The Tangles of Neaera's Hair
[March 5, 2010]
Flew to Catalina today for lunch. Oil temperature is no longer an issue, but I have not yet made a fairing around the oil cooling air outlet and so I have not done any speed checks to find out whether this new modification has increased drag to a measurable extent. I did notice that one of my temporary duct tape baffle seals had prolapsed into the outlet. What I found most interesting today however was the impresson that after landing the engine idled more smoothly at low rpm than it used to, and after shutting down I was able to turn the propeller with no more effort than at any other time. Before I changed the starter, the engine was very hard to turn over immediately after being shut down. Can it really be that the lightweight starter was exerting that much resistance?
[February 25, 2010]
Finally I have arrived at the end of a couple of tunnels. The matter of the starter has been resolved by putting the old 16-pound unit back on the engine. Now, with the help of batteries kept in tiptop shape by my battery tender, the engine cranks like mad. Sky-Tec, who made my lightweight starter, offers a special deal, a new 5-pound starter with internal clutch (to spare the engine clutch) for $250 and your old starter. Oddly enough, they did not offer to pay the $815 bill for the overhaul of my starter adapter, which their original idiotically designed starter had ruined. Eleven pounds is a lot, but I'm not sure it's worth $1,600. Maybe to the Pentagon.
On another front, I removed the duct extension that I had added to pick up oil cooler air from just behind the prop, and found that the oil runs just as cool without it. The key to a 20-25 deg. C reduction in oil temperature was, first, to pick up the oil cooling air before it had a chance to be heated by the exhaust pipes, and, second, to provide an outlet for it that was not affected by the cowl flaps. Incidentally, removing the duct extension also had the happy effect of bringing down the temperature of the left front cylinder to where it had been before; evidently the suction from the oil cooler duct was starving it.
A tuft test of the region around the outlet revealed horrible flow; the tufts were jumping around like a bunch of dervishes. Actually, I have never seen a dervish. But anyway, I need to provide turning vanes and perhaps some sort of hood to smooth that out, and also a bellmouth at the intake end.
Finally, I made the mistake, when changing batteries, of failing to note the fuel quantity from the totalizer. Lacking any means to visually confirm the fuel level, I have hitherto relied on tapping on the underside of the tank; the resonance of the skin changes when there is fuel on it, and I have a graph that relates the fuel quanitity to the outboard end of the fuel pool. Needless to say, this is a very approximate method. It came to me today, however -- it's incredible how long it can take for such an obvious idea to dawn -- that I could measure the fuel surface quite precisely by attaching a vinyl hose to a sump drain and noting the fuel level in the open end of the hose; my design software calculates tank volume for any pitch and roll attitude and fuel surface height. It appeared that there was 8.2 gallons in the right wing and 5.2 in the left. Using the tapping method, I had guessed 10 and 5.
[February 18, 2010]
At last the mystery of the balky starter appears to have been resolved. It seems that the first generation of the lightweight "high-torque" starters like my Sky-Tec lacked a clutch to disconnect them from the engine. The starter clutch inside the engine is a hefty coil spring that tightens around a shaft under load. The tension of the starter, which is a geared permanent magnet motor and does not turn freely when it is not energized, keeps the spring from relaxing, and eventually it wears to the point that it is no longer able to grip the shaft. The typical first symptom is exactly what happened: the prop stops at a compression peak and the starter makes a whirring sound. I removed the starter drive assembly from the engine and took it to Pacific Continental Engines, an overhauler on the field, where the guy I talked with said that if I had a Sky-Tec starter of the type whose driving nubbin cannot be turned by hand, I should throw it in the trash. This was discouraging news, but at least I still have my old starter. I then ran into Claude Morgan, who occupies the hanger two south of mine and has a Swift with a Continental 360 like mine. He turned out to be quite familiar with the problem, and said that he had put the old "18-pound starter" -- mine weighs only 16 -- back on his engine to avoid ruining the starter clutch. I am going to call Sky-Tec, whose website now makes a great point of how their current starters have electromagnetic clutches that prevent exactly what happened to me, and see whether they have a trade-in program. I'm not optimistic.
Incidentally, I was told that another cause of failures of Continental starter clutches is synthetic oil, which is so slippery that the coil spring can't get a good grip on the shaft. Lycoming engines don't have this problem (or the other one), because their starters engage by means of a small gear that pops forward to mesh with a large one. The system, called a Bendix drive, is out in the open air, unlike Continental's, which is inside the engine and bathed in oil.
Speaking of oil, I found out today that I had been right about one thing, at least: the inverted oil filter. I unscrewed it, and not a drop of oil came out.
[February 17, 2010]
I swapped my old 1970's starter motor for the Sky-Tec. It displays the same reluctance to turn over, so whatever the problem is it is probably not the starter. On the advice of Paul Lipps I checked the voltage drop all along the starter circuit with the small starter. I found nothing out of the ordinary, but since the small starter keeps whirring even when the prop is not turning, I wonder how much load it is really experiencing. Evidently its electromagnetic clutch is not engaging, and so it is never experiencing any torque to speak of. Tomorrow I will repeat the voltage drop survey with the old starter; at least when it bogs down, it stops dead.
My glideslope quit working a while ago, and I pulled the receiver, an ancient Collins GLS-350, today. It was incredibly difficult to get out, even though the instrument panels swings aside. It is held in place by a sliding shoe that is moved by a single screw; but I had put the head of that screw as nearly out of reach as it could possibly be. I'm going to arrange a better mount for it, although after this I will probably never have to remove it again.
[February 12, 2010]
I took out the batteries and worked for a couple of hours on assembling the charging socket and plug. After wiring up the part that goes inside the cowling I realized that it was going to be exposed to radiant heat from the exhaust and I could not use the wire that came with the battery tenders. I'll rewire that part on Monday. I tried cranking the engine with the mags and fuel pump off. There was very little voltage drop -- from 27 to 24 volts or so -- but that was not surprising since it was apparent that the starter motor is whirring but the prop is barely turning. I think there must be something wrong with the starter motor clutch. Bad news, if true.
[February 10, 2010]
Having built a sort of chimney on the top, that is downstream, side of the oil cooler, I reluctantly cut a hole in cowling top and made a test flight. The OAT on the ground was 19 C. The oil temperature rose to about 90 C during a climb to 8,500 feet, but then dropped to 78 C, which is the vernatherm setting, in cruise (27/2200, 141 kias, 8.4 gph). It was unaffected by my closing the cowl flaps; this was the result I was hoping to achieve. I still need to fair the edges of the hole in the cowling, provide some vanes to extract a few grams of thrust from turning the flow aft, and improve the sealing of the chimney -- I am temporarily using duct tape as a baffle seal.
The batteries were a huge disappointment, however. The starter barely turned the engine over. Actually, since it cranked equally weakly when being boosted by a Jet Center start cart at San Luis Obispo two weeks ago, the problem may not be the batteries at all. I will clean all the connections tomorrow and try it again. I had resolved to carefully watch the voltmeter during cranking to see how much drop there was under load, but then I forgot to do it. Maybe I'll remember tomorrow. I hope the problem is not the starter motor itself; that would be either expensive (buy another one) or heavy (install the gigantic original starter from 1970-something).
[February 3, 2010]
I've learned one or two things about batteries in the last few days. A couple of the important ones are that you don't replenish low fluid in a lead-acid battery with battery acid -- heck, it seemed so natural! -- and that a battery that sits unused for long periods needs to be on a continuous low charge to prevent accumulation of lead sulfate on its plates. A reader of this every-lengthening account, Glenn Stone, acquainted me with the notion of a "battery tender," which is a sort of trickle charger with the brains to maintain a "float" voltage just high enough to prevent sulfation and low enough to avoid eroding the plates. I bought a couple of them at Walmart ($20 bucks each, brand name Schumacher, look pretty solid) and hooked them up to my batteries yesterday, and today a couple of nice green lights indicate that the batteries are fully charged. I temporarily disconnected the tenders and measured the voltage at 26.6. I don't know if that's what it should be, but it seems high enough; it is slightly above the natural potential of 12 lead-acid cells, which would be around 25.2 to 25.6, and I suppose that it would drop rather quickly. I am going to install a socket in the bottom of the cowling to allow easy connecting and disconnecting of the tenders. The reason I needed two of them, if it's not obvious, is that I have two 12-volt batteries connected in series. They do not necessarily discharge and charge exactly equally, and in any case while 12-volt battery tenders are easily acquired, 24-volt ones appear, not surprisingly, to be rarer and more expensive.
[January 31, 2010]
The engine barely started for the SBP trip; in fact I had to get a fellow to come over and put away my homemade start cart and lock the hangar for me. Pleasant flight to SBP, the mountains unusually snowy after the previous week's storms.
The following morning my host, Kurt Colvin, who teaches engineering at Cal Poly and owns a Husky, and I found my wings heavily encrusted with frost. That took a while to go away, and then, of course, the engine would scarcely turn over; cold is no friend to batteries. Kurt tried without success to hand-prop it, and finally a start cart had to come over from the Jet Center. The engine should have whirled like a top, but it still cranked only weakly; it did start, however. On getting home and inspecting the batteries I found them to be heavily sulfated. In the course of acquiring new ones -- I use two 20-a.h. Yuasa motorcycle batteries in series -- and reading up on how to charge them, I learned that I have not been doing my batteries a favor for all these years by replenishing them with battery acid rather than distilled water; that just accelerates the sulfation by increasing the concentration of sulphuric acid, which apparently evaporates more slowly than the water. It is also advisable, it seems, to keep them on a "float" charger -- a steady 50-100 mA -- during periods of disuse. It is humbling to discover that I am still ignorant of such elementary things.
[January 19, 2010]
While rummaging through photographs to use as part of a presentation I'm giving to an EAA chapter in San Luis Obispo this coming weekend, I came upon this shot of an early, and abortive, project of mine called Tern, which is briefly described in the portion of this website devoted to the earlier Melmoth (Home > Topics > Melmoth 1 - mostly pictures).
The paths of glory lead but to the grave.
A couple of people have suggested punching a hole in the oil filter a few minutes before unscrewing it to ensure that all the oil in it drains out. I was assuming that since the filter is above the engine and the circuit is open to the air through the crankcase, that would not be necessary; but maybe it will. If so, I will have to do it with something other than the recommended centerpunch, since the firewall, which is made of a ceramic/carbon/nomex sandwich and is very light, is not intended to withstand hammer blows.
I have been working on a design for a four-seat single-engine jet, a project originated by Austin Meyer of X-Plane fame, who apparently wishes to put to the test the adage that the way to make a small fortune in aviation is to begin with a large one. Here is what my design looks like; the rainbow colors represent pressures on the airplane surface, the red end of the spectrum being low pressure and the blue end high:
[January 13, 2010]
In accordance with my policy of veering off from time to time into some irrelevant activity, I removed the oil filter from its position on the right side of the nosewheel well/engine mount and put it on the firewall. Viz:
The idea was mainly to make it easier to get at, but also to see whether putting it into an inverted position would make it easier to change wthe filter without having to take elaborate precautions to avoid spilling oil all over the place. An inverted filter drains into the engine when it is shut down, except for oil that is below the top of the screw-on spigot; that, however, is supposed to be retained by a rubber flap around the perimeter of the filter. So in theory you should be able to remove the filter without any oil escaping from it at all. We'll see. Inverted filters are used on some cars, for instance MG-Bs (not much of a recommendation) and some Ferraris (hardly more). They are suspect in MGs because of the delay in developing oil pressure on startup; but in the airplane that should not be a problem, because oil does not even flow to the filter until the vernatherm valve opens. Since that happens gradually, I think the air in the filter should enter the engine in a fine stream of bubbles without affecting the lubrication. I made one circuit today to check for leaks. Everything seemed normal. I had moved the thermocouple (see below) to the top plug on the right middle cylinder; there it registered about 50 deg F higher than on the bottom, which is expected. I also looked at the bubble catchers in the flap hydraulics; nice and dry, and no air to speak of inside.
Paul Lamar, who is a guru of the rotary-engine community, said in one of his communications the other day that every 90-degree fitting in the oil plumbing raises the oil temperature, and that removing one could bring the oil temperature down 10 to 20 degrees. I have four of them. I don't understand, however, how they can affect the oil temperature, since the lubrication system is positive-displacement. They may raise the oil pressure a little, but I don't understand why they would have a detectable effect on temperature.
[January 7, 2010]
I've made a couple of flights now with the spark plug thermocouple; it seems to match up pretty well with the description in the previous entry, but I'm still not persuaded that temperature readings from a bayonet thermocouple should really be interpreted as being incorrect when cooling is updraft. I discussed this yesterday with Mike Melvill, who has updraft cooling in his Long-EZ. He observed that the tip of the bayonet, which is quite long, is buried deep within the cylinder head, close to the cylinder wall, and it is hard to imagine that blowing cool air on the other end of it could have much effect on its reading. That is my impression as well. We also agreed about the heat load in the cylinders being concentrated on their undersides -- see the previous entry. If the bayonet thermocouple reads low, perhaps it simply means that the hottest part of the cylinder is cooling better -- which would be a good thing, not a bad one. I wish I could find some serious technical analysis of this topic, rather than hand-me-down guidance in online discussion groups.
The last leak that I fixed on the flaps has had a remarkable effect. It didn't seem to be that bad a leak, but since I fixed it I have not yet had to add hydraulic fluid anywhere, and the flaps have been staying in synch with one another and extending fully at each use. It's too early to declare victory, especially since I haven't looked under the seats lately, but I'm encouraged.
[December 29, 2009]
The holidays have been a time of complete inactivity on the airplane front. However, Dick Eklund, who handles plans sales and support for the Thorp T-18, has sent me a couple of spark plug termocouples and a calibrated CHT gauge. With its help I hope to get some idea of the relation beween the CHT as indicated by the bayonet probes, which are on the lower and therefore colder sides of the cylinder heads, and the factory CHT recommendation, which assumes downdraft cooling. I came across one plausible-sounding discussion of this topic on a Cozy site; here it is, slightly amended and amplified by me:
Lycoming says that cylinder head temperatures should never exceed 500 deg.F (260 C), but for maximum service life, cylinder head temperatures should be maintained below 435 deg.F (224 C) during high performance cruise, and below 400 deg.F (204 C) during economy cruise. High performance cruise is 75% power and 150 deg.F on the rich side of peak EGT. Economy cruise is less than 75% power and leaned to just above roughness. These temperature limits assume downdraft cooling and temperatures measured at the bayonet location under the cylinder, which is the hottest side with downdraft cooling. For updraft cooling you need to correct for the temperature difference across the cylinder, so add 40 deg.F (22 C) to the reading in climb and up to 70 deg.F (39 C) when leaned in cruise. If you are measuring CHTs with thermocouples under the bottom plugs, the temperatures are approximately correct without correction. If you are measuring CHTs with thermocouples under the top plugs, subtract 40 deg.F (22 C) from your readings to make them comparable to bayonet readings on the hottest side of the cylinder. So if you are using bayonet sensors on the bottom of the cylinders, your indicated temperatures should range from 300 deg.F (150 C) to 350 deg.F (175 C). Continental's recommended temperature for a bayonet thermocouple with downdraft cooling is 370 F (188 C); this would roughly correspond to 150 C for updraft cooling.
If, as I hope, this information is correct, it would suggest that I have been running 20-30 C hotter in economy cruise than I think I have. Unfortunately, the weasel words "up to 70 deg.F" leave room for doubt, and it is not clear why there should be different corrections for climb and for cruise. The matter is complicated by the fact that the bottoms of the cylinders, which with downdraft cooling would experience the greatest heat stress because the exhaust outlets are there and are provided with very little finning, would presumably be better cooled by updraft flow, while the tops of the cylinders, which have lots of fins but less concentrated heat, might receive less cooling but also need less. One might suppose that the temperature difference between tops and bottoms would be smaller with updraft cooling; the thermocouple readings from the top and bottom of a cylinder should shed some light on that. In the meantime, I can easily bring the CHTs down by opening the cowl flaps a little; that also reduces the oil temperature by a few degrees.
[December 14, 2009]
Finally, a palpable result. OT initially sat at about 80 C, then crept slowly to 85. This was with cowl flap open, that is, a decent delta-p (pressure drop) across the cooler. When I closed the cowl flaps the temperature went up to 88. Unfortunately, since I violated a basic rule of experimentation by making two changes at once (extending the duct intake to guaranteed cool air, and lagging the exhaust pipe near the duct) I do not know to what I owe the improvement. But the sensitivity to delta-p inclines me to think that it would be a good idea to provide the oil cooling air with a separate exit. For some reason, the temperature probe did not work on this flight, and so I could not confirm the temperature of the air within the duct.
[December 13, 2009]
On Friday I extended the oil cooler intake duct to a position just within the nose air inlet with the idea of picking up air before the engine gets a chance to heat it. I tried this before, but with such a tortuous duct that I was not sure that temperature gains were not being erased by duct losses. Anyway, in the next day or two I'll fly with this setup. The temperature probe is inside the duct; its lead is taped to the surface of the duct. I lagged the portion of the exhaust manifold that passes close by the oil cooler on the chance that a significant amount of heat is being radiated into the duct walls from the pipe. Here's the present setup:
You wouldn't guess it from the picture, but the cross-sectional area of the mouth of the duct is about 25% greater than that of the SCAT hose.
[December 9, 2009]
Yesterday I flew with the temperature probe in the oil cooler inlet duct. The temperature there was 34 C, the same as I measured behind the engine in the high-pressure plenum. The OAT was 10, so a considerable amount of heating of the cooling air is taking place before it actually gets to do any cooling. This may have to do with the location of the main air inlet just behind the propeller and below the spinner. It obliges air to flow around the oil sump and through an obstacle course of exhaust pipes and whatnot before getting to the cylinders and oil cooler. I have toyed with the idea of replacing the medial inlet with two inlets placed low on the cowling and some distance away from the propeller, something like this, but less ugly (that this is a T-34C, and the temperature was 34 C, moves me to think, annuit coeptis):
Such an inlet might improve the cooling air flow path. Despite the pre-heating of the cooling air, however, the cylinder head temps on this flight were about 150 C with the cowl flaps completely closed. CHT is not a problem.
[December 3, 2009]
Sifting through some old slides of Melmoth 1, I came upon a picture of the instrument panel that I think may have been taken while en route from Key West to Cozumel in the summer of 1974. It is interesting to compare it with a picture of the panel of Melmoth 2, taken in June, 2007 en route from Paso Robles to Los Angeles. Many of the instruments are the same, so it's easy to compare their readings.
First, performance. M1 -- this was early in its career -- was indicating 144 knots at 6,500 feet at 21.5/2500, that is, 161 ktas at maybe 70% power and a surprisingly rich mixture. The fuel flow is probably around 9.5 gph. M2, cruising at 11.500 feet at 26/2200 and lean of peak EGT, is indicating 141 knots, for a true airspeed of 169 knots at 8.8 gph (that's the fuel flow/totalizer at the upper right corner). This confirms my general observation that M2 is slightly faster and more efficient, despite being a four-seater; the big difference is its wingspan, which is over 35 feet to M1's 23. M1's cylinder head temps are at or above 200 C; M2's are 160 and 190, the 190 being the right rear (#1) cylinder, surprisingly enough after I figured out why it was running hot (April, 2007). I now cruise at between 150 and 180 C; but M1's oil temperature is about 65 C, whereas M2's is 100. The big difference in power settings is due to M2's being turbocharged and M1's having been naturally aspirated at the time the picture was taken. The manifold pressure gauge, by the way, is the same in both photos. It is a twin-engine gauge, and at some point I had the needles painted red and blue. The blue needle (needle #1 in 1974) is static pressure; it serves as a backup altimeter if you read it backwards from 30. The red needle (#2) is the manifold pressure.
[December 2, 2009]
Finally back to the hangar after a couple of weeks of holiday cooking and hanging out with our son and his wife and now seven-month-old daughter. I took out the #1 bubble catcher, which was still leaking hydraulic fluid, chased the threads, and potted an AN fitting into it with JB Weld. That should work. I then made a flight to check oil temperature with the duct as it appears in the photo below -- no hose, no bellmouth, just a way of getting at air that has not been playing footsie with the exhaust pipes. The result was not too promising: still 100 degrees C, even though the OAT was 13. I'll put the temperature probe inside the duct next.
[November 14, 2009]
A morning both eventful and unsatisfactory. I got out to the airport at 6:20 a.m. and attached the duct to the oil cooler. I didn't want to cut an expensive piece of 3.5" SCAT until I knew exactly how much I'd need, so I crammed about 40 inches of the stuff into the cowling and tied it down with safety wire. The front end is about 10 inches behind the air inlet. I then took off to test the cooler. There ensued another one of those educational glitch-parades that make test flying so amusing. The cable connecting the flap handle to the flap valve jumped its track when I was putting the flap handle back into the neutral position after setting the flaps for takeoff, but I was unaware of it. When I went to retract the flaps, the flap handle jammed, with the result that the hydraulic pump ran continuously. I had to pull a breaker to stop it. But rather than retract, the flaps went to the landing position, because the valve was not following instructions from the handle. So I flew around the pattern at 80 knots, got the gear down by briefly re-setting the breaker, and taxied back to the hangar. The problem was easily corrected, and I re-tensioned the cable so that it would not misbehave again, at least not immediately. I then went out to fly again. This time the left flap, which is always the troublesome one, did not extend symmetrically, so I left the flaps up and took off. Disappointingly, the oil temperature went up to about 90 C. This is better than it was, but it was a chilly morning, at least by LA standards, and it's hard to separate the effects of cooler ambient air from those of the duct. I had of course been hoping that the temperature would go to the factory-recommended 77 C and stay there. So now the question is whether the long, somewhat tortuous duct is impeding the flow, or the lack of large improvement is due to about ten other possibilities I can think of.
One observation I made that was of interest (to me, at least) was that the temperature behind the engine, on the "cold" side of the baffles, was around 40 C -- that is, quite a lot lower than the temperature at the inlet to the oil cooler. So the oil cooler seems to be getting a specially heated stream of air; this may help explain why the oil temperature is high, but the cylinder head temperatures aren't.
[November 13, 2009]
I got the oil cooler duct done just too late to add a bit of SCAT hose going to the air inlet and make a test flight. I hope to do it over the weekend. The duct is entirely flush-riveted, with the flush heads inside.
It will be interesting to see how this affects the oil temperature and also how the oil temperature is affected by the cowl flap position. I suppose that ideally the oil cooler would have its own air outlet, so that it experienced maximum delta-p at all times. On the other hand, you don't want to be putting more air through the cooler than it needs. The engine temperature is regulated by the vernatherm valve, which controls the flow of oil to the cooler. In principle you would like the vernatherm to be fully open when the oil temperature is at the recommended 170 deg. F; that would mean that the amount of oil cooling available is exactly the amount needed, and no extra air is being sent through the oil cooler. But I am getting ahead of myself. The first thing to find out is whether the duct brings the oil temperature down or not.
[November 10, 2009]
I am once again indebted to my alert Swedish correspondent, Jan Carlsson, who continues thinking after I stop, for pointing out that it is not impossible, as I said yesterday, that the static pressure in the plenum be greater than q. The source of the extra pressure would be the propeller. Duh.
[November 9, 2009]
On Sunday Hans Kandlbauer and I collected another batch of cowl pressure data. We had generally smooth air, which is needed because the water manometer is very sensitive to little jiggles. Nevertheless, some of the results were suspect; the pressure in the bottom plenum was a little higher than q at low speeds, which is impossible. For what it's worth, however, here is the variation of delta p, the pressure drop across the engine, at a range of cowl flap positions and airspeeds. There is some scatter in the data, especially at 100 knots.
The cowl flap position values are the size of the opening at the aft edge of the flap. Because of the deformation of the cowling under pressure and the placement of the limit microswitch, and flaps stop slightly short of fully closed. At 140 kias, zero is really 0.25; at 80 kias, it is more like 0.15. The line colors are indicated airspeed in knots. It is interesting to note that the last half-inch of travel, between the "climb" position (1.5) and the "ground cool-down" position (2), yields barely any gain. Otherwise, however, the variation of delta p with respect to outlet area is pretty linear. The outlet area at 1.5 is about 60 sq. in., which is approximately equal to the inlet area.
[November 5, 2009]
There's supposed to be a guy at the airport who has an oven with provisions for vacuum-forming plastic lenses. I go by his hangar every day, but he never seems to be there. In the meantime, I've gotten interested in the oil temperature question and am making a duct, as suggested by Jan Carlsson, to pick up cool air brfore it has had a chance to flow over the exhaust pipes. Every once in a while I treat myself to a little nostalgic metal work -- my first airplane was all-metal -- and I remember how much fun it is. Sheet aluminum is like a child: It doesn't want to do what you want it to do, so you have to trick it or compromise with it. (Some people beat on it, but I am of the non-violent generation.) Here is the duct after a few hours of work:
That's a spare oil cooler -- I didn't have to take it off the engine. The entry to the wedge diffuser below the cooler is 10 square inches -- a wild guess -- and I just happened to have some 3.5-inch SCAT, which is the same size. The duct bends down 90 degrees and forward 30, while transitioning from a 3.5-inch circle to a 4 x 2.5-inch rectangle.
While measuring the temperature of the air entering the oil cooler last week, I took a few pictures of tufts on the rear window. There is some slight unsteadiness along the centerline at the extreme aft end of the canopy, but the view is probably worth it, since the rear seats face aft. Yes, the upholstery of the pilot's seat is still a pillowcase.
[October 30, 2009]
After my last posting I received an email from Jan Carlsson of JC Propeller Design in Sweden, suggesting that the reason for my high oil temperature was that the exhaust pipes were pre-heating the air going into the oil cooler. I didn't believe that this could be the case, since the cylinder head temperatures are quite low, and they would be under the same influence. Today I measured the temperature at the entrance to the oil cooler, and found that I was wrong and he was right; the temperature was in the neighborhood of 60-65 C, or around 150 F. Small wonder the oil is hot. Jan suggests a duct from the air inlet to the oil cooler; another possibility would be a separate air inlet on the cowling side, which would make quite a crowd of inlets, since the induction air NACA scoop is there already. A third possibility would be an insulated plenum built into the bottom of the cowling, fed from the front inlet, supplying both the oil cooler and the induction and supplanting the NACA induction-air inlet. I'll think about this for a while. I also need to repeat the test, and measure the temperature of the air emerging from the cooler, to be sure that I am separating radiative from convective components properly.
The gadget with which I measured the temperature, by the way, I got at Radio Shack in November, 2003. It's intended for letting you know when the meat on your barbecue is ready, and consists of a probe, a transmitter, and a remote receiver that displays temperature. It cost about $25.
[October 28, 2009]
On Sunday Hans Kandlbauer and I collected cowl pressure data using a water manometer with two circuits, one comparing the high- and low-pressure plena (this is "delta-p", the pressure drop across the engine), the other low-pressure (as I thought) and static. The results looked pretty nonsensical until I realized that the low-pressure vs. static data were really high-pressure vs static. Then they made sense, but just to be sure I'm going to run the tests again. The confusion was due to the ambiguous labeling of some pressure hoses I had installed years ago; "low" could mean low pressure or low (that is, below the engine) plenum; obviously, in an updraft system the physically lower plenum has the higher air pressure.
The aim of all this data gathering is to understand why the oil temperature is higher than expected. It runs between 90 and 110 deg. C, depending on OAT (Southern California tends to be way above standard almost all year long) and cowl flap position. The factory recommendation is 170 F, or 77 C. The oil cooler is part of the engine, and the whole arrangement is the same as it was on Melmoth 1, except that the air flow is in the opposite direction and the length of the hoses going from the engine to the oil filter is greater (an extra three feet or so of 1/2 inch tubing). The filter is of concern because I have installed a diverter between the engine and the oil cooler; oil heading for the cooler gets sent through the filter first. The filter is a few inches away from an exhaust pipe, and I suppose that some radiant heating must be taking place, but certainly not enough to account for the observed temperature increment. The oil pressure runs about 45 psi in cruise, and since the oil pump is a positive-displacement device there is no reason to think that the impedance of the plumbing and the filter itself (which is a Bosch automotive model) is responsible. Just to make sure, I intend to short-circuit the diverter, bypassing the filter. I will also calibrate the oil temperature probe, though I have done this before and have no reason to suppose that its behavior has changed.
On Melmoth 1, the oil temperature maintained the factory Vernatherm setting of 170 F. One possible explanation for the difference now is that because the CHT probes are on the bottoms of the cylinder heads, they indicate cooler, for a given overall heat content in the cylinder head, than they would with downdraft cooling. That would imply that I should be aiming for CHTs lower than the recommended 370 F, which would mean a larger cowl flap opening, which would mean higher delta-p. It's evident that the minimum cowl flap opening of 18 square inches, which I normally use when cruising, results in a buildup of pressure above the engine and a consequent drop in delta-p; at 140 kias with the cowl flaps closed, we measured a delta-p of just four inches of water, which is less than a third of the total pressure. But even with the cowl flaps open and the CHTs abnormally low, the oil temperature never drops to 170 F.
[October 22, 2009]
Today I finally managed to record the tuft test of flow attachment on the stabilizer during the landing. CG was about as far forward as it gets, with full flap and no airbrake (the airbrake produces a nose-up pitching moment, and so it reduces the tail load). The video is short and somewhat difficult to interpret. It begins as the airplane crosses the airport boundary; the trimmed elevator angle is about -5 degrees. The approach speed is too high and so the flare goes on for some time; you can see the stabilizer hunting farther and farther upward, beginning about 9 seconds in. The landing itself is not detectable on the tape; but at 17 seconds the elevator suddenly deflects fully upward. At that point, the main wheels are already on the ground and I am holding the nosewheel off. When the elevator is fully deflected, the flow on it is separated; but there is practically no flow reversal while the plane is airborne.
[October 21, 2009]
Several people wrote to suggest that the low airspeed reading on landing might be due to a particularly steep pitch attitude -- that is, to pitot, not static error. But with full flap the pitch attitude on landing is actually quite flat, so I don't think that's it. This weekend I am planning to do some landings while someone in the right seat watches the GPS. I'm not certain this will tell me much, however, since the apparent position error is in the range of 3-5 knots, and uncertainty about the wind could be in that range as well. We'll see. I have also hooked up the little camera that I mounted on the tail a while ago; it is looking up at the horizontal tail, which I have tufted in order to see whether the elevator flow is separating during the landing flare. Another task in this little set of tests will be to record pressures in the cowling at various speeds and cowl flap settings, using a water manometer.
I have also made the male tool for the wingtip lenses, and yesterday I laid up a couple of plies of glass over it in order to make temporary covers for the holes in the leading edges where the lights will eventually be. These covers will also serve, later, as templates for trimming the plexiglas lenses. The actual mold for the lenses will be a plaster female, and I hope to draw the heated plexiglas into it with a slight vacuum.
[October 9, 2009]
I had some email discussion this morning with John Roncz regarding the landing speed of 48 kias. We agreed that it is implausibly low, implying a CL for the complete airplane of more than 2.6. John said he would have expected something closer to 2.2-2.3, which would give a stalling speed of around 53 knots. So the question is, why is the indication so low? One explanation would be position error; but a position error of 5 knots would require a high, and unlikely, positive pressure at the static ports. I then ran a Cmarc analysis of the airplane, flaps down, in and out of ground effect. At an angle of attack of six degrees, the predicted CL for the complete airplane was 2.17; in ground effect, at the same angle of attack, it was 2.54. This difference pretty closely corresponds to the disparity between the expected and the observed stalling speeds, but this may be mere coincidence, since I am not sure that a wing should be expected to stall at exactly the same angle of attack in and out of ground effect. Since Cmarc predicts CL but not the stall itself, these analyses may or may not have much relevance to the question; but they do suggest that an airplane might possibly touch down at a speed somewhat lower than its stalling speed out of ground effect.
Incidentally, at Melmoth 2's wing loading of about 20 pounds per square foot and at landing CLs in the vicinity of 2.0, a change of 0.1 in the maximum lift coefficient produces a change of one knot in the stalling speed. The landing rollout is proportional to the square of the speed at touchdown, and so each added knot of landing speed represents a change of about four percent in the landing distance. If the braking distance is 500 feet with a touchdown speed of 50 knots, it will be 600 feet for 55 knots. The extra 100 feet would be covered in about 1.3 seconds during the flare. That is why speed control during the approach is so important for maximum performance landings -- more important, usually, than small differences in maximum lift coefficient.
[October 8, 2009]
Finally, I managed to shoot some tape of the flap with tufts.
A video of one circuit around the pattern at Whiteman is on YouTube. Unfortunately, in order to get as much of the flap as possible into the frame I was obliged to tilt the camera about 40 degrees. This test was flown at 2,200 pounds, with 100 pounds of ballast in the baggage compartment in order to be able to trim hands-off at approach speed, or anyway what the Safe Flight angle of attack device thinks is approach speed (about 73 knots with full flap; 1.3 Vs would be more like 65). All tufts are attached and steady during takeoff and climb. When the flap is retracted, a large area of unsteady or reversed flow appears near the trailing edge of the wing. I have discussed this earlier (3/17/09); it is probably due to the thickness of the laminar airfoil, which is 18% out to BL 48. The outboard set of tufts, which are at about BL 125, are in better shape; the thickness there is more like 15%. It is unlikely that a wing root fairing would have any effect on this separation; the tufts at the bottom of the frame are at BL 48, and the side of the fuselage is at BL 25. Accelerating to about 100 kias, which is five knots above the theoretical speed for best rate of climb, removes most of the unsteadiness.
The flow attachment with full flap is just about perfect right down to touchdown, except in the wake of the middle track. This is not especially surprising, since the maximum deflection is only 30 degrees with respect to the wing chord line; if it were 40 degrees, there might be more separation. Around the middle track, the flow is attached over the front portion of the airfoil, so it is generating some lift, but completely separated over the aft portion. The reason the disturbance seems to be located mainly on the inboard side of the track is that the rear spar has forward sweep, and the flap track is at a right angle to it. It is therefore angled outward with respect to the air stream.
Touchdown occurs, as I noted yesterday with condign skepticism, at an indicated 48 knots.
[October 7, 2009]
Yesterday I tufted the left wing and flap and set up a video camera to record some takeoffs and landings. I put 50 pounds of ballast into the baggage compartment in order to make it possible to trim to approach speed with full flap. Today I flew to Santa Paula, bought 40 gallons of fuel, and flew back, reaching back over my left shoulder to turn the camera on and off. Unfortunately, I couldn't see the monitor, and upon inspecting the tape at Whiteman I discovered that I had recorded, in all, approximately three seconds in cruise somewhere over the Santa Clarita valley. I'll try again tomorrow. I did observe 48 knots just before touching down at Whiteman. I suspect position error, because that would imply a CL of 2.6. Doting father though I am, I cannot imagine that my flap is performing quite that well.
[October 2, 2009]
Flew Wednesday and today, staying in the pattern, trying to refine my landings with flap. It's apparent that even at 70 kias I'm still carrying too much speed on final; the plane floats quite a bit after I flare, even with the airbrake open. (On one touch and go I failed to retract the airbrake; it cut into the climb rate, but not dangerously. The main tipoff was buffetting due to separated flow in the wake of the brake.) The problem is that when I am flying alone the CG is so far forward that I can't trim for the proper approach speed. I think next week I will put some ballast into the baggage compartment in order to get the CG to a more natural position.
The flaps are working well, although they still do not extend fully; they stop about half an inch short of the end of the track. This is due to air still trapped in the hydraulic system; I expect that it will disappear over time, because some of it will get entrained as foam during each cycle and will end up in the bubble catchers. It appears that the flaps take 13-15 knots off the landing speed. The clean power-off stalling speed was 68 knots during initial flight test; the 200-pound weight gain since 2002 would increase that by about 5%, or 3 knots, at 2,000 pounds. (Today the airplane weighed about 1,900 pounds.) It now seems to touch down at around 50 or 51. The additional weight has also taken a bite out of the initial climb rate. Back when I could fly at 1,750 pounds or less and used 40 in. Hg. for takeoff, the initial climb was 2,000 fpm or more; now I use just 34 inches and with the added weight see only about 1,500 fpm.
It has been suggested that the intermittent problem with the push-to-talk switch could be temperature related, since it tends to occur initially and then correct itself after some time has passed. That might point to the audio panel, since it is the only thing in the mic key circuit that changes temperature.
[September 28, 2009]
Tried to fly today, not having done so for almost seven weeks. First, the batteries were low and wouldn't turn the engine over. I started it with the help of my ground cart, which consists of a homemade creeper with a couple of ancient auto batteries on it. Under normal circumstances they have a combined voltage of 8.7, but if I connect my homemade charger to them -- the Oneirodyne Amazo-Charge, as my old friend Peter Christie would have said -- they start the plane right up. And did. I taxied out, only to find that the mic key again (this last happened at Santa Fe in June) would not key the transmitter. Frustrated, I returned to the hangar and, just to have done something useful, checked the #2 flap master cylinder, which I re-sealed last week, for signs of leakage. There were none. I then gave the mic key one last try. People like to say that the definition of insanity is doing something over and over and expecting a different result, but this is quite false, and in fact in this case the result was different-- the XMIT light on the radio came on. By this time it was getting late and the plane was already back in the hangar, so, to paraphrase Lillian Roth, I'll fly tomorrow.
I really need to find the solution to this mic key problem. It is not the key switch -- which is on the sidestick -- itself; the problem remains even if I insert a manual key in the headphone mic line. It always seems to occur after startup, not during the course of a flight, and it resolves itself spontaneously sooner or later. It is as if an electrical bubble had gotten caught in one of the wires -- but there is no such thing as an electrical bubble.
My reading about Kelly Johnson and the Skunk Works has reminded me that many of the most satisfying days of my life have been spent on my airplanes, working from handwritten notes or scribbled sketches, and using the airplane itself as a mockup -- all techniques espoused by Johnson in contrast to the highly systematic and formal ones customary in aerospace. He tried to replace the drudgery of the factory floor with the excitment of the home workshop, and the oppression of the group with the passion of the individual.
[September 22, 2009]
There was nothing very mysterious about the leak in the #2 flap master cylinder, as it turned out; the static O-ring that seals the two parts of the cylinder when you screw them together was torn nearly in half in not one but two places. Oddly, it looked fine in its groove when I opened up the cylinder, and even after I removed it. It wasn't until I twisted the ring 90 degrees out of its natural set that the rip suddenly appeared. The damage must have happened during assembly. A new O-ring cost $1.35; some airplane parts are cheap. I wasn't sure how to lubricate it for re-assembly, but finally decided to leave the groove dry and to grease the inner faying surface thoroughly. I'm not sure that made sense; time will tell. Everything worked fine when I put it back together, but it will take a few cycles to know for sure.
[September 18, 2009]
I got back to the airport today for the first time since returning from the East on Tuesday. The hangar was as changeless as an Egyptian tomb. I hesitated to take the flap synchronizer apart in order to repair the leaks, since I expect to need to use the airplane next week, and I am very busy researching an article on Kelly Johnson, of Lockheed Skunk Works fame, for the Smithsonian's Air & Space magazine. I finally decided to go ahead, and managed, in the course of three hours, to repair the small fifth cylinder whose job is to restore everything to proper alignment after each flap retraction. The inside of the cylinder was badly scored, I'm not certain why, but it may have been galling between the aluminum piston and the aluminum cylinder. I ended up replacing the tube -- twice, actually, since I hastily drilled some holes in the wrong places the first time around. That's par for the course for me. I hope the #2 master cylinder, which drips, will be easier to fix; I suspect it's just a matter of a twisted or damaged O-ring, or some crud that got under the O-ring in my negative clean room.
[September 4, 2009]
We are staying in a friend's house at the mouth of the Pamet, a pygmy river that rises a stone's throw from the Atlantic near the tip of Cape Cod and flows three miles westward into Massachusetts Bay. Each evening Nancy and I go down to the harbor a little before the sun sets, walk some distance up the Pamet, and then turn as the sun vanishes below a small dune and walk back, stopping to admire the seabirds feeding in the slack tide and the ineffable mother-of-pearl palette of cloud, sky and water. We come here every year, and every year before coming I make a mental list of the things I am going to accomplish while here -- new or improved features in my computer software, a chapter in a never-finished book about the first Melmoth, the missing 20 percent of a film script that I wrote several years ago and that concerns, strangely enough, a pilot -- it's sort of Shane meets Medea, with wings. Each year, I do none of these things, falling, instead, into a daily cycle of shopping, cooking, reading, making minor house repairs and going to the beach, a routine that somehow swells to occupy every second of the time. This evening from our vantage point along the river we could see our son on the distant stone breakwater, casting for blues, a tiny erect figure against the twilit sea. He had waded across the harbor to get there, and probably underestimates the difficulty of returning in darkness, which is gathering as I write this. But he is a resourceful fellow, and will be back in time for dinner. He would not miss a lobster risotto.
[August 20, 2009]
I'm going away Saturday night for three weeks on the east coast, and leaving the plane here; so there will be a slack period in this otherwise gut-wrenching narrative. Because of having a lot of writing to do before leaving, I have not been at the hangar as much as usual; so I went there today to secure a few things, put tools away, and have a last (for a while) look at the plane. I did a little wiring, just to feel that I had accomplished something, and made a list of things that will need to be taken care of when I return, including the hydraulic leaks, the obligatory bi-annual static certification, and the glideslope receiver, which has stopped working. And, of course, I must figure out how to make lenses for the wingtip lights, and build the flasher circuit that Paul Lipps designed. At the rate I go, all this should take me well into November.
[August 14, 2009]
The #2 flap master cylinder is leaking again, as is the mysterious "driver" cylinder that is responsible for getting everything back into alignment at the end of each flap cycle (see diagram at October 13, 2008). For that matter, the airbrake cylinder has been leaking for a while too, so I have a bit of maintenance to catch up on. I don't remember the first Melmoth being quite so hydraulically incontinent as this, but I continue to believe that once I find and correct the cause of every leak, the system will cease to require much maintenance. At present, three of the four master cylinders are bone-dry, as are both inboard flap actuators and possibly the left outboard one as well. None of the connections in the plumbing is leaking any more, and not a single nylon line has blown out in the past two or three weeks -- this must be some sort of record. The right outboard actuator still seems to leak a bit. I tentatively attribute the proneness of the outboard cylinders to leak to their being subject to side loads, although I provided quite a lot of lateral slop where they connect to the flaps. Well, not for nothing does the airplane have "EXPERIMENTAL" written on the side of it.
[August 8, 2009]
Yesterday I took our daughter Lily up in the plane; she was the last remaining family member who had not flown in it. We moseyed around the west end of the San Fernando Valley at 4,500 feet, crossed the Santa Monica Mountains to Malibu, circled over the ocean and retraced our steps. I was in a quandary as to whether to tell Nancy before we did this, and decided not to. There was no good solution; she was going to be unhappy about it either way. I didn't, and she was, but we got back alive, so there wasn't too much to complain about. Lily liked it, and started talking about family trips to Baja -- "as soon as the drug war is over."
I saw the South African guys on Thursday, a few hours before they took off for Hawaii. They made it in 21 hours. Nice chaps. They are going to be over water practically the entire remainder of their return to SA, but they have only one more leg left that's as long as the LA-Maui one.
[August 2, 2009]
I got the bulbs from a downtown warehouse operation that didn't even have a sign outside, although it has a brightly-colored web presence. It was fun, something like venturing into a Moroccan souk. But I didn't work much on the plane last week because I was writing an article about Steve Fossett's accident and also fixing bugs in Loftsman that John Roncz uncovered in the course of designing an oddly shaped little aircraft. I finished the wingtip light assemblies and barely began making the tooling for forming the acrylic lenses for them.
On Wednesday I'm supposed to go down to Torrance to chat with a couple of South African guys who are flying around the world in an LSA they are promoting. They must have lots of Sitzfleisch -- long-suffering buttocks -- the longest legs for the 120-mph airplane being on the order of 24 hours. They're supposed to leave Oshkosh for Los Angeles tomorrow, and LA for Hawaii on Thursday. They have a website that tracks their progress.
[July 25, 2009]
The project du jour being the tip lights, and the halogen bulb sockets used by Grimes appearing less and less suitable as I chopped more and more off them to make them fit behind the position light bulbs, I finally abandoned them altogether and began searching on line for a substitute. In due course, having visited several ghostly online catalogs without benefit of phone number or geographical location, I identified, from their mug shots, some candidate sockets. It happened that at the same time I was repairing our washing machine, which had begun to leak water from the siphon break in its "injection hose" -- for such is the rather grandiose name of the rubber hose that delivers water into the tub. Searching, again, on line, I found the part, but it appeared that its cost would be nearly doubled if I wanted to have it in my hands in less than a week. Casting my memory back to the days when one turned to the Yellow Pages for appliance parts -- Los Angeles is, after all, a largeish city -- I resorted to that moldering volume and quickly located the hose a few miles south of my house. Encouraged by this experience, I began to hunt around for halogen sockets the same old-fashioned way, and was soon directed to a certain hardware store three miles from my house, Virgil's, which, remarkably, had a whole drawer full of a socket that looks just right -- though the sales personnel assured me that I must be mistaken about wanting a 24-volt bulb, since there was certainly no such thing in existence. Actually, there is. Twelve and 24-volt circuits seem to be used in outdoor lighting, no doubt so that dogs can urinate on the fixtures without dramatic effect. It is odd to notice, by the way, that these so-called 6.35 mm bi-pin bulbs cost, say, $3.99 each in one on-line catalog, and $7.99 in another. In fact, at the place where they are $7.99, everything is $7.99, including the sockets that I got from Virgil's for $3.19 apiece.
[July 20, 2009]
Yesterday I flew to Catalina with a couple of friends -- the landing fee is now a flat $25, so I don't go there much any more -- and on the return trip let one of them fly. He is a professional pilot and experienced in small aircraft (just "airline pilot" is no guarantee a person can land even a C-172). It is usually instructive to have another person fly the plane, and this time was no exception. One thing I learned was that it is apparently customary in this world for the mic key to be a trigger on the front of the stick grip. I have such a trigger, but it is the autopilot interrupt; the mic key is a thumb switch on the side of the stick. So Hans's first few transmissions went nowhere, because he was clicking the wrong switch; but it sounded as if he were transmitting, because the intercom was providing the expected sidetone.
When I take off I usually use 34/2800 initially, then come back to 30/2500 to climb. (Maximum T/O power would be 41/2800.) I habitually reduce power before raising the gear and flaps. But Hans maintained 35/2800 much longer than I normally would, while remaining at a relatively low climbing speed (80 knots with takeoff flap) and I noticed that the #3 CHT (right middle) got up to 240 C (464 F). It was a hot day, about 30 F above standard. It was still hotter at Whiteman -- around 100 when we took off -- but because of my habit of early power reduction and acceleration to 100 kias, the CHT had not gotten above 400. This made me realize that although I consider my cooling system satisfactory, it may actually not be adequate for a protracted climb at high power and low speed on a hot day. I don't know if production planes are any better, but it seems to me they must be.
We used 25/2200 for a leisurely return trip at 4,500 feet, indicating 126 knots at 6.5 gph.
[July 16, 2009]
On cutting the notch for the position light in the right wingtip, I found that much of the blue foam core in the curved transition from the wing panel to the upturned tip had been eaten away by gasoline that sometimes splashes out the tank vent during fueling. I recognized the look immediately, because a few weeks ago Mike Melvill had shown me similar gasoline erosion in the wings of his LongEZ. As it happens this doesn't matter much, since the tips are strong enough even without the core, and in fact I had deliberately carved out a similar portion of the core in the root of the left wingtip when I put the roll trim servo there. The vents open into the cavity between the wing and the tip, which is pressurized with a small flush inlet in the lower surface and vented to ambient pressure at the aft end; the idea was to provide a vent that did not protrude from the wing and would not ice up. It should have been obvious to me, after seeing Mike's wing, that something similar must have been happening in my tips; but I didn't make the connection.
I will build up the front of the core again, this time with fuel-resistant foam, lay up a shear web over it to restore the stiffness lost by cutting the hole, and then mount the light assembly on a floating rib running fore-and-aft. The light, here still in the pliers and tin snips stage, is basically just the standard Grimes unit with the back end of the teardrop cut off and the halogen bulb socket turned crosswise and crowded up against the nav light lens to make the whole thing as short as possible.
[July 14, 2009]
The position lights won out, since I'm still not sure which direction the pre-swirl for the turbo inlet should go. I'm heavily modifying a set of Grimes wingtip lights that I happen to have -- heaven knows why or where I got them -- and putting them under clear lenses where the wing transitions from a straight taper to the upturned dihedral-enhancing tips. There's just barely sufficient room. I'm not sure yet how I will form the lenses, but I will find out in due course, no doubt after ruining and discarding a great deal of Plexiglass. There will also be small white halogen bulbs that will blink -- a sort of poor man's strobe. I don't as a rule fly at night, but for such a complex airplane to be without lights seems incongruous.
This being Bastille day, the music station that I usually have on at the hangar played a rousing Marseillaise, all four or five stanzas -- I lost count. (We forget that the Star Spangled Banner -- a splendid anthem, in my opinion -- also has a whole bunch of extra stanzas.) The refrain of the Marseillaise includes the words "Qu'un sang impur abreuve nos sillons!" -- a remarkably sanguinary sentiment that, roughly translated, means "Let the foreigners' blood irrigate our furrows!" Actually, it doesn't say "foreigner" -- the exact words are "impure blood" -- but one gets the idea. I'm not sure which brand of blood was meant when the words were written in 1792; Prussian, perhaps, or Austrian.
[July 10, 2009]
After fixing a few small things, including a loose connection on the #1 CHT probe and a broken wire on the induction air temperature probe (which has not worked for years -- not that it mattered, since I never use enough boost to worry about excessively hot intake air anyway) I started making a mold for a new turbo inlet box. The turbo air inlet faces aft and is only a few inches away from the firewall; air coming into it has to make a sudden 90-degree turn. Currently, I'm using a "banjo box" to accomplish this -- although it would better be termed a "lute box." This is an expanding chamber with the turbo inlet bellmouth on one side. The idea is that air slows down and spreads out on entering the banjo box, and then gets sucked into the bellmouth. At some point I started to think that on the analogy of a tub drain, the right-angle turn might be made more efficiently if it relied on a spiralling path, like that of the turbo scroll itself. There is some question in my mind about whether introducing some pre-swirl into the inlet flow will mess up the impeller aerodynamics; but the turbo is usually running so far off point anyway that it may make no discernible difference at all. Anway, the idea of the whole project is to improve the breathing of the turbocharger. Actually, I should be working on navigation lights; maybe I'll do both projects simultaneously.
[July 2, 2009]
A benefit of seldom washing the plane is that the dirt on it forms streaks when I fly through moisture, and those streaks tell something about air flow. Today I noticed a faint streak that ran along the left side of the fuselage, starting a couple of feet above the wing. It paralleled the wing surface nicely, then went more or less straight aft for several feet before taking a little jog upward just before the baggage compartment door. The jog puzzled me for a moment, and then I realized that it was caused by by leakage around the door. The leakage is not outward, as you might expect, but inward, because the pressure in the cabin is lower than ambient, being dominated by outward leakage around the windows. This is why cabin vents should not be placed at the back end of the cabin; the pressure there is comparatively high, whereas the pressure in the vicinity of the largest cabin cross-section is low.
[June 29, 2009]
Yesterday we flew back home from Little River. The trip used 23 gallons to go about 420 nm, which works out to 18 nmpg. It's interesting to see how different the block mileage is from the instantaneous mileage. For most of the flight the engine was using about 7.7 gph, at a shade above 50% of power. Our true airspeed was about 159 knots, and so our mileage ought to have been better than 20 nmpg. We had light headwinds, about five knots at the start of the trip and 10 near the end. We did do quite a lot of climbing; we started at 9,500 and eventually ascended to 13,500, where the density altitude was 16,500, for a better ride. I suppose that the time spent climbing at 120 knots groundspeed cut into the mileage, and of course taxiing, runup and takeoff (27 gph!) do too; but I'm still surprised that the difference should be so large. I lean to 25-50 LOP immediately after takeoff and climb at 60% power or so, and 500 fpm. Maybe this is not actually the most economical way to gain altitude. The thing about climbing is that the rate really doesn't matter, because the work required to raise a certain mass to a certain height is a fixed quantity, regardless of how rapidly the job is done. (I was reflecting, as I repeatedly climbed the 85 steps from the beach to the house where we stayed north of Fort Bragg, that our sense that the rate at which work is done affects the total amount of energy expended is due to the way our bodies tire when we work rapidly but don't when we maintain a slower pace.) What affects the cost of climbing to a given altitude is the aerodyamic efficiency of the airframe and the specific fuel consumption of the engine. The aerodynamic efficiency is best around the best rate of climb speed, so that tends to take care of itself so long as you don't cruise-climb (but cruise-climbing may result in a shortened trip time; I haven't looked at that question, which is related to the Carson Speed, since the CAFE races in the 1980s). The specific fuel consumption improves as power output rises, and so it should really be more sensible to climb at a higher power setting, provided that the mixture remains the same.
It might, incidentally, be possible to recover most of the energy expended in climbing by shutting off fuel to the engine and allowing it to windmill with open throttle and coarse pitch during the descent; but passengers could object.
[June 23, 2009]
We got up at 5:00, took off at 6:09, and landed at Little River exactly three hours later, having enjoyed smooth air and a steady tailwind. Everything -- the GPS tracker, the mic key -- worked, except, of course, the flaps. The unreliability of the flaps is troubling; I will probably end up replacing all of the nylon lines with real aircraft stuff, even though it's so damn expensive. What was so odd about this failure was that it occurred when I was extending the flaps before takeoff, and there was no air load on them at all.
In this picture, taken as we crossed the Sierra Nevada into California, if you knew the geometry of the airplane you could infer the time of morning from the shadow of the horizontal tail on the wing. The Steve Fossett crash site is out there somewhere, probably behind the trailing edge.
[June 22, 2009]
I am writing this in Cedar City, Utah, where Nancy and I stopped for lunch on the way from Santa Fe to Little River, at Mendocino on the California coast north of San Francisco. We ran into quite a lot of turbulence on the way, and since turbulence is not Nancy's favorite part of flying -- actually, the only part of any flight she likes is parking at the end -- we decided to stay here tonight and leave at the crack of dawn, when the sun has not yet begun to heat up the desert surface. The plane had a couple of glitches at Santa Fe; the press-to-talk switch on the stick stopped working, and a borrowed substitute wouldn't work either. I arranged for a takeoff clearance by cell phone, but when I pulled up to the runway the transmitter resumed working, for no apparent reason. Then, just before takeoff, as I started to extend the flaps, I heard the dreaded pop and saw that the left flap was deploying unevenly. Evidently another one of those infernal NyloSeal fittings had blown off. So no flaps for the rest of this trip. Then the GPS tracker refused to recognize the GPS; it does that from time to time, again for no apparent reason, and pulls itself together on the next flight. And it appears that there is still a very minute fuel seep at the middle flap track on the right wing. I'll probably just live with it; sometimes leaks seal themselves.
June 13, 2009]
Having repaired -- I hope -- the leaks, I put the wing back onto the airplane at the end of the week.
Knowing, now, that one wing weighs 92 pounds, I was able to calculate the actual limit load factors for various fuselage loadings. Each wing, according to my 14-year-old dot-matrix computer printouts, was designed for an ultimate lifting load of 6,450 pounds, distributed spanwise in a manner halfway between a semi-ellipse and the geometric shape of the wing. This results in a moment of 386,000 inch-pounds at the outermost attachment bolt. Adding the weight of the main landing gear (35 pounds each) and the protruding portion of the centersection (which is integral with the fuselage), I arrived at a deduction of 135 pounds. Doubling all of this, so as reflect the whole airplane rather than just half of it, I subtracted 270 pounds from the measured (well, partly measured, with a small increment for the weight of the flap synchronization system) empty weight of 1,585 pounds, and got 1,315 pounds for the empty weight of the fuselage. (Even knowing the answer, I doubt I could come up with a weight breakdown that would account for it.) Then, I considered three loading conditions: single pilot, two 190-pound persons with 100 pounds of baggage, and four 170-pound persons with 50 pounds of baggage; these add, respectively, 200 pounds, 480 pounds, and 730 pounds to the fuselage weight. Dividing the three totals into the lifting load of 2 x 6,450 or 12,900 pounds, and dividing again by the conventional safety factor of 1.5, I arrived at limit load factors of 5.7, 4.8, and 4.2 G respectively. Weight creep -- or faulty estimation during design -- took its toll; I had intended, originally, that the plane be acrobatic at some loading. It falls slightly short, but no matter -- I am not particularly acrobatic myself.
I am aware that these numbers are slightly optimistic, because the weight of fuel is not uniformly distributed spanwise unless the tanks are full -- that is, unless I have won the lottery and put 142 gallons of fuel into my tanks. Partial fuel weight is concentrated inboard, and so it imposes some additional stress on the wing. The more fuel there is the more it spreads outward, however, and, although I have not yet run the numbers, I feel pretty confident that no fuel load could push the limit load factor, even at the maximum fuselage weight, below the Normal Category value of 3.8 G.
[June 5, 2009]
With the help of Russ Hardwick I removed the right wing in order to fix a couple of small fuel leaks. At the same time, I intended to calibate the fuel quantity senders. There are two in each wing, one inboard and one outboard, and in order to calibrate them it is necessary to be able to alternate between full and empty a few times. This is most easily done, obviously, by flipping the wing over. I also wanted to weigh the wing, in order to be able to calculate the actual weight of the fuselage. The senders are now calibrated, and the wing turned out to weigh 92 pounds, which is quite a bit more than the 52 pounds it weighed without tips, ailerons, flap tracks, controls, filler and paint.
The wing was easy to remove, once I had disconnected all of the electrical, hydraulic and fuel lines and the mechanical controls that connect it to the fuselage. After six and a half years, the faying surfaces showed no sign of fretting or corrosion. The main spar joint consists of two groups of 3/8-inch high-strength bolts, and it seems likely that under normal conditions friction due to clamping action, rather than the shearing strength of the bolts, transmits the load from the wing panels to the centersection. The outboard joint has four bolts and the inboard only three because the lift force is shared between them, whereas the bending moment is upward at the outboard attachment and downward at the inboard. The strips of reddish-brown color along the upper edges of both the wing and the centersection are non-structural; in order to reduce the cabin height, the centersection spar, which is made of carbon fiber and is black, is not as deep as the root profile, but only deep enough to contain the landing gear, which retracts under the seats. The four nutplates on the centersection spar are for the bolts that hold the front landing gear bearing block in place.
One simple rule that I seem to have been unaware of when I designed this wing is that there ought to be enough space between two structures to allow you to get your hand in. In this case, there isn't; to gain access to the fuel quantity sender, which is in the middle of the large round inspection plate, or to the low-fuel warning float, which is the little black thing in the recess, you have to remove the wing. Very clever. The three lines emerging from the tank are fuel feed, vapor return, and sump drain. I believe that the two shades of green on the aluminum reinforcing plate reflect the areas that were squeezed tightly together (darker green) and those that air could reach (lighter).
[May 31, 2009]
From time to time I have toyed with the idea of reversing the position of the intake manifold runners on my engine. The point would be to eliminate the transverse tubes which now obstruct the flow of cooling air toward the exits. For some mysterious reason this thought has come back to me with more force than usual, and I am thinking that I might actually do it. A little floor-based mocking-up exercise with tracing paper and the factory installation drawing, videlicet
I flew to Paso Robles yesterday with my friend Russ Hardwick. At 12,500 feet, density altitude around 14,000, speed was 174 knots at 8.4 gph.
[May 29, 2009]
Back from our trip east, I did a series of touch and go's today to get more familiar with the takeoff and landing checklist sequences and to get a better feeling for power settings, stick forces and so on during a pattern approach. (I usually fly a straight-in approach to Whiteman.) In the course of six landings, the lowest speed I saw before touching down was 52 knots, as compared with 68 knots without flaps. This suggests a CL of around 2.05 (1.2 clean). It's not clear how close to a full stall that was, and the flaps are stopping a little short of fully deflected because of small amounts of air in the hydraulic lines, so the figure of 2.2 that I mentioned earlier may yet prove to be correct. As always with high-lift devices, however, the exact CLmax is less important than controlling the flare, touchdown point and braking to minimize the required field length. I was able to trim to approach speed (about 73 knots) with takeoff flap (10 degrees), but with full flap (30 degrees), which I used only after turning final, I had to hold some back stick to keep the speed down. The CG was very near the forward limit. Fifteen inches of manifold pressure gives a good 600-700 fpm descent in the pattern with 10 degrees of flap. It appears as if I have a little too much speed on final. If touchdown speed is 52 knots, I should be flying the approach at 67 knots (1.3 Vs). It may be that the angle of attack indicator is not correct when the flaps are extended. But 73 knots is just 1.4 Vs, and it's easy to bleed off the extra speed by cutting the power and starting to flare a little early.
[May 15, 2009]
What was I thinking? Of course it isn't "done." No lights yet, the glideslope is inop, no gear position indicators, wings leaky and incompletely painted, no wastegate. Here is a to-do list which I began in 2002, before the plane first flew. When an item got done, I moved it to the end of the list and changed the font.
M2 to do
left front armrest
extend right console down to floor to prevent fouling torque tube
move aileron hinges
make left main gear doors flush
gear sway brace overcenter lock indicator lights
enlarge turbo banjo box
outboard sender, nav, strobe wiring
mechanically attach root fairings
remove wings:
calibrate all 4 senders
fuel leak in right wing, high, near root
fuel leak at right outboard sender?
fuel leak at middle track
why are low-fuel warning senders weird?
sand, smooth and repaint undersides
toe deflectors above brake pedals
replace nose gear actuator link
replace nose gear retract link
replace nose gear strut?
paint window margins
finish hard static plumbing
cabin/panel lights
nav lights
rotating beacon
alternate static
gas springs for main gear downlocks
canopy seals
window retention screws
adjustable wastegate
smaller alternator
tape pulley brackets
wire colors reversed on pwr/gnd from panel to alt/batt
oxygen system
NG actuating cylinder leak
**********************************************************************
Done
transponder
fuel flow/totalizer
static ports
oil separator
pitot-static-transponder certification
change oil and filter
swing compass
install nose strut gas spring
fit and install middle gear doors
correct position of inboard gear doors; why low?
new tow points
new tires
troubleshoot manual lowering
install and plumb nose gear cylinder
adjust gear control cable tension
reflector plate above cowl floor below turbo
reflector plate on air box
reinforce floor under torque tube support
repair cowl floor under turbo
enlarge cowl inlet
oil cooler radiation shield
overhaul Dukes pump
passenger seat
safety window hinge pins
gas springs for windows
fix short in radio rack
repair and revise turbo mount
put pop rivets in window latch mounting plates
provide cowling water drains
install #2 comm, both navs
replace anti-arcing diode on starter solenoid
move oil separator
fair cowl outlets
NAV antenna
hydraulic reservoir overboard drain
install autopilot
install rear armrests
seat upholstery
engine mount front fairing
reinforce right aileron torque tube support
wing trailing edge skin reinforcement
move air inlets to corners of engine mount
seal around exhaust pipe
carpets
contour wing upper surfaces
service EGT
service artificial horizon
service autopilot
fill and fair wing joints
paint removable parts
paint
reinforce floor under brake pedals
bracket to hold down right baffle shelf
replace leaking brake fluid hose
check voltage regulator wiring per Lipps letter
bracket to hold air duct away from exhaust
prime interior
seal holes in firewall
replace Lord mounts
longitudinal restraint for turbo
straighten lower end of nose gear half-fork
straighten NG retract link
reinforce or replace NG retract link
tiedown rings
electric tank switcher
get artificial horizon
revised turbo inlet air ducting
shift gear lowering backup hex
airbrake
use balsa core for cowl outlets
add camlocs to top cowl
cabin heat
rudder trim tab
#2 comm antenna
floor under rear seats
wingtips
shim front engine bearers
move fuel distributor
display compass card
stall warning horn
provide ventilator valves
repair #2 VOR
12 v outlet
glideslope antenna
marker beacon antenna
improve battery heat shield
replace voltage regulator
repair and reinforce battery connections
battery box insulation and blast tube
flap root fairings
boarding step fairings
move pilot's ventilator to panel
NACA engine air inlet
airbrake warning light
rear seat rails
outboard flap track fairings
airbrake position indicator
install GPS tracker
revise trim system
shimmy damper leak
nosewheel doors
rear seats
make cowl outlet ramps movable
pilot's seat
intercom
GPS rack
exhaust gas deflector plate w/afterbody
outboard flap actuator plumbing
back seat ventilator
roll trim
fill and fair grooves around windows
make new middle flap tracks
flap synchronizer
reinforce middle flap track attachment area
reinforce inner wing skins
A couple of the not yet done items deserve clarification. The nose strut is sufficiently strong, but the diameter of the piston (1.25 inches) is on the small side, and as a result it is difficult to pressurize correctly; either it is too soft and tends to bottom, or it is too stiff and tends to extend fully and stay that way. I have a vague plan of revising one of the old main struts from Melmoth 1 to serve as a nose strut; the piston's diameter is 1.625 in., and it should be less sensitive. I think the turbo would breathe better if the banjo box, through which air entering it makes a sudden 90-degree turn, were larger and differently configured. The wing root fairings are currently held in place mainly by aluminum tape; the idea was to use screws, eventually. As for the wastegate, it is currently the fixed type, with the result that the air throttle butterfly is often partly closed; I think that efficiency would benefit from having the butterfly open and regulating power with the wastegate; but I'm not sure about it, or how big a difference, if any, it would make.
[May 12, 2009]
Leaving tonight for the east. I'll be away two weeks. Someone asked me the other day whether the airplane was "done." In a way it's never done, but I had to admit that, in terms of what I set out to do, it's done. Oops -- no oxygen system yet! Not done yet -- thank God!
[May 6, 2009]
I made a short flight today, and encountered an interesting phenomenon after landing. A good wind was coming down the runway; the ATIS was calling it 10 with gusts to 15, but from the windsock I would have judged it to be more like a steady 15 knots. Anyway, after touching down I wanted to make the first turnoff, but when I applied the brakes the tires just seemed to skid. I had never encountered this behavior before and didn't understand what was happening until I thought about it again a couple of hours later. It was the flaps; even with the airplane in a level atittude they were taking enough weight off the main wheels that I was not getting effective braking. In order to make a short field landing, I would have to retract the flaps as soon as the wheels are on the ground -- equivalent to airliners raising their spoilers after touchdown. Just have to be sure to grab the right handle. (I made the turnoff anyway.)
My passenger pointed out that I still had a hand-lettered sign next to the flap handle saying "FLAPS (INOP)". Before leaving the hangar, I put a little acetone on a paper towel and erased it. The flaps are definitely working.
[May 4, 2009]
I drained the hydraulic fluid from the #2 master cylinder, replaced the Nyloseal fittings with AN flare fittings, pressurized it with air, submerged it in a bucket of water, and found that it did not leak a bit. The suspect joint between the piston and the shaft is evidently tight after all. The leak must have been at one of the two Nyloseal fittings. I re-installed them with more teflon tape, but I'm not confident of that being a permanent fix. Still, the news was basically good; if this cylinder is free of structural leaks, the others probably are too. Sooner or later, one can always get the better of leaky fittings.
Speaking of leaks, after reflection I decided not to take the leaky wing off this week. Nancy and I are going to the east coast next week (not in Melmoth -- too expensive) to introduce ourselves to our granddaughter, who was born on April 21. That would have given me only a few days to work on the wing. Instead, I will wait until after a certain event on May 30 to take the wing off; I will then have a couple of weeks to work on it before needing the use the plane again.
[May 2, 2009]
Nancy and I spent Monday through Thursday of last week visiting friends who have a house in the Sierra about halfway between Fresno and Yosemite. On Friday I removed the leaking master cylinder from the flap synchronizer, but did not have time to do anything with it. It's not actually clear where the leak is -- I thought it was at the main joint where the two pieces of the cylinder join, but I found some fluid inside the piston shaft, which would mean that the threaded joint between the piston and the shaft, which I sealed with Loctite and tested with compressed air, has begun to leak. Having found this apparent leak on the cylinder I had removed, I checked the others and found a drop of fluid at the end of a couple of other piston shafts. The floor below them was dry, so those leaks, if leaks they be, are very slow. They would be comparatively easy to repair, in any case, but I'm not certain that this is the only leak in the cylinder that I removed.
I'm planning to remove the right wing next week to deal with several fuel leaks, including one that kicks in whenever I put in more than about 25 gallons of fuel. I have not had a wing off since spring of 2002; it will be interesting to peer into all the dark places and see how they're doing.
[April 22, 2009]
A milestone of sorts: after six and a half years, Melmoth 2 finally flew with four people aboard. Mike Melvill was in the left seat. Ray Henning and his friend Mary Cunningham rode in the back seats, whose acrobatic entry procedure they accomplished with a good grace. We flew from Tehachapi down to Shafter, north of Bakersfield, where we picked up Ray's T-18 to bring it up to Mike's hangar. It will be stored there until it is sold. Mike has a lot of pictures up on the walls, and he gave us a tour, reminiscing about some of his adventures, which include a 38,000-mile circumglobal flight with Dick Rutan, mostly over water, in two Long-EZs. I thought it was remarkable to reflect that this entire career, this extremely rich life, had been set in motion many years ago by the decision of Mike and his wife Sally (who had eloped and married in their teens) to send away for plans for a weird-looking airplane designed by an unknown character named Burt Rutan.
[April 19, 2009]
Yet another video. This one is from the first up-and-away flight, on November 1, 2002. (I had made three short runway hops the day before.) The reasons for the weird temperatures that cut the flight short were two: the oil cooler plumbing was messed up, so that no oil was going through the cooler, and the selector switch that toggled between oil and induction air temperature readings, which share a single instrument, was mislabeled, so that the extremely high oil temperatures appeared as air temperatures, and vice versa. The high oil temperature was the cause of the drop in oil pressure. My comments, after landing, that the engine seemed to lack power are in the category of first-flight observations that are forgotten later. The drag of the landing gear must have made me feel that the airplane didn't have much pep. Anyway, it's never seemed that way since; it has plenty of power. Indeed, except for takeoff I never even use power settings as high as 30/2500 any more.
[April 17, 2009]
I should have added to the discussion below that since the maximum possible lift coefficient of the flapped portion of the wing is much higher that that of the unflapped portion, it would seem that the most likely point for the stall to begin would be just outboard of the flap. It remains to be seen whether this is the case.
In the meantime, now that the flaps, which have occupied me for so long, are working, I have sunk into a sort of pastoral stupor. The only thing I did on the airplane in the past few days was to mount a tiny video camera at the tail; the idea is to tuft the underside of the horizontal and see what the flow looks like during the approach to a stall, particularly with a forward CG.
I did post a couple of new videos on YouTube. Now that I have overcome my natural reluctance to appear ridiculous, I am willing to post just about anything. One of them, which only a parent could love, is of me pushing the plane into the hangar; the other, which is of slightly greater interest (if only because it contains an instance of that piece of film magic called a wipe), shows the extension and retraction of the Fowler flap.
[April 13, 2009]
The main reason for tufting the wing while testing the flaps was to get warning of an incipient outboard stall. It is often said that the outboard portion of a flapped wing is operating at a lower effective angle of attack than the flapped portion, and so the stall will not begin at the tip. Actually, the lift coefficient of the outboard panels is greatly increased by the upwash produced by the flap. Here are plots of spanwise variation of pressure coefficient along the quarter-chord line of the wing, without and with flaps. In both cases the angle of attack is zero. A negative pressure coefficient represents reduced pressure on the wing skin, a positive one increased pressure; lift exists when the pressure on the top of the wing is lower than that on the underside.
The numbers are hard to read, but the vertical scale goes from +1.0 (bottom) to -2.0 (top) -- it is customary to plot pressure coefficient with negative values going upward -- and the horizontal scale, which represents fractions of semispan, goes from 0 (centerline) to 1.0 (tip). The outboard end of the flap is at about .68 on the horizontal scale. The noteworthy things, I think, are that the lift increment supplied by the flap does not drop off suddenly at the end of the flap, but declines gradually toward the tip; and that a significant portion of the lift increment due to the flap -- the lift can be visualized as the area between the upper and the lower lines -- takes the form of increased pressure on the bottom surface of the wing. When the flap is retracted, the lower surface pressure is uniformly negative; when the flap is down, it is largely positive, becoming somewhat negative only about a third of the way out along the aileron. These differences are due to the flap greatly accelerating flow over the upper surface, while retarding it over the lower surface; our old friend Bernoulli is at it again.
The influence of the flap is felt even across the fuselage; the pressure coefficient at the centerline is -0.6 with flaps down and -0.45 with flaps up.
[April 10, 2009]
The other day, when I was visiting with Burt Rutan, he came out to look over my airplane before I left, and remarked that he had done one of the first layups on it. This was true: He and Mike Melvill came down to Whiteman in August, 1981 and laid up the inner skins of the top and bottom halves of the aft fuselage. This was my introduction to wet layup; I took over from there. The tail cone, from the fin post bulkhead to about the trailing edge of the wing, was made by heating 3/4-inch thick foam sheets in a homemade oven to soften them, and then bending them and gluing them into place in a fixture consisting of particle-board cradles. After the inner skins had been laid up by Burt and Mike, I added frames, then joined the top and bottom. Finally, I sanded the outer surface to give it continuous longitudinal contours. The outer skin was done in my garage during the winter of 1981.
In the picture below, which was taken while I was still a tenant in the big hangar at Whiteman, the frames have been added and the top half has been lifted out of its fixture and set down upright on top of it. The slanted bulkhed in the lower half is the footrest for the back seats. At this point, I felt that I would be finished in another year or so.
[April 9, 2009]
I flew today with full flap. The trim change is not excessive, at least with 50 pounds of ballast in the baggage compartment. I haven't stalled it yet, but it appears that the stalling speed will be around 50 knots at a weight of 1,900 pounds; this corresponds to a CL of 2.2, which is about what I hoped to achieve. (Theoretical section coefficients like 2.8 and 3 reported for big Fowler flaps are two-dimensional values; the complete airplane doesn't do that well because only part of the wing is flapped, the flap has tip losses, there's a download on the tail, and so on.) The flap hydraulics remained pretty dry, with just a couple of remaining drips. Unfortunately there is a new fuel seep in the right wing where I added the track reinforcement gusset, but that shouldn't be too hard to fix.
[April 7, 2009]
I flew out to Mojave on Monday to visit Burt Rutan, whom I first met in 1975, before the first VariEze had been built. I used to see him for lunch very regularly, but I had not talked with him in a long time. He had lost 40 pounds last year and had a close brush with death from constrictive pericarditis, but he now looked sleek and rosy-cheeked. He spoke of the SpaceShipOne project in tones of fond awe and retrospective amazement, and expanded enthusiastically on the absurdities of some of his interactions with government agencies charged with regulating not-yet-existent technologies like thrill rides to space.
Today, I worked on adding a pressure relief valve to the retraction side of the flap hydraulics; I will finish that tomorrow. It appears that one each of the master and actuator cylinders is leaking; the rest aren't, so I feel that I am slowly gaining the upper hand.
[April 1, 2009]
Today I extended the flap to 20 degrees. The hydraulic pressure was close to the relief value setting -- 550 psi -- but the flaps seemed to be traveling freely. I had put a 50-pound ballast into the baggage compartment; this moved the CG to around 20% of chord and alleviated the out-of-trim condition created by the flap. The trim change due to the additional flap deflection was slight. Lots of hydraulic seepage, however, some of it coming from the master cylinders themselves, some from the NyloSeal fittings.
[March 31, 2009]
I realized after taxiing to the runway today that I had not removed the floor panel covering the flap synchronizer, and so could not see the temporary hydraulic pressure gauge. The point of the flight was to find out what pressure is required to extend the flaps fully. I didn't want to taxi back, so I flew anyway, climbed to 7,500 feet, and extended the flaps to 15 degrees. With the CG about as far forward as it ever gets and the airbrake (which produces a nose-up trim change) extended, there was insufficient trim authority to hold approach speed (70 kias); hands off, the nose came down to the "fast diamond" on the angle of attack indicator, that is, something like 1.4 Vs. More flap deflection will tax the trim tabs even more. It's hard to tell, at this point, whether this will be a problem worth doing something about. I could increase the chord of the trim tabs or, alternatively, only extend full flap on short final. One question, which I will be able to answer with a couple of sandbags once I am comfortable with full flap, is whether the trim shortage occurs only with an extremely forward CG. Another question is how much elevator deflection is required to hold up the nose with full flap; I put a gauge on the stick to enable me to read elevator deflection in flight.
[March 29, 2009]
In an attempt to stay abreast of the times, I have uploaded to YouTube a mercifully brief video of Melmoth 2 landing at Santa Paula, shot a few days ago by Paul Lamar, whom I was going to see. The title is "Melmoth 2 landing at SZP". The flaps are at the takeoff setting, and the airbrake is down. My daughter Lily, if she learns of this, will declare it the nadir of vulgar self-promotion.
[March 27, 2009]
I have been concerned about possible flap asymmetry in case of a failure of one of the NyloSeal lines. This afternoon I blocked the flap in place at about 15 degrees deflection and then ran the pump to try to lower it further. Sure enough, one of the fittings popped off. After cleaning up the mess I tightened all of the fittings -- some of them took a full turn or more, which surprises me since I thought I had tightened them pretty firmly when I first assembled them. I don't understand how you're supposed to know when they are properly tightened. When I get the whole system to stay together during, say, a 10-second run at the relief valve setting, which is 550 psi, I'll feel more comfortable about going past the takeoff setting in flight.
The left outboard flap actuator continues to seep fluid from the retraction-line fitting -- a pipe-thread AN fitting, not NyloSeal. I would despair of ever getting some of these fittings to seal if I did not have the example of others to show that it can be done.
Yesterday for the first time I tried a takeoff with the takeoff flap setting; the airplane naturally ascended in a flatter than usual attitude, and felt like an elevator.
[March 23, 2009]
This strange sight is not a structural failure; it is a static load test of the outboard flap track. The idea was to apply a lifting force to the end of the track using the floor jack (the blue thing), with a bathroom scale (the square white thing) between them. The red jack was following the wing without applying any force to it, so that it would not fall very far if the flap track failed. It didn't.
While I was crawling around under the wing I noticed that hydraulic fluid was leaking from the outboard actuator. I removed it and re-installed all the fittings, replacing one that had a deep longitudinal scratch of unknown origin in the conical portion of the male AN flare fitting. The procedure for debugging the hydraulics seems to be to keep dismantling and reassembling things until, for whatever reason, they stop leaking. They can then, I hope, be ignored for many years.
[March 19, 2009]
There's a TFR today that will preclude any flying.
I should clarify something about the flow separation I noted a couple of days ago. I did not make sufficiently explicit that the picture showing reversed flow over a portion of the wing root was taken at 85 kias, which is the flaps-up approach speed. Now, this kind of separation at approach speed has no operational significance. It would matter only if it still existed at the best rate of climb speed, which is around 100 kias at low weights, but at that speed the separation has disappeared. Its presence at the lower speed is of mainly academic interest. I suppose that the fact that the separation vanishes when the flap extends a few inches might have some relevance to the initial climb rate after takeoff, but that influence would be very slight and, again, operationally inconsequential.
I should also explain my use of the terms "approach speed" and "climb speed." Early in flight testing, Mike Melvill identified 68 kias as the power-off stalling speed. The pilot-static system has not been calibrated down to that low a speed, but it is generally accurate and so I assume that 68 kias is about right. It corresponds to a CL for the complete aircraft of about 1.2 at the tested weight. (This is rather on the low side, and might be attributed to the low Reynolds number of the wing at landing speed; the chord, just inboard of the upturned tip, is 20 inches.) Under the conventional definition of approach speed as 1.3 Vs, the corresponding approach speed should be 88 knots. I rely mainly on the Safe Flight angle of attack device to regulate my approaches, however, since it automatically compensates for weight. When I first installed it according to the instructions, which suggest a "typical" chordwise location of the sensing tab, it yielded an approach speed of 85 kias, which seemed close enough to 88 and provided a comfortable flare. The angle of attack instrument has three reference points on its face, corresponding respectively (and roughly) to a slow approach (1.2 Vs), a normal approach, and best rate of climb (1.4 Vs). The angle of attack sensor is on the flapped part of the wing, and so in principle it compensates for flap deflection, since what it is actually sensing is the direction and dynamic pressure of flow in the vicinity of the tab (which looks just like a stall warning tab). The indication is somewhat affected by speed, however, since if the airplane is heavier, say, or the flap is down and the airplane is moving more slowly, the pressure felt by the tab may be different even though the location of stagnation is the same. At any rate, since the AoA indicator is my primary reference for approaches, I am using it to define "approach speed." Thus, when I say that the approach speed is 10 knots lower with the flap in the takeoff position, what I mean is that the AoA indicator is pointing to the "approach" marker (a green band in the middle of the indicator), not that I have measured the stalling speed and then multiplied it by 1.3
[March 18, 2009]
Today I intended to begin extending the flap past the takeoff setting; this would presumably entail larger trim changes and higher hydraulic pressures during extension. When I retracted the flap after takeoff, however, I heard a pop. Sure enough, the same nylon fitting had failed as failed on the 13th. After returning I replaced the nylon line with an armored high-pressure Aeroquip hose, which won't fail. I'm puzzled by the pressure spike that is apparently occurring in the line going to the cylinder that is labeled "Driver" in the diagram under October 13, 2008. I can't see why it would see higher pressures -- and during retraction, besides -- than two other nylon lines that are in parallel with it. Maybe they will be the next to fail.
As expected, if I taxi with the flap extended the middle roller bounces against the track, making a disagreeable rattling sound.
[March 17, 2009]
After repairing the popped hydraulic connection yesterday, today I tested the flaps as far as the takeoff setting. At this point the leading edge of the flap has translated aft almost to the trailing edge of the wing, and the flap chord line is deflected about 10 degrees with respect to that of the wing. The transition from takeoff to landing flap involves little additional aft travel, but the deflection increases to 30 degrees. Here is the scheme at the inboard track, at BL 25, where the total travel is 14 inches:
The takeoff setting reduces the approach speed, as indicated by the Safe Flight lift meter (alias angle of attack indicator), by 10 knots. I don't know what the reduction in minimum speed is, but the flap made a remarkable difference in the landing rollout. Without flaps (that is to say, for the past six and a half years) I have turned off Runway 12 at Whiteman at the third taxiway, with heavy braking; today I turned off at the second (at midfield) , and had to add power to get to it. Although I never minded not having the flaps before, now that I have them it would be difficult to go back to not using them.
At approach speed -- 75 kias with takeoff flap -- the flow attachment is good. Here are tuft shots with the flap about one inch short of the takeoff setting:
Interestingly (and disappointingly) this is not the case with the flap retracted; there is a pool of separated flow aft of 75% of chord, near the wing root:
Extending the flap a few inches improves this situation, but probably adds enough parasite drag to cancel the benefit:
There is still a great deal of testing to do.
[March 13, 2009]
This afternoon I finally operated the flaps in flight for the first time.
As far as it went, the experiment was an aerodynamic success but an hydraulic failure. Having slowed to approach speed (85 kias) at 7,500 feet, I extended the flaps, by small increments, to about half of the actuator travel -- the middle of the flap moved aft about six or seven inches while deflecting less than five degrees. This is much less than the takeoff setting, which involves about 11 inches of aft travel and 10 degrees of deflection. I had tufted the left wing and flap. At the approach angle of attack, I noted some separation in one tuft near the trailing edge of the wing at buttline 48. Even a slight flap extension reattached all upper-surface flow. The tufts on the flap upper surface were straight and steady. At half-extension, approach speed was reduced by seven knots. There was scarcely any trim change. I cycled the gear and the airbrake and did not observe any effect on the flap.
I then retracted the flap and extended it again. In the course of this operation one of the nylon hydraulic line connections popped off, flooding the area under the rear seats with hydraulic fluid and obliging me to return to the airport. The landing, with about four inches of flap extension, seemed unusually smooth and stable, but I may just have been paying more attention than usual.
Although the test ended prematurely, it looked promising -- particularly the lack of trim change, the good flow attachment, and the sizeable reduction in approach speed even with a fraction of the full Fowler travel. Some potential areas of concern are lifting of the long cantilevered slot lip, vibration or flutter of the flap, and flexing of the outboard track, which is an odd shape and difficult to analyze. The only sign of any problem that I observed today was lifting of the slot lip by maybe 1/4 inch. It will probably be necessary to anchor it at a few points.
[March 5, 2009]
Still no electrical power in the hangar, and since the temperature dropped about 10 degrees overnight the epoxy was too cold to pump and the filler on the wing surfaces was not yet sandable. I took off the cowling to inspect the engine, and found that one rocker cover screw had backed out and one exhaust flange nut had fallen off. Fixed those things. One convenience of updraft cooling is that since the bottom of the cowl has to be more or less airtight, stuff that falls off the engine stays in the airplane.
Last night, I figured out the relationship between the outermost shoreline of fuel, as determined by the fingernail tap test, and the amount of fuel in a tank. Here is the result:
Since the dihedral angle is rather small, the roll attitude has a fairly powerful influence on the results. The circled numbers are conservative, the actual values at buttlines 75, 92 and 130 being 6.5, 12.9 and 34.3 gallons, respectively. Those three buttlines were selected because they correspond to obvious landmarks on the wing; 75 is the middle flap track, 92 the angle of attack/stall warning sensor on the left wing, and 130 the outboard flap track. Now I have to decide whether to rely on memory, carry a copy of the chart in my flight bag, write the numbers on the underside of the wings, or all three.
[March 3, 2009]
I took 29 gallons of fuel from the right tank; with the 26 I took from the left tank a while ago, that makes about 20 gallons more than the totalizer said I had. I last initialized the totaliser 155 hours ago. Assuming an average fuel burn of 8.5 to 9 gallons per logged hour, the totalizer would be off by about 1.5% on the high side. My fuel quantity indicators are not overly reliable at any reading other than zero, so I can't use them to reset the totalizer from time to time. The only thing to do will be simply to add a gallon to the reading after every seven or eight hours of flying. The good side of this is that I am using less fuel than I thought, and so the airplane must have slightly less drag than I thought, since all of my power estimates, which are the basis of drag estimation, are based on fuel flow, and furthermore the plane has been heavier than I thought.
One of the difficulties of my fuel tanks, which consist of the entire interior of the wings, is that it is not possible to check fuel level visually. Since each wing holds 71 gallons, the tanks are never full or even nearly so. I noticed yesterday, however, that there is quite a difference between the sounds produced by tapping with one's fingernails on the underside of the wing where the skin is under fuel and where it is not. Since Loftsman allows calculating fuel quantity for any height of the fuel surface and any pitch or roll angle, it would be a simple matter to create a graph correlating approximate fuel quantity with the spanwise station at which the tapping sound changes.
I was so bold as to make a work schedule over the weekend. According to it I would be able to fly next Tuesday. All went according to plan yesterday, but today the electricity in the hangar was off, and that slowed me down a bit. I may catch up tomorrow, which, if the schedule is to be believed, will be a light day.
[February 26, 2009]
I've filled the holes in the upper surfaces of both wings with foam. It's been chilly in the hangar, and the microballoon paste that holds the foam cures rather slowly, so I haven't yet been able to sand the patches smooth and skin over them. I expect to get the foam filler into the hole in the bottom of the left wing tomorrow. I'll then move the fuel in the right wing into the left wing and add that final gusset. If things go well I should be able to skin all the other patches next week.
[February 18, 2009]
Dodged a couple of bullets. Returning to the hangar on Monday, I found the bolts that I had used to locate the lower-surface gusset too tightly bonded to be removed even with my largest screwdriver. Fortunately, I was able to get them out with a pair of channel-lock pliers, merely wrecking a couple of bolt heads in the process. Then, yesterday, I laminated the second ply of the gusset and two plies of carbon cloth into place, only to find that I could not maintain a vacuum in the vacuum bag, evidently because of the porosity of the fuel tank skin. So I cobbled up a sort of poor man's vacuum bag, consisting of a piece of foam rubber, a piece of plywood, and a wooden crutch pushing up against the plywood from the floor. This morning I found that the lamination had cured very nicely, and looked just as though it had been vacuum-bagged. Here is the completed gusset on the lower surface of the left wing:
The four bolts are bonded into place with JB Weld, a hard commercial epoxy that fills any voids between the bolt and the gusset. It now remains only to fill up the cavity with foam and skin over it.
Because of the difficulty I experienced in vacuum-bagging the lamination, I am changing the design somewhat. I will attach the second layer of each gusset to the first with the same Click Bond adhesive I used to bond the first to the wing skin, and then lay the two graphite plies over the top of both in lieu of passing one of the plies between them.
[February 13, 2009]
With rain roaring on the hangar roof, I finished digging out the sandwich core on the underside of the left wing and bonded the gusset into place. Sanding while semi-supine under the wing was no fun, but I found that by holding the vacuum cleaner nozzle between my drawn-up knees I was able to intercept most of the falling junk before it fell into my eyes and nose. I used a couple of wood crutches to hold the phenolic gusset in place during cure. Viz:
The procedure for this operation, once I overcame my reluctance to destroy the pristine surface of the wing, was first to cut through the outer skin with a very small grinding wheel in a Dremel-like tool, and then to pry the outer fiberglass skin away from the foam core. (This is one of the upper-surface gussets.)
Next, I dug out the foam with a chisel. This brought me down to the layer of epoxy-microballoon paste that forms the interface between the laminate and the core.
Using coarse sandpaper and a considerable amount of effort, I then sanded away the surprisingly durable microballoon layer. The inner graphite skin, which is the principal wing structure and also the liner of the 71 gallon fuel tank, was now exposed.
Finally, I bonded the gusset into place.
A second, shorter gusset will be added on top of the first one. The final reinforcement will consist of two plies of .100 phenolic with bidirectional carbon cloth between and over them and overlapping the exposed carbon surrounding the gusset. The extra thickness is needed not for compressive strength, but to handle the bearing loads on the four 1/4-inch bolts that join the gussets to the aluminum fittings within the flap cove. (The four holes are now 3/16 in diameter; they will be drilled and reamed when the complete gusset is in place.)
Finally, the outer skin surrounding the hole will be sanded to form a shallow scarf joint, the hole will be filled with foam and microballon paste, and a couple of plies of bidirectional glass cloth will be laid up over the top, dressed, and then, if past experience is any indication, clumsily painted. The whole procedure is repeated four times
[February 12, 2009]
A slight bump in the road. After bonding the upper-surface gusset to the right wing -- the acrylate goop cured much more rapidly today, no doubt because it was warmer than yesterday -- I began prepping the lower surface of the left wing. No sooner had I scraped away some of the foam core than gasoline began to seep out. Evidently the inner skin is somewhat porous, and it is the closed-cell foam core that is providing the final barrier to fuel leakage. There was no discoloration in the foam core, nor any apparent deterioration, so at least the fuel is not devouring the foam or migrating through it. (Auto fuel, with its aromatics, might be a different story.) I learned only after closing my wings that it is customary to coat the inside of integral composite tanks with a layer of pure epoxy. That would have involved a weight penalty of about six pounds, since the wing is entirely wet. In any case, draining 27 gallons of fuel from the wing into a collection of borrowed containers took me the rest of the afternoon. Tomorrow I should be able to bond the gusset on the underside of the left wing. I had intended to do each step of this operation at all four locations before going on to the next step, but evidently I will have to complete the repair to the left wing before draining fuel from the right wing and moving it to the left, which is my only remaining container.
[February 11, 2009]
Removing the wedge of outer skin and foam core from the wing proved to be remarkably difficult. This was gratifying; the sandwich is extremely tough and well-bonded. The outer skin, which consists of two plies of unidirectional material at right angles stitched together, 45/45 to the wing axis, had to be removed with pliers, and came off not as a sheet, as I expected, but in narrow, ragged strips, one layer at a time. The inner skin, the graphite one, is also hard as rock; I expected a little flexing, but detected none. Today I bonded the first gusset into place with the Click Bond stuff, which turned out to be easy to use. It's an acrylate adhesive, like Super Glue, but with a creamy consistency and a comparatively slow cure. You squish two components out of the envelope (I used three envelopes to be safe; I could probaly have gotten away with just two) and mix them up. They start off white, then turn yellowish as the reaction begins. By the time the goop has stiffened up, after 20-30 minutes, it is a dull green color. I was worried that I might end up permanently bonding into place the four clecos that I used to hold down one end of the gusset, so I kept taking them out, one at a time, and wiping them off. They seemed not to stick. Tomorrow I should be able to bond the second upper-surface gusset into place and get one, perhaps both, of the bottom surface holes prepared. I'm beginning to feel quite excited about the prospect of using the flaps.
[February 9, 2009]
The flaps and the middle track fairings are now installed. Apart from some minor seeps, the hydraulic actuation system is working properly. Many of the leaks involve the nylon hydraulic hose fittings, whose pipe threads are slightly smaller than those on AN fittings. After assembling a lot of the components, I found that several winds of teflon thread tape (which I first thought would be unnecessary because the fittings themselves are plastic) seem to prevent seepage, but I have not yet gone back through all the fittings to add the tape. The flaps still aren't ready to be used in flight, however. I have made the phenolic gussets that will be added, in a belt-and-suspenders sort of way, to the wing structure at the middle track attachments. All of my structural epoxy is quite out of date, and on Mike Melvill's advice I ordered a bunch of packets of Click Bond adhesive to attach the gussets. This is an adhesive used for nutplates, surface-mounted studs, and things of that sort, and Mike says it is exceptionally strong. These bonds don't actually have to be especially strong, because the load is spread out over a large area. Super glue would probably do fine. But if the stuff is really bulletproof, so much the better.
Installing the gussets will require removing a triangular patch of the outer skin, sanding down to the carbon inner skin, bonding the gussets to it, and then re-filling the hole and applying a new outer ply with a scarf joint to the existiing skin around its perimeter. The wing skin sandwich consists of a non-structure fiberglass outer ply, a foam (Divinycel) core about a quarter-inch thick, and a structural carbon inner skin. Hence the need to attach the gussets to the inner skin -- it is the one that carries most of the wing loads. This procedure should be quite easy on the upper surfaces, but difficult on the undersides of the wing, where I will have to work lying on my back with sanding grit falling in my face.
[January 28, 2009]
I took the flaps off the airplane in order to do the final laminations, attach the middle track fairings, etc. I won't get them back on until next week. Here is the middle flap track attachment. When the picture was taken the bolts were just slipped temporarily into place, but as of yesterday all of this is permanently assembled.
As I originally designed it, the upper and lower attachment fillings were a single piece; but I belatedly realized that in the event of the tension bolts at the bottom tearing out, the aileron pushrod would be jammed and the airplane would become uncontrollable -- which, indeed, it might be anyway if one flap went adrift. This attachment is at BL75.00, that is, 75 inches out from the airplane centerline; the flap extends from BL25.00 to BL140.00. The clevis-like object in the background is an idler supporting the aileron pushrod; there are a couple of these on each pushrod. They reduce the length of unsupported segments of the 3/4-inch diameter pushrod, which otherwise would not be able to take compressive loads without buckling. The 1/4-inch aluminum tube with the wire tied to it is the pitot line; the pitot head is located near the tip of the left wing.
[January 20, 2009]
Discedit frutex, ubi patriam ulterius lacerare non potest.
[January 17, 2009]
Here are the lower attachment fitting for the center flap tracks, ready to install. Photoshop provided the annual-report-style coloring; they are really just alodined aluminum, not nickel-plated unattainium. They are 3.5 inches wide; all the holes are 1/4-inch. They nest at the bottom of the flap cove, against the rear spar, with two bolts going through the spar into bathtub fittings inside the wing (which is an integral fuel tank), and four bolts threaded into the fittings through gusset plates embedded in the bottom skin. The skin sandwich is a little more than 1/4 inch thick, so the gusset and its bolts will disappear below the surface. The gusset is an elongated triangle, about six inches long, that will be bonded to the carbon-fiber inner skin of the sandwich along an internal rib.
A load of about 2,400 pounds (limit) is applied to the center lug by the fully-extended flap. It resolves itself into a 1,200-pound tensile component, which the gusset carries into the wing skin, and a 1,800-pound vertical component, reacted by a similar downward force from the upper fittings through a 1/4-inch-thick carbon-fiber reinforcing plate embedded in the rear spar. It is customary to apply a fitting factor of 2.0 for critical attachments like these (the standard factor of safety for most primary structure is 1.5), but these fittings are still more massive than is strictly necessary. It was necessary to provide sufficient material around the holes, and I wanted to be sure that the fittings would not distort to any significant degree under load.
I will install these on Monday and cut the shallow notches in the flap leading edges that will be required for clearance when the flaps are retracted.
[January 13, 2009]
Things are finally getting back to normal. I got the upper attachment fittings bolted and bonded into the wings yesterday. I hoped to get the bottom fittings ready to install today, but my mill vise seized up and I had to stop working to fix it. It was interesting to take it apart and see how it's made; there is a lot of inherited ingenuity hidden in these little everyday bits of mechanical engineering. The problem was a crushed ball in a thrust bearing; I removed the fragments and put the thing back together temporarily, while I locate a repacement bearing. I need to drill and tap four 1/4-28 holes in each fitting and make a tool that will enable me to locate the holes from underneath the wing when the fittings are in place. The next step will be to make the four links, two to a side, that go between the tracks and the bottom attachments. Once that is done, the remaining task, before the flaps can be used, is to add top and bottom surface gussets to distribute the center flap track forces into the wing skins. That sounds as if it should take a week, so it may be done by the end of February.
I have noticed, while taxiing with the flaps down, that they vibrate quite a bit, and I am somewhat concerned that they will produce a disconcerting clatter against the middle tracks, which are simply ramps designed to support an upward load only. The rollers may need to have tires. Tires -- that is, bits of hard rubber hose pushed onto an aluminum core -- might have another advantage, namely that of compensating for the misalignment between the rollers and the track surface. The track surface is parallel to the bottom of the wing, but the flap, because it is tapered, describes a sort of distorted cone as it extends, and so the roller as often as not rides on one edge of the track or the other rather than perfectly flush with its surface.
[December 27, 2008]
Having eaten and drunk sufficient over Christmas to make a little famine seem like a good thing, I finally got back to the airport yesterday and spent a couple of hours renewing my acquaintance with the airplane. I drilled the blind bolt holes in the bottom attachment for the left wing's center flap track, and, thanks to my generally virtuous life hitherto, they aligned properly with the ones in the wing.
I've been curious about whether I could begin testing the flaps at partial extension even before I get the surface gussets for the center tracks added. I ran a Cmarc analysis of the flaps in the takeoff position and found that the air load on each one is around 210 pounds, as opposed to about 360 pounds in the landing position. (The moment arm is also a couple of inches shorter.) It was interesting to see that with the flap in the takeoff position, at 1,200 in/sec (68 mph) the lift is 700 pounds greater than it would be at the same geometric angle of attack with flaps retracted; but only 420 pounds of this is applied to the flaps themselves. The rest is owing to increased circulation (that is, more upper-surface suction) caused by the flap, but acting on the wing.
[December 20, 2008]
My prediction (12/8) that I would finishing the various laminating tasks by the 19th was of course incorrect. They always are. The reason was partly that preparation for some of the tasks took longer than expected, and partly that Los Angeles has had a cold snap, at least by our standards, and between the early nightfall (the hangar has no lights to speak of) and the Arctic conditions (daytime temperatures in the low 50s) my working hours have been shortened and the cure cycle of epoxy has been lengthened. Unfortunately, I now won't get back to the airplane until the day after Christmas, because of various holiday activities. I spent most of yesterday's hangar time trying to determine where to drill the holes in the lower track attachment fittings to match, within a few thousandths of an inch, the existing holes in the rear spar. It's a matter of cutting and fitting without being able to see what you're doing, and of course you can't back-drill because the other side of the rear spar is the inside of a fuel tank.
[December 13, 2008]
My week of laminating began with splicing the tops and bottoms of the "canoe" fairings for the middle flap tracks. These are the same fairings as I used on the outboard tracks, and I had made up the half-shells some time ago. To join them, I fastened the top and bottom molds together, slipped the shells inside, and laid up a tape along the seam. This was a little tricky, since the tape is on the inside and I could barely get my hand in. I had to make a special vacuum bag that resembled a sock turned partially inside-out. The inner portion slid inside the shell; coaxing it into place provided a sensation similar, I imagine, to that of artificially inseminating a cow. Both fairings turned out nicely. Here one is before and after the splicing. In the picture on the right the two halves of the mold are lying beside the fairing; if you squint, the upper half looks like a spent Jovian thunderbolt or, as we call them today, a belemnite guard.
This will be the end result:
Next week I'll bond these fairings to the flaps, align the nose fairings and provide them with attachment flanges, and notch the leading edges of the flaps to clear the lower attachment fittings.
[December 8, 2008]
Yesterday I flew up to Palo Alto to attend a lecture on electric airplanes by Morton Grosser, a onetime associate of Paul MacCready. Leaving LA I encountered headwinds of 40 knots, and then found the San Joaquin Valley completely socked in with dense fog. I dropped down to 6,500 feet and bent my course westward in order to stay in sight of land while performing thought-experiments about how best to make a dead-stick landing in zero-zero conditions. The headwind slackened progressively as I flew northward, and I got to PAO in 2.1 hours. I was surprised to see at least two TwinStars parked there; maybe the airplane is a fave with Silicon Valley types. I like the airport, but I wish they'd put up a few more signs to help you get back to it. There's nothing on the 101, which goes right past it, to tell you it's there, and even if you know to take the Embarcadero/Oregon Expressway exit there's still no sign on the off ramp to tell you which branch to choose. And even if you manage to stumble on the one well-hidden sign in which the city has seen fit to invest, there are no further signs to help you get your bearings as you get closer to the airport. It's really ridiculous for a place that presumably attracts a certain number of out-of-towners.
I made the return trip in two segments, stopping for a few hours at Paso Robles. I observed 139 kias at 8.4 gph on the first leg, and the same indicated airspeed at 8.9 on the second. Both were at 11,500 feet, but the MP/RPM settings were a little different. Even the 8.4 reading fell short of what should be possible if my F is what I said it is a while ago -- 2.25 sq. ft; that's more like 2.4. There are various possible explanations, including instrument error, mixture setting (since fuel flow is a surrogate for power), and added drag from somethng like a sagging gear door. Since I have so much else to deal with now, I guess I won't find out the answer for a while. The wind had kicked up when I got back to Whiteman, and it was blowing 18 knots at 70 degrees to the runway. The tower instructed me to make left traffic for 30 -- an unusual maneuver -- so that I would be flying my base leg with a headwind rather than a tailwind. A good idea; I'd never thought of it. The approach was bumpy with lots of crab angle, but the landing was smooth -- demonstrating once again that greasers are chance events.
Last Friday I added air to the nosewheel strut, as I do every winter when the temperaures drop. I felt today that the strut was too full, but I noticed that the airplane seemed to track better during takeoff and landing. I don't understand why that would be, but I noticed how much of the nose strut of a Bonanza is exposed, and wondered whether I have been wrong to keep mine with only a couple of inches of piston showing.
[December 3, 2008]
Then along came Thanksgiving, with its interruption, sometime welcome and sometimes not, of the routine of airplane work. During the few hours that I spent at the hangar between then and now, I made another brief dip into the slough of stupidity, inadvertently installing (temporarily) the upper flap attachment brackets and then, observing the misalignment of several degrees in the resulting track position, shaved some material off the bottom of the corresponding lower bracket to match the error in the upper ones. It seemed incredible to me at the time that my extremely careful measurements had yielded such a grossly faulty result, but there it was. Or rather, as I finally discovered, there it wasn't, because once I had installed the correct fittings it turned out that the angles were nearly perfect, and now I had to re-machine the lower bracket to correct my first correction. Fortunately, small amounts of material were involved, and the part, which is still only roughly shaped, remains perfectly usable.
Before I begin actually installing the tracks, I have to do several laminations involving the fairings or "canoes" that will cover the tracks. Trying to be realistic about time for once, I wrote up a schedule, and found that these small operations, which don't sound like much work at all, will probably take seven days. I'm currently staying with friends in the mountains near Fresno, and am going up to Palo Alto next Monday and to Paso Robles on Tuesday; so I probably won't get the laminations done until around the 19th. Just in time for the next Holiday Hiatus. But I suppose there is still a fair chance that I will get the brackets and tracks (but not the surface gussets, which were really the point of this whole exercise) installed by the first of the year. I could then begin flight testing the flaps through the first half or so of their travel.
[November 25, 2008]
This seems to be the stupid season. It finally dawned on me a couple of days ago that the design of the bottom flap attachment fitting would be much simplified if I cut a notch into the leading edge of the flap rather than distort the fitting so as to preserve the flap profile. For a long time I have been thinking about this fitting and how best to make it, without its ever dawning on me that since this portion of the flap is inside a fairing anyway, it's not going to produce any lift to speak of and so the shape of its leading edge is of no consequence. I have now made all of the upper fittings, am nearly done with the first of the two lower ones, and have partially made one flap track. On the other hand, I haven't flown in a month. There must be something wrong with my priorities.
[November 16, 2008]
After cutting away some chunks of glass and foam, I was able to get at the fittings that I had stupidly buried, and to sponge up quite a lot of hydraulic fluid that had pooled in the dead space between the rear spar and the bottom skin. It appears -- I'm not absolutely certain yet -- that the leak was in fact in the line that I first suspected, showing that one can sometimes jump to a conclusion with no evidence and still be right. Good news for prosecutors. I was never able to figure out why the line leaked -- it continued to leak even after I tightened all the fittings mercilessly -- and so I made a new piece of line and used a different flare fitting, and the problem seemed to go away. I now have the upper track attachments fitted to both the left and right wings, and will start on the lower attachments next week.
[November 11, 2008]
I've noticed lately that the hydraulic system seemed to be losing fluid. Since I didn't see any big pools of the stuff on the floor -- either the airplane's or the hangar's -- I speculated that some interaction between the flaps, landing gear, and airbrake, all of which are hydraulically operated, was causing fluid to be dumped overboard from the reservoir. Yesterday, however, I found a pretty big pool of fluid on the left front corner of the airplane floor under the back seats. I put folded paper towels under the nearby connections, expecting to find the leak that way. Today there was no fluid on the towels but a new puddle in the corner. I then realized that the fluid was coming from a closed-off dead space between the bottom of the rear wing spar and the inside of the fuselage bottom skin sandwich. Six hydraulic lines related to the flaps pass through this cavity. Unfortunately -- this was very stupid -- there are connections inside the cavity, but the places where the lines enter and leave the cavity are potted with epoxy -- not so completely potted, however, that fluid could not find a way to leak out. Evidently, at least one connection was not tight. At first I jumped to the conclusion that the line nearest the leak was the responsible one, and I dug it out. I then discovered that there was quite a lot of hydraulic fluid inside the cavity, and I left it to drain overnight. As I was driving home I realized that there was no reason to think that the line alongside which the fluid was escaping from the cavity was the leaky one; it could have been any of the six, and the fluid could be flowing from one side of the airplane to the other before leaking out. The reason I had ill-advisedly potted all these connections into place was to isolate the wheel wells from the cabin; now I think I will have to open up a tunnel on each side so that the lines are accessible, and just pack it with Play-Doh or something to keep the wind from blowing in.
In the meantime, I've been fitting the middle flap track attachments to the left wing. This is fairly tricky, since the top fittings go into a very small and cluttered space, and they need to be drilled to match existing holes that I can't get at. So far, I've had pretty good luck. The underside of the track also needs to match the trajectory of the roller. I'm using a dummy track -- just the front end of a track -- to locate the front limit of the roller travel. Here's the dummy track in place in the left wing's flap cove, seen from below and above:
The tube is the aileron pushrod; it is supported by an idler every four feet. The two lines running under the top skin go to the outboard actuator; the lower line is for the pitot tube, which is located at the left wingtip. The clecos will be replaced by 1/4" bolts, and a gusset will spread compressive loads into the inner skin of the sandwich. Only the inner surface of the sandwich is stressed; it is made of carbon, while the outer skin is glass.
Here is the same dummy track lying on a drawing of the complete track. The track is not a slot; it is a ramp, and a single roller on the top of the flap travels along it.
I had a mechanical drawing class in high school, but I seem to have forgotten everything I learned about neatness and clarity. My drawings are all palimpsests -- masses of erasures, pentimenti, multiple views and even different objects occupying the same space on the page.
[November 7, 2008]
In the past couple of weeks I've received innumerable emails concerning the YouTube video that seems to show an exhibition acrobatic airplane losing its right wing in the course of a vertical snap roll, recovering in knife-edge flight, and rolling level just in time to land safely. Non-pilots, who in this case proved more sensible than their license-toting counterparts, generally wrote to ask whether this were really possible. Amazingly, however, a lot of pilots and engineers who should have known better accepted it as the real thing, even though it's pretty obvious -- particularly when the airplane touches down, bounces once, and immediately stops, just like a model -- that it's not. It seems that the tape is actually a clever piece of viral advertising for a clothing line. I'm not sure how you get to the clothing pitch; it must have something to do with an interview with the pilot to which you're supposed to find your way. Anyway, as far as the plausibility is concerned, and apart from the visibly inappropriate dynamics of the landing, I don't believe that any full-size airplane is sufficiently light and powerful to climb vertically on propeller thrust alone, as we see the airplane doing; and a vertical snap roll is a relatively low-stress maneuver that would not be likely to break a competition acrobatic airplane. In fact, it would probably not even bend a Cessna.
I spent the week making aluminum fittings for attaching the middle flap tracks to the wings.
[November 5, 2008]
The oranges are juicier today, the juice sweeter. Ex africa semper aliquid novi.
[November 4, 2008]
I mocked up the left middle flap track, using miscellaneous bits and pieces that I made years ago and then decided to discard. Surprisingly, it all fits together pretty well, although I had to re-route the pitot line around the flap attachment. I machined a sample upper attachment fitting out of maple; today I'll buy some 2024 plate and some new bandsaw blades and start making the real pieces.
First, however, to vote.
[October 22, 2008]
I did a short flight to test the behavior of the trim tab link, whose effect is to double the trim tab area. Nothing surprising. The trim authority at low speed was certainly not doubled, but I think that is because what limits it is not tab area but rather separation, and once the flow on the tab separates it doesn't matter that much whether you have one or two of them. This may turn out to be a problem when the flaps are down, but then again they may increase the downwash angle at the tail sufficiently to limit the amount of trim they require. I didn't test the nose-down trim authority with aft CG, but since that involves high speeds and small tab deflections, there is no separation issue and I'm pretty sure there will be no difficulty.
On the time-honored principle that one should always have two projects going at the same time, I am going to begin work on moving the aileron hinge lines aft to increase their aerodynamic balance and reduce the stick forces in roll, which have always been too high. I have hesitated over this project for a long time because of uncertainty about how best to contour the overhung nose of the aileron. An elliptical, well-streamlined nose makes a larger gap; the gap can be narrowed by making the nose of the aileron more blunt, but that leads to separation at large deflections, reducing the aileron authority. Hoerner reports a 20% increase in section drag due to an aileron slot; applied to 20 square feet of wing area, this represents an equivalent flat plate increment of 0.04 sq. ft. At 60% power, that represents .07 gph, or, at current prices, less than 40 cents an hour, so maybe I shouldn't be concerned. Hoerner does show that the drag increment can be almost entirely eliminated by thinning the airfoil section by 15% just ahead of the aileron. I could do that. There is also the option, seen on may sailplanes, of plastic gap seals that slide on the aileron surface like wipers and flex as the aileron nose rises above the wing surface -- another possibility.
[October 17, 2008]
The flaps now operate so routinely that the process of forgetting the past four weeks of fiddling with them is well underway.
I mentioned on October 10 that I was going to shorten the actuators, but a reader, Ken Phillips (of Cincinnati, I believe), suggested that it might be simpler and less pontincendiary just to add aluminum spacers sliding on the piston shafts to limit the actuator travel. I did so. The left cylinder now reaches its full extension just as the flap reaches its full retraction -- the inboard actuators are installed shaft-forward, so that they extend to retract the flap -- but the right one still wants to go a little too far. I'm going to shorten both piston shafts just a little, by 1/4 inch or less, so that the rod ends that screw into them are not bottomed. That way I'll have some adjustment available in case things move around with use, as they have a mysterious way of doing.
This matter of the travel limits of the inboard actuators involves two variables, the actuator travel and the location of the actuator anchor point on the airframe, relative to the retracted position of the flap. If I had planned things a little better I might not have had any problems, but one of the bad things about composite structures is that you can't drill out rivets or remove bolts and reposition anchor points. Once an anchor is drilled and bonded, there it is. It happens that I unwittingly placed my anchors in such a way that only by restricting the actuator travel to precisely the required amount, with the rod ends screwed all the way into the shafts, could I avoid applying hydraulic pressure to the stopped flap, with undesirable effect (see September 27 below). But then no further adjustment was available. No harm will be done by shortening the shafts a little, however, and that will allow fine-tuning of the retracted flap position.
To celebrate the apparent capitulation of the flap hydraulics, I started working on the linkage joining the two trim tabs, a simple job that I hoped to finish today, but didn't.
[October 13, 2008]
A visitor asked that I post a schematic of the flap hydraulics.
This sketch is simplified; it shows only one master/slave circuit, whereas there are four, and the single walking beam shown is really a bellcrank with five arms, four for the master cylinders and one for the "driver." See January 17, 2008 and January 8, 2005.
The only part that may be a little difficult to grasp is the equalizing function which is indicated in the detail on the left. A very small passage in the wall of the master cylinder allows fluid to pass from the pressure to the vent side when the piston is up against the flaps-retracted stop. As soon as the piston moves slightly (1-2 mm) on the extension cycle, this passage is blocked by the O-ring. The purpose of the passage is to allow the flap to retract fully even if some of the captive fluid has leaked out of the lines between the master cylinders and the flap actuators. The purpose of the single-acting "driver" cylinder is to drive the walking beam and the attached master cylinders to their limits.
[October 10, 2008]
The flaps seem to be working now without any significant leaks, but there is still a problem with the length of the inboard actuators. The best solution I see, since it is not practical to move the points where the actuators are attached to the fuselage, is to reduce the length of both cylinders by about 0.6 inch in order to ensure that they reach their end stops before the flaps do, or at least no later. (This was the cause of the bent shaft I described on September 27. I thought I had fixed the problem, but I was wrong.) I should be able to get that taken care of on Monday. The one synchronizer cylinder that was leaking is now sealed. A small scar from the lathe chuck happened to fall right under an O-ring; it was easily removed with emery paper.
It will be a relief to work, for a change, on some system that does not involve hydraulic fluid.
My statement in the previous entry that all-flying tails automatically compensate for changes in the wing downwash angle was false. I was not thinking clearly when I wrote that. It must be that the immediate, transitory pitching effect of a flap is mainly influenced by the position of the horizontal tail with respect to the wing wake. The long-term effect of putting flaps down, however, is always a more nose-down pitch attitude, if speed is unchanged.
[October 5, 2008]
A longtime correspondent, Dan Fritz, challenged my opinion that deploying flaps would make the airplane pitch down. After reflecting on it, I think he's right: more likely, it will pitch up. What had made me think it would pitch down was my experience with Melmoth 1, and also with my friend Russ Hardwick's Cherokee Arrow, which I flew quite a bit while I was between Melmoths. But both of those airplanes had stabilators, which automatically compensate <<Author's note: This statement is incorrect; see above.>> for the change in effective decalage (the difference in incidence between the wing and the horizontal tail) that the flaps produce. Melmoth 2 has a fixed stabilizer, and it will almost certainly respond to a change in decalage by initially pitching up. Of course, to maintain speed it will ultimately have to settle into a new attitude with the nose lower than before; but it will be necessary to add nose-down trim to get it there.
I spent several hours today wrestling with leaks in both ends of the left outboard flap actuator. It was looking pretty good when I left the hangar, but I'm still not certain that it's fixed.
[October 3, 2008]
I believe that the struggle between me and the flap hydraulics is finally tilting in my favor. The right flap now behaves properly, and the inboard end of the left one keeps pace with it. The outboard end of the left flap is not cooperating, but it has an evident leak, and I have come to suspect that leaks, not trapped air bubbles, were responsible for the initially crazy behavior of the system. I have been gradually eliminating minor leaks all week, and it was after I fixed a pretty significant one -- due to a damaged O-ring -- in the right inboard actuator that the right flap suddenly began working properly. I suspect that fixing the drip in the left outboard actuator will have a similar effect there. Surprisingly, the only cylinder that was completely leak-free from the outset was the one whose shaft got bent and had to be straightened. No doubt there is a moral in that, somewhere.
By luck -- I did not have much leeway in the sizing of the actuating cylinders -- the flap speed appears to be about what you'd want: not exasperatingly slow, but slow enough to allow the pilot to make trim adjustments and to stop the flap if something asymmetrical begins to happen. I am curious to see how the flaps and the airbrake interact -- operationally, that is, not aerodynamically. The airbrake produces a strong pitch up, whereas I believe that the flaps will cause the airplane to pitch down. I imagine that the landing sequence will be to open the airbrake in order to slow the airplane to gear speed (100 knots), then lower the gear, then extend the flap to the takeoff setting, which involves about 10 inches of aft travel and a wing area increase of about 16 square feet, but almost no angular deflection of the flap. Landing flap -- 30 degrees deflection -- would be used only for the final portion of the approach. I hope for a reduction in approach speed (at, say, 2,000 pounds) from 85 to 75 knots. It will be some time before the flaps can be used in flight, however, because I still have to make and install the center flap tracks, which will bear about half of the total flap load.
[September 27, 2008]
This was an exciting week, at least on the scale of what goes on in my hangar. After cycling the synchronizer cylinders alone last week, I installed the actuator cylinders and plumbed them. The inboard ones, which are inside the fuselage and readily accessible, were easy, but the outboard ones are crammed into a small cove in the trailing edge of the wing along with a lot of other stuff like aileron actuators, and I had to learn a particular installation sequence in order to get them in at all. Here's what the little cove looks like with the cylinders and their plumbing in place; for scale, the piston (the slender steel cylinder at right) is 3/8" in diameter.
The pushrod running across the upper half of the picture is 3/4" in diameter and actuates the left aileron. The curvy aluminum thing at right is the outboard flap track. The coiled up wires near the center of the picture are for the outboard fuel quantity indicator, which is not yet in service. The flap actuating cylinder is mounted in a yoke; the cylinder itself is not clearly visible, but it resides in a tunnel in the fuel tank.
With the actuator in place, I more or less charged the lines between the synchronizer cylinders and the actuator with fluid, and tried running the system. The first thing I found out was that I had crossed the lines going to the right outboard actuator, and it was trying to retract the flap while the other three actuators were extending. I fixed that. The flap then operated, albeit haltingly and unevenly, an indication that I had not successfully bled the system. Then disaster struck. After fully retracting the flap, I discovered that the piston shaft of the left inboard actuator was bent like a pretzel. Well, maybe not a pretzel, but at least some non-straight thing. Viz, after removal:
It didn't take long to understand what had happened. Either I once figured this out and then forgot about it, or I never figured it out at all, but the inboard actuators, which are extremely long and slender and are installed backwards, so that they pull the flap down and push it up, have to be adjusted so that they reach their internal stop before the flap reaches its up stop; otherwise the full system pressure is applied to the extremely skinny actuator, and it buckles. At first I wasn't sure I would even be able to get the actuator out of the plane, because they have to be at least partially retracted in order to be removed; but I was able to partially retract the piston despite its elegant hyperbolic arc, and it did come out fairly easily. More surprisingly, I was also able to straighten the piston. My time ran out on Friday before I had a chance to test it again; maybe on Monday I will finally emerge from these woods. Then I can start cleaning up; the airplane and hangar are littered with hydraulic-fluid-soaked paper towels, and look like one of those scenes in ER when the patient is bleeding out.
[September 19, 2008]
Today marked some sort of milestone. I began to bleed the flap hydraulics by running fluid through them from the pump. In order to do this I first re-plumbed the system, bypassing the flap actuator lines, so that the synchronizer module was connected directly to the hydraulic pumpand reservoir. At first nothing happened. Then I became aware that because the lines were more or less empty, the pump was sending fluid from the reservoir to the synchronizers, but returning mostly air to the reservoir. I kept replenishing the reservoir, and gradually got more and more action out of the synchronizers. I also began to discover leaks, however -- that was expected -- and so I didn't completed the bleeding; I'll continue with it on Monday.
Like the gear and airbrake circuits, the flap circuit uses a two-way valve with a closed center. To actuate any of these services, you hold the handle up or down until the action is completed, and then return it to the center. The hydraulic pump runs whenever the handle is not in the center detent. (Actually, there is one exception: the motor does not run when the airbrake handle is moved to the "retract" position; springs retract the brake.) Closed-center valves are necessary because open-center valves would let hydraulic fluid flow freely throughout the system, and no pressure would ever develop. But they are also necessary to hold the flaps and airbrake in any extended position. The landing gear has overcenter up and down locks, but the closed-center valve, which traps fluid in the lines, also provides a backup to the downlocks which proved useful on one occasion (January 28, 2005). I have become aware, however, that hydraulic fluid expands considerably when heated -- 3% increase in volume between 60 and 140 deg F -- and that when the flaps are finally working I should not park in the sun for long periods with the flap fully extended. It is only when the flaps are extended that there is no way for the system to take up the expansion due to heating.
[September 17, 2008]
For the first time, I changed the oil wthout getting the engine hot first. The reason for hot oil changes is, I suppose, to thin the oil and speed its draining. Instead, I removed the plug on Friday and let the engine drain over the weekend. I suppose that one could argue that since running the engine before an oil change gets a lot of the oil up into the passages in the engine, from which it takes a while to drain down, and also spreads it over the engine's internal surfaces, a cold oil change has the advantage of having already allowed some of the oil "up in the engine" to find its way back to the sump. In any case, it was the cleanest oil change I've ever done, because it was so easy to remove the plug without having to avoid all that hot metal. I didn't spill a drop.
After examining the cabin air inlets, I'm puzzled about how water got into the back seat area. I don't see how it could have gotten in through the air inlet, but I can't see any other source for it either. The front is a different story; it's obvious that water could come in there, and would immediately leak down to the floor. I need, at the very least, to make a plug for that inlet. I pulled the rear seat carpets, which had had baggage piled on them for days while they were wet, and laundered them. Most of the mildew smell went away. I was disappointed to find, however, that the Velcro that held the carpet in place had a much greater affinity for itself than for either the floor or the carpet. I need to find a really bulletproof adhesive to stick the Velcro to the floor, and should probably get an upholstery shop to sew the other half of the Velcro to the carpets.
I hope now, with no more travel planned for the forseeable future, to finally get the flaps working.
[September 12, 2008]
We got back yesterday at about noon after spending three days -- parts of four days, actually -- crossing the country. The unexpectedly long return included many hours spent in FBOs' lounges waiting for clouds to lift. I had promised Nancy that we would conduct this entire trip VFR -- several unnerving experiences in Melmoth 1 apparently made her phobic about IFR flying -- and this proved to be a troublesome commitment, although necessary, since without it she would not have consented to make the trip at all. I suppose this no-IFR rule is my belated punishment for the bold go/no go decisions of my youth. She finally did consent to what turned out to be a five-minute climb through clouds to VFR on top when confronted with the threat of being weathered in for four days in Bartlesville, Oklahoma.
I learned on this trip that there are some liberals in Indiana, and that inner America is a culinary disaster area. The plane performed well, with no mechanical problems and cruising speeds in the 160-170 kias range on an average of 8.4 gph. Despite the engine's habit of oozing oil from many pores, the result of its having been stored for 20 years while I built the plane, it actually consumed comparatively little oil -- a quart every ten hours or so. You don't fly a homebuilt for 37 hours without discovering some problem, however, and I discovered after a few downpours -- while the airplane was parked, not flying -- that rainwater gets into the cabin, apparently through the NACA inlets on the right side and the hinge line at the top of the baggage door. The carpets got soaked at Taunton, and we never had a chance to dry them out before piling tons of luggage on them. They now have a mildewy smell.
[August 27, 2008]
After we collected our daughter from Williamstown, where she had spent the summer as an acting apprentice at the theater festival, we had an unbelievable amount of baggage to contend with. It barely fit in Dave Noland's SUV -- crossover, actually -- and just about filled M2, behind the front seats, to eye level. The thing next to my right foot is a bathroom scale that I brought along from LA, anticipating something like this. Actually, the stuff added up to less than 250 pounds, so the weight was not a problem so much as the bulk. Lily remained in New York, so at least we didn't have to shoehorn her in along with everything else. We landed at Taunton, MA, an airport with the most paranoid and inconvenient security arrangements I've ever seen, and, apart from a sightseeing trip out along Cape Cod, M2 will remain there until we return to California in a couple of weeks.
I used to skydive at Taunton when I was in college, and once came within five seconds of augering in when I somehow failed to locate the D-ring on my ripcord. I landed off the airport in a clearing among trees in somebody's yard, feeling like one of those soldiers who hoped that the Normandy farmyard into which they descended did not belong to a flintlock-toting pétainiste.
[August 17, 2008]
Not surprisingly, we left later on Wednesday than we had planned. We stopped for the night at Gallup instead of somewhere in Kansas, flew to eastern Indiana the next day, and arrived at Orange County (Montgomery, NY) at noon on Friday. Block performance did not match the spot numbers observed during local flights. In theory the plane gets 21 nmpg at 170 knots. In theory, you pick up an average 10 knots or so eastbound from the prevailing wind. But throw in a wind that perversely blew much of the time from the northeast and convective activity that had us at 2,000 agl a lot of the time, and we averaged 145 knots and 17.4 npmg. But the midwest is quite a bit more interesting from 2,000 feet than from 12,000, and the time passed quickly. Used one quart of oil and something like 127 gallons of fuel. The only thing, besides the wind, that didn't work perfectly was my David Clark headset, which began soaking my neck with silicon breast-implant goo somewhere in Nebraska.
[August 11, 2008]
We're leaving Wednesday for the east coast, and so today I was giving the plane a once-over that included draining the sumps. This is something I seldom do, because in almost six years I have never found any water or anything else in them, and the quick-drains have tiny O-rings that drip when little bits of dirt get stuck under them. Sure enough, the left one started to drip after I drained the sump -- nothing in it, as usual. Normally I can get it to stop dripping by letting a rapid stream of fuel flow through it -- I collect the precious stuff in a jar and pour it back into the tank -- but this time that didn't work, and so I had to remove the drain assembly from the airplane to clean the O-ring. This is a difficult and messy job that inevitably includes spilling a pint or so of fuel on the ground by way of my armpits. Eventually I got the drain out, however, and cleaned it. In the duct above it I discovered a little mass of trapped tank scum. On close examination it proved to include quite a variety of mysterious substances and, tragically, the corpses of several ants. Viz:
[August 9, 2008]
I was at Santa Rosa, north of San Francisco, yesterday and Thursday, being a judge in a contest run by the CAFE foundation as a part of a multi-year NASA-sponsored effort to improve the technology of general aviation airplanes. NASA is offering substantial cash prizes for the achievement of various goals. The ultimate target is a PAV -- personal aerial vehicle -- that is quiet, efficient, and capable of largely autonomous flight, including automatic navigation and landing. Originally this year's field was to consist of five competitors, but only three ended up participating: a Slovenian-born Pipistrel Virus (34-foot span version), an Urban Air Lambada, and a Flight Design CT, both of the latter built in the Czech Republic. All three are two-seat LSAs with Rotax engines, although the Virus had forfeited its LSA status by installing a variable-pitch propeller. The Lambada is a motorglider with a long, complicated wing; the Virus and CT are polliwog-shaped high-wing designs. The Virus is the more gracile of the two. The Lambada is an old-fashioned airplane, well-behaved in flight and gadget-free. It has the most unmistakeable aerodynamic buffet prior to the stall that I have ever seen; the entire airplane shakes violently, and the engine jumps up and down visibly in its mounts. The Pipistrel is loaded with high-tech equipment, including various electronic displays and an autopilot with altitude hold. It has camber-changing flaps and sailplane-type airbrakes, and a correspondingly varied set of cockpit controls. The CT is most like a conventional small trainer, with the expected controls and round instruments in the expected places. In the picture below, the airplanes (not counting the deceased Douglas in the background) are, left to right, the CT, the Pipistrel, and the Lambada, whose outer wing panels have been removed. The Lambada, which was still involved in some inflight data collection when the photo was taken, is carrying two temporary CAFE pitot-static booms under its wings.
I found the CT to be the least pleasant of the three in flight. I was surprised, in fact, that an airplane with its handling qualities could even come to market. It is directionally unstable; if you floor a rudder pedal the ball goes over the the edge of the inclinometer and just stays there; if you roll without rudder the effect is the same. I thought those flying qualities went out with the Fokker Triplane. It was also much slower, both climbing and cruising, than the Virus, which achieved a top speed of 163 mph in last year's competition; the CT's owner blamed its lethargy on an unhappy choice of a propeller for this contest.
[Note added December 20, 2008. It has come to my attention that I was wrong to say that the CT is directionally unstable. It is stable, since when disturbed by a rudder or aileron pulse it comes to rest flying somewhat sideways, and does not diverge from that position. I should have said that its handling suffers from a lack of directional centering, or, more broadly, that of more than 200 types in my logbooks since 1961, it has some of the most unpleasant handlng qualities I have encountered, combined with entirely lackluster performance. This may not be true of all CTs, however; I gather that there have been some changes from the factory.]
I had a long conversation with Pipistrel's 24-year-old chief designer, who expounded some aerodynamic concepts I had never heard of. It struck me that in different cultures, different ideas are taken for granted, so that, for instance, all sorts of physical disorders are attributed in France to the liver, an organ that goes almost unnoticed in the US, except among drunks.
[August 2, 2008]
I completed the neutral-point hunt yesterday with a flight with 200 pounds of ballast, CG at 40%. The flight was unremarkable and the resulting data set fell nicely into line with previous ones. The stick-fixed NP is evidently at FS130, which is 60% of MAC, just as DWT said. I am setting the aft limit of the CG envelope at FS125, or 45% of MAC. I did discover that there is insufficient trim authority for fast cruise with aft CG. I am currently using only one of two trim tabs, and I expect that hooking up the other one will solve this problem.
[August 1, 2008]
On Tuesday I added another 50 pounds of ballast and did another stick force sweep, which confirmed the neutral point location finding from the first two. I plan to do one more today, with the CG at 40%. This is equivalent to four 170-pound occupants, 40 gallons of fuel and 50 pounds of baggage, and is the design aft limit. It provides a 7-inch static margin, which is pretty ample. In order to go farther aft, I would need to get more sand.
During Tuesday's flight the angle of attack indicator hung in the middle of the gauge. It turned out that the plastic face plate under the needle had cracked and sprung out sufficiently to interfere with the needle. I made a new face plate out of aluminum. It is somewhat crudely painted -- I never have the patience to do things like that well -- but it will serve. A remarkable thing was that when I called Safe Flight, the New York manufacturer of the device, to get some guidance about dismantling it, I talked with Joe Inserro, the same person I talked with when I first got the instrument 35 years ago.
[July 28, 2008]
I was looking through some old documents relating to the design of Melmoth 2 and I was surprised to find that some very early estimates of weight and drag were not too far from the truth. For example, a 1983 weight buildup arrived at an empty weight of 1,375 pounds. The actual weight at the first flight was 1,397. Since then quite a bit has been added, so I don't know how self-congratulatory I should be about the first estimate, but an undated, handwritten document that I think also dates from the 1980s has "Assuming We [ie empty weight] = 1600 lbs," which is not too far from the present value of 1,585. I also did a drag breakdown (handwritten, undated) that came up with an F of 2.5 square feet, which was almost exactly right if you made (as I did) the most pessimistic assumptions about laminar flow on the wings. The current estimate is about 2.3 sq ft.
A dot-matrix printout from an old longitudinal stability program I wrote puts the power-off neutral point at FS 124.11. That seems too far forward; Digital Wind Tunnel puts it at 129.97 or about .60 mac. Today I did a couple of flights to measure static longitudinal stability as a function of CG location. I first flew with a forward CG (113.43; .25 mac is 117.86, and mac is 35.26). I then loaded 100 pounds of sand (in bags) into the baggage compartment, which moved the CG to 118.40. (Actually, I added 10 gallons of fuel as well, but that has a relatively small effect on the CG location.) On both flights, I trimmed for 120 knots, then, without retrimming, accelerated to 160 and then slowed to 90, recording the stick forces required to maintain speeds at intervals of 10 or 20 knots. On the ground, I plotted the results and eyeballed a straight line through each series. Now, in principle I am measuring pounds of stick force per knot, but not having calibrated the Futek I'm just calling it millivolts (mV) per knot. The forward CG line has a slope of .27 mV/knot; the more aft one .19. I just about gasped when I extrapolated to the CG location at which the stick force slope would be zero, that is, the neutral point: 130.2. Given the many approximations involved in the test, that result is for all practical purposes identical to the one computed by Digital Wind Tunnel. It was interesting to see that although the airplane was obviously less stable with the ballast, it didn't feel subjectively worse; it still had good speed stability on final approach and felt normal throughout the speed range. Tomorrow I will add another 50 pounds and repeat the test.
[July 25, 2008]
I intended to make the first flight test with the stick force sensor, which I installed yesterday. But I got involved in plumbing the bubble catcher, and used up all my time on that. Here's the stick force thing:
I had to make the L-shaped adaptor between the bullet-shaped sensor, hereinafter "the Futek," and the sidestick mount. The red and blue wires coming out of it are for a press-to-talk switch. The two shielded conductors coming out of the Futek carry both the incoming excitation voltage, which I'm taking from the airplane's 12-volt bus (the airplane electrical system is 28 volt, but the Futek is limited to a maximum of 20 volts), and the output voltages, which are on the order of a few millivolts. One group is for the lateral axis, the other for the longitudinal. I tested it by lifting the weight of the elevator with the stick; it registered around 8 mv, and was quite well damped, so I think it should be possible to get good readings in flight. I have it hooked up to a $15 digital voltmeter that reads in increments of .1 mv, and I'm looking at the X axis, that is, pitch, only. Javier Arango, who will be the ultimate user of all this stuff, is ordering a data logger that will store continuous stick force information in two axes, as well as about ten other channels of data which we have yet to dream up (stick position would be an obvious candidate). Flight path and three-axis rate and acceleration information will be recorded by the Appareo gadget described on June 14.
Today's progress, such as it was, consisted of beginning to connect the lines between the synchronizer, the bubble catcher, and the hydraulic actuators for the flaps:
What you're seeing is the compartment beneath the back seats. The front of the airplane is to the left. The floor panels and the seats are supported by four carbon-fiber rails. Each aft-facing rear seat is located by several pins and locked down by a single bolt. The aluminum door in the middle of the floor will eventually have the oxygen outlets under it. The structure along the left side of the picture is the rear spar and main landing gear well; on the right edge are the tracks for the retractable boarding steps. About a third of the synchronizer plumbing is in place.
[July 17, 2008]
We got back from Cape Cod last night at midnight.
I flew a bit today, and thought a bit about what I need to do between now and a month from now when, if all goes according to plan, we will return to Cape Cod, this time in Melmoth 2. One big item is the leak in the right wing tank, which will require removing the wing. That's not a particularly difficult job, or at least it shouldn't be -- it's been on and off many times -- but I don't exactly look forward to doing it. It will pay some dividends, however, such as an opportunity to weigh a wing in its more or less completed form. That in turn will tell me the weight of the fuselage, and allow me to recalculate the actual factor of safety of the wings. It was 10 (ultimate) with two aboard when I designed the plane, but I underestimated the fuselage weight then. The reason for wanting to fix the wing tank leak now, rather than continue to let it go, is that it is located fairly high up in the tank and isn't a problem when there is less than 25 gallons (that is, 50 total) in it. That's fine for local flying, but for a cross-country trip I like to be able to carry 60 or 70 gallons (the total capacity is 142).
Another thing I want to get out of the way is the experimental determination of the neutral point. I described the procedure on June 14. Knowing the neutral point would help to determine the weight limit for rear seat passengers, among other things.
[June 18, 2008]
I finally got the bubble catchers assembled. Temperatures at the airport are forecast to be in the 97-109 range tomorrow and the next day, so I may not get this installed. Still in shock over the Lakers' total capitulation to the Celtics, I am going to Cape Cod to recuperate for three weeks -- plus my son is getting married there on July 12 -- and won't get the flaps moving on their own power until the latter part of July. Here's what the bubble machine looks like. Each tower is an inch in diameter and four inches tall.
[June 14, 2008]
As part of Javier Arango's project of collecting flight test data on his WWI airplanes, I ran some tests in my airplane with an Appareo GAU1000 flight data recorder which Javier had acquired. This is a little self-contained gadget about the size of a Rubik's cube. It costs $2,000, and performs what would have been considered miracles a decade or two ago, but are now merely routine digital tricks. Using GPS and solid-state gyros and accelerometers, it records location, speed, altitude, acceleration in three axes, pitch and roll rate, and so on. Display software allows you to replay your flight, a la Flight Simulator, but I find that aspect less interesting than the ability to measure a lot of variables like pitch attitude, roll rate, takeoff acceleration, and so on. One puzzling thing, however, is that the reported rates of climb are on the low side, not just in terms of my expectations but also in terms of the altitude changes and times recorded by the instrument itself. I suspect a programming error, but I have e-mailed the manufacturer to try to clear this up. The sevice samples its various parameters ten times a second, then smoothes and stores them at quarter-second intervals. Data can be downloded to Excel for futher manipulation. I expect to have a lot of fun with this (until Javier takes it back).
Another gadget Javier got, and which I am going to test first, is a stick force gauge. You can locate the neutral point with this thing by observing the stick force necessary to hold a speed 20 knots, say, below the trimmed speed, and then putting a couple of hundred pounds of sandbags in the baggage compartment and repeating the experiment. With an aft CG the stick force will be less, and a straight-line extrapolation through these two values to a stick force of zero gives you the CG location for zero longitudinal stability. Of course the thing that really matters is pilot comfort, and so the decision about how far forward of that point to put the aft limit of the CG range is a subjective one; but it will be interesting to compare the measured value with the one calculated by Digital Wind Tunnel. Likewise the phugoid period, which can be conveniently measured by the Appareo.
On Friday I picked up the bubble catchers from Flyte-Weld, and will start installing them on Monday, by which time I expect to have recovered from the depression and paralysis brought on by the collapse of the Lakers on Thursday.
[June 4, 2008]
Nancy and I went away for a week to stay with friends near Fort Bragg, on the Northern California coast. Their house overlooks the ocean and a rare (for the area) sandy beach, and we spent hours each day playing "beach boccie," which is a ballistic form of boccie ranging over both dry sand and smooth, wet -- but deceivingly undulant -- tidal flats. It was a lovely time, marred only by our having to drive ten hours each way because Los Angeles chose the day of our departure to undergo a freakish weather phenomenon preclusive of flight (at least for Nancy and me). It was interesting however, that the seats of my 12-year-old Geo Prizm were fidget-free for both long drives. I'm using those seats as models for my pilot's seat, but probably in vain because what matters is no doubt the depth and elasticity in a seat, not just its superficial shape, and those I cannot duplicate.
Today I finished making the parts for the bubble-catchers and took them down to Flyte-Weld, the welder near Burbank Airport whose work I was so pleased with a couple of years ago when I started this seemingly endless flap-actuation project. Chris Mogenson, the Hephaestos of this sooty forge, said he'd do the welding himself -- it's really a job shop whose welders do things by the hundreds, not four at a time -- but that it wouldn't be ready til late next week. I guess I need to find something else to occupy me in the meantime.
I've been having a hard time with the nylon tubing and fittings that I'm using. The description in the Aircraft Spruce catalog of how to assemble the stuff is pretty sketchy. To complicate matters, the 1/8-inch NPT threads on the nylon fittings are smaller than AN standard -- that is, they correspond to a portion of the tapered tap closer to its tip -- and they are really too small for a snug fit in holes that were tapped for AN pipe threads. Conversely, if you size a hole for the nylon fittings, you can't even start an AN fitting in it. I don't know whether an assembly lubricant should be used on the hose connections, or whether a thread sealing material, like teflon tape, or compound, like Tite-Seal, would be appropriate for the pipe threads. I have found nothing online. Of course, I'll figure it out eventually for myself, like most other things; but it's annoying to be so ignorant about such a commonplace product.
[May 20, 2008]
After trying to fill the synchronizer cylinders and lines without introducing any bubbles, I finally concluded that I need a bleeder in each of the four lines from the master cylinders to the actuators. Filling them is just too difficult and uncertain otherwise. These bleeders are actually air traps: vertical cylinders about 4 inches tall with a pressure-tight cap on the top. They're something like an inverted gascolator. Fluid enters and leaves at the bottom, but remains in the cylinder long enough for bubbles to collect at the top. I had one of these in Melmoth 1 and it worked fine. But this will delay the operation of the flaps for another couple of weeks, because I'm going to be away the week of May 23-30. Actually, even when the flap are operating they won't be working, because until I add the middle tracks they can't be used in flight.
[May 10, 2008]
The electrical connections for the flap are done. They were very simple, but some head-scratching was required to figure out how the flap and airbrake were wired, since I did not have a wiring dirgram for them. (Much of the plane has been built impromptu, without drawings, and although I always tell myself how important it is to document everything, I seldom get around to doing so.) I spent a while trying to puzzle out whether I had the flap valve rotating the right way; there was a 50-50 chance that I had it backward, and that the flap would go up when the handle went down. That would be easy to correct by simply swapping the cables at their connection points, but as far as I can tell from comparing the flap valve to the gear valve, I happened to get it right the first time.
I have worried quite a bit about the difficulty of bleeding the lines between the synchronizer and the flap actuators, but it occurred to me this morning that it is actually easy to purge air from the cylinders themselves, and the only bubbles that would be likely to be present would be in the lines. Since the internal cross-section of the smallest cylinder is some 30 times larger than that of the line, and since air does not compress to zero volume, even a four-inch-long void in a line would produce a shift of less than 1/8 of an inch in the position of the flap.
[May 7, 2008]
I had my first hydraulic flood today. The first of many, I'm sure. I was installing the flap actuating handle, and in the course of setting it up I cycled the flap control valve several times. The hydraulic pump wasn't running, but fluid ran from the reservoir to an open connection under the back seats, where the synchronizer is. By the time I noticed what had happened, the reservoir was practically empty, but the well under the seats wasn't.
The flap handle is now in place and working, except for the electrical connection, which I will do tomorrow. Like the gear and airbrake handles, the flap handle rotates a pulley which drives a two-way, center-closed valve, located under the passenger's seat, by means of a cable loop and a second pulley on the valve stem. The cable, which is about eight feet long, runs through flexible conduits. Those for the gear and airbrake are teflon-lined bicycle-brake cable housings; for the flaps I tried 3/16" nylon tubing, which is lighter and seems to work equally well. On the handle there is a cam that actuates the hydraulic pump by means of a single microswitch. The normal position of the handle is centered; to raise or lower the flaps, gear or brake you move the appropriate handle in the appropriate direction and hold it until the action is completed -- a matter of four or five seconds for the landing gear. You then return the handle to the central, valve-closed position. The hydraulic pump runs whenever the handle is out of center. I used this system because the more conventional one in Melmoth 1, which was also hydraulic but with electric rather than manual control, required a bunch of solenoid valves and microswitches and and quite a lot of plumbing and wiring. This one has no solenoid valves, three microswitches, and little plumbing or wiring.
The pictures below give some idea of how the system looks. The first one, below left, shows the flap handle mechanism not yet installed. The pulley, handle, and microswitch are visible, as are the cable, its nylon housings, and the barrel-and-set screw thing that keeps the cable from slipping on the pulley. The next picture shows the handle in place in the panel; the NACA 4415-shaped grip is removable so that the handle can pass through the slot. When it is in its center, neutral position, the handle rests in a detent. The handle, which slides in and out about 1/4-inch with respect to the pulley, is spring-loaded forward and must be pulled slightly aft to clear the detent before being raised or lowered.
The last picture shows the other end of the cable loop. This is the hydraulic jungle under the right front seat (it is also visible, viewed from below, in the entry for January 31, 2007). The gray thing, lower left, is the hydraulic pump, which came from a T-33. The flap valve is the thing with the large, thin hexagonal nut holding it to a green aluminum mount. The cable and its barrel lock are just visible to the left of the check valve with the stamped assembly date of 1966. I hope I can remain functional for as long.
[April 30, 2008]
Last week I got 15 feet of high pressure nylon tubing from Aircraft Spruce, but it turned out that I needed 16 feet. While waiting for the additional tubing to arrive, I took the partially-built flap handle out of the panel in order to complete it. The first problem was to figure out what I had had in mind when I made it, some time back in the 1980s. It gradually became apparent that there was supposed to be a limit sensor that would shut off the hydraulic pump when the flap was fully retracted. This is a feature that the other hydraulic services on the airplane -- landing gear retraction and air brake -- do not have. You just hold the handle in the up or down position until the cycle is complete -- you can tell by a change in the sound of the hydraulic pump -- and then restore it to its neutral center position. When I originally built this thing I didn't anticipate the self-bleeding feature of the hydraulic synchronizer, which requires that the pump continue to run briefly even after the flaps reach their fully retracted position. So I discarded some ingenious-looking little levers and springs and was able to carve away some portions of the handle structure -- saving, I'm sure, a number of grams -- and added a cam and microswitch to turn the motor on at any time the flap handle is not in the neutral position.
During periods of mental idleness I've been trying to figure out how best to fill all the flap-related lines and cylinders with hydraulic fluid without admitting too many bubbles and also without making a huge mess. It's not going to be easy.
[April 16, 2008]
Having fixed the leaky cylinder -- a pipe-thread problem, as usual, solvable with Tite-Seal -- and hooked up the correct end of one actuating cylinder to a master, I confirmed that the travel ratio was precisely what I had calculated that it should be -- not surprisingly, the value of pi having been known with sufficient precision since at least the time of Archimedes. Next, I had to make internal stops to limit the travel of the master cylinders. I machined these today, and the cylinder travels are now within .003 or less of the intended values. So far, so good. Tomorrow I will epoxy the stops into the cylinders, reassemble them once and for all, and install them in the frame.
I had occasion to look at some old photographs of tuft tests of Melmoth 1's double-slotted flap. The quality of the flow attachment was astonishingly good. Here is a shot, taken some time in the 1970's with a camera mounted on the tail, just as I was about to touch down -- in other words, at close to the maximum lift coefficient.
[April 14, 2008]
Today for the first time I connected one of the master cylinders to some of the flap actuation cylinders (the purpose of the master-slave arrangement is to synchronize the four actuating cylinders). Hydraulic fluid is messy at first, like a baby. I found that one actuator cylinder leaked; I sprayed fluid all over the place when a hose connection that I hadn't sufficiently tightened popped off; and I attached the wrong side of the inboard actuator to the master cylinder -- I didn't realize this til I was driving home -- and so the travel measurements I took didn't mean anything. Tomorrow I'll repeat today's experiments, I hope with better results and less splatter.
[March 31, 2008]
I have been derelict. Our son and his fiancee visited from New York, Easter came and went, and there were various household and work duties to discharge -- in short, I have not progressed much. But I have at least installed a good deal of the under-floor plumbing for the flaps. For the first couple of days that I worked on that, I made no progress at all; mostly I just sat in the back of the plane staring at the empty space, shifting the synchronizer and the not-yet-installed oxygen bottle around to see how they would best fit, and trying to decide how to route tubing and locate connections so as to ensure accessibility and minimize the number of expensive fittings needed. It's somewhat like a jigsaw puzzle -- slow at first, but gradually gaining speed as more and more pieces fall into place.
Yesterday I had an e-mail exchange with George Braly of GAMI (the manufacturer of, among other things, injectors whose orifice diameters are tuned to each cylinder in order to ensure even mixture distribution) about the specific fuel consumption of my engine. The question arose because I was asked to repeat some of the windmilling glide tests I did a while ago and wrote about in Flying, and in order to draw conclusions from these tests it is necessary to know two basic parameters that govern the drag of the airplane. One is CDo, the parasite drag coefficient, and the other is e, the span efficiency factor, which is a correction applied to the geometric aspect ratio in calculating induced drag. I obtain e, which is 0.86, from computer analysis using Cmarc; CDo, which is harder to ascertain, comes from comparing measured performance with calculated performance. Performance calculations involve two semi-unknowns, propeller efficiency and specific fuel consumption. My performance calculation program, in Loftsman, uses mathematical models to approximate these parameters, which vary with speed, power, and various other conditions. I had obtained performance charts for my Hartzell propeller which indicated that its efficiency was higher than I thought -- I had assumed a peak of .86, but Hartzell claimed .89 -- and the question now was whether I could pin down sfc with equal precision (and credibility). The program was saying .44 to .45 lb/hp-hr at 55% power, and Braly thought that .44 was a plausible number. But in the course of the discussion he mentioned that the EGT at which best sfc is achieved gets closer to peak as power diminishes. In other words, one should run 75 degrees Fahrenheit LOP (that is, on the lean side of peak EGT) at 70 or 75% of power, but only 25 LOP at 55%. This was interesting to learn, though the actual impact of the information on fuel consumption is probably very slight. Braly also alluded to the well-known general principle that best efficiency is achieved at the lowest rpm and highest manifold pressure consistent with engine limitations; but the applicability of that rule is influenced by the propeller, which may become less efficient, not more, at a given true airspeed, as rpm drops. The loss of prop efficiency with diminishing rpm is very gradual, however, and so it may not really be a significant factor at all.
Unfortunately, the more optimistic view of the efficiency of the propeller, while in no way affecting the performance of the airplane, has obliged me to revise my estimate of its CDo from 0.0214 to 0.0222. How humiliating!
[March 11, 2008]
I finished riveting the flap synchronizer frames today -- my rivet gun couldn't manage the 3/16-inch AD rivets, but my 12-ton hydraulic press upset them nicely -- and was able to mock the thing up to better visualize the plumbing. It looks kind of cool, if you don't realize how stupid it is.
[March 9, 2008]
Although I can't operate my flaps yet, I can analyze them with CFD. Here are a couple of images of streamlines that I found very interesting. The first view, from above, shows the large amount of spanwise flow associated with the deflected flap, and particularly the vorticity generated at the flap root. The second view -- same streamlines -- is just to clarify the relationships in the first. Streamline colors correspond to pressure, and therefore inversely to velocity, with the red end of the spectrum being low pressure/high velocity, green neutral, and blue high pressure/low velocity. The green color of the model is arbitrary.
[March 7, 2008]
In the last three days I've flown twice to Mojave to look in on Ray Henning and his T-18, and once to Apple Valley to touch bases with John Roncz. Roncz had unexpectedly gone to Tehachapi, so I missed him, but the air was very smooth and so I was able to perform the test of cooling drag described on February 16. At 8,500 feet and my customary cruising fuel flow of 8 gph, which is about 55% power, opening the cowl flaps seemed to reduce indicated airspeed from 139 knots to 137. The two-knot difference corresponds to 0.1 sq. ft. of equivalent flat plate area, or about 5% of the total parasite drag.
I chased the T-18 for a while yesterday while Mike Melvill and Ray flew in the T-18. It climbs very well -- 1,500 fpm up to 8,000 feet at Mojave (field elevation 2,538) -- and the airspeed indicator matched mine, which is accurate, perfectly. Ray had earlier mentioned a high cruise of 168 mph indicated at 10,000 feet, which works out to over 200 mph. And he has not yet put the wheel pants on. He has the odd-looking Thorp pants, which cover only the inner half of the wheel; the stock joke about them is that they only slow the airplane down a little. Here's how it looked through my optically imperfect rear window; the dry lake is on Edwards AFB, and the snow-covered peak is 10,000-foot Mt. Baldy in the San Gabriels:
I'm getting close to assembling the flap synchronizer frames. They involve a great many parts that took forever to fit and drill, but I hope to rivet them Monday if I manage to alodine them over the weekend.
[February 24, 2008]
While I grimly revisit the Gestalt of metal airplane construction by drilling holes in what will be the frame supporting the flap synchronizer, others are more interestingly occupied. Last Tuesday Ray Henning trailered his blinding T-18 to Mojave, where Mike Melvill, never one to waste any time, helped put it together and then took it out for a test. The wind was gusting to 29 knots by the time he was on the runway, and besides the tailwheel steering was unacceptably sensitive, so he confined himself to a short lift-off. Yesterday, after replacing the tailwheel springs, Mike made a flight that was cut short after 15 minutes by the non-operation of the alternator and consequent loss of radio communication. Apart from the electrical problem, everything was good, including -- always importantly -- the stall.
I feel a bit envious, like someone who has college-age kids and whose friend has a new baby. Ray, I suspect, must be greatly relieved and impatient to fly the plane himself. He will have to be careful to avoid any heading that places the sun in a position in which it reflects into the cockpit from a wing. The joke going around Mojave is that the airplane took four years to build and 12 to polish.
[February 16, 2008]
Back home, and flew for a little while. I was looking for smooth air in which to perform a simple test. I was curious whether opening and closing the cowl flaps affects overall drag enough to have a noticeable effect on speed. I've never detected any, but I thought that perhaps a more sensitive test than indicated airspeed would be vertical speed. If I trimmed for level flight with the cowl flaps closed and then opened them, the plane would begin to descend if the drag increased. After repeating this test a few times, I ought to begin to get a consistent impression. Unfortunately, today was not the day. It was bumpy at all altitudes.
Costa Rica hands with birdwatching proclivities will marvel to learn that I took this picture within 12 hours of arriving in the country:
[February 6, 2008]
I'm going to Costa Rica fora weeka. M2 is staying here. No exciting updates til I return.
[January 29, 2008]
During a break in the rain late last week I flew seven touch-and-gos. I've never flown touch-and-gos in Melmoth 2 before, and they turned out to be instructive. I realized that because I usually approach the airport on a long straight-in from the northwest, I had grown accustomed to flying the VASI glide path from a couple of miles out. That was a mistake; it's way too shallow for my airplane or, I suspect, any light airplane. Besides, Whiteman has a telephone pole sticking up right at the end of runway 12, and even though I probably clear it by 30 feet I always feel as though it's about to gouge a hole in the underside of my wing. If you're on the VASI glideslope and miss the pole by a good margin, you have to drop down rapidly to land on the numbers and make the midfield turnoff -- which I seldom managed to do. Flying a series of circuits I realized that a steeper approach felt more comfortable, made for a more natural flare, and allowed me to touch down on the numbers.
For about a week I've been working up the courage to ask one of the local shops if I could use their shear and brake to make the channel elements for the flap synchronizer. A lot of shops, and individuals, don't like to let visitors use their equipment. Today I finally got up the courage to ask. I hadn't even finished the sentence when the mechanic said, "Sure, come on over, they're right there." I had all the parts made inside of an hour.
[January 22, 2008]
Today I found, in a nondescript metal building on San Fernando Road, just east of the old home of Industrial Metal Supply (where, between 1968 and 1973, I bought most of the metal for Melmoth 1), a sheet of .050 2024-T3, which I need for the synchronizer frame. It's become quite difficult to find aircraft alloys in small quanities -- "remnants", as they're called. Industrial, in a new and grander location a mile away, now carries only 6061-T6 and 5052. 5052 is too weak and soft to be of much use, but 6061-T6 is suitable for some applications and is weldable, unlike the stronger aircraft alloys 2024 and 7075. Burbank Metal Supply resembles the old Industrial in miniature, with stacks of miscellaneous materials, aluminum and stainless steel, some pristine, some scuffed and scratched, leaning against walls and stacked in racks. Irv Kaye, who walks very fast and has a somewhat scholarly air, was friendly and helpful, digging through piles of sheet until he found the one, two by three feet, that I needed. It cost $25 -- about eight times what it would have cost when I was building the first Melmoth.
Now I must find someone equally cooperative who will let me use a shear and brake to cut and bend the parts.
I should explain again what this synchronizer does. The flaps are hydraulically operated and are tapered, so the outboard actuators travel a shorter distance than the inboard ones. The job of the synchronizer is to apportion the flow of hydraulic fluid to the actuating cylinders in such a way as to keep the tips and roots in the proper relation to one another and to make sure the flaps move simultaneously. The four cylinders in the synchronizer do this by moving different amounts, kept in step with one another by the single bellcrank to which they are all attached.
Burt Rutan has repeatedly said that I don't need flaps -- his Catbird, an airplane similar to mine, doesn't have them -- and it's true that I have been flying for five years now without them and without missing them. But when I said a few days ago that this was a case of art for art's sake, I could have been speaking of any number of aspects of my airplane that are not really necessary -- or for that matter of the airplane itself.
[January 17, 2008]
Having assembled the cylinders and begun to mock up the flap synchronizer on a piece of tooling plate, I am beginning to feel that this is a case of art for art's sake, unjustifiable by any rational calculus balancing effort and reward. To say nothing of weight. But now that I am this far down the road, I may as well continue.
[January 5, 2008]
Yesterday I spent a couple of hours machining a few final pieces for the flap synchronizing system. One of the things I did was take a little material off each of four end caps for the cylinders. These are 3 inches in diameter, and I took away material to a depth of .140 in. over a width of about .6 in. It disappeared into a mess of chips and didn't look like much, but if you calculate the volume removed it turns out to be about a quarter-pound of aluminum. I guess that was worth 20 minutes. As someone in rehab from Christmas, I can testify that machining is faster than dieting. So those parts are at last done, and this afternoon I degreased, acid-etched, and alodined them in the kitchen sink.
[January 1, 2008]
Well, that's over.
Yesterday was the first time in a week that I've gotten out to the airport and either flown or worked on the plane. I did a little of each.
Nobody has ever asked what the Latin quotations on the home page and on the "Cooling" essay mean. But I'll explain anyway. The one on the home page, "album mutor in alitem..." is from an ode of Horace (Quintus Horatius Flaccus, 65 BC - 8 BC), in which he somewhat grotesquely imagines himself transformed by the fame of his poems into a far-flying bird; literally, it means "I am miraculously changed into a white bird, and light feathers sprout from my fingers and shoulders..." It gets weirder when his legs develop crusty chicken skin; but enough. On the "Cooling" page, the phrase is from the Transformations (usually called "Metamorphoses") of Ovid (Publius Ovidius Naso, 45 BC - 17 AD, a sexy old goat). Telling of the schemes of Dedalus for escaping from imprisonment on Crete, he wrote that the mythical tinkerer "sent out his mind into unknown arts," namely, flight -- sort of like me fumbling around with engine cooling, an art not called "baffling" for nothing.
It never ceases to amaze me that these 2,000-year-old texts come down to us intact.
[December 20, 2007]
Having leaned toward using composites for the supporting framework for the flap master cylinders, I leaned back toward aluminum after reflecting about just how, in detail, I would achieve the desired bearing strength at the cylinder pivots and compressive strength between them. It seemed as though it would be a comparatively complicated layup (two of them, in fact, since the apparatus is sandwiched between two frames, mirror images of one another), with very little weight saving, if any, over an aluminum trusswork of simple bent-up channels riveted to corner gussets of 1/8-inch plate. The corner gussets will be the bearers for the cylinder pivots and the central bellcrank (the "starwheel") to which they are all connected.
It was not until this afternoon, actually, that I ran through all the numbers to ascertain exactly what the stresses are. I am apparently of the "Build first, analyze later" school of design, like the people who did that bridge in Minneapolis. Actually, there were no surprises, since I had a good approximate idea of the forces involved just from mental calculations which I perform, in a fanciful effort to stave off Alzheimers, while falling asleep at night. The main piece of enlightenment that came out of today's more formal calculation was that it is not necessary to regulate the hydraulic pressure in the master cylinders to a lower level than that in the bleeder cylinder; all can run at 500 psi without inflicting excessive loads on the structure. I still need to machine five clevis fittings to join the the hydraulic cylinders to the starwheel, and then I believe it'll be O-ring and hydraulic fluid time.
My hangar neighbor Ray Henning, who has finally finished his T-18 (I think it's been about 30 years in the making), gave me some nylon tubing which will be an excellent, and economical, alternative to the many Aeroquip hoses I had stupidly intended to use.
It will be truly disheartening if this elaborate apparatus does not work as planned.
[December 9, 2007]
Yesterday Captain Tom Huff, the CO of the Naval Test Pilot School at Patuxent River, Maryland, stopped by on his way to the Air Force Test Pilot School graduation at Edwards, and we flew to Camarillo for lunch. I had him fly the plane on the way there, hoping for his assessment of it. Of course if he had thought it stank he probably would have been too polite to say so, but I got the impression that he liked it pretty well. For me, it was a pleasure to watch a skillful and precise professional pilot -- Huff is an F-18 guy, mainly, but he also flies a 210 -- fly my plane, after watching myself fly it for so long. I imagine that playwrights and composers seeing their work performed get a similar pleasure; another person brings something fresh to your perception of the familiar thing. Huff made a nice landing at Camarillo, and I made a rotten one at Whiteman, just to round out the experience.
I've been working steadily on the flap retraction system; the main thing that remains to be made, apart from the center tracks, is the frame that holds the four synchronising cylinders in the proper relation to one another. Originally I was planning to make it of .080 aluminum plate, but at some point it dawned on me that the loads between mounting pivots of the cylinders and that of the starwheel that keeps them in step with one another are compressive, and therefore need something with better column properties than thin plate to keep them in place. I kicked around various options and am currently planning on composite; it seems like the least expensive option, and the simplest to tool.
[November 28, 2007]
On September 17 I wrote about removing the fuel filter and finding in it a great deal of debris consisting, mostly, of bits of carbon fiber and light-colored grit that I think must be epoxy particles released by sanding. I discovered today, to my very great surprise, that by simply holding my Canon PowerShot A80 against the eyepiece of my microscope I can take a pretty good photomicrograph. Here are three shots, the first of the (almost) clean side of the filter, the second of the dirty side, and the third of some of the powder that I scraped off the filter surface. The carbon fragments are on average a couple of thousandths of an inch long.
[November 13, 2007]
I flew up to Paso Robles again, this time to talk with a machinist, Richard Galli, who is creating 10 reproduction LeRhone rotaries for Javier Arango. Everything on these engines is machined from huge hunks of solid steel billet -- no castings -- and Galli seems to me a genius with a mill and a lathe. I have no idea how he manages to make some of these parts -- which were originally made, however, in 1915, with machines much inferior to his but, he says, with no less precision in the final results.
The flights up and back -- about an hour each way -- were very smooth, with visibility unlimited and cloudless skies and an OAT of 9 degrees C at 12,000 feet. The autopilot and GPS tracker are working again; now I need to learn the millions of features of my old but highly serviceable Lowrance. So far, like, I suspect, many pilots, I have pretty much confined myself to the "GOTO" command. The other day I could have used the "runway extension" feature, which draws a line several miles out from the runway centerline. It was so murky in Los Angeles that I couldn't see Whiteman's VASI lights until I was inside two miles.
The plane seems to me to have slowed down a bit; I need to put it up on jacks and see whether the landing gear doors have gone out of adjustment. Then again, maybe the overall coating of dust and ash is disturbing the laminar flow.
[November 6, 2007]
I changed my oil today. It took three hours. Every time I do it I promise myself that I will come up with some kind of quick-drain to replace the stock drain plug; but I never get around to it. The problem is that there is very little room between the drain plug and the nose strut in its extended, and even less in its retracted, position. Getting at the plug to remove it is difficult, and made more so by the fact that the engine and the oil are hot. There are various kinds of quick-drains on the market, but even the "low profile" one in the Spruce catalog looks to me as if it takes up too much space. I need a drain that protrudes no more than 1/4 inch below the boss on the sump. I have an idea of how to make one, but as the misery of the oil change recedes in memory I will probably lose the impulse to do it, just as I have on every previous occasion.
[October 31, 2007]
Just got back from almost three weeks on the east coast, where, among more ordinary activities, I logged .7 in a Black Hawk at Pax River. Having been relieved of most of its military equipment, it climbed 3,000 fpm straight up.
By the way, the Peter Garrison who flew a Seneca into a building in Vancouver on October 19 was not I. I am not sure which of us was the real Peter Garrison, but in any case I am now the remaining Peter Garrison.
[October 5, 2007]
On Tuesday Russ Hardwick and I flew up to Paso Robles for lunch at Michael's, an airport restaurant of the better sort or, better, a restaurant of the better sort that happens to be located at an airport. We parked in front of the restaurant, alongside a handsome Lancair 360. After lunch we got into a conversation with the owner of the Lancair, who had bought it from someone who had had it built by a professional builder. "There are the people who like to build," the pilot declared, "and then there are the people who like to fly." Obviously, he preferred to fly and assumed that I preferred to build.
On the return, while descending into Whiteman, I throttled the engine back to idle and compared rates of descent with fine and coarse pitch. (The subject was on my mind because I had written in a couple of recent Aftermath columns that glide can be extended by putting the prop in coarse pitch.) Fine pitch, which causes the engine to turn at higher rpm and therefore absorbs more energy, yielded 1,200 fpm, against 1,000 fpm for coarse pitch. Now I am curious to know the zero-thrust sink rate; theoretically, it should be around 750 fpm under the same conditions. This figure, which emerges from my computer simulation, implies that the engine is absorbing about 15 horsepower when the propeller is in coarse pitch. I have a 1972 Lycoming report, Peformance Characteristics of the Continental IO-360-D Model Engine, which includes a plot of friction horsepower against rpm; it shows a nearly straight-line variation between 12 hp at 2,000 rpm and 28 hp at 2,800 rpm. (A close fit, if anyone cares, is 5.16x^2 - 4.27x.) I'm not sure whether this includes pumping losses, which could be at least partly eliminated on the test stand by plugging up the intakes and exhausts. I'm also not sure whether it's better to have the throttle open or closed in a power-off glide, or whether it even makes an appreciable difference. A vacuum cleaner runs faster with its intake plugged, but it's not a positive-displacement pump and so the analogy may not be a useful one.
To measure zero-thrust sink rates, I would have to put a microswitch on the engine block behind the propeller flange and detect the point at which the crankshaft, which has measurable end play, shifts from thrust to drag. Knowing the zero-thrust sink rate is one way to measure drag; the rate of sink represents the release of potential energy at a known rate, and can be translated into horsepower at least as reliably as fuel flow can.
Speaking of sink, I tried a lean climb on the trip to Paso. Rather than climb at 1,000 fpm at 28/2500 and 12 gph with a rich mixture, I set up 27/2400 and 8.4 gph at about 50 deg. F lean of peak, which gave 500 fpm. I later ran the math and found that the lean climb saves 0.2 gallons or, at current prices, about 90 cents; on the other hand, it takes about three minutes longer to cover the first 40 miles of the trip. Is my time worth 30 cents a minute? Depends whom you ask.
On Wednesday and Friday I worked at Homer Knapp's machine shop -- he is a motorcycle machinist and pilot whom I first met in the early 1970s in John Thorp's circle -- on the flap synchronization cylinders. They are now honed and the barrels and caps are threaded. There is still some machine work to do on the caps, but the honing and threading operations have loomed before me for years now and I'm glad to have them finally taken care of. Homer did the first three barrels and had me do the fourth, which I only slightly messed up. I did the inside threads on all four caps without ruining any of them -- a minor miracle.
On Thursday I bit the bullet and took my autopilot over to Mid-Continent Instrument at Van Nuys airport for repair; I also removed my quaint eight-day wind-up clock, which would run for barely eight minutes on a full winding. I thought it needed cleaning, and took it to the local watch repair place in Echo Park only to learn that the elderly horlogier had "passed." For the past two days, however, the clock has been ticking away merrily on my drafting table, evidently more at home there than in the airplane. Perhaps, like many people, it prefers lying on its back.
I got a message this afternoon that the autopilot is fixed and the bill is $185. Not bad for an airplane part. I can amortize it with 200 lean climbs.
[September 20, 2007]
I flew around for half an hour just to remind myself of where the buttons and knobs were. I was somewhere north of the San Fernando Valley, climbing through 6,000, scanning the sky like mad because this is the area through which flights inbound to Van Nuys and Burbank pass, when I briefly looked at the instruments and then looked out again to see a King Air passing in front of me a few hundred feet away. It was incredible that I could have failed to notice it moments earlier, since I was being quite conscientious about looking for traffic. It's difficult, after an experience like this, to have a lot of faith in "see and avoid." It also makes it seem particularly strange that Cessna's new light sport airplane, the 162, which is featured on the cover of Flying this month in a picture so murky that the airplane can barely be distinguished from the background, is a perfect clone of the 150, an airplane so notoriously difficult to see out of that its mere existence demonstrated the value of pure chance in avoiding midair collisions. Evidently the designers at Cessna, who should know, feel that visibility plays a relatively minor role in air safety.
[September 18, 2007]
I found the filter element at Kal Nelson's, or rather at K&P International, which has replaced Nelson's, the disappearance of latter enterprise being, as an employee of the new one said to me with a mysterious smirk, "a long story." After installing the new filter element, I cut the old one apart. It consists of 27 square inches of resin-coated paper. Under the microscope it is revealed to be a dense tangle of glossy orange fibers whose diameters are on the order of a few ten-thousandths of an inch. I found that the dirty side was loaded with a lot of debris but far from clogged. None of the long glass or carbon fibers had found their way to the clean side, but a few particles of amorphous whitish stuff resembling salt had, together with some very small fragments of carbon. Some of these, however, may have been transferred to the clean side by my less than professional handling of the sample. The filter seems on the whole to have been very effective. Possibly, however, it would be a hazard in freezing conditions if there were any water in the fuel. If the filter, which has no bypass, managed to become clogged with frost, it could shut down the engine. It would perhaps have been better to put it in the engine compartment, where it could have been kept warmer and would, besides, have been easier to get at.
The pictures below show the compartment that is below the pilot's thighs. The airbrake has been propped open to allow access to the compartment. The black object with the groove down the middle that runs across the top of both picures is the main spar. The filter housing is the bright aluminum thing on the left. Immediately to its right is the fuel shutoff, whose handle is on the other side of the bulkhead; to the right of that is the gascolator -- a genuine antique. Then comes a shaft that is part of the backup manual gear-lowering mechanism, and then, vanishing from the edge of the picture, is the electric boost pump. The next picture takes up where the first leaves off, with the electric boost pump (the red and maroon thing with the yellow label on the bottom); the two aluminum valves are fuel tank selectors, one controlling feed and the other return. They may be operated manually or electrically; the motor is the tan cylinder above the valves. The two springs are return springs for the airbrake, which is the black surface at the bottom of the picture; the cylinder that operates the airbrake is just above the springs. The back end of the hydraulic pump is at the extreme right.
There are some photographs of the other end of this action-packed compartment at January 31, 2007.
[September 17, 2007]
I have been making the fairings for the middle flap tracks at a relaxed pace, one a day. Today, having finished the fourth of six pieces, I thought I would go flying, but then decided first to drain the sumps and gascolator and check the fuel filter. The fuel tank sump drains disgorged, as usual, a few largeish grains of this or that -- you can never tell what the stuff is -- and no water whatever. They have never shown any water, although the tanks are never close to full; I suppose this is my reward for living in a dry climate. Often one or the other of them begins a slow drip after being drained, and it becomes a big production to get rid of whatever bit of smut is sticking to the tiny O-ring. This time that didn't happen, and I proceeded to the gascolator, which is located above the airbrake in the wing centersection. It always drains very slowly, yielding a deep blue liquid -- the dye in the avgas seems to collect here -- and a small amount of finely divided black grit that almost looks like some sort of melanoprotozoa when random turbulence -- or Brownian motion -- stirs it up. The gascolator, too, was kind enough to re-seal without starting to drip.
I then opened up the fuel filter, which, just between us, I have not looked into since 2002. The filter uses a pleated paper element, and there was quite a lot of scum in it; in fact, when I had mined most of the stuff out of the pleats it amounted to perhaps half a cubic centimeter of what appeared, once dry, to be a fine gray powder. Under a microscope, however, it revealed its true identity: a pick-up-sticks-like maze of black and transparent shafts of graphite and glass, mixed with clumps of shapeless light-tan debris which I take to be epoxy dust. Using as a gauge one of Nancy's hairs, which, by the way, was astonishingly clean and regular in shape, resembling an acrylic extrusion, and which I mic'd at .0017 inch, I estimate that the fibers are about two or three ten-thousandths of an inch in diameter. Most are three or four thousandths long, but a few are as long as .010 inch. I'm awfully glad I put in the filter; most airplanes don't have extremely fine fuel filters like this, but the debris the filter caught could have caused no end of trouble in the injectors.
I imagine that the filter element must be pretty well riddled with this gunk, and that I need to replace it rather than attempt to clean it. (It is customary, in any case, to replace paper filters and not to re-use them.) The element is a Purolator part, AN6237-1. I thought I had a couple of spares, but I could not locate them in the hangar. (Actually, it would have been miraculous if I had.) The local parts shop, Vista, didn't have one, but said they could get one by tomorrow. I decided instead to try my luck at Norton Sales, which has incredible amounts of incredible stuff, but, incredibly, didn't have this. I then thought I might find it online; all of the places offering it for sale, however, are electronics parts suppliers, so I'm afraid that if I order one I'll end up with a capacitor or something instead. Nothing at Aircraft Spruce. I'll try Luky's tomorrow -- the somewhat diminished avatar of the once magnificent Joe Factor Sales -- and then Kal Nelson; if those fail I'll be back at Vista, where I hope it doesn't turn out that they can't get them after all.
[September 8, 2007]
I revisited the stress analysis of my flaps more than three years ago (see March 11, 2004), and found that the loads that I assumed when I built them in the first place, some time well back in the twentieth century (why didn't I make my programs print the date on everything?), coincided closely with the new calculations -- showing, for one thing, that the old methods worked as well as the new ones, at least for this sort of rough analysis. But I have no records of what calculations I used to size the attachment points for the middle flap track. There are receptacles in the rear spar for four 1/4-inch bolts, two top and two bottom. The bolts are certainly adequate; but what provisions I made in the surrounding structure to spread the tensile and compressive loads, equal to the weight of a small car, into the skins and ribs, I don't know. I must have assumed, since I was completely absorbed in the design at the time, that I would never forget its details. Now, 15 years later, I have. I have lots of photographs of the wings under construction, but none of them shows how the lower attachment, the one in tension and the more critical of the two, connects to the ribs and skin, or what local reinforcements I may have added to the sandwich core, or whether I locally doubled or tripled the skins (as I should have). There are a few shots of the upper attachment, and I assume the lower ones were similar. In any case, they no longer seem to me adequate. This is a critical area, because a failure here would threaten the integrity of the aileron pushrods, and so I am having to redesign the attachments from scratch, more or less as though the original hard points did not exist. This should never have been necessary; one should document everything, either with drawings or photographs, no matter how unforgettable it seems.
My ancillary interest in Latin has drifted away from Vergil and, because my daughter will be reading Ulysses later this year and I am revisiting it after an absence of 45 years, alit upon a bit of ecclesiastical hocus-pocus to be intoned over the dying: liliata rutilantium te confessorum turma circumdet. This seems to me to mean "May a lily-bearing throng of blushing spirit-guides surround you." Perhaps some pilot-priest, if such there be, could set me straight about these inexplicably rosy-cheeked confessors. It is interesting to note, by the way, that the wish that follows this one is "iubilantium te virginum chorus excipiat" which means "May a chorus of rejoicing virgins receive you." Evidently, Muslims are not the only ones who expect to be greeted by virgins at the pearly gates. Seriously, however, it's quite obvious that the virgins here are symbols of angelic purity, and we may as well assume that their Islamic counterparts are as well, and not the frolicking lapdancers that many people seem to suppose.
[September 6, 2007]
Through good luck, it turns out that the fairings for the outboard flap tracks (see October 26 or December 4, 2006) will also work for the middle ones, and so I can re-use the original molds. This is the opposite of what usually happens, which is that I plan a part to serve several purposes and then find that it really won't serve any. Each fairing consists of three parts. It always feels as if it should be possible to make several at once, but today I managed just one. No hurry.
I have been thinking a lot lately about how to translate the famous line of Vergil, sunt lacrimae rerum et mentem mortalia tangunt. Taken in isolation it seems very beautiful and poignant and has a Japanese pity-of-things flavor, hardly the sort of thing you expect from pius Aeneas. In context I think the effect is much more mudane. But this matter is probably more suitable for some other website.
[August 29, 2007]
On the 22nd I had lunch with Mike and Sally Melvill at Mojave. In an effort to prevent the inside of the cockpit reaching the boiling point of plastic while the airplane was parked -- 20-knot winds made it impossible simply to leave the windows open -- I spread a white sheet over the seats and most of the floor. This seemed to help, although the Safe Flight angle of attack meter was still frozen when I took off -- heat has that effect on it -- and didn't begin indicating until ten minutes into the flight. It seems as though the cover ought to be on the outside, although it is awfully inconvenient to have to stretch a big canopy cover over the airplane in a stiff wind. I wonder how I dealt with this problem in the first Melmoth; I don't remember it being a big concern, other than the one time I burned my hands on the seatbelt buckle after parking in 114-degree temperatures at Palm Springs.
In the week since then I have not flown; I have been making a few final additions to the left flap, and next week will do the same to the right.
[August 16, 2007]
On the 14th I flew up to Oakland for lunch and returned in the afternoon. Southbound a little north of Gorman I had to get an IFR clearance to penetrate the smoke from a fire -- it is called the Zaca fire, I have since learned -- that I had somehow remained unaware of until that day, but that has been burning for a month in the mountains north of Santa Barbara and has consumed 84,000 acres. Just before I entered the opaque smoke, there was an extraordinary view to the west of a wedge of turquoise sky between layers of russet; unfortunately, I didn't have a camera with me to capture it.
During the flight I observed the continuous slight -- two or three amp -- charging of the battery that I have come to recognize as the sign of low battery water; I checked it yesterday and it was indeed low. This unexpected charging was a great and seemingly alarming puzzle a couple of years ago; now it's just a piece of routine service.
My progressive shaping of the seat back cushion is paying off; it seemed quite comfortable (but the flight, admittedly, was short -- less than two hours). Now I feel as if the seat bottom needs a deeper hollow for the buttocks, which will result in more thigh support. I'm taking off just a little at a time; I don't want to go too far.
[August 14, 2007]
Yesterday I had an opportunity to re-weigh the airplane. It has gained 180 pounds since its first flight, lord knows where, and now weighs about 1,575 empty. I have to say "about" because there was around 53 gallons of fuel aboard, and I have to say "around." The empty CG has also moved aft by more than an inch. The news from scales is seldom good. I was trying to comfort myself when I happened upon the specifications of a Cozy Mk IV, which supposedly weighs 1,000 pounds empty and cruises at 220 mph on a 180 hp Lycoming. That made me feel even worse.
[July 24, 2007]
While preflighting the plane on Friday I noticed what appeared to be a nut lying in one of the small drain holes that are supposed to let rainwater out of the cowling. Opening the side of the cowl, I discovered that the object was actually the head of a bolt. The nut was lying nearby. They had previously secured the turbocharger to a brace that is intended to keep it from vibrating fore and aft. I had just read a few days earlier that one should not use self-locking nuts in the engine compartment, and this seemed to bear out that rule. I replaced the bolt, whose threads were peened flat, with a new one of the drilled variety, and I replaced the self-locking nut with a castle nut and cotter pin.
I learned yesterday that Hans Georg Schmid had died in the crash of the Express 2000 in which he had intended to make two circumnavigations of the globe via meridians. He had just taken off from the airport at Basel, Switzerland, bound for Oshkosh, a 5,000-mile nonstop -- he loved long flights, and had circumnavigated the Earth before in a VariEze (or Long-EZ, I'm not sure which) -- when he either encountered downdrafts or could not develop full power, and struck the roof of a building a couple of miles from the runway.
I felt some connection to this project because my friend Hans Kandlbauer had been its chief engineer and aerodynamicist; I had also helped design the tip tanks. Although the airplane was very fully equipped (glass cockpit, etc) and loaded with 450 gallons of fuel, it had a 315-hp Lycoming and should have had a pretty reasonable rate of climb. For reasons that are not yet clear, Schmid, a retired Swiss Air Lines pilot with 16,000 hours, had elected to take off southward, with a light wind behind him and rising terrain and buildings ahead, whereas if he had taken off northward he would have been flying over flat and unpopulated terrain. The airplane was relatively unproven; it had just emerged from its 25-hour initial flight restriction, and this was, I believe, the first time it had flown with a full fuel load. Below, the airplane on its first flight, June 13, and Hans Georg in the shop in December, 2005.
[July 12, 2007]
It is often the case that, once the answer to a question is known, one is tempted to see whether one could have arrived at it analytically.
Theory of Wing Sections (p. 195) gives a CL increment of 0.6 for a 20-degree-deflected plain flap. Assuming that because of the dropoff in the spanwise lift distribution near the tip the effective CL is only a third of the theoretical value, that gives 0.2 * 1.2 * 205 * .87 * q for the maximum rolling moment, where 0.2 is the CL increment, 1.2 is the area of the flapped portion of the tip, 205 is the distance in inches from the centroid of lift of the tip to the CG, .87 is the cosine of the dihedral angle, and q is the dynamic pressure, which is roughly 16 lb/sq ft at 70 kias (rotation speed) and 64 lb/sq ft at 140 kias (typical cruising speed). The rolling moments from a fully-deflected trimmer run roughly from 700 lb-in at the lower speed to 2700 lb-in at the higher.
The next question is: How do those values compare in magnitude with possible fuel imbalances? Using Loftsman's tank analyzing routine, I obtained the weights and spanwise centroids of fuel loads from empty to full and made the following graph, which shows the incremental effect of each unbalanced gallon of fuel:
Each wing can hold about 70 gallons of fuel. As fuel is added the CG of the fuel moves outward, and the space occupied by added fuel moves outward as well. Consequently, the moment contributed by each additional gallon increases much more rapidly when the tanks are nearly full. At cruising speed and full tanks, the trimmer can neutralize an imbalance of 2700/1200 or around 2.3 gallons; with a more typical fuel load of 40 gallons, however, the figure is nearly 7 gallons.
Analysis by Cmarc, using the inviscid option (which is somewhat unconservative, that is, optimistic) and fully-deflected ailerons, gives a rolling moment at 70 kias (close to the flaps-up stalling speed) of about 45,000 lb-in -- obviously sufficient to counteract any probable fuel imbalance. But it is also obvious that the effect of the roll trimmer is very small compared with that of the ailerons, and that an aileron trim tab would have been a more powerful roll trimming device. Duh.
[July 11, 2007]
I finally test flew the roll trim flap. The good news is that there is no noticeable adverse yaw or side force from full deflection; the bad news is that there is not much rolling moment either. At approach speed you can barely tell whether the flap is deflected or not. At 140 kias the effect is much more marked, but by the time you've reached altitude and accelerated to cruising speed the fuel imbalance that the trim is supposed to compensate for will probably have burned off anyway.
The flap travel is about +-20 degrees. I was interested to see that with the flap going downward, separation occurs at or slightly before half travel. The rolling moment continues to increase, but probably at a lower rate that it would if the flow remained attached. The hinge is in the upper surface; the lower surface has a well-faired radius at the joint, and it is possible that the flow over it remains attached up to a larger deflection; but I can't see that side from the cockpit.
It remains only to paint the flap and forget about it.
[June 29, 2007]
A correspondent (Frank Shoemaker) inquired about the kind of analysis needed for a modification like the addition of the trim flap. Another (Paul Lipps) wrote to point out that a spring trim on the stick works just as well, and is simpler than an electrically operated flap. I concede Lipps' point without debate.
How much analysis I would do would depend on the type of movable surface I was adding. In this case, it is a trailing-edge flap attached to a MAC servo. The servo is a linear jackscrew, and so the flap is locked in position at all times and is not susceptible to flutter. (Even if it came loose from the servo, I think that it is too small and light, and the wing is too massive and stiff, for mutual excitation to occur. That is just an intuitive judgment, however. The flap might buzz, or even tear itself off the wing.)
As far as stress analysis is concerned, I never did any stress analysis of the upturned tips in the first place. I considered it self-evident, based on experience with foam-cored structures, that they would be strong enough. They have a spanwise ply of unidirectional carbon in both upper and lower surfaces as well as the two-ply 45-degree glass torsion box. I also figured that even if one failed it would not be a safety of flight issue. After building them I tried to bend one and found it to be sufficiently stiff that in my opinion air loads would not break it at up to 200 knots (Vne).
One can, however, do a back-of-an-envelope stress analysis. Dynamic pressure at 200 knots is 132 lb/sq ft. CFD analysis of the spanwise lift distribution suggests that the tips achieve only about 60% of the CLmax of the wing at their root (BL 200), tapering to zero at the tip. With the trim flap set 20 degrees down I would very conservatively assume an average CL of 1.0 for the tip, which has an area of 1.6 sq. ft. Because the tip tapers from a root chord of 21 inches to a tip chord of only six, I would put the spanwise centroid of pressure 5 inches from the inboard end of the tip. This works out to a compressive load in the skin at the root of 1.6 * 132 * 5 / 3 (3 is the section depth in inches), or around 330 pounds. This root moment can be simulated with a 20-pound force applied (by hand) to the tip of the structure. Of course the moment curve is different; a concentrated load at the tip puts an unrealistically large bending moment at mid-span. But in any case this is a limit-load test, not ultimate.
The flap itself, which is piano-hinged along its entire leading edge, undergoes only torsional loads, for which it is manifestly adequate. I added a strong rib to the inboard end, with a nutplate where the actuator attachment goes, and bagged a two-ply layup over it to ensure shear continuity between the end rb and the skin. There is no rib at the outboard end.
In the process of adding the trim mechanism, I hollowed out some of the foam core at the root of the left tip; also, making the trailing edge into a movable flap interrupted the torque box. To remedy these defects, I closed out the cove, added a glass shear web where the foam now ends, closed the nose of the flap, and placed a four-ply reinforcement in the unsupported portion of the upper skin, which, as a thin curved compression member, is the most critical element in bending. The reinforcement also serves as an anchoring surface for the servo motor. Most of these modifications are in the aft portion of the tip, however, whereas the principal load is carried by the fore portion, which remained unchanged.
When putting a flap on a swept panel, you always have to choose between aligning the end gaps with the airstream and making them more or less normal to the trailing edge. The latter option avoids interferences, but I find it aesthetically unacceptable, and so I opted for the former, with the result that the end gaps have to be larger than I would like.
[June 24, 2007]
Having hacked up the left winglet in pursuit of the nonexistent pitot leak, I decided that I may as well put in the roll trimmer. This involved cutting up the winglet even more, but by now I was hardened to it. I have a little trim motor that I bought in 1987, and have been storing since then in a cool dry place, for this very purpose. The trimming surface is a flap on the winglet. Because the winglet has a 30-degree dihedral angle, the trim surface will actually produce some lateral force that will have to be neutralized by the rudder. Probably it will be too small to notice, and in any case the point of the trimmer is just to reduce the stick force due to a temporary fuel imbalance at the beginning of a flight. Imbalances occur mainly when the plane has been parked for a long time on a slanted surface, or one main gear strut is less fully inflated than the other. It's just been a minor and occasional annoyance up to now, but I can imagine that with more fuel that I usually take on, and the center of gravity of the fuel consequently farther outboard, it could be quite a nuisance. On the other hand, when I get around to moving the aileron hinges aft in order to provide more aerodynamic balance and reduce their hinge moments, an asymmetrical fuel load may not be such a problem.
[June 14, 2007]
I finally got the pitot-static sign-off today. Adjusting the transponder was not excessively expensive. The funny thing was that when we repeated the pitot test the pressure still bled down. Then it finally occurred to me to ask the technician to remove his test attachment from my pitot tube and put his thumb over the end of it and repeat the test. It still bled down. So the leak was in their equipment, not in my system.
[June 12, 2007]
Wrong. That was not the leak. Today, at first, I concluded that the leak must be in the pitot head itself. I extracted it from the wing with some difficulty and submerged it in water while pressurizing it with my dental gadget. A stream of bubbles rose from what turned out to be a drain hole that was clogged with something or other. I cleared the hole, and then when I covered it the pitot head held pressure. But it now seems as if the whole system is holding pressure, so something I did at some point in the last two days, I don't know what, must have sealed the mysterious tiny leak, wherever it was.
The radio shop, of course, has not yet even looked at my transponder.
[June 11, 2007]
It was surprisingly difficult to locate the leak. I tried pressurizing the system and painting all the joints with soapy water, to no avail. I broke the plumbing down into segments and tested them one by one, using a dental syringe (quite a handy thing, actually; you're supposed to squirt between your teeth with it, I suppose, but it just happens to generate 200 knots in the ASI when fully compressed) and an inches-of-water gauge that I had forgotten I had, but found in a cabinet while looking for a second ASI. I sawed out a chunk of the trailing edge of the left tip and dug out the blue foam stuffing to uncover the short length of vinyl hose that runs from the pitot tube to the 3/16-inch aluminum tube that connects the wingtip to the instrument panel. I finally concluded that the slow leak was where the vinyl tube slipped over the copper tube sticking out of the pitot, which is the standard heated type. I hope I'm right; if it's not there, I have no idea where else it could be.
[June 10, 2007]
I took the plane to the local radio shop for the biennial pitot/static certification, which is required even for VFR flying here because Whiteman is within 30 nm of LAX. The first problem that arose was a leak -- slow, but not slow enough -- in the pitot plumbing; the second was that the transponder's pulse timing had drifted off and was outside the tolerances for the test (the end result being that it transmitted inaccurate altitudes, even though the encoder was generating accurate ones). The radio guy who I hope will be able to fix the transponder was away for the week, and so we borrowed an AT50A from another airplane and completed the altimeter and encoder checks, which were fine. I'll find out Tuesday about the transponder -- I have a bad feeling the guy is going to say, "Can't fix it, you'll have to buy a new one, but here, we have a great deal for you." Meanwhile, I've been trying to track down the pitot leak. I have a feeling that it's where the tip extensions attach to the wing, which is bad, because I was uncharacteristically reckless there and made no provision for getting access to the pitot tube. Now I'm going to have to cut some holes in the tip to get at the thing, but I guess I can view this as a divine nudge toward installing roll trim, which an airplane with full-span fuel tanks needs.
[June 3, 2007]
I made round trips to Mendocino and to Paso Robles in the past week. Nancy was with me on the Mendocino trip, and she didn't find her seat, which used to be the pilot's seat, overly comfortable. I didn't love the new pilot's seat either. I decided that one problem was that the seat back was not sufficiently concave (about an axis parallel to my backbone), and so support was mainly being provided to the center of my back. I ground some more concavity into the seat back after that trip. It felt better on the hangar floor, but on the next trip, an hour-long flight to PRB, I felt that my back was getting sore again. By this time I was starting to wonder whether the whole business was not just my imagination, but I tried putting a lumbar support, which I unzipped from a little seat-cushion-plus-lumbar thingum that I had from Oregon Aero, behind me. That immediately felt a great deal better, and seemed pretty comfortable for the return trip -- or at least it allowed me to feel that the locus of dissatisfaction was now the seat bottom rather than the back.
I used to get a sore back (and shoulders) playing the piano. I wonder whether it's really that certain activities, among them flying and piano playing (for me, at least, and possibly for those who heard me play), produce muscle tension that is absent when, say, I am sitting in a movie theater or in an easy chair reading a book. Or, more likely, I am simply getting older, and more prone to aches and pains. I don't remember the seat being a major source of concern when Nancy and I flew for 15 hours from Alaska to Japan in 1976; and Melmoth 1's seats were much cruder than Melmoth 2's.
The trip to PRB was for Chuck Wentworth's annual barbecue at Antique Aero. A whole slew of interesting airplanes showed up, including, among the military types, a Zero, a couple of P-40s, a Sea Fury, and the expected herd of Mustangs. Most of these were extremely spiffily painted and polished, but the one I liked best looked somewhat war-weary, its aluminum dull and its paint chipped. It looked like the real thing.
[May 23, 2007]
Russ Hardwick and I flew to Page, AZ on the 21st to visit a couple of slot canyons. I had been working for the past week on the duct that leads air from the flush scoop on the right hand side to the controllable ventilator (from an '89 Camry) for the back seats. The duct is a fairly elaborate thing with a diffuser about a foot and a half long (a diffuser is a gradually expanding duct, intended to reduce the velocity of air flowing through it without allowing the flow to separate from the tunnel walls). At the end of the diffuser is a flow reverser that turns the air about 150 degrees and feeds it into the ventilator, which faces forward because the seats face aft. The reverser even has a turning vane in it; it's all very fancy.
When Russ and I left for Page, I hadn't yet tested the ventilator in flight and I didn't know how much air would come out of it. I did know that there was no way for people in the front seats to adjust the ventilator, but I figured that it was a warm day in LA and it was warm in Page, and so it wouldn't be a problem if it were open.
It was already apparent when we were taxiing that the ventilator was doing a pretty good job. It really went to town after we took off, discharging torrents of air into the cabin. This was not too objectionable at first, but then we climbed higher and higher to stay above the inversion and the turbulence, and the outside air got colder and colder. The ventilator happened to be aimed right between the two front seats. My right shoulder and Russ's left froze until we let down at Page. It's remarkable that a NACA scoop more than ten feet back from the nose of the airplane, where the boundary layer must be pretty thick, and behind the point of maximum fuselage width, can still pull in so much air.
[May 9, 2007]
I flew to Santa Ynez for lunch. The air was extremely calm -- groundspeed exactly matched true airspeed -- and I got a good speed point. Speed takes a very long time to settle down -- several minutes. As I have often mentioned before, I determine drag area (or drag coefficient -- they amount to the same thing) by comparing observed performance with computed performance, using the performance prediction routine in my lofting program, Loftsman. The computer output is one or two decimal points more precise than in-flight observation; for example, when my fuel flow indicator flickers back and forth between 6.9 and 7.0, I call it 6.95, but it could be any number within two or three hundredths of that. Airspeed can be measured within maybe half a knot, assuming zero calibration error. Here is the Loftsman output for a weight of 1,900 pounds, a density altitude of 10,400 feet, and a power setting of 26 in Hg and 2,000 rpm. The collective EGT was about 60 degrees lean of peak. Indicated airspeed was 133 knots.
The items, from left to right, are true and indicated airspeed in knots, drag in pounds, thrust horsepower required (a function of speed and drag), estimated propeller efficiency (based on a highly generalized curve), brake horsepower required (which is thrust horsepower required divided by propeller efficiency), percent of rated power, ratio of parasite to induced drag, engine specific fuel consumption (again based on a generalized curve), fuel flow in gallons per hour, specific range (that is, nautical miles per gallon), and, finally, the "CAFE" product of true airspeed and miles per gallon. The highlighted line corresponds to yesterday's measurement.
The last item, which I call the CAFE product because it was the crux of the scoring formula for the old CAFE efficiency races, is related to the "Carson speed", the speed at which you get the "best" combination of speed and efficiency (as distinct from the L/D or best range speed, at which you get the best efficiency, regardless of speed). The best speed to fly, on this basis, would have been closer to 140 kias.
Cylinder head temperatures, with the cowl flaps closed, were:
1. 175 C.
2. 170
3. 170
4. 170
5. 150
6. 180
On the return trip I used a slightly higher power setting (26.7/2,200, fuel flow 7.8 gph) and saw a somewhat different temperature distribution:
1. 185
2. 160
3. 180
4. 175
5. 150
6. 190
So the general pattern is: #1 and #6 are warmest, #5 (not #2, as I always thought) is coolest, and the others are somewhere in between. The previously observed coolestness of #2 correlated well with its being the first cylinder to reach peak EGT; it was therefore running leaner, and hence cooler, than the others. The present observation does not correlate with anything in particular, but suggests that the earlier pattern was just a coincidence. At this point the cooling is sufficiently well-behaved that I think I will just stop paying attention to it.
[May 8, 2007]
I realized yesterday that for years I have been referring to the left front cylinder as #5. It is #6. I went back and corrected the error all through this narrative (I hope).
What else have I been doing wrong for years?
Cylinders on my engine are numbered from back to front, with odd numbers on the right because the cylinders are staggered with the right side farther aft. (Multiple engines, on the other hand, when they are on the wings, are numbered from left to right, like freeway lanes.) My engine's oil cooler is mounted on the crankcase directly behind the #2 (left rear) cylinder.
The reason the lack of finning on the exhaust port surface is not a problem with downdraft cooling, I think, is that air emerges from the baffle passages at high velocity, and so heated air is continually scavenged from the unfinned surface. When the flow is going in the other direction, however, air converges into the baffle passages from a wide range of angles, and does not pick up a lot of speed until it enters the baffles. The revised baffle provides a converging channel over the exhaust port, and also adds baffling that wraps around the undersides of the cylinder, increasing the velocity of airflow there.
[May 5, 2007]
Success again. I redid the baffles on the right rear cylinder (which modification took three days rather than the expected one) and pulled its temps down by 50 degrees F or so as well.
Yesterday was a peculiar-looking day, with a shelf of dense clouds over the San Fernando Valley but lots of clear areas to the west. I started a 1,000-fpm climb westward once I was out from under Burbank's Class C. The CHTs were running around 150 C with the cowl flaps fully open. I closed down the aft vents to half an inch or so and went up to 10,500 feet without the hottest cylinders getting above 200 C. The target (ie factory recommended) temperature is 370 F or about 185-190 C. Continuing westward, I set up 27/2300, or around 55% (8.2 gph). With the cowl flaps closed as far as they would go (1/4-inch gap at the aft ends) the temps settled at around 150-175 C. (Different cylinders are still at different temperatures.) The oil temperature is still a rather high 97 C.
Incidentally, the reason I keep bouncing back and forth between Celsius and Fahrenheit is that my CHT gauge is calibrated in Celsius, while Continental's documentation is in Fahrenheit.
The #2 cylinder, the one next to the oil cooler, is still the coldest, and #1 and #6 are still the hottest, , but the disparities are much reduced. I guess that further tinkering with the baffling could bring the CHTs still closer to one another, but I'm not sure it would matter.
After pointing westward for a while I checked the GPS groundspeed and found that I was doing 90 knots. So I turned around, and then I was doing 220. Too bad I wasn't going to Arizona.
[April 27, 2007]
Success. The revised baffling on left front cylinder brought the temperature down by about 50 deg. F; it is now in line, +-20 degrees, with all the other cylinders save one, the right rear, to which I should be able to apply the same treatment next week. The problem with the cylinder is that it has no finning to speak of in the vicinity of the exhaust port:
My baffles previously ended even with the centerline of the cylinder; the trouble with that arrangement, as I now see it, was that it did not provde enough air velocity, and therefore heat transport, on the lower half of the cylinder. I modified the baffles by extending them down around the bottom of the barrel and the inboard part of the head, and providing a barrier about 3/4 of an inch away from the finless portion of the casting around the exhaust port. The revised baffle looks like this:
The way in which the baffle, which is lying down on my junkheap of a work table with its lower edge to the right, matches the cylinder should be fairly clear. I'm sure that still more improvement is possible -- the barrier near the exhaust port is pretty crude -- but this went a long way. Here's the way it looks installed:
[April 24, 2007]
It finally occurred to me -- showing that if I think about something long enough, even the most obvious fact about it will eventually become apparent -- that what my two hottest cylinders, the left front and right rear, have in common with one another is that their exhaust ports are not next to another cylinder. The suggestion is that whatever flow guidance is provided by a neighboring cylinder for cooling air passing by the exposed side of the port, which has practically no finning, is not being provided by my baffles. This clue at least gives me something to work with.
I should have the flap actuator plumbing finished by the end of this week and be able to resume working on the synchronising cylinders. It's increasingly clear that I won't have the flaps working by Oshkosh -- my somewhat arbitrary target -- unless some phase of the project proves less, rather than more, time-consuming than expected. That would be unprecedented, however. Well, maybe they'll be working -- but only on the ground.
[April 17, 2007]
The NACA scoop for back seat ventilation works nicely. I tufted the inside of the fuselage behind it, and the tufts were straight and steady in flight, indicating a strong flow with little turbulence. What I want to do now is diffuse it over a distance of about two feet and turn it around 180 degrees toward the back seats (which face aft). I sat in the new pilot's seat for this flight; it's not right yet. More foam grinding ahead. Cruised around for half an hour making squiggles on the GPS map. 137 kias at 7,500 ft DA, 7.6 gph -- a bit below par. It's interesting to note that opening the cowl flaps about 1/2 inch pulls CHTs down by 40 deg F, but does not have a measurable effect on speed. Tomorrow I think I'll wash the plane -- it's embarrassingly dusty -- and then get back to the flap hydraulics.
[April 13, 2007]
Two weeks later and I'm still installing hydraulic lines. It's weirdly time-consuming, to say nothing of expensive (AN and Aeroquip fittings are not being given away these days, unfortunately), but I'm getting there. I took a short detour this past week to cut a Concorde-shaped hole in the right side of the fuselage for an air vent for the back seats. I haven't flown yet to see whether any air actually comes in through it. It's one of those flush NASA affairs, and it's hard to understand how it can work very well once the boundary layer has grown to a depth that's comparable to that of the inlet channel. I'll test it on Monday.
I've also been grinding away at the foam on the pilot's seat and then sitting on it for a minute or two to see how it feels. It's hard to judge; even park benches feel comfortable at first.
[March 31, 2007]
Something about me seems to be extremely irritating to upholsterers. On Friday I was shown the door by the second one. I was not heartbroken; he seemed to me to be even less conscientious and competent than the first, who was no great shakes. But at least I ended up with a bunch of foam, glued rather haphazardly to the seat frame, at no charge. It's just as well that he decided to kick me out before he covered the seats, because the way he had shaped the foam was not very comfortable anyway. I'm going to try my hand at it, imitating the seats in my Geo Prism, which seem fairly comfortable.
In the meanwhile I've been adding the plumbing to deliver hydraulic fluid to the outboard flap actuators, and thinking a lot about an alternative cooling air intake configuration that might make it easier to equalize temperature among the cylinders. Just thinking; there are plenty of other things to work on first. But it's something to do while going to sleep.
Here's the environment of the outboard actuator:
The flap has been lowered to reveal the cove just inboard of the aileron; the latter can be seen, deflected upward, in the lower right corner. The diagonal pushrod is the aileron actuator, supported, in the upper left corner, by one of several idlers. An inspection plate has been removed, revealing the outboard fuel quantity sender (partially in shadow) and an aluminum block (bottom center) with blue fittings protruding from its top and bottom. The purpose of the block is to provide an anchor for the ends of flexible hoses going to the actuator, which will be installed just outboard of the aluminum flap track, between it and the fuel quantity transmitter. The paired lines, which run about ten feet inboard to the fuselage, are what I've been installing; they are 3/16 inch in diameter, and are secured to the upper surface of the cover at 15-inch intervals by tiny phenolic pillow-blocks.
[March 14, 2007]
I flew for half an hour to test the effect of the exhaust pipe insulation on the temperature of the left front (#6) cylinder head. It went up. This was not entirely unexpected; the exhaust pipe is in intimate contact with the cylinder head, and if stays hotter because of the insulation, some of that heat would migrate into the head. It was a question of whether the benefit of not preheating the air approaching the cylinder baffles would outweigh the ill effect of keeping the pipe hotter. It didn't.
A speed point -- density altitude 10,000 ft., weight 1950 lbs, fuel flow 7.5 gph, IAS 138.5 kts -- confirms once again the value of 2.25 sq. ft. for F.
I took my pilot's seat to the tapiceria -- upholstery shop -- across the street from Whiteman for an estimate. The amiable and copiously tatooed owner said it would be around $200 to do the second one -- $150 labor and $45 for the foam. I already have the covering material from my unhappy episode with the uphostery guy on the airport, who wanted half again as much money for the same job and then did it badly.
[March 12, 2007]
It was 90 degrees today, but there was a good breeze at the airport and for some reason the metal hangar does not become unbearable on hot days. Neddy, my large, long-haired and black dog, seemed pretty comfortable sprawled on the asphalt. I did some laminating in the back of the plane and noticed that for the first time this year I had to take care not to drip sweat on the epoxy-soaked glass cloth. The anchorages for the inboard flap actuators are now in place, and I have nearly finished making the hard points that will be secured near the outboard ends of the flaps to anchor the flexible hoses going to the actuators. Once those are in place, I will be able to plumb the hydraulic lines from the fuselage to the outboard actuators, and then get on with the synchronizer. On Friday, tired of fiddling with the flaps, I wrapped the exhaust pipe below the left front cylinder with insulating stuff, but I have not yet flown the plane to determine whether the proximity of the pipe is actually the reason for that cylinder running hotter than its neighbors.
[February 28, 2007]
I spent a jolly hour or two on my knees in the back of the plane, sanding out clearance for the flap actuator, which passes though a couple of bulkheads in a very confined space. At first I tried to do it with files, rasps and sandpaper, and I reminded myself of those patient prisoners who break out by filing their way though steel bars with dental floss dipped in floor dust. I then had the inspiration to saw a slot in a piece of 3/8" aluminum rod and slip the end of a 20-year-old, and hence tightly curled-up, piece of 40-grip Norton abrasive cloth in it. This, chucked in an electric drill, cut through fiberglass and plywood beautifully. At the end of an unusually long afternoon I had the left actuator working without interference though its entire travel. The right one will be easier because now I know what needs to be done, but harder because I'm right handed, and it's on the wrong side for holding a drill motor while hunched up on my knees.
[February 27, 2007]
I went to get some
O-rings at A.C. DePuydt, Inc. I love that place. It's located in an LA suburb
with the arresting name of Commerce. You go to the Will Call counter with your
tiny order for a dozen rings. They always have what you want, even weird sizes
without AN or MIL numbers, and after they're pulled it from inventory they send
you around to the cashier, who is always charming, and in no time the invoice
has been typed up and you're out the door with a little brown paper bag in your
hand. This time the bill was $5.14. I think they have a $5 minimum; they give
you extra O-rings to fill in the gap. I took them to the hangar, where a bunch
of hydraulic cylinder parts that I'd made over the past couple of weeks were
waiting for them.
I started to assemble the four hydraulic cylinders that will operate the flaps. I found that the silver-soldered joints between the shafts and the pistons for the outboard cylinders were leaky -- I submerged them in water and applied compressed air to the hollow shafts -- and I'll need to put some epoxy inside. On the inboard cylinders I had threaded the shafts and the pistons and used penetrating threadlocker, on the advice of my machinist friend Homer Knapp. They came out without any leaks. I then tried to assemble the cylinders and found that on one of them the hole in the end plug through which the shaft emerges was too small for the shaft. The shaft, which is a piece of surplus stainless tubing that I picked up at Industrial Metal Supply, mics at .378, and I've been reaming the bores with a .377 reamer. To enlarge the reamer I used another Homer trick, namely sliding a hard steel edge along the front of the flutes, which I suppose must raise a tiny burr. After I had done this several times the shaft finally passed and I was able to assemble the cylinders, one of which see below. The overall length of the cylinder in its retracted position is 20 inches. The next step is to fit them to the airplane, which I will do tomorrow -- or at least start doing tomorrow.
[February 21, 2007]
Machining, machining. The four actuating cylinders for the flaps are almost ready, and the synchronizing cylinders are about halfway there.
In the meantime, about three weeks ago I had delivered the structure for the fourth seat -- which was to be the pilot's seat -- to the upholstery shop on the airport. I took the guy the first seat he had done for me last fall and asked him to duplicate it, except that I wanted the seat cushion to be about an inch thicker and that there be more of a lumbar support at the bottom of the seat back. Several weeks passed, and then he presented me with a seat which was indeed one inch thicker, but only right under the buttocks, so that sitting on it was something like sitting on a watermelon: no thigh support, no lateral support. The lumbar bulge seemed to extend the whole height of the seat back, which was now flat rather than slightly concave as it should be. After one flight to see what it felt like, I took it back to him and pointed out that the first seat he had made was comfortable and well-formed -- so he obviously knew how to make a seat, which is, after all, what he does for a living -- but the new one wasn't. First he explained to me that this was my fault, because I hadn't had him make both seats at once -- although if I had, I would then have had two seats that were too low and lacked lumbar support, rather than just one. After some more discussion, he said, "All right, come back in an hour." I couldn't do that, but I came back the next day only to find that his knickers had evidently gotten into such a knot that he had stripped all the upholstery and padding from the seat frame, and refused to have anything more to do with it.
Well, I never liked the guy much anyway.
[February 10, 2007]
I spent the past week machining parts for hydraulic cylinders, averaging one mistake per three parts, and planning just how this flap system is going to fit in the airplane, how many of which kind of AN fittings it will require, and how the hydraulic connections will be bled. In Melmoth 1, which used two hydraulic flap actuators, one driven by the exhaust of the other, I used a kind of settling tower, consisting of a cylindrical fuel filter bereft of its innards and mounted upside-down, to capture air in the line connecting the two cylinders. I replenished the hydraulic fluid in the trap at fairly regular intervals, but never did know where all the air was coming from. The system for Melmoth 2 would require four such traps, one for each of the lines connecting the master cylinders to the flap actuators. I'll see how it works without them before installing them; the system, without air traps, works beautifully in my imagination.
Early in the week I also overhauled the left main gear strut for the second time. I had done so a few months ago, but it soon resumed leaking hydraulic fluid like mad. It turned out to have a rolled O-ring, due, I think, to an area of corrosion on the bottom of the groove which must have developed during the struts' many years of idleness. I bought the two Cherokee gear struts (whose outer shape was heavily modified for this airplane, but their inner workings are untouched) quite early in the project, back in the early 1980s, and they proceeded to sit around, along with the engine, for twenty years. I was able to clean up the rough area with fine sandpaper and the tip of my pinkie, but until I've made a few landings I won't be sure it's really fixed. The left strut also leaked air for the first year or so after the airplane flew, and then finally sealed itself up; that leak was up top -- as a general principle, air leaks out the top, fluid out the bottom -- and I have no idea what made it go away, other than the mysterious force that seals some leaks over time while it makes others worse. The right main, on the other hand, has been perfect, requiring neither fluid nor air in more than four years of operation.
[January 31, 2007]
The age of miracles is not over. I managed to connect the hydraulic flap control valve to the plumbing leading aft without taking the whole plane apart. I had to grind a 9/16" crow's-foot wrench down to a wisp, but it worked. One of the lines I installed was a remnant from Melmoth 1; I like incorporating little bits and pieces of the old plane in this one.
The two pictures below show the plumbing that is now complete. The upper one is particularly confusing. It is taken from beneath the airplane with the airbrake open and the cover that usually separates this area from the cockpit removed. The top of the picture is forward; the blue corrugated surface in the background is the hangar ceiling.
There are three physically identical valves in the picture (how many monkeys are hiding in the forest?). The one in the center, which controls the landing gears, is closest to the camera and looks larger than the others, but it is the same size and shape as the one in the upper left hand corner (airbrake) and the one at top center in the background (flap). My great accomplishment of the past two days has been to install the two vertical lines that run from the flap valve down to fittings below the main spar, which is the black object running across the bottom of the picture. For scale, the lines are 1/4-inch. Anyone who has done mechanical work will wince at the thought of tightening the nuts on the flap valve.
The valves are operated by cables running through Teflon-lined bicycle-brake-cable housings to the panel. One cable is visible in the groove in the capstan on the landing gear valve in the center foreground. The cylindrical white object just above the main spar is the hydraulic cylinder driving the landing gear. This whole mess is located under the front passenger's seat.
The picture below shows the same area, but viewed from behind the main spar, so that the continuation of the flap plumbing into the right main wheel well can be seen. The two 1/4" lines coming from the airbrake compartment pass below the main spar and are reduced to 3/16". They run above the gear when it is retracted, and down the rear spar. They pass below it to reach the compartment below the rear seats, where the flap synchonization system will be located (along with the oxygen bottle). The white rod is part of the gear retraction system. In addition to the right main gear, it is connected to a bellcrank that rotates a torque tube linking the nose gear to the mains.
[January 28, 2007]
I'm finally working in earnest on the flaps.
The first step is to provide plumbing from the control valve, which is in place, to the compartment under the back seats where the synchronization system (see January 8, 2005 -- time flies!) will be mounted, and from there to the outboard actuators in the wings. I improvise these things as I go along, and I found myself in a jam with respect to the lines going out along the wings. It happens that the roller tracks embedded in the fuselage sides and the plates to which the rollers and the inboard ends of the flaps are attached combine to eliminate any practical passage, even for two little 3/16" hydraulic lines, from the wing into the fuselage. It now appears that the solution will be to pass the lines forward through the rear spar outboard of the main landing gear, follow the front side of the rear spar to a point inside the fuselage, and then run aft underneath the rear spar -- there's about an inch between the bottom of the spar and the bottom of the fuselage -- into the compartment.
I have already made the mounts for the outboard actuators (see December 4, 2004) and have begun the mounts for the inboard ones. The outboard actuators are ready to install, but I have not yet made all the parts for the inboard ones. Nor have I finished machining the master cylinders. I also need to make new center tracks, and I'm not yet quite firm on their design. There's quite a lot to do.
[January 15, 2007]
I feel irritated with myself for spending time on something as stupid as this exhaust pipe fairing when I should be working on the flaps. The fairing is almost done. Viz:
The aluminum cuff will be trimmed for clearance; when the picture was taken it was still untrimmed in order to help with alignment. I'm a little concerned that I haven't left enough clearance for the pipe, which bounces around, mostly sideways, on startup and shutdown. The fairing has some freedom of motion, however, to allow it to accommodate itself to the pipe. When this is done I definitely have to work on the flap and nothing else.
The other day I flew to Reno with Javier Arango in his CJ2. I have a GI bill Learjet rating of ancient vintage, but I seldom get to fly in a jet. It's a different world. Noise-canceling headsets create a tombal silence in an already quiet airplane. Almost everything is done by twiddling knobs; it's something like operating a very complicated elevator. Javier mentioned having installed a new engine in his Bonanza and the throttle linkage coming loose in flight five hours later. The engine went to full throttle (note to self -- put a full-throttle spring on M2) and he landed by modulating power with mixture. Good presence of mind.
A few days after our trip a CJ crashed on takeoff at Van Nuys, killing both pilots aboard.
[January 3, 2007]
After an unaccustomed five days without going to the airport, I finished the structure of the fourth seat yesterday and today. Tomorrow I'll take it to the upholsterer. I installed the mic and phone hookups for the back seats a couple of weeks ago; the only thing missing back there now is ventilation. As long as it's winter, that's not too urgent.
I started work on a fairing for the exhaust pipe, the main purpose of which is to keep the boundary layer more or less intact between the airplane and the exhaust stream.
I happened to stumble on an RV discussion group online, where someone had inquired about the pros and cons of "slapping" a turbocharger onto his engine. Most of the response was negative, predicting all kinds of dire consequences -- overheating, cylinder wear, valve trouble, even flutter (because flutter is a function of true, not indicated, airspeed). I was reminded of the years that I spent worrying about all the terrible things that might happen if I turbocharged my engine. I finally did so, and have never regretted it. For me the turbocharger is not so much a matter of higher cruising speeds at altitude, though that's sometimes nice; it's more about rate of climb. True, I did once have to land on a road when a turbo lubricating oil fitting broke; but that was a bad fitting, not a more general engine problem. I don't run excessively high power settings, cooling is not a problem, fuel consumption on a per mile basis is lower (because I'm going faster and still leaning to between 50 and 75 degrees lean of peak), and I can maintain a steady 1,000-fpm rate of climb up 12,000 feet, where I like to cruise. All this might be different, I admit, if I were trying to cruise at 75% power at 24,000 feet, and that may be what people are dreaming about when they inquire about turbocharging their homebuilts.
[December 20, 2006]
In the current issue of Flying (January, 2007) I mention an interesting paper by a former Naval Academy professor, Bernard H. Carson. A reader kindly sent me an electronic copy of it, which can be downloaded here. It is in the public domain, and may (and should) be distributed and reproduced at will.
[December 16, 2006]
I spent the week working on the structure for the fourth seat. Very dull stuff. Daydreaming while working, I happened upon the nettlesome topic of the airplane's parasite drag coefficient, which hovers at around .021. There are still a few things I can do to reduce drag, but I doubt I will be able to reduce that number by much. How do some airplanes manage to get down to .016? The answer, I realized (again, since I have realized this many times before and then let it slip my mind), in at least some cases, is in the relative sizes of wing and fuselage. The P-51, for example, has a small, slender fuselage compared to its wing. The Bellanca Skyrocket has a conventional, Mooney-, Bonanza- or Comanche-like relationship between wing size and fuselage size. Melmolth 2, however, has a relatively large fuselage and an abnormally small wing -- 104 square feet as against 170-180 for most factory-built four-seaters. Since parasite drag coefficient is referenced to wing area, while the fuselage contributes disproportionately to parasite drag, an airplane proportioned like Melmoth 2 ends up with a higher parasite drag coefficient than its actual cleanness deserves. Or at least that is what I would like to think.
[December 4, 2006]
Went up to Reno to talk with Richard Tracy about the Aerion, a supersonic (Mach 1.6) business jet that's under development. It's 140 feet long, seats 6 or 8 in lounge-like comfort, and is supposed to cost $80 million a copy. I don't have a whole lot of sympathy with the need of Fortune 500 executives, who are already far more lavishly rewarded than they could possibly deserve, to shave three hours off a golfing trip to Scotland; but at least the scheme is, as Oppenheimer said of the atomic bomb, "technically sweet," and Tracy is such a nice guy he makes you feel that everything is fine. On the return flight I squeezed back into Whiteman just in time; M2 still has no lights. The moon rose over the southern Sierra as the sun was setting into the Pacific -- one of those transfixing moments that are worth all the work that goes before.
[November 17, 2006]
Flew to Camarillo with two passengers. This was the first flight with a human being -- a woman whose weight I estimate (being, to be sure, no great estimator of women's weights) as 140 lbs -- in the back seat, but since I had carried greater weights back there before, it was not exactly a test flight. CG was around 28% of chord. Anyway, she liked the view.
[November 16, 2006]
Flew to Torrance to talk with Bob Archer, antenna guru, about how to improve on my VOR antenna without increasing drag. Archer sells some strangely-shaped antennas that fit into composite wingtips, but my wingtips are too small for them unless, as he suggested, one were to replace the longest element in the antenna, a strip that runs straight backward for about 20 inches, with a screw-in rod that one would remove when the airplane was parked where some hapless pedestrian was likely to bump into a long, inconspicuous protrusion. An alternative was to embed a quarter-wave dipole in the leading edge of the horizontal tail. The spar is carbon, but is far enough from the leading edge to act as a reflector. The result would be an antenna with good sensitivity forward and poor sensitivity to the rear. If you have sufficiently good sensitivity forward you don't really need terrific sensitivity to the rear, but such deficiencies as the horizontal tail antenna may have could be supplied by one in the wingtip.
I put some fuel into the airplane before the flight, and a few minutes after takeoff, and shortly after turning on the automatic fuel tank switcher, I noticed that the tank cap was missing from the right wing. This was the first time in my life that I have taken off with an unsecured fuel cap -- I once left an oil cap off, back in the '70s -- and I was doubly fortunate: that I did not attempt to take off using the right tank, since suction on the filler opening could have interfered with fuel flow after rotation, and that the automatic switcher did not go to that tank while I was flying over Los Angeles. I don't know whether upper-surface suction could have interfered with fuel flow (one could calculate this fairly easily, comparing upper-surface pressure with the head of fuel in the tank), but I would not care to find out the hard way. It's surprising, and instructive, that I could have overlooked the tank cap lying right there on top of the wing -- I retrieved it later from the airport office -- and that I had never before even reflected on the safety issues -- if any -- that an open tank might entail.
[November 15, 2006]
Flew out to Mojave. The not-loud-enough theory was correct. Without the earplugs, the intercom is fine.
I caught a glimpse through a partly open door of parts for the next White Knight being made in Scaled's huge new hangar. The wingspan will be over 150 feet, I believe. SpaceShipTwo will carry six passengers and two crew and go somewhat higher than SpaceShipOne did. I'm still wondering whether suborbital "space tourism" will catch on. I imagine elderly members of the overcompensated classes staggering out of SpaceShipTwo, covered with barf and white as a sheet, and muttering, "That was great!"
[November 7, 2006]
The intercom works fine, at least on the ground, with the radio on. My latest theory is that it just isn't loud enough. I use earplugs underneath my headset, and it's possible that the intercom simply isn't as loud as the radios and the earplugs are blocking it out. In Melmoth 1 I used to use a Plantronics with earplugs that had holes punched in them and slender plastic tubes glued in to conduct sound. That might solve the problem, but in the meantime I'll just try flying without the earplugs. After all, I don't wear suspenders either.
[November 6, 2006]
I flew up to Paso Robles today to take a ride in Javier Arango's Corsair. I sat in back and couldn't see the instrument panel, so I don't have a very nuanced sense of what was going on. The acceleration on takeoff was like a jet's -- the airplane is 1,000 pounds lighter than it was with armor, armament, and military radios, and it cranks up 55 inches for takeoff. It climbs rapidly, as befits an airplane with a low wing loading -- not too different from a Bonanza's -- and a very low power loading. Chuck Wentworth, whose restoration business Antique Aero is at PRB and who maintains Javier's fleet of planes, said that there are only about ten Corsairs left that are in flying condition or could be brought to flying condition without major work.
Javier owns an original Sopwith Camel -- they're really rare -- and I sat in it. It fits like a too-tight shoe. The fuel is in a pressurized tank right behind you, the open stacks of the engine are spitting fire about four feet in front of you, and there's barely room to turn your head. Javier thinks that the seat back bulkhead was installed at the wrong station during one of the airplane's many trips to the repair shop; it was used for training, and crashed on takeoff with regularity. I cannot fathom going out to get shot at in such a thing; it's scary just to sit in.
The intercom in Melmoth continues to be a puzzle. It works on the ground, but not in the air. It occurred to me today, while I was driving home, that it could be that turning on the comm radio interferes with it; I'll check that tomorrow.
[October 25, 2006]
Apparently I didn't do a very good job of checking out the intercom, because it didn't work at all during the trip. My final adjustments must have had the opposite of the intended result, or else that one final wire made one thing work and another not. No matter; I'll fix it. The autopilot and the GPS tracker seemed to work, but from time to time one or the other -- I could never tell which -- would do something goofy; just enough to make you feel nervous when you're reading a map. Actually, the plane isn't bad to hand-fly in smooth air; but with turbulence the high stick forces in roll get tiring.
The trip was actually a failure in one sense, because a couple of weather systems got into complicity against us, and, operating under a VFR-only rule, we ended up leaving the plane in Denver in order to be sure to get to Providence in time for our daughter's college's "Parents' Weekend." But in another sense it was successful, because at its end Nancy did not say, "I never want to ride in this airplane again." Actually, the Airbus from Boston to Denver was worse. Whoever invented row 24 in an A319 should be made to sit in it for all eternity.
The cowl flaps worked very well; it was possible to control cylinder head temperature very delicately, regardless of speed and power. Performance was consistent with my current drag estimates; one point I noted was 180 knots at 9 gph at 14,000 ft d.a.; that's 60% of power. The plane used one quart of oil in 11 hours. On the negative side, the VOR antenna is very inadequate, essentially unusable at more than 40 miles; and the new pilot's seat was just okay, not miraculously comfortable as I had hoped it would be. There's always something to fix or change -- fortunately.
[October 14, 2006]
The intercom was a two-day puzzle, until I consulted the 30-year-old Collins audio panel installation diagram and found that it called for one more wire than the Sigtronics schematic seemed to require. Once I installed that, it worked fine; my first eBay experience is, so far, a happy one. I opened up the turn coodinator/autopilot to find out what the screw can have been touching, and I found nothing; so I wonder now whether the screw was really the problem at all, or just pretending. It seems to be working at the moment, anyway.
Leaving tomorrow for Boston, VFR.
[October 9, 2006]
Having concluded finally that my autopilot, which had been intermittent, was really not working, I took it to a local avionics shop where they bench checked it. It was working fine after all. I had already checked the wire harness for continuity, and so suspicion now fell on the servomotor. The shop lent me an overhauled autopilot (the autopilot circuitry is contained within the turn coodinator), which I plugged in, while holding it in my hand, with the panel opened up and my own unit removed. Everything now worked, including the servo. I then hooked up my own unit and found to my surprise that it ran fine. So I reinstalled it, only to find that once it was screwed into the panel it no longer worked. It took another half hour of swapping and testing to determine that the cause of the trouble was the upper left mounting screw. Although it was well under the 5/8" maximum length specified by a label on the case, it was evidently interfering with something inside. I cut another 1/8" from it, and the autopilot then worked fine. I still need to take the turn coordinator out once again and open it up to find out what the screw was touching.
It's very handy that the panel is hinged at the centerline and swings out for maintenance.
[September 27, 2006]
Today brought both my upholstered pilot's seat and, finally, an under-$80 intercom from eBay. The seat is a little disappointing; the cushion is thicker and softer, as hoped, but there is not enough lumbar support. It may be possible to change this, since the upholstery of the seat back seems to slide on like a slipcover and Velcro shut at the bottom. I also need to revise the brackets that attach the back to the pan, because the padding on the back is so thick that the pan is not so long as I intended it to be.
I was becoming discouraged about the intercoms, having lost several to other bidders, and so I had bids running on four of them at once. I lost one, won the second, and now, as luck may choose to have it, I'll probably end up with the other two as well. In the meantime I creep ever closer to a final decision about the back seat ventilation. A correspondent pointed out that an intake low on the left side would present some risk of ingesting exhaust gases, but I realized today that since my oxygen bottle is going to be under the back seats rather than under the rear seats' footrest, some of the space under the footrest can be used for a duct carrying air from a single right-side inlet over to the left side.
[September 23, 2006]
I still haven't done anything about ventilation for the back seats. I've more or less decided that the best inlet location is on the side, just below the top of the armrest, to minimize the amount of ducting required. But I've also been fiddling with sealing the window frames, which are probably the source of most of the high-frequency noise in the cockpit. They are also the source of ventilation, however, since in order for air to come in, it has to have a place to go out, and the rate of air movement, given a certain set of ducts, is going to be some function of the pressure difference between inlet and outlet. Of all the places where cabin air could leak out, the highest-velocity, lowest-pressure region is that around the front and top edges of the windows.
Contrary to intuition, air does not just naturally come in the front and go out the back; in fact, John Thorp put the ventilation inlet on the T-18 on the back end of the canopy, where the pressure is higher than inside. On the assumption that the best places to exhaust air would be those where the pressure is lowest, I considered two options: the top of the canopy and the side of the fuselage just above the wing. The pressure near the wing, at about 55% of chord, turns out to be more than 50% lower than that at the best point on the canopy top, and that location would be easier to protect against rain and to soundproof as well. At the moment, it's the leading contender.
[September 19, 2006]
The structure of the pilot's seat is at the upholstery shop and the job is supposed to be done by next Monday. Meanwhile I've been trying to make some progress on the flap actuating cylinders. I ruined one of them in a lathe today; fortunately I had made five and need only four. Now I can't permit myself any more mistakes on the cylinders, but I am still free to ruin one piston and one cap.
I've been bidding on intercoms on eBay; so far I haven't snagged one. Trying to figure out how to get a little extra money, I reflected that I could sell my DME and ADF, which I have not installed in the plane, on eBay for a couple of thousand dollars; but then I wondered whether I would regret that if at some future time I wanted to install one or both. With GPS they seem a bit outdated, but they are IFR legal, and my handheld GPS is not. I was thinking about selling my magnesyn remote compass and inverter, too -- genuine World War II equipment, but they took Nancy and me to Europe and Japan -- but then I remembered that the sensor/transmitter, which was mounted in the tail cone, was chewed up by the propeller of the Cessna that destroyed Melmoth 1.
[September 13, 2006]
Sometimes the maintenance gods are kind. The encoder is in and working perfectly, the left main gear strut has new O-rings, and I talked today with an interiors guy about finishing off my new pilot's seat. The problem with the autopilot was just a bad connection at the servo. Not bad for five days, including a weekend.
[September 8, 2006]
Some time has passed. Nancy and I have just returned from a three-week trip to the east coast, where we left our daughter Lily at college. We are planning to go back in October to visit, this time in Melmoth 2. This is noteworthy, because Nancy, although she flew all over the world in Melmoth 1 (see Two Mike Uniform), has never even sat in Melmoth 2, let alone left the ground in it. She was never fond of flying, but I attributed this particular reluctance to a feeling that she needed to be sure that Lily was properly launched before risking her own life again in one of my contraptions.
While vacationing I worked a little on some design ideas. I sketched a controllable wastegate -- I am now using the fixed type, from a Turbo Arrow -- and thought about how best to provide ventilation for back seat passengers. I decided on a couple of NACA scoops low on the sides, because they would keep the internal ducting to a minimum. Before leaving, I hooked up an intercom that I had made from a kit twenty years or so ago, but it didn't work. I'm now scouting eBay for one that does.
I realized back in August that the failure of the cowl flaps to close completely was probably due to deformation of the cowl top under air loads, and would not be fixed by a spring; what it really needs is for the closing limit switch to be touched by the cowl flap itself rather than by the actuator. The oil temperature rises by about ten degrees Celsius when the cowl flaps are closed, so they are doing something. My encoder failed just before we left, and since returning I've been busy installing a new one; it has yet to be tested (a new pitot-static calibration is required, since my airport is within the 30-nm veil of LAX). Various other service obligations loom, including a leaky left main gear strut O-ring. Fortunately the strut drops out of the airplane pretty easily. At some point I also have to remove the right wing to deal with a fuel leak in it. The leak is high in the tank and is not a problem with less than 30 gallons or so in the tank; but for the cross-country trip I may want to be able to carry more than that. There is also the question of upholstery for the new pilot's seat; I will probably end up settling, for the time being, for a few throw pillows. Finally, the wing leveler, after being intermittent for a while, is now seemingly in a vegetative state. It's tedious taking care of all these glitches, because after a lot of time and expense you're just back where you started from. I prefer progress.
[July 25, 2006]
Sitting in the new back seat I realized that one thing I had forgotten was ventilation. Under the bubble canopy, in the present 100-degree weather, you would be grateful for a faceful of blowing air. The question is, where to take the air in. The cowling hot-air exhaust streams diverge around the canopy and follow the shoulder of the fuselage; the apparent options for a cool-air inlet are (1) right behind the canopy on the centerline or (2) somewhat low on the side. I'd like to use a flush inlet, as I did for the front seats. I'm not sure how well one would work in the wake of the canopy, where the boundary layer is fairly thick; on the other hand, the pressure is relatively high there. To avoid doing anything rash, I'm painting the cowl flaps and the surrounding portion of the cowling first.
[July 19, 2006]
Took a friend on a 45-minute low altitude air tour of Los Angeles. What a horrible sight. The new aft limit switch on the cowl flaps worked, but the flaps still would not close tightly; I need to install that spring. This was the first flight with my new pilot's seat, currently upholstered with a slab of foam rubber on the pan and an old Ensolite camping pad on the back. The former pilot's seat is now in the back, facing aft, and the airplane is three-quarters of the way to being the four-seater it was intended to be. At a density altitude of about 4,000 feet, performance on this leisurely tour was 120 kias at 5.7 gph.
[July 10, 2006]
Not yet having fixed the sticking microswitch, I took off for Palo Alto only to find that I could not move the cowl flaps from the fully-open ground position. I flew up to Palo Alto (1:40, 15 gallons) and spent the day at NASA Ames. It was pretty breezy when I got back to the Palo Alto airport, and I didn't want to take the entire cowling off, but I snaked my arm under it and managed after several tries to unstick the microswitch. This allowed me to operate the cowl flaps, as long as I didn't run the jackscrew into the aft (closed) stop.
It's very warm at altitude these days; at 15,000 DA I was getting 170 ktas at 8 gph, but I started getting misses if I climbed much higher. This was a problem on Melmoth 1 until I switched to pressurized Slick mags. The Slick is an inferior mag to the Bendix, or so I'm told, but it does have this one advantage. People say you can run the unpressurized Bendix mags at high altitude without missing (which is caused by spark jumping from one point to another because the insulating effect of the dense air in the cylinder is so much greater than that of the air in the mag), but I can't; maybe my harness is lousy. Anyway, I can't go much higher than 15,000 feet. Eventually, I'll have to put my Slicks back on; I took them off in 2003 because of a coil problem. They're fixed now, but I've never bothered to re-install them.
There are lots of neat things at Ames, including a wind tunnel with an 80 x 120 foot test section, but the one I liked best was a transparent trough of slow-moving water into which filaments of fluorescent dye, in ultraviolet-lit colors as vivid as those of marine tropical fish, are injected to help visualize the flow over models. This would be so much better to have at home than an aquarium...
[June 30, 2006]
The cowl flaps are working routinely, though I have not yet added a spring and so they still do not want to close completely. I now realize that since I have not installed the annunciator light that was supposed to show when the motor is running, I have no way of knowing whether the 1/4-inch gap that persists when I close the flaps is due to the motor being overloaded or just to hysteresis and tolerance buildup in the system. I'll get to that sooner or later. I measured the outlet areas; the aggregate area is 18 sq in closed and 98 open. The inlet area is about 70 sq in. The intermittency problem I noted earlier turns out to be due to a sticking microswitch; it should be easy to fix.
I had lunch at Mojave yesterday with Mike Melvill; we were joined by Dick Rutan, who has been flying a Columbia 400 and had some thoughts to offer on the subject of hypoxia. The gist was that after a certain age, even men of iron turn out to be made of flesh and blood. At one point Bruce Evans, who was the head shop guy on Voyager, stopped by our table with a friend. After introductions, it was apparent that the young man had no idea who Dick was. We all danced around the subject idiotically, and I later regretted not simply saying, "This is the first person ever to fly nonstop around the world; it took him and his companion nine days continuously in the air." I don't know whether our failure to be clear was due to a reluctance to appear boastful or to an in-crowd's desire to make the poor outsider feel foolish. Dick later mentioned that when he returned from that flight and complained to Burt that at one point, in rain, Voyager had gone into an uncontrollable dive -- the result of the canard losing lift because of water droplets disturbing the flow -- Burt's reply was, "Don't fly in rain." Dick mentioned this as an instance of a fratricide narrowly averted, but it was not clear to me whether he meant that Burt had nearly killed him, or that he had felt like killing Burt.
It was over 100 degrees, and under the Mojave sun the controls of the airplane had become so hot that when I left I had to use a spare baseball cap as a potholder in order to touch the sidestick.
[June 26, 2006]
Problems. Flight test indicated that there was insufficient power to fully close the flaps at cruising speed, and at a certain point the whole actuator just seemed to stop working. I assumed I had sheared a roll pin, or worse, but when I took off the top cowling and tested it on the ground it was running again. I wonder whether the motor has a built-in overtemp protection circuit.
Making extremely pessimistic assumptions about pressure distribution, I suppose I could be asking the jackscrew for as much as 75 pounds of force. Now that it seems apparent that the natural inclination of the flaps is to open -- this was not intuitively obvious to me before -- I suppose the next step is to add a spring to alleviate the closing loads.
The day was hot and, for southern California, unusually humid, with temperatures of 95 on the ground and 78 at 7,500 feet. During the climb to 7,500 feet at 100 kias, the temperature of the hottest cylinder did not exceed 410 degrees, and most were quite a bit cooler. Later I cruised for some time at 4,000 feet (7,000 density altitude) at 2,000 rpm, using 5.5 gph, with a true airspeed of 123 knots. This is close to the best range speed. Here is an excerpt from the calculated performance at 2,000 pounds:
[June 23, 2006]
More delay. I was unrealistic, it turns out, to think that I could set up the limit switches the way I did. After several mishaps that proved, at least, that the jackscrew is incredibly strong, I took the whole thing apart and revised the rocker to incorporate a separate part that contacts the limit switches and allows fine adjustment. I hope to get this installed this weekend and to be able to fly again next week. It still seemed rather slow running in the airplane, where the battery was at 24 volts; I don't suppose that raising the voltage to 28 will make a huge difference. If I can't get used to the speed, I can always double it by connecting the jackscrew to the rocker by the same bolt as secures the pushrods.
[June 19, 2006]
I ran the cowl flap actuator today with temporary wiring. Other than going rather slowly -- I believe this is due to my power supply, which consists of two ancient car batteries in series, providing only about 21 volts -- it seems to be fine. Most of the airframe wiring, including the quick-disconnect to the cowl top, is already installed in the airplane. Here is the test lashup:
It looks bigger than it is. The motor is about four inches long, and the pushrods going to the cowl flaps are quarter-inch diameter, .016 wall stainless steel tubing. The washers lying nearby (below) are #10. Here is a closer look at the actuator:
The whole thing rests on a sheet-aluminum shoe that bolts to the cowl top. (You're looking at it upside-down, of course; on the airplane, it hangs from the top surface of the cowling.) From left to right, there's the gearhead motor, an aluminum adapter/support, and a bearing block and jackscrew cannibalized from a Lear Siegler linear actuator. The jackscrew is fully retracted in the picture, and also hidden by the greenish dust cover. An aluminum rod end is pressed and pinned to the end of the jackscrew nut, and inserts in a clevis that projects from the top of a rocker. The rocker pivots around a bolt through the shoe and includes positive motion stops at plus and minus 30 degrees. The pushrods are bolted to the rocker halfway between the jackscrew connection and the pivot bolt, providing a mechanical advantage of 2:1. Two microswitches shut off the motor when the apparatus reaches its travel limits. The DPDT switch visible behind the motor is for testing purposes; the actual switch is a rocker located between the throttle and the trimwheel.
[June 10, 2006]
Nearly all the parts for the cowl flap mechanism are made. I had to recontour the inner skin of the cowl top, shorten the engine lifting lug and re-route the breather tube to accommodate the thing -- nothing is ever quite so simple as it seems when I first visualize it -- but all the parts fit now. I can turn the jackscrew easily with a screwdriver, so the starting and running friction, which I assume will anyway diminish with use, are not excessively high.
The trickiest component to make was a 7075-T6 aluminum bushing that connects the jackscrew to the electric motor. It is keyed to the jackscrew shaft and snugged up against the supporting ball bearing by a thin-walled nut that disappears from sight down inside the bushing. Everything is then locked with a roll pin. I've never cut a keyway before, and I don't have any real broaches or whatever tool is appropriate. I made a sort of stout chisel 3/32" wide by grinding down a 1/4" drill bit, and then scraped the keyway, which is 1/16" deep, using my drill press as an arbor press. Surprisingly enough, it worked. The only component still remaining to make is a bracket to support the two travel-limit microswitches. I will then install the assembly so that I can at least fly the airplane again, and put in the actuating switch, limit switches, monitoring LED, and wiring later. (The LED is to let me know when the motor is running; it goes out when the actuator reaches either end of its travel.)
[May 26, 2006]
Step by tiny step, the setup for actuating the cowl flaps with an electric motor is getting made. I found when I fitted the flaps to the cowling that the small misalignment at the trailing edge of the left flap could be easily eliminated, and they both fit pretty well now -- not that it even matters. Here they are in their fully-open (taxiing, parking with a hot engine) and fully-closed (low-power cruise or descent) positions, and as seen from underneath. The actuator motor will be secured to the top cowling, about a foot behind the flaps.
[May 6, 2006]
I finished the sheet-metal work on the second cowl flap yesterday. It did seem as though breaking the twisted torque box into smaller pieces of metal relieved most of the stress in it, but I won't be sure how good the fit to the cowling is until I've installed the flap hinges.
Back when I was planning to operate the cowl flaps manually, I was concerned about the direction and magnitude of the air loads they would experience, and I made up a little CFD model of the cowl (as a closed plenum with an inlet, a central obstruction representing the engine, and an outlet containing a turning vane). I didn't learn much from it, other than that CMARC can handle streamlines in strangely shaped spaces; but it produced an interesting image. Here it is. As usual, color represents pressure, with the warmer colors indicating lower pressure and higher velocity. It appears that there is a large area of low pressure on the aft portion of the turning vane, suggesting that its natural tendency will be to open rather than close.
[April 29, 2006]
As I hoped, progress on the second cowl flap has been faster than on the first, now that the kind and arrangement of all the pieces is established. I am making one small design change, however, because the first flap, although I assembled and riveted it in a rigid jig, once removed from the jig popped slightly out of shape. Its twisted shape is not one that comes naturally to sheet metal, and so, after you have forced the pieces into alignment and riveted them, when you remove the assembly from the jig it naturally seeks the position that minimizes stored stress. The distortion is slight -- about 1/16th of an inch at the trailing edge, which in theory was supposed to lie perfectly flush with the top of the cowling with the flap closed. Fortunately, the flaps would be closed only for descent, or possibly for low-power cruise in Arctic conditions, but never on the ground; and the trailing edge of the flap is not visible from the cockpit when it is in the closed position anyway. So, as people around here always say when rationalizing a blemish, "You'll never see it from Burbank."
I considered a couple of approaches to preventing this problem in the second cowl flap. One would be to forestall it by building a bit of excess twist into the jig, so that springback would bring the part to the desired shape. This would involve some guesswork, since the right flap, which I'm making now, is not of quite the same size or shape as the left. Another approach was to subdivide the inner skin of the torque box into three panels, each of which would incur a minimum of internal stress. I decided to go with the subdivision method.
In the meantime, I was thinking about how to wire the motor, which drives a jackscrew with a limit switch at each end of its travel. This is a very common kind of circuit, but since I always manage to come up with the most complicated way of doing things I asked a couple of friends to suggest how they thought it should be done. In the meantime I designed my own circuit. My two helpers submitted the same design, which requires one dpdt momentary-contact switch (or rocker) and two single-pole microswitches. My version was basically similar, but I managed to cram in a couple of dpdt relays as well. Industry is probably full of people like me; that's why there are so many stupid designs on the market.
[April 24, 2006]
Today I flew up to Paso Robles, about 140 nm northwest of here, on Javier Arango's invitation to fly with him in his Sopwith Strutter. The airplane's nickname refers not to a proud way of walking, but to the arrangement of struts between the fuselage and the upper wing; the rather ungainly full version is "one and a half strutter." It took a VOR approach to minimums to get into PRB, but the clouds broke by midmorning. Flying in the Strutter was fun; it's not exactly a responsive airplane, but it's an honest and very flyable one. It can barely break 100 mph in a dive, but it has a great rate of climb with its 160-hp rotary engine and 100-inch prop. Phil Makanna, who has a great book out about WWI airplanes, took this picture as we blew by. The lump in back is me.
Melmoth's autopilot and GPS tracker worked fine, contrary to expectation, and its speed and fuel consumption were still consistent with an equivalent flat plate area of 2.3 square feet and a parasite drag coefficient of .022. I've begun leaning early in my climb -- may as well cool the engine with air, which is free, as with fuel, which is now $4 a gallon -- but this is a tactic that can be used only with airplanes that climb adequately at low power settings, and by pilots who don't mind taking it easy. Northbound I cruised at 10,500 ft and 163 ktas, burning 7.5 gph. Returning, I flew at 11,500 and 8 gph, trueing 169 knots. Those power settings are 51% and 55% of power, respectively.
I have one of the adjustable cowl flaps finished, and will begin the other tomorrow; I hope that now that I know some mistakes to avoid, it will go more quickly than the first, which took ten days to make.
[April 8, 2006]
I flew around for a while on the 6th. There was a scattered layer of small cumulus at around 5,000 feet and glassy air above. The mountains along the north edge of town are all snow-capped and their lower flanks are green from recent rains. Terrific visibility. I collected some speed-power data that seemed to confirm that F is now around 2.3 sq ft. One indication, besides correlations between the airplane and the performance prediction program, is that a line through several speed-power points has a shallower slope than it used to; I take this to imply a smaller parasite drag component.
The autopilot, which I thought I had repaired (broken wire), is still not working.
Bored with the new seat, I spent several days modifying the old cowl flaps so that they would rotate as intended without bumping into anything inside the cowling. I think I've got that part down now, and today I made templates for the edge ribs. I've decided to use the electric motor initially and to test how much engine power I would be able to use, and for how long, without overheating, if the cowl flaps were to fail in the closed position. That will give me a basis for deciding whether to use an electric or a manual actuation system.
One of the advantages of the moveable cowl flaps will be a super-open position that will drain hot air from the cowling much more effectively on the ground. Although placing the injection manifold in the air inlet nearly eliminated the fuel-heating problems that use to plague me, the injectors are still on the hot-air side of the engine and long idling or taxiing eventually brings about some roughness.
[March 23, 2006]
I have been working on a new seat and, at the same time, on making the cowl flaps adjustable. Today I went to a local surplus store, Apex, where I promptly found a little 24-volt gearhead motor of exactly the same type as I use for switching fuel tanks automatically. It would be ideal for operating the cowl flaps, using the same type of 6-pitch double-lead jackscrew as I used for the revised pitch trim. But I'm vacillating about whether it would be preferable to operate them electrically or manually. Electrically is a little more convenient both in construction and in use, but there is a possibility of the system failing with the cowl flaps closed. A manual system has fewer failure modes and is more likely to give warning of impending failure. A combination, similar to electric trim in being basically a manual system with an electric motor to drive it, would be rather complicated. One of these days I'll make up my mind. In the meantime I'm making a new pair of cowl flaps to replace the scuzzy temporary ones at whose picture you may scoff in the entry for September 23, 2005.
[March 11, 2006]
The past month has been devoted to rear seats, or rather to providing the necessary seat and seatbelt anchors for seats that will be installed at some future time. I intend to make a new pair of front seats, applying lessons learned from several years of flying with the present ones, and to put the present seats in the back, where they will face aft. Getting into the rear seats is far from easy, and will require that the backs of both the front and the rear seats be able to fold down flat. Once you get seated, however, it's perfectly comfortable back there, with full legroom, more than 48 inches of shoulder width, and a splendid view. Each rear seat is held in place with three pins and a single screw, and rests on two graphite rails that underpin the floor. The flap master cylinders and the oxygen system will both be located in the subfloor space below the rear seats.
The lessons learned from the first pair of seats were three. First, and this seems rather obvious now, instead of making the supporting surfaces for the pan and back match the desired seat angles and contours and then adding padding on top, I should have made the supports as thin and as close to the outside envelope of the seats as possible, and provided all the tilt and contour with the padding. The new seats will be able to have twice the cushion depth of the original ones.
Second, the seat pans should be longer than I made them (copying a VW Jetta seat); they will be 18 or 19 inches long rather than 16, and will extend to within a couple of inches of the crook of the knee.
Finally, in M2 the seats are mounted on a flat floor with very little space beneath them. With the present seats, whose pans are tilted, the gap between seat and floor tapers from maybe an inch deep at the front to zero at the rear. It makes a great trap for pencils, film cassette canisters full of earplugs, and so on. If there is a space under a seat, it should either be deep enough to allow storing things (like charts) and reaching in to retrieve them, or else so shallow (and perhaps equipped with a seal of weatherstripping around its perimeter) that it can't swallow up debris and valuables.
There's more to aeronautical engineering than meets the eye.
[February 13, 2006]
The drag of a blind cavity -- one with no leaks other than its opening in the airplane surface -- is difficult to predict. Hoerner gives a drag coefficient of 0.01 based on the area of the opening, assuming that the entire break in the skin lies parallel to the flow direction and does not present a hole facing into the free stream. The reason the value is so small is that air generally blows right past the opening, while friction with the passing air merely causes the small mass of air inside the cavity to rotate at a comparatively low velocity. If the two air masses remain generally separate, they exchange little energy. I suppose, however, that if the geometry of the cavity is such that passing air enters it in one place and leaves at another, or if passing air is drawn into the cavity and then separates at its aft edge when rejoining the free stream, the drag may be greater.
My nosewheel well opening is 40 inches long, and is 10 inches wide for most of its length; the area of the opening is about 375 sq. in., or 2.6 sq. ft. At my usual cruising speed (around 135-140 kias) a change in indicated airspeed of one knot corresponds to about .1 gph in fuel flow and about .1 sq ft. in equivalent flat plate area. The apparent speed gain of 2-3 knots from adding the doors implies a drag coefficient ten times larger than Hoerner's. I conclude that either the higher speed is the result of wishful thinking on my part, or else there must have been some exchange of energy between the air inside the well and the air passing by. If the latter is the case, I attribute it to the location of the well very close to the front of the airplane and immediately behind the propeller, where the boundary layer is still quite thin, and perhaps also to the complicated collection of stuff inside the well with the gear retracted, which would have disturbed the circulation of air within the well.
[February 7, 2006]
I did a couple of speed checks with the new nosewheel well doors and was pleasantly astonished to find an increase of several knots. This remains to be verified over a number of flights, but my equivalent flat plate area seems to have dropped from 2.5 to 2.25 square feet.
Here is the door mechanism:
The first picture shows the right side of the well; forward is to the left. The gear is down; the green part of the well is the aluminum engine bearer cum nosewheel compartment; the reddish-brown area is part of the composite fuselage structure. On retraction, the large aluminum arm swings 90 degrees aft (that is, to the right), coming to rest against the stop block. On the way down it contacts a roller (hidden from view) on the end of the S-shaped bellcrank and pushes it downward. The other end of that bellcrank raises the right door by means of the short link just visible, and very overexposed, at lower right. At the same time, the motion of the bellcrank is conveyed through an idler to a torque tube running across the top of the well -- the green thing angling toward the upper left. In the other picture, which shows the left side of the well -- the front is now to the right -- the arm on the torque tube is connected by the slender green tube to the left door. The large stainless steel tube running from left to right is a nosewheel steering actuator.
As far as the payoff is concerned, my method of assessing performance changes is to correlate observed speeds and fuel flows with my performance calculation program, which does a fairly good job of keeping track of all the variables. I collect speed/fuel flow data at random, set up the program parameters to match the altitude and weight, and vary flat plate area until the observed performance matches the calculated. The program takes care of the induced-drag component, I hope accurately. In any case, here are some observed performance points, reduced to density altitude, fuel flow and indicated airspeed, with true airspeed added in parentheses. The final value is the calculated equivalent flat plate area. EGT is always about 60 degrees lean of peak (by TIT). Incidentally, to convert the equivalent flat plate area to a parasite drag coefficient (CDo), divide by the wing area, 106 square feet.
8/30/05: 14,000 ft, 8.6-8.7 gph, 138 kias (171 ktas); 2.6
9/2/05: 14,500 ft, 8.6 gph, 139 kias (173 ktas); 2.5
1/2/06: 13,500 ft, 8.2 gph, 139 kias (170 ktas); 2.4
1/14/06: 12,200 ft, 8.7-8.8 gph, 143 kias (172 ktas); 2.5
2/8/06: 12,000 ft, 7.7 gph, 140 kias (167 ktas); 2.25
2/8/06: 10,000 ft; 7.4 gph; 137 kias (160 ktas); 2.25
The change in equivalent flat plate area, evidently due to the nosewheel doors, is clear. Based on the present value, the maximum cruising speed at 150 hp, assuming a critical altitude of 17,000 feet, would be around 200 knots using 10.4 gph.
[February 4, 2006]
So it's true: everything takes two months. I finished the nosewheel doors today. My estimate of two or three weeks to do the left door -- I've have the right one working for a month -- was as usual optimistic, though not so much as it seems, since I made two three-day trips in the past month. I have not yet gathered any speed data yet; I'll do that next week.
[January 4, 2006]
As was the case last year, the year's-end holidays entailed so much cooking and cleaning up -- we entertain a lot -- that I scarcely got out to the airport at all. Today I finally finished up the right nosewheel door and did a short test flight. Everything worked as hoped. Now I have to mount the left door and install the linkage, consisting of two bellcranks, three pushrods and a torque tube, that connects the left door to the right. This should not be very complicated, and I hope to get it done in two or three weeks rather than the month the right door took. The flap actuation system has been pretty much on hold for this, as have the cowl flaps and the back seats.
[December 18, 2005]
I've been working for the past couple of weeks on the nosewheel doors. In the course of testing the actuation system, I found that in three years of operation the connection between the main and the nose actuators -- all three struts' retractors are mechanically interlinked -- had developed some play. The bellcrank that was supposed to be holding the nose strut up and locked by going overcenter was not, in fact, going all the way overcenter at all. Trapped hydraulic fluid holds the nose strut up anyway, but the full overcenter motion of that bellcrank was needed for closing the doors. After some floundering around and several false starts I realized that the best way to correct the problem was to adjust the lengths of some push-pull rods in the wing centersection. When I did this I was rewarded not only by proper actuation of the right-side door -- I have still to build the linkage for the left one -- but also, unexpectedly, by the right main gear doors' closing more snugly than they had ever done before.
The
system by which the three gears are linked to one another is pretty simple,
but the system by which the inboard main gear doors open to let the wheels go
by and then close again is a bit trickier. There are no cams or lost motion
devices; everything is bellcranks and links. I spent a lot of time, years ago,
perfecting the kinematics, and even more time writing a computer program that
displayed the motions of all the parts and analyzed the stresses in them. Unfortunately,
the program, originally written for DOS, now seems to display all of its text
in Armenian -- the result, no doubt, of some kind of dirty tricks by Microsoft.
But the animated gear action can still be seen. The actuation system for the
nosewheel doors, I confess, violates the no-lost-motion rule; using only bellcranks
and links, it's very difficult to get the doors fully open quickly enough to
clear the tire as it begins to drop out of the well.
Revisiting the whole system I now feel that, given the short moment arms available for some bellcranks and the relatively high forces involved, I was too ready to use small hardware and bearings. Their strength is sufficient, but I now think that sometimes it's better to use more massive components with lower surface loadings; they wear more slowly, remain in adjustment longer, and are more resistant to damage and overload. Perhaps this is why, though I got away with a single 3/8-inch bolt in a spherical bearing at each end of the main gear trunnions in Melmoth 1, Piper selected a thick-walled steel cup an inch or more in diameter for the same purpose in the Arrow.
At the same time, I have also been machining components for the flap master cylinders and preparing to install adjustable cowl flaps. After worrying for a long time about how best to actuate the cowl flaps electrically, I decided that they could equally well be manual -- a great simplification, and relief as well.
[November 30, 2005]
Yesterday I flew up to Paso Robles, where Javier Arango has a beautiful collection of very exact WW1 aircraft replicas. Most are flying with the original engines, and because there is a shortage of 110-hp Le Rhone rotaries in the world Javier is having a set of ten made to order by a first-rate machinist. The crankcases are machined from a 605-lb steel cylinder, and weigh 37 pounds when finished. Lots of chips. The French and British turned out something like 30,000 of these things between 1917 and 1919. Anyway, it was a beautiful day for flying, but a high and a low side by side were squirting the wind southwestward at a pretty good rate. I flew up at 10,500 feet to stay above the turbulence, and my ground speed was 115 knots. The return trip a few hours later made up for it, though; at 13,500, using 8.3 gph, the groundspeed was 220 to 230 knots, and I briefly saw 254 when I started to descend.
[November 21, 2005]
I flew to Santa Maria today to visit Paul Lipps, an exponent, like me, of the "piece of shit" school of craftsmanship. Nevertheless, he cares about neatness where it counts. When I was getting ready to leave he cast a disapproving eye on my wings, which have not been washed since before Oshkosh 2004. He wetted a towel and handed me a dry one, instructing me to follow along behind him. He cleaned off a year's worth of dead bugs and I wiped away the water drops and dusted off the top of the wing. It happened that I had collected some performance points on the flight up, and I collected more on the flight down. It appeared that about a tenth of a square foot had been shaved off my equivalent flat plate area. This is not so surprising as it sounds, since the difference between "standard roughness" and full laminar flow is about 60 "counts," that is, .006 square foot of equivalent flat plate per square foot of exposed wing area. My exposed wing area -- this is planform area, not wetted area -- is about 85 square feet, and so the difference in drag between the absolutely worst surface condition and the absolutely best would be half a square foot of equivalent flat plate. Of course my wing was neither the worst nor the best, but it's possible that there was enough crud on it to eliminate a good deal of laminar flow.
Paul reported losing several knots when the nosewheel door actuator on his Lancair 235 (which cruises 173 knots on 5.6 gph, running rich) broke and the door failed to close; that gave me hope that I may see some benefit from closing up that vast trench on my airplane.
It was a magnificent day for flying, especially in the late afternoon, with air of an aquarium-like limpidity, infinite visibility, and some ragged clouds to filter the light of a lowering sun. Although the trip takes only 45 minutes, I climbed to 11,500 feet and was glad I had. Los Angeles is not a city noted for its beauty, but on an afternoon like this "Earth has not anything to show more fair."
[November 12, 2005]
The trim system has been working well. I will not know whether it has sufficient authority for the full CG range, however, until I have the flaps working. I did replace the old pushrod with a straight half-inch-diameter hollow pushrod, which unclutters the area a bit more. The trim system changes removed about 10 ounces. That's how it always is: remove ounces from one tail, add pounds in another.
I modified the mount for the GPS coupler to angle it toward the pilot; it was hard to see the LEDs. I may eventually move it to the top of the panel directly in front of me, but for the time being it is to the right of the panel centerline. I don't like the way the mounting bracket protrudes from the panel; it seems to violate basic crash safety principles.
I finally began working on the master cylinders for the flap actuation system. I had to ask around to find a welder; they come and go, and I haven't used one in a long time. Flyte-Weld, near Burbank Airport, did a beautiful job joining the cylinders to their bases, and didn't charge much. As usual, I am designing the things as I go along, and making an extra one in case I screw up.
I am also finally fitting the nosewheel doors. I laminated the doors themselves probably a decade or so ago, attached hinges to them nearly a year ago, and am now putting the mating hinges in place on the edges of the wheel well. The operating mechanism for the right door is quite straightforward; the left one is a bit more complex, since the motivation comes from the right side of the well and has to find its way over the top of the retracted gear strut to reach the left side. I'm very curious to see whether any speed gain comes from closing up the well. You'd think a 10-inch-wide, 30-inch-long sharp-edged cavity in an airplane's surface would produce some drag, but Hoerner gives a CD of .01 referred to the area of the hole. That would be 3 square inches of equivalent flat plate, an improvement of 0.82% -- not enough to measure.
[October 19, 2005]
I
finished the new pitch trim mechanism yesterday and test flew it today. It works.
A chain rotates a sprocket (hidden from view in the picture) that is connected,
via a universal joint, to a telescoping shaft of two nested thin-walled square
brass tubes. The shaft has to telescope because its length changes by a couple
of inches as the elevator moves up and down. It connects, through a second universal
joint, to a 6-pitch double-lead jackscrew that is mounted on the bottom of the
elevator, supported by the squarish aluminum bearing block. The fore and aft
movement of the jackscrew nut positions the trim tab through a short link (upper
center, with the three lightening holes in it). I made the mistake of greasing
the brass tubes, which actually increases their resistance in cold environments;
but it will be easy to clean them.
The old system, pictures of which can be found in the "Pictures" neighborhood of this website, was much more complex because the trim tabs acted as servo tabs as well, intended to reduce pitch forces. It turned out, however, that pitch forces didn't need to be reduced, and there was insufficient trim authority to maintain cruising speed with a heavy load in the back seats or, for that matter, to trim to 1.3 Vs for landing approach with a forward CG. Whereas the old system provided only five degrees of tab travel for trim, this one provides 27. Since it uses only one of the two tabs, however, and lacks the moment-reducing servo effect, it is not five times more effective than the old system but perhaps only two times. It's also about half a pound lighter.
[October 1, 2005]
I dug up some old pictures. Construction of the airplane began in a hangar at Whiteman Airport, but soon moved to my house in Echo Park. Here is the fuselage in the garage, where it remained for about ten years:
The
garage was ten feet wide, the airplane eight, and the workbench two. The place
eventually became so crowded that I had to get down on my hands and knees to
move from one part of the airplane to another.
Mitzi Trumbo took this picture with a fisheye lens from atop a ladder just outside the garage door. The length of the fuselage and of each wing panel (at this point the wings were stored in the basement of the house) was determined by the length of the garage, which had been built in the era of the Model A Ford. Eventually further progress became impossible, and I moved back to a hangar at the airport.
A bunch of friends helped carry the plane out of the garage. This was early in the 1990s. The dramatis personae are, left to right, Tom Shima,Carl Byker (legs only), Matt Damon (then available for odd jobs), myself, Aaron Stockard (legs again), and Walter Field.
In the hangar, I began to progress more rapidly, and by the late '90s most of the parts were in close proximity to one another. The canopy had just been tacked into place when I took this picture. The piecemeal assembly of components cured at different times is evident, as is a somewhat casual approach to the application of leftover surface filler.
[September 23, 2005]
This morning I gathered some data about cowling pressures with the new cowl flaps, which are currently locked in the open position. I used two water manometers, one comparing the high pressure plenum (below the engine, fed by the cooling air intake) to the low pressure plenum (above the engine and vented to the outer world), and the other comparing the high pressure plenum to ambient (static) pressure. The ratio of the difference between the two plenums to the free stream dynamic pressure is called the engine pressure difference or pressure drop; the ratio of the high pressure plenum pressure to the dynamic pressure is called the pressure recovery. I found the pressure recovery to vary from .68 at 90 kias to .54 at 140. On the other hand, the engine pressure difference, which is boosted by the extraction effect of the cowl flaps, went from .86 at 90 to .84 at 140. The pressure drop seems fairly good, but the pressure recovery is mediocre, possibly because of poor diffusion of the inlet air.
Here is how they look -- namely, like bits of scrap metal found lying about. Actually, the left one is what was there before, but with different side flanges and in a different position; the right one was made from scratch. Despite protruding, they do not seem to affect performance. The idea is to make them rotate in such a way that the rear edges become flush with the cowling, closing off the rear outlet, in cruise, while the front opening narrows somewhat. The gray area behind the left outlet is just primer, and has no particular significance.
[September 16, 2005]
In the course of the random walk that passes for the development and refinement of Melmoth 2, I was suddenly seized, early this week, by an impulse to fiddle with the turning vanes (that is, cowl flaps) in the cowling air outlets. I cobbled up a new pair, which are not flush like the old ones, but rise up somewhat above the surface of the cowling on the principle that the plume of air emerging from the cowling does the same. They look like something from a Wilga, but they increase the outlet area and improve the cooling considerably, dropping CHTs by a good 40 deg F. Actually, I shouldn't say "good," because the CHTs are below the manufacturer's recommended values now, but that's all right; eventually the cowl flaps will be adjustable, and it will be possible to raise the temperatures to the desired level (380 F, says Continental).
The left front and right rear cylinders continue to be hotter than the others. I suppose they must be hotter for different reasons, since they have nothing in common that I can tell. My current theory, which I have held on and off for some time, is that the left front cylinder is being heated by the proximity of its own exhaust pipe, and the left rear by improper baffling. Time will tell.
I swapped the bad tenths digit on one VOR with the otiose hundreds digit. Why do they even have hundreds digits, since the number is always one? For spares, I guess. The same goes for COMs. The GPS tracker didn't work on the first test flight, so I read the instructions and learned that I had to enable downloading of the data stream to the tracker. Instructions are good.
[September 9, 2005]
On the cusp of September I made the 1,250 nm round trip to Santa Fe again, this time with unusually friendly winds; it took 7.1 hours and used 63 gallons of fuel. I thought I had taken off with 85 gallons and didn't refuel in Santa Fe, but was then surprised to see the fuel relatively low when I got back. Deciding it was high time that I at least calibrated the zero points on the fuel gauges, I drained the tanks and found that I had 11 gallons left, not 22 as I had imagined. Calibrating the gauges was difficult because the senders, which are the primitive resistance type with a float on an arm, came from the first Melmoth and are therefore at least 30 years old. They have some dead spots and produce some spurious zeros. I think I got a decent calibration, however, and at least I now have a proper initialization for the Alcor digital totalizer.
A couple of things went wrong on the way. Something slipped in the airbrake control, and the brake would blow closed after a few seconds. And a digit burned out in one of the Collins Microline VOR heads. The airbrake problem was easily fixed, but the digit seemed alarming -- they're $135 each -- until the guy in the local radio shop pointed out to me that the first digit in VOR frequencies is always a one, and so you can swap the first digit with the faulty one (which is the tenths digit) without losing any information.
There was a downpour while I was in Santa Fe, and when I exercised the controls before taking off I noticed that the stabilizer felt heavy; with full back stick the intersection fairing dumped a bunch of rainwater down the fin cove. I had never provided the fairing with a proper drain hole. I remedied that today, but it is not a perfect situation; it's still conceivable that water could collect inside the fairing and freeze.
Today I wired up the Porcine GPS tracker, but I won't have a chance to test it until Monday.
[August 13, 2005]
Having returned from vacation, I flew for 40 minutes or so yesterday to exercise the airplane and to further investigate the effect, if any, of the flap track fairings. At 10,500 feet, where the density altitude was a bit over 13,000, at 2,400/27 with the mixture about 60 deg. F. lean of peak, I got 166 ktas on 8.1 gph. Feeding this back through the performance prediction program, I find the same 2.55 sq. ft. equivalent flat plate area as before. I should have done a complete speed-power curve before and after installing the fairings, because I'm now stuck with only a few isolated performance points. A while ago (pre-fairings) I recorded 166 ktas on 8.3 gph, but slight differences in density altitude and mixture setting can easily account for a couple of tenths of a gallon per hour. At this speed, however, one-tenth of a gallon per hour is roughly equal to a knot. I'm sure that the fairings must have produced some benefit, but it's hard to measure a knot when your margin of error is two knots.
[July 21, 2005]
One of the irritations of the generally wonderful Internet is the amount of outdated information on it. I'm not innocent. The website of the software company in which I'm a partner, AeroLogic, is extremely cobwebby. Just keeping a commercial website up to date is a full time job. My ranting about this is due to my having spent an unreasonable amount of time trying to locate a small universal joint and sprocket for my revised pitch trim system. You can find the online parts catalogs easily enough, but the lists of suppliers are out of date, their phone numbers are disconnected, and so on. I'm having similar trouble with Lowrance, the GPS maker. I want to get a coupler that will allow my AirMap 300, donated by a kind friend, to talk to my autopilot. A fellow named Jim Ham sells these inexpensive ($250) couplers -- his website, I hope up to date, is www.porcine.com (get it? ham:porcine) -- but Lowrance no longer provides the required cable, even though the particular unit went off the market just four years ago, which seems pretty recently to me, but maybe not to a 21st-century electronics company. I will make a cable, but only after a tiresome wild goose chase in which Lowrance directed me to suppliers that had ceased operations and web pages that are no longer accurate but that continue to litter the web like unburied corpses. Well, no matter; sooner or later things get done, and the delays give bad ideas time to settle to the bottom. I'm off to Cape Cod for two weeks, the plane remains in the hangar, and nothing new will happen until well into August.
[July 5, 2005]
Based on a short flight today, the speed gain from the flap track fairings was on the order of one knot. Well, maybe less. Maybe half a knot. Maybe nothing. They look nice, though.
[July 3, 2005]
It took five days, and an uncommon (for me) number of hours per day, to remove the entire nose gear assembly, repair the failed bearing retainer, fit the new steering tiller, and inspect and refurbish stuff as needed. Actually, I made the new top for the tiller twice. The first attempt turned out to have all sorts of interferences that were perfectly obvious once I had made the part and installed it; apparently not so obvious, at least to me, when I was merely visualizing it. I should have made a test item out of wood first; it machines more quickly than aluminum.
I replaced O-rings in the shimmy damper and nose strut actuating cylinder, cleaned everything up, and felt pretty good when it was all back together. Even though I don't fly the plane all the time, it's frustrating to have it unflyable. I still need to jack it and cycle the gear, and then fly, perhaps on Tuesday.
The sliding-out of the bearing was due to two engineering errors. One was the lack of a retaining lip on the outboard side of the bearing holder; the other was the lack of a large-area washer on the inboard side. In general, it's good engineering practice to incorporate a large-area washer wherever a pressed-in bearing can slide out of a socket. I had omitted one here because I thought that the stiffness of the U-shaped retraction arm, which is trapped between the sides of the wheel well, would prevent the right side, through which all the landing loads go, from moving inward. Wrong.
[June 25, 2005]
During a preflight inspection on Friday I discovered that the spherical bearing that carries the principal drag load from the nose gear into the engine mount structure had slipped completely out of its socket. Here is the area of the failure; it's just aft of picture in the previous entry, below. (In this picture, taken some time ago, everything is still intact.)
The bearing in question was pressed and staked into the round aluminum plate that is secured with six rivets to the steel weldment. The unpainted aluminum arm (right) and link connect the nose gear retraction arm (white) to that of the mains. A small hydraulic cylinder (left) and a gas spring (black, with blue label) help to overcome the aerodynamic drag of the gear as it goes down. Interestingly, the bearing holder failed in tension, apparently as the nose dropped down onto the runway during rollout on the previous landing. Although I had let the nose down a little harder than usual, I was not aware of anything having broken. Events like this, though rare, demonstrate the value of a thorough preflight inspection.
The only damaged part is the round aluminum bearing holder, which will be easy to replace. I will provide the new one with a more substantial lip to retain the bearing. I pulled the entire nose strut out of the airplane on Friday afternoon. The timing of the failure was fortuitous, since I had been planning to modify the steering mechanism anyway (see previous entry below). This will give me a chance to inspect the whole assembly.
[June 22, 2005]
I returned yesterday from a week in Korea, where I was investigating the effects of kimchi -- fermented spiced cabbage. I thought it was awful stuff, but it seems beneficial to the body, at least in the short run: practically all Koreans looked extremely trim and fit, whereas almost all the westerners I saw, including me -- those hotel triptych mirrors will stand aye accursed in my calendar -- looked like undercooked puff pastries.
As far as I could tell there are no private planes in Korea, or, if there are, they don't fly very often.
Before leaving I changed the oil in the airplane. I continue to marvel that I could have made this most recurrent of minor maintenance tasks so difficult. I always end up sitting in a pool of oil and bleeding. I've decided that before I do anything else I'll modify the steering tiller, which is to blame. The present arrangement looks like this:
The T-shaped thing running up the backside of the nose strut is the tiller. Partly visible behind its left arm is the cover for the oil drain plug, which is nearly impossible to get at because of the crossbar on the T. I've decided to put off whatever my next task was going to be (trim? ailerons? cowl flaps?) and replace that T with a U-shaped yoke. (If you're curious, there are some views of the lower end of this steering shaft at the bottom of the "Pictures" page.) The whole thing disengages from the rudder pedals when the gear retracts. When the gear is down, the ends of the tiller are in contact with the tabs at the ends of the rectangular aluminum bar. The steering pushrod, which is connected to this pivoting bar, runs along the left side of the wheel well, hidden in this picture, and links directly to the rudder pedals without any intervening cables or springs.
[June 4, 2005]
Finally both of the flap track fairings are installed, though the right one still needs to be sanded, primed and painted. These minor-seeming projects end up taking forever -- I started working on the fairings in the middle of March -- but it's partly because of interruptions for work or travel, partly because of my only putting in an hour or two a day and only on weekdays, and partly because of the nature of composite work, which, at least on the scale on which I practice it, seems to break down naturally into a series of small projects each of which absorbs one day's effort.
Now I must decide what to do next. The leading candidates are nosewheel doors, oxygen system, aileron hinges, back seats, trim revision, cowl flaps, and landing flap actuators. No doubt I could come up with a dozen others if I jogged my memory with the long list called "M2 to do.doc." I feel the strongest tug toward the ailerons, because I think they would produce the most gratifying result with the least effort. Of course I always systematically underestimate the effort that any project will require, but never mind: that applies to all projects equally. The easiest job would be the trim revision, but I keep putting it off because I can't locate a certain aluminum pillow-block that I've had for about 30 years, and that would be just perfect for part of this job. I don't really need to use it, but it's so right that it would be a shame not to. So I keep searching through boxes of disjecta membra from the first Melmoth, in what would be a metaphor if my life were a novel. If I find it, the agenda may suddenly change.
Perhaps, on the other hand, I should stop working on the plane for a week or two and devote some time to giving rides to people to whom I've promised them; the list keeps getting longer.
[May 18, 2005]
Back from Baja.
Mirabile dictu, I think I detected just the faintest hint of out-of-center ball, apparently attributable to the wing with the flap track fairing having slightly less drag than the other. Unfortunately I do not have a well-established speed/power/EGT/fuel flow grid, based on inflight measurements, that would allow me to make delicate comparisons of drag. My method of estimating drag is to vary the drag parameter in my computer simulation until the predicted performance matches the actual. That was the source of my estimate of 2.55 square feet of equivalent flat plate area. Uncertainty about specific fuel consumption and propeller efficiency, however, could produce errors of several percent.
I have not recalibrated my computer/airplane comparison since installing GAMI injectors, which would be expected to bring about an improvement in specific fuel consumption. This will complicate interpreting the speed/power data that I will take after both flap track fairings are in place. On the other hand, one does develop a sense of the expected IAS for a given cruising conditions, and any change for the better or worse is noticeable; but it's necessary to guard against what I think of as the Windex tune up phenomenon -- the fact that a car seems to run better after its windshield has been cleaned.
[May 12, 2005]
I finally got one of the two flap track fairings installed. (See March 17 below for the CFD version of the same thing.)
I'm leaving tomorrow for a few days in Baja California, and spent the last couple of working hours today attaching big numbers (required for ADIZ crossings) to the sides of the airplane with shelf paper. I should have been painting the fairing. Maybe I'll slap a quick coat on it before I leave tomorrow. But my impatience to tuft the fairing may surpass even my impatience to see it white. I'm also curious to see whether flying with only one fairing produces even the slightest right yawing tendency.
[April 25, 2005]
A trip to Santa Fe in continuous light to moderate turbulence convinced me to up the priority of reducing the stick forces in roll. I downloaded from the Internet (may peace be upon it) a NACA wartime report on aileron balance nose shapes. Unfortunately it mainly tended to confirm my sense that this is a topic upon which nothing definitive can be said. It does appear, however, that I will be able to move the aileron hinges aft, recontour their noses, and considerably reduce the weight of the static balances, all without venturing out of the zone of the tried and true, where I prefer to linger. I also discussed last week with Russ Hardwick various ideas for converting the present elevator trim system, in which both tabs double as servo tabs to lighten stick forces, to one in which one tab will be a servo and the other a pure trim tab. I feel now as though we arrived at a satisfactory solution to that problem, and so I may raise its priority as well.
The GAMI injectors had the expected effect of making all cylinders arrive at peak EGT at more or less the same time, so that it is possible to lean to a lower fuel flow, but turbulence made it impossible to collect a good set of data points on fuel flow, speed, and EGT.
[April 15, 2005]
I've been away to Boston and Corsica for a couple of weeks. Before leaving I installed a set of GAMI injectors, which differ slightly in bore diameter in order to better equalize the mixture ratios among the cylinders. I have not yet collected EGT data in flight to compare them with the factory injectors. Before leaving on the trip I was working on the tooling for the flap track fairings; I hope to have the parts made in a week or two, other obligations permitting.
[March 17, 2005]
Here's what a basic CFD model of the flap track fairings looks like:
My best guess from the analysis is that each fairing produces about four ounces of drag at normal cruise. There will be four tracks, so a pound of drag. How this compares with the bare tracks cannot be known, but the change will in any case probably be too small to measure with an airspeed indicator. Cruising drag for the complete airplane is around 200 pounds.
[March 12, 2005]
I have always had several books going at a time, and I always have several tasks going on the airplane. I work on one until it becomes boring or I encounter some difficulty or expense to which I feel unequal, and then I put it aside and take up something else. Currently I have the nosewheel doors, the oxygen system, the flaps, and the back seats in various stages of suspended progress, and to divert myself from them I have begun what I hope will prove to be a quick, simple and satisfying project, namely the outboard flap track fairings.
They seem as if they should not take long. On the other hand, they will probably not accomplish much, except perhaps aesthetically. The problem with some fairings, these included, is that while they are more streamlined than the structures that they cover, they are also much larger -- witness the huge "canoes" housing flap tracks on Boeing airliners -- and so they end up removing only a fraction of the drag that you wish you could eliminate completely. In this case, the flap tracks are oriented at right angles to the rear spars, which sweep somewhat forward; the fairings, on the other hand, must align with the local flow. As a result, the fairings have to be considerably wider than they would be if their axes coincided with those of the flap tracks. Furthermore, because of the oblique alignment of the tracks the fairings need to expand to a certain width fairly near their leading edges, and retain it until fairly close to their trailing edges. This situation raises what could be called the Constellation vs DC-4 question: is it better to have a body that has a continuously curved profile, or one that is narrower, but has a parallel-sided portion in the middle?
It is a great luxury to be able to worry about things like this, rather than whether or not I will be blown to bits next time I leave my house.
[March 4, 2005]
Fuel being as expensive as it is, I've been trying to use as little of it as possible, and so cruising at around 50-60% of power. I have been seeing good agreement with my performance program's calculated fuel burns and speeds if I assume an equivalent flat plate area of 2.55 square feet. The other day I recorded 166 KTAS at 7.7 gph at 12,500 feet, which was a little better than expected but within the range of uncertainty due to mixture, prop efficiency, etc. I have not done any high altitude speed points, but if the trends hold the 75% power cruising speed at FL180 should be around 195 kts. This is a little disappointing -- I was hoping for 300 -- but there is still some cleaning up to be done.
[February 25, 2005]
I got a ride in this today. Pretty slick. Details will be in the October issue of Smithsonian Air & Space.
[February 22, 2005]
It's been raining regularly, and often very heavily, for almost a week. I've been working, rather desultorily I must admit, on the rails that will support the rear seats, on the oxygen system, and on the anchors for the inboard flap actuators.
The only aspect of this that is of the slightest interest is the oxygen system. I learned that the 76-cu. ft. cylinder that I have saved for the past 23 years, and for which a fitted cradle is built into the rear seat footrest, went out of date three years ago and is now, as somebody at one of the local oxygen equipment businesses said, a very large paperweight. It seems that it would be difficult to replace the exact bottle, which I believe may have been original equipment on some Cessna back in the 1970s, but smaller and lighter aluminum bottles are comparatively inexpensive and readily available. From various websites I learned that with proper breathing and regulating gadgetry oxygen consumption at reasonable altitudes (meaning just below 18,000 feet) can be pulled down to 0.4 liters or less per person per minute, which would mean that a 24-cu. ft. bottle would last two people more than 12 hours. That seems acceptable. My principal concern in assembling this system is to keep it cheap. A liter is about 61 cubic inches, by the way, and so there are about 28 of them in a cubic foot.
I have also been thinking about putting some sort of microswitches at the landing gear overcenter knuckles in order to avoid ambiguity (see below) about whether or not the gear is really down and locked. I wonder whether a thin piece of stainless steel, insulated from the surrounding metal and getting clamped in the knuckle when it goes overcenter, would not be a good deal simpler than actual microswitches. It's worth a try.
[January 28, 2005]
I had a close call
that may be worth describing. About ten days ago I happened to look under the
airplane and I noticed that the inboard main gear doors were hanging slightly
open. M2 is not a P-51, and this should not be; if the gear is down, the doors,
which are mechanically linked to the rest of the retraction system, should be
closed. My eyes went to the overcenter locks on the sway braces (the diagonal
links that hold the gear legs down), and sure enough, both of them were unlocked.
I remembered that two days earlier, returning from a flight, I had slightly
overshot the detent when returning the gear handle to the center position after
lowering the gear, and the pump had run momentarily. Just a blip. The "down"
indicator on the torque tube hadn't moved, as far as I could tell, so I didn't
give a countervailing downward blip. This was pretty stupid.
The interesting thing is that I landed, taxied back and parked with both sway
braces unlocked. But it turns out that since the valve is closed-center, the
whole mechanism was held in place by the trapped hydraulic fluid, which saved
my (belly) skin, not to mention propeller.
So the lessons learned were:
1. The down position indicator is not a perfect gauge of the overcenter position
of the sway braces.
2. I need some microswitches and warning lights for positive indication of overcenter.
3. Because of the closed-center valves, the gear is more or less safe even when
it is not fully locked.
4. Any pump sound, however slight, in the up direction is reason for an additional
shot of down pump.
Speaking of warning lights, since I installed a big red light to indicate that
the air brake is open, I have never forgotten to retract it after landing.
[January 8, 2005]
The holidays, together with an extraordinary amount of rain, have been fatal to progress. I've only been out to the airport a few times, and only flown three times -- a round trip to Santa Fe before Christmas and a 20-minute hop to heat the oil a couple of days ago -- in the past month. I have, however, spent a lot of time on the design of the flap master cylinder array, using little models cut out of file folders and sheets of letter paper taped together to supplement their area as needed. This is what it looked like a few days ago:
The geometry is fairly complex, and the whole thing needs to be strong enough to defend itself against the hydraulic forces in the cylinders. The tandem cylinders I first imagined have been replaced by four identical cylinders; the starwheel provides the differential travel for the inboard and outboard slave cylinders.
[December 4, 2004]
The eventual resolution of the outboard actuator problem involved moving the pivots to a point halfway between their original and their one-diameter-lower positions. As of Friday, both outboard actuators were properly positioned to extend and retract the flaps. Here is what they look like:
The round thing behind the wires on the left is the outboard fuel level sender. Just to the right of it is the tunnel for the hydraulic flap actuator, which is mounted in the partly-green yoke thing. The tube running across the top of the picture is the aileron pushrod; the aluminum plate is the outboard flap track. The gray thing overhead is the undersurface of the upper wing skin. For scale, the aileron pushrod is 3/4 inch in diameter and the hydraulic actuator shaft is 3/8.
In the meantime, after consulting with a couple of interested friends I have more or less frozen the plan for the master cylinders. The design, which is similar in principle to, but different in detail from, the one I described in the entry for November 4, calls for four master cylinders, one for each flap actuator. All four are connected to a four-armed bellcrank or starwheel; two of its arms are shorter than the other two in order to provide for the difference in extension distance between the inboard and outboard ends of the flap. This assembly is situated under the rear seats. A fifth cylinder drives the starwheel. If you think about this system you will be baffled by the additional cylinder -- why don't the four master cylinders drive the starwheel? -- so it's probably better not to think about it. Bleeder ports in the master cylinders allow the columns of trapped fluid between the master cylinders and the flap actuators to refill on each cycle.
There is still a good deal of work to do to connect the outboard cylinders to hydraulic lines running along the rear spar to the fuselage; there is very little space for flexible hoses in the vicinity of the actuators, but there is enough. I anticipate that installing and hooking up the two inboard actuators will be much more straightforward; they are inside the fuselage, where, theoretically at least, there are no interferences.
[November 24, 2004]
Having lowered the outboard flap actuator pivot pins on both sides to accommodate the actuators in their fully-extended position, I found that they were now too low when the flaps were retracted. I had anticipated this possibility, but had trusted to luck to forestall it. Luck failed me. I do not have an exact drawing of the wings as they really are, and so am reduced to finding dimensions by cut-and-try. It isn't the first time. After some head-scratching I figured out that by moving the point at which the actuator rod attaches to the flap forward about an inch and somewhat downward I could solve the problem. I mocked up a new attachment point on the left flap with phenolic sheet and JB Kwik, but the epoxy hadn't hardened when I had to leave the airport, and so I'm not sure yet whether this solution really is one. Tomorrow being an obligatory at-home day, I won't find out 'til Friday.
On Monday I was supposed to fly out to Mojave to interview Cory Bird about his beautiful Symmetry, which won best everything at Oshkosh last summer. My two motorcycle batteries, which are old and no longer hold a charge well, were too flat to start the engine -- the plane hadn't flown in a month -- but I recharged them and made a short flight later in the day just for the fun of it. An upper-level storm of some kind had passed through over the weekend, leaving snow on the mountains and a mass of cold, transparent and still air over Los Angeles. I climbed to 8,000 feet and meandered around for a while. The air was glassy; the visibility was unlimited in every direction; the engine seemed particularly smooth, the airplane particularly stable; the day was made for flying.
[November 14, 2004]
Last week I began machining the pistons for the flap actuators. I turn them somewhat oversize from a bar of cold-rolled steel, silver-braze them to the stainless-steel shafts, and then finish-machine them with the proper O.D. and an O-ring groove. I have done one so far, and have tentatively assembled one outboard actuator. The actuator pivots in a kind of yoke at the rear spar; its fore end is inside a 3-inch-diameter tunnel that projects forward from the rear spar about a foot into the fuel tank . On fitting the actuator to the wing I found that despite my drawings the rod end that connects the shaft to the flap was still too high up when the cylinder had used up its angular travel within the tunnel. Consequently I had to lower the pivot pins on the yoke, a task that was complicated by there being insufficient material on one side of the yoke for the new hole. I got around this problem on the left side of the airplane; I assume it will be repeated on the right, but I haven't checked yet. Next week's tasks include adding attachment lugs to the left flap for the actuator rod end, repeating the whole actuator-fitting procedure on the right side, making more pistons (four are required), and, time permitting, roughing in the mounts for the inboard actuators, which are inside the fuselage. I feel a nice momentum building.
[November 4, 2004]
How the flaps work:
The inboard ends of the flaps extend 14 inches, and the outboard ends nine and a half. The ends of the flaps must be at the same relative points in their travel at all times during extension and retraction, and the right and left flaps must extend in step with one another. The current design iteration for the flap hydraulics does away with the original idea of slaving the outboard actuators to the inboard ones. Instead, two pairs of tandem cylinders (double-acting cylinders mounted end to end on a common shaft), situated inside the fuselage, serve as master cylinders. During flap extension they vent fluid to the two actuators (inboard and outboard) on each flap. Because the two sections of each tandem unit have the same bore diameter and share a common shaft, they displace identical amounts of fluid, and so their respective slave actuators on the right and left sides will move at the same rate. The tandem cylinders are physically identical, but by connecting their shafts to a common rocker arm at different distances from a fulcrum the ratio of their rates of motion can be controlled and even finely adjusted. During flap retraction, fluid flows from the pump directly to all four actuators, but the mechanically linked master cylinders, now on the downstream sides of the circuits, still preclude their getting out of step. Master cylinders 2.5 to 3 inches in diameter would need to move less than 3 inches to produce the required flap travel.
The only significant
failure mode that I foresee with this arrangement is leakage, either in any
of the four lines connecting a master cylinder to an actuator or past the piston
O-rings in any of the cylinders. A rapid leak is unlikely, but would be serious
if the pilot or some as yet uninvented automatic monitoring system failed to
take note of it and stop the hydraulic pump. Slow seepage is more probable,
and could cause one end of a flap to fail to extend fully. It may be necessary
to provide a tee and a small manual valve in each line that would permit fluid
from the reservoir to enter the line while the trailing edges of the flaps are
being pushed forward at both ends. Melmoth 1 had such a system; it required
attention every few weeks.
[November 1, 2004]
While away for a week of camping in Death Valley, I mulled over various ways to keep the two flaps in step with one another during extension and retraction. Interferences have bedeviled my tentative solutions to this problem, most of which involve a cable loop in a figure-eight shape. I had recently investigated hydraulic flow dividers, and decided that they were probably unsuitable because, according to one website, they are only good to within 10%; I then sketched a homemade valve, mechanically linked to the flaps, that would proportion flow in response to inequalities in their positions. The proportioning valve idea made me nervous, however, because it seemed likely to oscillate at some characteristic frequency. Today while driving -- I do a lot of design thinking while driving -- I hit upon a new, simpler solution that I think is a good one. I would like to think that it's ingenious, but it may be that I'm just stupid to have taken so long to come up with it. I now feel that I can start working on making the flaps operable -- probably a more interesting project than the nosewheel doors or the cowl flaps.
[October 21, 2004]
Various minor modifications to the baffles have not yet yielded any substantial changes in the CHTs. I did climb to 11,500 yesterday and get a speed point: 179 kt at 9.7 gph. This was at 29.5/2,400 and peak EGT. It suggests an equivalent flat plate area a little smaller than I had supposed, but it is impossible to make very precise estimates because there is no way to know the specific fuel consumption or the prop efficiency -- that is, no way to know how much power 9.7 gph actually represents.
Noting, after I had shut down, that I had once again forgotten to retract the speed brake after landing, I decided to put other tasks aside for a few days and install a brake extension warning light. It would be bad to try to take off or go around with the brake extended. I also have an idea of how to add a simple mechanical airbrake position indicator using a short length of bicycle brake cable.
[October 18, 2004]
Yesterday I reviewed a pre-World War II report on cylinder baffles, and was reminded that one factor in their effectiveness is the width of the opening through which high pressure air reaches the cylinder fins. The optimum angle is about 145 degrees. Now, the #1 cylinder, which is the hottest, is unique in having a somewhat larger opening than that. I am going to try extending the baffle behind the cylinder in such a way as to confine the flow more. This is a complete stab in the dark. I am also experimenting with closing up the air outlets on the low pressure side (potentially on all cylinders) in order to keep the air in contact with the fins for a slightly longer time. I did this to one cylinder so far, the left middle one, because it and the right middle tend to have the same temperature. On a very brief test flight today the restricted cylinder appeared slightly cooler than the other, but because of weather I did not go high enough or fly long enough to reach stable cruising temperatures. In fact the #2 CHT never even got into the green.
[October 16, 2004]
The NACA flush engine air inlet continues to be highly satisfactory. I have not yet climbed up high enough to map the MP vs rpm boundary, but it seems as though I can now cruise at any non-oxygen altitude without having to run at 2,500 rpm continuous to generate enough MP. I have been cruising back and forth to Mojave at 7,500 feet at around 55% of power, using 2,100 rpm and 27 in. Hg. Fuel flow is 7.8 gph and IAS is 136 knots, TAS 156. I do not seem to be able to get much above 20 nmpg.
I have begun working on the nosewheel doors. It is not yet clear how I will open and close them, but there are so many different ways to do it that one or another of them is bound to work. It is also not clear that closing up the well will reduce drag much; Hoerner gives a rather low coefficient for the drag of sealed cavities. But is seems aesthetically unsatisfactory to leave a huge hole in the bottom of an otherwise fairly clean-looking airplane.
I flew over to Catalina Island the other day for lunch and found that they have upped the landing fee to $20. Too bad; jokes about $100 hamburgers notwithstanding, there are limits to what one will cheerfully pay for a quite average lunch.
By the way, here is the current appearance of Melmoth 2:
As cool weather approaches, the matter of the cowl flaps gains prominence. The engine cools too much during descents, even with the airbrake. Before reducing the cooling flow, however, I have to deal with the big temperature difference between cylinders 1 and 6, and all the others. I am still waiting for the light to go on there; I can't see yet why #1, the right rear cylinder, should be 90 deg F hotter than 2, 3 and 4. Presumably there is something bad about the configuration of the baffles, but at the moment it still has me, well, baffled.
[September 27, 2004]
Flight tested the NACA scoop today. Luckily, it shows obvious improvement over the previous inlet; at 10,000 ft. and 2,300 rpm, I get four or five more inches of manifold pressure than before. This does not prove the inlet is particularly good; only that it is better than the old one, which may have been particularly bad. But at any rate the additional pressure means additional speed at altitude, or the ability to operate at lower rpm.
Another improvement came from the experiment of lining the inner surface of the cowling side with aluminum foil. After landing, the outer surface of the lined portion was merely warm from the radiant heat of the exhaust and turbocharger, whereas it used to be almost too hot to touch.
The NACA scoop is integral with the side panel. A gasket of felt weatherstripping presses against the open end of an aluminum box covering the air filter.
[September 17, 2004]
After finishing the wing root fairings, I had intended to move on to the nosewheel doors. But I found myself dawdling in a way that suggested a certain lack of energy and enterprise, or perhaps anxiety over not having yet done all my homework with respect to the actuating mechanism, and so I turned to some simpler tasks. I improved the lip contour on the cabin air inlet (that should produce no dicernible change); built an attractive balsa wood fairing around the inlet scoop for the battery box blast tube, which now resembles a small gun port embedded in the cowling; and I set to work to install the flush engine air inlet in the left side of the cowling that was the motive for the tuft tests of a couple of months ago. The airplane is unflyable while I work on this, so I'm trying to get it done quickly. Perhaps I am too pessimistic, but I suspect that the difference here, too, (due, in theory, to reduced duct losses and lower induction air temperature) will be imperceptible. But I would never know if I didn't try it. And yes, I did read that recent article in Flying saying that NACA scoops are not much good.
[September 10, 2004]
I devoted the first week back from vacation to finishing off the wing root and boarding step fairings, thereby eliminating four unsightly holes in the surface of the airplane and replacing them with some rather sloppily painted white surfaces, viz:
[August 5, 2004]
I returned yesterday from the Oshkosh trip. The airplane performed well, flying 22.5 hours without a mechanical glitch and using about two quarts of oil. The longest leg was 6.5 hours from Fort Wayne, Indiana to Tucumcari, New Mexico via the southeast corner of Missouri (to get around a line of thunderstorms). Overall fuel consumption, including taxi and climb, was 9 gph with airspeeds of around 170 knots. I run 25-50 deg lean of peak, and on the final leg (Santa Fe to Whiteman) I was cruising at 166 ktas at 15,000 ft density altitude using 8.3 gph.
At the start of the trip I set the voltage regulator at 27 volts and the battery was well-behaved, maintaining a charging rate close to zero. In spite of all going well, however, I did make a list of things that need changing, including my silly placement of the pilot's fresh air vent at the center bottom of the panel, where it blasts any chart you try to unfold in front of you.
Oshkosh seemed quieter this year, with far fewer visitors than last and not much in the way of exciting new airplanes (at least ones within the reach of non-millionaires) except Cory Bird's impeccable Symmetry, which carried off all awards for which it was eligible.
[July 27, 2004]
I left for Oshkosh at 7:00 a.m., but soon noted that the temperature in the battery box was higher than I had ever seen it -- 55 C -- and the charging current had gone straight to 4 amps. Concerned about possible thermal runaway, I turned back after going only 70 miles. I spent the rest of the day talking with people about the problem and trying to figure out how to solve it. Eliding a number of tedious details, it is sufficient to say that the higher-than-normal temperature was probably due to my having replaced a leaky gasket where the turbocharger joins the exhaust collectors. This raised the temperature (I am guessing) of the exhaust pipe whose proximity is the principal cause of heating in the battery box. Until I decide to lag or otherwise shield that pipe, it seems as though the box will inevitably be rather warm. Warmer batteries have lower resistance and therefore accept more charging current, which tends to heat them even further. The newly-installed blast tube at least maintains equilibrium, as appears from the fact that the temperature held steady at 55 and dropped when I reduced power.
I realized later in the day that I could perhaps lower the charging current, and thus the amount of heat I am putting into the battery in the form of electrical energy, simply by lowering the system voltage. The voltage regulator is within easy reach in the cockpit, and there is nothing magical about the number 28. Twenty-six or 27 volts would do as well. So tomorrow morning I will again depart, armed with a somewhat improved (though still, for all I know, imperfect) understanding of what is going on with the battery.
Before turning back I had established a 146 kias cruise at 28/2500 at 12,000-ft density altitude, for a TAS of 174 knots, using 9.3 gph. This is a fairly typical performance point.
[July 21, 2004]
I've been working on a few modifications before leaving for Oshkosh. As usual, I began the least important one first, and it's taking far longer than expected. The things I was hoping to accomplish were to 1) add fairings at the wing root trailing edges, covering the flap tracks; 2) provide a small external air scoop to ventilate the battery box; 3) replace the long duct bringing intake air to the filter with a NACA scoop in the side of the cowling; 4) add a short diagonal brace to the nose gear half-fork to make it stiffer in bending and torsion; and 5) wash the airplane. It's becoming increasingly apparent that I'll be lucky to get the fairings contoured, but not primed or painted, and to ventilate the battery box.
[June 26, 2004]
I flew to San Luis Obispo to meet a friend who was traveling to Los Angeles. She had 184 pounds of baggage, which pushed the CG farther aft than it had ever been before, to 34.6% of chord. This is still well ahead of the aft limit, and, more to the point, represents an aft moment (ie, the lift that must be supplied by the horizontal tail to keep the airplane balanced) only about half as large as would occur with two 170-pound back seat passengers and 50 pounds of baggage. To my surprise and chagrin, however, I found that I ran out of nose-down trim just at cruising speed. The elevator deflection was very slight (the tail loading was only 2.4 lb/sq ft, even ignoring the nose-down contribution of the wing pitching moment), so it is not a question of lack of tail power, but rather of lack of trim authority. Now, it happens that the nose-up trim is also insufficient to trim for approach speed at forward CG. What limits the trim authority at both extremes is the fact that the trim tabs are also servo tabs, intended to reduce pitch control forces. The pitch forces are currently so light, however, that I could perhaps eliminate the servo function and use the tabs for trim only; that would greatly increase the available trim authority.
[June 11, 2004]
I flew to Mojave for lunch and also to record tufts on the top of the cowling. The tufts showed, as expected, some turbulence behind the outlets, growing more severe as the flow approaches the windscreen and the boundary layer thickens. It may be due to several factors. One that I have already identified is the very steep sweep angle of the outlets -- about 35-40 degrees. The streamlines on the turning vanes tend to align themselves with the leading edges of the vanes, and so the air emerges at an angle to the external flow. Shearing where the internal and external flows meet creates vortices. I suspect that the disturbed flow may re-stabilize itself as it accelerates on the windscreen, and so the ultimate drag penalty may be small, but until I install the final moveable outlet vanes there is no "actionable intelligence" to be taken from the present observations. There is also a larger unanswered -- and perhaps unanswerable -- question about whether the benefit of the forward outlets (see Cooling Flow) at the angles of attack actually encountered in real-life climbs justifies their existence at all. Two noteworthy things about the tufts are that the ones just outboard of the outlet wakes are straight and steady, and that there is no evidence of slipstream rotation (which I have always suspected of being a figment of someone's imagination anyway).
In the course of a conversation about induction air inlets someone suggested that it might be good idea to adopt the old Mooney approach of a pilot-selectable air filter bypass for the air entering the NACA scoop at high velocity. I don't know why this option, with which I have been familiar for about 30 years, didn't occur to me before, but now I'm thinking about bifurcated duct through which the engine would breathe filtered air from the cold plenum on the ground and unfiltered air directly from the NACA inlet in flight.
In case you don't feel like reading all the stuff below to find out what the induction problem is, it's basically that air enters the planned flush scoop on the cowling at about 300 feet per second, and it would enter the turbocharger at about 300 feet per second, but in between it would have to slow down to less than 30 feet per second to pass through the air filter (because the area of the air filter is more than ten times the inlet cross-section). Now, you lose a lot of the energy of the airstream unless you decelerate ("diffuse") the air in a very long and gradually expanding duct, for which there is obviously not room in the cowling. A well-designed filter bypass would let the air flow straight to the turbo inlet through a smooth duct little more than a foot long. It still isn't ideal; it has to make two 90-degree turns on the way. But the losses may still be less than in any of the alternative arrangements I've been able to think of. Also, any ram recovery, which is pretty much nonexistent in a filtered system, can be doubled or tripled by the turbocharger, and so might be worth trying to get for high-altitude flying. It's very difficult, however, to get good ram recovery from a flush NACA scoop over the full range of speeds, power settings and air densities encountered by a turbocharged airplane.
[June 3, 2004]
A couple of frames captured from some 40 minutes of in-flight videotape convey the essence of the information acquired, and also illustrate rather nicely, if it needed illustrating, the curved path of the air over the wing. The vertical white bar is an artifact of the camera, due to sunlight reflecting from the canopy.
The area of interest, so far as the engine air inlet is concerned, is at the left edge of the picture; in fact, it's just the first three columns of tufts, and the region immediately below the continuous black line, which is a horizontal reference. The rows of tufts are four inches apart vertically and roughly (not exactly) ten inches apart horizontally. The tufts immediately above the reference line are one inch from it.
The first image is during a 100 kias climb. The angle of attack is about three degrees, and the tufts in the inlet area are tilted upward at about that angle.
For comparison, here s the CFD prediction of streamline paths at an angle of attack of four degrees:
The image below is in cruise at around 140 kias; the tufts are now parallel to the horizontal reference line.
On a subsequent
flight I tufted only the vicinity of the proposed inlet, and provided not only
a horizontal reference but also a 10-degree angle reference which is visible
as a faint extension behind the uppermost of the three tufts.
This image (unfortunately none too clear), taken at the moment of touchdown
in a full-stall landing, flaps up, shows how closely the flow in that area tends
to match the flight path vector; the apparent angle of the tufts is somewhere
around 12 to 15 degrees, which is about the expected angle of attack of incidence
of the airplane at touchdown.
Whatever its intrinsic interest, all this effort to discover the local flow direction may have been mooted by my having stumbled, after repeated Googling of various combinations of NACA, submerged, flush, intake, inlet and scoop, upon a 1948 NACA Research Memorandum, A8B16, which states unequivocally that the influence of angle of attack upon the pressure recovery of a fuselage-side flush scoop is slight. On the other hand, another RM (A50E02) states that ram recovery diminishes with increasing angle of attack, but attributes this effect not to misalignment of the scoop with the flow, but rather to increased boundary-layer thickness. An even earlier report (Advance Confidential Report 5I20, from 1945) cautions that submerged inlets "do not ... have desirable pressure-recovery characteristics for ... oil coolers, radiators, or carburetors [because] the required diffusion of the air and the range of inlet-velocity ratios is too great..." In other words, a given NACA scoop works well only in a narrow range of flow rates, whereas pitot or ram-type scoops -- ones whose openings face directly into the wind -- can recover a large portion of free-stream dynamic pressure regardless of the amount of flow actually being admitted. On the one hand, therefore, an airplane that operates most of the time quite far from its maximum-performance points ought to have ram inlets; but on the other hand the turbocharger easily overcomes a small ram-pressure deficit, and the flush scoop has the advantage of minimal drag. Voters in the impending election might do well to reflect that "on the one hand ... on the other hand" may indicate not a waffling personality, but rather a realistic appreciation of the compexities of a situation.
[May 28, 2004]
Okay, the MB antenna worked fine, so that takes care of that.
One of the next projects on my list is to replace the long duct through which the engine is currently breathing with a flush inlet in the side of the cowling, close to the air filter and the turbocharger. At the least, this should bring the temperature of the inlet air down somewhat, and may improve the ram recovery. Sizing the inlet is a fairly simple matter of identifying a few performance points -- maximum rate of climb at 10,000 feet, for instance, or maximum cruise at 18,000 feet -- that might represent the highest rate of airflow to the engine, which inhales 1,300 pounds, or around 16,000 cubic feet, of air per hour at 2,800 rpm in its naturally aspirated form and a third more with 40 in. Hg manifold pressure. I concluded that an inlet area of 7 square inches, with dimensions of 5 x 1.4 inches, would be about right.
What is more difficult is determining the best orientation of the inlet. The range of fuselage incidences that are of interest is about 1 to 4 degrees. Unfortunately, I haven't been able to locate any information on the effect of misalignment on the pressure recovery of flush NACA scoops, though I have a faint recollection of having read somewhere that misalignments of 3 or 4 degrees are tolerable. My CFD software can predict streamline paths on the cowling, but to verify them I attached a small TV camera to one of the flap tracks, tufted the fuselage from the nose back to the aft end of the canopy, and recorded a flight with speeds of 80 to 150 kias and with the speed brake open and closed. The results confirmed the CFD predictions, and also showed no flow separation on the fuselage sides even at low speed, except with the speed brake out. This result encourages me to think that no wing root fillets will be needed -- the hoped-for effect of making the intersection between the wing upper surface and the fuselage a right angle and of having the maximum width of the fuselage coincide with the trailing edge of the wing. I was likewise relieved to see that while there is some loss of flow energy in the stupidly designed intersection of the fuselage and the aft canopy, it's slight and probably doesn't have much effect on performance.
All this research to find the best orientation for an air intake is in a sense quite silly. The extreme performance points are in any case seldom visited except during flight testing; furthermore, any reasonably forward-facing inlet of roughly adequate size will work fine, and besides, you never really know how good an inlet is because, at least with a project like mine, once you have arrived at a satisfactory solution to a problem you don't go on endlessly investigating alternatives. For that matter, there are so many other variables involved in engine breathing that the last degree of refinement in the inlet orientation may be overshadowed by some unsuspected (or, for that matter, suspected) deficiency elsewhere in the system. The main reasons for making a study of the duct environment are three. First, it's amusing to mess around with airplanes, and this is one form of messing around. Second, it will provide a pretty good idea of the the correct orientation for the inlet. Third (and this may seem identical to the second, but really it is somewhat different), it may prevent making some grotesque error in orientation and placement that would otherwise become obvious only in retrospect.
This was the first time I've used the tiny television camera, which cost $100 and plays into a digital camcorder in the cockpit, in flight. Sooner or later, I plan to use it to confirm proper closing of the wheel well doors, sealing of engine baffles, and flow patterns inside the cowling.
[May 23, 2004]
On Friday I added a marker beacon antenna -- a dipole consisting of two pieces of copper tape nearly a yard long -- under the floor beneath the back seats. That makes a full ILS. I haven't tested it yet, but will tomorrow. I assume it will work because the marker beacon is the least demanding of all the radios, receiving a single frequency at short range with the signal arriving from directly below, where no part of the airframe gets in its way.
A few days ago somebody said something about aft loading, to the effect that the basic criterion was that if the airplane were tipped back until its tail touched the ground, it should drop back onto its nosewheel. Some won't. I suddenly wondered whether I had ever made that simple calculation. Last night I did, and was relieved the find that at the aft limit, which is at 50% of chord (FS 126.4), the CG is still nearly two inches ahead of the main gear axles when the airplane is tipped 15 degrees nose up. Whew.
[May 20, 2004]
In the past couple of weeks I changed the oil; installed a new heat shield on the batteries; added a stall warning bleater; reinforced the left front engine baffles to prevent them from lifting under air loads; replaced the voltage regulator; put a ventilating valve from a Camry on the passenger side and made a duct to it from the NACA inlet on the right side of the fuselage; installed a 12-volt cigarette-lighter-style outlet for external gadgets like a handheld GPS; and installed a glideslope antenna in the left wing. A brief test flight this afternoon revealed the flow from the ventilator to be rather anemic. The glideslope seemed to work fine, however, as did the 12-volt outlet. I failed to notice the battery charging current, and so I don't know yet whether the replacement regulator solved that problem or not.
The glideslope antenna was a rather simple addition that took a couple of hours to do. I used two pieces of solid copper wire, probably 16 gauge or so, taken from a piece of household cabling. There is a recess in the leading edge of the wing to accommodate the Safe Flight angle-of-attack indicator. The leading edge is fiberglass over a foam core back to 5% of chord, where the carbon wing box-cum-fuel tank begins. I was able to poke the wires into the foam to the right and left from inside the recess, and connect them to a coax which I brought out through the same conduit as carries the angle-of-attack sensor wiring.
The 12-volt outlet is powered by both channels of a Narco MP-10 power converter; it can supply up to 2 amps.
[May 7, 2004]
The revised fuel system plumbing worked, and did seem to reduce rough running due to fuel heating.
On May 1 I flew to Flagstaff to join a camping trip of the primary school that my children formerly attended. In the course of that trip the battery began drawing an increasing charging current, even when I would have expected it to be fully charged. On landing I found the battery water somewhat depleted, but whether that was a cause or a consequence of the excessive charging I didn't know. The problem recurred on yesterday's interminable (headwinds, moderate turbulence) trip from Flagstaff to Livermore by way of Lancaster. A couple of people have suggested that a shorted cell in one battery (I use two 14-volt batteries for the 28-volt system) could be the cause.
Forty-five minutes out of Livermore I observed the fuel flow to be rising while the peak EGT dropped. Smelling no fuel, I assumed that whatever was wrong it was not a fuel leak, and I continued on to Livermore. There I found that a loose B-nut on the fuel pressure line to the panel was allowing fuel to spray all over the inside of the cowling, accounting for both high indicated fuel flows and low delivery of fuel to the cylinders. I fixed it this morning and returned to Los Angeles without further incident, though I took the precaution of shutting down the electrical system for most of the flight because of the continued peculiar behavior of the battery.
For reasons that I don't know, the CHT probe on the #1 cylinder (right rear) emerged from a long dormancy to reveal that that cylinder, not #6 (left front), as I had always thought, is the hottest. Equal CHTs still elude me.
I found on descending into Livermore that very high rates of descent (> 2000 fpm) are possible with the airbrake, and that the buffeting I had experienced at lower speeds disappears above about 140 kias. All the more reason that a brake position indicator would be desirable.
I measured a temperature rise of about 40 deg C above ambient in the air entering the oil cooler, owing, I assume, to the exhaust pipes and turbocharger. It appears that an insulated duct running within the cowling from the air inlet to the cooler might help bring down the oil temperature, which currently hovers around 97 deg C.
[April 22, 2004]
One of the chronic problems associated with updraft cooling has been rough running while taxiing for any length of time on hot days or after landing, when the heat rising from the engine would boil the fuel in the lines. Having been designed with downdraft cooling in mind, the engine has its throttle body, distributor block, injectors, and all the associated plumbing on the top. Engine heat soaks into them through conduction, convection, and radiation -- no avenue has been omitted. This week I revised the system, moving the distributor to a position below the front of the crankcase, just within the cowling air inlet. The throttle body remains atop the engine, as do the injectors, but everything else is now underneath. I hope this will solve the problem. Tomorrow I will do a long ground run with the cowling on; I'll flight test it on Monday.
[March 19, 2004]
I had lunch at Mojave with Mike Melvill. I mentioned the peculiar asymmetry of dihedral effect that I noted when I first flew with the canted wingtips. Mike quickly asked whether the rudder moved at the same rate, in proportion to pedal displacement, to the right and to the left. We then realized simultaneously that the geometry of the connection between the rudder pedals and the pulley that drives the rudder cable (with which he is all too familiar, having gallantly repaired it after it fell apart during some of his kick-and-punch flutter testing) was more likely than not non-symmetrical, and that this, rather than some mysterious aerodynamic or power-related phenomenon, was the probable cause.
[March 11, 2004]
I've spent several hours contouring the tips and am nowhere near finished. "Contouring" means coating the bare composite skin with microballoon-filled epoxy and sanding it down to a smooth, well-shaped surface. This is not difficult on ruled surfaces like wings and on generally convex or mildly concave ones like fuselages, but I find it very difficult on surfaces with rapid shifts from convex to concave curvature, such as occur in the curved transition from the tip panel to the wing. I will undoubtedly lose patience at some point and settle for a less than perfect result.
In the meanwhile I've been occupying my thoughts with several other projects, including front-seat armrests (a pretty simple matter) and a separate air intake for engine breathing. The air intake seems desirable because I've found that air taken in at the front cowling inlet picks up quite a bit of heat on the way back to the turbocharger. There are ducting losses as well. I polled a few people about how best to handle the transition from the small intake cross-section (about 8 square inches) to the air filter, which is more than ten times larger. The consensus seemed to be that lack of space makes an ideal diffuser impossible, and the best bet is just to spill the intake air directly into a plenum and live with the inevitable losses. I considered both recessed ("NACA scoop") and protruding ("pitot") inlets, and decided to use the recessed type, even though it may have slightly lower ram recovery, because it produces less parasite drag. Ram recovery would weigh more heavily with me if I planned to do a lot of flying at maximum speed and altitude, like an interceptor; but I don't. Quite a lot of mulling has gone into the details of this ostensibly simple modification, because the scoop will be in the left side panel of the cowling, which must be easily removable.
I've also been revisiting the design of my middle flap track. (The flaps are installed, but not yet operable.) I need to remove the wings briefly for various reasons, and while they're off I'm intending to reinforce the area around the middle track attachment.
Reinforcing the middle flap track attachment points requires knowing the air load acting on the flap. CFD analyses indicate that the load on a fully-deflected Fowler flap is quite constant over the useful angle-of-attack range because the local angle of attack is controlled by the wing, while the total load on the wing+flap combination naturally increases with angle of attack, or "alpha". As a result, the fraction of the total load borne by the flap increases as speed increases, going from 13% at +10 degrees alpha to over 35% at -5 degrees (the angle of attack for maintaining 90 knots, the design flap speed, at minimum weight). The air load on the fully-deflected flap is always about 350-370 pounds per flap,. (The area of the flap, by the way, is 9 square feet, that of the wing panel 44 square feet.)
A source of Fowler flap test data is NACA Technical Report No. 534, which reports that the air load on this type of flap -- which translates aft until its leading edge coincides with the trailing edge of the wing before deflecting downward, in this case, 30 degrees -- rises to "nearly 1.5 times the load that would result from uniform distribution of the total load over the total area." Taking "total area" to mean wing+flap and omitting the portion of the wing that is buried in the fuselage, at a 2,850-pound gross weight the average loading would be 1425/(44+9) or 26.9 lb/sq ft. The flap load would then be about 40 lb/sq ft, or around 360 lbs. What a coincidence. The same NACA TR also says that the maximum CL of the flap itself may go as high as 3.2; at 60 knots, that would put a 350-lb air load on each flap. Bingo!
Part 23 requires that a flap be designed for a maneuvering load factor of 2G and for 25 fps gusts either normal to or aligned with the flight path. The 2G maneuvering requirement is equivalent to pulling up to the stalling angle of attack while at 85 knots; increasing the angle of attack reduces the fraction of the lift carried by the flap, however, and the flap load remains unchanged. The normal gust would change the angle of attack by 15 degrees, which would have the same effect of driving the wing up to the stall. The gust parallel to the flight path, on the other hand, is an increase in airspeed without a change in angle of attack. Part 23 requires that Vf, the flap extension speed, be the greater of 1.8 times the flaps-down stalling speed and 1.4 times the clean stalling speed. My 90-knot value does not meet this criterion, nor is it required to, this being a homebuilt. The worst case for gust loading, however, is the minimum speed, not the maximum, because the change in dynamic pressure, a function of the square of speed, is proportionately greater. Adding a 25 fps horizontal gust to the 60-knot stalling speed increases the air load on the flap by 56%, to 560 pounds. A factor of safety of 50% brings the ultimate load requirement to 842 lb per flap, half of which is carried by the middle track, with the remainder shared more or less equally between the inboard and outboard tracks.
[March 1, 2004]
That "end of next week" estimate with which I ended the last entry was my usual self-deception. I never learn.
The wingtips were an unexpectedly long process. First Ray Henning and I hotwired styrofoam cores for the upward-canted, straight-tapered portions. I laid up 2-ply bidirectional skins on the undersides of the cores. I then bandsawed wedge-shaped styrofoam inserts about three inches wide and 21 inches long, and bonded them to the roots of the tapered segments to provide 30 degrees of tip cant. I then bonded those assemblies to the wing, relying on measurement and on the accuracy of the insert surfaces to jig them, and carved and sanded the curved transition to shape. I then laid up bridges from the wings to the cured bottom skins of the tapered portions, incorporating little NACA scoops for the fuel vents and tunnels for access to the outboard aileron hinge bolts. Finally I skinned the tops. Each wingtip thus required five overnight cure cycles, and since I did the two tips one after the other (in order to avoid making any fatal errors twice), the whole project took two weeks. They still need to be filled, smoothed and painted, but they are flyable as is.
Theoretically, the tips should increase the dihedral effect of the wing alone by 50%; their effect on the totality of the airplane is more difficult to analyze. The additional wingspan should increase the L/D ratio by about 5% (from 15.1 to 15.9) and rate of climb by about 1%. John Thorp once told me that shedding the tip vortex from the ailerons increases stick forces; and so there was some basis for expecting a reduction in roll forces by moving the tip vortices outboard.
Today I made a 20-minute test flight to get a subjective assessment of the effect of the tips. It's impossible to detect small differences in rate of climb or L/D ratio, and roll forces seemed about the same as ever (too high). On the other hand, roll-yaw coupling is definitely improved. I am puzzled, however, by the fact that most of the improvement is found when yawing and rolling to the left; the dihedral effect with right yaw is considerably weaker. I don't know why this would be, and several minutes of standing in front of the airplane and scratching my chin did nothing to enlighten me.
[February 13, 2004]
I'm
in the process of adding wingtips. The wings were originally designed for a
span of 420 inches (35 ft, 10.67 m), but I left 10 inches off each end to allow
tailoring the dihedral effect by canting the tips. Without the tips, the airplane
has barely positive dihedral effect; that is, it rolls only slightly in response
to rudder. The tips, which will in fact increase the span to 430 inches (35.8
ft, 10.92 m), are canted upward 30 degrees and have about 45 degrees of leading
edge sweep. Both the upward cant and the sweep are supposed to contribute to
the dihedral effect, for reasons that are fairly obvious if you consider that
the desired rolling moment results from sideslip. It will be interesting to
see whether they actually do. Something similar was done to improve the dihedral
effect on Rutan's White Knight (the suborbital rocket's mother ship) and it
was quite successful. I'm not certain that the rapid taper to a 6-inch chord
NACA 0009 section at the tip is a good idea; White Knight's tips are broader
and cambered.
I hope to test-fly the tips by by the end of next week.
[February 5, 2004]
I flew up to Mojave to do a series of landings with the airbrake open, but since the first one was perfect and showed no detrimental effect, I cancelled the rest of the test. It was a classic mild California winter day of blue skies and unlimited visibilities, both at Whiteman and at Mojave; lovely for flying. I noticed on departure that at climb power the engine cools better at lower speed -- that is, better at best rate of climb speed than at cruise climb speed. I attribute this oddity to the extraction effect of the foward outlets.
I added a capsule assessment of the cooling system to the essay on cooling flow.
[February 2, 2004]
My planned test flight last Friday didn't happen, because of a stomach flu. I finally got in a 45-minute flight today, before the current rainstorm arrived. The results were generally good. The heater works, and doesn't smell bad. The new rudder trim tab seems just right; the ball is now centered in cruise, whereas it used to be a tad out of the cage to the left. The #2 comm antenna, using a design suggested by Allen Podell, works much better than the #1 comm's copper-tape dipole in the leading edge of the fin. The aft edge of the top cowl now stays put regardless of the airspeed.
On the other hand, the deflector that I put into the cowling behind the air inlet in the hope of steering some extra air toward the #6 cylinder seems to have had no effect at all; that cylinder is still 20 deg. C. hotter than the others (190 v. 170) in cruise.
I tried landing with the airbrake open; it seemed as though the airplane was less stable laterally and directionally and harder to control in the flare, but I'll have to do it a few more times to be sure.
I measured the air temperature inside the cowling on top of the air filter box; it's 20 deg. C. above ambient. Next flight I'll measure the temperature inside the air box; if there's no difference, then I can get rid of the long SCAT hose bringing air from just behind the inlet back to the filter, which is against the firewall. I've been toying with the idea of putting a dedicated NACA inlet on the cowling side to feed the engine, but I haven't yet decided whether it's worthwhile and, if so, where the inlet should be. I'll have to change something eventually, because I know that the present duct is not large enough to supply the engine at critical altitude.
[January 25, 2004]
The heater is now installed, but still untested, so I don't know how effective it is, and probably won't know until some future flight in semi-dark subfreezing weather when I find out that what seemed adequate on a southern California afternoon really wasn't. It was not much trouble to build, but I may regret using .010 aluminum for its outer shell.
The number of to-do items that I can reasonably undertake before being obliged to deal with the flaps grows ever smaller.
[January 16, 2004]
I flew to Santa Fe on the 12th and returned on the 14th. It was a lucky choice of dates. A high in southern Arizona put 15 knots on my tail for the eastbound trip. Two days later the high had migrated into Utah and a low had established itself in northern Baja. Together they were squirting air back toward California, against the current. I averaged 180 knots going, takeoff to touchdown, and 184 coming back. The trip somewhat made up for the fact that in this imperfect world the majority of wind components are inevitably negative.
The airplane performed perfectly, except in two respects. First, the cold-soaked engine would not start at Santa Fe; I don't know if this is because the battery is too small, or because it's getting old. Second, it got quite chilly in the cabin when an overcast blocked out the sun. On returning home I immediately moved "add heater" to the top of the to-do list.
An odd thing I noticed after landing was that the fine splatter of oil that I usually find on the windshield after a few hours of flying was not there; nor were there the usual fine streaks of oil on the upper cowling. I cannot account for this change, unless it is related to lower than usual air temperatures, or simply to my having cleaned off the inner surface of the cowling while repairing the outlet lips.
Yesterday I finished installing the additional Camlocs to the top cowling, but I have not yet flown to test their effect. Today I began making a heater. Fortunately I had salvaged all the hard-to-build components from Melmoth I; all I need to do is build a new muff. Heat is taken from a 9.25-inch segment of exhaust pipe; the exhaust systems of turbocharged airplanes, being under pressure, run very hot, and so I expect this to be enough.
[January 8, 2004]
It turns out that the buffet and tailwagging produced by the airbrake diminish with speed to the point that at 100 kias you are not aware that the brake is open; so the warning light is probably a good idea.
I had moved the cowl air temperature sensor from the top of the baffles -- that is, the hot side -- to the bottom, right next to the rocker covers. In cruise the temperature was 21 C (OAT was 12.5 C), which is barely balmy; after landing and during taxi it rose to 42 C, which is just about half of the temperature above the engine. After shutdown, with no airflow in the cowling, however, it rose to 95 C. The sensor is on the left side of the cowling, where the turbocharger is; some of that heat is probably coming from the turbo. I need to get some readings on the right side for comparison.
Mike Melvill once suggested that I might want to install a drop-in door in the rear portion of the top cowl to allow hot air to escape after shutdown. It would close itself under ram pressure. I'm thinking about it.
[January 7, 2004]
Little has been accomplished in the last two weeks, on account of the holidays. I replaced the deformed fairings on the aft cowl outlet lips with balsa-cored ones, which will presumably not inflate to a preposterous shape when heated, as the styrofoam-cored ones did. I also began to install four additional Camlocs in the top cowling; the rear edge, which is under full ram pressure, bulged a little between the original ones. This would not have bothered me much, had the shortcoming not been situated just a few inches from the windscreen, where I was obliged to stare at it continually.
A couple of people asked the obvious question about the airbrake: What is the maximum speed at which it can be used? I designed it for 300 mph indicated; not that I expect ever to get going that fast, but if I did I suppose I would want to slow down as soon as possible.
With regard to the question of whether there ought to be a brake-open warning light or not, I am still undecided. I need to do some basic tests, for instance, to ascertain the influence of the airbrake on stalling and takeoff behavior. I bought a reed relay ($2) that I can, if need be, secure to the structure near the trailing edge of the airbrake and wire to a yellow light on the panel. A small chip of magnet bonded to the brake would trip the relay when the brake is closed, turning the light off.
I'm flying to Mojave tomorrow for the press unveiling at Scaled of the "Global Flyer," a jet-propelled version of Voyager that is supposed to circle the globe nonstop in 80 hours, without refueling, with all-purpose adventurer Steve Fossett at the controls. That will be an opportunity to gain a little more airbrake experience.
[December 17, 2003]
I spent the morning writing the inevitable (for all aviation writers and a few with no understanding of aviation at all) assessment of the Wrights for the local paper. Then I went to the airport, finished the installation and wiring for the airbrake, and test-flew it. It produces a distinct but gradual and perfectly controllable pitch up; the moment generated by pressure under the belly ahead of the wing obviously much exceeds that from drag below the thrust line. With the brake down there is a continuous rumble that should make any kind of warning light or position indicator unnecessary. The effect on descent rate is marked; no official numbers yet, but I think I got rid of 2,000 feet in less than a minute at 125 kias without reducing throttle. There was no discernible small of exhaust in the cockpit. I had removed one of the upper access panels so that I could look down at the airbrake. With it open, there was nothing between me and Valencia but a lot of air. Unfortunately, before I could do much testing one of the cowl outlet vanes sheared a rivet and its trailing edge popped up to an odd position. I returned to the airport at reduced speed.
[December 15, 2003]
Having modified the airbrake lever on the throttle quadrant to incorporate a microswitch that will turn the hydraulic pump on and off, I provisionally assembled the system in order to test it. Concerned that undetected internal leakage in the landing gear control valve might allow pressure from the airbrake actuator to back up into the landing gear cylinders, I put jacks under the wings and immobilized the nosegear drag link hinge with a C-clamp. These precautions turned out to be unnecessary. The brake opened at a good speed -- not too rapidly -- and closed gradually. The purpose of the test, other than to satisfy my curiosity about the basic operability of the whole system, was to determine which position of the control valve was "up" and which was "down." It may seem odd that there was no other way to determine this, but aviation is full of surprises.
[December 9, 2003]
I successfully