According to the technician at Aero Accessories from whom I picked up the overhauled alternator this morning, it's just a plastic connection designed to avoid dropping metal fragments into the engine in case the link fails. But I wonder whether he's right. In any case, he said that failure of the outer case of the alternator is something they see maybe once a year.
He assumed it was due to vibration wearing the aluminum threads, so that the steel bolts and safety wire all remain intact, but the whole structure comes loose. After some number of hours of use, this coupling wears out. It is no longer possible to secure it to the alternator shaft with the required torque, and it must be replaced. This was the case with mine. This experience has reminded me that I am not really in the airplane owner demographic, and my flying career will last only as long as not too many expensive parts of my plane break at once.
The problem with the alternator turned out to be the alternator. In the seven years since I installed t, it had shaken itself to pieces. This is a little hard to understand, because the engine is quite smooth and I feel that the vibration level in the plane as a whole is low, but, as the mechanic said, you can never tell about vibration. What was surprising, and instructive, about this was that I had inspected the alternator before taking the airplane to the mechanic, and noticed nothing; but my attention was directed to the wire connections, and since the alternator itself was ostensibly intact, with all its bolts and screws and safety wire in place, it never occurred to me to grab the end of it and shake it to see whether it was coming loose from the rest.
The mechanic asked when I had last had my prop balanced. Forty years ago, I said. He suggested that every hours would be a better interval.
I've seen flakey behavior in the charging system before, including on the previous flight, but always the system would pull itself together after a few minutes and do the expected thing, that is, initially indicate a charge as the battery recovers from starting the engine, then gradually drop to zero charge or close to it and maintain a steady 28 volts.
I tested my old epoxy a few days ago; it's still good. I don't have much graphite cloth, however; I have to decide whether to settle for glass or spend some money.
I'm tempted to use glass just because it's so much more cooperative. Graphite is so stiff, it's a pain on small radii like these. Maybe I can use a little of each; that would seem high-tech. I need to find out whether my out-of-date high temperature epoxy will still harden, and whether I have enough carbon cloth for the parts I suppose I could use glass; it's a question of stiffness, not strength, and so carbon would be preferable.
More important, I need to figure out how to split the parts in order to be able to get them free of the molds. The molds represent the inner surface of the parts; in other words, the parts themselves will be laid up over these molds. This morning I began to reflect that the ambient pressure source for the injectors and mags -- both of which are pressurized by the turbocharger -- and possibly also for the manifold pressure gauge, is a tap in the duct leading into the throttle body, and that this tap is at a right angle to the flow direction.
Since the flow speed in that duct is around mph, there might be some pressure drop, and so I may not be getting full pressure. I consulted my photos and found, first of all, that I was wrong about the MP source; it comes from the crotch of the Y downstream of the throttle body. At least I think it does; actually, every one of my photos manages to hide that area, which resembles the pudendum of a putto, as modestly as those fortuitous bits of foliage and fabric in paintings of yore do the corresponding parts of Venus, Mars or Jesus.
But it stands to reason that the MP pickoff would be downstream of the throttle; I was silly to think otherwise, however briefly. At any rate, I shall go to the airport today and visit the scene in person. Fortunately, my manifold pressure gauge has two needles, one of which tracks ambient pressure and provides, for anyone who can subtract, a crude but reliable backup altimeter.
I can temporarily hook that one up to the pressure tap that goes to the mags and injectors; the two needles will show the pressure drop, if any. The last time I reported on its behavior, in December, I had replaced its internal battery and it was now remembering to send position data to the autopilot; but it had stopped offering airports, NDBs and such stuff as Go To options, and was confining itself to waypoints, of which, incidentally, none were programmed.
In addition, its map would display road, airport, position and track data, but not airspace boundaries. I was pretty well resigned to this state of affairs when one day it suddenly remembered its airports and NDBs. Then it would not search properly; it would go up to about the middle of the alphabet and then jump back to the beginning. After a couple of restarts, however, it abandoned that annoying behavior and acknowledged the entire alphabet.
A couple of flights later, airspace boundaries suddenly appeared. It was like a stroke victim slowly relearning how to speak and walk. I do not know enough about electronics to understand how a device like this, which must have about the neurological complexity of C. The intercooler tanks will be laid up, using carbon fiber, over these molds.
The one on the left is the inlet. Actually, I am well and so is the airplane. The nation, maybe not so much. I have done very little work on the plane lately, for several reasons.
Plus, although I feel I am getting closer to the correct solution, I am still uncertain about some details of the intercooler plumbing. I am pretty sure, at least, that I have the position right. Here is the palimpsest upon which my runes are inscribed: I do not expect this to be comprehensible; I am including it just to show that I do occasionally pick up a pencil or, more often, an eraser, and inflict something upon a piece of paper.
The process has been somewhat impeded by my stupid choice of some redwood that happened to be lying around here as the material from which to make molds for the two high-pressure "tanks" that bring air into the intercooler and conduct it thence to the throttle body. Redwood is a material of constantly varying density, and singularly ill suited to mold-making. However, once I have made a mistake I am determined to persist in it. I am pretty satisfied with the inlet and outlet paths for the induction air, although the very tight degree turn to the throttle worries me a bit, just in terms of its effect on flow distribution in the log manifolds.
The cooling air is a different story, but it, at least, I can defer thinking about until a later time. The inlet path for cooling air is less obstructed, and the paths for the charge air both into the cooler and from the cooler to the throttle body identifiable as an orange sleeve in the photo are better aligned.
But I am still waffling about the whole idea, in part because of the weight of the intercooler itself -- around six pounds. I think it's bigger than it needs to be. Someone cautioned me against sawing off one end of it, but I don't know what difference it would make if I did so and just bonded a new end plate to it with a mess of JB Weld. At any rate, the non-airplane aspects of my life have been more than usually complicated lately, and I've spent less time than usual on the plane.
So between lack of time and uncertain motivation, the intercooler is making no headway at all. I don't like the arrangement, now that I've seen it, and am going to try a different one, with the large face of the core horizontal rather than vertical. After writing an Aftermath column in which the cause of the crash was the pilot's faulty handling of an aborted landing, I became curious about whether Melmoth 2 could climb with full flap and airbrake -- one of many things that I have never tested.
The airplane was extremely light, however. The only problem was heating; the CHTs rose rapidly because of the low airspeed. The proper technique for a go-around would be to maintain level flight initially while cleaning up and accelerating. The pitch changes with airbrake and flap retraction are quite marked, but easily managed if you're prepared for them. The temperatures were, on average, 20 degrees F above ambient with the deflector and 30 above without.
This suggests that maybe I ought to look into making up some sort of duct that runs directly from the peripheral intake to the oil cooler; at present the oil cooler duct takes in a mixture of deflected cold air from the peripheral duct and warm air from the plenum. Incidentally, these data were collected while cruising at 4, feet at ktas on 6. Today the unpredictable 1 Lowrance worked, to some extent. Now that I have replaced its internal battery, it remembers that it is supposed to be producing NMEA output for the autopilot coupler.
On the other hand, it seems to have forgotten its airport and navaid data, and now offers only user waypoints in response to the "Goto" command. I suppose it would not be that much trouble to program the waypoints I use most often. But would it remember them? The first time I tested it in flight I got the impression that it had had a remarkable effect; but as time went on the effect appeared to vanish.
The only way I will know for certain is by measuring the temperature in the duct with and without the deflector in place. My seemingly successful installation of a new battery in the 1 Lowrance has resulted in a unit that remembers its settings, but refuses to lock onto a satellite, even though it passes its self-tests okay. Meanwhile, the 2 unit, which is currently installed in the airplane, has developed a new problem: I suppose it is foolish of me -- perhaps I am a deranged US dotard -- to suppose that electronic devices almost 20 years old can be expected to function normally.
Different altitudes produce scatter, but on the whole the points line up fairly well. I recorded induction air temperature at 20, 25 and 30 in. Hg at 4,, 8,, 12, and 14, feet. I had intended to finish the series at 16, feet, but it became apparent that the temperatures were getting quite high and I did not want to venture past deg.
Here are the data I collected: The left-hand chart is simply the right-hand chart minus the OAT. The astute viewer will wonder why the temperature rise is so large even at low manifold pressure and low altitude, where no compression at all should be taking place. The reason is the peculiar design of the Piper "fixed wastegate" system that I have modified to incorporate a manually adjustable wastegate. This is an inefficient arrangement, obviously, but by using low rpm these tests were run at 2, rpm, but I often go lower I can open the throttle fully at 8, feet or so.
I seldom cruise lower than that -- more usually above 10, feet. It's evident, anyway, that there's a good deal of heat to be gotten rid of. One question on my mind was whether I needed to provide a separate cold air intake for the intercooler, rather than use the air already in the "cold" plenum. The temperature near the firewall is about 45 deg F above ambient -- this due to heating by the exhaust pipes and the turbocharger. But it might be worth a try, nevertheless.
Following his advice, I crammed a new battery in with padding to press the contacts against it, and voila, it remembers! But -- can it be TSO'd? I remember, during the construction of Melmoth 1, intensely visualizing the retraction linkage for the main landing gear while meditating at the Cimarron Zen Center of Rinzai-ji.
How, I pondered, is the gear koan to work? I am now at the same stage with the intercooler. My recollection of the details of the engine compartment is not so complete or exact that I can mentally map every attachment and duct path, but I have dozens of photographs of it to help me.