Restoring the A-10D Mitchell Wing
SN# 275
By
Episode VII
The Instrument Panel and Electrical System Continued, Alien Abduction and The Pod
The instrument panel blank came back from the machine shop about two weeks after I’d dropped off the aluminum plate. It looked good, very professional. In the weeks that it was gone, I’d spent a lot of time sitting in the cockpit with my cardboard mockup panel, looking for the ultimate arrangement of instruments. Visibility was a big factor here since my knees tended to obscure the lower outside corners of the panel and the stick obscured a good part of the mushroom’s stem. Pushing cardboard and paper cutouts of the various instruments around on the mockup finally yielded a workable arrangement.
Climbing in and out of the cramped cockpit I found that my shins were perilously close to the bottom outside edges of the panel. Although the rudders were workable, any slight shift forward in body position was likely to result in the panel being embedded in my legs just below the knee. To deal with this the Sharpie marker came out again along with my trusty box knife (cardboard is such a wonderful medium). After a quick redesign session the lower outside edges of the panel were raised to relieve the areas around my shins.
Satisfied that I had a workable arrangement I covered the aluminum panel blank with two-inch masking tape and set about marking the instrument cutout holes in pencil. An instrument layout template from Aircraft Spruce was a big help in getting this done. Interestingly, it turned out that I had a bit more space than I expected. This was used to push the instruments on the outside edges as high as possible in order to accommodate the new shin cut modifications on the lower edge of the panel. It looked good, so good that I wanted to get it completed as soon as possible, which in my case meant tossing it into the car and driving straight to the machine shop. No matter that it was 9:30 at night.
Driving up the long gravel driveway I was not surprised to see that all the lights were on and the big metal doors to the front of the shop were open. Framed in the doorway was the nose of a Chevy stock car in various stages of disassembly. My machinist was heavily into racing and it looked like he and his small crew were getting ready to do battle on the local track again Saturday morning. The shop’s combination watchdog and sleeping champion, hood ornament announced my arrival with a fusillade of barks and a particularly threatening growl that caused a grease-stained face to pop up from where the car’s steering wheel once was.
“Where’s Roger?” I asked. The face grimaced and a blackened hand pointed to a pair of feet jutting out from beneath a rocker panel. It took a few minutes, a shower or two of sparks and some rude remarks aimed at a bad weld, but eventually the shop owner emerged from bowels of the Chevy.
“Hey, it’s the airplane guy.” He said, flipping up his welding mask. “All you guys com’mere!” Three more bodies extracted themselves from unknown places in the stock car and stood staring at me. “This is the guy I was tellin’ ya about! Flies one a them ultralights. Told ‘ya he was real.”
“Gotta be crazy ‘ta do that,” said one.
“Yeah, I wouldn’t do it,” said another.
A third looked me up and down, frowned and just shook his head. There followed a brief discussion during which all parties agreed that I was likely not to survive more than a year and that I should pay up front for any work. They then disappeared back into the Chevy leaving me to consider my newfound celebrity status and to discuss my panel project with Roger.
“Have it for ya in a week or two, okay?” It was the standard answer.
“Okay” I said and waved at the crew’s various body parts visible outside the car. “See ya.” I waited a moment but the only response was a twitch of the dog’s ear as he passed gas on the hood. Being a celebrity just ain’t what it used to be.
Now that the instrument panel was on track I decided to attack the pod. The first effort was to pull it off the airframe, which took about an hour. In doing this it occurred to me that I really hadn’t worked out how I was going to support the panel when it was finally installed. There followed the usual soul-searching and doodling, mentally fishing for an inspired way to do the mounting. It took awhile, but eventually I came up with a simple set of “L” brackets and padded clamp arrangement that would support the top. The bottom would be hinged to a narrow aluminum cross bar to allow access behind the panel for repairs and alterations. A quick visit to my growing scrap aluminum pile produced the needed pieces of raw metal. When the sawing began, it occurred to me that I had done nothing to isolate the panel from vibration. Back to the drawing board. Two miniature Lord mounts and a small strip of neoprene foam solved the problem with only a minor alteration of the mounting scheme.
Satisfied that the mounting was usable I turned once again to the pod. The fiberglass repairs had left the interior rough and unsightly. I had a number of choices. The first and least weight gain was simply to leave it as it was. After all, who looks at the inside of the pod? Well, me for one, and I hated it. So, that was out. The next was a suggestion from my homebuilder buddy who had sprayed the inside of his composite kit with a stone textured paint. It looked pretty good. The rough texture hid a wide variety of flaws. But, would it cover my super flaws? I decided to spray out a small section and see. It was better, but still not great. The last option, and the one I was hoping to be forced into, was to replace the original cloth liner with vinyl. For a few extra bucks the upholsterer that made my seat had turned the extra material into a ribbed, foam-backed liner guaranteed to cover even my mega-flaws. I just had to find it, then get some spray adhesive and edging.
A quick visit to the upholstery shop (another “Hey it’s the airplane guy,” recognition thing) produced ten feet of black automotive edging, some installation hints and a handful of razor blades to do the final cutting/ fitting. I was ready. Well, maybe not. While jockeying the liner for the best fit I had my first opportunity to look closely at the repairs. The guy who did it had forgotten to fill in two large holes from a cross brace and a number of old rivet holes. Damn. Back to fiberglass repair mode. Fortunately, I now had some experience in this area from dealing with the wing tip shroud. It wasn’t long before the holes were filled and the pod sides repainted. Okay, now for the liner. Or, maybe not. Hassling with the liner fit I realized that I’d forgotten to install the pitot tube in the nose. The old one had simply been a piece of aluminum tube held in place by copious amounts of silicone caulking. Unable to easily reach the nose section I put the pod on the ground, using some cardboard and an old blanket as padding to protect the paint, and crawled inside. After a bit of prying and poking, the silicone finally came loose in one large cone shaped mass. A Pitot Pal plastic base was installed in its place. Now I was ready for the liner.
A word to the wise here: Never apply spray adhesive outside, with a gusty wind blowing. Staying upwind is almost impossible and skin sticks very well to vinyl and or fiberglass. Needless to say, it took awhile, but the liner finally yielded. The next step was to cut it to fit the outline of the fiberglass pod using the razor blades. This was not as straightforward as I’d hoped, but when I was done, it was a reasonable approximation with about ¼” of material projecting beyond the edge of the fiberglass shell.
The edging was next. I’d been advised that a professional simply wraps the material around the shell edge and pushes the edging over it. This turned out to be far more difficult than I expected, requiring finger strength and dexterity beyond that of mere mortals. An hour later I had only six inches of edging in place. Frustrated, I cut the liner back to the edge of the glass and tried pressing the edging over it. It didn’t work. I needed some kind of tool to help the process. Rummaging through the garage I located my putty knife and used it to hold the liner in place while I pushed the edging over it. The small success was gratifying but I had used up the greater part of a Saturday afternoon in the process. The pod was also quite a bit heavier now, and visions of weight and balance nightmares began to haunt me. I banished these by moving my attention back to the instrument panel.
A call to the machinist yielded only the answering machine. The cell phone number was the same. Hmmm, unusual, but it was, after all, a weekend and the stock car racing season was well underway. I decided to try again mid-week. Still no luck. This was not a good sign. Finally one evening I cranked up the old Subaru and drove over to the shop. There was no sign of life. A small, dim light at the house held some promise, so I wandered over and banged on the sliding glass door. A few minutes later a bleary eye peeked around the doorframe and scanned the yard, finally stopping on me.
“Yeah?”
“Where’s Roger? I’m here for my instrument panel.”
“He ain’t here. Who’re you?”
“The airplane guy. You know, the one who keeps filling up your answering machine with messages. When’s he coming back?”
“Dunno. Maybe next week.”
“Who’re you?”
“Son.”
“Where is he?”
“Dunno. I’ll tell ‘em you was here, okay?” With that the eye disappeared and a set of faded curtains closed over the door leaving me standing on the deck like a rejected brush salesman.
Another week came and went with no results except a sore fingertip from hitting the redial number on my telephone. It was then that I gave up. Roger was obviously the victim of an alien abduction. I imagined him clutching my half-finished panel to his chest screaming, “No! No! Not now, the airplane guy needs this!” as an army of bug-eyed, spindly gray X-Files types dragged him to a waiting UFO. No doubt my panel was now in a museum somewhere on the planet Melmac, next to the stuffed and mounted remains of a greasy guy in blue coveralls, moustache forever contorted in a silent scream.
A month had come and gone since the panel blank first left my garage. And in that time an article appeared in one of the EAA magazines on how to cut large instrument holes in aircraft panels using only an electric hand drill and some hole saws. Buoyed by this new knowledge I decided to do the job myself. And so it was, that I pulled the last of the aluminum sheet from the pile, marked the now familiar contours of the Mushroom Mark II design on it and began cutting. It was slow going with the fine metal blade in my jigsaw, but finally a new panel blank separated from the aluminum sheet. Masking tape came next and I recreated the instrument layout with a few minor modifications. My homebuilder buddy had loaned me two large hole saws. After checking the magazine article one more time I set about cutting the wooden saw guides and screwing them to the panel blank. The hole saw shank fit nicely into my drill press so I tightened down the chuck and started the cut. It was like magic, within seconds a perfectly round hole appeared in the blank. Excited by this success I decided to check the fit of the 3 1/8” ASI in the hole. It fell through, landing with a thunk on the bench. My morale sank to zero as I read 3 ½” diameter on the hole saw. Damn. Gary had thrown all his large hole saws in one box and I had blithely assumed that the largest was the 3”. Okay, chalk up another chapter in the book of stupid, time-consuming mistakes. Luckily, the aluminum sheet had just enough material left for one more panel.
A week later the second panel, complete with correctly sized instrument holes, was sitting on the bench. It was decision time again. I had sort of nurtured the idea of using some type of veneer on the panel to give it the look of solid wood. Real wood though might present a problem with exposure to the weather in an open cockpit. After experimenting with some thin strips of cedar, using various varnishes and coatings, I decided there had to be something better. It was then that I spotted the stone-fleck paint can that had been the subject of another experiment for the pod interior and I got an idea. Pulling out the old panel blank with the super-sized hole in the middle, I sprayed it with the textured paint. It looked pretty good except for the coverage, which tended to leave thin spots and shiny aluminum beneath them. This problem was solved by first spraying the panel with gray primer. The next problem was that the stone-fleck paint wasn’t waterproof. Reading the instructions on the can yielded answer in the form of multiple coats of clear lacquer. I was in business. A day later the real panel had been turned to synthetic gray granite, and the day after that, three coats of flat clear lacquer made it weather resistant. Now for the instruments.
The following weekend provided a most satisfying experience, turning the empty panel blank into a fully populated instrument panel. The good vibes were enhanced when it slipped neatly into place onto the mounting system. The only kink here was that the threads on one of the Lord mount screw studs would not accept the nut. A die of the proper thread was used to re-cut the stud and, voila! One deluxe instrument panel. A few short lengths of ¼” vinyl tubing from the pitot kit were pressed into service and I suddenly had a rudimentary static air system. The next effort would be wiring the panel switches, fuses and 12 VDC outlets followed by the electric instruments.
The wiring proved to be fairly uneventful except for the occasional misinterpretation of the schematic or changes inspired by a better idea. Sets of wires were grouped by function and lengths adjusted so that they would be near full extension with the panel rocked back toward the seat. As many connections as possible were soldered to prevent intermittent function caused by loose joints and switches tested to make sure they turned “on” in the proper direction. It was starting to look like something out of a real airplane, by God.
Wiring the CHT/EGT gauge was a real rush. I applied the tip of the soldering iron to the two sensors and for the first time, something actually moved on the panel. Better yet, both moved in the right direction when heated.
In the preceding months I had found and joined the Middleboro, MA Ultralight club. I was now flying on a semi regular basis with their flight instructor in an effort to keep up my limited skills and work toward a UL pilot’s rating with the EAA. About a third of these little adventures were delayed or cancelled by unexpected maintenance items required by the instructor’s aging Challenger II. One of them was a dead battery, which got me thinking that sooner or later I would encounter the same problem with the A-10. While charging the Challenger battery was fairly straightforward through a hinged panel in the nose, the A-10’s battery would end up out of reach in the forward part of the pod. The idea of cutting a panel into the repaired and painted pod was anathema, so I began to consider other alternatives. The original owner had installed a pair of banana jacks on the side of the pod where he could plug in his battery charger. I decided to use one of the 12VDC jacks, already installed, for double duty. A quick check of the schematic, a bit of wire and an SPDT switch was all that was needed. Bingo, instant charging port. I just had to modify a battery charger with a 12VDC power plug instead of the normal spring clips. Or, I could use one of those super-gell-cell-dead-battery-eliminator car accessories I’d seen in the mail order catalogs that continually choked my mailbox. It was a decision to be made later.
If there’s anything that characterizes restoring one of these things, its decisions, some being a bit more unexpected than others. And, it’s one of these unexpected ones that I face now. I need a new propeller. So what’s wrong with the Ultra Prop that I spent good money to upgrade to a three-blade not that long ago? It turns out to be a matter of flexibility. After repairing the right trailing edge of the wing that had been chewed multiple times by the prop, I had developed the dark suspicion that something was not quite right. But, I repressed it and went on with other matters, promising to give it serious thought some day in the future. And all was just fine until I developed an interest in gyrocopters. Joining the Popular Rotorcraft Association brought me a copy of Rotorcraft Magazine, which had an article comparing the characteristics of pusher props. One of the things that concerned the gyro guys was flex in the prop blades. As power is applied, they cone forward, some much more than others, and in turbulent conditions or sudden reductions in power, can end up coning backwards as well. It should be noted here that when a gyro taxis and goes into it’s take-off roll, the main rotor is tilted aft to spin up its RPM and generate lift. In some designs a poor choice in the pusher prop will bring it perilously close to the main rotor disk. Obviously this is not a good thing. Interestingly, the Ultra Prop had the most flexible blades of all the props tested. It also produced the least thrust. Going back to my A-10 owner’s manual I noted that the prop clearance from the trailing edge of the wing was very small compared to other ultralights. It was obvious that the A-10 had been set up with a stiff, two-blade wooden unit in mind. I contacted Larry Smith at Ameriplanes and asked what the “factory” was currently using. He replied that he was still providing the durable, two-blade, wooden 54”x24” models from Tennessee Props. He also apologized for not reminding me to move the engine back 2”-3” if I was considering using a composite propeller. It made sense, but this would mean making another engine mounting plate, something I really wasn’t up for, especially at this stage in the game. Undaunted, I got back on the computer and e-mailed a friend in Massachusetts who also has an A-10. I’d remembered talking to him at the Yankee Fly-In earlier in the summer. He’d broken his prop when his main gear legs collapsed during taxi at the fly-in and had installed a replacement. He replied that he’s now swinging a 50” diameter two-blade Ivo (the remnants of his three blade) and was very happy with its performance. The smaller diameter gives him more ground clearance (much needed in the Mitchell Wing) and the two blades seemed to be providing more thrust than the three. After a few quick pitch adjustments on the ground he was getting 6,400 RPM from the engine at full throttle with all the temperatures in the green. He also did not move the engine to the rear, as the Ivo was extremely stiff when cut to a 50” diameter (all their blades are cast for a 60” diameter and cut to custom lengths). Hmmm, the gyro guys gave the Ivo a good rating, too. What to do? Time for some research into props.
So, tune in next time as our hero struggles with prop selection, hurricanes and disintegrating backyard hangers.
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