Restoring the A-10D Mitchell Wing
SN# 275
By
Episode X
Technical Counseling, Decisions, More Work, Getting Funky with Hardware
I had come to a nexus. I was looking at three options, none of them pretty and I needed advice. After a few quick e-mails and a phone call or two, I was in contact with one of the Technical Counselors from the RI EAA chapter. Like me, Frank traveled a good deal and also like me he’d just returned from a long business trip. The phone call was longer than expected. I explained my situation and my options and generally vented a lot of frustration. Option #3 was gaining ground quickly as the final solution, even though the price of scrap aluminum was at an all-time low. After some quick calculation I figured I might be able to recoup some of the loss by selling the engines, the salvaged instruments and some parts, but when the dust settled I’d still be heavily in the red. No matter, I rationalized that it could all be chalked up to an expensive learning experience.
Frank went into a state of semi-shock at the mention of #3. A veteran of several homebuilt aircraft he was of the opinion that Experimental was the way to go. After all, I already had the Private Glider rating and had even gone to the trouble of getting the additional training to get the motor-glider endorsement. An ‘N’ number meant access and insurance. I could fly it anywhere, and instead of being shunned as an ultralight non-person, I’d likely end up as the ‘pilot’ of a unique flying-wing aircraft; in effect, a celebrity.
It was obvious that there was prejudice and basic injustice involved here, but I decided to shut it out and concentrate on completing my decision making process. What about the FAA inspection? It was Frank’s opinion that obtaining an airworthiness certificate was within the realm of possibility, unless I’d somehow up scaled a Revell B2 bomber model, held it together with duct tape and super-glued a Rotax to its rear. “So, what about tomorrow afternoon?” he asked.
This quick reaction was unexpected, but I decided that such things should not be put off. After all I’d be back on the road the following week, (as would he), and any leg up on the decision process would be helpful.
The following afternoon at two-thirty a white mini-van rolled up my driveway and Frank stepped out, complete with EAA briefcase. I’d arrived from work about a half hour before and was in the process of opening the backyard hanger to allow the escape of the usual tropical heat build-up and to shoo any small critters that might have moved in during the last week of my absence. His first impression was one of interested awe. I’d given him the Ameriplanes and Mitchell Wing.com websites the day before, so he was at least vaguely familiar with what a Mitchell Wing actually was. Seeing one for the first time, up close, however, was outside the norm of yet another RV-6 or Long EZ. He was amazed at the thick airfoil and the overall size of the wing, and, of course the fact there really was no tail.
The next hour and a half was spent going over the airframe, the use of hardware and overall workmanship. I explained the various problems I’d found and the fixes and tried without much success to avoid that fact that I’d stupidly bought a basket-case to begin with. On his side, Frank had a thousand questions and in his turn related his own experiences with a variety of aircraft he’d either built or rebuilt, alone or with a partner. It was a very positive experience.
The bottom line was this, the workmanship was good, the AN hardware was the right stuff and I’d done nothing that violated good practice. Of course, Frank was not an A&P or a DAR or FAA. I would have to trust his evaluation. He also outlined the darker side of registration. I would have to get a new airworthiness certificate if anything major was replaced on the aircraft. Thus, if I swapped props for a different pitch, I’d be seeing the FAA again. If I decided to use my alternate 277 engine while one was being rebuilt or serviced, I’d need another certificate. And of course there was the paperwork and documentation that would have to be kept with the plane. I’d need the original flight manual and logbooks for the engine, airframe and prop. I’d need an ID plate somewhere on the airframe in the cockpit and the obligatory EXPERIMENTAL designation somewhere on the A-10’s foreshortened fuselage/pod. I’d also have to get creative about putting the ‘N’ number somewhere. Lacking a fuselage and tail surface this meant squeezing it, perhaps, on the drag rudders.
Then there was the requirement for an annual inspection. The A-10 is not on the FAA’s 51% list which means that getting a repairman’s certificate may or may not happen depending upon what they think of the restoration effort. The fact that I rebuilt everything but the wing itself might not count. If this is the case, then I’d have to find an A&P who’d consider doing the inspection. Finding one willing to deal with such a unique aircraft was not going to be easy. Also, if I sold the A-10, the repairman’s certificate was not transferable, which means the new owner was locked in to using an A&P for the annual inspection.
And who would do the original airworthiness inspection? FAA will grudgingly do it for free assuming that you can wait for a clear space on their schedule. The price was certainly right, but I’d heard some very negative stories about inspectors with bias against Experimentals. What were the local guys like? I’d have to ask the EAA chapter members who’d gone down that path to see. It would take some time, but I decided to start attending the regular meetings to ask. On the other hand I could find a DAR. These Designated Airworthiness Representatives were generally A&Ps who could do the inspection and paperwork, but for a fee. How much? Out here in the Far East the range appeared to be from $300-$500. Some of them were also known to be a bit friendlier toward the Experimental world.
Weight and balance was another issue on the list. Since 1991 the people who manufactured the Mitchell Wing A-10s have been using the wheel weight percentage technique rather than the traditional weights and moment arms. Besides producing a more accurate measurement it was far less complex and less prone to error. Given the Mitchell Wing’s pitch sensitivity, this is a good thing. Unfortunately, the percentage procedure was not in the manual I had. In order to get the airworthiness certificate I’d need to produce the weight and balance calculation. Solution: e-mail Larry Smith and find out if there was a new manual with the procedure. Answer: Larry says the manual hasn’t changed since the eighties. He then provided a brief description of the Ameriplanes approved weight and balance technique. Basically, put the A-10 on a relatively flat surface, then, with a full fuel tank and the pilot in the seat, measure the weight on each wheel. Ensure that the two wheels not being weighed are resting on something to bring them to the height of the scale and don’t expect the two rear wheel weights to be the same. The weight on the nose wheel should be 17-22% of the total (weight of all wheels combined). The closer the number is to 17% the quicker the response. Moving toward 22% means more docile handling in pitch. Will all this be acceptable to the bureaucrats? I don’t know.
Ah yes, and the final insult. With the magic of registration comes the taxman. The ‘N’ number makes you visible to your state government for property tax purposes. Nifty. I can already feel their hot breath on my neck.
While in a quandary about all this, I got word from my friend Mike Fithian at Falcon East that he was available to rebuild the engines for my Lazair. The four hour drive to upstate New York gave me the opportunity to do some thinking. Overall, the positive aspects of registration were a wash when looking at the downside. It was, however, a fact of life that I would need insurance to get access to even a small airport. Ultralight access was dieing all around me. All they had to do to boot the ULs off the field was demand the same one million dollars of third party liability insurance that the General Aviation guys had to produce. The USUA policy, it turns out, is only good for $100,000 per incident and is unacceptable. Therefore, jumping through the hoops of UL pilot rating and aircraft registration to get it was unlikely to be productive.
When the facts came together I could see a pale image of the future. Registration, no matter how time consuming, costly and painful, would let me fly, eventually. And, that was the original goal in all this. Whether or not it would be cheaper than going back to the sailplanes was unknown. My guess (hope?) was that it would be. If not, I’d wasted a lot of time and money only to be shot down before take-off. The second thing that was becoming obvious was that my Lazair, a true FAR 103 ultralight in every aspect, might never fly. Access is everything unless you own your own grass strip, and those who do are few and far between in this part of the country. They also don’t open them to outsiders for, you guessed it, liability reasons. It was about here that a brief flashback to the open skies of Kansas pushed me into yet another option, or maybe daydream, I’m really not sure yet. Retirement isn’t that far off. I could bail out, buy some land and head west. Damn, even the wife could come along if she wanted to.
Work on the A-10 did, however, continue. More problems, as expected, had appeared. The first was actually an old one. When the right outer wing section was folded, the support came to rest on top of the wing about three inches to the right of the u-shaped locking point. Exactly how this had escaped notice at the factory is beyond me, but things are as they are. When I got the A-10 I’d noticed that the wingtip support had been unceremoniously bent to fit, badly, into the locking point. My intention was to drill out the 3/16” pop rivet and move the lock point to where it should have been. This would leave a small square scar in the new paint, but then I still had some paint left and with some careful sanding I might be able to repaint it.
I was also reconsidering the difficulty of replacing the rudder control cables. At best it would mean opening two holes in the Mylar undersurface of the wing big enough to get my hands into. At worst I’d end up replacing the entire Mylar center section, something I really didn’t want to deal with. Further, I wasn’t completely sure that I could find a supplier for such a large sheet of film in the right thickness.
While considering the above, I decided to work on something I had a reasonable chance of success in doing. Drilling the engine attachment bolts seemed like the ticket, so I pulled out my handy-dandy drill jig and set up my drill press. This little device allows you to drill the bolt head through adjacent hex faces thus eliminating the possibility of weakening the bolt head itself. The set up was fairly simple. What I had not expected was that it would take three drill bits and two hours to put a single 1/16” hole in one bolt. Those 8.8 grade metrics were a lot tougher than I expected. The attempt at a second hole met nearly immediate failure when the drill bit snapped and wedged itself irretrievably in the tiny guide hole. It also left a tiny piece of the bit tip in the bolt head itself. I finally gave up the effort to make the jig usable again and tossed it, ordering a new one from AC Spruce. I also discovered that I was using the wrong drill bits. At a minimum they should be cobalt steel, designed specifically for drilling hardened steel. Finding nothing harder I located a few cobalt drill bits and put them into my tool kit to wait for the arrival of the new drill jig.
My search for prop bolts took a short leap forward after reading an article by Dennis Demeter in the June 04 issue of Ultralight Flying! The subject was counterfeit hardware. This led to some research on the Internet concerning industrial fasteners (i.e. bolts) and the fact that a set of trustworthy SAE grade 8 bolts would do the job admirably. The real challenge was to find some US made, SAE grade 8, 5/16” diameter bolts of the proper grip and thread length. Armed with the US Department of Energy list of suspect bolt manufacturers and their head marks I searched the local auto and hardware specialty stores for the right stuff. Having become a bolt aficionado I was amazed at just how much of their selection was on the black list. The hardware people I dealt with were equally amazed when I asked if their fasteners were imported or domestic. I rarely got an answer because they simply did not know. Most just wrote me off as a lunatic or a wine buff gone over the edge. “Domestic grade eight? Threads rolled, not cut? Ah, no monsieur, but we do have an excellent imported SAE grade five with just a hint too much carbon in the steel. A recent vintage, it has an unusual head mark from a lesser known, but exclusive, source. I’m told that those who’ve tried them found the cadmium coating memorable and quite sincere.”
Enter the MSC Industrial Supply Big Book catalog. A recent addition to my growing arsenal of hardware sources, these guys actually know where their stuff comes from and what it can do. Not only could I get a reliable, US made SAE Grade 8, I could push the envelope with an L9. The only kink was that I’d have to buy a box of 100. No problem, a good bolt is something to be appreciated, and in the case of prop bolts, replaced at regular intervals. While I was at it I also decided to replace the socket head cap screws that held the prop hub to the reduction drive. Interestingly, the originals were, again, of unknown origins and questionable quality. This was corrected with another 100 bolt order of high quality US made units from MSC.
Within two days both the drill jig and the new bolts appeared on my doorstep. Heading straight for the garage I set up my drill press with one of the 1/16” cobalt drills and then aligned it with the tiny hole in the top of the jig. I used one of the vise-grip type material clamps that I got from Harbor Freight to hold the jig in place. After selecting one of the bolts I put the head in the jig and lightly tightened the socket head screw to hold it in place. I then used my all purpose calipers’ depth measuring gauge to ensure that the bolt head was centered in the jig. I then gently tightened the jig’s socket head screw while making sure that the bolt shank was parallel with the drill press table. After it was reasonably secure (heavy pressure is not required) I rechecked the drill alignment with the hole in the jig. Now for the magic. I put several drops of thread cutting oil on the shank of the drill until a large blob formed at the tip and lowered it into the jig. I had already set the drill speed to the fastest setting and flipped the switch. The instructions tell you to perform “peck drilling” throughout the drilling process. I had a reasonable idea of what this was, but I still called a few machinist friends to make sure I wasn’t doing something stupid. As it turned out I was right. Peck drilling is simply applying light pressure to the drill bit at intervals to allow the oil to carry the tiny particles of metal away from the tip. The secret here is to watch the oil carefully. When it fills with metal particles stop and put more oil on the drill. Never let it go dry. Using this technique I found that I could drill two holes in each of two bolt heads before the drill bit got too dull to cut a nice hole. It worked very well, so well that I drilled the four 8.8 metric engine mounting bolts and then went on to the SAE Grade 8 prop bolts. After a couple of holes I developed a gentle touch on the drill press that resulted in some very nice holes for safety wire. I include this detailed information because the instructions that come with the drill jig are very brief and it may save you from ruining a jig (as I did).
Coming home from work one day I decided that my decision making process needed some hard data to work from. Recruiting my youngest daughter to help, we measured the weights on all three wheels, the engine with its reduction drive, the electric starter, the exhaust system, prop, the stabilators, the intake silencer and anything else I could think of that would end up on the A-10. The total was 286 lbs, give or take a pound here and there. This fell within the expected range of a typical A-10 and was not too surprising. I had to dump 32 lbs to get it down within the FAR103 limit. The starter and the pod bought me 23 lbs right off the bat. With no starter, I didn’t need the battery, or the electrical system for that matter. And that meant the electric fuel pump could go. Losing the entire instrument panel would get me even more. It appeared that I could keep the five gallon tank, the seat cover and the nose wheel brake, along with the intake silencer. Hmmm…this was looking like a very decent possibility. Maybe I could even afford a windshield of some type. True, the finished product wouldn’t be as elegant or as aerodynamic as a stock A-10D, but I’d be 103 compliant. This option was suddenly real. But there was still the question of access. It was time for some careful inquiries.
My acquaintances in the EAA chapter were very helpful. The answer was “yes” there still are small airports in Rhode Island that do not deny Ultralights access. I had the answers but no decision. I could go in either direction, UL or Experimental. It would take some thought.
As it turned out I was back on the road for some business travel within a few days of getting the information I needed. It was during this little jaunt that I discovered another possible kink. While sitting in the airport I pulled out my August copy of Sport Aviation and found an article on wiring aircraft electrical systems. According to the article most homebuilts are wired with the wrong stuff, i.e. automotive wire, switches and terminals. It seems automotive wire and terminals use PVC for insulation. The military has recently banned the use of PVC because when it catches fire it produces toxic fumes that can have noxious effects on the aircrew. The new mil-spec wire and terminals were free of PVC. Hmmm, seems I used automotive wire to wire my panel. Was it PVC? The boxes didn’t say. I’d have to do some research to find out. Odds are that it was. On the other hand, before I go ripping out my electrical system to replace it with expensive mil-spec wire, I have to consider the fact that the A-10 is a single seat, open cockpit aircraft. Having sized the wire gauges to easily handle the limited current loads involved, the odds of anything actually catching fire were pretty remote. If a dead short did happen and the insulation began to burn (which could also happen with the mil-spec stuff) it was unlikely that the pilot (me) would be adversely affected by toxic fumes. In a closed cockpit homebuilt I could definitely see a problem, but not with a sixty MPH wind in my face.
The article also addressed switches, indicating that the additional vibration in an aircraft caused automotive switches to internally disintegrate over time. This too may be overkill for my A-10, as I took precautions to isolate the instrument panel from any engine vibration transmitted to the airframe. Interestingly, I picked up an Aircraft Spruce catalog to see what kind of switches I might replace mine with, and found the same units for sale there. Obviously these things must have something going for them. The real question is: What will the FAA look for if I go the Experimental route? I don’t know. So, I guess it’s time to get in touch with Frank and ask some questions.
Another problem, more cosmetic in nature was discovered when I put the newly painted rudders back on the outer wing sections. The color scheme on the Mitchell Wing decals that I got from Ameriplanes caused them to disappear against the yellow paint. I needed something different, so I enlisted the artistic aid of my youngest daughter. Giving her the original decal and complete artistic license she reproduced it in ink, by hand, with no color and then scanned it into her computer. From here she created a number of color schemes against a yellow background that I could choose from. It took awhile, but I finally made a decision and then called GG Grafix, a small business owned by one of the UL club members dedicated to making vinyl decals and graphics for race cars, aircraft and anything else that needs a touch of individuality. I brought the design to him on a floppy disk and turned him loose. A month later I got a call from Mike, who’d just returned from the Yankee Fly-In at Greenland, New Hampshire. He’d seen Paul Gibney’s A-10D and taken a critical look at the Mitchell Wing logos, noting the company decals were all the same, i.e. on one rudder the eagle faced forward and on the other it looked backward. He was professionally appalled and proposed to do mirror images for mine at no extra cost. Naturally I agreed and a few days later had two vinyl transfers in black with red flame outlines that looked in opposite directions.
I was still in the decision process concerning the experimental registration, so I turned my efforts toward remounting the engine and the reduction drive. Using my new found knowledge of fasteners I was able to procure high quality socket screws and grade-8 hardware to replace all the old stuff. As a precaution I took the Hegar reduction drive apart and found that the main bearing was in very good shape. Unfortunately, it had been assembled with an additional, homemade steel plate that didn’t make much sense. It also negated the use of a cotter pin to lock the large 7/8” slotted nut in place, which in turn held the prop shaft to the airplane. This was not a good thing. So I consulted the installation and adjustment instructions which consisted of one and a half photocopied, single sided pages of rather sketchy information provided by the company (who no longer makes them, of course). After some experimental assembly and disassembly it appeared that the plate was a shim intended to align the drive and driven pulleys, but it didn’t.
I decided to install the reduction drive frame on the new engine and see where things ended up and then deal with the shim issues. Unfortunately the instructions were a bit shy on torque values for the socket headed screws that attached the drive frame to the engine. It would take some time to look them up so I took the opportunity to move the wing locking fixture. This was something that appeared to be relatively quick and simple.
As always, however, nothing in this project is ever easy.
Drilling out the 3/16” stainless steel rivet that held the small, U-shaped lock point bracket went rather well. I pushed the blind side head into the foam and then deburred the hole. It was here I noticed that the factory installed position of the bracket was not as shown on the assembly video, nor was it even the same as the bracket for the left wing. Ordinarily I would have been a bit shocked by this, but then I’d already been desensitized by a variety of other issues so it passed with only slight chagrin. There had been a number of subtle design changes in the A-10D as the company passed through the various owners, therefore I decided to follow suite and simply slide the bracket outboard a few inches, assuming they had reason for this other than poor quality control.
I marked the new position and drilled the hole using the proper wire gauge drill size for a 3/16” rivet. I located some appropriately sized stainless pop rivets at a local marine supplier and prepared to make the installation. According to the assembly video this and its mate were the most difficult rivets to pull in the entire airplane. Not only were they large and steel, they were also dead center inside the U-bracket. This meant that the rivet gun head could not rest against the rivet. The factory people in the video recommended a small stand-off spacer be placed over the mandrel shaft against the rivet head. Apparently this was provided with the original kit and, naturally, I’d have to make one. My first attempt using one made from thick walled aluminum tubing was a disaster. When I started to pull the rivet, the steel rivet head deformed and lodged inside the standoff. I couldn’t get the spacer off the rivet and I couldn’t pull the rivet out of the wing because the mandrel had expanded the blind side. It took an unsupported hacksaw blade and a thin steel shield slid beneath the bracket to finally remove it. I also purchased a short length of ½” x ½” square steel stock that would be the basis of the new stand-off spacer. I cut off a 3/8” section and then filed it down until it rested neatly inside the new U-bracket (yes, the old bracket was damaged in the removal). I then drilled a hole in the spacer slightly larger in diameter than the mandrel shaft and went back to the wing. It took some additional filing and shortening, but eventually the new spacer did its job. Fortunately I had the rare foresight to have purchased a heavy duty rivet tool just for this kind of job. After a bit of grunting and swearing the mandrel finally popped off and the rivet was set. I was pleased to see that the wing support swung neatly into position inside the new bracket. A few strokes with a small round file allowed an AN3 bolt to act as a locking pin. It took over a week to do, but one has to take solace where he can find it.
Another good thing happened while this was going on. By accident, I stumbled across a small local machine shop that had remained hidden for the last thirty-four years in the middle of a residential area in Fall River, MA. The owner was a stocky, serious faced little man who eyed my old propeller squash plate with an experienced glance. He pulled a round section of 6061-T6 off the shelf and then turned it over to a teenaged machinist in a dirty baseball cap that covered most of his face. “How long to make two of these?” the boss asked.
The teenager lifted the bill of his cap, frowned at the lack of complexity, pulled his cap back down and mumbled “half hour, tops”.
“Fifteen bucks each,” the boss said. “Have em for ya in a couple days if junior here can handle it.” He grinned at the kid, who was not amused.
At the end of the week a miracle happened. I actually received a call from the shop telling me that the job was done. Not only was it done, it was done well. I forked over thirty in cash and smiled at the kid advising him that I’ll be back, in my best Terminator tones.
“Great,” he said from beneath the cap. “Bring something more interesting next time.”
I smiled evilly, shook hands and then went back to my garage, secure in the notion that I now had a potent weapon in the part replacement battles ahead. I was also fairly sure there would be no alien abductions from this shop.
So much for this installment. Tune in for Episode XI. I can’t wait to see which way this thing goes.
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