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I just got off the phone with an FAA airworthiness inspector, regarding my wing attach fitting wear problem. I have a quandry and would like to ask for help, especially from Forrest or anyone who is an official DER...
The FAA guy reminded me that the approved acceptable repair data (AC 43.13) says that for this problem you simply weld washers on the fittings over the holes, sort of round doublers for the wing fittings. That's just great if you have an airplane in pieces and are doing a restoration. It usually requires disassembly of the wing root fitting from the spar, as well as fabric removal. Not an attractive proposition for an otherwise restored, flying airplane.
We measured the wear on the fittings and it was only about 10 thousandths. An AN-5 bolt is .3125" diameter, and the largest worn dimension of the hole is .322". What we found was the the hole could be reamed out to a .322" uniform hole, and still leave enough metal on the fitting to NOT have an "edge distance" problem. There would still be more than one bolt diameter's worth of metal left between the edge of the hole and the end of the fitting. If we reamed out the holes to .322, and then machined an AN-6 bolt from .375 down to .322", then it would repair the wear perfectly, and leave enough metal on the fitting to be acceptably strong.
The problem is that this would require either a field approval complete with a DER signoff, or a letter from the aircraft manufacturer stating that it is an acceptable repair on a Taylorcraft model B.
However, this method would allow the repair to be made without taking a flying airplane and reducing it to pieces. Very attractive from my perspective!
The FAA was not happy about the idea of filling up the hole with weld, then drilling it back out.
Forrest, is there any existing engineering data or prior approval for this kind of a repair? Would the T-craft factory (under present circumstances) give me a letter saying that my proposal is an acceptable repair? Is there any other method of repairing this problem that does NOT require me to take a flying airplane down into pieces?
All assistance appreciated. Forrest, last few times I tried to e-mail you directly it didn't get through or was lost in your inbox.
Bill Berle
The FAA guy reminded me that the approved acceptable repair data (AC 43.13) says that for this problem you simply weld washers on the fittings over the holes, sort of round doublers for the wing fittings. That's just great if you have an airplane in pieces and are doing a restoration. It usually requires disassembly of the wing root fitting from the spar, as well as fabric removal. Not an attractive proposition for an otherwise restored, flying airplane.
We measured the wear on the fittings and it was only about 10 thousandths. An AN-5 bolt is .3125" diameter, and the largest worn dimension of the hole is .322". What we found was the the hole could be reamed out to a .322" uniform hole, and still leave enough metal on the fitting to NOT have an "edge distance" problem. There would still be more than one bolt diameter's worth of metal left between the edge of the hole and the end of the fitting. If we reamed out the holes to .322, and then machined an AN-6 bolt from .375 down to .322", then it would repair the wear perfectly, and leave enough metal on the fitting to be acceptably strong.
The problem is that this would require either a field approval complete with a DER signoff, or a letter from the aircraft manufacturer stating that it is an acceptable repair on a Taylorcraft model B.
However, this method would allow the repair to be made without taking a flying airplane and reducing it to pieces. Very attractive from my perspective!
The FAA was not happy about the idea of filling up the hole with weld, then drilling it back out.
Forrest, is there any existing engineering data or prior approval for this kind of a repair? Would the T-craft factory (under present circumstances) give me a letter saying that my proposal is an acceptable repair? Is there any other method of repairing this problem that does NOT require me to take a flying airplane down into pieces?
All assistance appreciated. Forrest, last few times I tried to e-mail you directly it didn't get through or was lost in your inbox.
Bill Berle
I am absolutely certain I could replace the fitting without disassembling the butt rib.....if the rib was covered over, you could cut out enough fabric to do the job w/o hurting the rest of the wing. No way in a hot place could you weld it in place, or, now that I think about it, do it if you have a wing tank in place.....good luck......Marcus 
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