Repair of Aluminum Spars
I'm looking into buying an HP-13, which is an all-metal, 70s era, home-built glider. This glider hasn't flown in many years and has a few problems that need to be addressed. My main concern is corrosion. The plans called for aluminum wingtip plates, but the original builder installed steel plates instead. Of course, the dissimilar metals caused corrosion which is visible on the wing skin. I have no way of telling if there is corrosion on the tip of the spar until I remove the skin and take the steel plate off.
My question is, if there is substantial corrosion to the tip of the spars, can it be cut off and new aluminum welded on and shaped?
If I recall aircraft structures in A&P school, welding is not permitted on aluminum primary structure (spars). If the glider was designed with and included an SRM (Structural Repair Manual), follow instructions therein. Otherwise follow direction found in AC 43-13-2B in repairs of aluminum structures. I believe there are a number of repairs involving riveted splices, doublers, etc., that are allowable under these circumstances. Whatever you do, make sure you are in consultation with an A&P with Inspection Authorization, because it sounds like what you are faced with is a major repair, which must be signed off by an IA on a FAA Form 337.
Probably not. Welding aluminum isn't a great idea in this situation. But you could probably splice the spars if the corrosion is a real issue. Being a homebuilt, you do not need an IA to approve or submit a 337, but for your safety you do should make repairs in accordance with accepted practice. If that means getting an IA or A&P to help you determine how to make an appropriate repair, that is certainly a good idea. One thing to consider is that someone will need to do condition inspections on the glider on an annual basis. That person can be an A&P or an IA. If that person is uncomfortable with your repair work, s/he won't sign off on your condition inspection.
Originally Posted by JeffCasto
If there is corrosion, if it is limited to the outboard skins or outboard spar tips, it should be relatively easy to repair, IMO. There are a number of RV builders in your area. You might find some help there.
you might get ahold of Bob Kuykendall at www.hpaircraft.com he might be able to provide some guidance.
congrats on the HP!
Thanks for the help, guys.
Tony, thanks for suggesting Bob as a resource. I'm sure he could give me excellent advice on anything HP related. I haven't bought it yet. It will depend on whether I can get it at a bargain price. It needs a fair amount of work, and I'm worried about corrosion in places that I can't see.
Someday, I would like to build a plane. This might be a good project to learn on.
Again, thanks for the cogent replies.
A spar repair is always a major repair, and it needs more than an IA and a Form 337: it needs APPROVED DATA. If there's no structural repair manual, it probably needs a field approval from the FSDO.
Originally Posted by firstname.lastname@example.org
Mike - I would agree with you if this was a certified glider - but this is a homebuilt, thus needs none of that. He just needs a suitable repair.
I would also add that the 43.13 can be used as approved data (as talked about on the first page) as long as it is not conflicting with any OEM data. However, before doing this on a spar repair I would get an email from either the ACO or FSDO concuring that the repair via the 43.13 was appropriate.
Originally Posted by Mike Busch
Scott, I must have missed the part about this glider not being certified. Obviously if it's an experimental, none of Part 43 applies, including the Appendix A stuff about major repairs, and the Appendix B stuff about Form 337s. My bad.
Indeed, AC43.13-1B can now be used as approved data for small unpressurized airplanes provided it doesn't conflict with manufacturer's data. It didn't used to be that way, but Bill O'Brien was instrumental in making this change before he retired from the FAA and shortly thereafter passed away. Bill was a wonderful friend to aviation maintenance, and is sorely missed.
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