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Concerning shimming the main gear attachment to the aft spar --



I had a perfect fit on one side, but a 0.050" gap on the other, which needed

six bid to shim.  That worked out well.  I don't think I would shim a quarter

inch gap with BID, however.  I'd use a piece of 6061 aluminum.  Alodine or

anodize it, first.



It really shouldn't matter what type of aluminum you use.  The loads are small

compared to the compressive stress of aluminum.  The shim wouldn't really be

loaded up in shear or bearing.  2024 is susceptible to stress corrosion

cracking (unlike 6061) but that's not an issue here.  Of course, it you have a

chunk of 2024 lying around, it'll do fine.



I don't think I'd use bare phenolic here due to concerns about long-term

degradation.  Of course, if you beveled the edges and put 2 BID over it for

water protection, you'd probably get good results and be substantially lighter

than the aluminum.  



- Rob Wolf