I made the flap hinge covers out of .025 2024-T3. Others have made them out of stainless, but I don't like cuts that much. The aft portions of each plate were secured to the flap with one-lug 6-32 nutplates; I made small aluminum spacers of .025 aluminum so that the nutplates wouldn't be canted by the offset from the rib. The bottom covers have a 45 deg bend and are relatively simple to make; the upper covers have a curve and I used my Harbor Freight 40 inch three-in-one roller to accomplish same. Each cover is different from the others and have to be individually trimmed to match the hinge bearings and pushrods. I used keyed rivnuts for the front screws, and applied Loctite to avoid "spinning rivnuts" which can occasionally happen. I still need to radius the corners of the covers, Scotch-Brite and otherwise smooth, degrease, Alodine and prime them.
