Gilding the Lily - Milled Inspection Covers

[SpruceForest]

So after a quick hop in the AirCam to do a little fam this past Sunday AM, we headed back to Carlo's hanger to start duplicating the Bearhawk factory's leading edge skin bending jig... that is a post for another day, given he is still prototyping and proofing the tool (wet wing has .032" leading edge across the entire fuel bay area, so not the easy bend of a stock Patrol).

Found these access covers on the bench while waiting for Carlo to finish rough-trimming some tubing. Not saying I'll be doing the same, but interesting idea to eliminate the knuckle-catchers when working inside an inspection hole. The bare aluminum panel is for the wet fuel tanks - there are three or four of them on the lower 0.040" skin for each wing... primed on the exterior, of course. The other panel is .040" milled to 0.020 less primer thickness for the aileron access. Putting the doubler/edge and nut plates on the cover reduces the size of the required opening, so allows for a little more freedom in siting the port for best access. As the plates are on the underside, the usual 'start a screw or two' for alignment works pretty well. Carlo's been a working A&P and IA since the early 1980's, so is familiar with the joys of working in tight spaces created by marginally-sized access openings and the pure pleasure of running a knuckle through a nut plate.

Fairly certain the machinist that did the work produced the matching cover routing guide and templates. Not the only areas where CNC is being used to produce stuff like this - will try to capture more of the stuff he's done..

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[fairchild1934]

another way to do the same end result might be to make the covers in two pieces. Outer piece flat .032. Inner piece .032 3003 what has been hydroformed against a form and a rubber pad. The inner piece gets riveted to the outer piece and acts as a stiffener. Could use some 2 part windshield sealant between them to exclude water. (and hence corrosion)
Tim

[SpruceForest]

Carlo actually looked at having me 3D-print hydro-forming patterns for that very job, but the machined versions allowed a marginally stiffer access panel, a smaller gap between wing skin and access cover, and slightly nicer cosmetics. Given he's built two award winners in two tries, I think the machined panels and improved cosmetics got the nod. Mine will likely be pressed out and not quite as pretty, but having worked inside a wing or two, anything which can be done to improve access and eliminate the Cusinart Effect on hands and forearms seems worthwhile.