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Varieze wing attach plates-structure questions


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To all of you experienced builders and flyers:

I'm an AP/IA with a small shop helping an owner resurrect his Varieze project purchased 2nd hand. This aircraft was begun in 1981, completed by a second builder/owner. It was taxi tested, received its C of A then the engine was stolen before its first flight. Its been sitting stored in Texas heat ever since. Tap testing the wing attach plate areas showed the presence of possible debonding in the areas of the plate to spar cap interface. A letter was received by the new owner from the previous owner/builder stating that he had reservations about the 1/4-28 tapped holes in the lower plates. He felt that the screws supplied by Wicks aircraft may not have been the right ones. The plates were purchased from Ken Brock manufacturing during the build. His suggestion was to access the screw heads, clean them up and attempt to loosen the screws to check for proper thread engagement. (!?). As I look at the plans and builder instructions, it looks like these screws are installed using flox and epoxy in the relief areas of the spars. I cannot imagine these screws moving even if they are not threaded correctly.

The real question I need answered is:

What are these screws intended to do? Is the spar cap layup multi-plys dependent on the epoxy to aluminum bond line for structural strength using the screws for clamping pressure or are these screws intended to provide for shear loads through the spar caps? The plans say that the drilling and tapping operation can be done after the plates are installed and the assembly is cured.


Multiple sign-offs are in the builders log books with signatures and some sort of abbreviations following by a third party as a "pre-closure" inspection. During my early day homebuilding experiences this was done by FAA inspectors (1960's). Who would have done this type of third party inspection in 1981? Designees? DAR's? Tech Counselors? If, in fact, these assemblies were inspected by qualified person(s) and the attach plate/spar cap bond structure was seen to be correct, safe and per-plans; I'd have a warm-fuzzy about this aspect of the aircraft. But as it stands, I'm telling the owner I won't be willing to sign a conditional on this aircraft without a show-stopping surgery to outer wing panels and attach plates.


Tom Holland


(541) 519-6692

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For Marc & others,


Attach plates dump the flight loads through both the (primary) AN525-416R-14 structural screws x 8 per plate set (=125,000 psi tensile per screw = approx 75,000 psi shear per screw x 8 x .125" x .125" x pi = 29,452.5# shear load capacity per screw set ) into the unidir spar caps and bid pad sets; and through the epoxy/aluminum bond (secondary) assuming the plate set was roughed-up per builder's instructions. His experience after viewing and disassembling a couple of VZE's following accidents lead him to believe that final overstress failures do not occur at the attach plate joints and that the closure inspections were done by FAA safety inspectors during the building time frame. He suggested several inspection procedures to assure that the screws were in place and extending into the spar cores as called out in the plans. Assuming no other big problems found, we're good to continue this project.



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