Thorp Air Command - T18.net

I have just found out that one of the outboard wing attach bolts on my project was oversize. The main spar lower attach bolt for the Left outboard wing is drilled out to 7/16 instead of 3/8 per the plans. All of the other wing attach bolts on the main spar are per plans at 3/8. I am seraching for more info on others who have encountered this problem in other projects or have flying examples with oversize bollts. SO far opinions have ranged from go fly it, to it is not per plans so fix it, to a formula from BH that included using the face area, minus the edge diameter, divided by the coriolis effect divided by the expansion contraction coeficient of my anal sphincter.....he lost me on that one. Will fix it if best but not excited about dissassembly and reassembly on this since things are so straight and well aligned as is.......HELP

Scott
812-881-7923c

Scott, I think a conversation with Richard Eckland would be the answer and not rely on us

Already called him...he replied...."if it is not per the plans, you become the engineer" was hoping for more of an analytical answer than that......but..... My training does not afford me knowlegde or experience to address this problem.

Check PM

Well, Scott.... I will give my two cents here at the risk being admonished by those with advanced degrees of which I have none. Last year I was 3 for 4 winning "discussions" with degreed professional structural engineers, but that was with regard to large concrete structures, not aircraft. So far this year I am 1 for 1.....I'm on a roll........or due for a smack down...one or 'tuther.

Here is what I would do upon initial consideration - Insert the oversized bolt and install nut - torque it correctly and fly the airplane. I know there is less "area" of the fitting (larger hole), but I do NOT think there is a degredation of either bending moments (of that attach fitting), shear capabilities, or (longitudinal) tension/compression loads given proper washers and torque. Regardless, it would take using finite element analysis(to minimize error and increase predictability) to determine that, as any "ultimate load" to failure (compared to John Thorp's calc'd or demonstrated values) would be too close to call IMHO, given the variables in building.....Friction plays a roll in that fitting as well.....YMMV and all other disclaimers apply here, but that's my story and I'm sticking too it.....until proven otherwise by those smarter than I, of which there are many.

If I were to apply a fix to it, an epoxied doubler (with or without rivets) would be what I would do - thickness unknown, but that's where I imagine Bob's calc comes into play. The reason for the epoxy is to give 100% contact and therefore load transfer/distribution back to where the loads have been pre-calc'd. Edit - use as little epoxy as possible (it is a polymer/plastic after all) but get 100% contact - use the clamp and squeeeeeeze method.

Structural guys must have a way of calc'ing this out, and it might not be too complex either - beyond me though. I commend you for being up front about it - I think a lot of builders might have been laise faire with a case of the effits and said/noted nothing. But I seriously think you are fine to fly - keep the G meter less than 6.....I keep mine below 3.5.

_________________
Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)