trim spar gap

[delusional]

after countersinking the trim spar pretty precisely and using the same dimpling process as for the skins I seem to have a gap roughly .010 pretty consistently all the way across.

So which is worse, countersinking just a bit more which seems to me might be excessive, though I understand that most of the strength of the spar lies in the web, not the flange, but a knife-edge doesn't sound so good. Or, can I "un-dimple" slightly and live with not very flush heads? Or is it really only of cosmetic interest and I should just build on? Or take up hot air ballooning...

BTW, the EAA counselor came by to look at my project and did _not_ run away screaming. Yipee.

 

[mcencula]

If I understand you correctly, that you've countersunk enough for a rivet to fit flush, and yet the dimples don't sit down fully in the countersink, this is a common issue. On thicker material (.040 or more), I'll over-countersink the lower layer by about 0.007. However, in your case I think what I'd do is try reproducing the problem with a couple pieces of scrap material of the same thickness and squeeze some test rivets. I bet the gap you're seeing will close right up.

Good luck.

 

[mculver]

A close-up photo would be good; however I also countersunk a bit deep on the Horizontal Stab spar for just this reason.

 

[delusional]

... in your case I think what I'd do is try reproducing the problem with a couple pieces of scrap material of the same thickness and squeeze some test rivets. I bet the gap you're seeing will close right up...

I tried it on some scraps of the same size and methods and it closed up real good.

Thanks

 

[dbaflyer]

Probably too late to help you, but maybe for others. When I went to rivet the bottom left elevator skin to the trim tab spar it wasn't fitting very well against the top and bottom skin. Turns out that my stiffeners (4 of them) were a bit too long and they were pushing up and out on my trim spar. Looking back at what went wrong, I did not have the stiffeners on the skin when I matched drilled the skin and trim spar. If I had it would have been very obvious the stiffeners were too long and easily trimmed at that point. Trimming them after they are riveted to the skin was much harder, but using a dremel and being careful it worked out.