Trim tab warp...

It appears that reports of my being complete with the empennage were premature....

Riveted the trailing edge of my left elevator straight and with no problems last night. Went to put on the trim tab and found that the tab was warped by about 5/16" on the trailing edge (see picture). I confirmed that it is the tab, not the elevator that is warped. The funny thing is, I had no idea the warp was there at all until I fitted it to the elevator, so I don't know where in the process I went wrong.

Obviously, I'm going to have to rebuild the tab, but what concerns me is how this happened in the first place. I don't want to merely repeat this warp the second time around (replacement parts are going to cost $40 + another $25 in shipping I'd guess).

Has anyone else had this problem or have any suggestions? Photo hopefully attached below.

http://www.cwu.edu/~moorest/Brazil_Web_Photos/Photos.htm

Thanks,

Steve

Hi Steve,

Welcome to the Multiple Trim Tab Club. I would guess that at least half of us have built two trim tabs (or more). The trick is to keep everything flat on a table whenever possible, especially during the riveting together step. Use lots of clamps or something to hold it still. My first trim tab was virtually identical to yours. My second one was fine as I was cognizant of the fact it is easy to twist the tab in the final riveting stages.

Cheers

Thanks, Mark, for the encouragement.

Just thinking aloud... I riveted the trim tab rivets (both top and bottom) in the V-blocks, so it was standing vertical, figuring that would keep it straight/. Now, I've been thinking that maybe having in laying flat and even weighted down would work better, although I can only do that with the top skin-spar-hinge rivets. The lower skin rivets would require the tab to be in the vertical position to get access to the back of the spar.

Anyway, thanks again.

Steve

Hey Steve

You can do the bottom rivets with the tab flat as long as your squeezer (pneumatic or hand) has the reach, specifically the vertical reach. This is what I did. I placed the tab flat on the table, and let it overhang the edge just enough to get the bottom flush set on the rivet head, and then jsut squeezed it.

Later

Mark, follow up...

Thanks Mark.

So did you just clamp the bottom skin to the workbench and allow the top skin to float while you riveted the bottom skin-spar rivets?

It seems like this (using clamps on the bottom skin) would have to be the case because riveting the bottom in whis fashion would preclude weightinng the trib tab down. And, yes, I do have a longeron yoke to squeeze those bottom rivets.

Thanks again.

Steve

Exactly. The top part of the trim tab was just standing free. I used deep jawed Vise Clamps (you know, the squeezable clamps from Vise Grip) to clamp the tab to the table top and then squeezed the bottom rivets. You might need some spacers in there for the clamps to hold without hitting the spar; I don't remeber. Then I used the same clamps to hold everything down while I squeezed the top rivets. Finally, I did the end rivets.

Pretty straight forward. Of course, I didn't think of doing it this way until my SECOND tab ;-)

Cheers