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The Dreaded Trim Tab!

330Jock

Well Known Member
You guys have me worried I'm about to ruin my whole airplane! Have read everything about trim tab bending and riblets after screwup. My big question is: how do you dimple for flush rivets unless you do it before you bend? The plans also say: do not final drill trim tab until they are squared with elevator. OK if I do everything perfect and wait until last to drill trim tabs, how do I get flush pull rivets in them?
 
On the RV-3B the tab is only .016, and it would have been easy to open it up far enough to dimple the holes. I say "would have been" because the design is somewhat different.

More than likely, once it's bent, you won't have any trouble with that step.

Dave
 
If it's anything like my 9, you will be drilling and dimpling those holes before the trim tab is closed up for good. You can shape the ends, cleco everything in place and drill, and then disassemble, open the tab up enough to put your dimpler in there, and go to town. You could use a pop-rivet dimpler as well, but I was able to slide the squeezer in no problem. Just finished my 2nd one (first one was ruined trying to rivet the horns on when they weren't totally flush; drilling out the rivets cracked the skin). When you go to attach the horns, remember that dimpling them will cause the flat surface to be distorted. Carefully work it back flat again so that it sit's perfectly flush before riveting. Also bend the tabs before attaching the horns. At least in the -9 instructions, it has you attach horns first, which makes riveting them easier, but bending the tabs almost impossible.

Chris
 
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You guys have me worried I'm about to ruin my whole airplane! Have read everything about trim tab bending and riblets after screwup. My big question is: how do you dimple for flush rivets unless you do it before you bend? The plans also say: do not final drill trim tab until they are squared with elevator. OK if I do everything perfect and wait until last to drill trim tabs, how do I get flush pull rivets in them?

if I remember well, the manual saying "do not final drill trim tab until they are squared with elevator." is referring to the hinge attachment to the elevator. You can better not drill those before the trim tab is aligned and clamped to the elevator. Otherwise, you may end up with edge distance problems on the hinge.

I have bend the tabs as per the plans. Once bend, I used a pop rivet dimplet to make the dimples. It worked quite fine.

Other solutions for close quarter dimpling are to drill a female die (I used my countersink bit) in a small steel bar. You can then lay the narrow end (like end of rudder or elevator ribs) over the drilled countersink and use it as female die. Put you make die on the shaft of the c-frame dimpler and give it a small whack.

good luck
 
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