Drilling, prepping, and riveting

Both ends of the trim tab itself have little tabs that must be bent over a bending block, similar to one end of the left elevator.

The trim tab horn is made for both the manual and electric trim systems, so it has to be modified for the particular system on your plane. Here I am drilling the horn to the trim tab.

Next the hinge gets drilled to the trim tab. I drilled a few holes at a time, cleaned the burrs out from between the parts, and then drilled a few more holes. I did the first few holes with the hinge halves separated. After I had enough holes to hold the thing together with clecos, I reassembled the hinge and held it at a 90 degree angle while drilling. I was told this would prevent it from binding once the job was complete.

And then, oops. As I was cleaning up the parts, I noticed a big dent that I put in the skin during the tab-bending process. I thought about ignoring it, but since a new trim tab skin is only $12, I ordered one. I wasn't very happy with the way my tab-bending came out anyway, so I welcome the opportunity (not) to try that again.

Here we are bending the tabs on the new skin; it's already drilled, prepped, and primed. The bend line for the inboard tabs is not parallel with the chord line. This requires the use of a spacer in order to prevent the corner of the bending block from making the dent shown above. The cardboard spacer is visible in the picture on the right.

Here's the trim tab after aligning the trailing edges and drilling the holes in the forward (elevator) side of the hinge. The trailing edge lines up perfectly.

Here I am squeezing the upper skin/spar/hinge rivets. Some of these are very hard to reach (the hinge gets in the way), and I had to grind down the top of my yoke in order for it to fit in the outboard end. I still managed to screw up a couple of them and then do further damage by drilling them out. I guess that's what the oops rivet is for.

Believe it or not, the bottom skin-to-spar rivets (done in a previous step) are actually the easiest ones, although they look darn near impossible because the shop heads are inside the skin behind the spar. Just have a helper hold the upper skin out of the way and back-rivet these.

And here's the finished trim tab. All that's left is to rivet the hinge to the elevator. The drawing called for CS4-4 blind rivets in the folded end tabs, but this didn't make any sense because the CS4-4s are flush rivets and the holes aren't dimpled. I used the same MSP-42s that were called for in the folded end tabs of the elevator.