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Finished the trim tab

I had another big day in the shed today. I started by back riveting the electric trim assembly together.

I then installed the servo motor and mounted it inside the elevator. It fit nicely and the servo arm is centred in the notch.

The plans then called for the rear spar to be riveted to the root rib. I couldn’t get any of my bucking bars into the correct position so I decided to modify one to fit. First, I measured the angle between the root rib and the rest spar.

Then I marked this angle on the back edge of my small bucking bar using my Sharpie.

Holding the bucking bar in my vice, I used my angle grinder to remove most of the back edge to get close to the marked line. I finished off using a file then some sand paper to make a nice, smooth face.

I could then use my modified bucking bar to easily set the rivets between the rear spar and the root rib.

I put the elevator to the side at this stage and went back to work on the trim tab. I replaced the horns with the ones supplied in the electric trim kit and match drilled them.

I then marked the required measurements on the trim tab hinge and match drilled the outboard hole.

I then match drilled the remaining holes onto the hinge. I then marked the small areas where the trim tab horns were proud of the edge, then used my Scotchbrite wheel to remove the overhanging areas.

I also marked where the hinge was proud of the skin and removed these areas also. Next I broke all the edges, deburred all the holes, dimpled where necessary, then handed them to Bill who shot all the inside and mating surfaces with self-etching primer.

Once the parts where dry, I back riveted the bottom spar flange and horns.

Next was mounting the trim tab to the elevator. Once again Bill was of great assistance here. I’d hate to try and do this solo and would recommend a second set of hands to do this bit. We started by roughly positioning the trim tab and used a cleco clamp on the inboard edge to hold the tab to the elevator. To ensure the min 3/32″ clearance to the outboard edge, we drilled a #40 drill bit through some scrap wood and placed it in the outboard gap.

We used a long metal rule to shuffle the trim tab so that it was aligned to the trailing edge of the elevator. Once I was happy with the position, I carefully match drilled the hinge. I managed to convince Bill to take a photo of my drilling, so you get to see more than just my feet for a change šŸ™‚

I then marked the inboard edge of the hinge where it was proud of the skin and used my Scotchbrite wheel to round all the corners and remove the proud areas. I then mounted the trim tab back onto the elevator and checked the trailing edge of the trim tab to ensure it was aligned with the trailing edge of the elevator. There was a slight twist on the inboard corner which I was able to remove by carefully twisting the trim tab with my hands. Once I was happy that both trailing edges were aligned and straight, I match drilled the trim tab inboard tabs. I then put cloches into the tabs and removed the trim tab form the elevator. Using my squeezer, I then set rivets in the upper flange of the trim tab, then set the blind rivets in the inboard tabs.

I then drilled two holes in the outboard tabs and set blind rivets in the holes. Here is a shot of the completed trim tab.

Before mounting the trim tab, I used a length of wood and slightly bent the leading, lower edge of the trim tab skin. I cut a notch in the wood so that it wouldn’t clash with the horns. This bend is required so that the trim tab won’t clash with the elevator when the trim tab moves downwards.

I also set the blind rivets on the outboard end of the rear spar, and for my mini-rib. Here is a shot of what they look like.

I finished off by mounting the trim tab onto the elevator. All good! Here is a photo. The trim tab is not in the neutral position which is why is looks like the trailing edge doesn’t align. trust me, it does. Honest!

Build time 7 hours (2 hrs elevator, 5 hrs trim tab).


About gstrack

Husband and father of 2. Control & Instrumentation Engineer. Flying nut. Gadget geek.


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