Ivan's RV-7

Bending the close-out elevator tabsTimer icon2h

July 9, 2022

A very stressful moment: bending the close-out elevator tabs!

Today I bent the elevator close-out tabs. There are a lot of reports of builders who had challenges with this procedure, so I tried to research as much as I can. The common issues seem to be blocks moving and cracks on the skin.

The manual suggests using wood bending blocks. Some builders make a bending brake, but I think it only works for the tab itself or the separate top and bottom skins, like in an RV-14. In an RV-7 I don't see a good way of clamping the brake.

So I went with the idea of bending blocks. As a first step, I re-did my bending blocks to make them wider so they have more friction.

For holding the blocks together, I tried using carpet double-sided tape to hold them in place (as somebody recommended), but I think it was the wrong tape: it only made parts slide easier as the glue of that tape was very gummy. Another idea I tried was to use a single-sided Gorilla Tape, thinking that it will increase friction. It did, but it adds some thickness, too. The most friction I got from a hot glue gun, but it is hard to get the hot glue to spread uniformly (and it adds a lot of thickness, too).

In the end, I decided to not use anything as blocks seem to stay in place with enough clamping force.

I did several test bends and found that if place blocks about 1/32" of an inch inside the bend line (deeper into the part), the bend line would be where I get the flat aluminum face. However, as it turned out later, I should have moved it 1/32" outside of the bend line (which is exactly what the manual says, duh). I don't know exactly why did I get the different results on the test pieces. Maybe, I was not hammering them hard enough with the rivet gun?

The new bending blocks.

This is what the bending process looked like.

The process of bending the tabs.

In the end, I got the line maybe 1/32" or 1/16" deeper than I initially thought. In the image below, the top blue line is where I anticipated the start of the bend (edge of the corner). As you can see, that line is on the corner. The bottom line was the line where I wanted to get the flat face of the aluminum. I did not check that line because it does not matter that much, the critical dimension was to get the bend line away from the relief holes enough that nothing cracks.

The bending lines.

I think it worked out okay in the end. My concern was also the trailing side of the bend: initially, it looked like I would not get enough "meat" there for the bend. However, since I miscalculated the location of the bend line, it turned out to be just fine.

This is what the finished part looks like. I deepened the relief holes just a bit to get them away from the bend.

The finished bend.

If I get perfect bends on the trim tab, I estimate the gap between the elevator and the trim tab to be about 1/8" (assuming the inboard edge and the trailing edges are aligned). This is just a 1/32" larger than the minimum gap of 3/32". Perfect.

Another concern I had is if the bottom tab pushed against the top tab bend and I got a crack there. There was a little scratch in the primer, so I removed the primer in that area and inspected the part as well as I could. I did not find any crack there.

Then I switched to the trim tab skin. I started rounding all the relief holes as best as I could, to minimize the chance of the skin cracking while doing the trim tabs.

Rounding the edges of the trim tab.