Elevator Trim Tab Trailing Edge

[cderk]

I've searched the archives and I've seen a number of posts regarding final bending of the elevator trim tab trailing edges. In my case, I'm working on an RV-10.

Here are some of my observations as well as a few photos.

1. Van's has you build a homemade brake for bending - its detailed in Section 5 of the plans. Basically (2) 2x8s with hinges. I bought pine boards - and maybe that was my first mistake. Maybe I needed the thickness of a 2-by versus a 1-by piece of wood to get decent hinges.

2. Unless you purchase expensive hinges, you cannot really get both boards sandwiched together without a small gap (~1/8") where the hinge pin is.

3. First pass, putting the trim tab between the boards and pushing down pretty darn hard - I wound up with the following results.





In these two, it appears that I still need to get the "crease" tighter. Problem is that I'm clamping down all the way on the brake.

Attempt two, I spun the trim tab around, so the "crease" is not up against the hinges, but at the outside of the brake - I figured the farther away from the hinges, the closer the 1x8s would be. I then put the brake on the ground, and basically walked on top of the trim tab, sandwiched between the two pieces of wood - all 165lbs of me.

I got the following results - much better, however in a few spots, its slightly concave... perhaps 1/32" or 1/16".





Is this something that I should try making better? My wife has accused me of being anal retentive (about everything, not this) and Van's tech support has accused me of being anal retentive...

Thanks
Charlie

[clutch22]

I see you are using large, short hinges. I would suggest running down to the local hardware store and getting some piano hinge. Lay the boards flat on top of each other, then screw the hinge into the boards. There will be no gap. I have no gap on mine. Having the piano hinge run the entire length of the brake could also help with a more consistent trailing edge if your boards are pine and more flexible than other types of wood.

[1001001]

In the RV-10 builder's manual there is a suggestion for this that I used. They have you take two 1x2 hardwood boards and radius the edges on one side. Then you use slip joint pliers to squeeze the blocks against the trailing edge, working along the edge and checking as you go. This worked pretty well for me. Mine aren't perfect but I got pretty close with this method. I had to do this as the long brake wasn't an option -- the previous builder of my kit had already bent the ends of the trim tab skins and those prevented the brake from closing enough to fully bend the trailing edge.

I would also go with heavier boards and make sure there is no gap between them. The brake I have (made by the previous builder) is really solid--made with two pieces of MDF board on each side, laminated together with screws and maybe glue. The MDF gives a very flat and smooth surface to the brake.

[cderk]

Good suggestions - I'll start with the piano hinges. That sounds pretty simple to change.

I did see the small pliers version, the only thing that scares me about that is how easy it would be to get ripples across the length.

[1001001]

Originally Posted by cderk

Good suggestions - I'll start with the piano hinges. That sounds pretty simple to change.

I did see the small pliers version, the only thing that scares me about that is how easy it would be to get ripples across the length.

I did get a couple of minor ripples but once you get a feel for how much you need to squeeze they are very minimal. I used slightly longer pieces of wood than recommended and I think that helped. I did not bother wiring them together.

[rvbuilder2002]

Originally Posted by 1001001

In the RV-10 builder's manual there is a suggestion for this that I used.

What Dave might be talking about is a portion of Section 5

Take a look at paragraph 5.7.

Answer to your basic question.... Yes, shape of trailing edges is important. It is not bad to be a bit anal about this process.

[1001001]

Originally Posted by rvbuilder2002

What Dave might be talking about is a portion of Section 5

Take a look at paragraph 5.7.

Answer to your basic question.... Yes, shape of trailing edges is important. It is not bad to be a bit anal about this process.

Yep, that's what i was referring to.

Question: my trailing edges pass the straight edge test but have some rather minor concavities here and there. They're generally about 1/64" to 1/32". Is this acceptable?

[longranger]

On your brake, instead of hinging them face to face, hinge them edge to edge. You get a lot more leverage that way, so be careful not to over bend.

Also, if you have access to the tools, plane or joint the edges for a nice straight fit.

[rvbuilder2002]

I try and get it as close as I can.
The light tapping with a block and small hammer process described for reducing the bend works well.
I have even done it on finished painted surfaces with a layer of felt glued to the block.

[cderk]

The piano hinge worked like a charm. First try, and the bend was almost perfect, maybe a little on the heavy side, but I think I'm in good shape.

As always - thanks for the tips.

for what its worth... bending the edges of the trim tabs really sucked. Should have gone the riblet route - would have probably looked a lot nicer.