Bending Elevator Trim Tab Skin

[Phil]

Hi Everyone,

I have a technique question on bending the elevator trim tab skins. No, not the closeouts but the trailing edge bend. I'll post the close out question in 2 weeks I'm sure.

The plans refer you to section 5 where you build a brake (Two boards and a hinge) to uniformly squeeze the skins down so it will align with a straight edge that is laid from the spar to the trailing edge.

In the perfect world, you'd just put the skins in the brake and squeeze them down. Unfortunately I tried that and found this isn't a perfect world.

Upon squeezing, the ends of the skin would hold their position quite well and even be perfectly straight. However the area in the middle of the skin would spring back and I would obviously get ballooning.

This meant I needed to (only) squeeze the middle section a little more so they would catch up with the ends. I tried to massage the middle section with my fingers, and now I have a non-so-uniform trim tab that resembles a scallop.

Is there a technique that someone has invented to squeeze these skins uniformly? I'm definitely not happy with the results I'm getting.

Phil

[danielhv]

I had no problem after building the brake specified in the plans... is that how you build yours? I made the initial bend with a wooden dowel in the bend of the trailing edge to prevent it from creasing... I found that I had to remove the wooden dowel and squeeze a tiny bit more to get a sufficient bend...

[Phil]

Here is a photo of the skin inside the brake.





Below is the ugly photo, though it's really not as bad as it appears. For this photo, I managed to get the light perfect to show you what I'm talking about.

I couldn't continue bending the skin in the brake because I would have had to over-bend the outer ends of the trim tab just to get the middle section to align with a straight edge. (Remember the middle was springing back and the outside edges weren't.) That's the point when I tried massaging it, but the result looks like *(@#.

[jimbo]

Phil,

I had the same problem. Make sure the boards in the break are perfectly even and parallel. Also increase the spacing between the boards at the hinge to at least equal the bend diameter at the trailing edge (or move the skin back in the break). You might try putting newspaper in the middle of the break to build up a spacing to apply more pressure in the middle of the skin. Obviously you will want to build up the thickness of the spacer (newspaper) gradually so it wouldn't create a crease in the skin.

My 2nd attempt turned out just OK and I accepted it. It is a frustrating piece to work on.

Jim
RV9A

[Rick S.]

Seems Van's is making Christmas party money out of selling new trim tab parts, I'm no exception...it took two tries on each side to be acceptable but not for the bend on the trailing edge, nailed that all four times...I had some really straight 2 x 6's struct select lumber and I used a piano hinge to hold them together. As you mentioned in forthcoming tasks, bending the ends is the trick...search the forums for a guide to that, if I did it over again I would make the mini rib to fit inside the tab instead of bending that !@##$%%^ tab over to close it out.

[Greg Arehart]

When I bent my tab for the 9, I used 2x6 lumber (I noticed the photo was 1x6) and put the tab to be bent between the two EDGES of the 2x6, not between the wider sides as shown in the photo in the previous post (you have to modify the position of the hinges as well - I actually just used three old door hinges I had lying around rather than a piano hinge). I also made sure that the edges of the lumber were nice and straight. By using the edges, I had a lot more leverage. One can more easily get that last bit of bend as compared to using the flat sides of the 2x6.

greg

[ao.frog]

Hi.

We taped a round rod with the desired diameter in the bend before bending it. (both elevators and trimtab)
That way the boards couldn't make the bend too sharp.
For boards, we used the wooden sides from a waterbed. They where thick, straight and made a fine bend.

You've to make sure to skins doesn't push the rod out of position (aftwards) when they are pressed together.

I picked up this technique here on the forum. (don't remember where though...)

Worked fine.


Good luck

[Bob Ellis]

Phil

I couldn't see a dowel rod/fibre glass rod inside the trailing edge. I believe this is to a) stop over bending and b) get the correct inside radius. See the method I used at this link that worked out fine for me.

Good luck

Bob Ellis
Fuselage kit arrives in 30 minutes!
www.rv-8.co.uk