trim tab twist

[bullojm1]

I just finished my trim tab and noticed that there was a twist in the tab, so that the root end of the TE of the trim tab is 1/16" higher than the tip end with a ruler along the elevator TE. It looked great until I put the line of rivets in it, but somehow it got twisted.

I know that Van's documentation says to align it "perfectly", and this doesnt sound perfect. Is this anything to be concerned about? I am about to throw this trim tab in the pile with the other skin!

Thanks,
Mike Bullock
http://rvplane.com

 

[DGlaeser]

For a 1/16 offset, I'd try to just twist it the other way to get it straight. It should be flexible enough to 'adjust' back to alignment.

Dennis Glaeser
7A Fuselage

 

[sf3543]

The trim tab is tough to get just right. It really needs to be lined up in the wooden V jigs and drilled while everything is held in place. Redrill the prepunched holes to #40 in assembly to get everything perfect. Rivet what you can in the jig and then take it out for the rest. Rivet a couple of rivets and then back in the jig to check for alignment.
If after all of this it is still off a little bit, you shouldn't be able to twist the trim tab at all, since it will be extremely rigid. However, you can adjust out some of the crookedness at the hinge line. Maybe even up to 1/16". Make some slight bends in the hinge eyelets in order to move the trailing edge up or down. It doesn't take much and you can move the trailing edge to line it up. Pick a happy medium between the eyelets and the line of the trailing edges, or whichever you like. Use a seamer to grab the eyelets and bend them up, or down, SLIGHTLY, bending a little more at the root and tapering to the other end where there wouldn't be any bend at all.
You could use this same method to straighten a slight out of line flap trailing edge and no one would ever notice the hinge being slightly altered.

 

[alpinelakespilot2000]

You can try to get the twist out, or you can just join the 2-trim-tab-club. There's a LOT of us out here. The materials only cost maybe 20-25 bucks. My first one had about 1/8 twist in it. The second has none.

What I think is key is to weight the thing down very well anytime you are doing any drilling and, where possible, when you are riveting. What might help as well is to use 3 or 4 pulled rivets on the bottom spar just to hold things in place while you use your squeeze for the rest. Again, the key for me was to always have it weighted down on a flat surface.

The V-blocks only work if they are all cut EXACTLY the same and perfectly aligned... if they are not you are almost guaranteed to get some twist.

Again, I would bet you that half of all builders have built more than one tab or that a lot of builders out there are flying (probably just fine) with a twisted tab. Maybe both.

Since it's only 1/16", I probably wouldn't worry about it, but good luck.

 

[jonbakerok]

I think I probably hold the record

You can try to get the twist out, or you can just join the 2-trim-tab-club. There's a LOT of us out here. The materials only cost maybe 20-25 bucks. My first one had about 1/8 twist in it. The second has none.

I built four of them before I got it right. Well, actually, #3 came out pretty good. In fact, I was so proud of it, I left it on my workbench to admire while I worked on other things. A couple of days later, I somehow managed to drop a ball-peen hammer on it. #4 was perfect... and I put it in a box and hid it under the bed.

 

[bullojm1]

I built four of them before I got it right. Well, actually, #3 came out pretty good. In fact, I was so proud of it, I left it on my workbench to admire while I worked on other things. A couple of days later, I somehow managed to drop a ball-peen hammer on it. #4 was perfect... and I put it in a box and hid it under the bed.

This one was #3. Here is my history:

#1: All the bends turned out really nice. When I put the spar on, I noticed that the skin bowed inward between the spar and the TE. In my effort to try to bend the bow out, I put a nice crack down the TE. Doh.

#2: I ordered #2 and #3 skins together, knowing how easy these things are to screw up. #2 ended its life shortly after my bending blocks put a nice ding in the top skin. Also, the TE bend wasnt all that nice. I now know to put the top skin facing the bench, so that only the bottom of the skin could get the little ding.

#3 started about 20 mins after #2 was started. Everything went well until I got the twist. I also noticed in this one that there was in inward bow from the get-go. The inward bow only appeared when the top skin was clecoed to the spar. I remember now that I had to pull the skin back about 1/32" to meet the top of the spar, hence giving me a bow.

I think that I am going to order #4 (and maybe #5 - they are only $12.50 each), new spar and new hinge brackets.

- Mike Bullock
http://rvplane.com

 

[rv6builder48138]

Trim Tab Twist

Hey, that could be the latest dance craze at Oshkosh.

Save yourselves the hassle of bending those $*(#*!(*!! end tabs. Make a couple of end ribs (since they're small, could we call them "riblets"?) out of .025 aluminum. Only took me four trim tab skins to figure that out.