Improving elevator skin bent tabs?

[tegwilym]

I got through the dreaded tab bending on our RV7 elevator skin and trim tab. It wasn't as hard as I feared from reading all the posts of fear and disastrous bends.

My tabs all turned out nice, but of course the top of the elevator skin half of the trim tab bend, came out a little odd. It's not horrible or anything, but I'd like to see if I can flatten it out just a little more before riveting the skin on the spar/ribs.

Does anyone have a good idea how to do this? I was thinking maybe put the skin on a back rivet plate or chunk of wood and tap it from the inside (it would be a tight fit, so not sure how yet) with the riveter on about 20 psi and going through a block of wood to keep the dings minimal.

Here are photos of how it looks. It all meets nicely along the sides, but I have a bit of a concave area above the crease as you can see. Again, totally flyable, but just wondering if you builders have a clever way of flatting this out? I'm just afraid of messing with it too much and causing a big disaster if it's not needed.

Thanks for ideas!
Tom

Not too bad looking, but could it be flattened?


A slight ridge along the fold.


I think the wood that was clamped on top of it may have held ti too tight while hitting with the mushroom riveter? I did put a block of wood against it and reveted through the wood for extra protection.

[Smilin' Jack]

It appears that your bend in the back of the elevator is not enough.(trailing edge)
What I did was to use the 2X6 brake I made for bending the rear of the elevator put in a 1/8 th inch dowel and bent the aluminum with the dowel taped inside the bend. I am afraid if you use a wood block you could crush the trailing edge with out some kind of support inside. If your bend is tighter then try a smaller dowel.

Your folds on the end look good
It is important to keep the trailing edge bends alike on both surfaces.
Jack

[wirejock]

I wouldn't mess with it because things always seem to get worse when I try to make them better. It looks to me like the interior block either was not a perfect match to the chord of the trailing edge, was not all the way against the trailing edge or slid forward during the bending process. I agree with Jack's comment on keeping the trailing edges of both elevators as close to the same as possible.
You could make a wedge exactly the shape you want for the trailing edge and secure it inside then gently massage the bend back to flat but there it may make a weak spot or worse, a crack.
I used the Vans method and was reasonably pleased with the result. The trim tabs are similar so be ready for them. I found the blocks need support on both sides to prevent them from sliding. Even with two sided tape everywhere, they still try to move. Here's a pic of the trim tab. Sorry for the size and it's turned sideways. Kinda hard to work with on a phone.

[tegwilym]

Originally Posted by Smilin' Jack

It appears that your bend in the back of the elevator is not enough.(trailing edge)
What I did was to use the 2X6 brake I made for bending the rear of the elevator put in a 1/8 th inch dowel and bent the aluminum with the dowel taped inside the bend. I am afraid if you use a wood block you could crush the trailing edge with out some kind of support inside. If your bend is tighter then try a smaller dowel.

Your folds on the end look good
It is important to keep the trailing edge bends alike on both surfaces.
Jack

Jack,
Looking at the photo again I do see that it looks like the trailing edge is a bit thick, but it's not. Kind of an illusion in the photo that it shows like that. I did use the 1/8 inch dowel on that when I bent it and then used the seamer to make fine adjustments.

Anyway, that's a different discussion!

Tom

[tegwilym]

Originally Posted by wirejock

I wouldn't mess with it because things always seem to get worse when I try to make them better.

Hi Larry!
Yeah, I'm kind of thinking the same way. Leave it as it is or risk messing it up worse. I did use wedges of wood cut at the same angle, then some double sided tape. I'm wondering if the tape was a little too think (and soft) and allowed it to compress a bit. I did have a lot of trouble pulling it out when I was done, and on the next fold I used smaller squares of tape rather than the full length. I was kind of thinking of putting the wedge block back in there, turning it upside down so the indented part was flat on the bench, putting a wider chunk of wood on the other side and then using the riveter to pound it down to the bench from the opposite side? If that makes sense using words rather than a drawing of my idea!
If all else fails I could cut them off and use the riblet method, but I think this isn't too bad overall. I have looked at photos of other's work, and saw another builder's fold in person a few days ago and despite the uneven skin, mine looks much straighter!
This is my second elevator skin, I replaced the first from a totally unlrelated thing, so I did have a spare to practice on. Of course the practice piece turned out much better! Grrr!
The trim tab itself is bend and done, I'm extremely happy with how that part worked out at least. :-)

Tom

[wirejock]

Tom
It looks to me like the wedge slid slightly away from the trailing edge and allowed the part to compress a little. Certainly not worth a do over but could be fixed if you really wanted.
The elevator skin is probably thin enough to massage out the bend.
I would make a wedge, insert it into to trailing edge and brace it so it won't slide. You want it tight against the trailing edge. Then put a piece of book tape on the outside and use the mushroom set in your hand to gently rub it back in the form you want. That way you can feel it and watch the part. Good luck.

[tegwilym]

Did it! I put the wedge block back inside then turned it upside down so the dented part was flat on the bench and pounded from the back. That didn't do a whole lot, so with the wedge in still, I very carefully blasted the ridge with a piece of wood between the metal and the rivet gun. I was able to even it out pretty nicely. This photo doesn't show it too well, but compare with the other photo it looks a lot better!

Thanks again guys for reading my venting. Sometimes it's just good moral support to post photos and publicly complain about my work for encouragement.

Onward to riveting the skin on the spar/ribs now.

Tom

[wirejock]

Looks great.
Before you rivet the skin, check the fit of the trim tab. Cleco it in place and check the gap. You can still adjust things now. It looks like you're in good shape though (pun intended)!

[tegwilym]

I didn't cleko it in place, but did visually line up the holes. Looks good from here. I got the skin riveted on and starting the trim tab now.
I'm starting to see the end of this empennage project.

Tom