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Bent top wing skin

Draker

Well Known Member
Merry Christmas everyone!

Some days it seems like it's disaster after disaster on the RV-7 project. Today's one of those discouraging days. After a mishap with the deburring wheel, I'm left with a pretty badly bent wing skin:

IMG_0312-L.jpg


IMG_0313-L.jpg


This is the trailing edge of my top right inboard W-702 skin, after a great deal of re-straightening on my part. Maximum deflection in the center of the bend is approx. 1/4 inch. Looking ahead in the plans, it looks like this section overlaps the flap, and there are no rivets going in here that could "aid" in its straightening. The fit against the flap looks pretty tight, so this would probably end up rubbing against that control surface. I'm afraid it looks like I'll need to be ordering a new skin, but before I do, I thought I'd ask if anyone has any good repair ideas.

Best wishes, VAF!
 
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Nothing to Loose

Since there is no choice except straightening or buying a new skin, I would go at it like there was nothing to loose.

I would put a piece of plywood under the area with a layer or two of soft cloth like a towel in between. Using a small round head bump hammer (body work hammer from HF would be about right) and gently tap back onto shape. The ply and cloth will have enough give when tapping to pull the surface in. Use a straight edge to repeatedly gage when the surface is flat. If it still has a little bit of roughness when finished, a little filler before paint will clean it up.
 
Wait till others chime in

This kind of repair has been discussed before. I found some of the methods pretty neat and effective. I would wait till other experts chime in, and practice on scrap, before doing it for points. I was surprise some of the stuff that was repaired nearly perfectly.
 
Skin damage

It's a top skin so what ever you do, it's going to show unless it's perfect. Ultimately it's what you can live with.
For the future, consider using a Vixen file to clean up long straight edges like skins. Much faster and safer. Two or three passes takes out the shear marks.
 
It's a top skin so what ever you do, it's going to show unless it's perfect. Ultimately it's what you can live with.
For the future, consider using a Vixen file to clean up long straight edges like skins. Much faster and safer. Two or three passes takes out the shear marks.

My trick here (stolen from Vlad) is to use a drywall sanding sponge, followed by a pass with 400 grit sandpaper. Edges end up really nice!
 
If I am looking at it correctly, the bent end is what goes over the flaps. Since there is no support for the edge like up against the fuel tanks, it will be difficult to repair. You might as well give it a try. Once you get it bent back up and flattened out, you may have to find someone with an air powered stretcher-shrinker to get it straight. They can work wonders.

Best of luck on your repair.
 
Wow, thanks to everyone so far with such good ideas. Definitely learned something the hard way yesterday: No more deburring large skins with the wheel. I'm also going to write the dollar amount on each part with a sharpie as I inventory from now on :D

I'm going to have a go at repairing it since there's nothing to lose, but will probably just end up re-ordering. Got another PM suggesting I try a sheet metal shrinker, so I'll be looking around locally for one to borrow (HF has them for more than the cost of a replacement skin). I think I've exhausted all other avenues that involve bending, banging, or squeezing--the metal is warped to the point where when I push on one side, it "pops" out the other. Don't think any amount of hammering is going to help it.

I'm planning to paint the airplane so I'm not concerned about cosmetic scratches, #1 concern is interference with flap.
 
Wow, thanks to everyone so far with such good ideas. Definitely learned something the hard way yesterday: No more deburring large skins with the wheel. I'm also going to write the dollar amount on each part with a sharpie as I inventory from now on :D

I'm going to have a go at repairing it since there's nothing to lose, but will probably just end up re-ordering. Got another PM suggesting I try a sheet metal shrinker, so I'll be looking around locally for one to borrow (HF has them for more than the cost of a replacement skin). I think I've exhausted all other avenues that involve bending, banging, or squeezing--the metal is warped to the point where when I push on one side, it "pops" out the other. Don't think any amount of hammering is going to help it.

I'm planning to paint the airplane so I'm not concerned about cosmetic scratches, #1 concern is interference with flap.

Try asking around to see where your local shops/pilots would take planes for extensive sheet metal repair.

If one shop stands out, call them. It's probably a good bet that there is a single employee that is the "expert" at straightening out aluminum parts.

If you can find this guy in N. CA take the skin directly to him. It is a long shot but worth a few phone calls. :)

There aren't many folks around who can do metal forming/repairs to high standards any more, but if you can find one and watch him work it's an amazing sight.
 
skin repair

years ago I see a sheet metal man use a table spoon ( round side down)on top and piece of plywood covered with with 3 shop rags on bottom . re flatten a spot like yours. try on some scrap first . did need sanding to finish. good luck
 
I?d go to a high end car dealer and ask them who they use to repair door dings, etc. Some of those guys are magicians and can make damage disappear that you might think would be impossible to repair except at a body shop. Worth a try before you pay for the part plus shipping.
 
The metal has been stretched. It needs to be shrunk and there is no reliable way to shrink an edge of thin 2024t3 that I know of. The lancaster shrinkers leave marks that will likely result in cracking. If it was in O condition you could shrink it but t3 is way more difficult.

I assume that is a prepunched skin. Go ahead and order a new one and chaulk it up to experience and be more careful (paranoid) with the new one. I would not use a power tool on the edge of a skin.

Just be glad that you don't have to try and redrill every hole in the right place like on an old -4 or -6 skin.

I have scrapped my share of skins. I know the feeling. The wasted hours hurt more than anything. But the skins aren't cheap either.
 
Another option is to find a local source for the right type of sheet aluminum, buy a sheet and cut and match drill it from the original. May be cheaper than the part plus shipping, or paying somebody to try to fix it.

Chris
 
Use a piece of wood on top and on the bottom and C- clamps to straighten the area. You will have some spring back and the inevitable stretching, but it should be minimal
 
Call Vans and see how much the part is. Stop worrying until you find out. Did the same thing with one of my AST tabs. Stressed over it. It was $24. Sure this skin will be more but it's in a bad spot and it will always bother you.
 
Like was noted earlier, skin is stretched, and where it is located, no Good way to make a repair you would be happy with. With what the total cost of the plane is going to be, the price of a new skin is rather minimal, and probably just as cheap as some exotic repair.
 
My vote is for a new skin. That is in a very visible spot and it'll always bug you even if nobody else notices. You may be able to get a lot of the bend out but the way aluminum stretches, it'll be a big chore and perfection may not be possible. Besides, there will be future parts of that project where you will have a nice piece of scrap to cut, shape, and bend into new parts. I received two bad flap skins. Van's replaced them. My project is done now, and parts of the old skins are in my hangar all hacked and chopped up where they were used for miscellaneous shims, brackets, test pieces, etc. Likewise, I got the larger instrument panel. I hacked and chopped the original panel and made a really nice bracket to mount my oil cooler to the firewall! I'm just saying that your original oops probably won't go to waste.
 
UPDATE:

In case anyone's curious, I put a little elbow grease and a metal shrinker into the skin and had the below results (bent skin on top, straight one below for comparison):

IMG_0325-L.jpg


IMG_0324-L.jpg


Much better, but at the end of the day, I will be re-ordering the skin anyway. I'm not happy with the score marks that the shrinker tool leaves, which as Scott pointed out may lead to cracks eventually.

Thanks very much for everyone's advice and best wishes for the new year!
 
Polish

...

I'm not happy with the score marks that the shrinker tool leaves, which as Scott pointed out may lead to cracks eventually.

...

Just for kicks, try polishing out all of the score marks with Scochbrite and measure the resulting metal thickness.

The results will be interesting for all of us.
 
Just for kicks, try polishing out all of the score marks with Scochbrite and measure the resulting metal thickness.

The results will be interesting for all of us.

I agree, I would try polishing out those marks before committing to a new skin. Your repair looks quite good, it will ride on top of the anti-scuff tape of the flap.
 
I would have no problem using it but I wouldn't thin the metal by fully polishing out the marks....
There is minimal localized loading of the skin at that point so the likelihood of future cracking is quite remote (just make sure the very edge of the skin is polished well). In fact it might be more likely if you thin the material excessively.

In my opinion a better fix would be to sand flat (just enough to assure there is nothing raised above the normal skin surface with 220 and then use a small amount of filler applied with a razor blade to fill what amount of groves is left. Sand the filler flush. Once a bit of filler primer is applied and block sanded it would probably be undetectable.
 
I would have no problem using it but I wouldn't thin the metal by fully polishing out the marks....
There is minimal localized loading of the skin at that point so the likelihood of future cracking is quite remote (just make sure the very edge of the skin is polished well). In fact it might be more likely if you thin the material excessively.

In my opinion a better fix would be to sand flat (just enough to assure there is nothing raised above the normal skin surface with 220 and then use a small amount of filler applied with a razor blade to fill what amount of groves is left. Sand the filler flush. Once a bit of filler primer is applied and block sanded it would probably be undetectable.

Ken, I agree, but the OP has already ordered a new skin, so removing all of the marks and thinning the skin in the process would give us all data on how much shrinking a skin can do to it's thickness.

It sounds like the skin in the picture has now been declared scrap. :)
 
After some scuffing and polishing, with most of the score marks gone, I'm down to 0.0275" at the thinnest part of the sheet.

IMG_0329-L.jpg
 
After some scuffing and polishing, with most of the score marks gone, I'm down to 0.0275" at the thinnest part of the sheet.

IMG_0329-L.jpg

Interesting, since if you take away the 11% thickness (5.5% per side) of the low strength pure aluminum Alclad layer you are left with 0.0285" of the higher strength aluminum. :)

I presume both sides were sanded/polished approx. the same amount.
 
Interesting, since if you take away the 11% thickness (5.5% per side) of the low strength pure aluminum Alclad layer you are left with 0.0285" of the higher strength aluminum. :)

I presume both sides were sanded/polished approx. the same amount.

About the same amount on each side because the scoring was as bad on both sides. It's not super smooth. The thickness of most of the repair is about 0.030+ but there are a few thinner areas.

I'm actually going to delay ordering the new skin--might be able to live with this. I'm in no hurry to get the top skins riveted on. I think it's worthwhile to ask a local EAA tech counselor to have a look at the repair job.
 
You may have to do something like this down the road to repair damage, but why would you want to put something like this on a new airplane ? It's a major skin and on top for all the world to see....just say'in.
 
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