Fuselage skin replacement

[mcgaughy]

Anyone with experience replacing the aft side skin f-773 and aft bottom skin f-778?

I have a small dent and wrestling with repair verses skin replacement. I'm concerned more problems could develop by skin removal. Kinda like open heart surgery for something a stent could rectify.

Thanks.
Ellis

 

[planenutz]

Some photos of the dent would make it easier to people to provide advice.

Replacing the entire skin isn't a five minute job and it comes with paint-matching hassles, however the pre-punch skins on the RV-7 make it a lot easier than the first generation kits because you have less realignment issues. The fact you have to replace two skins would suggest its a significant dent and in that case you might want to replace the skins. Or you might find that you can save one skin by replacing the other, perhaps? Again, photos would help.

Sometimes open heart surgery is the better option. It's not a difficult job, nor is it a very time consuming job as you should be able to get that completed in a full working week. You just have to get over the mental barrier that typically holds us back.

 

[mcgaughy]

Here are some pics the damage is right at the seam of the two skins.

 

[Sam Buchanan]

That would be a tricky repair on the current skins since it is in a joint line. Because this is a new airframe, and you are in construction mode already, and you don't want to think about this every time you gaze across the ramp at your new RV....I suggest spending an hour of so drilling out rivets so you can install new skins. Yes, this is discouraging at this point in the project, but I think you will be happier in the long run if you return the fuse to pristine condition.

 

[planenutz]

Yeah, I agree witih Sam. Its a shame but it might be the best way forward.

I don't recall - is the J-Channel separate or is the lower skin folded to form a J-Channel on the edges? I had a feeling it was the latter on those aircraft. I imagine the J-Channel will be stretched so try releasing the rivets along the joint first and see what happens. I can't really tell from your photos however if the side skin is not damaged you might find you only have to replace the lower skin.

 

[Ralph Inkster]

I’ve rebuilt 2 fuselages with major skin panel replacements. The one most similar to your damage had gaping holes in the side & crushed top turtledeck.
How I’d approach your repair,
1- support the fuselage so it doesn’t sag or twist,
2- leave the side skin mostly riveted on for now but cut access holes in damaged side skin so you can easily rivet the new belly skin on,
3- drill off the damaged belly skin,
4- rivet on the new belly skin, reach in thru the holes to ease bucking those rivets,
5- drill off the damaged side skin
6- think of any specialty brackets you want to put in the tail cone while you have easy access,
7- close it up, rivet the side skin back on,

You really gotta love those prepunched skins! The plane with the crushed turtle deck was a 6, so I had to match all those hand layout rivet lines, oh so fun.
Good luck

 

[jackking123]

There are some choices, if it's SMOOTH, no crease it is likely structurally acceptable.... You can go inside and use "PAINTLESS DENT REMOVAL" techniques that they use in car work... This is from inside with tools and it is a SLOW WORKING of metal, a massage, slowly working metal, to get metal to go back to it's "memory" position. There are bond on pull tabs you can use from outside and gently pull on the dent to pull it out. The "PDR glue tabs" are removed with a concentration of isopropyl alcohol directly on glue to loosen. Then you carefully peel tab off. It takes time to get the solvent to penetrate.

Removing panel and DRILLING OUT so many rivets MIGHT make many more issues. From what I see (and may not have all the facts) I would try and get it pushed out. You may want to HIRE a Pro to come to your shop and do it. They have tools to do this....

Then if there is a small wrinkle or wave remaining, yes Sir, FILLER and primer. It will look great. What filler, NOT bond-oh. They have much better light weight fillers, can't recommend anything. I am sure people have some suggestions. Prime and paint it will look good as new. If you want a polished plane, well this option is out I guess. Many RV's have filler when the do the paint job to take out dents.

It has to be structural, and that means no cracks, no crease or sharp edges. That means dent to size ratio 400 to 1 ? So 10 inch wide/long dent, max depth of dent 0.3". I am pulling this out of my hat, may be 200 to 1 is OK. I think if you WORK the dent out slowly (takes time to realign the atoms), by pushing and releasing, pushing and releasing, over and over, never bending in one step, over and over you will straighten it out, if not completely you will make it better, unless it is sharp creased. Watch videos of this process on car bodies. It is wizard stuff. I do understand steel and aluminum are different, but most metals have memory, malleability and ductility. You can bend metal back if you did not crack or crease it... but it's a bit of an art.

 

[mcgaughy]

There are some choices, if it's SMOOTH, no crease it is likely structurally acceptable.... You can go inside and use "PAINTLESS DENT REMOVAL" techniques that they use in car work... This is from inside with tools and it is a SLOW WORKING of metal, a massage, slowly working metal, to get metal to go back to it's "memory" position. There are bond on pull tabs you can use from outside and gently pull on the dent to pull it out. The "PDR glue tabs" are removed with a concentration of isopropyl alcohol directly on glue to loosen. Then you carefully peel tab off. It takes time to get the solvent to penetrate.

Removing panel and DRILLING OUT so many rivets MIGHT make many more issues. From what I see (and may not have all the facts) I would try and get it pushed out. You may want to HIRE a Pro to come to your shop and do it. They have tools to do this....

Then if there is a small wrinkle or wave remaining, yes Sir, FILLER and primer. It will look great. What filler, NOT bond-oh. They have much better light weight fillers, can't recommend anything. I am sure people have some suggestions. Prime and paint it will look good as new. If you want a polished plane, well this option is out I guess. Many RV's have filler when the do the paint job to take out dents.

It has to be structural, and that means no cracks, no crease or sharp edges. That means dent to size ratio 400 to 1 ? So 10 inch wide/long dent, max depth of dent 0.3". I am pulling this out of my hat, may be 200 to 1 is OK. I think if you WORK the dent out slowly (takes time to realign the atoms), by pushing and releasing, pushing and releasing, over and over, never bending in one step, over and over you will straighten it out, if not completely you will make it better, unless it is sharp creased. Watch videos of this process on car bodies. It is wizard stuff. I do understand steel and aluminum are different, but most metals have memory, malleability and ductility. You can bend metal back if you did not crack or crease it... but it's a bit of an art.

Thanks very much. After hours / days of research I've come to the same conclusion. I'm slowly working some of it out now. Considering adding some j-channel to both the seam in question as well as one down the bottom center. The j- channel weighs next to nothing and can't hurt.

 

[rph142]

Thanks very much. After hours / days of research I've come to the same conclusion. I'm slowly working some of it out now. Considering adding some j-channel to both the seam in question as well as one down the bottom center. The j- channel weighs next to nothing and can't hurt.

I dropped a bucking bar on my completed RV-3 wing while doing an avionics upgrade. I hired a mobile dent repair guy and he had it 95% gone in an hour. They can work wonders.

 

[jackking123]

Thanks very much. After hours / days of research I've come to the same conclusion. I'm slowly working some of it out now. Considering adding some j-channel to both the seam in question as well as one down the bottom center. The j- channel weighs next to nothing and can't hurt.

Yes reinforcement stiffener will be sufficient overkill. Strength is not an issue. Nice!!!

 

[jackking123]

I found the aerospace quality filler "Fill Bond EP007. Don't use bondo as it shrinks. This stuff is used by Kermit Weeks... who has a museum in Florida, Fantasy of Flight, restores aircraft...

 

[mcgaughy]

I found the aerospace quality filler "Fill Bond EP007. Don't use bondo as it shrinks. This stuff is used by Kermit Weeks... who has a museum in Florida, Fantasy of Flight, restores aircraft...

I'll pass along too to be wary of West Systems 410 as it causes problems in the sun under dark painted surfaces (fact check the manufacturer's data). Knowing this, I won't use it under any external surface even though it sands so nicely.

 

[lucaperazzolli]

Maybe you could find interesting this article : https://www.kitplanes.com/a-ground-loop-story/

 

[mcgaughy]

Maybe you could find interesting this article : https://www.kitplanes.com/a-ground-loop-story/

Thanks. Interesting article. I was surprised they flattened dimples in old skin, match drilled, then redimpled. At least that's how I briefly understood it. Had I changed a skin, I had simply planned to drill the new skin hole to 40 or 41 then deburr and dimple then rivet. My experience has been that once thin aluminum is riveted, the holes expand slightly although I've never measured it.

 

[Tommy123]

Thanks. Interesting article. I was surprised they flattened dimples in old skin, match drilled, then redimpled. At least that's how I briefly understood it. Had I changed a skin, I had simply planned to drill the new skin hole to 40 or 41 then deburr and dimple then rivet. My experience has been that once thin aluminum is riveted, the holes expand slightly although I've never measured it.

Yep they will as well as the hole expansion when dimpled. Personally I wouldn't reskin your plane for that dent, If it's smooth I'd live with it.