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Skin Scratches & Polish

KatieB

Well Known Member
Someday I want a polished airplane. As Tony Spicer said, "One polished airplane per lifetime is the right number." Or something like that. I hope to polish at least part of my old -3. The problem is, over the 30 years the pieces have been stored, moved & kicked around, there are some pretty deep scratches here and there in the skins, particularly the wing leading edges. Most of the parts are in surprisingly good shape for their age, but there are some areas on big pieces where I worry. There are no blue vinyl coverings, either. And of course there are the inevitable scratches that happen during the course of construction. Van emphasizes polishing out EVERY scratch in his instructions, enough to the point that I think he must have a good reason for it.

Question for those who have polished their airplanes: How deep of a scratch in .025 or .032 2024 alclad sheet is too deep to polish out with a Nuvite type polish? Going a step further, how deep is deep enough to threaten the structural integrity, even for a painted airplane? When should a builder cough up the dough for a new skin?
 
Katie,

If you can feel the scratch with your fingernail it can be
taken out. G6 is the best to do that.

It will reduce the scratches (NuVite) to almost nothing.

The thicker skins come out easier because you can be
more aggressive on them.

Can't comment on the depth of the replacement you
are talking about though.

Good luck and hurry up with that shop.

Boomer
 
It depends

Katie,

The real answer is that it depends. The location and orientation of the scratch has as much (or more) effect than the depth of the scratch. For example, when my fuselage side skins arrived, there was a deep scratch (more of a gouge, really) just aft of the access panel on the left tailcone skin. You can see the scratch as a faint grey line at the bottom of this picture:
20090405-01-tn.jpg


I didn't even bother talking to Van's because I knew this would have zero effect on the strength of the airframe. I'll just polish it and fill it so it looks good cosmetically once painted.

If a similar gouge was crosswise across one of the members for the the HS spar reinforcements, I probably would have had the piece replaced. If it was on the HS spar reinforcement, but was longwise, I'd probably polish it out and keep going.

Much of the metal on our airplanes is loaded to only a fraction of the strength of the material. However, it's necessary to use reasonable thickness sheet metal for reasons of durability during assembly and the life of the airplane and so that it's thickness is matched to the size rivets that will hold everything together. What I mean by that is if a skin could be 0.016 thick instead of 0.025, that might be fine for the structural strength of the skin, but 0.016 is awfully thin material to use with 3/32 rivets...so let's go with 0.020 or 0.025.

So, again, it really depends on the situation. If you have questions about specific scratches, I'd recommend taking some pictures and contact Van's to get their opinion.

Good luck.
 
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