Filling sheet metal before paint?

[Echo Tango]

Other than the cosmetic advantage of having no discernible "rivet lines" or imperfections (see: errant rivet gun) and a perfectly smooth skin, are there any speed/drag reasons to fill the skins with some light, sand-able compound to achieve a perfectly smooth surface?

I kind of like the idea of a composite-looking airframe and I was just curious if anyone has done this or decided not to do it. I'm finishing up my HS right now and the skin is pretty nice, but not perfect

[rbibb]

Don't waste your time IMHO. Any minor drag reduction achieved is at least partially offset by the weight added. Not a good trade-off for time for reward received. YMMV

[Echo Tango]

Originally Posted by rbibb

Don't waste your time IMHO. Any minor drag reduction achieved is at least partially offset by the weight added. Not a good trade-off for time for reward received. YMMV

I don't think the weight would be more than an extra pound or so, but I see your point. I still might do it for cosmetics as I prefer that "minimalist" look, but I was just curious if anyone had any experience with skin friction drag numbers or how little they might actually matter.

ive heard grumblings that countersunk rivets themselves are a waste of time at RV speeds, but i would put them in anyway just because they look nice

[Remag]

I have heard of people doing this before, however, should you ever have to make a repair or replace a skin, you will never find where your rivets are to drill them out.

If you want the composite look, you could try a Glasair but who would want to do that

[DanH]

There was a time when filling was in vogue. How many noticed that someone did it to the RV-1?

[Sig600]

If it cracks because of flex, you're going to ruin your paint job. There's an RV-8 on my field with a really nice paint job that almost looks "composite" thanks to being well done.

Not to beat a dead horse, but the RV-7 break up in Canada was partially attributed to the flutter margins being changed by the fact that it was filled and smoothed with filler.

[RickWoodall]

I filled my rivets lines. Thought i did a good job. Painter didnt like it and sanded it all off and redid it nicer. Plane before paint after i did filler 1080. Plane after all stripped, refilled properly and nicely painted 1100.

As for the breakup, that report made it almost sound like there was a LOT of filler on tail, also that plane was being flown WAY outside of the envelope. I dont think a little filler had much to do with that.

[Ironflight]

Originally Posted by DanH

There was a time when filling was in vogue. How many noticed that someone did it to the RV-1?

Just to leave no coubt....it wasn't Van!

[RV7Guy]

Originally Posted by Sig600

Not to beat a dead horse, but the RV-7 break up in Canada was partially attributed to the flutter margins being changed by the fact that it was filled and smoothed with filler.

There has been nothing to quantify this at all. There was wording that this "may" have contributed but nothing for sure.

If this is truly the case there would be RV's falling out of the sky with all the folks that have filled parts

[Mike S]

Originally Posted by Echo Tango

Other than the cosmetic advantage of having no discernible "rivet lines" or imperfections (see: errant rivet gun) and a perfectly smooth skin, are there any speed/drag reasons to fill the skins with some light, sand-able compound to achieve a perfectly smooth surface?

I was told to fill the stiffener rivet line on the front portion of my wing, the one between the spar, and the leading edge.

This was from the guy who designed the airfoil for VANs---Steve Smith, a member here at VAF.

Reason being, when the airfoil was designed, he did not expect the factory would add the stiffener, and its rivets to the shape of the airfoil. He was thinking it may improve the performance a minor amount.

This is specific to the ten..........dont know if any of the other models would benefit from it.