How to get skins smooth?

[BTP880]

I have not started building yet, however I spend a lot of time looking. I have noticed that on some builds the skin of the plane is super smooth with no waves, dimples, bumps ect. Like so:

https://drive.google.com/file/d/1z0P...ew?usp=sharing

I know body filler and sanding has a role to play but with planes like this one:

https://drive.google.com/file/d/1vXY...ew?usp=sharing

There are flaws here that I am suspicious that body filler could fix. My question is whats the difference? How do you build it so that you can get these super smooth skins? Is there a trick to it?

Not meaning to bash anyone's planes here! You have one I dont lol your already doing better then I am!

[Ralph Inkster]

Riveting practice, lots of it.
Also riveting a long line of rivets in a sequence that minimizes the amount of stretching help with smooth results.
Most RV builders try to avoid bondo like the plague.

[vfrazier]

Yeah, practice helps... but so do some of the tricks that you learn that aren't in the AC43-13-1B... like whacking the buck tail with a hammer while your gunner tells you when it looks about right. Not for the faint of heart, but it is a valuable trick to bump the rivet back out if it's modestly depressed.

There are many others, like bonding the skins, then driving the rivets. Or heat treating the rivets to soften. Not recommended unless you have a Phd in metallurgy, or are insane about winning an Oshkosh trophy.

Or just do it the military way... use 1/4" thick skins and shave off the boo-boos.

Of course, the crappy looking planes fly just as nice as the show stoppers.

Good luck!

[Mel]

Most consider it over-kill but while riveting our wings, we heated the skins to the point of hardly being able to touch them. Another gentleman riveting his wings at the same time (winter) did not. Our skins ended up drum tight. His had a lot of "oil canning". I'm not saying that this was the only difference as he was a first time builder and it was our 6th build, but it certainly helped.

Also the riveting pattern makes a difference. Always try to start at the center of the panel and work toward the corners. Aluminum DOES migrate during riveting.
For example when riveting the aft wing skins, start at the center of the sheet at the main spar. Alternate working left, right, and aft.

[wirejock]

Depends on what you refer.
An under dimpled skin will show pillowing around every dimple. The only way around it is to not let it happen. Practice on scrap to properly set up and use the C-frame or DRDT.
Oil canning as other mention is another story.

[Karetaker]

Camera angle and lighting. I can look across my wings in the cradle and they look wavy, (my opinion) but look at them from a different angle and they look glass smooth. (My opiinion)

[arffguy]

Shims, don't forget shims. Sometimes the bulkhead flanges don't match up well and the flanges have to be cutoff and replaced. Or the bulkheads need to be shifted or widened. Don't work strictly to dimensions, make the parts fit together well without the rivets in yet (this is a bigger issue on the older non-punched kits). No gaps between parts.

[Z-EDD]

Originally Posted by BTP880

I have not started building yet, however I spend a lot of time looking. I have noticed that on some builds the skin of the plane is super smooth with no waves, dimples, bumps ect. Like so:

https://drive.google.com/file/d/1z0P...ew?usp=sharing

I know body filler and sanding has a role to play but with planes like this one:

https://drive.google.com/file/d/1vXY...ew?usp=sharing

There are flaws here that I am suspicious that body filler could fix. My question is whats the difference? How do you build it so that you can get these super smooth skins? Is there a trick to it?

Not meaning to bash anyone's planes here! You have one I dont lol your already doing better then I am!

I?m not saying there aren?t techniques that lead to better skins, but the primary difference in the examples cited is in the photography, lighting and angle. If you look at any RV from the wrong angle the flaws will show up. Also there is a big difference in paint quality between those two.

[Bevan]

Backriveting is easy to master and yields great results (smooth skins) on the thinner sheetmetal of control surfaces.

Bevan

[DeeCee 57]

not mentioned yet, the dimple dies! Don?t skimp on costs here, just get the best tooling available.