How attach sheet metal to 4130 tubing?

Attachment 4177

I am converting a single place Stit's Playboy to two seats.
I stripped the fuselage and am repainting it.
Rather than use fabric, I would like to aluminum skin it;
and while I am at it, put a little curve in the fuselage profile.

How can I attach curved forms to the square fuselage without
penetrating the tubing. I do not want to use blind rivets, bolts,
or screws because I would like to linseed oil the inside tubing.

I could make slots in the forms and create some type of
aluminum strip clamp around the tubing but I wanted to check
with the group and see if someone else has used, or know of a
better mouse trap :)

There are already one or two pieces on the belly that was safety
wired, but that looks like it quickly compromised the paint and rusted.

FYI - I would create new forms with a flat edge against the tubing.

Thanks for the suggestions!

How about welding some tabs on the tubing and bolting the formers to the tabs.

That is how the one shown in the picture above was done.

Take a look at the way the Stearman is constructed. There were many very successful duster conversions that metalized the entire fuselage using the tube clamps to support a 'birdcage' assembly. Doing the welding on the frame invites cracks and other issues.

If you do not want to weld tabs onto the frame I would suggest clamps. Use heavy "Adel" style clamps, not padded , you want them TIGHT on the tubes. The other good clamp option is a Curtiss type, these you will likely have to make they will clamp very tightly and were used for assembly jigging and semi-permanent installations up through the '50s. The issue will likely be vibration so use heavy enough clamps and enough to keep the new bulkheads and frame solid. Keep any clamp on tubing tight you do not want it to be able to vibrate on the tube and chafe into it. I would also recommend that the clamp it's self be steel and attach any aluminum stand-offs/frames to the clamp. That will prevent galvanic corrosion on the structural truss.Attachment 4178 Let the clamp be the "sacrificial" piece for any future corrosion from dissimilar metals.

I saw somewhere in the last year (maybe here??) That someone is making the Curtiss clamps again.

No need to go any farther than any number of Stearman suppliers for the clamps required. They come in a variety of sizes and forms.