This is the setup I used for finish welding the fuselage. I built lightweight rotating stands to position the fuselage in any position necessary for ease of welding. The stands are constructed out of 1-1/4 x .083 wall box tubing and look like small engine stands.

All the welding was done with the TIG or Heliarc process. TIG uses argon shielding gas to keep the welds from oxidizing and your control of the heat is superior to gas welding. The problem with TIG is if you are not an accomplished welder, it is possible to get inferior welds because of your inexperience. TIG heats the material quickly and if you're not careful you will build in stresses you wouldn't with gas. It is also harder to get consistent penetration without a lot of practice.

Most of the major aircraft manufacturers use TIG for welding parts similar to the welding required for the Pup. I prefer it because you have better heat control and very little oxidation problems. I am stress relieving all my welds so that shouldn't be an issue.

If you are considering TIG welding your project, I would suggest that you spend a lot of time practicing. Do a lot of practice welds with the same joint configuration as you will see on your parts. After welding, try to break the welds in a vise or with a hammer. If any welds break, keep practicing. You should be able to completely flatten a sheet metal T joint without the weld breaking. You should do the same thing if you are welding with gas. Remember, your life is on the line. If you don't have complete confidence in the work you are doing, use someone you have confidence in or keep practicing.

Here are some articles for further reading.

FAQs on Welding 4130

TIG WELD 4130

Biplane Project