"Morgans" wrote in message
...

"Jarhead" wrote

My instructor had me butt weld some tubing in a vertical as well as a
horizonal position. Then grind off the weld until flush with the surface
of the tubing. Then cut the tubing into strips across the weld
approximately 3/8" wide. Then clamp each strip in a vise about an inch
away from the weld and bend the tubing back and forth until it breaks. A
break outside of the weld is a passing grade. A very humbling experience
at the time.

The big thing missing with that exercise is checking for pinholes in the
weld, which would cause a leak. If the joint leaks, it lets moisture into
the inside of the tubes and promotes rust.

Some tube framed aerobatic aircraft have a pressure tap fitted to the tube
in a prominent place. The tubes are assembled with holes joining one tube
to the next. After welding, linseed oil is put inside the tubing (to
prevent rusting), then rotated around and drained out. The fuselage tubes
are then pressurized with nitrogen. If on the preflight, the pilot sees
that the gauge has dropped to zero, then he/she knows that there is a
crack
in the frame somewhere, and to find it and fix it.

All in all, another very good way to make sure your airplane is not going
to
fall apart, with you in it. That would be a "bad thing." g
--
Jim in NC


Instead of filling with nitrogen, fill with argon while the frame is being
welded. This keeps the inside of the weld as clean as the outside. A low
flow rate is ample as it doesn't bleed to atmosphere as easily as the
outside of the tubing. The same pressure gauge will provide years of
confidence in the airframe integrity.

Stealth, send your welding samples to ETRS Pty. Ltd, 1 Acirl Street Ipswich
Qld, not sure of postcode. Their website http://www.etrs.com.au/ is being
updated at the moment, due to a company buyout, talk to Mike Lynham in
Ipswich about what samples are required for aircraft welding test. They will
destructively test and certify the welding.

Hope this helps,
Peter