"Ted Edwards" wrote in message
...
Ed Huntress wrote:

have long, thin tubes loaded in compression. Aluminum could help,
theoretically.

How, Ed? Long thin tubes approach the Euler formula in which only
elastic modulus and radius of gyration matter. For example

2{pick}S_r I_tube 2 .05 {rem} radius of gyration for 2"OD, .05"
wall
0.6896557112
2{pick}S_r I_tube 2 .15 {rem} radius of gyration for 2"OD, .15"
wall
0.6562202374

Not much change there but the equal weight .05" wall steel tube would
have three times the elastic modulus of the .15" aluminum tube and, in
fact, a slightly larger radius of gyration.

Ted

Because the tubes could be of larger diameter and *also* have thicker walls,
for the same weight -- thus producing a higher value "r."

In fact, that's how the Bobsy was designed, with aluminum tube space frames,
back in the '60s.

Ed Huntress