This was long over due.
Check it out.
http://www.rotaryeng.net/mm-instruct.html

Paul Lamar

Paul,
Bill Freeman suggests compression loads are different (higher), on the
bottom rail, did he ever give the calculations for that other than to
suggest to go larger diameter and thinner wall - enquiring minds need to
know (EMNTK).
George ( down under)

Read that again George. You missed something.

The lower tubes are always in compression.

Paul Lamar