I ran a finite element model with two 15-foot booms, one
made of 2.25 inch round, the other with 2.0 square.
One end was fixed and the other end was left free,
exposed to gravity in the Z axis and an 85-mph wind
in the Y axis.
Results:
Gravity sag: round, -2.27 in; square, -2.19 in
Horiz deflection 85mph wind load: 7.95 in round;
10.82 in square
Bending moment applied to mast: 4778 in-lbs round;
7441 in-lbs square
Like you said, round booms "trounce" square booms.
They certainly don't do your mast, tower and rotor
any favors.
73 Jim K6OK
========
Jim Thomson wrote:
## Its actually a lot worse. A 2.25 inch OD round boom
has a circumference of 7.069 inches. A 2.0 inch square
boom has a larger circumference of 8.0 inches.
## assuming same wall thickness, the 2 inch sq boom is
8 / 7.069 = 13.2% HEAVIER...and more expensive, if cost
per pound is the same. Circumference of the 2 inch sq boom
is 13.2 % bigger.
## A real world fair comparison would be equal
circumferences. In that case the round boom would have to
be 8 / pi = 2.546 inches in diameter. They would both
weigh..and cost the same.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|