[TowerTalk] Optibeam OBLY14-5

[JVarney]

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



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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.