Section Index  Owatonna Steele County Amateur Radio  08Oct2014 
Horizontal Element DroopThe information required for the calculation is:
The basic formula for a round tube is:
"I" is the moment of inertia for the geometric shape. It is calculated as:
I = π * ( Do^{4}  Di^{4} ) / 64 As an example, I for a piece of tubing 1/2" OD and 3/8" ID is:
I = π * (0.5000^{4}  0.3750^{4} ) / 64 "w" is the weight per inch of the tubing. This may be available directly from the supplier. It can be calculated by calculating the weight of a solid aluminum bar for the outside diameter and then subtracting the weight of a solid aluminum bar for the inside diameter. Aluminum weighs approximately 0.098 pounds per cubic inch. The formula for calculating the weight of a 1 inch long round aluminum bar is:
Weight = π * 0.098 * D^{2} / 4 As an example, a 1 inch length of a 1/2" round aluminum bar would weigh:
Weight = π * 0.098 * D^{2} / 4
Likewise, a 1 inch length of a 3/8" round aluminum bar would weigh 0.0015 pounds. Putting it all together, the estimated droop for a 48 inch long piece of 1/2" OD by 3/8" ID aluminum tubing is:
Droop = ( w * L^{4} ) / ( 8 * E * I )

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