[TowerTalk] K-factor Revisited

[Tom Rauch]

Hi All,

I'm not a mechanical engineer, without a tag I don't know which 
way to install a T-shirt, but one thing is obvious.

Square footage alone is NOT a valid rating.

Square footage tells us nothing about bending moment moments or 
rotational torque, neither does weight alone.

Five square feet of antenna can overload the rotator, if it is on a 
long boom. So could one square foot, and that would be true no 
matter what the antenna weighs. All it takes is a long level to 
multiply the pressure by the mechanical advantage of a lever.
That would be true for bending moment, and torque. 

Thrust bearings reduce or eliminate the bending moment problem, 
but they certainly can't help the torque problems. Torque problems 
can certainly have more to do with wind pressure than simple dead 
weight.

Because of this, I NEVER consider the recommended sq ft of a 
rotator in making a choice. I look at how much torque the rotor can 
safely produce, and how much torque it will take before failure  
when locked down (in the wind).

IMHO, "square foot" ratings are meaningless.


73, Tom W8JI
w8ji@contesting.com

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