Chuck, if "torque" is the only thing you're worried about, there's an
old trick to use. Visit a local motorcycle shop and buy a front spring
, the inside diameter of which will accommdate your mast. Take whole
thing to welding shop and have the spring welded ( at both ends ) to
the mast. THEN, have them CUT the mast in the center of the spring.
Generally, the spring should be about 12" above the rotor end of the
mast for short masts ( say where 6-8 feet are inside the tower ) and in
your case, 12-24 inches for any length mast you want to run.
When you energize the rotor, the initial torque is absorbed by the
spring, and the the whole mast will begin to rotate....when you stop
the rotor, the spring, having given up all it's torque by then, will
again absorbe the torque of the mast and antenna ( the antennas will
overshoot a little, then come back. Also, during high wind periods,
the rotor just sits there, while the spring absorbs the torque caused
by the antenna moving.
I would also recommend a thrust bearing about every 30 feet of mast.
But, using this system, you can use "black" pipe for the long
section of the mast, and then transition into your "antenna" mast.
As for the HDX, if you can't find new parts, have it repaired by
welding angle iron, or rebar bent to form the traditional "Rohn"
And don't even begin to worry about the spring...I don't know of any
antenna every put up which would even begin to stress it.
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