In a message dated 98-07-03 11:01:08 EDT, ditzian@greenepa.net writes:
> I have been warned that one problem with very long masts used for
> turning antennas is that there is rotational flexibility in the
> mast. By the time one has 50 feet of mast between a rotor (at
> the bottom of a tower, for example) and the antenna (at the top
> of the tower, sitting on a thrust bearing) one may expect a fair
> amount of turning in the breeze, or of lag in alignment between
> the rotor and the antenna when the rotor turns. Furthermore,
> this may result in some whiplashing of the whole system when the
> antenna is turned and then stopped.
>
A long mast like you're describing is essentially a torsion bar that
would absorb and dissipate much of the wind forces on the antenna(s) before it
gets to the rotator. This is a well known phenomena. It's the same thing as a
coil spring but straight instead of wound in a circle.
I don't think there would be significant whiplashing because the torsion
bar would be dissipating a lot of the forces. We're talking about a steel mast
too.
> My question is whether wood (for example, 2x4 lumber) would
> resist this rotational or torsional effect better than round
> steel pipe or tubing (probably pipe due to cost)? Assume that
> there is no weight on the mast (or lumber); the mast simply turns
> the antenna that is sitting on the thrust bearing that is sitting
> on the tower.
SNAP! Wood is strong IF it's the right density and IF there aren't any
knots in it But it's not a suitable tower material. It's okay for purposes of
your example though.
>
> Please do not bother to excuse the bandwidth; I wanted to use it
> and I did. This submission has been reviewed for correctness of
> spelling, grammar, and punctuation, but a human being did the
> review. The language has been tailored to the expected level of
> reading ability of a majority of readers of the TowerTalk
> reflector. I have attempted to offend the greatest number of
> readers. If there are more anti-PC comments that can be made, I
> cannot think of them. Your comments in matters related to this
> final paragraph are best directed to me at ditzian@greenepa.net.
> Comments on the technical questions are appropriate to
> TowerTalk@contesting.com.
Your sarcasm was noted but not necessary. Please refrain from this kind
of personal editorializing in the future. Tnx.
Cheers, Steve K7LXC
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