Excellent explanation!
There was no intention on my part to refute that normal 3-point guying will
not resist twisting.
For guyed towers where twist must be reduced to near zero, then one must
employ the 6 guy arm system, period. For ham radio, I would think this is
necessary only for those using their tower to mount a microwave dish. I am
thinking the comments about single torque arms doing nothing at all had to
be referring to this low twist requirement.
Keith
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Tom Rauch
Sent: Tuesday, August 03, 2004 8:09 PM
To: keith@dutson.net; TowerTalk
Subject: Re: [TowerTalk] Rohn Torque Bar confusion
> IMO, if you compare the above to a six point torque arm
system, well, there
> really is no comparison.
>
> Keith
But no one is saying they are equal Keith.
I see a serious flaw in the idea a guying system does nothing to reduce
twist. That idea only would be true if the guyline attached to the center
axis of the tower.
Consider a spoked wheel such as on a bicycle or even the drive wheel of a
motorcycle or car with wire wheels. If the guyline does not resist twist,
why do wire wheels resist huge amounts of torque without serious deflection?
The reason is pretty simple. When the tower twists all three guylines have
to reach a longer distance, tension increases a large amount. (You could
view the tower as a wheel.) All three guylines, when the tower starts to
wrap up, add force that opposes any twist. That's because the guylines are
no longer in line with the center line of the tower. Each guyline adds an
equal opposing force to any twist.
Now that isn't exactly like a wire wheel with 50 spokes, but it still is a
significant force when the twist tries to pull the guyline an extra inch or
two!
As a matter of fact, this is why tower with heavy insulators in guylines
feel so "twisty". They have more sag to suck up out of the guyline, so the
tower can twist and wobble more than a guyline with less sag.
If a tower with a radius of one foot is extended to two feet in radius by
the addition of a torque arm, the same increase in guyline end spacing would
cause twice as much resistance to torque.
The primary difference between a torque arm and a six wire star bracket is
the star bracket already starts with the wires "deflected" from being in
line with the center, so the initial movement is much less for a given
increase in guy tension. The fact it is six lines doesn't help, because
three are going slack while three are tightening.
That's how it looks to me in my head-cad.
I'm sure there is someone who can put numbers on this. The problem isn't
that complex. I do absolutely know the idea guylines do nothing to resist
twist is wrong, because I can't twist my tower that sits on a greased ball
at the base insulator and it has NO torque arms of any type.
73 Tom
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
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http://lists.contesting.com/mailman/listinfo/towertalk
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