Unless you have a very narrow lot or a fold over tower than needs to be
guyed while lowering, I do not know why you would want four guy wires? With
three anchors, a tower can be placed 1/2 of the anchor distance toward one
side of the property line. Of course the opposite side of the property would
need to be at least 1 guy anchor distance away with three guys. Guy cables,
anchors and towers come in various sizes making a three wire system more
than sufficiently strong while requiring less hardware than four. I am not
even sure where you could purchase a four wire tower bracket.
John KK9A
Grant Saviers KZ1W wrote:
I think Wilson is correct that maximum 4 guy tension occurs when wind is
aligned with that guy. That will also be minimum downforce on the tower.
However, when wind is splitting the angle between the 4 guy anchors,
maximum download force on the tower occurs, the sum of downforce from
both guys. 40% more than directly on one guy for the 4 guy example,
while the tension in each guy is reduced by 30%.
As the angle between the guy anchors increases, the total guy tension
needed to counteract the wind increases. At 120 degrees (3 guys) both
the tension per guy and downforce are higher than with 4 guys when the
wind splits the guy angle, the worst case.
I think some towers fail in buckling which is a downforce loading.
A very simplified model is the top guy counteracts the antenna wind
load, and the intermediate guys keep the tower from buckling or from
bending that exceeds the leg yield stress.
All of this ignores the wind load from guys, the preloads, and their
dead weight adding to tower downforce.
Well, that's at least how my ancient memory of vector mechanics figured
this out. Plus some prior posts.
Grant KZ1W
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