At 09:32 PM 12/18/2006, Eric Scace K3NA wrote:
>Yes, I saw a tram line part and the results were not pretty. The person
>operating the winch narrowly escaped injury by the antenna and by the
>parted line. This occurred early in my ham antenna career as was a real
>wake-up call to the forethought required for safe installation.
>
>A tram line's forces act against the dead weight and wind load of the
>antenna being installed. Because the tram lines come off at an angle,
>those forces are much larger. (Draw out a force diagram using high
>school physics.) Assume a tram line leaves the pulley holding up the
>antenna at a 45 degree angle up and toward the tower, and on the other
>side continues on at a 30 degree angle below horizontal in the opposite
>direction toward the ground. For a 100 lb antenna, the force on the
>line to the tower is 738 lbs and on the line to the ground is 602 lb.
I'm having a bit of trouble visualizing the forces here. Is the
antenna supported by pulley hanging from the tram line (a'la a
gondola lift at a ski area), so you're talking about the forces on
the support line. Or are you skidding the antenna up a guy wire, and
the tram line is just the hauling line pulling it up at the angle of the guy?
Either way, I have a hard time getting 45 degrees to turn into 7.38
or 1/7.38.
Can you point me to a diagram?
>That is the static case. Loads will vary when one attempts to start the
>antenna moving from that point.
>
>-- Eric K3NA
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