[TowerTalk] Tram rope

[Jim Lux]

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