[TowerTalk] Tension on tramline

[Jim Lux]

They're all cases of catenary curves, and a bit of googling will find a lot
of detail
Try http://home.earthlink.net/~w6rmk/math/catenary.htm for some equations
which might help.



----- Original Message -----
From: "Pete Smith" <n4zr at contesting.com>
To: <towertalk at contesting.com>
Sent: Sunday, April 04, 2004 6:47 AM
Subject: [TowerTalk] Tension on tramline


> I was talking the other day with a local antenna guy about tramming.  I
> mentioned reading various cautionary tales on towertalk about masts
getting
> bent as a result of the tension on tramlines when relatively heavy
antennas
> are being moved up and down.  He said he had never had this problem, but
> opined that this was because he always left sufficient slack in the
> tramline so that the tension didn't become too severe.
>
> I can visualize that in cases of extreme slack (i.e., where the tram line
> goes almost straight down from the tower to the load) the tension on the
> tram line would be almost zero, because virtually the entire antenna
weight
> would be borne by the rope that controls the antenna sliding down the tram
> line.  I have also experienced what happens when you try to pull a line
> bearing weight in the middle (like a center-fed sloper suspended from the
> top of a tower, at a 45-degree angle) really taut, in order to get the
> droop out.  The tension required seems to increase almost exponentially as
> you get closer to dead straight, and you can't ever get all the slack
> out.  The wire will break first.
>
> Is there a mathematical formula that will tell you roughly how much
tension
> is required at a given load weight and degree of slack?  Alternatively, is
> there a safe rule of thumb to tell you how much slack to leave in a tram
> line for a given load?
>
> 73, Pete N4ZR
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> is back, at www.pvrc.org
>
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