The math is not simple for a catenary with a suspended load. You
get a lot of mental exercise doing hyperbolic sines and cosines.
You can search on catenary, tension, suspension, etc and get lots
of relevant references. Any any decent physics book with a chapter on
mechanics should show everything you need.
Here is an interesting site for some background info. It is on two
pages and there are some links to other interesting sites.
http://www.brantacan.co.uk/suspension.htm
73--John W0UN
At 08:47 AM 4/4/2004, you wrote:
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
The World HF Contest Station Database
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and ask for Sherman, W2FLA.
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