In a message dated 98-05-18 16:50:20 EDT, baker@EC.Rockwell.COM writes:
<< I know a number of locals who have crank up towers and they have them
partially cranked up. For example a 70 foot Hy-Gain cranked to 50 feet.
Doing this they leave them set at this level all the time, regardless of
weather conditions. Is there a way to determine the gain in square footage
of wind load at heights lower than the rated wind load at full height?
Thinking along these same lines if a crank up is rated at 16 square feet
at 60 MPH, then if I have 7 square feet on the tower what is the wind speed
it should be able to handle (e.g. 70 MPH?)? >>
There are 2 articles that you should read on this topic. The first is
by Roger Cox, WB0DGF, of Hy-Gain and the other is by Bruce Horn, WA7BNM. Both
cover crank-up towers and their ratings along with charts relating to wind and
derating the crank-ups. Roger's article involves Hy-Gain towers and Bruce does
the calculations for an 89 foot US Tower self-supporter.
Both articles are available from Tower Tech for a buck each. Address is
Box 572, Woodinville, WA, 98072.
Cheers, Steve K7LXC
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