You really ask a tough question, because the answer is not really
simple. Aerodynamic drag depends upon a parameter called the Reynolds
Number, which is a function of dimension and velocity. Once the
Reynolds Number is known, look up the Coefficient of Drag. Drag is then
given by:
Drag = Cd * .5 * rho * A * V squared,
where:
Cd is the coefficient of drag,
rho is the density of the air (determined by temperature, barometric
pressure, and altitude)
A is the cross sectional area of the particular element (for cylinders,
use the diameter times the length)
and V is the velocity, in units appropriate to those used for
determining Cd.
This isn't really accurate because it doesn't adjust for ends and aspect
ratios.
If you are interested, I'll look up particulars for typical cylindrical
antenna elements.
Meanwhile, assume 30 pounds per square foot at 80 mph, or 40 pounds per
sq ft at 100 mph. These are the figures used in the standard for steel
towers, I believe its AIA 232. I'll look up that too, if asked. I
can't believe how lazy I am right now! Problem is, I'm on the computer
that doesn't have all the references, including titles to a couple good
books about aerodynamic drag.
73 de WOØW
n6tqs@arrl.net wrote:
>Hi people,
>We've just had some big winds through here, and most people haven't
>had too many problems (although one person has reported half of a 40M
>element completely vanished, and I have to climb a little to realign
>a beam for a friend).
>
>But, it's got me curious- what's the formula for the sideways force in
>pounds, given a wind velocity and antenna area?
>
>73, doug
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