It comes from the Bernoulli equation:
pressure = rho * v^2
where rho is the density
Pressure, for antenna drag, is measured in pounds/square feet
The classic "drag equation" is Drag Force = rho * v^2 * Area * Cd
where Cd is the Coefficient of Drag, which is form (and Reynolds number)
dependent.
In pounds, feet, and miles/hr, and using Sea Level standard pressure and
temperature, the equation is Force = v(mph)^2 * Area (square feet)/391
If you want to do dimensional analysis: F (kg m/sec^2) = rho (kg /m^3) *
v^2 (m^2/sec^2) * area (m^2)
in SI units..
force (which is mass*length/time^2), rho (mass/length^3), velocity
(length/time), area (length^2)
1/391 is the density in the relevant units (which gets really ugly, because
you're combining slugs, g, feet, miles, hours)
----- Original Message -----
From: "Ellen M." <rockmeln05@yahoo.com>
To: <towertalk@contesting.com>
Sent: Friday, February 11, 2005 8:07 AM
Subject: [TowerTalk] Wind Force
> Hello Tower Talk,
> I had a question pertaining to the equation, F=PA where F is the
windforce, P is wind pressure(lb./ft^2), and A is antenna wind area (ft^2).
P=0.004(or 0.00256) V^2. I was wondering how the 0.004 converts the mph(V)
into lb/ft^2(P) for wind pressure. Any ideas would really help me out.
>
> Thank you,
> Ellen M.
>
>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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