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## Re: [TowerTalk] wind load

 To: "Tower and HF antenna construction topics." Re: [TowerTalk] wind load jimlux "Tower and HF antenna construction topics." Fri, 19 Feb 2010 06:45:30 -0800 mailto:towertalk@contesting.com>
 ```Charles Coldwell wrote: > On Thu, Feb 18, 2010 at 1:34 PM, Stan Stockton wrote: >> I could be wrong about this but have always thought (from an old Rohn book) >> that 70 MPH equated to 30 pounds per SF of antenna. > > OK, so in my example if the maximum wind load at 70 MPH is 15 sq ft, > and we have 30 pounds per square foot, that works out to 450 pounds of > force. That sounds reasonable. > > If we believe the force grows as the wind speed squared, and that a 70 > MPH wind puts 30 pounds per square foot of force on the tower (and > that a 0 MPH wind puts 0 pounds), then the constant of proportionality > is 30/4900. So that means the general formula would be > > F = 3/490 * W * W * A I use V^2*Area/391 for area in square feet and V in mi/hr 1/391 is the density of air in funny units.. If you want in other units (e.g. you have wind speed in meter/sec and area in square meters), it's basically the half theair density (rho).. about 1.2 kg/m^3 or 0.075 lb/ft^3 Drag = 1/2*rho* Cd* A * v^2, where Cd is the drag coefficient, assumed 1 here. > > where F is the force in pounds, W is the wind speed in MPH, and A is > the antenna effective cross-sectional area in square feet. > > What's the title/author of the Rohn book? > _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```