How does this wind loading information apply to a bertical antenna which is
rigidly mounted at the base and flexes in the wind?
In addition, if the vertical antenna is mounted on top of a 22 ft tower,
which is anchored in concrete, how does this info apply?
22 ft tower is short in comparison and maybe can be considered nonmovable
and then the vertical can be seen as the same as if it were mounted on the
ground.
Dan Schaaf
K3ZXL
"In the Beginning there was Spark Gap"
www.k3zxl.com
 Original Message 
From: "Charles Coldwell" <coldwell@gmail.com>
To: "Tower and HF antenna construction topics." <towertalk@contesting.com>
Sent: Thursday, February 18, 2010 2:55 PM
Subject: Re: [TowerTalk] wind load
On Thu, Feb 18, 2010 at 2:02 PM, Gene Smar <ersmar@verizon.net> wrote:
>
> To get these figures into engineering terms, you'd have to convert the
> wind speed into poundspersquarefoot
> http://www.arraysolutions.com/Products/windloads.htm and multiply by the
> EFFECTIVE area of the antenna. Then this force is applied to the top of
> the
> tower; let's say the tower is 100 feet tall. In the example, the force of
> a
> 70 mph wind is 12.54 psf. The total forced applied to the tower at 100
> feet
> AGL would be 12.54 X 15 = 188 pounds.
Well, that is substantially less than the 450 pounds I came up with
from the "30 pounds per square foot in a 70 MPH wind" rule mentioned
upthread.
> The trick comes in determining what the effective area (sqft) of the
> antenna really is. Manufacturers are unclear in their literature in how
> they calculate the advertised areas of their antennas.
I suppose this is due to uncertainty in the drag coefficient since the
geometric crosssection should be unambiguous. Rewriting the Array
Solutions formula as
F = A * 0.00256 * W * W * Cd
the effective crosssection is the product A * Cd, where A is the
geometric crosssection, and Cd is 1.2 for long cylinders and 2.0 for
flat plates.
> That calculation showed that my D40 rotatable dipole had a spec from
> Cushcraft of 1.3 sqft, whereas the "shadow area" of the elements
> calculated
> out to be 3.55 sqft. Go figure.
Yeah, I can't make up that difference no matter how I play around with
drag coefficients.

Charles M. Coldwell, W1CMC
"Turn on, log in, tune out"
Winchester, Massachusetts, New England (FN42kk)
GPG ID: 852E052F
GPG FPR: 77E5 2B51 4907 F08A 7E92 DE80 AFA9 9A8F 852E 052F
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