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## [TowerTalk] windforces on antennas

 To: [TowerTalk] windforces on antennas baycock@HIWAAY.NET (Bill Aycock) Sun, 10 Jun 2001 14:13:19 -0500
 ```I am a retired "Aerospace" Engineer, who started his professional career called an "aeronautical" Engineer. At that time, we dealt mostly with low-speed aero characteristics, which is what we are concerned with, with antennas. The arguments over which area to use are all right, every one, and all wrong, every one, depending on how you apply the numbers. Calculating drag (wind force) is like Zen archery- first you shoot your arrow, then find it, then call that spot the target. Simple. In calculating drag, you need the effect of four factors- the characteristics of the air - the reference area of the object we worry about - the shape factor for that object ( called, usually, drag coefficient) and the velocity of the air passing the object. Note that I said "reference" area, not surface or projected area. It really doesnt matter, so long as the area you use matches the one used to calculate the form factor, or drag coefficient from measurements. If one is a little off, the other, since it is derived from data, compensates. In practice, what is done is to take a shape- calculate the area projected in some repeatable direction, place it in a wind tunnel, and measure the force for various wind speeds. The relationship gives the form factor. after that- you can add shapes together, make them larger or smaller, etc, and, so long as you use the same method, you can calculate the drag for other , similar shapes. THat is what the antenna manufacturers have done. They have standardized on a form factor for antennas from measurements, and they give you a reference area that, with the proper application of the wind speed, will give you the proper force. I know that Steve, our professional erector, has the proper specs and numbers that are used according to the "Code". I cant remember the number of that spec, but he has it. Bill-W4BSG - Bill Aycock --- Persimmon Hill Woodville, Alabama, US 35776 (in the N.E. corner of the State) W4BSG -- Grid EM64vr baycock@HiWAAY.net w4bsg@arrl.net List Sponsor: Are you thinking about installing a tower this summer? Call us for information on our fabulous Trylon Titan self-supporting towers - up to 96-feet for less than \$2000! at 888-833-3104 www.ChampionRadio.com ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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