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## [Towertalk] Wind pressure calculations (2/3 factor)

 To: [Towertalk] Wind pressure calculations (2/3 factor) richard@karlquist.com (Richard Karlquist) Wed, 27 Feb 2002 08:32:32 -0800
 ```I am trying to do a simple wind pressure calculation on an antenna, but I am confused about how to do it. I see conflicting information on towertalk archives and various ham vendor sites. Let me see if I can get a consensus on a very basic example. If I have a 1 inch diameter round tube 12 feet long in an 80 MPH wind, what is the wind pressure. The projected area is 1 square foot (ie the shadow the tubing would cast on a plane surface) The total frontal area is pi/2 times this or 1.59 square feet Some references say to multiply by 2/3 to get "effective area" whatever that means. Other references talk about 1.5, which is the reciprocal of 2/3 and close to pi/2. Anyway, some sort of area needs to be multiplied by some fudge factor and then needs to be multiplied by wind stagnation pressure. Am I correct in assuming this is 30 lbs per square foot for 80 MPH? I am thinking this is an ideal value in free space (ie pushed by an airplane traveling at 80 MPH). I see references to a "UBC basic wind speed of 80 MPH" where 80 MPH doesn't mean 80 MPH, rather it refers to a table of pressure vs height. I see at 70 feet this is something like 24 lbs/square foot. This seems to imply a ground effect. I'm not trying to apply for a building permit, I'm just trying to see if an antenna will survive 80 MPH winds. Can anyone boil this down to something simple? Rick Karlquist N6RK richard@karlquist.com www.n6rk.com www.karlquist.com ```
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