[TowerTalk] Array windload calculation.

[EUGENE SMAR]

Jim:

     AAAARRRRRGH!  DON'T use 0.66!  It's WRONG!  You'll underestimate the
wind load of your array.  The number you're mentioning is the ratio between
the shape factors for long, cylindrical (= 1.2) vs flat (= 2.0) shapes for
wind pressure on a structural member.  (Divide the two numbers and you get
0.6, but notice that the shape factor for long cylindrical shapes is,
nevertheless, greater than 1.0)

     I brought up this same subject last summer and learned that my
assumptions in windload design, e.g., 0.66 shape factor, were erroneous.
Check out the archives ca. June 10, 2001 for a lengthy thread or two on the
subject.  BTW - the net force on your EME booms will be at right angles to
the boom, NOT in line with the wind.  The magnitude will be Cos^2 of angle,
so the force drops off rapidly as you turn the boom into the wind.  (Don't
argue with me, argue with Gustav Eiffel.)

     Happy reading.

73 de
Gene Smar  AD3F

-----Original Message-----
From: WB9UWA Jim Shaffer <wb9uwa@gte.net>
To: towertalk@contesting.com <towertalk@contesting.com>
Date: Saturday, February 16, 2002 6:18 PM
Subject: [TowerTalk] Array windload calculation.


>
>Hi All,
>
>I am designing my next EME array and had some question about calculating
>windloading.
>The array will be primarily round tubing so I am applying a .66 correction
>factor to
>show the round tubing offering less wind resistance then a flat surface.
The
>problem I come
>up with when calculating horizontal tubing is what to do about orientation
>to the wind?
>Obviously the windload will change depending on wind direction. What is the
>proper
>fudge factor here?
>
>73, Jim Shaffer, WB9UWA.
>
>
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Where do you get ICE bandpass filters & beverage matching boxes?  The
same place that pays for the hosting of this list:  The eHam Store.
Order online at http://store.eham.net.
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