Sylvan:
I had to call ARRL at the number shown on their QEX web page for copies
of DIck's articles. They cost $3 US each (higher price if you're not an
ARRL member.) Try www.arrl.org and wind your way through their
publications pages.
As far as why the UBC says what it says, I don't have an answer. But I
can speculate. My previous post said that Dick's article had drag
coefficients for long tubes and for flat plates: 1.2 and 2.0, respectively.
If you divide 1.2 by 2.0 you come up with 0.6, the ratio of tubular to flat
plate drag coefficients. Most folks (myself included) had incorrectly used
this ratio as the "shape factor" when calculating wind loading. The UBC is
not wholly inaccurate though; the factor for tubing IS, in fact, about 2/3
that for flat plates.
Get copies of Dick's articles: "Determination of Yagi Wind Loads Using
the 'Cross-Flow Principle' ", by Dick Weber K5IU, Spring, 1993; "Aerodynamic
Balancing: Part
1", Weber, Comm. Quarterly, Summer, 1994; "Aerodynamic Balancing: Part 2",
Weber, Comm Quarterly, Winter, 1995. They may keep you from putting up a
risky tower system.
73 es GL de
Gene Smar AD3F
-----Original Message-----
From: Sylvan Katz <jskatz@sk.sympatico.ca>
To: EUGENE SMAR <SPELUNK.SUENO@prodigy.net>; Tower Talk
<towertalk@contesting.com>
To: <towertalk@contesting.com>
Date: Thursday, June 07, 2001 8:21 AM
Subject: Re: [TowerTalk] Wind Loading redux
>Eugene
>
>Your posting is extremely interesting. I have two questions:
>
>> However, I have since read three of Dick K5IU's various papers
>> (available through ARRL's QEX/Communications Quarterly) in which he cites
>
>(1) Are these available on the web?
>
>> Another point: The nonsense of multiplying the area of a Yagi
>element
>> by 0.67 or 0.6 or anything less than unity (1) to account for its shape
is
>
>(2) Why does footnote 8 in the UBC Table 16-H --Pressure Coefficients (C
q )
>states "Factors for cylindrical elements are two-thirds of those for flat
or
>angular elements"
>
>You note is timely as I am diligently working on a mast design for some
>Force 12 antennas.
>
>.. sylvan
>
>----------------
>Sylvan Katz
>VE5ZX & G0TZX
>Saskatoon, SK
>
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