TT:
The following three articles by Dick K5IU are (were?) available through
the ARRL back issues of Communications Quarterly:
o "Determination of Yagi Wind Loads Using the 'Cross-Flow Principle' ", by
Dick Weber K5IU, Spring, 1993;
o "Aerodynamic Balancing: Part 1", Weber, Comm. Quarterly, Summer, 1994;
o "Aerodynamic Balancing: Part 2", Weber, Comm Quarterly, Winter, 1995.
The first one is a not-too-mathematical explanation of the wind forces
on Yagis, the topic of this thread. The other two explain why we shouldn't
point our masts true north (please don't start!) and then proceed
unthinkingly to fasten all of the booms on the east (or west) side of the
mast.
Great beach reading!
73 de
Gene Smar AD3F
-----Original Message-----
From: dan hearn <dhearn@ix.netcom.com>
To: jljarvis <jljarvis@adelphia.net>
Cc: towertalk@contesting.com <towertalk@contesting.com>
To: <towertalk@contesting.com>
Date: Saturday, July 06, 2002 11:07 AM
Subject: Re: [Towertalk] Estimation of yagi windload
>Dick Weber, K5IU, did analysis of this problem in Determination of Yagi
>Wind Loads Using the "Cross Flow Principle" in Comm. Quarterly, Spring
>1993 issue. I believe this is the most comprehensive work on the subject
>to date. 73, Dan, N5AR
>
>jljarvis wrote:
>>
>> Towertalkians:
>>
>> In thinking about Eric's question of windload on a helix,
>> I came to realize I'd never seen a thorough approach to
>> windload on a yagi.
>>
>> * Does anyone have a reference to a published analysis?
>>
>> * Thinking about it:
>>
>> * To what degree are 'hidden' elements shadowed by
>> those before them? It probably depends on windspeed
>> and element diameter, as well as spacing.
>>
>> * My guess is, "not at all", in which case, one sums
>> the exposed area of the elements and degrades that by
>> whatever the flat/round factor is. (.70?)
>>
>> * Further, I suspect that maximum exposed area occurs
>> around 45 degrees, where one takes .707 of the exposed
>> boom area, plus .707 of the exposed elements area,
>> each multiplied by the flat/round factor, and then summed.
>>
>> I suspect a search in the IEEE journal might yield something;
>> that's my next step.
>>
>> Has anyone seen reference to wind tunnel studies, in support
>> of mathematical models/approximations?
>>
>> Jim Jarvis/N2EA
>>
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