Date: Wed, 13 Sep 2017 18:01:03 -0400
From: r young <ryoung158@gmail.com>
To: towertalk@contesting.com
Subject: [TowerTalk] Question wind loading beam
<I am planning on replacing my KT34A, which was listed with a wind load of 6
<sq feet.
My tower cannot handle anything very big big and did fine with the KT34a.
I was looking at the XR3 and XR4 by Innovantennas ( Force 12).
I was told this this
The XR3 and 4 are very similar in size, weight and wind-loading to the C3.
The XR3 has a wind area of 8.32 SqFt and the XR4, 9.19 sqft.
That is much higher than I expected for beams that seem compact.
Is there a different standard now? If so , what would the wind load be
for them using the method that had 6 sq feet for the KLM kt34a back in the
day. I think M2 now rates the KT34a even lower in load.
Appreciate any help.
Tks
## Both KLM and M2 use the 222-C method... which is no longer used these days.
Length X width of each ele section = projected area of a cylinder. With the
older 222-C spec,
they took the projected area of a cylinder, then multiplied by .666 to get
...effective area.
## IE: F12 would rate a yagi at say ..10 sq feet. Its actually 15 sq ft
of projected area.
15 X .666 = 10 sq ft. 10 sounds better than saying 15....from an advertising
perspective.
## Innovantennas, JK ants, and also optibeam, have done it correctly. Any of
the newer methods,
like 222- D, E,F, and also UBC-97 B, C.D use length X width for each
ele. IF the sum total of all
the ele projected areas is greater than the projected area of the boom, then
the total ele area is now listed
as the yagi wind load. That is typ for HF yagis. For VHF + UHF yagis, typ
the boom has greater area than
the sum total of the eles..so the boom projected area is listed.
## M2, Mosely, Hy-gain are still doing it wrong..and you have to take
their..effective area listings...and multiply
em all by 1.5 to get reality.
## Towers like UST etc are done correctly...with ant loads listed as
projected areas of a cylinder.
## For a superb writeup on this topic, look at K7NVs website.
http://k7nv.com/notebook/topics/windload.html
## JK ants, and optibeam, and innovantennas all use the.. generic
formulae..which is what you get
in a wind tunnel. Then factoring in height is not an issue.
Jim VE7RF
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