[TowerTalk] Question wind loading beam

[Jim Thomson]

Date: Wed, 13 Sep 2017 18:01:03 -0400
From: r young <ryoung158 at gmail.com>
To: towertalk at 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