[TowerTalk] Motorized UST tower... very smooth and dead

[Jim Thomson]

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From: "Robert Harmon" <k6uj at pacbell.net>
Sent: Wednesday, September 29, 2010 3:11 PM
To: "Jim Thomson" <jim.thom at telus.net>
Cc: <towertalk at contesting.com>
Subject: Re: [TowerTalk] Motorized UST tower... very smooth and dead

> The HDX-689 is rated for 60 sq ft not 50 sq ft.
>
> It has twice the capacity of the HDX-589.
>
> Bob
> K6UJ
>
>
###  I have both stress analysis spec sheets, which depict abt 8 x  wind 
load ratings   Which
one do you want ?

##  In a 70 mph wind, they rate it  at 62.5 sq ft  IF the ant eles/boom are 
 >2" OD
and 50 sq ft is els, etc. are  2" or less in OD.   Both those are based on 
PROJECTED AREA
OF A CYLINDER !       They rate the flat eq at  38.5 sq ft.  [ effective 
projected area of a cylinder, factoring
in the drag coef ].

## be careful here.   F-12 /M2 etc  rate their ants in the flat eq of a 
cylinder  IE: effective area.
F-12 calculates the projected area of all the ele's, adds em up , then 
multiplies by .67

##  The point here is..... don't assume you can put up  50 sq ft of F-12 
ants, you cant.   I'd use the
38.5 sq ft  flat rating of the HDX-689.   Rohn rates their towers in EPA 
[effective projected area/flat area eq], which
is a smart move.

## In the past, ant makers quote effective area, cuz it makes for smaller 
numbers.   Tower makers will quote
projected area's, cuz they end up being bigger numbers.   Both methods are 
legit, just don't mix them up.
On some yagi's, the quoted sq footage is way out to lunch. Most of the yagi 
mech stress programs  will
give you the effective area of all the els...and also the boom.

Jim   VE7RF