On 12/7/11 4:24 AM, Jim Thomson wrote:
> Date: Wed, 07 Dec 2011 00:19:21 -0500
> From: K8RI<K8RI-on-TowerTalk@tm.net>
> Subject: Re: [TowerTalk] Fwd: HDBX-48 figures for 90 mph zone
> To: email@example.com
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> On 12/6/2011 11:13 PM, HansLG@aol.com wrote:
>> In a message dated 12/6/2011 4:43:51 P.M. Eastern Standard Time,
>> firstname.lastname@example.org writes:
>> As I recall wind pressure "on a flat surface" at 70 mph is 20.6 lbs/sq
>> so if the tower is rated for
>> 18 sq ft at 70 mph, would it be too much of a stretch to say to the zoning
>> board that since wind pressure at 90 mph is 34 lbs/sq ft, by simple math,
>> the tower should be good for 10.9 sq ft at 90 mph ?
>> Gene / W2LU
> Regardless of wind area isn't there a boom length limitation on both the
> BX and HDBX series?
> Roger (K8RI)
> ## yes, I think they reduced it to just 10' years ago..and sales plummeted.
> Just fudge the ant wind load a bit, and perhaps 'take out' one section on
> Then when u install it, add the extra section back in. IF you ever did hit
> it with
> a 90 mph wind, and a big ant, ur gonna be in for an eye opener. That thing
> 70 mph = 20.6 sq feet. That's from 1976. 222- REV-D. It's now REV G !
> A Trylon T-500, 72' tall..is good for 22 sq feet @ 70mph....but only 6 sq feet
> at 100 mph. The tower itself will eat up all the windload. Toss in any
> you can kiss it goodbye. I wonder if the factory will even give you a
> rating for 90 mph ?
That's a tapered tower with a pretty large cross sectional area, of
angle iron. There's a pretty good chance that it would have an
available antenna area of less than zero with a 60% increase in wind
load. that square law thing really bites hard.
For those that are interested, the summarized analysis is in the back of
the BX manual
Gives cross sectional area for each section, heights of sections,
assumptions of strength for materials, etc.
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