Re[2]: [TowerTalk] Re: Projected Area (something rotten in

Hank Lonberg Hank.Lonberg@harrisgrp.com
Mon, 24 Aug 1998 7:30 -0800


     

Bill:

The equation used in TIA/EIA 222-F which is the latest revision and the UBC 
defines the basic wind speed stagnation pressure (a datum) value as:

        Qs = 0.00256V*V

        This is base on Bernoulli's equation which can be arrainged to give

        Qs=1/2*RHOair*V*V8

                Density(air) at 59 deg F and 29.92 in Hg is 0.0765 lbs/cf
                Rho=Density/g
                RHOair=.0765/32.2

        To express in MPH

        Qs= 1/2(.0765/32.2)(1/3600)*(1/3600)(5280/1)*(5280/1)*V*V

        Qs= 0.00256*V*V


I don't know of any safety factor in this derivation

Hope this helps

73

Hank /  KR7X

______________________________ Reply Separator _________________________________
Subject: Re: [TowerTalk] Re: Projected Area (something rotten in  Den
Author:  baycock@hiwaay.net (Bill Aycock) at ~INETMAIL
Date:    8/23/98 8:07 PM


Steve- There is a reference several of our more knowledgible tower Gurus 
have used that has been bothering me.  I have seen the equation for dynamic 
pressure given as q= 0.004 v^2, with an attribution to the specification 
EIA-222 Rev F, or one of the earlier revisions.  One of the functions of a 
spec is to define terms and the way they are both used and determined. That 
is one of the problems we are having with the definition of area, as it is 
to be used to fit antennae to towers, by way of load calculations.
     
My problem with the equation as given (more than once), is that it gives an 
answer about four times the accepted value.  By accepted value, I mean the 
one that would be given by any competent aerodynamicist when asked for the 
equation for dynamic pressure.  The problem comes from the value 0.004. In 
the classical equation, this term is about 0.00119, and is half the (mass) 
density of air at normal sea level conditions.
     
If the value given in the spec is such that it represents a built-in safety 
factor, they should say so. I dont have ready access to the spec, so I cant 
say how the equation is given in context, which is why I am asking you. The 
problem may be one of units, but my checks there dont look that way.
     
Can you clarify this for me ?
     
Thanks es 73
     
Bill
     
Bill Aycock   W4BSG
Jackson County, AL
EM64vr
W4BSG is "vanity" this time, but was 
earned by exam in 1954, the first time.
     
--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html 
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com 
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm
     
------------------------- Original message header: 
>MAIL FROM:<owner-towertalk@contesting.com>
>RCPT TO:<hank.lonberg@harrisgrp.com> 
>DATA
>Received: from dayton.akorn.net (dayton.akorn.net [205.217.100.11])     by dayt
on.akorn.net (8.8.5/8.8.5) with SMTP id VAA20087;     Sun, 23 Aug 1998 21:09:39 
-0400 (EDT)
>Received: by dayton.akorn.net (TLB v0.10a (1.23 tibbs 1997/01/09 00:29:32)); Su
n, 23 Aug 1998 21:09:29 -0400 (EDT)
>Message-Id:<3.0.5.32.19980823200757.009481b0@hiwaay.net> 
>X-Sender: baycock@hiwaay.net
>X-Mailer: QUALCOMM Windows Eudora Pro Version 3.0.5 (32) 
>Date: Sun, 23 Aug 1998 20:07:57 -0500
>To: "Steven H. Sawyers n0yvy" <sawyers@inav.net>, towertalk@contesting.com 
>From: Bill Aycock <baycock@hiwaay.net>
>Subject: Re: [TowerTalk] Re: Projected Area (something rotten in  Denmark) 
>In-Reply-To: <199808230427.XAA17040@soli.inav.net>
>References: <008f01bdcd7e$2da36be0$d05bfea9@guy> 
>Mime-Version: 1.0
>Content-Type: text/plain; charset="us-ascii" 
>Sender: owner-towertalk@contesting.com 
>Precedence: bulk
>X-List-Info: http://www.contesting.com/towertalkfaq.html 
>X-Sponsor: W4AN, KM3T, N5KO & AD1C
------------------------- End of message header.

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm