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
To: <towertalk@contesting.com>
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.
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