[Towertalk] Wind pressure calculations (2/3 factor)

[Richard Karlquist]

Here is a quote from the YS manual:

> it calculates the wind load on each element section.
> Wind Load = P (As)

> P = Wind Pressure (Lbs/Sq Ft) = .004(V^2)
> V = Wind Speed
> As = Effective Area of section =(Length)(Diameter)(2/3)

> 2/3 is the shape factor for cylindrical tubing.

Somewhere on the YS web site, there is a justification,
such as it is, for using this obsolete formula.  
Applying it to the example I gave would give an
effective area of 2/3 sq ft and a wind pressure
of 25.6 lbs/sq ft for a wind load of 17 lbs.
Notice that the wind pressure coefficient is .004,
not .00256 like you see elsewhere.

One thing has become a least a little clear:
you only use the 2/3 with the .004 wind pressure coefficient
and you do NOT use the 2/3 with the .00256 wind pressure
coefficient.  What you don't want to do is use
the 2/3 with .00256 and get an optimistic number.


Rick Karlquist    N6RK
richard@karlquist.com
www.n6rk.com
www.karlquist.com 

> -----Original Message-----
> From: Pete Smith [mailto:n4zr@contesting.com]
> Sent: Wednesday, February 27, 2002 9:43 AM
> To: Richard Karlquist
> Subject: Re: [Towertalk] Wind pressure calculations (2/3 factor)
> 
> 
> Go to the Yagistress web site.  K7NV has an excellent 
> tutorial there on
> area calculations, and you can also get a demo of the 
> Yagistress software
> that may be all you need.
> 
> http://yagistress.freeyellow.com/
> 
> 73, Pete N4ZR
> 
> Check out the World HF
> Contest Station Database at
> www.pvrc.org
> 
> 
> 
>