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

[Jim White, K4OJ]

sounds like a job for Yagistress Man

k4oj


----- Original Message ----- 
From: "Richard Karlquist" <richard@karlquist.com>
To: <towertalk@contesting.com>
Sent: Wednesday, February 27, 2002 8:32 AM
Subject: [Towertalk] Wind pressure calculations (2/3 factor)


> I am trying to do a simple wind
> pressure calculation on an antenna,
> but I am confused about how to do
> it.  I see conflicting information
> on towertalk archives and various
> ham vendor sites.  Let me see if
> I can get a consensus on a very
> basic example.
> 
> If I have a 1 inch diameter round
> tube 12 feet long in an 80 MPH wind,
> what is the wind pressure.
> 
> The projected area is 1 square foot
> (ie the shadow the tubing would cast
> on a plane surface)
> 
> The total frontal area is pi/2 times this
> or 1.59 square feet
> 
> Some references say to multiply by 2/3
> to get "effective area" whatever that
> means.  Other references talk about 1.5,
> which is the reciprocal of 2/3 and close
> to pi/2.
> 
> Anyway, some sort of area needs to be
> multiplied by some fudge factor and then needs to
> be multiplied by wind stagnation pressure.
> Am I correct in assuming this is 30 lbs
> per square foot for 80 MPH?  I am thinking
> this is an ideal value in free space
> (ie pushed by an airplane traveling at
> 80 MPH).
> 
> I see references to a "UBC basic wind speed
> of 80 MPH" where 80 MPH doesn't mean 80 MPH,
> rather it refers to a table of pressure vs
> height.  I see at 70 feet this is something
> like 24 lbs/square foot.  This seems to imply
> a ground effect.
> 
> I'm not trying to apply for a building permit,
> I'm just trying to see if an antenna will
> survive 80 MPH winds.
> 
> Can anyone boil this down to something
> simple?
> 
> Rick Karlquist    N6RK
> richard@karlquist.com
> www.n6rk.com
> www.karlquist.com 
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