[TowerTalk] Windload at 90 mph (was: Plumbing a tower)

[Chris Wendling]

Jim,
  
  Yes, I figured you used a Cd of 1.0, which is a reasonable starting place.
  Nice to know there is another "aero" guy on the towertalk list.
  
  Below is a link to some very good information on communication  structures and wind loads under various conditions of icing, etc.   I think you'll find it very interesting.
  
  73,
  CW-AI4MI
  
  
  <http://books.google.com/books?id=m-Uhn_O7O08C&pg=PA144&lpg=PA144&dq=coefficient+of+drag+for+wire+cable&source=web&ots=em_0WoRPLK&sig=ZeJ8s2lWzdEklgFL3Xu1JnQ2Af8#PPA133,M1>

Jim Lux <jimlux at earthlink.net> wrote:  Chris Wendling wrote:
> Clay,
>     
>     Yes, you're in the ballpark.
>     
>     The formula for drag is 1/2* rho*velocity-squared*frontal-area*coefficient-of-drag.
>     
>     I calculate about 26 lbs force for 90 mph for 1 sq-ft frontal projection area.
>     
>     This assumes a coefficient of drag of 1.3 - typical for tubing or wire profiles.
>     Also, the density of the atmosphere was assumed to be at STP (standard temp and pressure at sea level.)
>     
>  The largest error contributor to these calculations is most oftem the  estimate of the drag coefficient- Surface roughness, Reynolds number,  interconnections on the tower, etc., may yeild different results.


Indeed.. I just used 1.0 for Cd for rough and ready order of magnitude. 
I was thinking in terms of a tubular free standing tower (as opposed to, 
say, a lattice HDBX style)    1.3 might be a reasonable number of a 
smallish tube in that sort of wind, it would be near the peak in the 
Cd/Reynolds number curve.  Somewhere around I have a spreadsheet that 
figures this stuff out, with handy data taken from Blevins, Fluid 
Dynamics Handbook.