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@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.
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