[TowerTalk] Wind Surface Area

[jimlux]

Stan Stockton wrote:
> Seems like there is some factor for round tubing instead of square - 
> like 2/3 or something?
> 
> Stan, K5GO


Depends on the speed of the wind, or more properly the Reynolds number 
(Re).  This size/speed range is an area where the drag coefficient 
varies a lot with the Reynolds number (as in a 3:1 variation)..  If you 
want to be conservative, take 1.2 times projected area (because that's 
about as big as the Cd can get).

I use projected area as a rule of thumb (i.e. Cd=1), but mostly for 
computational convenience.

If your design is so close to ragged edge of failure that your estimate 
of the Cd of the tubes makes a difference, then maybe there are bigger 
design issues that need to be addressed?

Jim