[TowerTalk] Windload at 90 mph

[Chris Wendling]

Jim Lux <jimlux at earthlink.net> wrote:


The tricky thing, of course, is that structural members for ham towers 
in typical winds are in that horrible Reynolds number regime around 
100,000 where the Cd varies so quickly (and varies a lot depending on 
laminar vs turbulent).    I remember being amazed that the wing strut on 
a Cessna 150 has a lot less drag than a 1/4" steel cable in the same 
place would.


My standard tome on this kind of thing is Applied Fluid Dynamics 
Handbook, by Robert Blevins, published by Krieger.  It's a great 
compendium of all the formulas and empirical tables, all converted to be 
in the SAME systems of units. I wish they had it in pdf.

> 

Jim,
  
  You hit the nail on the head. Seems like such a simple, innocent  question when hams ask for the wind loading on their antenna's and  towers.
   
  Even with very specific information about a particular tower  construction, etc. there just is no simple answer.  I usually  provide a range, as we have done here: from about 20 to about 35 lbs  per sq ft projected area at 90mph.  But it is a fascinating area  of study.  My first aeronautical engineering course was about 40  years ago now, at OSU. How time flies. Great discussion, and thanks for  the book tip.
  
  73,
  CW-AI4MI