# [TowerTalk] Bang for the buck?

Jim Lux jimlux at earthlink.net
Sun Mar 28 07:10:11 EST 2004

```AE7I wrote:

Most of the crank-up towers are advertised with 70 mph ratings, but it is
difficult for me to translate that to 85 mph, as I understand that the wind
loading goes up exponentially.  Back of the envelope shows the wind force
will be 1.50 times higher at 85 than at 70...

HOWEVER... watch out, because the antenna square footage is only a part of
the total load.  The tower is also significant, and you might wind up with
ZERO area at the higher speed.

Example.. tower is 50 square feet, and there's 10 square feet of antennas on
it.... It's ok at 70  (that is, 60 Square feet*70^2 is some number within
the limit for the tower)... Now, jack the wind speed up to 85...so the loads
increase by 1.5... now you're at 50*1.5 for the tower alone with NO
antennas... and that's more than the limit.

>> Goes as the square of wind speed, as a general rule..
I would like to be able to handle about 15 sf of antenna on a
self-supporting crank-up tower with 10 foot mast extended about 6 feet above
the tower.

```