[TowerTalk] Rohn RSL tower - slightly off topic

Steve Maki lists at oakcom.org
Fri Jun 7 19:45:39 EDT 2019

On 06/06/19 19:18 PM, john at kk9a.com wrote:

> I missed the torque part however I wish someone could explain this in simple terms.

I'll give it a try.

Stick a tennis ball on top of a mast. It creates no rotational torque in 
the wind.

Stick the tennis ball on the side of the mast, it creates torque in the 
wind, like a wind vane.

Picture a balanced boom (balanced for wind...and weight if you like, but 
I don't believe the weight is important for this).

Picture the boom going right thru the mast (ala Telrex elements that 
went thru the boom).

A hypothetical symmetrical wind comes along. The boom does not rotate 
because everything is balanced.

Now move the boom to one side of the mast. The wind will now attempt to 
move the boom *downwind*, IOW, perpendicular to the wind on the downwind 
side of the mast, because of the lever arm created by the distance 
between the mast center and the boom center. Kinda like a weather vane.

Now add a second identical boom to the other side of the mast. Voila, 
things are balanced again for wind force vectors.

I have to say though that it would seem that because of the small lever 
arms involved, this concern is not worth putting much effort into. The 
effect can easily be dwarfed by antennas that are not wind balanced.

-Steve K8LX

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