[TowerTalk] Rohn RSL tower - slightly off topic

Steve Maki lists at oakcom.org
Fri Jun 7 19:51:46 EDT 2019

It just occurred to me that with a small lever arm and single long boom 
(which all booms are), equilibrium might occur well before the boom goes 
totally crosswind.

At this point I'm entering the area well above my pay grade.

-Steve K8LX

On 06/07/19 19:45 PM, Steve Maki wrote:

> 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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