A calculated solution to a wind balance situation becomes even more complex
when the boom is a lattice structure (tower sections) and therefore presents
a variable wind area that increases due to turbulence at higher wind speeds.
And I didn't want to use more tower sections for the sail... This was the
situation with my 4 el 80m yagi on a 76' boom. It isn't close to being wind
balanced when it is close to being weight balanced. There is about 30 feet
of tower on the reflector and about 46 feet on the other. If you're
wondering why it isn't better balanced for wind - I want to be able to reach
the feed point DE connections from the tower. My first try was to "fill"
the last 10 feet of the boom with aluminum plate. This proved to be not
nearly enough. I wound up putting about 15 sq ft of aluminum plate out
under the reflector end. Now in low winds it weather vanes up wind, in
moderate winds it is very undecided and higher winds make it point downwind,
as before. It's a lot less torque on the mast and rotor system in any case.
However since I added the 150 feet of 4.5 inch mast and mounted the rotor
(with shear pin) at the bottom, everything has become so much easier to work
on...
73 Don
VE6JY
----- Original Message -----
From: "Jim Jarvis" <jimjarvis@comcast.net>
To: <towertalk@contesting.com>
Sent: Sunday, January 09, 2005 18:36
Subject: [TowerTalk] Torque balancing...agreement!
>
> We read and learn. w0un and I are not in total agreement,
> but he's a bright and reasonable guy...and it's obvious that
> the problem is communications. We're describing the elephant
> from different appendages.
>
> I'm still looking for Weber's paper...but in the course of
> googling it, I came up with a TT post on the SAME TOPIC, made
> by me, in 2002. Did we ever resolve the question of windload
> on a helix?
>
> After I read Weber's paper, John and I will chat offline...if
> any concensus develops to help the guy trying to balance the
> kt34XA, one of us (not both) will post it.
>
> THAT SAID.... I submit the following observations:
>
> * Windload calculation and torque balancing are different problems.
> * John is right, the elements for the most part cancel out. If you
> place your hose clamps exactly the same way in all locations,
> they pretty much DO cancel out.
> * 45 degrees is the worst angle to calculate windload...and that
> problem is truly gnarly...but you don't have to solve it to
> "balance" the torque.
> * Adding weight to the nose, instead of offsetting the boom is the
> smartest idea I've seen so far. It may worsen the aerodynamic
> imbalance, though.
> * Even with weight added, the array isn't symmetrical, due to the
> clean 10m director, and maybe 5% differences between reflector
> and directors.
> * The nose will need a trimtab. I used 4" x 8.5", 15' from the mast.
> It could be slid, for tuning.
>
> Best regards,
>
> N2EA
> jimjarvis@ieee.org
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
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> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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