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Re: [TowerTalk] KT34XA Torque Balance

To: "Red" <>,"Tod - Minnesota" <>,"TowerTalk" <>
Subject: Re: [TowerTalk] KT34XA Torque Balance
From: "Michael Tope" <>
Date: Sat, 8 Jan 2005 00:08:31 -0800
List-post: <>
----- Original Message -----
From: "Red" <>
To: "Tod - Minnesota" <>; "TowerTalk" <>
Sent: Friday, January 07, 2005 5:32 PM
Subject: Re: [TowerTalk] KT34XA Torque Balance

> Hi, Tod and TTers;
> Tod presents 'an elegant solution."  Furthermore, by optimizing the
> length and diameter of the arm versus area of the vane, one can minimize
> the wind loading on the tower and mast.
> I recall that this aspect of antenna design and the calculations are
> addressed in David Leeson's book, "Physical Design of Yagi Antennas."
> I don't believe he includes calculations for any of the KT34 series, as
> he does for several popular antennas, but he offers all you need to
> calculate the wind induced torque.
> 73 de WOØW
> Tod - Minnesota wrote:

One caution, Red - John W0UN sent me an email letting
me know that the portion of Leeson's book that describes
the need to torque balance elements with dummy elements
is incorrect. It seems that Dick Weber K5IU has written on
this subject pretty extensively and that all you need to do is
to torque balance the boom, which by the way is way out
of balance on the KT34XA (the boom wind torque balance
point and the center-of-mass balance point are offset by
about 20"). If you look at what Weber writes you find out that
don't need to worry about the elements because the wind
forces on a symmetric element always act in the direction
perpendicular to the element (what he describes as the
"cross-flow" principle) which means that force on the
element gets applied in-line with the boom so there is no
net torque from the elements. The elements have to be
symmetric of course, but most are, so happily I no longer
need to worry about doing wind force calcs on the
nightmarishly complex KT34XA elements. All I have to do
is something like Tod suggests where I balance the forces
acting on the boom.

73 de Mike, W4EF.......................


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