[TowerTalk] Wind Loading redux
EUGENE SMAR
SPELUNK.SUENO@prodigy.net
Fri, 8 Jun 2001 11:23:42 -0400
Kurt:
I know you weren't picking on me. I appreciate your contributions to
the topic, both at present and in your previous work. (Plus your e-mails to
me last year on rotator bearings, etc.)
Early Bencher literature on their Skyhawk lists the following as
contributing to the design: Jim Breakall WA3FET, Tim Duffy K3LR, and Bob
Locher W9KNI. The Skyhawk's non-conducting compensators are mounted near
the 10M 2nd DIR. The boom compensator apparently offsets the torque
imbalance caused by having more boom on the REFL side of the mast clamp.
The element compensator offsets the imbalance caused by having more element
material on the REFL side of the clamp. Therefore, the whole array is
mounted at the CG (I presume. Haven't done the math yet.)
73 de
Gene Smar AD3F
-----Original Message-----
From: Kurt Andress <K7NV@contesting.com>
To: EUGENE SMAR <SPELUNK.SUENO@prodigy.net>
Cc: Tower Talk <towertalk@contesting.com>
Date: Friday, June 08, 2001 4:58 AM
Subject: Re: [TowerTalk] Wind Loading redux
>EUGENE SMAR wrote:
>>
>> Kurt:
>>
>> With my planned antenna arrays, I won't have appreciable mast torque
>> caused by off-center mounting of the boom on the mast. I'll have a
small
>> V/UHF vertical at the top, a D40 rotatable dipole (same length on either
>> side of the boom bracket) below that, and the Bencher Skyhawk
(purportedly
>> torque balanced by the element and boom compensator pieces.) If and when
I
>> install the 2M Yagi (KLM 144-148-13LBA), it will be mounted at the center
of
>> its boom; there's not enough element aluminum to worry about finding the
>> balance center of the boom.)
>>
>
>Sounds like you have it covered Gene!
>Except, that the mention of element compensators smells like some old world
>thought, which would be incorrect in light of the information you have
>shared. So, my nature would make me want to know enough to figure out how
>the element compensators on that antenna work. I have no direct knowledge
>of the Bencher antenna, other than someone suggested that it was designed
>with my software, by someone I don't know of, so I'm just another guy
>without enough information to understand it. Maybe you can help?
>
>> I think what you're cautioning us about is the case where we have
large
>> HF Yagi arrays in which the balance point (and mounting point) of the
array
>> is not the center of the boom. In these cases, wind blowing broadside to
>> the boom will want to turn the longer side of the boom away from the
wind,
>> creating torque on the mast/rotator/tower.
>>
>
>Yes, that's right, and it doesn't have to be a "large HF array", just a
>really imbalanced one to be a problem.
>The notorious "T2X sticky brake" thing probably has more to do with this
>than anything else. I have a perfectly (as good as it gets) balanced (mass
>& wind load) antenna on a Ham III that never...EVER...has the braking wedge
>fetch up, no matter how hard it is blowing. OTOH, I also have an antenna
>that is not perfectly balanced, and it fetches up the T2X wedge about 50%
>of the time in just about any wind over 15-20 mph. Call me crazy, but I
>think it shouldn't happen.
>
>We all get to decide how important any of this is to us and proceed
>accordingly. My point really was that people are buying and having problems
>with antennas, that are not properly balanced.
>You introduced this incarnation of the subject, I commented, because I do
>not think it is all fixed, by virtue of the fact that you now have some
>good reference information. I'm the first one to wish to never comment on
>the subject again, three years on this frequency is probably long enough!
>
>> Dick's papers on aerodynamic balancing discuss how to compensate for
>> such imbalances, e.g., fixing a weight onto the boom so the balance point
is
>> shifted to the center of the boom, or entending the shorter side of the
boom
>> with a piece of aluminum tubing sleeved onto the main boom, or installing
>> compensators.
>>
>
>Yes, this covers it properly, I'm glad you now have it...everyone else go
>get one!
>
>I'll add, there is another version of the sleeved piece on the boom to
>compensate. This just uses a boom that is longer than required, but
>centered on the mast, that allows the element ensemble to be placed so the
>element ensemble CG coincides with the boom center.
>It doesn't pass muster, according to our current paradigm of "what an
>antenna should look like," but it works just fine. One of my tribanders is
>done this way, and it never does the "hula" when it blows (just about every
>day).
>Fortunately, it was really easy to do, my neighbors don't know the
>difference, and I only had to please myself when I did it.
>
>My old software release incorporates all that you have recently discovered,
>so finding your favorite solution probably doesn't need to take several
>weeks to sort out, but that can't be nearly as much fun, and that's why we
>really do this.
>
>I just wanted to point out that the other source for antenna torque is
>there, as it was not covered in your latest comments on the subject. I
>think there are quite a few TT subscribers that do not posess the
>information you have been talking about. I apologize if you thought I was
>picking on you, that really wouldn't do much for me.
>
>> BOTTOM LINE: You have to do some "cypherin' " before you put up an
>> antenna/tower system. Apparently, there's more to ham radio than Ohm's
Law.
>>
>> GL es V=IR de
>
>F=MC/I, and I am not responsible for "I", it exists on its own merit,
>regardless of what I wish it would do! Sometimes, too much E=IR (the other
>"I") causes problems with F=MC/I, and the other way around. That pretty
>much defines the system design challenge.
>
>It really must be time to talk about "True North" again. I'm sure I'm done.
>TT is fortunate to have someone else step up and be willing to beat the
>drum!
>
>--
>Have fun with it,
>Kurt
>
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