I really don't know how many times, or in how many different ways, I
have to explain this. I thought I was just about as clear as I could
possibly be my last post.
Yes, your very last question is the case here. The swirlers are like I
said last time ... mini-tornadoes maybe 80 to 150 feet across. When one
of them hits the tower dead on, the wind pushes one end of the boom in
one direction, and the opposite side of the swirler pushes the other end
of the boom in the opposite compass direction ... but in the same
rotational direction. The torques add.
All this discussion about torque compensators just adds to the
confusion, and they would just make it worse. If you stop to think
about the force vectors involved, it doesn't even really matter whether
or not the antennas are torque balanced to begin with ... or which side
of the mast they are attached to. That's all garbage for this
situation. One antenna could even be mounted to the mast at the very
end of the boom and the net rotational force would still be the same as
if the antenna was perfectly balanced (in the case of swirling winds).
A simple drawing would illustrate that. If the boom was 20 feet long,
for example, F x 20 feet is the same as 2F x 10 feet. This isn't rocket
science.
It is however, as you say, a real problem ... which is why I have
stripped gears on my PST-61D. I've measured the wind speed in those
swirlers as high as 100 mph on a clear day in the spring when the
thermals are active, and repeated swirling gusts in the 70's and 80's
are not at all unusual. One a bad day they come through my lot in waves
of three, each about 3 minutes apart. I'd say about a third of the days
during April and May see sporadic wind gusts greater than 60 MPH.
I've considered a PST-71D, but it's quite the monster and there's no
guarantee it will work either. For the time being I have the mast
locked in a fixed position.
Dave AB7E
On 12/11/2017 5:37 PM, Jim Thomson wrote:
Date: Mon, 11 Dec 2017 00:46:45 -0700
From: David Gilbert <xdavid@cis-broadband.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] PST61 Rotor Reliability?
<I don't think you read my post.?? A paddle isn't applicable here at
<all.? In fact, it would make things worse by adding cross sectional area
<to the system.
<Dave AB7E
### Are your pair of optibeam yagis even Torque balanced to begin with,
probably not, since I dont see any form of tq comp used on any commercially
made yagi.
If not,your swirling winds will make your situation even worse.
That paddle the fellow was talking about is actually called a torque
compensator.
If you dont have an equal amount of boom on either side of the mast, it will
not be
tq balanced. If you have more boom on one side of the mast than the other
side,
it has been mounted at the center of gravity. If you do that, you require a
small tq comp plate
down at the shorter end of the boom.
## method 2 is to mount the boom to mast... dead center in the middle of the
boom. Then
use a small counter weight at the light end of the boom. Ditto with both yagis.
## with 2 yagis on a mast, they need to be mounted on opposite sides of the
mast.
## do all of the above, and most of your issues will be alleviated.
## I thought that prosistel made bigger rotors like the 71 and the 110 / 115
??
## My SMALL k7nv PP is good for 1250 ft lbs of tq, thats 15,000 inch lbs of
rotating tq.
Its lighter than my M2 OR-2800. OR-2800 only has 233 ft lbs of tq = 2800
inch lbs.
### on a PP, the final big gear is meshed,and driven by 3 smaller gears, every
120 degs.
PP also come in the medium and large size.
## are u saying your swirling winds are essentially blowing in 2 directions at
once, like N at
one end of boom, and S at other end of boom ?? With the boom oriented E-W. If
that’s the
case, you have a real serious problem. And any TQ imbalance will make it even
worse, a lot worse.
Jim VE7RF
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