[TowerTalk] PST61 Rotor Reliability?

[David Gilbert]

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 at cis-broadband.com>
> To: towertalk at 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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