Let's see...
90 degrees in 5 seconds extrapolates to 360 degrees (1 rev) in 20 seconds,
or 3 rpm. I understand most of those prop pitch motors have about 1000 to 1
gear reduction, so the motor must have rotated at about 3000 rpm. Yep,
that's screaming!
73, Keith NM5G
_____
From: TexasRF@aol.com [mailto:TexasRF@aol.com]
Sent: Wednesday, April 25, 2007 11:32 AM
To: kdutson@sbcglobal.net; TOWERTALK@contesting.com
Subject: Re: [TowerTalk] Mast slipping
First hand feedback: a full sized 80m 3-el yagi (1200 #) will windmill a
large prop pitch with about 45 mph wind. This is for a very well balanced
design with equal element spacing.
You can't imagine how disconcerting it is to be belted off next to one of
those big drives and hear it screaming as the antenna rotates 90 degrees in
about five seconds!
I had to scrounge up an original disc brake for the prop pitch motor to hold
that load in the gusty Texas winds.
Wonder how one calculates twisting torque when the load is balanced? There
seems to be a missing bit of information needed to do such a calculation;
variation in wind speed over an area of say 100ft in width.
73,
Gerald K5GW
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