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[TowerTalk] Re: Long mast, intermediate bearing

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Subject: [TowerTalk] Re: Long mast, intermediate bearing
From: (Dick Flanagan)
Date: Mon, 6 Apr 1998 20:42:10 -0800
At 8:01 PM -0800 4/6/98, Matt Kolb wrote:

>Even your smaller rotators (I
>am looking at the Yaesu G-800 manual as I speak) will easily handle 400
>lbs of vertical load while they will handle very little in lateral
>binding on the mast before they crap out.  The centering effect as well
>as the ball bearings make sure that the only pressures seen by the
>rotator are those of a purely vertical load....something that they
>appear to be designed to handle, hence the vertical load rating.

I have been chatting with Steve about this, but perhaps I should insert
this point of confusion (on my part) into this conversation.  I am
concerned about this "lateral binding on the mast."

For example, I have a 20' mast; 16 feet above the tower, 4 feet down to the
rotor.  That amounts to a 4:1 lever arm; for each pound of force pushing
the top of the mast to the left, there is a four pound force pushing the
bottom of the mast to the right.  It is the job of the rotor to contain
this lateral force at the bottom of the mast.  Correct?

To continue the example, with 20 sq ft of wind loading on the mast, one
could reasonably expect to see a 200 pound lateral force applied to the top
of the mast.  This would equate to an 800 pound lateral force being applied
to the rotor.  Correct?

This lateral force would seem to be just as critical to a rotor as any of
its other specifications, yet none of the rotor manufacturers appear to
state it.

Now, since rotors aren't being sheared apart in rampant numbers, this
doesn't appear to be a real-world problem, but I am curious about the
physical forces in effect here.  Any thoughts on this?

73, Dick

PS:  Be gentle.  I'm a software engineer and this is definitely hardware!

Dick Flanagan W6OLD CFII Minden, Nevada DM09db (South of Reno)

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