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Erecting Long Masts

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Subject: Erecting Long Masts
From: (Terry Dunlap)
Date: Thu, 19 Dec 1996 18:18:38 -0700
At 03:45 PM 12/19/96 PST, David O. Hachadorian wrote:
>Interesting question, here are some numbers.
>The way to figure this is to regard the bearing at the top of
>the tower as the fulcrum of a lever. All of the bending
>moments above the bearing must be equal in magnitude to
>the bending moments below the bearing.
>Here are several different ways to use a 20 foot mast, with
>22 square feet of antennas concentrated 2 feet below the top
>of the mast, 71 mph wind (20 psf). This is for a stiff, non-
>bending mast.
>a. 2 ft rotor to bearing, 16 ft bearing to antenna.
>bending moment = 22x20x16 = 7040 ft-lbs.
>side force on rotor = 7040/2 = 3520 pounds.
>b. 5 ft rotor to bearing, 13 ft bearing to antenna.
>bending moment = 22x20x13 = 5720 ft-lbs.
>side force on rotor = 5720/5 = 1144 pounds.
>c. 10 ft rotor to bearing, 8 feet bearing to antenna.
>bending moment = 22x20x8 = 3520 ft-lbs.
>side force on rotor = 3520/10 = 352 pounds. 

But these calculations are without an intermediate support, are they not?  An
intermediate support would effectively isolate the rotor from any of these.
Please excuse me if I'm missing the obvious, I'm just trying to understand
what's being presented.

73 de Terry KK6T

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