Re: [TowerTalk] Mast Load Question

[Jim Schnaidt <kj0m@mchsi.com>]

On May 26, 2004, at 10:13 PM, Dave Hachadorian, K6LL wrote:

> >
>
> In Statics, this is a "sum of the moments" problem. The clockwise
> overturning moments about the thrust bearing must equal the
> counterclockwise moments. You didn't specify the mast weight, but let
> me assume that it weighs 5 pounds per foot.
>
> clockwise:
> (45# ant)(12')(.707) + (80# mast)(8')(.707)
>
> counterclockwise:
> (rotor force)(4') + (20# mast)(2')(.707)
>
> Therefore:
> (4')(rotor force) = 382 + 452 - 28
> rotor force = 202 pounds

Thanks, Dave.

One question, though. Why the .707 in the calculation? Has this to do 
with the fact that the tower is laid over to about 45 degrees? I think 
the sin of 45 degrees is around .707. Is that correct?

It appears the bigger problem may be the ability of the tower raising 
fixture to handle the 250 extra pounds on the top of the tower when 
it's tilted over. I need to contact US Tower regarding this. Someone 
has emailed privately that someone told him 500# max at the top of the 
tower. With the chrome alloy mast and about 140# of antennas, I think 
I'm still within specs there but need to verify that. Otherwise, it 
seems the rotor bolt stress won't be near what I originally envisioned.

Thanks.

73,

Jim
KJ0M

._._.

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