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[TowerTalk] Effective Moment/K Force & Yaesu rotators

To: <>
Subject: [TowerTalk] Effective Moment/K Force & Yaesu rotators
From: (
Date: Wed, 11 Jul 2001 12:42:20 EDT
In a message dated 7/10/01 10:16:59 PM Pacific Daylight Time, writes:

> I messed up that post about my confusion about calculating "K" tremendously 
>  by not putting in the source of my confusion--> The Yaesu web site, and 
>  Texas Tower web site both leave out the mast in the calculation of the "K" 
>  factor , made sense to me. So I purchased my G1000DXA and waited for the 
>  UPS truck to bring my shiny new rotator, which I purchased with this new 
>  "scientific system" to assure my "safety freak" side all factors are 
>  covered. But when I open the box and read the manual there it is--> A half 
>  page explanation (with diagrams) that suddenly includes the weight of the 
>  mast in calculating the "K" factor. I didn't understand why--so I started 
>  making phone calls. I called Texas Towers and they didn't know for sure 
>  which was correct, next I tried Vertex and had no luck getting anyone but 
>  marketing who him-hawed around really not knowing what to do.
>  My brother is a C.P.E. but not a ham, he felt that in engineering a 
>  structure he would not consider the mast, but since he did not have access 
>  to the engineering information on the rotor he could not say whether the 
>  vertical loading should be included in the "K" factor or not. Yaesu's own 
>  literature contradicted itself. I still have not received a reply to my 
>  letter from Vertex/Yaesu.
>  I would like to feel completely comfortable with my decision to leave the 
>  mast out of the calculation, but if something happens and the rotator 
>  clamshell fails, and the antennas fall damaging part of my home......what 
>  will the insurance company determine? God forbid what if someone were 
>  or killed! The safety freak inside me has not been sleeping well waiting 
>  for an answer from Vertex/Yaesu (now 6 weeks overdue).
>  Thanks for your email at least I know there is someone else who feels that 
>  the concentric force of the mast is insignificant compared to the 
>  torque of the antennae when calculating "K".
>  At 10:31 AM 7/10/2001 -0600, N4KGwrote:
>  Hi Frank,
>  I have never understood why weight of the mast is a factor since
>  it has such a small radius. Also, the K factor is not a "real"
>  moment but a ficticous number that "sort of" indicates rotor
>  capability. The actual moments depend on WHERE the weight
>  is distributed. Empirical evidence is still the best criteria for
>  rotor selection, unfortunately.
>  Tom N4KG

    Frank - chill out and get some sleep. You're overreacting and I'll bet 
you a nickel that you never get a response from Yaesu/Vertex so don't worry 
about it. 

    Tom is correct. Effective Moment and K Force is an ESTIMATE from the 
factory based on their knowledge of the antenna loads and rotator capability. 

    Since EM/KF is weight times turning radius, the mast is insignificant. 
For example, a 70 pound 2" mast would have an EM/KF of 6.36 ft-lbs. The 
margin of error for an EM/KF is *much* higher than that. 

    The use of a foot-pounds of torque spec for rotators is more useful than 
the old "square footage" estimate since two antennas of identical square 
footage can have drastically different wind-induced torque forces and EM/KF's.

    BTW I picked up Yaesu's latest rotator brochure and there have been some 
changes to the specs. Some of the models now need 6-conductor control cables 
where they used 5-conductor previously. I heard they changed to DC motors or 
something like that. Also, the K Force for the G-1000 has been down-graded 
from 2020 ft-lbs to 1664 ft-lbs.

Cheers,    Steve     K7LXC
Tower Tech  


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