Pete Smith n4zr@contesting.com
Mon, 13 Dec 1999 09:48:01 -0500

At 07:57 AM 12/13/1999 -0600, n4kg@juno.com wrote:
>When pushing the load limits, a better measure of capacity
>is needed.  The problem with boom length only specifications
>is that they do not account for element size and weight.  The
>problem with Wt X Boom specifications is that they do not
>account for element  WEIGHT   DISTRIBUTION.  A 2L Yagi
>has ALL of it's element weight at the ends presenting a 
>worst case scenario.  A multi-element multi-band antenna
>has it's element weight (and often boom weight) distributed
>along the boom.  Thus two antennas with equal boom 
>lengths and equal weight can have VERY different torque
>requirements.  Examples: 2L40 vs. 3L20 or 2L80 vs. 5L20.
>It should be a simple matter to determine rotor stall torque.
>Simply attach an arm (boom) to a mast and measure the
>force in a restraint applied perpendicular to the boom.
>Force X distance (from the mast) = torque.  If the imbalance
>is a problem, apply two restraints at each end of the boom
>and sum the forces.  Any Mechanical Engineer worth his
>salt should be able to make this determination.  

Don't you also need to add in maximum wind-induced torque, if you're
looking for a true worst case?

73,  Pete N4ZR

Don't forget to update your entry in the contest station database

FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm