All,
I appologize if this has appeared before. But I can't see it
getting through the reflector here. We had network problems at
the time I first tried to send it. So i'm unconvinced that it is
getting out of house yet.
Eric
Hi pete,
I think you're probably OK from a mass times turning radius
standpoint (inertial moment).
1. The turning radius for the mast mass is one inch minus half
the wall thickness.
2. The material that comprises the Yagis is not uniformly
distributed around the center of rotation. It is (usually)
slightly concentrated towards the middle of the assembly. So
to use _half_ of the turning radius times the mass of the
antenna is slightly conservative (in most cases - probably
should check for the particular antennas).
However, that isn't the whole story. If the wind is blowing,
there are other significant forces to overcome. The magnitude of
these is entirely dependent on the particulars of the antennas
and how they are mounted to the mast. You might want to ask the
manufacturer what is the maximum torque applied to the mast for
some maximum wind speed (above which you won't be trying to turn
the assembly) for the antennas you have. If you can't get the
information out of the manufacturer, first let us know here on
the reflector, and then if you are sufficiently concerned, you
may want to computer model the mechanical assembly to see what
you may be in for.
If the manufacturer can't tell you this value, then how can we
believe anything else he says about the wind speed survivability
or effective wind cross section values for the antenna? The
manufacturer really should be able to specify the worst case
orientation and a torque for some particular value of wind speed.
If they can't or won't, I would have to be asking myself "What is
it that they don't know that would prevent them from being able
to provide this information?".
73, Eric N7CL
>From: brunet@us.ibm.com
To: <towertalk@contesting.com>
>Date: Wed, 1 Sep 1999 13:28:00 -0500
>
>It looks like the T2X can't handle a C31XR and a EF240X. The
>torque spec on the T2X is 3400 ft lbs (weight x turning radius).
>The turning radius of the EF240X is 25.1' the weight of the two
>antennas is 120 lbs and a 20' chrome moly is about 140 lbs for a
>torque of 25.1 x 260 = 6526 ft-lbs. Is this correct logic?
>
>Thanks, Pete
>
>=====
>Pete Brunet -- IBM Special Needs Systems, 11400 Burnet Road, MS 9171, Austin,
>TX
>78758
>(512) 838-4594 voice, (512) 838-2212 fax, brunet@us.ibm.com, ws4g
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