> Greetings,
>
> Perhaps I am wrong, but the whole idea of wind load on a rotator seems to
> be a misnomer. The only time that spec
> would be valid is for side load, not torque, and side load only counts if
> the rotator is outside of the tower. Wind load
> will entirely depend on the antenna design and how uneven the wind area is
> on either side of the mast which will
> produce the torque. If the antenna had 10 ft^2 on either side of the mast
> then the torque is 0 yet the wind rating
Even then it won't be zero as the antenna will tend to oscillate and that
will produce tremendous torque for short periods.
> would be 20 ft^2. I know I am simplifying things but torque ratings
> should be just that... measured in inch pounds or
> the like. If you want to compare rotators, then look for torque values,
> not wind load.
As far as I know the worm gear rotators are rated in inch pounds of torque
for holding and turning.
I need to get up the tower and pull the big rotator tomorrow. I'd rather go
play while the weather is nice, but then again I need to do the tower work
while the weather is nice and pulling the rotator is a *lot* of work
particularly as I need to let the antennas down for maintenance which takes
a climb that lasts most of the day.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com
>
> My two cents.... 73
>
> Rob VE6TR
>
>
>
>
>
> On Mon, 12 Jun 2006 18:11:14 -0700, Al Williams wrote:
>
>>Not only is it that the M2 rating of 35 sq feet is meaningless, also the
>>rotational torque inertia may even be more important!
>>See my previous posting on 4/28/06 at 9:08 am. There have been no
>>responses
>>to that previous concern.
>>
>>k7puc
>>
>>
>>----- Original Message -----
>>From: "Mike Harris" <mike.harris@horizon.co.fk>
>>To: "Al Williams" <alwilliams@olywa.net>; "Tower Talk"
>><towertalk@contesting.com>
>>Sent: Monday, June 12, 2006 5:27 PM
>>Subject: Re: [TowerTalk] Rotator Questions
>>
>>
>>> G'day,
>>>
>>>
>>> | The M2 2800 rating of 35 sq feet is comparable to my own rating of 400
>>> sq
>>> | feet (on an absolute calm day!). Without a specified wind speed the
>>> rating
>>> | is meaningless?
>>>
>>> An interesting point. Maybe there is someone out there who can offer
>>> clarification on this.
>>>
>>> I found the windloading of the Optibeam OB9-5 somewhat confusing:
>>>
>>> Windload at 130km/h 578N / 0.72m sq / 7.8 ft sq
>>>
>>> I received the following from Thomas at OB:
>>>
>>> <quote>
>>> on our web site you should find all the data which are usual, i.e. m2,
>>> feet2 and Newton.
>>> And we always calculate it at 130 km/h.
>>> So the windload on the 9-5 is 578 Newton = 0.72square meters = 7.8
>>> square
>>> feet.
>>>
>>> I am not doing the calculation, a friend of mine has written a program
>>> which is doing the work.
>>> The program checks what is the bigger wind resistance, the boom or the
>>> elements when pointing into the wind with the maximum surface.
>>> <unquote>
>>>
>>> From this I assume that the antenna at some angle to the wind has a
>>> maximum surface area of 7.8 ft sq and at 130km/h offers a windload of
>>> 578
>>> Newton.
>>>
>>> Maybe someone can comment upon this interpretation as well.
>>>
>>> My heavy duty 12 metre crank up/fold over tower has an unguyed and
>>> extended "area of headload" rating for "tubular aerials" at 130km/h
>>> (80mph) of 24.5 ft sq. At 100mph 14.4ft sq and 120mph 8.7ft sq. 80mph
>>> winds would be very unusual here and higher speeds even more so, an
>>> OB9-5
>>> on a PST61D on my tower should be pretty solid, even taking into account
>>> the wind area of the rotator and mast.
>>>
>>> We had a blow a couple of weeks ago that was 55kt sustained peaking 75kt
>>> that caused a little damage around town. My 6ft sq log and rotary 20m
>>> dipole above didn't complain. I couldn't telescope the tower if I
>>> wanted
>>> to 'cos the wind pressure stopped the top section from lowering under
>>> gravity. A pull down rope would seem useful in extreme circumstances.
>>>
>>> Regards,
>>>
>>> Mike VP8NO
>>>
>>
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>
>
>
>
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>
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