At 09:21 AM 1/12/2006, Jim Rhodes wrote:
>I am with the others. Is there a reason that you could not use a ring rotor
>or swing arm? A whole lot less engineering there. Is this thing tapered all
>the way up or is it an SSV type tower that has less taper the higher you
>go? I have seen installations that used a long mast section going through 2
>sections with a bearing plate between and a BIG rotator at the bottom of
>the mast. But with a tapered tower that could be a real challenge. And you
>need a BIG, STRONG mast to do it with for any real capacity. Rotating the
>whole tower would take a whole lot of steel to hold the thing down. I don't
>think it would be financially feasible to do it that way.
>
>If you decide to go through with it please keep us posted on the project &
>what you decide. We all like to learn from others experience.
>
>At 05:03 AM 1/12/2006, David J Windisch wrote:
>
> >Other peoples' ideas on mechanical arrangements for making all or part of a
> >96-ft self-supporting three-legged tower, 28ft-sqd at 80MPH, rotate, are
> >what I'm interested in reading.
There's a long and interesting history of the "rotate the entire
structure". Many early radio telescopes worked this way (like ones built
by the likes of Penzias, Reber, and Krauss)
The key is in resisting the up force on the upwind leg. One way is just
with sheer mass (the railroad wheel on a track approach). The other is
with a track that holds both up and down (think of roller
coasters). Just for grins, what sorts of forces are we talking about:
80 mi/hr is 80*80/391 lb/sf wind force, or, about 16.5 lb/sf. For your 28
sf antenna, I'll round up to 20 lb/sf and 30 sf for 600 lbs. You said the
tower is roughly 100ft high, so you've got a moment of 60,000 lbft. Let's
say the wind load on the tower itself is the same, for 120,000 lb ft total
moment. say your tower is 6 ft on a side at the base, so you'll have an
upforce of 20,000 lbs on the upwind side and a downforce of 20,000 lbs on
the downwind side. You'll need some moderately hefty wheels and bearings,
eh? No skateboard wheels here, you can see why the "railroad wheel on
rails" is the scheme of choice.
By the way, there's an interesting calculation of loads on the Eiffel tower
(which is about 10 times taller) at:
http://www.ce.jhu.edu/perspectives/studies/Eiffel%20Tower%20Files/ET_Internal%20Forces.htm
It's left as an exercise for the reader of this post to figure out how to
support and rotate the Eiffel tower (which weighs a mere 22 million
pounds). Come on folks... in comparison, the 6 stack of SteppIRs is
feeble. You *need* that 6 stack of 160m beams.
Jim...
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