Thanks, Jerry. A lot of buckshot in that one shell ! I had discussed
with my local friend the notion of putting a wooden dowel through
the tubing, and you give a fine exegesis for why that is a better plan.
Another idea that struck me this evening, is to double up the tubing
for the originally planned dipole, and make it into a single element
vertical made from double tubing - and then add wire radials that can
also play as light weight guy wire-rope supports.
HOWEVER... I tried there this afternoon, and it makes
the element way too heavy and it still sags a bit, so
doubling the tubing is not the solution, either.
The wife and I looked at fiberglass crappie poles today,
and we are thinking the Spiderbeam poles are now
the leading contender.
Yes... the expanding foam might work to _slightly_ dampen vibration
(the way Hy-Gain runs a rope inside some of its yagi beam elements to
dampen vibration.) But you and Rick both explain how it won't do enough
for the rigidity and support I am looking for.
Oh well... one more idea on the scrap heap ! I am, however, having
great fun working this out.
Thanks for the gloss on tubular engineering. As they used to say in
the 1980s.... "Totally tubular, man..." ;-)
=============== James -K8JHR ========================
On 1/8/2011 7:29 PM, Dr. Gerald N. Johnson wrote:
> were it bends (and sometimes breaks). Column load is more complex but
> bending is a part of failure if it doesn't buckle. Wood inserts help
> slow buckling too. I'm not so much a fan of foam, I don't think its
> strong enough in the tube to keep the tube round and full diameter,
> though foam faced with very thin metal shows a lot of strength, I think
> that structural foam is a lot more dense than foam in place out of a can.
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