[TowerTalk] Adding Expanding Foam inside boom

[Charles Gallo]

On Thu, April 26, 2018 9:20 am, Bob Shohet, KQ2M wrote:
> I would also expect that the rate and quality of the “curing” would be
> impacted by the ambient temperatures and humidity levels/climate at a
> given location.  In much of New England the temperature can easily vary
> by more than 120 degrees in the course of a year – and significantly more
> in the great plains states.  And the climate can very enormously from the
> generally wet/humid East to the desert SW. This has to have an impact.
>
> 73
>
>
> Bob  KQ2M

Of course there are foams (2 part) that mix on spray, and don't require
water vapor to cure

That said, what is the problem you are trying to solve?  Usually foams are
used to stop vibration/change resonance frequency.  Here is the question
(and I don't know the answer) - how often do we see fatigue
cracking/failure on the BOOM of an antenna?  Not the elements - heck, they
crack on some, but I don't think I've heard of booms failing except during
extreme events like ice/wind storms.

The foam might not give you ANY extra strength, and even you look at
strength/weight, I'm going to guess it'll be a net negative.  Now if you
know your boom has a vibration problem, we are talking another story. 
Even then, there are probably better ways to make the boom stiffer (put an
end cap on both ends, attach a cable that runs inside the boom from end
cap to end cap, and come up with a way to tension the cable - aka put the
boom under compression, or put a metal ROD in, and put the boom under
tension - both will change resonance)

The material that interests me.  I've heard that they make tube that is
similar to ACM sheet - basically a pair of Al tubes, with a composite in
between (ACM siding is polystyrene or similar)

I'm wondering if these materials might be the way to go in new designs -
they are about 90% as strong, but also less than half the weight.  I
wonder if we could go to some of the carbon fiber/aluminum composite
tubes, and get MORE strength, for LESS weight (for the same size), or
downsize, to go SAME strength, but less area and load.. (of course at
greater expense)