[TowerTalk] Adding Expanding Foam inside boom
grants2 at pacbell.net
Wed Apr 25 23:48:32 EDT 2018
I don't think there is any magic.
The mechanical properties of household construction foam can't add much
strength or dampening at frequencies that might matter.
Then it has to stick permanently onto the id and have sufficient
strength to not shear from bending.
And not absorb moisture, ever or degrade from heat/cold cycling. And
weigh very little.
Sounds to me like a project for Boeing Research.
Internal sleeving is the way to strengthen elements/booms as Leeson
points out in his book. No more wind resistance and the mechanical
properties are the same as the thicker wall solid tube. He also
advocates triple boom guys (one above, two down to a spreader) to
prevent uplift failures which for ridge/hill top locations such as his
QTH are a real problem.
Coupled structural resonances are numerous in tower + yagi structures,
but that is not addressed by any ham radio treatise I've read. Modeling
same would be prohibitively complex. Aluminum has no fatigue infinite
life threshold as does steel, so it is possible for elements to
eventually break from fatigue at low stress levels and many cycles. The
limit of cycles vs stress is in charts for many aluminum alloys/heat
treats. That happened to a vertical I had that vibrated strongly.
Telrex put polypro rope inside TH7DX element ends to absorb vibration
energy, presumably elements were subject to fatigue. A simple, durable,
& cheap fix if you have a such a problem .
On 4/25/2018 19:49 PM, Charles Morrison wrote:
> Has anyone tried this ?
> Can it improve survivability of very large yagis?
> It won’t prevent a boom failure, but could it help last a little longer?
> -Charlie N1RR
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> TowerTalk at contesting.com
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