[TowerTalk] Fwd: Tower Permitting Spec's
wes_n7ws at triconet.org
Tue May 1 15:28:42 EDT 2018
I had a vertical for 40-meters using a Cushcraft AV-80 for aluminum stock. This
had a fiberglass rod at the bottom for an insulator, a heavy wall bottom section
and several sections of 2" OD aluminum tubing with swagged ends telescoped
together. I believe it was originally claimed to be self-supporting but I
decided to guy it to reduce sway.
So I installed one set of rope guys approximately halfway up. In the lightest
of breezes I noted some vibration but stupidly ignored it. One morning I looked
out from the house and the whole top above the guys was gone. Closer inspection
revealed that it had partially fractured and had actually folded over on itself
as if it was hinged.
On 5/1/2018 9:10 AM, Richard (Rick) Karlquist wrote:
> When I built my first 90 foot vertical, I made the whole
> thing out of three 30 foot pieces of 4 inch OD aluminum
> irrigation tubing/pipe, guyed at the joints at 30 and
> 60 feet as well as at the top. I didn't know any better.
> It shimmied like crazy in the slightest wind. I
> eventually evolved the design to 30 feet of 4 inch,
> 30 feet of 3 inch 30 feet of 2 inch, again guyed at
> 30, 60 and 90 feet. It didn't shimmy because it was tapered.
> It would survive really bad storms,
> only to have the top section buckle 6 months later
> in no particularly high wind. I repaired it, and the
> same thing happened again. Again, I repaired it, and
> again, same problem. Turns out it was
> the dreaded aluminum fatigue. The fix was to add guying
> at the 75 foot level, in the center of the 2 inch section.
> Never had a failure since.
> Rick N6RK
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> TowerTalk at contesting.com
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