Thanks Chuck for the details. From your description the destruction
was initiated by a guy failure, possibly the guy sawing through the
tower leg. As Jim notes, the use of a proper guy bracket with a
suitably strong and tensioned guy would have saved the tower. BTW
my Delhi towers are guyed using the Delhi bracket, thimble and all,
and my rotors are mounted 10 or so feet below the top of the tower.
For years I thought about using torque arms, dithered, and found that
with properly tensioned guys I did not need torque arms. Yes I can
push the antenna boom and watch the tower twist below me, but it only
twists as far as the tensioned guys allow. We learn from our own
and others experiences.
Doug/VA5DX
Jim Jarvis wrote:
> Clearly, sheer winds from downbursts at leading edge
> of Tstorms can be catastrophic, and Chuck's tower was
> overloaded. BUT...
>
> If the guys had been connected using a triangular bracket,
> such as Rohn uses for mounting their torque arms on 25g,
> and if there had been torque arms, along with the torque
> tube to the low-mounted rotor...it's possible the stick would
> have survived.
>
> As I reflect on the one hbdx48 I saw fail, it related to the
> guys being looped around the legs. Compressed leg structure
> and no resistance to torque loading crumpled the section.
>
> Ignoring, for the moment, the prime maxim of "following the
> mfr instructions", I think this tower is viable for moderate
> arrays, if the torque load is moved off the upper sections.
Chuck Sudds wrote:
> Everything was put up and it appeared that this tower was going to do
> the job A-OK. Just to be sure that there would be little or no
> twisting, I installed three aircraft cable guys at about 46ft where the
> rotor would have normally mounted. I simply looped the cable around
> each leg and guyed the ends to existing structures on my property.
>
> The following May, we were hit with 100MPH straight-line winds which
> actually blew some rail cars off the tracks in this area! I knew they
> were coming by listening to the local weather spotters net but could do
> nothing but point the beam(s) into the wind. They hit the tower with so
> much force that the aircraft cable guys literally cut right through the
> legs of the HDBX48 metal on one leg! This caused the tower to actually
> fold over at the 6ft level, right where the new rotor plate was
> mounted! Had I mounted right at ground level, there is a chance, I
> guess, that it just might have survived ;)
> Chuck KØTVD
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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