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[TowerTalk] The Moment of Truth

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Subject: [TowerTalk] The Moment of Truth
From: (Stan Griffiths)
Date: Wed, 25 Jun 1997 12:19:42 -0700 (PDT)
>The Moment of Truth has arrived...
>If you're a regular, you saw my earlier posts about the tower project I am
>planning. To summarize in 25 words or less: It must be 70' tall, it must be
>a freestanding crankup (tubular strongly preferred for appearance), it must
>be motorized with remote control, and it must not fall over! (OK, that took
>28 words...)

Hi Dick,

I think the answer for you is to go back to your original "summary plan" of
25 words or less.  If you delete the last three words ("not fall over"),
then I think you have a workable plan.  It's that last requirement (it's not
supposed to fall over) that is a real killer.  Seriously, though . . .

>The only companies seriously in the running are U.S. Towers and Tri-ex. To
>my great disappointment, I have learned a thing or two on this reflector
>about windload specs and tower manufacturers. To summarize, although U.S.
>Towers advertises that their tubulars will handle 10 sq. ft. of antenna
>wind load at 50 MPH, their engineering specs clearly show it dropping to
>1.6 sq. ft. at 70 MPH! Sounds to me like the tower is virtually guaranteed
>to collapse at windspeeds over 50 MPH with any commercial tribander on the

Wonder what it would do at 90 mph and NO antenna on it . . .

>OK, so get one of their triangulars or one of the Tri-ex models. Once
>again, U.S. Towers specs their triangulars for 50 MPH. I don't have the
>engineering package in hand, but I shudder to think what it shows. On the
>other hand, the only reports I got of towers collapsing, and there were
>several, were from Tri-ex LM-470 owners. Yeah, they might spec the towers
>for 70 MPH, but why did I hear about so many collapsing when I got *no*
>reports of such from U.S. Towers tubular owners (who, like their Tri-ex
>counterparts, have a strong tendency to overload their towers, making my
>plans look tame by comparison)?

I wouldn't take much comfort in not hearing anyone confess to you that they
made a bad decision about the tower they bought.  Most people I know who
screw up big time don't like to talk about it much.  There are many more
failures out there than you will EVER hear about . . .

>So! My conclusion is: If you're going to own a crankup, it's got to come
>down when the wind starts a blowin'. No problem! I can whip up a wind speed
>alarm and maybe even an automatic lowering circuit (seems like all the
>Tri-ex owners are doing that.)

You should definitely have a "positive pull-down" feature on any crankup
that you intend to lower with even a few mph of wind present.  Automatic,
unattended, crank-down schemes really scare me.  I keep having visions of
the neighbor's kid standing inside the tower as it comes down . . . Of
course, this if for a lattice tower and not a tubular.

 It might even be possible to keep operating
>in gusty conditions if I lower the tower to 50' (more section overlap
>should result in greater structural strength, right? -- Does anyone know
>how much more?)

I have never seen anyone do any real estimates on this, although it stands
to reason that as you lower it, the whole system gets stronger and has less
stress on it.

>Thanks for putting up with all my questions --- I really am a worrier!

I would say "justifiably concerned" . . .

>again, yesterday we had a sudden freak storm that bent some of the tall
>trees on my property almost in half (an apple tree with a 4.5 inch trunk
>got sheared off right at the ground level.)

For those guys who tell you their tower has been up with no problems for 5
years, how long did the apple tree stand there without a problem . . . ?

>$7,000+ is a lot of money to
>fall over in a scrap heap when something like that happens (more like
>$9,000 if the beam and rotator get creamed...)

You can always earn more money to replace a crashed tower.  It is the
possibility of seriously injuring another person that worries me the most.

Good luck, Dick, with this project.  Above all, make it SAFE.


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