Kyle,
The standard MA550 comes complete with a house bracket, but is still only
rated for 10 sq. ft. @50 MPH, and you are right about the derating to 2.7
sq. ft. @70MPH. I'm not a PE, but I doubt that adding another bracket at the
20-foot level would increase the overall tower windload rating. While it
might make a failure at the concrete base or along the lowest section less
likely, it will not do anything to keep the two upper sections from
buckling. True, there's less bending force against those sections, but
they're still subject to failure.
I use an MA770MDP with a TH7. That's 9.5 sq. ft. wind load. Like the MA-770,
the freestanding MA770MDP is only rated for 10 sq. ft. at 50 MPH and derates
in a similar fashion at higher wind speeds. What do I do? I keep the tower
cranked down to about 50 ft. (where the TH7 works fine) unless I'm chasing a
rare one or contesting. I never leave the tower full up unattended or when
the wind gets above 20 MPH. If I'm away overnight, or if the wind gets much
past 25 MPH, I lower the tower all the way (full down, it would take a
hurricane to knock it over.)
I believe the Tri-Ex 70' SkyNeedle is rated considerably higher than the
U.S. Tower, but it's on the order of $10,000.
With a $2,000 budget, you can buy an MA550, bracket it to the house, and
keep it cranked down in high winds or when not in use. However, you will
quickly find that hand-cranking that tower frequently is a huge chore and
hard on the arm. If you can spring for more money, get the motorized
version.
73, Dick, WC1M
-----Original Message-----
From: Sandel, Kyle W <SandelKW@bp.com>
To: 'towertalk@contesting.com' <towertalk@contesting.com>
To: <towertalk@contesting.com>
Date: Sunday, April 05, 1998 2:41 PM
Subject: [TowerTalk] Low Visibility Installation
>We're leaving Alaska for Ohio in the next 60 days. Despite my "best laid
>plans" we purchased a home in a subdivision with CC&Rs. I'm still
optimistic
>that I can put up a tribander but my strategy will include a presentation
to
>the architectural review committee showing a very low impact
>installation--Force 12 C3S and a tubular crank up limited to 60 feet.
>
>One problem is finding the tubular crank up with a wind load rating of 4.9
>to meet the 70mph standard in OH. The US Tower's MA550 is advertised at 10
>sq ft at 50mph rating but drops to 2.7 at 70mph. Otherwise this is a
>satisfactory product.
>
>Here are my questions:
>
>1. Any experience with someone modifying the MA550 or like tower to meet
the
>needed windspeed spec either by reinforcement or house bracketing? US Tower
>just says "talk to a PE" which is, of course, the technically correct
answer
>and I've purchased the plans but I'm not planning on buying their tower or
>engaging a PE if the consensus is that there's no hope of this working. The
>new home is a two story so a bracket at 18 to 20 feet should be no problem.
>
>2. Any suggestions for other tubular-type towers that might get the desired
>result with a reasonable budget, say less than $2,000?
>
>3. I need a photo of a low visibility installation to show the
architectural
>committee. This is the opposite of the usual gigantic tower silhouetted
>against the sky. More like a really small tribander on a light tower backed
>by trees with a really big house underneath it.
>
>4. Can I get email addresses from the folks who've been on the reflector
>recently with their success stories about beating the P&Z boards using well
>documented public service, testimonials etc? I'll pay for copying and
>mailing of same.
>
>Thanks to all
>
> 73 Kyle AL7J
>
>--
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