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Re: [TowerTalk] Heights Towers Aluminum??

To: "W5LT" <W5LT@verizon.net>, <donovanf@starpower.net>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] Heights Towers Aluminum??
From: "Dennis Petrich" <radioart@charter.net>
Date: Thu, 14 Aug 2008 19:08:21 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Thanks Bob for taking the time to set us straight.  This info is timely 
because I'm interested in purchasing one of the HT soon.

Regrads,

Dennis, k0eoo


----- Original Message ----- 
From: "W5LT" <W5LT@verizon.net>
To: <donovanf@starpower.net>; <towertalk@contesting.com>
Sent: Thursday, August 14, 2008 6:33 PM
Subject: Re: [TowerTalk] Heights Towers Aluminum??


> There must have been more at work here than the marginal addition of some
> Heliax. I designed the fold-over mechanism for the Heights new tower 
> series
> a few years ago, in accordance with the Aluminum Association 
> Specifications
> and the Uniform Building Code, which include industry accepted design 
> safety
> margins.  I am assuming the tower that failed was one of the newer design
> (post 1995) units. The pre-1995 units were substantially over rated.
> The tower sections have two parameters: a moment rating and a shear 
> rating.
> Both must be considered in the tower design for wind and also the 
> tilt-over
> case. For a typical Yagi antenna and associated rotor & mast, the forces
> generated during fold-over are much less than (typically around 1/2) those
> that would be experienced during a rated wind load event. For example, my
> HTS tower is rated for 36 sq-ft projected area at 80 ft in my 70mph wind
> zone, which yields a wind pressure at the top of the tower of about 
> 700lbs.
> That force generates a shear force at the apex the top section of that
> magnitude, and a moment of 700 lbs x 8 ft = 2800 ft-lbs at the bottom of 
> the
> section. The top tower section must be chosen to carry those loads to the
> next lower section, in addition to the loads from the wind area (or
> self-weight) of the section itself. As the design progresses down the 
> tower,
> both the total moment and shear load grow and each tower section must be
> selected to carry both. The fold-over case loads are derived similarly.
> Analysis of the fold-over case for my tower shows that the shear and 
> moment
> loads are well balanced, that is, the actual load to the maximum design 
> load
> ratios are about equal for each section, and are less than half the
> corresponding section rating.
> It would be very unusual for a properly designed tower supporting its 
> rated
> wind load to fail in shear during the folding operation. The only way I 
> can
> think that could happen is that, as Frank suggests, the user added some 
> low
> wind resistance dead weight to the tower that exceeded the shear rating by 
> a
> significant margin. Perhaps a several hundred pound lead ball at the top?
> The engineering ratings of the Heights tower sections are provided on 
> their
> website, along with the methods to engineer you own tower configuration.
> 73s
> Bob, W5LT
>
> -----Original Message-----
> From: donovanf@starpower.net [mailto:donovanf@starpower.net]
> Sent: Thursday, August 14, 2008 9:11 AM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Heights Towers Aluminum??
>
> Don't forget that you must comply with the dead weight capacity of your
> tilt-over tower.  This is important, a nearby ham failed to comply with 
> the
> dead weight specification and his Heights fold-over tower collapsed as he
> tilted it up.  His mistake?  He forgot to count the weight of his Heliax
> feedlines!
>
> Everything you add to your tower must be counted against the dead weight
> specification, including all cables, masts, rotators and other 
> accessories.
> Give serious consideration to using an aluminum mast and light weight
> antennas, feedlines and control cables.
>
> Its especially important to minimize every pound of weight above the top 
> of
> the tower (i.e., mast and antennas and feedlines).  Every pound above the
> top of the tower adds very significantly to the moment on the lower tower
> sections and the tilting base.
>
> 73
> Frank
> W3LPL
>
> ---- Original message ----
>>Date: Thu, 14 Aug 2008 5:11:25 -0700
>>From: Dennis <radioart@charter.net>
>>Subject: Re: [TowerTalk] Heights Towers Aluminum??
>>To: W3OA <w3oa@roadrunner.com>, towertalk@contesting.com
>>
>>Thanks for taking the time to respond Dick.
>>
>>Very good input on some of the issues I would be faced with.   How do you
> rotate the antenna at 40' or is it stationaly?  Isn't there some kind of
> ring assembly for rotating antennas on the sides of towers?
>>
>>Thanks Dick, Dennis, k0eoo
>>
>>
>>---- W3OA <w3oa@roadrunner.com> wrote:
>>> Hi Dennis -
>>>
>>> I have a 60' Heights tower with a fold-over kit and 10 feet of mast out
>>> the top.
>>>
>>> It's been up for 5 years now and I'm very happy with it.
>>>
>>> You do need to watch how big an antenna you put on it.  If the antenna
>>> is too large you won't be able to lower the tower far enough to work on
>>> most of the antenna from the ground.  I suppose that's obvious but it's
>>> a trade I thought about for a long time before I decide to get a
>>> fold-over tower.  I ended up with two Force 12 C-4s, one at 40 feet and
>>> one at 70 feet.  I can reach the feed points using an 8 foot step 
>>> ladder.
>>>
>>> Another gotcha I found out through experience is that rotor brakes that
>>> hold an antenna just fine when the tower is up may not hold the antenna
>>> in position as the tower rotates down.  The antenna, of course, wants to
>>> rotate so its heavy end is pointed down and the break may not hold it in
>>> any other position.  This can be an even bigger problem with side
>>> mounted antennas.
>>>
>>> I'd do it again 'cause I don't want to climb a tower.
>>>
>>> Good Luck - Dick, W3OA
>>>
>>> Message: 6
>>> Date: Mon, 11 Aug 2008 20:46:23 -0500
>>> From: "Dennis Petrich" <radioart@charter.net>
>>> Subject: [TowerTalk] Heights Towers Aluminum??
>>> To: <towertalk@contesting.com>
>>> Message-ID: <A577548AEF344F668DEB831F901180B9@D5V7GZF1>
>>> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>>> reply-type=original
>>>
>>> Hello all who have aluminum towers.
>>>
>>> I am thinking of putting up the tilt-over self supporting aluminum tower
>>> from Heights Towers.  This one is 69' with the tilt-over kit and is 
>>> rated
> at
>>> 21sq' at 80mph. and will take a 12' mast.  I will be putting up 15sq' of
>>> antenna.
>>>
>>> Anyone of you have experence with such a thing??  The whole tower tilts
> over
>>> so you can work on the antenna from the ground, an idea I like very 
>>> much.
>
>>> You can see it on their web page.
>>> http://www.heightstowers.com/fold_over_kits.htm
>>>
>>> Thanks in advance for your comments
>>>
>>> Dennis, k0eoo
>>>
>>> >
>>>
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk mailing list
>>> TowerTalk@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
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