[TowerTalk] DANGER...RE: HDBX series of towers!!

[Guy L. Olinger]

I wonder if Rohn deliberately designed this weak so that it would break
before the twisting moment took down the tower?

73, Guy.

wbh3@chrysler.com wrote:
> 
> There have been a number of comments regarding the HDBX series of
> towers, especiallyt the HDBX-48 which I used to own and just sold.
> Many of the comments relate to the lack of any specifications from Rohn
> except  (and I quote)  from Rohn:
> 
> "Antenna types for HDBX should be limited to those having a maximum
> boom length of 10 feet.  No engineering data relating to the use of
> boom lengths in excess of 10 feet is available and the use of such boom
> lengths is not recommended."
> They go further to say:  "All towers are recommended to be bracketed
> for extra safety and to withstand gusty wind conditions."
> 
> The HDBX is also specified to have an 18 sq. ft.  capacity.
> 
> I installed a CDR rotator and KLM KT-34XA  (30 foot boom) about 2 feet
> above the top of the tower and the thrust bearing using the top plate
> and rotor plate supplied by Rohn.  The thickness (or maybe I should say
> thin-ness) of these two plates made me somewhat concerned at the time
> but I put it out of my mind.  Also, the fact that the attachement
> points on both plates were bent down did not cause me any concern.
> 
> All in all, the tower was fantastic.  I have been up on it in some
> pretty strong winds and,  although  I regretfully present a rather
> large windload  ( due to too many cold 807's), the tower with me at the
> top did not budge that I could tell.   There  has been twice when my
> finger has slipped off the rotator control unit thus bringing  the
> antenna  (and rotator) to an unplanned and fatally  fast stop, plus the
> antenna did swing in an arc of about 5 to 10 degrees in the wind
> (rotator slop).
> 
> All of this is leading up to the fact that  when I sold my tower, the
> gentleman who bought it called me up a couple weeks later and advised
> me that two of the tabs that secured the rotor plate to the tower legs
> had sheared in half and there was only 1 tab holding the rotor plate to
> the tower (along with the upper tower plate where the thrust bearing
> was mounted).    I think you all can fill in the rest of the scenario,
> i.e., plate fails, antenna windmills, coax wraps around tower, etc.
> 
> 6 May 98
> 
> Well, I just saw Steve's (K7LXC)  comments regarding stress failure of
> the rotor plate and top plate.  Also of note is David  Bunte, K9FN's
> thread from 2 May  98, subject HDBX towers relating to same problem.
> These cheap, crummy, #$@*&&# plates are less than 1/16 th.  inch thick
> .  I should have had my head examined for not replacing them from the
> start, but then I am new to towers.  Maybe that is why Rohn won't
> specify anything but the minimum for the tower.  It is hard to believe
> that a company with Rohn's reputation would allow something this poorly
> designed to be put on the market.  I don't care if you use even their
> 10 foot boom, the looseness in the rotor itself will let the antenna
> swing back and forth and fatigue th metal.  Even if you only have up a
> TV antenna, if you should accidentally let your fingers slip off the
> rotator switch and let everything come to a screeching halt (which I
> have done) you will eventually stresss the plates.
> 
> Steve:  Wish I had seen a thread something like  this 5 years ago!!!
> 
> Bill Haselmire - WX8S
> bg@tir.com
> 
> --
> FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
> Submissions:              towertalk@contesting.com
> Administrative requests:  towertalk-REQUEST@contesting.com
> Problems:                 owner-towertalk@contesting.com
> Search:                   http://www.contesting.com/km9p/search.htm

-- 
Guy L. Olinger
Apex, NC, USA
k2av@qsl.net

'AV since '74, previously K4VDL, K3FKJ, W2HVA.
(Remember those? Get in touch!)

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm