[TowerTalk] Am I asking for trouble? - tower loading

[Jerrry BOYD]

Let me share a story from about 20 years ago.  I had a UST crank up, HDX 555, with a 20 ft moly steel mast and a tail twister.  Th7DXX and a 2 element shorty forty on top.  Well below the 30 sq ft @ 50MPH rating of the tower.  This was in a southern CA coastal city where we generally did not get huge winds.

I was at work, only 4 blocks from home, when a storm blew in with gale force winds (peak gusts of 65 mph). One of my sons (a ham) was at home and called me to say that the tower and yagis were swaying side to side and he thought it was going to bend.  Rushed home and attempted to crank down the tower....unable to do so due to lateral forces of the wind.  Storm finally blew through.  The tower was actually bent to the point that it would NOT retract.  A fairly expensive crane got it down and the tower was tweaked enough that it was unusable.  A local engineer (also a ham) "speculated" that if the tower had been equipped with a motorized pull down system I might have been able to retract it in the wind but gravity didn't work because the sections bound on each other.

I WOULD NOT push the envelope unless I had (and I know several who have done this) a motorized pull down system linked to a wind speed detector that would automatically cause the retraction to occur if I were not home to manually activate it.  Even that is not fool proof because if there is a power failure the MPD won't work.
Jerry
N7WR 
  ----- Original Message ----- 
  From: john at kk9a.com<mailto:john at kk9a.com> 
  To: TOWERTALK at contesting.com<mailto:TOWERTALK at contesting.com> 
  Cc: jknodel at msn.com<mailto:jknodel at msn.com> 
  Sent: Sunday, October 15, 2006 5:49 PM
  Subject: [TowerTalk] Am I asking for trouble? - tower loading


  Why is this your only option.   You didn't say which UST model you are
  considering, so I will assume that it is the heaviest one in their catalog.
  Perhaps they or another crankup tower company can make a heavier one for
  you.  If not certainly AN Wireless, Rohn, Glen Martin, etc make very strong
  self supporting towers.  Sooner or later you will mistakenly leave the tower
  up or have it get stuck during a strong wind.  I'm not sure how much safety
  margin there is in the US Towers design or what will happen if it fails, is
  this a risk that you wish to take?

  John KK9A

  To: towertalk at contesting.com<mailto:towertalk at contesting.com>
  Subject: [TowerTalk] Am I asking for trouble? - tower loading
  From: "jknodel M Knodel"
  Date: Sun, 15 Oct 2006 10:57:46 -0700


  I would like to get everyone's opinion on this -

  I am planning on installing a US Towers crankup tower. These towers are
  rated for windloads at 50mph and 70mph. I want to stack 2 beams on the
  tower. These 2 antennas would exceed the tower's windload rating at 70mph
  but would be well within the rating for 50mph. I plan to install a wind
  speed meter and deligently crank down the tower every time the wind exceeds
  50mph.

  I cannot install a guyed tower at this location so this is my only option.
  The crankup with these antennas and cranking it down in winds over 50mph is
  my plan. Am I asking for trouble in doing this?? Thanks.

  _______________________________________________



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