[TowerTalk] free-standing tower vert plomb accuracy

[Al Williams]

According to FirstCall, the rejuvenated triex towers are selling well.
Other new owners
are likely to also be interested  in the following two part question:

  1. How accurate should a free-standing towers vertical plomb be?

  2. How to measure the vertical plomb?

(The motorized SKY470/LM470) does not have levelling nuts for adjusting the
towers' vertical plomb for leveling the tower.  The base fixture must be
levelled before the concrete sets.  The suggested method is to use a level
set on top of the three base mounting plate ears and move the base fixture
until level in all three directions between the three plate ears.  The
distance between mounting plate ears is 24 inches.)

I believe that with care, I can easily detect an error of .03 inch in 24
inches using an aluminum bubble vial level.  (I shimmed one end of the level
and measured the shim with a dial caliper.  Then turned the level
end-for-end to verifyy the accuracy of the level.)  If my calculations are
correct, this translates to 1.275 inches at the top of the 70' tower with
15' of mast extending.

Unknown is the tower mfr's vertical plomb inaccuracy of the mounting holes
and the tower legs themselves.

The stress analysis that I have reviewed (I am not a mech or civil engineer)
do not make any reference to the vertical plomb requirement.  My "feeling"
is that the tower rated at 15 sq ft at 70' height for  80mph wind can
withstand considerably more vertical plomb deviation than 1.275 inch--but
how much?????

k7puc




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