[Towertalk] Re: Help! Heavy Wind Batters Beam and Rotor

[K7LXC@aol.com]

In a message dated 4/22/02 9:54:43 PM Pacific Daylight Time, 
jsbmjb@theriver.com writes:

> I have a Force 12 C-36XR beam (36' boom, 108 lbs, 13.8 sq ft, 120 in-lbs
>  torque) mounted on a Tail Twister rotor with 5' of 2" chrome-molly mast
>  in Santa Cruz County Arizona (75 mph winds).  I'm located on top of a
>  hill and have days and days of 25 -35 mph winds.  So the antenna and
>  rotor are pounded with 12 - 16 hours of wind a day for 100 or more days
>  a year.
>  
>  The first failure and I hope the last, was all the bolts holding the
>  rotor to the rotor plate loosened and fell out.  The beam and rotor have
>  been removed from the tower and are on the ground.
>  
>  What changes do you recommend before I return them to the top of the
>  tower?  I would rather spend my time operating than tower climbing and
>  repairing my antenna and rotor.
>  
Hi, John --

    Well, the problem with the rotator base bolts isn't common but does 
happen as you've observed. Something M2 does is use aircraft-type bolts with 
drilled holes in the head so that they can be safety-wired. The T2X bolts are 
real common (the M2 ones are fine threaded) so you should be able to get them 
from an aircraft parts supplier. Check the yellow pages or do an internet 
search for sources. There are a couple of airplane owners on TT who can 
probably help you with this. Or you can drill them yourself. 

    You could probably use some LokTite on the threads - that'll discourage 
them from loosening. I think it's the blue version that will allow them to be 
removed at some point. There's another color that WON'T so be sure to ask the 
salesperson for the right one. Available at any auto parts store. 

    I'd also encourage you to do an inspection at least once a year - in your 
case maybe more. That way you'll catch something before it becomes a problem. 

    In the case of the F12 antenna, I'd put another row of rivets opposite 
the existing ones on the elements to really lock down the element joints. 
With just one row of rivets, the elements have been known to work loose in 
windy environs. Adding a third row so the rows are 120 degrees apart wouldn't 
hurt if you're a little ambitious. 

    Also adding a couple of bolts thru the boom-to-element clamps is highly 
recommended as well if they don't already have them. That's another place 
where the rivets have been known to work loose. 

    With that big antenna you get big stresses on the boom-to-mast clamp. In 
the last 2 months I've seen two that were just ripped apart - both were 
installations on ridge tops. You may want to add another plate (so the total 
one is thicker than stock). If the antenna isn't twisting around the mast 
now, then it probably won't in the future. But beefing up the mast bracket 
will eliminate that potential problem. 

    Other than that, you should be good to go. 

Cheers,
Steve     K7LXC
TOWER TECH -
Professional tower services for industry and amateurs