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## [TowerTalk] kt34xa torque balancing

 To: [TowerTalk] kt34xa torque balancing "Jim Jarvis" jimjarvis@ieee.org Sat, 8 Jan 2005 11:34:57 -0500
 ``` TT: I would recommend a trimtab which clamped around the boom, and permits it to be slid in or out, to fine-tune the solution. I did this with an XA 15 years ago, have long since lost the calculations, and don't have the manual, so won't share dimensions. The XA was mounted on a house-mounted wilson tubular mast. In gusts, with the tower nested down, it tended to rotate toward the back of the beam, causing the tower sections to rotate within themselves, until they hit the stop. Screech...bang. As this tower was firmly tied to the frame of my house outside our bedroom, sleep was difficult on windy nights. Here's a method of estimating the size of the trimtab: The manufacturer specifies 10 sq. ft. as the windload area for the antenna. The Boom... 32' x 3", accounts for 8 sq. ft. The mast to boom bracket adds about another half foot to that. (partly obscured by the boom, and 10.5" on a side).... So, the elements present around 1.5 sq. ft. to the total windload. Not much. I assumed that all trapped elements were identical, for purposes of windload, and I assigned them an exposed area of 1 ft ^2. (wrong..but maybe not TOO wrong). Then, I estimated the 10m director area had half as much drag as the trapped ones. (wrong, but maybe not too wrong.) >From there, it's a sum-of-moments problem. For each of the elements, multiply the offset from the mast x the estimated exposed area. (One end of the antenna has to be negative, obviously. Doesn't matter which.) Then simply sum it up, and figure out how big a trimtab you'll need, at what distance. The closer in it is, the bigger it has to be, obviously. (The boom-offset is probably not material... the center of mass vs. geometric center of boom is offset by 20". 20" x 3" = 60sq. in., so a 1 sq in. tab, 5' from the mast would balance this out. If that tab were located 15' out from the mast, I'd only need .3" sq. It's lost in the estimation errors.) I won't tell you the dimensions of my trimtab, except to say that it was less than 1 sq. ft. (consider.. 1 sq. ft. @ 15' from the mast would produce 15 ft. lbs torque...the problem isn't that big!) I leave it to you to calculate the ft. lbs and therefore area required. In my case, I cut it once, put it at 15', and the tower stopped screeching. It still moved a little in big gusts...but I could sleep at night! Never bothered sliding it in-out to perfect the solution, even though I could lower the tower and walk on the roof to do the job. N2EA jimjarvis@ieee.org _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] kt34xa torque balancing, Jim Jarvis <= Re: [TowerTalk] kt34xa torque balancing, W0UN -- John Brosnahan [TowerTalk] Torque balancing made easy, was kt34xa torque balancing, K8RI on Tower Talk Re: [TowerTalk] Torque balancing made easy, was kt34xatorque balancing, W0UN -- John Brosnahan Re: [TowerTalk] Torque balancing made easy,was kt34xatorque balancing, K8RI on Tower Talk Re: [TowerTalk] Torque balancing made easy,was kt34xa torque balancing, Michael Tope Re: [TowerTalk] kt34xa torque balancing, Michael Harris [TowerTalk] kt34xa torque balancing, Jim Jarvis Re: [TowerTalk] kt34xa torque balancing, W0UN -- John Brosnahan RE: [TowerTalk] kt34xa torque balancing, Tod - Minnesota RE: [TowerTalk] kt34xa torque balancing, W0UN -- John Brosnahan