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Re: [TowerTalk] Mast load question

To: Pete Smith <>
Subject: Re: [TowerTalk] Mast load question
From: Jim Schnaidt <>
Date: Wed, 26 May 2004 16:55:37 -0500
List-post: <>

On May 26, 2004, at 3:13 PM, Pete Smith wrote:

I may be all wet, but the chrome moly mast seems likely to me to weigh a lot more than the total of those two antennas. A conservative calculation would be to take the sum of the weight of the top antenna times its lever arm above the thrust bearing, plus the weight of the lower antenna times its (tiny) lever arm, plus the weight of the mast times 6 feet (the midpoint above the thrust bearing). If the thrust bearing offers no resistance at all to the mast tilting (big if), then the lateral load on the rotator bolts would be that first sum times 3 (because the arm below the thrust bearing is 1/3 as long). Could be several thousand pounds.

No, Pete, you're not all wet! You're exactly right. I should have recalled my high school physics. It really is a lever and W1 X L1 = W2 X L2. Therefore, you're absolutely correct in saying the force on the rotor bolts could be several thousand pounds and probably is all of that!

To be really safe, it seems to me that the smart thing would be to place a second bearing -- not a thrust bearing, per se, but one that can take the full lateral load you anticipate -- just above your rotator. That way all the forces are taken off before they reach the rotator.

Exactly right again. I need to do some engineering now. To the drawing board!

Thanks, Pete. I appreciate it! So simple, I should have seen it. Intuitively, I remembered the mechanical advantage (or disadvantage in this case) but just couldn't quantify it.





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