[TowerTalk] Mast load question

[Jim Schnaidt]

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.

73,

Jim
KJ0M

._._.