[TowerTalk] Analysis of mast slippage in rotor

[John Becker]

Thanks to all who responded on this issue.

It appears that there is no perfect solution. The weak link for the 
HAM-III and related rotors is the limited strength of a 1/4-20 U-bolt.

I'm reluctant to drill out the holes to accommodate a 5/16-18 U-bolt, 
but in looking at my test setup again, I came up with another idea. I 
could leave the existing U-bolts and backing plate just as they are and 
add a third larger U-bolt with a saddle (such as a muffler clamp but 
stainless) around the entire assembly midway between the original 
U-bolts. A U-bolt with a 3.5" ID should fit. This would add considerable 
pressure to the mast clamping action without modifying the rotor. Do any 
of you see a downside to this approach that isn't apparent to me?

One other thought comes to mind. The original design includes a bolt 
threaded through the center of the backing plate which is intended to be 
screwed down against the mast. I'm thinking that this actually may be 
counterproductive, because any force applied at this point would reduce 
the pressure between the mast and backing plate along the two 4.5" lines 
where they are in contact. Therefore, I'm considering the removal of 
this bolt. Your thoughts?

73,

John, K9MM