This is not strictly Rotary related, but I thought it might be of interest.

http://www.cozybuilders.org/Desert_Center/Prop_Bolt_Retention.html

Brian Trubee


He did it wrong. You don't need that much spring deflection. One or two springs
would have done the job in parallel instead of some in series. 0.012 deflection
for the springs is near nothing.


Paul Lamar ...No rotor no motor.

Paul,
Marc did it correctly.  You need enough deflection range on the
Belleville washers to allow the hub to expand over its full range while
the Bellvilles maintain a more nearly constant bolt tension.  In
essence, the low elastic modulus Bellevilles are being used to swamp the
high elastic modulus of the prop hub.  Marc's graph shows that as the
hub shrinks with dry "weather" conditions the hub would lose 50% of the
bolt tension without the Belleville washers.  But, with the Bellvilles
the tension loss is only about 8%.  The objective was to maintain the
600psi hub loading recommended in the Sensenich article without the need
to constantly re-torque the prop bolts.

The static analysis of this scheme makes it look like a pretty good
idea.  But, the presence of the Bellevilles is also swamping the high
elastic modulus of the prop bolts.  Under certain dynamic conditions the
prop hub loading could go to zero.  I'm not saying the idea will not
work.  But, this is clearly a possible avenue for trouble to develop.

Aubrey Thompson

I agree with all that. I am not saying the concept is wrong or won't work.
On the face of it you are correct but what must be known is just how
far the hub shrinks and expands with moisture content. I maintain it will
not change more than .012" so the deflection of two bell springs in parallel
for each bolt will do the job. Six for each bolt are not required. His graph
suggest that but no real expansion tests were done on the prop under very dry
and very wet conditions.

Also I would place a thin stop under the two springs to prevent bottoming
out the springs and over stressing them.

This is not strictly Rotary related, but I thought it might be of interest.

http://www.cozybuilders.org/Desert_Center/Prop_Bolt_Retention.html

Brian Trubee


He did it wrong. You don't need that much deflection. One or two springs
would have done the job in parallel instead of some in series.


Paul Lamar ...No rotor no motor.

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