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Propeller shaft design

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kubark42

Well-Known Member
Joined
Oct 19, 2020
Messages
90
I'm looking for information on propeller shaft design for a pusher prop. I have a belt-driven system where the pulleys mount directly to the propeller, so the shaft is more of a free-wheeling axle than it is a power-transmitting shaft. As such, I only have bending moments to worry about. Thus, calculating the loads and stresses is trivial.

No surprise that I want to make this as strong and light as possible. Design parameters AFAICT are two: 1) the distance between bearings and 2) the shaft's 2nd moment of area (i.e. inner vs outer diameters). (Cost isn't much of a factor, as a section of 4140 shaft material from McMaster is going to cost around $1/cm, so the final materials cost is well under $20.)

Where I need some input is calculating the design load limits as a function of desired TBO. On paper, the solid shaft is massively over-speced, and could almost be a thin-walled 4140 tube. Of course, that isn't accounting for 2nd order effects, such as resonance, fatigue, bearing point load deformation, etc... These are the things of which I have no knowledge.


Close up view:
Screen Shot 2021-01-16 at 2.08.12 AM.png

  • Gold: propeller
  • Red: bearings
  • Purple: pulleys
  • Blue: propeller shaft
Thoughts?

Side view:
Screen Shot 2021-01-16 at 2.08.31 AM.png
 
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