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:
Side view:
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:
- Gold: propeller
- Red: bearings
- Purple: pulleys
- Blue: propeller shaft
Side view: