While calculating propeller static thrust by using a famous Prop-power-calculator.xls (by Pé Reivers), I've noticed that no matter what "stock" configuration I put into the calculator, I do always get the propeller power required half or third of the engine power available.
Zivko Edge 540: Lycoming AEIO-540-EXP 300HP@2700rpm engine, HARTZELL 76" prop @ 11.5" pitch
Calculator given performance: 51HP, 154Kg thrust
Piper Sport: Rotax 912ULS 100HP@2400rpm engine, Woodcompo 67" prop @ 10" pitch
Calculator given performance: 17HP, 88Kg thrust
!NOTE - calculator is for 2-blade props, while above planes have 3-blade props. However, that doesn't change the mismaching in numbers a lot.
Above engine RPM's are with reduction applied (i.e. 1:2.43). That means the actual HP available is two-fold!.
I would imagine everything shouldbe the other-way around(?)
- Reduction rates of 1:0.5, RPM's * 2, engine power / 2
- Or propeller driven directly by the shaft
- Or prop diameter increased (not to practical perhaps)
- Or pitch inreased
- Or number of blades increased?
- Or all of above?
What am I missing here?