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Old 03-09-2005 | 02:51 AM
  #54  
adam_one
 
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Default RE: Prop effective speed

Yes. The limit comes from compressibility effect when the speed of the propeller blades approaches speed of sound in which case drag increases dramatically and efficiency falls off rapidly. I haven't seen any experimental data for thrust (Ct) and power (Cp) coefficients for propellers operating at supersonic speeds. That would be really interesting.
Of course, mechanical strength may also be a consideration.
Ok it sounds reasonable, but we may also think in terms of prop efficiency, which becomes zero when the forward speed is zero (static condition).

Efficiency = (thrust * velocity) / input power

Also propellers use to have their highest efficiency at a moderate rpm.