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(For this question use annex 081-035 issue date November 2005).
A typical curve representing propeller efficiency of a fixed pitch propeller versus TAS at constant RPM is:
  • A
    diagram 2.
  • B
    diagram 3.
  • C
    diagram 1.
  • D
    diagram 4.

Refer to figures.

The efficiency of any system is determined by the ratio of the output power to the input power. The force developed by the engine and delivered to the propeller via the shaft is the rotational force of the propeller, the propeller torque.
The power delivered to the propeller is the product of the torque and the angular velocity of the propeller shaft (Torque × Rotational Speed).
The thrust developed by the propeller is the product of the mass of air moved and the acceleration given to it by the propeller. The power developed by the propeller is the product of the thrust and the TAS (Thrust × Axial Speed).
Propeller efficiency is the ratio of the propeller power developed to the engine power delivered. A well-designed propeller is typically 80% efficient when operating at its optimum blade angle of attack.

Propeller Efficiency= ((Thrust × Axial Speed))/((Torque × Rotational Speed))

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