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Which statement is correct when comparing a fixed pitch propeller with a constant speed propeller?

I. A fixed pitch propeller improves propeller efficiency over a range of cruise speeds.
II. A constant speed propeller improves take-off performance as compared with a coarse fixed pitch propeller.

  • A
    I is incorrect, II is correct.
  • B
    I is correct, II is correct.
  • C
    I is correct, II is incorrect.
  • D
    I is incorrect, II is incorrect.
The purpose of a variable-pitch propeller is to either manually or automatically maintain the optimum angle of attack to maximize the lift/drag ratio of the propeller as the airplane speed changes. This characteristic is the most significant advantage of the constant-speed (fixed RPM) propeller over the fixed-pitch propeller because it is able to maintain maximum efficiency over a range of airplane speeds. Therefore, statement 1 is incorrect.
This facility not only improves the propeller efficiency but also decreases the fuel consumption.
A constant speed propeller is one that varies the pitch setting automatically to maintain a constant rotational speed, despite changes in other factors. A large blade angle or coarse pitch is suitable for high-speed flight (cruise). Therefore, statement 2 is correct.

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