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In comparison to both engines operative, the power required for a Performance Class B multi engined aeroplane to maintain level flight with the critical engine inoperative is...
  • A
    greater, due to the decrease in total drag.
  • B
    greater, due to the increase in total drag.
  • C
    doubled, as the aeroplane loses 50% of its performance.
  • D
    constant, provided the pilot counteracts the yaw.
If a twin-engine aircraft loses an engine total thrust is reduced by 50%, but the excess thrust (the thrust, minus aerodynamic drag) is reduced by more than 50% due to additional drag of the dead engine and the compensation of the yaw moment. The drag of the dead engine and propeller depends whether the propeller is windmilling, stopped or feathered.
  • Drag from a windmilling propeller is high. It is being driven by the relative airflow and is generating both drag and torque.
  • If a propeller is stationary, it is generating drag but no torque. Drag from a stationary propeller is less than from one which is windmilling.
  • A feathered propeller generates the least drag. There is no torque because it is not rotating, and the parasite drag is a minimum because the blades are edge on to the relative airflow.

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