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Regarding the main rotor aerodynamics during powered flight, what position does the angle of attack occupy?

  • A

    The term 'angle of attack' is another name for the blade pitch angle.

  • B

    It is inside the blade pitch angle.

  • C

    It includes the blade pitch angle.

  • D

    It coincides with the blade pitch angle.

Refer to figure.
Angle of Attack (AoA, α or alpha) is the angle between the Relative Airflow and the Chord line.

AoA constitutes one of the elements of the Coefficient of Lift (CL) and affects its value. More specifically, Lift increases (up to a point) as AoA increases.

The point of maximum lift is called "Critical AoA" or "Critical alpha" and the relationship is roughly linear up to 15º approximately for a symmetric aerofoil.

Beyond this point, the amount of lift produced decreases as the AoA increases further. The AoA beyond the point which lift starts to decrease is known as "Stalling AoA".

The blade pitch angle is defined as the angle between the blade chord line and the plane of rotation which acts around the feathering axis. Therefore, AoA is inside the the blade pitch angle.

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