Can the angle of attack change with no change in angle of incidence?

Can the angle of attack change with no change in angle of incidence?

• A. No
• B. Yes
• C. Only At High Speed
• D. Only At Low Altitude

Answer: (B)

AOA is determined by the angle between the blade’s chord and the oncoming relative wind. The angle of incidence is simply the blade’s pitch setting relative to the plane of rotation. If you fix the incidence (pitch) and keep it at a constant value, the direction and speed of the relative wind can still change as flight conditions change—such as when you start moving forward, climb or descend, or change rotor thrust. Those changes tilt the relative wind, so the angle between the blade’s chord and that wind—i.e., the angle of attack—can increase or decrease even though the blade’s pitch remains unchanged. In short, AOA can vary with changes in airspeed and inflow while incidence stays fixed.

AOA is determined by the angle between the blade’s chord and the oncoming relative wind. The angle of incidence is simply the blade’s pitch setting relative to the plane of rotation. If you fix the incidence (pitch) and keep it at a constant value, the direction and speed of the relative wind can still change as flight conditions change—such as when you start moving forward, climb or descend, or change rotor thrust. Those changes tilt the relative wind, so the angle between the blade’s chord and that wind—i.e., the angle of attack—can increase or decrease even though the blade’s pitch remains unchanged. In short, AOA can vary with changes in airspeed and inflow while incidence stays fixed.