Which term denotes the angle between the blade's chord line and the relative wind?

• A. Angle of Incidence
• B. Angle of Attack
• C. TAF
• D. Chord Line

Answer: (B)

The angle between the blade’s chord line and the relative wind is the angle of attack. This is the aerodynamic angle that determines how much lift the blade generates at any given flight condition—the relative wind is the net air flow seen by the blade, created by its rotation and the aircraft’s motion, and the chord line is the straight line along the airfoil’s cross-section. By changing pitch (collective), you tilt the chord line relative to that incoming air, increasing or decreasing the angle of attack and thus the lift, up to the point where stall may occur. The angle of incidence, in contrast, is a fixed geometry: the blade’s chord line relative to the plane of rotation. The term listed as TAF isn’t the standard term for this angle, and a chord line by itself isn’t an angle.