What is the acute angle between the chord line of the airfoil and the direction of the relative wind?

• A. Angle of Attack
• B. Pitch angle
• C. Angle of incidence
• D. Sideslip angle

Answer: (A)

The acute angle between the airfoil’s chord line and the direction of the relative wind is the angle of attack. This is the measure of how the wing meets the oncoming air—the wing’s chord line is the straight line from the leading edge to the trailing edge, and the relative wind is the incoming airflow. The angle between these two directions determines how much lift the wing can generate at a given airspeed; increasing it increases lift up to the point of stall.

Pitch angle, on the other hand, refers to the airplane’s nose-up or nose-down attitude relative to the horizon, not the airflow direction relative to the wing. Angle of incidence is the fixed angle between the wing’s chord line and the aircraft’s fuselage, set during installation. Sideslip angle is the sideways angle between the relative wind and the aircraft’s longitudinal axis, related to yaw.