What is meant by the angle of attack?

• A. The angle between the gust and the wing.
• B. The angle between the wing and the horizon.
• C. The acute angle formed between the chord line of an airfoil and the direction the air strikes the airfoil.
• D. The angle between the fuselage and the relative wind.

Answer: (C)

The angle of attack is the acute angle between the wing’s chord line and the direction of the relative wind hitting the wing. The chord line is the straight line from the leading edge to the trailing edge of the airfoil, and the relative wind is the airflow that the wing encounters, effectively the air moving opposite to the airplane’s flight path. When you pitch the nose up, the chord line tilts more into the oncoming air, increasing the angle of attack. Lift rises with angle of attack up to a critical point, after which the airflow can separate and a stall occurs.

The other descriptions don’t define the angle of attack: they refer to the fuselage’s relation to wind, the aircraft’s attitude relative to the horizon, or the gust direction relative to the wing, none of which capture the essential measure between the wing’s chord line and the relative wind.