What is the angle between the relative wind and the chord line of an airfoil called?

The angle between the relative wind and the chord line of an airfoil is referred to as the angle of attack. This angle is crucial in determining the aerodynamic efficiency of the airfoil, as it directly influences lift generation. When the angle of attack increases, the lift also typically increases to a point. However, if the angle becomes too steep, it can lead to a stall, where the airflow separates from the wing surface, resulting in a loss of lift.

Understanding the angle of attack is essential for pilots and engineers, as it impacts the performance and handling characteristics of the aircraft. Recognizing this concept allows for better control of the aircraft during various phases of flight, including takeoff, cruising, and landing.