Angle of incidence (aerodynamics)

The angle of incidence, also known as the angle of attack, in aerodynamics is the angle between the chord line of an airfoil and the relative wind. The chord line is an imaginary straight line joining the leading edge and trailing edge of the airfoil. The relative wind is the direction of the airflow relative to the airfoil.

The angle of incidence is a crucial factor in determining the lift and drag generated by an airfoil. As the angle of incidence increases, the lift generated by the airfoil generally increases, up to a certain point. Beyond this critical angle of incidence, known as the stall angle, the airflow separates from the upper surface of the airfoil, leading to a significant reduction in lift and a dramatic increase in drag. This phenomenon is called stall.

The angle of incidence is typically measured in degrees. A positive angle of incidence means that the leading edge of the airfoil is tilted upwards relative to the relative wind. A negative angle of incidence means that the leading edge of the airfoil is tilted downwards relative to the relative wind. An angle of incidence of zero means that the chord line of the airfoil is parallel to the relative wind.

In aircraft, the angle of incidence can be adjusted by the pilot using control surfaces such as elevators (for pitch) and ailerons (for roll), effectively changing the angle of attack of the wing relative to the oncoming airflow. The appropriate angle of incidence is dependent on factors such as airspeed, weight, and desired maneuver.