Angle of Attack Explained

What is Angle of Attack?

Angle of attack, often abbreviated as AoA and symbolized by the Greek letter alpha (α), is the angle between the chord line of a wing (a straight line from leading to trailing edge) and the direction of the relative airflow. For a whole aircraft, the reference line may be the longitudinal axis rather than the chord line, especially in three-dimensional analysis.

Angle of Attack vs. Attitude and Incidence

• Angle of Attack (AoA): The angle between the chord line (or longitudinal axis for the whole aircraft) and the relative wind.
• Attitude: The orientation of the aircraft's nose relative to the horizon (pitch), not to be confused with AoA.
• Angle of Incidence: The fixed angle between the aircraft's longitudinal axis and the wing root chord line, set during manufacture and not changed in flight.

Angle of Attack and Lift

• Increasing AoA generally increases lift up to a point. As AoA rises, the wing deflects more air downwards, generating more lift.
• Beyond a certain AoA, known as the critical angle of attack, airflow separates from the upper surface, causing a stall and a rapid loss of lift.

Local and Induced Angle of Attack

• Control surfaces (like elevators) can locally change the AoA, affecting lift and aircraft control.
• In real flight, downwash and wingtip vortices cause the local airflow to differ from the undisturbed flow, creating an induced angle of attack that reduces effective lift.

Angle of Attack Diagrams

• Diagrams typically show the chord line, relative airflow, and the angle between them, helping visualize how AoA changes with pitch and flight conditions.

Understanding these distinctions is crucial for safe and efficient flight, as improper management of AoA can lead to stalls or inefficient performance.