Angle d'attaque (AoA: Angle of Attack)

Qu'est-ce que l'angle d'attaque ?

Angle of attack (AoA) is the angle between a wing's chord line — an imaginary straight line from leading edge to trailing edge — and the direction of the oncoming relative airflow. It is one of the most important parameters in aerodynamics, directly controlling how much lift the wing generates. AoA is frequently confused with pitch attitude, but the two are distinct: an aircraft can be pointed nose-up while the AoA is low (during a zoom climb after pitching up rapidly), or nose-down with a high AoA (during an accelerated stall).

Fonctionnement

As AoA increases from zero, the wing generates progressively more lift because:

• More air is deflected downward, increasing the reaction force (Newton's 3rd Law component).
• The pressure differential between lower and upper wing surfaces widens.
• The coefficient of lift (CL) increases linearly with AoA in the normal range.

This relationship continues until the critical AoA is reached — typically 15–20° for subsonic airfoils — at which point airflow separates from the upper surface and a stall occurs. The flight envelope defines the safe range of AoA across all speeds and altitudes.

At low speeds, maintaining sufficient lift requires a higher AoA. At high speeds, a lower AoA generates the same lift. Pilots indirectly control AoA through back pressure on the control column and throttle management.

Importance en aviation

AoA sensors are safety-critical instruments. They feed data to stall warning computers, flight management systems, and fly-by-wire control laws. The angle-of-attack indicator (sometimes called an alpha indicator) is increasingly common in cockpits as a primary tool for energy management during approach. NASA research shows that AoA-based approaches are more consistent than airspeed-based approaches, particularly at varying weights.

The Boeing 737 MAX MCAS system was designed to address AoA-induced pitch behavior caused by repositioned engines. Its malfunction, triggered by faulty AoA sensor data, led to two fatal accidents (Lion Air 610, Ethiopian Airlines 302) and a 20-month worldwide grounding.

Impact concret

The F/A-18 Super Hornet can operate at AoAs exceeding 70° during high-alpha maneuvers, far beyond what conventional airliners can achieve. Carrier approaches are flown at approximately 8° AoA, referenced directly by the Fresnel lens optical landing system. The Airbus A320's flight envelope protections maintain AoA below alpha-max regardless of pilot input, providing a hard boundary against inadvertent stalls during normal operations.