The critical angle of attack is the maximum angle between a wing's chord line and the oncoming airflow before the wing stalls. Beyond this point, smooth airflow separates from the upper wing surface and lift collapses suddenly.
How It Works#
Every wing generates lift by accelerating air over its curved upper surface. This creates lower pressure above the wing and higher pressure below, producing an upward force. The angle of attack (AoA) is the angle at which the wing meets the incoming air.
As AoA increases, lift increases with it. The wing works harder, pulling more air across its surface. But this only holds up to a point.
At the critical AoA, roughly 15 to 18 degrees for most general aviation wings, the airflow can no longer follow the wing's upper surface. It breaks away in a turbulent, chaotic separation. Lift drops sharply and drag spikes. This is a stall.
The critical AoA is a fixed aerodynamic property of a wing's shape. It does not change with airspeed, altitude, weight, or bank angle. A wing stalls at the same AoA whether it is flying fast or slow, loaded or light.
Example in Aviation#
A student pilot is practicing slow flight in a Cessna 172. The instructor asks them to pull back gradually on the yoke while keeping altitude. Airspeed decays, and the AoA climbs steadily toward the critical value. The stall warning horn activates at a few degrees before the critical AoA. If the student continues pulling back, the wing exceeds its critical AoA and stalls, pitching the nose down.
The key point here: the stall was not caused by low airspeed alone. It was caused by exceeding the critical AoA. The airspeed just happened to be low because that is how the critical AoA was reached in this case.
Why It Matters#
Pilots must understand that a stall can happen at any airspeed and any attitude. An aggressive pull during a steep turn, a botched go-around, or an abrupt pitch input on final approach can all drive the wing past its critical AoA. Confusing "stall" with "low airspeed" is a dangerous and common misconception.
AoA indicators are increasingly common in light aircraft and give pilots a direct readout of how close the wing is to its critical limit. Understanding this concept is the foundation of stall and spin awareness training.
Key Takeaways#
- The critical AoA is the point where airflow separates and lift collapses.
- For most general aviation wings, the critical AoA is roughly 15 to 18 degrees.
- A wing can stall at any airspeed if the critical AoA is exceeded.
- The critical AoA is fixed by wing shape and does not vary with flight conditions.
- Stall recovery requires reducing AoA, not simply adding power or raising the nose.