Understanding the Critical Angle of Attack

In my time flying over the flat terrain of southern Wisconsin, I have noticed that student pilots often associate stalls with slow airspeeds. While it is true that we usually practice stalls at low speeds, a wing can stall at any speed if the critical angle of attack is exceeded. The angle of attack is the angle between the chord line of the wing and the direction of the relative wind. As you increase this angle by pulling back on the yoke, the air has a harder time following the upper curve of the wing. At a specific point, usually around 16 to 18 degrees for a common Cessna 172, the airflow becomes turbulent and separates from the surface, causing a sudden loss of lift.

Consider an aircraft performing a steep turn at a high bank angle. To maintain altitude, the pilot must pull back to increase lift. This increases the load factor, often referred to as G-loading. In a 60-degree level bank, the aircraft experiences 2 Gs of load, and the stall speed increases by approximately 40 percent. If the pilot pulls too aggressively to tighten the turn, the wing hits that critical angle while the airspeed indicator might still show a speed well above the normal 1-G stall speed. This is known as an accelerated stall, and it happens much faster than the gentle power-off stalls practiced in the local training area.

Ground track and pitch attitude can be deceptive. On a windy day near Burlington or Waukesha, your nose might be pointed toward the horizon while your actual flight path is descending. In this scenario, the relative wind is coming from below, which puts you much closer to the critical angle than you might realize. Understanding that the wing does not care about your ground speed or your orientation to the horizon is fundamental to safe maneuvering.

Hazard Warning: Attempting to pull out of a low-altitude dive too abruptly can exceed the critical angle of attack and induce an accelerated stall with insufficient altitude for recovery.