FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightEasy
A commercial pilot applicant asks a CFI at what point during a slow, gradual increase in pitch the wing will stall. The instructor should explain that a stall always occurs when the wing reaches:
- Aa load factor of exactly 1.0 G
- Ba specific indicated airspeed regardless of angle of attack
- Cthe maximum lift-to-drag ratio angle of attack
- Dthe critical angle of attack, regardless of airspeed
Show answer & explanationAnswer & explanation
Correct answer: D. the critical angle of attack, regardless of airspeed
A stall is caused solely by exceeding the critical angle of attack, at which the airflow separates from the upper surface of the wing. This can occur at any airspeed, attitude, or power setting.
Why the other options are wrong
- A. Load factor affects stall speed but a 1.0 G stall is only one specific case, not the definition.
- B. Stall speed varies with weight, load factor, and configuration—it is not fixed.
- C. Best L/D angle of attack is well below the critical angle and does not cause a stall.
Critical Angle of Attack
The angle of attack at which airflow separation over the wing becomes so great that further increases in AOA produce a rapid decrease in lift, causing a stall.
- Stall occurs at critical AOA, independent of airspeed
- Can happen in any attitude or airspeed
- Typically 16-20 degrees for most wings
- Load factor and weight change the speed at which critical AOA is reached, not the angle itself
Memory trick: 'Angle, not speed' decides the stall