Stall
In aerodynamics, a stall is a flight condition that occurs when the angle of attack (AoA) exceeds a critical value, leading to a sudden reduction in lift. While often associated with low airspeed, a stall is fundamentally caused by excessive angle of attack, not insufficient speed alone.
Aerodynamics of stalls
A stall occurs when the angle of attack (AoA) exceeds the critical angle at which the wing can no longer produce sufficient lift. It is not caused by low airspeed alone—although airspeed and AoA are closely related.
- The critical AoA is typically around 16–18° for most general aviation aircraft.
- As the critical AoA is approached, airflow separates from the upper surface of the wing, resulting in a sudden loss of lift, a nose‑down pitch tendency, and often a wing drop.
Factors affecting stall speed
The stall speed is not fixed; it changes with configuration, weight, and load factor. FlightGear models all these effects realistically.
- Landing gear and flaps
- Extending flaps lowers the stall speed because it increases the wing’s camber and lift coefficient. Likewise, lowering landing gear adds drag and changes the pitch attitude, but its main effect on stall speed comes from the change in configuration. In FlightGear you can feel this by comparing stall speeds with flaps up versus full flaps.
- Weight
- Stall speed increases with weight. Heavier aircraft need a higher angle of attack to produce the required lift, so the critical AoA is reached at a higher indicated airspeed. Use the aircraft weight and fuel load menus to experiment.
- Center of gravity (CG)
- A forward CG makes the aircraft more stable but increases the stall speed slightly because the tail must produce more downforce. An aft CG reduces stall speed and can make stall recovery more challenging—especially in spin‑prone aircraft.
- Load factor and bank angle
- In a turn, the load factor increases, and stall speed rises with the square root of the load factor. For example, a 60° bank (2 g) increases stall speed by about 40%. FlightGear’s turn coordinator and accelerometer (
/instrumentation/g-meter) help you visualise this relationship.
Power-off and power-on stalls
Power‑off stalls
Power‑off stalls typically occur during approach and landing phases. Common scenarios:
- Final approach with excessive nose‑up trim or too slow airspeed.
- A steep turn in the pattern, especially when base‑to‑final is overshot.
- Abrupt pitch‑up during a go‑around before the aircraft has accelerated.
In FlightGear, practice these scenarios by setting up a short approach, then pulling the throttle to idle and trying to maintain altitude with back pressure until the stall warning sounds.
Power‑on stalls
Power‑on stalls are most common during takeoff and climb, or when practicing go‑arounds. Look out for:
- A high pitch attitude immediately after takeoff, especially with a low‑power aircraft.
- Aggressive climbing turns, such as those used to avoid obstacles.
- Attempting to climb too steeply after a go‑around while the flaps are still extended.