Stalling and Spinning: Stall Recognition, Recovery, Spin Aerodynamics and Prevention
This domain tests the stall and the spin as aerodynamic events with fixed triggers and defined recoveries. Items ask for the cause, the indications, the effect of weight, load factor and configuration, and the correct recovery sequence.
The stall
- A stall occurs at the critical angle of attack, about 15–16°, not at a particular speed.
- Vs = √(2W/(ρ S CLmax)). It rises with √W, with √n, with altitude, and with any reduction in CLmax from ice, contamination or loss of power.
- Recognition: stall warning horn or stick shaker, buffet, mushy controls, high sink rate and an angle-of-attack indicator.
Stall recovery
- Reduce the angle of attack with forward stick, keep the wings level, apply power, then recover without a secondary stall.
- Aileron use near the stall can aggravate a wing drop; use rudder instead.
Spins
- A spin is an aggravated, autorotating stall: one wing is more stalled than the other and yaw is present as well as stall.
- Incipient, developed and recovery phases each have characteristic rotation rate, pitch attitude and airspeed.
- Recovery: power idle, ailerons neutral, full rudder opposite to the rotation, elevator forward to break the stall, then recover from the dive.
Worked example
An aircraft stalls at 60 kt at 1000 kg. At 1200 kg the stall speed is 60 × √1.2 = 65.7 kt. In a 2.5 g manoeuvre it is 60 × √2.5 = 94.9 kt. Same wing, same CLmax, same stall angle - only the speed at which the critical angle is reached has changed.
Traps
- The stall angle does not change with weight, density or speed.
- Aileron input during a spin can worsen the autorotation.
- A spiral dive is not a spin: airspeed rises rapidly and the recovery is different.
- Ice reduces CLmax and raises Vs; the stall warning may also trigger early or late.
- A stall in a turn is not cured by pulling harder; the angle of attack must be reduced.