Stalling and spinning
Overview
Stalling and spinning tests the critical AoA stall, the factors that change stall speed, and spin recognition and recovery.
Core rules
- A stall occurs when the wing exceeds the critical AoA, at any speed, attitude or power setting.
- V_S = √(2W/(ρSC_Lmax)). Increasing weight, load factor, altitude or ice raises stall speed.
- In a level turn V_S(n) = V_S√n, where n = 1/cos φ.
- A spin is an aggravated stall with yaw: one wing is more stalled than the other, causing autorotation.
- Phases: entry, incipient, developed, recovery. Recovery: PARE - power idle, ailerons neutral, rudder opposite the yaw, elevator briskly forward.
- Stalls in turns, accelerated stalls and cross-controlled stalls are examiner favourites.
Worked example
V_S = 50 kt at 1 g. In a 60° banked level turn n = 1/cos 60° = 2, so V_S = 50√2 = 70.7 kt. The aircraft stalls 21 kt faster than in straight flight.
Traps
- Believing a stall needs low speed - an accelerated stall can occur at high speed.
- Adding power before breaking the stall in a spin recovery.
- Forgetting that a forward CG slightly increases stall speed but improves recovery margins.