1 — What a Stall Actually Is
Lesson 2 ended at the critical angle of attack — the top of the lift curve. A stall is simply what happens when you go past it. It is not about running out of speed, running out of engine, or pointing too high at the sky. It is about one thing only: the angle of attack exceeding the critical angle, at which the airflow can no longer follow the upper surface of the wing.
Once the angle of attack passes the critical angle, the airflow can no longer follow the upper surface and separates. Lift collapses, drag rises sharply and the nose drops — the wing is stalled. This depends on angle of attack alone, not on airspeed.
When the flow separates, three things happen together: lift collapses, drag rises sharply, and because the wing’s centre of pressure moves, the nose drops. That nose-drop is the wing’s built-in attempt to reduce the angle of attack and start flying again — the basis of every stall recovery.
2 — Stall Speed, Weight and Load Factor
So why publish a stall speed at all? Because for a given weight and load, there is a speed at which level flight demands the critical angle. Two things move it:
- Weight — a heavier wing needs more lift, so it reaches the critical angle at a higher speed. Stall speed rises with weight.
- Load factor — in a manoeuvre the wing supports more than the aeroplane’s weight. In a
level turn the load factor is
n = 1 / cos φ, and stall speed rises with√n.
Drag the bank angle and watch the stall speed climb — even though the stalling angle never changes:
Illustrative wings-level stall speed Vₛ₁g = 50 kt.
3 — Stall Warning and the Spanwise Stall
Certification requires a stall warning with a margin before the stall — usually an aerodynamic buffet (turbulent air from the wing root shaking the tail) and a stall-warning horn or light triggered by the changing stagnation point. Recognise these and you can stop the stall before it develops.
Wings are also designed to stall progressively. With washout (the tip set to a lower angle of attack than the root), the root stalls first. That keeps the ailerons, out at the tips, effective deep into the stall — so you keep roll control and the stall stays straight rather than dropping a wing.
4 — The Spin
A spin is a stall with yaw. If one wing is more deeply stalled than the other — from yaw, or from a wing dropping at the stall — that wing makes less lift and more drag. It drops and goes slower; the other rises and speeds up; the difference sustains itself. This autorotation is the spin: both wings stalled, the aeroplane descending in a steep, rotating, nose-low corkscrew.
5 — Why This Matters to the Pilot
Nearly every fatal loss-of-control accident is a low-level stall or stall–spin — typically slow, banked and distracted in the circuit. The defence is not a number on the ASI; it is angle-of-attack awareness: keep the wing flying, stay coordinated (ball centred so a stall doesn’t become a spin), and respect that pulling g or steepening the bank raises the speed at which the wing will let go.
All speeds and figures here are illustrative; your aircraft’s real stall speeds (Vₛ, Vₛ₀) and spin-recovery procedure come from its POH/AFM.
