Stalling — Page 191, Lesson 226

Let’s pick this up right where the spin itself leaves off. We’ve talked about how a spin develops, and now I want to walk you through what actually changes the spin’s behaviour — and that comes down to two things: the total mass of the aeroplane, and where its centre of gravity sits. First, mass. The heavier the aeroplane, the more slowly it tends to enter the spin initially. But here’s the catch — as the spin progresses, the spin rate may actually tend to increase. Why does that matter? Because a heavier aeroplane carries more angular momentum. Angular momentum is the rotational equivalent of inertia — it’s the tendency of a spinning object to keep spinning. So in a heavily loaded aeroplane, that higher angular momentum means it takes more time and more altitude to recover from a spin. You need to arrest that rotation, and the heavier you are, the harder that is. Now, centre of gravity location is even more significant than mass. It affects the aeroplane’s resistance to entering a spin in the first place, and it affects every phase of the spin itself. Let me break that down into three cases. Case (a): CG towards the forward limit. This makes the aircraft more stable. Because it’s more stable, control forces are higher — the controls feel heavier — and that makes it less likely that a pilot will make large, abrupt control movements. If you trim the aeroplane and release the controls, it will tend to return to level flight on its own. But there’s a price: the stall speed will be higher. So a forward CG protects you from spins, but it raises the speed at which the wing stalls. Case (b): CG towards the aft limit. This decreases longitudinal static stability — that’s the aeroplane’s natural tendency to return to its trimmed attitude after a disturbance. It also reduces pitch control forces, so the controls feel lighter. That combination tends to make the aeroplane easier to stall. And once a spin is entered, the further aft the CG, the flatter the spin attitude becomes. So an aft CG makes spins easier to enter and flatter once you’re in them. Case (c): If the CG is outside the aft limit — beyond the certified range — or if you don’t reduce power promptly, the spin is more likely to go flat. Now, a flat spin is a specific and dangerous condition. It’s characterized by a near-level pitch and roll attitude, with the spin axis near the CG. Here’s the counterintuitive part: the altitude lost in each turn of a flat spin may actually be less than in a normal spin. But the extreme yaw rate — often exceeding 400 degrees per second — results in a high descent rate. Let me put that number in perspective: 400 degrees per second means the aeroplane is rotating more than a full turn every second. The relative airflow in a flat spin is nearly straight up, which keeps the wings at high angles of attack — so the wings stay stalled. And more importantly, that upward flow over the tail may render the elevator and rudder ineffective. If you lose elevator and rudder authority, recovery becomes impossible. That’s why a flat spin is so feared. Now let’s move to spin recovery. Recovery from a simple stall is achieved by reducing the angle of attack, which restores the airflow over the wing. But spin recovery is different — it additionally involves stopping the rotation. And here’s the key point I want you to hold onto: the aerodynamics of a spin are extremely complex, and they can dictate vastly different recovery procedures for different aeroplanes. So there is no universal spin recovery procedure that works for all aeroplanes. Don’t ever assume one technique will save you in every type. The recommended recovery procedure for some aeroplanes is simply to reduce power to idle and release pressure on the controls — essentially let the aeroplane recover itself. At the other extreme, the design of some aircraft is such that recovery from a developed spin requires definite control movements, precisely timed to coincide with certain points in the rotation, and you may need to do this for several turns. So the range is from “do almost nothing” to “precisely choreographed control inputs over multiple rotations.” Let me show you the geometry of what we’re talking about — the flat spin attitude versus a normal spin. So to tie it together: mass affects how fast the spin develops and how much altitude you need to recover. CG location affects stability, control forces, stall speed, and whether the spin goes flat. And a flat spin, with its near-level attitude and extreme yaw rate, can rob you of elevator and rudder authority entirely. That’s why spin recovery is type-specific — there’s no one-size-fits-all procedure.