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STALLS AND SPINS
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By John Lorenz
 Many pilots’ fear of a stall fills the cockpit like a physical presence during practice. The belief that a stall will lead to a spin that augers you into the ground before you can howl “Bernoulli lied!” is usually fear of the unknown, deriving from an unfamiliarity with the progression from stalls to spins. We’re not really sure how close to a spin we are when the airplane stalls, we don’t know which kinds of stalls lead to spins, and we only have a vague idea of how to stop an incipient spin. Getting comfortable with stalls helps a pilot realize that not all stalls are bait for the spin monster, and, in a perverted sort of way, even intentional spins are fun after you get used to them, since the stall to spin pattern is predictable and controllable.
The first stage is the buffet, nibbling at the edge of the stall. Continue beyond the buffet to a full stall, and, if the rudder is being mismanaged so that the ailerons are deflected, one wing will drop as the nose goes down. If the wing has lost all lift and goes down quickly, this is the beginning of a spin. Early corrective control inputs will arrest it, but if they are not made before the wings get to vertical, the falling wing tucks under and now you’ve started a spin, which takes several hundred feet of altitude to recover from. It takes time for opposite-rudder input to stop the plane’s rotation, and then you then have to recover from a steep dive.
Stalls at altitude, with rudder inputs that keep the ailerons neutral and the ball centered, don’t lead to spins and are readily recoverable no matter how fast or how much the nose drops. The airplane returns to controllable flight, even if the wing drops, if you learn the two secret control inputs known only to the Mystical Order of Super-Pilots: 1) leggo the damnfool yoke, and 2) rudder, rudder, rudder to pick up a falling wing. Releasing the yoke lets the nose drop, reducing the angle of attack thus breaking the stall, and also lets the airplane accelerate downhill to a safe airspeed. Opposite rudder speeds up the falling wing thus reducing its angle of attack and giving it more lift. Recovery from any remaining dive is easy as long as you don’t pull up too abruptly and induce a secondary stall. The amount of altitude lost in a stall depends on how far you let the nose drop while holding the yoke back, how soon power is re-applied, and how soon the nose is pulled up once flying speed is regained. There is no reason to dread a coordinated stall at altitude other than for the uncomfortable, sudden drop. However, uncoordinated stalls at low altitude are an entirely different story -- a spin develops from a sloppy stall, and spins consume altitude.
An intentional spin is easiest to enter by adding full rudder during a stall. This slows one wing while speeding up the other, giving them different angles of attack and thus differential lift. An accidental spin on the other hand usually results from a stall with the ailerons deflected. This also gives the left and right wings differential lift due to the different angles of attack. The wing with the downward-deflected aileron has a greater angle of attack and thus develops a deeper stall than the wing with the upturned aileron, which retains some lift at the stall. As a corollary, a yoke turned to the right, as in trying to raise a falling left wing, lowers the aileron on that wing and deepens its stall, hastening its downward fall. Aileron inputs during a stall have a reversed-control effect.
An airplane has differential aileron deflection, and thus wants to spin, if you stall it with your feet off the rudder pedals in a climb, holding heading with the ailerons. It will try to spin if you stall in a slip, or if you stall and try to pick up a falling wing with opposite aileron. It will try to spin if stalled in the all-to-common base-to-final skid, where the rudder pedal is unintentionally held into the turn causing the pilot to hold opposite aileron to prevent the bank from oversteepening. A stall precedes every spin, but stalls don’t cause spins. They just set up the conditions where a spin can occur.
We give student drivers the obscure advice to “steer in the direction of the skid” on icy roads and hope they figure it out if they ever need it. Likewise, we tell student pilots about spins, but in flight we only teach them to avoid situations that lead to spins: stay out of the water and you won’t drown. Accident statistics suggest that this spin awareness and prevention strategy has been successful. However, we have left pilots with only a tenuous grasp of the importance of the rudder and how to use it, and no clue of what to do to break out of an incipient spin. If the goal is to improve pilot understanding and proficiency, pilots must do enough stalls to get comfortable with lifting a dropping wing with opposite rudder and neutral ailerons, and with breaking a stall by releasing the yoke. These are counter-intuitive responses when the horizon is doing unnatural things, but the gut reaction, full aft yoke to bring the nose up and opposite aileron to lift the wing, actually only develops the spin by prolonging the stall and killing any remaining lift in the down-going wing. |
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