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Stalls and Spins

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Stalls and Spins
Stalls and Spins
Stalls and resulting spins have caused aircraft accidents since the beginning of flight. Even though airplanes have evolved to have better stall characteristics, stalls and spins continue to be a leading cause of accidents (Landsberg).
A stall occurs when airflow separates from all or part of the upper surface of a wing, resulting in sudden loss of lift. This is caused by exceeding the critical angle of attack (angle of attack is the angle between the relative wind and the chord line of the airfoil). Below the critical angle, airflow over the wing surface is relatively smooth. Above the critical angle, the thin layer of air above the wing, or "boundary layer," becomes turbulent and separates from the airfoil (Dole and Lewis, 53). Lift is destroyed and drag increases, causing the aircraft to rapidly lose altitude. Pilots are trained to recover from this condition. However, if the stall occurs too low to the ground, there may not be enough altitude to recover. A study of aircraft accidents from 1992 to 2002 reveals that approximately 80 percent of fatal stall accidents occurred within 1,000 feet of the ground (Landsberg). Stalls are usually associated with slow flight in a nose-up attitude, but they can occur at any airspeed or attitude.
Spins are of even greater concern because recovery requires more altitude and more actions on the part of the pilot. Simply stated, a spin is an autorotation resulting from one side of the wing stalling more than the other. Spins cause rapid loss of altitude. If the pilot does not recover, the aircraft will spin into the ground. Aircraft design affects the ease of entering and recovering from spins. Adding devices to improve stall characteristics will generally reduce spin-related accidents; preventing a stall or making it gentler can reduce accidental spins. Straight-wing aircraft must stall before they will spin (swept-wing aircraft do not necessarily have to stall first) (Dole and Lewis, 186). Favorable Stall



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