Stalling, Spinning, and Recovery

7.1 The Cause of the Stall

• A stall is a loss of lift resulting from the separation of airflow from the wing's upper surface.
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•  It is caused by exceeding the
• critical angle of attack (AOA), which is typically around 16 degrees.
•  A stall is an aerodynamic phenomenon related to AOA, not airspeed. An aircraft can be
• stalled at
• any speed, in any attitude, if the critical AOA is exceeded.

•  The primary cause is the
• adverse pressure gradient on the rear portion of the wing becoming too strong for the
• boundary layer's kinetic energy, causing the flow to stop, reverse, and separate. 149149149149

7.2 Stall Recognition and Behavior

• As an aircraft approaches a stall, the pilot may observe:
•  Flight controls becoming less effective ("mushy").
•  Speed is low and decreasing for a given power setting.
•  Nose attitude is higher than normal.
•  Aerodynamic buffeting as the separated, turbulent air from the wing root strikes the tailplane.
•  Activation of a stall warning device (e.g., horn or stick shaker).
• At the stall itself, the aircraft may experience a wing drop, a sharp nose drop, and a loss of
• altitude.

7.3 Stall Recovery

• The only way to recover from a stall is to restore smooth airflow over the wing.
• 1. Reduce the Angle of Attack: The primary and most critical action is to move the control
• column forward to reduce the AOA below the critical angle.
• 2. Apply Maximum Power: Simultaneously apply maximum authorized power to minimize
• altitude loss and accelerate the aircraft back to a safe flying speed.
• 3. Level the Wings: Use rudder to prevent wing drop on straight-wing aircraft. On swept-
• wing aircraft, ailerons may be recommended.
• A
• secondary stall can occur if the pilot pulls back on the control column too aggressively
• before the aircraft has regained sufficient airspeed.

7.4 Factors Affecting Stall Speed (Vs)

• The indicated stall speed is affected by several factors:
•  Weight: Stall speed increases with the square root of the change in weight. A 20% weight
• reduction results in an approximate 10% reduction in stall speed. 163163163163
•  Load Factor (g): In a turn, lift must be increased to maintain altitude, which increases the
• load factor. The stall speed increases with the square root of the load factor. 164164164164For
• example, in a 60° level turn, the load factor is 2g, and the stall speed increases by about 41%.
•  Configuration (Flaps/Slats): High-lift devices increase the Cʟₘₐₓ, which decreases the stall
• speed. 166166

•  Center of Gravity (CG): A forward CG requires a greater tail-down force to maintain
• balance, which means the main wing must produce more lift overall. This results in a higher
• stall speed. An aft CG reduces the required tail-down force, resulting in a
• lower stall speed.
•  Power: Engine thrust has a vertical component that helps support the aircraft's weight, and
• propeller slipstream over the wing increases lift. Therefore, the power-on stall speed is
• lower than the power-off stall speed.
•  Wing Contamination: Ice, frost, or even dirt on the leading edge disrupts the airflow,
• reduces Cʟₘₐₓ, and increases the stall speed.
•  Mach Number: At high altitudes and speeds, compressibility effects can cause flow
• separation at a lower AOA, reducing Cʟₘₐₓ and increasing the stall speed. 170170170170This
• leads to the phenomenon of "coffin corner," where the high-speed buffet (Mach buffet) and
• low-speed buffet (stall) converge.

7.5 Spinning

•  A spin is an aggravated stall that results in
• autorotation, a helical flight path where the aircraft is descending while rotating.
•  It occurs when one wing is more stalled than the other. The more-stalled (down-going) wing
• has both less lift and more drag, which causes the aircraft to roll and yaw into the spin.
•  Spin Recovery: The generic recovery procedure is:
• 1. Power to IDLE.
• 2. Ailerons NEUTRAL.
• 3. Rudder FULL OPPOSITE to the direction of rotation.
• 4. Elevator PUSH FORWARD to break the stall.