12.68 Stalling and Spinning

12.68.2 Describe the stalling angle of attack, with reference to:

(a) disruption of streamline flow over the upper surface of the aerofoil;

The stalling angle of attack is the angle of attack at which the airflow over the upper surface of an airfoil becomes disrupted, causing a loss of lift and an increase in drag. This disruption of the streamline flow over the upper surface of the aerofoil is due to the separation of the boundary layer from the surface of the airfoil. At low angles of attack, the airflow over the upper surface of the airfoil remains attached to the surface, creating a smooth, streamlined flow. As the angle of attack increases, the airflow over the upper surface of the airfoil begins to separate from the surface, creating turbulent flow and reducing the effectiveness of the airfoil. At the stalling angle of attack, the airflow over the upper surface of the airfoil becomes fully separated, creating a large wake of turbulent air behind the airfoil. This reduces the lift generated by the airfoil and increases the drag, causing the aircraft to lose altitude and airspeed. Pilots must be aware of the stalling angle of attack for their particular aircraft, and must avoid flying at angles of attack that are too high. Proper training and practice can help pilots develop the skills necessary to recognize and recover from a stall.