[L1] 1 Overview [L2] 1) Definition [L4] - A phenomenon occurring on aircraft wings where lift decreases suddenly. [L4] - A phenomenon where lift decreases when the wing reaches or exceeds the critical angle of attack. [L2] 2) Angle of Attack (AoA) [L4] - The angle formed between the chord line of the airfoil and the relative direction of motion of the fluid. [L5] * The angle between the chord line, which is the straight line connecting the leading edge and trailing edge of the airfoil, and the relative direction of motion of the air. [L4] - As the angle of attack increases, the maximum lift coefficient increases together, but there is a tendency to decrease rather than increase once it exceeds a certain angle. [L2] 3) Terms Related to Stall [L4] - Aircraft Wing (Airfoil) [L4] - Critical Angle of Attack: The angle at which the airflow flowing over the wing surface separates from the wing when the angle of attack exceeds a certain amount, resulting in a state where sufficient lift cannot be generated to support the aircraft's load. [L1] 2 Occurrence and Countermeasures of Stall [L2] 1) Occurrence of Stall [L4] - It always occurs at the same angle of attack (e.g., 16 degrees), and the most important thing is that the angle of attack is unrelated to speed, attitude, or weight. [L5] * Aircraft stall is linked to the angle of attack regardless of the aircraft's speed, density, altitude, or weight. [L4] - The larger the angle of attack, the greater the lift generation. [L4] - At a high angle of attack, the aircraft can maintain the same altitude even if speed is reduced, compensating for reduced thrust. [L4] - If the angle of attack exceeds a certain amount, separation occurs in the airflow on the upper and lower surfaces of the wing, which is called the critical angle of attack (16~20 degrees). [L2] 2) Prevention of Stall [L4] - Lift, the force capable of lifting the aircraft's weight, must always be greater than gravity, and this condition must be maintained during flight. [L4] - To maintain the aircraft's altitude, lift must be greater than gravity, which can be resolved by reducing the aircraft's own weight or increasing lift. [L4] - Stall is affected only by the angle of attack and is not affected by surface roughness or weight. Since the streamline flowing over the wing is assumed to be laminar flow, surface roughness also has no effect.