Flight relies on aerodynamic forces, with lift countering an aircraft’s weight. Understanding how wings generate lift is central to how aircraft remain airborne, enabling passenger travel and global cargo transport.
Understanding Lift
Lift is the aerodynamic force that directly opposes an aircraft’s weight, holding it in the air. Wings, shaped as airfoils, generate this force by interacting with moving air. As air flows around an airfoil, a pressure differential forms, with lower pressure above and higher pressure beneath the wing, pushing it upward. The wing’s shape also deflects air downwards, and by Newton’s third law, this action creates an equal and opposite upward reaction force.
Understanding Angle of Attack
While wing shape is fundamental to generating lift, the angle of attack (AoA) also influences this process. AoA is the angle between the wing’s chord line—an imaginary line from leading to trailing edge—and the oncoming air (relative wind). This angle directly impacts the aerodynamic forces on the aircraft. The angle of attack differs from the aircraft’s pitch angle, which is the angle between the aircraft’s nose and the horizon; these two angles are not always the same and can vary independently.
How Angle of Attack Increases Lift
Increasing the angle of attack leads to greater lift. As the wing tilts upward, it deflects more air downwards, resulting in a stronger upward reaction force by Newton’s laws. Raising the angle of attack also accentuates the pressure difference between the wing’s upper and lower surfaces. Airflow over the curved upper surface speeds up, creating a more pronounced low-pressure zone, while higher pressure beneath the wing exerts a greater upward push. This combined effect of increased air deflection and enhanced pressure differential results in higher lift.
The Limit: Critical Angle and Stall
There is a precise limit to how much lift can be generated by simply increasing the angle of attack. As the angle continues to rise, the wing eventually reaches its “critical angle of attack,” also known as the stall angle. This is the specific angle at which the wing produces its maximum possible lift. If the angle of attack increases beyond this critical point, the smooth airflow over the upper surface of the wing can no longer adhere to the wing’s curvature and begins to separate. This separation of airflow leads to a sudden and significant loss of lift, a condition known as a “stall.” Beyond the critical angle, increasing the angle of attack paradoxically causes the lift to decrease rapidly, making the wing much less effective at supporting the aircraft.