Aircraft achieve flight due to lift, an aerodynamic force that counteracts gravity. Lift is produced by the interaction of the airplane with surrounding air. The angle of attack is the angle between the wing’s chord line—an imaginary line from the leading edge to the trailing edge—and the direction of the oncoming airflow, or relative wind. This angle is a fundamental factor in controlling how much lift an aircraft generates.
Understanding How Wings Generate Lift
An aircraft wing generates lift through aerodynamic principles. The curved shape of the wing and its interaction with air create a pressure difference. As air flows over the curved upper surface of the wing, it speeds up, resulting in lower pressure above the wing. Simultaneously, air flowing beneath the flatter lower surface travels more slowly, leading to higher pressure. This pressure differential creates a net upward force on the wing.
The wing also generates lift by deflecting air downwards. As the wing moves, it pushes air downwards. By Newton’s Third Law, the wing’s downward push on the air creates an equal and opposite upward force on the wing, contributing to lift. Both the pressure differential and downward air deflection produce the overall lift force that supports an aircraft.
How Tilting the Wing Increases Lift
Increasing the angle of attack magnifies lift, leading to a greater upward force. When the wing tilts upward relative to the oncoming air, it increases the amount of air deflected downwards. This greater downward redirection of air results in a stronger upward reaction force on the wing, in accordance with Newton’s Third Law.
Tilting the wing also enhances the pressure differential. As the angle of attack increases, the airflow over the upper surface becomes even more accelerated, leading to a further reduction in pressure above the wing. Concurrently, the underside of the wing presents a larger surface area to the oncoming air, increasing the pressure below it. This amplified pressure difference contributes substantially to the overall lift.
Lift generally increases proportionally with the angle of attack up to a certain point. For many airfoils, a symmetrical wing will generate lift roughly in proportion to its angle of attack within a practical range. This direct relationship allows pilots to control the amount of lift produced by adjusting the wing’s angle relative to the airflow. This control is fundamental for various flight maneuvers, including takeoff, climbing, and maintaining altitude.
The Limit of Increasing Lift
While increasing the angle of attack generally increases lift, there is a critical point beyond which this relationship breaks down. This specific angle is known as the “critical angle of attack,” and it represents the angle at which the wing produces its maximum possible lift. For many general aviation aircraft, this critical angle typically falls within the range of 15 to 18 degrees. Exceeding this angle leads to a rapid decrease in lift, a condition known as an aerodynamic stall.
A stall occurs when the smooth airflow over the upper surface of the wing separates from the wing. This separation creates turbulent, recirculating air over the wing, which drastically reduces the wing’s ability to generate lift. The aircraft’s controls may become less responsive, and the wing can no longer support the aircraft’s weight, causing it to descend. It is important to understand that a stall is a consequence of exceeding the critical angle of attack, not necessarily of low airspeed. Recovery from a stall typically involves reducing the angle of attack to re-establish smooth airflow over the wing.