What common feature differentiates an airfoil from a flat surface?

An airfoil is specifically designed to generate lift, which distinguishes it from a flat surface. The shape of an airfoil typically has a curved upper surface and a flatter lower surface, allowing it to create a pressure difference over and under the wing when air flows around it. This pressure difference results in an upward aerodynamic force known as lift. Additionally, the angle of attack, which is the angle between the chord line of the airfoil and the oncoming airflow, plays a crucial role in enhancing this lift production.

In contrast, a flat surface, while it may produce some lift at high angles of attack, is not designed for efficient lift generation and often produces more drag without significant lift, particularly at lower angles of attack. Thus, the ability of an airfoil to efficiently generate lift under various conditions and its optimized shape for this purpose are critical features that set it apart from flat surfaces.