lift-to-drag ratio

The lift-to-drag ratio is a measure of an airfoil's efficiency. An airfoil is a specially shaped surface, like an airplane's wing, that generates both lift and drag when it moves through the air. Lift is the force that pushes the airfoil upward, perpendicular to the airflow, while drag is the force that resists its motion, acting in the same direction as the airflow.12

A higher lift-to-drag ratio indicates that an airfoil is more efficient, producing more lift for less drag. For example, a hand held flat out a car window experiences high drag and low lift, resulting in a poor lift-to-drag ratio. When tilted slightly, it generates more lift and less drag, improving the ratio. High-speed aircraft often use thin, streamlined airfoils for low drag and low lift, whereas slower aircraft may use thicker airfoils for higher lift, even if it means more drag.21