Why are wings useful for flight?

A wing is a surface designed to deflect air. Its airfoil, curved on top with the trailing edge angled downward, forces the airflow passing over it to change direction and leave heading downward. By Newton's third law, if the wing pushes the air down, the air pushes the wing up. From a pressure standpoint, the air accelerates over the upper surface and slows beneath the lower one, so the pressure above the wing is lower than below it: the difference, integrated over the whole surface, is lift. Both descriptions are the same physics seen from different angles.

Lift grows with the square of speed, with wing area and with angle of attack. A transport aircraft generates with its wings a force equal to its own weight in exchange for drag that is only a fraction of that: the lift-to-drag ratio of a commercial jet is around 17 to 1, and that of a glider exceeds 50 to 1. That means the engines only need to supply thrust equivalent to a small part of the weight. A rocket, which has no wings, must overcome its entire weight with direct thrust and burns propellant at a much higher rate.

Long, narrow wings, like a glider's, generate lift with little induced drag, but they are heavy and hard to manoeuvre. Short, swept wings, like a fighter's, penalise efficiency at low speed but allow fast flight. Airliners seek a balance with moderate sweep, high aspect ratio and high-lift devices, flaps and slats, which increase curvature and area when it is necessary to take off and land at low speeds.