A swept wing is a wing that has an angle backward or forward. Most of the initial aircraft had a straight wing. There are many advantages of swept wing over a straight wing. By sweeping of wing, a wing sees an effectively smaller value of airflow velocity or Mach number. By sweeping the wings of a subsonic aircraft the drag divergence is delayed.

Swept wing with normal and tangential stream velocity components

If \(\Lambda\) is the sweep angle of the swept wing than critical Mach number for an airfoil is less than actual critical Mach number for a swept wing which is less than critical Mach number for an airfoil/\(\cos\Lambda\). Wing sweep increases the critical Mach number of the airfoil. However, wing sweep reduces the lift. There is a decrease in the coefficient of lift.

For a supersonic aircraft in a supersonic flight, wing sweep decreases the wave drag. A thin wing with a large angle of sweepback has the smallest wave drag.

Swept wing