Compared with a straight wing of similar area and aspect ratio, a swept wing has a lift coefficient that is:

• A. Higher at subsonic speeds
• B. Lower at subsonic speeds
• C. Higher at all speeds
• D. Less throughout subsonic and supersonic speeds

Answer: (D)

Sweeping a wing reduces the lift coefficient for a given flight condition because the flow interacts with the wing as if the angle of attack were smaller. The wing’s sweep turns the wing planform away from the flow, so the velocity component that actually contributes to generating lift normal to the wing is reduced. That means, at the same airspeed and true angle of attack, a swept wing produces less lift per unit area than a straight wing of similar area and aspect ratio. This reduction in lift holds across subsonic speeds and, with the same caveat about speed-related effects, also applies toward the transonic and lower supersonic ranges. The practical takeaway is that sweep lowers lift for a given condition, even though it raises the speed at which compressibility effects become problematic, which is why sweep is used for higher speed capability rather than higher lift at a fixed AoA.