CL of a swept wing compared to a straight wing with comparable area and aspect ratio is

• A. Less in both supersonic and subsonic
• B. Greater in subsonic only
• C. Less in subsonic only
• D. Greater in both supersonic and subsonic

Answer: (A)

The ability of a wing to generate lift per unit of angle of attack (lift coefficient) is reduced when the wing is swept, even if the area and aspect ratio are kept the same. Sweeping the wing changes how the flow meets the wing: the flow’s normal component to the wing’s surface is smaller, so the wing’s circulation and the pressure differences that produce lift are weaker. In subsonic flight this shows up as a lower lift-curve slope and a smaller CL for a given flight condition. In supersonic flight, sweep still reduces the effective lift generation per unit angle of attack, even though it helps with drag and wave effects, so the overall lift coefficient remains lower than that of a straight wing with identical area and AR. To compensate, a higher angle of attack (and thus more drag) would be needed to achieve the same lift as the straight wing.