Which statement about swept wings and lift coefficient is true?

• A. CL is less for swept wings compared to straight wings with same area and AR in both subsonic and supersonic
• B. CL is greater for swept wings in subsonic but less in supersonic
• C. CL is unaffected by wing sweep
• D. CL is greater for straight wings in all flight regimes

Answer: (A)

Sweeping a wing changes how effectively it can generate lift at a given geometry. For the same wing area and aspect ratio, a swept wing tends to produce a smaller lift coefficient than an unswept (straight) wing in both subsonic and supersonic flight.

In subsonic flow, sweeping reduces the lift-curve slope and shifts the lift distribution because the flow is redirected along the wing, increasing downwash and promoting spanwise flow toward the wingtips. These effects lower the pressure difference that the wing can sustain for a given angle of attack, so the lift coefficient is reduced.

In supersonic flow, the main aerodynamic advantage of sweep is delaying the onset of drag rise by increasing the critical Mach number, but the lift generated at a given true angle of attack is still less than that of a straight wing with the same area and AR. The sweep angle reduces the effective cross-flow that contributes to lift, effectively lowering the lift coefficient for the same geometric wing.

Therefore, the statement that the lift coefficient is lower for swept wings than for straight wings with the same area and aspect ratio holds across both subsonic and supersonic regimes. The other options contradict this understanding by claiming no change, or a higher lift coefficient under some conditions, which isn’t supported by how sweep alters lift generation.