With MCDR and MCRIT, which statement about sweepback is correct?

• A. Sweepback increases
• B. Sweepback decreases
• C. Sweepback unchanged
• D. Sweepback varies

Answer: (A)

As Mach number moves toward the transonic range, delaying the onset of shock waves on the wing becomes crucial. Sweeping the wing reduces the flow’s effective speed normal to the leading edge, which pushes the speeds at which shocks form and drag rises to higher values. So, to withstand higher speeds before drag rises sharply (toward MCDR and MCRIT), the useful effect of sweepback becomes greater. That’s why sweepback increases in this context. The other possibilities don’t align with the goal of delaying drag divergence: less sweep or no change would actually bring on the drag rise sooner, and saying it simply varies is too vague to capture the directional influence of sweep at these Mach numbers.