What does the area rule imply for drag in transonic flow?

What does the area rule imply for drag in transonic flow?

• A. Drag depends solely on wing area and is independent of fuselage shape.
• B. Drag correlates with cross-sectional area; smooth area distribution minimizes wave drag.
• C. Cross-sectional area distribution is irrelevant to drag in transonic flow.
• D. Wave drag is minimized by maximizing fuselage cross-section.

Answer: (B)

In transonic flow, wave drag arises from shock waves forming as the aircraft stretches toward and beyond Mach 1. The area rule shows that drag is tied to how the cross-sectional area along the aircraft changes with length. If A(x)—the cross-sectional area at each station along the fuselage and wings—varies smoothly, the shocks are weaker and the overall wave drag is reduced. So the total drag relates to the distribution of cross-sectional area, not just to the size of a single part like the wing. Designers blend and shape the fuselage and wing to keep A(x) as uniform as possible, which minimizes wave drag. That’s why the correct idea is that drag correlates with cross-sectional area and that a smooth area distribution minimizes wave drag. The other statements ignore the importance of how area is distributed, suggest that increasing fuselage size alone reduces drag, or claim area distribution is irrelevant, which isn’t consistent with transonic drag behavior.

In transonic flow, wave drag arises from shock waves forming as the aircraft stretches toward and beyond Mach 1. The area rule shows that drag is tied to how the cross-sectional area along the aircraft changes with length. If A(x)—the cross-sectional area at each station along the fuselage and wings—varies smoothly, the shocks are weaker and the overall wave drag is reduced. So the total drag relates to the distribution of cross-sectional area, not just to the size of a single part like the wing. Designers blend and shape the fuselage and wing to keep A(x) as uniform as possible, which minimizes wave drag.

That’s why the correct idea is that drag correlates with cross-sectional area and that a smooth area distribution minimizes wave drag. The other statements ignore the importance of how area is distributed, suggest that increasing fuselage size alone reduces drag, or claim area distribution is irrelevant, which isn’t consistent with transonic drag behavior.