Which statement about the area rule is true?

Which statement about the area rule is true?

• A. In transonic regimes, drag correlates with cross-sectional area; smooth area distribution minimizes wave drag, guiding fuselage and wing shaping.
• B. Area rule has no practical implications for design.
• C. Drag is solely a function of wing area.
• D. Cross-sectional area distribution should be maximized.

Answer: (A)

The area rule shows that, in transonic flight, drag is strongly tied to how the cross-sectional area of the aircraft varies along its length. When the flow reaches near sonic speeds, wave drag comes from shock waves whose strength is influenced by how abruptly the cross-sectional area changes. If the area distribution is smooth and the overall cross-sectional area is kept as compact as possible for the vehicle length, the shocks are weaker and the wave drag is reduced. This is why shaping the fuselage and wings to achieve a smooth, minimized area distribution is the design strategy in transonic regimes. That’s why the statement stating this relationship and the benefit of a smooth area distribution is true. The other ideas don’t fit: the area rule has clear practical design implications; drag is not determined only by wing area; and maximizing cross-sectional area distribution would actually increase, not reduce, drag.

The area rule shows that, in transonic flight, drag is strongly tied to how the cross-sectional area of the aircraft varies along its length. When the flow reaches near sonic speeds, wave drag comes from shock waves whose strength is influenced by how abruptly the cross-sectional area changes. If the area distribution is smooth and the overall cross-sectional area is kept as compact as possible for the vehicle length, the shocks are weaker and the wave drag is reduced. This is why shaping the fuselage and wings to achieve a smooth, minimized area distribution is the design strategy in transonic regimes.

That’s why the statement stating this relationship and the benefit of a smooth area distribution is true. The other ideas don’t fit: the area rule has clear practical design implications; drag is not determined only by wing area; and maximizing cross-sectional area distribution would actually increase, not reduce, drag.