The lift-to-drag ratio achievable in supersonic cruise, compared with subsonic cruise, is
Answer: A
Wave drag adds a whole component that simply does not exist subsonically, and the thin, low-aspect-ratio wing a supersonic aircraft needs is poor at generating lift cheaply. Ratios around seven are typical in supersonic cruise against fifteen to twenty for a subsonic transport.
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Nacelle placement on a transonic transport matters aerodynamically because
Answer: B
A nacelle adds cross-sectional area over its length and its own flow field interacts with the wing's supersonic pocket. Placed carelessly it strengthens the shock and provokes separation; placed well it can be nearly neutral, which is why nacelle position is settled early and changed reluctantly.
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Wing-body blending on a modern transport is used partly to
Answer: C
A fillet or blended junction avoids the abrupt area change and the corner flow that a plain intersection would produce, cutting both wave drag and the interference drag caused by two boundary layers meeting. It is the area rule applied with a lighter touch than a waisted fuselage.
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An aircraft has a critical Mach number of \( 0.72 \) unswept. What sweep is needed for a critical Mach number of about \( 0.85 \)?
Answer: D
Requiring \( 0.85 \cos\Lambda = 0.72 \) gives \( \cos\Lambda = 0.847 \), so \( \Lambda = 32 \) degrees. This is exactly the range found on real transports, and it shows how the familiar 30 to 35 degrees of sweep follows directly from a cruise Mach number near 0.85.
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A wing of aspect ratio \( 9 \) is swept \( 30 \) degrees. Measured perpendicular to the leading edge, the effective aspect ratio is nearest to
Answer: A
The effective value scales as \( AR \cos^2\Lambda = 9 \times 0.866^2 = 9 \times 0.75 = 6.75 \). Sweep therefore costs aspect-ratio efficiency as well as maximum lift, which is part of why designers use no more sweep than the cruise Mach number actually requires.
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Assertion (A): Transport wings are swept about thirty to thirty-five degrees rather than sixty.
Reason (R): Sweep costs maximum lift and effective aspect ratio, so no more is used than the cruise Mach number needs.
Select the correct answer from the options below.
Answer: B
Both are true and the second explains the first. A cruise near Mach 0.85 requires only about thirty-two degrees to bring the section down to a comfortable normal Mach number, and every further degree would cost low-speed performance and induced-drag efficiency for no cruise benefit.
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Assertion (A): Laminar flow control is harder to achieve on a swept wing than on an unswept one.
Reason (R): The spanwise pressure gradient produces an inflected crossflow profile that is highly unstable.
Select the correct answer from the options below.
Answer: C
Both statements are true and the second is the reason for the first. Crossflow instability transitions the boundary layer far earlier than Tollmien-Schlichting waves alone would, so the natural laminar run on a swept wing is short and active suction is usually needed to extend it.
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Consider the following statements about supersonic cruise efficiency:
1. Wave drag adds a component absent from subsonic flight.
2. The thin, low-aspect-ratio wing needed is a poor lift generator.
3. Lift-to-drag ratios comparable with a subsonic transport are readily achieved.
Which of the statements given above is or are correct?
Answer: D
The first two are correct and between them explain the third's falsity. Supersonic cruise ratios around seven compare poorly with fifteen to twenty subsonically, and that gap is the central economic obstacle to supersonic transport rather than any single technical failure.
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Consider the following statements about nacelle and junction design on a transonic wing:
1. A nacelle contributes to the aircraft's cross-sectional area distribution.
2. A blended wing-body junction reduces interference drag.
3. Junction shaping has no effect on the strength of the wing shock.
Which of the statements given above is or are correct?
Answer: A
The first two are correct. The third is false: shaping at the junction alters the local pressure field and can strengthen or weaken the shock on the inboard wing appreciably, which is why so much transonic design effort goes into fillets and nacelle position.
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Match each aircraft feature in List I with the design principle behind it in List II.
List I
A. Concorde's ogival delta
B. The F-102's waisted fuselage
C. A modern transport's supercritical wing
D. The F-14's variable sweep
List II
1. Smoothing the streamwise area distribution
2. Keeping the leading edge subsonic while retaining vortex lift
3. Weakening the shock that closes the supersonic pocket
4. Serving both low-speed loiter and a supersonic dash
Select the correct match.
Answer: B
Each of these aircraft is a textbook illustration of one principle. Taken together they trace the development of transonic and supersonic wing design from the area rule of the 1950s through variable sweep to the supercritical sections that every airliner now uses.
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