The chief reason a supersonic transport has proved economically difficult is
Answer: C
Wave drag and the poor lifting efficiency of a thin, slender wing together halve the lift-to-drag ratio relative to a subsonic transport, and fuel burn per seat-mile follows directly. The engineering was demonstrated decades ago; it is the economics, along with the sonic boom overland, that has proved intractable.
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Which best summarises why wing design differs so sharply between the subsonic and supersonic regimes?
Answer: D
The whole tension of the subject lies in that one sentence. A long wing is cheap in induced drag but expensive in wave drag; a slender swept wing is the reverse. Every planform from the sailplane to the delta is a position taken on that trade, and variable sweep was an attempt to avoid taking one.
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A canard-delta configuration is used on aircraft such as the Eurofighter partly because the canard
Answer: A
The canard's own vortex passes over the wing and delays breakdown of the wing's leading-edge vortex, extending the usable incidence range. It also trims the aircraft with a lifting rather than a downloading surface, which suits a delta whose aerodynamic centre moves a long way between subsonic and supersonic flight.
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A close-coupled canard differs from a conventional tailplane chiefly in that it
Answer: B
A tailplane usually trims a nose-down moment by pushing down, which subtracts from the lift the wing must make. A canard trims by lifting, so it adds. The cost is a destabilising contribution that must be handled by relaxed static stability and a flight control computer.
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The sonic boom overpressure reaching the ground from a supersonic aircraft depends most strongly on
Answer: C
The near-field pressure signature coalesces during its descent into the familiar N-wave, and how strong it arrives depends on how much volume and lift the aircraft distributes over how much length, and on how far the wave has travelled. Stretching the aircraft and flying higher both soften it, which is the basis of current low-boom design.
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A supersonic aircraft cruises at \( M = 1.8 \). The minimum leading-edge sweep for a subsonic edge is nearest to
Answer: D
The Mach angle is \( \arcsin(1/1.8) = 33.7 \) degrees, so the sweep must exceed \( 90 - 33.7 = 56.3 \) degrees. The distractor 33.7 degrees is the Mach angle itself, which is the complement of the answer and the commonest slip in this calculation.
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Assertion (A): Relaxed static stability is common on canard-delta fighters.
Reason (R): A canard placed ahead of the centre of gravity is destabilising in pitch.
Select the correct answer from the options below.
Answer: A
Both are true and the second explains the first. A lifting canard moves the neutral point forward, so the aircraft is deliberately flown with the centre of gravity behind it and stabilised artificially. The reward is trim without a download and a marked gain in manoeuvrability.
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Consider the following statements about the sonic boom:
1. Its strength depends on the aircraft's length, weight and altitude.
2. It reaches the ground continuously along the flight track, not only at the moment of transition.
3. It can be eliminated entirely by careful shaping.
Which of the statements given above is or are correct?
Answer: B
The first two are correct. The third overstates what shaping can do: careful distribution of volume and lift along a long airframe can soften the signature substantially, which is what low-boom research pursues, but the pressure disturbance cannot be made to vanish while the aircraft is supersonic.
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Consider the following statements about a close-coupled canard on a delta:
1. Its vortex delays breakdown of the wing's leading-edge vortex.
2. It trims the aircraft with an upward load rather than a download.
3. It makes the aircraft more statically stable in pitch.
Which of the statements given above is or are correct?
Answer: C
The first two are the aerodynamic case for the configuration. The third is reversed: a lifting surface ahead of the centre of gravity moves the neutral point forward and is destabilising, which is precisely why such aircraft rely on relaxed stability and full authority flight control systems.
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Which of the following is NOT a recognised approach to reducing the sonic boom reaching the ground?
Answer: D
A thicker wing adds volume abruptly and strengthens the signature, which is the opposite of what low-boom design seeks. The other three all spread the disturbance over a greater length or a greater propagation distance and soften the wave that arrives.
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