The forebody of a hypersonic vehicle typically serves as
Answer: C
The vehicle and its propulsion cannot be designed separately at these speeds, since the forebody shock system performs part of the compression. That integration is why hypersonic vehicles look so unlike conventional aircraft.
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The afterbody of a hypersonic vehicle usually acts as
Answer: D
A full nozzle would be impossibly large at hypersonic pressure ratios, so the vehicle's underside completes the expansion. The resulting thrust vector passes through the airframe rather than through any discrete engine component.
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A combined cycle propulsion concept exists because
Answer: A
A turbine engine works from rest to about Mach 3, a ramjet from 2 to 6 and a scramjet above that. Handing over between them, or combining them in one flow path, is the only way to span the whole range with air breathing propulsion.
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A turbine based combined cycle engine handles the low speed range using
Answer: B
The turbine engine accelerates the vehicle to a speed at which ram compression becomes adequate, and is then bypassed or shut down. The transition between modes is one of the hardest parts of the whole design to make work reliably.
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The X-43A and X-51A flight programmes demonstrated
Answer: C
Both vehicles were boosted to operating speed before their engines took over for a brief powered phase. Those flights proved the principle while showing how far the technology remains from practical sustained operation.
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A ramjet's thrust falls at very high Mach numbers because
Answer: D
Shock losses grow steeply and the high combustor temperature dissociates the products, absorbing energy that never reaches the nozzle. Both effects worsen with Mach number and together set the upper limit of the cycle.
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The inlet of a scramjet must
Answer: A
Partial compression through oblique shocks raises the pressure without the temperature penalty of full deceleration. Getting that shock system right across a range of Mach numbers is one of the principal design challenges of the engine.
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Thermal choking in a scramjet combustor occurs when
Answer: B
Adding heat to a supersonic flow drives it towards Mach one, and reaching that point disrupts the whole flow path. The combustor is often given a diverging area specifically to allow heat addition without approaching the condition.
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Compared with a rocket, an air breathing hypersonic engine offers
Answer: C
Correct answer: Much better specific impulse
An air breathing engine takes its oxidiser from the atmosphere and so carries only fuel, while a rocket must lift both. A hydrogen scramjet reaches a specific impulse of the order of 3000 seconds against about 450 for a hydrogen-oxygen rocket, roughly seven times better. The rocket keeps the advantages of working from rest, in vacuum, and at any speed, and it is far simpler; the air breather’s single but decisive advantage is the fuel it does not have to carry.
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A ramjet is well suited to
Answer: D
Its simplicity, light weight and freedom from rotating machinery suit an expendable vehicle in that speed band. The requirement for a booster to reach operating speed is acceptable when the vehicle is launched rather than taking off.
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