Propulsion Integration Questions and Answers

Answer: C

Correct answer: 3.1 m

Read down the clearance column against the 0.40 m requirement. The 3.1 m fan gives 0.41 m, just sufficient; the 3.4 m fan gives 0.28 m and fails.

Note how quickly the margin disappears: each 0.3 m of fan diameter costs about 0.15 m of clearance, since the nacelle grows by roughly the same amount and half of it hangs below the centreline. That is the arithmetic behind the flattened nacelle bottoms and lengthened landing gear seen on re-engined aircraft.

Answer: D

Correct answer: Removing bleed addresses the larger share

The two bleed items total 2.8 per cent of the 3.4 per cent lost, against 0.6 per cent for the gearbox. Eliminating bleed therefore attacks more than four fifths of the offtake penalty.

That is the case for a bleedless architecture, in which cabin air is compressed electrically and the wing is anti-iced electrically. The saving is real but not free: the electrical system grows heavier and the generators larger, so the net benefit depends on the mission.

Answer: A

Correct answer: Underwing pod, for relief and access

The table shows the underwing pod alone scoring well on both bending relief and access, which are the two criteria that matter most on a large long-range transport - relief because the wing is long and heavily loaded, access because the aircraft must be turned round quickly and maintained economically.

Its penalty is the large engine-out moment, paid for with a bigger fin. That trade has been accepted on essentially every large transport built since the 1960s.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason gives the two decisive advantages. The engine mass hanging outboard acts downward against the wing's upward bending in flight, allowing a lighter structure - and the relief grows with load factor, so it is greatest where the structure is most critical.

A pod hanging clear beneath the wing is also far easier to inspect, access and change than a buried or rear-mounted installation. Together these outweigh the larger engine-out yawing moment the position imposes.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the second explains the first. Engines on the rear fuselage occupy the space where a conventional tailplane root would sit, and their efflux and wake pass through it.

Mounting the tailplane on top of the fin lifts it clear of both. The arrangement brings its own difficulty - a T-tail can be blanketed by the wing wake at high angle of attack, giving a deep stall from which recovery may be impossible - which is why such aircraft carry stick pushers.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason is the whole justification for the mechanism. A supersonic inlet decelerates the flow through oblique shocks whose angles depend on the flight Mach number, so a fixed geometry is correctly matched at one speed only.

Variable ramps or a translating centrebody reposition the shock system across the envelope, keeping pressure recovery high and avoiding buzz. The cost in weight, complexity and maintenance is accepted because a mismatched inlet loses far more in thrust than the mechanism weighs.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason is why the limit exists. As the aircraft slows it no longer outruns its own reversed efflux, so the hot gas curls forward and can be drawn back into the inlet.

Re-ingestion raises inlet temperature, distorts the flow into the compressor and risks a surge; the same flow field lifts debris from the runway towards the engine. Stowing at a specified ground speed avoids both, at the cost of giving up the last of the reverse thrust when it is least effective anyway.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the saving. Bleed air is taken from the compressor after the engine has already done work compressing it, and that work is discarded rather than recovered by expansion through the turbine.

A bleedless architecture drives cabin compressors and anti-icing electrically instead, recovering most of the two to three per cent that bleed costs. The saving is offset by a heavier electrical system and larger generators, so the net gain depends on the aircraft and its mission.

Answer: C

Correct answer: A is false but R is true

The assertion is false. An overwing nacelle sits above the wing's upper surface - the most aerodynamically sensitive region on the aircraft, where the flow is accelerated and the pressure recovery is delicate. Interference drag there is higher, not lower, than for an underwing pod.

The reason is true, and gives the genuine motives for overwing mounting: the wing shields engine noise from the ground, and it keeps the intake well clear of runway debris. Those benefits are bought at a drag penalty rather than accompanied by a drag benefit.

Answer: D

Correct answer: Both A and R are true, but R is not the correct explanation of A

Both statements are true, but the reason works against the assertion rather than for it. The twin's shorter arm would, on its own, give it the smaller moment.

The twin nonetheless suffers the larger moment because each of its engines carries twice the thrust: with equal total thrust \( 4T \), losing one gives \( 2T \times 8 = 16T \) against \( T \times 12 = 12T \). The explanation is the thrust per engine, not the arm - the arm is a mitigating factor that the thrust overwhelms.