Propulsion Integration Questions and Answers

Answer: A

Correct answer: Statement I is incorrect but Statement II is correct

Statement I is incorrect: bleed extraction carries a definite thrust and fuel penalty, of the order of a few per cent.

Statement II is correct and explains it. The air is tapped from the compressor after the engine has already done work compressing it, and that work is then discarded rather than recovered by expansion through the turbine. The cost is why bleedless architectures, with electrically driven cabin compressors and anti-icing, have been adopted despite the weight of the electrical system they require.

Answer: B

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second is the mechanism of the first. Jet mixing noise is generated by the large turbulent structures at the shear layer between the fast jet and the still air around it.

Chevrons shed streamwise vortices that break those structures into finer ones. The acoustic energy shifts to higher frequencies, which the atmosphere attenuates far more rapidly over the distance to the ground, and the low-frequency content that carries best is reduced. A small thrust penalty is accepted in exchange.

Answer: C

The inlet delivers the flow to the fan face at low Mach number, the compressors raise its pressure, the core burns and expands it, and the nozzles convert what is left into velocity. Each stage depends on the one before it doing its job.

Answer: D

Correct answer: 2, 4, 1, 3

The chain runs from the failure to the design consequence. Thrust becomes asymmetric (2) the moment the engine fails. A yawing moment develops, augmented by the windmilling drag of the dead engine acting on the opposite side (4).

The rudder is applied and the aircraft held straight (1), and the fin and rudder are sized from the balance that requires (3). The last step is the design one: the surfaces exist to meet this case, so the case must be established before they can be sized.

Answer: A

Correct answer: 2, 4, 1, 3

The moment is thrust times arm, so the ordering follows the arms. A rear-fuselage engine (2) is closest to the centreline at two or three metres. A wing-root buried engine (4) is next, being tucked against the fuselage.

An underwing inboard pod (1) is further out, and an underwing outboard pod on a four-engine aircraft (3) is furthest of all, often twelve metres or more. The last case is what sizes the fin, which is why four-engine aircraft carry proportionally large vertical tails.

Answer: B

The engine states its demand, the capture area follows, the diffuser then slows the flow to what the fan wants, and the off-design penalty is assessed last. Choosing an area before knowing the demand would be arbitrary.

Answer: C

Correct answer: 2, 1, 3, 4

The sequence follows the landing roll. Main wheels touch down and the spoilers deploy (2), dumping lift so that weight transfers to the wheels and the brakes can work.

Reversers are deployed and the fan flow turned (1), and they are most effective at high speed where their momentum change is greatest. As speed falls, wheel braking takes over as the main retarding force (3), and the reversers are stowed at the specified speed (4) - before they begin re-ingesting their own efflux and any debris it has raised.

Answer: D

Correct answer: Only three

Three pairs are right. An underwing pod gives wing bending relief and easy access; a rear-fuselage installation gives a small engine-out yawing moment; and a wing-root buried engine gives low drag and a clean exterior.

The fourth is wrong. An overwing pod does not have the lowest interference drag - the flow over the wing upper surface is the most sensitive region on the aircraft, and putting a nacelle there disturbs it badly. Overwing mounting is chosen for ground clearance and debris protection, at a drag penalty.

Answer: A

Correct answer: Only three

Three pairs are right. A boundary layer diverter keeps low-energy fuselage flow out of the inlet; a variable ramp matches the shock system to Mach number; and the diffuser slows the flow so it arrives at the fan face at an acceptable Mach number.

The fourth is wrong. Chevrons are at the exhaust, not the inlet, and their purpose is to reduce jet mixing noise by promoting finer-scale mixing. They have no effect on inlet pressure recovery whatever.

Answer: B

Correct answer: All four

Every pair is correct, and together they make the point that no installation is without cost. An underwing pod's long moment arm gives a large engine-out yawing moment; rear-fuselage engines shift the centre of gravity aft and require a heavier rear fuselage.

Buried engines are difficult to change and force the wing box to be cut about; and a high bypass ratio reduces ground clearance under a low wing. Choosing an installation means choosing which of these penalties to accept, which is what makes propulsion integration a genuine design trade.