Propulsion Integration Questions and Answers

Answer: C

Correct answer: Only three

Three pairs are right. Cabin pressurisation and wing anti-icing both run on compressor bleed air, which arrives hot and at pressure; electrical generation is driven mechanically from the accessory gearbox.

The fourth is wrong. Thrust reversers are deployed hydraulically or electrically, not by bleed air. The general division is worth remembering: pneumatic services take bleed from the compressor, mechanical services take shaft power from the gearbox, and actuation is hydraulic or electric.

Answer: D

Correct answer: Only three

Three pairs are right. Pressure recovery is the total pressure at the fan face divided by the free stream total pressure; spillage drag arises from air the inlet captures but does not swallow; and inlet buzz is an unsteady shock oscillation at a supersonic inlet.

The fourth is wrong. Bypass ratio is the ratio of the mass flow through the fan bypass duct to that through the core, not a ratio of diameters. The diameters do rise together, but the definition is one of flow.

Answer: A

Correct answer: A small engine-out yawing moment

An underwing pod sits far from the centreline - often seven metres or more, and twelve on the outboard station of a four-engine aircraft - so its engine-out yawing moment is the largest of any common arrangement. That is the position's principal drawback, and it sizes the fin.

The other three are genuine advantages: the engine mass relieves wing bending, a podded engine hangs clear for easy access and change, and keeping the engine below and ahead leaves the wing upper surface aerodynamically clean.

Answer: B

Correct answer: Exhaust nozzle chevron geometry

Chevrons are at the exhaust, downstream of everything the engine does, and they cannot affect what happens at the inlet. Their business is jet mixing noise.

The other three all bear on recovery directly: ingesting a fuselage boundary layer brings in low-energy distorted flow, the position of the shock system at supersonic speed determines how much total pressure survives the deceleration, and the diffuser shape governs whether the flow reaches the fan face without separating.

Answer: C

Correct answer: Higher jet velocity and more mixing noise

Raising the bypass ratio lowers jet velocity and reduces mixing noise. A larger mass of air is accelerated less to produce the same thrust, and since mixing noise scales with a high power of jet velocity, the reduction is dramatic - it is the main reason modern turbofans are so much quieter than early jets.

The other three are genuine consequences: a larger nacelle diameter, reduced specific fuel consumption from the improved propulsive efficiency, and the ground clearance problem that larger nacelle creates under a low wing.

Answer: D

Correct answer: Boundary layer diverter

A boundary layer diverter is an inlet component: a wedge or gap that holds a fuselage-side intake clear of the surface so that low-energy boundary layer air passes outside rather than being ingested.

The other three are structural items in the mounting chain. The pylon front spar fitting attaches the pylon to the wing, the thrust link carries the engine's forward force into that structure, and fuse pins are the deliberately weakened elements that let the engine separate cleanly under a severe overload.

Answer: A

Correct answer: Higher aircraft mass

A heavier aircraft needs more retarding force, but its mass does nothing to make the reverser itself less effective or more hazardous - the reverser turns the same fan flow whatever the aircraft weighs.

The other three are all genuine low-speed problems. As forward speed falls the aircraft no longer outruns its own reversed efflux, so the hot gas can be re-ingested, and the same flow field draws loose debris towards the inlet. This is why reversers are stowed at a specified ground speed rather than held in to a stop.

Answer: B

Correct answer: Ground clearance beneath the nacelle

The nacelle grows with the fan, so a 3.1 m fan in place of a 2.8 m one adds roughly 0.3 m to the diameter and therefore about 0.15 m to the depth below the pylon. On a low-wing twin the static clearance may already be only half a metre, and it must survive oleo compression, tyre deflection and bank.

Gearbox ratios and bleed are matters of engine design rather than integration, and the engine-out moment depends on the arm, which a re-engining does not change.

Answer: C

Two heavy engines moving far aft shifts the centre of gravity and changes what the tail must do, and a T-tail usually becomes necessary as well. Wing bending relief is lost at the same time, so the wing structure itself grows heavier.

Answer: D

Correct answer: Raise the nacelle above the runway

Foreign object damage on a rough field is a geometry problem: the inlet is close enough to the surface that its suction lifts stones and grit into the engine. Raising the nacelle - by longer gear, a different pylon geometry, or moving the engine up and forward - attacks that directly.

None of the others touches the cause. Chevrons address exhaust noise, a variable inlet addresses supersonic shock matching, and raising the bypass ratio makes the nacelle larger, which lowers the clearance and makes matters worse.