Propulsion Integration Questions and Answers

Answer: C

As the aircraft slows, the reversed flow can outrun it and be drawn back into the inlet, carrying hot gas and debris. Reversers are therefore stowed at a specified ground speed rather than being held in to a full stop.

Answer: D

Correct answer: Low-slung underwing pods

An underwing pod on a low-wing aircraft sits close to the ground, and its inlet draws hard enough to lift stones, grit and debris from the runway into the engine.

The other positions are all further from the surface: rear-fuselage engines are high and well aft, overwing pods are shielded by the wing itself, and buried wing-root engines take their air from an inlet set well above the ground. Ground clearance is one of the sharpest constraints on low-wing installations, and it grows tighter as bypass ratio rises.

Answer: A

Correct answer: Pressurisation and anti-icing

Bleed air is hot compressed air tapped from the compressor, and its two principal uses are cabin pressurisation and air conditioning, and anti-icing of the wing leading edges and engine inlets. Both need air that is already hot and at pressure, which is exactly what the compressor delivers.

Generators, fuel pumps and hydraulic pumps are driven mechanically from the accessory gearbox instead. Bleed is not free: the air has had work done on it, so extracting it costs thrust - which is why bleedless architectures have appeared.

Answer: B

Correct answer: The generator, fuel pump and hydraulic pump

The accessory gearbox is driven by a shaft from the engine's high-pressure spool and carries the mechanically driven accessories: the electrical generator, the fuel pump, the hydraulic pump, the oil pumps and often a starter.

The distinction from bleed air is worth holding: mechanical loads come off the gearbox, pneumatic loads come from compressor bleed. Environmental control compressors run on bleed air, and thrust reversers are usually driven hydraulically or electrically rather than from the gearbox.

Answer: C

Correct answer: Fail so the engine separates cleanly

Fuse pins are deliberately weakened links in the engine mount, designed to shear under a load far above anything normal operation produces - a seizure, a severe imbalance after a fan blade loss, or a ground impact.

The reasoning is that an engine departing cleanly is survivable, whereas a pylon that stays attached and twists can tear open the wing box and its fuel tanks. During normal running the pins carry the steady thrust and inertia loads without any intended flexibility; they are structure until the moment they are not.

Answer: D

Correct answer: Give rapid access for line maintenance

Fan cowls are hinged at the top so that they swing open like a pair of doors, exposing the accessory gearbox, the pumps, the generator and the plumbing within a minute or two and with no loose fasteners to drop into the engine.

Turnround time is money, and a large proportion of line maintenance is done through these panels. Hinges add weight and a slight aerodynamic penalty compared with a flush bolted panel, so the arrangement is chosen for access despite those costs, not because of them.

Answer: A

Correct answer: Thrust and the engine's distance from the centreline

The yawing moment is a force times a moment arm, so it is the thrust of the remaining engine multiplied by its distance from the centreline:

\[ N = T \times y \]

Both terms matter, which is why a rear-fuselage installation at two or three metres produces a far smaller moment than a wing pod at seven. In practice the failed engine's windmilling drag acts at its own arm on the opposite side and must be added. Mass and bypass ratio play no part.

Answer: B

Correct answer: Reduce jet mixing noise

Chevrons are the serrated triangular cut-outs at the trailing edge of a nacelle or nozzle. They generate streamwise vortices that promote finer-scale mixing between the jet and the surrounding air.

Mixing noise arises from the large turbulent structures at the boundary between fast and slow air; breaking them into smaller structures shifts the noise to higher frequencies, which attenuate faster in the atmosphere, and reduces the low-frequency energy that carries to the ground. The cost is a small thrust loss, accepted for the noise benefit.

Answer: C

Correct answer: Ground clearance becomes critical

A higher bypass ratio means a larger fan, and a larger fan means a larger nacelle. On a low-wing aircraft with an underwing pod, the nacelle must still clear the ground with the gear compressed and the aircraft banked.

That constraint has driven several familiar solutions: flattened nacelle bottoms, longer landing gear, and engines moved forward and up on the pylon. Thrust reversers and bleed air remain perfectly feasible, and the engine's weight is not what limits the installation - its diameter is.

Answer: D

Putting the engine above the wing keeps it well clear of debris and lets the wing screen the noise from the ground. The penalties are interference drag and awkward maintenance access, which is why the layout remains rare.