Propulsion Integration Questions and Answers

Answer: A

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. A fuse pin is ordinary structure until the moment it is not: it must carry every flight and ground load, including manoeuvre, gust, landing impact and thrust, with full fatigue life and no intended movement.

Its weakness is calibrated to lie above all of those and below the load that would fail the wing, so it shears only in a severe overload - a seizure, a fan blade loss, an impact - letting the engine depart before the wing box is torn open.

Answer: B

Correct answer: 1 and 2 only

Statement 1 is correct: the engine mass outboard relieves wing bending in flight. Statement 2 is correct: a pod hanging clear beneath the wing is the easiest of all installations to access and change.

Statement 3 is false and inverts the position's chief drawback. An underwing pod sits far from the centreline - often seven metres, twelve at an outboard station - so it produces the largest engine-out yawing moment of any common arrangement, which is what sizes the fin.

Answer: C

Correct answer: 1 and 2 only

Statement 1 is correct: pressure recovery is total pressure at the fan face over free stream total pressure. Statement 2 is correct: spillage drag arises when the engine swallows less than the inlet captures, the excess spilling around the cowl lip.

Statement 3 is false. A pitot inlet decelerates the flow through a single normal shock, and at Mach 2.5 that shock destroys around half the total pressure. Supersonic flight requires a system of weaker oblique shocks with variable geometry to position them.

Answer: D

Correct answer: 1 and 2 only

Statement 1 is correct: on a high-bypass turbofan most of the mass flow is in the fan stream, so that is what the reverser turns. Statement 2 is correct: reversers are not credited in the certified distances, which assume brakes and spoilers alone.

Statement 3 is false and reverses the truth. Reversers are most effective at high ground speed, where the momentum change is greatest; at low speed their effect falls away and re-ingestion becomes a hazard, which is why they are stowed.

Answer: A

Correct answer: 1 and 2 only

Statement 1 is correct: a higher bypass ratio improves propulsive efficiency and so lowers specific fuel consumption. Statement 2 is correct: it requires a larger fan and therefore a larger nacelle.

Statement 3 is false and inverts the effect. Raising bypass ratio reduces jet mixing noise, because the same thrust is obtained by accelerating a larger mass of air through a smaller velocity change - and mixing noise scales with a high power of jet velocity.

Answer: B

Correct answer: A-2, B-1, C-4, D-3

Each component is matched to its function. The pylon (A) positions the pod and carries its loads into the wing (2); the nacelle (B) is the fairing enclosing the engine (1).

The diffuser (C) slows the captured flow before the fan face (4), since the compressor requires a low inlet Mach number; and the thrust reverser (D) turns the fan flow forward to retard the aircraft (3). The four span structure, aerodynamic fairing, internal flow and a control device respectively.

Answer: C

Correct answer: A-2, B-1, C-4, D-3

Each position is matched to its dominant penalty. The underwing pod (A) suffers a large engine-out yawing moment (2) from its long arm. Rear-fuselage engines (B) bring an aft centre of gravity and a heavier rear fuselage (1).

Wing-root buried engines (C) are difficult to change and force the wing box to be cut about (4). An overwing pod (D) suffers interference drag and poor access (3), the nacelle sitting on the wing's most sensitive surface.

Answer: D

Correct answer: A-2, B-1, C-4, D-3

Each phenomenon is matched to where it arises. Inlet buzz (A) occurs at a supersonic inlet with an unstable shock system (2). Spillage drag (B) occurs at the inlet when the engine swallows less than is captured (1).

Re-ingestion (C) occurs during reverse thrust at low ground speed (4), when the aircraft no longer outruns its own efflux. Jet mixing noise (D) arises at the exhaust shear layer (3). Two belong to the inlet, one to the exhaust and one to a transient ground condition.

Answer: A

Correct answer: A-2, B-1, C-3, D-4

Each offtake is matched to what it powers. Compressor bleed (A) supplies cabin pressurisation and anti-icing (2), being hot and already at pressure. The accessory gearbox (B) drives the electrical generators and pumps (1) mechanically.

The fan stream (C) provides most of the reverse thrust on a high-bypass engine (3), since it carries most of the mass flow; and the core exhaust (D) contributes the remaining share of net thrust (4). Pneumatic, mechanical and two propulsive paths.

Answer: B

Correct answer: Relief of wing bending in flight

Bending relief is exactly what rear-fuselage mounting gives up. With no mass hanging outboard, nothing opposes the wing's upward bending in flight, so the wing structure must be heavier than an equivalent aircraft with underwing pods.

The other three are genuine advantages: the nacelles sit high and well clear of the runway, the engine-out yawing moment is small because the arm is short, and the wing is left uninterrupted for full-span high lift devices.