Engine Performance and Matching Questions and Answers

Answer: A

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

Both are true and the reason is the argument. The design point is one condition used for sizing the components; idle, taxi, climb and part power cruise are all away from it, and they account for essentially the whole of the engine’s operating life. Performance and handling at those conditions therefore matter at least as much as the design point figures.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are the genuine matching conditions, together with speed compatibility on a shaft. Statement 3 is wrong and is the point worth taking away: the operating point is wherever those conditions are simultaneously satisfied, and there is no reason it should coincide with any component’s peak efficiency. Only at the design point is the match arranged to fall near the best points.

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 are correct. Statement 3 is not: corrected mass flow is defined precisely so as to remove the pressure dependence from the physical flow, so it is the corrected value that is independent of inlet pressure while the physical flow falls steeply with it - which is why an engine passes far less mass at altitude than at sea level for the same corrected condition.

Answer: D

Correct answer: 1 and 2 only

Statements 1 and 2 describe the two transient hazards correctly. Statement 3 is wrong in an important way: electronic control does not abolish the physics, it enforces the schedules that respect it. A modern engine is safe during a slam acceleration because the control limits the fuel, not because surge has ceased to be possible.

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 describe how deterioration is measured and used. Statement 3 is the reverse of the truth - wear opens clearances, erodes blade profiles and degrades seals, all of which reduce compressor efficiency. That falling efficiency is precisely the cause of the rising exhaust temperature described in statement 1.

Answer: B

The three requirements are independent and must hold simultaneously. Where they intersect is generally not where any component would prefer to be, and that compromise is precisely what makes matching a design discipline.

Answer: C

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

Each correction removes exactly the dependence that matters for that quantity. Speed corrects on temperature alone, because blade Mach number depends on the speed of sound. Flow corrects on both, since it scales with density and with velocity. Thrust corrects on pressure alone, being a force proportional to pressure times area. And fuel flow, being a heat release, corrects on both.

Answer: D

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

Four influences on surge margin, distinguished as much by their timescale as by their sign. Opening the turbine nozzle lowers the working line and improves the margin permanently. Bleed extraction raises it while the bleed is drawn. Rapid acceleration raises it only during the manoeuvre. And deterioration erodes it slowly and irreversibly over the engine’s life.

Answer: A

Two of the four raise the exhaust temperature and are separated only by what the shaft speed does. Reading the pattern rather than any single instrument is the whole basis of diagnosing a fault without opening the engine.

Answer: B

Correct answer: Equal compressor and turbine pressure ratios

No such condition exists. The turbine expansion ratio is generally lower than the compressor pressure ratio, because the combustor loses some pressure and the propelling nozzle needs the rest to produce thrust. The three real conditions are continuity of mass flow between components, balance of turbine work against compressor demand, and common speed for components on one shaft.