Engine Performance and Matching Questions and Answers

Answer: C

The engine could produce more on a cold day, and that surplus is spent maintaining the rating as conditions worsen. Predictable performance across a range of conditions is worth more to an operator than the extra thrust on a good day.

Answer: D

Worn seals, eroded blades and increased tip clearances all force the engine to run hotter for the same output. The temperature margin remaining before the limit is what determines when the engine must be removed for overhaul.

Answer: A

Correct answer: The gap between the temperature reached and the certified limit

The margin is what is left before the engine reaches its certified exhaust gas temperature limit at a given rating. A new engine has a large margin; as it deteriorates it must run hotter for the same thrust and the margin shrinks. When it reaches zero the engine can no longer make its rated thrust legally, and it comes off for overhaul - so the margin is effectively the engine’s remaining life.

Answer: B

A drop in compressor efficiency, a change in turbine flow capacity and a combustor problem each leave a different signature across the measured parameters. Recognising the pattern narrows the fault before the engine is opened.

Answer: C

Correct answer: Speed, temperature and torque

Each limit protects a different failure mode: rotational speed guards against centrifugal stress in the discs and blades, temperature against creep and oxidation in the turbine, and torque against the shaft and any reduction gearbox. Which one binds first depends on the condition - temperature on a hot day, torque or pressure on a cold one - and the control enforces whichever comes first.

Answer: D

Each spool of a twin or triple spool engine has its own map and its own locus. The two are coupled through the gas path, so a change affecting one appears on the other even without any mechanical connection between them.

Answer: A

Correct answer: Lowers the working line, increasing surge margin

A larger propelling nozzle passes the same flow at a lower pressure, so the whole engine runs at a lower pressure ratio for a given corrected flow. That moves the working line down away from the surge line, which is why a variable nozzle is one of the standard tools for recovering margin - at some cost in thrust or specific fuel consumption.

Answer: B

Idle, taxi, climb, descent and part power cruise are all off design conditions. Matching that behaves well only at one point produces an engine that is difficult to start, slow to accelerate and prone to surge everywhere else.

Answer: C

Air removed after compression is work already spent that returns nothing, and its absence changes the flow balance the components had been matched for. Performance figures are therefore quoted with the bleed and power offtakes stated explicitly.

Answer: D

The same physical engine at sea level and at altitude appears as one curve when the parameters are corrected. That collapse is what makes a compressor map or an engine characteristic a usable design and diagnostic tool at all.