Engine Performance and Matching Questions and Answers

Answer: A

Dividing by the appropriate functions of inlet temperature and pressure removes the dependence on ambient conditions. That collapse is exactly what makes a single map a usable design and diagnostic tool across the whole envelope.

Answer: B

Each component's deterioration produces a distinct pattern across the measured parameters. An unchanged turbine flow capacity alongside a compressor efficiency loss points clearly to the front of the engine rather than the back.

Answer: C

Air taken after compression has absorbed work and then leaves without doing any in the turbine. The engine must work harder to produce the same thrust, which is why performance figures always state the offtakes assumed.

Answer: D

It is placed by the matching conditions rather than by any preference of the designer. Its distance from the surge line is the surge margin, which must remain adequate through transients and through the engine's whole service life.

Answer: A

The relation follows from the way blade Mach numbers depend on temperature. Cold air gives a higher corrected speed at unchanged shaft rpm, which is why an engine behaves differently on a cold day even at the same physical speed.

Answer: B

Once sonic conditions exist in the throat, nothing downstream alters the flow passing through it. That fixed capacity ties the compressor's operating point directly to the turbine's geometry, which is why nozzle area is such an effective lever.

Answer: C

Cutting fuel faster than the shaft slows leaves the mixture below the limit that sustains a flame. The fuel control schedules it for the same reason it schedules acceleration, protecting the engine at both ends of the throttle range.

Answer: D

Each component's deterioration produces a distinct pattern across the measurements rather than moving one reading alone. Recognising that pattern narrows the diagnosis considerably before the engine is opened for inspection.

Answer: A

Each component would prefer a different condition, and the engine runs where the three requirements intersect. That compromise is the essence of matching and the reason off design behaviour needs such careful attention.

Answer: B

Correct answer: The two nozzle area changes

Both nozzle changes act the same way: enlarging a choked or nearly choked throat lets more flow pass at a given pressure, so the compressor is asked for more flow and less pressure ratio, and the working line drops. Bleed extraction works through a quite different route - removing air between the compressor and turbine - and rapid acceleration is a transient of the fuel schedule.