Gas Turbine Engine Construction and Operation
Core concepts
Know the sections and their jobs: inlet, compressor (axial or centrifugal), diffuser, combustion chamber (can, annular, can-annular), turbine (nozzle guide vanes and rotor blades), exhaust, and accessory gearbox. Understand how compressor stages raise pressure while turbine stages extract energy to drive the compressor and accessories. Learn the meaning of pressure ratio, bypass ratio for turbofans, and the difference between turbojet, turboprop, turboshaft, and turbofan. Study turbine blade cooling, clearance control, and the importance of avoiding overtemperature. Understand starting sequence, light-off, and why bleed air is used for anti-ice and cabin pressurization.
Traps to expect
Questions test whether you know that the turbine drives the compressor, not the other way around, and that most thrust in a high-bypass turbofan comes from the fan, not the core. Watch for confusion between compressor stall (flow breakdown) and surge (violent reversal). Know that a hot start is indicated by rapidly rising exhaust gas temperature, and that hung starts mean the engine fails to accelerate. Do not confuse N1 (fan/low-pressure spool) with N2 (high-pressure spool).
Worked example
If a turbofan has a bypass ratio of 5:1, then for every 1 part of air through the core, 5 parts go through the fan duct. Rule of thumb: bypass ratio = fan mass flow ÷ core mass flow, so total flow is the sum of both.
Study habit
Trace the air path from inlet to exhaust and note pressure and temperature at each station. This makes performance and troubleshooting questions far more intuitive.