Engines, Turbine Engines
A B2 systems-level overview: the Brayton cycle and gas path, engine types and spools, and electronic engine control (EEC/FADEC).
Turbine engines, summary notes
- The gas turbine works on the continuous-flow Brayton cycle, intake, compressor, combustor, turbine, exhaust, and produces thrust by Newton's third law, F = ṁ·(V_jet − V_inlet): a mass of air is accelerated rearward.
- Engine types differ only in where the energy goes: turbojet (all thrust from the jet), turbofan (most thrust from the bypass fan, quiet and efficient), turboprop (most power to a propeller) and turboshaft (all power to an output shaft).
- Modern engines are multi-spool: the low-pressure spool (N1, fan/LP compressor + LP turbine) and the high-pressure spool (N2, HP compressor + HP turbine) run at their own speeds; the gas generator supplies gas to drive the fan/power turbine.
- For the B2 (avionics) technician the engine is essentially a controlled, instrumented system: an ELECTRONIC ENGINE CONTROL (EEC)/FADEC reads the sensors and schedules the fuel and start sequence, so the B2 focus is the sensors, wiring, connectors and the EEC, not the internal mechanical detail covered in Module 15.
- The parameters the aircraft systems set and watch are engine speed (N1/N2), gas temperature (EGT/ITT), thrust (EPR or N1) and fuel flow, plus oil and vibration.
- ⚠ Exam trap: a turbofan makes most of its thrust from the BYPASS fan, not the core jet; and the FADEC/EEC is a full-authority ELECTRONIC controller that schedules fuel, the B2 syllabus treats the engine at systems/indicating level, not the deep mechanical detail of Module 15.
- Thrust
- F = ṁ·(V_jet − V_inlet)
From a B2 (avionics) standpoint, what does 'FADEC' do and what does the technician mainly work on?
FADEC (Full Authority Digital Engine Control) is the electronic engine controller: it reads engine sensors (speeds, temperatures, pressures, throttle) and has full authority to schedule fuel flow, the start sequence and limit protection. The B2 technician deals with the electrical/electronic side, the sensors, harnesses, connectors, the EEC unit and the indicating channels, rather than the internal gas-path hardware.
Gas turbine, the running turbojet
Turbine engines concept map
Turbine Engines (B2)
Turbine engines quiz
Turbine Engines, quiz
1. A turbine passes 50 kg/s and accelerates the gas from 200 to 500 m/s. The thrust is:
15 kN25 kN10 kN2. A gas turbine operates on which cycle?
The Brayton (constant-pressure) cycleThe Otto cycleThe Carnot cycle3. Thrust is produced by:
Accelerating a mass of air rearward (Newton's third law)Intake suction onlyConstant-volume combustion4. A turbofan produces most of its thrust from the:
Bypass fanCore jetTurbine wheel5. The gas-path order in a gas turbine is:
Intake, compressor, combustor, turbine, exhaustCompressor, intake, turbine, exhaustTurbine, compressor, combustor, intake6. On a two-spool engine, N1 refers to the:
Low-pressure spool (fan/LP)High-pressure spoolAccessory gearbox7. FADEC stands for:
Full Authority Digital Engine ControlFan And Duct Exhaust ControllerFuel And Direct Engine Cooling8. The EEC/FADEC schedules the engine's:
Fuel flow and start sequence, with limit protectionCabin pressure, by regulating the bleed air taken from the compressor to the packsLanding gear retraction, sequencing the doors and locks against the engine power setting