Piston and turbine engines, propellers, fuel systems, lubrication and engine indications
Scope
This domain covers piston and turbine engine cycles, propeller control, fuel and oil systems, and engine indications. Expect mixture, detonation, N1/N2, EGT, governor operation and fuel type questions.
Piston engines
- Four-stroke Otto cycle: induction, compression, power, exhaust. Mixture control gives best power rich of peak and best economy lean of peak.
- Detonation is uncontrolled explosion after spark; pre-ignition is ignition before spark. Both raise cylinder head temperature.
- Turbo/supercharging: the wastegate controls manifold pressure; critical altitude is where full throttle gives maximum allowable manifold pressure.
Turbine engines
- Brayton cycle: intake, compression, combustion, exhaust. Axial compressor, annular combustor, turbine. N1 is the fan/LP spool; N2 is the HP spool. EGT is a limiting indication.
- FADEC controls fuel and starting; surge is a compressor airflow stall.
- Start sequence: motoring, ignition, fuel on, light-off, idle.
Propellers
- A constant-speed governor senses RPM by flyweights; underspeed directs oil to fine pitch, overspeed to coarse. Feathering reduces drag; reverse/beta range is for ground use; prop sync matches RPM.
Fuel and oil
- Jet A-1 for turbines; Avgas 100LL for piston engines. Vents prevent tank collapse; boost pumps, crossfeed and jettison are system features.
- Turbines use dry-sump oil systems; many piston engines use wet-sump. Monitor pressure, temperature and chip detector.
Worked example
If RPM falls below the selected value, governor flyweights move inward and the pilot valve ports oil to the propeller to decrease blade angle (fine pitch). Lower blade angle reduces load and RPM rises back to the setting.
Traps
N1 is not N2. EGT limit is not a target. Beta range is not for flight. Avgas in a turbine is catastrophic. A chip detector warning requires inspection, not reset.