ANAC GMP Theoretical Exam (Powerplant Group) cheat sheet

Newton's second law: thrust equals mass flow rate multiplied by the velocity increase imparted to the air or exhaust gases, plus any pressure-thrust term.

Brayton (gas turbine) cycle stages: intake compression, constant-pressure combustion heat addition, expansion through turbine, exhaust rejection; thermal efficiency rises with pressure ratio.

Otto cycle for reciprocating engines: four strokes - intake, compression, constant-volume combustion/power, exhaust; ideal efficiency = 1 − 1/r^(γ−1) where r is compression ratio.

Power available is propulsive power (thrust × true airspeed for jets, or shaft power × propeller efficiency); power required is drag × true airspeed; excess power gives climb capability.

Specific fuel consumption: TSFC = fuel flow / thrust (jets); BSFC = fuel flow / brake power (piston and turboprop); lower values indicate better efficiency.

Compression ratio in a piston engine is cylinder swept volume plus clearance volume divided by clearance volume; higher ratio raises thermal efficiency but is limited by detonation.

Propulsive efficiency = thrust power / (thrust power + kinetic energy lost in the exhaust jet); it improves as exhaust velocity approaches flight velocity.

Engine station numbering: 1 inlet, 2 compressor face, 3 compressor exit, 4 combustor exit/turbine inlet, 5 turbine exit, 7 exhaust nozzle; pressure and temperature rise through compression and combustion, fall through turbine and nozzle.

Horizontally opposed air-cooled layout: crankcase, opposed cylinders, pistons, connecting rods, crankshaft, camshaft, valve train, and accessory case driven from the crankshaft.

Four-stroke valve sequence: intake valve opens near top dead center and closes after bottom dead center; exhaust valve opens before bottom dead center and closes after top dead center; valve overlap aids scavenging.

Firing order and crankshaft design determine even firing intervals; a four-cylinder flat engine typically fires 1-3-2-4 with 180° crank throws.

Detonation is uncontrolled rapid burning producing high peak pressures and temperatures; pre-ignition is ignition before the spark, often caused by a hot spot such as a glowing carbon deposit or spark plug electrode.

Mixture distribution, ignition timing, compression ratio, and cylinder head temperature all influence detonation margin; rich mixture at high power and low CHT protect the engine.

Valve clearance is set cold with a feeler gauge; incorrect clearance causes noise, loss of lift, or valve burning. Hydraulic lifters maintain zero lash automatically.

Cylinder compression test: a reading below the manufacturer's minimum or a large spread between cylinders indicates ring, valve, or head gasket leakage; a differential (leak-down) test locates the source.

Engine power ratings: takeoff, maximum continuous, and cruise; manifold pressure and RPM limits define the operating envelope, and oversquare operation (high MP at low RPM) is restricted.

Axial compressor: alternating rotor and stator rows; each stage adds a small pressure rise; variable inlet guide vanes and bleed valves prevent surge and stall at low RPM.

Centrifugal compressor: impeller, diffuser, and manifold; simpler and more surge-tolerant, used in small engines and as the final high-pressure stage of some designs.

Combustor types: can, annular, and can-annular; annular is compact, gives even temperature distribution, and is common in modern engines.

Turbine: nozzle guide vanes accelerate and swirl hot gas onto rotor blades; blades are cooled by internal passages and film cooling and use thermal barrier coatings.

Turbofan: bypass ratio = bypass mass flow / core mass flow; high bypass ratio gives high propulsive efficiency and lower specific fuel consumption at subsonic speeds.

Free-turbine turboshaft and turboprop engines have a gas generator (compressor, combustor, turbine) driving a separate power turbine connected to the output shaft.

Engine pressure ratio (EPR) and fan or compressor speed (N1) are common thrust parameters; exhaust gas temperature (EGT) indicates turbine temperature margin and is a primary limit.

Hot section distress: EGT margin loss, blade creep, and cracking are monitored by borescope inspection and trend monitoring.

Piston fuel system: tank, selector valve, boost pump, fuel strainer, engine-driven pump, fuel/air control unit (carburetor or fuel injection servo), and distribution to cylinders.

Carburetor icing risk is highest at temperatures between roughly −10 °C and +20 °C with high humidity; carburetor heat is applied before ice forms and causes a rich mixture and RPM drop.

Fuel injection advantages: even mixture distribution, no carburetor icing, better fuel economy, and easier starting; the mixture control is set for density altitude.

Magneto ignition: self-contained rotating magnet and coil generating high voltage; two independent magnetos provide redundancy; the ignition switch grounds the primary circuit to shut off the engine.

Impulse coupling provides a retarded spark at low cranking RPM; spark plug fouling from lead deposits causes roughness that may clear after leaning.

Dry-sump lubrication: oil tank, pressure pump, oil cooler, filter, and scavenge pumps; wet-sump stores oil in the crankcase. Oil pressure and temperature must be monitored.

Air cooling: cylinder fins, baffles, and cowl flaps control airflow; cowl flaps open in climb and closed in cruise to regulate cylinder head temperature.

Starting: starter motor or air turbine starter, ignition, fuel, and, for turbines, starter-assisted motoring to a stable idle; hot starts occur when fuel is excessive or light-off is delayed.

Propeller pitch is the angle between the blade chord and the plane of rotation; geometric pitch is the design angle, effective pitch accounts for slip.

Blade element theory: thrust and torque vary along the blade span; the blade is twisted so each section operates at an efficient angle of attack.

Fixed-pitch propellers are matched to cruise or climb; a climb propeller has lower pitch for higher static RPM.

Constant-speed propeller: governor uses flyweights and oil pressure to change blade angle, maintaining selected RPM as load changes.

Feathering rotates blades to near zero thrust to reduce drag after engine failure; reverse pitch produces negative thrust for braking and ground handling.

Piston engine controls: throttle controls manifold pressure, propeller control sets RPM, mixture control sets fuel/air ratio; power settings are read from the POH.

Turbine controls: thrust lever sets power; FADEC or hydro-mechanical unit schedules fuel to protect against overspeed, over-temperature, and surge.

Propeller balance and track: dynamic balance reduces vibration; track adjustment aligns blade tips within manufacturer tolerance.

Scheduled inspections: preflight, 100-hour, annual, and progressive; calendar and hour limits from the manufacturer and the approved maintenance program apply.

Oil analysis and spectrometric wear-metal trends detect bearing and cylinder wear before failure; sudden changes in iron, aluminum, or copper merit investigation.

Borescope inspection of cylinders and turbine hot section reveals valve condition, carbon deposits, blade cracks, and burn-through without disassembly.

Compression and leak-down tests: differential test measures leakage past rings and valves; air escaping through the oil filler indicates ring wear, through the exhaust valve indicates valve leakage.

Vibration analysis and trend monitoring of EGT, RPM, and fuel flow identify imbalance, bearing distress, and compressor fouling.

Troubleshooting logic: verify the symptom, isolate the system, test components in order, and confirm correction; record findings in the maintenance record.

Fuel system checks: filter contamination, pump pressure, and injector flow; air in fuel lines causes rough running and hard starting.

Ignition troubleshooting: magneto drop check, spark plug condition (color, gap, electrode wear), and harness resistance tests.

Maintenance, preventive maintenance, and alterations must follow approved data; major repairs and alterations require approved data and a return to service by an appropriately rated person or organization.

Airworthiness directives are mandatory; compliance must be recorded and the applicable AD status verified before return to service.

Maintenance records must include description of work, date, signature, certificate number, and reference to approved data; the aircraft log and engine log are separate records.

Life-limited parts have mandatory retirement times tracked by serial number and hours or cycles; installation and removal must be recorded.

A release to service (maintenance release) certifies that work was performed and the unit is airworthy; it is issued by qualified maintenance personnel.

Engine and propeller type certificates define the approved configuration; unapproved parts must not be installed.

Weight and balance and performance data change with engine or propeller modifications; the flight manual and placards must reflect the approved configuration.

Continued airworthiness includes service bulletins (some mandatory by AD), inspection programs, and reporting of defects or unairworthy conditions as required by the authority.

Dirty dozen human factors: fatigue, complacency, distraction, pressure, stress, lack of communication, lack of teamwork, lack of resources, lack of awareness, lack of knowledge, norms, and lack of assertiveness.

SHELL model: Software, Hardware, Environment, and Liveware interact; mismatches at the interfaces produce error; error is managed, not blamed.

Hazardous materials: fuel, oil, solvents, and hydraulic fluid require correct storage, labeling, PPE, and disposal; fuel spills are contained and reported.

Engine ground safety: intake suction and exhaust blast zones are lethal; propeller arcs are kept clear, and engines are started only with chocks, fire extinguisher, and clear communication.

Fire safety: correct extinguisher class for fuel, oil, and electrical fires; fuel and ignition sources are separated during maintenance.

Noise and emissions: high-bypass engines reduce noise and NOx; community noise limits and emissions standards apply to engine design and operation.

Fatigue management: duty limits, rest, and checklists reduce error; critical tasks such as control rigging and torque values are independently verified.

Environmental compliance: waste segregation, spill prevention, and proper handling of refrigerants and fire-extinguishing agents under applicable regulations.