ANAC GMP Theoretical Exam (Powerplant Group) flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Brayton cycle

The ideal thermodynamic cycle for gas turbine engines, comprising compression, constant-pressure heat addition, expansion, and exhaust rejection; efficiency increases with pressure ratio.

Otto cycle efficiency

For an ideal reciprocating engine, thermal efficiency equals one minus one divided by compression ratio raised to the specific heat ratio minus one; higher compression improves efficiency.

Specific fuel consumption

Fuel flow per unit of output: thrust specific fuel consumption divides fuel flow by thrust, brake specific fuel consumption divides by shaft power; lower values mean better efficiency.

Propulsive efficiency

Thrust power divided by total jet power; it rises as exhaust velocity approaches flight velocity, which is why high-bypass engines are efficient at subsonic speeds.

Compression ratio

Cylinder swept volume plus clearance volume divided by clearance volume; it determines the ideal Otto efficiency and is limited by detonation and fuel octane.

Detonation versus pre-ignition

Detonation is uncontrolled rapid burning after normal ignition, raising peak pressure; pre-ignition is ignition before the spark, often from a hot spot such as a glowing deposit.

Valve overlap

The period near top dead center when both intake and exhaust valves are open; it aids scavenging of burned gases and improves volumetric efficiency.

Differential compression test

Air is applied through the spark plug hole at top dead center and leakage is measured; escaping air at the oil filler indicates rings, at the exhaust indicates valves.

Variable inlet guide vanes

Movable vanes at the compressor inlet that change airflow angle with speed, preventing surge and stall and improving compressor efficiency at low rotational speeds.

Annular combustor

A single continuous combustion chamber around the engine axis; it is compact, gives uniform exit temperature, and reduces pressure loss compared with can designs.

Bypass ratio

Bypass air mass flow divided by core engine mass flow; high bypass ratios improve propulsive efficiency and reduce specific fuel consumption at subsonic speeds.

Engine pressure ratio

Turbine exhaust pressure divided by compressor inlet pressure; it is a thrust-related parameter used to set and monitor power on many turbofan engines.

Exhaust gas temperature

Temperature measured at the turbine inlet or exhaust; it indicates hot-section temperature margin and is a primary operating limit protecting turbine blades.

Carburetor icing conditions

Ice forms in the venturi when temperature is roughly minus ten to plus twenty degrees Celsius with high humidity; carburetor heat is applied before ice accumulates.

Magneto operation

A self-contained engine-driven generator producing high voltage for spark plugs; two magnetos give independent ignition, and the switch grounds the primary circuit to stop the engine.

Dry-sump lubrication

Oil is stored in a separate tank, pumped under pressure to bearings, then scavenged back; it allows inverted flight and better cooling than a wet sump.

Cowl flaps

Adjustable panels behind the engine that control cooling airflow; opening them in climb lowers cylinder head temperature, closing them in cruise reduces drag.

Hot start

A turbine start in which excessive fuel or delayed light-off raises exhaust temperature beyond limits; it requires motoring to clear fuel and inspection before further attempts.

Constant-speed propeller

A propeller whose blade angle is changed by a governor to hold the selected RPM as load and airspeed vary, converting engine power efficiently across the flight envelope.

Propeller feathering

Rotating blades to near zero angle of attack so they produce little thrust and minimum drag, used after engine failure to reduce asymmetric drag and vibration.

Geometric pitch

The theoretical distance a propeller would advance in one revolution if it moved through a solid medium without slip; effective pitch is reduced by slip.

Manifold pressure

Absolute pressure in the engine intake manifold, read on the cockpit gauge; the throttle controls it and it is a primary power indicator for piston engines.

Airworthiness directive

A mandatory instruction issued by the authority to correct an unsafe condition; compliance is required and must be recorded before the aircraft or engine is returned to service.

Maintenance release

A certification, signed by qualified maintenance personnel, that the described work was performed in accordance with approved data and the unit is airworthy.

Life-limited part

A component with a mandatory retirement time in hours or cycles; its history is tracked by serial number and it must be removed before the limit is reached.

Approved data

Information approved by the authority, such as type certificate data sheets, manuals, and approved drawings, required for major repairs and alterations.

Borescope inspection

Optical inspection through spark plug holes or inspection ports to examine cylinder walls, valves, and turbine blades without disassembly, detecting cracks, deposits, and burn-through.

Oil spectrometric analysis

Laboratory measurement of wear metals in oil samples; rising iron, aluminum, or copper trends can reveal bearing, ring, or bushing wear before failure.

Trend monitoring

Recording engine parameters such as exhaust gas temperature, fuel flow, and speed over time so gradual degradation and abnormal changes are detected early.

Compressor fouling

Accumulation of dirt and deposits on compressor blades that reduces airflow and efficiency, raising exhaust gas temperature and fuel consumption; washing restores performance.

Dirty dozen

Twelve human-factor precursors of maintenance error, including fatigue, complacency, distraction, pressure, stress, and poor communication, teamwork, awareness, and knowledge.

SHELL model

A human-factors framework describing interactions among Software, Hardware, Environment, and Liveware; mismatches at these interfaces create error in maintenance and flight.

Foreign object damage

Damage to engine components caused by ingested debris such as stones, tools, or birds; prevention requires intake inspection, clean aprons, and tool control.