PNG CASA Basic Gas Turbine flashcards

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

Brayton cycle

The ideal gas turbine cycle: compression, constant-pressure heat addition in the combustor, expansion through the turbine and exhaust. Its efficiency depends mainly on pressure ratio and turbine inlet temperature.

Isentropic relation

For an ideal gas, T2/T1 = (P2/P1)^((γ−1)/γ). It links compressor or turbine pressure ratio to temperature ratio and is used to compute ideal work and efficiency.

Specific fuel consumption

Fuel mass flow divided by net thrust or shaft power. Lower values mean better economy; rising SFC with unchanged settings signals engine deterioration.

Surge margin

The margin between the compressor's operating point and its surge line. Bleed valves and variable stator vanes increase it at low speed; fouling or back pressure reduces it.

Annular combustor

A single continuous liner around the shaft, giving the most uniform exit temperature profile and shortest length. Can and can-annular types use discrete cans instead.

Turbine blade cooling

Compressor bleed air passes through internal passages and film-cooling holes in the blade. It protects the superalloy from gas temperatures above its melting point but costs cycle efficiency.

Fir-tree blade root

A serrated root that fits matching slots in the turbine disc. Centrifugal load holds it in place, with locking features preventing axial movement.

Accessory gearbox

A gearbox driven from the HP spool that drives the fuel pump, oil pump, hydraulic pump, starter/generator and tachometer generators.

Dry-sump oil system

A pressure pump feeds oil to the bearings and scavenge pumps return it to the tank. This allows inverted flight and prevents oil accumulating in the bearing chambers.

Oil filter bypass valve

A spring-loaded valve that opens when the filter differential pressure is too high, keeping oil flowing to the bearings but allowing unfiltered oil through.

Fuel control unit

The unit that meters fuel using inputs of N1/N2, inlet temperature and pressure, throttle position and EGT. It schedules acceleration and deceleration limits.

Ignition exciter

A capacitor-discharge unit that produces high-voltage pulses for the igniter plugs. Weak output causes difficult light-off and a slow EGT rise during start.

Hung start

The engine lights but fails to accelerate to idle, usually from low starter power, low fuel flow or a misrigged control. Abort before the start EGT limit is exceeded.

Hot start

EGT exceeds the start limit because of excess fuel, weak ignition or low airflow. Shut off fuel and motor the engine to purge before any restart attempt.

EGT margin

The difference between observed take-off EGT and the EGT limit. A shrinking margin indicates hot-section deterioration and drives maintenance planning.

Flat rating

The engine delivers constant thrust or power up to a defined outside air temperature, then output decreases above that break temperature as density falls.

Take-off rating

The maximum thrust or power approved for take-off, normally time-limited (commonly five minutes) and certified at a defined sea-level static condition.

Life-limited part

A component with a published cycle or hour limit that must be removed from service when the limit is reached, regardless of its condition.

Maintenance release

A certification that the work was completed in accordance with approved data and that the engine is fit for return to service, signed by authorized personnel.

Airworthiness directive

A mandatory requirement issued by the authority to correct an unsafe condition. It must be complied with within the stated time and recorded in the engine records.

Borescope inspection

Internal inspection of compressor and turbine blades without disassembly. Findings are recorded with stage, location and description for engineering assessment.

Chip detector

A magnetic plug in the oil system that collects metallic particles. Debris type and quantity indicate bearing or gear wear and guide the inspection scope.

Vibration trend

Vibration rising with N1 or N2 indicates imbalance, bearing wear, blade damage or FOD. Trending against speed isolates the affected spool.

Wet start

Fuel is introduced but ignition does not occur. The engine must be motored to purge the fuel before another start to avoid fire or a hot start.

Intake danger zone

The area in front of a running engine where suction can draw in personnel or loose items. Never stand in the intake plane during start or ground running.

Just culture

A reporting culture that encourages maintenance error reporting without blame for honest mistakes, while still holding individuals accountable for gross negligence.

Fire handle

A cockpit control that shuts off fuel and bleed air to the engine and arms the fire extinguisher, isolating the affected engine.

Thermal efficiency

Net work output divided by heat added in the combustor. It rises with pressure ratio and turbine inlet temperature in the Brayton cycle.

Propulsive efficiency

Thrust power divided by jet power. High-bypass turbofans improve it by moving a larger mass of air at lower velocity.

Variable stator vanes

Compressor vanes whose angle is scheduled with speed to keep the airflow matched to the blades, maintaining surge margin at low speed.

Torquemeter

A device that measures the torque delivered by a turboprop or turboshaft engine. Torque is the primary power indication for those engine types.

Trend monitoring

Recording N1/N2, EGT, fuel flow and oil data over time. A sustained trend shift triggers maintenance action before a limit is reached.

Approved data

The current manual, service bulletin or airworthiness directive used to perform and release maintenance. Superseded or unapproved data must not be used.