CAA NZ Basic Turbine Knowledge (Aeroplane) flashcards
CAA NZ Basic Turbine Knowledge (Aeroplane) · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Brayton cycle efficiency
- Ideal thermal efficiency of a gas turbine cycle is η = 1 − 1/(PR^((γ−1)/γ)), where PR is compressor pressure ratio and γ is specific heat ratio (about 1.4 for air).
- Specific thrust
- Specific thrust is thrust per unit mass flow: F/ṁ = (1+f)Ve − V0, where f is fuel-air ratio, Ve exhaust velocity, V0 flight velocity.
- Propulsive efficiency
- Propulsive efficiency ηp = 2V0/(Ve+V0); it is highest when exhaust velocity is close to flight velocity, typical for high-bypass turbofans.
- Engine station numbering
- Standard SAE ARP755 station numbers: 0 free stream, 1 inlet entry, 2 compressor inlet, 3 compressor exit, 4 combustor exit, 5 turbine exit, 7 nozzle exit.
- Axial compressor stage
- An axial compressor stage consists of a rotor row followed by a stator row; each stage increases pressure and decreases axial velocity.
- Annular combustor
- An annular combustor is a single annular chamber around the shaft, common in modern turbofans for compactness and uniform exit temperature.
- Twin-spool engine
- A twin-spool engine has separate low-pressure and high-pressure compressors and turbines on concentric shafts, allowing each spool to operate at optimal speed.
- Thrust bearing
- A thrust bearing absorbs axial loads from the compressor and turbine, maintaining rotor axial position; often a ball bearing.
- Synthetic turbine oil
- Synthetic ester-based oils (MIL-PRF-23699) are standard for turbine engines due to high-temperature stability and resistance to coking.
- Oil scavenge pump
- Scavenge pumps return oil from bearing compartments to the oil tank; multiple scavenge stages are common to ensure efficient return.
- Labyrinth seal
- A labyrinth seal is a non-contact seal with a series of ridges that restrict oil leakage from bearing compartments; pressurisation further prevents leakage.
- Fuel control unit (FCU)
- The FCU is a hydromechanical unit that meters fuel to the engine based on throttle position, compressor speed, and altitude, preventing overtemp and flameout.
- FADEC
- Full Authority Digital Engine Control (FADEC) is an electronic system that computes fuel flow and variable geometry positions, often with dual-channel redundancy.
- Duplex fuel nozzle
- A duplex fuel nozzle has two fuel circuits (primary and secondary) to provide good atomisation at low and high fuel flows.
- Fuel/oil heat exchanger
- A fuel/oil heat exchanger uses fuel to cool engine oil, while warming the fuel to prevent ice formation in the fuel system.
- Igniter exciter
- The exciter is a high-energy capacitor discharge unit that supplies power to the igniter plugs for engine starting and relight.
- Air turbine starter
- An air turbine starter uses bleed air from an APU or ground cart to rotate the engine for starting; common on large turbine engines.
- Hot start
- A hot start occurs when EGT exceeds limits during start, often due to excessive fuel or low starter power; action is to cut fuel and continue motoring.
- Hung start
- A hung start is when engine RPM stagnates below idle, often due to insufficient starter power or fuel control fault; the start must be aborted.
- EGT
- Exhaust Gas Temperature (EGT) indicates turbine temperature; it is highest during start and takeoff, and exceedance can damage the turbine.
- N1
- N1 is the low-pressure spool speed (fan speed) and is the primary thrust parameter for turbofan engines.
- N2
- N2 is the high-pressure spool speed, indicating core engine speed; it is used for starting and monitoring engine health.
- Vibration monitoring
- Vibration sensors detect imbalance, bearing damage, or foreign object damage; high vibration requires maintenance action.
- Thrust reverser
- A thrust reverser deflects fan or exhaust gases forward to decelerate the aircraft on the ground; it must be stowed and locked for flight.
- Derated thrust
- Derated thrust is a reduced takeoff thrust setting that extends engine life and reduces maintenance costs while maintaining safety margins.
- Flat rating
- Flat rating means an engine maintains its rated thrust up to a break temperature; above that, thrust decreases with increasing temperature.
- Compressor stall
- Compressor stall is a disruption of airflow through the compressor, causing a bang, EGT rise, and N1 fluctuation; action is to reduce throttle.
- Flameout
- A flameout is the loss of combustion in the engine, often due to fuel starvation or icing; action is to attempt a relight.
- APU
- The Auxiliary Power Unit is a small gas turbine that provides electrical power and bleed air for engine starting and air conditioning on the ground.
- Bleed air
- Bleed air is compressed air extracted from the engine compressor for anti-ice, pressurisation, and air conditioning; it reduces engine thrust.
- Borescope inspection
- A borescope inspection uses a flexible scope to examine compressor and turbine blades for cracks, erosion, and foreign object damage without disassembly.
- Oil analysis
- Oil analysis monitors wear metals in engine oil to detect early signs of component failure and trend engine health.