EASA Module 14 flashcards
EASA Module 14 · Build recall with a focused review session.
31 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Brayton cycle
- The thermodynamic cycle of a gas turbine: isentropic compression, constant-pressure heat addition, isentropic expansion and constant-pressure heat rejection. Efficiency increases with pressure ratio and turbine entry temperature.
- Specific fuel consumption
- Fuel mass flow divided by thrust (TSFC) or by shaft power (SFC). It measures economic efficiency; lower values are better and TSFC improves with higher bypass ratio at subsonic speed.
- Compressor surge
- A violent reversal of airflow through the compressor, often following blade stall. It produces a bang, fluctuating fuel flow, falling RPM and rapidly rising exhaust gas temperature, and needs immediate throttle reduction.
- Choked nozzle
- A nozzle is choked when flow reaches Mach 1 at the throat. For a convergent nozzle this occurs at a pressure ratio of about 1.89, after which further pressure rise does not increase mass flow.
- Turbine blade cooling
- HP turbine blades are cooled by compressor bleed air through internal passages and film holes, and coated with a thermal barrier. This allows gas temperatures above the creep limit of the blade alloy.
- Bypass ratio
- Mass flow through the fan duct divided by mass flow through the core. High bypass ratios give better propulsive efficiency and lower noise, which is why modern civil turbofans use them.
- Compression ratio
- The ratio of cylinder volume with the piston at bottom dead centre to the volume at top dead centre. Higher ratios raise thermal efficiency but increase detonation tendency and require higher octane fuel.
- Detonation
- Spontaneous ignition of the unburnt end gas ahead of the flame front, producing a sharp pressure rise and knocking. It is caused by high compression, lean mixture, hot intake air or low octane fuel.
- Pre-ignition
- Ignition of the mixture before the spark occurs, usually from a glowing plug, carbon deposit or overheated valve. Unlike detonation it is not caused by the fuel's octane rating and can destroy pistons quickly.
- Volumetric efficiency
- The mass of air actually inducted divided by the theoretical mass the swept volume could hold at ambient conditions. It falls with throttle restriction, high RPM and hot intake air.
- Stoichiometric ratio
- The chemically correct air-to-fuel mass ratio for complete combustion, about 14.7:1 for petrol. Richer mixtures give more power, leaner mixtures give better economy but raise cylinder head temperature.
- Magneto check
- During run-up each magneto is selected alone to confirm the other is live. A dead magneto is hidden when the switch is in BOTH, so an engine may stop when switched off.
- FADEC
- Full Authority Digital Engine Control: a dual-channel computer that schedules fuel flow, variable stator vanes and bleed valves, and provides overspeed and over-temperature protection without a mechanical backup.
- Hot start
- A turbine start in which exhaust gas temperature exceeds the limit before or shortly after light-up, usually from too much fuel or low starter speed. Fuel and ignition must be cut off immediately.
- Hung start
- A start in which the engine lights but fails to accelerate to idle RPM, with N2 stagnating and EGT rising. Causes include weak starter, low bleed pressure or incorrect fuel scheduling.
- Dry-sump oil system
- An oil system with a separate tank, pressure pump and one or more scavenge pumps. It allows the tank to be positioned for aircraft attitude and prevents oil collecting in the engine.
- Igniter plug
- A high-energy capacitor-discharge plug producing roughly 15 to 20 kV to ignite the fuel-air mixture during starting and for relight. Only one of the two is normally needed in flight.
- Bleed air
- Air tapped from a compressor stage for cabin pressurisation, anti-icing, starting and hydraulic reservoirs. Large bleed extraction reduces available thrust and raises exhaust gas temperature.
- Thrust reverser lock
- A mechanical or hydraulic lock plus control logic that prevents reverse thrust selection in flight. Deployment is only possible with weight on wheels and throttle at idle.
- Geometric pitch
- The theoretical forward distance a propeller would advance in one revolution if it moved through a solid medium. Effective pitch is smaller because of slip, the difference between the two.
- Helix angle
- The angle between the relative airflow and the plane of rotation at a blade section. It increases with forward speed and decreases with radius, so blade angle rises towards the tip.
- Blade angle
- The angle between the blade chord line and the plane of rotation. Angle of attack equals blade angle minus helix angle, so blade angle must be increased for higher forward speed or RPM changes.
- Constant-speed propeller
- A propeller whose blade angle is varied by a governor to hold a selected RPM. Flyweights and a speeder spring control oil flow to the pitch-change piston as load or speed changes.
- Feathering
- Turning the blades to a very coarse angle so they align with the relative airflow and produce almost no thrust or drag. It is used after an engine failure to reduce asymmetric drag.
- Reverse pitch
- Moving the blades past the fine pitch stop to a negative angle of attack so they produce rearward thrust. Used on the ground to shorten landing roll and improve manoeuvring.
- Propeller slip
- The difference between geometric pitch and effective pitch, caused by the air yielding as the blade produces thrust. Slip increases with load and is expressed as a percentage of geometric pitch.
- Propeller efficiency
- Thrust power divided by shaft power, expressed as a percentage. It peaks when the blade angle of attack is small, and falls at high tip Mach numbers because of compressibility losses.
- Static balance
- Balancing a propeller as a stationary assembly so its centre of gravity lies on the axis of rotation. It is done on a knife-edge or bearing stand before installation.
- Dynamic balance
- Balancing the propeller while it rotates, using an analyser to measure vibration and adding weights to correct the imbalance. It reduces vibration that static balancing cannot detect.
- Propeller tracking
- Checking that all blade tips follow the same plane of rotation by rotating the propeller past a fixed reference. Excessive track error indicates a bent blade or damaged hub.
- Windmilling
- A propeller or fan rotating under the influence of airflow alone after engine shutdown or failure. It causes drag and, in a turbine, may allow a relight if fuel and ignition are restored.