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AVIA 204 - FM2B > Turbine Engines and Complex Aircraft Systems > Flashcards

Turbine Engines and Complex Aircraft Systems Flashcards

1
Q

Turbine Engines

A
  • Have a much higher power to weight ratio than an internal combustion engine
  • Much more expensive to build and maintain
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2
Q

Ramjet

A
  • A jet that continuously burns fuel and produces thrust
  • Used for missiles supersonic airplanes
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3
Q

Turbojet Basics

A
  • More advanced type of ramjet
  • Several compressor blade stages compress the airflow into the engine
  • Similar to the 4 stroke cycle
  • Intake, compression, ignition, exhaust
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4
Q

Turbojet Principles of Operation

A
  • Air from the atmosphere flows into the compressor where its pressure is increased
  • Usually multiple stages of compression
  • Fuel is added to the high pressure air and burned in the combustion chamber
  • Self sustained once started
  • Hot air from combustion chamber flows through turbines, which extract energy to drive the compressors
  • Exhaust or nozzle is responsible for delivering the flow to the atmosphere
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5
Q

Axial Compressor

A
  • Air flows directly from the front to the rear of the compressor
  • Each stage increases the pressure of the air by an approximate factor of 1.2
  • many more stages of compressor than turbine
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6
Q

Centrifugal Compressor

A
  • Increases pressure of the air by a factor of 4
  • Not as common on large engines as axial because airflow changes direction and frontal size of the engine is larger
  • Used in shorter engines such as APU’s or turboprops in conjunction with axial stages
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7
Q

Combustion Chamber

A
  • Where fuel and air is mixed and ignited
  • passes flow to turbine
  • Only 25% of air from compressors is mixed with fuel and burnt
  • Rest is used to cool air after burning
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8
Q

Annular Combustion Chamber

A
  • One continuous combustion chamber
  • Advantage is that airflow is already in-line with it and discharge is set up for turbines
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9
Q

Can-type Combustion Chamber

A
  • Small individual combustion chambers
  • Advantages are easier to test and repair
  • Disadvantage is airflow changes to and from cans
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10
Q

Can-annular Combustion Chamber

A

Individual flame tubes with common inner and outer casing

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11
Q

Turbines

A
  • Purpose is to extract energy from flow to drive the compressor
  • Hot gases coming from the combustion chamber drive the turbine which in turn drives the compressor
  • Turbine blades get extremely hot, so they use bleed air from the compressor to cool them down
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12
Q

Turbofans

A
  • Newest and most common type of jet engine
  • Some air coming through the inlet bypasses the jet and produces thrust similar to a propeller
  • Provides better low speed power for take-off and landing, but reduces power slightly at cruise
  • Ratio of air into jet and bypass air is called “by-pass” ratio
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13
Q

Multiple Spool Engines

A
  • Most modern turbofan engines are multiple spools or concentric shafts so different stages of the engine can rotate at different speeds
  • Improves efficiency, provides easier starting, and reduces the chance of compressor stalls
  • Modern high-bypass turbofan will have 2-3 spools
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14
Q

The Turbo Prop

A
  • Propeller shaft attached to turbojet
  • Helicopter rotor attached to turbojet is a turboshaft
  • Combination of turbine and propeller
  • Can got o much higher altitudes than an internal combustion engine while being more efficient than a turbo fan
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15
Q

PT6 Engine

A
  • Most popular turbo prop ever built
  • Used in PC-12
  • Reverse flow engine
  • Free turbine
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16
Q

Bleed Air

A
  • On most turbine engines, bleed air is extracted from the compressor section to feed various aircraft systems
  • This hot compressed air can be used to run deicing systems including pressurization, heating, and air conditioning
  • In modern turbofan, air is ducted out of the axial compressor stages
16
Q

Free Turbine

A
  • Turbine engines usually have a direct drive shaft connecting the turbine and compressor
  • Free turbine uses the force of the air going through the system to power the gearbox, which is connected to prop or rotor
  • Free turbine results in less time required to perform maintenance, less ground noise, and operates over a wider range of air pressures and velocities
17
Q

Turbine Ignition Systems

A
  • Turbine engines usually only require ignition during the starting phase
  • Spark plugs are used during start, but the flame is self-sustaining afterwards
  • In-flight conditions may require continuous ignition
18
Q

Electronic Engine Control

A
  • Modern turbine engines incorporate electronic controls to more efficiently manage thrust settings
  • Engine computers prevent operating limitations from being exceeded
  • Computers may work in conjunction with autothrottle or an FMC
  • Starting is much easier
  • Computers work constantly to maximize efficiency and fuel economy
19
Q

Controlling Turboprops

A
  • Power is measured in torque, set using throttle
  • Propeller set by prop levers
  • Reverse thrust is applied by moving power levers down past idle
  • Condition levers select engine fuel supply on or off
20
Q

Turbine Instruments

A
  • N1 gauge shows percent of maximum RPM on the low pressure compressor shaft
  • N2 gauge shows percent of maximum RPM on the high pressure compressor shaft
  • ITT (Interstage Turbine Temperature) shows temp within the turbine section of engine
  • EGT shows EGT
21
Q

Controlling Turbojets and Turbofans

A
  • Power usually set using N1 or EPR (Engine Pressure Ratio)
  • Only a throttle and fuel shutoff valve required for each engine
22
Q

Starting Turbine Engines

A
  • When starting, must first reach a specific operating RPM before fuel can be introduced to the combustion chamber
  • Air must be compressed at a given RPM for combustion to occur
  • Engines use several methods to spool the engine up for starting
  • Methods include APU, Air Start, and Starter Generators
  • On multiple spool engine, only high pressure shaft is spun to start engine
  • Once ignition occurs, HP shaft accelerates and starts to feed the turbine stages of any other shafts
23
Q

Starting Turbine Engines - APU

A

Compressed air is ducted from the APU to spool up the HP shaft

24
Q

Starting Turbine Engines - Air Starts

A
  • Can use ground cart or have bottles of compressed air stored on board
  • Compressed air sent through the HP gas generator
  • Can be bleed air from opposite engine
25
Q

Starting Turbine Engines - Starter Generators

A
  • Commonly used on turboprops, smaller jet engines, or APU’s
  • Uses an electric motor to spin compressor to its operating RPM
  • Once engine is running, used a generator to power the aircraft’s electrical systems
  • Power insufficient for large engines
26
Q

Hot Start

A
  • ITT climbs rapidly towards limit, pilot must cut off fuel
  • Usual cause is insufficient engine RPM at the time of ignition
  • Too little airflow and too much fuel
  • Can ruin the engine if not caught in time
27
Q

Hung Start

A
  • Engine starts, but doesn’t accelerate to normal operating RPM
  • Result is a low RPM. high ITT condition, as fuel is burning but airflow isn’t sufficient for cooling
  • Do NOT add fuel
  • Must cut off fuel supply
28
Q

Compressor Stall

A
  • Compressor blades stall
  • Engine is receiving insufficient intake airflow
  • If compression is reduced enough, expanding gasses from combustion chamber can overcome the force of compressed air from the compressor
  • Exhaust will then flow forwards, not a good thing
  • Loud bang, engine RPM and temp fluctuations
  • Reduce power and increase airspeed
  • Compressor stalls can damage engine if consistent
  • Movable stator blades provide protection against compressor stalls
29
Q

Reverse Thrust Turboprop

A

Blades move past the full coarse position into the beta range

30
Q

APU

A
  • Mini Engine
  • Centrifugal compressor provides some electrical power and bleed air
  • Used on ground to save fuel by not running a full size engine
31
Q

Electrical Systems

A
  • Electrical power needed to operate hydraulics
  • Left and right bus bars connected with a bus tie to redirect power
  • Generators produce Ac power and Transformer Rectifier units convert it to DC
32
Q

Fuel Systems

A
  • Tanks are located in the wings and belly of the fuselage
  • Some aircraft use a trim tank to move aircraft’s C of G during flight
  • Fuel usually burned from centre tank first, then the wings
  • Jet fuel may freeze at altitude
  • Fuel heat-exchangers use warm oil or bleed air to run adjacent to fuel lines to prevent freezing
  • Heat exchanger also used to cool engine oil
  • If fuel tanks not heated, additive called Prist may be added to prevent freezing

AVIA 204 - FM2B (10 decks)

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