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
2
Q
Ramjet
A
- A jet that continuously burns fuel and produces thrust
- Used for missiles supersonic airplanes
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
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
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
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
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
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
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
10
Q
Can-annular Combustion Chamber
A
Individual flame tubes with common inner and outer casing
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
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
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
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
15
Q
PT6 Engine
A
- Most popular turbo prop ever built
- Used in PC-12
- Reverse flow engine
- Free turbine
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
Starting Turbine Engines - Air Starts
- 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
Starting Turbine Engines - Starter Generators
- 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
Hot Start
- 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
Hung Start
- 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
Compressor Stall
- 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
Reverse Thrust Turboprop
Blades move past the full coarse position into the beta range
30
APU
- 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
Electrical Systems
- 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
Fuel Systems
- 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
