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Engine Systems Introduction Flashcards

1
Q

What creates thrust for the aircraft?

A

Propulsion system

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2
Q

What are the two main ways propulsion systems operate?

A
  1. Thrust developed by a gas turbine engine

2. Indirectly by a propeller (rotor) driven by piston or gas turbine engine.

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3
Q

What is the combustion process ?

A

Air and liquid hydrocarbons are compressed and then ignited.

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4
Q

What cycle do aeronautical piston engines use? What fuel do they use?

A
  1. Four stroke petrol cycle.

2. Utilize AVGAS

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5
Q

What is the piston attached to which is then attached to something else?

A

Piston –> Connecting rod –> Crankshaft

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6
Q

What are the four cycles in a piston engine?

A
  1. Intake
  2. Compression
  3. Power
  4. Exhaust
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7
Q

What occurs during the intake cycle of piston engine?

A
  1. Intake valve opens and fuel/air mixture is drawn into the cylinder.
  2. Cylinder pressure reduces as cylinder travels downwards.
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8
Q

What occurs during the compression cycle of piston engine?

A
  1. Both valves close

2. Cylinder pressure increases as piston travels upwards again.

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9
Q

What occurs during the power cycle or piston engine?

A
  1. Both valves are closed.
  2. Cylinder reaches TDC and spark plug fires, igniting the compressed fuel/air mixture.
  3. Resulting explosion forces the piston back down the cylinder.
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10
Q

What occurs during the exhaust cycle of piston engine?

A
  1. When piston reaches BDC, exhaust valve opens
  2. Piston comes back up and forces exhaust gases out exhaust valve
  3. Exhaust valve closes at TDC and process starts all over again.
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11
Q

What are two methods used to artificially increase the pressure available to the intake manifold by using a compressor on the engine intake air?

A
  1. Supercharger

2. Turbochager

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12
Q

What is a supercharger?

A

Centrifugal compressor directly driven by the engine through a system of gears that rotates the impeller at approximately nine times the engine RPM.

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13
Q

What system can be used to reduce the risk of over-boosting?

A

Manifold Air Pressure (MAP) Control

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14
Q

What determines the operating speed of a turbocharger?

A

Exhaust energy and the load on the compressor which is related to MAP.

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15
Q

Which has greater Friction Horsepower (FHP) losses, supercharger or turbocharger?

A

Supercharger.

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16
Q

What are some advantages of a piston engine?

A
  1. Low cost
  2. Low fuel consumption
  3. Suitable for smaller engines
  4. Simple engine and prop controls
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17
Q

What are some disadvantages of a piston engine?

A
  1. Higher weight and size for a given thrust output
  2. Relatively low power output < 300 BHP
  3. Less reliable and higher maintenance requirements.
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18
Q

What are some gas turbine characteristics?

A
  1. Allows higher cruising levels with higher transit speeds for greater economy.
  2. Utilizes cheaper fuel with the enhanced safety characteristics provided by its higher flash point
  3. Has fewer moving parts and a higher power-to-weight ratio.
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19
Q

What are the primary categories of gas turbine engines?

A
  1. Turbojet
  2. Turbofan
  3. Turboprop
  4. Turboshaft
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20
Q

How does the gas turbine engine move?

A

Spins smoothly and continuously.

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21
Q

What occurs during the start of a gas turbine engine?

A

External source is used to spin the engine until there is sufficient airflow for combustion, and then sufficient exhaust flow for the engine to achieved self-sustaining RPM.

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22
Q

What are the 5 stages of a gas turbine engine?

A
  1. Air Inlet
  2. Compression
  3. Combustion Chamber
  4. Turbine
  5. Exhaust
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23
Q

What occurs during the inlet stage?

A

Air is directed by the air inlet into the compressor.

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24
Q

What occurs during the compression stage?

A

Air is compressed, volume decreases, increasing temperature and delivered to the combustion chamber.

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25
What occurs in the combustion chamber during engine start/after engine start??
1. Fuel is injected and mixed with compressed air in the combustion chamber. 2. During engine start, fuel is ignited by igniter plugs 3. After engine start, fuel/air mixture is burned continuously with high temperatures.
26
When does combustion cease?
When the engine is shut down by turning off the fuel supply?
27
What occurs in the turbine phase?
Power is extracted from the gas flow to drive the compressor.
28
What is the difference in exhaust gases in a turboprop/turbojet engine?
1. Exhaust gases are used to provide thrust in a turbojet 2. In a turboprop engine, the exhaust gases are directed through an additional turbine to drive a prop through reduction gearing.
29
What can occur if there is an overtemperature or overspeed condition that lasts for more than a few seconds?
Internal engine components can be destroyed.
30
When do the hottest temperatures in the engine cycle occur?
During the starting cycle
31
What must occur before fuel is introduced into the combustion chamber?
Engine must reach a minimum rotational speed.
32
What is bypass air in a turbofan?
Air ducted around the hot core of the engine through an inlet fan that is driven by the turbines of the gas generator section.
33
What is the bypass ratio (BPR)?
Ratio of mass flow of air through the bypass duct to mass flow of air through the primary gas path.
34
What does a high bypass ratio indicate?
That most of the airflow is directed around the gas generator.
35
What BPRs do high bypass turbofan engines have?
> 3 : 1
36
What are there often two stages of compression/power extraction?
To optimize and maximize engine compression.
37
What BPRs do a low bypass turbofan use?
Less than 1:1
38
What advantages do low bypass turbofans provide?
1. Lower frontal area which reduces drag and enables installation in fuselage. 2. Greater efficiency at high speeds 3. Reduced rotational inertia enabling more rapid engine power changes 4. Increased thrust for a given engine weight.
39
What is used to allow a low bypass turbofan to operate at a wider speed range?
Variable geometry in the exhaust and intake sections.
40
What is an afterburner and which engine can it be used in?
Fuel is sent into exhaust and unburnt oxygen is ignited again providing extra thrust. Only in low bypass turbofan engines.
41
What can be used to provide a variation in afterburner thrust?
Variable exhaust nozzle.
42
What provides thrust in a turboprop?
Propeller
43
When is turboprop most efficient?
At low/medium altitudes and speeds up to 350 kts.
44
Why does the efficiency of the propeller deteriorate at speeds > 350 kts and high altitudes?
Development of shock waves on the blade tips.
45
What are two types of turboprop configurations?
1. Direct Drive | 2. Free Turbine
46
What type of A/C are turboshafts used on?
Helicopters.
47
What occurs to result in either compressor stall/surge?
Loss of laminar flow through the compressor section of a gas turbine.
48
What conditions can result in compressor stall?
1. If compressor operates outside of critical limits of RPM, pressure ratio and mass flow. 2. If it operates outside of these limits, any breach can affect the Relative Airflow (RAF) over the compressor blades.
49
What occurs if the compressor blade exceeds the Critical Angle of Attack (AoAcrit)?
1. Compressor blade stalls 2. Airflow over the blade separates into a cell of highly turbulent air behind the blade 3. Air flows around the turbulence instead of smoothly around the blade 4. Next blade spinning round encounters the turbulent air cell which might be large enough to stall the subsequent blade as well and a rotational stall occurs.
50
Will a stall often clear with little or no action from the pilot?
Yes
51
What are some compressor stall symptoms?
1. Audible rumbling noises 2. Popping sound, banging if more sever 3. Vibration 4. Reduced engine RPM, thrust and fuel flow 5. Increase turbine gas temperature
52
What is compressor surge?
When all stage of the compressor stall, the pressure in the combustion chamber is high enough to force the flame forward, which is referred to as a compressor surge.
53
What are some compressor surge symptoms?
1. Audible noises (muffled rumblings to violent banging and vibration) 2. Flames or a 'fireball' (from the engine exhaust and/or the intake) 3. High engine temperature (EGT, ITT, TIT).
54
What are some instances where a compressor stall or surge is more likely to occur?
- Rapid engine acceleration - Engine over-fueling - Disturbed airflow on the ground - Foreign object ingestion - High AoA or sideslip
55
What are some pilot interventions in the event of a compressor surge?
1. Throttle reduction to reduce fuel flow and combustion chamber pressure 2. Engine may need to be shutdown and restarted to clear a surge.
56
What does the engine fuel system provide?
Fuel to the engine to maintain the RPM at a selected value irrespective of aircraft altitude, attitude or speed.
57
What are the main fuel components on the engine side of the fuel system?
1. Fuel Cooled Oil Cooler (FCOC) 2. Fuel filter 3. High pressure fuel pump 4. Fuel Control Unit (FCU)
58
Why is a Fuel Cooled Oil Cooler (FCOC) required?
At high altitudes or extremely low temperatures for extended periods, fuel can condense out of the fuel and freeze, resulting in the fuel flow stopping.
59
What does the Fuel Cooled Oil Cooler (FCOC) do?
It is a heat exchanger in which engine lubricating oil is used to heat the fuel to ensure that ice cannot build up, while the fuel provides cooling for the engine oil.
60
Where can debris enter the fuel?
1. Through tank vents | 2. Through open line refueling points
61
What does the low pressure fuel filter do and where is it installed?
1. Ensures contaminants are filtered out. | 2. Installed between the FCOC and the engine driven fuel pump.
62
What doe the high pressure fuel pumps do and how are they driven?
- Deliver a continuous supply of fuel at the desired volume during all engine operating settings. - Driven by the engine.
63
Why are fuel pumps rated at a greater flow capacity than the maximum engine requirements?
To ensure the engine demands never exceed fuel supply volume.
64
What two types of HP fuel pumps are used?
1. Piston-type | 2. Spur Gear
65
What is the Fuel Control Unit (FCU) and how is it driven?
- Manages fuel flow to the engine by delivering precise amount of fuel for combustion and anticipates a variety of inputs that affect the combustion air/fuel ratio. - Engine driven
66
What are some factors that FCUs consider?
- Power lever angle - Inlet Air temperature - Inlet air pressure - Aircraft speed - Combustion pressure - Engine RPM - Turbine gas temperature
67
What is Basic Fuel Control FCU?
A fuel control system that consists of a strictly mechanical interface between the throttle and the engine's Fuel Control Unit (FCU).
68
What is Supervisory Control FCU?
Electro Hydro-Mechanical Fuel Control
69
What is Full Authority Control FCU?
Electro Hydro-Mechanical Digital system (Fly-By-Wire)
70
What functions does the engine oil system have?
1. Cushioning moving parts 2. Cleaning engine internals 3. Carrying away engine wear debris 4. Protecting against corrosion
71
What are the components of the lubrication system?
1. Oil Tank 2. Oil pump 3. Filter assemblies 4. Oil Cooler 5. Non-Return Valve (NRV) 6. Monitoring instruments 7. Magnetic chip detectors
72
What are the two types of oil coolers?
1. Fuel Cooled Oil Cooler | 2. Air Cooler Oil Cooler
73
What does the Engine Bleed Air System supply?
Small percentage of air for: 1. Internal Cooling of the engine 2. For use within A/C pneumatic systems.
74
What are 4 things engine bleed air is used for in a general sense?
1. Engine cooling 2. Bearing sealing and pressurization 3. Engine anti-icing 4. Bleed air services
75
What are the main areas of the engine that required cooled air?
1. Combustors | 2. Turbines
76
What percentage of air enters the combustor snout compared to that which flows around the combustor and then enters at a later period?
1. 20% through the snout | 2. 80% flows around and then in at a later stage.
77
What parts of the turbine need to be cooled?
Turbine discs and blades.
78
Which stage of compression is air for engine anti-icing taken from?
Later HP stages as it is the warmest.
79
What are some areas that hot air is used to prevent ice build up in?
1. First stage compressor inlet guide vanes 2. Engine nose cone 3. Air cooled oil cooler inlet 4. Compressor inlet cowling
80
What are some systems other than the engine that rely on bleed air as a source of pneumatic power?
1. Cabin pressurization and air conditioning 2. Airframe anti-ice systems 3. Hydraulic reservoir pressurization 4. Galley functions such as potable water pressurization 5. Engine starting
81
Where are indications of failures or exceedance of engine parameters outside limits usually displayed?
Through the aircraft alerting system
82
Where is routine engine monitoring information usually displayed?
On gauges in the cockpit.
83
What does the power of a gas turbine engine refer to?
The amount of thrust or torque that is generated by the engine.
84
What are some example power indication systems?
1. Torque indicator 2. Thrust indicator 3. Engine Pressure Ratio (EPR) indicator
85
For a turboprop engine, how is power output expressed and what may this be displayed in?
Power expressed as torque. - PSI - Ft lbs - Percentage of allowable range
86
For a turbofan or turbojet, what is the most common form of power indication? Explain what it is
- Engine Pressure ratio | - Ratio of exhaust output pressure to the inlet pressure.
87
Which type of engine are torque indicators used on?
1. Turboprop | 2. Turboshaft
88
What are some methods of measuring torque?
1. Hydraulic Torque Indication System which using planetary gears that provide oil pressure that goes to the torque gauge. 2. Torque Shaft Indication System which propagates an electrical signal in proportion to the toque between two shafts (one reference and one experiencing the torque)
89
How does a thrust indicator work?
Measurements of pressure in propeller slipstream / jet engine exhaust and compares that to a reference pressure (normally static pressure).
90
What type of engines are EPR indication systems only used for?
Axial flow turbojet engines
91
What are the fuel flow indicating systems used for? What units are normally displayed?
Indicating and displaying the amount of fuel being consumed in a certain period of time. Lbs, litres or gallons per hour
92
What are the two basic types of fuel flow indicating systems ?
1. Rotating vane (Vane that depending on its position, will transmit a voltage that is converted into a fuel flow rate) 2. Impeller (rotating impeller that the greater the fuel flow, the greater the fuel flow)
93
How is engine temperature monitoring accomplished?
Using thermocouple probes.
94
What keys temperatures are taken for engine temperature measurements? what units are these temperatures?
1. Turbine Inlet Temperature (TIT) 2. Intermediate turbine temperature (ITT) 3. Exhaust gas temperature (EGT) Units are Celsius
95
How is engine oil pressure measured and what units?
Pressure detection transmitter is placed in the oil system inlet side that sends pressure signals to the displays. Units are PSI
96
How is oil temperature measured?
Using a thermistor
97
What is used to measure and indicate engine speed? What are the units?
Tachometer | Percent of Rated RPM (Percent RPM)

Ground School Systems 1 (12 decks)

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