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at 103 > AT103 Review Through Exam 3 > Flashcards

AT103 Review Through Exam 3 Flashcards

1
Q

Early Gas Turbine Engine Inventors/Users

A

1232 - Chinese began to use rockets as weapons.
1872 - Dr. F. Stolze designed the first true gas turbine engine. This engine never ran under its own power.
1939 - The aircraft company Ernst Heinkel Aircraft flew the first flight of a gas turbine jet, the HE178.
1941 - Sir Frank Whittle designed the first successful turbojet airplane, the Gloster Meteor. In 1942 he shipped an engine prototype to General Electric in the United States. America’s first jet plane was built the following year.
1942 - Messerschmitt Me 262, the world’s first operational jet fighter.

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2
Q

Brayton Cycle vs. Otto Cycle

A

Brayton is the same as Otto except events occur at the same time and events occur at different locations within the engine

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3
Q

Convergent vs. Divergent

A

C: Velocity decreases, Pressure and Temperature increase
D: Velocity increases, Pressure and Temperature decrease

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4
Q

Non-Air vs. Air Breathing

A

NA: Carries all the needed oxygen within their fuel
AB: Takes air

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5
Q

Types of Air Breathing Turbine Engines (4)

A

Turbojet
Turboprop
Turboshaft
Turbofan

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6
Q

Turbojet Engines

A

Takes air in through the air inlet
Compresses the air
Mix compressed air with fuel
Air and fuel mixture ignited and burned
Hot gases passes through turbine
Air forced out of a specially shaped exhaust nozzle forming a high-speed jet

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7
Q

Turboprop Engines

A

Drives a propeller
A derivative of the turbojet engine

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8
Q

Two methods to drive propeller

A

Connecting the propeller to the compressor
Connecting the propeller to a turbine separate from the core engine (Free-Turbine Engine)

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9
Q

Turboshaft Engines

A

Commonly used for helicopters
More efficient at constant RPM required by helicopters
Most drives output shaft with multistage free turbine
Reduction gearbox is remote from the engine

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10
Q

Turbofan Engines

A

Increased propulsive efficiency
Lower Noise
Lower fuel consumption
Lengthened blades in early stage(s) of low-pressure compressor
Air from the fan section flows around the outside of the core engine
Fan can produce 30-75% of the total thrust

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11
Q

Bypass Ratio

A

Ratio of the mass or air moved by the fan to the mass of air moved by the core engine

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12
Q

Types of Bypass Ratios (3)

A

Low-Bypass (Less than 2 : 1)
High-Bypass (Ratio of 4 : 1 or greater)
Ultra-High-Bypass (Exceeds 30 : 1)

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13
Q

What is thrust measured in?

A

pounds (lbs)

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14
Q

What is thrust determined by? (3)

A

Change in momentum experienced by air flowing through the engine
The momentum of the fuel
The force caused by the difference in pressure across the exhaust nozzle multiplied by the area of the nozzle

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15
Q

Types of thrust (2)

A

Net
Gross

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16
Q

Net thrust

A

Thrust produced by the engine while in flight

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17
Q

Gross thrust

A

Thrust produced by the engine while engine is static and not moving

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18
Q

Thrust indication for smaller jet engines

A

Compressor speed in % RPM
RPM is approximately proportional to the trust being produced by the engine

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19
Q

Thrust indication for larger jet engines

A

Engine Pressure Ratio (EPR)
Ratio of the turbine discharge total pressure to the compressor inlet total pressure

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20
Q

Methods of increasing thrust (3)

A

Water Injection
Duct Heater
Afterburners

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21
Q

Thrust Horsepower

A

Can be computed when engine thrust (lbs) and aircraft speed (mph) are known

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22
Q

What are turboprops rated in?

A

ESHP

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23
Q

What do turboprops take into account for? (2)

A

Shaft horsepower to the propeller
Thrust developed at the exhaust

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24
Q

Engine Station Designations (11)

A

AM or 0 - Ahead of the Engine
1 - Entrance to the aircraft air inlet duct
2 - Fan (N1 compressor) inlet
3 - N2 compressor inlet
4 - Burner inlet
5 - N2 Turbine inlet
6 - N1 Turbine inlet
7 - Diffuser
8 - Afterburner combustion chamber
9 - Afterburner duct
10 - Exhaust nozzle discharge

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25
Q

Gas Turbine Engine Sections (2)

A

Cold
Hot

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26
Q

Parts of the Cold Section (3)

A

Inlet air duct
Compressor
Diffuser

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27
Q

Parts of the Hot Section (3)

A

Combustion
Turbine
Exhaust system

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28
Q

Inlet Air Duct

A

Usually considered a part of the airframe
Responsible for supplying a constant undisturbed flow of subsonic air to the compressor
Designed specifically to match the engine being used

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29
Q

Types of inlet air ducts (2)

A

Subsonic
Supersonic

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30
Q

Subsonic inlet ducts

A

Usually a divergent type
Air flowing into a divergent duct… Velocity decreases Pressure increases

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31
Q

Turboprop Engines

A

Propeller reduction gearbox interferes with air flow

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32
Q

Ways to deliver air in turboprop engines (3)

A

Ducted Spinner Inlet
Conical Spinner Inlet
Under-scoop Inlet

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33
Q

Pratt & Whitney PT6 Engine

A

Reverse flow

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34
Q

Foreign Object Damage (FOD)

A

Common practice to cover engines when not in use

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35
Q

Warm compressor air is routed to prevent…

A

inlet ice formation (bleed air)

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36
Q

Supersonic inlet ducts

A

Air must be below the speed of sound entering the compressor
A convergent-divergent (CD) inlet duct is used

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37
Q

Supersonic air entering slows down until…

A

the narrowest part of the duct

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38
Q

What happens when supersonic air enters the narrowest part of the duct?

A

Air is reduced to speed of sound and a normal shockwave forms
Air becomes subsonic after flowing through the normal shockwave
Air is further slowed through divergent duct

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39
Q

Variable inlet ducts are used to accommodate…

A

different air speeds

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40
Q

How do variable inlet ducts accommodate different air speeds? (2)

A

Lowering or raising a wedge
Moving a taper plug in or out of the duct

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41
Q

Types of Compressors (2)

A

Centrifugal
Axial-Flow

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42
Q

Advantages of Centrifugal Compressors (4)

A

Rugged
Light Weight
Ease of Construction
High Pressure Ratio for each stage of compression

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43
Q

Centrifugal Compressor components (3)

A

Impeller
Diffuser
Manifold

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44
Q

Centrifugal compression ratio

A

6 : 1 to 7 : 1

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45
Q

Centrifugal Compressors

A

Volume of air moved depends on the diameter of the compressor

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46
Q

Disadvantages of diameters too large (2)

A

Tip speed increases and efficiency decreases
Difficult to streamline the engine

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47
Q

Types of Centrifugal Compressors (2)

A

Double-Entry
Multi Stage

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48
Q

Double-Entry Centrifugal Compressor

A

Difficult to design inlet ducts for front and rear air supply

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49
Q

Multi Stage Centrifugal Compressor

A

High pressure rise per stage
Experiences pressure loss between stages

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50
Q

Axial-Flow Compressors

A

Air passes straight through the compressor
Made up of stages of rotor blades between stages of fixed stator vanes
Rotor blades and stator vanes are airfoil shaped and positioned to form a series of divergent ducts

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51
Q

Axial-Flow Compressor disadvantages (2)

A

Heavier than centrifugal compressors
Costly to manufacture

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52
Q

Axial-Flow Compressor advantages (2)

A

Higher overall compression ratio
Easier to streamline

53
Q

Types of Axial-Flow Compressors (2)

A

Single-Spool
Dual-Spool

54
Q

Single-Spool Axial-Flow Compressors

A

Stages of compressor is limited

55
Q

What happens when there are too many stages in a Single-Spool Axial-Flow Compressor? (3)

A

Rearmost stages become inefficient
Front stages become overloaded
Airflow through compressor become restricted and can lead to compressor surge

56
Q

Dual-Spool Axial-Flow Compressors

A

Rearmost compressor = High-pressure compressor (N2)
Driven by forward stage turbine (High-pressure turbine)
N2 compressor is governed by the fuel control and used by the starter to start the engine due to its lighter weight

57
Q

Three-Spool Axial-Flow Compressors

A

Fan = Low-pressure (LP) compressor (N1)
Intermediate-pressure (IP) compressor (N2)
High-pressure (HP) Compressor (N3)
All driven by separate turbines (three shafts)

58
Q

Path through Three-Spool Axial-Flow Compressor

A
  1. N1, N2, N3 Compressors
  2. Diffuser
  3. Combustion
  4. Turbine
  5. Exhaust system
59
Q

Hybrid Compressor Engine

A

Uses both axial-flow and centrifugal compressors

60
Q

Blade Attachment

A

Blades are loosely attached to the compressor drum or disk
Centrifugal forces from a running engine will hold the blades in their intended position
Commonly attaching by the dovetail or fir tree method

61
Q

Blade Design

A

Blades have twists designed to produce the correct pressure gradient along the length as velocity changes
Much like small propellers
To maximize efficiency (seal):
Abradable strips are mounted in the compressor housing and/or the blade tip

62
Q

What counteracts Bernoulli’s Principle

A

Blade twists

63
Q

Guide Vanes and Stator Vanes

A

Usually fixed (Variable controlled hydraulically with fuel from fuel control)
Turns air so it flows correctly for the rotor blades
Stator Vanes have airfoils positioned to create divergent ducts (decrease velocity and increase pressure)

64
Q

Diffuser Section

A

At the rear or the compressor
Diverging area for air to decrease velocity and increase pressure
Highest pressure point in the engine

65
Q

Causes of Surges and Stalls (5)

A

Excessive rotor blade angle of attack
Obstruction to inlet
Excessive pressure in the burner section
Abrupt flight maneuvers
High crosswind during takeoff and low airspeed

66
Q

Combustion Section Requirements (7)

A

Minimum pressure loss in gases
High combustion efficiency (low smoke emission)
Low risk of flame blowout
Combustion occurring entirely within the combustor
Uniform temperature distribution throughout the gases
Low enough temperature of gases leaving combustor to prevent turbine damage
Combustor design provides easy starting

67
Q

What are Combustors made out of?

A

Thin sheets of corrosion resistant metal

68
Q

Most Common Types of Combustors (3)

A

Multiple-Can
Can-Annular
Annular

69
Q

Multiple-Can Combustors

A

Usually between 8-10 cans are used
Igniters installed in only 2 cans
Crossover tubes connects the cans

70
Q

Advantage of Multiple-Can

A

Individual cans can be removed

71
Q

Disadvantages of Multiple-Can (2)

A

Uneven temperatures
Can cause turbine failure when cans fail due to extreme temperature differences

72
Q

Can-Annular Combustors

A

Consist of individual cans mounted on an annular duct
Hot gases are collected, then directed into the turbine

73
Q

Advantages of Can-Annular (3)

A

Individual cans can be removed
Shorter cans (lower pressure drop)
Uniform temperatures even with a clogged fuel nozzle

74
Q

Annular Combustors

A

Makes the most efficient use of space
Efficient mixing of fuel with air
Requires minimum amount of cooling air
Provides even temperature air
Cannot be replaced without removing the engine from the aircraft

75
Q

Turbine Section

A

The power-producing component
¾ of the gases from combustion section is converted to SHP to drive compressor and fan

76
Q

Types of Turbines

A

Axial Turbine
Radial-Inflow Turbine

77
Q

Turbine Inlet Guide Vanes (TIGV)

A

Mounts between the combustion section and first stage turbine
Forms a series of convergent ducts to increase velocity and decrease pressure
Directs air to turbine blades at the right angles
Highest temperature point in the engine

78
Q

Highest pressure and temperature points in the engine

A

Pressure: Diffuser Section
Temperature: Turbine Inlet Guide Vanes (TIGV)

79
Q

Turbine design

A

Normally made of heavy nickel alloy forging
Blades are attached with a fir-tree method (accounting for thermal expansion)
Turbine disk and blades are sometime machined out of a single piece of material and are called “blisk”

80
Q

Turbine Blade Designs (3)

A

Reaction Blade
Impulse Blade
Reaction-Impulse Blade

81
Q

Reaction Blade

A

Produce turning force by aerodynamic action (airfoil)

82
Q

Impulse Blade

A

Produce turning force by the energy required to change the direction of airflow (bucket)

83
Q

Reaction-Impulse Blade

A

Combo of Reaction and Impulse Blades

84
Q

Turbine Cooling

A

Amount of power a gas turbine engine can produce is limited by the maximum temperature the turbine inlet can tolerate
Turbine Inlet Temperature (TIT)
Turbine cooling improves efficiency
Flowing compressor bleed air through hollow guide vanes and rotor blades

85
Q

Causes of Turbine Failures (3)

A

Creep
Metal Fatigue
Corrosion

86
Q

Creep

A

Deformation of metal that is continually under high centrifugal loads and temperatures

87
Q

Metal Fatigue

A

Weakening of metal subjected to repeated cycles

88
Q

Corrosion

A

Electrolytic action that occurs when alloying agents combine with elements in the air to form salts
Accelerated by exposure to extremely high temperatures

89
Q

Turbine Engine Exhaust

A

Energy remaining after exhaust gases passes through the turbine are utilized to produce thrust
Exhaust system must straighten and accelerate the exhaust gases
The end of the tail pipe is the exhaust nozzle or jet nozzle
The outlet area determines the velocity of gases leaving the engine
Most turbojet and low-bypass turbofan have an outlet area in a choked condition

90
Q

Gases are accelerated to the speed of sound at the end of the tail pipe and can…

A

no longer accelerate

91
Q

For turbine engines equipped with afterburners

A

Variable-Area Nozzle

92
Q

Variable-Area Nozzle

A

Opens or closes automatically based on the fuel flow of the engine
Earlier afterburner engines have only two positions
Modern afterburner engines control their nozzles with the electronic engine control (EEC)

93
Q

For efficiency

A

The divergent portion of the nozzle must vary automatically as airflow changes
Some nozzles use a wall of air to form the divergent portion boundary of the nozzle

94
Q

Noise Suppressors

A

Noise is one of the primary complaints
The amount of noise relates to the velocity of the exhaust gases
The distance the noise travels relates to the frequency of the sound
The amount of noise cannot be decreased without sacrificing thrust
First sounds to be heard are always the low-frequency
Increasing the frequency will shorten the distance of the noise

95
Q

Thrust Reversers

A

Used to assist the brake system in slowing down the aircraft after landing
Same function as propellers with reverse- pitch capability
Turbojet and turbofan engines reverses some of its thrust to aid deceleration
Thrust reversers diverts 40-50% of the engine’s rated forward thrust rearward
Used on the ground to decrease landing roll
Some aircrafts use thrust reversers to allow descent at a steep angle without building up excessive speed (Very limited)
Operates by deflecting part of the exhaust gases or fan discharge air forward
Actuated by the pilot using the control mounted on the engine throttle
Throttle is retarded to the idle position, then the reverse thrust control in moved

96
Q

Afterburners

A

The air flowing out of the exhaust is hot and contains large amounts of oxygen
First used on a civilian aircraft by the Concorde
Although afterburners use more fuel, it also helps aircraft reach cruising altitude quicker
Also known as a “reheat” system in the United Kingdom
When operating the afterburner, back pressure on the turbine would increase if exhaust nozzle stays the same
Variable exhaust nozzles are used to control turbine back pressure

97
Q

Vector Thrust

A

Either through changing the direction of the exhaust nozzle or the turbine engine entirely
British Aerospace Sea Harrier is one of the first to use vector thrust for vertical takeoff capabilities
To increase the thrust produced by vector-thrust engines, plenum-chamber burning (PCB) is used
Similar to afterburners, fuel is injected into the fan-discharge air and burned
Increase thrust by as much as 50%

98
Q

Lubrication System in Gas Turbine Engines

A

Absorb large amount of heat
Typically 5 – 8 gallons of low viscosity synthetic oil
Oil circulates through the engine at a high flow rate
Normally about a pint an hour is consumed

99
Q

Turbine shaft bearings

A

Absorb large amount of heat

100
Q

Similarities to reciprocating engines (5)

A

Lubrication reduce friction in the gears and bearings
Absorb heat from the bearings
Protect metal parts against corrosion
Pick up and carry contaminants into filters
Routed through an oil-to-fuel heat exchanger

101
Q

Lubrication System Subsystems (3)

A

Pressure Subsystem
Scavenge Subsystem
Vent Subsystem

102
Q

Lubrication System Components (3)

A

Oil Filters
Oil Coolers
Chip Detector

103
Q

Oil Filters

A

Wire-mesh screen can remove contaminants up to 40 microns
Pleated fiber filter up to 15 microns

104
Q

Oil Coolers

A

Modern oil coolers are of the oil-to-fuel type
Serves dual purpose
Removes heat from the oil
Warms the fuel

105
Q

Chip Detector

A

Magnetic chip detectors are installed in the scavenger system
Picks up ferrous metal flakes or chips
They are easily removed for routine inspection
Some are connected into an electrical circuit that indicates metal particles by illuminating a warning light on the flight deck

106
Q

Turbine Engine Fuels (2)

A

Jet A / A-1
Jet B “Wide-Cut Fuel”

107
Q

Jet A Fuel

A

Similar to commercial kerosene
Similar to the military JP-8
Jet A starts to freeze at -40°F
Jet A-1 starts to freeze at -58°F

108
Q

Jet B Fuel

A

Blend between gasoline and kerosene
Similar to the military JP-4
Jet B starts to freeze at -60°F

109
Q

Tetraethyl Lead (TEL)

A

Causes deposits to form on the turbine blades

110
Q

Lubrication Properties of Avgas (2)

A

Avgas does not lubricate as well as kerosene (lubricity)
Can cause excessive wear on fuel control system

111
Q

Microbial Growth in Jet Fuel Tanks

A

Microscopic organisms live and multiply at the interface between water and fuel forming scum
The scum holds the water that is in contact with the tank structure causing corrosion

112
Q

Scum Prevention Methods

A

Additives (Ethylene Glycol Mono-methyl Ether, PFA 55MB, Prist)
Mixed into the fuel at the refinery or
Injected into the fuel as it is pumped into the tanks

113
Q

Turbine engines use a…

A

continuous combustion process (not timed)

114
Q

Ignition is only needed normally during the…

A

start sequence

115
Q

Unlike aviation gasoline, turbine engine fuel requires a…

A

much hotter spark for ignition

116
Q

Ignition system is normally turned on during (4)

A

Takeoff
Landing
Flight into Turbulent Conditions
When Engine Anti-Ice System is Actuated

117
Q

In case of a turbine engine flameout

A

2 Ignition Exciters
2 High-Tension Leads
2 Igniters

118
Q

Cooling-down period is called a…

A

“duty cycle”

119
Q

Two types of ignition systems

A

Intermittent-Duty System
Continuous-Duty System

120
Q

To start a gas turbine engine

A

The compressor is first rotated with a starter
Ignition system is energized
When the engines reaches a specified RPM, fuel is sprayed into the combustors and the engine starts
Once engine accelerates to a self-sustaining idle speed, the starter and ignition systems are turned off
Start sequence is usually programmed so the pilot only needs to initiate the action (press and hold a button)
For dual-spool axial-flow engines, the starter rotates the N2 compressor

121
Q

Commonly Used Started Types (2)

A

Air Starters (Large Engines)
Electrical Starters (Small Engines)

122
Q

Air Starters

A

Light weight with good amount of torque produced
Requires large volumes of low pressure compressed air
APU, GPU, and cross-flow of compressor bleed air
Air starters have their own lubrication system in the starter housing
Magnetic chip detector is built into the drain plug

123
Q

Electrical Starters

A

Series-wound electric starters
Connected to the engine through a ratcheting starter jaw similar to reciprocating engines
Starter jaw engages a mating jaw on the engine starter drive
Once engine is self-sustaining, the starter jaw moves away from the jaw in the engine
Electrical power is then stopped to the starter

124
Q

What connects to the crankshaft?

A

Connecting rod

125
Q

The top limit of the stroke is called

A

Top Dead Center (TDC)

126
Q

Parts of a spark plug (3)

A

Electrodes
Ceramic Insulator
Metal Shell

127
Q

Fine Wire Spark Plug

A

Similar construction to the massive electrode type
Electrodes are made of platinum and iridium
Platinum and iridium ensure maximum conductivity and minimum wear
Most superior spark plug

128
Q

Too high volatility will form bubbles in the fuel lines causing…

A

“vapor locks”

at 103 (5 decks)

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