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AT 103 > AT 103 Third Exam > Flashcards

AT 103 Third Exam Flashcards

(72 cards)

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1
Q

!! What are the advantages of a fuel injected system !!

A

Freedom from vaporization icing
more uniform delivery of air fuel mixture to each cylinder
improved control of fuel/air ratio
instant acceleration after idling with no tendency to stall
increased engine fuel efficiency and power

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2
Q

what is bendix

A

a servo

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3
Q

Difference between fuel injected and carburated

A

carburator - mixer
Fuel injected - meterer
fuel air mixture in fuel injected does not mix in the Venturi

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4
Q

carb vs injected similarity

A

both have an air inlet tube that goes through a Venturi
throttle regulates air through system

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5
Q

What does the idle valve do

A

connected to throttle linkage so that at idle, another part will open to let a little bit of fuel in in order to not over lean the mixture

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6
Q

What are the two functions of the fuel divider

A

ensures equal distribution of metered fuel to the nozzles
provides isolation of each nozzle for clean engine shutdown

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7
Q

What operates the fuel divider

A

fuel flow pressure

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8
Q

where does the air - fuel mixture meet?

A

right at the point before entering the cylinder

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9
Q

What are the two ways to produce thrust for turbine engines

A

aerodynamic action
jet reaction

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10
Q

How does aerodynamic action work

A

uses propellers
lift is produced along the horizontal plane
large mass of air through small change in velocity

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11
Q

how does jet reaction work

A

mass of air is heated inside the engine and discharged at high velocity through a shaped nozzle
Mass of air and amount determines thrust
(Small mass of air through large velocity change)

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12
Q

Who demonstrated the first jet propulsion (and when)

A

Heron of Alexandria
Egypt
first century AD

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13
Q

Quick turbine development history!

A

1232 Chinese weapon rockets
1872 Dr F Stolze first true gas turbine engine - never ran under own power
1939 - Ernst Heinkel Aircraft HE 178
1941 - Sir Frank Whittle designed Gloster Meteor
1942 - Messerschmitt Me 262 world’s first operational jet fighter

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14
Q

What is the Otto cycle

A

intake
compression
power
exhaust

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15
Q

What is the Brayton cycle

A

Otto cycle but with events occurring at the same time, however in different locations within engine

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16
Q

What happens in a convergent duct (supersonic)

A

air compresses
velocity decreases
pressure increases
density increases

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17
Q

What happens in a diverging duct (supersonic)

A

air expands
velocity increases
pressure decreases
density decreases

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18
Q

How does air flow through a chocked nozzle

A

velocity increases when converging, exhaust accelerates to speed of sound and forms shockwave creating pressure differential across nozzle that contributes to thrust

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19
Q

How does a non-air-breathing engine work

A

carries needed oxygen in fuel
generate heat by chemical reaction between fuel and oxidizer

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20
Q

how does turbojet work

A

takes in air
compresses
mixes compressed air with fuel
air fuel mixture ignited/burned
hot gasses pass through turbine
air forced out specially shaped exhaust nozzle

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21
Q

Benefits of the turbofan engine

A

increased propulsive efficiency
lower noise
lower fuel consumption

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22
Q

What does a bypass engine with a 4:1 ratio mean

A

(High bypass engine)

for every 4 molecules that enter, only one actually goes through the engine, the other three go into the bypass for cooling

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23
Q

What is thrust measured in

A

pounds

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24
Q

What is thrust determined by

A

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

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25
!! What is net thrust !!
thrust produced by the engine in flight
26
!! what is gross thrust !!
produced by the engine while engine is static and not moving ((test stand))
27
Thrust total =
thrust (core engine) + thrust (fan)
28
thrust indication for a small jet
% RPM
29
large jet engine indication
engine pressure ratio (ratio of the turbine discharge total pressure to the compressor inlet total pressure)
30
What is the inlet air duct
part responsible for supplying the constant, undisturbed flow of subsonic air to compressor (usually considered part of the airframe)
31
What are variable inlet ducts for
accommodate different air speeds by lowering/raising a wedge or moving a taper plug in or out of a duct
32
Centrifugal compressors advantages
rugged light weight ease of construction high pressure ratio for each stage
33
what happens if a centrifugal compressor is too big
tip speed increases and efficiency decreases difficult to streamline engine
34
pros/cons of axial-flow compressor
heavy costly higher compression ratio easier to streamline
35
single spool axial flow compressor characteristics
limited stages rearmost stages become inefficient/front stages become overloaded airflow can become restricted and can lead to compressor surge
36
In a dual spool axial flow compressor, which compressor starts the engine and why
N2 due to lighter weight
37
compressors are made up of
rotor blades and fixed stator vanes which are shaped and positioned to form a series of divergent ducts
38
Why do blades have a gap at idle
centrifugal force creates the seal as the engine speeds up
39
where is the highest pressure point in the engine
diffuser section
40
what is the diffuser section
diverging area for air to decrease velocity and increase pressure
41
Advantages / Disadvantages of multi-can
A: individual cans can be removed D: uneven temperatures which can cause turbine failure due to the extreme difference
42
can-annular advantages
can remove cans shorter cans with lower pressure drop uniform temperatures even with a clogged fuel nozzle
43
Pros / Cons of annular combusts
most efficient minimum cooling even temperature air Cannot be replaced without removing engine
44
What is the turbine section
power producing component of the engine
45
Where is the hottest gas inside the turbine engine
turbine inlet guide vanes
46
What is a reaction blade
produces force by aerodynamic action (airfoil)
47
what is an impulse blade
produces turning force by the energy required to change the direction of airflow
48
what is creep
deformation of metal that is continually under high centrifugal loads and temperatures
49
what is metal fatigue
weakening of metal subjected to repeated cycles
50
what is corrosion
electrolytic action that occurs when rallying agents combine with elements in the air to form salts
51
Lubrication primary characteristics of turbine oil
Low Viscosity High Film Strength (does not break under high pressure) Low volatility (does not evaporate at low air pressures of high altitude)
52
secondary characteristics of turbine oil
high flash point low pour point good anti-foaming low carbon deposit
53
what is the wet sump system
pressurized oil lubricates rotor coupling and bearings accessory drive gears are splash lubricated
54
dry sump system
after lubricating/cooling, oil is returned to tank by scavenger pumps
55
Pressure subsystem
supplies correct amount of clean lubrication oil at the proper pressure and temperature
56
scavenge subsystem
picks up oil after it has performed functions and returns oil to oil tank
57
Vent subsystem
provides slight pressure on the oil in the oil tank to allow positive flow of oil
58
where is oil usually filtered in a turbine engine
right after the pressure pump and again before being sprayed
59
What is the chip detector
system that detects ferrous metal flakes or chips in the oil system (canary in a coal mine)
60
What is the oil pressure system reading
difference between pressure produced at the oil pump and the pressure of air in the vent system
61
What is the difference between Jet A, A-1, B
Jet A: freezes at -40F Jet A-1: freezes at -58F Jet B: freezes at -60F
62
Kerosene vs Avgas
K: 6.7 pounds per gallon Av: "6" pounds per gallon Kerosene has a lower heat energy per pound but higher per gallon
63
What is the issue with turbine fuel viscosity
contaminants and water are suspended in jet fuel and take a long time to get picked up by the tank pumps water can also freeze
64
what do fuel nozzles do
vaporize fuel to mix with air
65
if fuel flow is increased too quickly...
over rich mixture may result excessive TIT or produces compressor surge fire may go out
66
if fuel flow is reduced too quickly
engine may experience lean die-out
67
where is the TIT read
at the turbine inlet guide vanes
68
What does FADEC do
controls all engine functions and eliminates need for backup hydro-mechanical control controls engine power through direct control of EPR
69
advantages of FADEC
no engine trimming required improved engine starts constant idle speed saves fuel by improved engine bleed air management fully modulates active tip clearance automatically limits critical engine pressures and speeds, reducing wear and possible damage
70
What happens if both channels fail
actuator motors are spring loaded to fail safe positions fuel flow goes to minimum
71
how does the turbine ignition system work
continuous combustion process so ignition is only needed during start
72
what are the three different types of instrument gauges
temperature pressure mechanical movement

AT 103 (3 decks)

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