MOD 3-4 Flashcards
(118 cards)
1
Q
what is modular designed
A
The ability to replace parts of the engine.
2
Q
where we convert the ram pressure to static pressure without loss of total pressure
A
Divergent duct
3
Q
ram recovery point is?
A
when the pressure rise due to ram effect is going to increase the pressure at the face of the compressor is equal to the ambient pressure
4
Q
what is duct pressure efficiency ratio?
A
ability of the duct to convert kinetic energy to potential energy (velocity to static pressure) whit out loss in total pressure.
5
Q
which is considered the cold section of the engine ?
A
inlet and compressor
6
Q
which is considered the hot section of the engine
A
when gases leave the diffuser combustion
7
Q
purpose of the combustion section ?
A
place for mixing fuel and air for combustion, as well as mixing and expansion gases, full energy is converted to heat and velocity. Pressure held constant
8
Q
performance requirements
A
-high combustion efficiency -stable -uniform temp distribution -easy starting -small -low smoke -low carbon
9
Q
why the air velocity most be slow at the combustion section?
A
So that the flame is not moved toward the turbine (high ITT) or blown out completely (flame out)
10
Q
what is flame out ?
A
is when the air is moving so fast that it blows out the flame
11
Q
why the pressure must be constant on the combustion section ?
A
high pressure flows to low pressure so if there was a pressure rise it would cause a surge which would cause a stall
12
Q
combustion section components
A
-case -perforated inner liner -fuel metering orifice -ignition source -drain
13
Q
3 .types of combustion sections
A
- Can 2.Annular 3. Can-annular
14
Q
what means reverse flow ?
A
air flow changes direction 2 times on the combustion section
15
Q
can type advantages ?
A
-Each can, may be removed without separating the engine cases - Each can has it’s own fuel/air pattern control.
16
Q
what is primary air
A
-25%-33% of air trough the engine -swirls upstream -low velocity (stabilization zone) -turbulence(just at the head of the combustion liner )
17
Q
what is secondary air
A
67% to 75% of the air going through the engine • Dilution air – big holes • Cooling air – small holes • Film cooling • Cools the flame – is heated (energy transfer) • Presents a uniform flame front (temp. and press.) to the first stage turbine nozzle
18
Q
What is an advantage of the modular design on a gas turbine engine?
A
Modules can be replaced individually. The engine is not required to be removed and sent to an overhaul shop for repair
19
Q
What is the cross-sectional shape of an inlet duct?
A
Divergent
20
Q
The inlet duct converts energy in the gas, causing the _____to decrease and the _____to increase
A
velocity, static pressure
21
Q
One function of an inlet duct is to deliver and even ______ and _____ to the face of the compressor
A
pressure, velocity
22
Q
The air pressure in the inlet duct at ram recovery point is the same as _____
A
Ambient pressure
23
Q
If the duct pressure efficiency ratio is1:1 or 100%, the _____ will be the same at the inlet as it is at the outlet.
A
total pressure
24
Q
The manufacturing and repair instructions for an inlet duct will is the responsibility of the _____ manufacturer
A
airframe
25
The bell mouth inlet duct is used primarily for \_\_\_\_\_
testing engines in a test cell
26
The air coming into the bell mouth inlet duct sees _____ % of the orifice/inlet size
100
27
In addition to having the same function as a sub-sonic inlet duct, the supersonic inlet duct has the additional function of \_\_\_\_\_.
Slowing the velocity of the air to sub-sonic speeds
28
The compressor is considered part of the _____ section
cold
29
On the Brayton Cycle graph, the compressor is described by line from point _____ to \_\_\_\_\_
A-B
30
If the engine has a low pressure compressor (N1) and a high pressure compressor (N2), which one is shown on the Brayton Cycle graph?
Line A to B represents all the compressors if there is more than one rotating group (N1 and N2)
31
List the 3 types of compressors
axial centrifugal axial-centrifugal
32
mayor parts of the compressor
impeller ,diffuser, manifold (The impeller is what puts energy (velocity) into the gas)
33
What are the 3 major parts of a centrifugal compressor?
Impeller•Diffuser•Manifold
34
List 2 advantages of a centrifugal compressor
Simplicity –easy to manufacture•Rugged (compared to axial compressor)•Low cost (relative)•Less FO
35
List 1 disadvantage of a centrifugal compressor
About 80% efficient•Limited stages (2)•Large frontal area
36
Why is there a limit of 2 stages of compression when using a centrifugal compressor?
Limited to 2 stages by the law of diminishing returns with more than 2 stages the loses will equal the gain
37
Why does the static pressure rise as the gasses travel through the centrifugal compressor impeller?
add velocity at the same time that is converting the velocity in static pressure
38
Indications of Stall
Vibration•Slow power lever response•Mild stall –no loud noises, maybe a rumbling sound•Explosive stall (loud bang) –can cause extensive damage
39
What are the 2 major parts of an axial compressor?
rotor(add energy and converts it) and stators (converts energy)
40
AoA is affected by ?
engine RPM air flow velocity FCU acceleration rate
41
The axial compressor is limited to a\_\_\_\_\_ compression ratio per stage. This happens when the compressor is running at the most efficient RPM it was designed to run. This is close to 100% RPM.
1.2:1
42
preventing stalls
lower angle of attack (derating the engine) use a bleed valve employ a two spool rotor variable IGV and variable vanes vary the exhaust nozzle size
43
what is flat rate ?
engine performance limit by thrust, the manufacture will determine that , because we don't want to exceed ITT or RPM
44
what kind of performance limitations an engine has and must never exceed
-wheels speeds -Turbine temperature -torque or thrust for which the AC was certified (flat rate, airframe limitations)
45
What is Standard Day Barometric Pressure: _____ OAT: _____ Altitude: \_\_\_\_\_
29.92 inches of mercury 15 degrees Celsius at sea level
46
As temperature increases, density \_\_\_\_\_\_\_\_\_\_
decreases
47
As pressure decreases, density
decreases
48
In the stratosphere the temperature stabilizes at\_\_\_\_ so even as altitude\_\_\_\_\_, the temperature does not change (assuming Standard Day)
-69.7˚F - increases
49
The profile of the exhaust nozzle is a convergent duct so static pressure\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
decreases and velocity increases
50
As the subsonic gases exit the nozzle (convergent duct), the static pressure will\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ until sonic velocity is reached in the throat of the nozzle.
decrease and the velocity will increase
51
As the subsonic gases exit the nozzle (convergent duct), the static pressure will\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ until sonic velocity is reached in the throat of the nozzle.
decrease and the velocity will increase
52
on the thrust formula is the aircraft is not moving, nozzle not \_\_\_\_\_\_\_\_\_\_\_
choked
53
on the thrust formula is the aircraft is moving, nozzle is \_\_\_\_\_\_\_\_\_\_\_
choked
54
When is a nozzle considered a choked nozzle
As the subsonic gases exit the nozzle (convergent duct), the static pressure will decrease and the velocity will increase until sonic velocity is reached in the throat of the nozzle.
55
How does atmospheric temperature affect thrust?
Higher density = higher mass airflow Lower density = lower mass airflow
56
How does atmospheric pressure affect thrust?
As the pressure increases, the temperature increases reducing the density of air entering into the engine thrust decreases
57
Ram pressure\_\_\_\_\_\_\_ thrust, ram temperature _______ thrust
increases, decreases
58
If the result of ram pressure rise is added to the ram temperature rise, the resultant is called the
ram effect
59
Increase in altitude results in a decrease in \_\_\_\_\_\_\_\_\_\_\_\_\_\_
temperature and pressure
60
Why does the thrust decrease at a faster rate as aircraft altitude increases above 36, 089 ft?
because less density less drag
61
Fg = Fr = Fn =
-gross thrust -ram drag - net thrust
62
what is a RPM speed indication
eddy current, probe produces a magnetic field using aircraft electrical power, passing blade gear tooth disrupts the field magnetic lines of flux (phonetic wheel)
63
how a monopole indicator works?
similar to eddy current has a permanent magnet instead to used the power of the aircraft
64
what is a phonic wheel
is a gear that does not drive anything but gives us the pulse to a speed indication
65
tachometer generator parts ?
-generator -driven from accessory drive -indicator -synchronous motor and flux coupling
66
What is EPR ?
engine pressure ratio or tail pipe ratio is the ratio between Pt2 ( face of the compressor ) and Pt7 (pressure total tail pipe)
67
what is IEPR
Integrated EPR average of fan exhaust pressure and gas generator gas pressure , divide by the Pt2
68
exhaust section purpose
• Imparts a high exit velocity to the exhaust gases as they exit the engine • TF and TJ engines – Choked nozzle at high RPMs
69
A convergent-divergent exhaust nozzle causes an increase in \_\_\_\_\_\_by increased acceleration of the exhaust gases.
Thrust
70
Forces acting 90° to the walls of the duct resulting in the increase \_\_\_\_\_\_\_\_\_\_-
Thrust
71
purpose of the nozzles of the Vectored Thrust
the four controlable nozzles allow the thrust produce by the turbo fan engine to vectored downward to takeoff and aft for forward flight
72
name the parts of the exhaust
A.Exhaust cone
B. exhaust collector
C.strut
The exhaust collector bolts to the engine housing just aft of the turbine. The tail pipe bolts to the ring around the collector
73
A convergent-divergent exhaust nozzle causes an increase in thrust by increased acceleration of the exhaust gases.
what is A, B and C
A. Subsonic convergent section
B.Supersonic Divergent Section
C. gas attains sonic velocity
74
Characteristics of thrust reverses
- For use on turbo jet and turbo fan engines
- Deployed on the ground
- Slow aircraft
- Reduces wear on the brakes
- Not always made by the engine manufacturer. Can be a 3rd party manufacturer but fitted to specific engines
75
Thrust reversers types?
Pre-Exist
Post-Exist
76
what kind of thrust reverser is this one ?
Pre- Exist
77
what kind of trust reverse is this ?
Post-Exist
Target type
78
what kind of thrust reverse is this?
A clamshell-type thrust reverser.
79
what Reverser deploiment conditions have to be met in order to deploy thrust reversers?
- Weight on landing gear (squat switch)
- Power lever – idle
80
Thrust Augmentation types
- Afterburner – re-heat, Take-off or increased thrust requirement
- Water or Water/methanol injection • Take-off only
81
Characteristics Thrust augmentation afterburner
Add fuel after the last turbine • 300% increase in fuel burn – 50% increase in thrust • Works like a ram jet • Usually has a variable geometry exhaust nozzle • Open when accelerating to full power, then restricts to choke the nozzle after A/B initiated
82
Thrust augmentation Water or Water/Methanol Injection characteristics
-Used for take-off only
* Injected in the inlet, compressor, or diffuser
* Methanol keeps water from freezing (if stored during flight)
* Water only (consumed on take-off then remainder is jettisoned)
83
On the Brayton Cycle graph, the exhaust section of a turbofan or turbojet engine is represented by a line that goes from point _____ to point \_\_\_\_\_
D TO E
84
when we use Thrust augmentation ?
when we need a lot of performance and performance recovery (like hot day, not enough, density air is really low orwhen need to get to sonic velocity )
85
Noise comes from the _____ and the \_\_\_\_
noise suppresion is done by ?
Inlet , exhaust
Fan Noise • Fan design can reduce noise • Inlet can be lined with sound absorbing material
• Exhaust noise • Reduce shear zone differential
86
The cone that follows the last turbine, makes a _____ duct inside the exhaust duct.
divergent
87
When is water or water/methanol used?
take off
88
An afterburner thrust augmentation systems injects extra fuel. Where in the engine is the fuel added?
Add fuel after the last turbine
89
How does a turbofan engine reduce the noise produced by the exhaust of the engine?
- Fan design can reduce noise
- Inlet can be lined with sound absorbing material
- Reduce shear zone differential (exhaust)
90
The turbine section of the engine is represented by a line from point _____ to point _____ of the Brayton Cycle graph.
C to D
91
The profile shape of the turbine vane is a _____ duct.
convergent
92
The purpose of the turbine vane is to increase _____ and decrease \_\_\_\_\_
velocity ,pressure
93
The purpose of the turbine is to \_\_\_\_\_
extract energy to drive the compresor or in turbo prop/shaft to run the gearbox
94
The combination type turbine blade has the _____ section at the tip and the _____ section at the root
reaction,impulse
## Footnote
reactio= extract velocity and pressure
Impulse = extracts velocity only
95
If a turbine disk has 50 blades, and extracts 750 Hp out of the gasses, how much does each blade extract?
15 hp= (750/50)
96
If there are 3 turbine disks, and they extract a total of 750 Hp out of the gasses, how much does each disk extract?
same amount each disk
97
The _____ type of turbine shroud has the least amount of losses due to clearances
rotating (more mass, less losses)
98
.Refer to the vector diagram that describes the velocity of the gasses at the root and the tip of the turbine blade, why is U for the root of the blade, less than U for the tip of the blade?
vane assembly converts more pressure to velocity at the root of the blade than at the tip.
99
Turbine Engine Pneumatic Systems • Provide a source of air for:
– Cabin pressurization – Cabin heating and cooling – Engine and airframe anti-ice systems – Labyrinth seals – Internal cooling – Fuel control (FCU)
100
Pneumatic System Operation
Shut-off valves control the extraction of bleed air from the compressor (this is a different valve from the compressor bleed valve that is used to prevent compressor stall.
101
Oil Systems Purpose:
Supply oil under pressure to - clean - cool - lubricate
102
Typical Oil System
Tank/sump/reservoir • Pump • Relief valve • Filter • Oil pressure indication • Nozzles and jets • Scavenge pump • Chip detector • Oil cooler • Tank/sump/reservoir
103
purpouse Chip Detectors
Indicate when ferrous metal is present in the oil • Impending failure indicators - ΔP indicators – Button (usually red) pops out when a differential pressure across a filter exceeds a threshold pressure
104
Starting Systems Purpose:
To accelerate the engine to the point where the turbine is producing enough power to continue the engine’s acceleration up to idle speed
105
whats the Length of Start Cycle
Starter continues to accelerate the engine even after light off, until the engine has selfsustaining acceleration to idle • A “hot start” or a “hung start” could result if the starter is disengaged too soon or if the battery voltage is low (electric starter)
106
Types of Starters
Electric motor • Electric motor/generator – Starter/generator • Pneumatic or air turbine • Gas turbine starter (small turboshaft that is used to start the bigger engine) • Hydraulic motor starter
107
What is the purpose of a gearboxon a gas turbine engine?
Provide a place for mounting accessories for operation and control of the engine and airframe systems
108
List 4 things that the pneumatic system provides air for.
Cabin pressurization – Cabin heating and cooling – Engine and airframe anti-ice systems – Labyrinth seals – Internal cooling – Fuel control (FCU)
109
List the 2 types of spark igniters used in turbine engines
spark type
glow plug type
110
What is the purpose of the engine oil system?
lubricate
cool down
clean
111
In a typical engine oil system, what is the component that follows next in line to the scavenge pump(s)?
112
What component protects the engine from oil starvation, if the oil filter completely plugs?
bypass valve
113
A labyrinth seal has oil pressure on one side and air pressure on the other. Which pressure is higher? Why?
air pressure is higher and hight pressure follows low pressure keeping the oil on the other side
114
What is the purpose of a chip detector in an engine oil system?
detect any ferrous material
115
.What could cause a “hung” start?
if we turn off the starter too soon before gets to the sustaineble acceleration we can get a hung start, fire addinf fuel but the engine is not acceleration
116
.What does self-sustaining acceleration mean?
when the engine is capable to mantain idle accelation
117
.What is the difference in the drive mechanism for a starter motor, and a starter/generator?
118
3.How many amps of power would a pneumatic starter draw when it is initially engaged?
1500 amps
