Chapter 1 Flashcards
1
Q
What is Newton’s third law of motion
A
For every force acting on a body there is an equal and opposite reaction
2
Q
The purpose of a compressor
A
Give a predetermined pressure rise throughout the compressor
3
Q
Two types of compressor
A
Centrifugal and axial
4
Q
What are the two types of centrifugal flow compressor
A
Double entry and single entry
5
Q
What does the centrifugal compressor do
A
To raise the pressure of air by centrifugal action cause flow to radially move outwards along a divergent duct vanes to impeller tip , causing acceleration in the air and rise in pressure
6
Q
What does a impeller shaft move on
A
Ball and roller bearing
7
Q
Why is it important to keep clearances as small as possible in the compressors
A
Prevent excessive air leakage
8
Q
Centrifugal advantages
A
Robust , cheap simple
Low surge tendency
Flexible - relatively efficient
Withstand icing and fod
Balancing is relatively easy
Simple to maintain
9
Q
Centrifugal disadvantage
A
Low compression ratio
Large frontal area
High impeller tip speed
No straight through airflow
10
Q
What does a diffuser do
A
Converts the velocity created by the centrifugal rotation of the impeller and coverts it into extra pressure and temperature
11
Q
What is an axial compressor
A
Consists of one or more rotor assemblies the carry blades of aerofoil sections
12
Q
What is the set up of a axial compressor / one stage
A
One stage = set of rotors followed by set of stators
13
Q
Explain the movement
A
Air drawn into compressor
Air accelerated by rotating blades and swept rearwards
Pressure rise if due to energy imparted to the air in the rotor
Air is decelerated in the flow satire passage and kinetic is turned to pressure
14
Q
How do we maintain velocity in a axial compressor and what is it called
A
The shape between the drum and the outer casting , forms convergent duct
Called cascade effect
15
Q
What is the twist called along the compressor blades called
A
Stager angle
16
Q
Advantages of axial flow compressor
A
Higher compression ratio
Straight through airflow
Smaller frontal area High
Capacity for further development
17
Q
Disadvantages of axial flow compressor
A
Complex
Expensive
Will not accept ram air
Slow to accelerate
18
Q
What is Stall
A
The breakdown of airflow over one or more stages of the compressor
19
Q
What is a surge
A
The event that occurs when compressor delivery air pressure is less that combustion pressure leading to hot combustion gases flowing backwards through the compressor
20
Q
Cause of stall in compressor
A
FOD , Icing , flight manoeuvre or over fueling
21
Q
What is surge
A
The result of a servers stall
Is it the inequality between the pressure found in the combustion chamber and that of the compressor delivery
22
Q
How do you identity stalk
A
Audible rumbling
Loss of rpm
High jet pipe temperature
Vibration
23
Q
How to identify surge
A
Loud bangs of varying severity possibly accompanied by flames from the intake
Rise in JPT
Loss of rpm
Extensive damage of engine
24
Q
What are the types of airflow control in the compressor to stop stall and surge
A
Inlet guide vanes
Variable stator vanes
Twin spool
Compressor discharge valve
25
Describe variable inlet guide vanes
Can be variable
Found before first set of rotors of an axial compressor Air accelerated
Designed to be stationary or automatic
If automatic operation is prevalent to mass airflow and speed of the engine
Purpose : makes sure the air hits the blades at the right AOA
26
What is a compressor discharge valve
Bleeds air from the compressor
Assists engine start / helps avoid stall and surge during start , acceleration and deceleration
Compensates for compressors over efficiency at low RPM
Connected to FCU with butterfly type linkage
27
When the compressor discharge valve is
Open , what is the pressure / engine power doing
Closed what is the pressure/ engine power doing
Open , acceleration / deceleration
Closed, at full engine power , the turbine is at the optimum speed
28
FOD damage for compressors
Change in aerodynamics of the blade profile
Resulting in
Change in air flow through the engine
Resulting in
Lead to deterioration, malfunction and even engine failure
29
Detection of compressor blades
Visual inspection through either the intake / front stage blades or specific ports
30
Blade bending is it repairable
Is repairable is minor using file or abrasive cloth and bend out damage area
Must be carried out by authorised person
And in accordance to the right aircraft publication
31
Purpose of combustion system
Realease chemical energy from fuel
Minimum loss
Uniform velocity
Must be reliable
Have a life as long at the overhaul life of the engine
Must be possible to re-light in flight
32
Components of at basic combustion chamber
Flame tube
Outer air casting
33
What is a flame tube
Contains flame during combustion
Must withstand high temps
34
What is a outer air casting
Subjected to Lowe temps
Maufactured from alloy steel
Overheating will show discolouration
35
Flame tubes: how much percentage for total compression delivery is used in atomised fuel combustion
And what does the another percentage do
18/20%
Enters the rear of the primary zone :
Cools the hot gases
Shapes the flames to prevent it contacting the sides of the flame tubes
36
What is the air/ fuel ratio for the combustion chamber
60:1
37
What are the two combustion system layouts in use
Annular and reverse flow
38
What is an annular chamber
Uses the whole of the annulus ( the space between the compressor and drive shaft ) for combustion
Surrounded by an outer casing to form part of the structure of the engine
39
Benefits of the annular combustion system
Good utilisation of the area
Structural part of the engine
Annular gas flow
High efficiency
Large total combustion area
40
What is reverse flow combustion chamber
It is also annular but the airflow is initially reversed in the direction of airflow
This shortens overall length
Lose a bit of energy
41
What are Combustion chamber drains and what does combustion chambers use specifically
What does it contain and how does it work
Allows residue fuel in the chamber to drain overboard
Automatic drain valve
Simple spring and plate valve , as the pressure reduces the spring will open and close as pressure increase
42
Reverse flow benefits
Annular construction
Reduces engine length
Extensively used in helicopters
43
What is a fuel nozzle or burners
Introduce the fuel into the combustion chamber in a state in which it will burn efficiently
44
What is a fuel nozzle or burners
Introduce the fuel into the combustion chamber in a state in which it will burn efficiently
45
What is are the two types of Burners
Atomiser and vaporiser
46
What is the requirements for a burner
Introduce the fuel at the right state
Operate in a wide range of operating conditions
47
Name the three types of atomisers
Duplex
Rotary atomiser
Airspray nozzle
48
What is a duplex atomiser
two types of fuel supplied depending on quantity required
Design includes a main and primary manifold and two independent orifices
Variable flow rate
Efficient atomisation at low flows ( needed at high altitudes )
Uses a spring to open and close the orifices
49
What is a rotary atomiser
Fed through a hollow compressor shaft
Hits an internal dam
Uses centrifugal motion to eject the fuel in an atomised spray
50
Air spray nozzle what is it
Mixes proportion of the primary combustion air and injected fuel
Burns more efficiently due to aerating the spray, reduce Carbon formation and exhaust smoke
51
What are the advantages of Airspray nozzle
Low pressure required atomised fuel
Allow use of a simpler high pressure pump
52
How does a vaporiser work
Fuel fed from feed tubes to the vapourising tubes
Heated by combustion
Fuel is therefore vaporised before passing into flame tube
This type of system requires a torch igniter to initiate combustion
53
Advantages for vaporiser
Effective over a wider operating range that atomiser
Combustion control easier
Produce less smoke
Flame can be stabilised at the front of combustion chamber drains
Combustion zone is shorter
Fine filters used to protect the burner from debris
54
What is the purpose of a turbine
To extract sufficient energy from the gas stream to drive the compressor and accessories
55
Purpose of a turbine
Extract energy
Turn gas into mechanical energy
Provide necessary driving torque
56
What is the construction of a turbine
Nozzle guide vanes
Rotating turbine disc
Turbine blades
57
Shape nozzle guide vanes
Aerofoil shape
Convergent duct
Hollow
Cooled by compressor delivery pressure
58
What happens to airflow in the nozzle guide vains
Pressure decrease
Temp decrease
Velocity increase
59
What is a turbine disc
Made from nickel based alloy
Either integral or bolted to the flange
Due to heat and stressed classed as critical component
60
How can you cool turbine blades
Flow of cooling air across the face of both discs
61
Describe an Turbine blades
Aerofoil in shape
Combination of impulse 50% and reaction 50% section
62
What is the twist call along the turbine blades called
Stagger angle
63
What does a turbine blades have to do?
A stagger angle
Forms convergent duct in direction of flow
64
Does the velocity increase in the convergent duct in the turbine blades
No cause the propose of the turbine blades is to take as much energy as it can
65
What attaches the blades to the turbine disc
Shroud
Fir-tree root
Locking plate
66
What is blisk and shrouding
A method of resisting the high stresses imposed on the blade roots , blades are permanently attached to the disk
Shrouding , a casing is put around it to stop the gas from leaking due to centrifugal force
67
Factors that effect a turbine
Fatigue
Thermal shock
Corrosion
Oxidisation
High temperature
Centrifugal force
High rotational speed
High frequency gas flow
68
What is Turbine blade creep
This is the heating of the blades that result in a elongating of the blades due to the centrifugal loads exerted on them
69
What cause the elongation of turbine blades in normal service
Centrifugal force
High temperature
Running hours
70
When is creep likely to occur , in what time periods
Primary - new engine
Secondary - normal service use
Tertiary - excess temperature and running hours
71
What happens to PTV through the NGVs ( nosal Gide veins)
P decrease
T decrease
V increase
Due to convergent duct
72
What happens PTV in the Turbine blades
P decrease
T decrease
V decrease
Convergent duct
73
Typical maintenance on turbines
Turbine tip clearance
Bearing wear / fatigue
Run down check. Run down time in limits ( pilot times it )
Overheating checks ( look for burnt blades )
FOD Damage
Compressor
Turbine
Exhaust
Corrosion erosion , prevented by compressor washing
74
What two devices help in reducing stall /surge
Cdv -compression discharge valve
Variable stators
Inlet guide viens
Twin spool
75
What is the purpose of the exhaust cone
Protect the rear face of the turbine disc from overheating
76
What three sections make up an exhaust
Exhaust unit
Jet pipe
Propelling nozzle
77
What are other names for turbine entry temperature
JPT
TET
EGT
TGT
TIT
78
What temperatures on the turbo prop and turbo shaft engines approximately
90-100*c
79
What is used to protect the A/C structure against heat , what is it made of , and shape and why this shape
Insulation blanket
Stainless steel
Dimpled , to increase strength
80
Maintenance for exhaust system
Cracking
Corrosion
Security of attachment
81
How to increase power of the engine , what would it increase
Weight
Frontal area
Overall fuel consumption
82
What is the basic formula for engine momentum
Thrust =mass airflow rate x(velocity out-velocity in )
83
How can mass airflow be increased
Injecting water into the compressor
Or injecting into the combustion gas flow
Or both
84
Describe compressor water injection what happens , and how that improves mass airflow
Water is injected into the compressor the water droplets evaporate allowing additional fuel to be burned without exceeding the engines temperature limits
Cooled air also increases in design thereby improving mass airflow
85
Does the compressor water injection and combustion system water injection work the same ?
Yes
86
Where are most injection system now fitted
Older types of turbo-prop aircraft
87
How to increase exhaust gas velocity ?
Reheat ( after burning )
88
How does reheat work
Only a certain percentage of air is burned so mixing and burning fuel with this sunburnt air further accelerates the gases and provides and increase to the basic thrust
89
Where is noise predominately made , what causes it and how is it stopped
Fan/ compressor
Cause by rotating assembly in their bearings and complex aerodynamic interactions
Reduced by installing noise suppressing acoustic liners into engine cowlings , change design of intake creating a extended lower lip (scarfed intake)
Jet pipe/ exhaust
Reduced by changing the way gas muses with ambient or bypass air
Early aircraft used ‘lobe’ type exhaust : mixes exhaust gas and reduce the shockwave produced in hot stream
Newer design : serrations in the trailing edge of the nozzle/ nacelle
90
What are the advantages of a continuous work cycle
Smoother continuous running engine
More power for given engine size
Lightweight combustion chamber and low octane fuels
91
Disadvantages for a continuous working cycle
High flame temperature
Contains critical components-turbine
92
Name types of intakes and what they used for
Pitot ( subsonic)
Divided ( subsonic)
Variable throat (supersonic)
Bellmouth ( low forward speed)
93
Name types of protection devices for engine intakes , are they passive or active
Intake grilles ( passive)
Ice shield ( passive)
Momentum separator ( passive)
Sand filter (active)
Particle separator ( active)
94
Name types of accessories to the engine
Starter motor
Fuel control unit
Engine oil pumps
Macho generator
Alternator/ generator
Centrifugal breather
95
Non driven items fitted to accessories gearbox
Scavenge filter
Drain plugs
Oil temperature bulbs
Magnetic plugs
96
Where is the drive taken for accessory units
Rotating shaft
Via internal gearbox
To external gearbox
97
What common methods are used to transfer power and how are they different
Splined drives ( at least four splines )
Serrated drives ( triangular , tapered or parallel
98
Internal gearbox gears
Made from aluminium
99
External gearbox gears
Made from magnesium to reduce weight
Location of external gearbox is dependent on size and shape of the engine casting
Found at the front , centre and rear of the engine
100
External gearbox gears
Made from magnesium to reduce weight
Location of external gearbox is dependent on size and shape of the engine casting
Found at the front , centre and rear of the engine
