AGK Engines Flashcards
Ignition Timing…
Is performed by the magnetos .
Is necessary as it takes a finite time for the mixture to burn.
Which engine initiates combustion by the heat of compression
Deisel engine
Which engine uses a spark to initiate ignition
Petrol engine
Name the strokes in a 4 stroke engine
Induction, Compression, Power, Exhaust
Flame rate of aviation fuel mixed with air
60/80 ft per second
(18-24m)
The crank assembly is comprised of…
Crankshaft
Connecting rods
Pistons
Hydraulic tappets are used to…
automatically adjust the tappet clearance
Why are valves often filled with sodium ?
To take heat away
Name 4 EMF variables
Magnet size
Conductor length
Perpendicular angle
Rate of charge
How long should the starter operating light take to switch off ?
30 Seconds
An impulse coupling..
Gives you a higher energy retarded spark.
A high tension booster is…
A vibrator directly connected to the high tension side. (shower of sparks)
A low tension booster is…
A set of pulses to the primary circuit (low tension side)
Pre flight magneto checks are…
Drop check
Dead cut check
RPM drop range on a drop magneto check
Drop of 100-175 indicates normal magneto operation.
Drop greater than 400 means there may be a faulty spark plug and should be reported immediately.
A blocked spark plug gap is said to be …
Fouled
A spark plugs body forms an…
Electrode
AVGAS is made up of ?
15% carbon 85% hydrogen
Octane rating is…
A measure of resistance to detonation
Detonation flame rate ?
1000 ft/s
what colour is AVGAS 100LL
Blue
and environmentally better
What colour is AVGAS 100
Green
and environmentally worse
A fuel sample must be…
Clear and bright
Free of sediment
No entrained water
have a max water content of 30ppm
Detonation causes
Fuel with too low octane (poor anti knock)
Incorrect (weak) mixture
Anything that could unduly raise temperature or pressure.
High engine temperature
Pre ignition causes
Hot debris within the cylinder
(typically carbon deposits)
Ignition malfunction (damaged spark plug)
High cylinder temperatures
Mixture ratios
20:1 Lean (increased detonation risk)
15:1 Chemically correct (ideal ratio)(EGT Peak)
8:1 Rich (increased detonation risk)
Takeoff and cruise mixes should be..
Takeoff 11:1
Cruise 17:1
Ineffective crank angle is ?
The period of relatively little movement of the piston around the TDC and BDC
Inlet valve lag is when…
The inlet valve remains open just after BDC as the compression stroke begins to help fill the chamber. The valve closes just after the piton leaves the ineffective crank angle.
Inlet valve lead is when…
Inlet valve opened early, just before TDC, exhaust valve is still open at the end of the exhaust stroke
Exhaust valve lead is when…
Both valves are closed at the start of the power stroke, most of the work is done before the piston reaches BDC, so the exhaust valve opens before the end of the power stroke. Provides a longer period to clear the cylinder of waste gasses.
Exhaust valve lag is when…
The exhaust valve remains open until slightly after the TDC, remaining gas exits under its own momentum.
TDC
Top Dead Center
BDC
Bottom Dead Center
Where does valve overlap occur ?
Around TDC between the exhaust and induction strokes.
Prime carburettor icing temperature and key condition ?
+18 to +25 C
and high humidity levels
Low power levels
Carb icing prevention ?
Carburettor heating
Carb icing symptoms ?
Loss of rpm
Reduced inlet MAP
Decreased EGT
Rough running
Jammed throttle
Engine stops
Carburettor alternative ?
Fuel injection, fuel is injected to the cylinders directly so no need for a carburettor.
Diesel engine is primed how ?
By using the accelerator pump
Fuel must …
Have a lot of energy
Be able to form a vapour
Be able to burn quickly
AVGAS has a SG of …
0.72 at 15 C
what can occur if fuel vaporises in the fuel lines or pumps. This causes partial or complete loss of engine power.
Vapour lock
What is the extremely rapid chemical decomposition of the mixture after burning has begun. May be heard as knocking sound.
Detonation
What is the ignition of the mixture before the spark plug has sparked. Caused by hot spots in the cylinder.
Pre-ignition
Symptoms for pre-ignition and detonation ?
Rough running
Power loss
Overheating
What is added to fuel to reduce detonation ?
Lead
AVGAS 100LL (Low lead)
What is the stoichiometric fuel mix ?
15:1, but cannot be used as engine would overheat
Which engine has a lower power to weight ratio, Why ?
Diesel
They are heavier but have the same output as a lighter petrol engine and lower max RPM. But it has a greater compression ratio
What is a carburettors purpose ?
To mix fuel and air to the correct ratio. Fuel is supplied by an engine driven pump. Air is supplied via the air intake.
How is mixture manually controlled ?
A mixture control lever in the cockpit
At low power setting the butterfly valve is… ?
Almost closed
Pre-ignition is ?
The ignition of mixture before the spark plug has fired
RPM gauge measures ?
Crankshaft RPM
Manifold pressure gauge ?
Measures manifold pressures in InHg
Boost pressure gauge ?
Measures manifold pressure in PSI relative to sea level pressure
Oil pressure gauge ?
Measures oil pressure just after the oil filter
Oil temperature gauge ?
Measures oil temperature in oil return line
CHT gauge ?
Measures the temperature of the hottest cylinder
EGT gauge ?
Measures the temperature of the exhaust gas stream
Fuel pressure gauge ?
Measures the fuel pump output pressure
Induction temperature gauge ?
Measures the carburettor inlet temperature
Camber line and chord line are between ?
Leading and trailing edge
Chord is the length of the chord line
Does a petrol or diesel engine have greater thermal efficiency ?
Diesel.
It has a higher compression ratio; 20:1 whereas petrol engines only have a 10:1 ratio.
What device is fitted to measure cylinder head temperature effectively ?
A Thermocouple
Engine PWR output ?
Torque x RPM
how is magneto switched off ?
Grounding the magneto
What happens to AoA of a fixed pitch prop as A/C accelerates along a runway ?
Decreases
Rich mixture in climbing segments results in ?
A gradually rich mixture as you climb (less dense air)
Why does a cylinder have 2 spark plugs ?
It reduces time for complete combustion
How is impeller driven ?
Diversion of exhaust gasses by waste gate, using energy that would otherwise be wasted
What is the angle between the blade chord and the plane of rotation ?
Blade pitch
Flat rating is used in what ambient conditions ?
Cold
What does jet thrust vary with
Altitude
Air density
Air speed
Engine RPM
Hot and high conditions are associated with… ?
The least thrust available from the engine
Propulsive power is … ?
Thrust x Aircraft velocity
RAM effect is associated with ?
High airspeed
Combustion occurs at a constant … ?
Pressure
What does a compressor do to gas flow ?
Gives it energy
Flat rating is used in what conditions ?
Cold
Constant speed propeller… ?
Adjusts pitch to ensure propeller runs at optimum RPM for airspeed
How is blade pitch altered ?
PCU in the propeller hub
Coarse pitch …?
Absorbs most power, creates most rotational drag
Fine pitch… ?
Absorbs the least power
Creates a lot of rotational drag if not running (Engine failure)
What prevents blades from going fully coarse on engine shut down ?
Centrifugal latch
Feathered blades are ?
Fully coarse to provide the minimum drag
Un-feathering is ?
Putting the blades to a finer pitch to allow engine restart in flight
What is fitted to multi engine aircraft to prevent problems caused by asymmetric drag ?
Auto-feather system
How is reverse thrust achieved ?
By setting the pitch to behind fully fine
(Beta range)
How is reverse thrust prevented ?
Weight on wheels operated fine pitch stop
How is cabin noise reduced ?
Synchronising or synchrophasing to avoid build up of pressure waves
How to avoid over boosting ?
Rev up: Power back
When must CSU operation be checked ?
Before flight, done by operating RPM lever
Which system always has a governor fitted ?
Constant speed, variable pitch
What sound frequency is produced from a propeller engine commonly
90 Db
Fining blade pitch … ?
Increases RPM
What pitch is wanted for landing and takeoff ?
Fine pitch
Ideal cruise pitch ?
Coarse
How is the propeller driven ?
Engine torque (RPM)
Impact on AoA on a variable pitch prop with increase or decrease of TAS and RPM ?
It remains the same
Effect of TAS on AoA on a fixed pitch prop ?
AoA is inversely proportional to TAS
(TAS increases AoA decreases)
What does LP spool comprise
LP compressor or fan
LP turbine
Shaft
What does HP spoil comprise
HP compressor
HP turbine
For optimal efficiency… ?
Fan must run at relatively low RPM
Core must run at a very high rpm
Multiple spools allow this to happen
Bypass ratio is ?
The ratio of bypass air mass flow to core mass flow.
( air entering the core Vs air going in bypass duct.
If 10 tonnes of air enter inlet, and 1 comes out the exhaust, bypass ratio is 9:1)
What do some turbine engines have to drive the propeller ?
Free turbine
Pure turbojet has no ?
Bypass duct
Exhaust jet velocity is very high instead
An engine which uses a gas turbine to drive a helicopter rotor is a ?
Turbo shaft
Advantage of multi spool designs is ?
Each spool runs at its optimum speed
Most moderns commercial jet aircraft use ?
Turbofan engines
Read part of pitot-style inlet forms a …?
Divergent duct
Pitot style inlet cannot guarantee stable inlet conditions:
When contaminated with ice
At very high angle of attack
In severe turbulence
I’m very high crosswinds
Air inlet fan has sensors to detect
Inlet temperature
Inept pressure
(Amongst other things)
Nacelle functions ?
Reduce compressor noise
Provide structure for bypass duct
Streamline engine installation
Protect external engine components
Two types of compressor ?
Centrifugal
Axial flow
Compression ratio on a centrifugal compressor ?
4.5:1 per stage
A maximum of 2 stages in series can be employed
What is a “stage” in an axial flow compressor ?
A set of rotating rotors and stationary stators, axial flow compressor comprises many stages
Axial flow compression ratio ?
1.1-1.2:1 (10-20%) per stage
What happens to Velocity pressure and temperature going through a rotor ?
Velocity - Increases
Pressure (static) - decreases
Temperature - Increases
What happens to velocity, pressure and temperature in a stator ?
Velocity - decreases
Pressure (static) - increases
Temperature - increases
Variable Inlet guide veins … ?
Swivel to deliver air at correct AoA to first stage of compressor
Why is clearance between rotor sections and compressor case very small ?
To prevent tip losses
Diffuser role ?
Converts kinetic energy into static pressure
Stall or surge indicators
Low RPM
Banging noises
High temp
Axial compressors are vulnerable to … ?
Foreign object damage
Positives of centrifugal compressor
Less prone to surges
Less susceptible to FOD
Shorter, so more compact engines
Reasonably Efficient
Negatives of a Centrifugal compressor
Low compression ratio
Less efficient than an axial flow compressor
Requires larger frontal area
Axial Flow compressor P+N
Very efficient
High compression ratio
Vulnerable to FOD
Can suffer aerodynamic instability
Stall and surge cheats
Multiple stools
Bleed valves
Variable inlet guide veins (VIGV) or variable station valves (VSVs)
Stall and surge avoidance
Before flight check for ice and damage
Avoid starting in cross or tailwind
Avoid extreme angles of attack
The entire axial flow compressor is located in … ?
A convergent duct to help sustain airflow against rising static pressure
Flow reversal through an axial flow compressor is called ?
Compressor surge
Diffuser at the back of an axial flow compressor uses a …. Duct ?
Divergent
External air bleed- alternate name + uses
Customer bleed
To supply hot air or high pressure to aircraft systems, such as air con or anti icing
Can be switched off manually.
Internal Air bleed functions
Spinner anti icing
Pressurised internal cavities
Pressurised bearing housings
How to stop an internal engine over heat ?
Turn off engines
Role of combustion chamber ?
To mid air and fuel to allow efficient burning
Pressure across Gas turbine engine ?
GTE is a constant pressure engine, combustion does not create an increase
How does the distribution of air go into the combustion chamber ?
20% goes through a ‘snout’ in ceramic lining, 80% goes around
Air fuel ratio in GTE
45-130:1
In the flame is 15:1
What does a primary airflow feed ?
Combustion flame, via a swirled valve and recirculating vortex.
Reducing airflow speed to 3 m/s
Where is gas ignited ?
Primary zone
What does a combustor drain do ?
Allows pooled fuel to drain away preventing a hot start or torching
Cannular combustion chambers
Multiple chambers, Lots of little flames, lots of cooling tubes.
Turbo annular combustion chamber
Radially placed, multiple flame tubes with different nozzles.
Annular combustor (modern)
Fuel nozzles arranged radially injecting into one large flame tube
Air spray injectors
Takes in air to creates a swirl and mixes it with fuel to make a toroidal flame in the primary zone, controlled by FADEC
Advantage of air spray injectors ?
Low carbon emissions
Lower pollutants
What is the most sensitive part of the GTE
The turbine assembly is most temperature and pressure sensitive part and is life critical
What happens to turbine size heading away from heat
It increases
What does the turbine drive ?
Compressor, front fan, accessory gearbox
Compressor stage is ?
Rotating rotor
Stationary stator
Turbine stage is made up of
Stationary nozzle guide vein (NGV)
Rotating turbine rotor
What does the turbine do ?
Extract kinetic energy to creat rotation of turbine discs and thus the spool shaft
Impact on T, sP, V across the turbine
Decreases
How is the turbine system housed ?
In a divergent duct
Impulse turbines
Driven by a fluid jet against the blade, rotation is only achieved through this action, causing an impulse force which drives the turbine.
Impulse turbine nozzle and rotor setup
Nozzle - convergent (creates a jet flow which strikes the blades)
Rotor - constant area
Reaction turbine
Is designed in the opposite to impulse and utilises newton’s 3rd law. Air accelerated through convergent ducts creating a reaction force
Reaction turbine rotor and stator set up
Nozzle - constant area
Rotor - convergent shape (accelerates air through it)
P/V/T across an impulse turbine (NGV/Rotor)
NGV
P- Decreases
V - Increases
T - Decreases
Rotor
P - Decreases
V - Increases
T - Decreases
P/V/T across an Impulse/reaction turbine (NGV/Rotor)
NGV
P - Decrease
V - Increase
T - Decrease
Rotor
P - Decrease
V - Increase
T - Decrease
P/V/T across a reaction turbine (NGV/Rotor)
NGV
P - No change
V - No change
T - No change
Rotor
P - Decrease
V - Increase
T - Decrease
How are blades connected to discs
Fir tree connection, increases surface area whilst creating multiple load paths
How is blade stress monitored ?
HCF - high number of small stresses (vibrations)
LCF - low number of large stresses
How is blade stress reduced ?
Reducing blade temp
Single Crystal tech sees alloys moulded in a specific manor to reduce it
Active clearance control (ACC) role ?
Ensures minimum loss within turbine, using hot bleed air to expand the turbine case to maintain small tip clearances.
How is blade tip losses reduced ?
Shrouding
Typical exhaust system composition
Jet pipe
Propelling nozzle
An exhaust cone
Purpose of exhaust system ?
To maximise thrust by accelerating air rear wards
When does the propelling nozzle become choked ?
When nozzle velocity reaches M1.0
P/V/T effect in exhaust
P + T fall
V may increase
How is exhaust noise reduced ?
Shrouding high velocity core exhaust gas with cold bypass air. Mixer units can be used instead
What does scarfing do ?
Reduces noise on modern A/C
How is reverse thrust produced ?
By reversing some of the hot stream with blocker doors or clamshells or buckets
How is reverse thrust produced on high bypass engines ?
Reverse thrust is produced by reversing some of the bypass air through cascade vanes and doors in the nacelle
How is inflight reverse thrust prevented ?
Interlocks.
Airbus won’t let reverse thrust be used at low speeds.
Cold stream reversal is used on ?
Larger, high bypass engines
Minimum number of reverse thrust protections ?
3
One on flight deck
(Visual indication of doors, green for in operation, Amber for unlocked)
Two operated by engine
How are blocker doors operated ?
Hydraulically
How are clamshells and buckets operated
Pneumatically
How is engine temp measured?
Thermocouple
Thermocouple composition?
Two dis-similar metals joined to form a junction with a loop, a small voltage is produced when exposed to heat
EGT ?
Exhaust gas temperature
TGT
Turbine gas temperature
TET
Turbine engine temperature
JPT
Jet pipe temperature
How are rotating shafts supported
Needle roller bearings
How are thrust loads generated by shafts transferred to the main engine casing ?
Ball bearings, so shafts must have both types of bearing
How are bearings lubricated and cooled ?
By engine oil
Why does the filter have a bypass ?
Incase it becomes blocked
What surrounds each set of bearings
A bearing chamber
Main lubrication system components are (7)
Oil pressure pumps
Scavenge pumps
Oil reservoir
Oil cooler/fuel heater
Filters
Magnetic chip detectors
Air/Oil separator
Labyrinth seal use ?
To prevent loss of oil from bearing housing
If you notice engine run down time has decreased, this means ?
There’s a damaged abradable lining/seal (grabbing abradable seal)
Pre flight lubrication checks
Oil quantity check - (sight glass)
Oil leaks - (walk around)
Shortly after engine start oil pressure should rise after 30 secs. If not may indicate a leak
What does rising oil quantity indicate ?
Fuel leaking into oil lube system
How is filter blockage indicated ?
CLOG
Smell of damp socks or acrid smoke may indicate ?
Internal engine issue
Purpose of engine fuel system ?
To provide fuel to the combustor at the correct pressure under all conditions
Fuel delivery is dependent on ?
Core rotation speed (N2)
FADEC stands for
Full Authority Digital Engine Control
Heart of the FADEC is a ?
Engine electronic controller (EEC), which has two channels for redundancy
FADEC power supplies ?
FADEC alternator/ generator - in flight
A/C electrical system - below 20% of N2 before and after
Major FADEC functions are
Deliver correct amount of fuel
Maintain sufficient HP pump output at low RPM
Fuel shut off when commanded
Overspeed protection
Controlling compressor airflow (BLD valves)
Ensuring manifold draining on shutdown
Reverse thrust
ACC
(Clue is F stands for Full ) Anything engine related
If you have a single channel failure ?
No loss of functionality, FADEC fault would be displayed
Dual channel failure ?
(Bank & PP answer is ) engine is will fail/ shutdown
( Mick says it will revert back to last selected power setting)
Jet fuel is a form of ?
Kerosene or parrafin oil
Most commonly Jet A and Jet A-1
(Jet A-1 has additives)
Jet A flash and waxing point ?
Flash +38°C
Waxing -40°C
Jet A-1 flash and waxing point
Flash point +38°C
Waxing point -47°C
Fuel additive blend is ?
Fuel system icing inhibitor (FSII)
Anti static additives
Oxidation and corrosion inhibitors
What fuel cane be used on cold climates (Canada, the poles) ?
Jet B
70% gasoline
30% kerosene
(Jet B is banned in Europe for commercial operations for safety and environmental concerns)
Fuel waxing ?
Fuel turns to a slushy substance and can CLOG all components within the system. Any water will for slush way before waxing point.
How is fuel starvation prevented ?
Fuel heater is now placed before the filters
De-rating means ?
The engine is set to have lower thrust in ideal conditions using less fuel.
However max thrust isn’t available if it becomes required
Flex thrust is ?
A temporary limitation on max thrust created by entering an assumed temperature which is higher than ambient, so engine produces less thrust saving fuel.
Max thrust (TO/GA) is available if required
How are de-rate and flex thrust set
By the crew via the CDU
Thrust may be indicated by ?
ratio of inlet to outlet pressure (EPR) or speed of the tan (N1)
Increase of vibration means ?
Trouble ahead
2 types of engine starter motor are ?
Air (pneumatic) starter - driven by compressed air
Electric (starter/generator) - driven by AC to start accessory gearbox, becomes a generator at ground idle.
Dry start
Low staggering RPM
No EGT
No fuel flow
- could be HPSOV malfunction
Hung start
Low staggering RPM
High EGT
Low fuel flow
- could be a compressor stall
- low bleed pressure
- engine failing to reach self sustaining speed
Hot start
Normal RPM increase
Rapid and excessive EGT rise
Normal fuel flow
-possible following a previous failed start attempt
Wet start
Low staggering RPM
No EGT
Some indicated fuel flow
- dry run should be carried out before re-trying
Multi engine spool start, difference in rotational speeds
N1- 20-25%
N2- 50-60%
Torching may result in ?
A tailpipe fire
This will not illuminate any warning
It may or may not be indicated by EGT
APU auto shutdown reasons
Fire warning
Excessive EGT
Low oil pressure
High oil temperature
Airspeed/Altitude limit exceeded
APU overspend
High bleed Air temperature
Typical APU capacity limits
Electrical power and Air bleed - 11’000ft
Air bleed - 17’000ft
Electrical power;
60KVA- 32’000 - 41’000ft
90KVA- sea level - 32’000ft
APU start up to - 41’000ft
Battery start not available above - 25’000ft
The APU supplies
Electrical and (optionally) pneumatic power
Starting sequence for an GTE on the ground ?
Starter, rotation, ignition, fuel
What is specific range in a jet aeroplane ?
Nautical miles flown per unit mass of fuel
Advantages of multi-spool engines ?
One smaller air starter driving only one spool can be used
In a GTE an un geared fan has the same RPM as ?
The low pressure compressor
What is the energy delivered by a free turbine DEPENDANT on ?
Rotational speed of the HP spool
Bypass ratio is the ratio of ?
Hot air mass flow to cold air mass flow
Converging duct induces ?
Decrease in pressure, increase in exhaust gas velocity
(pressure into speed)
