AGK - Engines Flashcards
What comes after ‘suck’ in the Otto Cycle
Squeeze (Compression)
What’s after ‘blow’ in the Otto cycle
Sleeps
What are the main reasons that the ‘4 stroke cycle’ can only be considered hypothetical?
Ineffective crank angle
Finite combustion time
the volume within cylinder between TDC and top of cylinder is called?
Clearance Volume
Total amount of fuel and air mixture drawn into cylinder is called?
Charge
What is the charge inside the cylinder ignited by?
Spark Plugs
What is the principle of energy transfer of a piston engine?
Chemical > Heat > Pressure > Mechanical
Name the 4x strokes in the theoretical 4 stroke cycle
Induction > Compression > Power > Exhaust
How many full rotation will the crank shaft traveled within a 4 stroke cycle ?
2
Stroke definition
distance the piston travels between its lowest and highest points
Ignition occurs…….
Between the compression and power stroke
Top most limit of the piston
Top Dead Centre (TDC)
The average pressure exerted on the piston during power stroke is called ?
Mean Effective Pressure (MEP)
Most of the work on the power stroke is done ______ the piston reaches BDC
Before (therefore the exhaust valve opens before the end of power stroke)
The exhaust valve remains open until slightly after TDC (exhaust valve lag), why is that needed?
Longer time available to clear the cylinder of exhaust gas via residual pressure and momentum
At high RPM, piston is travelling so fast that ignition is further ______ in order for the power stroke to receive peak pressure
Advanced
The crankshaft can be directly connected to?
The Propeller
The crankshaft can also be indirectly connected to the propeller via?
A Gearbox
The ‘up down’ motion of the piston is called?
Reciprocal movement
Definition of ineffective crank angle
Close to TDC and BDC, there is very little linear displacement of the piston despite the angular rotation speed remains unchanged
What does the practical 4 stroke cycle exploites? And how?
The ineffective crank angle and finite combustion time
Altering the valve timing in relation to stokes and altering the ignition timing
Inlet valve _____ and ______ maximise the amount of charge that enters the cylinder
Lead , lag
The mixture inside the cylinder is only compressed when both inlet and outlet valves are ______
Closed
1 Pascal or pressure is______
Small in the grand scheme of things as it is only 1N per square metre
Humidity is
A measure of the amount of Water Vapour within a volume of gas
For any gas, at a given temp and pressure, the number of molecules present must be _______ for a particular volume
Constant (therefore as humidity increase, H2O replaces more N2 and O2 within a given volume of air, and as H2O has less mass vs N2 and O2, the volume of air will decrease in mass)
Boyle’s Law
P1 V1 = P2 V2
Absolute temperature of a gas is ________ in Boyle’s law
Constant
Charles Law
For a specific mass of gas, at constant pressure
V is proportional to T
Combines Gas Law
PV / T = Constant
Mechanism of heat transfer (not met version)
Convection
Conduction
Radiation
Newton’s Laws of motions are:
It’s okay I trust you got this right. If not please refer to POF, I can’t be bothered typing them all.
Thrust produced by a prop or jet engine depends on Two things :
The ‘amount’ of air and how much is that amount of air being accelerated
Formulas for Thrust
F = M x (V [jet] - V [flight])
1 horse power is approximate equal to _____ watts
740 watts
What is Torque?
A twisting force
Amount of Torque depends on?
Force applied
The length of the arm which force is applied and the angle between the two.
SI unit for Torque
Newton Metre - NM
Mechanical efficiency of an engine is expressed as a ratio between ?
The useful power produced to the theoretical power produced
Modern piston engines are about _____% efficient
80
The more work that an engine has to do to power it’s own components the ______ efficient it will be.
Less
Engine power is determined by the _____ of mixture ignited in the cylinder
Mass
More mass more power
Multiple cylinders produce ______ power delivery
Smoother
______ and ______ of cylinders can be increased to increase power
Number and size
Firing interval of an engine is determined by?
Diving 720 degrees by the number or cylinders
Engines can be classified by:
Number of cylinders Cylinder arrangement Method of cooling Type of fuel and induction system Type of fuel used Prop drive arrangement
Rotary engines have _____ crankshaft and ______ rotating cylinders
Fixed, rotating
Radial engines have ______ cylinders and ______ crankshaft
Fixed, rotating
Radial engines have the advantage of being ______ and ______ and have a ______ surface area for cylinder cooling.
Small, light, large
What’s the major disadvantage of radial cylinder configuration
Imposes significant constraints of aircraft design resulting in high drag
Another major draw back of radial engines is that ______ can pool in the cylinders that are inverted.
Oil
In-line engines have ______ ______ frontal area but ____ difficult to cool. Hence usually limited to _____ cylinders.
Relatively small, more, 6
In-line engines are often ______
Inverted
What is the most common engine cylinder arrangement?
Horizontally opposed engine (box or flat)
What are the benefits of having horizontally opposed engine cylinder arrangement ?
Short, rigid that sits easily within a streamlined nacelle, which reduces drag.
Horizontally opposed engines typically have _ , _ or _ cylinders.
4,6,8
Horizontally arranged engines are usually ______ cooled
Air
Cylinder comprises of 2 main components
Head and Barrel
Barrel in the cylinder of aero engine is typically made from?
Steel
Aero engines always have at least _____ spark plugs as an in built redundancy for safety
2
2 sets of spark plugs in aero engine is connected to ______ ______ magnetos
Two separate
As well as safety, using 2 spark plugs per cylinder ensures ______ and ______ ______ fuel burn, improving combustion efficiency.
Quicker and more even
Top of the piston is called the ______
Crown
The lower part of the piston is called the ______
Skirt
_______ rings are fitted around the top of the piston to prevent gases from escaping
Compression
What connects the piston to the crankshaft?
Connecting rod
The connecting rod is connected to the ______ ______ of the crankshaft at the ______ ______
Crank pin, big end
To save weight, aero engines tend to have ______ strokes
Short
Cylinder firing sequence
1342
What’s the benefit of alternating the firing order of cylinders
To reduce stresses on the crankshaft
The crank shaft, connecting rod and pistons are collectively known as?
The crank assembly
The camshaft operates the valves via?
Push rods
Camshaft always rotate at what speed?
Half the speed of crankshaft
Inlet and exhaust valves are ______ valves
Poppet
Inlet and exhaust valves are opened by ? And closed by?
Opened by camshaft and closed under spring pressure
How many springs are located around the valve stem for redundancy. The are also wound in what manner?
2.
Wound in opposite directions.
Inlet valve is normally ______ than exhaust valve
Larger
The moving parts of an engine must be lubricated to reduce ______ and ______
Friction, wear
Engine oil has which secondary functions?
Cooling,
Cleaning carbon deposits and metal flakes
Protecting against corrosion
Hydraulic operations
What are important indicators of engine health?
Oil temperature and pressure
Aero engine oil is typically…… . And its viscosity reduces with ______ temperature
A Mineral oil.
Increased
Aero engine oil must be able to maintain……
Suitable viscosity over a wide range of temperatures.
Apart from maintaining viscosity in wide range of temperatures, what other properties must engine oils have?
Have low evaporation rate
Inhibit corrosion
Inert
Discourage the formation of sludge
To meet engine oil requirements, additives are used to form compound oils. What are identification prefixes?
W80, AD100
Engines have ______ ______ or ______ ______ lubrication systems
Dry sump, wet sump
In the dry sump system, the oil is held in a ______ mounted ______ from the engine, but in the wet sump the oil is held in the ______ of the crankcase
Tank, remotely, bottom
Oil pressure in a dry sump typically reaches _______ to ______ psi.
60 - 70
Spent oil in a the dry sump is pumped back to the tank via a _______ pump
Scavenge
Oil returns from the engine via the scavenge pump and ______ line and spills onto a ______ plate
Return (scavenge), deaerator
The de-aerated oil recycled into the hot well of the tank to allow good circulation to establish _______. The hot well then gradually heats the cooler oil in the tank which eventually be able to flow ______ through the hot well.
Quicker.
Through
Magnetic plugs are?
Also known as chip detectors that are fitting in the oil return line. Ferrous particles from the engine are caught by the magnets and these particles can be examined to give an indication of wear and failure of components
Oil pump in a dry sump is ______ driven
Engine
The wet sump system uses the same components as the dry sump except?
No return (scavenge) line or scavenge pump. And no oil tank reservoir
The crankshaft splashing through the oil helps to lubricate the working surfaces. This is known as ?
Splash lubrication
Dry sump system oil check after flight
Immediate
Wet sump system oil check after flight
About 20 mins after shut down
Excessive cooling of the oil can cause the oil to ……..
Congeal in the matrix and block it
In the dry sump system the oil cooler is fitted in the _________ ______. In the wet sump system the cooler is normally fitted in the ______ ______ to the engine.
Return line.
Pressure supply.
Oil pressure should typically indicate within ______ seconds of engine start.
30
Hydraulicing occurs when oil ______ into the cylinders when they are ______. To avoid damage to cylinders, manually turn the prop to work the valves to allow oil to ______ from the cylinder.
Leaks, inverted, escape
Liquid cooling system extract heat from the engine by running a mixture of ______ and ______ through galleries built into the crank case.
Water and glycol
Hot fluid in the cooling system is piped into the radiator and cooled by ______ ______.
Ram air
Aero engines can be air cooled instead of liquid cooled to save ______ and ______ working components.
Weight., reduce
Temperature on the cylinder is measure at the ______ ______. And sensors are fitted on ______ cylinders, where the ______ temperature is displayed
Cylinder head. All. Highest
Cylinder head temperature is controlled by:
Amount of power produced
Aircraft speed
Temperature of cooling air
Mixture ratio
Engine is more likely to overheat when…….
Using high power during a climb
During start of the engine, the starter motor drives the engine via a ______ or ______ ______ on the engine flywheel
Gearbox, Tooth gear
As soon as engine starts, an ______ clutch disengages the Drive from the motor.
Overrun
If starter warning lamp remains on for more than _____ seconds after engine start, the starter motor have failed to ________. The engine must ______ ______.
30, disengage, shut down
Magnetos generate ______ tension electricity to power the spark plugs.
High
The purpose of the ignition system is to provide ______ of sufficient strength and duration at precisely the right moment in the cycle to ensure efficient ________
Sparks, combustion
The critical components of the ignition system are ________ to ensure that any single failure doesn’t result in total loss of engine ______.
Duplicated, power
Magnetos are ______ ______
Engine driven
The generator section of the magneto comprises a ______ pole rotating permanent magnet.
4
Primary winding, also called the ______ ______ circuit is wound around the soft iron stator. It comprises of a few turns of ______ wire.
Low tension, thick
The secondary circuit, also called the ______ ______ circuit, is wound over the primary circuit. The secondary winding contains many more turns of ______ wire and so it acts as a step-up transformer
High tension, thin (fine)
The primary circuit is continuously ______ and ______ by a contact breaker. This has two effects:
1) it converts continuous flow of AC current into a series of ______
2) The collapse of the magnetic field around the primary winding produces a surge of energy in the secondary winding, resulting in a series of ______ voltage, ______ current pulses of electricity that are distributed to the distributor.
Broken, reform
1) pulses
2) high, low
What’s the purpose of the distributor in the ignition system?
Alternately distribute the high voltage pulses of electricity to spark plugs
The collapse of the magnetic field caused by the opening of contact breaker points can induce a current in the primary winding, it can be sufficiently strong to produce ______ at the contact breaker points, which can cause damage to the breakers.
Arching
A ________ is fitted in parallel with the contact breaker to prevent arching.
Capacitor
The high tension voltage delivered to the spark plugs need to be in the region of ______ volts
30000
As well as the magneto, the engine also drives the contact breaker rotor and distributor rotor via a spindle, therefore their operating speed _____ directly with engine ______
Vary, RPM
Each magneto is controlled by its own ______ switch
Ignition
The ignition switch lead is called the ______ lead
P
When the ignition switch is open, the ignition circuit is ______. The provides a _____ ______ protection in flight.
Live, fail safe
On the ground, a disconnected wire results in a _________ live circuit
Permanently
Advantage of 2 spark plugs per cyclinder?
Quicker rise to peak cylinder pressure by providing more even burn of the fuel gas mixture.
The magneto is ________ to reduce the possibility of internal arching at altitude.
Pressurised.
Magneto’s output voltage is directly proportional to ______ ______
Engine RPM
An impulse coupling comprises a ______ loaded clutch mounted between the drive spindle from the engine and the magneto shaft. The drive spindle winds up the spring in the clutch, and as its released, the spring ______ and spins the ______
Spring, unwinds, magneto
What is the common ‘extra’ component between the LT and HT booster.
Using the aircraft battery
In the LT booster, a second set of ______ ______ points in the LT booster coil circuit ensures a sufficiently retarded spark. The circuit is switch ______ once engine has started.
Contact breaker, off
in the HT booster, a current is fed from the ________ to power the primary winding. A ______ ______ in the coil interrupts the primary winding circuit produce a continuous stream of high-voltage impulses, in the secondary HT circuit.
Battery, trembler interrupter
On a spark plug, a small ______ is set to separate the two electrodes. When HT voltage is applied, a strong ______ is created as the current arch the gap, this ignites the fuel air mixture.
Gap, spark
If the gap in the spark plug is too small the spark may be too ______. If the gap to too big there may…………..
Weak,
Maybe no spark at all
When oil , carbon and lead deposits from the fuel blocks the gap in the spark plug and causing the failure to spark, this is known as?
Fouling
Mag drop check is carried out ______
Twice
First mag drop check is done ______ ______ at about ______ to ______ RPM.
Second mag drop check is done during ______ ______ at about ______% of max engine RPM
After startup, 1000 to 1200
Power checks, 75%
No drop in RPM during mag drop check indicates one half of the ignition system is ______ ______ .
Not earthed
Excessive RPM drop and rough running indicates _________ ________
Ignition problem
if the amber starter warning lamp remains on for more than ______ after engine start the motor may have _____ to disengage. The engine must be _____ _____
30 seconds
Failed
Shut Down
The magneto is an….
AC generator, transformer and distribution system providing high voltage current to the spark plugs. It is independent of the aircraft battery and electrical system.
Engine rotation drives _____ which deliver high tension _____ to the spark plugs.
Magnetos
Electricity
The Ignition system must…
Provide sparks at precisely the right moment in the cycle to ignite the mixture.
Most light aircraft aero engines have __ magnetos
and each magneto powers a _____ _____ in each cylinder.
2
Spark plug
When the ‘P’ switch is closed the magneto is _____ and when it is open the magneto is _____
Off
On
The switch must be closed to _____ the circuit. This provides a fail safe _____, but is unsafe _____
Earth
In flight
On the ground
2 advantages of spark plugs:
Helps accelerate the combustion process
Is fail safe
Magneto’s output voltage is _____ _____ to
engine RPM.
Directly proportional
Magnetos are pressurised to reduce the possibility of
_____ _____ at altitude.
Internal Arcing
A mag drop (Magneto check) is carried out _____
Twice
The First mag drop is just after start at about _____ - _____ RPM. Each magneto is switched off in turn. The RPM should _____ but the engine should continue to ______ ______.
1000-1200 RPM
Drop
Run smoothly
The second mag drop is at about _____ of max RPM. Each magneto is _____ _____ in turn. RPM drop must be ______ _____.
75%
Switched off
Within limits
Spark pulgs can have a build up of _____ _____ which can lead to the plug _____
Dirt and oil
Fouling
The low tension booster is only live when _____ the _____.
Cranking
Engine
Impulse coupling is creating _____ _____ and _____ _____
High tension
Retarded Sparks
In a mag drop what indicates a failure of one half of the ignition circuit?
A complete dead cut
What indicates one half of the ignition system is not being earthed.
No drop in RPM
What indicates an ignition problem
Excessive RPM drop and rough running
A 300-400 RPM drop or rough running indicates
Malfunctioning spark plug
A dead cut check before shut-down is to confirm
The ignition system isn’t live.
3 characteristics of AVGAS:
Must contain a significant quantity of energy
Must be able to form a vapour, but not too readily
Must be able to burn quickly but controllably
AVGAS 100LL has a flame rate of
60-80ft/s (18-24m/s)
The number on the fuel is the
Octane rating (resistance to detonation )
LL at the end of the fuel stands for
‘Low Lead’
Under abnormal conditions the mixture may _____ rather than _____
Detonate
Burn
Detonation:
The extremely rapid spontaneous combustion of part of the mixture after the burning has begun
Result of detination:
Rapid, violent and uneven rise in pressure in the cylinder with flame rates around 300m/s (1000ft/s)
Detonation can often be heard as a
Knocking sound
The 4 principal causes of detination are:
Fuel with poor anti-knock qualities
Incorrect mixture ration
Anything that raises the temp. or the pressure of the mixture before it is burned.
High engine temp,.
The higher number on the octane rating is the ______ _____ anit-knock properties and the lower is the ______ _____.
Rich mixture
Lean mixture
The most effective additive for controlling detonation is
Having lead in the fuel
AVGAS 100LL is dyed _____
Blue
AVGAS 100 is dyed _____
Green
Older pistons ere designed to run on _____. This is dyed _____
80/87
Red
Mixture ratio 15:1 is
Stoichiometric (chemically correct)
Mixture ratio 12:1 is
30% rich, used for the take-off and climb
Mixture ration >15:1 is
Lean, good for cruise economy
_____ heat at high power settings, _____ _____, and high power settings at _____ _____ all increase
the risk of detonation.
Carburettor
Overheated cylinders
Low RPM
A lean mixture produces higher engine _____ because the slower burn gives more time for _____ _____ _____ to the body of the engine.
Temperatures
Heat to transfer
With a lean mix, the slower burn gives _____ _____ but _____ _____ _____.
Reduced power
Reduced fuel consumption
Indirect injection
Injects the fuel to the air flow just before the fuel inlet/
In a carburetor, filtered fuel is pumped into a _____ whose level is controlled by a _____ _____.
Chamber
Float valve
A basic carburetor system is not sufficient because (4 things):
It takes no account of air density.
It would result in a progressively richer mixture as
engine speed and/or altitude increases.
Ram-air effect in the inlet would weaken the mixture
with increased airspeed.
No provision for special mixture settings required at
very low and very high power settings.
A pressure balance duct ensures that the _____ of the intake and float chamber remain _____
Pressure
The same
A diffuser takes pressure off the _____ _____ and _____ fuel output.
Float chamber
Reduces
A mixture control valve _____ pressure in the float chamber to allow controlled _____ _____
Controls
Fuel mix
The basic float carburettor pumps fuel into the chamber whose level is controlled by a ______ valve
Float
A basic carburettor is insufficient because:
1) does not take into account density of the air
2) will result in progressively richer mixture as engine speed/ altitude increase
3) Ram-air effect in the inlet would weaken the mixture
4) no provision to ‘select’ a mixture ratio on demand
In a carburettor, the ______ ______ ______ ensures that the correct mixture ratio is maintained across a range of air speeds and flight controls
Pressure balance duct
The perforations in the diffuser ensures that correct mixture ration is maintained across _______ ______ and flight conditions
Air Speeds
As air density decrease with altitude, the mass of air passing through the throat of carburettor ______. This results in a progressively ______ mixture as the aircraft climbs. A pilot can control it via a ______ control.
Reduces. Richer. Mixture
A very small throttle openings the pressure drop in the Venturi is ______, resulting in an insufficient flow of fuel from the main jet. The solution is to insert a ______ running jet especially designed for low power conditions.
Small, slow
The slow running jet is designed to provide a ______ mixture at idle.
Rich
At high power settings, a power enrichment system is required to provide the ______ mixture needed to cool the cylinders
Rich
In the economiser system, the needle that allow extra fuel flow to the jet is ________ except during high powered settings
Closed
The phenomenon ‘when the throttle is opened rapidly, the lag of the fuel flow causing a reduction in mixture ratio’ is known as?
And what device can be fitted to minimise it?
Lean cut
Accelerator pump
The carburettor throat produces a ______ in temp because the reduction in pressure and the evaporation of fuel. It can be as much as ______ degrees.
Drop, 25
Symptoms of Carb icing are?
loss of RPM Reduced performance Reduced inlet manifold pressure Decreased EGT Rough running Jammed throttle Engine cut out
In terms of carb icing, the most dangerous conditions occur when in ______ or ______ during relatively warm days with relatively high humidity.
Cruise, decent
In a fixed pitch prop, first sign of carb icing is an unexplained ______ in RPM.
In variable prop, first sign of carb icing is a drop in ______ ______ ______.
Drop, manifold absolute pressure (MAP)
There are two type of fuel injection:
In the ______ injection, fuel is delivered just before the inlet valve.
In the ______ injection, fuel is injected directly into the cylinders.
Indirect, Direct
Indirect systems are ______ and ______ because there’s no need for more complex timing systems
Cheaper, simpler
Fuel injection removes the need to use a ______ in the air intake, thus reducing the likelihood of intake icing. It also provides more ______ and ______ reliable fuel delivery and ______ throttle response
Venturi, even, reliable, quicker
When using indirect fuel injection, the metering valve is controlled by the ______, where when the the throttle butterfly opens the metering valve also opens allowing more fuel to flow.
To control the fuel air mixture, a ______ ______ ______ is needed.
Throttle, mixture control valve
The manifold valve ______ all the metered fuel between all the cylinders. It will also stop the fuel flow when the mixture control is set to ______ ______ ______.
Divides, Idle Cut Off
Powerful engines and Diesel engines use ______ fuel injection.
Direct
A very _____ mixture is needed on engine start up
Rich
Carburettor engines use which methods to ‘prime’ before start up?
Manually operated plunger
Exercise the Throttle
Manual or electric pump
Air intakes are prone to ______ ______ which have same symptoms as carb icing.
Impact icing
Fuel injected engines have an alternate air source which also ______ the intake air filter
Bypasses
Fuel injection systems will not show a drop in RPM when ______ ______ is selected
Alternate air
Leaning at higher power setting leads to ______.
Detonation
Density altitude is the pressure altitude adjusted for any temperature deviation from _ _ _
I S A
Density altitude is used to assess an aircraft’s ______ ______
Aerodynamic performance
The power delivered by the aircraft’s engine is affected by the ______ and ______ of the atmosphere
Density, composition
3 Power output and their definitions
Take - off power - maximum power the engine can produce
Rated power - the ‘continuous power’ available at a particular RPM setting, MAP or both.
Cruise power - A percentage of maximum take off power
At ______ atmospheric density, the engine produces more power, but it will also need more power to turn the prop in the same density.
High
Power available from a prop at sea level will _______ as TAS increases, then it will reach a ______ before decreasing.
Power available at altitude vs TAS is _____ as above although at a ______ power output in comparison to sea level
Increase, peak
Same, lower
Altitude boosted ______ pump compressed air into cylinders to delay drop in power due to lower density at ______ density altitude. However it will need a control system to prevent ______ boosting on the ground.
Supercharger, higher, over
______ boosted supercharger increases the maximum power available at sea level. However they will require ______ engine structure and better ______ ______.
Ground, stronger, cooling system
A ______ pressure gauge or a ______ air pressure gauge measures the pressure of the air being supplied at the inlet manifold.
Boost, manifold
The boost pressure gauge indicates pressure ______ to standard ______ ______ pressure
Relative, sea level
The manifold air pressure gauge displays ______ pressure in the manifold, measured in ______ __ ______
Absolute, inches of mercury
Before start up, the MAP and boost gauge indicate atmosphere pressure - ______ boost
Static
When the engine is running, MAP initially ______ but then returns to the ______ ______ value - the reference RPM.
Drops, static boost
Two types of super charging units.
Supercharger and Turbo-charger
Superchargers are ‘______ superchargers’ and are powered by the ______. They are fitted ______ of the carburettor and compresses the fuel air mixture.
Internal, crankshaft, downstream
Turbo-chargers are ‘______ superchargers’, they are powered by the ______ ______ stream. They are fitted ______ from the carburettor so compresses only air.
External, exhaust gas, upstream
The disadvantage of the internal supercharger is that they are typically ______ and _____, hence they have been largely abandoned in modern engines.
Huge, heavy
The turbo-charger comprises a ______ linked to an ______ by a short shaft.
Turbine, impeller
The impeller is a type of ______ or radial compressor.
Centrifugal
Advantages of the turbocharger
- no power taken from the engine to drive the turbocharge
- the drive train is less complex
- the exhaust driven turbine takes time to spool, therefore can lag in power delivery
The speed of the turbine in the turbocharger depends on the amount of ______ ______ directed into is vanes. A overboost valve provides rudimentary protection against overboosting by bleeding ______ pressure overboard.
Exhaust gas, excess
For a given power setting, a point is eventually reached where the waste gas controller has completely ______ the waste gate
Closed
Above critical altitude, manifold pressure and engine power will ______
Reduce
In the turbo charged engine, back pressure occurs because all the ______ now enters the turbine. This reduces ______ ______ and engine for a given value of MAP will ______
Exhaust, volumetric efficiency, decrease
On an internal supercharger, critical altitude is known as the ______ ______ ______
Full throttle height
A absolute pressure controller controls the ______ ______ actuator to maintain the right amount of boost across a range of ambient conditions
Waste gate
Engine start - waste gate is held ______ because of spring pressure.
Idle power - little exhaust gas so waste gate moves to fully ______ position
Take off - waste gate is ______ ______
Open
Closed
Partially open
Climb - during a climb, at constant power, the waste gate tend to ______ as the air density decreases
Critical altitude - the waste gate is fully ______. The turbine is at maximum speed.
Above critical altitude - the waste gate is fully ______, although the maximum value of MAP is reduced.
Close
Closed
Closed
With a absolute pressure controller system, at MAP values lower than maximum, the turbocharger runs ______ than it needs to.
Faster
The differential controller controls the waste gate at ______ throttle position except ______ ______.
All, fully open
Due to hot exhaust gas temperatures, an ______ is sometimes fitted at the induction manifold to cool the mixture.
Intercooler
Rated altitude is the maximum altitude at which maximum continuous power can be ______ on a supercharged engine
Maintained
To prevent ______ ______, when shutting down, the engine should be left to run at _____ ______ to allow its temperature to stabilise.
Thermal shock, low power
Diesel engines utilise the heat generated in the ______ stroke to ignite the ______. Therefore they have no need for ______ ______ , and therefore no need for distributors and ______
Compression, charge (fuel air mixture), spark plugs, magnetos
Diesel engines always use ______ injection whereas petrol engines may use ______, ______ or ______ fuel injection systems
Direct, carburettors, direct or indirect
To produce sufficiently high temperature in Diesel engines, compression ratios are ……. from ______ to ______. The high compression ratio improves the engine’s ______ ______
Typically higher, 14:1 to 28:1, thermal efficiency
Kerosene is ______
Jet A1 or AVTUR
Specific gravity of Jet A1
0.8 - 0.9
Jet A1 has ______ flash point then AVGAS
Higher
Jet A1 is a ______ lubricant and so require a specially designed fuel pump.
Poor
Advantages of Diesel engines
- inherently more fuel efficient
- require less schedule maintenance
- ideally suited for turbocharging
- simpler and more reliable as there’s no need for an extra ignition system
- kerosene is safer and cheaper than AVGAS
Disadvantage of Diesel engine
The higher operation pressure requires stronger and heavier designs.
In a Diesel engine, just _____ TDC, a metered quantity of fuel is ______ into the cylinder, it will immediately ignite.
Before, injected
Diesel have _____ risk of detonation so diesels can operate at much ______ mixture ratios, therefore there’s no mixture control lever required and the ______ ______ is controlled by the amount of fuel injected into the cylinder.
No, leaner, power output
Diesel fuel injection systems must operate at anything up to _____ psi, as the high pressure experienced in the cylinders.
24000
Two types of diesel fuel injection systems
Common rail, direct injection
in a diesel direction injection system, the pump must :
- Sense RPM and air density
- adjust the timing of the fuel pulse
- rapidly generate fuel pulses in appropriate sequence for each injector
The ______ ______ acts as an accumulator for high pressure fuel which is then fed to the electronically operated injectors. The ______ ______ ______ controls the fuel pressure and the injectors.
Common rail, engine control unit (ECU)
Injectors incorporate a mechanically operated spring loaded ______ valve injectors, which opens when the fuel pressure exceeds the spring force.
Poppet
The ______ ______ contain electronically heated coil encased in a sheath filled with magnesium oxide power. They provide heat to the cylinder when the engine is cold during start up
Glow plugs
Diesel engines have _______ power to weight ratios typically
Lower (as they are heavier)
Diesel engines uses a ______ cooling system with a mixture of ______ and ______. The air-cooled heat exchanger disperses the heat energy absorbed by the ______.
Liquid, water, anti-freeze, coolant
A prop must comprise of ______ or more blades attached to a central ______. The hub is usually covered by a fairing called a ______
Two, hub, spinner
The frontal area that the prop blades move though when rotating is called ______ ______
Propeller disc
The blade angle is?
Angle between chord line and plane of rotation
Typically there’s a twist in the blade where the blade angle ______ from root to tip
Decrease (blade ‘washout’)
The blade angle is taken to be the actual bade angle of the blade section __ % out from the hub to towards the tip.
75
On a fixed pitch prop, when TAS increases, AOA _____
Decrease
Blade AOA is defined as?
Angle between chord line and relative airflow
Prop efficiency increases as TAS ______, up to the point where AOA becomes smaller than ______ degrees
Increases, 4
A fixed pitch propeller is designed to be most efficient in the ______
Cruise
For a fixed pitch prop, the higher the RPM for a given TAS the ______ the AOA
Larger/ bigger
A fixed pitch propeller provides the maximum thrust during take off roll because?
High RPM, High angles of attack, slow TAS
A fully fined prop blade has ____ degree blade angle an a feathered prop blade has ____ degrees blade angle
0, 90
A feathered prop produces the ______ drag in flight. Which is used during an engine failure
Minimum
In a variable pitch prop, the pitch of the blades can be changed so that
The blades AOA can be kept to most efficient at more speeds
When an engine fails and torque lost, the propeller will ______ . Where a large aerodynamic force is generated in the opposite direction to flight (______), and a smaller component which provides the driving force to keep the propeller rotating (______)
Windmill, drag, torque
When prop is feathered, there is no aero/ mechanical driving force, thus is will be ______
Stationary
The propeller hub is attached to the ______ or ______ of the engine, either directly or though a ______
Drive shaft, crankshaft, gearbox
On more powerful prop engines, a ______ ______ may have to be used to translate the large amounts of power generated at high engine RPM.
Reduction gearbox
The principle of a reduction gearbox is
A relatively small but high speed gear on the crankshaft driving the relatively large low speed gear attached to the propeller shaft. Allowing the engines and propeller to function at their respective optimum RPM.
On a variable pitch propeller, thrust is increase by increasing the blade angle rather than ______
RPM
On a vari-pitch prop, any increase of AOA increases ______ ______, therefore any thrust will require an increase of ______ , if RPM is to remain constant
Torque drag, power
Two types of pitch control unit
Single acting and double acting
The mechnism that is responsible for changing the blade pitch is?
Pitch control unit
For a single acting PCU on a single engine aircraft, it typically drives the blade pitch to coarse only (single acting), with help of a spring during engine failure, the blade will have tendency to _____ _____
towards Fine
Apart from retaining some ability to produce thrust, a fined off windmilling prop on a single engine aircraft have the added benefit of?
Help any attempt to restart the engine
On single acting PCUs for twin engines aircraft, upon engine failure the prop will coarsen to avoid ______ ______, by reducing the blade ‘area’ that is presented to the airflow.
Asymmetric drag
A double acting PCU provides pressure to both sides of the piston to fine or coarsen the pitch, why is this needed?
Oil pressure is needed on both side of the piston to overcome the centrifugal and aerodynamic forces created by the blades.
Constant speed unit has 1 job
Match torque drag to engine torque
If engine torque is higher than torque drag, the CSU must ______ the blades so that torque drag increase
Coarsens
When CSU overspeeds, the flyweights will push against the CSU speeder spring and the landed valve will allow oil to flow to ______ the pitch
Coarsen
When CSU underspeeds, the flyweights relax away from the CSU speeder spring and the landed valve will allow oil to flow to ______ the pitch
Fine
When the landed valve is in a position that creates a hydraulic lock is when the CSU is __ ______
On speed
In case of absence of oil pressure during engine malfunction, a feathering system must have a separate ______ ______.
Oil reservoir
In the beta range the power lever directly controls the ______ ______, whisky the propeller RPM are maintained within safe levels by an under-speed governor
Pitch angle
On fixed pitch prop, power is indicated by ______
On vari-pitch prop, power is a function of mass flow which is indicated by______
RPM
MAP
RPM lever is usually ______
Throttle level is usually ______
Blue
Black
If you need to increase power significantly on a variable-pitch prop you must ……
First set a higher RPM then increase throttle
At relatively low RPM and high power, it is possible to ______ the engine
Overboost
upon starting up, it is advisable to check:
- Operate the RPM lever to encourage oil flow in CSU
- Feathering check, momentarily set blades to feather to see is RPM drops rapidly
During landing configuration, RPM level must be set to ______ ______ in anticipation of a possible go around
Fully fine/ fully forward
The Brayton cycle
Compression, Combustion, Expansion, Exhaust
Thrust =
M x (Vjet - Vflight)
Diffuser
a divergent duct between the compressor and the combustion sections, the area of highest pressure
Factors that affect thrust:
Altitude
Speed (above M0.4 due to ram effect)
Ambient temperature
Engine bleed
Air taken from the engine to power other systems, reduces the mass flow through the engine, thus reduces thrust.
Intake heating
reduce air density therefore reduce mass flow through the engine
Specific fuel consumption (SFC)
Ratio of fuel mass consumed to produce a unit of thrust per unit of time.
The _____ the SFC the better
Lower
Thermal efficiency
Efficiency with which fuel energy if converted to kinetic energy.
Propulsive efficiency
Efficiency with which kinetic energy is translated into propulsive force.
At _____ speeds, high velocity exhaust from turbo jets wastes more energy than the flow slipstream from a prop.
Low
At _____ speeds, exhaust gas velocity is much reduced relative to the air flow speed.
High
The Air inlet
Provides a reliable steady flow of air to the compressor
The Compressor
compresses the air
The combustion chamber
burns the fuel with
The turbine
extracts energy from the exhaust gases to drive the compressor
The exhaust
accelerates the air at maximum thrust
Modular construction aids what?
Makes it possible to change major engine sections without dismantling the entire engine
Spool
an assembly comprising a compressor and turbine connected by a shaft
Axial flow
the passage of air through the engine
Advantages of bypass engines
Bypass air does not need to be combusted to achieve its acceleration - more thermally efficient
Bypass air is given a smaller acceleration - propulsive efficiency is greater at lower speeds
The two compressor sections are more efficient because they individually run at their optimal speed
Because less air enters the core, the section is smaller and lighter
Bypass air reduces the noise
A Twin spool high pressure bypass comprises of a ___________ and a __________
LP spool
HP spool
A triple spool high bypass has a bypass ratio exceeding _____
5:1
The fan in a triple spool high bypass engine can produce as much as _____ the total thrust
85%
At air speeds of up to 300kts and at medium altitudes the _____ engine is more efficient
Propeller
Direct couple engine
The single spool is mechanically connected to the propeller
Free spool engine
There is no connection between the gas generation section and the power section of the shaft.
Modern turboprops propellers rotate at speeds of _____ - _____
800 - 1000RPM
Gas turbine engines can rotate at up to _____
40,000RPM
direct drive turboprop engines require a _____ _____
reduction gearbox
Air should be _____ and not have any _____ when entering an engine
Uniform
Turbulence
There is a _____ _____ at the intake section of a Pitot intake to ______ thrust due to the Ram effect
Slight divergence
Increase
The risk of surge is reduces by doing a….
rolling takeoff
Auxiliary intakes
secondary air doors around the circumference of the engine to increase airflow into the engine for more power.
Suction zone
Area where objects can be sucked into the engine
Inlet icing can:
Disrupt laminar flow into the engine
Starve the engine of air, causing a flame out
Can damage the engine blades
The Nacelles function is to:
Streamline and protect the outer-casing of the engine
Provide easy maintenance access
Create the cold air bypass duct
The less work a turbine has to do to drive the compressors, the more _____ it can produce
Thrust
Axial flow compressor
air flows parallel to the axis of the engine
Centrifugal compressor
air flows radially from the center of the compressor to it’s perimeter
A Centrifugal compressor comprises of:
An impeller
A diffuser
A casing to house it
Process of a Centrifugal compressor:
Air enters through the eye
It’s picked up by rotating vanes and propelled outwards by a centrifugal force
Then enters the diffuser vanes which converts the kinetic energy to pressure energy.
In a Centrifugal compressor: velocity, pressure and temperature _____
Increase
The impeller and the diffuser each account for ___ the overall rise in pressure.
1/2
If thee clearance between the rotating impeller and the stationary diffuser is to small, it can cause _____. And if it’s too big, it can cause _____
Buffet
Low Pressure
A greater mass flow can be achieved by a…..
Double entry impeller
In a Axial flow compressor, Rotors add _____ to the airflow by accelerating air towards a set of _____ _____
Energy
Stator blades
In the rotor disc, Velocity, pressure and Temperature _____
Increase
Stator blades convert _____ energy into _____ energy
Kinetic
Pressure
In stators, the velocity _____, static pressure _____ and the temperature __________
Decreases
increases
increase is maintained.
The pressure rise across a single stage is usually only about _____
10-20%
Axial flow compressors usually achive pressure ratios of _____ up to _____ with outlet temps of _____
35:1
50:1
6-700°C
The speed and direction of the air approaching each compressor blade is determined by what 2 factors:
The rotation of the blade speed
Speed of the air
The AoA on the blade _____ from root to tip due to the rotational velocity
differs
The amount of twist is known as the _____ _____
Stagger angle
If a stage stalls, this can lead to a _____
Surge
A deep surge
the reversal of airflow through the compressor
Variable Inlet guide vanes are _____ the first stage of the compressor. They adjust their _____ to in sure that air is directed onto the first stage at the correct angle
before
angle
Variable Stator vanes….
Ensure that air leaving one compressor stage arrives at the next at the correct angle.
Across the rest of the stages
Multi-spool designes allow each compressor to run at _____ speeds. And they _____ the need for air control systems
Optimum
reduce
Inter stage bleed valves:
reduces the load on the compressor
Compressor stall can be caused by:
Damage to the blades
Ice on the blades
Extreme incidence angles
not enough airflow
Symptoms of a compressor stall:
High EGT/TGT Reduced thrust Rumbling/banging sounds from the compressor Fluctuating RPM and fuel flow Compressor surge
Compressor surge
the compressor’s output mass flow falls below the point where it can sustain the adverse pressure gradient
Flames seen exiting the intake - accompanied by a loud bang
Deep surge
Possible cause of surge
Over fueling
Compressor stall
Possible to clear surge by…
reducing throttler to idle, resorting stable intake conditions
Centrifugal compressors are _____ likely to suffer from surge
Less
To avoid surge/stall
Before flight, check for ice/damage
Avoid strong crosswind/tailwinds
Avoid extreme AoA
Low pressure compressor blade construction:
Larger -> smaller
Snubbs keep spacing of the blade and prevent aerodynamic instability
Made from titanium outer-layer (sandwich structure)
Wide chord
Ultra high bypass fan blades construction
Complex twist
Large spacing
Modern blades made of composite
Axi-centrifugal compressors achieve…
High compression ratios for a relatively short engine.
Bleed air systems:
Air taken from several points through the compressor
Used for multiple tasks
reduce power : thrust ratio
Increase fuel consumption
Due to effect on performance, some systems cannot be used for take-off, approach + landing
Internal air systems are used for:
Internal engine + accessory cooling
Bearing chamber sealing
Prevention of hot gas ingestion into turbine disk cavities
Engine anti-icing
High pressure air is used to cool:
Turbine blades, engine anti-ice
Low pressure air is used to cool
bearings
Auxiliary gearbox -
Provides power to the aircraft’s hydraulic, electrical and pneumatic systems
modern combustion engines can be __% efficient
98%
Requirements for combustion
High combustion efficiency and max. heat release
Combustion stability
Reliable and consistent ignition during start + in-flight relight
Exhaust gas temp. doesn’t exceed the turbine blades temp. limit.
Promote low emissions, low fuel combustion and high durability.
Flow feeds into a diffuser section at ____
150m/s
Only __% of the air is introduced immediately into the flame tube - Primary air.
20%
kerosene burns with a flame rate of ____
3m/s
combustion temp can peak _____ - _____°C
2100 - 2300°C
The dilution zone
reduces the temp. of the gases to between 1000 - 1700°C
Secondary zone
where secondary air enters through ports in the walls of the flame tube.
Multiple combustion chamber system:
Used on older designs
Individual but interconnected chambers
Tubo-Annular combustion chamber
Individual flame tubes inside a single air casing.
Annular combustion chamber
Short (75% of the length of a turbo-annular) Combustion in one section costlier + harder to manufacture Multiple igniters less emissions
Reverse flow annular combuster
Shorter engine
air fed rear to front
Air spray injector:
channels air through an inner swirl chamber and outer swirl vanes.
An annular fuel nozzle sits between the two so that the fuel is ejected between two turbulent air streams
Spray inject operate lower fuel pressures
Ignition systems:
Can hold their voltage for at lease 1 min
Powered by the High Energy ignition unit (HEIU)
High power output (12J) for shirt periods (alt. starts + ground starts)
Low power (3 - 6J) output for continuous ignition
