The Aeroplane Engine Flashcards
What is the most common engine design for GA aircraft today?
Horizontally-opposed
In the cylinder, what absorbs all the power from the cylinder and transfers it to the propeller?
Crankshaft
What forms a link between the crankshaft and piston?
Connecting rod
What does the connecting rod do?
Connects the crankshaft and piston
What does the crankshaft do?
Absorbs power from the cylinders and transfers it to the propeller
What does the inlet valve do?
Lets fuel/air mixture into the cylinder
What lets the fuel/air mixture into the cylinder?
Inlet valve
Where does the fuel/air mixture become compressed and burnt (combusted)?
The cylinder(s)
How do used gases leave the combustion process>
Through the exhaust valve
What ignites the compressed fuel/air mixture?
Spark plugs
What does the term ‘reciprocating’ refer to in ‘reciprocating engine’?
The back and forth motion of the pistons
Energy process in piston cylinders?
Conversion of chemical energy to heat energy to mechanical energy
What does the chemical energy consist of in pistons?
Fuel
The basic process of combustion in each cylinder?
Fuel/air mixture is burned
Heat energy causes gases to expand
Piston driven down the cylinder
Four-stroke cycle’s 4 stages:
Intake
Compression
Power
Exhaust
In the intake stroke, what causes air (and fuel) to flow into the cylinder?
Decreased pressure
In the intake stroke, what happens to the pressure?
It reduces
In the intake stroke, how is pressure reduced?
The piston moves downwards
In the intake stroke, what valves are open?
Inlet valve
In the intake stroke, what valves are closed?
Exhaust valve
In the compression stroke, what valves are open?
None
In the compression stroke, what valves are closed
Both inlet and exhaust valve
In the compression stroke, what happens to the piston?
It moves to the top of the cylinder
In the compression stroke, what happens to the pressure?
It increases
In the compression stroke, how does pressure increase?
The piston moves upwards
In the compression stroke, what mainly happens to the fuel/air mixture?
The temperature increases
In the compression stroke, the main result of increased cylinder pressure is what?
Rising temperature of fuel/air mixture
In the power stroke, what causes the piston to drive downwards?
Expansion of combusting gases
In the power stroke, what is the effect of expanding gases in combustion?
Piston moving downwards
In the power stroke, how is the fuel/air mixture altered?
It is ignited and thus expands in combustion
In what stroke (stage) does combustion occur?
Power stroke
In the exhaust stroke, what valve is open?
Exhaust valve
In the exhaust stroke, what valve is closed?
Inlet valve
In the exhaust stroke, what happens to the cylinder?
Piston moves upwards
In the exhaust stroke, as the piston approaches the top of the cylinder head, what happens?
Inlet valve opens and cycle continues
How many times does the crankshaft in the Otto cycle rotate?
Twice
How many strokes in the Otto cycle provide power?
One
How to work out the number of ‘power strokes’ from the number of cylinders?
The number of cylinders = number of power strokes
Relationship between number of power strokes and crankshaft rotations?
Crankshaft rotations is two and power strokes is the same as number of cylinders
How does fuel quality change with engine compression?
Higher compression requires higher-qaulity fuel
What is the penalty of higher performance in engines (and higher fuel-quality)?
Greater cylinder wear
What is the compression ratio?
Ratio of total volume to clearance volume
When does total volume occur?
Bottom dead centre (BDC)
When does clearance volume occur?
Top dead centre (TDC)
When does swept volume occur?
When the piston is in the course of a stroke
Name of volume when piston is in the course of a stroke?
Swept volume
Name of volume at top dead centre?
Clearance volume
Name of volume at bottom dead centre?
Total volume
Total Volume / Clearance Volume =
Compression Ratio
Term given to piston reaching top of travel, furthest from crankshaft?
Top Dead Centre
Term given to piston reaching bottom of travel, closest to crankshaft?
Bottom Dead Centre
Term given to distance the piston moves between TDC and BDC?
Stroke
Term given to diameter of the cylinder?
Bore
What is the bore?
Diameter of a cylinder
What is a stroke?
Distance between TDC and BDC
What item controls the timing of valve opening and closing?
Camshaft
The camshaft is gear-driven by what?
Crankshaft
Relationship between camshaft and crankshaft movement?
Camshaft operates at half crankshaft speed
What rotates at the half-rate of the crankshaft?
Camshaft
How often does an inlet valve open in the four-stroke piston cycle?
Once
How often does an inlet valve open for every two rotations of crankshaft?
Once
How often does the crankshaft rotate fully in a four-stroke cycle?
Twice
Camshaft is said to rotate at what speed?
Half engine speed
What process allows the maximum time for air-fuel intake to occur?
Inlet valve opening prior to TDC and not closing until BDC
The inlet valve opening prior to TDC is known as?
Valve lead
The inlet valve closing not until BDC has passed is known as?
Valve lag
The inlet and exhaust valves being open at the same time is known as?
Valve overlap
When does the ignition spark occur?
Just before TDC and the power stroke commencing
What major process occurs just before TDC and the power stroke commencing?
Ignition spark
What electrical setup does a typical light aircraft’s ignition system have?
Ignition systems in parallel circuit
What provides the necessary high tension electrical current for the spark plugs?
Magnetos
Magnetos provide what?
Electrical current for the spark plugs
Typically, how many spark plugs in a cylinder?
Two
Magneto is mechanically driven by what?
Engine
What term is given to the coil of wire wrapped around a conductor in a magneto?
Armature
In a magneto, what is the purpose of the secondary coil of wire?
Acts as a transformer
What does the transformer do in a magneto?
Transforms primary voltage into a much higher voltage
Basic operation of a magneto?
Magnet rotates near a conductor
Current induced in armature around conductor
Secondary coil transforms into high voltage
High voltage fed to spark plugs
What component controls the timing of the spark plugs from a magneto?
Breaker points
What function do breaker points perform in a magneto?
Break the primary current which induces a high voltage in the secondary current
What component ensures the spark plugs operate at each correct order for the out-of-phase cylinders?
Distributor
How often does the distributor finger rotate?
Once in every complete four-stroke cycle
Once in every two turns of the crankshaft
What is an ignition harness?
The leads bound together in a distributor
Instead of heavy-duty wiring between the battery and starter motor, what is done instead?
Starter motor is remotely controlled using a solenoid-activated switch
A solenoid is typically used for what process?
Electric starter motor
Why would a starter warning light remain illuminated after engine start?
The starter relay sticks and the solenoid has not disconnected
How many sparks are necessary for a start-up?
One spark per cylinder
If only one spark is necessary per cylinder, what provides the spark in ignition?
Left magneto
What happens to the magnetos during ignition?
Left magneto provides high tension supply to spark plugs
Right magneto is de-energised
Spark occurring at fixed number of degrees prior to TDC is known as?
Spark advance
What is kick-back?
Premature ignition of gases during start-up
Crankshaft turns in wrong direction
Two functions of impulse coupling?
Accelerate rotating magnet momentarily to generate a high voltage
Retard ignition-timing at low-cranking
How does impulse coupling generate a high voltage?
By winding up a coiled spring without magnet rotation, energy is stored and released
Magnet accelerates rapidly and generates a large current
What happens to impulse coupling once the engine has started and running at normal RPM?
Coiled spring no longer effects magnet
Spark is produced normally by the engine rotating the magnet
Advantage of impulse coupling in terms of what powers it?
Doesn’t depend on any electrical source so can run without a battery
In impulse coupling, what initially happens as the engine is turned over?
Magnet is prevented from rotating
When impulse coupling prevents a magnet from rotating during initial ignition, what happens to the excess energy?
It winds up a coiled spring
What happens to the Right Magneto system when Left is selected?
It is earthed
Burned gases in an engine are known as what?
Exhaust
How does a tachometer measure RPM?
Engine moves a drive-shaft
Drive-shaft rotation moves a flyweight assembly
Angle at which flyweight assembly moves correlates to an RPM
Typically, a tachometer relies on what major component to read RPM?
Flyweight
