AGK Engines Flashcards
What perfoms Ignition Timing and why is it important?
Performed by magnetos
Is necessary as it takes a finite time for the mixture to burn
Which engine ignites combustion by the heat of compression?
Diesel Engine
Which engine uses a spark to initiate ignition
Petrol Engine
Name the strokes in a 4 stroke engine
Induction, Compression, Power, Exhaust
Induction Stroke
Inlet Valve opens just before TDC
Volume Increase
Pressure/Temp decrease
Inlet valve closes just before BDC
Compression Stroke
Inlet/Exhaust valve closed
Stroke starts when piston is on the up
Volume decreases
Pressure/Temp increases
Just before TDC, mixture is ignited
When is the mixture ignited and how?
Just before TDC
Spark plug - burns fuel instantaneously
Power Stroke
Rapid rise in P/T
Inlet/Exhaust closed
Volume increases
Pressure/Temp decreases
Only stroke to produce POWER
Exhaust Stroke
Starts at BDC, as piston begins to rise
Volume decrease
Pressure/Temp increase
Piston pushes out the waste gases
Flame rate of aviation fuel mixed with air
60/80ft per second
The cramk assembly is compromised of…
Crankshaft
Connecting rods
Pistons
Hydraulic tappets are used to…
Automatically adjust the tappet clearance
Why are valves often filled with sodium?
To take away heat
Crank assembly
Connecting rods
Pistons
Crankshaft
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 is…
Gives a higher energy retarded spark
A high tension booster is…
A vibrartor directly connected to the high tension side (secondary circuit) and then Primary circuit
(Shower of sparks)
A low tension booster
A set of pulses to the primary circuit
(Low tension side)
Pre flight magneto checks are…
Drop Check
Dead Cut check
What should happen if magneto check (Drop/Dead) reveals an issue?
Aircraft shut down
Fault logged in the AML
RPM drop range on a DROP magneto check
Drop of 100-175rpm indicates normal magneto operation
Drop greater than 400rpm means there may be a faulty spark plug or p lead - report immediately!
How to perform a Drop check
At 1000-1200rpm switch each magneto off in turn
Monitor for a drop in rpm and engine sound
Engine should continue to run
What does a dead cut check ensure?
ignition switch circuit is operating correctly
Means engine can be shut down electrically
Should a DEAD cut check be performed before or after DROP check?
After and when engine is at 75%rpm (2000,2200rpm)
How to perform dead cut check
Ignition - switch OFF briefly
Engine rpm should rapidly decay (magnetos switched off)
ignition - switch ON before engine completely stops
If one magneto fails in flight, what happens?
None of the cylinders will stop firing
What powers the spark plugs during engine start up?
Magnetos
What converts continuous AC to a series of pulses?
Magneto
Design of ignition switch system…
Fail sake during flight
Allows engine to still fire even if switch fails
Potential hazard to anyone close to a stationary prop
What does a closed ignition switch do?
Grounds magneto and makes the ignition circuit safe
A blocked spark plug is said to be…
Fouled
A spark plugs body forms an…
Electrode
AVGAS is made up of?
15% carbon
85% hydrogen
An octane rating is
A measure of resistance to detonation
Detonation flame rate?
60-80 ft/s
What colour is AVGASLL?
Blue
Better for environment
What colour is AVGAS 100?
Green
Environmentally worse
What does LL stand for?
Low Led
What colour is AVGAS 80?
Red
Only for authorised certain aircraft
A fuel sample must be…
Clear and bright
Free of sediment
No entrained water
have a max water content of 30ppm
What does ppm stand for?
Parts per million
Causes of detonation…
Fuel with too low octane
incorrect (weak) mixture
Anything that could unduly raise temperature/pressure
High Engine temperature
Detonation flame rate?
1000ft/s
What is pre ignition?
Ignition of mixture before spark plug has fired
What causes Pre ignition?
Hot debris within cylinder (often carbon deposits)
Ignition malfunction (damaged spark plug)
High cylinder temp
Does detonation occur before or after pre ignition?
After
Mixture ratios
20:1 Lean (increased detonation risk)
15:1 Chemically correct (ideal ratio)
8:1 Rich ( increased detonation risk)
Takeoff mix
11:1
Rich mixture (for large power output), makes cylinder cooler
Cruise mix
17:1
Lean, it increases range
CHT and EGT
Cylinder head temp
Exhaust gas temp
How are mixture ratios measured?
By mass
Why does a 15:1 mix (ideal), create high CHT?
flame rate is slower, so is in contact with cylinder head for longer
What is Ineffective crank angle?
Period of relatively little movement of the piston around TDC and BDC
Inlet valve lag is when…
Inlet valve remains open just after BDC as the compression stroke begins
Helps fill chamber
Valve closes just after the piston leaves ineffective crank angle
Inlet valve lead is when…
Inlet valve open early, just before TDC (end off exhaust stroke)
Exhaust valves still open at the end of exhaust stroke
Exhaust valve lead is when…
E valve opens before BDC on P stroke
Longer time to clear cylinder waste gases
Exhaust valve Lag is when…
E valve is open until slightly after TDC
Remaining gases exit under own momentum
TDC
Top Dead Centre
BDC
Bottom Dead Centre
Where does valve overlap occur?
Around TDC between exhaust/induction strokes
What is Torque?
The capacity to do work (leverage)
ibs, ft, nm
Torque equation
Force (F) x Distance (D)
Force Equation
Pressure (P) x Area (M^2)
Piston Engine Principles
Chemical Energy
Heat Energy
Pressure Energy
Mechanical Energy
How to check health of engine?
Oil temp gauge
Oil Pressure gauge
CHT gauge
Secondary functions of engine oil?
Protect against corrosion
Cleaning engine
Cooling engine by absorbing heat and dissipating it to surrounding atmosphere
An ideal oil should be…
Discourages sludge formnation
Inhibits corrosion
Suitable viscosity over wide range of temps
Auxiliary spark augementation methods
Impulse coupling
Low tension booster
High Tension booster
Excessive engine cooling in a decent can cause damage to the engine, why?
Thermal shock
Impulse coupling components…
HUB CAM with flyweights
Spring
Shell (BODY)
Power Equation
Torque x RPM
What is the ‘stroke’
Distance between TDC and BDC
How many degrees does the crank shaft rotate?
720 degrees
How many strokes in 1 cycle?
4
How many degrees does the crankshaft rotate between TDC and BDC
180 degrees
The … rotates 1/2 speed of the crankshaft
Camshaft
What does a carburettor do?
Mixes fuel and air before it reaches the engine
What does CBP stand for?
Contact Breaker Point
’
What components seal the skirt rings?
Piston rings
What component lifts the push rods?
Cams
What does pressure do inside a carburettor?
Allows fuel to flow
Carb icing symptoms
Loss of rpm
Recued inlet MAP
Decreased EGT
Rough running
Jammed throttle
Engine stops
Carburettor alternative?
Fuel injection, fuel injected straight into cylinders
What is added to fuel to reduce detonation?
Lead
What is the pressure like inside the float chamber of a carburettor?
Atmospheric
RAM effect
When air is taken aboard an aircraft in flight, it undergoes an increase in pressure
Q
1/2 pV^2
Engine flywheel gear sequence
Starter motor
Starter overrun clutch
Flywheel gear
The higher compression ratio in a diesel engine means that the engine block has … than similar powered petrol engine
Less weight
What do thick primary windings do in the magneto?
Create big pulses which are then sent to the spark plug
What does the CBP do?
Cuts the current at the peak and then goes back to zero and builds up again
What happens to the pressure on a cold engine start up?
Goes into the amber range on the gauge
~ This has to return to green before taxiing
Dry Sump Schematic
Liquid Cooling System
When is the cow flap opened and closed?
Closed during decent - otherwise cylinders will be over cooled
Opened during t/o to increase cooling
What should engine oil be?
Correct specification
Unopened bottle
What type of piston engine loses power during initial part of the climb to high altitude?
Normally aspirated
Where are intercoolers located?
Between turbocharger and inlet manifold
Waste gate principles…
Sensitive to ambient pressure
Controlled by waste gate controller
Controls rotational speed of the turbocharger
Oil pressure gauge
Oil temperature gauge
Measures oil pressure just after the oil filter
Measures oil temperature in oil return line
Where does a propeller make the most amount of thrust?
75% blade radius
Camber line and chord line are between?
Leading and trail edge
Does a petrol or diesel engine have a greater thermal efficiency?
Diesel
Higher compression ratio 20:1. But Petrol one has 10:1
What is the blade angel?
Angle in-between Chord line and Plane of Rotation
What is the most efficient AoA and when is it reached?
4 Degrees
Reached in the cruise
The effect of TAS on a fixed pitch propeller
As TAS increases, AoA decreases
As TAS decreases AoA increases
FYI, AoA is large at the start of T/O but as TAS increases, the propeller becomes more efficient
The effect of RPM on a fixed pitch propeller
As RPM increases, AoA increases
As RPM decreases, AoA decreases
Why are the Propeller blades twisted?
To preserve the AoA across the whole blade
Blade pitch angle must be reduced from root to tip
Effects on efficiency with different AoA
Optimum AoA (4 degrees) - Designed cruising speed (efficient)
High AoA - Higher than cruising speed (efficiency decreases)
Low AoA - Lower than causing speed (efficiency decreases)
What happens to the AoA if TAS increases/decreases in a Variable Pitch Propeller?
Stays the same
What happens to the AoA if RPM increases/decreases in a Variable Pitch Propeller?
Stays the same
Feathered, Coarse and Fine diagrams
What happens if ice forms on the spinner/propellers?
Anti ice system takes away the ice, either by,
Electrical heater system
Fluid dribbled over area
What does a reduction gearbox do?
Reduces RPM produced by propellers
What happens when forces are equal and opposite on a propeller assesmbly?
Stable propeller RPM can be achieved
What is a centrifugal twisting moment (CTM)
Each end of blade produce opposing moments
Counteracted by centrifugal weights at the blade root
Tendency to ‘fine off’
Weights help at low RPM as centrifugal force drops off
What is Aerodynamic Twisting Moment (ATM)
Blade CP is ahead of the pitch change axis
Aerodynamic force generates a movement around the axis point driving the propeller towards coarse
Which is more dominant, CTM or ATM and why?
CTM is more dominant because…
Wind milling prop causes both actions to combine - prop drives to fine due to increased drag
SEP…
MEP…
PCU…
Single Engine Piston
Multi Engine Piston
Propeller Control Unit
If propeller control lost, why is it better for the props to be in the ‘fine’ position?
Can land/GA
Incraese airflow round the props, increase in thrust if it were to turn back on
Change in exhaust back pressure causes…
Increase in volumetric efficiency
What does FADEC reduce?
Number of controls In cockpit
Engine handling task
On a constant speed prop, excessive power demand may be indicated by…
Boost warning light
If you increase power substantially, the overboots warning light will come onion you don’t adjust the…
RPM Lever
High SFC indicates…
Poor efficiency
On a constant speed prop, phrase for throttle and RPM lever relationship is
‘Rev up - throttle back’
On a petrol engine, mixture adjustment can be finessed by referring to…
EGT gauge
For a fixed pitch prop at any alt, increasing RPM does what to the power output?
Increases power output
On a petrol engine, lean mixture required in the cruise is set using the…
Mixture control lever
On a constant speed prop, power is indicated by MAP and
Torgue gauge
On a fixed pitch prop, power is approx indicts by
RPM gauge
On a constant speed prop, power is estimated by meaning MAP in the … and/ or by meaning the …
Manifold
EGT
FADEC stands for…
Full Authority digital engine control
Can carburettor engines ben fitted with FADEC?
No
Does oil temp increase in the climb with a low speed and high power?
Study increase in oil temp
