Ignition and Engines Flashcards
What are the components of a mageneto?
Primary Coil - few turns, heavy wire
Secondary Coil - lots of turn, light wire
Soft Iron Core - coils are around it
Magnet - rotates
Cam - switches contact breaker off and on
Contact Breaker - on the primary circuit.
Capacitor - Prevents arcing across the contact breaker. Also helps with build up of current
Ignition Switch - turning on removes the primary coil grounding.
How does a magento work?
Magnet rotates, createing current in the primary coil.
When the Cam Opens - the circuit is broken, causing magnetic field to collapse
Secondary coil is energised
Distruibtor sends to the correct spark plug(s)
What does ‘off’ on the ignition switch do?
Creates a short circuit to ground.
preventing the sparks from being produced
Why would a magneto be pressurised?
To prevent arcing at high altitudes
When the starter is moved to on - what does it do?
Break the primary to ground circuit.
( the primary is grounded by default… to reduce accidental problems )
How does an Impulse Coupling work?
Magneto spark is not strong at < 1,000 RPMs
* Used on start up.
* Spring, which is wound.
* The unwinding accelerates the rotor in the magneto
* Producing good spark are low RPMs ( on start )
What does it mean to say the ignition is retarded?
Prevents backfiring
The spark is retarded to fire after the piston is at top of dead center ( usually 15 degrees or more ).
Used for starting.
How does a low tension booster work ( Magnetos)
Magneto spark is not strong at < 1,000 RPMs
* Used on start up.
* Tension Coil produces extra voltage from Battery, to primary coil.
* Spark is retarded 20 or 30 degrees from top of center
What are the 4 types of cylinder arrangement?
Inline
V - usually for more than 6 cyclinders
Radial
Opposing
What are the angles for V cyclinder arrangements?
And why does it matter?
90 degrees
60 degress
45 degrees
reduce crankshaft length and vibration
What are the advantages of Horizontal Opposing
Short Crank Shaft
Good for air cooling
What is the definition of a HP?
550lbs lifted vertically per second
Equal to 746 watts
Types of HP
Brake HP
Indicated HP
Friction HP
Thrust or Shaft HP
How are Brake HP, Indicated HP and Fricition HP related
BHP=Indicated - Friction
What causes CO2?
Incomplete combustion.
Steps for suspected CO2 in cabin
Turn off Cabin Heat
Max Fresh Air
Open window if environment, POH allow
Supplementary Oxygen
Lean Fuel
Inform ATC
Land as soon as practicable
Seek medical attenion on landing
Get inspection of aircraft
Main parts of a float carb - and how it works
Parts
Main Jet
Venturi
Throttle
Float Chamber
Pivoted Float
Needle Valve
Process
Air passes the venturi
Travels faster - creating low pressure
Fuel sucked in and mixed
Throttle controls weight of mixture send to engine.
Need valve automatically adjusts for fuel level
What happens at low rpm to the mixture?
Mixture gets weak, as the throat is nearly closed.
Need
Idle Bleed
Idling Jet
Means that fuel by passes the venturi.
Note: Not sure ‘how this works’
How does the mixture control work?
Needle valve to main jet.
Mixture fully open means valve is fully open ( max fuel)
Mixture fully closed means valve is fully closed ( idle cut off )
Main components of a fuel injection system
An engine driven fuel injection pump
fuel/air control unit
fuel manifold unit
fuel nozzles
What is the difference between Direct and Indirect Fuel injection systems
Direct
Fuel is put onto the cylindar head
Indirect
Value is put in above the inlet valve
Advantages of Fuel Injection
Better Fuel Distribution
Less suspectiable to icing
Smooth acceleration
What are the stages in 4 stroke engine?
Compression
Power
Exhaust
Intake
What causes detonation?
Fuel temp gets too high and spontanously ignites
Affects all Cylinders
Usually means the engine is overleaned
Sounds like pinking or knocking
What causes pre-ignition (and impacts)
Cause
Fuel ignited too early.
Incorrect timing adjustment
Carbon built up
Affects
Affects 1 cylinder
results in rough running
loss of power
engine damage.
How to fix detonation?
Enrich the mixture
Increase airspeed
Reduce throttle
Why do high compression engines need high octane fuel?
Compression is higher
So fuel is more likely to detonate
So high octane ( = more detonation resistance ) is needed
At a fixed RPM - what is the relationship between mixture, power, Cylinder Head temp and Specific fuel consumption
Richer = more fuel consumption
Power has a best mixture setting
Cylindar temp is max on the leaner side
What are the mixture ( air to fuel ) ratios at high power, idle and cruise
Parts of a Crankcase
Breather
Crankshaft Bearing Support
Mounting face for accessories
Cylinder mounting face
Webs - for structure
How does the Crankshaft work?
To create rotating force
Has 1 crankthrow per cylinder
Crankthrow has 1 ??? + 2 crankheads
Describe the Piston head and rings
3 rings:
- Compression - keeps gases in
- Oil control - provides oil, prevents it from getting to the head
- Oil scrapper - collects oil and gravity has it fall back to the sump.
Main parts of the cyliender barrel
Mounting Flange - to connect to Crankcase
Threads - to connect to the head
Cooling fins -
Parts of the valve mechanism and how it works
Camshaft - controlled timing gears. 1/2 crankshaft speed
Tappets - up and down from the crankshaft
Pushrods - connect from Tappets to rockers
Rockers - press down on the Value spring to open the value.
Where/what is the tappet gap?
Gap between the rocker and the valve inlet.
Old school - manual adjustment
Modern - auto hydrolic
Why 2 Springs for valve inlets?
Different diameters to prevent valve bounce.
4 stoke cycle is…
Induction
Compression
Power
Exhaust
Value timing - what is it and key impacts
Timing of when values are opened and closed.
Inlet - opened usually 10 degree before TDC
Exhuast - opened usually 10 degrees before BDC
Why does cyclinder pressure matter during the cycle?
It assists with induction and scavanging
What is Valve Overlap - what does it achieve?
The inlet value opens, while the exhuast value is still open.
Creates a low pressure, sucking fuel in - while also pushing exhuast out.
Within the engine strokes - what is induction and scavenging?
????
Ignition timing - when is the spark usually created?
10 degrees before TDC
Helps with timing of the power stroke
In the power stroke - when is the max power ( relevant to TDC)?
Usually 10 degrees after TDC
With ignition timing, what is Advanced vs Retarded?
When would each be used?
Advanced - spark fires before TDC
Retarded - spark fires after TDC
Usually advanced - except during start, usually retarded.
For efficency this timing should be adjusted depending on RPM. Does not matter in light aircraft due to the low range.
