10 Questions
What is the effect of shielding around the ignition lead on capacitance?
It increases the capacitance
What is the additional energy requirement due to ignition lead capacitance?
More magneto primary current is required to fire the plug
What is the purpose of a dual ignition system in an aircraft?
To increase reliability of the ignition system through redundancy
What is the function of the spark plug in an ignition system?
To conduct a short impulse of high-voltage current through the combustion chamber wall
What component controls all units in an aircraft ignition system?
Ignition switch
What happens when one magneto or spark plug fails in a dual ignition system?
The engine runs normally with a slight decrease in power
What is the effect of shielding on the magneto's energy requirement?
The magneto requires more energy
What type of ignition system is typically used in certificated aircraft?
Dual ignition system
What is the purpose of the magneto in an ignition system?
To produce enough energy to charge the capacitance and fire the plug
What is the effect of a failed magneto in a single ignition system?
The engine stops running
Study Notes
Ignition System
- A magneto ignition system generates current by using a permanent magnet, coil of wire, and relative movement of the magnetic field
- Typical voltage output of a magneto ignition system is around 20 kV
Magneto Operation
- Magneto generates electrical power by rotating the permanent magnet and inducing current flow in the coil windings
- Current flow generates its own magnetic field, which collapses across a second set of windings to produce a high-voltage
- This high-voltage is used to arc across the spark plug gap
Magnetic Circuit
- The magnetic circuit consists of a permanent multi-pole rotating magnet, soft iron core, and pole shoes
- Electrodes of the distributor block are numbered consecutively in the direction of distributor rotor travel
Ignition Harness
- The ignition harness contains insulated wires for each cylinder, connecting the magneto distributor block to the spark plug
- The ignition harness leads provide a conductor path for the high-tension voltage to the spark plug and shields stray magnetic fields
Importance of Shielding
- Unshielded magnetos and ignition leads can act as antennas, picking up random frequencies and causing electromagnetic interference
- Shielding prevents radiation of energy into the surrounding area and increases capacitance, requiring more magneto primary current to fire the plug
Dual Ignition System
- Standard certificated aircraft incorporate a dual ignition system with two individual magnetos, separate sets of wires, and two spark plugs per cylinder
- This design increases reliability through redundancy, allowing the engine to continue running normally even if one magneto or spark plug fails
Ignition Switches and Spark Plugs
- Ignition switches control all units in the aircraft ignition system
- Spark plugs conduct a short impulse of high-voltage current through the wall of the combustion chamber
Generates electrical power through the rotation of a permanent magnet and coil windings, producing a typical voltage output of 20 kV.
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