Magneto Ignition System

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