How It Works: Magneto - AOPA Lecture Notes

Overview

• Presenter: Julie Summers Walker
• Publication Date: December 1, 2019
• Illustration by: Steve Karp

Magneto: The Source of the Spark

• Magneto is a self-contained high voltage generator.
• Provides ignition to the engine via spark plugs.

How Magneto Works

• A magnet spins near a coil of wire.
• Faraday’s Law: Any relative motion between magnet and wire induces current flow.
• Spin of magnet generates strong magnetic force held by a primary coil.
• Contact points open, causing rapid magnetic flow.
• High voltage generated in secondary coil ignites spark plug, firing the engine.
• Two magnetos (left and right) in most general aviation (GA) aircraft.
  • Each fires one of two spark plugs per cylinder.
  • Redundancy ensures engine continues running if one fails, albeit less efficiently.

Applications and Historical Context

• Primarily used in:
  • Lawn mowers
  • Chain saws
  • Old tractors
  • Light aircraft
• Advantages:
  • Self-contained, independent of battery/electric systems.
  • Engine runs during battery or electrical failure.
• FAA historically requires ignition to be separate from aircraft’s battery/electric system.
• Modern electronic ignition systems gaining popularity due to better performance.

Additional Resources

• Learn more about P-lead: Link

About the Author

• Julie Summers Walker: AOPA Senior Features Editor, joined AOPA in 1998.
• Student pilot, working towards solo.