Understanding Magneto: The Engine Igniter

May 6, 2025

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.