What Is a Magneto and How Does It Work?

If you have ever been around an aircraft with piston engines, you might have heard the term "magneto" thrown around in discussions about the ignition system. While the term may be familiar to some, there is the question of what exactly a magneto is and how it works to power an aircraft's spark plugs to get the engine up and running. In this blog, we will answer these questions as we explore the basics of aircraft piston engines, all while discussing the vital role magneto systems play in these assemblies.

Understanding Aircraft Piston Engines

Before we delve into the fundamentals of magneto systems, it is essential to grasp the basics of aircraft piston engines. This is due to the fact that they are commonly found in small aircraft, powering propellers with a mechanical arrangement that generates thrust. In a piston engine, the primary function is to convert fuel and air into mechanical power, and this process involves four stroke cycles: intake, compression, power, and exhaust. The power cycle is the one that interests us, as it is here where spark plugs come into play.

The Aircraft's Ignition System

To ignite the air-fuel mixture during the power stroke, aircraft rely on an ignition system. The two primary components of this system are the spark plugs and the magneto. The ignition system's main objective is to create a high-voltage electrical spark at the precise moment the piston is ready to begin the power stroke. This spark ignites the compressed air-fuel mixture, resulting in a controlled explosion that drives the piston and turns the engine's crankshaft.

The Magneto System

Magnetos are self-contained ignition systems that generate high-voltage electrical pulses for spark plugs. Unlike many other electrical systems, a magneto does not rely on an external power source, such as a battery or an alternator. Instead, it operates independently, making it highly reliable and suitable for aircraft. The magneto system typically consists of several key components, including a permanent magnet, a primary coil, a secondary coil, a distributor, and a set of breaker points.

The Permanent Magnet

At the heart of the magneto system lies a permanent magnet which generates a continuous magnetic field, and it is mounted on the magneto's rotor while it spins with the engine. As the rotor rotates, it induces a flow of electrons in the coil windings, thanks to the principles of electromagnetic induction.

Primary and Secondary Coils

The primary coil is a winding of wire that surrounds the magnet's magnetic field, and when the rotor spins, it causes the magnetic field to collapse and expand within the primary coil. This variation in the magnetic field induces a voltage in the primary coil, generating low-voltage electrical current.

The secondary coil is also wound around the magnet, but it typically has many more wire turns than the primary coil. This high number of turns amplifies the induced voltage to create a high-voltage spark.

Distributor and Breaker Points

The distributor plays a crucial role in the magneto system, as it directs the high-voltage electrical pulses from the secondary coil to the spark plugs in the correct firing order for the engine. This ensures that each spark plug ignites the air-fuel mixture at precisely the right moment in the engine's four-stroke cycle.

The breaker points are a pair of contact points within the magneto that open and close as the rotor spins. These points are connected to the primary coil and act as a switch to control current flow in the primary circuit. When the breaker points open, it causes the magnetic field to collapse, inducing a high-voltage pulse in the secondary coil. This pulse is then sent to the spark plugs.

How the Magneto System Works

With a grasp of the fundamental components of the magneto system, let us explore how these elements seamlessly unite to generate the vital sparks propelling the aircraft engine.

  1. As the aircraft's piston engine rotates, the magneto's rotor, along with the permanent magnet, spins with it.
  2. The rotating magnet induces a fluctuating magnetic field within the primary coil.
  3. The breaker points open and close as the rotor spins, controlling the flow of current in the primary circuit. When the points open, the magnetic field collapses, creating a voltage spike in the secondary coil.
  4. The high-voltage pulse generated by the secondary coil is then directed to the distributor.
  5. The distributor routes the high-voltage pulse to the appropriate spark plug in the firing order, ensuring that the spark occurs at the right time in the engine's power cycle.
  6. When the spark plug receives the high-voltage pulse, it generates a spark at the electrode gap, igniting the air-fuel mixture and initiating the power stroke.


In conclusion, comprehending the intricacies of the magneto system is imperative for those with an interest in aircraft piston engines and their ignition systems. With its self-contained design, autonomy from external power sources, and precision in generating high-voltage sparks at the perfect timing, the magneto assumes a pivotal role in ensuring the smooth and dependable operation of an aircraft's engine. Consequently, maintaining a reliable magneto and conducting routine inspections and testing are vital to upholding quality and dependability.

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