What is an Aircraft Magneto and How Does It Work?

Posted on November 13, 2018 James Hinds Aircraft

Whether you’re driving a car or piloting a plane, to start the engine, all you really do is turn the ignition key or push the start button. That’s all it takes. But have you ever wondered how such a simple movement causes the spark plugs to fire and the engine to start? The answer is a magneto, a simple and highly reliable electrical generator.

Aircraft magnetos are engine driven electrical generators that use permanent magnets and coils to produce high voltages to fire the aircraft spark plugs. Because aviation runs on redundancy, in every aircraft piston engine, there are two independent ignition systems. There are two aircraft spark plugs per cylinder and a left and right aircraft magneto. The left and right magnetos each fire one plug per cylinder, allowing smoother and more complete combustion of the fuel mixture while still allowing for the redundant safety net in the event that one of the magnetos fail.

Aircraft Magnetos, as you would expect by the name, generate a voltage with the help of magnets. Each magneto is equipped with a permanent magnet on a rotor that spins in close proximity to a high-output coil of wire with two windings. The first winding is made with heavy copper wire and the second with finer wire. As the magnet spins, a magnetic flux is generated and passed through the first winding, creating a magnetic flux linkage. The number of magnetic flux linkages is not constant and generates a voltage as the number changes. However, this is not enough to fire the spark plugs. The second winding creates a voltage that is about 100 times stronger when the breaker points connected to the first winding open, collapsing the magnetic field and prompting a large change in magnetic flux linkages. The change in magnetic flux linkages creates a voltage that is amplified to 20,000 volts and released to ignite the spark plug by the second winding.

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