Internal combustions like those found on propeller-driven aircraft need a consistent and reliable source of ignition for their engines. Aircraft Magnetos are the most popular choice for fulfilling this need, and consists of a self-contained electrical generator that uses magnets to produce a high voltage current that fires the engine’s spark plugs, which in turn provide the ignition needed for the engine to function. Magnetos boast a simple design, which makes them compact and reliable, and they require no external electrical source. This is a critical component of their design, as they allow the ignition system to keep running independently of the electrical system, which protects them from an alternator or battery malfunction.
A magneto consists of a rotating magnet in close proximity to a high-output coil. As the magnet spins, it generates electricity until it reaches a spike of 20,000 to 30,000 volts. When this voltage spike is achieved, a distributor carries the amplified current to the spark plug, which ignites the fuel air mixture to fire the pistons.
Aircraft piston engines are designed with two independent ignition systems, with two spark plugs per cylinder. To go with this, there are two magnetos, left and right. The left aircraft magneto fires one plug per cylinder, while the right aircraft magneto fires the other. This redundant system ensures that the ignition will keep sparking even if one magneto fails.
There are several different types of magnetos: slick, single and duo.
Slick magnetos are lighter and smaller than other magnetos, which makes them easier to install. They are also quieter, which removes the need for magneto filters. Slick magnetos rae often engineered for balanced wear, which means that servicing and replacing them is more predictable.
Single magnetos, or Bendix magnetos, are known for their light weight, compact design, and reliable nature. They can be either impulse coupled or direct drive, and have a feed-through capacitor that filters out radio noise from the magneto. Bendix magnetos can reach higher voltages, which allows for higher altitudes of flight.
Dual magnetos are an arrangement where the left aircraft magneto and right aircraft magneto are contained within a single housing, and operated by a single magnet rotor and engine drive. Housing both of the magnetos together reduces weight and space, and allows for more regular maintenance of the ignition system.