Unless you’re lucky enough to fly a turbine or an engine with an electronic ignition system, the internal combustion engines you fly behind or between likely operate using a simple system involving a magnet, coil, condenser and contact points. As the spinny thing in the accessory case turns the magneto drive shaft, the magnet rotates and imparts electrical energy to the coil. When the points close, a jolt of electricity is sent from the coil to the respective spark plug wire to the attached spark plug and, kaboom, the cylinder fires. At least that’s the way it’s supposed to work.
Meanwhile, a second magneto does the same thing, preferably at the same time, to a second spark plug in the same cylinder. Between two magnetos and two spark plugs operating in sync, the engine will deliver power with a bit more efficiency than a conventional engine with only one spark plug per cylinder, everything else being equal. There’s also a so-called “dual” magneto, which uses only one drive shaft but fits two ignition harnesses. The design can simplify installation and maintenance but at the expense of some redundancy. And redundancy is always good.
