The starter is a system on the aircraft designed to use electrical power from the batteries to rotate the engine at a speed high enough allow for combustion. The system consists of a source of electricity (battery), wiring, switches, and solenoids to operate the starter and starter motor. See the video below for a visual explanation: <div class='iframe-container'><iframe width="560" height="315" src="https://www.youtube.com/embed/kFsl5r34lCI?si=QOscDG1jvZhADOe6" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe></div> # Why use a solenoid? Rather than provide power directly to the starter motor, the ignition switch is wired through a solenoid that transfers that power to the motor. This is because the power required by the starter motor is large, and conncting the starter directly to it would require a large switch and heavily insulated wiring. Another advantage of the solenoid is the linear motion it produces when engaged. When supplied with power, the core of the solenoid shifts back, and since it is connected to the pinion, this allows it to push the pinion forward and lock with the flywheel. # The Pinion The pinion is what connects to the flywheel and allows it to rotate the engine to a sufficient rpm for starting. It uses a helical gear to rotate it slightly as it engages on the flywheel to mesh smoothly and prevent any possible damage. In addition to this, a one way clutch is used to ensure that the starter motor is not oversped when the engine starts running.