Bring the spin

The starter motor on an airplane engine is a part of a clever starting system that is more complex than you might think.

When you twist the ignition switch key on most training aircraft, you’ll notice three detents followed by a spring-resisted segment. The first detent turns on the right magneto, the second detent the left magneto, the third detent both magnetos, and the final twist momentarily completes a low-current electrical circuit that closes high-current-capacity points on the starter contactor, connecting the battery directly to the starter and resulting in starter motor rotation.

Starters on Lycoming engines (shown in the illustration) connect to the engine through a starter drive that extends to mesh its pinion-gear teeth with the engine’s ring-gear teeth when the starter motor begins to rotate, and retracts once the engine roars to life so that the starter is not damaged by the fast-turning engine.

After the engine starts, releasing the ignition key moves the ignition switch to the Both magnetos setting, cutting power to the starter contactor and starter motor.

Unless otherwise stated in the aircraft pilot’s operating handbook, Lycoming advises the pilot to engage the starter for a maximum of 10 seconds at a time, followed by 20 seconds of cool-down time between starting attempts. This is because the starter motor generates a significant amount of heat and has no cooling fan. An overheated starter can damage internal components and require repair.

Some airplane starters are energized with a push button and others with a pull knob. Lycoming engines typically have the starter mounted on the front of the engine while Continental and Rotax engines have the starter mounted on the back of the engine. Regardless, similar principles apply.

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