Definition
A heavy, rotating metal disc attached to the engine's crankshaft that stores rotational energy and smooths out the power pulses produced by the cylinders firing. In the starting system, the flywheel carries a ring gear around its outer edge that the starter motor's pinion gear engages to crank the engine over.
Plain English
A heavy spinning wheel bolted to the engine. It evens out the engine's running and gives the starter something to grab onto when spinning the engine to life.
Context Anchor
Seen in engine starting-system discussions, especially when describing how the starter turns the engine before it begins running on its own.
Derivation
From 'fly' (to move quickly) and 'wheel.' The name reflects its job: a wheel that keeps moving quickly to carry momentum between power pulses.
Why Pilots Care
Provides the mass needed for reliable starter engagement and smooth crankshaft rotation between power strokes, reducing vibration and wear during start and operation.
Analogy
A spinning bicycle wheel does not stop the instant you stop pushing it; it keeps moving for a while. A flywheel uses that same stored spinning motion to help smooth the engine’s rotation.
Intuition Check
Do not think of a flywheel as one of the aircraft’s landing wheels. In this context, it is an engine part that spins inside the powerplant system.
Example Sentence 1
When the pilot turned the ignition key to START, the starter motor engaged the flywheel and began turning the engine over.
Example Sentence 2
The flywheel’s weight helps the propeller keep turning smoothly between the power strokes of a four-cylinder engine.