Definition
A type of aircraft engine starter that uses a heavy flywheel spun up to high speed and then mechanically engaged with the engine crankshaft to crank it over for starting. Energy is built up in the flywheel first (by hand crank or electric motor), then released through a clutch to turn the engine.
Plain English
A starter that first spins a heavy wheel up to a high speed, stores energy in it, and then connects that spinning wheel to the engine to turn it over and start it.
Context Anchor
Seen in aircraft engine starting-system descriptions, especially for older or larger piston engines that need a strong burst of turning force to start.
Derivation
Inertia comes from the Latin iners, meaning 'inactive' or 'idle.' In physics, inertia is the tendency of a moving mass to keep moving. The starter is named for how it works: a heavy flywheel is wound up to high speed, and the inertia stored in that spinning mass is what cranks the engine when released.
Why Pilots Care
Enables reliable starting of large or cold engines while reducing battery load and avoiding damage from direct high-torque cranking.
Analogy
Like winding up a child's pull-back toy car: you build up energy in the spring first, then release it all at once to make the wheels turn.
Grounding Statement
The starter stores energy in a spinning wheel before using it to turn the engine.
Intuition Check
Do not read “inertia” as meaning the starter is weak or slow. Here it means the starter uses the stored motion of a spinning mass to help turn the engine.
Example Sentence 1
The mechanic energized the inertia starter for several seconds, waited for the flywheel to reach full speed, then engaged it to crank the radial engine.
Example Sentence 2
In cold weather operations the inertia starter allowed the crew to crank the engine without draining the aircraft battery.