Definition
A type of internal combustion engine in which each piston completes four separate strokes — intake, compression, power, and exhaust — to produce one power event. The intake stroke draws in the fuel-air mixture, the compression stroke squeezes it, the power stroke ignites it to drive the piston down, and the exhaust stroke pushes the burned gases out. Most piston aircraft engines operate on this 4-cycle (also called four-stroke) principle.
Plain English
An engine that goes through four steps to make power: suck in fuel and air, squeeze it, burn it, then blow the leftovers out. Then it starts again.
Context Anchor
Seen in aircraft piston-engine discussions, especially when describing how a typical light-airplane engine produces power.
Derivation
Cycle' comes from the Greek 'kyklos' meaning 'circle' or 'wheel' — something that goes around and repeats. A 4-cycle engine repeats the same four-step sequence over and over for as long as it runs.
Why Pilots Care
Understanding the 4-cycle sequence helps pilots recognize normal engine sounds, diagnose rough running, and perform accurate preflight and in-flight checks on piston aircraft.
Intuition Check
Do not read 4-cycle as four separate engine cycles. It means one repeating engine cycle made of four piston strokes.
Example Sentence 1
Most general aviation airplanes are powered by 4-cycle piston engines similar in principle to a car engine.
Example Sentence 2
During the engine run-up the pilot listened for the smooth rhythm produced by the 4-cycle power strokes.