Definition
An engine operating cycle in which the piston completes four separate strokes — intake, compression, power, and exhaust — to produce one combustion event. The crankshaft rotates twice for each complete cycle. Most piston aircraft engines use this cycle.
Plain English
The piston moves up and down four times to do one full job: pull air and fuel in, squeeze it, burn it for power, and push the leftover gases out. The crankshaft turns twice to complete this cycle.
Context Anchor
Seen in aircraft engine theory, maintenance training, and descriptions of how piston aircraft engines produce power.
Derivation
‘Stroke’ here means a single movement of the piston from one end of its travel to the other. ‘Cycle’ means a repeating sequence. So ‘four-stroke cycle’ literally means a repeating sequence built from four piston movements.
Why Pilots Care
Virtually all light-aircraft piston engines use this cycle; knowing the sequence helps pilots understand power response, fuel mixture effects, and basic troubleshooting during flight.
Analogy
Think of it like breathing: take air in, squeeze it, use it, then breathe the waste out. The engine repeats those steps very quickly to keep producing power.
Intuition Check
Do not read “stroke” here as a sudden hit or medical event. In an engine, a stroke is one full piston movement inside the cylinder.
Example Sentence 1
The Lycoming O-360 is a typical four-stroke cycle engine, with each cylinder firing once every two crankshaft revolutions.
Example Sentence 2
During preflight, the pilot noted smooth operation through each phase of the four-stroke cycle by listening to the engine sound.