Definition
The first of the four strokes in a four-stroke reciprocating engine cycle, during which the piston moves down from the top of the cylinder to the bottom while the intake valve is open, drawing a fresh fuel-air mixture into the cylinder.
Plain English
The step where the piston moves downward and pulls a fresh mix of fuel and air into the cylinder, ready to be burned.
Context Anchor
Seen when studying how a reciprocating aircraft engine produces power during the four-stroke cycle.
Derivation
‘Intake’ comes from ‘in’ + ‘take,’ literally meaning to take something in. ‘Stroke’ refers to one full movement of the piston from one end of the cylinder to the other. Together: the stroke during which the cylinder takes in its charge.
Why Pilots Care
Correct understanding of the intake stroke is essential for grasping how an engine produces power and why valve timing and mixture control directly affect performance and safety.
Intuition Check
Do not think of “stroke” here as a medical event or a brush mark. In an engine, a stroke is one complete piston movement in one direction.
Example Sentence 1
During the intake stroke, the descending piston pulls the fuel-air mixture into the cylinder through the open intake valve.
Example Sentence 2
Proper ignition timing depends on the intake stroke having fully charged the cylinder before the compression stroke begins.