Definition
A propeller arrangement in which two propellers are mounted on concentric, coaxial shafts driven by the same engine, with one propeller turning clockwise and the other turning counterclockwise. The two propellers are positioned one behind the other on the same thrust line, and the opposing rotation cancels the torque and gyroscopic effects that a single large propeller would produce.
Plain English
Two propellers stacked on the same shaft, spinning in opposite directions, both pulling (or pushing) the aircraft along the same line. Because they spin opposite ways, the twisting forces they create cancel each other out.
Context Anchor
Seen in aircraft systems descriptions, aircraft operating handbooks, and discussions of propeller-driven aircraft with unusual or high-performance propeller installations.
Derivation
From Latin contra, meaning 'against,' and rotate, meaning 'to turn.' The name simply describes two propellers turning against each other on the same axis.
Why Pilots Care
The opposing rotation cancels the twisting force that would otherwise pull the aircraft left or right, allowing straighter climbs and reduced control input at high power.
Intuition Check
Do not read “contrarotating” as just “more than one propeller.” The important point is that the two propellers turn in opposite directions on the same centerline.
Example Sentence 1
The contrarotating propellers on the aircraft eliminated the strong left-turning tendency normally felt during a high-power takeoff.
Example Sentence 2
During preflight the mechanic inspected the gearbox that drives the contrarotating propellers to confirm proper synchronization.