Internal-combustion engine in which the combustion chambers and cylinders rotate with the driven shaft around a fixed control shaft to which pistons are attached.
The gas pressures of combustion are used to rotate the shaft. In the Wankel engine, the most fully developed and widely used rotary engine, a triangular rotor rotates with an orbital motion in a specially shaped casing, and forms rotating crescent-shaped combustion chambers between its sides and the curved wall of the casing.