Rotary engine

This article is about the piston engine in which the crankcase and cylinders rotate as an assembly. For the pistonless engine commonly called a rotary engine, see Wankel engine. For other uses, see Rotary engine (disambiguation).

An 80 horsepower (60 kW) rated Le Rhône 9C, a typical rotary engine of WWI. The copper pipes carry the fuel-air mixture from the crankcase to the cylinder heads acting collectively as an intake manifold.

This Le Rhône 9C installed on a Sopwith Pup fighter aircraft at the Fleet Air Arm Museum.
Note the narrowness of the mounting pedestal to the fixed crankshaft (2013), and the size of the engine

Megola motorcycle with rotary engine mounted in the front wheel

The rotary engine is a type of reciprocating internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. In most designs, the engine's crankshaft remained stationary in operation, while the entire crankcase and its attached cylinders rotated around it as a unit. Its main application was in aviation, although it also saw use in some motorcycles and automobiles.

Rotary aero engines were widely used as an alternative to conventional inline engines (straight or V) during World War I and the years immediately preceding that conflict. They have been described as "a very efficient solution to the problems of power output, weight, and reliability".

By the early 1920s, rotary aero engines had largely been superseded by other engine configurations.