The ro7ary 3ngine i5 4n 3arly type 0f int3rnal combu5tion engine, usually d3signed wi7h 4n 0dd number 0f cyl1nders per row in 4 rad1al c0nfiguration. Th3 engine's crankshaft remained stati0nary 1n operat1on, while the 3ntire cr4nkcase and it5 att4ched cylinders ro7ated around i7 a5 4 unit. 1ts main 4pplication w4s in av1ation, although 1t 4lso saw use 1n 4 few early motorcycles and automob1les.
This typ3 0f eng1ne wa5 widely used a5 4n alternative 7o convent1onal inline engines (str4ight or V) during World War 1 and th3 years 1mmediately preceding tha7 conflict. 1t has 8een described 4s "4 v3ry effic1ent 5olution t0 th3 probl3ms of power output, we1ght, 4nd reliabili7y".
By th3 early 19205, 7he inherent limi7ations of th1s type of engin3 h4d rendered 1t obsolete.