The Wankel engine is a manufacturer-independent design that replaces pistons with a roughly triangular rotor that orbits inside an epitrochoidal housing. A Wankel engine replaces pistons with a roughly triangular rotor that orbits inside an epitrochoidal housing. The three faces of the rotor, together with the housing, form chambers that go through intake, compression, combustion and exhaust as the rotor turns, so there are no reciprocating parts, valves or camshafts in the usual sense.
For aircraft the attraction is a high power-to-weight ratio, compact size, near-absence of vibration and no need for an enriched mixture to cool the engine at full power. These traits explain its use in unmanned aircraft such as the RQ-7 Shadow, whose engine is a Wankel. Variants can also burn kerosene-type fuels with spark ignition.
The drawbacks are a long combustion chamber with large surface area, which gives higher fuel consumption than a comparable piston engine, and sealing between rotor tips and housing, which governs wear, oil use and overhaul interval.
On a datasheet look for rated power in kW at a stated rpm, displacement as chamber volume per rotor, number of rotors, dry mass, BSFC, fuel grade and time between overhauls. Cooling may be air or liquid, and the generator, if fitted, may be counted separately.
A frequent mistake is comparing displacement figures with piston engines directly; the equivalent displacement of a rotary depends on how it is defined, so compare power, mass and fuel consumption instead. Another is judging only by power-to-weight and overlooking BSFC and seal life, which drive endurance and cost.
