The term '''''rotary combustion engine''''' has been suggested as an alternative name for these engines to distinguish them from early (generally up to the early 1920s) aircraft engine+s and motorcycle engine+s also known as ''rotary engine+s''. However, both continue to be called ''rotary engines'' and only the context determines which type is meant.
The basic concept of a (pistonless) rotary engine avoids the reciprocating motion of the piston with its inherent vibration+ and rotational-speed-related mechanical stress+. the Wankel engine is the only successful pistonless rotary engine, but many similar concepts have been proposed and are under various stages of development. Examples of rotary engines include:
Pistonless rotary engine+ A pistonless rotary engine is an internal combustion engine that does not use pistons in the way a reciprocating engine does, but instead uses one or more s, sometimes called rotary pistons.