Rotary engine was first conceived by a German named Felix Wankel in the
1920's but it wasn't until the late 50's that one was ever built.
unusual design of the engine uses triangular pistons called rotors which
rotate rather than move up and down as most internal combustion engines
do. A clear explanation can be found at
rotary engine is compact, lightweight and contains about 10% of the
moving parts of conventional piston engines. They also produce the
equivalent power of a piston engine with twice it's capacity.
drawbacks of the rotary engine are that they have a high fuel
consumption and have been often been accused of being unreliable.