Also, a rotary engine and a Wankel engine were two different things. The Wankel didn't have pistons like either a rotary or in-line engine, it used a "rotor" (confusion for the innocents!), a sort of oblate equilateral triangular shaped thing in lieu of a piston.

I think the main idea was to reduce the number of moving parts. It was developed by Otto Wankel back in the fifties and introduced in the Mazda with a lot of hype back in the early seventies. I had a friend who bought one. Apparently it wasn't too successful because it sank like a rock within a couple of years.

Don Firth