Wankel rotary engine powered thousands of aircraft. One of several problems: It spewed castor oil on its pilots.

Bore and Stroke: 146 mm (5.8 in.) x 165 mm (6.5 in.) Following World War I, French Gnome-Rhone ended its production of rotary engines, and began building radial engines under license from English ...

While modern engines feature many tweaks and improvements on the original ideas, they usually aren't as interesting as the strange contraptions engineers experimented with in the early days. Take, for ...