#radial engine

Want to really annoy a Mazda fan with a Wankel engine without whispering "apex seals" into their ear? Tell them it's not a real rotary engine.

Before the pistonless Wankel design, "rotary engine" meant something very different, where the entire engine would be spinning along with whatever it was driving. The main use for this was very early airplanes. The propeller would spin, and so would the engine! You get the benefit of increased airflow and less worry about gears, since the crankshaft is basically the airplane itself and the engine spins around it.

There aren't any reciprocating parts, and you can use a lighter construction overall. The downside: A "total loss" oil system. There's no easy way to get oil back to the middle of the engine to send it back through the cylinders, so oil must be burned along with the fuel.

The increasing scale of airplanes after the First World War lead to them quickly becoming obsolete compared to water-cooled and massive radial designs. Its last gasp was in helicopter applications, but even then there were better ways to do it.

The rotary engine had one other neat use outside of aircraft: motorcycles! A small rotary engine fit very neatly inside of the wheels, and could turn the wheel to directly drive it.

Anyways, the whole purpose of this post is vocabulary.

Rotary engine: Whole engine spins

Radial engine: Cylinders turn a crankshaft and are arranged in a circle (most common)