A radial engine is a reciprocating internal combustion engine with a single crankshaft, which has cylinders arranged in a circle (in one or more rows) perpendicular to the axis of the crankshaft so that all cylinders make the same angle with each other.

This article will explain how the radial engine works, its use, and a brief history.

An X engine is a four-cylinder or four-row single-shaft piston internal combustion engine. The cross-section of the X engine forms the shape of the letter X, hence the name.

An X engine is a special type of radial engine, but if it has only four cylinders, it is also a flat engine.