Axial engine

Axial engines (sometimes known as barrel or Z-crank engines) are a type of reciprocating engine with pistons arranged around an output shaft with their axes parallel to the shaft. Barrel refers to the cylindrical shape of the cylinder group (result of the pistons being spaced evenly around the central crankshaft and aligned parallel to the crankshaft axis) whilst the Z-crank alludes to the shape of the crankshaft.