aripile

Aripile, often spelled aeolipile or aeolipila and sometimes referred to as Hero's engine, is an ancient device described as a simple steam-powered turbine. It is widely regarded as one of the earliest machines to convert steam pressure into rotational motion.

The device typically consists of a sealed vessel, such as a metal globe, containing water. The globe is mounted on a bearing and fitted with one or more hollow tubes that extend outward from the vessel and curve so that their jet ends point away from the surface. When the vessel is heated, water inside turns to steam and escapes through the nozzles, producing a reactive force that spins the assembly about its axis.

Operation relies on jet propulsion principles: the escaping steam exerts thrust on the nozzle ends, causing rotational motion. The design demonstrates basic thermodynamics and the conversion of heat energy into mechanical motion, though it is inefficient and capable of only limited work.

Historically, aripile is commonly attributed to Hero of Alexandria in the 1st century CE, with descriptions appearing in works such as Hero’s Pneumatica. Surviving accounts are fragmentary, and it is unclear how widely the device was built in antiquity. In modern times, replicas and reconstructions are presented in museums and classrooms to illustrate early ideas about steam power and propulsion.

Legacy varies in classification; it is sometimes called the first steam turbine or an early example of turbine-like behavior. While not a practical engine, the aripile is significant as a historical demonstration of propulsion physics and the early study of steam power.