An aeolipile, aeolipyle, or eolipile, from the Greek "Αἰόλου πύλη," , also known as a Hero's (or Heron's) engine, is a simple, bladeless radial steam turbine which spins when the central water container is heated.

Torque In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...

is produced by steam jets exiting the turbine. The Greek-Egyptian

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...

and

engineer Engineers, as practitioners of engineering, are professionals who Invention, invent, design, build, maintain and test machines, complex systems, structures, gadgets and materials. They aim to fulfill functional objectives and requirements while ...

Hero of Alexandria Hero of Alexandria (; , , also known as Heron of Alexandria ; probably 1st or 2nd century AD) was a Greek mathematician and engineer who was active in Alexandria in Egypt during the Roman era. He has been described as the greatest experimental ...

described the device in the 1st century AD, and many sources give him the credit for its invention. However,

Vitruvius Vitruvius ( ; ; –70 BC – after ) was a Roman architect and engineer during the 1st century BC, known for his multi-volume work titled . As the only treatise on architecture to survive from antiquity, it has been regarded since the Renaissan ...

was the first to describe this appliance in his ''

De architectura (''On architecture'', published as ''Ten Books on Architecture'') is a treatise on architecture written by the Ancient Rome, Roman architect and military engineer Vitruvius, Marcus Vitruvius Pollio and dedicated to his patron, the emperor Caesa ...

'' (). The aeolipile is considered to be the first recorded

steam engine A steam engine is a heat engine that performs Work (physics), mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a Cylinder (locomotive), cyl ...

or reaction

steam turbine A steam turbine or steam turbine engine is a machine or heat engine that extracts thermal energy from pressurized steam and uses it to do mechanical work utilising a rotating output shaft. Its modern manifestation was invented by Sir Charles Par ...

, but it is neither a practical source of power nor a direct predecessor of the type of steam engine invented during the

Industrial Revolution The Industrial Revolution, sometimes divided into the First Industrial Revolution and Second Industrial Revolution, was a transitional period of the global economy toward more widespread, efficient and stable manufacturing processes, succee ...

. The name – derived from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

word Αἴολος and

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word ''pila'' – translates to "the ball of

Aeolus In Greek mythology, Aiolos, transcribed as Aeolus (; ; ) refers to three characters. These three are often difficult to tell apart, and even the ancient mythographers appear to have been perplexed about which Aeolus was which. Diodorus Siculus m ...

", Aeolus being the

Greek god In ancient Greece, deities were regarded as immortal, anthropomorphic, and powerful. They were conceived of as individual persons, rather than abstract concepts or notions, and were described as being similar to humans in appearance, albeit larg ...

of the air and wind. Because it applies steam to perform work, an Aeolipile (depicted in profile) is used as the symbol for the U.S. Navy's Boiler Technician Rate, as it was for the earlier Watertender, Boilermaker, and Boilerman ratings.

Physics

The aeolipile usually consists of a spherical or cylindrical vessel with oppositely bent or curved

nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe (material), pipe. A nozzle is often a pipe or tube of varying cross ...

s projecting outwards. It is designed to rotate on its axis. When the vessel is pressurised with steam, the gas is expelled out of the nozzles, which generates thrust due to the

rocket A rocket (from , and so named for its shape) is a vehicle that uses jet propulsion to accelerate without using any surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely ...

principle as a consequence of the 2nd and 3rd of

Newton's laws of motion Newton's laws of motion are three physical laws that describe the relationship between the motion of an object and the forces acting on it. These laws, which provide the basis for Newtonian mechanics, can be paraphrased as follows: # A body re ...

. When the nozzles, pointing in different directions, produce forces along different lines of action perpendicular to the axis of the bearings, the thrusts combine to result in a rotational moment (mechanical couple), or

torque In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...

, causing the vessel to spin about its axis. Aerodynamic drag and frictional forces in the bearings build up quickly with increasing rotational speed (

rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or r⋅min−1) is a unit of rotational speed (or rotational frequency) for rotating machines. One revolution per minute is equivalent to hertz. Standards ISO 80000-3:2019 def ...

) and consume the accelerating torque, eventually cancelling it and achieving a

steady state In systems theory, a system or a process is in a steady state if the variables (called state variables) which define the behavior of the system or the process are unchanging in time. In continuous time, this means that for those properties ''p' ...

speed. Typically, and as Hero described the device, the water is heated in a simple

boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, centra ...

which forms part of a stand for the rotating vessel. Where this is the case, the boiler is connected to the rotating chamber by a pair of pipes that also serve as the pivots for the chamber. Alternatively the rotating chamber may itself serve as the boiler, and this arrangement greatly simplifies the pivot/bearing arrangements, as they then do not need to pass steam. This can be seen in the illustration of a classroom model shown here.

History

Both Hero and Vitruvius draw on the much earlier work by

Ctesibius Ctesibius or Ktesibios or Tesibius (; BCE) was a Greek inventor and mathematician in Alexandria, Ptolemaic Egypt. Very little is known of Ctesibius' life, but his inventions were well known in his lifetime. He was likely the first head of th ...

(285–222 BC), also known as Ktēsíbios or Tesibius, who was an inventor and mathematician in

Alexandria Alexandria ( ; ) is the List of cities and towns in Egypt#Largest cities, second largest city in Egypt and the List of coastal settlements of the Mediterranean Sea, largest city on the Mediterranean coast. It lies at the western edge of the Nile ...

Ptolemaic Egypt Ptolemaic is the adjective formed from the name Ptolemy, and may refer to: Pertaining to the Ptolemaic dynasty * Ptolemaic dynasty, the Macedonian Greek dynasty that ruled Egypt founded in 305 BC by Ptolemy I Soter *Ptolemaic Kingdom Pertaining ...

. He wrote the first treatises on the science of compressed air and its uses in pumps.

Vitruvius's description

(c. 80 BC – c. 15 BC) mentions aeolipiles by name:

Hero's description

Hero (c. 10–70 AD) takes a more practical approach, in that he gives instructions how to make one:

Practical usage

It is not known whether the aeolipile was put to any practical use in ancient times, and if it was seen as a pragmatic device, a whimsical novelty, an object of reverence, or some other thing. A source described it as a mere

curiosity Curiosity (from Latin , from "careful, diligent, curious", akin to "care") is a quality related to inquisitive thinking, such as exploration, investigation, and learning, evident in humans and other animals. Curiosity helps Developmental psyc ...

for the ancient Greeks, or a "party trick". Hero's drawing shows a standalone device, and was presumably intended as a "temple wonder", like many of the other devices described in '' Pneumatica''.

, on the other hand, mentions use of the aeolipile for demonstrating the physical properties of the weather. He describes them as: After describing the device's construction (see above) he concludes: In 1543, Blasco de Garay, a scientist and a captain in the Spanish navy, allegedly demonstrated before the

Holy Roman Emperor, Charles V Charles V (24 February 1500 – 21 September 1558) was Holy Roman Emperor and Archduke of Austria from 1519 to 1556, King of Spain (as Charles I) from 1516 to 1556, and Lord of the Netherlands as titular Duke of Burgundy (as Charles II) fr ...

and a committee of high officials an invention he claimed could propel large ships in the absence of wind using an apparatus consisted of copper boiler and moving wheels on either side of the ship. This account was preserved by the royal Spanish archives at Simancas. It is proposed that de Garay used Hero's aeolipile and combined it with the technology used in Roman boats and late medieval galleys. Here, de Garay's invention introduced an innovation where the aeolipile had practical usage, which was to generate motion to the paddlewheels, demonstrating the feasibility of steam-driven boats. This claim was denied by Spanish authorities.Museo Naval, Catálogo guia del Museo Naval de Madrid, IX edición, Madrid, 1945, page 128.

Physics

History

Vitruvius's description

Hero's description

Practical usage

See also

References

Further reading