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 An aeolipile (or aeolipyle, or eolipile), also known as a Hero engine, is a rocket style[1] jet engine[2] which spins when heated. In the first century AD, Hero of Alexandria described the device,[3] and many sources give him the credit for its invention. The aeolipile he described is considered to be the first recorded steam engine or reaction steam turbine.[4] The name – derived from the Greek words "aeolos" and "pila" – translates to "the ball of Aeolus"; Aeolus being the Greek god of the wind. A device called an aeolipile was described in the first century BC by Vitruvius in his treatise De architectura, however it is unclear whether it is the same device, or a predecessor, as there is no mention of any rotating parts.[5]
[edit] Description and physics The aeolipile consists of a vessel, usually a "simple" solid of revolution, such as a sphere or a cylinder, arranged to rotate on its axis, having oppositely bent or curved nozzles projecting from it (tipjets). When the vessel is pressurized with steam, steam is expelled through the nozzles, which generates thrust due to the rocket principle[6] as a consequence of the 2nd and 3rd of Newton's laws of motion. 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, causing the vessel to spin about its axis. Aerodynamic drag and frictional forces in the bearings build up quickly with increasing rotational speed (rpm) and consume the accelerating torque, eventually canceling it and achieving a steady state speed. Typically, and as Hero described the device, the water is heated in a simple boiler 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 to the right. [edit] History.jpg) Both Hero and Vitruvius draw on the much earlier work by Ctesibius (285-222BC). Since it is unknown whether or not Ctesibius himself was the inventor, awarding proper credit for creating the first aeolipile may never be achieved. [edit] Vitruvius's descriptionVitruvius (c. 80 BC – c. 15AD) mentions aeolipiles by name: "Æolipylæ are hollow brazen vessels, which have an opening or mouth of small size, by means of which they can be filled with water. Prior to the water being heated over the fire, but little wind is emitted. As soon, however, as the water begins to boil, a violent wind issues forth." [5] [edit] Hero's descriptionHero (c. 10 - 70 AD) takes a more practical approach, in that he gives instructions how to make one:
[edit]In recognition of the Aeolipile's contribution to steam engineering, the U.S. Navy chose a semblance of the Aeolipile for the Boiler Technician rating badge. [edit] Practical usageIt is not known whether the aeolipile was put to practical use as an 'engine' in ancient times. Hero's drawing shows a stand-alone device, and was presumably intended as a temple 'wonder', like many of the other devices described in Pneumatica. [3] Vitruvius, on the other hand, mentions use of the aeolipile for demonstrating the physical properties of the weather. He describes the aeolipile as
After describing the device's construction (see above) he concludes:
[edit] See also
[edit] References
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