A kind of jet engine was built by the Ancient Greek Hero Alexander in the first century AD. It was a ball driven round by jets of steam escaping from two nozzles.
The first jet engines were built at the same time in the 1930s by Pabst von Ohain in Germany and Frank Whittle in Britain.
Ohain’s engine was put in the Heinkel HE- 178 which first flew on 27 August 1939; Whittle’s was put in the Gloster E28 of 1941. The first American jet was the Bell XP-59 Aircomet of 1942.
Jets work by pushing a jet of air out the back. This hits the air so fast that the reaction thrusts the plane forward like a deflating balloon.
Jet engines are also called gas turbines because they burn fuel gas to spin the blades of a turbine non-stop.
Turbojets are the original form of jet engine. Air is scooped in at the front and squeezed by spinning compressor blades. Fuel sprayed into the squeezed air in the middle of the engine burns, making the mixture expand dramatically. The expanding air pushes round turbines which drive the compressor, and send out a high-speed jet of hot air to propel the plane. This high-speed jet is noisy but good for fast warplanes and the supersonic Concorde.
Turboprops are turbojets that use most of their power to turn a propeller rather than force out a hot air jet.
Turbofans are used by most airliners because they are quieter and cheaper to run. In these, extra turbines turn a huge fan at the front. Air driven by this fan bypasses the engine core and gives a huge extra boost at low speeds.
Ramjets or ‘flying stovepipes’ are the simplest type of jet engine, used only on missiles. They dispense with both compressor and turbine blades and simply rely on the speed of the jet through the air to ram air in through the intake into the engine.