The first reaction engine, the aeolipile (a ball that rotated as a reaction to escaping steam), was constructed by the inventor Heron (or Hero) of Alexandria. Developments through the centuries have resulted in two general types of reaction machines, the true rocket and the airstream engine, commonly known as the jet engine. Unlike a jet engine, a rocket engine carries with it chemicals that enable it to burn its fuel without drawing air from an outside source. Thus a rocket can operate in outer space, where there is no atmosphere. Fritz von Opel, a German automobile manufacturer, made the first flight entirely by rocket power in 1939. The American R. H. Goddard did much of the important pioneer work in modern rocket development.
The second category of reaction motor, the jet engine, is a development of the late 18th-century gas turbine engines, which directed combustion gases against the blades of a turbine wheel. Not until 1908 was it suggested that an aircraft could be driven by jet propulsion. René Lorin, a French engineer, proposed using a reciprocating engine to compress air, mix it with fuel, and thus propel the aircraft by the pulses of hot gas produced by combustion of the mixture. Henri Coanda, a Romanian engineer, experimented with a reaction-powered aircraft in 1910, and observed the phenomenon now known as the Coanda effect. In 1939 the English engineer Frank Whittle developed a jet engine that powered a full-sized aircraft, and a year later Secundo Campini in Italy flew for 10 min using a thermal jet engine.
Jet-propelled aircraft have replaced propeller-driven types in all but short-range commercial applications; turboprop planes, in which a propeller is turned by a turbine engine, are used for short-range flights. The SR-71 Blackbird, a U.S. jet spyplane, holds the current speed record of 2,193.17 mph (3,529.56 kph) for a piloted air-breathing airplane, but NASA's experimental scramjet-powered pilotless X-43A bested this, almost reaching Mach 7 (about 5,300 mph/8,500 kph) and later Mach 10 (about 7,600 mph/12,200 kph) in brief test flights in 2004. The experimental X-51A, also pilotless, reached Mach 5 (3,800 mph/6,100 kph) in a 2010 test flight. The Australian-led HyShot Flight Program successfully tested a British-designed scramjet engine in 2006.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.