Jet propulsion, propulsion of a vehicle by reaction to the rapid expulsion of a gas backward. The reaction imparts an equal forward momentum to the vehicle. The chief use of jet propulsion is to power airplanes. The first jet engine was designed and built by Sir Frank Whittle (1937), but the first jet-engine aircraft to fly was German (Aug. 1939). Jet engines are internal-combustion engines. The turbojet is the commonest form. Air enters the inlet diffuser and is compressed in the air compressor. It then enters the combustion chamber, where the fuel is injected and ignited, and the hot, expanding exhaust gases pass through a turbine that drives the compressor and engine accessories. The gases are expelled through the jet nozzle to provide the thrust.
See also: National Aeronautics and Space Adminstration.