Powered Flight - Methods of Propulsion - Jet Propulsion - Jet Aircraft

Jet Aircraft

Airbreathing jet engines provide thrust by taking in air, compressing the air, injecting fuel into the hot compressed air mixture in a combustion chamber, the resulting accelerated exhaust ejects rearwards through a turbine which drives the compressor. The reaction against this acceleration provides the engine thrust.

Jet engines can provide much higher thrust than propellers, and are naturally efficient at higher altitudes, being able to operate above 40,000 ft (12,000 m). They are also much more fuel-efficient at normal flight speeds than rockets. Consequently, nearly all high-speed and high-altitude aircraft use jet engines.

The early turbojet and modern turbofan use a spinning compressor and turbine to provide thrust. Many, mostly in military aviation, add an afterburner which injects extra fuel into the hot exhaust.

Use of a turbine is not absolutely necessary: other designs include the crude pulse jet, high-speed ramjet and the still-experimental supersonic-combustion ramjet or scramjet. These mechanically simple designs require an existing airflow to work and cannot work when stationary, so they must be launched by a catapult or rocket booster, or dropped from a mother ship.

The bypass turbofan engines of the Lockheed SR-71 were a hybrid design – the aircraft took off and landed in jet turbine configuration, and for high-speed flight the afterburner was lit and the turbine bypassed, to create a ramjet.

The motorjet was a very early design which used a piston engine in place of the combustion chamber, similar to a turbocharged piston engine except that the thrust is derived from the turbine instead of the crankshaft. It was soon superseded by the turbojet and remained a curiosity.

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Famous quotes containing the word jet:

    But every jet of chaos which threatens to exterminate us is convertible by intellect into wholesome force. Fate is unpenetrated causes.
    Ralph Waldo Emerson (1803–1882)