Jet airliners are not, in fact, jet airliners. Though the first of the breed, the de Havilland Comet, really was powered only by sleek turbojets that fitted elegantly into its wings, it did not take engineers long to work out that a turbojet works best not by itself but as part of a bigger whole.
A turbojet takes in air through a revolving compressor, mixes the compressed air with fuel, burns the mixture in a combustion chamber and ejects the exhaust out of the back to provide thrust, having first run it through a turbine which, via a shaft running along the engine’s axis, turns the compressor. Modern engines, however, also use the jet’s revolving shaft to spin either a propeller, creating a turboprop, or a ducted set of blades, creating a turbofan (see diagram). Both of these arrangements—and particularly turbofans—move more air, and thus create more thrust, than the turbojet within is capable of generating by itself. For long-haul flight, therefore, turbofans are preferred.
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