A jet is an engine that works by expelling a fluid jet backward so that the reaction to this exhaust propels the vehicle forward. Both the jet engine and the rocket engine are types of reaction engine, but whereas the rocket engine is self-contained and can work in a vacuum a jet engine can only function in the atmosphere.
The balloon jet and Newton's third law
If an inflated balloon is untied and released it flies across a room. It may be thought that the balloon is moving because the stream of escaping air is pushing against the atmosphere, rather as a row boat is propelled by the oars pushing back against the water. But this is not so. The balloon would fly just as well in a vacuum where there was nothing for the escaping air to push against; in fact it would fly better. The explanation lies in the fact that the pressure of the air in an inflated balloon is equal and constant in all directions. It it were not, the balloon would be continually moving in the direction in which the pressure was greatest. When, however, the neck of the balloon is opened there is nothing for the compressed air to push against at that point and so is is able to escape. But the pressure on the opposite side of the balloon is still there and, since there is no longer any counter pressure to balance it, it can move the balloon. Thus the balloon flies across the room in the opposite direction from the escaping air.
Early history of the jet engine
Many centuries later, Isaac Newton constructed a model carriage which was jet propelled. This, too, relied upon steam escaping under pressure from the rear of the vehicle to provide a forward thrust.
The practical application of jet propulsion, however, is a fairly recent innovation. The first jet-propelled aircraft were the German Heinkel 178, which made its inaugural flight in 1939, and the British Gloster E.28/39 powered by Frank Whittle's turbojet, which first flew in 1941.
Parts of a jet engine
Types of jet engineThe main types of jet engine are:
Related categories AERODYNAMICS AND AERONAUTICS
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