Ramjets

The ramjet is a jet engine for very high­speed aircraft. It has no fan or compres­sor. The engine has to be moving at about 600 miles per hour (965 kilome­ters per hour) before it starts working. At that speed, air rams into the engine so fast that a compressor is not needed to compress it. The shape of the engine enables this to happen. With no fan or compressor, there is no need for a tur­bine. Ramjets work best in aircraft flying at more than twice the speed of sound.

SEE ALSO:

• Aircraft Design • Fighter Plane

• Jet and Jet Power • Propeller

• Rocket • Thrust

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TECH^TALK

EXTRA THRUST

Some aircraft are able to swivel their engine exhaust nozzles to point in different directions. This action is called thrust vectoring. It was invent­ed for aircraft such as the Harrier Jump Jet, which takes off straight up in the air by pointing its engine nozzles downward; it then swings the engine nozzles backward to fly normally. Some fighter planes use thrust vectoring to help them maneuver fast in air battles. The engine nozzles of the F-22 Raptor, for example, swivel in this way.

A fighter plane also sometimes needs a sudden burst of power or speed to take off or to escape trou­ble in an air battle. Fighters do this by using an afterburner, which sprays fuel into the jet engine’s exhaust nozzle. The fiery, hot jet of gas leaves the engine, and the fuel instantly burns and gives the plane an extra push. Afterburners are normally used only for short periods because they use up fuel very quick­ly. The F-22 Raptor was designed to fly at supersonic speeds for long periods without using afterburners.

This ability, called supercruise, gives the fighter plane an advantage over an enemy plane that may run out of fuel in mid-combat.