The US Air Force has assigned the 'X' status to the new Scramjet powered X-51. The X was first used in the 1940s to identify eXperimental supersonic aircraft.

This new X-51 uses a truly cutting edge engine technology called Scramjet (supersonic combustion ramjet) which accepts supersonic air flows into the combustion chamber of the engine. As the air flow enters the engine it is funneled and compressed as fuel is entered into the chamber. This mixture is then ignited to take the already supersonic air speed to velocities between Mach 12 and Mach 24 (theoretical top speed). Current maximum air speeds range from Mach 3.2 for the USAF SR-71 Blackbird recon plane to over Mach 30 for the Apollo space flight.

The scramjet technology requires an additional engine to propel the aircraft into the sound barrier 'before' the supersonic engine can compression the high speed air flow.

The first successful flight of a scramjet engine was accomplished by the University of Queensland in Australia. They reached speeds of Mach 7 in their trials, or seven times the speed of sound.

Taking the concept one step further, the scramjet technology (as envisioned in the X-51) could also be used as a hypersonic non-explosive missile. Ballistics, whether from a rifle or a missile, shows a relationship between mass and velocity of the projectile. This means that a lighter object can have a higher impact effect than a heavy object if the lighter version is traveling at a higher speed. This means that a scramjet powered missile could have incredible destructive effect without the need of an explosive charge. Tomahawks, the current standard for mid to long range missiles, by comparison, top out at 550 mph.



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