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 This page is intended for college, high school, or middle school students. For younger students, a simpler explanation of the information on this page is available on the Kid's Page.

As an aircraft moves through the air, the air molecules near the aircraft are disturbed and move around the aircraft. Exactly how the air re-acts to the aircraft depends upon the ratio of the speed of the aircraft to the speed of sound through the air. Because of the importance of this speed ratio, aerodynamicists have designated it with a special parameter called the Mach number in honor of Ernst Mach, a late 19th century physicist who studied gas dynamics.

For aircraft speeds which are greater than the speed of sound, the aircraft is said to be supersonic. Typical speeds for supersonic aircraft are greater than 750 mph but less than 1500 mph, and the Mach number M is greater than one, 1 < M < 3. In supersonic flight, we encounter compressibility effects and the local air density varies because of shock waves, expansions, and flow choking.

The first powered aircraft to explore this regime was the Bell X-1A, in 1947. It and subsequent experimental aircraft proved that humans could fly supersonically. The aerodynamics of these early aircraft is used on modern supersonic fighter aircraft. There have been several efforts to develop cost-effective supersonic airliners. The Russian TU-144 and the Anglo-French Concorde went into service in the early 1970's but were financial failures. Because of the high drag associated with supersonic flight, fighter aircraft use high thrust gas turbine propulsion systems. On the slide we show an F-14 which is powered by two afterburning turbofan engines. The wings of supersonic fighters are swept in planform to reduce drag. The F-14 is unique because the amount of sweep can be varied by the pilot; low sweep for good low speed performance, high sweep for supersonic flight. For Mach numbers less than 2.5, the frictional heating of the airframe by the air is low enough that light weight aluminum is used for the structure.

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