Jet aircraft

A jet aircraft (or simply jet) is an aircraft propelled by one or more jet engines. Jets are nearly always fixed-wing aircraft, though a wide range of different types of jet aircraft exists– both for civilian and military purposes.

Most jet aircraft need to fly at high speeds– either supersonic, or just below the speed of sound (transonic) in order to achieve efficient flight. They typically cruise around Mach 0.8 (981 km/h (610 mph)), and at altitudes around 10,000-15,000 m (33,000-49,000 ft) or higher, where jet engines operate most efficiently. This contrasts propeller-powered aircraft, which achieve peak efficiency at much lower speeds and altitudes.

Jet aircraft are usually designed using the Whitcomb area rule, which states that the total area of the cross-section of an aircraft must be approximately the same as that of a Sears-Haack body. The application of this rule minimizes the production of shockwaves, which waste energy.

Frank Whittle, an English inventor and RAF officer, began development of a viable jet engine in 1928, while Hans von Ohain in Germany began to work, independently, on similar concepts in the early 1930s. Thus, in August of 1939, the world's first jet aircraft, the Heinkel He 178, took its maiden flight.