Jet aircraft

A jet aircraft (or simply jet) is an aircraft (nearly always a fixed-wing aircraft) propelled by jet engines (jet propulsion).

Whereas the engines in propeller-powered aircraft generally achieve their maximum efficiency at much lower speeds and altitudes, jet engines and aircraft achieve maximum efficiency (see specific impulse) at speeds close to or even well above the speed of sound. Jet aircraft generally cruise at faster than about M 0.8 (609 mph, 981 km/h or 273 m/s) at altitudes around 10,000–15,000 metres (33,000–49,000 ft) or more.

Frank Whittle, an English inventor and RAF officer, developed the concept of the jet engine in 1928,Hans von Ohain in Germany, a decade later developed the concept independently at the end of the 1930s. He wrote in February 1936 to Ernst Heinkel, telling him of the design and its possibilities. However, it can be argued that the English engineer A. A. Griffith, who published a paper in July 1926 on compressors and turbines, also deserves credit.

Zimbabwe

Coordinates: 20°S 30°E / 20°S 30°E / -20; 30

Zimbabwe (/zɪmˈbɑːbweɪ/), officially the Republic of Zimbabwe, is a landlocked sovereign state located in southern Africa, between the Zambezi and Limpopo Rivers. It borders South Africa to the south, Botswana to the west, Zambia to the northwest, and Mozambique to the east and northeast. The capital and largest city is Harare.

Since the 11th century, present-day Zimbabwe has been the site of several organised states and kingdoms as well as a major route for migration and trade. The British South Africa Company of Cecil Rhodes first demarcated the present territory during the 1890s; it became the self-governing British colony of Southern Rhodesia in 1923. In 1965, the conservative white minority government unilaterally declared independence as Rhodesia. The state endured international isolation and a 15-year guerrilla war with black nationalist forces; this culminated in a peace agreement that established universal enfranchisement and de jure sovereignty in April 1980. The country then rejoined the Commonwealth of Nations (later suspended in 2003), and became a member of the United Nations and the Southern African Development Community (SADC).

Zimbabwe (disambiguation)

Zimbabwe can refer to:

Great Zimbabwe

Great Zimbabwe is a ruined city in the south-eastern hills of Zimbabwe near Lake Mutirikwe and the town of Masvingo. It was the capital of the Kingdom of Zimbabwe during the country's Late Iron Age. Construction on the monument by ancestors of the Shona people began in the 11th century and continued until the 15th century, spanning an area of 722 hectares (1,780 acres) which, at its peak, could have housed up to 18,000 people. It is recognised as a World Heritage Site by UNESCO.

Great Zimbabwe served as a royal palace for the Zimbabwean monarch and would have been used as the seat of political power. One of its most prominent features were the walls, some of which were over five metres high and which were constructed without mortar. Eventually the city was abandoned and fell into ruin.

The earliest known written mention of the ruins was in 1531 by Vicente Pegado, captain of the Portuguese garrison of Sofala, who recorded it as Symbaoe. The first European visit may have been made by the Portuguese traveler António Fernandes in 1513-1515, who crossed twice and reported in detail the region of present-day Zimbabwe (including the Shona kingdoms) and also fortified centers in stone without mortar. However, passing en route a few miles north and about 35 miles south of the site, he did not make a reference to the Great Zimbabwe riddle.