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 (609mph, 981km/h or 273m/s) at altitudes around 10,000–15,000 metres (33,000–49,000ft) 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.
Tonga ([ˈtoŋa]; Tongan: Puleʻanga Fakatuʻi ʻo Tonga), officially the Kingdom of Tonga, is a Polynesian sovereign state and archipelago comprising 177 islands of which 52 islands are inhabited. The total surface area is about 750 square kilometres (290sqmi) scattered over 700,000 square kilometres (270,000sqmi) of the southern Pacific Ocean. It has a population 103,000 people of whom 70% reside on the main island of Tongatapu.
Tonga became known as the Friendly Islands because of the congenial reception accorded to Captain James Cook on his first visit in 1773. He arrived at the time of the ʻinasi festival, the yearly donation of the First Fruits to the Tuʻi Tonga (the islands' paramount chief) and so received an invitation to the festivities. According to the writer William Mariner, the chiefs wanted to kill Cook during the gathering but could not agree on a plan.
Tonga's population is 358, making it the seventh most populous village in Tuvalu. It is the main village of the island of Nanumanga, comprising 52% of the population of the island. The only other village is on the island Tokelau.