Jet aircraft

A jet aircraft (or simply jet) is an aircraft (nearly always a fixed-wing aircraft) propelled by jet engines. Whereas the engines in propeller-powered aircraft generally achieve their maximum efficiency at much lower speeds and altitudes, jet engines achieve maximum efficiency at speeds close to or even well above the speed of sound. Jet aircraft generally cruise most efficiently at about Mach 0.8 () and at altitudes around or more. The idea of the jet engine was not new, but the technical problems involved could not begin to be solved until the 1930s. Frank Whittle, an English inventor and RAF officer, began development of a viable jet engine in 1928, and Hans von Ohain in Germany began work independently in the early 1930s. In August 1939 the turbojet powered Heinkel He 178, the world's first jet aircraft, made its first flight. A wide range of different types of jet aircraft exist, both for civilian and military purposes. After the first instance of powered flight, a large number of jet engine designs were suggested. René Lorin, Morize, Harris proposed systems for creating a jet efflux. After other jet engines had been run, Romanian inventor Henri Coandă claimed to have built a jet-powered aircraft in 1910, the Coandă-1910. However, to support this claim, he had to make substantial alterations to the drawings which he used to support his subsequently debunked claims. In fact the ducted-fan engine backfired, setting the aircraft on fire before any flights were ever made, and it lacked nearly all of the features necessary for a jet engine - including a lack of fuel injection, and any concern about hot jet efflux being directed at a highly flammable fabric surface. During the 1920s and 1930s a number of approaches were tried. A variety of motorjet, turboprop, pulsejet and rocket powered aircraft were designed. Rocket-engine research was being carried out in Germany and the first aircraft to fly under rocket power was the Lippisch Ente, in 1928. The Ente had previously been flown as a glider. The next year, in 1929, the Opel RAK.