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An aircraft is a machine that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil,〔(【引用サイトリンク】title=Aircraft - Define Aircraft at Dictionary.com )〕 or in a few cases the downward thrust from jet engines. The human activity that surrounds aircraft is called ''aviation''. Crewed aircraft are flown by an onboard pilot, but unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Aircraft may be classified by different criteria, such as lift type, aircraft propulsion, usage and others. ==History== (詳細はflight go back many centuries, however the first manned ascent – and safe descent – in modern times took place by hot-air balloon in the 18th century. Each of the two World Wars led to great technical advances. Consequently, the history of aircraft can be divided into five eras: *Pioneers of flight, from the earliest experiments to 1914. *First World War, 1914 to 1918. *Aviation between the World Wars, 1918 to 1939. *Second World War, 1939 to 1945. *Postwar era, also called the jet age, 1945 to the present day. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「aircraft」の詳細全文を読む スポンサード リンク
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