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The Vertical Take-Off and Landing Experimental Aircraft (VTOL X-Plane) program is an American research project sponsored by the Defense Advanced Research Projects Agency (DARPA). The goal of the program is to demonstrate a VTOL aircraft design that can take off vertically and efficiently hover, while flying faster than conventional rotorcraft.〔(DARPA Awards Contracts in Search of a 460 MPH Helicopter ) - News.USNI.org, 19 March 2014〕 There have been many previous attempts, most of them unsuccessful.〔〔Whittle, Richard. "(The Next X-Plane )" ''Air & Space/Smithsonian'', October 2015. Accessed: 26 September 2015.〕 A helicopter with a conventional rotor layout has a theoretical top speed of , after which it suffers from dissymmetry of lift. Some designs have successfully created hovering and high-speed aircraft, including the Bell Boeing V-22 Osprey tiltrotor that can fly at and the Sikorsky X2 compound helicopter that flew at , but both made significant aerodynamic compromises to hovering efficiency or range. DARPA's goal is to demonstrate a VTOL aircraft that can achieve a sustained top speed of 300 to 400 knots ().〔 All competitors for the program opted to demonstrate their concepts using an unmanned aerial vehicle even though it was not required, but the technologies are intended to be applied to manned aircraft as well.〔(DARPA’s Selects Four Developers for new X-Plane Program ) - Defense-Update.com, 18 March 2014〕 ==Requirement and programme== DARPA announced the programme in February 2013 with a requirement to create a new aircraft that uses the best features from both vertical take-off landing technology and that used for conventional aircraft.〔 The hybrid aircraft will try to improve on four areas: *Speed - achieve a top speed of at least 300 kts.〔 *Hover - increase hover efficiency to at least 75 percent.〔 *Cruise efficiency - achieve a lift-to-drag ratio of at least 10.〔 *Load - ensure the solution can carry a useful load of at least 40% of the projected gross-weight.〔 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「VTOL X-Plane」の詳細全文を読む スポンサード リンク
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