The US Defense Advanced Research Projects Agency (DARPA) is to undertake in July 2014 conceptual design reviews for the four vertical take-off and landing (VTOL) X-Plane contenders a Boeing programme official disclosed on 24 June 2014. Announced by DARPA in early 2013, the VTOL X-Plane programme is geared at demonstrating efficient hover and high-speed flight. The specific requirements are that the aircraft achieve a top sustained flight speed of 300 kt to 400 kt; raise aircraft hover efficiency from 60% to at least 75%; present a more favourable cruise lift-to-drag ratio of at least 10, up from the current 5-6; and carry a useful load of at least 40% of the vehicle’s projected gross weight of 10,000-12,000 lb (4,500-5,450 kg).
Of the four contenders, Boeing’s Phantom Swift is currently the only one to have been built (as a 17% scale model) and flown…While DARPA did not specify whether the aircraft be manned or unmanned, all of the entrants have opted for unmanned.
Excerpt from DARPA to progress VTOL X-Plane as Boeing reveals Phantom Swift details, IHS Jane’s International Defence Review, June 25, 2014