The US Defense Advanced Research Projects Agency (DARPA) is to undertake conceptual design reviews for the four vertical take-off and landing (VTOL) X-Plane contenders in the coming weeks, a Boeing programme official disclosed on 24 June.
Speaking at the company's St Louis facility in Missouri, Brian Ritter, programme manager for Phantom Swift, said that initial reviews of the solutions being proposed by Aurora Flight Sciences, Boeing, Karem, and Sikorsky will be undertaken at the end of July. This will be followed with a preliminary design review by the end of 2015.
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. Speaking to reporters at St Louis, Ritter disclosed details of the Phantom Swift, which plans to achieve DARPAs goals through the use of ducted-fan technology.
"The combination of body-fans and tilt-wing fans for improved controllability is the unique feature of the Phantom Swift," Ritter said, adding: "In the challenge of efficient hover and high-speed flight the answer is in ducted-fan technology, and this is something that Boeing is now investing heavily in."
In its full-sized configuration the Phantom Swift will measure 15.2 m (50 ft) from wingtip to wingtip, 13.4 m (44 ft) from nose to tail, and weighs in at to 5,450 kg (12,000 lb). With two downward facing fans in the main body of the aircraft for vertical lift, payloads would be housed in bays in the nose, mid-section, and tail of the Phantom Swift.
While the demonstrator will be powered by a conventional General Electric CT7-8 engine, the long-term plan is to incorporate an all-electric drive as soon as the technology makes it feasible. In high-speed cruise the lift fans are shut down and doors are closed for greater aerodynamic performance (forward propulsion is provided by the wingtip thrusters).
While DARPA did not specify whether the aircraft be manned or unmanned, all of the entrants have opted for unmanned. However, Ritter said there is potential for the full-scale Phantom Swift to be manned, and that Boeing sees a whole family of platforms based on the aircraft.
With Phase 1 contracts for the USD130 million VTOL X-Plane programme awarded to the four competitors, Phase 2 and Phase 3 will see the entrants downselected to one platform with the goal of flight trials in the 2017-18 timeframe.