Boeing subsidiary Aurora Flight Sciences has revealed new details about its prototype fan-in-wing aircraft and released an animation of the craft’s vertical lift rotors.
The still-unnamed design is part of a Pentagon X-plane effort to demonstrate technologies and integrated concepts that can “enable a transformational combination of aircraft speed and runway independence”.
The secretive Defense Advanced Research Projects Agency (DARPA) is overseeing the project, which it calls Speed and Runway Independent Technologies, or SPRINT.
The term runway independence is typically taken to mean the capability for vertical take-off and landing (VTOL), although Washington is also exploring alternatives like amphibian aircraft capable of taking off from water. Through SPRINT, the US military is seeking to develop a prototype aircraft capable of both VTOL operations and of flying at the faster speeds typical of fixed-wing jets.
Aurora had previously indicated it would pursue a blended-wing body aerostructure housing internally ducted fans to generate vertical lift. The company is now providing more detail about its proposed design, including the number and placement of its rotors.
The latest rendering of the uncrewed craft, released on 20 May, shows a blended-wing-body design with a prominent V-shaped tail and two oblong air intakes mounted low on each side of the nose.
Aurora says the demonstrator will have three “fan-in-wing” (FIW) vertical lifting rotors: two amidships and one centred near the front of the aircraft. An animation provided by the company shows that the fans will be covered by doors that will flip open during vertical flight and close for forward travel.
Aurora says it could add more lifting fans to future designs to provide additional capabilities.
“The choice of three lift fans reflects the team’s strategy to simplify the demonstrator and streamline its path to flight test,” the company says. “The FIW technology could be scaled to four or more lift fans to meet future aircraft requirements.”
Without offering specifics, Aurora says the design “leverages existing engine solutions”, which the company says will shorten the development timeline and reduce engineering risk.
DARPA has set an airspeed target of 400-450kt (740-830km/h) for the SPRINT aircraft. Aurora claims the blended-wing design will be able to maintain a cruising speed of 450kt.
In addition to the VTOL capability required by DARPA, Aurora also says its SPRINT aircraft will have “super short take-off and landing” (SSTOL) capability and be able to take off and land conventionally.
The Pentagon defines short take-off and landing aircraft as those capable of clearing a 15.2m (50ft)-high obstacle within 450m of commencing take-off and, when landing, of stopping within 450m after passing over a 12.2m-high obstacle.
While examples of such a craft exist, including the Lockheed Martin F-35B and BAE Systems/Boeing AV-8B Harrier II, SPRINT appears to be targeting mobility applications rather than an expeditionary fighter.
DARPA is partnered on the effort with US Special Operations Command, whose missions often require depositing troops and equipment into austere or far-flung hostile locations.
Aurora says it is seeking to demonstrate “game-changing capability for air mobility” with its SPRINT aircraft.
The new design details come less than two weeks after Aurora’s design was chosen by DARPA as the first proposal to advance to the latest stage of the SPRINT competition. Based on feedback from DARPA, the company’s choice of blended-wing body combined with FIW vertical lift appears to show promise. Aurora was advanced to the next stage of the SPRINT development process on 30 April, winning a nearly $25 million contract from DARPA.
None of the programme’s other competitors, including Bell, Northrop Grumman and Piasecki Aircraft, have yet been approved for Phase 1B, which covers additional design maturation and is expected to last 12 to 18 months.
Aurora says it hopes to complete a preliminary design review of its SPRINT proposal with DARPA in 12 months and have a working prototype ready to fly within 36 months.
