The U.S. Defense Advanced Research Projects Agency (DARPA) has tasked Bell Textron with an X-plane demonstrator high-speed VTOL aircraft for its Speed and Runway Independent Technologies (SPRINT) program. On Wednesday, the manufacturer announced its selection for Phase 2 of this program, saying it is responsible for design, construction, ground testing and certification of the demonstrator in the build-up to Phase 3, which would involve flight testing.
During Phase 1A and 1B of the SPRINT program, Bell competed with Boeing subsidiary Aurora Flight Sciences. DARPA’s objective is to support the development of a VTOL aircraft that can fly at speeds of between 400 and 450 knots. Its tiltrotor concept has been selected in preference to the Aurora design that featured a blended-wing-body concept incorporating three vertical lift rotorfans. Northrop Grumman and Piasecki Aircraft were also involved in Phase 1 of the process.
Bell’s SPRINT design is based on a new folding rotor propulsion concept it refers to as “Stop/Fold.” According to the U.S. company, the rotors have been engineered to produce the required lift without generating adverse downwash conditions that can compromise safety on the ground. The projected downwash is between 60 and 90 mph, with a disk loading of 10 to 25 pounds per sq ft and a hover efficiency of between 4 and 6 pounds per sq ft.
The manufacturer has said the design could support development of aircraft ranging in gross weight between 4,000 and 100,000 pounds. It envisages that the aircraft could operate in VTOL mode, or with a short takeoff and landing capability that would require no more than 400 feet of runway, including unprepared or damaged surfaces.
Bell has been working on its SPRINT concept for more than a decade, with activities including demonstrations of the folding rotors, integrated propulsion, and flight controls at the Holloman Air Force Base. It has also evaluated the design in the National Institute for Aviation Research’s wind tunnel at Wichita State University.
According to the Textron division, its latest high-speed VTOL technology builds on past accomplishments including the X-1 rocket-powered aircraft and the XV-15 tiltrotor design that led to the V-22 Osprey and AgustaWestland AW609 models. “This technology will bring a new era of next generation vertical lift aircraft that will deliver revolutionary warfighting capability,” commented Jason Hurst, Bell’s executive vice president of engineering.