• 25 Dec 2023 04:31 AM
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Four Companies Dash for DARPA’s SPRINT

By Dan Gettinger, Managing Editor
Vertiflite, Jan/Feb 2024

On Nov. 1, the US Defense Advanced Research Projects Agency (DARPA) announced that it had selected four companies — Aurora Flight Sciences, Bell, Northrop Grumman and Piasecki Aircraft — to design prototypes for a high-speed vertical takeoff and landing (HSVTOL) X-Plane.

The four companies will participate in Phase 1A of the SPeed and Runway INdependent Technologies (SPRINT) program, a joint effort by DARPA and US Special Operations Command. This period of the three-phase project will see the competitors develop conceptual designs for an HSVTOL and, in Phase 1B, engage in preliminary designs and risk reduction efforts.

DARPA plans to eventually choose one of the four companies to build a prototype of its design for an HSVTOL, the first test flights of which are expected in 2027.

DARPA’s Tactical Technology Office (TTO) Director Dr. Mike Leahy revealed the HSVTOL program in January 2023 at the Society’s 10th Annual Electric VTOL Symposium. DARPA released the broad agency announcement solicitation for the SPRINT program on March 9 (see “DARPA SPRINTs Toward High-Speed VTOL,” Vertiflite, May/June 2023). The agency is seeking an aircraft that can cruise at speeds of up to 450 kt (830 km/h), carry a payload of 5,000 lb (2,270 kg) and hover in austere environments.

The SPRINT program is not, however, expected to result in a pre-production aircraft. Rather, DARPA will seek to “validate technologies and integrated concepts” for high-speed and runway independent operations that can be applied to different sizes of aircraft, according to the agency’s solicitation.

The SPRINT program builds on an earlier initiative, the Air Force’s High-Speed VTOL Challenge, launched by AFWERX technology incubator in 2021 (see “Air Force Picks 11 Companies for High-Speed VTOL Program,” Vertiflite, March/ April 2022). Of the four SPRINT competitors, three — Bell, Northrop Grumman and Piasecki Aircraft — were involved in AFWERX’s Challenge.

Aurora Flight Sciences announced on Nov. 15 that it is working on a blended-wing-body design for its bid for SPRINT. For vertical lift, the concept will feature lift fans embedded in the wings. In designing its SPRINT concept, the Virginia-based Boeing subsidiary will leverage experience on programs like the Boeing X-48 blended wing body aircraft and Aurora Excaliber, a jet-powered VTOL drone.

Bell is developing a concept for an uncrewed aircraft known as the Sea-based Logistics Unmanned Rearm/Refuel Platform (SLURRP), according to a Nov. 27 report in Aviation Week. The SLURRP is the smallest variant of a family of HSVTOL aircraft conceived of by Bell, each of which feature Bell’s concept for a folding tiltrotor propulsion system. In September, the Textron subsidiary announced that it had begun testing a folding rotor testbed at the Holloman High Speed Test Track in New Mexico (see “Rotorcraft News,” Vertiflite, Nov/Dec 2023).

While neither Northrop Grumman nor Piasecki Aircraft have disclosed their designs for the SPRINT program, both were involved in AFWERX’s Challenge. For that initiative, Northrop worked with Jetoptera to design a blended-wing-body airframe for the latter’s patented fluidic propulsion system (FPS). Northrop subsidiary Scaled Composites helped Jetoptera design and test a subscale demonstrator of the aircraft.

For its contribution to the AFWERX HSVTOL Challenge, Piasecki conceived its PA-1469, which featured two aft-mounted turbofan engines with vectoring exhausts and two tilting ducted propellers for vertical lift. That design also included a cargo ramp, one of DARPA’s requirements for the SPRINT aircraft.

In addition to AFWERX’s Challenge, the SPRINT program draws on a rich history at the Department of Defense of efforts over more than a half-century in exploring high-speed VTOL aircraft concepts. With SPRINT, DARPA is aiming to prove that the elusive dream of high-speed vertical lift is achievable for this new mission set.