The Pentagon’s High Speed Vertical Take-Off and Landing (HSVTOL) X-plane competition will likely fund assembly of only one of two competing designs.
Both Bell and Boeing subsidiary Aurora Flight Sciences have advanced to the final round of design development in the HSVTOL effort, which seeks to deliver an experimental aircraft capable of taking off and landing vertically and of achieving speeds typical of fixed-wing jets.
The competition is being funded by the US Defense Advanced Research Projects Agency (DARPA) in conjunction with US Special Operations Command (SOCOM).
Speaking at the annual Special Operations Forces Week conference in Tampa, Florida on 7 May, the head of SOCOM’s fixed-wing procurement office said he expects to see DARPA make a single-source selection for HSVTOL in the near future.
“They’re on the way to down-selecting, in the not-too-distant future, a single design that will build towards an X-plane demonstrator,” says US Air Force Colonel Justin Bronder.
Bronder notes the winning HSVTOL design will likely make its first flight in 2027 or 2028.
Unlike traditional military competitive procurement competitions, DARPA research programmes carry no guarantee of leading to a lucrative contract for large-scale orders.
Instead, technology matured under DARPA programmes is forwarded to the various Pentagon procurement offices for further consideration.
“There’s some definite interest from the air force and potentially other services to hopefully pick up that technology demonstrator for future consideration,” Bronder says.
He suggests that contested logistics and air mobility across long distances or within austere environments are missions for which the new aircraft could be appealing.
The two finalist proposals vary wildly in their approach to solving the X-plane challenge, which calls for cruise speeds of 400-450kt (740-833km/h) and ability to hover from unprepared surfaces.
Bell’s design is centred around a novel “Stop/Fold” rotor system that resembles a tiltrotor while in vertical and low-speed horizontal flight. However, the concept will feature a third mode for high-speed horizontal flight, in which the rotor blades fold down and the aircraft functions more like a conventional jet.
Aurora has proposed a novel blended-wing-body jet with three internally housed fan-in-wing rotors that generate vertical lift.
An animation released by the company shows that the fans would be enclosed behind doors, which would lay flush with the fuselage, during forward travel. The doors would be open for vertical flight.
Both companies have completed windtunnel tests using sub-scale models of their HSVTOL designs in recent months.
