Sikorsky has reached a milestone for its blown-wing tailsitter uncrewed air system (UAS), which the helicopter manufacturer is developing as the progenitor of a new family of VTOL aircraft. In test flights, the autonomous twin prop-rotor prototype was able to successfully transition from vertical lift to horizontal flight and back again.

According to Igor Cherepinsky, director of Sikorsky Innovations—the airframer’s rapid prototyping group—the UAS has transitioned dozens of times during testing. The wing-shaped, electric-battery-powered vehicle weighs 115 pounds, has a wingspan of 10 feet, and is controlled by the airframer's Matrix flight autonomy system. The company believes the UAS can be scaled up as a cargo carrier.

“They’re products on their own, but they’re also helping us with the physics for a much larger aircraft,” said Cherepinsky during a pre-Verticon show press visit to the company’s Stratford, Connecticut headquarters. “We’re looking at a family of products that has a high degree of commonality when it comes to systems.”

Indeed, the shape of the autonomous UAS represents the wing of the planned follow-on tilt-wing aircraft in the family. “For regional air mobility, we are in the process of building the hybrid electric demonstrator (HEX),” said Cherepinsky.

That will be a 9,000-pound UAS, which will use a single General Electric turbine spinning generators to develop electricity to power a pair of rotors mounted in the actuator-operated tilt wing. Cherepinsky believes hybrid power will be required, given the current development status of batteries. “No electric power source that we see in the near future could provide support for this vehicle,” he said.

Asked why Sikorsky favors the tilt-wing design over the tiltrotors pursued by other manufacturers, Cherepinsky replied, “We understand what happens in the hover with a tiltrotor where you are taking a vertical drag penalty. We believe tilting the wing, getting the wing out of the way in a hover buys you back a whole bunch of performance.”

Hybrid-Electric Testbed Will Be Ready Soon

The Lockheed Martin subsidiary is currently building the HEX’s power systems testbed. “That has all the dynamic components, all the drive train,” explained Cherepinsky, adding Sikorsky plans to run that vehicle on the ground, as well as hover it. “We have the parts, we’re putting the vehicle together, we’ll have power on shortly, and then ground runs and first flight within 12-to-18 months is our current schedule.”

One of the other considerations for the HEX design is that the OEM wants to use it as a test case for next-generation manufacturing. “Part of the cost of the vehicle tends to be old-style manufacturing processes, forgings and castings,” said Cherepinsky.

Those types of components traditionally tend to have long lead times and are difficult and expensive to modify. “This aircraft doesn’t have any of that. We’re 3-D printing components including motor housings, gearbox housings, gears,” he added.

Sikorsky plans for the HEX to serve as a stepping-stone to an eventual scaled-up commercial hybrid-electric aircraft. “Last but not least is the actual product that we are studying as a regional mobility concept that is a nine- to 12-passenger machine, which has a 400+ mile range, that cruises comfortably in the high 200-knots range, and that is a pretty compelling hovering machine,” Cherepinsky said.

It would feature the same drivetrain as HEX but with four rotors on the wing and a weight between 14,000 and 15,000 pounds. “These are not meant to be long-term hovering machines, that’s not the mission,” noted Cherepinsky. “The question is, how do I efficiently perform vertical takeoff, hover for tens of minutes at a time…get efficiently on wing and go far very fast, and do the same thing on the other end?”

For hovering applications, he believes the helicopter—Sikorsky’s primary product range—will continue to fill that role for the foreseeable future.

As part of plans for its eventual hybrid-electric family, the rotorcraft manufacturer is also exploring what it describes as the E-76 concept, a hybrid-powered helicopter using one of its midsize S-76s as a starting point. “We’re not necessarily planning to convert S-76s into electric power, but we can use that platform as a study of what would happen if I took an S-76-class aircraft and added hybridization,” explained Cherepinsky. “We believe there are benefits there.”