• 28 Apr 2025 04:06 PM
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Sikorsky Innovations: Adding Up to Something Big

By Frank Colucci
Vertiflite, May/June 2025

Sikorsky leverages additive manufacturing to prove the physics of its Rotor Blown Wing and make production rotorcraft lighter, cheaper and faster.

The battery-powered Rotor Blown Wing (RBW) demonstrator configuration number five (RBW-5) — built by the Sikorsky Innovations rapid prototyping shop (see “On a Wing and a Pair,” Vertiflite, July/Aug 2024) — transitioned from vertical takeoff to wing-borne cruising flight for the first time in January.

A power system testbed (PSTB) without wing or fuselage has begun ground-testing the turboshaft, generator and motors for a bigger hybrid-electric experimental (HEX) tilt-wing aircraft. Paced by PSTB progress, the 9,000-lb (4,100-kg) HEX air vehicle should fly in 2027 or 2028 and could pave the way for a potential 14,000–15,000-lb (6,400–7,000-kg) tilt-wing aircraft to succeed the company’s S-76 helicopter. Sikorsky, a Lockheed Martin Company, has invested heavily in additive manufacturing for rapid prototyping and affordable production, including parts for its current helicopter programs. Innovations director Igor Cherepinsky told a February media tour, “Sikorsky products have longevity. When we make these, they will be out there for decades and decades and decades … A year or two to revolutionize manufacturing is absolutely worth it to us.”

The RBW concept promises the vertical takeoff and landing (VTOL) performance of helicopters and the speed and range of fixed-wing aircraft. During efficient fixed-wing cruise, hybrid-electric versions would recover the power expended by the booster battery during takeoff.

The Promise of RBW

Today’s twin-proprotor RBW-5 proof-ofconcept demonstrator models Sikorsky’s RBW entry into the Defense Advanced Research Projects Agency (DARPA) AdvaNced airCraft Infrastructure-Less Launch And RecoverY (ANCILLARY) competition. The 120-lb (64-kg) autonomous uncrewed aircraft system (UAS) demonstrator proves the physics behind a family of larger crewed and uncrewed tilt-wings. Traditional tailsitters and tilt-wing aircraft use propellers, but RBW uses a proprotor with cyclic and collective blade-pitch control. Cherepinsky noted, “We’re adding a helicopter twist to the tilt-wing, which on our tailsitter has been very successful.”

With its 10-ft (3-m) span bathed in constant rotorwash, the RBW-5 uses commercial-off-the-shelf electric motors to explore the concept. By the time of the Stratford, Connecticut, briefing, the demonstrator had transitioned more than 100 times from vertical to horizontal flight and back to refine fly-by-wire (FBW) control laws for itself and larger aircraft. “Our biggest rule is we follow the physics,” said Cherepinsky.

The RBW-5 has no vertical tail surfaces but integrates fixed-wing control movements with rotor pitch changes to transition from vertical to wing-borne flight around 80 kt (150 km/h). “Part of the thing that makes it work is the blown wing,” noted Cherepinsky. The tilt-wing eliminates the downwash losses suffered by tiltrotors in a hover. “We believe tilting the wing in a hover … buys you back a whole bunch of performance. It brings up some interesting issues, which is why these are not conventional tiltwings.” If Sikorsky wins the ANCILLARY Phase II and Phase III contracts, the company plans to build a 300-lb (140- kg) hybrid-electric demonstrator for flight tests.

DARPA’s ANCILLARY UAS aims to launch and recover from ship decks or unprepared sites. With its electric drive and flight control system components integrated in wing nacelles, the operational Sikorsky RBW would carry intelligence, surveillance and reconnaissance (ISR) sensors or cargo in its center-wing bay. Bigger, crewed versions would hold its horizontal cockpit and passenger cabin level while the wing tilts to obviate the pilot contortions necessary to land past tailsitters. “We’ve had conversations with military and commercial operators. There’s clearly a desire for onboard pilots,” said Cherepinsky. “For planes that carry people, there’s going to be room for at least one pilot up front. All these vehicles will be capable of flying autonomously or with an operator.”

With or without a pilot, Sikorsky’s Matrix autonomous flight controls could also tailor the HEX tilt-wing aircraft to prioritize performance or operating costs in different missions. “There is no such thing as the perfect aircraft,” conceded Cherepinsky. However, hybrid-electric propulsion makes it possible to optimize the size of turboshafts and supplemental batteries for the application. Together, Matrix controls, electric propulsion and widely variable speed proprotors could, for example, trade noise footprint for maximum performance at different points in the mission.

The PSTB for the 9,000-lb (4.1-t) HEX demonstrator will hover with a single GE Aerospace CT7 turboshaft powering the 1.2 MW-generator that in turn powers separate Sikorsky-built motors to spin twin proprotors. “It’s not as easy as it sounds,” acknowledged Cherepinsky. Sikorsky Innovations engineers studied tilt-wings versus mechanically more complicated tiltrotors, multicopters and other unconventional configurations.

Cherepinsky explained, “We understand the physics of these vehicles, and we believe it’s much more optimal to have [fewer] motors.” A bigger tilt-wing for regional air mobility might have four proprotors blowing across its span. Sikorsky engineers have already drawn a notional RBW with a 60-ft (18.3-m) span and 30,000-lb (13.6-t) gross weight. Cherepinsky explained, “We are interested in areas where a normal helicopter used to operate and [we can] double the range.” A notional 9–12-passenger regional air mobility RBW could cover 400–550 nm (740–1,020 km) at speeds from 200–300 kt (370–555 km/h). Sikorsky has been building motors and flight controls for the vehicles in-house and now makes system commonality and vertically integrated manufacturing central themes in its advanced concepts. Most parts for the hybrid-electric aircraft will be 3D printed in-house.

Additive Answers

The RBW-5 proof-of-concept took advantage of additive manufacturing (AM) in the fabrication of plastic parts. The bigger HEX leverages metal AM for dynamic parts. HEX aerostructures would be built with composite fiber placement, and Cherepinsky said, “We are holistically looking at how we’re going to build this. We don’t [just] want to build a demonstrator … We’re trying to figure out what manufacturing in the future is going to look like.”

Sikorsky built its Advanced Manufacturing Technology Center (AMTC) at the Stratford helicopter plant to take manufacturing cost and time out of the company’s current and future aircraft and to free itself from overburdened, unpredictable suppliers. Cherepinsky explained, “Additive manufacturing of high-strength, flyworthy components enables the designer to go from idea to functioning part in days as opposed to months … This approach is a game-changer for rapid prototyping.”

AM processes build parts from wire, powder or rod rather than machining them from billets, forgings or castings (see “Parts Just Add Up,” Vertiflite, Sept/Oct 2013). Sikorsky now 3D prints aluminum, titanium and magnesium components, as well as plastic parts. At the AMTC, Lockheed Martin fellow Kishore Tenneti noted that no outsourced casting is usable without repeated, timeconsuming machining and inspections to meet Sikorsky specifications.

3D printing eliminates the irregular casting process completely. Tenneti said, “In addition to controlling our own destiny, we’re driving out the casting problems and reducing the lead time on these parts.” A transmission housing that typically took 18 months to deliver from a casting supplier was 3D printed in two weeks. When unsatisfactory parts from a radiator supplier slowed Black Hawk production, Sikorsky devised a 3D-printed replacement now in qualification.

The AMTC in Stratford started in 2014 with a single industrial-size 3D printer. It now has 28 thermoplastic AM machines and five metal AM machines. Another metal machine is due this year.

During the AMTC media tour, Sikorsky director of aircraft systems design Bob Perchard offered, “All the technology here was initially geared toward making shop floor aids/tools for our hourly employees to rapidly have a solution for something that was very complex. We can 3D print something and get a new tool out to them the next day. Now, we’re producing 3D-printed production parts that are flying away on aircraft fielded to our customers.” Metal parts up to 8 ft (2.4 m) diameter and 40 ft (12.1 m) long can be 3D printed in-house.

Whatever the material, AM processes can also produce complex geometries that are impossible with traditional manufacturing and make lighter parts by combining multiple components into one piece. Integrating fittings, fasteners and other details into workpieces, for example, results in a lower overall part count, and the ability to go directly from design to finished component with minimal touch-time generates more savings. Printing multiple copies of parts without additional labor also provides notable savings with low-volume components.

3D-printed avionics junction boxes and environmental control ducts for S-70 Black Hawk/Seahawk helicopters cut lead times 55–70%. Both parts were well suited for 3D printing due to their relatively simple designs. The choice of fabrication technology was based on part design, material properties, cost and print speed. The avionics junction box was made from ULTEM polyetherimide (PEI) resin using fused deposition modeling (FDM). The environmental control ducts with more complex stiffeners and curves were made of a nylon polymeric material infused with carbon.

What Next?

The S-102 Raider X Future Attack Reconnaissance Aircraft (FARA) competitive prototype — cancelled in February 2024 by the Army just before first flight — had around 200 AM components, including an additive aluminum transmission housing that cut weight 20–30% and incorporated internal features impossible with traditional processes. The technology is applicable to future production blocks of the Sikorsky Black Hawk under the next multiyear contract from the Department of Defense.

The S-104 HEX demonstrator effort has already used three additive manufacturing technologies to make dynamic, flight control and airframe parts. Laser powder bed fusion (LPBF) uses a high-power laser to melt and fuse metal powder, layer by layer, into solid parts. It has produced 3D-printed gearbox housings.

Additive friction stir deposition (AFSD) made HEX swashplates and main-rotor shafts. A high-speed rotating stirring tool printhead deposits feedstock at temperatures below the melting point, and dynamic friction causes the material to heat, soften, deform and bond. The result is metal parts with a fine crystalized grain microstructure that is equiaxed (the same size in all directions).

FDM used by Sikorsky to 3D print thermoplastic junction boxes and other components extrudes melted plastic through a nozzle. Layers build up to quickly make accurate parts from digital design tools.

Sikorsky's vice president and general manager Rich Benton came to the helicopter maker from Lockheed Martin Training and Solutions and reflected on his new assignment with refreshing enthusiasm and insight. He told the assembled press at Stratford, “This is the most amazing factory that Lockheed Martin has. It’s 2.2 million square feet [20.4 hA] of manufacturing awesomeness.”

About the Author

Senior contributing editor Frank Colucci has written for Vertiflite for 30+ years on a range of subjects, including rotorcraft design, civil and military operations, testing, advanced materials, and systems integration.