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United Therapeutics adds hydrogen to its electric helicopter plans

By Elan Head | May 10, 2024

Estimated reading time 7 minutes, 11 seconds.

United Therapeutics, the biotechnology company that sponsored development of an electric-powered Robinson R44 helicopter, is continuing to advance the concept as a hydrogen fuel cell-powered aircraft.

Mikaël Cardinal, VP of program management at the United Therapeutics subsidiary Unither Bioelectronics, revealed the company’s progress May 9 at the Vertical Flight Society’s Forum 80 in Montreal, Quebec. Cardinal said that his team has been working on a prototype of a hydrogen-powered R44 for about a year-and-a-half, and its first hover is “hopefully imminent.”

United Therapeutics began developing a battery electric-powered R44 in 2016 in partnership with the Southern California firm Tier 1 Engineering. That project made a splash in December 2018 when it set a Guinness World Record for the farthest distance traveled by an electric helicopter.

As Vertical reported at the time, the 30-nautical-mile (55-kilometer) flight was no mere publicity stunt. Rather, it was an early milestone in a deliberate strategy to develop a fleet of zero-emissions vertical-lift aircraft to carry organs from United Therapeutics facilities to patients in need — an ambition that also encompasses partnerships with the eVTOL developers EHang and Beta Technologies.

United Therapeutics collaborated with Tier 1 Engineering on three generations of the battery-powered e-R44. In October 2022, the third-generation e-R44 with a magni250 motor from magniX performed the first all-electric cross-country helicopter flight from Jacqueline Cochran Regional Airport to Palm Springs International Airport in California’s Coachella Valley.

At the time, the partners indicated that they were working toward a supplemental type certificate (STC) for the battery-electric conversion. Ultimately, however, United Therapeutics decided that the 20-minute missions of which the battery-electric R44 was capable were too limiting for what it wanted to achieve.

“It’s not an optimal system — it’s not as performant as a clean-sheet design eVTOL aircraft,” Cardinal said of the battery-electric R44. Nevertheless, he said, the project still generated “a lot of valuable learnings on the different aspects of electric propulsion system integration into existing airframes, which is part of our overall strategy in our technology portfolio.” United Therapeutics expects that electric conversions of existing airframes will encounter fewer barriers to certification than clean-sheet eVTOLs, even though it has invested in those as well.

As the company explored how to extend the range of its battery-electric helicopter — around 40 nm (75 km) without reserves — hydrogen fuel cells emerged as a promising solution. Quebec-based Unither Bioelectronics decided to bring its hydrogen research and development in-house, sourcing commercially available technologies and assembling them into an iron bird for initial ground testing.

“In the last eight months, we’ve transitioned from this to the actual airframe and started the integration of the electric propulsion unit, along with the tank and the fuel cell system,” Cardinal said. “We are currently building more knowledge data sets that will inform . . . the safe-for-flight configuration of the experimental airframe.”

Based on what the company has learned so far, it believes that a range of over 175 nm (325 km) will be achievable using liquid hydrogen as a fuel source. “With those range predictions, we believe it could be a very interesting product from a commercial viability perspective in terms of range and payload,” said Cardinal.

The prototype incorporates two low-temperature proton exchange membrane (PEM) fuel cell stacks along with a booster battery pack that is used to meet transient power demands. The hydrogen fuel tank is mounted in the rear of the aircraft, aligned with the fairing underneath the tail boom. Cardinal said that the company plans to perform initial test flights using gaseous hydrogen and transition to liquid hydrogen later this year.

Along with thermal management in a hover, liquid hydrogen storage is one of the principal challenges facing the project. Cardinal said that Unither Bioelectronics is using a fully customized, vacuum-insulated composite tank that has demonstrated a very low boil-off rate. The system is also lightweight with a structural weight fraction of 35 percent, “so with a 67-pound [30-kg] overall system weight we’re able to hold 44 pounds [20 kg] of liquid hydrogen” — sufficient to meet the company’s range goals, he said.

“In Quebec, we are lucky, we have a green liquid hydrogen supply very close to where we are leading our R&D activities,” Cardinal noted. Looking to the future, he said, the relatively small quantity of hydrogen required for United Therapeutics’ helicopters could conceivably be met by on-site production facilities, “so we’re envisioning local liquefaction hubs across the network to feed the fleet as we perform the organ delivery missions.”

Cardinal said that Unither Bioelectronics views itself as a “system integrator” rather than a technology developer, and is working with a variety of external suppliers that are targeting the aviation market. However, the company has not yet finalized or announced any suppliers, as it is still in the R&D phase. “We’re not married to any specific player in the supply chain,” he said.

Because the R&D has been taking place in Quebec, Unither Bioelectronics has been liaising with Transport Canada Civil Aviation on the project, recognizing that regulators will also need time to get up to speed on this new technology and develop appropriate certification standards.

Eventually, the company aims to achieve an STC for its integrated solution, which may or may not be for the R44. “We are planning for an STC on a Robinson airframe — let’s put it that way,” Cardinal told Vertical.

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