• 20 Apr 2023 05:55 AM
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H2-Aero Symposium: Zero Emissions Aircraft Take Flight

By Dan Gettinger and Jesse Schneider
Vertiflite, May/June 2023

With ZeroAvia and Universal Hydrogen making first flights of their large demonstrator airplanes, the momentum is building for practical hydrogen-electric aviation.

The Vertical Flight Society hosted its Second Annual H2-Aero Symposium in Long Beach, California, on March 28–30. In the spirit and model of the first symposium (see “H2-Aero: Leading the Way to Carbon-Free Aviation,” Vertiflite, May/June 2022), this year’s event brought together leaders from industry, academia and government to discuss the outstanding technical and policy challenges that face the hydrogen aviation community, as well as to celebrate the many achievements that have taken place in the past year. The Symposium was chaired and organized by Jesse Schneider, CEO/CTO of ZEV Station and chair of the VFS H2-Aero Team.

More than 120 people attended the symposium in-person and virtually. The three-day event featured eight sessions and over two dozen speakers, as well as a tour of Shell’s nearby heavy-duty vehicle hydrogen facility and the first in-person meeting of the new SAE International AE-5CH Hydrogen Airport Taskgroup.

Hydrogen Aircraft

As part of his keynote, H2-Aero Team Chair Jesse Schneider presented the VFS Whitepaper: Multimodal Hydrogen Airport Hub, which was developed by the VFS H2-Aero Team during 2022 as a direct output of last year’s symposium, and was updated in March 2023. Schneider described the whitepaper as “a guidebook for enabling hydrogen for both aircraft and airports, first by leveraging the megatrend of hydrogen for heavy duty trucks and then growing into a hub.” The H2-Aero whitepaper describes the necessary policy, standards and fuel cell aircraft sandbox demonstrations, as well as sizing of future hydrogen hubs.

Although sustainable aviation fuel (SAF) — i.e., derived from non-fossil sources, with a lower carbon footprint than conventional jet fuel — is needed in the near term to reduce CO2 emissions, it does not solve the local emissions issue and can consume up to three times more energy than hydrogen to produce with electrolysis. “Hydrogen at scale, starting with 60 tonnes per day for a small airport hub, can help start the path to net-zero carbon emissions in aerospace and play a role as a follow-on fuel to SAF,” Schneider said.

In his keynote presentation, Jason Heron — the Clean Fuels Manager for Airbus Americas Research and Technology, responsible for coordinating clean aviation fuel activities for Airbus in the Americas — explained the scope of the challenge facing the aviation industry and Airbus’ efforts to accelerate the introduction of sustainable fuels including hydrogen.

Although aviation contributes around 2.5% to global emissions today, observed Heron, it “could go to 10% very quickly and that could be very detrimental to the aviation industry.”

Airbus has achieved a 50% reduction in CO2 emissions per passenger kilometer compared to 1990 levels, Heron said. To reach the company’s goal of zero emissions, Airbus is looking at improved air traffic operations, new engine and aircraft technologies, and clean fuels such as hydrogen. In the short-to-medium term, however, SAF will remain the company’s primary alternative to conventional fuels, until hydrogen becomes available. Airbus estimates that production of SAF must scale by 600% to meet the estimated demand by 2030.

Airbus is exploring a range of hydrogen-based solutions, including hydrogen combustion and hydrogen fuel cells, as well as synthetic fuels, using a net-zero carbon fuel derived from renewable hydrogen and CO2. Cost will remain a key driver in the adoption of hydrogen-based fuels, said Heron. The Department of Energy (DOE) goal of $1/kg (45¢/lb) is around 80% less than the cost of renewable hydrogen fuels today. In Airbus’ view, liquid hydrogen must utilize cryogenic storage, which presents additional engineering challenges; the company is not focusing on gaseous hydrogen.

In addition to working on its designs for a fleet of ZeroE hydrogen-powered aircraft, which the company unveiled in 2020, Airbus is also interested in other ways of integrating hydrogen. The company sees an opportunity in hydrogen hubs, particularly in the US. Amid the growth in electric ground vehicles, hydrogen could be used to support the increasing level of electrification at airports, which is rapidly outpacing the capacity of existing infrastructure.

In January, ZeroAvia conducted the maiden flight of a Dornier 228 powered by the company’s ZA600 hydrogen-electric engine (see “Electric CTOL/STOL News,” Vertiflite, March/April 2023). Dr. Alex Ivanenko, ZeroAvia’s general manager for rotorcraft and new segments, summarized the company’s progress in developing hydrogen-based motors and power supplies. The company is working on two types of electric motors: the 600- kW ZA600, which is expected to be commercially available in 2025, and the ZA2000, a next-generation motor expected to enter commercial service in 2027 in the 2,000–5,000-kW range for larger aircraft.

ZeroAvia acquired Ivanenko’s HyPoint last year and is continuing development of its high-temperature proton-exchange membrane (HTPEM) fuel cell systems (see “Future Fuel: HyPoint’s Hydrogen Revolution,” Vertiflite, Sept/Oct 2021). Ivanenko described HTPEM technology as essential for fuel cell systems greater than 1 MW for rotorcraft and electric vertical takeoff and landing (eVTOL) aircraft, as it can dramatically decrease the weight of the system compared to low- and medium-temperature fuel cell systems, though the latter are well suited for single-engine aircraft.

One of the primary challenges posed by hydrogen for aviation is that the fuel cells remain heavier than current piston engines, which for aircraft operators translates to a reduction in payload or range. Hydroplane, said CEO Dr. Anita Sengupta, saw an opportunity to develop a fuel cell stack and powerplant for aviation applications that would address these issues. In doing so, Hydroplane seeks to improve the efficiency of the fuel cell stack, while achieving a reduction in volume and maintaining a comparable range to combustion engines — a significant improvement over lithium battery-based energy storage systems.

Hydroplane is working towards its first demonstration flight of a specially configured Piper Archer single-engine aircraft this year, as early as this summer. Hydroplane hopes to offer the powertrain to government users, original equipment manufacturers (OEMs) and pre-existing aircraft owners who are looking for a zero-emissions option. “With our design, it will be a drop-in replacement for them — that’s the entire goal of the company,” said Sengupta. Given the advantages in operational range offered by the Hydroplane solution, advanced air mobility (AAM) applications are an excellent use-case for this technology, said Sengupta, as it would allow operators to take advantage of traditional aviation infrastructure instead of relying on vertiports.

Hydroplane would also consider licensing the technology for non-aviation applications such as heavy-duty trucks. While the electrification of AAM aircraft marks progress towards reducing CO2 emissions, most emissions in the transportation sector — approximately 60% — are from heavy-duty vehicles. “It’s a great opportunity for us to develop a technology that decarbonizes the majority of transport emissions,” said Sengupta.

The second day of the symposium began with keynote presentations from hydrogen aviation executives. Chris Gilmore, head of advanced concepts at Universal Hydrogen, opened his presentation describing the successful completion of the maiden flight on March 2 of their hydrogen-powered test aircraft, a Dash 8-300, and of how the company overcame engineering challenges to reach that point (see “Electric CTOL/ STOL News,” Vertiflite, May/June 2023). In a detailed video, company CEO Paul Eremenko highlighted the vision: “This is the largest airplane ever to fly on hydrogen fuel cells. It’s a flight test platform for the first ever commercial plane to run on sunshine and emit nothing but water.”

Gilmore showed a photo of the powertrain installation, illustrating one of the engineering challenges the team sought to overcome: reducing the intense heat generated by the system. “The thermal management system is not simple,” said Gilmore, noting that it needed to use both liquid cooling and ingest enough air to reject the heat, all while meeting the weight and performance requirements of the aircraft. Universal Hydrogen is working towards its certified product, an ATR 72 transport, which will need engines capable of delivering approximately 2 MW of shaft power. While the test flight in March involved gaseous hydrogen, the next step is for the company to use liquid hydrogen.

In addition to the powertrain, Universal Hydrogen is devoting considerable resources to developing a modular approach to refueling the aircraft; delivering the hydrogen efficiently from a generation plant to the aircraft is a major challenge. The company’s specially designed capsule tanks are designed to be filled at depots before being transported to the airport and inserted directly into the airplane. This approach, argued Gilmore, maximizes the use of existing freight vehicles and ground support equipment, simplifying the fueling process and reducing infrastructure costs. Implementing this system will require ensuring that these modules are certified for both ground and air transportation, and that ground personnel are trained to handle them. Doing so could, however, go a long way towards figuring out how to realize hydrogen-powered flight sooner than many have thought possible, something that Gilmore describes as one of the main motivators for the team at Universal Hydrogen.

Gilmore also highlighted the unique benefits on gaseous hydrogen fuel cells plus batteries for increased range at a minimum cost for eVTOL aircraft. This was originally presented by Eremenko at the second VFS H2eVTOL Council meeting in February 2021 (see “The H2eVTOL Council’s Pioneering Year,” Vertiflite, Jan/Feb 2022), which galvanized VFS efforts to support hydrogen-electric propulsion systems for aviation.

John Piasecki, CEO of Piasecki Aircraft Corp., detailed the company’s progress on designing the PA-890, a hydrogen-powered, slowed-rotor, winged compound helicopter. By combining the compound helicopter technology and the hydrogen fuel cell, Piasecki is aiming for an aircraft that addresses regional aerial mobility (RAM) requirements, namely one capable of flying 200 nm (370 km), plus mandatory instrument flight rules (IFR) reserves.

“The main objective of this, beyond reducing emissions, is to reduce cost,” said Piasecki. “From our perspective, the biggest impediment of the broader application of vertical flight capabilities is cost, and the primary cost driver for vertical flight is the turbine engine.” Piasecki’s partner in the project is ZeroAvia, which is working to develop the 660-kW hydrogen fuel cell that provides the power to both the main rotor and the swiveling tail rotor. As Piasecki put it: “Hydrogen is plentiful, it is clean and it is super high energy.” Powered by ZeroAvia’s HTPEM hydrogen fuel cell, Piasecki is aiming for a 50% reduction in direct operating costs, a 1,660-lb (750-kg) payload and a certification target of 2028.

To realize these goals, Piasecki is engaged in two parallel projects. The first project is its HAXEL demonstration project, for which Piasecki is modifying an EDM aerotec COAX 2D helicopter to serve as a proof-of-concept demonstrator (see “Piasecki to Fly World’s First Hydrogen Helicopter,” Vertiflite, May/June 2022). The company has completed a critical design review and is implementing intermediate design reviews to facilitate getting to flight as soon as possible.

For the second, Piasecki is developing a full-scale hydrogen fuel cell system for the PA-890 to validate key parameters and inform the development of US Federal Aviation Administration (FAA) certification requirements. The company is currently in the second of its three-phased approach to building the modular design for the full-scale demonstrator.

The company is also considering the infrastructure requirements of its hydrogen fuel cell-powered aircraft. Piasecki observed that the distributed and runway-independent nature of vertical flight operations will require solutions that can adapt to the requirements of its customers. “Logistics and infrastructure are core issues that our customers absolutely need to have confidence in and a path forward before they fully commit and adopt the technology,” said Piasecki. The company will seek to leverage existing standards development and work to characterize the investments required by customers to acquire and operate the technology. It will be essential to do so, explained Piasecki, in parallel with aircraft development to ensure that operating the vehicle is cost effective.

Bartini Aero CEO Dr. Ilya Khanykov gave an insightful presentation on the benefits and challenges of hydrogen-powered eVTOL aircraft, including from a business perspective, i.e., maximizing revenue opportunity and minimizing cost opportunity. The Bartini air taxi concept uses the ZeroAvia (née HyPoint) HTPEM fuel cell. Initiated in 2017, the configuration was wind-tunnel tested in 2022 and 2023. Bartini has recently launched certification discussions with the European Aviation Safety Agency (EASA) of two-seat configuration; a four-seater is also planned.

Research and Development

The final session focused on hydrogen research and development. Dr. Anubhav Datta of the University of Maryland made a compelling case for the critical role that universities are to play in developing the future workforce for the hydrogen aviation industry. The current situation is marked by a lack of basic data on a range of topics associated with hydrogen fuel cells for aviation, as well as by a near total lack of sustained funding for research into this field in the United States. As a result, universities do not have the resources to develop aviation-focused cryogenic hydrogen laboratories where such data could be produced and evaluated in a structured setting, nor for the curriculum to educate the future workforce. Absenting this funding, said Datta, the hydrogen aviation industry will soon find itself confronted with a severe shortage in qualified engineers.

The unique facilities and critical mass of faculty situated at the government-backed Vertical Lift Research Centers of Excellence (VLRCOE) — comprised of more than a dozen universities led by University of Maryland, Georgia Tech and Penn State — offer a solution for addressing the workforce challenge and for developing the data underpinning a more sustainable future in aviation. As Datta put it: “If there was ever a right time for aviation-focused research and flying a demonstrator to acquire true data, it is probably now.”

Bell’s Joe Rainville gave a comprehensive overview of fuel-cell and hydrogen technologies. He presented that hydrogen-electric vertical flight aircraft are viable and would provide advantages over a comparable aircraft powered by batteries or traditional fuel.

Hydrogen-electric powertrains would have two-to-three times higher endurance than a battery-electric propulsion system, Rainville said. Hydrogen “fuel cells are predicted to have a significantly longer service life than batteries or potentially a gas turbine,” he added, noting that “fuel cells are quiet and smooth,” and generate power that leads to only water vapor and oxygen-depleted air being emitted. There are challenges, he cautioned. “Fuel cells make about as much heat as they do power,” he noted, adding that a fuel-cell driven system is “more complex than a pure battery-electric system.”

The final presentation of the H2-Aero Symposium was from Gernot Hacker, AVL List GmbH. AVL is supporting the German Aerospace Center’s (DLR) BALIS project with a fuel cell composite testbed for up to 1.5 megawatts (MW) of power. The test field forms a development environment for hybrid-, hydrogen- and electric-drive concepts for passenger aircraft with a capacity of up to 60 people. The BALIS comprises test infrastructure and main components of the propulsion system itself. These include full-scale fuel-cell systems, the hydrogen tank, electric motors, a battery system and the cooling system, as well as control and feedback control systems. The great variability and functional variety of the test environment allows research and development in line with diverse framework conditions, specifications, and guidelines. “The BALIS laboratory is a novel testing environment which enables development and validation of the complete hydrogen and fuel cell systems for aviation. This unique test center will help develop high-power powertrains possible [of achieving] zero-emission flying,” he said.

H2-Aero Ecosystem

There were also notable presentations and session chairs from Elizabeth Collins, National Renewable Energy Laboratory (NREL); Lt. Col. Mike Dunn, US Air Force, North Spark Defense Laboratory; Roberto Licata, Dassault Systèmes; David Franks, SAE International; Helen Leadbetter, UK Civil Aviation Authority (CAA); Jonathan Torres, FAA Airports, Emerging Entrants Division; Tom Mourmouras and Griffin Valentich, Shell Hydrogen; Project NAPKIN’s Mark Kelk, Cranfield Aerospace Solutions, Ltd.; hydrogen advisor Monterey Gardiner, Cryogenic Consulting; Keith Malone, Hydrogen Fuel Cell Partnership (HFCP); and Connor Dolan, Fuel Cell & Hydrogen Energy Association (FCHEA).

VFS thanks all who participated, presented and supported the H2-Aero Symposium. In particular, Bartini, Piasecki, SAE International and ZEV Station were sponsors, and M4 Engineering, Toray and ZeroAvia were exhibitors.

SAE AE-5CH Hydrogen Airport Taskgroup

On the final day of the event, Shell provided a tour of its nearby hydrogen refueling station and SAE International hosted the first face-to-face meeting of its AE-5CH Hydrogen Airport Taskgroup, which is working on Aerospace Information Report (AIR) 8466, “H2 Fueling of Aircraft, in both gaseous and liquid form.”

Dr. Kazunori Nagasawa of NREL presented their novel modeling software, Hydrogen Filling Simulation (H2FillS); the freely available thermodynamic model can be used to evaluate new gaseous H2 aircraft fueling protocols. Finally, Erik Gustafson of Chart industries presented the state of the art of subcooled liquid hydrogen (sLH2) developments for heavy-duty vehicles.

There were a number of key decisions made. The VFS H2- Aero whitepaper’s hydrogen aircraft matrix was adopted as a basis for the SAE AIR 8466 fueling limits and performance guideline. In addition, the AE-5CH taskgroup agreed that there should be a harmonization for hydrogen technology for aircraft and that sLH2 specifically will be used as the technology for the first fueling guideline from 100 kg (220 lb) for an eVTOL aircraft to 1,300 kg (2,866 lb) for a regional airplane.

About the Authors

Jesse Schneider is the CEO/CTO of ZEV Station, a startup establishing a multimodal EV-charging and hydrogen-fueling station. He has over 25 years in automotive electric and fuel cell vehicles at BMW AG and Mercedes-Benz, as well as other OEMs and suppliers.

Dan Gettinger is the managing editor of Vertiflite magazine and the Electric VTOL News newsletter.