July 25, 2023
As aviation moves toward a goal of net-zero carbon emissions by 2050, innovators are considering a number of sustainability solutions. Although business aviation is responsible for just .04% of global transportation emissions, the industry is supporting a wide range of initiatives including sustainable aviation fuel (SAF), book-and-claim, carbon offsets and new technology.
Advocates say hydrogen-powered aircraft propulsion has the potential to provide a less expensive and carbon-free alternative.
Greener, Cheaper Range
Most companies currently developing hydrogen-electric aircraft are focusing on the regional airline market. Nonetheless, experts believe the resulting technology could eventually result in new zero-emission aircraft for the business sector.
ZeroAvia is producing hydrogen-powered engines for small regional turboprops and sees hydrogen as a good solution for scheduled commercial operations with predictable demand to support production volumes. That said, business aircraft operations with predictable operations or along common routes could be candidates for early adoption.
“There is certainly a need for cleaner propulsion in business aviation, as many business leaders will attest,” said James McMicking, chief strategy officer at ZeroAvia.
Stuttgart, Germany-based H2Fly – now owned by U.S. electric vertical takeoff and landing aircraft (eVTOL) developer Joby Aviation – is pioneering hydrogen-electric aviation in its HY4 demonstrator aircraft. The HY4, a four-place hydrogen-fuel-cell powered aircraft, first flew in 2016.
Hydrogen-fueled powerplants offer promising technology for regional air travel with a maximum range of 2,000 km – about 1,080 nm, according to H2Fly Founder Josef Kallo. The company has partnered with Deutsche Aircraft to power a modified Dornier 228 demonstrator aircraft using hydrogen fuel cells.
“The technology of electric hydrogen airplanes is moving very fast, and we have seen huge gains on power density side which leads to us to believe we can achieve greater range,” Kallo said.
Supernal, a subsidiary of Hyundai Motor Group, is developing a hydrogen-powered eVTOL intercity aircraft with a regional range. Paul McDuffee, Supernal’s senior principal, airspace integration, said hydrogen can mean utilizing the current regulatory environment without exemptions and waivers, since with hydrogen propulsion, the system essentially creates its own power and can have a much longer range.
“Hydrogen fuel cells eliminate the capacity issues that come with traditional battery power,” said McDuffee. “This could mean a better use case for business aviation.”
“Hydrogen has been used as an energy source for a long time and now may be its moment in the sun,” he added. “It is used in space programs, boats, busses and other vehicles, so we’re learning from those proven successes. With the byproduct being water, how clean you get?”
In addition to being a sustainable alternative to fossil fuels, hydrogen could result in a lower-cost solution to air travel, especially under current tax structures for fossil fuels.
“With the global drive to scale clean hydrogen, production costs will continue to decline, and it will become increasingly available across the aviation network, making hydrogen an even more attractive option for wider business aircraft use,” said McMicking.
Hydrogen-electric aircraft also promise lower maintenance costs when compared to traditional powerplants.
The past decade – really, the past six or seven years – have demonstrated significant breakthroughs in hydrogen-powered aircraft research, development and testing.
“We’re at a unique moment where technology can be driven in fast-forward,” said Kallo.
“The HY4 has demonstrated on the ground, at full power/high dynamics of power provision, that liquid hydrogen storage can deliver very accurately and efficiently the fuel that’s needed to power the aircraft,” Kallo added. “That was the missing piece. Now I can say the technology works.”
McMicking reported, “The next needed breakthrough is delivering higher temperature fuel cells which can reduce the weight and complexity of the systems and thus improve the overall specific power of these clean engines, this will enable improvements in payload and range. The second will be the move to liquid hydrogen as the fuel, which can more than double the volumetric energy density, thus reducing the amount of space required to carry hydrogen fuel, the primary limitation of hydrogen-powered aircraft.”
Hurdles to Widescale Implementation
Infrastructure, regulatory frameworks and cost of research and development are hurdles to widescale implementation of hydrogen propulsion systems.
Infrastructure is a clear challenge for any new fuel or energy system. Widescale implementation of SAF is hampered by production and distribution challenges. For electric aircraft utilizing lithium-ion batteries, developing a grid robust enough to support charging is a challenge.
Infrastructure will also be a challenge for hydrogen-powered aircraft.
“Infrastructure is expensive; hydrogen is cheap,” said Kallo. “We want emission-free hydrogen, also known as ‘green hydrogen’, which is not produced from natural gas or fossil fuel resources, so we need primary renewable energy from solar or wind farms to produce the hydrogen.”
This is a worthy investment, though, as hydrogen could be the cheapest of the fuel sources currently in use or development. ZeroAvia contends the investment for developing infrastructure for the production of synthetic aviation fuel, which will make up the bulk of SAF produced in the coming years, is a more significant investment than that required to develop green hydrogen infrastructure.
Regulatory hurdles are another challenge to widespread adoption of hydrogen as an energy source.
“Resources are being devoted to hydrogen aviation in many countries across the world, so we can be confident that certification will come,” said McMicking. “However, to be an early adopter and reap the benefits that will bring, it is important that policymakers and regulators are active in exploring and supporting the technology.”
McDuffee considers regulatory hurdles from an AAM perspective, including the current FAA rulemaking for powered-lift aircraft.
“If there is no relief for fuel/energy reserves once AAM aircraft are being operated in a more routine fashion, there will be significant challenges to advancing AAM.” he said. “Battery power alone is far from meeting IFR reserves by regulation for anything more than intercity operations. AAM lacks operational experience, so we should look for propulsion options, like hydrogen, which would allow for more operational experience in the NAS [National Airspace System] under current regulations.”
A third challenge is the cost to develop lightweight components. Kallo explained lightweight components will allow higher performance in the propulsion system, but design and certification costs make these components very expensive in the first generation.
ZeroAvia believes its engines for small regional turboprops will be available as early as 2026. By 2030, the company estimates their hydrogen propulsion system could power regional jets with up to 60 passenger seats with a range of up to 560 nm. The same technology could be used in the mid-size and large cabin business jet markets.
Supernal plans to launch in 2028, beginning with intercity eVTOLs, and H2Fly is also targeting 2028 for its regional aircraft entry to service.
ZeroAvia believes technology to enable larger, longer-range aircraft should be available by the 2040s, but that technology would require new airframe designs – retrofitting today’s wide-body aircraft designs would not be feasible. This means the propulsion technology could be available before the aircraft designs are.
“Our mission is a hydrogen-electric engine in every aircraft, because we have concluded it will be the most economical and environmentally friendly propulsion solution, and we understand the technology path to get us there,” said McMicking.
While these companies are focusing largely on regional airline travel, with the exception of Supernal’s eVTOL model, developing the technology and infrastructure for hydrogen-fuel-cell powerplants can only benefit business aviation’s sustainability efforts.
New technologies, when combined with better aircraft design for improved aerodynamics, more effective performance in traditional engines and more efficient routing, are critical to meeting the global aviation industry 2050 net-zero emissions goal.