In a significant leap forward for the future of air mobility, Joby Aviation has successfully tested a hydrogen-electric version of its S4 electric vertical-takeoff-and-landing (eVTOL) aircraft. This breakthrough comes as Joby continues its pursuit of certification for its battery-powered air taxi and gears up for the launch of commercial services.
The modified S4 prototype, now equipped with a hybrid battery/hydrogen-electric propulsion system, completed a 523-mile flight over Marina, California, in June. This distance far exceeds the 155 miles achieved by the battery-electric version of the S4 in 2021. Supported by the U.S. Air Force’s Agility Prime program, this technology demonstrator marks a pivotal step in extending the range and capabilities of eVTOL aircraft.
“At a high level, 90% of the systems on the aircraft stay the same,” said Joby founder and CEO JoeBen Bevirt. “We add the fuel cell, the liquid hydrogen system, modify the batteries, and we get an aircraft with dramatically more range and endurance.”
Innovations in Hydrogen-Electric Propulsion
The demonstrator features a series-hybrid battery/hydrogen-electric propulsion system. While retaining the six tilting propellers and electric motors of the baseline S4, the system uses a fuel cell to recharge the batteries during flight. A 40-kg liquid hydrogen (LH2) tank, developed internally by Joby, is installed in the fuselage, along with a fuel cell from Joby’s subsidiary H2Fly and a heat exchanger for cooling.
This technological advancement highlights Joby’s vertically integrated approach, enabling optimized design and construction of critical components such as the dewar (insulated tank), fuel cell, compressors, and battery system. This synergy was crucial for the efficient development of the hydrogen-electric propulsion system.
“One of the unique things we were able to achieve is to draw on the existing pool of technology and pull out the battery-electric energy source and introduce this hybrid battery/hydrogen-electric solution,” said Didier Papadopoulos, aircraft OEM president at Joby. “The key takeaway is the power of electric propulsion to allow you to think in a very flexible way about how you develop new aircraft architectures.”
Strategic Implications and Future Prospects
Joby’s development of the hydrogen-electric demonstrator has been undertaken by a small, focused team, ensuring minimal diversion of resources from the certification of the battery-electric S4 and preparations for Part 135 commercial air taxi services. This strategy leverages existing work and investments, allowing for significant expansion in capabilities with relatively modest additional investment.
Joby envisions a complementary role for hydrogen-electric and battery-electric aircraft. Battery-electric models will serve short-distance, intra-metropolitan trips, while hydrogen-electric aircraft will handle regional journeys, offering extended range and operational efficiency. Airports are poised to become key hydrogen distribution centers, facilitating the growth of hydrogen-electric air travel.
“Hydrogen is one of the best energy carriers in the world because it’s three times lighter than jet fuel and because we can convert the chemical energy that it contains into propulsion twice as efficiently as a small turbine can convert jet fuel into propulsion,” Bevirt explained.
While Joby has not specified a timeline for the development and fielding of the hydrogen-electric air taxi, the company draws confidence from its progress with battery-electric aircraft certification. The relationships and regulatory groundwork established with the FAA are expected to be advantageous as discussions about hydrogen-electric certification commence.
“H2Fly started [working on hydrogen-electric propulsion] about 10 years ago, and now we are at a point where we’re able to integrate with the airframe that we have today and demonstrate,” Papadopoulos said. “That sets the stage for the next steps, moving into the certification framework and what the aircraft is going to look like.”
Bevirt anticipates that hydrogen-electric air taxis will significantly boost demand for liquid hydrogen infrastructure at airports, propelling a major shift in aviation sustainability and operating economics.
“I think the aviation world writ large doesn’t realize what a game changer hydrogen will become for aviation, from a sustainability standpoint but also the operating economics,” Bevirt said. “Hydrogen-electric, in my view, is going to be one of the greatest disruptions in aviation in multiple generations.”
This milestone in Joby Aviation’s journey represents a transformative moment for the aviation industry, setting the stage for a new era of sustainable, efficient air travel.
PHOTO CAPTION: Joby Aviation eVTOL Joby’s CEO lauds the performance of the internally developed liquid hydrogen tank and fuel cell heat exchanger (under the nose). Credit- Joby Aviation