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The planned ZERA-Lite modified Caravan uses liquid hydrogen and fuel cells for zero-emission propulsion.
UK startup Zero Emissions Aerospace (ZeAero%) has unveiled plans to retrofit the Cessna Caravan with a liquid hydrogen fuel cell propulsion system as a step toward developing a zero-emission 19-seat regional aircraft.
Founded in 2019 and based in Bristol, England, ZeAero% is building a 200-kW integrated propulsion system demonstrator, with ground testing planned for next year, says founder and CEO Matthew Orchard.
ZeAero% has launched a follow-on fundraising round to build a 500-kW propulsion system for ground and flight testing, aiming for supplemental type certification (STC) in the Caravan for entry into service in 2030-31, he says.
The startup is aiming for a range of 400 nm with the reengined Caravan, dubbed the ZERA-Lite, while retaining the nine-passenger payload. By comparison, a rival Caravan fuel cell conversion using gaseous hydrogen offers a 250 nm range.
“Initially, we probably had too ambitious ideas and the last five years have been good for us to really understand where the technology is going,” says Orchard, who held several senior engineering management roles over a 17-year career at Airbus.
“We went back to basic physics, looking at the Part 23 space because if we are going to radically change the technology, we need to learn to crawl before we run,” he says. “The only credible combination we came up with was liquid hydrogen [and fuel cells].”
ZeAero% is developing a modular fuel cell system powered by liquid hydrogen that scales from 500 kW to “a couple of megawatts,” Orchard says. “We would love to do something in the 19-seat space, but to start with we’re working on an STC conversion of the Caravan because it has a good payload fraction. You can stick a somewhat heavier propulsion system in it and you still have some useful payload.”
The Caravan also has a certified cargo pannier. “It’s a good place to put the fuel storage system without penalizing the aircraft too much,” he says. “And unlike some of the gaseous systems, we don’t need to expand the aero shape that much to do that.”
ZeAero% is aiming to get the modified Caravan onto the market for £30-40 million ($40-54 million). “That’s with the proviso that we don’t try to develop everything ourselves,” Orchard says. “To develop everything, you could easily spend £120 million on it, but we are not.”
So far, ZeAero% has been supported with funding from the government’s Innovate UK agency and Aerospace Technology Institute. Innovate UK lists three projects totaling £1.83 million in funding running from May 2023 to February 2027.
This includes the £1.5 million Sparrowhawk project to build the 200-kW liquid-hydrogen propulsion demonstrator. The first hardware for the “pump-to-prop” ground test rig has been delivered to ZeAero%’s recently opened facility in Bristol, Orchard says.
ZeAero% is using a double-walled vacuum-insulated liquid hydrogen tank. The demonstrator has aluminum inner and outer walls, but the startup plans to move to a carbon-fiber outer tank that is integrated with the aircraft structure to save weight.
The company has also developed technology to use waste heat from the fuel cells to vaporize and condition the liquid hydrogen for delivery to the fuel cells. “We were not keen on having a cryogenic pump,” Orchard says.
“We have a solution that avoids in-tank pumps and, by using the waste heat from the fuel cells, we probably gain about a 10% reduction in the cooling air needed,” he says. ZeAero% also plans to use additive manufacturing to enable complex heat-exchange geometries.
Using liquid hydrogen, ZeAero% is targeting a range of 1,000 nm for its proposed 19-seat ZERA-19. “Effectively, we can tanker fuel for 500 nm, take on a complete payload or passengers or cargo and return to base without refueling,” Orchard says.
Range and a 10% reduction of operating cost over a 19-seat turboprop “have been big drivers of our technology,” he says. “We’re confident with a clean sheet design we can get to 1,000-plus nm,” he says.
ZeroAvia has postponed certification of its gaseous-hydrogen fuel cell propulsion retrofit because of funding issues. Orchard says ZeAero%’s approach differs in starting with liquid hydrogen and avoiding the need to later change fuel system technologies.
The startup also is not doing everything in-house, instead working with specialist suppliers of system elements including fuel cells, compressors and electric engines. “I also think starting humbly and building slowly has worked to our advantage,” he says.
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