Hydrogen-fueled airliner concepts to-date have been criticized for their lack of growth potential in range and payload, but a new design outlined by the UK’s Aerospace Technology Institute (ATI) indicates the potential for a viable design capable of carrying 279 passengers on non-stop flights up to 5,250 nm.
Developed under the UK government-backed FlyZero project, the midsize concept is the largest of several aircraft designs produced through the ATI study that targets zero-carbon-emission commercial air travel by the end of the decade. Early in 2022, findings from the project will be published. This will include three final aircraft concepts covering the regional, single-aisle and midsize sectors, along with technology roadmaps, market and economic reports and a sustainability assessment.
The ATI study group said the findings “will help shape the future of global aviation with the intention of gearing up the UK to stand at the forefront of sustainable flight in design, manufacture, technology and skills for years to come.”
Specifically referencing the midsize concept, the group said the design “would meet the demands of a unique sector of the market between single-aisle and widebody aircraft operations which together account for 93% of aviation’s carbon emissions.”
Characterized by a distinctively bulged forward fuselage, the midsize design incorporates “cheek” cryogenic fuel tanks on either side of the lower lobe as well as an aft fuselage-mounted fuel tank. Designers say the liquid hydrogen will be stored at minus 253C (20K) and the use of cheek tanks will “also serve to keep the aircraft balanced as the fuel burns off and eliminate the need for any additional aerodynamic structures.”
Fuel will be fed to turbofans adapted for hydrogen combustion and supported on a 54-m-span (177-ft.-span) high-aspect ratio wing. As the wing does not need to carry fuel it will be easier to optimize for a higher cruise lift coefficient, ATI says. “The concept demonstrates the huge potential of green liquid hydrogen for air travel not just regionally or in short-haul flight but for global connectivity. Liquid hydrogen is a lightweight fuel, which has three times the energy of kerosene and sixty times the energy of batteries per kilogram and emits no CO2 when burned,” the group added.
Through the development of the FlyZero concepts, the project has identified a wide variety of airframe structures, systems and propulsion technologies which—together with the infrastructure and ground equipment for refueling—will require rapid development to deliver zero-carbon-emission flight. These include dry wing designs (without fuel tanks), cryogenic hydrogen tanks and fuel systems, fuel cells, electrical power systems and hydrogen gas turbines.
“Liquid hydrogen helps the volume geometric challenge to some degree, but there is still a challenge that we’re looking to address at aircraft level as to where we put the tanks, where we position them, the center of gravity effect that can have, and the insulation challenge,” said Simon Webb, FlyZero’s chief engineer for propulsion.
Speaking to Aviation Week, he said the extremely low storage temperatures are a “big challenge in terms of refueling at the airport, storage of the fuel and then the onboard cryogenic tank and the fuel delivery system and the equipment that goes with the types of pumps and valves. Some of the technology is there in the space industry, for example, but aviation has quite different requirements in terms of its life, the reuse or the weight of it, the cost of it.”
Commenting on progress to-date, FlyZero project director Chris Gear said: “I do believe you could fly an experimental vehicle and validate these arguments. And some of the work we’ve done has really shown that because liquid hydrogen is so much lighter than kerosene—you can basically counter the weight penalty for carrying the tanks. It’s very easy to develop an aircraft that could fly across the Atlantic on a liquid-hydrogen solution and so we do see that as a real possibility.”
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