Last week, the Aerospace Technology Institute (ATI) delivered on its promise to present two more FlyZero concepts for regional and short-haul aircraft this year. They are part of a technology and research project from the UK government. FlyZero’s three concepts for hydrogen-based aircraft.
“Three next-generation aircraft concepts have been created as part of the FlyZero project to help understand and demonstrate the potential of zero-carbon emission technologies in aviation”, ATI says in a media statement released on March 11. “The concepts also highlight the crucial future technology opportunities for the UK and additionally, each has its own specific objectives. The FlyZero regional aircraft is designed to demonstrate the feasibility of a fuel cell-powered aircraft, while the narrowbody explores how hydrogen could replace carbon-based fuels in the largest and most competitive commercial aviation sector. Finally, the FlyZero midsize assesses the potential for hydrogen to cover long-haul routes, overturning the view that hydrogen aircraft would be limited to shorter routes.”
After assessing all zero-carbon energy sources, in its report, the FlyZero project team has identified green liquid hydrogen as the most promising fuel for large commercial aircraft. But the team also says that further research and development is needed on six so-called hydrogen technology bricks: power systems (hydrogen gas turbines), hydrogen storage and fuel systems, fuel cells (to convert hydrogen and oxygen into electricity), thermal management, electric propulsion systems, and aerodynamics. Another seven technology bricks have been identified that impact the design and operations of a zero-carbon aircraft: aircraft systems, sustainable cabin design, materials, manufacturing, design and validation, lifecycle impact, and airports, airlines, and airspace consequences.
Regional aircraft
For its regional aircraft, the ATI project team took the in-service ATR 72-600 as a reference and at first sight, its concept seems very similar. It has a high wing a T-shaped tailplane. At 28 meters, the FZR-1E concept is just 80 centimeters longer than the ATR, but the fuselage is wider at 3.5 meters versus 2.7 meters for the French/Italian aircraft with the 75 seats in a 3×2 arrangement. Span is 31 meters compared to 27.1 meters for the ATR. Maximum Take-Off Weight (MTOW) is 28.8 tonnes for the concept and 22.8 for the ATR.
The regional aircraft concept of FlyZero looks very similar to an ATR 72, but underneath the skin, you can see the differences. (FlyZero)
But looking more closely, you see the differences. On the FZR-1E, the passenger cabin extends just aft of the high wing. That’s because, behind the bulkhead, there are two vacuum-insulated storage tanks for liquid hydrogen. Under the cabin floor are the fuel cells that produce electricity for the six electric motors on the wings. Originally, the fuel cells were to be positioned aft in the fuselage, but for space, weight, and weight distribution have been moved to the belly-center position.
ATI says that the concept airplane is calculated to require ten percent more energy than the ATR, while the heavy fuel cells are also a negative factor. But it expects further improvements in fuel cell development that improve energy efficiency: “Up to a point, the weight penalty for over-sizing the fuel cell stack is offset by the reduced weight of the thermal management system and reduced fuel consumption. Therefore, the system take-off power to cruise power ratio will differ from a normal combustion aircraft and the key to this is understanding how to manage transient heat loads at the extremes of the operating envelope.”
An interesting feature likely to be found on many future hydrogen airliners is a water tank to store water that is produced in the exhaust of the hydrogen fuel cells. Dripping the water onto taxiways and runways at airports was deemed not to be acceptable, as it could make them slippery and impact safety. That’s why a tank is required that store the water until it can be released during flight.
The FZR-1E is designed for a maximum range of 800 nautical miles/1.481 kilometers and a speed of 325 knots/602 kilometers per hour, but a typical mission will be 375 nm/695km long. The higher speed of the concept will reduce its block time to 1.6 hours compared to 1.9 hours for the ATR. Block fuel energy will be higher at 56.4 megaJoules versus 52 mJ for the kerosene-powered turboprop.
