With the global aerospace community committed to a greener future, a Boeing-led research team has successfully flown what it says is the world’s first manned aircraft powered by hydrogen fuel cells. Fuel-cell technology itself is not new, and is gaining acceptance in ground-vehicle applications, but this aviation initiative by Boeing Research and Technology-Europe (BR&TE) looks destined to play an important part in the ongoing search for more environmentally friendly ways of flying.
Nobody in Boeing’s Phantom Works organization is suggesting that this is going to lead to a 737 replacement powered by fuel cells, but the results of the program will undoubtedly encourage new applications to emerge in due course, perhaps for UAVs, small manned aircraft, or next-generation auxiliary power units. The big breakthrough this time is the achievement of sustained straight and level flight relying on fuel-cell power alone, producing zero emissions—just water and heat.
“This is a most inspiring way toward a greener future,” said John Tracy, Boeing’s Chief Technology Officer and Senior Vice President-Engineering, Operations, and Technology, during a test flight at Ocana, a small general aviation airfield just a few miles south of Madrid. “We have new technologies and some of the best engineers in Europe working together to provide affordable solutions to environmental challenges. One of the greatest contributions we can make is to pioneer new technologies to give us a tangible, powerful lead that will take us to progressive new products. This is vital so that future generations can enjoy the benefits of global air transport.”
The baseline airplane platform is a 53.5-ft-wingspan Dimona, a two-seat composite-structure motor-glider manufactured by Diamond Aircraft Industries of Austria. The modified hybrid power system comprises hydrogen-gas-fuelled proton-exchange-membrane fuel cells and a lightweight lithium-ion battery power pack linked to an electric motor that is coupled to a conventional propeller. The hybrid system generates a total of 45 kW, with the fuel-cell element providing 23 kW—sufficient for cruise—and the lithium-ion batteries providing another 22 kW of power for takeoff. The batteries are disconnected once target altitude has been reached.
Replacing the conventional powerplant aboard the airplane and integrating the new hybrid system was a major engineering and systems-integration task that required removing almost everything from in front of the engine compartment bulkhead and re-fitting the space with the electric motor, fuel-cell stacks, water tanks, and air filter, with all necessary pipe work and electrical connections.
Fitting the new power management and distribution system and motor controller/inverter system units in the second pilot seat position, with the battery pack and hydrogen tank behind the pilot, required careful attention to such related issues as maintaining an acceptable center of gravity to ensure safe airplane handling at all stages of the flight profile. Even the weight of the pilot became an important factor in calculating how the reconfigured airplane would fly. Balance was crucial.
The tank contained 34 L of compressed hydrogen gas and there were two forward-mounted 10-L water tanks. Although the team was keen to use standard components wherever possible, a high proportion of the overall propulsion system was custom-built for this application. The brushless electric motor was originally designed to power an automobile. Cockpit instrumentation was modified to provide the pilot with suitable warnings should there be an “over-powering” problem, or temperature issues. But the engine performed very well during the test flights and both the pilot and ground observers noted almost silent operation compared to a normal light aircraft. With the hybrid power system functioning as intended, the fuel cells converting the fuel directly into electricity without combustion or mechanical energy, there were zero carbon-dioxide emissions, the wastewater being used to cool the fuel-cell stack.
First test flight took place in early February, with two more in both late February and early March, completing the planned initial flight-test program. Using the full hybrid power combination, the modified Dimona, bearing Boeing Phantom Works markings, taxied out at Ocana and then took off and climbed steadily to 3300 ft over the airfield site. The takeoff run was slightly longer than normal but the climb rate was smooth and uneventful. The aircraft flew at 62 mph for approximately 20 min on power solely generated by the fuel cells.
BR&TE is located in Madrid, Spain, but the Fuel Cell Demonstrator Airplane program has been a truly international effort, spread over five years. The U.K. company Intelligent Energy was responsible for the design, development, and assembly of the fuel-cell system. Gore of Germany built the membrane electrode assemblies, Madrid-based IIC built the thermal-management system for the electric motor (supplied by UQM Technologies of the U.S.), Saft of France designed and assembled the auxiliary batteries and emergency backup battery, and the MT-Propeller (from Germany) propeller was modified by Madrid’s TAM to mechanically couple to the electric motor. BR&TE worked closely with Madrid’s Inventia in developing a CATIA model for the demonstrator aircraft and on the preliminary design for the installation of all the components. Also from Madrid, avionics group Aerlyper performed the minor airframe modifications, while Air Liquide was responsible for the detailed design and assembly of the onboard fuel system and refueling station.