Putting fuel-cell-powered aircraft into the air

  • 18-Oct-2008 11:01 EDT
antares_stuttgart.jpg
The first flight of the Antares DLR-H2 is expected to take place in 2008. The aircraft wa­s first exhib­ited in late September at the Stuttgart International Airport.­­­

Higher levels of electrification in aircraft are on their way but will not be taking over an entire aircraft any time soon, said Denis Chapuis, Vice President R&D, EADS France, during a synergy forum in Hamburg titled, “Aircraft Meets Automotive: Systems Architectures.”

“Currently we have four different types of power in aircraft: electric, hydraulic, pneumatic, and mechanical,” he said. “Will we go all electric? No. Batteries are not sufficient for aircraft use. There is no other source. The fuel cell is not there.”

But is that really so? Change is coming. Even fuel-cell ­skeptic Chapuis ­acknowledged the change that is taking place in aeronautics. “The aircraft 10 years ago is not the same as the aircraft today,” he said.

Very much like in the automotive industry, the fuel cell has the potential to split the expe­rt community in two groups: believers and skeptics. Among the many cons is the criticality of cooling, says Chapuis. “Replacing other forms of energy with electric power does not only raise the question of how to provide that electric energy, but the power such electronics require introduces a new dependency between energy supply and cooling. If we lose cooling, we will lose the electric function. Look at an Airbus A330, for example. It has 1.6 MW installed power, 1.2 MW of which is pneumatic. It is a challenge to do this electrically.”

Looking at fuel-cell technology from the manufacturing and economic point of view, there is another major obstacle: In contrast to the U.S. and Japan, there is no developed supplier base for power electronics in Europe that would be ready to meet an industry demand.

That said, the complete lack of an alternative to jet fuel as a sole power source—at least for auxiliary aircraft functions—asks for further development.

­The German aerospace research center (Deutsches Zentrum für Luft- und Raumfahrt, DLR) is an organization that has been driving the use of fuel cells in aircraft for over five years. After demonstrating the potential of fuel cells as a 20-kW APU during a flight with the Airbus A320 ATRA (Advanced Technology Research Aircraft in cooperation with Airbus Germany) earlier this year (see AEM Technology Update, April 2008), the DLR has unveiled an aircraft that is completely powered by PEM fuel cells.

The new motor glider, called Antares DLR-H2, was jointly developed by the DLR Institute for Technical Termodynamics, located at Stuttgart, together with Lange Aviation, Zweibrücken. The aircraft is based on the one-seater motor glider Antares 20E, which has been in production for several years. The Antares DLR-H2 has a wing span of 20 m but a mass of only 600 kg—60 kg less than the standard motor glider. The Antares DLR-H2 was first exhibited at Stuttgart International Airport at the end of September, with first flight scheduled for 2008.

The fuel-cell-powered motor glider has two additional under-wing pods. The left one holds a 350-bar hydrogen tank, and the right pod contains the 20-kW (25-kW-peak) fuel-cell system that drives a motor powerful enough to make the research glider a self-launching aircraft, claims the DLR.

The brushless fixed-shaft electric dc-dc motor is practically identical to the motor of the conventional Antares 20E. This motor has been developed especially for Lange and is claimed to currently be the only EASA-certified electric aircraft motor in existence. It normally runs at 190 to 288 V. Pulling up to 160 A, the 42-kW motor can deliver up to 216 N·m in the series version aircraft.

The DLR fuel-cell system is quite like the system to be used in wide-body aircraft for onboard energy supply, and it supplies the electrical energy for the powertrain, which consists of power electronics, motor, and propeller. According to the DLR, the performance of the aircraft could be increased substantially by using up to four external pods or by future fuel-cell innovations.

Using electric power for propulsion, however, is only a way of qualifying the technology’s potential. Fuel cells are not expected to be usable as primary propulsive energy sources for passenger aircraft within the foreseeable future. Instead, the DLR's research is aimed at developing fuel cells under real operational conditions so they can be used as reliable onboard power supplies in civil aviation.

“In this context, the fuel cell is an important alternative to existing ways of providing energy,” said Dr. Hans Müller-Steinhagen, Director of the DLR Institute for Technical Thermodynamics. The Antares DLR-H2 flying test bed makes sense as it provides a cost-efficient test environment for developing fuel-cell systems, also optimizing the test time of the DLR's research Airbus A320 ATRA.

The full potential of the fuel cell, however, is not limited to electric power supply. “The special benefit of the fuel-cell concept for civil aviation is a multifunctional approach,” said Dr. Andreas Friedrich, head of the Electrochemical Energy Technology department at DLR.

For example, per each kilowatt of electric power the fuel cell produces, it also “emits” half a liter of pure water. During a transatlantic flight, this could result in a water supply anywhere between 500 and 3000 L, depending on the type of aircraft, says the DLR. As a result, the water supply and tank could be considerably reduced.­

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