The world's first piloted aircraft powered by fuel cells
The Antares DLR-H2 research aircraft is the world's first piloted aircraft to be powered exclusively by fuel cells, ensuring that it takes off, flies and lands without emitting any carbon dioxide. The fuel used is hydrogen. Electrical energy is generated as a result of the direct electrochemical reaction – without combustion – between hydrogen and oxygen in the ambient air. The only product yielded by this particle-free reaction is water.
The official maiden flight of the Antares DLR-H2 took place in Hamburg on 7 July. In a test in November 2009, in which an altitude of 2558 metres was reached, functionality of the fuel cell at the reduced pressure encountered at altitudes exceeding 2000 metres was demonstrated.
The propulsion system of the aircraft was developed at the Stuttgart-based DLR Institute of Technical Thermodynamics, in cooperation with project partner Lange Aviation. The Antares 20E, a motorised glider that Lange Aviation has produced for some years, was used as the basis. The fuel cell system and the hydrogen storage system were installed in two external pods fitted below the wings, which were specifically reinforced for this purpose. A specially developed fuel cell operating at an electrical efficiency of up to 52 percent rounded off Antares' electric drive system in 2009. The system had already been tested in the wide-bodied Airbus A320 ATRA, supplying the auxiliary power. Now, the energy delivered by this system is fed into the electrical power train, which has been developed and certified for flight use by Lange Aviation. The power train consists of power electronics, a motor and a propeller.
A new fuel cell system
In 2012, higher-performance and more compact fuel cell systems were incorporated in cooperation with Hydrogenics. The improved systems occupy a smaller volume, so the project engineers arranged the stacks and air intake in the upper half of the pod and a cooling air duct now runs beneath the payload carrier. In addition to the extremely limited space available for installation, when fitting components it is, at all times, necessary to consider specific aviation requirements concerning mass distribution, safety and lightweight construction.
The developers selected a new, larger pressure vessel that, at 350 bar, now holds five kilograms of hydrogen to replace the previous tank in the external pod on the starboard wing, which provided a capacity of just two kilograms. Sensors placed in all areas of the fuel cell system monitor the hydrogen concentration in the air to ensure operational reliability. To monitor all operational conditions as thoroughly as possible, numerous additional sensors have been installed throughout the aircraft.
Other forms of propulsion
Hybridisation with a Li-Ion battery will help further enhance the aircraft's performance. It is expected that coupling the fuel cell with the extremely quiet and high-performance, electrical propulsion system for light aircraft will set new standards in terms of range, in comparison to piston-driven engines.
Antares DLR-H2 as a flying test laboratory
Although fuel cells will not be suitable as primary sources of energy for commercial aircraft in the foreseeable future, they do represent an interesting and important alternative to the energy systems currently used in civil airliners, and would provide reliable on-board power supply. High efficiency goes hand in hand with minimal exhaust emissions, low noise generation, safe flight operations and high passenger comfort. The research conducted at DLR is geared towards using fuel cells as a reliable source of on-board power under real operational conditions in commercial aviation.
The Antares DLR-H2 enables DLR to test different fuel cell system architectures under conditions relevant to aviation, including low pressure, varying temperature, acceleration and vibration. In addition, optical sensors have been installed as a payload in order to monitor traffic along major roads, hence permitting timely registration of the current traffic status and the transmission of this information, for instance to avoid congestion.
Cooperation between aviation and energy researchers
Aviation and fuel cell researchers worked together closely at DLR during the fuel cell aircraft project Antares DLR H2.
All aerodynamic properties of the aircraft were optimised again to enable ultra-efficient flight. The aim was to prevent turbulent airflow across all surfaces. Integrating the external pods presented a significant aeroelastic and aerodynamic challenge. In this area, the expertise that the DLR Institute of Aeroelasticity contributed ensured a perfectly tailored installation of the pods without compromising the dynamics of the aircraft. The additional air resistance, when compared with the production model Antares 20E, is less than 10 percent, with a possible additional load of more than 200 kilograms. Even at a speed of up to 300 kilometres per hour, Antares DLR-H2 will fly entirely without flutter; it should be noted, however, that the current maximum speed is around 176 kilometres per hour.
Fuel cell system directly coupled with the motor control
The method used to connect the fuel cell system with the power train was equally innovative – the wide range of input voltage levels means that the motor can be operated between 188 and 400 volts while providing an efficiency of over 92 percent. This eliminates the step of voltage stabilisation; the fuel cell system can therefore be designed in such a way that it is directly connected to the motor control unit. This cuts back on components and costs while increasing efficiency; the overall efficiency of the propulsion system, from the tank to the power train and the propeller, is roughly twice as high as standard engines based on combustion technology, providing up to 40 percent under optimal operating conditions. Combustion engines deliver a mere 18 to 25 percent of the energy from kerosene or diesel for propulsion. Therefore, the DLR Institute for Aeroelasticity, the Bern University of Applied Sciences and Lange Aviation have all made an important contribution.
Technical Data for the Antares DLR-H2
|Wing span||20 metres|
|Fuselage length||7.4 metres|
|Length of the external pods||2.87 metres|
|Empty weight||approx. 460 kilograms|
|Maximum weight||875 kilograms|
|Max. fuel cell power||approx. 33 kilowatts|
|Fuel cell efficiency||up to 52 percent|
|DLR Flight Operations||Stuttgart|
Fuel cells in aviation
In a first stage of development, DLR, together with Airbus Germany and one other supplier, have installed a fuel cell system to supply emergency power to the hydraulic pumps used to control the DLR Airbus A320 ATRA research aircraft. In the summer of 2011, the aircraft taxied for the first time with a fuel-cell-powered motor driving its nose wheel. DLR and Airbus are cooperating in a further research project intended to replace the entire auxiliary power unit with a fuel cell system. Auxiliary power units provide the electrical systems with power while the main engines are shut down. Among other things, this powers the air conditioning system and compressed air systems on board an aircraft. With the Antares DLR-H2, in future, specific fuel cell systems designed for applications within aviation can be tested and optimised at low cost; this applies equally to the test times for the DLR research aircraft Airbus A320 ATRA.
The Antares DLR-H2 is based on the motorised glider Antares 20E, which is produced by the company Lange Aviation, based in Rhineland Palatinate. DLR developed the fuel cell system in cooperation with Hydrogenics. The German Federal Ministry of Transport, Building and Urban Development (Bundesministerium für Verkehr, Bau und Stadtentwicklung; BMVBS) and the National Organisation Hydrogen and Fuel Cell Technology (Nationale Organisation Wasserstoff- und Brennstoffzellentechnologie; NOW GmbH) supports the research project.