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Against the backdrop of climate change, the aviation industry is increasingly becoming the focus of debate in wider society. Innovations geared towards more environment-friendly air transport are becoming more prevalent. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) presented its expertise and research work relating to alternative fuels, electric flight, uncrewed flight and atmospheric research at the German National Aeronautics Conference on 21 August 2019 in Leipzig. The DLR research aircraft HALO and Do 228 (D-CFFU), and the flying helicopter simulator EC-135 FHS were there.

“Essentially, we believe that the aviation sector has two main tasks. Firstly, to improve current aircraft, because they are going to be flying for some time to come, and secondly, to pave the way for new aircraft,” says Rolf Henke, DLR Executive Board Member for Aeronautics Research. “With present-day aircraft, a lot remains to be done in terms of aerodynamics, weight, propulsion and synthetic fuels. In terms of tomorrow’s aircraft, there is still a great deal of research work that needs to be carried out. Electric flight has a huge potential for reducing noise and pollution, and can make environment-friendly flight possible on short- and medium-haul routes. Our vision is a ‘zero-emission aircraft’.”

  Rolf Henke at the German National Aeronautics Conference

DLR research themes at the German National Aeronautics Conference in detail

‘Electric Flight Demonstrator’ conceptual design

Hybrid electric propulsion systems are a key technology and vital precursor to the realisation of electrically powered flight. They offer the potential to significantly reduce emissions of carbon dioxide, nitrogen oxides and noise on the way towards a ‘zero-emission aircraft’. In future, electric propulsion systems will be used both in urban air mobility and for commuter aircraft, thus enabling new aircraft configurations. Previously, only small, battery-powered aircraft have been in operation, with small, hybrid-electric aircraft undergoing flight tests. However, DLR is now working with industry partners Siemens¹, MTU Aero Engines and RUAG Aviation to prepare a feasibility study for a 19-passenger test aircraft based on a Dornier Do 228.

The study shows that there are good prospects of success for converting and testing a national ‘Electric Flight Demonstrator’ with a completely electric propulsion system in the 500-kilowatt power class. The development stages would be battery-powered flight and hybrid-electric operation with an additional gas turbine generator. This test platform – the size of a commuter aircraft – will facilitate extensive research and further development of hydrogen as an energy source. This will increase the potential of electric flight to achieve a fair environmental balance when flying on short- and medium-haul routes. The Do 228 D-CFFU, which DLR uses for Earth observation research, showed the size of such a test aircraft at the German National Aeronautics Conference, in the form of a special display.

Alternative fuels in air transport

Synthetic fuels such as those produced from natural gas (Gas to Liquid, GtL) or biomass (Biomass to Liquid, BtL) have huge potential for environment-friendly flight. Unlike conventional kerosene, the chemical composition of synthetic fuels can be controlled by selecting appropriate manufacturing processes. Independent of the engine design, this enables better combustion properties and less pollutant formation.

In its Emission and CLimate Impact of alternative Fuels (ECLIF) project, DLR and its partners conducted flight tests to investigate the role of ice crystal formation in the generation of contrails at high altitudes and the emission of pollutants by these fuels. The objective here is ‘fuel design’. This is the design and optimisation of low-emission fuels for the future, with precisely defined properties such as the lowest possible soot formation, thus reducing the climate impact of contrails. An exhibit at the conference showed two flames – one with conventional kerosene and one with a GtL-based fuel – demonstrating the different soot output of the two fuels. Due to its significantly lower aromatic hydrocarbon content, the GtL fuel generates much less soot than conventional kerosene.

Atmospheric and climate research with HALO

The High Altitude Long Range (HALO) research aircraft, a modified Gulfstream G550, is a globally unique research platform for conducting measurements to assist with addressing current issues in atmospheric and climate research and Earth observation. This is thanks to its combination of range, maximum altitude, payload capacity and extensive instrumentation options. The focus is on measurements for which the aircraft’s maximum altitude of up to 15 kilometres and range of up to 8000 kilometres with 10 hours of flight time are decisive. The flying laboratory, which can be equipped with a variety of different measurement systems, was on display at the conference.

From September 2019, HALO will spend a month in Río Grande, a city in southern Argentina. Using a new, laser-based light detection and ranging (lidar) system, the researchers are planning flights over the surrounding oceans and towards Antarctica, in order to measure atmospheric gravity waves at altitudes of up to 80 kilometres. Atmospheric gravity waves affect the weather and are a factor in understanding Earth’s climate system. HALO is a joint initiative by German environmental and climate research institutions.

Uncrewed and crewed flying as a team

The aircraft of tomorrow will also include uncrewed aerial vehicles. The sector is currently experiencing rapid growth, along with the emergence of novel concepts and technologies. New ‘urban air mobility’ is resulting in the potential for air transport in and between cities. However, these new elements of the air transport system pose an enormous challenge when it comes to managing lower-level airspace. DLR is making the research infrastructure necessary for addressing this problem available to its partners in the form of the new National Experimental Test Center for Unmanned Aircraft Systems in Cochstedt, near Magdeburg. In the autumn of 2018, DLR Cochstedt conducted a test in which the DLR EC 135 FHS and an uncrewed superARTIS light helicopter flew in formation, as is required during reconnaissance flights following natural disasters. Both aircraft were on display at the conference to showcase the research topic of joint crewed and uncrewed flight. Last year, superARTIS also demonstrated the uncrewed delivery of relief supplies in the Dominican Republic.

¹ In June 2019, Rolls-Royce and Siemens signed an agreement for the sale of the Siemens eAircraft unit. The transaction is expected to be completed by the end of 2019.