No fear of flying

It is possible to reduce the climate impact of air traffic by at least 80 percent while remaining economically competitive. For four years, 20 research institutes have been working on designs for low-emission commercial aircraft. This week, the German Aerospace Center (DLR) presented the results of the "EXACT" (Exploration of Electric Aircraft Concepts and Technologies) project to 170 participants from industry and research at the DLR site in Hamburg-Finkenwerder.

Björn Nagel, Director of the DLR Institute of System Architectures in Aeronautics in Hamburg, states: "Research into ecological aircraft concepts has shown that the impact of aviation on the climate can be reduced by at least 80 percent without increasing costs." Nagel continues: "In the Exact project, we have now comprehensively analyzed and evaluated the most promising aircraft concepts and technologies."

Both the complete life cycle of the aircraft and the process of extracting, transporting and supplying renewable fuels were comprehensively considered in the analysis of the climate compatibility of new aircraft configurations. This enabled the researchers to identify the aircraft configurations with the greatest ecological and economic potential.

Three aircraft concepts have emerged as the most promising, low-emission and economical for short and medium-haul flights for 250 passengers:

Battery hybrid drive surprisingly good
What was surprising at first glance was the fact that the battery-electric hybrid concept came out on top. Due to the high mass of the batteries and the rather short ranges, battery operation was previously considered more suitable for smaller aircraft for short-haul use. "However, the plug-in hybrid architecture actually makes it possible to power larger, market-relevant aircraft," says Daniel Silberhorn, head of the Exact project. Sustainable production with a very high recycling rate and a long service life for the batteries are then key ecological boundary conditions. Low production costs and fast recharging ensure the economic viability of the aircraft. Silberhorn believes that a battery-powered aircraft could travel 500 kilometers, and a hybrid-electric aircraft with sustainable fuels could even travel up to 2,800 kilometers.

Short-haul turboprop aircraft

The technology for turboprop aircraft has already been in practical use for many years, albeit primarily in regional applications. At a lower cruising speed, the aircraft consumes significantly less fuel. This option is therefore not only ecologically advantageous, but is also worthwhile for airlines from an economic perspective. When operated with fossil fuels, the impact on the climate is already reduced by more than 40 percent compared to jet engines; if sustainable fuels were used, the impact on the climate would be reduced even further. The aircraft in question has a range of 2800 kilometers.

Economic efficiency of hydrogen propulsion

Hydrogen-powered aircraft can reduce the impact on the climate by at least 80 percent, according to the Excat project. Whether they are also economically attractive, however, depends largely on the production costs for hydrogen and synthetic kerosene, according to the experts. Fuel cells to support the aircraft on the tarmac, during descent or in the on-board systems would result in a significant reduction in emissions with a range of up to 1500 kilometers.

Simulation from energy generation to recycling

DLR has developed a simulation framework for the Exact project. It enables calculations to be made based on a large number of parameters - from energy production and aircraft design to climate impact and the overall assessment of the air transportation system. The project has thus shown in detail what new climate-friendly aircraft could look like. For each possible propulsion technology, there is also information on how the corresponding components or lightweight structures must be designed. This in turn helps with product pre-development and production planning.

"Since the beginning of the project, we have gradually compared a wide range of technology options with each other and have thus arrived at the three favorites," says Daniel Silberhorn. In a follow-up project, the aim is to define technical details such as the exact aerodynamic properties of the aircraft or the precise weight of a hydrogen tank in more detail. Together with aircraft manufacturers, suppliers and research institutions, the design process of a potential new aircraft is to be continuously adapted. "Our research results in virtual products in which the interaction of different technologies is mapped. In cooperation with industrial companies, we want to concretize the potential and the boundary conditions for the transfer to the next real product," says Björn Nagel. (aum)