The research and development of a new generation of ecofriendly airliners not only require new technological steps on airframe design and aerodynamics, engines, and fuels, but foremost needs a big step in digitalization. Right now, the level of digitalization and computerization isn’t high enough to fully understand how various technical solutions interact with each other and can influence a design. This is one of the challenges highlighted in a recent study from the German Aerospace Center DLR. Eco-airliner not possible without next step in digitalization. DLR or Deutsches Zentrum für Luft- und Raumfahrt recently published a strategy report called “On the way to emission-free”. The report describes the technological steps and other challenges that are to be overcome when developing the technology for commercial aircraft in 2050 that will have the lowest carbon emissions possible. While at first sight, the report seems very similar to other studies like those from Clean Sky (now Clean Aviation) or Destination 2050 that was prepared last year by a group of European stakeholders, like ACI Europe and Airlines 4 Europe (A4E), it mostly identifies some of the challenges to meet the 2050 target. DLR identifies four main themes that need to be further researched and developed: emission-free propulsion, energy-efficient aircraft, emission-free air transport, and digitalization. Only a combination of these themes will allow the industry to become climate-neutral in 2050, DLR says. On emission-free propulsion, the report says that disruptive technologies, materials, and manufacturing processes are needed to improve efficiency. As a first step, all medium- to long-haul aircraft that enter service from 2030 should fly on 100-percent sustainable aviation fuels (SAFs) and synthetic fuels. This will reduce carbon dioxide emissions but attention is also needed for the reduction of nitrogen and soot particles. At the same time and during this decade, the industry needs to develop hybrid-electric propulsion systems using hydrogen that deliver an output of 1 to 2 mW. Interestingly, the report hardly mentions battery-powered electric propulsion, probably because batteries are seen as too heavy and lack the energy density of other options. Hybrid-electric has huge potential but requires the development and testing of (light-weight) fuel cells, high-output aggregates, and a full understanding of the effects of using supercold liquid hydrogen on systems. “This requires a systematic research and development of safe, reliable, and low-emission hydrogen burners as well as the safe handling and control of hydrogen and an increased proportion of water vapor in the hot gas area.” One of the topics that takes research is that of hydrogen tanks, as DLR told AirInsight last year. DLR expects that only by 2040 the first regional aircraft with fuel-cell hydrogen technology will be available, which is about ten years later than what companies like ZeroAvia and Universal Hydrogen are saying. Longer-term – around 2040-2050 -, DLR foresees ultra-high by-pass engines with open rotors with direct hydrogen burn as the future platform for engines. Better aerodynamics should reduce fuel burn by fifty percent As SAFs and hydrogen are expected to be more expensive than kerosene, it will be necessary to reduce fuel burn as much as possible. Not only should this come from more efficient engines but also from low-drag aircraft designs, so that only half of the current power is required to propel it. DLR says a fifty-percent reduction in energy requirements should be the target. Of this, forty percent should come from improved aerodynamics, including longer and thinner wings with a higher aspect ratio, and improved laminar airflow suitable for speeds over Mach 0.75. The optimal integration of the ultra-high by-pass engines into the airframe design is another area that needs to be improved. The remaining ten percent should come from lighter designs that include load reduction methods that combine sensor and control concepts and sensor-based structure monitoring. Ultra-lightweight is the solution here. The third objective – emission-free air travel – looks at improved air traffic management. The German agency notes that in Europe, initiatives like the Single European Sky and SESAR exist, but they don’t sufficiently cover the operational and technological implications of CO2 and non-CO2 reducing measures. The effects of technologies that should reduce emission can only be observed if you look at the entire air transport system, says DLR. The agency is already working on new operational concepts and technologies that include communications, navigation, surveillance, air traffic management, and safety that not only look at traditional modes of air transport but also take urban air mobility into account. Graphic from the DLR report in German. The black line shows how CO2 will increase to 450 percent from 2020 levels if no action is taken. The purple line shows that emissions will still grow to 50 percent if energy-efficient technologies like better aerodynamics are combined with traditional engine technologies. The blue line reduces emissions to 30 percent by introducing SAFs and synthetic fuels. Emissions can do down to 17 percent if hydrogen is introduced on regional to medium-haul routes. (DLR) Without any measures, carbon emissions from air travel will quadruple (450 percent) by 2050 compared to 2020 levels, the study says. Introducing energy-efficient technologies combined with current engine technology will not be enough to curb this trend as emissions will continue to grow to some fifty percent of 2020 levels. SAFs, synthetic fuels results, and optimized air traffic management can bring emissions down to thirty percent of 2020. If on top of all measures hydrogen-based propulsion is introduced on regional to medium-haul flights, carbon emissions will end at seventeen percent of 2020 levels. That’s the most optimum scenario in the DLR study, which defies claims that air transport can get to zero carbon emissions if it moves to hydrogen. Digital models not detailed enough for getting a full understanding Getting to this level and having all the technologies available will take serious effort. Developing and testing them individually might not be the problem. It is the combination of them and the interaction that needs to be fully understood. This is where DLR’s worries about digitalization come in. “Physical phenomena are currently not precise and for the most extensive virtualization of design, development, and approval calculable quickly enough.” The use of different software systems that often are not connected results in the lack of realistic data models of future designs, which makes it impossible to develop them. The aerospace agency recommends the development of precise numeric methods and algorithms, including so-called reduced-order models, for the development and validation of designs. There also needs to be a new platform for the exchange of data and models, plus the development and use of new virtual solutions. This includes a ‘digital twin’ of a design before it is actually built, something that is already used by various OEMs like Airbus and Dassault Systems and recently also mentioned by Boeing as the way to design their next airliner. DLR is not an aircraft manufacturer, so the solution that is being studied and developed will never end up in a DLR aircraft. But the agency says it is acting as a virtual manufacturer: “DLR considers always the aircraft and air travel in the context of an inclusive system. Due to this system competence, it takes over the role of a virtual manufacturer and binds in other actors in aviation research as well as the aviation industry.” DLR claims it is the only agency that has the methods and competence for aviation to provide highly precise and application-oriented models of future products.
