Aircraft Design Implications of Alternative Fuels for Future Hybrid-Electric Regional Aircraft Configurations Jonas Mangold* and Andreas Strohmayer* *Institute of Aircraft Design, University of Stuttgart Pfaffenwaldring 31, 70569 Stuttgart Abstract Air transport is a driver of economic prosperity, as it connects millions of people and provides a fast way to travel. However, the environmental impact, such as emissions like CO2, NOX or noise, is more and more in the focus of the broad public. The goal of the FUTPRINT50 project is to develop a more environmentally sustainable aircraft with a hybrid-electric powertrain for Entry-Into-Service in 2035/2040, carrying 50 passengers over a range of 800 km. Electrification of the powertrain can offer advantages over conventional architectures, as electric components operate at higher efficiencies and have a higher specific power. This for example could enable novel propulsion concepts, such as distributed electric propulsion. An all-electric aircraft would produce no in-flight emissions, but remains limited in range due to the low specific energy of current battery technology. A hybrid-electric propulsion system could compensate for this disadvantage. Combining a conventional primary energy source with the electrified powertrain can increase the range compared to an all-electric design and still can reduce emissions compared to conventional aircraft. However, to limit the environmental impact, alternative fuels are necessary for an environmentally friendly hybrid-electric propulsion concept. Sustainable Aviation Fuels (SAF) and Hydrogen (H2) are the most promising fuels to further greening transportation and aviation. Using SAF leaves the engine and the fuel system mostly unaltered, as the same properties of SAF and Jet A-1 are targeted. This is an advantage, as it basically allows conventional aircraft engines to be used, enhanced by hybridization. H2 has apparent benefits as a fuel for aviation due to its higher specific gravimetric energy compared to kerosene. On the other hand, H2 requires more storage volume due to its much lower density. In FUTPRINT50, several power train architectures and corresponding aircraft configurations are investigated, looking at both SAF and LH2 as primary energy carriers. Hybrid-electric propulsion and alternative fuels affect the aircraft itself substantially. SAF would be a CO2-neutral intermediate solution, as only small changes to aircraft and airport infrastructure are required. In contrast, fuel tank and related systems would significantly change for LH2. A possible arrangement of the LH2 tank aft of the rear pressure bulkhead can be a reasonable solution. However, in terms of aircraft design, this can for example affect the aircraft\'s stability and increase trim drag. Thus, the empirical knowledge based on classical designs can no longer be generally applied to such configurations, and the design methodology has to be adapted. Combined with the variations of energy management strategies, this results in many new open variables and options to lower emissions in the different flight segments. In conclusion, the presentation will focus on this influence of alternative fuels on aircraft design.