Design of a Hybrid Electric Propulsion System within a Preliminary Aircraft Design Software Environment

The ambitious climate objectives set by the European Commission within the scope of ACARE Flight Path 2050 call for significant improvements in terms of efficiency for future aircraft configurations [1]. One of the main drivers for these improvements is the development of novel propulsion systems. Therefore, stakeholders in the aviation sector are increasingly interested in electric propulsion concepts, due to higher efficiency and reduction of local emissions. While in small aircraft for general aviation applications (CS-23) full electric propulsion concepts seem realistic for medium-term applications, in the field of large aircraft (CS-25) these concepts are not feasible in a 2030-2050 timeframe. By contrast, hybrid electric propulsion concepts are scalable with regard to flight range and payload and are considered to achieve similar operational flexibility as present-day conventional technologies. Thus, a variety of hybrid electric propulsion technologies has been investigated within preliminary aircraft design research projects in recent years. Within the scope of the presented research, a design methodology has been implemented into the aircraft design suite MICADO (Multidisciplinary Integrated Conceptual Aircraft Design and Optimization Environment) to evaluate electric propulsion concepts on a preliminary level in a short time and with the necessary flexibility to investigate a broad design space. As a first approach, the concept of an uncoupled parallel hybrid electric propulsion system, consisting of two gas turbine engines and two electrically driven ducted fans powered by batteries, has been chosen and integrated into an Airbus A320-200 aircraft. Preliminary results have shown a block fuel reduction only for design ranges below 900 NM depending on the conducting material. In consideration of realistic assumptions for specific battery weights, a mission energy (or even cost) reduction cannot be achieved yet, which is in line with research findings from other organizations. Therefore, further studies considering improvements such as a more feasible aircraft configuration, different propulsion system architectures and variable degrees of hybridization throughout the flight mission are planned for future research work.