Sizing of the series hybrid-electric propulsion system of general aviation aircraft

Abstract

Hybrid-electric aircraft possess the potential to reduce the CO2 emissions of general aviation aircraft. However, optimized propulsion systems are needed to leverage the advantages and lower the fuel consumption. In order to identify optimized designs, the characteristics of the individual propulsion elements are needed and suitable trends for mass, power and efficiency are required for modern propulsion components. Additionally, part load efficiency and altitude characteristics need to be investigated. The fuel consumption of an aircraft depends further on the aircraft mass and the aerodynamic drag. Hence, the influence of an increased propulsion system mass on the aircraft mass and the parasitic and induced drag is considered. Additionally, the required power reserve is determined to compensate a failure of a combustion engine or a battery pack during take-off. In a further investigation, the energy reserve is identified which is required after such component failure during cruise flight. The derived trends are implemented into a sizing program and optimized propulsion systems are determined for a 4-seat hybrid-electric aircraft with a cruise speed of 220 km/h as well as a 9-seat hybrid-electric aircraft with a cruise speed of 400 km/h.