The effects of the degree of hybridisation on the design of hybrid-electric aircraft considering the balance between energy efficiency and mass penalty

The growing interest in the application of the hybrid-electric concept demands a rigorous method applied to balancing the energy efficiency improvement with the mass penalty. In hybrid-electric aircraft (HEA) design, it is necessary to avoid excessive usage of energy, which is caused by deliberate hybridising in pursuit of high electrical energy conversion efficiency. This paper presents a design method to achieve multi-objective designs conducted within a framework of multi-disciplinary design exploration appropriate for HEA, meeting the requirement of minimising the maximum take-off mass (MTOM) and fuel saving. A theoretical analysis proposes the existence of the optimum design area of HEA. This is followed by a series of demand-focused numerical design experiments that have verified the existence and position of the optimum design area by taking the mission of a short-range narrow-body airliner as the design target, considering the predicted technology timeline until 2050. Compared to a fuel-powered twin-turbofan aircraft, 65.56% fuel-saving, 16.4% reduction in flight operation cost, 44.58% reduction in block CO2emission, and 75% improvement in the cost-specific air range (COSAR) are achieved via hybridisation using the proposed design optimisation method.