Hybrid fuel-electric multi-engine testbed– results of the research

Purpose The research aims to investigate the challenges associated with designing a hybrid electric propulsion system for light airplanes and its operations. Design/methodology/approach This paper presents the results of an experimental campaign conducted on a hybrid fuel-electric propulsion system testbed. Two main aspects of the system were examined. The first applies to the chosen electric motor’s simultaneous work with two- and three-blade propellers. The goal was to assess the aerodynamic characteristics of the propellers and determine their optimal operating points. Measurements were conducted under static conditions (i.e. with external flow velocity equal to 0 m/s). The second aspect refers to the power generator set consisting of an internal combustion engine and an electric machine connected by the gearbox and other necessary equipment (the cooling system, the exhaust system, the converter, etc.). The main goal of these studies was to create a map of the specific fuel consumption by the set with respect to the power generated and rotational speed. It was expected that the optimal operating point (the maximal ratio of the generated power and the consumed fuel) would occur within a specific rotational speed range and the throttle opening under a specific load from the electric machine. Findings Based on measured results, the pitch angle of the propeller was selected for four modes of propulsion operation: takeoff, climbing, emergency and cruising. A three-blade propeller with a pitch angle equal to 15° appeared to be the best. During the research, it turned out that the chosen propulsion system is more controllable by requested rotations per minute than torque, even if the built-in proportional-integral-derivative controller controllers enable both operating modes. Practical implications The results will facilitate designing light airplanes with hybrid fuel-electric propulsion systems driving two propellers. Originality/value Only one airplane with a serial hybrid fuel-electric propulsion system driving two propellers has been built and tested. Unfortunately, no detailed and publicly available data on its propulsion system was found. Therefore, the current paper shows such information for the first time.