Conceptual All-Electric Retrofit of Helicopters: Review, Technological Outlook, and a Sample Design

The diffusion of electric system on-board has started after 2000 due to the need of fulfilling new regulations regarding environmental impact of aviation and of reducing maintenance costs. This process has led to the more-electric aircraft concept design, for which several hydraulic and pneumatic systems have been replaced by electric drives. The main obstacles to the switch to electric propulsion and energy storage/production (all-electric aircraft) are the unfavorable energy-to-weight and power-to-weight ratios of battery and fuel cell that represent the two viable technological solutions for energy storage and power generation. Helicopters make no exception in the transition to electric systems, although with a significant lag with respect to fixed-wing aircraft. Nevertheless, it is expected that, in the future, the technological progress will make electric propulsion a standard solution also for rotorcraft. This paper presents a review of the steps toward electrified aircraft taken by the aviation industry in the past decades (mainly concerning fixed-wing vehicles) and the conceptual all-electric retrofit of a case study lightweight helicopter. Different batteries and fuel cell solutions are examined, and the performance (range and endurance) and economic aspects (life cost and investment plan) are critically analyzed, considering both the currently available technology and the expected future developments.