Operational Energy and Power Reserves for Hybrid-Electric and Electric Aircraft

Abstract

Power and energy reserves in hybrid-electric and electric aircraft propulsion systems are required to counter propulsion component failures and to cope with disorder in flight operations. In the first section of the paper, a failure of a battery pack or a combustion engine during take-off is considered and an equivalent level of safety to conventional aircraft is suggested. In the next section, a required energy reserve for a propulsion component failure during cruise flight is evaluated. Therefore, a range to reach a suitable airport for an emergency landing is determined for Europe and the USA by calculating the distance to the nearest diversion airport for a mesh of possible aircraft positions. The median, the 95th percentile and the 99th percentile of this diversion range is then determined by a cumulative frequency analysis - the investigation is carried out for different runway lengths which represent different aircraft classes. Furthermore, safety margins are discussed which are required for flight operation. The same methodology is then applied to determine the operational flight reserve which is required to reach a suitable alternate airport from a destination airport and the results are discussed.