Energy-Based Preliminary Sizing and Hover Performance Assessment of Hybrid-Electric VTOL Aircraft

Abstract

Electric vertical take-off and landing (VTOL) aircraft are considered a promising solution for fast and sustainable Urban Air Mobility (UAM), as they combine the advantages of vertical flight with the highly efficient flight of fixed-wing aircraft. However, the specific energies of today’s batteries still significantly limit the range and endurance of such vehicles. A more viable intermediate step towards sustainable UAM is represented by hybrid-electric aircraft. However, in the preliminary design phase, sizing of dual-power systems is a major challenge, particularly for complex and widely-varying VTOL configurations. To address this challenge, we present a simple, configuration-independent sizing methodology to estimate the relative weight and size of the propulsion system of hybrid-electric VTOL aircraft for a set of given mission parameters. The approach is demonstrated using a comprehensive case study. Since we introduce weight-specific parameters such as the energy-change-to-weight ratio, the presented methodology does not require prior knowledge of the initial aircraft weight or any other in-depth knowledge of the aircraft configuration. In this context, equations to calculate the hover endurance and the vertical climb performance are also derived. The proposed design methodology can provide valuable insight during the early design process of new VTOL concepts by showing which hybrid-electric VTOL configurations are feasible in terms of the required energy storage characteristics. Since the methodology is configuration-independent, it can provide a basis for new preliminary development tools for hybrid-electric VTOL aircraft.