Methodology for multidisciplinary aircraft design under consideration of hybrid-electric propulsion technology

Abstract

Against a background of increasing energy demand and rising fuel prices, hybrid-electric propulsion systems have the potential to significantly reduce emissions of aircraft, particularly in the light aircraft sectors.

Within this thesis, a novel design methodology for aircraft using hybrid-electric propulsion is presented. This methodology can be used stand-alone, or it can be integrated into existing aircraft design frameworks. It allows for the design of optimal aircraft under consideration of the additional degrees of freedom due to hybrid propulsion systems. To achieve this goal, the components of hybrid-electric propulsion systems are modeled in a way suitable for conceptual aircraft design. The models of the individual components are then assembled to a global propulsion system model.

Thorough testing of the models and the methodology is performed, and adequate results are obtained. Test cases are two real-world sizing exercises of different aircraft, and a comparison against a different design method, which was developed in parallel to this work by another researcher. The validation process confirmed the correct implementation of the method and the sensible modeling of the aircraft's components and physics.

The methodology is used to assess the impact of this new design approach on aircraft performance, efficiency, and overall configuration design. For this purpose, four different aircraft are considered: a typical general aviation design, an unmanned surveillance aircraft, a vertical take-off and landing aircraft, and a short take-off and landing aircraft. The vertical- and short-take-off aircraft will be considered because these capabilities are highly demanding with respect to the propulsion system. Therefore, aircraft designed for such capabilities might offer a high payoff if hybrid propulsive methods are considered.

The analyses conducted within this thesis indicate that hybrid-electric propulsion systems offer practically no benefit compared to conventional designs for aircraft that are intended to be flown as fast as possible for most of their mission. Aero-propulsive coupling might change that result. However, modeling and assessing such effects is not part of the scope of this thesis. That topic should be assessed in further research.

Nevertheless, hybrid-electric propulsion can indeed be of benefit for aircraft that require high excess power but only use that power for short periods at a time. In these cases, significant savings of energy and cost are possible compared to current conventional designs.