Preliminary design of hybrid-electric regional aircraft with reduced environmental impact

Abstract

Nowadays, the aviation industry faces unprecedented challenges in the context of environmental sustainability. Due to their smaller size and shorter route profiles, regional turboprop airplanes are identified as the ideal test bed for the integration of cutting-edge technologies. The integration of alternative propulsion systems, such as hybrid-electric architectures and alternative aviation fuels, is a necessary stride toward reducing regional aviation’s environmental footprint, but their true potential can only be unlocked through a multidisciplinary approach. In light of the major impact of design choices on the technical, economic, and environmental performance of new aircraft, emphasis is placed on the role that the preliminary designer may have in influencing the industry’s trajectory toward sustainability. Literature on hybrid-electric regional aircraft highlights the sensitivity of the expected advantages to the assumed technological levels. This stresses the importance of a careful technology foresight, when the purpose is to provide a prospective analysis of the benefits expected in a specific time horizon. Furthermore, increasing sensitivity to the environmental problem imposes holistic considerations, which do not neglect life-cycle and cost considerations even in the preliminary design phases. The present thesis work, titled “Preliminary Design of Hybrid-Electric Regional Aircraft with Reduced Environmental Impact”, aims to explore the challenges and opportunities that lie in integrating sustainability into the heart of aircraft design, posing the following research question: How can preliminary aircraft designers support the transition to a future sustainable regional aviation, with a specific focus on hybrid-electric and hydrogen-based technologies, while including life-cycle considerations? By addressing this multifaceted problem, the initial candidate’s efforts have been focused on the development of a design framework for hybrid-electric aircraft in collaboration with the DAF research group of the University of Naples "Federico II". In this sense, active participation in several European research projects supported the candidate’s research and the development of know-how on the topic. Thus, classic design methodologies have been adapted and generalized in order to manage innovative propulsion architectures as well as conventional aircraft. In particular, a general mathematical model is proposed, capable of describing a huge variety of propulsion systems involving alternative energy sources. The model is able to degenerate into specific architectures based on thermal engines, batteries, hydrogen fuel cell systems, or any combination of them. The model has been included in an in-house flexible design workflow that allows for an accurate, consistent, and complete design of new concepts. The workflow combines the generalized powertrain description with sophisticated methods for mass estimation, aeropropulsive interaction effects, and a design approach based on mission analysis. An extensive study has been conducted to support the determination of a transition roadmap towards economically and environmentally sustainable regional aviation. Focusing on a 50-passenger regional platform, several future scenarios have been defined, representative of the most promising technologies available for three reference entry into service years. Starting from market-driven top-level requirements, a wide design exploration has been performed, using an accurate approach based on surrogate models and mission analysis. Detailed life cycle and cost analyses have been carried out for each scenario, highlighting that trade-offs emerge when considering innovative technologies. As an outcome of this activity, extensive and scalable life cycle inventory datasets have been generated and published in collaboration with expert partners, representing a first step toward the integration of sustainability considerations at the preliminary design level. Finally, the technical, economic, and environmental results of the study have been critically compared, electing the most promising scenarios. Sustainable aviation fuels and battery systems have been identified as valid transition technologies, while waiting for hydrogen-based propulsive systems to mature sufficiently. The conclusions have been summarized in a set of recommendations for aviation stakeholders and policymakers, seen as necessary steps toward the alignment with European environmental objectives.