The aviation sector faces significant challenges due to competition and environmental demands, necessitating innovative solutions for future aircraft. Enhancing energy efficiency requires not just optimizing existing technologies but also adopting radical advancements in airframe and propulsion systems. This thesis explores the impact of various promising technologies—such as laminar flow control, load alleviation, advanced materials, boundary layer ingestion, ultra-high bypass ratio turbofan engines, and sustainable energy sources—on designing sustainable, energy-efficient aircraft. The study aims to identify configurations that leverage these technologies, assessing their overall influence on aircraft performance and cost. It encompasses a range of aviation sectors, from short-range regional to long-range transatlantic and business jets. A multi-fidelity design environment is developed, integrating conceptual design methods and energy system models for diverse aircraft designs. An initial sizing methodology is introduced, allowing robust sizing of both conventional and unconventional configurations through optimization algorithms. Multiple configurations are analyzed for each sector to identify optimal candidates that meet mission requirements. The findings indicate that advanced airframe technologies can significantly enhance aircraft performance and enable previously unfeasible configurations. Additionally, the results r
