HYLENA will investigate, develop and optimize an innovative, highly efficient, hydrogen powered electrical aircraft propulsion concept. This is based on the integration and combination of Solid Oxide Fuel Cells (SOFC) with turbomachinery in order to use both the electric and thermal energy for maximisation of propulsive efficiency. This game-changing engine will exploit the synergistic use of: a) an electrical motor: the main driver for propulsion, b) hydrogen fueled SOFC stacks: geometrically optimized for nacelle integration, c) a gas turbine: to thermodynamically integrate the SOFC. This concept will achieve significant climate impact reduction by being completely carbon neutral with radical increase of overall efficiency for short and medium range aircrafts. The HYLENA methodology covers on: - SOFC cell level: experimental investigations on new high-power density cell technologies - SOFC stack level: studies and tests to determine the most light-weight and manufacturable way of stack integration - Thermodynamic level: engine cycle simulations of novel HYLENA concept architectures - Engine design level: exploration, through resilient calculation and simulation, of the best engine design, sizing and overall components integration - Overall engine efficiency level: demonstration that HYLENA concept can reach an efficiency increase of more than 50 % compared to state-of-the-art turbofan engines - Demonstration level: a decision dossier for a potential ground test demonstrator to prove that the concept works in practice during a second phase of the project The HYLENA consortium consists of one aircraft manufacturer (Airbus), 3 universities and 2 research institutes covering the expertise in aircraft design, propulsion system design, SOFC technology, hydrogen combustion and climate impact assessment. This project is fully complementary to Clean-Aviation to investigate a low level TRL concept and bring it to TRL3 in 42 months prior to a demonstrator in phase 2.