HYLENA will investigate, develop and optimize an innovative, highly efficient integrated hydrogen powered, electrical aircraft propulsion concept for short and medium range. It will achieve significant climate impact reduction by being completely carbon neutral with radical increase of overall efficiency. The full synergistic use of: a) an electrical motor (as the main driver for propulsion), b) a contoured hydrogen fueled SOFC stacks (geometrically optimized for nacelle integration), c) a gas turbine (to thermodynamically integrate the SOFC), will act as an enabler for hydrogen aviation and will allow for efficient and compact engine concepts. This disruptive propulsion system will be called HYLENA concept. HYLENA aims to evaluate and demonstrate the feasibility of a “game changing” engine type which integrates Solid Oxide Fuel Cells (SOFC) into a turbomachine, in order to utilize the heat generated by the fuel cells on top of its electrical energy. The combination of e-motor, turbomachine and contoured SOFCs fueled with H2 will deliver high overall efficiency and performance versus state-of-the-art turbofan engines. Indeed, HYLENA Figures of Merit consist of minimizing CO2 emission; negligible NOX and an unmatched overall efficiency versus state-of-the-art turbofans which corresponds to an outstanding performance increase. It will also enable to extend the flight range for the same fuel tank size. The HYLENA project will deliver: 1. On SOFC cell level: Experimental investigations on SOFC cell technologies and identification of the most promising one(s) for aeronautical applications; 2. On SOFC stack level: Studies and tests to determine the most compact/light/manufacturable way of stack integration; 3. On thermodynamic level: Cycles simulations of the proposed novel HYLENA concept architecture and down selection of the most performing one; 4. On engine design level: Exploration, through resilient calculation and simulation, of the best engine design, sizing and overall components integration; 5. On overall engine efficiency level: Demonstration that HYLENA concept can reach very high efficiency levels with limited weight and complexity; 6. On demonstration level: A decision dossier for a potential ground test demonstrator to prove that the HYLENA concept works in practice during a second phase in the continuity of this project.

The potential of Distributed Electric Propulsion (DEP) for future aircraft has been evaluated with Scaled Flight Testing (SFT). Scaled flight testing can contribute to a reduction of risk and cost in the development of a radically new aircraft. The flight dynamics and control of the aircraft have specifically been addressed. The validity of results of scaled flight testing for predicting the full-scale aircraft properties was addressed in a first campaign. A 1:8.5 scaled version of a typical large passenger aircraft was built, tested in the wind tunnel and was subsequently flight tested. During the flight tests an accurate flight test instrumentation system measured the scaled aircraft flight parameters, such as motion, control surface deflections and air data. Results of the scaled flight testing have been compared with full-scale test results which validates the scaled flight testing methodology. In a second campaign the methodology is applied to investigate and demonstrate the benefits of distributed electric propulsion. Aircraft with the same external shape have been used in the two test campaigns, modifying only the propulsion: the twin turbo-jet propulsion of the first campaign was replaced by propulsion with six propellers in the second campaign. This paper presents the highlights and key results of the development, manufacturing, wind tunnel tests, ground tests, taxi tests and flight tests of both campaigns.