The technical work of exFan started out with investigating the aircraft boundary conditions and the hybrid energy system with the goal of identifying favourable operating conditions, synergies and advantageous aircraft integration as well as providing a concept of the hybrid energy system to reduce heat generation and system weight.
For this, an environmental model that represents the ambient conditions at different altitudes and climatic conditions as well as a rough sizing model for all components of the propulsion system were developed. Different aircraft configurations were investigated and a baseline configuration was chosen. A parametric analysis was performed that set the optimum operating conditions for the exFan. Using the sizing models for all components and the aircraft itself, a baseline aircraft with corresponding system topology layout and system architecture was defined. In parallel, the requirements for the exFan concept and baseline cases for the life-cycle assessment of the exFan were set-up.
As the aircraft level was defined, the project moved on to develop a concept for the exFan in a multidisciplinary approach: Knowledge on the interaction of exFan components was gathered and concepts for the electric machine, gearbox, fan, heat propulsor, thermal management and energy system were set up with the goal of reducing weight in respect to the whole aircraft. At this point, a flexible aircraft model had been developed, that is able to give feedback on concept decisions with conflicting optimization criteria (e.g. increasing fuel cell efficiency vs. reducing fuel cell weight). For the exFan concept, mass, build volume and performance over a design mission was defined for each component and a 3D representation of the concept was developed to demonstrate component assembly and envisioned aircraft integration. Strategies to achieve take-off during hot ambient conditions were developed.
To further improve heat exchanger efficiency and durability, several surface treatment techniques are being evaluated, such as chemical polishing and electroless nickel-phosphorus (NiP) coatings. These methods are being tested on complex geometries manufactured via additive manufacturing, including internal channel structures. The treatments aim to enhance corrosion and fouling resistance, improve heat transfer, and reduce aerodynamic drag, all contributing to the overall performance and longevity of the propulsion system.
