Multidisciplinary Optimisation of an eVTOL UAV With a Hydrogen Fuel Cell

To explore the use of hydrogen fuel cells as a feasible alternative on Unmanned Aerial Vehicles (UAVs), a class I concept was designed at the Portuguese Air Force Research Centre (CIAFA). This work focuses on the Multidisciplinary Design Optimisation (MDO) methodology that was used to improve the 3h endurance of the baseline concept that had a Maximum Take-Off Weight of 21.6 kg, using 148 g of hydrogen and a 800 W fuel cell to power conventional flight operations. Another propulsive system comprised of batteries and rotors is used for Vertical Take-Off and Landing (VTOL). MDO was performed with the aid of OpenAeroStruct, a low fidelity software that combines Finite Element Analysis (FEA) and Vortex Lattice Method (VLM) to model lifting surfaces. Initially, a cruise and a load flight conditions were used with structural parameters and geometric twist as design variables. In a second approach, complexity was increased by including taper, wing chord and span as design variables in the problem formulation. Lastly, a third flight condition was introduced to ensure stall requirements were met. The use of MDO led to a 21% increase in endurance with a smaller wing, while satisfying all imposed constraints. This work marks an important milestone in the development of a future prototype at the CIAFA.