Design and Testing of a Vertical take-off and Landing UAV optimized for carrying a Hydrogen Fuel-cell with Pressure Tank

Flight endurance is still a bottleneck for many types of UAV applications. While battery technology improves over the years, for flights that last an entire day, batteries are still simply insufficient. Hydrogen powered fuel-cells offer an interesting alternative but pose stringent requirements on the platform. The required cruise power must be sufficiently low and flying with a pressurized tank poses new safety and shape constraints. This paper proposes a hybrid transitioning unmanned air vehicle that is optimized towards carrying a hydrogen tank and fuel cell. Hover is achieved using twelve redundant propellers connected to a dual CAN network and dual power supply. Forward flight is achieved using a tandem wing configuration. The tandem wing not only minimizes the required wing span to minimise perturbations from gusts during hover, but it also handles the very large pitch inertia of the inline pressure tank and fuel cell very well. During forward flight, eight of the twelve propellers are folded while the tip propellers counteract the tip vortexes. The propulsion is tested on a force balance and the selected fuel-cell is tested in the lab. Finally a testing prototype is built and tested in-flight. Stable hover, good transitioning properties and stable forward flight were demonstrated.