Issue 41 Unmanned Systems Technology December/January 2022 PteroDynamics X-P4 l Sense & avoid l 4Front Robotics Cricket l Autonomous transport l NWFC-1500 fuel cell l DroneX report l OceanScout I Composites I DSEI 2021 report

64 Dossier | Northwest UAV NWFC-1500 fuel cell power without needing multiple generators, power converters and potential points for thermal losses between the power unit and the BLDC lift motors (as a hybrid engine system would). Faced with equally compelling scientific and economic cases, NWUAV therefore began developing its hydrogen- electric technology in 2017 and unveiled it earlier this year. Development strategy The company gives particular thanks for the advice and expertise shared by the NRL in the development of its fuel cell, particularly from Dr Ben Gould of the NRL’s Alternative Energy Section, who is considered a leading expert in PEMFC engineering. The key strategy adhered to by NWUAV has been to produce a system as modular and scalable as its NW-44 and NW-88 engines, which would meet generally similar SWaP requirements, given the company’s close knowledge of customers in their weight classes. “There’s a lot of scepticism about hydrogen power – as there was among our own team initially – so we’ve worked hard to answer every possible question about the practicality of running UAVs on PEMFCs that could pose an issue as we went down this road,” Ratcliffe adds. “We also worked heavily on packaging, weight reduction and many other mission-critical specifications. And while there was some new science to get to grips with, modern propulsion systems still universally rely on the same core bodies of engineering knowledge to produce them, such as thermodynamics, materials science, fluid dynamics, electrical engineering, control theory, data buses and more. So our engineering team already had much of the necessary aptitude.” The NRL’s engineers meanwhile did much of the chemistry and physics calculations to provide the groundwork for planning out the system’s architecture, so that NWUAV could focus on commercial concerns such as packaging and designing for manufacture. System architecture The NWFC-1500 features 48 cell layers in its PEM stack, with around 1 V per layer. The system measures roughly 40.6 cm in length by 17.3 cm in diameter. Ratcliffe and his team have designed the system to be as small relative to its stack as possible, judging that a tighter integration package will be key to its end- users and hence maximising the power- to-volume ratio (with 50 A typical output via a 24 V DC supply). To further assist systems integrators, mounting structures can be designed and supplied ad hoc using additively manufactured Nylon-12 structures supplied by NWUAV’s sister company, Northwest Rapid Manufacturing, and electrical connectors can be chosen freely. “As with our UAV engines, we’ve designed it to have flexible, modular packaging, power engineering, connector selection and other factors that can be adapted to new platforms and mission sets, because unmanned systems engineers have to cater for a huge range of applications, so it doesn’t pay to be set in stone with too much,” Ratcliffe adds. The balance of plant (BoP) is designed to be tailored to the bay of whichever aircraft or other vehicle the NWFC-1500 is being integrated into, but as standard the fuel cell and all ancillary systems fit into the system dimensions mentioned above, for easy installation. “That also means, unlike engines, we can easily integrate the NWFC-1500 into other types of vehicles, such as surface vessels or land vehicles,” Ratcliffe notes. December/January 2022 | Unmanned Systems Technology The stack is composed of membrane electrode assemblies from Gore and bipolar plates from Borit Manufacturing We’ve worked hard to answer every possible question about the practicality of running UAVs on PEMFCs that could pose an issue