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

63 PEMFCs versus lithium-ion “When you look at the full breadth of power units in the UAV market, IC engines are relatively expensive and require quite a bit of maintenance,” observes Jeff Ratcliffe, CTO at NWUAV. “That’s fine for a military market in exchange for 12-24 hours in the air at a time, but the commercial market – which has grown tremendously over the past six years – is very cost-sensitive, and it’s no coincidence that it has worked almost entirely on battery and electric-motor powertrains up to now. “However, there are severe limitations in terms of chemistry and physics on how much energy you can store in batteries of a given weight, since you are storing both halves of an electrochemical reaction onboard for the entire flight.” Ratcliffe and his team therefore saw huge potential in endurance and efficiency terms between IC engines and battery-electric powertrains. He had also tracked the US Naval Research Lab’s (NRL’s) XFC programme, which had begun in 2006 to develop the hydrogen fuel cell-powered Ion Tiger UAV that flew for the first time in late 2016 (and which incidentally was being designed to be launched from a submarine). The project caught NWUAV’s attention for having resolved numerous conflicts in terms of the SWaP, packaging, maintenance, ramp rates and more that had plagued other attempts to power small electric aircraft with hydrogen. “Rather than having to oversize a battery for a UAV, or oversize the chemicals inside the pack, having a fuel cell means you can pump those chemicals through a system, some stored offboard and some drawn directly from the surrounding atmosphere, and generate electricity while carrying only half of the chemical types that a battery uses for its oxidation-reduction reactions,” Ratcliffe observes. “And instead of keeping inert by- products on board as a battery does, we throw ours overboard as water, which makes it a clean, pollution-free option.” PEMFCs versus IC engines Being satisfied that the physics and chemistry would make the SWaP of a fuel cell viable for long-endurance UAVs, NWUAV also investigated the economics of PEMFCs to judge whether hydrogen- electric power made sense from a long- term supply perspective. In addition to being better suited to the increasingly strict emissions requirements in areas that many commercial unmanned vehicle developers aim to supply, the company (through consultations with the NRL and others) learned that many of the materials in a PEMFC are designed to last for 5000-20,000 hours before needing to be replaced – an order of magnitude improvement over many IC engine pistons, crankshafts and other components. “If you calculate the lifecycle and per-hour costs of an air vehicle, and divide that capital cost by the utility time of PEMFC materials compared with IC engine parts, you get a significantly lower cost of operations,” Ratcliffe says. “And fuel cells are still, relatively speaking, a brand new industry, so those costs and replacement rates are going to go down even further in the years ahead as order volumes increase and production technology improves, whereas IC engines and batteries are already comparatively more mature.” He adds that the company did consider hydrogen-powered IC engines as a clean power solution. However, NWUAV predicts that distributed-lift types of VTOL- transitioning architectures will become dominant among UAVs in the near future, meaning its ideal solution was something that would efficiently produce DC Northwest UAV NWFC-1500 fuel cell | Dossier Rather than having to oversize a battery, or oversize the chemicals in the pack, a fuel cell allows you to pump the chemicals through a system Unmanned Systems Technology | December/January 2022 The fuel cell and balance of plant can be assembled flexibly and modularly for a wide variety of unmanned vehicles