Unmanned Systems Technology 024 | Wingcopter 178 l 5G focus l UUVs insight l CES report l Stromkind KAT l Intelligent Energy fuel cell l Earthsense TerraSentia l Connectors focus l Advanced Engineering report

69 Intelligent Energy fuel cell | Dossier Instead, roughly one-quarter more air is drawn through the intake vents and across the power electronics and the fuel cells, before exiting through each of the two fans’ ducts with the purged hydrogen and humid air. Rather than push one fan to a higher rpm for the extra air, the dual-fan design makes the 800 W fuel cell quieter thanks to having two fans running at a lower rpm. It also reduces the overall parasitic losses taken from powering the cooling system. The electronics module has four vents in total: on the top, underneath and on the left and right sides, but with no vent on the front. This helps to baffle the air coming towards the fuel cell as the UAV is in flight. “Imagine you’re running a fan to cool a fuel cell when you’re hovering,” Kelly says. “It’s running at a particular rate, then suddenly you command the UAV to move at 40 kph, which would mean you have the equivalent of a 40 kph wind entering the electronics section – it could play havoc with the control of the system. Baffling that airflow reduces that effect.” Each fan is driven by a T-Motor F20II brushless electric motor with a 3750 Kv value (or rpm per volt) and an rpm range of 19,000 to 34,000 (with 23,000 rpm at peak operation). Each propeller is a 3 in diameter, triple-bladed bullnose prop with a 3.5 mm pitch. These fit within a combined ventilation space of 4500 mm 2 across the two exhaust ducts. “At peak fan power, we move 4.3 m 2 of air per minute,” says Kelly. “Total air draw is determined primarily by feedback from the thermistors in the fuel cell, telling the controls to increase or decrease cooling to the cell stack.” The team found that to move the quantities of air they needed, a typical computer cooling fan would have weighed three to four times more than the T-Motor alternative. That would have made it impossible to make the design light enough for small UASs. As Kelly comments, the Kv value and propeller were the primary draws of the F20II, giving it the necessary ratios of air draw versus size and weight. “The rpm per volt makes them much quicker to start and stop,” he adds. “You don’t get that near-immediate response time with standard cooling fans for electronics.” The cooling system developed initially used CFD software to simulate airflow and thus identify target requirements for air draw, before moving on to bench- testing fan motors. Once levels of air flow and efficiency had been studied, IE began testing them in fuel cell modules. The motors are run at a power consumption rate of around 20 W, up to a peak of 50 W. While they are capable of being run at higher rates, those rates help maintain an internal operating temperature of around 50 C, usually cycling between 40 and 60°C. “Our control system determines the best operating temperature given Unmanned Systems Technology | February/March 2019 Four intake vents are designed around the front section of the module, so air is first drawn directly through the electronics If you want to put a payload in a particular place, and make sure your CoG is right, you can just move the fuel cell forwards or back