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7 Platform one Unmanned Systems Technology | December/January 2021 A Norwegian start-up is developing an ice protection system for UAVs (writes Nick Flaherty). In-flight icing is one of the risk factors limiting the use of UAVs on BVLOS missions. It occurs when a UAV flies into a cloud and encounters supercooled water droplets, which then freeze on the surface of the aircraft. This accretion leads to severe aerodynamic disturbances, which can lead to a loss of control or even a crash. To mitigate this risk, UAVs can be equipped with an ice protection system that detects and removes the ice by heating it, rather than relying on de-icing chemicals sprayed on before launch. However, heating systems can drain the battery of UAVs. Ubiq Aerospace has therefore developed a system called D-Ice that combines sensors, machine learning and wires embedded in the leading edge of fixed-wing UAVs. “The problem was pitched by the US Coast Guard, which were flying Puma unmanned platforms. They were having a lot of issues, not just flying but taking off, so they were having to cancel flights,” said Kim Lynge Sorensen at Ubiq. “The problem is that the ice builds up not just on the leading edge but also on the propellor and the sensors, especially the air speed sensor. Autopilots use that information for how they fly the craft. “The only thing that really makes sense for small unmanned systems is electrothermal. It’s the only solution where you don’t have an immediate impact on the system, as you don’t have the added weight of chemical systems,” he said. Ubiq’s de-icing system operates in cycles. It measures the temperature and humidity using dew point calculations, and switches on optical sensors to detect the formation of any ice. The sensors are built into the airframe, along with an LED laser and photodiode to measure the diffraction, which changes once ice forms on part of the wing. When the sensors detect ice starting to form, it is allowed to grow. Conducting carbon filaments in the leading edge are shaped to allow the ice to grow more in certain places than others. Once the ice reaches a critical size, extra heating melts the ice at the interface of the surface, and the whole sheet of ice is shed from the wing by the airflow. The heating can then switch off until the ice builds up again. This requires less energy than constantly heating the wing, Sorensen said. The positioning of the sensors and heating elements is determined through CFD combined with aerodynamic models of the effects of ice, which change rapidly. “Using smart algorithms we were able to say where the ice forms, using thermal modelling based on the thermodynamics of the airflow,” Sorensen said. D-Ice is available as an embedded custom component in a manufacturing process, or as a retrofit solution for existing unmanned aircraft. Airborne vehicles De-icer runs hot and cold The D-Ice system switches on only when icing on a UAV’s wings is detected