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Unmanned aerial vehicles (UAVs) are an emerging technology with a large variety of commercial and military applications. In-flight icing occurs during flight in supercooled clouds or freezing precipitation and is a potential hazard to all aircraft. In-flight icing on UAVs imposes a major limitation on the operational envelope. This report describes the unsettled topics related to UAV icing. First, typical UAV applications and the general hazards of icing are described. Second, an overview of the special technical characteristics of icing on autonomous and unmanned aircraft is given. Third, the operational challenges for flight in icing conditions are discussed. Fourth, technologies for ice protection that mitigate the icing hazard are introduced. Fifth, the tools and methods required to understand UAV icing and to develop aircraft with cold-weather capabilities are presented. Finally, an assessment of the current and future regulations regarding icing on UAVs is provided.

In-flight atmospheric icing is a severe hazard for propeller-driven unmanned aerial vehicles (UAVs) that can lead to issues ranging from reduced flight performance to unacceptable loss of lift and control. To address this challenge, a physics-based first principles model of an electric UAV propulsion system is developed and identified in varying icing conditions. Specifically, a brushless direct current motor (BLDC) based propeller system, typical for UAVs with a wing span of 1-3 meters, is tested in an icing wind tunnel with three accreted ice shapes of increasing size. The results are analyzed to identify the dynamics of the electrical, mechanical, and aerodynamic subsystems of the propulsion system. Moreover, the parameters of the identified models are presented, making it possible to analyze their sensitivity to ice accretion on the propeller blades.