In-flight icing on unmanned aerial vehicles is a severe hazard and imposes limits on the operational envelope. Icing has been shown to lead to substantial aerodynamic performance losses on lifting surfaces and propellers. To quantify the performance loss of the propeller in icing conditions, this study proposes a model that describes the performance of a fixed-wing UAV propeller in icing conditions. For the development of this model, experiments in an icing wind tunnel have been performed to evaluate the performance loss of the propeller in different icing conditions. From the thrust and torque measurements, a model for the transient performance of a propeller in icing conditions has been developed. The model calculates thrust and torque as a function of the temperature, liquid water content, advance ratio, and the rotation rate of the propeller. This model contains an estimator for the ice accumulation on the propeller, the ice shedding forces of the propeller, and the performance of the iced propeller. This model can for example be used to estimate the flight performance of UAVs in icing conditions. It could also be applied for path and mission planning tools, autopilot, flight simulators, performance-based ice detection and the design of ice protection systems.
<div class="section abstract"><div class="htmlview paragraph">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. The experiment data analysis shows that the propeller power efficiency is highly sensitive to icing, with a 40% reduction in thrust and a 16% increase in torque observed on average across the tested motor speeds and airspeeds. The resulting reduction in propeller efficiency can be as high as 70% in the worst-case scenario. These findings provide valuable insights into the impact of ice accretion on electric propeller systems and contribute to the development of effective ice protection systems for safer UAV operation in cold environments.</div></div>
<div class="section abstract"><div class="htmlview paragraph">Urban air mobility (UAM) is a fast-growing industry that utilizes electric vertical take-off and landing (eVTOL) technologies to operate in densely populated urban areas with limited space. However, atmospheric icing serves as a limitation to its operational envelope as in-flight icing can happen all year round anywhere around the globe. Since icing in smaller aviation systems is still an emerging topic, there is a necessity to study icing of eVTOL rotors specifically. Two rotor geometries were chosen for this study. A small 15-inch rotor was selected to illustrate a multirotor UAV drone, while a large 80-inch rotor was chosen to represent a UAM passenger aircraft. The ice accretion experiments were conducted in an icing wind tunnel on the small 15-inch rotor. The icing simulations were performed using FENSAP-ICE. The ice accretion simulations of the 15-inch rotor sections at –5 °C show a large, rather streamlined ice shape instead of the expected glaze ice characteristics. At –15 °C the numerical ice accretion presents the typical rime ice shape. The results of the 80-inch rotor simulation present more varied ice shapes, which could indicate higher sensitivity towards the icing condition. Ice horns formed at temperatures close to freezing and the flow separation aft of the ice led to significant aerodynamic penalties. The 3D ice accretion simulation of the 80-inch rotor shows discrepancies with the 2D results as it does not predict ice accretion at the outer region of the blades at – 15 °C. This could be due to the higher stagnation temperature, increased friction, and three-dimensional crossflows preventing ice accumulation. The performance degradation simulations show that ice accretion causes significant aerodynamic penalties, especially in cases where horn ice accretion forms. Finally, the anti-icing loads required to mitigate ice accretion thermally were calculated. Both rotors require high power consumption for a fully evaporative IPS design.</div></div>
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