Full-Scale EVTOL Rotor Icing Wind Tunnel Testing
Authors:   The Pennsylvania State University, Karli Geoffrey ,   Georgia Institute of Technology, Yan Sihong , Palacios Jose 
Published: September 2024

In recent years, the electrically powered Urban Air Mobility (UAM) market has witnessed significant growth, fueled by advances in electric motor and high-power-density lithium battery technologies. This surge of interest has prompted an exploration into the design and functionality of electric vertical take-off and landing (eVTOL) vehicles, particularly those with multi-tilt-rotor configurations. These eVTOL vehicles, capable of operating at higher RPMs than traditional helicopters, face unique challenges, especially under adverse environmental conditions such as icing. Aircraft airframe icing is known to severely compromise the operational efficiency and safety of aerodynamic surfaces, posing a significant threat to the operational capabilities of eVTOL vehicles. This paper presents the development and testing of a full-scale eVTOL rotor test stand that was designed to assess the impact of icing on these novel vehicles. The study focuses on evaluating eVTOL configurations under specific atmospheric conditions outlined in the Federal Aviation Regulation (FAR) Appendix C. The research aims to provide insights into the dangers imposed by icing and to collect experimental ice shapes in these unique configurations. This comprehensive data will aid in validating icing models and could help contribute to the formulation of eVTOL icing rules and regulations, improving the safety and viability of these vehicles in commercial airspace. A full-scale eVTOL rotor test stand was developed and tested in the Rail Tec Arsenal icing wind tunnel. In total 23 experimental conditions yielding 62 reference points were analyzed. The samples were compared to current state of the art 2D modified LEWICE prediction software based on maximum leading edge thickness and horn height. Of the 13 rime cases, 100% were within ±30% of the experimental results. 73.9% of mixed cases were within these bounds and 34.6% of glaze cases satisfied this criteria. Only a single horn out of 23 cases (4%) was within these bounds. Horn structures and other large features were unable to be successfully captured by 2D prediction models. Current 2D modeling software is sufficient at predicting leading edge ice thickness at temperatures at or lower than −10°C. Accuracy decreased as temperature increased, and other factors like SLDs negatively affected the prediction accuracy. It was empirically determined that there was no observable spanwise LWC variation during testing that could account for model uncertainty. Additionally, LWC changes through the rotor plane were also measured. A comparison between full and truncated blades was also performed. Straight-cut, truncated tips have a negative effect on ice shape development that is unaccounted for in 2D ice accretion models. Finally, it was determined that for an eVTOL trying to land after accreting ice in cruise, there would be an approximately 15%-30% additional power requirement (RPM held constant), dependent on icing conditions. The overarching goal of this work was to showcase the implications of icing on eVTOLs, with the ultimate goal of ensuring their operational integrity in diverse climatic conditions. This research represents a necessary step towards establishing eVTOLs icing testing, for efficient, and reliable urban air mobility.