Evaluation of Visual Failure versus Aerodynamic Limit for a Snow Contaminated Anti-Iced Wing Section during Simulated Takeoff

Under contract to Airlines for America (A4A), APS Aviation Inc. (APS), in collaboration with the National Research Council of Canada (NRC), completed an aircraft ground icing exploratory research project at the NRC 3 m × 6 m Wind Tunnel in Ottawa in January 2019. The purpose of this project was to investigate the feasibility of using aerodynamic data to evaluate the performance of contaminated anti-icing fluid, rather than the traditional visual fluid failure indicators that are used to develop Holdover Times (HOTs). The aerodynamic performance of a supercritical airfoil model with anti-icing fluids and snow contamination was evaluated against the clean, dry performance of the airfoil in order to calculate the associated aerodynamic penalty. The visual failure of the fluid was also evaluated for each run, and the visual and aerodynamic results were compared against each other for each contamination exposure time. The results demonstrated that the visual failure of a fluid was not directly linked to the aerodynamic performance of the fluid, and the margin between the two was a function of the fluid used, the model configuration, and the test temperature. The results support the premise that in specific operational conditions, certain fluids may offer protection for a period of time after the visual failure. This margin of protection is likely dependent on the same variables as the current holdover times, including precipitation type and intensity, fluid type, and outdoor air temperature and aircraft configuration.