Aerodynamic Comparison of Freezing Rain and Freezing Drizzle Conditions at the RTA Icing Wind Tunnel 2019-01-2023
The simulation of icing conditions in icing wind tunnels (IWTs) is essential for the certification of aircraft components and offers unique possibilities for research purposes. Up to now only the conditions defined in Appendix C of the EASA Certification Specification 25, respectively the FAA Code of Federal Regulations Title 14 Part 25 were used for the certification processes in IWTs. In addition, Appendix O was introduced in 2014 to cover supercooled large droplet (SLD) icing conditions such as freezing drizzle and freezing rain, which pose a major risk for flight safety. The simulation of SLD icing in IWTs is, due to the different behavior of the large droplets, very challenging and not all required conditions have successfully been recreated yet. RTA Rail Tec Arsenal Fahrzeugversuchsanlage GmbH has focused on the simulation of in-flight icing conditions since 2012 and increased effort was put in the simulation of SLDs in recent years. During several research projects it was shown that the correct droplet size distributions for freezing drizzle and freezing rain MVD > 40 µm can be created. With further improvements to the spray system a cloud uniformity within certain tolerances also has been achieved over areas large enough to cover an unscaled wing section. In order determine the ice accretion with the most severe influence on the aerodynamic performance a NACA0012 wing section with a wingspan of 1.8 m and a chord of 1 m was exposed to different icing clouds including Appendix C conditions, freezing drizzle and freezing rain. The aerodynamic coefficients were recorded over a large angle of attack range and the characteristics of the different ice accretions were analyzed and documented using high resolution 3D scan technology. It was the first time that an unscaled wing was iced under artificial freezing rain conditions.
Wolfgang Breitfuß, Michael Wannemacher, Florian Knöbl, Hermann Ferschitz
International Conference on Icing of Aircraft, Engines, and Structures