Icing on Full-Scale Swept Wings in Flight and Icing Wind Tunnel

Inflight ice accretion on aircraft wings has been critically important for development and certification of transport category aircraft. With recent efforts toward certification by analysis, it is becoming increasingly important to characterize ice accretions in icing wind tunnels, the primary source of validation data for higher-fidelity three-dimensional ice shape analysis codes to be used in aircraft certification, in comparison with those in natural icing environments. In this study, a series of natural icing flight tests and icing wind tunnel tests were conducted on a transport category aircraft. The results were compared at similar test conditions on protected and unprotected surfaces of swept wings and empennage. For unprotected surfaces, both tests resulted in scallop ice, with natural icing flight test resulting in significantly smaller ice accretions. For protected surfaces, runback ice was formed on the lower wing surface in both tests, with natural icing flight test resulting in significantly less and sparser runback ice. Differences in scallop ice structures, limitations of icing wind tunnels, and scaling methods are considered the potential contributing factors to the differences. The results indicate a need for further studies on case-to-case comparison of ice accretions in the two test methods focusing on full-scale aircraft conditions.