## 4 Conclusions  
The aim of this paper was to propose a detailed comparative procedure to assess the ability of passive ice protection materials in assisting the manual de-icing of a rotorcraft. The proposed procedure consisted of the characterization of materials under several laboratory tests in order to determine their characteristics of wettability and their icephobic behavior. Finally, their assessment under a multi-tool analysis was conducted to evaluate if they can assist in the manual de-icing, which includes conditions resembling operational reality. The multi-tool analysis allowed for the classification of materials depending on which tools were used, the number of passes necessary, and different atmospheric icing conditions. The comparison scale used five tools that are commercially available. The four icing conditions at \(-10\)\({}^{\circ}\)C simulated in the laboratory included the following: high-intensity freezing rain, low-intensity freezing rain, dry snow, and partially melted and refrozen snow. Five different materials were used to evaluate the proposed procedure: aluminum, as a reference; two silicone-based coatings, Nusil and Surfellent; an epoxy-based coating Wearlon; and finally a commercial ski wax, Swix.  
The wettability characteristics, which were determined for all materials tested, provided valuable insight into their icephobic behavior. All materials tested were more hydrophobic than aluminum. The material with the most significant icephobic behavior was the Nusil silicone coating with an average reduction factor of 12.2. This was determined by considering the adhesion reduction factor of the CAT, the PO and the reduction factor in freezing delay. The following coatings, Surfellent, Swix, and Wearlon, also showed some icephobic behavior, however, to a lesser extent, with average reduction factors of 7.4, 7.1, and 3.2, respectively. By evaluating the materials with the MTA, all materials behaved in a different manner. Although Nusil appeared to be promising under ice adhesion, it performed poorly under snow conditions. On the other hand, Surfellent and Swix received high scores by clearly assisting the manual de-icing in most conditions. Overall, the Surfellent coating received the highest score, indicating that it could assist the manual de-icing in these targeted conditions.  
The overall results show that it is important to undertake several tests including different ice and snow precipitation before concluding a material to be icephobic. On the other hand, having such a procedure, including predictor tests and real operational techniques, certainly allows for a better characterisation of the material(s).  
This procedure could easily be adapted to different fields of application by varying the type of frozen precipitation, the type of tools, and even the weight percentage of the results to adequately assess the efficiency of the materials in question. The improvement of the MTA could be undertaken by further instrumenting or automating the process, ensuring repeatability. Finally, this procedure could also be used as a development tool for the optimization and assessment of new materials.  
Conceptualization, J.-D.B., D.P., S.S., M.R. and G.M.; methodology, J.-D.B., D.P. and M.R.; validation, J.-D.B. and G.M.; formal analysis, J.-D.B.; resources, D.P., S.S. and M.R.; writing--original draft preparation, J.-D.B., D.P. and S.S.; writing--review and editing, M.R. and G.M.; supervision, G.M.; project administration, G.M.; funding acquisition, J.-D.B. and G.M. All authors have read and agreed to the published version of the manuscript.  
Funding: The authors would like to thank the Department of National Defense of Canada for funding the research under contract W7714-217494.