# Superhydrophobic Coating Solutions for Deicing Control in Aircraft
## 3 Superhydrophobic Surface with Icephobic Behaviour for Aircraft Applications
### SHS Tested in Flight Conditions
From the test, it was observed that the SHS allowed to save energy equal to 33% for glaze ice and about 13% for rime concerning the anti-icing system without coating (reference). Also, the hydrophobic coating allowed for saving energy but in smaller quantities than SHS. From this preliminary work, the increase in hydrophobicity allowed reducing energy consumption for ice protection but no tests about the durability and resistance of SHS were conducted. [PERSON] et al., over the years, proposed different studies in which they analyzed the yield of SH materials under real application conditions. In these works, [27; 32] the SH coating was prepared by spray coating technique where several layers of nanometric hydrophobic silica dispersed in Tetrahydrofuran were deposited on different substrates with or without a polyurethane primer layer. In [27] the authors found that higher CA was reached when the silica dispersion was prepared by ultrasonication, in fact, superhydrophobic behavior was reached only after this step. Reference and SH-coated samples  
Figure 6: Ice shape pictures for both metallic and SHS materials, taken immediately before the shedding event. Case nomenclature is A, D glaze ide, B, mix condition and C rime. Ice shape profile has been enhanced to ease visual comparisons. SHS case A seems to have a lot of ice on the top surface not enhanced, but this is correct because that ice section is made only by light ice feathers, which would have been shed earlier and separately from the leading edge ice. Reprinted from Cold Regions Science and Technology, 100, [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], Pages 50–58, Copyright (2014), with permission from Elsevier [30]. (Ra = 0.3 \(\upmu\)m) were subjected to an aging test according to the MIL standard in which real flight conditions at 16,000 m in altitude were simulated (variation of humidity and temperature) for about 16 h, 10 times. After the aging test, the SH coating maintained its wettability in particular when a primer PU (Polyurethane) layer was applied and measurement of CA at \(-12\)\({}^{\circ}\)C and 0.5 bar showed a decrease in wettability losing superhydrophobicity (<130\({}^{\circ}\)). An evolution of the work is found in [32] where an SH coating, produced following the procedure in [33], was applied on the NACA0015 (symmetrical airfoil with a 15% thickness to chord ratio developed by the National Advisory Committee for Aeronautics) wing profile has been subjected to an IWT test, the temperature ranged from \(-3\) to \(-23\)\({}^{\circ}\)C at an altitude of 3000 m, LWC 0.3 g/m\({}^{3}\) and two-speed tests 50 and 95 m/s. Superhydrophobicity was maintained after the IWT test campaign but the effectiveness of the SH coating on ice prevention/reduction depended on the tested conditions (glace or rime and exposure time) and, in general, for long exposure time it could be considered as a support to an active system and not for use only as an anti-icing system. [PERSON] et al. [34] conducted validation tests in IWT on a hybrid anti-icing system (CA = 150\({}^{\circ}\) RoA = 8\({}^{\circ}\)) prepared by combining icephobic polytetrafluoroethylene (PTFE) coating and electrothermal heating (ICE-WIPS). The IWT test chosen conditions appeared in Federal regulation and they selected wind speed of 75 m/s, T = \(-10/-8\)\({}^{\circ}\)C and different LWC. The experiments provided raw data concerning the reduction in power consumption and it was observed that, in relationship to the existing heating system, the ICE-WIPS reduced power consumption by 30 to 70% depending on icing conditions. The work, however, did not provide data regarding the durability and the maintenance of properties thus resulting partly deficient for actual applications. [PERSON] et al. [35] recently developed an SH duplex coating system devoting a great deal of attention to its environmental durability.