# Superhydrophobic Coating Solutions for Deicing Control in Aircraft
## 3 Superhydrophobic Surface with Icephobic Behaviour for Aircraft Applications
### SHS Tested in Flight Conditions  
Some works devoted to ice prevention employing superhydrophobic surfaces for aerospace applications draw incomplete or preliminary conclusions because the tests to which the materials are subjected are not in line with real application conditions. To date, the tests that most closely simulate real-world conditions are those involving the use of an Icing Wind Tunnel (IWT) in which is possible to reach the relevant droplet's impact velocity (50 m/s or higher) at low temperatures (up to \(-30\)\({}^{\circ}\)C) generating both rim and glaze ice or specific aging test according to standards. Fortunately, to date, the research employing these tests is increasing and this improves knowledge and the chances, through careful study, of finding a solution to the long-standing problem of ice accretion during flight. Among the earliest works devoted to the study of the properties of superhydrophobic coatings for aeronautics applications using tests conducted under standard conditions (IWT and others) are those by [PERSON] et al. [29] and [PERSON] et al. [30]. In [29] different surfaces, from hydrophilic to superhydrophobic, were analyzed in IWT (air speed 28 m/s, T = \(-17\)\({}^{\circ}\)C) varying icing conditions by acting on the nozzle for the liquid water clouds generation following Icing certification (FAR29, Appendix C--Icing Certification for icing condition requirements). The SH coating (CA = \(161^{\circ}\pm 2\)) was obtained by depositing a thin layer of Teflon by spray coating technique on the wing surface (etched aluminum). To define how a surface was effective in reducing ice adhesion, values of heating power required to avoid ice formation were taken as quantitative parameters. They found that the use of SH coating for aluminum reference provides a reduction in heating power  
Figure 5: Pictures of samples acquired at \(-27\)\({}^{\circ}\)C. Reference with water droplets before (**a**) and after (**b**) the icing at \(-27\)\({}^{\circ}\)C; coated sample with water droplets before (**c**) and after (**d**) the icing at \(-27\)\({}^{\circ}\)C. Reprinted with permission under the terms of the Creative Commons CC BY license from [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], Superhydrophobic coatings as anti-icing systems for small aircraft, Aerospace. 7 (2020) [26]. up to 80% to keep the edge of the wing ice-free and a significant reduction of runback ice in high LWC and complete prevention in low LWC conditions. Furthermore, it was observed that the grown ice consists of isolated structures, features that facilitate their breakage and removal. Unfortunately, the present study did not provide data regarding the characteristics of the coating after the test. In [30] the authors tested two SH commercial materials (surface roughness 1.1 and 2.42 um) and two common metals (baseline) (surface roughness 0.5 um) to evaluate the icephobic properties in helicopter blades employing an Adverse Environment Rotor Test Stand facility (T up to \(-25\,\mathrm{\SIUnitSymbolCelsius}\) and about 60 m/s) following the Federal Aviation Administration (FAA) advisor circular. The authors found that at high LWC on SH-FAS material, the ice-shedding capability could be slightly enhanced compared to the other samples. However, the authors observed that the adhesion reduction for the two SH samples did not depend on wettability because similar CA show differently in time ice conditions. Nevertheless, it was observed that SHS exhibited a reduced thickness of the grown ice (Figure 6) but on the other hand, it was pointed out that adhesion stress increases as roughness increases, and the SH samples started to deteriorate after four shedding tests. Also, [PERSON] et al. [31] tested different commercial hydrophobic and superhydrophobic (CA = 152) coatings under glaze and rime conditions in IWT. Different temperatures were settled to simulate different ice conditions at a constant speed of 21 m/s.