## 3 Results
### IWT Tests
Results, displayed in Figure 14a,b, show that in rime ice conditions, the \(t_{ice}\) measured on A1 and A2 was similar to or higher than those measured on AR; whereas in glaze ice conditions, in test 3 and test 6, the \(t_{ice}\) measured on A1 was reduced by \(-12\) and \(-34\%\), respectively, with respect to the AR site; lower differences were observed in all other cases. This was because, at the stagnation point (\"A\" in Figure 13a for an attack angle equal to zero), the ice accretes in spite of the surface properties since the local velocity of the airflow there is zero. For the A1 surface in test 4, in fact, the ice accreted only at the stagnation point. The extension length of the compact ice \(L_{ci}\) was measured after each test and compared to the corresponding reference. Values were subtracted of the corresponding \(t_{ice}\) and reported in Figure 15.  
Results show that in rime ice conditions (test 1 and test 2), the ice accreted along the coated airfoil generally increased with respect to the reference. In detail, _Lci_ measured on the A1 site in test 1 and test 2 was \(+5\%\) and \(-5\%\), respectively, compared to those measured on the AR. In both tests, _Lci_ on the A2 site was higher than the AR (\(+39\) and \(+22\%\), respectively). A different scenario could be observed in glaze ice conditions (tests 3, 4, and 6) and in test 5, for which _Lci_ measured on A1 and A2 was considerably lower than those measured on the AR (from \(-12\) to \(-100\%\)). By supposing that in all cases the high hydrophobicity of the surface caused the droplets to easily roll on the surface, these results seemed to give evidence that the lower the temperature, the faster the freezing of droplets. As a consequence, in test 1 and test 2, the droplets froze before rolling away, increasing _Lci_. Whereas in tests 3-6, the droplets slipped away, froze as isolated droplets, or did not freeze at all. Hence, as the temperature increased, the effect of the superhydrophobicity increased and the difference of _Lci_ (\(\Delta\)Lci) measured on coated and reference surfaces became larger (Figure 16). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**TEST** & **Static T** & **V** & **Total T** & **Altitude** & **LVC** & **MVD** & **Mach** & **Test Duration** & **Flight Path** \\
**ID** & [\({}^{\circ}\)C] & **[m/s]** & [\({}^{\circ}\)C] & **[m]** & **[g/m\({}^{3}\)]** & **[\(\mu\)m]** & & **[s]** & **[km]** \\ \hline
1 & \(-22.98\) & \(94.9\) & \(-18.55\) & \(3001\) & \(0.602\) & \(22.08\) & \(0.299\) & \(79\) & \(7.50\) \\
2 & \(-22.95\) & \(94.5\) & \(-18.57\) & \(83\) & \(0.553\) & \(19.92\) & \(0.298\) & \(77\)Figure 12: Pictures of ice accreted on A1, A2, and AR samples during the IWT test 1 (**a**), test 2 (**b**), test 3 (**c**), test 4 (**d**), test 5 (**e**), test 6 (**f**). The superhydrophobicity of A1 and A2 was preserved after the IWT test campaign. The 3D scan acquired after test 6 was overlapped with the neat airfoil 3D reconstruction (Figure 17). In the inset (Figure 17d,e), a magnification of the airfoils with an assessment of the lengths of the compact ice _Lci_ accumulated starting from the leading edge was also reported. These values were in good agreement with those measured and reported in Figure 15, and listed in Table 4. The comparison was made by adding the thickness of the ice accumulated at the stagnation point. Figure 14: Accreted ice thickness \(t_{ice}\) on A1 and AR (**a**), and on A2, and AR (**b**), during the IWT tests. Figure 13: Schematic drawing of the accreted ice shape. With an angle of attack equal to zero, A represents the stagnation point (**a**). Measurement of the samples’ chord length after each test (**b**,**c**). Figure 15: Length of the compact ice _Lci_ accreted from the leading edge alongside the airfoils A1 and AR (**a**), and A2 and AR (**b**) during the IWT tests. Figure 16: Percentage variation in _Lci_ of coated surfaces with respect to the references as a function of the tests’ temperature.