## 1 Introduction  
Aircraft icing has been widely recognized as a severe weather hazard to flight safety in cold climates [1], since the ice accretion on aircraft surfaces alters the flight aerodynamics, reducing lift and increasing weight and drag, thus leading to dangerous stall conditions with a temporary or permanent loss of control of the aircraft. Currently, to hinder the ice accretion dangers, active Ice Protection Systems (IPS) requiring energy are being employed, either to prevent icing (anti-icing) or to remove ice once it has been formed (de-icing). The use of active IPS, which can be thermal, electro-mechanic [2], electro-thermal [3], pneumatic, or a glycol-based fluid type [4], implicates an increase in construction complexity, weight, manufacturing, and management costs, an increase of onboard power consumption, and then an increase of CO\({}_{2}\) emissions [5]. It would be highly desirable and advantageous if surfaces could passively reduce or delay the ice formation and facilitate ice removal. While active methods rely on energy input from an external system for the anti-/de-icing operation, passive methods take advantage of the physical properties of the airframe surfaces (e.g., surface wettability) to prevent, delay, or reduce ice formation and accretion [1], and avoid/reduce the run-back of ice [6]. In this contest, superhydrophobic coatings owing to their extraordinary water repellency and no requirement for additional energy consumption can be viewed as excellent candidates for icephoicity in this area [7, 8]. However, whether or not superhydrophobicity implies icephoicity, is a debated topic [9, 10], and, generally, it is a misunderstanding to believe that to design a surface with high contact angles should consequently lead to an icepphobic surface [9]. [PERSON] et al. [11] found that the anti-icing capability of surfaces depends not only on their superhydrophobicity but also on the surface morphology; [PERSON] et al. [12] found that icephobic properties of superhydrophobic surfaces can be compromised in the case of frost formation, so under high humidity, the surface turns into a hydrophilic surface; [PERSON] et al. [13] found that the superhydrophobic surfaces cannot reduce the ice adhesion, and the ice adhesion strength on superhydrophobic surfaces is comparable to that observed for superhydrophilic surfaces, because of the mechanical interlocking between the ice and the surface texture. During a flight, ice accretion is usually due to supercooled water droplets impinging on aircraft surfaces, and the icephobicity of a surface not only depends on intrinsic surface properties but also on the ice formation conditions [5]. Therefore, it would be highly recommended and helpful to assess the icephobicity of these coatings through a test conducted at aircraft cruise velocities and in relevant icing conditions. However, most studies use droplets' impact velocities below 10 m/s [14; 15] or freezing conditions not in line with typical aircraft icing conditions [13; 16]. To the best of our knowledge, only in a few studies of superhydrophobic surfaces were tested in an Icing Wind Tunnel (IWT) at relevant speed, i.e., 50 m/s or higher, and by generating both prime and glaze ice [17; 18; 19]. Other studies were focused on the effect of hydrophobic/superhydrophobic coatings on the reduction of power supply needed to keep the aircraft surfaces ice-free when combined with active Ice Protection Systems (IPS) [6; 9; 20; 21; 22]. Table 1 represents a short review of these studies, performed to the best of our knowledge. Table 1 highlights that IWT tests at a speed higher than 50 m/s were carried out only by combining coatings with active IPS [20]. In this scenario, the present work aims to test at 50 and 95 m/s and at temperatures ranging between \(-3\) and \(-23\)\({}^{\circ}\)C, two superhydrophobic coatings applied on two NACA0015 wing profiles, without any active IPS. Selected IWT test conditions take into account common performances of General Aviation, CS-23, and CS-25 categories [23].