Ice accretion on external aircraft surfaces due to the impact of supercooled water droplets can negatively affect the aerodynamic performance and reduce the operational capability and, therefore, must be prevented. Icephobic coatings capable of reducing the adhesion strength of ice to a surface represent a promising technology to support thermal or mechanical ice protection systems. Icephobicity is similar to hydrophobicity in several aspects and superhydrophobic surfaces embody a straightforward solution to the ice adhesion problem. Short/ultrashort pulsed laser surface treatments are proposed as a viable technology to generate superhydrophobic properties on metallic surfaces. However, it has not yet been verified whether such surfaces are generally icephobic under representative icing conditions. This study investigates the ice adhesion strength on Ti6Al4V, an alloy commonly used for aerospace components, textured by means of direct laser writing, direct laser interference patterning, and laser-induced periodic surface structures laser sources with pulse durations ranging from nano-to femtosecond regimes. A clear relation between the spatial period, the surface microstructure depth, and the ice adhesion strength under different icing conditions is investigated. From these observations, a set of design rules can be defined for superhydrophobic surfaces that are icephobic, too.can reduce dramatically lift and increase drag, influencing the maneuverability of the aircraft. Ice protection systems (IPS) are installed to allow aircraft flying safely in icing conditions. At the present time, IPS are not supported by coatings or surfaces that facilitate the ice removal-due to the still too low maturity and robustness of such technological solutions. Yet, surface functionalization is a promising strategy for manufacturing icephobic surfaces [3] aiming to delay ice accretion and/ or to reduce ice adhesion [4,5] and therefore to reduce the electrical or thermal energy required by the IPS.In the last two decades, several approaches for producing icephobic surfaces were presented in literature. For example, it has been proven that polishing the surfaces can reduce the mechanical interlocking with the accreted ice, hence facilitating the ice removal. [5] Coatings can lower the surface free energy and thus reduce the strength of the bonding between ice and surface. [6] On slippery liquid-infused porous surfaces the supercooled water droplets impinge on a liquid instead of a solid surface, which offers a double advantage: interfacial slippage of water or ice occurs (nonzero slip velocity)-which reduces ice adhesion [7] -and interlocking of ice with a liquid interface cannot occur. However, employing coatings or chemicals to

Surface contamination by ice poses a hazard to industries ranging from power transmission to transportation by ground, sea and air. The aviation industry is particularly affected by icing phenomena that manifest as a reduction in fuel efficiency and compromised aerodynamic lift, which can impair flight safety. [1] Consequently, there is a worldwide scientific effort to understand the physics of icing, aiming to develop effective and efficient anti-icing and de-icing strategies. [2] Icing can occur while aircraft are on the ground or in the air. On the ground, when freezing precipitation contaminates the surfaces of an aircraft, safety protocols delay that aircraft's scheduled flight. In fact, contamination necessarily needs to be removed since it alters aerodynamic properties and, like on a snow-covered car, ice fragments can be sheared off by aerodynamic drag and fly into the engines. A typical ground de-icing operation consists in directly spraying an aircraft with a mixture of warm water and glycol. [3] Generally, ice contamination in the air is caused by the impact of supercooled water droplets found in clouds. Depending on several conditions, droplets may either stick to a surface at the point of impact or flow along the surface in the direction of airflow. In the latter case they form a thin film of water, where surface tension forces them into rivulets. [1,4] While fixed-wing aircraft cruise at altitudes above where icing can occur, helicopters operate at altitudes where supercooled water droplets are known to occur (temperature range between −40 and 0 °C). [5] Aviation safety authorities demand to avoid flying into known icing conditions and, as an additional precaution, they enforce through certification, the equipment of ice protection systems (IPS) to all commercial aircraft. [6] IPS can provide either anti-icing, de-icing, or both countermeasures. [1,7] Thermal anti-icing describes a condition where all impinging water droplets are evaporated by a high-temperature surface. A de-icing countermeasure is one where ice is removed from a surface once it has reached a subjectively critical size. [7] Commercial airliners, for the most part, are equipped with thermal IPS that use hot air drawn from the compressor of their turbofan engines, which is diverted to critical surfaces Forward facing aerodynamic surfaces such as rotors and wings are susceptible to ice build-up when exposed to atmospheric icing conditions. If not removed, accumulated ice on aircraft surfaces affects aerodynamics or rotation balance, which can ultimately lead to increased fuel consumption, reduced operational performance and to potentially hazardous situations. Laser surface structuring is proposed as an alternative technology to coatings for achieving icephobic properties and support anti-icing and de-icing processes on aerodynamic surfaces. However, to authors' knowledge, no study available in the literature reports on the icing behavior of microtextured curved aerodynamic profiles and the effect of the laser surface treatment on the...

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