TECHNICAL FIELD AND STATE OF THE ART

The invention concerns an aircraft probes intended to be attached to an aircraft.

Conventionally on an aircraft probes measuring external environment and airflow parameters are arranged at various places on an outer surface of the aircraft.

Aircraft probes generally comprise a base that is attached to the aircraft, a housing extending essentially vertically from the base, wherein said housing comprising a body extending from the leading edge to the trailing edge, defining at least an airfoil portion extending at least partially from the base to the end of the housing, an airflow inlet having a first surface substantially parallel to an incoming airflow, a primary airflow passage from the airflow inlet to a primary airflow outlet, and a sensor assembly disposed within a sensor flow passage.

When an aircraft is flying under icing conditions, ice may form and adhere to the walls of a probe, thereby disturbing the functioning of the probe if too much ice accumulates. In addition, should ice form or enter inside the window integrating the sensor it may cause measurement inaccuracies or even prevent the functioning of the sensor.

Various solutions have been put forward to overcome these malfunction problems due to the formation of ice on the probe. The predominant anti-icing means is a heating mechanism provided to heat the body of the probe and thereby prevent ice from forming on the walls of said probe. In many conditions ice still forms on sections of the probe despite the operation of electrical heaters. Other parts of an aircraft are also susceptible to ice formation, and again heating is the predominant means to address the problem of ice formation.

Another means for managing the problem of ice formation on aircraft surfaces is inducing hydrophobic behavior on the surfaces of aircraft parts. For example, patent application WO2004078873 discloses hard, ice-phobic coatings which can be applied to airfoil surfaces to reduce ice adhesion on airfoil surfaces which are surfaces designed to produce reaction forces from the air through which it moves. Patent application WO2014148909 discloses an ice-phobic coating layer that will make it hard for under- cooled water and ice-like structures to attach and subsequently grow. The coating layer is applied either directly or as a multi-layered film. Use of a metallic icephobic plating comprising nickel and applied to at least a portion of the flowpath surface has also been known in the art, as disclosed by patent application WO2009134526.

Although coatings like the ones disclosed in the above mentioned patent applications claim to have good mechanical strength, durability of coatings under flight conditions and for long periods is an industry concern that still remains.This is especially true for leading edges of aircraft components where the surface is subjected to high speed impact of particles.

It is the objective of this invention to induce superhydrophobic, hydrophobic, or icephobic properties on at least parts of the surface of a probe by nano and micro texturing of the alloy of the probe itself rather than by application of coatings; such surface properties are expected to have much better durability.

It is well known in the art the use of laser for inducing hydrophobic properties on a metal surface.

For example, US2015136226 (A1 ) discloses a method for treating a metal or metal alloy to modify optical and hydrophobic properties of the metal or metal alloy, the method comprising: exposing a surface region of the metal or metal alloy to laser pulses sufficient to alter a surface structure of the metal or metal alloy to form a plurality of nano- scale structure shapes on the surface region and a plurality of micro-scale structure shapes on the surface region.

Other patent applications disclose methods for inducing hydrophobicity directly on different metal surfaces: For example, CN104498957A discloses a laser treatment method for inducing hydrophobicity on titanium alloy surface; CN104907698A discloses a laser treatment method for rendering super-hydrophobic a zinc alloy surface; CN104907701A discloses a laser treatment method for inducing super-hydrophobicity on stainless steel surfaces.

One of the problems with laser treatment of metal surfaces is that they can be slow. Especially treatment of complex surfaces, such as the surfaces of an aircraft probe, where there are changes of curvature and a 5-axis CNC machine may be required to guide the laser beam can be slow and expensive. US20140314995 (A1) discloses a laser processing method that is intended to be fast wherein the solid surface is covered with a transparent medium during laser processing and the laser beam incidents through the covering medium and irradiates the solid surface. The problem with such methods that utilize covering medium is that such medium would typically have low durability in flight conditions and would thus be unsuitable for aerospace applications.

Superhydrophobic materials are characterized in that water deposited on a surface will form a contact angle at least greater than 140 °. There are many such materials known in nature and perhaps the most publicized one is the lotus leaf. Most of such materials exhibit hierarchical structures, that is, a structure within a structure at micro and nano scales. Hierarchical structures have been possible to replicate and several methods are known to the art for creating hierarchies of nano and micro scale structures. For example, US20130330501 A1 discloses such hierarchical structure that can be applied on a variety of substrates. The hierarchical surface includes a primary structure having at least one primary characteristic features; a secondary structure having at least one secondary characteristic features, wherein the size of the at least one secondary characteristic features are larger than the size of the at least one primary characteristic features. The primary structure and the secondary structure synergistically provide improved mechanical properties and control of the wetting characteristics over that of the primary structure or the secondary structure alone. Hierarchies of structures have been created with the objective of better control of surface properties, locally, without regard of the overall geometry of an object.

It is therefore an objective of the present invention to propose an aircraft probe, which enables the probe to function under any weather conditions, in particular in the presence of frost and/or snow, without perturbing the measurements taken, and which utilizes superhydrophobic, hydrophobic, icephobic properties integrated directly into the surfaces of the probe rather than through coatings, and in a way that delivers cost effectively excellent anti-icing performance over long service life. A further objective of the invention is to create superhydrophobic, hydrophobic, or icephobic properties on the surface of a probe utilizing laser treatment, and taking full advantage of hierarchical structures at different scales. SUMMARY OF THE INVENTION

It is now found by the inventors that excellent resistance to ice formation can be achieved on aircraft probes, with high durability, by inducing surface functional properties partly or wholly by laser treatment, at selective areas, forming certain patterns. Said functional properties comprising hydrophilic or hydrophobic or superhydrophobic and or icephobic or omniphobic properties.

The above surface functional properties will make it hard for super-cooled droplets and ice-like particles to attach and subsequently grow as an ice formation on the probe surfaces. The above surface functional properties will also make it easy to remove any ice that may be formed on the surface.

In a preferred embodiment, the induced surface properties are arranged in surface patterns according to the geometry of the surface and the position on the probe.

This and other aspects and advantages of the present disclosure will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the disclosure, for which reference should be made to the claims. Moreover, the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures described herein.

LIST OF EMBODIMENTS

1. The first embodiment concerns a probe in the form of an airfoil wherein airflow across the sensing element is created by a cross channel from high pressure side of the airfoil to the low pressure side of the airfoil, as illustrated in figures 1A to 1 B. A probe of such general geometry is referred to as Probe Type A.

2. A second embodiment concerns a probe having an air intake that is essentially perpendicular to the direction of travel, as illustrated in figures 2A to 2D. A probe of such general geometry is referred to as Probe Type B. BRIEF DESCRIPTION OF DRAWINGS

Other features and advantages of the invention will appear in the following description. Embodiments of the invention will be described with reference to the drawings, in which:

- FIGS. 1 A-1 B illustrate in two isometric views an exemplary probe of type A;

FIG. 2A illustrates an isometric view of exemplary probe of type B;

FIGS. 2B-2C illustrate a side view of exemplary probe of type B;

FIG. 2D illustrates an isometric view of the air intake of exemplary probe of type

B;

- FIG. 2E illustrates an isometric view and a front view of a probe with macro scale features as indentations;

FIGS. 3A and 3B illustrate generic hierarchical structures;

FIG. 4 illustrates micro scale structures with troughs and peaks, having nano scale structures superimposed;

- FIGS.5A and 5B illustrate structures with varying distance between them;

FIG. 6A-6C illustrate examples of topographical patterns;

FIG. 7. Illustrates topographical patterns of surface functionalization superimposed on a curved surface having meso scale features;

FIG. 8 illustrates an example of a surface having hierarchies of structures both in a vertical orientation and in a horizontal orientation, said surface being able to preserve its properties under conditions of flight;

Fig 9 illustrates an example of meso scale features on a surface used to protect a downstream surface against abrasion from direct particle impact.

Fig 10: illustrates an example of a continuous path of the laser beam

DETAILED DESCRIPTION OF THE INVENTION

There follows a detailed description of embodiments of the invention by way of example only with reference to the accompanying drawings.

Figures 1 A and 1 B show an aircraft probe Type A for resisting the formation and propagation of ice which comprises a base (1 ) that is attached to the aircraft, a housing (2) extending, preferably vertically, from the base comprising a body extending from the leading edge (3) to the trailing edge (4), defining at least an airfoil portion extending at least partially from the base to the end of the housing. The airfoil portion comprises the upper airfoil (2a), and the lower airfoil (2b). The upper airfoil comprises a front section (2a1 ), and a back section (2a2).

Fig. 1 B further shows the airflow inlet (5) having a first surface facing (or substantially parallel to) an incoming airflow, a primary airflow passage is formed between the airflow inlet (5) and the primary airflow outlet (6) shown in Fig. 1A. A sensing element (7) at the primary airflow passage measures airflow parameters such as, for example, temperature.

The surface of the housing (2) has functional properties, these functional properties comprise any of the following: hydrophilic, hydrophobic, superhydrophobic, icephobic, omniphobic properties. These properties are induced partly or wholly by laser treatment on the surface of housing. Also, surface functional properties are arranged in topographical patterns.

Figure 2A shows a second embodiment of the invention, an aircraft probe for resisting the formation and propagation of ice which comprises a base (101) that is attached to the aircraft, a housing (102) extending, preferably vertically, from the base comprising a body extending from the leading edge (103) to the trailing edge (104), defining at least an airfoil portion extending at least partially from the base to the end of the housing. An inlet opening (105) allows air to flow through the housing and an outlet opening (106) allows air to exit the housing. Figure 2B illustrates an example of a probe wherein the leading edge (103) may be inclined in relation to the base (101 ).

Figures 2C and 2D show the airflow inlet channel (105) of the probe according to the second embodiment of the invention, having a first surface essentially perpendicular to the incoming flow (105a), an inner channel surface facing (or essentially parallel to) an incoming airflow (105b), wherein a primary airflow passage (105c) is formed between the airflow inlet and the primary air flow outlet (106).

Fig.2C further shows a cross sectional view of the second embodiment of the invention wherein a sensor assembly (107) disposed within a sensor flow passage (108).

Fig. 2D shows an isometric view of the upper section of the body of a probe of Type B, distal from the base. The exterior surface of the air intake channel is distinguished in the part that may have direct particle impact (109a) and the part that is somehow shielded and does not have direct particle impact (109b). Apart from the inlet opening (105), the exterior surface of the air intake channel may, in some embodiments as illustrated for example in figure 2B, not be exposed to direct particle impact,

The surface of the housing (102) has functional properties, these functional properties comprised of hydrophilic or hydrophobic or superhydrophobic and or icephobic or omniphobic properties, which are induced partly or wholly by laser treatment on the surface of housing. Also, surface functional properties are arranged in topographical patterns.

Hydrophilic or hydrophobic or superhydrophobic and or icephobic or omniphobic properties, can be induced on a surface through micro and/or nano features. Such features are created directly on the metal or alloy surface of a probe by appropriate laser treatment. Figure 3A shows nano scale structures (15) and micro scale structures (16) having hydrophilic or superhydrophobic and or icephobic or omniphobic properties formed on a surface. Such nano and micro scale structures are induced partly or wholly by laser treatment on the surface of the aircraft probe.

Scientists and engineers for several years have attempted to mimic nature in creating hydrophobicity, and it has been discovered that nature works in hierarchical structures, as it is most widely known by the lotus effect. The inventors have found that hierarchical structures can be created directly on a metal or alloy surface directly by laser.

Figure 3B shows an example of hierarchical order of the structures having different dimensional scales. The second or third order structures are in the nano scale range and are superimposed on the first order micro scale structures. Nano or micro structures can also be superimposed on structures of greater scales following similar hierarchy of scales. Hierarchical structures can also have different orientations to the surface, including parallel, vertical and inclined orientations.

Hierarchical structures can also be formed though projections as well as indentations on the surface. Figure 4 shows nano and micro scale structures at different dimensional scales having troughs (17) and peaks (18). A laser beam for example can displace material and create a though and deposit that material nearby to create a peak at nano or micro scale level. Other processing methods such as for example microembossing, electoerosion can also create patterns with structures comprising troughs and peaks, and the scale of these features generally depends on the capabilities of the processing method. Some processing methods may be more suited to create an underlying pattern at meso or micro scale upon which laser treatment may be applied to create nano scale structures.

Nano or microscale structures need not be homogeneous across a surface area. In fact, the inventors have found that by introducing variability in these structures, it is possible to vary surface functional properties such as degree of hydrophobicity or degree of resistance to wear. One of the attributes of nano or microscale structures that can be varied is the distance between one structure to another structure. For example, this could be the distance between structures resembling pillars. Figure 5A shows a surface having micro and nano scale structures where the distance Ln and Lm between the nano and micro structures respectively is constant. Figure 5B shows a surface having micro and nano scale structures where the distance Ln and Lm between the nano and micro structures respectively is not constant but varies instead. For example as shown the distance between the micro structures has increased from Lm-1 to Lm-2 and the distance between the nano structures has increased from Ln-1 to Ln-2. These distances may vary in any suitable way either increase or decrease or according to the functional requirements.

By varying the distance between structures the inventors have found that it is possible to create surface functional properties to match one desired property such as for example degree of hydrophobicity, against another desired property, such as for example resistance to abrasion from particle impact, and against manufacturing cost. It can be understood that the higher the density of nano/micro structures, i.e. the smaller distance between said nano/micro structures, the longer the laser processing time and hence the greater the processing cost per unit surface area.

The creation of nano/micro structures can induce surface properties such as superhydrophobic, hydrophobic, and or icephobic or omniphobic properties or hydrophilic properties. Different areas of the surface can therefore have different functional properties depending on the processing that they receive and hence the structures upon them. It is known from prior art that patterns of surface properties can have interesting effects. For example, US7402195B2 teaches that alternating regions of liquid repelling and liquid attracting material promote droplet formation on a surface. The inventors have found that interchanging regions of hydrophobic and hydrophilic properties on the surface of an aircraft probe can be used to direct in a controlled manner what is known as "runback water", that is water that forms after ice melts in areas of the probe that are heated and runs upstream the airflow. Furthermore, the inventors have found that interchanging regions of hydrophobic surface of different degrees of hydrophobicity present a cost effective way of achieving easy removal of ice or low ice adhesion on a large surface area of an aircraft probe.

Alternating regions of surface functional properties form patterns across the surface of the probe; these patterns are referred to as topographical patterns. Figure 6A shows such topographical patterns comprising regions of interchanging patterns of hydrophilic or hydrophobic or superhydrophobic or icephobic or omniphobic properties. The figure shows a top view of a surface (19) having two different types of structures, type "A" and type "B". For example, Type "A" can comprise hierarchical structures of micro and nano scale features which renders the surface superhydrophobic. And for example, type "B" can comprise micro scale structures which render the surface hydrophobic. Such alternating topographical patterns with different properties make the surface behave differently when water impinges or ice starts to develop. For example a hydrophilic topographical pattern could be formed on part of the surface to promote water coalescence or a superhydrophobic topographical surface could be formed on a portion of the leading edge to delay the formation of ice.

The distance L between the above mentioned topographical patterns can either be constant or varying as shown in Figures 6B and 6C respectively. Said distance L may vary along any direction. For example, in one embodiment this distance varies along the direction of the airflow, and for example in another embodiment this distance varies along the axis of the housing from the base of the probe, i.e. essentially perpendicular to the probe.

Furthermore, the above mentioned interchanging patterns may have one or more of the following characteristics:

• Interchanging regions of different shapes

• Interchanging regions of functionalized and non-functionalized surface areas

• Interchanging regions of hydrophilic and hydrophobic properties

· Interchanging regions of different degrees of hydrophobicity

• Interchanging regions of varying shapes

• Interchanging regions of varying size of the repeating patterns • Interchanging regions of whose shape or size follows a rule or equation

• Interchanging regions of varying size of the repeating pattern along the direction of the airflow

• Interchanging regions of varying size of the repeating pattern along the length of the leading or trailing edges

Topographical patterns with structures at nano and micro scale may be combined with geometric features of the probe surface at meso scale. Figure 7 shows the topographical patterns combined with meso scale geometrical features of the probe surface. Topographical patterns (20a, 20b) of micro and nano scale features, which induce surface functionalization, may exist on a curved surface, as illustrated in Figure 7, or on an essentially flat surface, and may in both cases be combined with meso scale features. Meso scale features may be of the order of 0.05 to 1.0mm. Different patterns may also result in different surface properties such as areas of hydrophobic and areas of hydrophilic properties. Topographical patterns with structures at nano and micro scale may also be combined with geometric features of the probe surface at macro scale. For example, Figure 2E shows a probe with indentations (202a) on the airfoil shaped body, said indentation acting as ice-weakening interfaces. These features at macro scale are found to have a much enhanced behavior when combined with said topographical patterns of surface functionalization.

The topographical patterns may be formed at different processing steps and may be superimposed. For example, the micro scale structures may be formed using a first method and then the nano scale structures superimposed on the micro scale structures using a second method different from the first.

The patterns of functionalized areas can be arranged in such a way as to resist abrasion over time and thus preserve their properties for a longer time. For example, the leading edge, as it is more prone to abrasion than other areas of the probe, can have patterns of micro and nano scale structures which are more resistant to direct impact with particles. For example, as shown in figure 2C or 2D, the exterior surface of the air intake channel is distinguished in the part that may have direct particle impact (109a) and the part that is somehow shielded and does not have direct particle impact (109b). On surface 109a, the surface may be functionalized with micro and nano features that are more resistant to abrasion, while on surface 109b there may be nano and micro features that are less resistant to abrasion.

Preservation of properties against deterioration due to abrasion or other mechanisms, may also take place due to features at the micro and nano scale. Such an arrangement of patterns is shown in Figure 8, the irregular structures (21) both at the micro (22) and nano (23) scale range can provide superhydrophobic properties to a surface. When abrasion occurs these structures will wear out in a manner that the overall superhydrophobicity will not be affected significantly thus making such structures more resistant to abrasion.

Areas of the probe that are not exposed to the incoming flow may have micro and nano structures less resistance to abrasion.

Furthermore, micro and nano structures that are less resistant to abrasion may be protected by geometrical features at meso scale to prevent or at least reduce direct particle impact. For example such geometrical features are shown in Figure 9 wherein meso scale features can form shielding surfaces (24) that are slightly inclined to the incoming flow and which provide a means for shielding the micro and nano scale structures that are formed on adjacent surfaces (25).

As explained earlier, it is found to be beneficial to selectively treat different areas of a probe. According to a first embodiment of the probe, it can be seen from figures 1 A and 1 B, areas of the probe where the surface is partly or wholly functionalized by laser treatment. These areas correspond to one or more of the following parts of the probe:

• at least a portion of the leading edge surface (3)

• at least a portion of the trailing edge (4)

• at least a portion of the airflow inlet (5)

· at least a portion of the primary airflow passage from the airflow inlet to a primary airflow outlet (6)

• at least a portion of the body where there is runback water (2)

• at least a portion of areas where heating is applied to melt any ice formed (3,2)

• on any surface prone to the formation of ice

According to a second embodiment of the probe, it can be seen from figures 2A to 2D, areas of the probe where the surface is partly or wholly functionalized by laser treatment. These areas correspond to one or more of the following parts of the probe: • at least a portion of the leading edge surface (103)

• at least a portion of the trailing edge (104)

• at least a portion of the airflow inlet (105)

• the leading edge of the mouth formed for airflow inlet (105a)

· the inner and lower surface of the airflow inlet (105b)

• the inner side and upper surface of the airflow inlet (105c)

• at least a portion of the primary airflow passage from the airflow inlet (105) to a primary airflow outlet (106)

• at least a portion of the outer surface of the airflow inlet channel, said portion of outer surface being susceptible to direct particle impact (109a)

• at least a portion of the outer surface of the airflow inlet channel, said portion of outer surface not being susceptible to direct particle impact (109b)

• at least a portion of the body where there is runback water (102)

• at least a portion of areas where heating is applied to melt any ice formed (103, 102)

• on any surface prone to the formation of ice

The hydrophilic, hydrophobic, superhydrophobic, icephobic, or ominiphobic properties are induced on at least part of the surface of the probe by using at least partly a laser texturing method directly on the alloy surface of the aircraft probe or on a pretreated alloy surface of the aircraft probe.

Pre-treatments may include:

• cleaning and/or polishing

• coating with another material

• chemical, electrical, or electrochemical etching

· micro-embossing

The inventors have further found that when processing the surface area of a probe the path that the laser beam flows can be critical in order to avoid unintended discontinuities in the treatment and in order to process the intended areas within the shortest possible time thus reducing treatment cost. Figure 10 shows one example of a laser beam path arranged in such a way as to minimize the processing time. In the illustrated example, the laser beam path follows a continuous path (31) along curved lines (32) without abrupt change of direction to minimize the processing time. The curved path is optimized for following surfaces of the probe and surfaces having high curvature. Such surfaces of high curvature for the probe are for example the leading edge (103), the trailing edge (104), or the edge of mouth of the airflow inlet (105a).