Patent Description:
During flight ice may accumulate on exposed portions of aircraft, such as leading edges of wings, horizontal and vertical tail planes, and high-lift devices, in particular if the aircraft, such as an airplane, flies through a cloud containing supercooled water droplets or if droplets impact on a supercooled airframe structure.

Different systems for preventing ice formation (anti-icing) and removing ice that has formed (de-icing) are generally known. Usually the ice protection system on commercial airliners mainly includes pneumatically operated systems employing bleed air heating or expanding inflatable rubber boots.

The known systems are usually rather energy inefficient or are not suitable for new aircraft types that are envisioned as a more electrified aircraft system architecture. A commercial transport aircraft with a more electric system aircraft architecture was recently introduced to the market using an electro-thermal ice protection system. This system still uses continuous operation (so-called anti-icing mode) and rather heavy metallic heaters.

A further issue for which de-icing is relevant is possible contamination of microperforated leading edges, such as a vertical tail plane leading edge. The microperforations improve laminarity of the aerodynamic boundary layer. The boundary layer of air can be sucked in through the microperforations. A negative pressure on the in-facing side of the leading edge allows the aerodynamic boundary layer from the out-facing surface to be controlled such that the result is an increase of laminar boundary length around the tail plane, reduction of drag, and improvement of fuel-efficiency. For further illustration reference is made to <CIT> and <CIT>.

In addition to heating based systems, <CIT> and <CIT> disclose superhydrophobic coatings to further reduce the adhesiveness of ice and simplify its removal.

<CIT> discloses an ice-protection system for a rotorblade of a tiltrotor aircraft. The ice-protection system has heating elements that are resistance-tailored to the application.

<CIT> discloses an ice removal system, where heaters can be individually powered depending on where ice is detected.

<CIT> discloses a de-icing/anti-icing system having heating elements made of carbon nanotubes.

<CIT> discloses an ice protection heater element having a carbon-allotrope heater with micro perforations.

<CIT> discloses an active superhydrophobic surface structure that can be switched between a superhydrophobic and ordinary state.

<CIT> discloses a system for anti-icing with a control unit that is connected to multiple electrical leads, temperature sensors and ice detectors.

<CIT> discloses a kind of anti-icing method based on a superhydrophobic electric heating cover.

<CIT> discloses a hybrid electrical ice protection system including a first set of heaters and a second set of heaters to implement three ice protection methods in various combinations. The ice protection methods include the fully-evaporative anti-ice protection method, the wet running anti-ice protection method, and the de-ice method.

It is the object of the invention to improve de-icing systems for aircraft.

The object is achieved by the subject-matter of the independent claims. Preferred embodiments are subject-matter of the dependent claims.

The invention provides a de-icing system configured for preventing the formation of and/or removing ice on a leading edge portion of an airfoil of an aircraft, the de-icing system comprising a heating foil that is adhesively bondable to the leading edge portion and that has a plurality of heating elements that are configured to be selectively energized for heating, an ice detecting device configured for detecting the presence of ice on the leading edge portion, and a control device configured for periodically and selectively energizing the heating elements based on the ice presence measured by the ice detecting device. The control device is further configured to energize a first group of the heating elements such that a first linear heating pattern parallel to the leading edge portion is formed, in order to create a predetermined breaking line. The control device is further configured to energize a third group of the heating elements such that a plurality of second linear heating patterns that are parallel to each other and orthogonal to the first heating line are formed. The control device is configured to progressively energize and de-energize the heating elements so as to transition between different heating patterns in such a manner that the heating elements are energized progressively further away from the predetermined breaking line.

Preferably, the ice detecting device is integrated within the heating foil. Preferably, the ice detecting device includes a temperature sensor, preferably a thermocouple.

Preferably, the heating elements include carbon based material or a carbon based thin film configured to produce heat when energized. Preferably, the carbon based material or the carbon based thin film include any one of graphite, graphene and graphene related materials (GRM), or carbon nano tubes (CNT).

Preferably, the control device is further configured to cyclically energize and de-energize the first group.

Preferably, the control device is further configured to cyclically energize and de-energize the third group.

Preferably, the control device is further configured to energize a second group of the heating elements such that a square heating pattern arranged adjacent to a predetermined breaking line of the leading edge portion is formed.

Preferably, the control device is further configured to energize a second group of the heating elements such that a U shaped heating pattern that has its opening facing towards a predetermined breaking line of the leading edge portion is formed.

Preferably, the control device is further configured to energize a second group of the heating elements such that a T shaped heating pattern that has its stem adjacent to a predetermined breaking line of the leading edge portion is formed.

Preferably, the control device is further configured to energize a second group of the heating elements such that a triangular heating pattern that has its base adjacent to a predetermined breaking line of the leading edge portion is formed.

Preferably the heating triangle pattern is interposed between two consecutive third groups of heating elements.

Preferably, the control device is further configured to energize a second group of the heating elements such that a V shaped heating pattern that has its tip facing away from the predetermined breaking line of the leading edge portion is formed.

Preferably the heating V shaped pattern is interposed between two consecutive third groups of heating elements.

Preferably, the control device is further configured to energize a second group of the heating elements such that a triangular heating pattern that has a tip arranged with a distance from and facing a predetermined breaking line of the leading edge portion is formed.

Preferably, the control device is further configured to energize a second group of the heating elements such that a heating pattern having a pair of heating columns that extend orthogonal to a predetermined breaking line of the leading edge portion is formed, wherein in one of the columns extends further than the other column.

Preferably, the control device is further configured to energize a second group of the heating elements such that a row heating pattern that extends parallel to a pre-determined breaking line of the leading edge portion is formed.

Preferably, the control device is further configured to energize a second group of the heating elements such that a heating pattern of a plurality of heating rows that extend parallel to a predetermined breaking line of the leading edge portion, wherein the heating rows extend between the third group of heating elements.

Preferably, the control device is further configured to cyclically energize and de-energize the second group.

Preferably, the control device is configured to cyclically energize and de-energize the heating elements.

Preferably, the control device is configured to progressively energize and de-energize the heating elements, preferably the second group, so as to transition between different heating patterns in such a manner that the heating elements are energized progressively further along the predetermined breaking line.

Preferably, one or more heating patterns, a specific heating pattern or all heating patterns are repeated along the predetermined breaking line. Preferably, the heating patterns on one side of the predetermined breaking line are offset along the predetermined breaking line relative to the heating patterns on the other side of the predetermined breaking line.

Preferably, the de-icing system further comprises a superhydrophobic coating that is applicable to the leading edge portion, wherein the superhydrophobic coating comprises a silicone nanofilament network.

The invention provides an airfoil for an aircraft comprising a leading edge portion and a preferred de-icing system, wherein the heating foil is arranged at, preferably adhesively bonded to, an inner side of the leading edge portion, wherein the ice detecting device is arranged so as to allow for detection of ice on an outer side of the leading edge portion.

Preferably, the leading edge portion includes a plurality of microperforations configured for preserving laminarity of an aerodynamic boundary layer adjacent to the airfoil, wherein a superhydrophobic coating that has a silicone nanofilament network is arranged on an outer surface of the leading edge portion and/or a side wall portion of the microperforations.

Preferably, the airfoil is configured as a horizontal tail plane, a vertical tail plane, a high-lift device or a rotor blade.

The invention provides an airfoil for an aircraft comprising a leading edge portion that includes a plurality of microperforations configured for preserving laminarity of an aerodynamic boundary layer adjacent to the airfoil, wherein a superhydrophobic coating that has a silicone nanofilament network is arranged on an outer surface of the leading edge portion and/or a side wall portion of the microperforations.

Preferably, the airfoil includes a preferred de-icing system, wherein the heating foil is arranged at, preferably adhesively bonded to, an inner side of the leading edge portion, wherein the ice detecting device is arranged so as to allow for detection of ice on an outer side of the leading edge portion.

Preferably, the airfoil is configured as a horizontal tail plane, a vertical tail plane, a wing or a high-lift device.

The invention provides an aircraft comprising a preferred de-icing system and/or a preferred airfoil.

The invention provides a de-icing method for de-icing a leading edge portion of an airfoil of an aircraft using a heating foil attached to the leading edge portion, the heat foil having a plurality of heating elements, the method comprising the steps of:.

Subsequently advantageous effects of the invention are described in more detail. It should be noted that not all advantages need to be present at the same time or the same intensity.

Standard heating systems (e.g. bleed air or metallic heating wires) enable anti-icing operations on e.g. the wing. Hereby, the surface (e.g. wing) is continually heated. On the other hand, heating foils can exhibit a higher power density and a quicker response which enables operation in de-icing mode. In de-icing mode, ice may grow until a critical thickness is reached. Then, the heating foils are turned on and due to thermal shock, cracks are generated in the ice layer and the ice is shed off. Turning the heating foil on and off can be done automatically by using ice detection sensors and thermocouples preferably implemented into the heating foil.

Since the heating foils are not continually turned on, energy is saved with this operation method. De-icing mode also prevents run back ice contrary to the anti-icing mode. In anti-icing, the constant heating forms liquid water which may freeze again behind the heated surface. The use of a commercially available (printed) heating foil (foil + heatable ink + foil) with a high power density (e.g. > <NUM> W/cm<NUM>) allows for deicing.

Another idea is that the thin film heaters are based on graphite, carbon nanotubes (CNT) or graphene and related materials (GRM), which can be much lighter and more energy efficient than conventional metallic heaters. Preferably, the heaters are cyclically heated.

This technology can also be used for microperforated surfaces used for hybrid laminar flow control (HLFC) systems. The heating foil is preferably attached to the backside of the micro-perforated skin (pore diameter of approx. <NUM>) with a corresponding perforation. Another preferred use case is the implementation of a heating system on top of drones' rotor blades e.g. with a battery as a power supply attached to the middle section of the rotor blade holder.

Furthermore, if contaminants resulting from the impact of insects, engine exhaust aerosols, and ice blocked the microperforated holes, the functionality of the HLFC system could be impaired. The ideas described herein also prevent at least the icing over of the pores thereby maintaining the functionality.

Another improvement over manual de-contamination on-ground is surface functionalization, which prevents contaminants from sticking to the surface, thereby allowing aerodynamic forces to remove contaminants during flight. Usually some type of fluorination would sufficiently reduce the strength of adhesion that contaminants have to a surface.

However, for high impact velocities of contaminants during flight there is further improvement in preventing contaminants from entering and clogging the microperforations. A superhydrophobic coating, which is preferably arranged not only on the outer surface but also within the microperforations, allows both for air to pass through the microperforations and from contaminants, in particular ice, from getting stuck over and inside of the microperforations.

Embodiments of the invention are described in more detail with reference to the accompanying drawings.

Referring to <FIG>, an embodiment of an aircraft <NUM> is depicted. The aircraft <NUM> includes a fuselage <NUM>. A pair of wings <NUM> are attached to the fuselage <NUM>, in a manner known per se. The wing <NUM> may include one or more high-lift devices <NUM>.

The aircraft <NUM> further comprises a horizontal tail plane <NUM> and a vertical tail plane <NUM>.

The wing <NUM>, the high-lift devices <NUM>, and the horizontal and vertical tail plane <NUM>, <NUM> are examples of an airfoil <NUM>.

The airfoil <NUM> may comprise a separate leading edge member or an integrated leading edge member, collectively described herein as a leading edge portion <NUM>.

Referring to <FIG> and <FIG>, the aircraft <NUM> includes a de-icing system <NUM>. The de-icing system <NUM> comprises a heating foil <NUM>. The heating foil <NUM> is arranged on an inward facing side of the leading edge portion <NUM>.

The de-icing system <NUM> further comprises an ice detecting device <NUM> that is preferably integrated into the heating foil <NUM>. The ice detecting device <NUM> includes a thermocouple <NUM> that is arranged on the inward facing side of the leading edge portion <NUM>. The ice detecting device <NUM> may alternatively or additionally include an optical sensor with or without optical fibers, an acoustic sensor for detecting surface acoustic waves, and/or a pressure sensor.

The de-icing system <NUM> further comprises a control device <NUM>. The control device <NUM> is connected to the heating foil <NUM> and the ice detecting device <NUM> in order to control a de-icing process.

Referring to <FIG>, the heating foil <NUM> includes a plurality of heating elements <NUM>. The heating elements <NUM> are preferably of a carbon-based material, such as graphite, graphene and related materials (GRM) or carbon nanotubes (CNT). The heating elements <NUM> are configured as a thin film and preferably sandwiched in between electrically isolating thin foils. The heating foil <NUM> is configured such that individual heating elements <NUM> may be energized by the control device <NUM> depending on the detection of ice by the ice detecting device <NUM>.

As depicted in <FIG>, the heating elements <NUM> may be configured as heating stripes <NUM> that are arranged substantially in parallel to the leading edge portion <NUM>.

As depicted in <FIG>, in another embodiment, the heating elements <NUM> may be configured as heating rectangles <NUM>. The heating elements <NUM> are arranged in a plurality of heating rows <NUM> and heating columns <NUM>.

Referring now to <FIG>, embodiments of a de-icing cycle are described in more detail.

As depicted in <FIG>, initially a first group <NUM> of the heating elements <NUM> is energized. The first group <NUM> forms a first linear heating pattern <NUM>. The first linear heating pattern <NUM> is parallel to the leading edge portion <NUM>. The first linear heating pattern <NUM> generates a pre-determined breaking line for ice that has accumulated on the airfoil <NUM>.

Subsequently, the control device <NUM> energizes a second group <NUM> of the heating elements <NUM>. The second group <NUM> is configured as a square heating pattern <NUM>. The square heating pattern <NUM> is arranged adjacent to the first group <NUM>. The square heating pattern <NUM> is repeated multiple times along the extension of the first group <NUM>. Furthermore, the square heating patterns <NUM> above the first linear heating pattern <NUM> are offset along the direction of the leading edge portion <NUM> relative to the square heating patterns <NUM> below the first linear heating pattern <NUM>.

The control device <NUM> further energizes heating elements such that the energized heating elements are progressively further away from the first group <NUM>.

As depicted in <FIG>, subsequent to the square heating pattern <NUM>, the second group <NUM> is energized such that a U shaped heating pattern <NUM> is generated. The opening of the U is facing the first group <NUM>. Furthermore, leg portions <NUM> of the U shaped heating pattern <NUM> are arranged adjacent to the first group <NUM>.

Similarly, to the square heating patterns <NUM>, the U shaped heating patterns <NUM> are offset along the extension of the first linear heating pattern <NUM> and depending on whether the U shaped heating pattern <NUM> is above or below the first linear heating pattern <NUM>. Preferably, the U shaped heating patterns <NUM> are arranged such that a meandering heating pattern <NUM> is generated.

Further in this embodiment, the second group <NUM> is energized by the control device <NUM> such that a T shaped heating pattern <NUM> is generated. A stem portion <NUM> of the T shaped heating pattern <NUM> is arranged adjacent to the first linear heating pattern <NUM>. The stem portion <NUM> extends orthogonally relative to the first linear heating pattern <NUM>.

Again, a plurality of T shaped heating patterns <NUM> is offset along the first linear heating pattern <NUM>. The T shaped heating pattern <NUM> are arranged such that each stem portion <NUM> is adjacent to the first linear heating pattern <NUM> and a crossbar portion <NUM> connects the respective stem portions <NUM> on one side of the first linear heating pattern <NUM>. In other words, all heating elements <NUM> with the exception of a rectangular de-energized portion <NUM> are energized.

Finally, in this embodiment, the second group <NUM> is de-energized, while the first group <NUM> is kept energized.

Referring to <FIG>, another embodiment of a de-icing cycle is described in more detail. Regarding the first group <NUM>, the de-icing cycle is identical to the previously described de-icing cycle.

Different from the previous de-icing cycle, the second group <NUM> is configured as a pair of heating columns <NUM>. The heating columns <NUM> extend orthogonal to the first group <NUM>. One of the heating columns <NUM> is shorter than the other one of the heating columns <NUM>. As depicted from top to bottom in <FIG>, the heating columns <NUM> are energized and de-energized such that the heating columns <NUM> seem to progress along the direction of the leading edge portion <NUM> from left to right. It should be noted that a progression in the opposite direction is also possible.

Referring to <FIG>, the first group <NUM> is energized in the same way as in the previously described embodiments. The second group <NUM> is energized by the control device <NUM> such that a triangular heating pattern <NUM> is generated. The triangular heating pattern <NUM> is preferably configured as an isosceles triangle. The triangular heating pattern <NUM> is arranged such that a base portion <NUM> is arranged adjacent to the first group <NUM>, whereas a tip portion <NUM> is facing away from the first group <NUM>. The triangular heating pattern <NUM> are again offset along the direction of the first linear heating pattern <NUM> and preferably have a different offset depending on whether the triangular heating pattern <NUM> is above or below the first linear heating pattern <NUM>. As depicted in <FIG>, the triangular heating pattern <NUM> are preferably arranged such that a meandering heating pattern <NUM> is created.

Further in this embodiment, the control device <NUM> energizes the second group <NUM> such that a V shaped heating pattern <NUM> is created. Similarly to the U shaped heating pattern <NUM>, leg portions <NUM> of the V shaped heating pattern <NUM> are arranged adjacent to the first linear heating pattern <NUM>. Furthermore, a tip portion <NUM> of the V shaped heating pattern <NUM> is facing away from the first linear heating pattern <NUM>.

As depicted in <FIG>, the previously energized triangular heating pattern <NUM> and meandering heating pattern <NUM>, respectively, are de-energized in this state.

As further depicted in <FIG>, the second group <NUM> is again energized in a triangular heating pattern <NUM>, however, the base portion <NUM> and the tip portion <NUM> are flipped.

In other words, the control device <NUM> energized the heating elements <NUM> such that the heating elements <NUM> are progressively energized further away from the first linear heating pattern <NUM>, whereby none of the heating elements <NUM> is energized twice during progression of the de-icing cycle.

Referring to <FIG>, another embodiment of a de-icing cycle is depicted, which is a variant of the de-icing cycle according to <FIG>. In addition to the first group <NUM> and the second group <NUM>, which exhibits the same progression as in the previously described embodiment, a third group <NUM> of heating elements is energized. The third group <NUM> creates a second linear heating pattern <NUM> that extends orthogonally from the first linear heating pattern <NUM>. The first group <NUM> and third group <NUM> are permanently energized.

Furthermore, as depicted in <FIG>, the second group <NUM> is energized such that the respective patterns are formed between two neighboring second linear heating patterns <NUM>.

In case of the triangular heating pattern <NUM>, the third group <NUM> is arranged such that it forms a symmetry line of the triangular heating pattern <NUM>.

Referring to <FIG>, the heating foil <NUM> is configured as having the heating stripe <NUM>. As depicted in <FIG>, the first group <NUM> again forms a first linear heating pattern <NUM> that extends substantially in parallel to the leading edge portion <NUM>.

As further depicted in <FIG>, the second group <NUM> is energized so as to form a row heating pattern <NUM> that extends parallel to the first linear heating pattern <NUM>.

The control device <NUM> is configured such that the heating stripes <NUM> are energized progressively away from the first linear heating pattern <NUM>. In other words, the patterns are created such that the heat seems to move away from the first linear heating pattern <NUM>.

Referring now to <FIG>, another embodiment of a de-icing cycle, which is a variant of the de-icing cycle of <FIG>, is described. In this embodiment, the heating foil <NUM> in addition to the heating stripes <NUM> further comprises of orthogonal heating stripes <NUM> that orthogonally extend from the first group <NUM>. The orthogonal heating stripes <NUM> form the third group <NUM> in this embodiment.

The second group <NUM> is energized by the control device <NUM> such that the heating stripes <NUM> are energized progressively moving outward from the first group <NUM>, where in the second group <NUM> is arranged between two neighboring orthogonal heating stripes <NUM>.

It should be noted that different de-icing cycles may be repeatedly executed in order to break off ice that has accumulated on the leading edge portion <NUM>.

Referring to <FIG>, the leading edge portion <NUM> is described in further detail. The leading edge portion <NUM> includes microperforations <NUM>. The microperforations <NUM> are part of a hybrid laminar flow control (HLFC) system. Thus, the microperforations <NUM>, which usually have a diameter of around <NUM> micrometers should be kept clean of contaminants <NUM>.

The leading edge portion <NUM> includes a superhydrophobic coating <NUM>. In this embodiment, the superhydrophobic coating <NUM> is only arranged on the skin of the leading edge portion <NUM>.

Referring to <FIG>, a cross section through the leading edge portion <NUM> is depicted. In this embodiment, the superhydrophobic coating <NUM> is not only arranged on the skin of the leading edge portion but also on a sidewall <NUM> of the microperforations <NUM>. It should be noted that in this embodiment, a flow channel <NUM> is kept free of the superhydrophobic coating <NUM>.

Referring to <FIG>, a further embodiment of the leading edge portion <NUM> that is similar to the embodiment depicted in <FIG> is depicted. In this embodiment, the superhydrophobic coating <NUM> is arranged on the skin <NUM>, the sidewall <NUM>, and within the entire volume of the microperforation <NUM>. The superhydrophobic coating <NUM> is sufficiently porous so as to not impede the function of the microperforations <NUM> in the HLFC system (see microscopic image depicted in <FIG>).

Silicone nanofilament (SNF) networks <NUM> grown on surfaces have been shown to have water-repelling properties. When the SNF networks <NUM> are fluorinated, they also show oil-repelling properties.

By growing a network of fluorinated SNFs <NUM> on the surface of a microperforated airfoil <NUM>, such as a VTP, the outer airfoil surface will gain these oil-and water-repelling properties.

Referring to <FIG>, the results of experiments are depicted, which show the effects of the superhydrophobic coating <NUM>. The superhydrophobic coating <NUM>, as used herein, includes a silicone nanofilament network <NUM>, which has in and of itself water-repelling properties. The superhydrophobic coating <NUM> may also be configured as a superoleophobic coating, if the silicone nanofilament networks are fluorinated and thus additionally exhibit oil-repelling properties.

<FIG> shows the interfacial adhesion strength of four different types of impact ice (ice formed by impacting supercooled water droplets in-flight) on three different surfaces. The first surface is the native oxide layer on a metal alloy whose primary component is titanium (Ti6Al4V).

The second surface is that described in <CIT>, specifically, the same alloy anodized such that the oxide layer grew in the shape of nanotubes, and which was subsequently fluorinated using a commercial perfluoropolyether solution.

The last surface is the same as the second, except instead of fluorinating it using the commercial solution, SNFs <NUM> were grown on the nanotubes and subsequently fluorinated using the method described below.

The results show that for rime and mixed/glaze conditions, the fluorinated SNFs surface is at par with the commercially fluorinated surface. For mixed/rime, and glaze, however, the fluorinated SNFs <NUM> showed lower adhesion strength to ice, thus proving improved performance.

For every icing condition, the fluorinated SNFs <NUM> and the commercially fluorinated nanotubes showed lower ice adhesion strength than the "bare" native oxide surface. The experiments show that fluorinated SNF networks <NUM> in general also exhibit ice-phobic properties and are durable enough to endure several icing/de-icing cycles.

By growing a network of fluorinated SNFs <NUM> inside of the perforations of the microperforated VTP, oil and water are repelled by the perforation walls, and will therefore not remain stuck inside the perforations.

In one embodiment, the silicone nanofilaments cover the surface of the micropores but do not bridge the diameter (<FIG>). Due to the small pore size and the am-phiphobicity of the fluorinated silicone nanofilament network, droplets of water and oil greater than the micropore diameter are completely repelled, while smaller droplets are hindered in their passage through the microperforations.

In addition, the sidewalls <NUM> are coated, so the effective diameter accessible to a droplet is slightly decreased; from a probabilistic point of view, the coating on the rims and on the "entrance" of the walls reduces the number of configurations (in terms of impact point and trajectory) that can result in a droplet going through the hole.

Furthermore, by growing a network of fluorinated SNFs inside of the perforations of the microperforated airfoil <NUM>, such that the network covers the entire diameter of the microperforations <NUM>, no foreign matter composed of oil or water could enter the pores. Since the SNF network is itself porous, it does not prevent air from passing through the microperforations <NUM>.

In another embodiment, the silicone nanofilament network <NUM> bridges the entire diameter of the micropores (<FIG>). Due to the porous nature of the nanofilament network, gases such as air can easily pass through the pores, thus retaining the intended functionality of the permeable drag reduction device. The network of SNFs effectively blocks any contaminants of passing through the pores of the micro-perforated plate; liquid contaminants simply bounce off.

The method consists of growing superhydrophobic Silicone Nanofilaments (SNFs) on the surface of the microperforated airfoil <NUM> through a gas phase silanization process known in the art.

SNFs cover the micro-perforation walls and fill them in the radial direction, creating a porous structure with spacings one or two orders of magnitude lower than the micro-perforation diameter. A subsequent fluorination makes the SNFs oleophobic or superoleophobic and therefore reduces the adhesion that both liquid and particulate contaminants have to the surface. Moreover, the combined silanization and fluorination treatments reduce the adhesion of ice to the surface.

Typical airfoils, such as the VTP comprise a metal alloy containing primarily Ti, and possibly containing additional elements such as V, Fe, Sn, Ni, Nb, Mo, Zr, Y, Hf, Ta, Ce, Tb , Nd, Gd, Dy, Ho and Er and/or additionally at least one further element selected from the group comprising Zn, Mn, Ag, Li, Cu, Si, Al or Ca.

The metallic plate is anodized in order to produce a nanoporous layer comprising nanotubes including titanium dioxide using a process described in <CIT>. The resulting nanotubes have diameters in the range of <NUM> to <NUM>.

Prior to silanization, microperforated airfoils are pre-treated with an alkaline solution which may contain surface active compounds. One example of such treatment is sonication for <NUM> minutes in a <NUM>%v/v aqueous solution of Deconex <NUM> universal (by Borer Chemie AG), after which samples are rinsed with deionized water and dried with N<NUM> gas flow.

In our instance, the process employs a silanizing mixture comprised of at least one component of formula I and at least one component of formula II:.

With this method, the micro-perforations walls are completely covered with a layer of SNFs with diameter in the range <NUM> - <NUM>. The so-obtained porous coating has a thickness in the order of micrometre to tens of micrometres, which can partly or completely fill the micro-perforations in the radial direction.

This gas phase process is particularly suited to coat surfaces with complex shapes at the sub-millimetre range, such as the airfoil microperforations <NUM>, when compared to conventional liquid- or spray-based processes. Moreover, scale-up of this process to coat large (<NUM><NUM>) substrates has been demonstrated (<NPL>).

Fluorination can be carried out either as a solvent phase or vapour phase process, as described in the art (<NPL>; <NPL>).

Prior to chemical modification, SNFs are activated by exposition to O<NUM> plasma. The material is then exposed to at least one fluorinating agent of formula III:.

where Rc is a perfluorinated or polyfluorinated alkyl chain C(<NUM>-<NUM>), X<NUM> is a hydrolysable group, such a as a halogen or alkoxy group.

This process introduces fluorine-containing groups that are covalently linked to the surface. As such, it is superior in quality and stability to conventional treatments with perfluoropolyether (PFPE) compounds that are instead only bound to the surface through weak interactions.

Regarding further information regarding the silicone nanofilament networks, reference is made to the manuscript "<NPL> et al.

Referring now to <FIG>, an embodiment of a de-icing method is described in more detail.

The de-icing method includes a sensing step S10. In the sensing step S10 the ice detecting device <NUM> detects, whether there is ice formation on the airfoil <NUM>.

The de-icing method further includes a measuring step S12. The measuring step S12 is executed after the sensing step S10. In the measuring step S12, the control device <NUM> based on the data of the detecting device <NUM> determines the intensity of ice formation, e.g. as thickness increase per time unit in arbitrary units.

The de-icing method further includes a comparing step S14. The comparing step S14 is executed after the measuring step S12. In the comparing step S14 the intensity of ice formation that was determined in the measuring step S12 is compared with a predetermined threshold of an acceptable ice formation intensity.

If the measured intensity is below the threshold, the de-icing method is continued in the measuring step S12.

If the measured intensity exceeds the threshold, the de-icing method is continued in a de-icing step S16. In the de-icing step S16, the heating foil <NUM> is energized by the control device <NUM> such that any of the previously described heating patterns is generated or any of the previously described de-icing cycles is performed.

After the de-icing step S16 is performed, the method skips to the measuring step S12.

Claim 1:
A de-icing system (<NUM>) configured for preventing the formation of and/or removing ice on a leading edge portion (<NUM>) of an airfoil (<NUM>) of an aircraft (<NUM>) , the de-icing system (<NUM>) comprising a heating foil (<NUM>) that is adhesively bondable to the leading edge portion (<NUM>) and that has a plurality of heating elements (<NUM>) that are configured to be selectively energized for heating, an ice detecting device (<NUM>) configured for detecting the presence of ice on the leading edge portion (<NUM>), and a control device (<NUM>) configured for periodically and selectively energizing the heating elements (<NUM>) based on the ice presence measured by the ice detecting device (<NUM>), wherein the control device (<NUM>) is further configured to energize a first group (<NUM>) of the heating elements (<NUM>) such that a first linear heating pattern (<NUM>) parallel to the leading edge portion (<NUM>) is formed, in order to create a predetermined breaking line, wherein the control device (<NUM>) is further configured to energize a third group (<NUM>) of the heating elements (<NUM>) such that a plurality of second linear heating patterns (<NUM>) that are parallel to each other and orthogonal to the first heating line are formed, characterized in that the control device (<NUM>) is configured to progressively energize and de-energize the heating elements (<NUM>) so as to transition between different heating patterns in such a manner that the heating elements (<NUM>) are energized progressively further away from the predetermined breaking line.