Method of fabricating an aircraft aerodynamic structure

Abstract

Disclosed is a method of fabricating an aircraft aerodynamic structure 200 for an aircraft, the method comprising moulding the aircraft aerodynamic structure (118, figure 2a) such that the aircraft ae

Description

TECHNICAL FIELD

[0001] The present invention relates to an aircraft aerodynamic structure, comprising a surface configured to mitigate adhesion of insects, and a method of fabricating the aircraft aerodynamic structure. BACKGROUND

[0002] Aircraft are subject to insect encounters in flight. The insect encounters often result in insect carcases becoming adhered onto aerodynamic surfaces of the aircraft. The adhered insect carcasses negatively affect the aerodynamic properties of the aerodynamic surfaces of the aircraft, resulting in reduction of lift generated and increase in undesirable air flow disruption. Therefore, it is desirable to reduce the occurrence of insect carcases becoming adhered to aerodynamic surfaces of aircraft. SUMMARY

[0003] A first aspect of the present invention provides a method of fabricating an aircraft aerodynamic structure for an aircraft, the method comprising moulding the aircraft aerodynamic structure such that the aircraft aerodynamic structure comprises an aerodynamic surface, the aerodynamic surface comprising a topography configured so that the aerodynamic surface has a water contact angle of at least 80 degrees and a surface roughness of 0.2 microns to 50 microns, whereby the topography is configured to mitigate adhesion of insects to the aerodynamic surface when the aircraft aerodynamic structure is incorporated into the aircraft and encounters the insects during flight of the aircraft.

[0004] When the aircraft is in flight, it will intercept various flying insects which would, without the present invention, result in insect carcasses becoming adhered to an aerodynamic surface of the aircraft. Such insect adhesion is known to cause performance reduction in aircraft, in particular impacting the lift that can be generated at aircraft wings. It is impractical to clean aircraft wings before each flight. It is therefore desirable to prevent or reduce such insect adhesion.

[0005] The method according to the first aspect enables an aircraft aerodynamic structure to be made which reduces or eliminates the adhesion of insects on impact. To reduce adhesion means to either reduce the likelihood of adhesion at each instance of insect impact onto the aircraft aerodynamic surface, or to reduce the strength with which the insect is adhered to the aircraft aerodynamic surface in an instance of adhesion, or both. This is achieved by moulding the aircraft aerodynamic structure such that it comprises an aerodynamic surface having the topography described above. Moulding is a technique that is relatively inexpensive, and applicable to many materials. Moulding is a process that comprises replicating a pattern from a mould. The pattern of the mould is a negative of the topography.

[0006] Optionally, the aerodynamic surface has a surface energy of less than 50 mJ / m2. Further optionally, the surface energy is less than 40 mJ / m2.

[0007] Optionally, the moulding the aircraft aerodynamic structure comprises moulding the aircraft aerodynamic structure of an elastomeric material. Elastomeric materials are suitable for moulding of the topography. This is because aircraft aerodynamic structures of elastomeric material already may be produced by moulding, and therefore producing the surface topography thereon does not require additional manufacturing steps. This improves performance, at no or low additional cost, resulting in greater efficiency.

[0008] Optionally, the topography comprises a regularly repeating pattern. A regularly repeating pattern is relatively easy to produce. In particular, it is relatively simple to produce a mould with a regularly repeating pattern as opposed to a random or irregular pattern. Therefore, the topography comprising a regularly repeating pattern is also simple to produce.

[0009] Optionally, the topography comprises channels formed by a repeating pattern of peaks and troughs, such that the channels will be aligned with a flow of air over the aircraft aerodynamic surface structure, in use. Such channels aligned with the flow of air may provide superior aerodynamic properties to the aerodynamic surface structure in comparison to other possible topography patterns, as the flow of air is relatively less disturbed, and occurrences of turbulence are minimised. This has positive effects on the performance of the aircraft aerodynamic structure and of the aircraft.

[0010] Optionally, the topography comprises a plurality of patterns selectively applied to the aircraft aerodynamic structure based on an intended location of the aircraft aerodynamic surface structure on the aircraft. Selectively applying particular patterns at plural respective locations of the aircraft aerodynamic structure, tailors the properties of the aircraft aerodynamic structure in use to each of the plurality of locations on the aircraft. This balances the insect adhesion mitigation with the aerodynamic performance of each location, as required for each of the plurality of locations.

[0011] Optionally, the method comprises performing a surface treatment on the aircraft aerodynamic structure. The performing the surface treatment further enhances the properties of the aircraft aerodynamic structure by, for example, applying a coating to further reduce the insect adhesion, and / or by modifying and refining the surface topography produced by moulding.

[0012] Optionally, the surface treatment is one of: a chlorinating treatment; and a coating application treatment. Further optionally, the coating comprising one or more of the following: ethylene-vinyl acetate, copoly(imide fluorinated alkyl ether), fluorinated silane, fluorinated aliphatic compounds, silicones, fluorine-containing polymers.

[0013] A second aspect of the present invention provides an aircraft aerodynamic structure, obtained by the method of the first aspect of the present invention.

[0014] A third aspect of the present invention provides a moulded aircraft aerodynamic structure for an aircraft comprising an aerodynamic surface, the aerodynamic surface comprising a topography configured so that the aerodynamic surface has a water contact angle of at least 80 degrees and a surface roughness of 0.2 microns to 50 microns, whereby the topography is configured to mitigate adhesion of insects to the aerodynamic surface when the aerodynamic surface encounters the insects during flight of the aircraft.

[0015] Optionally, the aircraft aerodynamic structure of the first aspect or second aspect is an aircraft wing. Alternatively, the aircraft aerodynamic structure may be a horizontal stabiliser, a vertical stabiliser, or an aerodynamic structure for elsewhere on an aircraft.

[0016] Optionally, the aircraft aerodynamic structure of the first aspect or second aspect is a morphable surface structure, comprising: elastomeric material forming the aerodynamic surface and having a glass transition temperature, and a controller configured to control a temperature management system that is for changing a temperature of the elastomeric material, the controller configured to control the temperature management system on the basis of a command received at the controller.

[0017] A capacity for controlling the shape of part of an aircraft is desirable to modify its characteristics for various functions. For example, different wing lengths may be more optimal for cruising than for take-off or landing. Maintaining a continuous aerodynamic surface is desirable for reducing drag during flight and thus optimising aircraft performance. The morphable surface structure provides a way of maintaining, with fewer or no steps and gaps, a continuous aerodynamic surface across aircraft parts, for example parts of an aircraft wing, which may be subjected to a shape change during aircraft operation. Being able to change a temperature of the elastomeric material allows the elastomeric material to have the required visco-elastic properties over an entire operating temperature range of an aircraft, including when the ambient temperature would otherwise cool the elastomeric material to below the glass transition temperature.

[0018] A fourth aspect of the present invention provides an aircraft comprising the aircraft aerodynamic structure of the first aspect or second aspect of the present invention.

[0019] Optionally, the aircraft aerodynamic structure is releasably attached to the rest of the aircraft.

[0020] Optional features of any one of the aspects of the present invention may be applied equally to any other one of the aspects of the present invention, where appropriate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0022] Figure 1 shows a schematic view of an aircraft;

[0023] Figures 2A and 2B show schematic partial cross sections of a wing of the aircraft of Figure 1 with a morphable aerodynamic structure comprising an aerodynamic surface, in Figure 2A with a moveable part of the wing at a first position relative to a fixed part of the wing and in Figure 2B with the moveable part of the wing at a second position relative to the fixed part of the wing;

[0024] Figure 3A and 3B show example embodiments of an aerodynamic surface each comprising an example topography.

[0025] Figure 4 shows an example embodiment of the method of fabricating an aircraft aerodynamic structure in accordance with the present invention. DETAILED DESCRIPTION

[0026] An example aircraft 100 is shown in Figure 1. The aircraft 100 comprises a fuselage 102 and a pair of wings 104 extending from the fuselage.

[0027] In this described embodiment, each of the wings 104 comprises a morphable aerodynamic structure 110. A different shape of the wings may be advantageous during take-off and / or landing of the aircraft than the optimal shape at cruising altitude. The morphable aerodynamic structures 110 of the wings 104, i.e., aerodynamic structures that are able to change shape, are provided to facilitate a shape change of the wings 104 in order to give the wings a more optimum shape for given circumstances.

[0028] The morphable aerodynamic structures 110 in this embodiment are located at, and define, surfaces of the respective wings 104. This is schematically shown in Figures 2a and 2b by way of example, in schematic partial cross-sectional views of one of the wings 104. The morphable aerodynamic structure 110 comprises a fixed portion 111 and a moveable portion 112. The moveable portion 112 is movably connected to the fixed portion 111, in this example by way of a hinge 113 but other connection mechanisms are used in other examples. Actuators (only one 114 of which is shown in Figure 2) are each pivotally connected to each of the fixed and moveable portions 111, 112 and actuatable to move the moveable portion 112 relative to the fixed portion 111 to thereby actuate a shape change of the morphable aerodynamic structure 110 and, thus, the wing 104. In this example, extension of the actuator 114 causes extension and dropping of the flap 112 (as shown in Figure 2b), and retraction of the actuator 114 causes retraction of the flap 112 (as shown in Figure 2a).

[0029] The morphable aerodynamic surface structure 110 also comprises an aerodynamic surface 118 formed by an elastomeric material 116, which has a glass transition temperature Tg. A controller 120 is provided to control a temperature management system (not shown) for changing a temperature of the elastomeric material 116, the controller 120 configured to control the temperature management system on the basis of a command received at the controller 120. The controller 120 is configured to communicate wirelessly with the temperature management system, and to wirelessly receive the command. The temperature management system comprises a heating system, which is for heating the elastomeric material 116 to facilitate a shape change of the structure 110 and for improving resistance to bird strikes, and a cooling system, which is for cooling the elastomeric material 116 to increase its hardness and therefore improve its resistance to e.g., sand erosion.

[0030] The morphable aerodynamic structure 110 is an example of an aircraft aerodynamic structure according to the present invention. Co-pending UK Patent Application No. 2303945.6 describes such a morphable aerodynamic structure and a method of operation thereof in more detail.

[0031] The aerodynamic surface 118 comprises a moulded topography configured to mitigate adhesion of insects to the wing 104 during flight. An example topography according to an embodiment of the present invention is shown in Figure 3A. That figure depicts a close-up of an area 200 of the aerodynamic surface 118, schematically and not to scale.

[0032] The area 200 comprises a ridged topography, made up of alternating peaks 210 and troughs 220. Each peak 210 is about 50 microns in height H, with respect to a lowermost point of the troughs 220. The peaks 210 are elongate and extend along a length, into the page of Figure 3 A, such that each trough 220 acts as a channel to guide airflow over the aerodynamic surface 118. Each of the channels extends in a direction along which a flow of air would pass over the wing 104 when the aircraft 100 is in flight.

[0033] The topography in Figure 3A results in reduced wetting with respect to a flat surface of the same material by effectively reducing the contact area of the aerodynamic surface with an impacting liquid. Wetting refers to a spreadability of a liquid over a surface, and is quantified by a contact angle. The contact angle is an angle a wall of a droplet of the liquid makes with a surface. A low contact angle corresponds to high spreading, and a high contact angle corresponds to low spreading of the liquid. Low wetting and high contact angle are a way of characterising a low affinity of a substance to a surface.

[0034] Another parameter to characterise a surface is a surface energy or surface free energy of that surface. The aerodynamic surface 118 has a surface energy of about 40 mJ / m2. In other embodiments of the aerodynamic surface, the surface energy may differ, but it preferably is lower than 50 mJ / m2 A surface energy of a surface can be determined, for example, from measurements of contact angles as explained above with known test liquids. From this data, a surface energy can be calculated, selecting an appropriate mathematical model for such calculation based on the material of the surface.

[0035] The topography shown in Figure 3 A is that of the area 200 of the aerodynamic surface 118. The remainder of the aerodynamic surfacel18 also comprises a topography, which in this embodiment is the same as that in the area 200.

[0036] In accordance with the present invention, a water contact angle of the aerodynamic surface 118, that is a contact angle as described above when measured with water as the liquid, is on average at least 80 degrees. The water contact angle is measured by water contact angle goniometry, for example by the First Ten Angstroms FTA 1000B contact angle goniometer.

[0037] A second example topography, in accordance with another embodiment of the invention, is shown in Figure 3B. The second example topography is in an area 250 of an aerodynamic surface according to another embodiment of the invention. The area 250 comprises a pattern of alternating high peaks 260, low peaks 265 and troughs 270. In this embodiment, the high peaks 260 and the low peaks 265 have dissimilar height, shown schematically in Figure 3B, but otherwise the topography has the same parameters to the example of Figure 3 A. In this embodiment, the high peaks 260 and low peaks 265 and the troughs 270 have variable spacing and width, in dependence on where they are located on the aerodynamic surface. In this example, the area 250 is located near a leading edge of a wing. The topography of the aerodynamic surface is different near a trailing edge of the wing.

[0038] In Figures 3 A and 3B two example surface topographies are shown, schematically depicted as comprising rounded peaks separated by troughs, forming channels along a direction of airflow. In other examples, a topography may be present that comprises a series of localised features rather than elongated channels. In other examples, a topography with sharp features may be present. The sharp features may comprise sharp peaks forming channels, or pyramidal formations, for example. In other examples, a topography with an irregular pattern may be present. The irregular pattern may comprise a random pattern with variable sizes and spacing of features. In all examples, the topography has a surface roughness of 0.2 microns to 50 microns. The surface roughness of a material is, in this case, understood as an average of the absolute values of the vertical deviation of surface features from a mean line, for a given area of the material. This may be determined, for example, by optical (such as laser microscope) or contact (such as profdometer) or other (such as atomic force microscopy) instruments capable of producing a 3D measurement of a surface.

[0039] For example, in the area 200, wherein the peaks 210 are about 50 microns in height H, the average deviation from the mean line, and therefore the surface roughness, would be about 25 microns.

[0040] The aircraft aerodynamic structure may be, in other embodiments of the present invention, a static structure, i.e„ not a morphable structure, and / or may have an aerodynamic surface that is not formed from an elastomeric material. In the present example, the aircraft aerodynamic structure is removable from the rest of the aircraft in order to be replaced, in case of deterioration is service. In other embodiments, the aircraft aerodynamic structure may be permanently fixed to the rest of the aircraft.

[0041] An example embodiment of a method of fabricating an aircraft aerodynamic structure is shown in Figure 4. The method 300 is a method of fabricating the aircraft aerodynamic structure 110 of the wing 104 of the aircraft 100. In other embodiments of the method, a different embodiment aircraft aerodynamic structure, in accordance with the present invention, may be fabricated.

[0042] The method 300 comprises moulding 302 an aerodynamic surface of an aircraft aerodynamic structure. In this example, the moulding 302 comprises moulding the aerodynamic surface 118 of the aircraft aerodynamic structure 110. The moulding 302 comprises producing a topography having a water contact angle of at least 80 degrees and a surface roughness of 0.2 microns to 50 microns, as outlined with respect to the abovedescribed examples. In this example of the method 300, the moulding 302 comprises producing the topography of area 200 shown in Figure 3 A. In this example, the moulding 302 comprises making a mould with a negative of the topography of area 200 and moulding an elastomeric material in the mould, in order that the elastomeric material, once moulded, has the topography. In other embodiments of the method, a mould may be produced with a negative of a topography of a different embodiment, such as that of the area 250 shown in Figure 3B, or another topography according to an embodiment of the present invention.

[0043] The method 300 comprises performing 304 a surface treatment on the aircraft aerodynamic structure, and more specifically on an aerodynamic surface of the aircraft aerodynamic structure. In this example, the performing 304 the surface treatment comprises performing the surface treatment on the aerodynamic surface 118 of the aircraft aerodynamic structure 110.

[0044] The performing 304 the surface treatment comprises, in this example, proving a coating of ethylene-vinyl acetate to the aerodynamic surface 118. In other embodiments of the method of fabricating an aircraft aerodynamic structure, the performing the surface treatment may comprise providing a coating of another coating material or materials and / or a chlorinating surface treatment, for example. The coating material may be selected from: ethylene-vinyl acetate, copoly(imide fluorinated alkyl ether), fluorinated silane, fluorinated aliphatic compounds, silicones, fluorine-containing polymers. Plural coating materials may be used. Indeed, plural surface treatments may be performed in some embodiments.

[0045] The performing 304 the surface treatment is optional, and so may be omitted altogether in some embodiments of the method 300.

[0046] It is to be noted that the term “or” as used herein is to be interpreted to mean “and / or”, unless expressly stated otherwise.

Claims

1. A method of fabricating an aircraft aerodynamic structure for an aircraft, the method comprising moulding the aircraft aerodynamic structure such that the aircraft aerodynamic structure comprises an aerodynamic surface, the aerodynamic surface comprising a topography configured so that the aerodynamic surface has a water contact angle of at least 80 degrees and a surface roughness of 0.2 microns to 50 microns, whereby the topography is configured to mitigate adhesion of insects to the aerodynamic surface when the aircraft aerodynamic structure is incorporated into the aircraft and encounters the insects during flight of the aircraft.

2. The method of fabricating the aircraft aerodynamic structure of claim 1, wherein the aerodynamic surface has a surface energy of less than 50 mJ / m2.

3. The method of fabricating the aircraft aerodynamic structure of claim 1 or claim 2, wherein the moulding the aircraft aerodynamic structure comprises moulding the aircraft aerodynamic structure of an elastomeric material.

4. The method of fabricating an aircraft aerodynamic structure of any one of the preceding claims, wherein the topography comprises a regularly repeating pattern.

5. The method of fabricating an aircraft aerodynamic structure of any one of the preceding claims, wherein the topography comprises channels formed by a repeating pattern of peaks and troughs, such that the channels will be aligned with a flow of air over the aircraft aerodynamic surface structure, in use.

6. The method of fabricating an aircraft aerodynamic structure of any one of the preceding claims, wherein the topography comprises a plurality of patterns selectively applied to the aircraft aerodynamic structure based on an intended location of the aircraft aerodynamic surface structure on the aircraft.

7. The method of fabricating an aircraft aerodynamic structure of any one of the preceding claims, wherein the method comprises performing a surface treatment on the aircraft aerodynamic structure.

8. The method of fabricating an aircraft aerodynamic structure of claim 7, wherein the surface treatment is one of:a chlorinating treatment; anda coating application treatment, the coating comprising one or more of the following: ethylene-vinyl acetate, copoly(imide fluorinated alkyl ether), fluorinated silane, fluorinated aliphatic compounds, silicones, fluorine-containing polymers.

9. An aircraft aerodynamic structure, obtained by the method of any one of claims 1 to 8.

10. A moulded aircraft aerodynamic structure for an aircraft comprising an aerodynamic surface, the aerodynamic surface comprising a topography configured so that the aerodynamic surface has a water contact angle of at least 80 degrees and a surface roughness of 0.2 microns to 50 microns, whereby the topography is configured to mitigate adhesion of insects to the aerodynamic surface when the aerodynamic surface encounters the insects during flight of the aircraft.

11. The aircraft aerodynamic structure of claim 9 or claim 10, wherein the aircraft aerodynamic structure is an aircraft wing.

12. The aircraft aerodynamic structure of any one of claims 9 to 11, wherein the aircraft aerodynamic structure is a morphable surface structure, comprising:an elastomeric material forming the aerodynamic surface and having a glass transition temperature, anda controller configured to control a temperature management system that is for changing a temperature of the elastomeric material, the controller configured to control the temperature management system on the basis of a command received at the controller.

13. An aircraft comprising the aircraft aerodynamic structure of any one of claims 9to 12.

14. The aircraft of claim 13, wherein the aircraft aerodynamic structure is releasablyattached to the rest of the aircraft.

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