Riblet panels and methods of assembling and applying same

Abstract

A method of assembling a riblet panel (200, 300a-d, 400a-d, 500, 600a-c, 700a-d, 800) for attaching riblets (202, 302a-d, 402a-d, 502, 602a-d, 702a-d) to a surface over which a fluid flows, the method comprising: preparing a plurality of riblet films, each riblet film comprising one or more riblets (202, 302a-d, 402a-d, 502, 602a-d, 702a-d); and attaching the plurality of riblet films to a common laminate film in a predetermined arrangement, wherein the riblet panel (200, 300a-d, 400a-d, 500, 600a-c, 700a-d, 800) is configured to adhere to the surface; and wherein the predetermined arrangement is configured such that, when the riblet panel (200, 300a-d, 400a-d, 500, 600a-c, 700a-d, 800) is adhered to the surface, the one or more riblets (202, 302a-d, 402a-d, 502, 602a-d, 702a-d) of the plurality of riblet films are configured to reduce the skin friction of the surface when the fluid flows over them.

Description

RIBLET PANELS AND METHODS OF ASSEMBLING AND APPLYING SAMECROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Australian Provisional Patent Application No 2024903951 filed on 29 November 2024, the contents of which are incorporated herein by reference in their entirety.FIELD OF THE INVENTION

[0002] The present disclosure relates to riblet panels and the use of such riblet panels for attaching riblets to a surface to alter the skin friction of the surface as a fluid flows over it.BACKGROUND OF THE INVENTION

[0003] Riblets are microstructures that can be used to alter the skin friction of a surface as a fluid flows over it. For example, to reduce the skin friction component of aerodynamic drag of an aircraft, it is known to apply riblets to the external surface of the aircraft such that the riblets are generally aligned or oriented with the airflow direction over the aircraft. As the airflow directions over different sections of an aircraft differ, the riblets need to be applied to the aircraft with different orientations in different sections so as to maximise the drag reduction benefit.

[0004] Figure 1 shows an example aircraft 10 having a fuselage 12, wings 14, a vertical stabiliser 16, and horizontal stabilisers 18. The fuselage 12, wings 14, vertical stabiliser 16, and horizontal stabilisers 18 each define an aerodynamic surface of the aircraft 10. Airflow directions over the aircraft 10 may be different at different sections of the aircraft 10. For example, the airflow direction over a front section of the fuselage 12 may be different to the airflow direction at a rearward section of the fuselage 12. Further, different sections of the aircraft 10 may include only one or more than one airflow direction. For example, the airflow direction over a front section of the fuselage 12 may only be in a single direction (e.g. horizontal), while other sections of the fuselage 12 may include airflows that have different directions (e.g. airflows that are substantially horizontal, airflows that are angled upwards towards the rear of the aircraft 10, and / or curvilinear airflows). As an example, Figure 2 shows different airflow directions 11 over a section of the fuselage 12 of the aircraft 10. As can be seen from Figure 2, there are different1006254568airflow directions over this section of the fuselage 12. These airflow directions include linear airflow directions and curvilinear airflow directions.

[0005] It will be appreciated that applying riblets at different orientations to align with different airflow directions over different sections of an aircraft may be a time consuming and tedious process, particularly if there are a significant number of different airflow directions over the aircraft. Further, if the riblets are not applied to the correct section of the aircraft and / or they are not correctly oriented when applied to the aircraft, the riblets may not align with the airflow direction over the particular section of the aircraft to which they are applied. This may reduce the drag reduction benefit or, in some cases, even increase aerodynamic drag of the aircraft, thereby reducing the aerodynamic efficiency of the aircraft. It will be appreciated that an aerodynamic surface having a significant number of different airflow directions may increase the likelihood of riblets being incorrectly oriented and / or positioned on the aircraft, which may potentially increase the aerodynamic drag of the aircraft. It will also be appreciated that an aerodynamic surface having a significant number of different airflow directions will increase the number of individual riblet sections to be oriented to flow, increasing the complexity and cost of riblet installation.

[0006] Riblets can also be applied to other surfaces over which a fluid may flow in order to reduce the drag and / or improve particular characteristics of the surface as the fluid flows over it. For example, in addition to aircraft, riblets may be applied to land based vehicles (e.g. cars, trucks, trains, etc.), water based vehicles (e.g. surface boats / ships, submarines, etc.), rotating elements (e.g. propellers, impellers, turbine / fan blades, etc.) and fluid transporting elements (e.g. pipes). It will be appreciated that one or more of the problems and deficiencies discussed above with respect to the application of riblets to the external surface of an aircraft may also arise in the context of applying riblets to such other surfaces over which a fluid may flow.SUMMARY OF THE INVENTION

[0007] According to a first aspect of the invention, there is provided a method of assembling a riblet panel for attaching riblets to a surface over which a fluid flows, the method comprising: preparing a plurality of riblet films, each riblet film comprising one or more riblets; and attaching the plurality of riblet films to a common laminate film in a predetermined arrangement, wherein the riblet panel is configured to adhere to the surface; and wherein the predetermined1006254568arrangement is configured such that, when the riblet panel is adhered to the surface, the one or more riblets of the plurality of riblet films are configured to reduce the skin friction of the surface when the fluid flows over them.

[0008] According to a second aspect of the invention, there is provided a panel to be adhered to a surface over which a fluid flows, the riblet panel comprising: an adhesive laminate film; and a plurality of riblet films attached to the adhesive laminate film in a predetermined arrangement, each riblet film comprising one or more riblets configured to reduce the skin friction of the surface when the fluid flows over them, wherein the riblet panel is configured to adhere to the surface.

[0009] According to a third aspect of the invention, there is provided a method of attaching riblets to a surface over which a fluid flows, the method comprising: identifying at least one datum on the surface; applying an initial riblet panel to the surface such that it is aligned with the at least one datum; and applying one or more subsequent riblet panels to the surface such that each subsequent riblet panel is aligned with and abuts or overlaps a portion of a riblet panel that was applied immediately prior, wherein each of the initial and subsequent riblet panels comprises: an adhesive laminate film; and at plurality of riblet films attached to the adhesive laminate film, each riblet film comprising one or more riblets configured to reduce the skin friction of the surface when the fluid flows over them, wherein the riblet panel is configured to adhere to the surface.

[0010] According to a fourth aspect of the invention, there is provided a method of attaching a riblet panel to a surface of a wing of an aircraft, wherein the riblet panel comprises one or more riblets configured to reduce the skin friction of the wing, and the riblet panel is provided in the form of a roll having an exposed end and an internal end, the method comprising: identifying at least one datum on the aircraft; aligning the exposed end of the roll with the at least one datum; rolling out the riblet panel on the surface of the wing to the internal end of the roll; and adhering the riblet panel to the surface of the wing.

[0011] Throughout the present disclosure, reference will be made to ‘a riblet sub-assembly’, ‘a riblet panel’ and a ‘riblet assembly’. It will be appreciated that each of these terms is intended to describe a particular form of the ‘riblet panel’ defined above.1006254568BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Preferred embodiments of the invention will be described, by way of examples only, with reference to the accompanying representations;

[0013] Figure 1 shows an exemplary aircraft and aerodynamic surfaces of the aircraft;

[0014] Figure 2 shows examples of different airflow directions over a section of the fuselage of the aircraft of Figure 1;

[0015] Figure 3 shows a method of producing riblet sub-assemblies for an aerodynamic surface of an aircraft and applying those riblet sub-assemblies to the aerodynamic surface according to an embodiment of the present disclosure;

[0016] Figure 4 shows a fuselage of an aircraft divided into a plurality of vertical sections according to an embodiment of the present disclosure;

[0017] Figure 5 shows a fuselage of an aircraft divided into a plurality of horizontal sections according to an embodiment of the present disclosure;

[0018] Figure 6 shows an exemplary embodiment of a vertical riblet sub-assembly produced using the method of Figure 3;

[0019] Figure 7 shows another exemplary embodiment of a vertical riblet sub-assembly produced using the method of Figure 3;

[0020] Figure 8 shows a cross-sectional view of the vertical riblet sub-assembly of Figure 6 or 7 taken across a longitudinal axis of the vertical riblet film;

[0021] Figure 9 shows a plan view of the vertical riblet sub-assembly of Figure 6 or 7;

[0022] Figure 10 shows a plan view of a horizontal riblet sub-assembly according to an embodiment of the present disclosure produced using the method of Figure 3;

[0023] Figures 1 la-d show cross-sectional views of further embodiments of riblet subassemblies produced using the method of Figure 3, where the cross-sectional views are across a longitudinal axis of the riblet sub-assemblies;1006254568

[0024] Figures 12a-d show cross-sectional views of yet further embodiments of riblet subassemblies produced using the method of Figure 3, where the cross-sectional views are across a longitudinal axis of the riblet sub-assemblies;

[0025] Figures 13 shows a perspective view of a riblet panel according to another embodiment of the present disclosure produced using the method of Figure 3;

[0026] Figures 14a-c show cross-sectional views of yet further embodiments of riblet panels produced using the method of Figure 3, where the cross-sectional views are across a longitudinal axis of the riblet panels;

[0027] Figures 15a-d show cross-sectional views of yet further embodiments of riblet panels produced using the method of Figure 3, where the cross-sectional views are across a longitudinal axis of the riblet panels; and

[0028] Figure 16 shows an example of a riblet assembly to be applied to a top surface of a wing of the aircraft of Figure 1 produced using the method of Figure 3.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] At least preferred embodiments of the present disclosure are directed to riblet panels that may reduce the time taken to apply riblets to an aerodynamic surface of an aircraft and may reduce the likelihood of riblets being incorrectly oriented and / or positioned on the aerodynamic surface of the aircraft. Correctly orienting and / or positioning riblets on an aerodynamic surface may improve the drag reduction performance of the riblets compared to riblets that are incorrectly oriented and / or positioned on the aerodynamic surface.

[0030] Figure 3 illustrates a method 100 of producing and applying riblets to an aerodynamic surface of an aircraft according to an embodiment of the present disclosure. The method 100 includes mapping an aerodynamic surface of an aircraft to determine airflow directions over multiple sections of the aerodynamic surface (step 102), producing a riblet panel, which in this embodiment takes the form of a riblet sub-assembly, to be applied to one of the sections of the aerodynamic surface based on determined airflow directions over that section (step 104), and applying the riblet sub-assembly to its respective section on the aerodynamic surface (step 106).1006254568

[0031] At step 102, one or more aerodynamic surfaces of an aircraft are mapped to determine airflow directions over different sections of the one or more aerodynamic surfaces of the aircraft.

[0032] Determining airflow directions over an aerodynamic surface of an aircraft may include dividing the aerodynamic surface into a plurality of sections and determining airflow directions in each of those sections. Figure 4 shows an aircraft 40 having a fuselage 42 (i.e. an aerodynamic surface) that is divided into a plurality of vertical sections 44, where each vertical section 44 is horizontally adjacent another vertical section 44. Figure 5 shows an aircraft 50 having a fuselage 52 that is divided into a plurality of horizontally extending sections 54 that are arranged in a grid, where a longitudinal edge of each section 54 is vertically adjacent a longitudinal edge of another section 54 and a lateral edge of each section 54 is horizontally adjacent a lateral edge of another section 54.

[0033] Airflow directions are determined over each section (e.g. sections 44 or sections 54) of the aerodynamic surface (e.g. fuselage 42 or fuselage 52). Airflow directions over each section of the aerodynamic surface may be determined using computer models of the aircraft (e.g. computational fluid dynamics), wind tunnel testing, flight data obtained from actual flights of the aircraft, or combinations thereof. Figure 2 shows examples of determined airflow directions 11 over a section of a fuselage of an aircraft.

[0034] Although it has been described above that the aerodynamic surface of the aircraft is divided into a plurality of sections and that then airflow directions over each section are determined, it will be appreciated that airflow directions over the aerodynamic surface may be determined first and that then the aerodynamic surface may be divided into a plurality of sections to determine airflow directions over those sections. Further, it will be appreciated that the aerodynamic surfaces of an aircraft can be divided into sections having different shapes and / or dimensions to that illustrated in Figures 4 and 5.

[0035] At step 104, riblet sub-assemblies are produced that are to be applied to the aerodynamic surface of the aircraft. Using the airflow directions determined in step 102, each riblet sub-assembly is produced based on airflow directions over the section of the aerodynamic surface to which the riblet sub-assembly is to be applied. Accordingly, a set of riblet subassemblies will be produced for the aerodynamic surface of the aircraft, where each riblet subassembly is to be applied to a particular section of the aerodynamic surface of the aircraft. Each1006254568riblet sub-assembly is dimensioned to cover the section of the aerodynamic surface to which it is to be applied.

[0036] Each section of the aerodynamic surface(s) mapped at step 102, including the determined airflow directions over each of those sections, may be projected onto a planar section (i.e. a two-dimensional representation of the respective section of the aerodynamic surface). This may provide a two-dimensional representation for each section of the aerodynamic surface of the aircraft with the respective airflow directions over the section of the aircraft mapped to the two- dimensional representation of that section. The two-dimensional representations of the sections of the aerodynamic surface(s) of the aircraft may be used to produce the riblet sub-assemblies.

[0037] Figure 6 shows a riblet panel, which in this embodiment takes the form of a riblet subassembly 200a, that is to be applied to the forward vertical section 44i of the fuselage 42 of the aircraft 40. For aircraft 40, it may be determined at step 102 that there is only a substantially single airflow direction over the forward vertical section 44 This single airflow direction is generally indicated by the arrows 60.

[0038] The riblet sub-assembly 200a has riblets 202a that correspond to the single airflow direction 60. In particular, when the riblet sub-assembly 200a is oriented with its longitudinal edges extending vertically, the riblets 202a extend horizontally over the riblet sub-assembly 200a. The riblets 202a are oriented on the riblet sub-assembly 200a such that, when the riblet sub-assembly 200a is applied to the vertical section 44x of the aircraft 40, the riblets 202a will substantially align with the single airflow direction 60 over the vertical section 44x of the aircraft 40.

[0039] Figure 7 shows another riblet sub-assembly 200b, which in this embodiment is to be applied to a rearward vertical section 44xof the fuselage 42 of the aircraft 40. For aircraft 40, it may be determined at step 102 that there are substantially three different airflow directions over the vertical section 44x. Arrows 70, arrow 72, and arrows 74 generally indicate a first airflow direction, a second airflow direction, and a third airflow direction over the rearward vertical section 44x, respectively.

[0040] The riblet sub-assembly 200b has first riblets 202b i that correspond to the airflow direction 70, second riblets 202b2that correspond to the airflow direction 72, and third riblets 202b3that correspond to the airflow direction 74. In particular, when the riblet sub-assembly1006254568200b is oriented with its longitudinal edges extending vertically, the first riblets 202bi extend horizontally over the riblet sub-assembly 202b, the second riblets 202b2extend at an angle 03over the riblet sub-assembly 202b, and the third riblets 202b3extend at an angle 02over the riblet sub-assembly 202b. The angle 03and the angle 02are different from each other. It is clear from Figure 7 that the first riblets 202bbthe second riblets 202b2, and the third riblets 202b3extend in different directions over the riblet sub-assembly 200b.

[0041] The first riblets 202bbthe second riblets 202b2, and the third riblets 202b3are each oriented on the riblet sub-assembly 200b such that, when the riblet sub-assembly 2002b is applied to the rearward section 44xof the aircraft 40, the first riblets 202bbthe second riblets 202b2, and the third riblets 202b3will substantially align with the first airflow direction 70, the second airflow direction 72, and the third airflow direction 74, respectively.

[0042] Although the riblets 202 in Figures 6 and 7 have been illustrated as being rectilinear, it will be appreciated that the riblet sub-assemblies 200 may have one or more curvilinear riblets (not shown) that will at least substantially align with curvilinear airflow directions over the section of the aircraft to which they will be applied. For example, referring to Figure 2, one or more riblet sub-assemblies 200 may have one or more curvilinear riblets that will substantially align with the curvilinear airflow direction I la located within box 13. It will be appreciated that other riblet sub-assemblies 200 may include curvilinear riblets that will substantially align with curvilinear airflow directions over different sections of the aircraft to which they will be applied.

[0043] A riblet sub-assembly 200 may be produced for each of the other vertical sections 44 of the aircraft 40 using a similar method to that described above. In particular, each riblet subassembly 200 may have riblets 202 extending in a single direction or in two or more different directions depending on airflow directions determined at step 102 for the respective vertical section 44 of the aircraft to which the riblet sub-assembly 200 is to be applied such that, when the riblet sub-assembly 200 is applied to its respective vertical section 44 of the aircraft 40, the riblets 202 of the riblet sub-assembly 200 will substantially align with respective airflow directions over that vertical section 44 of the aircraft 40.

[0044] It will therefore be appreciated that a set of riblet sub-assemblies may be produced for the fuselage 42 of the aircraft, where each riblet sub-assembly 200 of the set of riblet subassemblies is to be applied to a particular vertical section 44 of the fuselage 42 of the aircraft 40.1006254568Each riblet sub-assembly 200 is produced with riblets 202 pre-oriented in one or more directions on the riblet sub-assembly 200 based on airflow directions over the particular section of the fuselage 42 to which the riblet sub-assembly 200 is to be applied. Accordingly, when each riblet sub-assembly 200 of the set of riblet sub-assemblies is applied to its particular section 44 of the fuselage 42, the pre-oriented riblets 202 of the riblet sub-assembly 200 will substantially align with respective airflow directions over its particular section 44 of the fuselage 42.

[0045] With regard to aircraft 50, it will be appreciated that a set of riblet sub-assemblies for the fuselage 52 of the aircraft 50 may be produced using a similar method to that described above with respect to the fuselage 42 of the aircraft 40. In particular, riblet sub-assemblies having riblets extending in one or in more than one direction over a respective riblet subassembly may be produced for each of the horizontally extending sections 54 of the fuselage 52 of the aircraft 50 in a similar manner to that described above with respect to the fuselage 42 of the aircraft 40 having vertical sections 44.

[0046] Riblet sub-assemblies 200 that are to be applied to vertical sections 44 of the aircraft 40 will be referred to below as “vertical riblet sub-assemblies 200”. Riblet sub-assemblies that are to be applied to horizontal sections 54 of the aircraft 50 will be referred to below as “horizontal riblet sub-assemblies 200”. Reference to “riblet sub-assemblies 200” below is referring to either or both of the vertical and horizontal riblet sub-assemblies 200.

[0047] Each riblet sub-assembly 200 of the set of riblet sub-assemblies may have a unique identifier (not shown). The unique identifier of each riblet sub-assembly 200 identifies to which specific section of the aerodynamic surface the riblet sub-assembly 200 is to be applied. Such identifiers may be markings (e.g. numbers, letters, symbols, alignment shapes) on any layer of the riblet sub-assembly 200, or on any protective layer (e.g. application tape) applied to the riblet sub-assembly 200 to protect the riblet sub-assembly 200 prior to being applied to an aircraft. Identifiers can be printed onto or formed in (e.g. by inscribing, etching, etc.) any layer of the riblet sub-assembly 200. The unique identifiers of each riblet sub-assembly 200 may match corresponding identifiers in engineering drawings of the riblet sub-assemblies (e.g. applied to an aircraft). In this embodiment, the unique identifiers of each riblet sub-assembly 200 may allow a person to determine where the respective riblet sub-assembly 200 is to be applied on an aircraft based on the corresponding identifier in the engineering drawings.1006254568

[0048] Although the above method has been described as producing riblet sub-assemblies to be applied to a fuselage of an aircraft, it will be appreciated that the above method may be used to produce riblet sub-assemblies for other aerodynamic surfaces of an aircraft (e.g. wings, vertical stabiliser, horizontal stabilisers, etc.). It will also be appreciated that riblet subassemblies may be produced for an aerodynamic surface of an aircraft that is divided into sections having different shapes and / or dimensions to that illustrated in Figures 4 and 5, where each riblet sub-assembly is dimensioned to cover the section of the aerodynamic surface to which it is to be applied.

[0049] Figure 8 shows an exemplary cross-sectional view of a vertical riblet sub-assembly 200 according to an embodiment of the present disclosure. The vertical riblet sub-assembly 200 has riblets 202, a riblet carrier 204 and a riblet carrier adhesive 208 that together form an adhesive riblet film 206. The riblets 202 may be the riblets of any of the vertical riblet subassemblies 200 of the set of riblet sub-assemblies described above. The vertical riblet subassembly 200 comprises further layers disposed underneath the riblet film 206, including a laminate roll carrier 210 and a laminate roll adhesive 212. The laminate roll carrier 210 and the laminate roll adhesive 212 together form an adhesive laminate film 214.

[0050] The riblet carrier adhesive 208 is disposed between, and couples together, the riblet carrier 204 and the laminate roll carrier 210. The laminate roll carrier 210 is configured to be coupled to and carry the riblet film 206. The laminate roll adhesive 212 is connected to the laminate roll carrier 210 and is configured to couple the vertical riblet sub-assembly 200 to an aerodynamic surface of an aircraft. From Figure 8, it can be seen that the vertical riblet subassembly 200 is a laminate having several layers.

[0051] Figure 9 shows a plan view of a vertical riblet sub-assembly 200 looking down on the riblets 202 of the vertical riblet sub-assembly 200. The vertical riblet sub-assembly 200 may have a riblet film connecting portion 216 arranged along its trailing edge 211 (i.e. downstream edge) and a laminate film connecting portion 220 arranged along its leading edge 213 (i.e. upstream edge).

[0052] Referring to Figure 8, the riblet film connecting portion 216 extends beyond the downstream longitudinal edge 218 of the laminate film 214 and the laminate film connecting portion 220 extends beyond the upstream longitudinal edge 222 of the riblet film 206. The riblet1006254568film connecting portion 216 of a first vertical riblet sub-assembly 200 is configured to be coupled to the laminate film connecting portion 220 of a second vertical riblet sub-assembly 200 that is be applied to the aerodynamic surface adjacent to and downstream of the first vertical riblet sub-assembly 200. The laminate film connecting portion 220 of the first vertical riblet subassembly 200 is configured to be coupled to the riblet film connecting portion 216 of a third vertical riblet sub-assembly 200 that is to be applied to the aerodynamic surface adjacent to and upstream of the first vertical riblet sub-assembly 200. In this arrangement, the riblet film connecting portions 216 of the vertical riblet sub-assemblies 200 and air flowing over the aerodynamic surface during flight will extend in a generally common direction. This may reduce the likelihood of air flowing under the riblet film connecting portion 216 of a vertical riblet subassembly 200 and lifting the riblet film connecting portion 216 from the laminate film connecting portion 220 of an adjacent downstream vertical riblet sub-assembly 200.

[0053] With respect to Figure 4, the vertical riblet sub-assembly 200 that is to be applied to the forward most vertical section 44 x may omit a laminate film connecting portion 220 and the vertical riblet sub-assembly 200 that is to be applied to the rearmost vertical section 44nmay omit a riblet film connecting portion 216.

[0054] It will be appreciated that the horizontal riblet sub-assemblies 200 may have a similar construction to that described above with respect to the vertical riblet sub-assemblies 200. However, the riblet film connecting portions 216 and the laminate film connecting portions 220 of the horizontal riblet sub-assemblies 200 may be slightly different to the riblet film connecting portions 216 and the laminate film connecting portions 220 of the vertical riblet sub-assemblies 200. Figure 10 shows a top view of an exemplary embodiment of a horizontal riblet subassembly 200 looking down on the riblets 202 of the horizontal riblet sub-assembly 200. The riblet film connecting portions 216 of the horizontal riblet sub-assemblies 200 may be arranged along one longitudinal edge and along one lateral edge of the horizontal riblet sub-assembly 200, while the laminate film connecting portion 220 of the horizontal riblet sub-assemblies 200 may be arranged along the other longitudinal edge and the other lateral edge of the horizontal riblet sub-assembly 200. Accordingly, as illustrated in Figure 10, horizontal riblet sub-assemblies 200 may be oriented with the riblet film connecting portion 216 arranged along the bottom longitudinal edge and the rear lateral edge of the horizontal riblet sub-assembly 200, while the laminate film connecting portion 220 is arranged along the top longitudinal edge and the front lateral edge of the horizontal riblet sub-assembly 200. Alternatively, horizontal riblet sub- 1006254568assemblies 200 may be oriented with the riblet film connecting portion 216 arranged along the top longitudinal edge and the front lateral edge of the horizontal riblet sub-assembly 200, while the laminate film connecting portion 220 is arranged along the bottom longitudinal edge and the rear lateral edge of the horizontal riblet sub-assembly 200.

[0055] The riblet film and laminate film connecting portions 216, 220 of the embodiments of riblet sub-assemblies 200 described above may facilitate the creation of an overlap between adjacent riblet sub-assemblies 200. Such an overlap may assist in reducing the likelihood of the riblet sub-assemblies 200 peeling away from the aerodynamic surface to which they are applied. The riblet film connecting portion 216 and the laminate film connecting portion 220 of the riblet sub-assemblies 200 are configured to connect to the laminate film connecting portion 220 and riblet film connecting portion 216 of adjacent riblet sub-assemblies 200 such that the junction between adjacent riblet sub-assemblies 200 is substantially flush. This may reduce protrusions at the junctions between adjacent sub-assemblies 200, which may trip air flowing over the junctions and increase aerodynamic drag. It will be appreciated that, in other embodiments and applications, an overlap may be achieved in alternative ways, or may be unnecessary or undesirable where an abutment or even spacing between adjacent riblet sub-assemblies is sufficient or desirable.

[0056] For example, an alternative embodiment of horizontal riblet sub-assemblies may omit the riblet film connecting portion 216 from the bottom longitudinal edge and the laminate film connecting portion 220 arranged along the top longitudinal edge. In such an embodiment, vertically adjacent horizontal riblet sub-assemblies may be applied such that the bottom longitudinal edge of one horizontal riblet sub-assembly abuts the top longitudinal edge of another horizontal riblet sub-assembly. Such an embodiment may simplify the application process and may be appropriate where the top and bottom longitudinal edges run substantially parallel to the direction of fluid flow over the surface.

[0057] The alternative embodiment horizontal riblet sub-assemblies described above may retain the riblet film connecting portion 216 arranged along the rear lateral edge and the laminate film connecting portion 220 arranged along the front lateral edge. However, in another alternative embodiment, the riblet film connecting portion 216 and / or the laminate film connecting portion 220 may be omitted from the lateral edges.1006254568

[0058] In a further alternative embodiment, the riblet sub-assemblies 200 may omit the laminate film connecting portion 220 disposed along the leading edge of the riblet sub-assembly 200 (e.g. the leading edge 213 of the vertical riblet sub-assembly 200 in Figure 9 or the left vertical edge of the horizontal riblet sub-assembly 200 in Figure 10) but may include the riblet film connecting portion 216. In this embodiment, at least a portion of the leading edge (e.g. the leading edge 213 of the vertical riblet sub-assembly 200 in Figure 9 or the left vertical edge of the horizontal riblet sub-assembly 200 in Figure 10) is configured to be coupled to the riblet film connecting portion 216 of an adjacent upstream riblet sub-assembly 200. Further, for this embodiment, the rearward most riblet sub-assemblies 200 (e.g. the riblet sub-assembly 200 to be applied to the vertical section 44nin Figure 4 and the riblet sub-assemblies 200 to be applied to the rearward most horizontal section 54 in Figure 5) may omit riblet film connecting portion 216.

[0059] In yet another alternative embodiment, the riblet sub-assemblies 200 may omit the riblet film connecting portion 216 but may include the laminate film connecting portion 220 disposed along the leading edge of the riblet sub-assembly 200 (e.g. the leading edge 213 of the vertical riblet sub-assembly 200 in Figure 9 or the left vertical edge of the horizontal riblet subassembly 200 in Figure 10). In this embodiment, at least a portion of the trailing edge (e.g. the trailing edge 211 of the vertical riblet sub-assembly 200 in Figure 9 or the right vertical edge of the horizontal riblet sub-assembly 200 in Figure 10) is configured to be coupled to the laminate film connecting portion 220 of an adjacent downstream riblet sub-assembly 200. Further, for this embodiment, the forward most riblet sub-assemblies 200 (e.g. the riblet sub-assembly 200 to be applied to the vertical section 44i in Figure 4 and the riblet sub-assemblies 200 to be applied to the forward most horizontal section 54 in Figure 5) may omit the laminate later connecting portion 220.

[0060] The riblets 202 may be drag-reducing microstructures. The drag-reducing microstructures may have heights between about 5 microns to 200 microns, widths between about 0.5 micron to 150 microns, and spacing between adjacent microstructures between about 10 microns to 200 microns.

[0061] The riblets 202 may be formed using any suitable methods known in the art. For example, the riblets 202 may be formed using direct contactless microfabrication, lithography, stamping, imprinting, nanoimprint lithography, etching, ablation, or injection moulding. As a particular example, the riblets 202 may be formed using methods described in the Applicant’s1006254568International Application No PCT / AU2020 / 050543 filed on 29 May 2020, the contents of which are incorporated by reference in their entirety.

[0062] Riblet film 206 may be formed from the riblets 202 being attached directly to the riblet carrier 204 through chemically or physically bonding. In some embodiments, this direct attachment may occur during the process of forming the riblets 202 themselves, e.g. the riblets 202 are cured directly onto the riblet carrier 204. In some embodiments, a primer may be applied on the riblet carrier 204 prior to forming the riblets 202 on the riblet carrier 204. The primer may improve adhesion between the riblets 202 and the riblet carrier 204. The riblet carrier 204 may be provided with the riblet carrier adhesive 208 applied to it prior to applying the riblets 202 to the riblet carrier 204. Alternatively, the riblet carrier adhesive 208 can be applied to the riblet carrier 204 after the riblets 202 have been applied to the riblet carrier 204. The riblet carrier adhesive 208 may have a protective layer (not shown) applied to the surface of the riblet carrier adhesive that is to be coupled to the laminate roll carrier 210. This protective layer is to prevent the riblet adhesive layer 208 adhering to other surfaces and to prevent contaminants adhering to the riblet adhesive layer 208 prior to the riblet carrier layer 204 being adhered to the laminate roll carrier 210.

[0063] The riblet film 206 may be rolled up to form a roll (not shown). All the riblets 202 of the riblet film 206 may be formed on the riblet carrier 204 with a common orientation (e.g. extending substantially parallel, substantially perpendicular or at an angle to the long dimension of the roll).

[0064] Each riblet sub-assembly 200 may be formed by cutting one or more sections from the roll of riblet film 206 and applying each cut section of riblet film 206 to the laminate roll carrier 210 of the adhesive laminate film 214. Each section of riblet film 206 cut from the roll will be referred to below as a “riblet section”. Any protective layer adhered to the riblet adhesive layer 208 of each riblet section is removed prior to each riblet section being attached to the laminate roll carrier 210. Each riblet section cut from the roll of riblet film 206 may be attached to the laminate roll carrier 210 using any suitable method known in the art. For example, each riblet section may be attached to the laminate roll carrier 210 of the adhesive laminate film 214 using chemical or physical methods of bonding, such as cold lamination, hot lamination, handapplication via squeegee, hot or cold pressing, arbor, rollers, adhesive, or plastic welding.1006254568

[0065] As an example, with regard to Figure 6, one or more riblet sections may be cut from a roll of riblet film 206 and applied to the laminate roll carrier 210 of the laminate film 214 in a particular orientation to form the riblets 202a for vertical riblet sub-assembly 200a. As another example, with regard to Figure 7:• one or more riblet sections may be cut from a roll of riblet film 206 and applied to the laminate roll carrier 210 of the laminate film 214 in a particular orientation to form the riblets 202b x for vertical riblet sub-assembly 200b, where the riblets 202b x extend horizontally;• one or more riblet sections may be cut from a roll of riblet film 206 and applied to the laminate roll carrier 210 of the laminate film 214 in a particular orientation to form the riblets 202b2for the vertical riblet sub-assembly 200b, where the riblets 202b2extend at an angle Ox; and• one or more riblet sections may be cut from a roll of riblet film 206 and applied to the laminate roll carrier 210 of the laminate film 214 in a particular orientation to form the riblets 202b3for the vertical riblet sub-assembly 200b, where the riblets 202b3extend at an angle 02.

[0066] Accordingly, a riblet sub-assembly 200 may be formed by applying one or more riblet sections cut from a roll of riblet film 206 to the laminate roll carrier 210 of an adhesive laminate film 214 in particular orientations based on airflow directions over the section of the aerodynamic surface to which that particular riblet sub-assembly 200 is to be applied.

[0067] The riblet sub-assembly 200 may be provided with a release liner (not shown) covering the exposed face of the laminate roll adhesive 212, which is then removed when the riblet sub-assembly 200 is to be applied to its respective section of the aerodynamic surface. The riblet sub-assembly 200 also may be provided with an application aid or protective tape (not shown) covering the exposed face of the riblets 202, which is then removed when the riblet subassembly 200 is to be applied to its respective section of the aerodynamic surface. The riblet subassembly 200 may further be rolled up to form a roll (not shown), to help facilitate storage, transport and application.

[0068] Each riblet sub-assembly 200 may be perforated (not shown). The perforations may reduce the likelihood of pressurised air outgassing during flight. Without perforations, any outgassing may cause the riblet sub-assemblies 200 to detach from the surface of the aircraft.1006254568Perforations may be formed through the riblet sub-assemblies 200 using laser perforation techniques, hot or cold needle perforation techniques, or any other suitable techniques known in the art that are capable of forming perforations in the riblet sub-assemblies 200. Alternatively and / or additionally, each layer of the riblet sub-assemblies 200 may be formed from gas permeable materials to address the above discussing outgassing issue. In another embodiment, one or more layers of the riblet sub-assemblies 200 may be perforated prior to assembling riblet sub-assemblies 200. In another embodiment, one or more layers of the riblet sub-assemblies 200 may be perforated and / or one or more layers of the riblet sub-assemblies 200 may be formed from gas permeable materials. The perforations and / or gas permeable materials may also allow air bubbles to escape from underneath the riblet sub-assemblies 200 when they are being applied to a surface of an aircraft (e.g. using a squeegee).

[0069] At step 106, each riblet sub-assembly 200 produced at step 104 is applied to its respective section of the aerodynamic surface. It will be appreciated that certain configurations of the riblet sub-assembly may improve the ease and / or efficiency of this application step. For example, vertical riblet sub-assemblies, such as those depicted in Figures 6 to 9, may be produced with a long, narrow, high aspect ratio that allows their short upper edge to be quickly and easily applied to the aerodynamic surface. The remainder of the riblet sub-assembly can then be progressively applied in the downwards direction whilst under the tension force applied by gravity.

[0070] As discussed above, each riblet sub-assembly 200 may have a unique identifier that identifies the specific section of the aerodynamic surface to which the riblet sub-assembly 200 is to be applied. In some embodiments, the identifier may be provided on the application aid or protective tape. The identifiers may reduce the likelihood of a riblet sub-assembly being incorrectly applied to a section of the aerodynamic surface it is not meant to be applied to.

[0071] The set of riblet sub-assemblies may be applied to the aerodynamic surface by first applying one of the riblet sub-assemblies to the aerodynamic surface. At least one datum on the aerodynamic surface may be used as a reference to correctly position and / or align the first riblet sub-assembly 200 in its respective section on the aerodynamic surface. Subsequent riblet subassemblies 200 may be applied to the aerodynamic surface by aligning at least one of their edges with an edge of a riblet sub-assembly 200 that has already been applied to the aerodynamic surface. The at least one datum may be a fixed, unfixed, or temporary datum. Examples of fixed1006254568datums include windows, doors, wing edges, existing painted lines on the aircraft (e.g. emergency cut zones), fuel hatches, aircraft liveries, any other markings on the aircraft, or any other features of the aircraft. An example of an unfixed datum includes identifiers on a riblet sub-assembly 200 (e.g. printed lines) that can be used to align that riblet sub-assembly 200 with another riblet sub-assembly 200. Examples of temporary datums include laser levels projected onto the aircraft or tape markings applied to the aircraft prior to applying the riblet subassemblies 200 to the aircraft.

[0072] In another embodiment, a datum could be measured off a fixed datum. For example, a window of an aircraft could be used as a datum and a respective riblet sub-assembly 200 may be applied offset from this datum by a certain distance and / or angle.

[0073] For aircraft 40, a set of vertical riblet sub-assemblies may be produced at step 104 that are to be applied to the fuselage 42 of the aircraft 40, where each vertical riblet sub-assembly 200 of the set of vertical riblet sub-assemblies is to be applied to a specific section 44 on the fuselage 42. As discussed above, each vertical riblet sub-assembly 200 of the set of vertical riblet sub-assembly may have an identifier that identifies the specific vertical section 44 of the fuselage 42 to which the vertical riblet sub-assemblies 200 are to be applied.

[0074] The set of vertical riblet sub-assemblies for the fuselage 42 of the aircraft 40 may be applied to the fuselage 42 by first applying the vertical riblet sub-assembly 200 for the rearmost vertical section 44nof the fuselage 42 and then sequentially applying vertical riblet subassemblies 200 for adjacent upstream vertical sections 44 until finally the vertical riblet subassembly 200 for the front most vertical section 44i is applied. The riblet adhesive layer 208 of the riblet film connecting portion 216 of each vertical riblet sub-assembly 200 is connected to the laminate film connecting portion 220 of the adjacent downstream vertical riblet sub-assembly 200. The set of vertical riblet sub-assemblies is applied to the fuselage 42 starting from the rearmost vertical section 44nand moving toward the front most vertical section 44x because this allows the riblet film connecting portion 216 of a vertical riblet sub-assembly 200 that is about to be applied to the fuselage 42 to be easily connected to the laminate film connecting portion 220 of the adjacent downstream vertical riblet sub-assembly 200 that has already been applied to the fuselage 42.1006254568

[0075] The fuselage 42 of the aircraft 40 may include a vertical datum. The first vertical riblet sub-assembly to be applied to the fuselage 42 (e.g. the vertical riblet sub-assembly for the rearmost vertical section 44n) may be applied to the fuselage 42 using the vertical datum as a reference to correctly position and / or align the first vertical riblet sub-assembly 200 in its intended section (e.g. the rearmost vertical section 44nof the fuselage 40). Applying the first vertical riblet sub-assembly 200 to its intended vertical section 44 on the fuselage 40 may include aligning one of the longitudinal edges of the first vertical riblet sub-assembly 200 to the vertical datum. Subsequent vertical riblet sub-assemblies 200 may then be applied by aligning their longitudinal edge 211 with the longitudinal edge 213 of an adjacent downstream vertical riblet sub-assembly 200 that has already been applied to the fuselage 40, such that the two longitudinal edges 211, 213 abut or overlap (depending on whether a riblet film connecting portion and / or a laminate film connecting portion is / are present). The vertical datum may be any of the datums discussed above.

[0076] The fuselage 42 of the aircraft 40 may also include a horizontal datum. Applying the first vertical riblet sub-assembly 200 to its intended vertical section 44 on the fuselage 40 may thus also include aligning one of the lateral edges of the first vertical riblet sub-assembly 200 to the horizontal datum. Alignment of subsequent vertical riblet sub-assemblies 200 in the vertical direction may then be achieved by aligning their lateral edges with the horizontal datum or the lateral edge of an adjacent downstream vertical riblet sub-assembly 200 that has already been applied to the fuselage 40. The horizontal datum may be any of the datums discussed above.

[0077] Similar to aircraft 40, for aircraft 50, a set of horizontal riblet sub-assemblies may be produced at step 104 that are to be applied to the fuselage 52 of the aircraft 50, where each horizontal riblet sub-assembly 200 of the set of horizontal riblet sub-assemblies is to be applied to a specific section 54 on the fuselage 52. As discussed above, each horizontal riblet subassembly 200 of the set of horizontal riblet sub-assemblies may have an identifier that identifies the specific section 54 of the fuselage 52 to which the horizontal riblet sub-assemblies 200 are to be applied.

[0078] The application order for the set of horizontal riblet sub-assemblies for aircraft 50 may differ depending along which edges the riblet film connecting portions 216 and the laminate film connecting portions 220 are arranged. If the riblet film connecting portion 216 is arranged around the bottom longitudinal and rear edges of the horizontal riblet sub-assemblies 200 and the1006254568laminate film connecting portions 220 are arranged around the top longitudinal and front edges of the horizontal riblet sub-assemblies 200, the horizontal riblet sub-assemblies 200 may be applied by:• applying the horizontal riblet sub-assemblies 200 in rows starting with the bottom row first and moving sequentially upwards, where each row of horizontal riblet subassemblies 200 is applied sequentially starting at the rearmost section 54 of the row and moving forward toward the front most section 54 of the row;• applying the horizontal riblet sub-assemblies 200 in columns starting with the rearmost column first and moving sequentially forward, where each column of horizontal riblet sub-assemblies 200 is applied sequentially starting at the bottommost section 54 of the column and moving upward toward the topmost section 54 of the column; or• first applying the horizontal riblet sub-assembly 200 for the bottom rear comer section 54, then applying the horizontal riblet sub-assembly 200 for the adjacent upstream section 54 or the horizontal riblet sub-assembly 200 for the adjacent higher section 54 next, where each following horizontal riblet sub-assembly 200 applied may be the horizontal riblet sub-assembly 200 for the adjacent upstream or the adjacent higher section 54.

[0079] If the riblet film connecting portion 216 is arranged around the top longitudinal and front edges of the horizontal riblet sub-assemblies 200 and the laminate film connecting portions 220 are arranged around the bottom longitudinal and rear edges of the horizontal riblet subassemblies 200, the horizontal riblet sub-assemblies 200 may be applied by:• applying the horizontal riblet sub-assemblies 200 in rows starting with the top row first and moving sequentially downwards, where each row of horizontal riblet sub-assemblies 200 is applied sequentially starting at the front most section 54 of the row and moving rearward toward the rearmost section 54 of the row;• applying the horizontal riblet sub-assemblies 200 in columns starting with the front most column first and moving sequentially rearward, where each column of horizontal riblet sub-assemblies 200 is applied sequentially starting at the topmost section 54 of the column and moving downwards toward the bottommost section 54 of the column; or• first applying the horizontal riblet sub-assembly 200 for the top front comer section 54, then applying the horizontal riblet sub-assembly 200 for the adjacent downstream section 54 or the horizontal riblet sub-assembly 200 for the adjacent lower section 54 next, where1006254568each following horizontal riblet sub-assembly 200 applied may be the horizontal riblet sub-assembly 200 for the adjacent downstream or the adjacent lower section 54.

[0080] With any of the application orders described above for the set of horizontal riblet subassemblies, the riblet adhesive layer 208 of the riblet film connecting portion 216 of each horizontal riblet sub-assembly 200 is connected to the laminate film connecting portion 220 of a horizontally adjacent horizontal riblet sub-assembly 200 and the laminate film connecting portion 220 of a vertically adjacent horizontal riblet sub-assembly 200. These application orders allow the riblet film connecting portions 216 of each horizontal riblet sub-assembly 200 to be easily connected to the laminate connecting layer portions 220 of adjacent horizontal riblet subassemblies 200 that have already been applied to the fuselage 42.

[0081] The fuselage 52 of the aircraft 50 may include a horizontal datum. The first horizontal riblet sub-assembly 200 to be applied to the fuselage 52 (e.g. the horizontal riblet sub-assembly 200 for the bottom rear corner section 54 or the riblet sub-assembly 200 for the top front comer section 44) may be applied to the fuselage 52 using the horizontal datum as a reference to correctly position and / or align the first horizontal riblet sub-assembly 200 in its intended section 54 (e.g. the bottom rear corner section 54 or the top front corner section 54). Applying the first horizontal riblet sub-assembly 200 to its intended horizontal section 54 on the fuselage 50 may include aligning one of the longitudinal edges of the first horizontal riblet sub-assembly 200 to the horizontal datum. The fuselage 52 of the aircraft 50 may also include a vertical datum. Applying the first horizontal riblet sub-assembly 200 to its intended horizontal section 54 on the fuselage 50 may thus also include aligning one of the lateral edges of the first horizontal riblet sub-assembly 200 to the vertical datum. Subsequent horizontal riblet sub-assemblies 200 may then be applied to the fuselage 50 by abutting or overlapping one of their edges with an edge of a horizontal riblet sub-assembly 200 that has already been applied to the fuselage 52, and aligning another of their edges, which is perpendicular to the abutting or overlapping edge, with either of the two datums or with a parallel edge of the horizontal riblet sub-assembly 200 that has already been applied to the fuselage 52. For fuselage 52, it will be appreciated that at least one longitudinal edge and at least one lateral edge of a horizontal riblet sub-assembly 200 will be aligned with a longitudinal edge and a lateral edge of adjacent horizontal riblet sub-assemblies 200, respectively. The horizontal and vertical datums may be any of the datums discussed above.1006254568

[0082] Each riblet sub-assembly 200 of the set of riblet sub-assemblies may be applied to its respective section on the fuselage 42 or 52 using any suitable methods known in the art. For example, each riblet sub-assembly 200 may be applied to its respective section on the fuselage 42 or 52 using a squeegee to press the laminate roll adhesive 212 of the riblet sub-assembly 200 into contact with the surface of the fuselage 42 or 52. Each riblet sub-assembly 200 may be applied to its respective section on the fuselage 42 or 52 using other tools, such as, rollers, brushes, or any other suitable tool known in the art that is capable of applying the riblet subassemblies 200 to the surface of the aircraft.

[0083] The junction between the edges of adjacent riblet sub-assemblies 200 may be sealed. The junctions / edges between adjacent riblet sub-assemblies 200 may be sealed. Such sealing may prevent / restrict the laminate adhesive layer 212 from being exposed to fluids (e.g. hydraulic fluid, oils, fuel, water, etc.) that may reduce the performance of the laminate adhesive layer 212 and / or to reduce mechanical strain the laminate adhesive layer 212 may be exposed to (e.g. rain or particle impact, shear forces encountered during flight). Accordingly, sealing the junctions / edges between adjacent riblet sub-assemblies 200 protects vulnerable edges of the riblet sub-assemblies 200, particularly the laminate adhesive layers 212, from damage and ultimately delineation. Sealing may be provided by applying a liquid material that cures in place to seal the junctions / edges between adjacent riblet sub-assemblies 200. The junctions / edges between adjacent riblet sub-assemblies 200 may be sealed by application of a top coat applied over the aircraft and the riblet sub-assemblies 200. In this example, the riblets may be covered by a protective layer (e.g. an application tape) before the top coat is applied and, after the top coat is applied, the protective layer may be removed before the top coat dries.

[0084] As described above, the riblet sub-assemblies 200 may omit the riblet film connecting portions 216 and the laminate film connecting portions 220. In this embodiment, the riblet subassemblies 200 are applied to the fuselage 42 or 52 so that the edges of adjacent riblet subassemblies 200 either abut or are displaced from one another. The edges between adjacent riblet sub-assemblies 200 may be sealed as described above.

[0085] As described above, the riblet sub-assemblies 200 may omit the riblet film connecting portion 216 but include the laminate film connecting portion 220 on a leading edge of the riblet sub-assembly 200. In this embodiment, at least a portion of the trailing edge of each riblet subassembly 200 (apart from the rearmost riblet sub-assemblies 200) overlaps the laminate film1006254568connecting portion 220 of an adjacent downstream riblet sub-assembly 200 and the horizontal edges between adjacent riblet sub-assemblies 200 either abut or are displaced from one another. The overlap portions and the horizontal edges between adjacent riblet sub-assemblies 200 may be sealed as described above.

[0086] As described above, each riblet sub-assembly 200 is produced with riblets 202 preoriented in one or more directions based on airflow directions over the particular section of the aerodynamic surface the riblet sub-assembly 200 is to be applied. Only after the riblet subassembly 200 is produced is it applied to its respective section on the aerodynamic surface. After the riblet sub-assemblies 200 are applied to their respective sections on the aerodynamic surface, the riblets 202 of each riblet sub-assembly 200 will substantially align with respective airflow directions over the particular section of the aerodynamic surface to which they are applied.

[0087] As the riblet sub-assemblies 200 having pre-oriented riblets 202 results in the riblets 202 being substantially aligned with respective airflow directions over the section of the aerodynamic section to which they are applied, this may reduce the need to separately prepare and apply individual riblet films to the aerodynamic surface that correctly align with airflow directions. For example, referring to Figure 7, the riblet sub-assembly 200b has three sets of riblets 202bi, 202b2, and 202b3that extend in different directions. Applying riblet sub-assembly 200b to its respective vertical section 44xon the fuselage 42 of the aircraft 40 results in three sets of riblets (i.e. riblets 202bb202b2, and 202b3) being simultaneously applied to the fuselage 42. It will therefore be appreciated that this reduces the need to separately apply three different sets of riblet films to the corresponding vertical section 44xof the fuselage 42. Further, increasing the number of separate sets of riblets to be applied to an aerodynamic surface may increase the likelihood of riblets being incorrectly positioned and / or aligned, which may increase the aerodynamic drag of the aerodynamic surface, thereby reducing the aerodynamic efficiency of the aerodynamic surface. It will be appreciated that the riblet sub-assemblies 200 having preoriented riblets 202 may reduce the number of components (e.g. separate sets of riblets) to be applied to an aerodynamic surface. This may reduce the likelihood of riblets 202 being incorrectly positioned and / or aligned on the aerodynamic surface.

[0088] Once the first riblet sub-assembly 200 is applied to the aerodynamic surface, each subsequent riblet sub-assembly 200 is applied by aligning one of its edges with an edge of a riblet sub-assembly 200 that has already been applied to the aerodynamic surface. Given the1006254568riblets 202 of a riblet sub-assembly 200 are pre-oriented prior to being applied to the aerodynamic surface, applying a riblet sub-assembly 200 by aligning one its edges with an edge of an already applied riblet sub-assembly 200 will result in the riblets 202 of the riblet subassembly 200 substantially aligning with respective airflow directions in the section of the aerodynamic surface. This again reduces the need to separately apply riblets at different orientations on the aerodynamic surface. It will be appreciated that separately applying riblets in different orientations on an aerodynamic surface may be a time consuming process, especially if the aerodynamic surface has a significant number of different airflow directions.

[0089] The riblet sub-assemblies 200 having pre-oriented riblets 202 may therefore simplify the process of applying riblets to an aerodynamic surface by reducing the number of components that need to be applied to the aerodynamic surface and the need to apply multiple sets of riblets at different orientations on the aerodynamic surface. Pre-orienting the riblets 202 may also allow riblet sub-assemblies 200 to be produced in configurations that facilitate a physically simpler application process, e.g. vertical riblet sub-assemblies with a long, narrow, high aspect ratio as discussed above. The riblet sub-assemblies 200 may also simplify the process of applying riblets that substantially align with airflow directions of an aerodynamic surface. This is because to align the riblets 202 with respective airflow directions requires simply aligning an edge of a riblet sub-assembly 200 with an edge of a riblet sub-assembly 200 that has already been applied to the aerodynamic surface. Reducing the number of components to be applied to an aerodynamic surface and simplifying the process of applying riblets to an aerodynamic surface may reduce the time required to apply riblets to the aerodynamic surface. This may reduce the downtime required for an aircraft when applying riblets to the aircraft.

[0090] It will be appreciated that the set of riblets produced using method 100 may be specific to an aerodynamic surface of a particular aircraft. It will be appreciated that riblet sub-assemblies may be produced for, and applied to, other aerodynamic surfaces of that aircraft using method 100. Further, riblet sub-assemblies may be produced for, and applied to, aerodynamic surfaces of different types of aircraft using method 100.

[0091] The above method 100 describes using determined airflow directions over an aircraft to produce riblet sub-assemblies 200 having pre-oriented riblets 202 that, when applied to the aircraft, will substantially align with the airflow directions over the particular section of the aircraft to which they will be applied. In some embodiments, whilst the orientation of the riblets1006254568may vary over the surface of the aircraft depending on the determined airflow directions, the design or configuration of these riblets, e.g. the shape / profile (both in cross section and long section), height and width of each riblet as well as the spacing between adjacent riblets, may remain constant. For example, a riblet configuration known to reduce skin friction within certain speed and altitude ranges may be globally applied to an aircraft with a cruising speed and altitude within these ranges.

[0092] In alternative embodiments, the riblet configuration may vary over the surface of the aircraft according to local wall shear stresses. Accordingly, it is also envisaged that the above method 100 may additionally include determining local wall shear stresses over different sections of the aircraft (e.g. at step 102). The local wall shear stresses may be determined using computer models of the aircraft (e.g. computational fluid dynamics) or any other suitable method known in the art. These determined local wall shear stresses (e.g. determined at step 102), may be then used to optimise the riblet configuration for each riblet sub-assembly 200 in order to reduce the local wall shear stresses at the section of the aircraft to which each riblet subassembly 200 is to be applied.

[0093] Accordingly, at step 104, for each riblet sub-assembly 200, the orientation of the riblets 202 may be determined from airflow directions over the section of the aircraft to which the riblet sub-assembly 200 is to be applied, and the spacings, size (height and width), and / or shape (i.e. the configuration) of the riblets 202 may be determined from the local wall shear stresses experienced at the section of the aircraft to which the riblet sub-assembly 200 is to be applied. It will be appreciated that this may result in different riblet sub-assemblies 200 having riblets 202 with different riblet configurations, and / or riblets 202 of a single riblet sub-assembly 200 having different riblet configurations.

[0094] Figures 1 la-d show cross-sectional views of riblet sub-assemblies 300a-d according to further embodiments of the present disclosure. The cross-sectional views are taken across a longitudinal axis of the riblet sub-assemblies 300a-d.

[0095] Riblet sub-assembly 300a has riblets 302a, a riblet carrier adhesive 308a, a laminate roll carrier 310a, and a laminate roll adhesive 312a. The riblets 302a are applied to the riblet carrier adhesive 308a, to form an adhesive riblet film, which is coupled to the laminate carrier layer 310a. The laminate adhesive layer 312a is connected to the laminate carrier layer 310a to1006254568form an adhesive laminate film, and is configured to couple the riblet sub-assembly 300a to an aerodynamic surface. The riblets 302a may be applied to the riblet carrier adhesive 308a using any of the methods described above with respect to applying riblets 202 to riblet carrier 204. It will be appreciated that riblet sub-assembly 300a is similar to riblet sub-assembly 200 but omits the riblet carrier 204.

[0096] Riblet sub-assembly 300b has riblets 302b, a riblet carrier 304 and a riblet carrier adhesive 308a, which together form an adhesive riblet film. The riblets 302b are applied to the riblet carrier 304b. The riblet sub-assembly also has an adhesive laminate film in the form of a laminate roll adhesive 312b, and the riblet carrier adhesive 308b couples the riblet carrier 304b to the laminate roll adhesive 312b, which is configured to couple the riblet sub-assembly 300b to an aerodynamic surface. The riblets 302b may be applied to the riblet carrier 304b using any of the methods described above with respect to applying riblets 202 to riblet carrier 204. It will be appreciated that riblet sub-assembly 300b is similar to riblet sub-assembly 200 but omits the laminate roll carrier 210.

[0097] Riblet sub-assembly 300c has riblets 302c, a riblet carrier 304c, and a double-sided laminate roll adhesive 312b. The riblets 302c are applied to the riblet carrier 304c to form an adhesive riblet film. The double-sided laminate roll adhesive 312c is an adhesive laminate film that is connected to the riblet carrier 304c and configured to couple the riblet sub-assembly 300c to an aerodynamic surface. The riblets 302c may be applied to the riblet carrier 304c using any of the methods described above with respect to applying riblets 202 to riblet carrier 204. It will be appreciated that riblet sub-assembly 300c is similar to riblet sub-assembly 300b but omits the adhesive layer 308b of the riblet sub-assembly 300b.

[0098] Riblet sub-assembly 300d has a riblet film in the form of riblets 302d and an adhesive laminate film in the form of laminate roll adhesive 312d. The riblets 302d are applied to the laminate roll adhesive 312d, which is configured to couple the riblet sub-assembly 300d to an aerodynamic surface. The riblets 302d may be applied to the laminate roll adhesive 312d using any of the methods described above with respect to applying riblets 202 to riblet carrier 204. It will be appreciated that riblet sub-assembly 300d is similar to riblet sub-assembly 300c but omits the riblet carrier 304c of the riblet sub-assembly 300c.1006254568

[0099] The riblet sub-assemblies 300a-d may be formed using any of the methods described above for forming riblet sub-assembly 200 (e.g. lamination). In embodiments where a separate riblet carrier layer is not present, e.g. riblet sub-assemblies 300a & 300d, additional tensile strength may be imparted to the riblet sub-assembly by embedding mesh, scrim or some other fibre within same layer in which the riblets are formed. The riblets 302a-d of the riblet subassemblies 300a-d may be formed and pre-oriented on the riblet sub-assembly 300a-d using any of the methods described above for forming and pre-orienting riblets 202 on riblet sub-assembly 200. Accordingly, the riblet sub-assemblies 300a-d may have riblets 302a-d pre-oriented in one or more directions on the riblet sub-assembly 300a-d based on airflow directions over the particular section of an aerodynamic surface to which the riblet sub-assembly 300a-d is to be applied. Therefore, when the riblet sub-assembly 300a-d is applied to that particular section of the aerodynamic surface, the pre-oriented riblets 302a-d of the riblet sub-assembly 300a-d will substantially align with respective airflow directions over that particular section of the aerodynamic surface.

[0100] Figure 12a-d shows a cross-sectional views of riblet sub-assemblies 400a-d according to further embodiments of the present disclosure. The cross-sectional views are taken across a longitudinal axis of the riblet sub-assemblies 400a-d.

[0101] Riblet sub-assembly 400a has riblets 402a, a riblet carrier 404a, a riblet carrier adhesive 408a, a decorative layer 416a, and a laminate roll adhesive 412a. The riblets 402a are applied to the riblet carrier 404a. The riblet carrier adhesive 408a couples the riblet carrier 404a to the decorative layer 416a. The laminate roll adhesive 412a is connected to the decorative layer 416a and is configured to couple the riblet sub-assembly 400a to an aerodynamic surface. The riblets 402a may be applied to the riblet carrier 404a using any of the methods described above with respect to applying riblets 202 to riblet carrier 204. It will be appreciated that riblet subassembly 400a is similar to riblet sub-assembly 300b but further includes the decorative layer 416a laminated between the riblet carrier adhesive 408a and the laminate roll adhesive 412a.

[0102] Riblet sub-assembly 400b has riblets 402b, a riblet carrier 404b, an riblet carrier adhesive 408b, a decorative layer 416b, a laminate roll carrier 410b, and a laminate roll adhesive 412b. The riblets 402b are applied to the riblet carrier 404b. The riblet carrier adhesive 408b couples the riblet carrier 404b to the decorative layer 416b, which is coupled or applied to the laminate roll carrier 410b. The laminate roll adhesive 412b is connected to the laminate roll1006254568carrier 410b and is configured to couple the riblet sub-assembly 400b to an aerodynamic surface. The riblets 402b may be applied to the riblet carrier 404b using any of the methods described above with respect to applying riblets 202 to riblet carrier 204. It will be appreciated that riblet sub-assembly 400b is similar to riblet sub-assembly 200 but further includes the decorative layer 416b laminated between the riblet carrier adhesive 408b and the laminate roll carrier 410b.

[0103] Riblet sub-assembly 400c has riblets 402c, a decorative layer 416c, a laminate roll carrier 410c, and a laminate roll adhesive 412c. The riblets 402c are applied to the decorative layer 416c. The decorative layer 416c is applied or connected to the laminate roll carrier 410c. The laminate roll adhesive 412c is connected to the laminate roll carrier 410c and is configured to couple the riblet sub-assembly 400c to an aerodynamic surface. The riblets 402c may be applied to the decorative layer 416c using any of the methods described above with respect to applying riblets 202 to riblet carrier 204.

[0104] Riblet sub-assembly 400d has riblets 402d, a riblet carrier 404d, a decorative layer 416d, and a laminate roll adhesive 412d. The riblets 402d are applied to the riblet carrier 404d. The decorative layer 416d is laminated between the riblet carrier 404d and the laminate roll adhesive 412d. The laminate roll adhesive 412d is configured to couple the riblet sub-assembly 400d to an aerodynamic surface. The riblets 402d may be applied to the riblet carrier 404d using any of the methods described above with respect to applying riblets 202 to riblet carrier 204. It will be appreciated that riblet sub-assembly 400d is similar to riblet sub-assembly 300c but further includes the decorative layer 416d laminated between the riblet carrier 404d and the laminate roll adhesive 412d.

[0105] The decorative layer 416a-d of each riblet sub-assembly 400a-d may include at least a portion of an image that faces in the direction of the riblets 402a-d. So that the decorative layer 416a-d is visible from the riblet side of the riblet sub-assembly 400a-d, the riblets 402a-d and each layer above the decorative layer 416a-d in the riblet sub-assembly 400a-d are transparent. As each decorative layer 416a-d may include at least a portion of an image, when several riblet sub-assemblies 400a-d are applied to an aerodynamic surface, the decorative layers 416a-d of those riblet sub-assemblies 400a-d may together form a complete image.

[0106] Alternatively, the decorative layer 416a-d of each riblet sub-assembly 400a-d may include one or more colours. In this embodiment, when several riblet sub-assemblies 200 are1006254568applied to an aerodynamic surface, the one or more colours of those riblet sub-assemblies 200 may together define at least part of the livery of the aircraft.

[0107] The decorative layer 416a-d of the riblet sub-assembly 400a-d may form part of either the riblet film or the laminate film of the riblet sub-assembly 400a-d. For example, if the decorative layer 416a-d has the same or similar dimensions as the section of the aerodynamic surface where the riblet sub-assembly 400a-d will be applied, the decorative layer 416a-d may be incorporated into the laminate film. Alternatively, one or more of the riblet films within a riblet sub-assembly 400a-d may comprise at least a portion of the decorative layer 416a-d, such that the combined riblet films define the overall decorative layer 416a-d for that riblet sub-assembly 400a-d.

[0108] The riblet sub-assemblies 400a-d may be formed using any of the methods described above for forming riblet sub-assembly 200 (e.g. lamination). The riblets 402a-d of the riblet subassemblies 400a-d may be formed and pre-oriented on the riblet sub-assembly 400a-d using any of the methods described above for forming and pre-orienting riblets 202 on riblet sub-assembly 200. Accordingly, the riblet sub-assemblies 400a-d may have riblets 402a-d pre-oriented in one or more directions on the riblet sub-assembly 400a-d based on airflow directions over the particular section of an aerodynamic surface to which the riblet sub-assembly 400a-d is to be applied. Therefore, when the riblet sub-assembly 400a-d is applied to that particular section of the aerodynamic surface, the pre-oriented riblets 402a-d of the riblet sub-assembly 400a-d will substantially align with respective airflow directions over that particular section of the aerodynamic surface.

[0109] The riblet sub-assemblies 300a-d and 400a-d may also include riblet film connecting portions and laminate film connecting portions similar to the riblet film connecting portion 216 and the laminate film connecting portion 220 described above with respect to riblet subassemblies 200.

[0110] In the above embodiments, a riblet panel is formed by a riblet sub-assembly comprising multiple riblet films applied to a common adhesive laminate film that is configured to adhere to the aerodynamic surface. In these embodiments, the riblets of the riblet panel are thus applied to the aerodynamic surface with the common adhesive laminate film interposed1006254568between the aerodynamic surface and the riblet films such that the riblets 202, 302a-d, 402a-d are exposed.

[0111] Figure 13 shows a riblet panel 500 according to another embodiment of the present disclosure. The riblet panel 500 of this embodiment comprises a plurality of riblet films (though Figure 13 only depicts a single adhesive riblet film 506) applied to an adhesive laminate film, which in this embodiment takes the form of an adhesive laminate roll carrier 510. In this embodiment, adhesive riblet film 506 comprises riblets 502, a riblet carrier 504, and a riblet carrier adhesive 508. The riblet panel 500 further comprises a release liner 518.

[0112] The riblets 502 are attached to an upper surface of the riblet carrier 504 and the riblet carrier adhesive 508 is attached to a bottom surface of the riblet carrier 504. The release liner 518 is attached to a bottom surface of the riblet carrier adhesive 508 and is configured to prevent the riblet carrier adhesive 508 adhering to other surfaces and to prevent contaminants adhering to the riblet carrier adhesive 508 before application of the riblets 502 to an aerodynamic surface. The adhesive laminate roll carrier 510 is adhered to the riblets 502 so that the riblets 502 are covered by the adhesive laminate roll carrier 510 and disposed between the adhesive laminate roll carrier 510 and the riblet carrier 504.

[0113] The riblets 502 may be the riblets of any of the riblet panels 200 of the set of riblet panels described above. The riblets 502 may be attached to the riblet carrier 504 using any of the methods described above with respect to attaching riblets 202 to riblet carrier 204.

[0114] As described above, each riblet panel 500 includes a plurality of riblet films 506. To apply the riblets 502 of each riblet film 506 of a riblet panel 500 to an aerodynamic surface, the release liner 508 is removed to expose the riblet carrier adhesive 508 of each riblet film 506 of the riblet panel 500. At this point, the plurality of riblet films 506 of the riblet panel 500 are still adhered to the adhesive laminate roll carrier 510. While the adhesive laminate roll carrier 510 is adhered to the riblets 502 of each of the riblet films 506 of the riblet panel 500, the exposed riblet carrier adhesive 508 of each riblet film 506 is adhered to the aerodynamic surface. At this point, the plurality of riblet films 506 of the riblet panel 500 have been adhered to the aerodynamic surface with the adhesive laminate roll carrier 510 still adhered to the plurality of riblet films 506 of the riblet panel 500. Subsequently, the adhesive laminate roll carrier 510 of the riblet panel 500 is removed from the riblets 502 of the plurality of riblet films 506 to expose1006254568the riblets 502 of each of the plurality of riblet films 506 of the riblet panel 500. The adhesive strength of the riblet carrier adhesive 508 to the aerodynamic surface is greater than the adhesive strength of the adhesive laminate roll carrier 510 to the riblets 502 so that the riblet film (i.e. the riblets 502, the riblet carrier 504, and the riblet carrier adhesive 508) is not removed from the aerodynamic surface when removing the adhesive laminate roll carrier 510 from the riblets 502.

[0115] Similar to that described above (e.g. at step 104), multiple riblet panels 500 may be produced for an aerodynamic surface. Each riblet panel 500 may be produced based on airflow directions (e.g. determined at step 102) over the section of the aerodynamic surface to which the riblet panel 500 is to be applied. Each riblet panel 500 is therefore produced with riblets 502 preoriented in one or more directions based on airflow directions over the particular section of the aerodynamic surface to which the riblet panel 500 is to be applied. Therefore, when each riblet panel 500 is applied to its particular section of the aerodynamic surface (e.g. fuselage 40), the pre-oriented riblets 502 of the riblet panel 500 will substantially align with respective airflow directions over its particular section of the aerodynamic surface. Accordingly, a set of the riblet panels 500 will be produced for the aerodynamic surface, where each riblet panel 500 is applied to a particular section of the aerodynamic surface.

[0116] The set of riblet panels 500 may be applied to the aerodynamic surface using a similar method to that described above with respect to the set of riblet panels 200. For example, an initial riblet panel 500 may be applied to the aerodynamic surface by aligning the initial riblet panel 500 with a datum on the aerodynamic surface. Subsequent riblet panels 500 may then be applied to the aerodynamic surface by aligning a subsequent riblet panel 500 to a riblet panel 500 that was previously applied to the aerodynamic surface.

[0117] Each riblet film 506 may be produced by cutting riblet sections of predetermined shapes from a riblet film sheet. In one embodiment, the riblet film sheet may be unrolled from a roll of adhesive riblet film comprising the riblets 502, riblet carrier 504, and riblet carrier adhesive 508. Accordingly, cutting riblet sections from the roll of riblet film forms adhesive riblet films 506 as depicted in Figure 13.

[0118] In one embodiment, each riblet film 506 cut from the riblet film sheet may be provided with its own, individual release liner 518. Such an individual release liner 518 may have formed part of the riblet film sheet, or may be applied to the riblet film 506 after it has been cut from the1006254568riblet film sheet. In an alternative embodiment, all the riblet films 506 of a riblet panel 500 may be applied to a single, common release liner 518.

[0119] Each riblet film is 506 is applied to the adhesive laminate roll carrier 510 with a desired orientation such that the plurality of riblet films is attached to the adhesive laminate roll carrier 510 in a predetermined arrangement. If each riblet film 506 is provided with its own release liner 518, each riblet film 506 may be individually applied to the adhesive laminate roll carrier 510 with the desired orientation. Alternatively, each riblet film 506 may be pre-arranged into its desired orientation and the individual, adjacent release liners 518 may be attached to each other (e.g. via tape) before the riblet films 506 are applied to the adhesive laminate roll carrier 510. This may expedite the process of applying the riblet films 506 to the adhesive laminate roll carrier 510. It also allows the release liners 518 to be removed together as a unit, rather than having to remove each release liner 518 individually. This may simplify and expedite the process of removing the release liners 518 prior to applying the riblet panel 500 to the aerodynamic surface.

[0120] If all the riblet films 506 are applied to a single, common release liner 518, each riblet film 506 is applied to the release liner 518 with the desired orientation. Subsequently, the riblet films 506 provided on the single, common release liner 518 are applied to the adhesive laminate roll carrier 510 in the predetermined arrangement to form the riblet panel 500. The riblets 502 of each riblet panel 500 will therefore be pre-oriented with the desired orientation so that, when the riblet panel 500 is applied to the respective section of the aerodynamic surface and the adhesive laminate roll carrier 510 is removed, the riblets 502 will substantially align with respective airflow directions over that particular section of the aerodynamic surface.

[0121] In an alternative embodiment, the riblet film sheet may be unrolled from a roll of nonadhesive riblet film comprising the riblets and riblet carrier, but not the riblet carrier adhesive. Accordingly, cutting riblet sections from the roll of riblets forms non-adhesive riblet films (not depicted). In this embodiment, each riblet panel may be assembled using a similar method to that described above but further including applying the riblet carrier adhesive to the riblet carriers of each non-adhesive riblet film. The riblet carrier adhesive may be first applied to a common release liner. In this case, the non-adhesive riblet films may be applied to the riblet carrier adhesive before then being applied to the laminate roll carrier, or vice versa. Alternatively, the non-adhesive riblet films may be first applied to the laminate roll carrier, the riblet carrier1006254568adhesive may be then applied to the non-adhesive riblet films and then the common release liner may be applied to the riblet carrier adhesive.

[0122] Figures 14a-c show cross-sectional views of riblet panels 600a-c according to further embodiments of the present disclosure. The cross-sectional views are taken across a longitudinal axis of the riblet panels 600a-c.

[0123] Riblet panel 600a has riblets 602a, riblet carrier 604a, riblet carrier adhesive 608a, release liner 618a, laminate roll carrier 610a, and laminate roll carrier adhesive 612a. The riblets 602a, riblet carrier 604a, and riblet carrier adhesive 608a together form a riblet film. The laminate roll carrier 610a and the laminate roll carrier adhesive 612a together form a laminate film. The riblet panel 600a is similar to the riblet panel 500 but the riblet panel 600a includes the laminate roll carrier adhesive 612a disposed between the riblets 602a and laminate roll carrier 610a. In this embodiment, unlike the riblet panel 500, the laminate roll carrier 610a may not itself be adhesive and the laminate roll carrier adhesive 612a is configured to attach the laminate roll carrier 610a to the riblets 602a.

[0124] Riblet panel 600b has riblets 602b, riblet carrier adhesive 608b, release liner 618b, laminate roll carrier 610b, and laminate roll carrier adhesive 612b. The riblets 602b and riblet carrier adhesive 608b together form a riblet film. The laminate roll carrier 610b and the laminate roll carrier adhesive 612b together form a laminate film. The riblet panel 600b is similar to the riblet panel 600a but the riblet panel 600b omits the riblet carrier 604a of the riblet panel 600a. For riblet panel 600b, the riblets 602b are attached to the riblet carrier adhesive 608b instead of a riblet carrier 604a as with riblet panel 600a.

[0125] Riblet panel 600c has riblets 602c, riblet carrier adhesive 608c, release liner 618c, and laminate roll carrier 610c. The riblets 602c and riblet carrier adhesive 608c together form a riblet film. The laminate roll carrier 610c defines a laminate film. The riblet panel 600c is similar to the riblet panel 500 but the riblet panel 600c omits the riblet carrier 504 of the riblet panel 500. For riblet panel 600c, the riblets 602c are attached to the riblet carrier adhesive 608c instead of a riblet carrier 504 as with riblet panel 500.

[0126] Similar to that described above, the release liner 618a-c is configured to be removed from the riblet carrier adhesive 608a-c to expose the riblet carrier adhesive 608a-c. The exposed riblet carrier adhesive 608a-c is configured to adhere to an aerodynamic surface to attach the1006254568riblets 602a-c to the aerodynamic surface. The laminate film of the riblet panels 600a-c is configured to be removed from the riblets 602a-c to expose the riblets 602a-c.

[0127] Figures 15a-d show cross-sectional views of riblet panels 700a-d according to further embodiments of the present disclosure. The cross-sectional views are taken across a longitudinal axis of the riblet panels 700a-d.

[0128] Riblet panel 700a has riblets 702a, riblet carrier 704a, riblet carrier adhesive 708a, decorative layer 716a, decorative layer adhesive 720a, release liner 718a, and adhesive laminate carrier roll 710a. The riblet carrier adhesive 708a is disposed between and connects the riblet carrier 704a and the decorative layer 716a. The decorative layer adhesive 720a is disposed between and connects the decorative layer 716a and release liner 718a. The riblets 702a, riblet carrier 704a, riblet carrier adhesive 708a, decorative layer 716a, and decorative layer adhesive 720a together form a riblet film. The laminate roll carrier 710a defines a laminate film. The riblet panel 700a is similar to the riblet panel 500 but the riblet panel 700a includes the decorative layer 708a and decorative layer adhesive 720a disposed between the riblet carrier adhesive 708a and release liner 718a.

[0129] Riblet panel 700b has riblets 702b, riblet carrier 704b, riblet carrier adhesive 708b, decorative layer 716b, decorative layer adhesive 720b, release liner 718b, laminate carrier roll 710b, and laminate carrier roll adhesive 712b. The riblets 702b, riblet carrier 704b, riblet carrier adhesive 708b, decorative layer 716b, and decorative layer adhesive 720b together form a riblet film. The laminate roll carrier 710b and laminate roll carrier adhesive 712b form a laminate film. The riblet panel 700b is similar to the riblet panel 700a except that the riblet panel 700b includes the laminate roll carrier 712a disposed between the laminate roll carrier 710b and riblets 720b. In this embodiment, unlike the riblet panel 700a, the laminate roll carrier 710b may not itself be adhesive and the laminate roll carrier adhesive 712b is configured to attach the laminate roll carrier 710b to the riblets 702b.

[0130] Riblet panel 700c has riblets 702c, riblet carrier adhesive 708c, decorative layer 716c, decorative layer adhesive 720c, release liner 718c, laminate carrier roll 710c, and laminate carrier roll adhesive 712c. The riblets 702c, riblet carrier adhesive 708c, decorative layer 716c, and decorative layer adhesive 720c together form a riblet film. The laminate roll carrier 710c and laminate roll carrier adhesive 712c form a laminate film. The riblet panel 700c is similar to the1006254568riblet panel 700b except that the riblet panel 700c omits the riblet carrier 704b of the riblet panel 700b. For riblet panel 700c, the riblets 702c are attached to the riblet carrier adhesive 708c instead of a riblet carrier 704b as with riblet panel 700b.

[0131] Riblet panel 700d has riblets 702d, riblet carrier adhesive 708d, decorative layer 716d, decorative layer adhesive 720d, release liner 718d, and adhesive laminate carrier roll 710d. The riblets 702d, riblet carrier adhesive 708d, decorative layer 716d, and decorative layer adhesive 720d together form a riblet film. The adhesive laminate roll carrier 710d defines a laminate film. The riblet panel 700d is similar to the riblet panel 700a except that the riblet panel 700d omits the riblet carrier 704a of the riblet panel 700a. For riblet panel 700d, the riblets 702d are attached to the riblet carrier adhesive 708d instead of a riblet carrier 704a as with riblet panel 700a.

[0132] For riblet panels 700a-d, the release liner 718a-d is configured to be removed from the decorative layer adhesive 720a-d to expose the decorative layer adhesive 720a-d. The exposed decorative layer adhesive 720a-d is configured to adhere to an aerodynamic surface to attach the riblets 702a-d to the aerodynamic surface. The laminate film of the riblet panels 700a-d is configured to be removed from the riblets 702a-d to expose the riblets 702a-d.

[0133] The decorative layer 716a-d of each riblet panel 700a-d may include at least a portion of an image that faces in the direction of the riblets 702a-d. So that the decorative layer 716a-d is visible from the riblet side of the riblet panel 700a-d, the riblets 702a-d and the layers between riblets 702a-d and decorative layer 716a-d (e.g. the riblet carrier and / or riblet carrier adhesive) are transparent. As each decorative layer 716a-d may include at least a portion of an image, when several riblet panels 700a-d are applied to an aerodynamic surface, the decorative layers 716a-d of those riblet panels 700a-d may together form a complete image.

[0134] Alternatively, the decorative layer 716a-d of each riblet panel 700a-d may include one or more colours. In this embodiment, when several riblet panels 700a-d are applied to an aerodynamic surface, the one or more colours of those riblet panels 700a-d may together define at least part of the livery of the aircraft.

[0135] The riblet panels 600a-c and 700a-d may be formed using any of the methods described above for forming riblet panel 500 (e.g. lamination). The riblets 602a-c and 702a-d of the riblet panels 600a-c and 700a-d may be formed and pre-oriented on the riblet panel 600a-c and 700a-d using any of the methods described above for forming and pre-orienting riblets 5021006254568on riblet panel 500. Accordingly, the riblet panels 600a-c and 700a-d each have multiple riblet films that are attached to the laminate film in a predetermined arrangement such that the riblets 602a-c and 702a-d are pre-oriented in one or more directions on the riblet panel 600a-c and 700a-d based on airflow directions over the particular section of an aerodynamic surface to which the riblet panel 600a-c and 700a-d is to be applied. Therefore, when the riblet panels 600a-c and 700a-d are applied to that particular section of the aerodynamic surface, the preoriented riblets 602a-c and 702a-d of the riblet panel 600a-c and 700a-d will substantially align with respective airflow directions over that particular section of the aerodynamic surface.

[0136] The laminate film of each of the riblet panels 500, 600a-c, and 700a-d may be an application aid or tape that does not completely cover the riblets of the riblet panel, or a protective tape that has a size and shape sufficient to cover the riblets of the riblet panel.

[0137] As the riblet panels 500, 600a-c, 700a-d comprise multiple riblet films that are attached to the laminate film in a predetermined arrangement such that the riblets 502, 602a-c and 702a-d are pre-oriented on the riblet panel 500, 600a-c and 700a-d, applying a single riblet panel 500, 600a-c, 700-a-d to a section of an aerodynamic surface applies multiple riblet films 506, 606a-c, 706a-d with the riblets 502, 602a-c, 702a-d substantially aligning with airflow directions over that section of the aerodynamic surface. This reduces the need to separately orient and apply multiple riblet films at particular orientations to that section of the aerodynamic surface so that the riblets will substantially align with airflow directions over that section of the aerodynamic surface. Accordingly, similar to that described above with respect to riblet subassembly 200, the riblet panels 500, 600a-c, 700a-d may simplify the process of applying riblets to an aerodynamic surface by reducing the number of components that need to be applied to the aerodynamic surface and the need to apply multiple sets of riblets at different orientations on the aerodynamic surface. Reducing the number of components to be applied to an aerodynamic surface may therefore reduce the time required to apply riblets to the aerodynamic surface, which may also reduce the downtime required for an aircraft when applying riblets to the aircraft.

[0138] For each riblet sub-assembly 200, 300a-d, 400a-d, the laminate film will have dimensions and / or a shape that substantially corresponds with (e.g. substantially matches) the dimensions and / or shape of the section of the aerodynamic surface to which the riblet subassembly 200, 300a-d, 400a-d is to be applied. In contrast, for each riblet panel 500, 600a-c, 700a-d, as the laminate film will be removed, the laminate film does not have to have1006254568dimensions and / or a shape that corresponds with (e.g. matches) the dimensions and / or shape of the section of the aerodynamic surface to which the riblet panel 500, 600a-c, 700a-d is to be applied. This is because the laminate film of the riblet panels 500, 600a-c, 700a-d need only be dimensioned so that they can carry all the riblet films 506, 606a-c, 706a-d of a riblet panel 500, 600a-c, 700a-d prior to application of the riblet panel 500, 600a-c, 700a-d to an aerodynamic surface.

[0139] Figure 16 shows a riblet assembly 800 according to another embodiment of the present disclosure applied to a top surface 19 of a wing 14 of an aircraft 10.

[0140] The riblet assembly 800 extends from a base edge 802 to a tip 804, between a leading edge 806 and a trailing edge 808. The base edge 802 is positioned adjacent the wing root 21 of the aircraft 10 and the tip 804 is to positioned proximate the wing tip 22. The leading edge 806 is positioned proximate the trailing edge of the slats 23 of the wing 14. In alternative embodiments where the aircraft 10 does not have any slats 23, the leading edge 806 of the riblet assembly 800 may be positioned proximate and extend along the leading edge 24 of the wing 14. The trailing edge 808 of the riblet assembly 800 is positioned proximate and extends along the trailing edge 25 of the wing 14. The riblet assembly 800 is provided with pre-oriented riblets (not shown) that extend from the leading edge 806 to the trailing edge 808, and which will substantially align to the different airflow directions over the areas of the wing 14 to which they will be located when the riblet assembly 800 is applied to the top surface 19 of the wing 14.

[0141] It will be appreciated that the wall shear stress of the air flowing over the wing 14 will vary from the leading edge 24 to the trailing edge 25 of the wing 14. Accordingly, it will be appreciated that correspondingly varying the design or configuration of the riblets, e.g. the shape / profile (both in cross section and long section), height and width of each riblet as well as the spacing between adjacent riblets, of the riblet assembly 800 based on the wall shear stress will increase the desired skin friction reduction effect. In the depicted embodiment, this variation is achieved in a discrete manner by the riblet assembly 800 utilising 3 separate riblet designs or configurations: a first design with a riblet configuration optimised to reduce wall shear stress immediately downstream of the leading edge 24 of the wing 14; a second design with a riblet configuration optimised to reduce wall shear stress immediately upstream of the trailing edge 25 of the wing 14; and a third design with a riblet configuration optimised to provide the wall shear stress with a smooth transition between the first and second designs. It will be appreciated that,1006254568in alternative embodiments, the variation in riblet design or configuration may be achieved in a continuous manner, utilising the manufacturing methods described in the Applicant’s International Application No PCT / AU2020 / 050543 filed on 29 May 2020.

[0142] Accordingly, the riblet assembly 800 has a leading region 810 (identified in Figure 16 by the darkest grayscale shading) comprising riblets (not shown) of the first design, a trailing region 814 (identified in Figure 16 with the lightest grayscale shading) comprising riblets (not shown) of the second design and a central region 812 disposed between the leading and trailing regions 810, 814 and comprising riblets (not shown) of the third design. The leading region 810, central region 812, and trailing region 814 extend from the base edge 802 to the tip 804 of the riblet assembly 800, with the leading region 810 extending along the leading edge 806 of the riblet assembly 800 and the trailing region 814 extending along the trailing edge 808 of the riblet assembly 800. The configurations of the riblets in the leading region 810, central region 812, and trailing region 814, i.e. the first, second and third designs, may be determined using any of the methods described above.

[0143] Whilst not shown in Figure 16, the orientation of these pre-oriented riblets is indicated by the line segments extending between the upstream and downstream edges of each region. Accordingly, it can be seen that all riblets of the trailing region 814 have a single, parallel orientation. In contrast, while the riblets of the leading and central regions 810, 812 are aligned with the ribs of the trailing region 814 in the area adjacent the base edge 802 of the riblet assembly 800, their alignment varies as the distance from the base edge 802 increases. The airflow directions over the wing 14 may be determined and / or obtained using any of the method described above.

[0144] Although the riblet assembly 800 has been described and illustrated as having three different designs and regions (i.e. leading, central, and trailing), it is envisaged that the riblet assembly 800 may have more or less than three different designs and regions. For example, the riblets of the entire riblet assembly 800 may have a common design or configuration and thus riblet assembly 800 may have only a single region.

[0145] The riblet assembly 800 may comprise a single riblet sub-assembly, i.e. be a single riblet panel that is applied to the top surface 19 of the wing 14. Alternatively, the riblet assembly 800 may be comprised of multiple riblet sub-assemblies (e.g. riblet sub-assemblies 200) that are1006254568individually applied to the top surface 19 of the wing 14 to form the riblet assembly 800, similar to the embodiments described above with respect to Figure 4 and 5.

[0146] It will be appreciated that providing the riblet assembly 800 as a single riblet panel may reduce the time required to apply the riblet assembly 800 to the top surface 19 of the wing 14 compared to applying multiple riblet sub-assemblies (e.g. riblet sub-assemblies 200) that together form the riblet assembly 800. For example, after manufacturing at an offsite production facility, the riblet assembly 800 may be rolled up from the tip 804 to the base edge 802 and transported to the application site as a riblet assembly roll (not shown). The riblet assembly 800 may then be applied to the top surface 19 of the wing 14 by initially positioning the base edge 802 adjacent the wing root 21, with the ends of the base edge 802 used to position the roll in the longitudinal direction of the aircraft 10, and then subsequently rolling out the riblet assembly 800 to the tip using any of the application methods described above. It will be appreciated that, in alternative embodiments, the riblet assembly 800 may be rolled up in the reverse direction, i.e. from the base edge 802 to the tip 804, or in the transverse direction, i.e. from the leading edge 806 to the trailing edge 808 or vice versa, with the subsequent rolling out step occurring in the relevant opposite direction, respectively.

[0147] The riblet assembly 800 may have a similar construction to any of the riblet panels described above. For example, the riblet assembly 800 may have a construction similar to that described and illustrated with respect to the embodiments of Figures 8, 1 la-d, 12a-d, 13, 14a-c, and 15a-d.

[0148] Figure 16 shows a riblet assembly 800 for the top surface 19 of the right wing 14 of the aircraft 10. It will be appreciated that a riblet assembly 800 to be applied to the top surface of the left wing of the aircraft 10 will be a mirror image of the riblet assembly 800 shown in Figure 16.

[0149] Further, the shape of the riblet assembly 800 shown in Figure 16 substantially corresponds with the shape of the top surface 19 of the wing 14 such that the riblet assembly covers almost the entire top surface 19 of the wing 14. It will be appreciated that, in alternative embodiments, sufficient skin friction reduction may be achieved with a riblet assembly that covers less area of the top surface of the wing and / or has a shape that does not substantially correspond with the shape of the top surface of the wing. It also will be appreciated that the riblet1006254568assembly 800 shown in Figure 16 is for a specific aircraft and that a riblet assembly 800 made for the top surface of a wing of a different aircraft may have a different shape. It will be further appreciated that a riblet assembly 800 made for the top surface of a different aircraft may have more or fewer regions of riblets of different configurations compared to the three regions of the riblet assembly 800 shown in Figure 16, depending on the airflow characteristics over the wing of the particular aircraft.

[0150] Although method 100 includes mapping step 102, production step 104, and application step 106, this does not require a single party to carry out all three steps. It is envisaged that different parties may carry out one or more of steps 102, 104, and 106. For example, a first party may map one or more surfaces of a first type of aircraft to determine airflow directions over those surfaces, a second party may produce riblet sub-assemblies based on the mapping performed by the first party, and a third party may apply the riblet sub-assemblies produced by the second party to respective surfaces of an aircraft of the first type. In this example, the second party may obtain information relating to the airflow directions determined by the first party and produce multiple sets of riblet sub-assemblies for one or more surfaces of an aircraft of the first type. The second party may then supply those sets of riblet sub-assemblies to a one or more third parties who apply each set of riblet sub-assemblies to respective surfaces of an aircraft of the first type. It is also envisaged that the second party may obtain information relating to the airflow directions determined by the first party, produce sets of riblet sub-assemblies for one or more surfaces of an aircraft of the first type, and apply those sets riblet sub-assemblies to the respective surfaces of the aircraft of the first type. It is also envisaged that the first party may perform all of steps 102, 104, and 106.

[0151] The riblet panel embodiments described above, i.e. riblet sub-assemblies 200, 300a-d, 400a-d, riblet panels 500, 600a-c, 700a-d, and riblet assembly 800, have been described and illustrated as having riblets that are pre-oriented based on airflow directions previously determined and mapped to a respective section of the surface to which the riblet panels are applied. However, it will be appreciated that some applications of the present disclosure do not require the steps of determining and mapping the flow of a fluid over the surface to which the riblet panel is to be applied. For example, it may be sufficient for the riblets of the riblet panels to reduce the skin friction of the surface to which they are applied if the riblets are oriented such that they will substantially align with predominant fluid flow direction(s) and / or expected fluid flow direction(s) over the section of the surface to which the riblet panels will be applied. 1006254568Regardless of how the specific arrangement of the riblet films on a riblet panel is determined to ensure that its riblets are configured to reduce the skin friction of the surface to which it is applied, assembling a riblet panel with multiple riblet films attached to a single laminate film means that adhering the single riblet panel to the surface results in multiple riblet films being attached to the surface. Accordingly, similar to that described above, having riblet panels that each include multiple riblet films may simplify the process of attaching riblets to a surface by reducing the number of components that need to be individually adhered to the surface. This may therefore reduce the time required to attach riblets to the surface, which may also reduce the downtime required for an aircraft when attaching riblets to the aircraft.

[0152] Although the method 100 has been described above for producing riblet panels for an aerodynamic surface of an aircraft, it will be appreciated that the method 100 may also be used to produce and apply riblet panels to other surfaces over which a fluid may flow. For example, the method 100 may be used to produce and apply riblet panels to aerodynamic surfaces of other vehicles (e.g. cars, motorbikes, trains, trucks). Further, it is envisaged that the method 100 may also be used to produce and apply riblet panels to hydrodynamic surfaces of marine vehicles (e.g. shipping vessels, cruise ships, speed boats, yachts). Still further, the method 100 may be used to produce and apply riblet panels to surfaces that rotate (e.g. wind turbine blades, propellers, impellers, turbines, fans, etc.) or to stationary surfaces over which a fluid may flow (e.g. the external surface of a pipe) or through which a fluid may flow (e.g. the internal surface of a pipe).

[0153] Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and / or combined with other pieces of prior art by a skilled person in the art.

[0154] By way of clarification and for avoidance of doubt, as used herein and except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additions, components, integers or steps

[0155] It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or1006254568evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.1006254568

Claims

CLAIMS1. A method of assembling a riblet panel for attaching riblets to a surface over which a fluid flows, the method comprising: preparing a plurality of riblet films, each riblet film comprising one or more riblets; and attaching the plurality of riblet films to a common laminate film in a predetermined arrangement, wherein the riblet panel is configured to adhere to the surface; and wherein the predetermined arrangement is configured such that, when the riblet panel is adhered to the surface, the one or more riblets of the plurality of riblet films are configured to reduce the skin friction of the surface when the fluid flows over them.

2. The method of claim 1, wherein each riblet film of the plurality of riblet films is prepared before any riblet film of the plurality of riblet films is applied to the common laminate film.

3. The method of claim 1, wherein at least one riblet film of the plurality of riblet films is applied to the common laminate film before all the riblet films of the plurality of riblet films are prepared.

4. The method of any one of claims 1 to 3, further comprising: obtaining flow directions of the fluid flowing over the surface when the surface moves with respect to the fluid; mapping the obtained flow directions to at least one planar section projected from the surface; and applying the plurality of riblet films to the common laminate film in the predetermined arrangement such that the riblets of the plurality of riblet films substantially align with the flow directions mapped to the at least one planar section.

5. The method of any one of claims 1 to 4, further comprising: obtaining wall shear stresses of the fluid flowing over the surface when the surface moves with respect to the fluid; mapping the wall shear stresses to at least one planar section projected from the surface; and1006254568preparing riblets of the plurality of riblet films with a riblet configuration comprising at least one of riblet height, riblet width, riblet shape and riblet spacing designed to reduce a wall shear stress mapped to the at least one planar section.

6. The method of any one of claims 1 to 5, wherein preparing the plurality of riblet films comprises cutting predetermined shapes from a sheet of riblets.

7. The method of claim 6, wherein the sheet of riblets is unrolled from a roll of adhesive riblet film comprising an adhesive layer configured to adhere the riblet film to the surface and provided with a release liner for protecting the adhesive layer of the adhesive riblet film.

8. The method of claim 6, wherein the sheet of riblets is unrolled from a roll of nonadhesive riblet film and preparing the plurality of riblet films further comprises adhering the plurality of riblet films to a common release liner in the predetermined arrangement with an adhesive layer configured to adhere the riblet film to the surface.

9. The method of claim 8, wherein the plurality of riblet films is adhered to the common release liner prior to being applied to the common laminate film.

10. The method of claim 8, wherein the plurality of riblet films is adhered to the common release liner after being applied to the common laminate film.

11. The method of any one of claims 1 to 10, wherein the common laminate film is an adhesive laminate film and attaching the plurality of riblet films to the adhesive laminate film comprises adhering riblets of the plurality of riblet films to the adhesive laminate film such that the riblets are covered by the adhesive laminate film.

12. A riblet panel to be adhered to a surface over which a fluid flows, the riblet panel comprising: an adhesive laminate film; and a plurality of riblet films attached to the adhesive laminate film in a predetermined arrangement, each riblet film comprising one or more riblets configured to reduce the skin friction of the surface when the fluid flows over them, wherein the riblet panel is configured to adhere to the surface.100625456813. The riblet panel of claim 12, wherein each riblet film comprises an adhesive layer configured to adhere the riblet film to the surface and a release liner provided on the adhesive layer.

14. The riblet panel of claim 12, further comprising a common adhesive layer configured to adhere the riblet panel to the surface and a common release liner provided on the common adhesive layer15. The riblet panel of any one of claims 12 to 14, wherein the adhesive laminate film covers the one or more riblets of the plurality of riblet films.

16. The riblet panel of any one of claims 12 to 15, wherein the one or more riblets of each riblet film have the same orientation.

17. The riblet panel of any one of claims 12 to 15, wherein the one or more riblets of one riblet film have an orientation that is different to an orientation of the one or more riblets of another riblet film.

18. The riblet panel of any one of claims 12 to 17, wherein at least one of a riblet height, a riblet width, a riblet shape and a riblet spacing of the one or more riblets of one riblet film is different to a respective riblet height, riblet width, riblet shape and / or riblet spacing of the one or more riblets of another riblet film.

19. The riblet panel of any one of claims 12 to 17, wherein the one or more riblets of each riblet film have the same riblet height, riblet width, riblet shape and riblet spacing.

20. A method of attaching riblets to a surface over which a fluid flows, the method comprising: identifying at least one datum on the surface; applying an initial riblet panel to the surface such that it is aligned with the at least one datum; and applying one or more subsequent riblet panels to the surface such that each subsequent riblet panel is aligned with and abuts or overlaps a portion of a riblet panel that was applied immediately prior,1006254568wherein each of the initial and subsequent riblet panels comprises: an adhesive laminate film; and at plurality of riblet films attached to the adhesive laminate film, each riblet film comprising one or more riblets configured to reduce the skin friction of the surface when the fluid flows over them, wherein the riblet panel is configured to adhere to the surface.

21. The method of claim 20, further comprising removing the adhesive laminate film from each of the initial and subsequent riblet panels.

22. The method of claim 20 or 21, wherein each of the initial and subsequent riblet panels accords with any one of the riblet panels of claims 12 to 19.

23. The method of any one of claims 1 to 11, the riblet panel of any one of claims 12 to 24 or the method of any one of claims 25 to 27, wherein the surface is an aerodynamic surface of an aircraft.

24. A method of attaching a riblet panel to a surface of a wing of an aircraft, wherein the riblet panel comprises one or more riblets configured to reduce the skin friction of the wing, and the riblet panel is provided in the form of a roll having an exposed end and an internal end, the method comprising: identifying at least one datum on the aircraft; aligning the exposed end of the roll with the at least one datum; rolling out the riblet panel on the surface of the wing to the internal end of the roll; and adhering the riblet panel to the surface of the wing.

25. The method of claim 24, wherein the steps of rolling out and adhering occur simultaneously.

26. The method of claim 24, wherein the steps of rolling out and adhering occur consecutively.

27. The method of any one of claims 24 to 26, wherein, in its unrolled state, the riblet panel has a shape that substantially corresponds with a shape of the surface of the wing.100625456828. The method of any one of claims 24 to 26, wherein the at least one datum is a fuselage of the aircraft and the riblet assembly is rolled away from a wing root of the aircraft towards a wing tip of the aircraft.

29. The method of any one of claims 24 to 28, wherein the rib assembly comprises a riblet panel according to any one of claims 12 to 19.

30. The method of any one of claims 24 to 29, wherein: the riblet panel comprises a plurality of riblet films and an adhesive laminate film attached to the riblets of the riblet films; and the method further comprises removing the adhesive laminate film from the riblet panel after it is adhered to the surface of the wing.1006254568

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