Ridged foil for reducing air resistance of an aircraft

Abstract

The invention relates to a ridged foil (10) for reducing the air resistance of an aircraft, comprising a suspension (20) with magnetic particles contained therein, wherein depending on the course of a magnetic field acting on the ridged foil (10), the acting magnetic field can be made visible at least locally by changing the orientation of the magnetic particles. The ridged foil (10) according to the invention allows the inspection of the aircraft structure located below the ridged foil (10) through the ridged foil.

Description

TECHNICAL FIELD

[0001] The invention relates to a ridged foil for reducing the air resistance of an aircraft, to an aircraft having such a ridged foil, and to a method for testing an aircraft structure to which such a ridged foil is applied. BACKGROUND

[0002] The term "ridge" denotes a profile on a surface, which is realized as an assembly of microscopically small grooves or ribs. Ridges are used on the flow surfaces of aircraft for reducing flow resistance and thus fuel consumption.

[0003] One form of applying ridges to an aircraft is achieved by manufacturing so-called ridged foils having ridges and applying them on the (aerodynamic) surfaces at locations where a corresponding reduction of flow resistance is desired on the aircraft.

[0004] However, it can be disadvantageous in the use of such ridged foils at times that the ridged foils usually cover the aerodynamic surfaces on which they are applied and thus limit the line of sight to the aircraft surface structure lying underneath in these areas. As a result, it is not always possible to visually inspect the structure in these areas. This can make the implementation of maintenance tasks difficult and thus at least partially limit the use of ridged foils.

[0005] It is an object of the present invention to provide a ridged foil which overcomes or at least mitigates the disadvantages of the prior art. SUMMARY

[0006] It is an object of the present invention to be achieved by a ridged foil for reducing the air resistance of an aircraft having a suspension body having magnetic particles contained therein, wherein depending on the course of a magnetic field acting on the ridged foil, the acting magnetic field can be made visible at least locally by changing the orientation of the magnetic particles.

[0007] In the ridged foil according to the application, the suspension with the magnetic particles contained therein functions as a so-called flux detector. Here, the suspension is a substance with a carrier liquid and freely rotatable magnetic particles contained therein. The function of the flux detector is based on the fact that the freely rotatable particles orientate themselves depending on whether a magnetic field generated from the outside impinges substantially orthogonally or substantially parallel to the plane of the flux detector. If the magnetic field impinges orthogonally on the flux detector, the magnetic particles orientate themselves in such a way that they reflect only a small portion of the light. The flux detector thus appears comparatively dark. In contrast, when the magnetic field extends parallel to the plane of the flux detector, the magnetic particles function as a kind of small mirror, whereby the flux detector appears bright. Depending on the number of magnetic particles in the suspension, a finely structured display of the magnetic field can thus be provided. It should be understood that the reflection effect of the light impinging on the magnetic particles also occurs in principle in all other (intermediate) angles and achieves a corresponding variable light / dark progression.

[0008] The ridged foil according to the application, which is arranged on one side thereof with a plurality of ridges (ridges designed as very small ribs), can advantageously make irregularities in a structure to which the ridged foil is applied visible (when a magnetic field acts at least locally on the structure and the ridged foil) by making itself to some extent function as a flux detector. This is because irregularities in the structure, for example cracks or other disturbances, influence the progression of the magnetic field lines under the influence of the magnetic field acting on this structure region. The influence is achieved in such a way that the progression of the magnetic field lines in the region of the irregularity on the structure is generally different from the progression that would be expected without the irregularity, for example without the crack (the progression of the actual magnetic field deviates from the expected progression of the ideal magnetic field).

[0009] Thereby, for example, irregularities in a structure can be made visible for maintenance purposes by the ridged foil according to the application, although these irregularities can not be seen only externally through the ridged foil (even if the ridged foil is designed to be transparent, because, for example, a crack is formed under the structure surface). By the ridged foil according to the application, cracks that can occur in the underlying structure can be detected or made visible (if the penetration depth of the magnetic field is sufficient). The use or application of the ridged foil is thereby simplified.

[0010] In other words, the ridged foil for reducing the air resistance of an aircraft according to the application comprises ridges arranged parallel to one another designed on one side of the foil and a suspension with magnetic particles contained therein. The typical dimensions of the ridges can vary, for example, as follows: the ridge height (from the ridge base up to the ridge tip) is between 0.01 mm and 0.04 mm; the ridge width (average) is between 0.005 mm and 0.02 mm. The usual spacing between adjacent ridges can be, for example, between 0.02 mm and 0.08 mm.

[0011] The ridged foil according to the application has a foil thickness of approximately 0.05 mm to 0.25 mm (not taking the ridge height into account). It is to be understood that this specification can vary depending on the area of application (i.e. depending on where the ridged foil is arranged on the aircraft or which flow speed regime results). The ridged foil is typically designed to be flexible and transparent or translucent. The foil material can for example be selected from the following group of plastics: PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PEN (polyethylene naphthalate), PP (polypropylene), PA (polyamide), and PE (polyethylene). In the framework of the present application, a suspension is to be understood as a substance with a carrier liquid and freely rotatable magnetic particles contained therein.

[0012] In a preferred embodiment of the ridged foil, the ridged foil comprises a layer with a plurality of microcapsules, wherein the suspension is distributed onto and accordingly contained in the microcapsules. By means of the microcapsules onto which the suspension is distributed, a better orientation of the magnetic particles within the microcapsules can be achieved. As the magnetic particles are thus able to rotate more easily within the capsule interior, the sensitivity of the ridged foil according to the application can be improved when the magnet is displayed optically. The magnetic particles can then in principle also change their position within the microcapsule interior more easily and more quickly. The suspension can for example be an oil and / or preferably be gel-like. The magnetic particles can for example be nickel particles, iron particles and / or chromium iron particles. The magnetic particles are then suspended in an oil or gel-like carrier liquid within the microcapsule interior. The magnetic particles can for example be designed as so-called "Flakes". In the framework of the present application, a suspension is to be understood as a substance with a carrier liquid and freely rotatable magnetic particles contained therein. The layer with the microcapsules can likewise be selected from the above-mentioned group of plastics.

[0013] In a further advantageous embodiment of the ridged foil, the magnetic particles comprise colloidal nickel. Colloidal nickel shows a favourable fast response behaviour at the field strength of the magnetic field to be introduced. Magnetic particles designed in this way are particularly easy to respond to changes in the magnetic field and are therefore particularly suitable for making irregularities in the structure located below the ridged foil visible.

[0014] It is also preferred that the ridged foil is embodied in such a way that the suspension and / or the layer comprising the microcapsules is applied to a substrate which serves as a carrier foil. By means of the substrate which serves as a carrier foil, the ridged foil according to the application additionally acquires stability, tear resistance and robustness.

[0015] It is also advantageous if the ridges are designed as ribs with pointed ends which are arranged substantially parallel to one another. In this way, the ridged foil according to the application has the advantageous effect of reducing the air resistance of the aerodynamic surface provided with the ridged foil to a high degree. The ridged foil is usually arranged on the aerodynamic surface in such a way that the flow extends parallel to the ridges.

[0016] In an equally preferred embodiment, the ridges have a substantially triangular cross section. This cross-sectional shape of the ridges is advantageous in terms of effectively reducing the resistance of the aerodynamic surface provided with the ridged foil.

[0017] Further preferably, the ridged foil also has an adhesive layer for bonding the ridged foil to the aerodynamic surface. In this way, the installation of the foil according to the application can be achieved on an industrial scale. The foil can be relatively easily processed, for example advantageously by a flat and horizontally lying foil. It is also possible to easily use on curved aerodynamic surfaces and to prevent damage to the aerodynamic surface when applying the ridges. Alternatively, the ridged foil according to the application can itself be designed as an adhesive foil without providing an additional adhesive layer.

[0018] The object of the application is also achieved by an aircraft which is provided with a ridged foil designed according to the application, which is applied to the aerodynamic surface of the aircraft. This aircraft substantially utilizes the same advantages exhibited by the ridged foil according to the application. That is to say, in this aircraft, by locally introducing a magnetic field into the region of the structure provided with the foil, irregularities which can be present in the structure can be made visible by the changed magnetic field, even if the structure is covered by the ridged foil. It is also possible even in the case where the ridged foil according to the application is not designed to be transparent itself, or the irregularities are slightly deeper in the structure and are not visible from the outside without the ridged foil.

[0019] Finally, the object of the present application is also achieved by a method for testing an aircraft structure to which a spine foil is applied, wherein the method has the following method steps: generating a magnetic field, acting on the aircraft structure to be tested locally with the magnetic field, displaying the generated magnetic field by means of the spine foil, and evaluating the displayed magnetic field. By means of the method according to the present application, irregularities in the structure to which the spine foil is applied can advantageously be made visible. The presence of irregularities in the structure, for example cracks or other material changes such as fatigue phenomena, changes the course of the magnetic field lines in the region of the irregularities compared to the case in which no irregularities are present in the structure. It can thus be deduced whether irregularities in the structure are present in the case in which the local course of the magnetic field displayed by the spine foil deviates from the expected course of the magnetic field. If necessary, the structure can then be tested in more detail by means of other testing methods. Maintenance of the aircraft is simplified and accelerated by means of the testing method according to the present application. In a preferred variant of the method, the actual magnetic field displayed is compared with an ideal magnetic field for the evaluation.

[0020] The above-mentioned aspects and other aspects, features and advantages of the present application are likewise achieved by the examples of embodiments described below with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0021] The same reference signs are used in the drawings to denote the same or at least similar elements, components or aspects. It should be noted that one embodiment will be described in detail below, which is merely illustrative and not restrictive. In this text, the word "aufweisend" does not exclude other elements, and the indefinite article "ein" does not exclude a plurality. However, the mention of certain features in different embodiments does not limit the subject matter of the present application. Combinations of these features can also be used advantageously. The figures are not drawn to scale, but only have schematic and illustrative features. In the drawings:

[0022] Figure 1a a top view of the ridge side of a spine foil according to an embodiment of the present application is shown,

[0023] Figure 1b a cross section through the spine foil according to Figure 1 along the line A-A is shown,

[0024] Figure 1c a magnified partial detail view of Figure 1b is shown,

[0025] Figure 2a a perspective view of an aircraft structure to which the spine foil according to Figure 1 is applied in a first magnetic condition is shown,

[0026] Figure 2bA perspective view of a structure, according to Figure 1, on which a ridged foil is applied, is shown in a second magnetic case.

[0027] Figure 3 A flowchart illustrating the method steps for testing an aircraft structure to which a ridged foil sheet has been applied is shown, and

[0028] Figure 4 A front view of an aircraft with a ridge foil is shown. Detailed Implementation

[0029] Figures 1a to 1c A ridged foil 10 for reducing air resistance in an aircraft is shown. The ridged foil 10 has an assembly on one side consisting of multiple shaped bodies (so-called ridges 12), which are designed as ribs 14 or grooves. The ridges 12 are arranged substantially parallel to each other and have triangular cross-sections, each forming a tip 16 at one end. The ridges 12, or the ridged foil 10, are typically oriented or arranged such that they extend substantially parallel to the flow direction 18. Ridges 12 or ridged foil 10 are used on the aerodynamic surfaces of an aircraft to reduce flow drag and thus reduce fuel consumption (see [link to documentation]). Figure 4 ).

[0030] The ridged foil 10 includes a levitation body 20 having magnetic particles 22 contained therein (see...). Figure 1c (Partial detail diagram). The suspension 20 is a substance having a carrier liquid 24 and magnetic particles 22 contained therein. The suspension 20 is distributed on a plurality of microcapsules 26 arranged in a layer 28 of a ridged foil 10, and the microcapsules contain the suspension 20 having magnetic particles 22. In other words, the ridged foil 10 includes a layer 28 having a plurality of microcapsules 26, wherein the suspension 20 is distributed on and contained therein in a plurality of subsets on the microcapsules 26. The magnetic particles 22 may be, for example, colloidal nickel, and the carrier liquid 24 may be, for example, an oil or a gel-like liquid, which allows the magnetic particles 22 to be stored in the carrier liquid 24 in a way that allows them to rotate freely.

[0031] A layer 28 comprising microcapsules 26 is applied to a substrate 30 serving as a carrier foil. On the side of the ridged foil 10 opposite to the ridge 12, the ridged foil 10 also has an adhesive layer 32 for bonding the ridged foil 10 to an aerodynamic surface.

[0032] Figure 2a and Figure 2b Partially and exemplaryly, an aircraft structure 34 is shown with a ridged foil 10 (e.g., by means of an adhesive layer 32) applied to its aerodynamic surface 36. For greater clarity, in Figure 2a and 2bIn the middle, the ridge 12 and the layers 30, 32 are not shown. In Figure 2a In the middle, the aircraft structure 34 is not damaged or the aircraft structure 34 does not have structural irregularities. In Figure 2b In the middle, the aircraft structure 34 has structural irregularities 38 (as structural irregularities 38, for example cracks that can exist in the aircraft structure 34).

[0033] By Figure 2a and 2b The magnetic fields 40', 40" that are not shown in the middle are introduced locally into the structure 34, the corresponding magnetic fields 40', 40" act locally on the aircraft structure 34 to be tested, and due to the presence or absence of irregularities 38 or cracks ( Figure 2b and 2a ), a different run of the field lines of the magnetic fields 40', 40" occurs in the aircraft structure 34 or directly in the region of the surface 36, which is exhibited by the magnetic fields 40', 40".

[0034] The different run of the field lines of the magnetic fields 40', 40" characterizes the magnetic situation, which is visible by the ridged foil 10, since depending on the magnetic fields 40', 40" acting on the ridged foil 10, the acting magnetic fields 40', 40" can be made visible at least locally by changing the orientation of the magnetic particles 22. Thus, a visibility is achieved, since the suspension 20 with the magnetic particles 22 contained therein acts as a flux detector. The freely rotatable particles 22 are oriented depending on the angle of incidence of the externally generated magnetic fields 40', 40" onto the freely rotatable magnetic particles 22. Depending on the angle of incidence, the magnetic particles 22 are oriented locally such that they reflect only a small or a large part of the light. Thus, the ridged foil 10 appears locally darker or brighter and a brightness run is obtained, which can be seen on the appearance of the ridged foil 10, which characterizes the respective magnetic situation 40', 40".

[0035] On the basis of the different run of the field lines of the magnetic fields 40', 40" that are visualized through the ridged foil 10, it can be concluded whether irregularities 38, for example cracks, exist in the aircraft structure 34 or not. This advantageously allows the aircraft structure 34 to be examined for irregularities 38 that are located under the ridged foil 10, for example for the purpose of maintaining the aircraft.

[0036] In Figure 3In the middle, a method for testing an aircraft structure 34 to which a ridged foil 10 is applied is shown schematically. The method comprises the following method steps: first, in a first step 42, a magnetic field 40 is generated; then, in a second step 44, the magnetic field 40 is introduced locally onto or into the aircraft structure 34 to be tested (i.e. the magnetic field 40 acts locally). Thereby, in a further step 46, the generated magnetic field 40 is displayed or made visible by means of the ridged foil 10. Finally, the displayed magnetic field 40 is evaluated in a last step 48. For the evaluation, the displayed actual magnetic field 40" can be compared to an ideal magnetic field 40'.

[0037] Finally, Figure 4 An aircraft 50 with a ridged foil 10 is shown, which is applied on an aerodynamic surface 36 of the aircraft 50. By locally introducing a magnetic field 40', 40" through the ridged foil 10 into the surface area of the aircraft structure 34, the aircraft 50 or the aircraft structure 34 located underneath the aerodynamic surface 36 can be inspected (e.g. for cracks).

Claims

1. A ridged foil (10) for reducing the air resistance of an aircraft (50), comprising: a suspension (20) with a carrier liquid and freely rotatable magnetic particles (22) contained therein, wherein the magnetic field acting on the ridged foil (10) can be made visible at least locally by a change in the orientation of the magnetic particles (22) depending on the course of the magnetic field, and wherein the magnetic particles are oriented locally such that they reflect only a small or a large portion of the light depending on the angle of incidence of the magnetic field incident on the magnetic particles.

2. The ridged foil of claim 1, wherein, The ridged foil (10) comprises a layer (28) with a plurality of microcapsules (26), wherein the suspension (20) is distributed onto and contained in the microcapsules (26) accordingly.

3. The ridged foil according to claim 1 or 2, wherein, The magnetic particles (22) comprise colloidal nickel.

4. The ridged foil of claim 1 or 2, wherein, The suspension (20) and / or the layer (28) comprising the microcapsules (26) is applied on a substrate (30) serving as a carrier foil.

5. The ridged foil of claim 1 or 2, wherein, The ridges (12) are designed as ribs (14) arranged essentially parallel to one another with a pointed end (16).

6. The ridged foil of claim 1 or 2, wherein, The ridges (12) have an essentially triangular cross section.

7. The ridged foil of claim 1 or 2, wherein, The ridged foil (10) also has an adhesive layer (32) for bonding the ridged foil (10) to an aerodynamic surface (36).

8. An aircraft with a ridged foil (10) according to one of claims 1 to 7, which is applied on an aerodynamic surface of the aircraft.

9. A method for testing an aircraft structure, a ridged foil (10) according to one of claims 1 to 7 being applied to the aircraft structure, the method having the following method steps: - generating (42) a magnetic field, - locally acting (44) the magnetic field on the aircraft structure to be tested, - displaying (46) the generated magnetic field by means of the ridged foil (10), and - evaluating (48) the displayed magnetic field.

10. The method of claim 9, wherein, In the evaluation (48), the displayed actual magnetic field (40") is compared with an ideal magnetic field (40').

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