GB2595486A

GB2595486A - Removal of debris from aerodynamic surfaces

Info

Publication number: GB2595486A
Application number: GB2007990.1A
Authority: GB
Inventors: Durston Nicholas
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2020-05-28
Filing date: 2020-05-28
Publication date: 2021-12-01
Also published as: GB202007990D0

Abstract

An aerodynamic surface 1 comprising an elastic film 20 covering at least its leading edge region 16. A film stretching and displacement mechanism (e.g. rotatable rollers 21, 22 attached at film ends) displaces and stretches the film relative to the aerodynamic surface along a chordwise direction. The film may comprise a polymer material or silicone. The film may cover an upper skin panel of an aircraft wing box. The leading edge may be formed by a moveable leading edge device surface (e.g. droop nose device, or a slat). The aerodynamic surface may comprise lower 15 and upper 14 slots, wherein the first and second ends of the film extend through the slots into an internal space of the aerodynamic surface. Stretching the film may remove frozen debris 31 (ice or insect contamination) from a contaminated region 30 of an aerofoil surface. The film may thus clean, deice, or decontaminate the region.

Description

REMOVAL OF DEBRIS FROM AERODYNAMIC SURFACES

TECHNICAL FIELD

100011 The present invention relates to aerodynamic surfaces and methods for removing debris from such aerodynamic surfaces.

BACKGROUND

[0002] It is desirable to reduce the amount of aerodynamic drag experienced by an aircraft. Drag can be reduced by ensuring that airflow over at least the leading edge part of a wing is laminar. Maintaining laminar flow requires the surface of the wing to be very smooth, as any discontinuities (e.g. joints between skin panels, fastener heads, or the like) may cause the flow downstream of the discontinuity to become turbulent.

[0003] Surface smoothness at the leading edge of a wing is reduced by debris, such as insect debris or ice, which accumulates during flight. A mechanism for removing this debris, or reducing its aerodynamic effect, as early as possible during a flight, is therefore desirable.

SUMMARY

[0004] A first aspect. of the present. invention provides an aerodynamic surface comprising an elastic film and a film stretching and displacement mechanism. The elastic film is disposed on the aerodynamic surface such that the film covers at least a leading edge region of the aerodynamic surface. The film stretching and displacement. mechanism is for displacing the film relative to the aerodynamic surface along a chordwise direction and for stretching the film along a chordwise direction.

[0005] Optionally, the film covers an upper region of the aerodynamic surface immediately aft of the leading edge region.

[0006] Optionally, the aerodynamic surface comprises a wing box and the film covers an upper skin panel of the wing box.

[0007] Optionally, the aerodynamic surface comprises a leading edge moveable device, wherein the leading edge region of the aerodynamic surface is formed by an outer surface of the moveable device.

[0008] Optionally, the aerodynamic surface comprises a lower slot in a lower region of the aerodynamic surface, and wherein a first end of the film extends through the lower slot into an internal space of the aerodynamic surface.

[0009] Optionally, the aerodynamic surface comprises an upper slot in an upper region of the aerodynamic surface, and wherein a second end of the film extends through the upper slot into an internal space of the aerodynamic surface.

[0010] Optionally, the upper slot is located at a join between a fixed leading edge structure of the aerodynamic surface and a wing box of the aerodynamic surface.

[0011] Optionally, the upper slot is located at a join between a fixed trailing edge structure of the aerodynamic surface and a wing box of the aerodynamic surface.

[0012] Optionally, the film stretching and displacement mechanism comprises a first roller fixedly attached to a first end of the film and a second roller fixedly attached to a second end of the film, and is configured to displace the film by one or more of: - rotating the first roller and the second roller in the same direction, by the same amount; - rotating the first roller and the second roller in the same direction by different amounts; - rotating the first roller and the second roller in opposite directions by different amounts; - maintaining one of the first. roller and the second roller stationary and rotating the other of the first roller and the second roller.

[0013] Optionally, the film stretching and displacing mechanism is configured to stretch the film by one or more of: - rotating the first roller and the second roller in the same direction by different amounts; - rotating the first roller and the second roller in opposite directions by the same amount; - rotating the first roller and the second roller in opposite directions by different amounts; - maintaining one of the first roller and the second roller stationary and rotating the other of the first roller and the second roller.

[0014] Optionally, a total length of the film is at least 50% greater than a distance on an outer surface of the aerodynamic surface between the first roller and the second roller.

[0015] Optionally, a second end of the film is fixedly attached to an upper region of die aerodynamic surface, and the film stretching and displacement mechanism comprises a roller fixedly attached to the first end of the film and is configured to simultaneously displace and stretch the film by rotating the roller.

[0016] Optionally, the film is configured such that the coefficient of friction between an inner surface of the film and an outer surface of the aerodynamic surface is low enough to permit sliding therebetween.

[0017] Optionally, the aerodynamic surface comprises multiple separate portions of elastic film and multiple separate film stretching and displacement mechanisms distributed along the span of the aerodynamic surface, wherein each portion of film is associated with a different one of the film stretching and displacement mechanisms.

[0018] Optionally, the aerodynamic surface is an aircraft wing.

[0019] A second aspect of the invention provides an aircraft comprising an aerodynamic surface according to the first aspect.

[0020] A third aspect of the invention provides a method for removing debris from an aerodynamic surface, the method comprising: - providing a stretchable material on an outer surface of a leading edge part of the aerodynamic surface; - operating the aerodynamic surface such that debris becomes deposited on a region of the stretchable material; and - stretching the stretchable material along a chordwise direction of the aerodynamic surface.

[0021] Optionally, the method further comprises displacing the stretchable material relative to the aerodynamic surface along a chordwise direction relative to the aerodynamic surface.

[0022] Optionally, displacing the stretchable material is performed simultaneously with stretching the stretchable material.

[0023] Optionally, displacing the stretchable material is performed before stretching the stretchable material.

[0024] Optionally, stretching the stretchable material is performed at a time when the debris is frozen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [0026] Figure la is a cross-section through a forward part of an example aerodynamic surface according to the invention, with the film in a first position; [0027] Figure lb is a cross-section through the forward part of the example aerodynamic surface of Figure lb, with the film in a second position; [0028] Figure 2 shows two cross-sections through a contaminated region of the film of the example aerodynamic surface of Figures la and lb, in unstretched and stretched states of the film; [0029] Figure 3a is a cross-section through the forward part of a further example aerodynamic surface; [0030] Figure 3b is a cross-section through the forward part of a further example aerodynamic surface; [0031] Figure 4 is a cross-section through a complete further example aerodynamic surface; [0032] Figure 5 is a cross-section through the forward part of a further example aerodynamic surface; [0033] Figure 6 is a perspective view of an example aircraft comprising an aerodynamic surface according to the invention; and [0034] Figure 7 is a flow chart illustrating an example method for removing debris from an aerofoil according to the invention.

DETAILED DESCRIPTION

[00351 The examples described herein each relate to aerodynamic surfaces. Each such aerodynamic surface according to the invention has an outer aerodynamic surface, and comprises an elastic film disposed on the outer aerodynamic surface, and a film stretching and displacement mechanism. In each case the elastic film covers at least a leading edge region of the aerodynamic surface. The film stretching and displacement mechanism is for displacing the film relative to the outer aerodynamic surface along a chordwise direction and for stretching the film along the chordwi se direction.

[0036] For the purposes of this document, the chordwise direction is considered to be substantially normal to a leading edge of the aerodynamic surface. It should also be noted that the term -aerodynamic surface" is intended to refer to a complete structure, such as a wing, which has an aerodynamic profile. It is not intended to just refer to a surface part of such a structure. The term -displacement" as used herein refers to a change in the relative position of a point on the film and a point on the structure of the aerodynamic surface which underlies the film. Displacements of the film relative to the underlying aerodynamic surface structure in accordance with the invention are along an outer surface part of the aerodynamic surface. It is not intended that any part of the film moves in a direction normal to the underlying outer surface part during a displacement operation according to the invention.

[0037] Aerodynamic surfaces according to the invention are advantageously able to mitigate the aerodynamic effects of debris which becomes deposited on the aerodynamic surface during flight. In particular, the film stretching and displacement mechanism enables a region of debris to be moved away from an aerodynamically significant region of the aerofoil structure to a different, less aerodynamically significant, region (such as aft of the stagnation point/line on the lower surface of the aerodynamic surface 1). Furthermore, the film stretching and displacement mechanism enables a region of film on which debris is present to be stretched in a manner such that the aerodynamic effect of the debris is reduced, and/or such that removal of some or all of the debris is facilitated. In at least some examples the combined mitigating effect of the stretching and displacement may be sufficient to permit laminar flow to be maintained over the aerodynamic surface, even after debris has become deposited on it.

[0038] Figures la and lb are cross sectional views of a leading edge part of an example aerodynamic surface 1 according to the invention. In this example the aerodynamic surface 1 is a laminar flow aircraft wing. The primary structural element of the wing is a wing box comprising upper and lower skin panels 11, 12, each of which extends between a front spar 13 and a rear spar (not. shown). A fixed leading edge (FLE) structure 10 is attached to the front spar 13 using any suitable attachment mechanism (not shown). A fixed trailing edge (FTE) structure (not shown) is attached to the rear spar using any suitable attachment mechanism. The aerodynamic surface 1 has an outer aerodynamic surface, which is formed by the outer surfaces of the upper and lower skin panels 11, 12, the FLE structure 10, and the FTE structure.

[0039] An elastic film 20 is provided on the outer aerodynamic surface of the aerodynamic surface 1, such that the film covers a leading edge region 16 of the structure 1. The leading edge region 16 encompasses the foremost extremity of the aerofoil profile, across the full smtnwise length of the aerodynamic surface 1. The leading edge region 16 may be a spanwise extending band, which extends for a short distance above and below the foremost extremity of the aerofoil profile. The leading edge region 16 may be a region which encompasses most or all of the debris 31 which becomes deposited on the aerodynamic surface during flight. In the example of Figures la-b the film 20 additionally covers an upper region of the aerodynamic surface 1 immediately aft of the leading edge region 16, and a lower region of the aerodynamic surface 1 immediately aft of the leading edge region 16. The upper region extends aftwardly to a forward edge of the upper skin panel 11 and the lower region extends aftwardly to a forward edge of the lower skin panel 12.

[0040] The elastic film 20 forms part of the aerodynamic external surface of the aerodynamic surface 1 and is designed to minimise turbulent air flow over the leading edge. The film 20 may be under tension, to help ensure that it remains in close contact with the underlying surface of the aerodynamic surface I. Preferably the film 20 is configured such that the coefficient of friction between an inner surface of the film 20 and an adjacent outer surface of the aerodynamic surface 1 is sufficiently low to enable easy sliding of the film 20 over the outer surface of the aerodynamic surface 1. The film 20 may have a smooth external surface to give the leading edge a closely toleranced surface profile in order to minimise the turbulent effects caused by imperfections on the surface of the leading edge. Alternatively, a rough 'shark-skin' or 'lotus-leaf' profiling may be given to the film 20 to further minimise drag and/or to minimize ice build-up. The film 20 may have a close tolerance thickness distribution.

[0041] The film 20 is stretchable, at least in the chordwi se direction. Preferably the film is stretchable even at temperatures below 0°C. Preferably the film 20 has a high elastic strain. For example, the film 20 may have an elastic strain of at least 200%. In some examples the film 20 may have an elastic strain of at least 500%. Other desirable properties for the film 20 are: it is able to function in temperatures -60°C to +60°C, is resistant to erosion, is producible in large sheets, is UV/water/fuel/hydraulic fluid/oil resistant, has reasonable impact resistance (i.e. bird strike, hail, runway debris), is easy to roll, it is lightweight, is low friction (to allow sliding over the wing structure), resistant to lightning strike, easy to replace during routine maintenance, recyclable/bio-degradable; and is transparent to allow visual inspection of underlying structure. The film may comprise a polymer material, such as latex (synthetic or natural) or silicone. The film 20 may be further enhanced by applying an anti-icing coating. The film 20 could also be coated or profiled to act as an environmental protection barrier to prevent the wing from being damaged from rain or hail. The film 20 may also provide an element of bird-strike protection. In some examples the film 20 may be printed with messages and/or advertising, which can change in a scrolling manner as the film is displaced.

[0042] The aerodynamic surface 1 comprises an upper slot 14 in an upper region and a lower slot 15 in a lower region. In this example the upper slot is located at a joint between the upper wing skin 11 and the skin of the FLE structure 16, and the lower slot is located at a joint between the lower wing skin 12 and the skin of the FLE structure 16. Each slot 14, 15 provides a path for one of the ends of the film 20 to extend through into an internal space of the aerodynamic surface 1. A seal 23, 24 engages with the film 20 as it passes through each of the slots 14, 15. The purpose of the seals 23,24 is to prevent (as far as possible) air flowing through the slots 14, 15, and to minimise the size of the discontinuities on the outer external surface caused by the presence of the slots 14, 15. In other examples, the slots 14, 15 may open into spaces which are not connected. In such examples, there should not exist an issue with air flow through the slots and so the seals 23, 24 may not be present.

[0043] The aerodynamic surface 1 further comprises a film stretching and displacement mechanism, which is configured to both displace the film 20 relative to the aerodynamic surface along a chordwise direction, and stretch the film along the chordwise direction. hi the example of Figures la-b, the film stretching and displacement mechanism comprises first and second controllably rotatable rollers 21, 22 each of which is housed within an internal space of the aerodynamic surface 1. In particular the first (upper) roller 21 is housed within a first internal space to which the first slot 14 provides access and the second (lower) roller 22 is housed within a second internal space to which the second slot 15 provides access. In this particular example the first internal space and the second internal space are each part of the same internal space, which is an internal space of the FLE structure 10.

1110441 The rotation of the rollers 21. 22 may be driven by any suitable driving mechanism such as electrical, hydraulic or pneumatic driving mechanism. Any such driving mechanism may be connected to a control system of the aircraft, such that the rotation of each roller 21, 22 is individually controllable by the control system.

[0045] A first end of the film 20 is fixedly attached to the first roller 21 and a second, opposite, end of the film 20 is fixedly attached to the second roller 22. In any given operational state of the stretching and displacement mechanism, the film 20 is at least partially wound around at least one of the first and second rollers 21,22. In some operational states the film 20 is at least partially wound around both of the first and second rollers 21, 22. The stretching and displacement mechanism is configured to maintain a nominal pre-selected tension in the film 20 when the film is not being stretched. The amount of film wound around one of the rollers 21, 22 will therefore depend on the total length of the film 20 and the amount of film wound around the other roller 21, 22. In general, the more film is wound around the first roller 21 the less film is wound around the second roller 22, and vice versa.

[11046] The total length of the film 20 may be at least 50% greater than a distance on the outer surface of the aerodynamic surface between the first roller 21 and the second roller 22. In some examples the total length of the film 20 may be as small as possible whilst permitting sufficient displacement of the film for a debris-covered region 30 of the film (hereinafter referred to as a contaminated region) to be moved away from the leading edge region 16 of the aerodynamic surface 1. In some examples, the total length of the film 20 is sufficient to enable a large enough displacement of the film 20 that the contaminated region 30 does not overlap with the leading edge region 16 after the displacement. Making the length of the film 20 as small as possible advantageously minimizes the weight of the film 20 In other examples, the film 20 may be long enough to be used for multiple flight cycles without cleaning or replacement, as will be explained further below.

[0047] The first and second rollers 21, 22 are individually driven by high-torque motors (not shown) of any suitable design. Each roller 21, 22 is rotatable in both the clockwise and anti-clockwise directions, by a selected amount. The motors driving the rollers 21, 22 may be controlled by control signals received from, e.g., an avionics system of an aircraft in which the aerodynamic surface 1 is comprised. The film stretching and displacement mechanism is configured to displace the film by rotating the first roller 21 and the second roller 22. If the film 20 is desired to be displaced without simultaneously stretching it, the first and second rollers 21, 22 are rotated by the same amount, in the same direction. The film stretching and displacement mechanism is configured to stretch the film by one or more of: rotating the first roller and the second roller in the same direction by different amounts; rotating the first roller and the second roller in opposite directions by different amounts; rotating the first roller and the second roller in opposite directions by the same amount: maintaining one of the first roller and the second roller stationary and rotating the other of the first roller and the second roller.

[0048] The rollers 21, 22 may be operated so as to move the contaminated region 30 to a lower surface of the FLE structure 10. This is desirable because the aerodynamic effect of debris 31 deposited on the aerodynamic surface 1 will be less when the debris 31 is located on a lower region of the aerodynamic surface I. Figure lb shows the wing 1 after the film stretching and displacement mechanism has been operated to move the contaminated region 30 to a lower surface of the FLE structure 10. It will be appreciated that the length of film 20 wound around the first roller 21 must be at least as great as the distance by which it is desired to move the contaminated region 30, before the displacement is effected. In at least some examples it may also be possible to operate the rollers 21, 22 so as to move the contaminated region 30 to an upper surface of the FLE structure 10.

[0049] To displace the film 20 from the position shown in Figure 1 a to the position shown in Figure lb without simultaneously stretching the film 20 the first and second rollers 21, 22 are rotated anti-clockwise (in relation to the orientation shown in Figures la-b) by the same amount. Non-contaminated film is fed from the first roller 21 through the first slot 14 onto the upper surface of the FLE structure 10, while the used film is pulled through the second slot 15 and wound around the second roller 22. The contaminated region is thereby moved away from the leading edge region 16 to the position shown in Figure lb, where die contamination has less aerodynamic effect. Meanwhile, as the film 20 forms a continuous sheet, the contaminated region of film is replaced at the leading edge 16 by a section of non-contaminated film. It is noted that the rollers 21, 22 may be rotated further to move the contaminated region further away from the leading edge region 16 if required (if more film is available on the first roller 21). That is, the distance over which the contaminated region moves is directly dependent on the amount by which the rollers 21, 22 are rotated. In some examples the contaminated region 30 may be moved far enough that it passes through one of the gaps 14, 15 and is no longer on an outer surface of the wing I. If it were desired to move the contaminated region 30 instead to the upper surface of the FLE structure 10, the same process would be performed except that the first and second rollers 21, 22 would be rotated in the opposite direction (i.e. clockwise in relation to the orientation shown in Figures la-b).

I00501 Alternatively or additionally to displacing the film 20 the rollers 21, 22 may be operated to stretch the film 20 by a selected amount. The stretching may be done simultaneously with translating the contaminated region 30 away from the leading edge region 16. Alternatively or additionally, the stretching may be done after the contaminated region 30 has been moved away from the leading edge region 16. Stretching the film 20 may achieve one or both of two beneficial effects.

[00511 The first beneficial effect is removal of some or all of the debris 31. This can be achieved if the stretching is performed after the aircraft has reached a high enough altitude for the debris 31 to be frozen. The debris 31 becomes brittle when it freezes, meaning that stretching the film 20 causes some or all of the debris 31 to break up and detach from the film 20. To achieve the first beneficial effect, it may be advantageous to first displace the film 20 to move the contaminated region 30 away from the leading edge region 16, and then to stretch the film at a later time (i.e. a time by which the debris 31 is expected to be frozen). Where the film 20 is stretched with the intention of achieving the first beneficial effect, the film stretching and displacement mechanism may be operated so as to release the film 20 from the stretched state (that is, to allow to film tension to return to the nominal value) shortly after a desired amount of stretching has been achieved. To achieve maximum removal of frozen debris 31, it may be advantageous to perform the stretching operation multiple times.

I00521 The second beneficial effect is a reduction of the aerodynamic effect of the debris 31. This can be achieved if the stretching is performed at lower altitude, when the debris 31 is not frozen. Stretching the film 20 when the debris 31 is not frozen causes the shape of the debiis 31 to change. In particular, the edges of the debris 31 are expected to become flattened and spread out. The overall height of the debris 31 is also expected to be reduced. This shape change is illustrated in Figure 2. Part (i) of Figure 2 shows the debris 31 when the film 20 is in an unstretched state and part (ii) shows the debris 31 when the film 20 is in a stretched state. The flattened shape of the stretched debris 31 is expected to be less disruptive to laminar airflow over the wing 1 than the unstretched shape. Where the film 20 is stretched with the intention of achieving the second beneficial effect, the film stretching and displacement mechanism may be operated so as to maintain the film 20 in the stretched state throughout cruising flight.

I00531 To simultaneously stretch and displace the film 20, the first and second rollers 21, 22 are rotated by different amounts. This may mean that the first roller 21 is rotated clockwise by a first amount and the second roller 22 is rotated clockwise by a second, different amount. This may mean that the first roller 21 is rotated anti-clockwise by a first amount and the second roller 22 is rotated clockwise by a second, different amount. In either of these cases, the amount by which one of the first and second rollers 21.22 is rotated may be zero. That is, either one (but not both) of the first and second rollers 21, 22 may be maintained stationary during the simultaneous stretching and displacing operation. It will be appreciated that if one of the rollers 21, 22 is maintained stationary, the displacement of the film 20 that occurs is as a result of the film 20 stretching, and no additional displacement is possible. This means that only a limited amount of movement of the contaminated region is possible. This operational mode also applies to examples of the invention in which the film stretching and displacement mechanism comprises only one roller -one such example is described below with reference to Figure 5.

[0054] In the example of Figures la-b, to simultaneously stretch the film 20 and displace it to the position shown in Figure lb, both rollers 21, 22 are rotated anti-clockwise but the second roller 22 is rotated by a greater amount than the first roller 21. The greater the difference between the amounts of rotation of the first and second rollers 21, 22, the greater the amount of stretching is experienced by the film 20. The distance by which the film 20 displaces is determined by the amount of the rotation of the roller which is rotated by the smaller amount (in the example of Figures la-b this is the first roller 21).

[0055] To stretch the film 20 without simultaneously translating it, the first and second rollers 21, 22 arc rotated by the same amount but in opposite directions. In particular, according to the illustrated orientation, the first roller 21 is rotated clockwise and the second roller 22 is rotated anti-clockwise. More generally, the first and second rollers 21, 22 are rotated in directions such that the surfaces of the rollers which face the outer surface of the wing 1 move away from each other whilst the opposite surfaces of the rollers which face the interior of the wing 1 move toward each other. In other words, each roller 21, 22 is rotated in a direction such that more film becomes wound around that roller.. As noted above, stretching the film 20 without simultaneously displacing it may advantageously be performed after a separate displacing (without stretching) operation has already taken place to move the contaminated region 30 away from the leading edge region 16. However; it is also possible to stretch the film 20 and then to displace it after it has been stretched. In such examples the film 20 may be displaced whilst in a stretched state, or alternatively the film tension may be allowed to return to the nominal value (by operating the rollers in the reverse manner to how they were operated to stretch the film 20) before the displacing is performed.

[0056] The aerodynamic surface 1 may comprise multiple separate portions of elastic film 20 distributed along the span of the aerodynamic surface. In such examples, the aerodynamic surface may also comprise multiple separate film stretching and displacement mechanisms distributed along the span of the aerodynamic surface, with each portion of film being associated with a different film stretch and displace mechanism..

[0057] Figures 3a and 3b arc cross-sectional views of two alternative example aerodynamic surfaces 3, 4 according to the invention. In these examples, the aerodynamic surfaces 3, 4 are each wings with a leading edge moveable device. In particular, the wings 3, 4 each comprise a slat 51, which is attached to a wing box of the respective wing 3, 4 by any suitable attachment mechanism (not shown). In other examples the leading edge devices may he droop nose devices, or any other type of leading edge moveable device. The wing boxes 3, 4 are of the same design and each comprise upper and lower skin panels 52, 53, extending between a front spar 54 and a rear spar (not shown). Seals 43 and 44 are provided on the leading edges of the upper and lower skin panels 52, 53, which have substantially the same construction and function as the seals 23,24 of the example aerodynamic surface 1. The wing boxes and components thereof of Figures 3a-b are substantially the same in construction and arrangement. as the wing box and components thereof of the example aerodynamic surface 1.

[00581 Each slat 51 can be moved by an actuation mechanism (not shown) from a retracted position in which it abuts the respective wing box, to an extended position in which a gap is present between the slat 51 and the wing box. Figures 3a and 3b show the aerodynamic surfaces 3, 4 with the slats 51 in the extended position. The discussion of the example aerodynamic surfaces 3, 4 applies equally to other slat arrangements, for example arrangements in which the slat abuts a FLE structure of the aerodynamic surface when in the retracted position, rather than the wing box directly. As in the example of Figures la-h, the aerodynamic surfaces 3, 4 each comprise an elastic film 40 having the same properties as the film 20 described above. In these examples the film 40 is arranged on the respective aerodynamic surface 3.4 so as to maintain a closely defined surface profile, this time over the slat 51. Each example aerodynamic surface 3,4 comprises a film stretching and displacement mechanism having substantially the same construction and function as the film stretching and displacement mechanism of the example aerodynamic surface 1, except for the differences described below.

[00591 In each example aerodynamic surface 3, 4 the film 40 is able to be stretched and displaced over the external surface of the slat 51 by rotatable rollers 41a, 42a, 41b, 42b which are housed in an internal space of the respective aerodynamic surface 3, 4. Unlike in the example aerodynamic surface 1, the internal spaces of the aerodynamic surfaces 3, 4 are defined partly by the slats 51 and partly by the respective wing boxes, and only exist as substantially closed spaces when the slats 51 are in the retracted positions. When the slats 51 are in the extended position, there exist upper and lower gaps 55, 56 between each slat 51 and the respective wing box. These gaps 55, 56 allow the film 40 to be fed between the rollers 41a, 42a, 41b, 42b and the external surface of each slat 51 when the slat is in the extended position. Each slat 51 is configured (for example by having cut-out portions on its trailing edges) such that an upper slot having substantially the same configuration as the first slot 14 and a lower slot having substantially the same configuration as the second slot 15 is present when the slat 51 is in the retracted position. The upper and lower slots enable the film 40 to pass into the internal spaces of the aerodynamic surfaces 3, 4 when the slats 51 are in the retracted position.

[0060] The rollers 41a, 42a of the example aerodynamic surface 3 are substantially identical in design and construction to the rollers 41b, 42b of the example aerodynamic surface 4, and to the rollers 21, 22 of the example aerodynamic surface 1. However, the rollers are positioned differently in each of the three example aerodynamic surfaces 1, 3, 4. In the example of Figure 3a, the rollers 41a, 42a are each mounted to the structure of the slat 51 by any suitable mounting mechanism (not shown). In particular, the first roller 41a is mounted to an upper inner surface of the slat 51 and the second roller 42a is mounted to a lower inner surface of the slat 51. In this example, the slat 51 is configured such that, in the retracted position, an inner surface of the slat together with a generally forward-facing surface of the wing box defines an internal space of the aerodynamic surface 3. The rollers 41a, 42a are located within this internal space.

[0061] By contrast, in the example of Figure 3b the rollers 41b, 42b are each mounted within the same internal space of the aerodynamic surface defined by the inner surface of the slat 51 and the forward-facing surface of the wing box, but are each mounted on the wing box. In this particular example, the first roller 41b is mounted (by any suitable mechanism) to a lower surface of the upper skin panel 52 and the second roller 42b is mounted (by any suitable mechanism) to an upper surface of the lower skin panel 53. In principle, however, each roller 41h, 42b could he mounted to any suitably-located structural member, such as the front spar 54. In this example, the film 50 bridges the gaps 55, 56 which are present between the upper and lower wing skins 52, 53 and the slat 51 when the slat 51 is in the extended position. For some applications, it may not be desirable aerodynamically to block the gap between the slat and the wing box when the slat is extended, in which case the roller arrangement of the Figure 3a example is preferred. For other examples (including examples in which the leading edge device is a droop nose device) the reverse may he true, in which case the roller arrangement of the Figure 3h example is preferred.

[0062] Figure 4 shows a further alternative example aerodynamic surface 5 according to the invention. The aerodynamic surface 5 is substantially identical in many aspects to the example aerodynamic surface 1 of Figures la-b, and therefore components of the aerodynamic surface 5 which arc identical to the corresponding components of the aerodynamic surface I have been indicated in Figure 4 using the same reference numerals as used in Figures la-b and will not be further described. A complete cross-section through the aerodynamic surface 5 is shown in Figure 4, such that the rear spar 18 and FTE structure 17 are visible. The differentiating features of the example aerodynamic surface 5 of Figure 4 could also be applied to the example aerodynamic surface 4 of Figure 3b.

[0063] The primary difference between the example aerodynamic surface 5 and the example aerodynamic surface 1 is the location of the first (upper) roller 61. Rather than being positioned within the same internal space of the aerodynamic surface 5 as the second (lower) roller 22 (which is positioned substantially identically to the second roller 22 of the aerodynamic surface I), the first roller 61 is positioned within a different internal space of the aerodynamic surface 5 to the second roller 22. More particularly, the first roller 61 is positioned within an internal space of the FTE structure 17. In this example the first roller 61 is mounted (by any suitable mechanism) to the rear spar 18. The location of the first slot 64 of the aerodynamic surface 5 is consequently also shifted rearward compared to the location of the first slot 14 of the aerodynamic surface 1. In particular, the first slot 64 is located at a join between the upper skin panel 11 and the FTE structure 17.

[0064] The relatively rearward location of the first slot 64 means that the elastic film covers a relatively larger amount of the outer surface of the aerodynamic surface 5 (as compared with the example of Figures la-h). The film 20 may cover approximately 50% of the outer surface of the aerodynamic surface S. The film 20 may cover up to 50% of the "wetted" outer surface of the aerodynamic surface 5. The film 5 covers the upper skin panel 11 as well as the FLE structure 10. Consequently, the total length of the film 20 may be greater in the aerodynamic surface 5 than in the aerodynamic surface 1.

[0065] The relatively rearward location of the first slot 64 is advantageous for maintaining laminar flow, and thereby reducing drag. This is because the slot is a discontinuity in the upper region of the aerodynamic surface which could cause a transition from laminar to turbulent flow. It is aerodynamically advantageous for this transition to occur as far aft as possible.

[00661 Figure 5 is a cross-sectional view of a further alternative example aerodynamic surface 6 according to the invention. The aerodynamic surface 6 is substantially identical in many aspects to the example aerodynamic surface 1 of Figures la-h. and therefore components of the aerodynamic surface 5 which are identical to the corresponding components of the aerodynamic surface 1 have been indicated in Figure 5 using the same reference numerals as used in Figures la-b and will not be further described. The differentiating features of the example aerodynamic surface 6 of Figure 5 could also be applied to the example aerodynamic surface 4 of Figure 3b or the example aerodynamic surface 5 of Figure 4.

[00671 The primary difference between the example aerodynamic surface 6 and the example aerodynamic surface 1 is that the first (upper) roller is omitted. Instead, an upper edge 64 of the film 20 is fixedly attached to the aerodynamic surface 6. hi the illustrated example the edge 64 is attached to an outer surface of the upper skin panel 11. In other examples the edge 64 could be attached to the FLE structure 16, or an FTE structure (not shown). Omitting the first roller means that the options for how the film 20 can be stretched and displaced are limited. In particular, only operational modes equivalent to those described above in relation to Figures la-b in which the first roller 21 is maintained stationary can be used. It will be appreciated that stretching and displacement of the film 20 cannot be performed independently in this example.

[0068] However; omitting the first (upper) roller is advantageous because it simplifies the film stretching and displacement mechanism, thus reducing its weight, and also because the need for a slot in the upper region of the aerodynamic surface 6 is eliminated. It is expected that it would be possible to achieve a sufficiently smooth surface at the attachment location of the edge 64, sufficient that this join would not cause a transition from laminar to turbulent flow.

[0069] Figure 6 shows an example aircraft 600 comprising example aerodynamic surfaces according to the invention. In particular, each wing 601a, 601b of the aircraft 60 comprises an aerodynamic surface according to the invention, and may have any or all of the features of the example aerodynamic surfaces 1, 3, 4, 5, 6 described above. The two wings 601a, 601b arc substantially identical, except for being mirror images of each other, and the film stretching and displacement mechanisms of each wing may typically be operated simultaneously, in the same manner, during the operation of the aircraft 600. The aircraft also comprises further aerodynamic surfaces, namely two horizontal stabilizers 602a, 602b, a vertical stabilizer 603, and two nacelles 604a, 604b. Any or all of these further aerodynamic surfaces may comprise an aerodynamic surface according to the invention. The illustrated example aircraft 600 is a commercial airliner, although the invention may equally be applied to any other aircraft having at least one aerodynamic surface.

[0070] The aircraft 600 further comprises various control systems (not shown). One or more of these control systems may be configured, in conjunction with appropriate sensors also provided on the aircraft, to monitor the elastic films for contamination and/or damage. Such monitoring may be performed either directly by examining the film surface, or indirectly by monitoring the efficiency of the aircraft in flight. An automated control system may be provided on the aircraft 600 that is configured to operate a film stretching and displacement mechanism to displace and/or stretch the film 20 when contamination/damage is detected. Alternatively or additionally, such a control system may be configured to operate the film stretching and displacement mechanism to displace and/or stretch the film at pre-determined points in a flight cycle (such as when a pre-determined altitude is reached, or when a certain phase of the flight cycle is entered). In some examples the film stretching and displacement mechanisms may be directly operated by aircraft crew.

[0071] When the aircraft 600 takes off, it passes through a region (from ground level up to a height of approximately 600 metres) where insects are widespread. When collisions occur, the insects impact the films on the wings 601a, 601b across a relatively narrow region at the leading edge of each wing 601a, 601b, creating a correspondingly narrow band of debris (a contaminated region) on each of the films 20. The contaminated regions 30 may be contained within the leading edge regions 16 of each wing, or may overlap with the leading edge regions. The contaminated regions, being positioned precisely at the leading edge of the wing 1, could prevent or hamper the achievement of a laminar boundary layer over the aerodynamic surface 601a, 60 1 b To avoid this, the film stretching and displacement mechanism associated with each of the wings 601a, 601b can be operated (e.g. by a control system of the aircraft 600), in any of the manners described above in relation to Figures la-b, to move the contaminated regions away from the leading edge regions to different parts of the wings 601a, 601b 1 where the debris will have less aerodynamic effect. This may typically be done after the aircraft 600 has risen above the insect-filled region, but before the cruise phase has begun.

[0072] Alternatively or additionally, the Film stretching and displacement mechanisms can he operated to stretch the films, in any of the manners described above in relation to Figures la-b, in order to further mitigate the aerodynamic effects of the debris. The stretching will typically be done after the aircraft has risen above the insect-filled region, but before (or shortly after, if it is desired to wait until the debris has become frozen) the cruise phase has begun. The stretching may be performed multiple times.

[0073] When the aircraft 600 comes in to land, it again passes through the insect-filled region. Again, collisions with insects occur and contamination builds up on the leading edge regions of the wings 601a, 601b. If the films have not been displaced relative to their positions during cruise, then the leading edge regions will coincide with different regions of the films from the regions which they coincided with during take-off, due to the displacement of the films effected by the film stretching and displacement mechanisms after take-off. A further contaminated region is thereby created on each film. However; for at least some applications it may be desirable to operate the film stretching and displacement mechanisms to displace the films back to the position they had during take-off, before the aircraft passes through the insect-filled region. This means that the previously-contaminated region becomes contaminated again, and the rest of the films remain pristine. This may enable the time period between full cleaning or replacement of the films to be extended.

[0074] After landing and before the next flight of the aircraft 600, any of the displacement operations described above in relation to Figures la-b may be performed to move the contaminated regions (and/or the further contaminated regions) away from the leading edge regions of the wings 601a, 601b. Depending on the lengths of the films, whether or not contaminated regions are "reused" for landing, and the conditions experienced by the aircraft during its operation (flying through clouds and rain is expected to have a cleaning effect) it may be possible for the aircraft 600 to undergo multiple flight cycles before there is not enough clean film left to achieve laminar flow during cruise. If there is not enough clean film left to achieve laminar flow during cruise, this typically means that it is not possible to operate the film stretching and displacement mechanisms to position the films such that the regions of film encompassed by the leading edge regions are free of debris. During at least sonic periods whilst the aircraft is on the ground. each entire film may be cleaned or replaced, so that the films no longer comprise any contaminated regions.

[0075] In examples in which the aircraft 600 comprises further aerodynamic structures according to the invention, the film stretching and displacement mechanisms of those further aerodynamic structures may be operated in substantially or identically the same manner as the film stretching and displacement mechanisms comprised in the wings 601a, 601b during the operation of the aircraft 600.

[0076] Figure 7 illustrates a method 700 for removing debris from an aerodynamic surface. The aerodynamic surface may be any of the example aerodynamic surfaces described above, and/or any aerodynamic surface of the example aircraft. 600, and/or any aerodynamic surface of any other aircraft which may accumulate debris during its operation.

[0077] A first block 701 of the method 700 comprises providing a stretchable material on an outer surface of a leading edge part of the aerodynamic surface. The stretchable material may be an elastic film 20, 40 according to the above-described examples, and may be provided on the aerodynamic surface in any of the manners described above.

[0078] A second block 702 of the method 700 comprises operating the aerodynamic surface such that debris becomes deposited on a region of the stretchable material. The debris may typically become deposited on a region of the stretchable material which is present on a leading edge region of the aerodynamic surface. Operating the aerodynamic surface such that. debris becomes deposited on a region of the stretchable material may comprise an aircraft. in which the aerodynamic surface is comprised flying through a region in which many insect are present, and or in which atmospheric conditions cause ice to accumulate on the aerodynamic surface. Operating the aerodynamic surface as required by block 702 may comprise operating an aircraft in which the aerodynamic surface is comprised in the manners described above in relation the example aircraft 600 of Figure 6.

[0079] A third block 703 of the method 700 comprises stretching the stretchable material along a chordwise direction of the aerodynamic surface. The stretching may be performed by a film stretching and displacement mechanism comprised in the aerodynamic surface, which may have the features of any of the example film stretching and displacement mechanisms described above in relation to Figures la-b, 3a-b, 4 and 5. The stretching may be performed in any of the manners described above in relation to Figures la-b. The performance of block 703 may be performed under the control of a control system of an aircraft in which the aerodynamic surface is comprised. Block 703 may be performed at a time when the debris is frozen. Block 703 may be performed in response to one or more predefined criteria being met. Such pre-defined criteria may include any or all of: altitude, flight phase, aircraft speed, temperature, elapsed flight time, Mach number, Coefficient of Lift, state of the boundary layer, or the like. Block 703 may be performed in response to the detection of debris on the aerofoil. Block 703 may be performed in response to a manual command, e.g. from the flight crew of an aircraft in which the aerodynamic surface is comprised.

[0080] A fourth, optional block 704 of the method 700 comprises translating the stretchable material relative to the aerofoil outer surface along a chordwise direction relative to the aerodynamic surface. The translating may be performed by a film stretching and displacement mechanism comprised in the aerodynamic surface, which may have the features of any of the example film stretching and displacement mechanisms described above in relation to Figures la-b, 3a-b, 4 and 5. The translating may be performed in any of the manners described above in relation to Figures la-b. The performance of block 704 may be performed under the control of a control system of an aircraft in which die aerodynamic surface is comprised. Block 704 may he performed in response to one or more predefined criteria being met. The pre-defined criteria may be (but need not be) the same as the predefined criteria for the performance of block 703. The pre-defined criteria for performing block 704 may include any or all of: altitude, flight phase, aircraft speed, temperature, elapsed flight time, Mach number, Coefficient of Lift, state of the boundary layer, or the like. Block 704 may be performed in response to the detection of debris on the aerofoil. Block 704 may be performed in response to a manually input command, e.g. from the flight crew of an aircraft in which the aerodynamic surface is comprised. Block 704 may be performed simultaneously with block 703. Block 704 may be performed before or after block 703.

[0081] Although the invention has been described above with reference to one or more preferred examples or embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

[0082] Although the invention has been described above mainly in the context of a fixed-wing aircraft application, it may also be advantageously applied to various other applications, including but not limited to applications on vehicles such as helicopters, drones, trains, automobiles and spacecraft.

[0083] Where the term "or" has been used in the preceding description, this term should be understood to mean -and/or", except where explicitly stated otherwise.

Claims

CLAIMS: 1. An aerodynamic surface comprising: an elastic film disposed on the aerodynamic surface such that the film covers at least a leading edge region of the aerodynamic surface; a film stretching and displacement mechanism for displacing the film relative to the aerodynamic surface along a chordwise direction and for stretching the film along a chordwise direction.
2. An aerodynamic surface according to claim 1, wherein the film covers an upper region of the aerodynamic surface immediately aft of the leading edge region.
3. An aerodynamic surface according to claim 1 or claim 2, wherein the aerodynamic surface comprises a wing box and the film covers an upper skin panel of the wing box.
4. An aerodynamic surface according to any preceding claim, comprising a leading edge moveable device, wherein the leading edge region of the aerodynamic surface is formed by an outer surface of the moveable device.
5. An aerodynamic surface according to any preceding claim, wherein the aerodynamic surface comprises a lower slot in a lower region of the aerodynamic surface, and wherein a first end or the film extends through the lower slot into an internal space of the aerodynamic surface.
6. An aerodynamic surface according to claim 5, wherein the aerodynamic surface compiises an upper slot in an upper region of the aerodynamic surface, and wherein a second end of the film extends through the upper slot into an internal space of the aerodynamic surface.
7. An aerodynamic surface according to claim 6, wherein the upper slot is located at a join between a fixed leading edge structure of the aerodynamic surface and a wing box of the aerodynamic surface.
8. An aerodynamic surface according to claim 6, wherein the upper slot is located at a join between a fixed trailing edge structure of the aerodynamic surface and a wing box of the aerodynamic surface.
9. An aerodynamic surface according to any preceding claim, wherein the film stretching and displacement mechanism comprises a first roller fixedly attached to a first end of the film and a second roller fixedly attached to a second end of the film, and is configured to displace the film by one or more of: rotating the first roller and the second roller in the same direction, by the same amount; rotating the first roller and the second roller in the same direction by different amounts; rotating the lirst roller and the second roller in opposite directions by different amounts; maintaining one of the first roller and the second roller stationary and rotating the other of the first roller and the second roller; and is configured to stretch the film by one or more of: rotating the first roller and the second roller in the same direction by different amounts; rotating the first roller and the second roller in opposite directions by the same amount; rotating the first roller and the second roller in opposite directions by different amounts; maintaining one of the first roller and the second roller stationary and rotating the other of the first roller and the second roller.
10. An aerodynamic surface according to claim 8, wherein a total length of the film is at least 50% greater than a distance on an outer surface of the aerodynamic surface between the first roller and the second roller.
11. An aerodynamic surface according to claim 5, wherein a second end of the film is fixedly attached to an upper region of the aerodynamic surface, and wherein the film stretching and displacement mechanism comprises a roller fixedly attached to the first end of the film and is configured to simultaneously displace arid stretch the film by rotating the roller.
12. An aerodynamic surface according to any preceding claim, wherein the film is configured such that the coefficient of friction between an inner surface of the film and an outer surface of the aerodynamic surface is low enough to permit sliding therebetween.
13. An aerodynamic surface according to any preceding claim, comprising multiple separate portions of elastic film and multiple separate film stretching and displacement mechanisms distributed along the span of the aerodynamic surface, wherein each portion of film is associated with a different one of the film stretching and displacement mechanisms.
14. An aerodynamic surface according to any preceding claim, wherein the aerodynamic surface is an aircraft wing.
15. An aircraft comprising an aerodynamic surface according to any preceding claim.
16. A method for removing debris from an aerodynamic surface, the method comprising: providing a stretchable material on an out.er surface of a leading edge part of the aerodynamic surface; operating the aerodynamic surface such that debris becomes deposited on a region of the stretchable material; aml stretching the stretchable material along a chordwise direction of the aerodynamic surface.
17. A method according to claim 16, further comprising: displacing the stretchable material relative to the aerodynamic surface along a chordwisc direction relative to the aerodynamic surface.
18. A method according to claim 17, wherein displacing the stretchable material is performed simultaneously with stretching the stretchable material.
19. A method according to claim 17, wherein displacing the stretchable material is performed before stretching the stretchable material.
20. A method according to any of claims 16 to 19, wherein stretching the stretchable material is performed at a time when the debris is frozen.