Leading edge system for an aircraft, provided with an assembly for absorbing impacts

Abstract

The system (10) comprises a casing (12) having an outer surface (12a) and an inner surface (12b), internally defining a cavity (14), and comprising a front portion (20) susceptible of undergoing a collision with a striking mass (M) and being penetrated and crossed by the latter. There is an assembly (22) for absorbing impacts, situated in the cavity (14) downstream of the front portion (20). The assembly (22) comprises a cloth (24; 26; 28) separate and spaced apart from said front portion (20), joined to the inner surface (12b) of the casing (12), and configured to be hit by the striking mass (M) crossing the front portion (20), so as to envelop and contain the striking mass (M) in order to absorb the energy resulting from the collision. The cloth (24; 26; 28) has its periphery (24a, 24b; 26a, 26b; 28a, 28b) glued in a distributed manner to the inner surface (12b) of the casing (12). Furthermore, the cloth (24; 26; 28) is loose and can freely unfurl in the cavity (14).

Description

[0001] TITLE: "LEADING EDGE SYSTEM FOR AN AIRCRAFT, PROVIDED WITH AN ASSEMBLY FOR ABSORBING IMPACTS"

[0002] * * *

[0003] DESCRIPTION

[0004] Technical field

[0005] The present invention relates to a leading edge system for an aircraft, wherein such system is provided with an assembly for absorbing impacts.

[0006] Technical background

[0007] When in flight, aircraft may undergo undesired highspeed collisions with striking masses, which may represent a major issue in terms of safety, particularly while taking off and landing. Such undesired collisions include, for example, those occurring between an aircraft and a bird, referred to as "bird strikes". Such collisions have particularly important consequences when they occur in proximity to the aircraft' s leading edges.

[0008] It is in fact of paramount importance to ensure that a structure undergoing a bird strike can still guarantee a safe flight until landing. In particular, the composite structures employed in the aircraft industry have a more fragile behaviour than metal structures, and it is therefore more difficult to absorb the energy of an impact. Moreover, latest-generation structures are also required to contribute to reducing fuel consumption thanks to their low weight and their ability to facilitate a natural laminar flow, while also being particularly economical.

[0009] In an attempt to limit the damages and effects caused by such collisions, some aircraft parts, and particularly leading edge systems, are generally provided with impactabsorbing assemblies to ensure flight safety.

[0010] US 10, 556, 701 B2 describes an energy absorbing arrangement of a leading edge, which comprises an inner barrel comprising a centreline axis, an outer barrel, a webbing extending between the outer barrel and the inner barrel. The webbing is configured to be offset from the nose lip by a distance, the webbing being folded together to form a plurality of folds, the plurality of folds being stitched together via a plurality of stitches, wherein the webbing is configured to absorb energy from an object in response to the object passing through the nose lip and applying a force to the webbing.

[0011] However, the arrangement disclosed in US 10, 556, 701 B2 has a few drawbacks. For example, the fact that there are stitches that rigidly constrain the webbing to the outer barrel and to the inner barrel creates hard points in the structure. Such hard points will tend to cause punctual stiffening when the webbing is hit by an object, resulting in breakage of the webbing and adversely affecting the ability to absorb impacts.

[0012] For completeness' sake, further prior-art documents related to leading edge systems are mentioned below.

[0013] US 8, 322, 657 B2 describes a panel having an impact protection membrane. In particular, there is an aircraft leading edge panel having an outer aerodynamic surface and an inner surface carrying the elastomeric impact protection membrane. The membrane comprises a woven or knitted fabric, which is impregnated with an elastomeric material. The membrane and the panel may be bonded by an adhesive or cocured to bond the membrane to the panel. The membrane provides impact protection to the panel by de-bonding from the face of the panel and absorbing at least part of the energy of an object impacting the panel.

[0014] EP 3 248 864 Al describes an aerodynamic surface for an aircraft comprising a torsion box having a front spar, and a composite leading edge section that comprises an outer surface shaped with an aerodynamic leading edge profile, an inner surface internally arranged with respect to the outer surface, and a blanket arranged between the outermost point of the inner surface and the front spar, essentially acting as a barrier. The blanket is made of fibre material and is joined to (and also kept under tension by) at least two opposing areas of the inner surface for absorbing a bird strike, to prevent damage to the front spar. However, the blanket is kept under tension within the opposing areas of the inner surface.

[0015] EP 1 963 095 Bl describes a device for protecting an aircraft structure, which comprises a skin made of GLARE ( GLAss- fibre REin forced aluminium) . When a force acts upon it, the skin deforms to absorb the force, so that damage to the aircraft structure is prevented. Therefore, the skin behaves like a substantially rigid barrier.

[0016] EP 2 130 762 Bl describes a leading edge structure for wing structures and empennage, comprising an outer shell suitable to define a front portion of an airfoil. The outer shell is formed of a bent plate made of fibre-reinforced thermoplastic resin composite material. The structure further comprises an inner shell having a convex profile that is oriented in the same direction as the profile of the outer shell. The inner shell is formed of a bent plate of fibre-reinforced thermoplastic resin composite material and is bonded to the outer shell at the longitudinal edges thereof. There is at least one reinforcing element transversally extending to connect the outer shell and inner shell to each other, which is formed of at least one piece of fibre-reinforced resin composite material and is fixed at opposite ends to the outer shell and inner shell, respectively. In this case as well, however, impact absorption is provided through the adoption of a substantially rigid barrier.

[0017] EP 2 196 309 Bl describes a leading edge structure that comprises two or more multilayer panels at least partially overlapping and suitably curved with at least partially congruent concavities. Each multilayer panel includes at least the following three layers: a first layer consisting of a metal foil, a second intermediate layer of fibre-glass securely fixed to the first layer, and a third metal honeycomb layer securely fixed to the second layer. This document does not consider the use of cloths, membranes, or the like for absorbing the impact of an external element.

[0018] EP 2 995 552 Al describes an airfoil portion that comprises an outer skin member and an inner stiffening member. Either the outer skin member or the inner stiffening member, or both, are arranged to delimit a chamber. The chamber is configured to contain an inner pressure, wherein the inner pressure differs from a pressure external to the chamber. The stiffening member behaves like a rigid barrier to absorb the impact of an external element.

[0019] US 2017 / 0259902 Al describes an aircraft aerodynamic surface that includes an upper skin, a lower skin, and a front spar, and a leading edge having an external shell and an impact resisting structure. The external shell may be shaped with an aerodynamic leading edge profile, being configured to provide Laminar Flow Control (LFC) to the leading edge. The impact resisting structure is transversally arranged between the external shell and the front spar, and is configured for absorbing a bird strike to prevent damage to the front spar. Also, at least one of the external shell and the impact resisting structure is fitted with the upper and lower skins . In this case as well, a rigid construction is used to absorb the impact of external elements .

[0020] US 6, 627,296 Bl describes an impact resistant structure which comprises a substantially sinusoidally shaped elastically collapsible open-celled fluted layer, whereby in an impact event, the flutes are free to move, absorbing the impact forces due to the flutes resiliently collapsing in an accordion-like fashion, and returning substantially to the original shape after the impact without permanent damage to the structure. In this document as well, the use of cloths for impact absorption is not taken into account.

[0021] Lastly, US 7, 923, 096 describes a leading edge system having the technical features mentioned in the preamble of the independent claim.

[0022] Summary of the invention

[0023] It is one object of the present invention to provide a leading edge system which can solve the problems suffered by the prior art. In particular, according to the present invention, a leading edge system is provided which offers improved impact absorption performance over those made in accordance with the prior art.

[0024] According to one aspect of the present invention, this and other objects are achieved through a leading edge system having the technical features set out in the appended independent claim.

[0025] Due to the fact that the system comprises an assembly for absorbing impacts, which in turn comprises at least one cloth with its periphery glued in a distributed manner to the inner surface of the system casing, and to the fact that the cloth is loose and can freely unfurl in the cavity defined by the casing, the energy of a striking mass can be effectively absorbed by the cloth. In particular, energy absorption occurs through an improved bagging effect caused, for example, by deployment of the cloth and / or by phenomena of gradual and progressive separation of its periphery from the inner surface of the casing. In particular, the system essentially avoids any hard points (typically created through the use of mechanical connection members and / or by application of stitched areas) for joining the cloths to the inner surface of the casing, thus allowing for diffusive dissipation of kinetic energy and resulting more effective than the systems made in accordance with the prior art.

[0026] It is understood that the appended claims are an integral part of the technical teachings provided in the following detailed description of the present invention. In particular, the appended dependent claims define some preferred embodiments of the present invention that include some optional technical features.

[0027] One advantage of the system made in accordance with the present invention lies in the fact that the assembly for absorbing impacts is light, simple, and economical to manufacture .

[0028] Another advantage of a system made in accordance with the present invention lies in the fact that the system for absorbing impacts can be installed without requiring any intervention on the outer surface of the system casing, in particular avoiding the use of any fastening and / or connection means crossing said casing transversally. Installation is thus possible also in a casing made as one piece (e.g. of the "one-piece inlet" type) . A further advantage of a system made in accordance with the present invention lies in the fact that it is compatible with the use of electric anti-icing protection devices.

[0029] According to another aspect of the present invention, a leading edge system for an aircraft is provided, wherein such system comprises:

[0030] - a casing having an outer surface and an inner surface, internally defining a cavity, and comprising a front portion susceptible of undergoing a collision with a striking mass and being penetrated and crossed by the latter, and

[0031] - an assembly for absorbing impacts, situated in the cavity downstream of said front portion, wherein said assembly comprises a plurality of cloths arranged in succession one after the other downstream of the front portion, separate and spaced apart from the front portion, wherein each cloth is joined to the inner surface of said casing and is configured to be hit by said striking mass crossing the front portion, so as to envelop and contain the striking mass in order to absorb the energy resulting from the collision; wherein each cloth has at least one part of its periphery glued in a distributed manner to the inner surface of the casing; wherein each cloth is loose and free to unfurl in the cavity; and wherein, in said succession of cloths, each next cloth has fewer waves than the associated preceding cloth.

[0032] Further features and advantages of the present invention will become apparent in light of the following detailed description, provided herein merely as a nonlimiting example and referring, in particular, to the annexed drawings as summarized below. Brief description of the drawings

[0033] Figure 1 is a partial longitudinal sectional view of a leading edge system for an aircraft, in particular for an engine nacelle. The system includes an assembly for absorbing impacts, and is made in accordance with an exemplary embodiment of the present invention, which employs a plurality of cloths.

[0034] Figure 2 is a magnified partial view of the system shown in Figure 1, showing an exemplary mode of connection between the periphery of a plurality of cloths of the assembly for absorbing impacts and the inner surface of a system casing, in particular of an outer barrel.

[0035] Figure 3 is a partial longitudinal sectional view of the same system shown in Figure 1, wherein a striking mass has penetrated through a front portion of the system casing and is hitting the cloths of the assembly for absorbing impacts .

[0036] Figure 4 is a perspective view of a leading edge system for an aircraft, in particular for an airfoil. The system includes an assembly for absorbing impacts, and is made in accordance with an exemplary embodiment of the present invention, which employs a plurality of cloths.

[0037] Figure 5 is a side view of a phase of a bird strike test carried out on a leading edge system for an aircraft, obtained in accordance with an exemplary embodiment of the present invention. In particular, in Figure 5 the system is shown during a phase before the bird strike.

[0038] Figure 6 is a side view showing a phase of the same bird strike test that follows the one shown in Figure 5, wherein the system is shown when a bird hits the cloth located in the rearmost position.

[0039] Figure 7 is a side view of a phase of the same bird strike test that follows the one shown in Figure 6, wherein all cloths are fully extended backwards.

[0040] Figure 8 is a side view of a phase of the same bird strike test that follows the one shown in Figure 7, showing the end of the test.

[0041] Figures 9 and 10 are partial and longitudinal sectional views corresponding, respectively, to Figure 1 and Figure 3, showing some preferred dimensional parameters of some components and elements of a system made in accordance with an exemplary embodiment of the present invention. In Figure 10, for clarity, the cloths of said system are omitted. Detailed description of the invention

[0042] With reference to Figures 1 to 3, numeral 10 designates as a whole a leading edge system for an aircraft, made in accordance with an exemplary embodiment of the present invention. In particular, system 10 as shown herein by way of example concerns the leading edge of an engine nacelle. However, as will become apparent to a person skilled in the art while reading the present detailed description, the system may also be used for different leading edges of an aircraft. More generally, this system may be incorporated into any aerodynamic component of an aircraft, e.g. selectable from the group including: an engine nacelle, an airfoil, a tail, a rudder, and a radome, without however departing from the scope of the present invention.

[0043] In the detailed description that follows, terms or expressions such as "axial" or "axially", "longitudinal" or "longitudinally", "radial" or "radially", "transversal" or "transversally", "inwards" or "internally", and "outwards" or "externally" refer to a central axis (not shown) of the engine nacelle to which system 10 belongs.

[0044] System 10 comprises a casing 12 susceptible of undergoing a collision with an external striking mass M, which is shown in Figure 3 only. Striking mass M may be, for example, a bird during a so-called bird strike event. Casing 12 has an outer surface 12a and an inner surface 12b, and internally defines a cavity 14. Outer surface 12a and inner surface 12b are numbered in Figure 2 only.

[0045] In the embodiment illustrated herein, casing 12 has a substantially tubular shape, e.g. a barrel-like or cask-like shape, and comprises, in a per se known manner, an outer barrel 16 substantially cylindrical in shape and situated in a transversally external position. Furthermore, casing 12 comprises an inner barrel 18 substantially cylindrical in shape and situated in a transversally internal position. Outer barrel 16 and inner barrel 18 define therebetween an annular interspace that forms cavity 14 of casing 12. Furthermore, casing 12 comprises a nose lip 20 that annularly connects the front ends of outer barrel 16 and inner barrel 18, closing cavity 14 at the front. Casing 12 further comprises a bulkhead 21 that closes cavity 14 at the rear.

[0046] Note that Figure 1 shows only a part of the longitudinal section of casing 12 of system 10, particularly the top part thereof. Its bottom part (not visible in the drawings) is symmetrical relative to the central axis of the engine nacelle .

[0047] System 10 further comprises an assembly 22 for absorbing impacts. As shown in Figure 3, assembly 22 is situated in cavity 14 downstream of a front portion of casing 12 which is susceptible of undergoing a collision with a striking mass M and being penetrated and crossed by the latter; in the illustrated embodiment, said front portion consists of nose lip 20. In particular, assembly 22 protects bulkhead 21 from a collision with striking mass M. Preferably, assembly 22 comprises a plurality of cloths 24, 26, 28, which are separate and spaced apart from nose lip 20 and are joined to inner surface 12b of casing 12. Cloths 24, 26, 28 are configured to be hit by striking mass M as it crosses the front portion consisting of nose lip 20, so as to envelop and contain striking mass M in order to absorb the energy resulting from the collision. In Figure 3, by way of example, the trajectory followed by striking mass M is indicated by a dashed-dotted arrow intersecting nose lip 20.

[0048] In particular, cloths 24, 26, 28 are arranged in succession one after the other downstream of the front portion consisting of nose lip 20. In the illustrated embodiment, the plurality of cloths comprises three cloths, including a front cloth 24, an intermediate cloth 26, and a rear cloth 28. Front cloth 24 is situated downstream of nose lip 20, intermediate cloth is situated immediately downstream of front cloth 24 and immediately upstream of rear cloth 28, and rear cloth 28 is situated immediately downstream of intermediate cloth 26 and upstream of bulkhead 21.

[0049] Alternatively to the above, as will be apparent to a person skilled in the art, further embodiment not illustrated herein may use an assembly comprising just a single cloth or a different (greater or smaller) number of cloths.

[0050] In the embodiment illustrated herein, since assembly 22 is to be installed between outer barrel 16 and inner barrel 18, each one of cloths 24, 26, 28 has an annular shape that defines a radially external periphery 24a, 26a, 28a and a radially internal periphery 24b, 26b, 28b, which are glued in a distributed manner to inner surface 12b of casing 12. The number of cloths, the distance between the cloths, and the bonding lengths can be determined as a function of the estimated mass and impact speed of striking mass M.

[0051] By way of non-limiting example, cloths 24, 26, 28 may be continuous throughout their extension (in particular, having an annular shape in the illustrated embodiment) , or may be made up of a plurality of overlapping segments or parts. In particular, in embodiments not shown in the drawings, overlapping may occur in the same cloth, taken singularly, with a plurality of cloth segments, wherein each cloth segment has an edge portion laterally or angularly overlapping (and, for example, fixed to it by glueing or, alternatively, by means of other systems) an associated edge portion of the next cloth segment. Optionally, the edge portions belonging to the cloth segments that make up a preceding cloth may be laterally or angularly offset from the edge portions belonging to the cloth segments that make up the next cloth; in particular, when the cloths have an annular shape, said edge portions may form some sort of clocking arrangement. In particular, peripheries 24a, 26a, 28a, 24b, 26b, 28b are joined to inner surface 12b without the use of any mechanical connection elements and / or without application of stitches.

[0052] With particular reference to Figure 2, a dashed-dotted line shows the distributed bonding between radially external peripheries 24a, 26a, 28a and inner surface 12b of casing 12 (in particular, of outer barrel 16) . In particular, radially external peripheries 24a, 26a, 28a are glued in a distributed manner to outer barrel 16, while radially internal peripheries 24b, 26b, 28b are glued in a distributed manner to inner barrel 18. As will be apparent to a person skilled in the art, each one of cloths 24, 26, 28 generally has its periphery (radially external periphery 24a, 26a, 28a and / or radially internal periphery 24b, 26b, 28b) glued in a distributed manner to inner surface 12b of casing 12. In more detail, each one of cloths 24, 26, 28 preferably has it entire periphery (radially external periphery 24a, 26a, 28a and / or radially internal periphery 24b, 26b, 28b) glued in a distributed manner to the entire inner surface of casing 12.

[0053] With particular reference to Figure 2, each one of radially external peripheries 24a, 26a, 28a defines a substantially cylindrical lateral wall extending in the direction of the longitudinal axis (not shown) of the engine nacelle. In turn, each one of radially internal peripheries 24b, 26b, 28b defines a substantially cylindrical lateral wall extending in the direction of the longitudinal axis of the engine nacelle. The radially external face of the lateral walls defined by radially external peripheries 24a, 26a, 28a is annularly glued in a distributed manner to outer barrel 16, whereas the radially internal face of the lateral walls defined by radially internal peripheries 24b, 26b, 28b is annularly glued in a distributed manner to inner barrel 18.

[0054] Furthermore, cloths 24, 26, 28 are loose and free to unfurl in the cavity 14 when they are hit by striking mass M. In other words, the width of cloths 24, 26, 28 in the transversal direction is oversized, being greater than the width of cavity 14, which, in the illustrated embodiment, is defined by the transversal distance d between outer barrel 16 and inner barrel 18. In the illustrated embodiment, in the succession of cloths, the ratio between the width of each next cloth 26, 28 and the width of cavity 14 is lower than the ratio between the width of the associated preceding cloth 24, 26 and the width of cavity 14.

[0055] Front cloth 24 and intermediate cloth 26 have a plurality of folds or waves configured to freely unfurl when striking mass M hits cloths 24, 26. In particular, intermediate cloth 26 has fewer waves than front cloth 24. In more general terms, with particular reference also to other embodiments not shown herein, in the succession of cloths, each next cloth (which in the illustrated embodiment is intermediate cloth 26) has fewer waves than the associated preceding cloth (which in the illustrated embodiment is front cloth 24 ) .

[0056] In the embodiment illustrated in Figures 1 to 3, the waves are formed in a respective loose portion (not numbered) belonging to each one of cloths 24, 26. Each loose portion is situated centrally relative to the respective radially external periphery 24a, 26a and the respective radially internal periphery 24b, 26b of the associated cloth 24, 26. In particular, the loose portion of each cloth 24, 26 is formed substantially as a central annular portion situated between said peripheries 24a, 26a and 24b, 26b. Moreover, each loose portion is configured to be free to extend and unfurl in cavity 14 when the striking mass hits the respective cloth 24, 26.

[0057] Preferably, in the succession of cloths 24, 26, 28, each next cloth 26, 28 has a smaller area than the associated preceding cloth 24, 26. In the illustrated embodiment, front cloth 24 has a larger area than intermediate cloth 26. In turn, intermediate cloth 26 has a larger area than rear cloth 28.

[0058] In particular, as will be further described below, peripheries 24a, 24b, 26a, 26b, 28a, 28b of consecutive cloths 24, 26, 28 partially overlap (and are glued to) each other .

[0059] Preferably, in the succession of cloths 24, 26, 28, radially external periphery 26a, 28a of each next cloth 26, 28 is also glued (in addition to being glued to inner surface 12b of casing 12, in particular of outer barrel 16) to radially external periphery 24a, 26a of the associated preceding cloth 24, 26. Likewise, radially internal periphery 26b, 28b of each next cloth 26, 28 is also glued (in addition to being glued to inner surface 12b of casing 12, in particular of inner barrel 18) to radially internal periphery 24b, 26b of the associated preceding cloth 24, 26. In the illustrated embodiment, radially external periphery 26a of intermediate cloth 26 is also glued to radially external periphery 24a of front cloth 24; likewise, radially internal periphery 26b of intermediate cloth 26 is also glued to radially internal periphery 24b of front cloth 24. Furthermore, radially external periphery 28a of rear cloth 28 is also glued to radially external periphery 26a of intermediate cloth 26; likewise, radially internal periphery 28b of rear cloth 28 is also glued to radially internal periphery 26b of intermediate cloth 26.

[0060] Preferably, in the succession of cloths 24, 26, 28, the initial or proximal portion of radially external periphery 26a, 28a of each next cloth 26, 28 is glued to the final or distal portion of radially external periphery 24a, 26a of each preceding cloth 24, 26. In addition, the initial or proximal portion of radially internal periphery 26b, 28b of each next cloth 26, 28 is glued to the final or distal portion of radially internal periphery 24a, 26a of each preceding cloth 24, 26. In the illustrated embodiment, the initial or proximal portion of radially external periphery 26a of intermediate cloth 26 is glued to the final or distal portion of radially external periphery 24a of front cloth 24, and the initial or proximal portion of radially internal periphery 26b of intermediate cloth 26 is glued to the final or distal portion of radially internal periphery 24b of front cloth 24. Likewise, the initial or proximal portion of radially external periphery 28a of rear cloth 28 is glued to the final or distal portion of radially external periphery 26a of intermediate cloth 26, and the initial or proximal portion of radially internal periphery 28b of rear cloth 28 is glued to the final or distal portion of radially internal periphery 26b of intermediate cloth 26.

[0061] Preferably, the final or distal portion of radially external periphery 24a, 26a, 28a and of radially internal periphery 24b, 26b, 28b of each cloth 24, 26, 28 is glued to inner surface 12b of casing 12.

[0062] In order to maximize the energy absorption performance in the distributed bonding region, cloths 24, 26, 28 may overlap with pitches and overlapping areas so sized as to maximize the number of glued surfaces and the debonding length of cloths 24, 26, 28.

[0063] Preferably, casing 12 may be made from sheet, in particular of metal material, or from laminated material, in particular composite material. As aforementioned, casing 12 may be made as one piece, or else may comprise a plurality of panels, e.g. in a sandwich arrangement.

[0064] Preferably, cloths 24, 26, 28 may be made of composite material, e.g. having a reinforcement containing fibres, in particular carbon fibres and / or Kevlar fibres. Moreover, reinforcement fibres may be treated with fluids having favourable rheological characteristics, such as, for example, non-Newtonian fluids, suitable for absorbing additional energy resulting from the collision with the striking mass. In further embodiments, cloths 24, 26, 28 may be made, whether partly or completely, in the form of open- mesh nets .

[0065] With reference to Figure 4, the following will describe a leading edge system 10 made in accordance with another exemplary embodiment of the present invention.

[0066] Those parts and elements which are similar to - or which perform the same function as - those of the previously described embodiment have been assigned the same alphanumerical references. For brevity, the description of such parts and elements will not be repeated below, and reference should be made to the description of the embodiment shown in Figures 1 to 3.

[0067] In particular, system 10 concerns a leading edge of an airfoil, wherein, differently from the embodiment illustrated in Figures 1 to 3, casing 12 does not have a tubular shape defined by an inner barrel and an outer barrel. On the contrary, casing 12 defines a substantially convex shape also having an outer surface 12a and an inner surface 12b.

[0068] Unlike the embodiment illustrated in Figures 1 to 3, cloths 24, 26, 28 do not have an annular shape with respective radially external peripheries and respective radially internal peripheries. In Figure 4, in fact, cloths 24, 26, 28 have respective upper peripheries 24a, 26a, 28a and respective lower peripheries 24b, 26b, 28b joined in opposite positions to inner surface 12b of casing 12.

[0069] With reference to Figures 5 to 8, there is shown a sequence of phases of a bird strike test carried out on a leading edge system for an aircraft obtained in accordance with an exemplary embodiment of the present invention. The tested system was the one of the embodiment shown in Figure 4.

[0070] Figure 5 shows system 10 during a phase that precedes the bird strike event.

[0071] Figure 6 shows system 10 during a phase in which a bird has hit rear cloth 28, which is located in the rearmost position .

[0072] Figure 7 shows system 10 during a phase in which the cloths are fully extended backwards.

[0073] Figure 8 shows system 10 during a phase in which the test has ended.

[0074] System 10 shown in Figures 6 to 8 was constructed as a full-scale prototype of carbon resin representative of a leading edge of a mass-produced regional aircraft (in particular having a midsection of 815 mm x 285 mm) with a longitudinal development of 2, 000 mm.

[0075] System 10 was subjected to a bird strike test by following the same procedures as used for certifying civil aircraft, with the following significant parameters:

[0076] - bird weight: 4 lbs

[0077] - nominal bird speed: 300 nodes; recorded bird speed: 155 m / s (301 nodes) .

[0078] The above parameters are typical of CS-25 (FAR25) certified civil aircraft. Therefore, the test procedure and environment were fully representative of real conditions.

[0079] As clearly visible in Figures 7 and 8, during the test the bulkhead 21, which is located, by way of example, at a distance of 655 mm from the furthest point of casing 12, was not impacted and / or damaged. This implies that the test was fully successful, without bulkhead 21 undergoing any deformation. Moreover, the debonding shape of rear cloth 28 is evidence of the excellent diffusive performance of this mode of dissipation of impacting kinetic energy.

[0080] With reference to Figures 9 and 10, there is shown a system 10 like the one of the embodiment illustrated in Figures 1 to 3, wherein some preferred dimensional and geometric parameters are indicated.

[0081] In brief, as previously described with reference to the embodiment illustrated in Figures 1 to 3, there are a plurality of cloths including front cloth 24, intermediate cloth 26 and rear cloth 28 (e.g. made of composite material, in particular having a reinforcement containing Kevlar fibres) . Cloths 24, 26, 28 are installed inside casing 12 of leading edge system 10 by (hot or cold) glueing and left loose .

[0082] In Figure 9, references hl, h2 and h3 designate distances or heights of cloths 24, 26, 28. In more detail, hl designates the front distance between the regions where radially external periphery (or upper periphery, in the embodiment shown in Figure 4) 24a and radially internal periphery (o lower periphery, in the embodiment shown in Figure 4) 24b of front cloth 24 are respectively glued to inner surface 12b of casing 12; said front distance hl may also be defined as "height" of front cloth 24. Likewise, h2 designates the intermediate distance between the regions where radially external periphery (or upper periphery, in the embodiment shown in Figure 4) 26a and radially internal periphery (or lower periphery, in the embodiment shown in Figure 4) 26b of intermediate cloth 26 are respectively glued to inner surface 12b of casing 12; said intermediate distance h2 may also be defined as "height" of intermediate cloth 26. Lastly, h3 designates the rear distance between the regions where radially external periphery (or upper periphery, in the embodiment shown in Figure 4) 28a and radially internal periphery (or lower periphery, in the embodiment shown in Figure 4) 28b of rear cloth 28 are respectively glued to inner surface 12b of casing 12; said rear distance h3 may also be defined as "height" of rear cloth 28.

[0083] In Figure 9, references 11, 12, 13 designate a series of transversal widths of cloths 24, 26, 28, which refer to their loose (or free) portions configured to operatively extend and unfurl inside cavity 14. In more detail, 11 designates the front width (measured transversally) of the loose portion of front cloth 24, situated between radially external periphery (or upper periphery, in the embodiment shown in Figure 4) 24a and radially internal periphery (or lower periphery, in the embodiment shown in Figure 4) 24b of said front cloth 24. Furthermore, 12 designates the intermediate width (measured transversally) of the loose portion of intermediate cloth 26, situated between the radially external periphery (or upper periphery, in the embodiment shown in Figure 4) 26a and radially internal periphery (or lower periphery, in the embodiment shown in Figure 4) 26b of said intermediate cloth 26. Furthermore, 13 designates the rear width (measured transversally) of the loose portion of rear cloth 28, situated between radially external periphery (or upper periphery, in the embodiment shown in Figure 4) 28a and radially internal periphery 28b (or lower periphery, in the embodiment shown in Figure 4) of said rear cloth 28.

[0084] Furthermore, in Figure 10 references al, a2, a3 designate the action angles of, respectively, debonding forces Fl, F2, F3 acting upon the regions where cloths 24, 26, 28 are respectively glued to inner surface 12b of casing 12. For clarity, cloths 24, 26, 28 are omitted in Figure 10. In particular, front action angle al relates to a front debonding force Fl acting upon the region of peripheries 24a, 24b where front cloth 24 is glued. Intermediate action angle a2 relates to an intermediate debonding force F2 acting upon the region of peripheries 26a, 26b where intermediate cloth 24 is glued. Lastly, rear action angle a3 relates to a rear debonding force F3 acting upon the region of peripheries 28a, 28b where rear cloth 28 is glued.

[0085] Preferably, as shown in Figures 9 and 10, each one of widths 11, 12, 13 is greater than the respective heights hl, h2, h3 of the respective cloths 24, 26, 28. In particular, each one of widths 11, 12, 13 is greater than the respective heights hl, h2, h3 by at least 20%. Even more in particular, the oversizing of widths 11, 12, 13 compared to heights hl, h2, h3 decreases as a function of the (axial or longitudinal) distance between the respective cloth 24, 26, 28 and the front end of casing 12. For example, cloths 24, 26, 28 may be sized to obtain ll=2*hl, 12=1, 5*h2, and 13=1, 2*h3; in this way, during a collision caused by, for example, a bird strike event, during the advancement of striking mass M cloths 24, 26, 28 can define wide action angles al, a2, a3, e.g. ranging between 100° and 170*, with values decreasing as the distance of the respective cloth 24, 26, 28 from the front end of the casing increases (i.e. al > a2 > a3) .

[0086] This results in cloths 24, 26, 28 being able to operate substantially simultaneously in the event of a collision with a striking mass M. Thus, instead of undergoing bending stress, cloths 24, 26, 28 are only, and more favourably, subjected to membrane stress (i.e. tensile stress, much like a sail) . Therefore, a considerable component of forces Fl, F2 and F3 causes the glued junction to work substantially under peel conditions relative to the bonding region of cloths 24, 26, 28 at their respective peripheries 24a and 24b, 26a and 26b, 28a and 28. Therefore, forces Fl, F2 and F3 are essentially prevented from acting in a direction perpendicular to said bonding region of cloths 24, 26, 28, which would be unfavourable because they would stress the bonding in a direction normal to the bonded surface. Between the cloth and a normally stressed bonding, in fact, the yielding part is the bonding, at least for standard epoxy adhesives and composite structures.

[0087] Of course, without prejudice to the principle of the invention, the forms of embodiment and the implementation details may be extensively varied from those described and illustrated herein by way of non-limiting example, without however departing from the scope of the invention as set out in the appended claims.

Claims

CLAIMS1. Leading edge system (10) for an aircraft; said system comprising :- a casing (12) having an outer surface (12a) and an inner surface (12b) , internally defining a cavity (14) , and comprising a front portion (20) susceptible of undergoing a collision with a striking mass (M) and being penetrated and crossed by the latter; and- an assembly (22) for absorbing impacts, situated in the cavity (14) downstream of said front portion (20) , said assembly (22) comprising a plurality of cloths (24; 26; 28) arranged in succession one after the other downstream of said front portion (20) , wherein each cloth is separate and spaced apart from said front portion (20) , joined to the inner surface (12b) of said casing (12) , and configured to be hit by said striking mass (M) crossing said front portion (20) , so as to envelop and contain said striking mass (M) in order to absorb the energy resulting from said collision; wherein each cloth (24; 26; 28) has at least one part of its periphery (24a, 24b; 26a, 26b; 28a, 28b) glued in a distributed manner to the inner surface (12b) of the casing ( 12 ) ; and wherein each cloth (24; 26; 28) is loose and free to unfurl in said cavity (14) ; said system being characterized in that, in said succession of said cloths (24; 26; 28) , said at least one part of the periphery (26a, 26b; 28a, 28b) of each next cloth (26; 28) is glued in a distributed manner also to said at least one part of the periphery (24a, 24b; 26a, 26b) of the associated preceding cloth (24; 26) .

2. System according to claim 1, wherein at least one ofsaid cloths (24; 26) has a plurality of waves configured to freely unfurl when said striking mass (M) hits said at least one of said cloths (24; 26) .

3. System according to claim 1 or 2, wherein, in said succession of said cloths (24; 26; 28) , each next cloth (26; 28) has a smaller area than the associated preceding cloth (24; 26) .

4. System according to any one of the preceding claims, wherein, in said succession of said cloths (24; 26; 28) , an initial or proximal portion of said at least one part of the periphery (26a, 26b; 28a, 28b) of each next cloth (26; 28) is glued in a distributed manner to a final or distal portion of said at least one part of the periphery (24a, 24b; 26a, 26b) of each preceding cloth (24; 26) .

5. System according to any one of the preceding claims, wherein the final or distal portion of said at least one part of the periphery (24a, 24b; 26a, 26b; 28a, 28b) of each cloth (24; 26; 28) is glued in a distributed manner to the inner surface (12b) of the casing (12) .

6. System according to any one of the preceding claims, wherein, in said succession of said cloths (24; 26; 28) , each next cloth (26) has fewer waves than the associated preceding cloth (24) .

7. System according to any one of the preceding claims, wherein said casing (12) is made from sheet, in particular of metal material.

8. System according to any one of claims 1 to 6, wherein said casing (12) is made of laminated material, in particular laminated composite material.

9. System according to any one of the preceding claims, wherein said casing (12) is made as one piece.

10. System according to any one of the preceding claims,wherein each cloth (24; 26; 28) is made of composite material, e.g. having a reinforcement containing fibres, in particular carbon fibres and / or Kevlar fibres.

11. System according to any one of the preceding claims, wherein each cloth (24; 26; 28) is made, at least partly, in the form of an open-mesh net.

12. System according to any one of the preceding claims, wherein each cloth (24; 26; 28) has a loose portion located centrally relative to said at least one part of said periphery (24a, 24b; 26a, 26b; 28a, 28b) and configured to extend and unfurl freely in said cavity (14) when it is hit by said striking mass (M) .

13. System according to claim 12, wherein said loose portion of each cloth (24; 26; 28) has a width (11; 12; 13) which is greater than the respective distance (hl; h2; h3) between the regions where at least one part of the periphery (24a, 24b; 26a, 26b; 28a, 28b) of each cloth (24; 26; 28) is glued in a distributed manner to the inner surface (12b) of the casing ( 12 ) .

14. Aerodynamic component of an aircraft, said component comprising a leading edge system (10) according to any one of the preceding claims.

15. Component according to claim 14, selected from a group including an engine nacelle, an airfoil, a tail, a rudder, and a radome .

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