• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    A blade (10) with a weak radar signature comprises a rigid working skin (13), a leading edge spar (12) and a central spar (15) produced from dielectric materials and filling elements (17a, 17b) each formed of a material absorbing electromagnetic waves. Alternatively, the skin (13), the spars (12,15) and filling elements (17a, 17b) are assembled as a core (11) providing the structural strength of the blade (10) and surrounded with a covering coating (18) comprising a rigid and profiled external skin (19a, 19b), made from dielectric materials, and a layer (20a, 20b) of a flexible and light synthetic material, absorbing electromagnetic waves and providing the filling between the core (11) and the external skin (19a, 19b), in such a way as to form a radar screen. The blade is adapted in particular to the rotors of military helicopters.
    公开号:NL8801562A
    申请号:NL8801562
    申请日:1988-06-20
    公开日:1998-01-05
    发明作者:
    申请人:Aerospatiale；
    IPC主号:
    专利说明:

    - Propeller blade with weak radar signature -
    The invention relates to a propeller blade with a weak radar signature, intended for equipping aircraft rotors heavier than air, in particular aircraft rotors heavier than air with an at least partly rotating support surface, such as rotor planes and planes with horizontal and vertical drive, and more specifically helicopters for military use *
    The object of the invention is to propose a propeller blade, in particular a helicopter rotor, the construction of which consists of parts which have been specially selected and which are used to reduce the radar echo of the propeller blade and thus of the rotor disc which is the rotation of the various propeller blades with which the rotor is designed is generated, in order to increase the inconspicuity or stealth of the aircraft equipped with at least one such rotor, with the aim of making it detectable to a lesser extent with electromagnetic wave beams from radar installations.
    On the one hand, the idea underlying the invention is based on the known principle that all elements conducting electricity reflect the electromagnetic waves. After all, the detection provided by a radar installation is based on the reception of at least a part of the reflected fraction of incident electromagnetic waves that are aimed at a target to be detected. Thus, in order to produce a propeller blade with a weak radar signature, or in other words an "inconspicuous" propeller blade, the propeller blade must be made less reflective to electromagnetic waves. Moreover, it is also known that every incident electromagnetic wave is converted into a reflected wave and into a broken wave with every change of the medium in which the wave propagates. Thus, the idea underlying the invention rests, on the other hand, on the need to destroy the fractured portion of an incident electromagnetic wave hitting a propeller blade in the fastest manner possible to prevent the fractured wave from propagating inside the propeller blade, bouncing off the inner walls of the propeller blade or generating a resonance phenomenon in the cavities of the propeller blade construction, then leaving the latter in the form of a reflected wave that can be received by a radar installation.
    The object of the invention is therefore to propose a propeller blade, the construction of which offers a good compromise between transmitting a sufficiently large capacity, that is to say a sufficiently subsidence capacity for reflecting, and a sufficiently large capacity for absorbing electromagnetic waves because the radar signature of the propeller blade will be very weak.
    To this end, the propeller blade according to the invention is made of composite materials, it is of the kind comprising: - at least one longitudinal beam of wire layers of fibers of high mechanical strength, which are made into a whole by a polymerized synthetic resin, a working rigid shell which participates to the structural strength of the propeller blade and at least consists of a layer of cloth of mechanically very strong fibers, made in one piece with a polymerized synthetic resin, and - at least one filling element of a light synthetic material, arranged in the working shell, characterized in, that the working shell and each longitudinal beam are made of dielectric materials and the material of each filling element is a material that absorbs electromagnetic waves, and / or the working scale, each longitudinal beam and each filling element are assembled in a structural heart that provides the structural strength of the propeller blade and is surrounded by a covering l layer with a rigid and profiled outer shell of dielectric materials, and a layer of a flexible and light synthetic material that absorbs electromagnetic waves and provides the filling between the structural heart and the outer shell to form a radar barrier.
    The invention thus proposes three main embodiments of the radar inconspicuous propeller blade.
    In a first embodiment, all essential building elements of the propeller blade, and in particular all working elements, consist of either dielectric materials or materials that absorb the electromagnetic waves.
    This leads to refraining not only from using metal parts, but also from parts containing boron or carbon, although the latter material is particularly favorable in terms of its performance over other replacement materials, such as glass or aramid fibers, and in in particular, the fiber sold under the KEVLAR brand.
    As a result, the invisibility to radar of the propeller blade according to this first embodiment can only be obtained by increasing the mass, keeping all other things equal, compared to a "non-invisible" propeller of the same architecture and provided of elements which are constructed and are optimally made of materials which may be conductive, for example of cloth or of carbon fibers, and this applies in particular to the rigid working shell of the screw blade.
    In a second embodiment of the propeller blade according to the invention, all parts that provide the structural strength of the propeller blade are regrouped and assembled in a structural heart and the latter is surrounded by a two-layer covering layer, the outer layer of which is a rigid shell and is profiled to the aerodynamic profile required of the propeller blade, and is made of dielectric materials, while the inner layer is a flexible and absorbent filler layer that forms a radar shield. In this case, the electromagnetic waves pass through the outer shell upon encountering the propeller blade and are then "captured" and absorbed into the filler layer. As a result, it remains possible to use electrically conductive materials, and in particular carbon in the form of fibers, wire layers and / or cloth, to assemble the elements of the structural heart, while maintaining a weak radar signature for the propeller blade.
    Because the coating that forms the radar at the same time in use forms a protective shield of the structural heart against shocks (against stones and branches) and other attacks from the environment, and thus against damage, the result is that the constituent elements of the structural heart can be optimized in terms of properties and can be executed with a minimal thickness without having to think about the attacks mentioned.
    This makes it possible to gain a sufficient amount of mass from the structural heart to a dielectric screw blade to compensate for the extra mass of the cladding layer surrounding the structural heart.
    This second embodiment is not limited to the cases in which the structural heart comprises at least one wire layer longitudinal beam and a working layer in the form of fiber layers which encloses at least one filling element, as proposed above, but extends to all possible structures of the structural heart, both when the cross section of the heart (according to the chord of the propeller blade) has a contour which is substantially parallel to the profile of the outer shell of the cladding layer, in which case the filling layer of flexible and absorbent material is preferably a blade to compensate for the tolerance differences between the contour and the profile, or in the case where the structural heart has a cross section with a contour with flat edges, based on simple geometric shapes, such as triangular and quadrangular, in which case the filling layer is made of flexible and absorbent material is preferably a thick layer to compensate for the differences and in shape between the contour and profile of the outer shell of the cladding layer. In addition, it should be noted that such an arrangement also allows the contour of the structural heart to be shaped - 5 - with an approximately aerodynamic profile with a high tolerance, compensated by the application of the cladding layer, but all the more so. more facilitates a cheap implementation of the structural heart.
    Finally, in the third embodiment, which seeks to achieve maximum invisibility to propeller radar with a certain increase in mass accepted, is a structural heart consisting of dielectric or absorbent elements and surrounded by a coating with a dielectric outer shell and a flexible and absorbent filling layer that forms the radar screen. In particular, a propeller blade according to this third embodiment can be imagined to be a propeller blade according to the second embodiment, the structural heart itself of which is at least substantially completely constructed as a propeller blade according to the first embodiment which has been presented above.
    In these various embodiments, at least one filler element, but preferably each of the filler elements housed in the working shell, is made of a cellular material or a relatively hard foam, and filled with electrically conductive particles. This filled material, like the foam materials normally used in the manufacture of propeller blades from "non-invisible" composites, may have a density which varies over a considerable range of values. In the case of the invention, the specific gravity of the filled material used is advantageously in a range ranging from practically 50 to practically 200 kg / m 3, where the filling represents about 5% by weight of the filled material.
    Likewise, in the second and third embodiments in which the propeller blade includes a clad layer, the absorbent filler material that forms a radar shield for the structural heart is advantageously a cellular material or a foam material filled with electrically conductive particles .
    Advantageously, the filled material or materials are used to create the filler or fillers housed in the working shell and / or filler layer and radar shield when the propeller blade is such a coat includes a polyurethane foam filled with electrically conductive particles. The latter can be carbon particles, for example, carbon powder or carbon granules, but advantageously the filling consists of carbon fibers which all behave like a small antenna or a dipole which converts the electromagnetic wave encountered into electric current and then the corresponding energy consumed by the Joule effect, which ensures a very effective absorption in the absorbent foam.
    In the first embodiment and in the third embodiment, the wire layers of each longitudinal beam and the webs of each layer of the working shell are advantageously formed with fibers selected from aramid fibers and glass fibers, and the resin or resins are assembly is advantageously selected from epoxy resins, polyesters or thermoplastic resins.
    The invention also proposes to improve the invisibility for radar of the propeller blade by making special provisions on non-structural parts of the propeller blade. In particular, in the various embodiments envisaged, each counterweight and any static and / or dynamic equilibrium mass with which the propeller blade is equipped are made of a composite material consisting of particles of at least one metal oxide, preferably heavy, which are held together in at least one poly -merized synthetic resin. In the same manner, the mass of the support is in the form of a block of a dielectric composite material. In addition, the nose protection is advantageously provided with at least one elastomer band, which is preferably selected from the polyurethanes and the silicone, but it is also possible that the nose protection is in the form of a cap of thermoplastic resin, preferably reinforced with a reinforcement of dielectric fibers, this fiber reinforcement occurring, for example, in the form of a nonwoven layer of fibers, the cap forming an anti-erosion layer.
    In a propeller blade according to the second embodiment of the invention, the optimization of the structural heart is advantageously provided by the fact that at least one longitudinal beam and / or at least one layer of the working shell of the structural heart are provided with thread layers and / or or a carbon fiber fleece.
    In this case, as in the case of a propeller blade according to the third embodiment of the invention, the coating layer is advantageously a non-working coating, the outer shell of which is preferably a thermoformed, non-structural shell of a thermoplastic resin, optionally at least partially armed with dielectric fibers.
    The choice of a thermoplastic resin to perform the rigid and profiled outer shell of the non-working cladding layer is advantageous not only because this material is dielectric, but also as the material has excellent qualities in terms of surface condition, behavior in exhibits erosion, impact resistance, and repairability making it easy for the user to intervene because this coating is not structural. This will allow minor damage to be repaired by the user without having to return the propeller blade to the factory. The choice of a thermoplastic resin makes it possible to eliminate the long finishing operations such as the stopping, sanding and touch-up phases in the manufacture of the propeller blade, as well as painting if the chosen thermoplastic resin is colored in mass, with as resulting in significant manufacturing and maintenance savings.
    Furthermore, when a propeller blade according to the first embodiment, i.e. without a cladding layer, is of the type having tabs attached to the trailing edge of the propeller blade, the latter being characterized in that each tab is an element of insulating materials and in the shape of a wedge, the edge of which is glued directly to the lip of the trailing edge of the propeller blade.
    In the various embodiments it is advantageous for the reinforcing the frame of the propeller blade that it additionally comprises a central longitudinal beam which is composite and preferably dielectric and extends over the wing width of the propeller blade practically in the center of its chord, and of which the transverse ends along the chord are both connected by means of a composite saddle which is preferably also dielectric, one on the inside of the top surface portion and the other on the inside of the bottom surface portion of the working rigid shell to engage with the latter and a longitudinal beam in the nose define a nose chamber filled with a front filler element, a back filler element similarly filling the portion of the rigid working shell extending behind this mid-length beam to the rear edge of the propeller blade.
    Irrespective of the particular design of the structural elements of the propeller blade according to the invention, the propeller blade having a weak radar signature and made of composite materials, when produced in accordance with the second and third embodiments, is generally characterized in that it comprises: - a structural heart, preferably with an approximately aerodynamic profile that provides the structural strength of the propeller blade, and - a covering layer surrounding the structural heart and consisting of: - a rigid outer shell with a desired aerodynamic profile, made of dielectric materials , and - a layer of a non-working adaptive material that is light and flexible and provides padding between the heart and the outer shell and absorbs the electromagnetic waves to form a radar shield.
    In all cases where the propeller blade is covered with a coating layer, it is advantageous to facilitate the operations in assembling, disassembling, exchanging and possibly repairing this coating, that the coating consists of two complementary layered parts, each one of the two complementary parts of the absorbent material layer that form the radar shield, and comprising one of the two complementary parts of the dielectric outer shell, the two complementary layered parts of the cladding being arranged around the structural center and connected together, and preferably , to the structural heart, for example by gluing.
    In general, in the screw blades according to the invention, all connections are advantageously glued connections, and in the cases where fastening screws will nevertheless be used, for instance for fastening the screw blade block to the running part thereof, plastic screws will be used, for example Nylon or TorIon (registered trademarks).
    The invention will be better understood and other features and advantages of the invention will become apparent upon reading the description given below, non-limiting, of some embodiments described with reference to the accompanying drawings, in which: Fig. 1 is a view of a cross section according to the chord of a first example of a helicopter rotor propeller blade without coating, fig. 2 is a cross-sectional view according to the chord of a second example of a helicopter rotor propeller blade provided with a coating layer, and fig. 3 is a perspective sketch with partial omissions of a truncated section of the running portion of the propeller blade, the cross section of which is shown in Figure 2.
    The screw blade 1 shown in Fig. 1 is provided with a nose longitudinal beam 2 which consists of a bundle of unidirectional wire layers of dielectric fibers of high mechanical strength, for example glass fibers, these wire layers are held together by a thermosetting impregnation resin which is polymerized and which is also a dielectric resin, for example an epoxy resin.
    This longitudinal beam has a cross section which is substantially in the shape of a C due to the circumstance of the convex curvature of the top surface and the bottom surface, as well as the hollow recess of its rear surface which is thus practically a rear wing of the subcutaneous skin 2a and a rear wing. of the upper skin 2b.
    In addition, the longitudinal beam 2 also has a small hollow recess in its nose surface, the function of which will be explained below.
    The longitudinal beam 2 thus assembled is known in a known manner with a base or an insert by means of which it can be connected to a rotor hub, and this longitudinal beam 2 is intended to absorb mainly the centrifugal forces to which the propeller blade in use is exposed. .
    The propeller blade 1 is also provided with a working rigid shell 3 which is profiled to the aerodynamic profile ultimately desired for the propeller blade. This working shell 3 is accomplished by stacking a plurality of layers of membranes of high mechanical strength dielectric fibers held together by, for example, a polymerized resin, by layers of glass fibers or of aramid fibers which are crossed and whose warp and weft threads are substantially at an angle of 45 ° with the direction of the nose of the propeller blade, these layers having been previously impregnated with a thermosetting resin, for example of the epoxy type, and hot-polymerized.
    This shell is conventionally carried out with finishing steps including, optionally, caulking, stopping, sanding and finally a painting phase for covering the outer surface of the shell 3 with a paint layer that absorbs the electromagnetic waves.
    The longitudinal beam 2 is placed in the region of the nose of the shell 3 to which the beam is rigidly connected by the polymerization of the resins along its convex top surface and convex bottom surface and its rear wings 2a and 2b, such that the concave recess on its front with the scale 3 determine a space occupied by counterweights for re-centering and static and / or dynamic equilibrium masses 4. These counterweights and equilibrium masses 4 are made of a composite material consisting of a granular filling of a heavy metal oxide, for example lead oxide held together by a polymerized resin. These counterweights and balancing masses 4 are not part of the reinforcing frame of the propeller blade which is, however, completed with a working longitudinal beam 5 in the longitudinal direction and in the center. This longitudinal beam 5 may be a dielectric composite extending substantially over the entire wing width of the propeller blade at the center of its chord, having a cross section practically Z-shaped, with a central portion forming the core 5c and consists of a sheet of honeycomb material, covered on both sides with layers of fiberglass fleece, previously impregnated with a thermosetting resin and two wings 5a, 5b, both of which have been created by superimposing the extensions of the impregnated fiberglass layers on the surfaces of the central core 5c.
    The pressure side wing 5a rests against the top surface of a pressure side support member 6a itself of dielectric composite material, for example, formed by superimposing a plurality of layers of pre-resin impregnated and longitudinally laid glass fibers, this pressure side support member 6a being applied with its bottom surface against the inner surface of the pressure side portion 3a of the shell 3, and analogously the suction side wing 5b rests against the bottom surface of a suction side support member 6b of dielectric composite material obtained by superimposing a number of layers of glass fiber webs previously impregnated with resin and which are laid in the longitudinal direction, which wing is arranged with its top surface against the inner surface of the suction side part 3b of the shell 3, but in a position closer to the longitudinal beam 2 than the wing 5a and the pressure side support member 6a. Simultaneously polymerizing the thermosetting impregnating resin of the different parts of the core 5, the support members 6a and 6b and the nonwoven layers of the shell 3 ensures a rigid connection of the longitudinal beam 5 by means of the support members 6a and 6b directly with the part on the pressure side and the suction side part of the working rigid and dielectric shell 3. In this way, the longitudinal beam 5 with the dielectric acting scale 3 and the dielectric longitudinal beam 2 define a structural front chamber on the nose side which is filled with a pre-filling body 7a, while the dielectric longitudinal beam 5 with only the dielectrically acting shell 3 in its rearwardly divided portion defines a structural rear chamber which is also filled with a rear shim 7b. The shims 7a and 7b both consist of a light and relatively rigid polyurethane foam filled with carbon fibers.
    This filled foam can be obtained in accordance with the directions of the method and using the solid particle fill dispersion apparatus in polyurethane foams described in US 3,256,218. In particular, this patent describes a method of dispersing solid particles and fibrous particles, the dimensions of which are at least as large as the average diameter of the cells of the foam, with a substantially uniform distribution or dispersion of the fibers or fibers of the filling in the cell mass, as well as a practically uniform distribution of the elements forming the polyurethane foam, over the entire volume occupied thereby. The filled foam used to create the filler bodies 7a and 7b exhibits a density of light between about 50 and about 200 kg / m 3, and the carbon fiber fill represents about 5% by weight of the filled foam. This behaves like a "semiconductive" material and is thus more reflective than the unfilled polyurethane foam, but also and above all more absorbent to electromagnetic waves. After all, the carbon fibers that are in large numbers in the foam all behave like a small antenna or a small dipole that converts the electromagnetic waves into electric current, which results in heating of the fiber by the Joule effect, which in turn creates a consumption and dissipation of the energy transported by the incident wave. Thus, foam bodies 7a and 7b are obtained which absorb the electromagnetic waves which have passed the dielectric shell 3, the front part of which is protected by a protective cap 8 on the nose. This cap 8 is also non-conductive and is either built up from one or more bands of elastomeric material, for example polyurethane or silicone resin, which are glued to the dielectric shell 3, or performed by thermoforming a thermoplastic resin, optionally reinforced with glass fibers, for example of a layer of glass fiber fleece which forms an anti-erosion layer, the thermoplastic cap being glued to the dielectric shell 3.
    "If the propeller blade is provided with tabs 9, the latter are in the form of small triangular and elongated elements, or in the form of wedges, of a rigid and insulating material and they are each with an edge directly on the lip of the trailing edge 3c which is formed by the union of the trailing edge of the subcutaneous part 3a and the upper skin part 3b of the shell 3, thus obtaining a propeller blade which exhibits a weak radar signature because it is at the same time not reflective and highly absorbent for electromagnetic waves due to performing the structural and non-structural elements in dielectric materials and due to the presence of the pads in absorbent filled foam.
    The second example of a propeller blade 10, shown in Figures 2 and 3, includes a structural heart 11, formed in the form of a primary structure containing all the structural and essential elements of a helicopter propeller blade with a known structure, similar to that of the propeller blade of FIG. 1, and the creation of this structural center 10 is very close to the establishment of the prior art propeller blade, except for the choice of materials if just above with reference to FIG. 1 describes the propeller blade described.
    This structural heart 11 is provided with a nose longitudinal beam 12 which consists of device wire layers of mineral or organic fibers with a high mechanical strength, preferably of glass or of aramid fibers, and these wire layers are held together by a thermosetting and polymerized impregnation resin. The longitudinal beam 12 has a cross-section which is practically in the shape of a C due to the convex curvature of the top and bottom surfaces and the hollow recess of its rear surface such that a rear wing 12a on the compression side and a rear wing 12b on the suction side.
    A small hollow recess is still shown in the front face of the longitudinal beam 12, which recess in known manner includes a base or an insert for its connection to a rotor hub.
    The structural heart 11 is also provided with a working rigid shell 13 with a transverse profile that is without parallel much parallel to the final aerodynamic profile desired for the propeller blade. This working shell 13 is accomplished without finishing, i.e., without caulking, stopping, sanding or painting, by stacking a number of layers of mineral or organic fiber webs of high mechanical strength held together by a polymerized resin. For example, the working shell 13 consists of two crossed layers of carbon fiber webs, the warp thread and the weft thread of which have an angle of approximately 45 ° to the direction of the nose of the screw blade, these two layers having been previously impregnated with a thermosetting resin, for example of the epoxy type, and are polymerized hot. The longitudinal beam 12 is placed in the area of the nose of the shell 13 to which it is rigidly attached by polymerizing the resins along the convex top surface and the convex bottom surface and the convex surfaces of its rear wings 12a and 12b, such that the concave recess in its front face with the scale 13 defines a space occupied by counterweights or equilibrium masses 14 constructed in a heavy metal.
    The structural center also includes a working longitudinal girder 15 which is longitudinal and centrally located, and is constructed of a composite material and extends substantially the entire width of the propeller blade at the center of its chord and has a cross section which is practically Z-shaped, with a central portion 15c forming a core consisting of a honeycomb panel covered on both sides with layers of carbon fiber fleece impregnated with a thermosetting resin and two wings 15a and 15b both obtained by superimposing the extensions of the pre-impregnated carbon fiber webs of the faces of the central portion 15c. The pressure side wing 15a rests against the top surface of a pressure side composite material support 16a formed by a stacking of a plurality of layers of carbon fiber web which are longitudinally laid and previously impregnated with a thermosetting resin, the support member 16a with its bottom surface is placed against the inner surface of the pressure side portion of the damage 13, and analogously the suction side wing 15b rests against the bottom surface of a suction side support member 16b, which is of a composite material rigidized by stacking a number of layers of carbon fiber web, also longitudinally laid and previously impregnated with a thermosetting resin, the support member 16b being placed with its top surface against the inner surface of the suction side portion of the shell 13, but in a position closer to the longitudinal beam 12 than the wing 15a and the pressure side support member 16a. The simultaneous polymerization of the thermosetting impregnating resin of the different parts of the longitudinal beam 15, the support members 16a and 16b and the layers of the shell 13 provides a rigid connection of the longitudinal beam 15 via the support members 16a and 16b directly with the parts at the bottom and the top of the rigid and working shell 13. Thus, the longitudinal beam 15 with the working scale 13 and the longitudinal beam 12 defines a structural antechamber which is preferably filled with a pre-fill body 17a, while the longitudinal beam 15 with only the working scale 13 in the rearwardly facing portion of the shell defines a structural back chamber which is also preferably filled with a rear shim 17b. The shims 17a and 17b both consist of a light synthetic material which is relatively rigid, with cells or of foam, for example of polyurethane foam, or else of artificial honeycomb material in layers, in order to display the desired shapes.
    The creation of the structural heart 11 thus comes close to the creation of the screw blade according to Fig. 1 with the exception of the selection of the materials which can be optimized in terms of properties such as dimensions, in particular thickness. independent of the conductivity or non-conductivity of these materials when using carbon fleece layers, and on the other hand the lack of finishing of the working shell 13 and especially of its shape which is only substantially parallel to the desired aerodynamic and final profile, and achieved without great shape accuracy with a tolerance in the approximate profile thus obtained which may be relatively large, but which is always compensated by applying around the structural heart 11 a coating layer 18 described below. It is clear that the realization of the structural heart 11 has become all the easier.
    The coating layer 18 is a non-working coating, composite and layered, with two superimposed layers, none of which participates in the structural strength of the propeller blade. This coating 18 is built up by assembling around the structural heart 11 of a pressure side half cladding layer 18a and a suction side half cladding layer 18b which are complementary.
    Each of these two half-coatings 18a and 18b is provided with a rigid and thin outer layer of a thermoplastic resin which can be colored in the mass, which is thermoformed in the desired precise profile to the part 19a on the pressure side and the part 19b the suction side of a rigid external shell (19a-19b) that is thin, non-operating and dielectric, but which only bears the aerodynamic forces and is profiled with precision in accordance with the desired precise aerodynamic profile.
    Both half-coatings 18a and 18b are provided with an inner layer formed in a light synthetic foam, flexible and deformable, and filled with electrically conductive particles to form an adjustment layer 20a on the pressure side and an adjustment layer 20b on the suction side, respectively. shapes intended to fill the clearance between the profiled outer shell (19a-19b) that does not work, and the working inner shell 13 by compensating for or absorbing the differences in orm that exist between the contour of the inner shell 13 and the accurate profile of the outer shell (19a-19b), and at the same time forming a radar shield for the structural heart 11. The foam used to create the filler and fitting layer (20a-20b) is a flexible foam of poly -urethane filled with carbon fibers that form a layer that absorbs the electromagnetic waves in the same conditions as the absorbent pad and 7a and 7b of the propeller blade described with reference to Fig. 1.
    After all, the thermoplastic and dielectric outer shell (19a-19b) allows electromagnetic waves to be absorbed by thermal dissipation resulting from the heating of the carbon fibers in the foam of the layer (20a-20b), so that this absorbent layer acts as radar trim. At the same time, this filling and adjusting layer (20a-20b) of the covering layer 18 adjusts the non-working profiled shell (19a-19b) around the structural heart 11. In the zone of the nose of the blade, both half outer shells 19a and 19b a portion 19c slightly thickened inwardly to form the protection of the nose, and the thickness of the foam adjustment sheet 20a and 20b is greater than the thickness near the trailing edge. The average thickness of the deformable and filled foam layer is about 5 mm, while the average thickness of the profiled and dielectric outer shell is about 1 mm.
    To facilitate the application of the cladding layer 18 to the structural heart 11, each filled foam sheet 20a or 20b is glued to the hollow inner surface of the associated half shell 19a or 19b to obtain two half claddings 18a and 18b which are then wrapped around the structural heart 11 and both are glued to the opposite surface at the top or bottom, placing one against the abutting surfaces of the nose edge and the rear edge of the propeller blade.
    The use of any mass-colored thermoplastic resin to build up the external and profiled shell (19a and 19b) allows to take advantage of the properties and properties peculiar to this material, which are perfect above its dielectric properties surface condition hence the savings on lengthy and difficult soaking and finishing steps such as sanding, stopping, painting and better erosion compared to conventional paints. In addition, the outer shell (19a-19b) and the padded foam adjustment and padding layer (20a-20b), gathered together to form the cladding layer 18, simultaneously form a protective shield for all structural elements regrouped in the heart 11 of the propeller blade , with regard to medium-sized shocks which are the most numerous, for example due to stones and rocks and collisions with branches. In the event of local damage to the coating layer 18, since the latter is not structural, it is possible for the user to carry out simplified repairs using parts of the same composite materials.
    In the event of more serious damage, the propeller blade is taken back to the factory, where the cladding layer 18 is disassembled to allow checking of the integrity of the structural heart 11, and a repair is carried out, if necessary, to ensure this integrity. adjust. In addition, if necessary, and more or less locally, the coating layer 18 is repaired or simply replaced by another identical coating which also has a dielectric outer shell and a flexible and absorbent padding layer if the original coating is too damaged and has become unusable for re-use. usable screw blade. It should be noted that the non-vital character of the cladding layer 18 allows, when lost in the farce, to take advantage of the aerodynamic properties which are certainly worse but still sufficient, of the approximate profile of the structural heart 11 to allow the aircraft to return to its base.
    To improve the resistance to impact and erosion, it is possible to reinforce the synthetic resin of the profiled outer shell (19a-19b) by means of a limited fiber input provided that the latter are non-conductive, or even by this shell ( 19a-19b) to be made with a non-conductive fiber nonwoven layer which serves as an anti-erosion layer, stiffened by a polymerized impregnation resin.
    Thus, a propeller blade with a weak radar signature is also obtained, the structural elements of which are well protected by the cladding layer which simultaneously forms a radar shield and a protective shield.
    In addition, this non-working cladding layer 18 is not vital, but it is consumable and interchangeable, making it possible to develop the profile of the propeller blade over the width as well as over the chord in a modular manner through the cooperation of half cladding layers 18a on the underside. and 18b at the top with the desired curvature or curvatures. The profile of a propeller blade can be changed completely while retaining its absorption properties with regard to electromagnetic waves, or this profile can be modified or converted, provided it remains substantially within the profiles of the same generation starting from the same structural center 11 as a basis.
    It is important to note that the extra mass resulting from the presence of the coating layer 18 can be compensated by optimizing the constituent elements of the structural heart 11.
    After all, since the latter is protected by the cladding layer 18, its constituent elements can all be made with the minimum thickness or optimized in terms of properties without having to worry about the various attacks and collisions to which the propeller blade may be exposed during use.
    It is clear that the structural heart 11 can only be checked for its covering with the covering layer 18. After the latter has been put in place and glued, the final inspection of the propeller blade consists of an inspection of the exterior.
    It is also important to note that the cross-sectional contour of the strucutal heart 11 may be very different from the aerodynamic profile of the outer shell 19: for example, the structural heart 11 may be contoured with flat sides and, to be more precise, a contour in the form of a flattened hexagon obtained as a result of a triangular cross section of one front part of the side member and of the working shell, as well as a triangular cross section of the rear part of this working shell up to the trailing edge, while the central part of the heart 11, practically between the longitudinal beam and the central core, can have a rectangular cross-section. However, based on simple geometric shapes, such a contour defines a profile which, although very approximate compared to that represented by the outer shell 19, remains sufficiently effective on the aerodynamic plane to preserve the non-vital character of the cladding layer 18 and enable the aircraft to be brought to safety when this coating 18 becomes detached from the structural heart 11 which serves as the basis. In this case, the compensation for the largest differences between the shapes of the contour of the wart 11 and of the profile of the shell 19 is obtained by the layer (20a-20b) of filled foam in the form of a relatively thick layer.
    A third example of a low radar signature propeller blade that favors radar blade propulsion installations in relation to its weight is obtained by creating the structural center 11 of the propeller blade shown in Figures 2 and 3 with the same materials if they are used to create the propeller blade of FIG. 1, only the rear edge tabs 9 and the leading edge protection 8 will not be adopted. In other words, the propeller blade of Figure 1, without its tabs 9 and its leading edge protection 8, can be used as a structural heart instead of the center 11 of the propeller blade of Figures 2 and 3.
    Thus, a dielectric and absorbent structural heart is obtained, which itself is surrounded by an inoperative coating with a dielectric outer shell and a filler layer for adaptation that absorbs, and forms a radar shield.
    It is clear that such a propeller blade exhibits the maximum absorption properties in combination with minimal reflection properties of the electromagnetic waves.
    权利要求:
    Claims (14)
    [1]
    1. Low radar signature propeller blade, in particular for an aircraft heavier-than-air rotor, with an at least partially rotating support, such as a helicopter, where the propeller blade (10) is composed of composite materials and is of the type comprising: - at least one longitudinal beam (12) of wire layers of fibers of high mechanical strength, which are assembled by a polymerized synthetic resin, - a working rigid shell (13) that participates in the structural strength of the screw face (10) and at least consists of a layer of cloth of mechanically very strong fibers, made in one piece with a polymerized synthetic resin, and - at least one filling element (17a, 17b) of a light synthetic material, arranged in the working shell (13), characterized in that the operating shell (13) and each longitudinal beam (12) are made of dielectric materials and the material of each shim element (17a, 17b) is a material that absorbs etetic waves and / or the working shell (13), each longitudinal beam (12) and each shim (17a, 17b) are assembled in a structural center (11) that provides the structural strength of the propeller blade (10) and is enclosed by a covering layer (18) with a rigid and profiled outer shell (19a-19b) of dielectric materials, and a layer (20a-20b) of a flexible and light synthetic material that absorbs electromagnetic waves and provides the padding between the structural heart (11) and the outer shell (19a-19b) to form a radar shield.
    [2]
    Propeller blade according to claim 1, characterized in that at least one filler element (17a, 17b) housed in the working shell (13) is made of a cellular material or of a relatively hard foam, filled with electrically conductive particles.
    [3]
    A propeller blade according to claim 2, characterized in that the specific gravity of the filled material used is in a range ranging from about 50 to about 200 kg / m3, the filling representing about 5% by weight of the filled material.
    [4]
    Propeller blade according to any one of claims 1 to 3, with a covering layer (18), characterized in that the filling material, flexible and absorbent, which forms a shield for the structural heart (11), is a cellular material or a foam filled with electrically conductive particles.
    [5]
    Propeller blade according to any one of claims 2 to 4, characterized in that the used filled material or the used filled materials for creating a filler element (17a, 17b) and / or the filler layer and shielding layer (20a -20b) of the coating layer (18) is a polyurethane foam filled with carbon particles.
    [6]
    Propeller blade according to claim 5, characterized in that the carbon particles forming the filling are carbon fibers.
    [7]
    Propeller blade according to any one of claims 1 to 6, characterized in that the thread layers of each longitudinal beam (12) and the web of each layer of the working shell (13) are made of fibers selected from the aramid fibers and glass fibers, and the cohesive resins which also provide the stiffening, are selected from the epoxy resins, polyester resins or thermoplastic resins.
    [8]
    Propeller blade according to any one of claims 1 to 7, of the type provided with at least a counter-centering counterweight and / or at least one static and / or dynamic equilibrium mass (4), characterized in that each counterweight and each equilibrium mass is made of a composite material consisting of particles of at least one metal oxide, preferably a heavy metal oxide, which are held together in at least one polymerized resin. Propeller blade according to any one of claims 1 to 8, of the type provided with a protection of the nose (8), characterized in that the protection consists of at least one band of an elastomer, preferably selected from the polyurethanes and the silicone resins.
    [9]
    Propeller blade according to any one of claims 1 to 8, of the type provided with a protection of the nose (8), characterized in that this protection is provided in the form of a cap of a thermoplastic resin, preferably reinforced with a dielectric fiber reinforcement.
    [10]
    Propeller blade according to any one of claims 1 to 10, with a covering layer (13) surrounding the structural heart (11), characterized in that at least one longitudinal beam (12) and / or at least one layer of the working shell (13) of the structural heart (11) contain wire layers and / or a fleece of carbon fibers, respectively.
    [11]
    Propeller blade according to any one of claims 1 to 11, with a coating layer (18), characterized in that a coating layer is a non-working coating. Propeller blade according to claim 12, characterized in that the outer shell (19a-19b) is a non-structural shell thermally formed from a thermoplastic resin, optionally reinforced with at least partially dielectric fibers. IA. Propeller blade according to any one of claims 1 to 3 and 5 to 10 without coating and of the type, provided with tabs (9) attached to the rear edge, characterized in that each tab (9) is an element of insulating material and in the form of a wedge glued directly to the lip (3c) of the rear edge of the propeller blade (1) with the edge.
    [12]
    Propeller blade according to one of Claims 1 to 14, characterized in that it furthermore comprises a central longitudinal beam (5) of composite material and preferably dielectric material extending along the width of the propeller blade (1) practically in the middle of its chord and the ends (5a, 5b) of which are transverse to the chord are both connected by means of a support member (6a, 6b) of composite material and preferably of dielectric material, the one (5b) the interior of the part (3b) on the suction side, and the other (5a) on the interior of the part (3a) on the pressure side of the working rigid shell (3) so as to have the latter and a longitudinal beam along the nose ( 2) to form a nose chamber filled with a pre-filler element (7a), a rear filler element (7b) similarly extending the part of the working rigid shell (3) behind the central longitudinal member (5) to the rear edge (3c) of the screw sheet (1).
    [13]
    A propeller blade with a weak radar signature, in particular for an aircraft rotor heavier than air, in particular for an at least partially rotating support surface, such as a helicopter, the propeller blade consisting of composite materials, characterized in that the propeller blade is provided with: - a structural heart (11), preferably with an approximately aerodynamic profile, which provides the structural strength of the propeller blade (10), and - a covering layer (18) surrounding and containing the structural heart (11) a rigid outer shell (19a-19b) and with the required aerodynamic profile, made of dielectric materials, and a layer (20a-20b) of a non-working, light and flexible adaptive material that provides padding between the heart (11) and the outer shell (19a-19b) and that it absorbs the electromagnetic waves in such a way that a radar shield is formed.
    [14]
    Propeller blade according to any one of claims 1 to 13, 15 and 16, with a covering layer (18), characterized in that the covering layer (18) consists of two complementary layered parts (18a, 18b) and each of which has one of the two complementary parts (20a, 20b) of the layer of absorbent material forming the radar shield, and one of the two complementary parts (19a, 19b) of the dielectric outer shell, the two complementary layered parts (18a, 18b ) of the coating layer (18) are placed around the structural heart (11) and bonded together as well as with the structural heart (11).
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    同族专利:
    公开号 | 公开日
    GB8814781D0|1998-11-25|
    IT8867528D0|1988-06-07|
    GB2327925A|1999-02-10|
    CA1341239C|2001-05-22|
    GB2327925B|1999-06-02|
    FR2748719B1|1999-05-07|
    CA1340376C|1999-02-02|
    DE3821588C1|1998-02-26|
    FR2748719A1|1997-11-21|
    引用文献:
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    US4006479A|1969-02-04|1977-02-01|The United States Of America As Represented By The Secretary Of The Air Force|Method for dispersing metallic particles in a dielectric binder|
    US4083656A|1975-03-21|1978-04-11|Textron, Inc.|Composite rotor blade|
    FR2381662B1|1977-02-28|1982-01-29|Aerospatiale|
    US4316700A|1979-04-03|1982-02-23|Schramm Burford J|Unitary, bonded-together helicopter rotorblade|
    DE3307066A1|1983-03-01|1984-09-13|Dornier Gmbh, 7990 Friedrichshafen|MULTILAYER FIBER COMPOSITE|DE102008024644B4|2008-05-21|2018-07-26|Airbus Defence and Space GmbH|Rotor blade with integrated radar absorber for a wind turbine|
    DE102010039705B4|2010-08-24|2020-02-27|Airbus Operations Gmbh|Structural element for an aircraft and spacecraft and method for producing such a structural element|
    FR2964941B1|2010-09-16|2013-03-08|Eurocopter France|MINIMIZED VULNERABILITY BLADE|
    GB2485524A|2010-10-26|2012-05-23|Vestas Wind Sys As|Foam core containing radar absorbing materials for composite structures|
    US9033672B2|2012-01-11|2015-05-19|General Electric Company|Wind turbines and wind turbine rotor blades with reduced radar cross sections|
    US9033671B2|2012-01-11|2015-05-19|General Electric Company|Wind turbines and wind turbine rotor blades with reduced radar cross sections|
    FR3000463B1|2012-12-27|2016-02-05|Eads Europ Aeronautic Defence|ENERGY ABSORPTION DEVICE FOR AN AIRCRAFT STRUCTURE ELEMENT|
    CN106542079B|2016-11-25|2019-03-01|江西洪都航空工业集团有限责任公司|A kind of structure-type wave-absorption covering design method|
    CN113687323B|2021-10-26|2022-03-08|中国航发四川燃气涡轮研究院|Low-scattering shell for binary vector engine and application thereof|
    法律状态:
    1998-01-05| A1A| A request for search or an international-type search has been filed|
    1998-10-01| BB| A search report has been drawn up|
    1998-10-01| BC| A request for examination has been filed|
    2000-03-01| BV| The patent application has lapsed|
    优先权:
    申请号 | 申请日 | 专利标题
    FR8709079|1987-06-26|
    FR8709079A|FR2748719B1|1987-06-26|1987-06-26|LOW SIGNATURE RADAR BLADE|
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