DE3821588C1 - Wing with weak radar echo - Google Patents

Abstract

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.

Description

The invention relates to a wing blade with weak radar echo, for the assembly of rotors on aircraft, esp special rotors of aircraft with at least partially rotating structure, in particular rotary wing aircraft and convertible aircraft, especially military helicopters purposes.

The object of the invention is to create a wing blade, especially for the rotor of a helicopter, the structure is built from resources that are specially selected and used to follow the radar echo of the sheet and Lich to reduce the rotor disc, which by the Dre hung of the different leaves with which the Rotor is equipped to maintain discretion or confidentiality mission of one with at least one such rotor equipped aircraft to increase and this for the to make electromagnetic radar bundles more difficult to detect.  

The basic idea of the invention is based on the one hand on the be known principle of all electrical conductors, the electromagnetic reflect table waves; by means of a radar On the other hand, the detection is not based on the reception at least part of the reflected fraction of the impact emit electromagnetic waves that are detected on a Are aimed. For the realization of a wing blade with low radar echo, which can also be called a "discrete" wing sheet can designate, the reflectivity of the Flü gel sheet for electromagnetic waves can be reduced. Furthermore, it is well known that any electromagnetic Wave with every change in the medium in which they are spreads into a reflected wave and into a broken one ne wave is implemented. The basic idea of the invention be therefore rests on the other hand on the need for the broken one Nen portion of an electrical impinging on a wing suppress the tromagnetic wave as quickly as possible to prevent this broken wave that is inside ren of the wing blade continues on the inner walls of the wing is reflected or a resonance phenomenon caused in the cavities of the wing structure to closing from the wing in the form of a reflected To emit wave that are caught by a radar can.

The invention thus relates to a wing blade, the Structure represents a good compromise between one sufficiently high permeability, i.e. a sufficient ge wrestle reflectivity, and a sufficiently high Ab sorption capacity for the electromagnetic waves, so the radar echo of such a wing is very weak.

For this purpose, the wing is made according to the invention Combined materials manufactured and contains:

• - At least one spar of thread layers with fibers of high mechanical strength by means of a polymerized synthetic resin are agglomerated,  
• - a rigid, load-bearing shell that matches the mechanical one Structural strength of the wing blade contributes and little least a layer of fiber fabric of high mechanical Strength as well as with polymerized synthetic resin has agglomerated and
• - At least one filling element made of a light synthetic Material which is arranged in the supporting shell;

it is characterized in that the supporting shell and each spar are made from dielectric fabrics where in the material of each filler element for the electroma is magnetic wave absorbing material, and / or the load-bearing shell, every spar and every filling element in one Structural core are assembled, which the Structural Fe Stability of the wing blade guaranteed and by a ver clothing is surrounded, which is a rigid and profiled exterior shell made of dielectric materials as well as a flexible and lightweight layer of synthetic material, wel ches absorbed the electromagnetic waves and the filling guarantee between the structural core and the outer shell to form a radar screen.

The invention proposes three main embodiments of the "dis "wing blade.

In the first embodiment, all the essentials are components of the wing, especially all load-bearing Elements, either of dielectric materials or of sol Chen built materials that absorbed electromagnetic waves beers.

This not only avoids the use of me metallic components, but also of such components, containing boron or carbon during this last material compared to other substitutes such as Glass or aramid fibers, in particular of the commercial type drawing KEVLAR, is particularly powerful.  

It follows that the "radar discretion" of the wing leaf in this first embodiment only at cost a mass increase with otherwise the same ratio compared to a "non-discreet" wing blade Geometry can be achieved that has elements that made from possibly conductive substances and opti are lubricated, for example from fabrics or carbon fibers, which in particular for the rigid supporting shell of the Wing blade applies.

In a second embodiment of the Flü according to the invention Gelblattes are all components that make up the structure Stability of the wing blade result in a structural core grouped and assembled, which by a two-layer surrounded casing, the outer layer of which is rigid Shell is made according to the desired aerodynamic pro fil of the wing blade is profiled and made of dielectric Materials, while the inner layer is flexible and absorbent fill layer that is a radar screen forms. In this embodiment, if the electromagnetic waves hit the wing, they cross the outer shell and are then in the fill layer "captured" and absorbed. It therefore remains possible to conduct capable materials, especially carbon fibers in the form of thread layers or fabrics to the elements of the structural core, with the low radar echo remains preserved.

Because the cladding forming the radar screen at the same time a protective shield for the structural core against impacts (Stones and branches) forms, as well as against different ones Influences from the environment, i.e. against damage gene, the components of the structural core with regard their characteristics optimized and trained with minimal thickness without the harmful environment mentioned above to consider rivers.  

Because of this, it is possible to manufacture to gain sufficient mass of the structural core, in Ver equal to a wing made of dielectric materials, by the mass disadvantage of the ver to compensate for clothes.

This second embodiment is not on the case limits, in which the structural core at least one spar lay of thread and a supporting shell made of layers of Contains fiber fabrics, which around at least one filling element closes, as explained above, but extends to all possible structures of the structural core, whether the Cross section of the same (along the chord of the wing blade) has a contour that is substantially parallel to the Pro fil is the outer shell of the cladding, the then Filling layer made of flexible and absorbent material preferably a film to compensate for tolerance deviations between the contour and this profile, or whether the structure turkern has a cross section with a facet contour, which is based on simple geometric shapes, for example se triangles and quadrilaterals, the filling layer then flexible and absorbent material preferably a pole star layer to compensate for the various forms between contour and profile of the outer shell of the cladding. It should also be noted that such an execution is also allows the contour of the structural core to be large Tolerance approximate shape of an aerodynamic profile which compensate by attaching the panel is made to be an economical manufac to facilitate the development of the structural core.

In the third embodiment, which is a particularly high "Radar discretion" of the wing blade while accepting one realized certain mass disadvantage, includes the wing a structural core made of dielectric or absorbent Elements covered by a dielectric Outer shell and more flexible and absorbent, a radar  screen-forming filling bowl is surrounded. In particular, can a wing according to this third embodiment as a such appear after the second embodiment, at which in turn the core of the structure is essentially like a Wing after the first embodiment described above form is formed.

In these different embodiments, at least a filling element, but preferably each of the wear in the the shell filled filling elements, from a relative rigid cell load loaded with conductive particles material or foam material formed. This freighted Ma material can be made in the same way as the foam materials usually for the production of "non-discreet" flues composite gel sheets, have a density that varies within a wide range. At fiction According to embodiments, the density of the used be freight material advantageously in an area which ranges from about 50 to about 200 kg / m³, the Chartering material about 5% by weight of the freighted material matters.

In the second and in the third embodiment, at which is the wing blade has a covering absorbent filling material of the radar screen Structural core advantageously a cellular dimension material or foam material containing conductive particles is freighted.

The freighted work is or are advantageous material or the freighted materials used for the manufac tion of the filling elements accommodated in the supporting shell and / or the fill and radar screen layer of the panel be used when the wing blade has such a bond dung, a polyurethane foam with electrical conductive particles is loaded. These particles can Be carbon particles, e.g. B. powder or carbon grains,  however, the chartering material is preferably made of Carbon fibers, each of which resembles a small antenna ne or a dipole behaves to the elec convert the tromagnetic wave into an electrical current, so that the corresponding energy through the Joule effect is consumed, resulting in a very effective absorption in the absorbent foam is guaranteed.

In the first and in the third embodiment the thread layers of each spar and the fabric of each layer of the supporting shell preferably formed from fibers under the aramid and glass fibers are selected, while the resins used for agglomeration preferably under Epo oxide resins, polyester resins or thermoplastic resins are selected.

The invention further proposes the "radar discretion" to increase the blade by taking special measures the structural parts of the same. Especially are all opposites in the different embodiments weights and static and / or dynamic balancing weights the blade is made of a composite material, which consists of particles of at least one heavy metal oxide, which in at least one polymerized synthetic resin are agglomerated. Furthermore, the mass carrier in the form of a block of dielectric composite material forms. For the protection of the front edge is preferably white thereafter provided a strip of an elastomer which preferably made out of polyurethanes and silicones chooses; but it is possible to protect the front edge to form as a hood made of thermoplastic resin, before preferably with an insert made of dielectric fibers strengthens, this reinforcing insert made of fibers for example as the shape of a layer of fiber fabrics, which form an erosion protection layer.  

In a wing according to the second embodiment the optimization of the structural core preferably through the The fact ensures that at least one spar and / or we at least one layer of the supporting shell of the structural core with thread layers and / or a fabric made of carbon fibers is provided.

In this case, as in the case of a wing blade after the third embodiment, the lining is preferred a non-load-bearing covering, the outer shell of which is preferred like a thermoformed resin, not shell belonging to the structure is, if necessary, at least part is reinforced with the electrical fibers.

Choosing a thermoplastic resin for manufacturing the rigid profiled outer shell of the non-load-bearing Ver clothing is not only advantageous because this measure material is dielectric, but also insofar as this Material excellent properties in terms of upper surface quality, erosion resistance, shock resistance Stability and repair ability because simple Interventions by the user are possible because this cladding is not a structural part. Small damages can on the be repaired by the user without the wing blade to send back to the factory. Choosing a thermoplastic Resin also enables production to be avoided with lengthy finishing phases, for example Spach tending, grinding and mending, as well as avoidance the paint job when the chosen thermoplastic resin is in the mass is colored, so that overall considerable savings manufacturing, maintenance and repair.

If a wing blade according to the first embodiment, that is without cladding, is provided with approaches, which on the Trailing edge of the wing blade are attached, so this is characterized in that each approach is an element insulating material in the form of a wedge that is with  Narrow side directly on the edge strip of the trailing edge of the wing blade is glued.

In the various embodiments, it is for reinforcement Kung the skeleton of the wing blade advantageous that this further a central composite spar, preferably from di has electrical material that spans the span of the wing blade essentially in the middle of its tendon extends while its transverse ends facing towards the Seh ne run, each over a composite panel of preference wise dielectric material with the inner surface of the flü top side or the inner surface of the underside of the wing rigid supporting shell are firmly connected to this Shell and a box with a spar at the front edge structure to be made with a front filler is filled, with a rear filling element also those Fills part of the supporting rigid shell, which differs from the Back of the central spar to the trailing edge of the Flü gel leaf stretches.

Regardless of the special training of the structural elements te of the wing blade according to the invention, this is a clot The radar echo has a wing made of composite materials, if it is after the second and third embodiment is generally further characterized in that it contains:

• - A structural core, preferably with approximately aerodynamic profile, which is the structural strength of the wing sheet guaranteed, and
• - a cladding surrounding the structural core, comprising:
  • - A rigid outer shell with the desired aerodynamic profile made of dielectric materials and
  • - A layer of a non-load-bearing shape adjustment material, which is light and smooth and takes over the filling between the core and the outer shell and absorbs electromagnetic waves to form a Ra screen.

In all cases where the wing blade is a fairing it is for assembly, disassembly, changing and, if necessary to repair the panel advantageous that this from consists of two complementary layer components, each one of two complementary parts of the radar screen forming layer of absorbent material and one of two complementary parts of the dielectric outer shell comprises, wherein the two complementary layer components of the Covering around the structural core and firmly attached to each other the and preferably also connected to the structural core are, for example by gluing.

In general, all of the wing blades according to the invention Connections preferably glued; if however attachment screws are used, for example for fastening of the wing shaft on the running wing part, so Plastic material screws are used, for example made of nylon or Torlon (trademark).

Further features and advantages of the invention result from the following description of several embodiments and from the drawing to which reference is made. In the drawing show:

Figure 1 is a cross section along the chord of a first embodiment of a rotor blade for a helicopter without fairing.

Figure 2 shows a cross section along the chord in a two-th embodiment of a rotor blade for a helicopter, the blade being provided with a covering. and

Fig. 3 is a perspective view with parts shown torn off at a portion of the running part of the blade, which is shown in Fig. 2 in section Darge.

. The vane 1 shown in Figure 1 comprises a beam 2 at the front edge, which is of a bundle rectified extending thread layers of dielectric fibers of high mechanical strength, for example glass, is formed; these thread layers are agglomerated by means of a synthetic, thermosetting and polymerized impregnating resin, which is also a dielectric resin, for example epoxy resin.

This spar has a substantially C-shaped cross section due to the convex curvature of its wing underside and wing top and the concave cavity be ner back, in this way a rear wing 2 a on the wing underside and a rear wing 2 b on the wing top form. In addition, this spar 2 has a small concave recess on its front surface, the task of which is explained below.

The spar 2 thus constructed comprises, in a known manner, a wing shaft, by means of which it is connected to the hub of a rotor; this spar 2 is intended to absorb the majority of the centrifugal forces to which the wing blade is exposed during operation.

This wing 1 also includes a rigid working or supporting shell 3 , which is equipped with the desired aerodynamic profile of the wing.

This supporting shell 3 is built up by stacking several layers of a fabric made of dielectric fibers of high mechanical strength and agglomerated by means of a polymerized synthetic resin, for example from layers of glass fiber or aramid fiber that are crossed and their warp and weft fibers around 45 ° inclined towards the direction of the leading edge of the wing, these layers are pre-impregnated with a thermosetting resin, for example of the epoxy type, and are polymerized warm. This shell is formed in a conventional manner, with finishing steps, which may include closing joints, spatulas, sanding and painting, in order to provide the outer surface of the shell 3 with a layer of lacquer which absorbs electromagnetic waves.

The spar 2 is arranged in the zone of the front edge of the shell 3 , with which it is rigidly connected by polymerization of the resins, along its convex wing top and wing underside and along its rear wings 2 a and 2 b and in such a way that the concave recess on its front with the shell 3 defines a receptacle, which is taken up by counterweights for centering and static and / or dynamic balancing masses 4 .

These counterweights and balancing masses 4 are produced from a composite material consisting of a granular fertilization mass of a heavy metal oxide, for example lead oxide, agglomerated with a polymerized synthetic resin. These counterweights and balancing weights 4 do not belong to the mechanically fixed skeleton of the Flügelblat tes, which in turn is completed by a supporting central longitudinal beam 5 . This longitudinal spar 5 of the electrical composite material extends essentially over the entire span of the wing blade in the middle of its chord and has an approximately Z-shaped cross section, with a central part which forms the web 5 c and consists of a plate in a honeycomb structure , which is covered on each side with layers of glass fiber fabric, which are pre-impregnated with a thermosetting resin, and two legs 5 a, 5 b, which are each formed by superimposing the extensions of the impregnated glass fabric layers on the surfaces of the central leg 5 c.

The leg 5 a on the underside of the wing rests on the upper surface of a dielectric composite plate 6 a on the underside of the wing, which is formed, for example, by overlaying several layers of resin pre-impregnated glass fibers that run in the longitudinal direction, this Ver composite plate 6 a with its underside against the inner surface of the wing bottom 3 a of the shell 3 is applied; in an analogous manner, the leg 5 b rests on the upper side of the wing on the lower surface of a dielectric composite plate 6 b on the upper side of the wing, which is formed by superimposing several layers of glass fibers pre-impregnated with resin, which run in the longitudinal direction, and with their upper surface against the inner surface of the inner top 3 b of the shell 3 is created, but closer to the spar 2 than the leg 5 a and the composite plate 6 a. The simultaneous polymerization of the thermosetting resin, with which the different parts of the legs 5 , the composite panels 6 a, 6 b and the Gewebela conditions of the shell 3 are impregnated, ensures a rigid connection of the spar 5 via the composite panels 6 a, 6 b directly with the top and bottom of the rigid load-bearing and dielectric shell 3 . In this way, the spar 5 with the supporting dielectric shell 3 and the dielectric spar 2 limits a box structure on the front or front edge, which is filled with a front filling body 7 a, while the dielectric spar 5 with the dielectric supporting shell 3 alone , forms in Demjéni gene part, which is directed towards the trailing edge thereof, a rear body structure at the trailing edge, wel che also with a filler is filled, namely the rear packing 7 b. These packing elements 7 a and 7 b each consist of a light and relatively rigid foam made of carbon loaded with polyurethane. This loaded foam can be made by a method and apparatus for distributing solid cargo particles in polyurethane foam as described in U.S. Patent 3,256,218. This publication describes in particular a method for distributing solid and fiber-shaped particles, the dimensions of which are at least as large as the mean diameter of the cells of the foam, with a substantially uniform distribution of the fibers or fiber pieces in the cellular mass, and essentially one uniform distribution of the elements that make up the polyurethane foam in the entire volume it occupies. The loaded foam, which is used to produce the packing 7 a and 7 b, has a density between about 50 and about 200 kg / m³, while the cargo material made of carbon fiber pieces makes up about 5% by weight of the loaded foam material. This behaves like a "semiconductor material" and is therefore more reflective than a non-loaded polyurethane foam, but at the same time - and above all - more absorbing for the electromagnetic waves. The large number of carbon fiber pieces present in the foam behave like a small antenna or a small dipole, which converts the electromagnetic waves into electric currents, which cause the fiber pieces to be heated by the Joule effect, which means that the wave that strikes them carried energy is consumed and dissipated. This gives foam body 7 a and 7 b, which absorb the electromagnetic waves that could penetrate the electrical shell 3 , the front part of which is protected by a protective cover 8 for protecting the front edge. This protective hood 8 is also non-conductive and either built up from one or more elastomer strips, for example made of polyurethane or silicone, which are glued to the dielectric shell 3 , or formed by thermoforming a thermoplastic resin, which can optionally be reinforced with glass fibers, example, a layer of glass fibers, which forms an erosion protection layer, while the thermoplastic protective hood is glued to the dielectric shell 3 .

If the wing blade is provided with lugs 9 , these are realized in the form of small, triangular or wedge-shaped elements made of rigid and insulating material, each of which stripes are glued directly to the edge on the trailing edge 3 c with their narrow side, which is glued by the union the parts 3 a and 3 b of the shell 3 on the wing upper side and wing underside at the trailing edge forms ge. This gives a wing blade that causes a low radar echo, because it is both of low reflectivity and of high absorbency against the electromagnetic waves, since both the structural elements and the non-structural elements consist of dielectric substances and fillers from sorbing loaded foam are provided.

The second embodiment of the wing blade 10 shown in FIGS. 2 and 3 comprises a structural core 11 which is designed in the form of a primary structure which comprises all the essential structural elements of a helicopter wing blade of a known structure, comparable to the wing blade according to FIG. 1 , while the structure of the structural core 11 comes very close to that of a conventional wing, with the exception, however, of the choice of materials, if one considers the wing described above with reference to FIG. 1.

This structural core 11 comprises a spar 12 at the front edge, which is formed from rectified thread layers of mineral fibers or organic fibers of high mechanical strength, preferably of glass or aramid fibers, these threads being agglomerated by means of a thermosetting and polymerized synthetic impregnating resin are. This spar 12 has a substantially C-shaped cross section, due to the convex curvature of its surfaces on the wing top and bottom and on the basis of the concave recess of its back, so as to have a rear leg 12 a on the underside of the wing and a rear leg on the To form wing top. A small concave recess is also provided on the front side of the spar 12 , which has a wing shaft for connection to a rotor hub in a known manner.

The structural core 11 also includes a rigid supporting or working shell 13 , the cross profile, without greater accuracy, runs essentially parallel to the final aerodynamic mixing profile that is desired for the wing blade. This load-bearing shell 13 is carried out without finishing, that is, without filling in joints, spatulas, sanding and painting, by stacking several layers of fabrics made of mineral fibers or organic fibers of high mechanical strength, which are agglomerated by means of a polymerized synthetic resin. For example, the load-bearing shell 13 consists of two crossed layers of carbon fiber fabrics, the warp threads and weft threads of which are inclined by approximately 45 ° to the direction of the leading edge of the wing blade, where these two layers are pre-impregnated with a thermosetting resin, for example of the epoxy type, and are thermally polymerized . The spar 12 is arranged in the zone of the front edge of the shell 13 , to which it is rigidly connected by polymerizing the resins along its convex surfaces on the top and bottom of the wing and with its rear legs 12 a and 12 b, the concave Recess on its front with the shell 13 forms a receptacle, which are taken by counterweights or from equal masses 14 , which are made of a heavy metal.

The structural core also includes a load-bearing and central longitudinal spar 15 , which is made of composite material and extends substantially over the entire span of the wing blade in the middle of its chord and has a Z-shaped cross section in wesentli Chen, with a central part having a web 15 c forms, which consists of a plate in honeycomb structure, which is covered on both sides with layers of carbon fibers, which are impregnated with a thermosetting resin, and consists of two legs 15 a, 15 b, each of which is pre-impregnated by the extensions of the extensions Carbon fiber fabric from the surfaces of the central leg 15 c are formed. The leg 15 a on the underside of the wing rests against the top of a composite side 16 a on the underside of the wing, which is formed from a stack of several layers of carbon fiber fabrics, the fibers of which extend in the longitudinal direction and which are pre-impregnated with a thermosetting resin, the composite plate 16 a is created with its underside against the inner surface of the shell 13 on the underside of the wing; in an analogous manner, the leg 15 b is placed on the upper side of the wing against the underside of a composite panel 16 b on the upper side of the wing, this composite panel 16 b consisting of a stack of several layers of carbon fiber fabric, the fibers of which also run in the longitudinal direction and which are coated with a thermosetting resin are pre-impregnated. The composite plate 16 b is applied with its top against the inner surface of the shell 13 on the upper side of the wing, but in a position that is closer to the spar 12 than the leg 15 a and the composite plate 16 a. The simultaneous polymerization of the thermosetting resin with which the various parts of the spar 15 , the composite panels 16 a, 16 b and the layers of the shell 13 are impregnated ensures a rigid connection of the spar 15 by means of the composite panels 16 a and 16 b directly with the parts of the rigid and load-bearing shell 13 on the top and bottom of the wing. In this way, the spar 15 with the supporting shell 13 and the spar 12 limits a box structure on the front or on the front edge, which is preferably filled with a front filler 17 a; the spar 15 delimits with le diglich the supporting shell 13 in that part which faces the trailing edge thereof, a rear box structure on the side of the trailing edge, which is filled in if necessary, namely with a rear filling body 17 b. These packing 17 a and 17 b are each formed from a light, relatively rigid, wavy or foam-like synthetic resin material, for example made of polyurethane foam, or consist of a synthetic layer material with a honeycomb structure in order to have the desired designs.

The realization of such a structural core 11 comes close to the design of the wing blade according to FIG. 1, with the exception, however, that on the one hand another material selection takes place which can be optimized with regard to the characteristics and dimensions, in particular with regard to the thickness, regardless of the electrical ones Conductivity properties of these substances, when using layers of carbon fibers, and on the other hand no finishing of the supporting shell 13 is carried out, in particular its shape, which is only approximately parallel to the desired aerodynamic end profile, this shell without great dimensional accuracy and with a relative large tolerance of their approximate profile is produced, but this is always compensated for by the attachment of a covering 18 described above around this structural core 11 . It is evident that the realization of the structural core 11 is considerably simplified in this way.

The cladding 18 is not load-bearing and is constructed as a layered composite structure from two superimposed layers, each of which does not contribute to the structural strength of the wing blade. This panel 18 consists of that around the structural core 11 around a half panel 18 a on the wing underside and a half panel 18 b on the wing top side are added, which are complementary to each other. Each of these two half panels 18 a, 18 b comprises a rigid and thin outer layer made of thermoplastic resin, which can be colored in the mass and is precisely thermoformed with the desired profile to the part 19 a on the underside of the wing or part 19 b on the To form the top of the wing of a rigid, thin and non-load-bearing outer shell, which is dielectric, but can only withstand aerodynamic stresses; it is precisely shaped with the desired aerodynamic profile.

Each half panel 18 a, 18 b further comprises an inner layer made of a light synthetic foam which is flexible and deformable and loaded with conductive particles to form a shape-matching layer 20 a on the wing underside or a shape-matching layer 20 b on the wing top, which are intended to form the space between the profiled and non-load-bearing outer shell ( 19 a, 19 b) and the load-bearing inner shell 13 by absorbing and / or absorbing shape differences between the contour of the inner shell 13 and the exact profile shape of the outer shell ( 19 a, 19 b) can be compensated and at the same time a radar screen for the structural core 11 is formed. The foam used to make the fill and conformal layer ( 20 a, 20 b) is a flexible polyurethane foam loaded with carbon fiber pieces to form a layer absorbing the electromagnetic waves under the same conditions as the absorbent fillers elements 7 a and 7 b of the leaf described with reference to FIG. 1. The thermoplastic and dielectric outer shell ( 19 a, 19 b) lets the electromagnetic waves pass through, which are absorbed by heat dissipation due to the heating of the carbon fiber pieces in the foam of this layer ( 20 a, 20 b), so that this absorbing layer acts as a radar screen works. At the same time, this filling and shape adaptation layer ( 20 a, 20 b) of the cladding 18 ensures the adaptation of the profiled, non-load-bearing shell ( 19 a, 19 b) around the structural core 11 . In the zone of the front edge, each outer half-shell 19 a, 19 b has a part 19 c which is slightly thickened inwards in order to provide protection for the front edge; the thickness of the foam-Forman fitting film 20 a, 20 b is greater than its thickness near the trailing edge. The average thickness of the loaded deformable foam layer is 5 mm, while the average thickness of the profiled dielectric outer shell is about 1 mm.

To facilitate the assembly of the panel 18 around the structural core 11 , each loaded foam sheet 20 a, 20 b is glued against the concave inner surface of the corresponding half-shell 19 a and 19 b to produce the two half-panels 18 a, 18 b then placed around the structural core 11 and glued to its opposite surface on the wing underside or wing top and glued together at the merging planes of the leading edge and the trailing edge.

The use of a thermoplastic resin, which may be colored in the mass, for the production of the profiled outer shell ( 19 a, 19 b) enables the exploitation of the qualities and properties of this material, which besides the electrical properties in a perfect surface texture , which means that lengthy and difficult finishing steps such as sanding, filling and painting can be eliminated, and are more resistant to erosion than conventional paint coatings. In addition, the outer shell ( 19 a, 19 b) and the shape-matching and filling layer ( 20 a, 20 b) made of loaded foam, in association with one another to form the cladding 18 , simultaneously form a protective screen for everyone in the core 11 of the wing blade combined structural elements with regard to joints of medium size, which occur particularly numerous and occur, for example, from stone chipping and contact with branches. If the cladding 18 is damaged locally, since it is not a structural element, it is possible for the user to carry out simple repair work himself, which can happen with parts of the same material quality. In the event of severe damage, the wing blade is dismantled and sent back to the factory, where the covering 18 is then removed in order to check the condition of the structural core 11 ; if necessary, a repair can be carried out to repair damage to the structural core. In addition, the fairing 18 may be repaired more or less locally, or it may simply be replaced by another, the same fairing, which also has a dielectric outer shell and a flexible and absorbent filler layer if the original fairing is too thick damaged and no longer usable to obtain a reusable wing. Of particular importance is also that the fairing 18 is not absolutely necessary for the function and if the fairing is torn off during flight, the aerodynamic properties of the approximate profile of the structural core 11 can be used to ensure the return of the aircraft To make it possible to land, since these aerodynamic properties of the structural core are not as good, but are still sufficient.

To increase the shock and erosion resistance, it is possible to reinforce the resin, which is in the profiled outer shell ( 19 a, 19 b), with a relatively small amount of fibers, provided that these are not conductive, or it can this shell ( 19 a, 19 b) by a layer of non-conductive fiber fabrics, which acts as an anti-erosion layer and is reinforced by a polymerized synthetic impregnating resin.

In this way, a wing blade is still created, which generates a weak radar echo and whose Structural elements are well protected by the cladding, which forms both a radar screen and a protective shield. In addition, the non-load-bearing cladding 18 is not absolutely necessary for the flight function, but is wear-resistant and interchangeable, which also makes it possible to change the profile of the wing blade both along the span and along the tendon, which can be done in modular form by the half-claddings 18 a, 18 b for the wing underside and wing top with the desired curvatures. You can change the profile of a wing blade, its absorption properties th against electromagnetic waves, however, or adjust or change this profile, on the condition, however, that one starting from the same structure core 11 remains essentially within the profiles of the same generation Ge.

It should also be emphasized that the mass disadvantage due to the presence of the cladding 18 can be compensated for by optimizing the elements that make up the structural core 11 . Since this is namely protected by the United clothing 18 , its components can each be realized in minimal thickness or in optimized characteristic data without having to take into account the various interfering influences and impacts to which the wing blade is exposed during operation.

The structural core 11 can obviously only be checked before it is provided with the cladding 18 . After this covering has been applied and glued on, the final inspection consists of an external inspection.

It is also important to note that the contour of the cross section of the structural core 11 can deviate considerably from the aerodynamic profile of the outer shell 19 :
For example, the structural core 11 may have a faceted structure, in particular a contour in the form of a flattened hexagon, which is obtained when the front part of the spar and the supporting shell has a triangular cross section and the rear part of this supporting shell also has a triangular cross section has, which extends to the trailing edge, while the central part of the structural core 11 , which is located substantially between the spar and the central leg, may have a rectangular cross section.

Such a contour on the basis of simple geometrical shapes corresponds to a profile, which is only a rough approximation to the profile of the outer shell 19 , but is still aerodynamically good enough to make the cladding 18 unnecessary and the existence of the Secure aircraft when this panel 18 should be torn from the structural core 11 . In this case, the compensation of the more or less large differences between the shapes of the contour of the structural core 11 and the profile of the shell 19 is ensured by the loaded foam layer ( 20 a, 20 b) in the form of a relatively thick padding.

A third embodiment of a wing blade, which produces a weak radar echo and in which the "radar discretion" is preferred over the weight, consists in that a structural core 11 of the wing blade shown in FIGS . 2 and 3 is made of the same materials as those used to manufacture the wing blade of FIG. 1, only the lugs 9 on the trailing edge and the protective hood 8 on the leading edge not being adopted. So it can be the wing shown in Fig. 1 without the lugs 9 and without the protective cover 8 on the front edge as a structural core instead of the structural core 11 of the blade according to FIGS. 2 and 3 who used the. In this way, a dielectric and absorbing structural core is obtained, which in turn is provided with a non-load-bearing cladding with a dielectric outer shell and an absorbent filling and shape-matching layer forming a radar screen.

Such a design of a wing blade has its own maximum absorption in combination with the properties minimal reflection for the electromagnetic Waves on.

Claims (18)

1. Blade which causes only a weak radar echo, in particular for the rotor of an aircraft, especially with an at least partially rotating supporting structure, such as a helicopter, made of composite materials and with:

• at least one spar ( 12 ) made of layers of thread consisting of fibers of high mechanical strength, which are agglomerated by means of a polymerized synthetic resin,
• - A working or load-bearing rigid shell ( 13 ) which takes part in the structural strength of the wing blade ( 10 ) and comprises at least one layer of a fiber fabric made of fibers of high mechanical strength, which are agglomerated by means of a polymerized synthetic resin, and
• - at least one filling element ( 17 a, 17 b) made of a light synthetic material, which is arranged in the supporting shell ( 13 ),

characterized in that the supporting shell ( 13 ) and each spar ( 12 ) are formed from dielectric's materials and the material of each filling element ( 17 a, 17 b) is a material which absorbs the electromagnetic waves, and / or the supporting one Shell ( 13 ), each spar ( 12 ) and each filling element ( 17 a, 17 b) are composed of a structural core ( 11 ), which ensures the structural strength of the wing blade ( 10 ) and is surrounded by a covering ( 18 ), the one rigid and profiled outer shell ( 19 a, 19 b) made of dielectric materials and a flexible, light and the electromagnetic waves absorbing layer ( 20 a, 20 b) comprises a synthetic material, which the space between the structural core ( 11 ) and Fills the outer shell ( 19 a, 19 b) to form a radar screen. 2. Blade according to claim 1, characterized in that at least one filling element ( 17 a, 17 b), which is received in the supporting shell ( 13 ), consists of a relatively rigid cell material or foam and is loaded with conductive particles. 3. wing according to claim 2, characterized in that the density of the loaded material used in a range is from about 50 to about 200 kg / m³ extends, the chartering material about 5% by weight of the freight material. 4. Blade according to one of claims 1 to 3, which has a lining ( 18 ), characterized in that the flexible and absorbent filling material, which forms a screen for the structural core ( 11 ), is a cell or foam material, which with conductive Particle is loaded. 5. Wing according to one of claims 2 to 4, characterized in that the material or the materials which are used for the realization of a filling element ( 17 a, 17 b) ver, and / or the filling and screen layer ( 20 a, 20 b) the cladding ( 18 ) consist of a polyurethane foam which is loaded with carbon particles. 6. Blade according to claim 5, characterized in that the carbon particles that make up the chartering material form, are pieces of carbon fiber. 7. Blade according to one of claims 1 to 6, characterized in that the thread layers of each spar ( 12 ) and the fabric of each layer of the supporting shell ( 13 ) are formed from fibers which are selected from aramid fibers and glass fibers, while the resin or the resins for agglomerating and the stiffening are selected from epoxy resins, polyester resins or thermoplastic resins. 8. Blade according to one of claims 1 to 7, of the type with at least one counterweight for centering and / or a static and / or dynamic balancing mass ( 4 ), characterized in that each counterweight and each balancing mass are made of a composite material that is formed from particles of at least one metal oxide, preferably heavy metal oxide, which are agglomerated in at least one polymerized synthetic resin. 9. Wing according to one of claims 1 to 8, of the type with a protection ( 8 ) for the front edge, characterized in that this protection comprises at least one strip of an elastomer, which is preferably selected from polyurethanes and silicones. 10. Blade according to one of claims 1 to 8, of the type with a protection ( 8 ) for the front edge, characterized in that this protection is realized in the form of a hood made of thermoplastic resin, which is preferably reinforced by a reinforcement made of dielectric fibers is. 11. Blade according to one of claims 1 to 10, with a lining ( 18 ) which surrounds the structural core ( 11 ), characterized in that at least one spar ( 9 ) and / or at least one layer of the supporting shell ( 13 ) of the structure Turkerns ( 11 ) each comprise thread layers and / or fiber fabrics made of carbon fibers. 12. Blade according to one of claims 1 to 11, with a panel ( 18 ), characterized in that this panel is a non-load-bearing panel. 13. A blade according to claim 12, characterized in that the outer shell ( 19 a, 19 b) is a non-structural, thermoformed shell made of a thermoplastic resin, which is optionally at least partially reinforced by dielectric fibers. 14. Blade according to one of claims 1 to 3 and 5 to 10, without cladding and of the type with lugs ( 9 ) which are attached in the region of the trailing edge, characterized in that each lug ( 9 ) is an element made of insulating material and is in wedge shape, which is glued with its narrow side directly onto the edge strip ( 3 c) on the trailing edge of the wing blade ( 1 ). 15. Wing according to one of claims 1 to 14, characterized in that it further comprises a central, preferably dielectric composite spar ( 5 ) which extends along the span of the wing ( 1 ) substantially in the middle of its chord and from its transverse ends (5 a, 5 b), along the chord, the one (5b) via a preferably composite dielectric plate (6b) rigidly connected to the inner side of the portion lying on the upper wing surface (3 b) and the other (5a) rigid with the inner face of the part lying on the Flügelun bottom ( 3 a) of the rigid supporting shell ( 3 ) is connected to form a box structure for the front edge with this shell and a spar ( 2 ) on the front edge, which by a front filler ( 7 a ) and a rear filling element ( 7 ) is filled, which also fills that part of the load-bearing rigid shell ( 3 ) which extends from the back of the central spar ( 5 ) to the trailing edge ( 3 c) of the wing blade ( 1 ) extends. 16. Blade, which produces only a weak radar echo, in particular for the rotor of an aircraft, in particular with at least partially rotating supporting structure, such as He likopter, made of composite materials, characterized in that it comprises:

• - A structural core ( 11 ) with a preferably approximate th aerodynamic profile, which ensures the structural strength of the wing blade ( 10 ), and
• - A covering ( 18 ) which surrounds the structural core ( 11 ) and comprises:
  • - A rigid outer shell ( 19 a, 19 b) with the desired aerodynamic profile and made of dielectric materials and
  • - A layer ( 20 a, 20 b) made of a non-structural form fitting material that is flexible and light and fills the space between the structural core ( 11 ) and the outer shell ( 19 a, 19 b) and absorbs the electromagnetic waves to a radar screen to build.

17. Blade according to one of claims 1 to 13, 15 and 16, with a panel ( 18 ), characterized in that this panel ( 18 ) consists of two complementary layer construction ( 18 a, 18 b), each of which is one of two complementary parts ( 20 a, 20 b) of the radar screen form the layer of absorbent material and one of two complementary parts ( 19 a, 19 b) of the dielectric outer shell, wherein the two complementary layer components ( 18 a, 18 b ) of the cladding ( 18 ) around the structural core ( 11 ) and connected to each other as well as to the structural core ( 11 ).