Aircraft radome incorporating a lightning protection system, and aircraft comprising such a radome

An aircraft radome includes a composite structure including, or according to the circumstances configured to define, at least one housing extending along the radome from a base of the radome. The housing receives an electrically conductive strip in contact with an inner surface of an outer wall, or according to the circumstances flush with the outer wall, of the composite structure. A conductive base is situated in the region of the radome base and connected to a ground of the aircraft. The composite structure of the radome is devoid of any perforations or through-passages in the region of the electrically conductive strip, and a first end of the electrically conductive strip is in contact with the conductive base.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application of PCT/EP2021/074728, filed 8 Sep. 2021, which claims benefit of Serial No. 2009090, filed 8 Sep. 2020 in France, and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications.

TECHNICAL FIELD

The invention relates to the technical field of radomes for aircraft. In particular, it concerns radomes incorporating a lightning protection system. The invention also relates to an aircraft equipped with such a radome.

TECHNICAL BACKGROUND

Classically, the aircrafts comprise a primary structure with outer walls mostly made from composite structures. The composite structures have a very favourable strength to weight ratio for use in such apparatus. The radome forming the protective outer wall of the antenna also incorporates such composite structures.

However, these composite structures can be damaged by lightning. Indeed, a lightning strike generates very high densities of electrical charge locally, which can damage them. These electrical charges cannot be evacuated by these composite structures, which are electrically insulating. Therefore, a lightning protection system is used, such as a metal mesh integrated into these composite structures, to ensure the evacuation of the electrical charges towards the ground of the aircraft. However, in the case of the radome, there is a design constraint since it must interfere as little as possible with the signals transmitted and received by the antenna. It is therefore not possible to provide a lightning protection system such as a metal mesh, which would be harmful to the quality of radio exchanges.

To protect the radome from lightning strikes, the aeronautical industry generally uses electrically conductive strips, usually made of aluminium or copper, integrated into the radome. These strips are electrically connected to the ground of the aircraft.

For example, electrically conductive strips protruding from the outer surface of the radome have been proposed. The disadvantage of such electrically conductive strips positioned on the outer surface, and therefore not flush with the outer surface, is that they create discontinuities in the flow of the flux around the aircraft and therefore reduce the aerodynamic performance thereof.

More recently, it has been proposed to limit aerodynamic disturbances by using a lightning protection system in which electrically conductive strips are placed on a face of the radome not exposed to the air flux, in particular, on the inner face of the radome.

The document U.S. Pat. No. 8,004,815 B2 discloses an aircraft radome comprising such a lightning protection system. The lightning protection system comprises an external wall10, an inner wall11and a plurality of electrically conductive strips13located on the inner wall11and on an unexposed face of the external wall10. The lightning current is received by means of metal studs15flush with the exposed face of the external wall10. The metal studs15comprise a threaded cylindrical portion passing through the electrically conductive strips13, which in turn allows the latter to receive the lightning current. Furthermore, the threaded cylindrical portion of the metal studs15extends well beyond the electrically conductive strips13. In fact, nuts17are arranged on the other side of the electrically conductive strips13in order to cooperate with the threaded cylindrical portion of the metal studs15and allow the electrically conductive strips13to be fixed.

However, such a system requires the radome to be drilled at several points in a line. This increases the risks in terms of long-term mechanical strength and the risk of water infiltration into the composite structure or even inside the radome. Furthermore, due to the use of metal studs, the metal surface area receiving lightning is very limited compared to that of an externally projecting strip, which increases the risk of local damage to the radome due to lightning strikes.

The document EP 2 219 950 B1 discloses a radome comprising a composite structure3comprising a lightning protection system in which electrically conductive strips of copper or aluminium are flush with an outer surface9of the radome. In this regard, the outer surface9has a hollow profile into which the electrically conductive strips1extend. Each electrically conductive strip1is attached to the composite structure3by means of a number of attachment means8,10. The attachment means8,10consist of screws10and nuts8. The screws10extend across the electrically conductive strip1. Each of them has a surface2flush with the outer surface9and an external thread which cooperates with a drilling hole in the electrically conductive strip1which has equivalent cooperation means for this purpose.

In such a system, as the external surface9is pierced at several points at the level of the electrically conductive strips1, this increases the risks in terms of long-term mechanical resistance and the risks of water infiltration into the composite structure or even into the interior of the radome. Indeed, during a lightning strike, the material of the external surface is necessarily pulverised due to the energies involved. Repeated lightning strikes are therefore likely to degrade the outer surface even more rapidly through holes (e.g., due to drilling) in that surface.

There is therefore a need to provide an aircraft radome with an aerodynamic lightning protection system, to limit the risks in terms of long-term mechanical strength as well as the risks of water ingress into the composite structure and the radome.

SUMMARY OF THE INVENTION

To meet this need, the invention proposes an aircraft radome comprising:a composite structure defining at least one housing located inside or outside the composite structure and extending along the radome from a base of said radome, said at least one housing receiving an electrically conductive strip and said conductive strip being either in contact with an inner surface of an external wall of the composite structure when said at least one housing is inside the composite structure or flush with the external wall of the composite structure when said at least one housing is outside the composite structure,a conductive base located at the level of said radome base and connected to a ground of the aircraft,

said composite structure being devoid of any perforations or passages through the external wall at the electrically conductive strip and a first end of said electrically conductive strip being in contact with the conductive base.

According to various features of the invention which may be taken together or separately:when the electrically conductive strip is flush with the external wall, an inner surface of the electrically conductive strip conforms the contours of the housing;the composite structure further comprises an inner wall and a core, for example in the form of a honeycomb, located between the external wall and the inner wall;the core is made of a single material along the radome;the radome further comprises at least one other housing formed in the external wall;the other housing is located in the extension of the housing and receives a second end of the electrically conductive strip and means for attaching said second end of the electrically conductive strip to the external wall;the attachment means is flush with portions of the external wall other than a portion where the second housing is formed;the attachment means is in the form of a patch attaching the second end of the electrically conductive strip in said at least one other housing;when the electrically conductive strip is in contact with the inner surface of the external wall of the composite structure, the housing comprises a U-shaped longitudinal portion comprising two longitudinal legs and a transverse leg, said housing comprising two hooking tabs at the inner surface of the external wall, said hooking tabs extending from the longitudinal legs;the composite structure further comprises an inner wall and a core, for example in the form of a honeycomb, located between the external wall and the inner wall, the housing extending through the thickness of the core;the core comprises, in a volume V3having as a base the housing and having as its height the distance between the housing and the inner wall, a material different from a material of the rest of the core;the radome comprises adhesion strips located at interfaces between the material and the rest of the core;the external wall has a thickness of between 0.15 mm and 1 mm;the first end of the electrically conductive strip bypasses the composite structure at the base;said first end of the electrically conductive strip is U-shaped;said first end of the electrically conductive strip comprises a first longitudinal leg extending into the housing, a second longitudinal leg contacting the base and a transverse leg connecting the first and second longitudinal legs bypassing the composite structure at the base;the composite structure comprises only the external wall, the housing and the electrically conductive strip, the inner surface of the external wall directly facing the interior of the radome;the electrically conductive strip is straight between the first end and the second end.

The invention further relates to an aircraft comprising an antenna capable of transmitting and receiving a radio frequency signal and a radome as previously described.

DETAILED DESCRIPTION

With reference toFIG.1, the invention relates to an aircraft nose radome1intended to protect an antenna located in the foremost part of the aircraft. However, in the context of the invention, the radome can also be a tactical radome placed in front of the aircraft underneath it. The radome may also be a SATCOM (Satellite Communication) radome used to protect satellite antennas on the aircraft. This type of radome is usually placed on an upper part of the aircraft. Still within the scope of the invention, the radome can also be placed on the rear part of the aircraft, in particular on an upper fairing of the aircraft, also on a side of the aircraft, etc.

In the following description, it has been chosen to describe the invention more precisely in the context of an application to a nose radome, without the invention therefore being limited to this single application.

The radome1comprises a base2which physically separates it from the rest of the aircraft (not shown). It comprises an electrically conductive base3(not visible inFIG.1), located at the base2, which allows the radome1to be electrically connected to ground of the aircraft.

In addition, the radome1comprises a composite structure10configured to provide lightning protection.

The composite structure10comprises an external wall12made of an electrically insulating material and an electrically conductive strip22, for example of aluminium or copper. Due to its external positioning, the external wall12is susceptible to electricity from lightning while the aircraft is in flight. In this regard, the electrically conductive strip22is arranged with respect to said external wall12so as to conduct electricity generated by lightning strikes to the conductive base3. The arrangement of the electrically conductive strip22with respect to the external wall12will be described in more detail below with reference to the various embodiments.

According to a first aspect of the invention, a first end24of the electrically conductive strip22is in contact with the conductive base3. Thus, as the conductive base3is connected to the ground of the aircraft, the electrically conductive strip22is also electrically connected to the aircraft ground via said conductive base3. The electricity received by the lightning strike can thus be conducted to the aircraft ground, thus preventing any damage to the external wall12, which is insulating by nature, by pulverising the material of said external wall12. The composite structure10thus configured allows to protect the radome1from lightning strikes. We will come back to this in the description relating toFIGS.4,5,9and10.

According to a second aspect of the invention, the composite structure10is devoid of perforations or passages passing through the external wall12at the level of the electrically conductive strip22. In other words, the external wall12of the composite structure may not comprise, in particular, through perforations resulting from machining or human intervention. This is made possible because the electrical connection of the electrically conductive strip22to the aircraft ground is made by the contact between the first end24and the conductive base3. More generally, the external wall12may not comprise any through passages. A “passage” is a place where a fluid can pass through. A perforation is therefore a particular type of passage. In other words, a passage is not necessarily a perforation, the term passage referring more generally to any place through which a fluid may pass through the external wall12.

As discussed in the preamble to this detailed description, this is not typically the case with composite structures of the prior art, in which means for attaching and/or grounding the electrically conductive strip always pass through at least the electrically conductive strip and the external wall. Thus, in the event of repeated lightning strikes to the composite structure, the latter being perforated at the attachment and/or grounding means of the electrically conductive strip, there is an increased risk that the size of these perforations will increase by spraying the material at their location and that ultimately the structural integrity of the radome will be compromised and fluid may leak into the radome.

The absence of through perforations in the external wall12, i.e., perforations passing through the external wall12, at the level of the electrically conductive strip22prevents premature wear of the composite structure10and favours a good mechanical resistance of the radome1even after several lightning strikes. Indeed, the external wall12forms a physical interface between the exterior of the radome1and the interior of the composite structure10. In some cases, as will be seen below, it can form with the electrically conductive strip22the interface between the outside and the inside of the radome.

It should be noted that “at the level of the electrically conductive strip22” means the volume of the composite structure10located around the sectional plane of the electrically conductive strip22, the sectional plane of the electrically conductive strip22being defined as the plane normal to the external wall12passing through the longitudinal axis of the electrically conductive strip22.

It is therefore understood that the volume of the composite structure10located around the electrically conductive strip22, including the electrically conductive strip22itself, is a volume in which there must be no fluid or electrical passage (lightning strikes) to the interior of the composite structure to avoid degrading its mechanical strength.

The aforesaid volume is therefore not limited to the embodiments presented in the present description only, but may adopt variable geometries according to any configuration of the electrically conductive strip22with respect to the external wall12which, without being illustrated or exemplified in the present invention, would be as previously defined.

For example, in the event that it is the electrically conductive strip22itself which by its configuration is likely to create a passage for fluid from the outside to the inside of the radome, the volume of the composite structure10located at the electrically conductive strip22corresponds at least to the volume of said strip itself.

Furthermore, with regard to the “through perforation(s)”, what is important in the context of the invention is that it does not pass through the external wall12.

A perforation going through the external wall12may consist of a succession of perforations which by virtue of their close positioning or in a chain create a communication between the exterior of the radome and the interior of the composite structure. For example, two drillings made in the external wall12without each of them passing completely through the external wall12if said drillings or passages are arranged to create a pathway for a fluid, for example air.

As will be explained below, the external wall12does not comprise any perforations or passages to the interior of the composite structure10. The external wall12is therefore completely continuous. Incidentally, as discussed above, all of the elements of the radome, including the electrically conductive strip22, are arranged so as never to pass through the thickness of the external wall12themselves.

According to another aspect of the invention, the radome1can be protected from premature wear without compromising the aerodynamic properties of the aircraft. In this regard, the composite structure10defines at least one housing20located inside or outside the composite structure10and extending along the radome from the base2. The housing20receives the electrically conductive strip22and according to the embodiment, either the electrically conductive strip22is in contact with an inner surface13of the external wall12when the housing20is inside the composite structure10or it is flush with said external wall12when the housing20is outside the composite structure10. By being positioned in this way, the electrically conductive strip22does not generate asperities on the surface of the external wall12, which asperities are likely to replicate on upper layers (e.g., antistatic, anti-erosion and protective coating layer) and thus does not disturb the air flow on the radome1. As a result, the positioning of the electrically conductive strip22does not have an adverse effect on the aerodynamic properties of the aircraft.

FIGS.2to5illustrate a first embodiment of the invention in which the electrically conductive strip22is flush with the external wall12, said housing20being outside the composite structure10. The housing20is understood to be “outside the composite structure10” when the housing20, although belonging to the composite structure10, is positioned on the side of external portions11of the external wall12.

With reference toFIG.2, in this first embodiment the housing20is formed directly in the external wall12. In other words, the housing20is an integral part of the external wall12. Advantageously, the housing20is in the form of a hollow profile formed in the external wall12. The hollow profile shape of the housing20is not only adjusted to the contours of the electrically conductive strip22, but also the depth of the hollow profile and thus of the housing20is adapted so that the electrically conductive strip22is flush with the external wall12. The shape of the hollow profile is “fitted” in that the housing20conforms to the shape of the electrically conductive strip22while being tightly packed around said electrically conductive strip22.

Indeed, the hollow profile is made during the moulding of the radome1by adequately combining the constructional principle of the radome1with the dimensions of the electrically conductive strip22. This means that already at the design stage, the dimensions of the electrically conductive strip22constitute a constraint to be taken into account when defining the dimensions of the housing20. In this respect and from a practical point of view, the moulding of the radome at the level of the housing20is carried out on a male cavity in a die mould. This method of forming the housing20avoids modifying the structure of the radome1by adding densified zones. It should be further noted in relation to this embodiment that the electrically conductive strip22is not attached to the housing20using through attachment means, otherwise a drilling would also be formed in the external wall12, in which the housing20is formed. Preferably, the electrically conductive strip22is bonded into the housing20. For this structural bonding, an adhesive such as 3M EC2216 may be used. Alternatively, it is also possible to carry out a cofiring by means of a self-adhesive film or prepreg to enable the electrically conductive strip22to be attached to the housing20.

As can be seen inFIG.3a, the electrically conductive strip22advantageously comprises an inner surface21conforming to the contours of the housing20. Thus, the inner surface21has a profile substantially identical to that of the hollow profile formed by the housing20. In addition, the electrically conductive strip22comprises an outer surface23flush with the external portions11of the external wall12other than a portion where the housing20is formed. The external surface23precisely follows the profile of the portions11. In other words, the external surface23is substantially flush with an imaginary surface passing through two lines M and N of the external wall12delimiting the housing20from the portions11and following the shape of the portions11. These lines M and N are illustrated inFIG.1(in perspective) and3a(in section). The portions11and the outer surface23thus define the shape of the contour, i.e., the “wet” surface, of the radome1. The arrangement of the electrically conductive strip22and the housing20in relation to the external wall12thus ensures that the air flow over the radome1is not impeded. In view of the above, it should be noted that the depth of the housing20thus corresponds to the distance between a bottom of the housing20and the imaginary surface passing through the two lines M and N.

Furthermore, as illustrated inFIG.3b, the electrically conductive strip22comprises a second end26and the composite structure10comprises a second housing30formed in the external wall12and receiving the second end26and means28for attaching the second end of the electrically conductive strip in the second housing30.

The second housing30is in line with the housing20, i.e., it adjoins the housing20and like the latter, the second housing30is free from through perforations as it is formed in the external wall12.

Advantageously, the attachment means28is fixed above the electrically conductive strip22in the second housing30, thereby protecting the second end26of the electrically conductive strip from becoming detached due to air flux. Indeed, unlike the first end24of the electrically conductive strip22, the second end26is oriented in the opposite direction to the air flux. Indeed, when the aircraft is in flight, the air flux flows from the front of the radome towards the base2. Preferably, the attachment means28is wider than the electrically conductive strip22itself so as to improve the attachment of said strip22.FIG.1further illustrates an example of an embodiment in which the attachment means28has a triangular shape overlapping and projecting beyond the second end26.

The attachment means28may be in the form of a patch, i.e. a generally flat and adhesive element, put in place during the draping phase by creating a reservation for the second end26. More precisely, the attachment means28comprises several adhesive faces, one being the face in contact with the electrically conductive strip22and at least two other faces in contact with lateral edges of the second housing30.

The radome1according to the invention also takes into account aerodynamic stresses at this second end26. In this respect, the attachment means28advantageously flush with the portions11of the external wall12other than a portion where the second housing30is formed. In other words, a face of the attachment means28exposed to the air flux is substantially coincident with an imaginary surface passing through the two lines M and N of the external wall12and following the shape of the portions11, in a manner similar to the external surface23of the electrically conductive strip at the level of the housing20. It should be noted that it does not matter whether the face of the attachment means28facing the outside of the radome is adhesive or not, since antistatic, anti-erosion and protective coatings cover the entire compositional structure10once it is completed. What is important is that the side of the attachment means28facing the outside of the radome is flush with the portions11so that during the subsequent deposition of these coating layers there is no obstacle to disturb the flow of air.

Like the housing20with the electrically conductive strip22, the second housing30forms a hollow profile fitted to the contours of the second end26and the attachment means28and its dimensions are adapted so that said attachment means28is flush with the external wall12. In this regard, as illustrated inFIG.3b, the second housing30may be deeper than the housing20, as in addition to receiving the second end26of the electrically conductive strip, the second housing30receives the attachment means28. During manufacture, the male cavity used to form the radome1is therefore adapted to take account of this dimensioning. It should be noted that, for simplicity, the second housing30is shown inFIG.3bwith a similar shape to that of the housing20, but that the second housing30may have a different shape. For example, this shape could be the triangular shape shown inFIG.1.

As previously mentioned, the composite structure10is devoid of perforations through the external wall12at the electrically conductive strip22. In this embodiment of the radome1, the composite structure10is also devoid of any mechanical parts for attaching the conductive strip22to the composite structure10in a volume V1of the composite structure10having as a base, in a geometrical sense, the external surface23of the electrically conductive strip and having as a height, in a geometrical sense, a thickness ES of the composite structure10(illustrated inFIG.2). It should be noted that the composite structure has substantially the same thickness ES along the radome1. The composite structure10thus has a structural homogeneity in the volume V1that allows it to better resist repeated lightning strikes, which results in the elimination of the risk of water infiltration in the composite structure10as well as the elimination of stress concentrations around the drilling zones under external mechanical stresses.

In this regard, the composite structure10may further comprise an inner wall16and a core14located between the external wall12and the inner wall16. In other words, by selecting volume V1as the observation window, the composite structure10comprises successively the inner wall16, the core14, the external wall12and the electrically conductive strip22from the inside of the radome to the outside of the radome. However, by selecting a viewing window outside of volume V1, the composite structure10comprises successively the inner wall16, the core14and the external wall12from inside the radome to outside the radome. In this viewing window, the core14is in contact with both an inner surface13of the external wall and an inner surface15of the inner wall.

The core14is, for example, in the form of a honeycomb, also called “nida” in the following, or of foam. Advantageously, the core14is made of a single material along the radome1. In other words, in this embodiment, the core14is in the form of a nida along the radome1. Thus, in addition to its structural homogeneity due to the absence of a part in the volume V1, the structural homogeneity of the composite structure10is also due to the fact that it is made of the same material in the volume V1but also outside this volume. This avoids the need to densify the drilled areas, thus saving manufacturing time and obtaining a radome with limited ground. This also simplifies the manufacturing method of said composite structure10.

With reference toFIG.4, the first end24of the electrically conductive strip advantageously bypasses the composite structure10at the level of the base2. In other words, the first end24of the electrically conductive strip is configured to bypass the external wall12, the core14and the inner wall16to contact the conductive base3. Bypassing the composite structure10at the base2avoids the need to drill the radome1to connect the electrically conductive strip22to aircraft ground. This avoids the previously mentioned disadvantages of through-perforations in the radome at the electrically conductive strip22.

Preferably, the first end24of the electrically conductive strip is U-shaped. That said, generally any shape that allows bypassing of the composite structure10could be suitable, the U shape being by no means limiting. The first end24of the electrically conductive strip comprises a first longitudinal leg24aextending into the housing20. The first longitudinal leg24afaces towards the outside of the radome1and is located in the vicinity of the base2. The first end24of the electrically conductive strip comprises a second longitudinal leg24bin contact with the conductive base3. More specifically, the second leg24bis at least partially in contact with the conductive base3. In other words, the second longitudinal leg24bneed not be entirely in contact with the conductive base3. The first end24of the electrically conductive strip further comprises a transverse leg24cconnecting the first and second longitudinal legs24a,24bbypassing the base2. In the example embodiment shown inFIG.4, the transverse leg24ctakes the form of an arc extending laterally towards the outside from the composite structure10, but it could take any other form as long as it connects the first and second longitudinal legs24a,24band bypasses the composite structure10at the base2. That being said, preferably, the transverse leg24bypasses the composite structure10in a close manner, which also allows it to improve the retention of the electrically conductive strip22.

In this regard, it should be noted that the bypassing is possible at the base2because the radome1is a part of the aircraft which is not only independent of other parts of said aircraft but also can be manufactured independently of other parts. Thus, bypassing the composite structure10with the electrically conductive strip22can be achieved at the time of manufacture of the radome1without undue technical difficulty by the manufacturer. Furthermore, the electrically conductive strip22has a thickness—between a few tenths of a millimetre and a few millimetres—which is sufficiently small not to prevent the assembly of the parts and not to generate any sealing defect in the external structure of the aircraft. At the same time, the adhesive used during the structural bonding process is used to seal the space left free and in the case of a cofiring, a paste seal will be used. The bypassing of the composite structure10by the electrically conductive strip22is therefore not only advantageous because it avoids through perforations which in the long run can cause problems of mechanical strength of the composite structure10, or even sealing problems, but also because it is technically easy to implement in a manufacturing method of the radome.

The base3is connected to the composite structure10by means of screws and non-through inserts. These pass through the second longitudinal leg24b, the inner wall16and the core14without passing through the first longitudinal leg24aand the external wall12. Only the second longitudinal leg24b, the inner wall16and the core16are therefore drilled, the first longitudinal leg24aand the external wall12remaining intact. The composite structure10therefore does not comprise any perforation in the external wall12, in particular in the area of the electrically conductive strip, but only at the aforementioned location. The composite structure10and the conductive base3are thus rigidly connected.

According to a variant illustrated inFIG.5, the composite structure10is advantageously a monolithic structure. By “monolithic structure” is meant that the composite structure10is devoid of a core14. In other words, the composite structure10comprises only the external wall12, the housing20and the electrically conductive strip22, the inner surface13of the external wall being directly opposite the interior of the radome. The monolithic structure has several advantages. In addition to saving material, the monolithic structure is also simpler to implement.

This is because when the composite structure10is in the form of a monolithic structure, the electrically conductive strip22can be straight between the first end24and the second end26, as the monolithic structure has a much smaller thickness than the composite structure10with a nida-shaped core14, so that it can be aligned with the conductive base3. Therefore, it is entirely possible to use a straight electrically conductive strip22between the first end24and the second end26. The manufacturing method of the radome1is further simplified. In this case, the composite structure10is connected to the radome1by screwing the composite structure10to the conductive base3. However, it should be noted that this attachment is not made at the electrically conductive strip22, but in a portion of the conductive base3that does not face the strip22.

FIGS.6to11illustrate a second embodiment of the invention in which the electrically conductive strip22is in contact with the inner surface13, said housing20being within the composite structure10. By the housing20is meant “inside the composite structure10” the fact that the housing20, although belonging to the composite structure10, is positioned on the side of the inner surface13of the external wall12.

With reference toFIG.6, in the second embodiment of the invention the housing20is closed by the external wall12, said external wall12completely covering the housing20and the electrically conductive strip22. In effect, the housing20is in the form of an open pocket or reservoir which would be open to the exterior at one face if it were not closed by the external wall12at said face. Incidentally, as the housing20accommodates the electrically conductive strip22, the latter is therefore encapsulated between the housing20and the external wall12. The arrangement of the electrically conductive strip22and the housing20with respect to the external wall12thus avoids creating asperities on the external wall12.

Advantageously, the external wall12has a thickness of between 0.15 mm and 1.00 mm. The external wall12thus has a thickness suitable for conducting the lightning energy to the electrically conductive strip22, and possibly being perforated in the event of a lightning strike on said external wall12, while limiting the quantity of pulverised material. Indeed, the energy at which the material is ionised during a lightning strike may be sufficient to pulverise a large quantity of material from which the external wall12is made. This must be limited as it is risky. Thus, the thickness range of the external wall12represents a compromise between the need to conduct the lightning energy to the electrically conductive strip22and limiting the amount of pulverised material. In this regard, the fact that the electrically conductive strip22is in contact with the inner surface13of the external wall keeps the thickness to a minimum.

With reference toFIG.7, the housing20has an Ω (“omega”) shape comprising a U-shaped longitudinal portion from which two hooking tabs20dextend.

The U-shaped longitudinal portion extends between the front of the radome, at a second end26of the electrically conductive strip, and the base2. In this embodiment, the second end26extends into the housing20and without being retained by an attachment means. Indeed, as the electrically conductive strip22is covered by the external wall12, no means for attaching the second end26is required as it is not susceptible to being unstuck by the air flux.

The U-shaped longitudinal portion comprises a transverse leg20aand two longitudinal legs20b,20cextending from the transverse leg20a. Since the electrically conductive strip22is disposed in the U-shaped longitudinal portion, the dimensions of the U-shaped longitudinal portion are adapted to the dimensions of the electrically conductive strip22. Incidentally, as the electrically conductive strip22is in contact with the inner surface13of the external wall, the length of the longitudinal legs20b,20cis substantially equal to the thickness of the electrically conductive strip22.

As for the two hooking tabs20d, they extend from the U-shaped longitudinal portion, giving the housing a general Ω shape. More specifically, each hooking tab20dextends from the other end of the longitudinal legs20b,20crespectively which is not connected to the transverse leg20a.

To form the “pocket” an additive to the moulding tool is added during this phase of the radome manufacturing method. This additive is then removed to allow insertion of the final metal strip. Preferably, said electrically conductive strip22is retained in the housing20which constitutes the pocket by a gluing or riveting or screwing method. It should be noted that in this area, it does not matter if the composite structure10is perforated since this area is never in direct contact with lightning strikes.

In the embodiment shown inFIG.7, the composite structure10may further comprise an inner wall16and a core14located between the housing20—and the portions of the inner surface13below the housing20—and the inner wall16. Let a volume V2of the composite structure10having as a base, in the geometrical sense of the term, an orthogonal projection of the housing20on the inner surface13and as a height, in the geometrical sense of the term, a thickness ES of the composite structure. Selecting as the observation window the volume V2, the composite structure10comprises successively, in this example of embodiment, the inner wall16, the core14, the housing20, the electrically conductive strip22and the external wall12, from the inside of the radome to the outside of the radome. Obviously, in the area of volume V2where the hooking tabs20dare located, the composite structure10comprises successively the inner wall16, the core14, the hooking tabs20dof the housing and the external wall12. However, by selecting an observation window outside the volume V2, the composite structure10comprises successively the inner wall16, the core14and the external wall12. In the latter observation window, the core14is therefore in contact with both the inner surface13of the external wall and an inner surface15of the inner wall.

In the example embodiment shown inFIG.8, the structure of the core14in a volume V3having as its base the housing20and having as its height the distance between the housing20and the inner wall16differs from the structure of the core14in the rest of the composite structure. It should be noted that the volume V3differs from the volume V2in that it does not include the volume between the housing20and the external wall12. In this embodiment, the volume V3comprises a material14aconsisting of a foam or densified zone, while the remainder14bof the core14is in the form of a honeycomb or nida14b. In practice, the volume V2constitutes a “reserve” which allows to differentiate the material14afrom the rest of the core14bas required, depending on the mechanical requirements. This reserve is produced by machining or thermoforming. In order to join the foam14ato the nida14b, the composite structure10may further comprise adhesion strips25located at the interfaces between the material14a, i.e., the foam14a. One interface being in close proximity to one of the hooking tabs20d, the other in close proximity to the other of the hooking tabs20d. Preferably, the adhesion strips25consist of intumescent areas. These are made by exposing the foam14ato heat which allows it to swell and better adhere to the nida.

Whilst in the example embodiments ofFIGS.7and8, the composite structure10comprises a core14in the form of a nida, this is not always the case, as will be seen in the description relating toFIGS.10and11.

With reference toFIG.9, the first end24of the electrically conductive strip advantageously bypasses the composite structure10at the base2. This bypass is similar to that seen with reference toFIG.4but differs only in the nature of the layers bypassed. Indeed, as seen previously, the electrically conductive strip22is not arranged in the same way with respect to the external wall12. Thus, in this embodiment, the first end24of the electrically conductive strip bypasses the housing20, the core14and the inner wall16to come into contact with the conductive base3. As a reminder, bypassing the composite structure10at the base2avoids the need to drill the radome1to connect the electrically conductive strip22to the aircraft ground. This avoids the disadvantages of through-perforations in the radome at the electrically conductive strip22. As before, the base3is connected to the composite structure10by means of screws and non-through inserts. These pass through the second longitudinal leg24b, the inner wall16and the core14without passing through the first longitudinal leg24aand the external wall12. Only the second longitudinal leg24b, the inner wall16and the core16are therefore drilled, the first longitudinal leg24aand the external wall12remaining intact.

As in the first embodiment, the first end24of the electrically conductive strip is therefore U-shaped. The description of the U-shape and its arrangement in the composite structure therefore applies to the present embodiment except for the nature of the contoured layers.

According to the variant illustrated inFIGS.10and11, the composite structure10is advantageously a monolithic structure meeting the same definition as that previously seen in relation to the first embodiment. In other words, the composite structure10comprises only the external wall12, the housing20and the electrically conductive strip22, with the inner surface13of the external wall12and the side of the housing20opposite that facing the external wall12directly facing the interior of the radome. The advantages of such a monolithic structure are the same as those previously seen in relation to the first embodiment. In particular, in this embodiment the electrically conductive strip22is notably straight between the first end24and the second end26.

The invention also relates to an aircraft comprising an antenna capable of transmitting and receiving a radio frequency signal and a radome1as previously described. The radome1allows the antenna to be protected from lightning strikes while maintaining good mechanical strength, even after repeated lightning strikes.

The aircraft may be a fixed wing aircraft (e.g., aeroplane) or a rotary wing aircraft (e.g. helicopter).