Patent Application
20230331368
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.
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 wall 10, an inner wall 11 and a plurality of electrically conductive strips 13 located on the inner wall 11 and on an unexposed face of the external wall 10. The lightning current is received by means of metal studs 15 flush with the exposed face of the external wall 10. The metal studs 15 comprise a threaded cylindrical portion passing through the electrically conductive strips 13, which in turn allows the latter to receive the lightning current. Furthermore, the threaded cylindrical portion of the metal studs 15 extends well beyond the electrically conductive strips 13. In fact, nuts 17 are arranged on the other side of the electrically conductive strips 13 in order to cooperate with the threaded cylindrical portion of the metal studs 15 and allow the electrically conductive strips 13 to 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 structure 3 comprising a lightning protection system in which electrically conductive strips of copper or aluminium are flush with an outer surface 9 of the radome. In this regard, the outer surface 9 has a hollow profile into which the electrically conductive strips 1 extend. Each electrically conductive strip 1 is attached to the composite structure 3 by means of a number of attachment means 8, 10. The attachment means 8, 10 consist of screws 10 and nuts 8. The screws 10 extend across the electrically conductive strip 1. Each of them has a surface 2 flush with the outer surface 9 and an external thread which cooperates with a drilling hole in the electrically conductive strip 1 which has equivalent cooperation means for this purpose.
In such a system, as the external surface 9 is pierced at several points at the level of the electrically conductive strips 1, 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.
To meet this need, the invention proposes an aircraft radome comprising:
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:
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.
Further objects, features and advantages of the invention will become clearer in the following description, made with reference to the attached figures, in which:
With reference to
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 radome 1 comprises a base 2 which physically separates it from the rest of the aircraft (not shown). It comprises an electrically conductive base 3 (not visible in
In addition, the radome 1 comprises a composite structure 10 configured to provide lightning protection.
The composite structure 10 comprises an external wall 12 made of an electrically insulating material and an electrically conductive strip 22, for example of aluminium or copper. Due to its external positioning, the external wall 12 is susceptible to electricity from lightning while the aircraft is in flight. In this regard, the electrically conductive strip 22 is arranged with respect to said external wall 12 so as to conduct electricity generated by lightning strikes to the conductive base 3. The arrangement of the electrically conductive strip 22 with respect to the external wall 12 will be described in more detail below with reference to the various embodiments.
According to a first aspect of the invention, a first end 24 of the electrically conductive strip 22 is in contact with the conductive base 3. Thus, as the conductive base 3 is connected to the ground of the aircraft, the electrically conductive strip 22 is also electrically connected to the aircraft ground via said conductive base 3. The electricity received by the lightning strike can thus be conducted to the aircraft ground, thus preventing any damage to the external wall 12, which is insulating by nature, by pulverising the material of said external wall 12. The composite structure 10 thus configured allows to protect the radome 1 from lightning strikes. We will come back to this in the description relating to
According to a second aspect of the invention, the composite structure 10 is devoid of perforations or passages passing through the external wall 12 at the level of the electrically conductive strip 22. In other words, the external wall 12 of 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 strip 22 to the aircraft ground is made by the contact between the first end 24 and the conductive base 3. More generally, the external wall 12 may 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 wall 12.
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 wall 12, i.e., perforations passing through the external wall 12, at the level of the electrically conductive strip 22 prevents premature wear of the composite structure 10 and favours a good mechanical resistance of the radome 1 even after several lightning strikes. Indeed, the external wall 12 forms a physical interface between the exterior of the radome 1 and the interior of the composite structure 10. In some cases, as will be seen below, it can form with the electrically conductive strip 22 the interface between the outside and the inside of the radome.
It should be noted that “at the level of the electrically conductive strip 22” means the volume of the composite structure 10 located around the sectional plane of the electrically conductive strip 22, the sectional plane of the electrically conductive strip 22 being defined as the plane normal to the external wall 12 passing through the longitudinal axis of the electrically conductive strip 22.
It is therefore understood that the volume of the composite structure 10 located around the electrically conductive strip 22, including the electrically conductive strip 22 itself, 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 strip 22 with respect to the external wall 12 which, 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 strip 22 itself 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 structure 10 located at the electrically conductive strip 22 corresponds 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 wall 12.
A perforation going through the external wall 12 may 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 wall 12 without each of them passing completely through the external wall 12 if said drillings or passages are arranged to create a pathway for a fluid, for example air.
As will be explained below, the external wall 12 does not comprise any perforations or passages to the interior of the composite structure 10. The external wall 12 is therefore completely continuous. Incidentally, as discussed above, all of the elements of the radome, including the electrically conductive strip 22, are arranged so as never to pass through the thickness of the external wall 12 themselves.
According to another aspect of the invention, the radome 1 can be protected from premature wear without compromising the aerodynamic properties of the aircraft. In this regard, the composite structure 10 defines at least one housing 20 located inside or outside the composite structure 10 and extending along the radome from the base 2. The housing 20 receives the electrically conductive strip 22 and according to the embodiment, either the electrically conductive strip 22 is in contact with an inner surface 13 of the external wall 12 when the housing 20 is inside the composite structure 10 or it is flush with said external wall 12 when the housing 20 is outside the composite structure 10. By being positioned in this way, the electrically conductive strip 22 does not generate asperities on the surface of the external wall 12, 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 radome 1. As a result, the positioning of the electrically conductive strip 22 does not have an adverse effect on the aerodynamic properties of the aircraft.
With reference to
Indeed, the hollow profile is made during the moulding of the radome 1 by adequately combining the constructional principle of the radome 1 with the dimensions of the electrically conductive strip 22. This means that already at the design stage, the dimensions of the electrically conductive strip 22 constitute a constraint to be taken into account when defining the dimensions of the housing 20. In this respect and from a practical point of view, the moulding of the radome at the level of the housing 20 is carried out on a male cavity in a die mould. This method of forming the housing 20 avoids modifying the structure of the radome 1 by adding densified zones. It should be further noted in relation to this embodiment that the electrically conductive strip 22 is not attached to the housing 20 using through attachment means, otherwise a drilling would also be formed in the external wall 12, in which the housing 20 is formed. Preferably, the electrically conductive strip 22 is bonded into the housing 20. 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 strip 22 to be attached to the housing 20.
As can be seen in
Furthermore, as illustrated in
The second housing 30 is in line with the housing 20, i.e., it adjoins the housing 20 and like the latter, the second housing 30 is free from through perforations as it is formed in the external wall 12.
Advantageously, the attachment means 28 is fixed above the electrically conductive strip 22 in the second housing 30, thereby protecting the second end 26 of the electrically conductive strip from becoming detached due to air flux. Indeed, unlike the first end 24 of the electrically conductive strip 22, the second end 26 is 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 base 2. Preferably, the attachment means 28 is wider than the electrically conductive strip 22 itself so as to improve the attachment of said strip 22.
The attachment means 28 may 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 end 26. More precisely, the attachment means 28 comprises several adhesive faces, one being the face in contact with the electrically conductive strip 22 and at least two other faces in contact with lateral edges of the second housing 30.
The radome 1 according to the invention also takes into account aerodynamic stresses at this second end 26. In this respect, the attachment means 28 advantageously flush with the portions 11 of the external wall 12 other than a portion where the second housing 30 is formed. In other words, a face of the attachment means 28 exposed to the air flux is substantially coincident with an imaginary surface passing through the two lines M and N of the external wall 12 and following the shape of the portions 11, in a manner similar to the external surface 23 of the electrically conductive strip at the level of the housing 20. It should be noted that it does not matter whether the face of the attachment means 28 facing the outside of the radome is adhesive or not, since antistatic, anti-erosion and protective coatings cover the entire compositional structure 10 once it is completed. What is important is that the side of the attachment means 28 facing the outside of the radome is flush with the portions 11 so that during the subsequent deposition of these coating layers there is no obstacle to disturb the flow of air.
Like the housing 20 with the electrically conductive strip 22, the second housing 30 forms a hollow profile fitted to the contours of the second end 26 and the attachment means 28 and its dimensions are adapted so that said attachment means 28 is flush with the external wall 12. In this regard, as illustrated in
As previously mentioned, the composite structure 10 is devoid of perforations through the external wall 12 at the electrically conductive strip 22. In this embodiment of the radome 1, the composite structure 10 is also devoid of any mechanical parts for attaching the conductive strip 22 to the composite structure 10 in a volume V1 of the composite structure 10 having as a base, in a geometrical sense, the external surface 23 of the electrically conductive strip and having as a height, in a geometrical sense, a thickness ES of the composite structure 10 (illustrated in
In this regard, the composite structure 10 may further comprise an inner wall 16 and a core 14 located between the external wall 12 and the inner wall 16. In other words, by selecting volume V1 as the observation window, the composite structure 10 comprises successively the inner wall 16, the core 14, the external wall 12 and the electrically conductive strip 22 from the inside of the radome to the outside of the radome. However, by selecting a viewing window outside of volume V1, the composite structure 10 comprises successively the inner wall 16, the core 14 and the external wall 12 from inside the radome to outside the radome. In this viewing window, the core 14 is in contact with both an inner surface 13 of the external wall and an inner surface 15 of the inner wall.
The core 14 is, for example, in the form of a honeycomb, also called “nida” in the following, or of foam. Advantageously, the core 14 is made of a single material along the radome 1. In other words, in this embodiment, the core 14 is in the form of a nida along the radome 1. Thus, in addition to its structural homogeneity due to the absence of a part in the volume V1, the structural homogeneity of the composite structure 10 is also due to the fact that it is made of the same material in the volume V1 but 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 structure 10.
With reference to
Preferably, the first end 24 of the electrically conductive strip is U-shaped. That said, generally any shape that allows bypassing of the composite structure 10 could be suitable, the U shape being by no means limiting. The first end 24 of the electrically conductive strip comprises a first longitudinal leg 24a extending into the housing 20. The first longitudinal leg 24a faces towards the outside of the radome 1 and is located in the vicinity of the base 2. The first end 24 of the electrically conductive strip comprises a second longitudinal leg 24b in contact with the conductive base 3. More specifically, the second leg 24b is at least partially in contact with the conductive base 3. In other words, the second longitudinal leg 24b need not be entirely in contact with the conductive base 3. The first end 24 of the electrically conductive strip further comprises a transverse leg 24c connecting the first and second longitudinal legs 24a, 24b bypassing the base 2. In the example embodiment shown in
In this regard, it should be noted that the bypassing is possible at the base 2 because the radome 1 is 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 structure 10 with the electrically conductive strip 22 can be achieved at the time of manufacture of the radome 1 without undue technical difficulty by the manufacturer. Furthermore, the electrically conductive strip 22 has 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 structure 10 by the electrically conductive strip 22 is therefore not only advantageous because it avoids through perforations which in the long run can cause problems of mechanical strength of the composite structure 10, or even sealing problems, but also because it is technically easy to implement in a manufacturing method of the radome.
The base 3 is connected to the composite structure 10 by means of screws and non-through inserts. These pass through the second longitudinal leg 24b, the inner wall 16 and the core 14 without passing through the first longitudinal leg 24a and the external wall 12. Only the second longitudinal leg 24b, the inner wall 16 and the core 16 are therefore drilled, the first longitudinal leg 24a and the external wall 12 remaining intact. The composite structure 10 therefore does not comprise any perforation in the external wall 12, in particular in the area of the electrically conductive strip, but only at the aforementioned location. The composite structure 10 and the conductive base 3 are thus rigidly connected.
According to a variant illustrated in
This is because when the composite structure 10 is in the form of a monolithic structure, the electrically conductive strip 22 can be straight between the first end 24 and the second end 26, as the monolithic structure has a much smaller thickness than the composite structure 10 with a nida-shaped core 14, so that it can be aligned with the conductive base 3. Therefore, it is entirely possible to use a straight electrically conductive strip 22 between the first end 24 and the second end 26. The manufacturing method of the radome 1 is further simplified. In this case, the composite structure 10 is connected to the radome 1 by screwing the composite structure 10 to the conductive base 3. However, it should be noted that this attachment is not made at the electrically conductive strip 22, but in a portion of the conductive base 3 that does not face the strip 22.
With reference to
Advantageously, the external wall 12 has a thickness of between 0.15 mm and 1.00 mm. The external wall 12 thus has a thickness suitable for conducting the lightning energy to the electrically conductive strip 22, and possibly being perforated in the event of a lightning strike on said external wall 12, 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 wall 12 is made. This must be limited as it is risky. Thus, the thickness range of the external wall 12 represents a compromise between the need to conduct the lightning energy to the electrically conductive strip 22 and limiting the amount of pulverised material. In this regard, the fact that the electrically conductive strip 22 is in contact with the inner surface 13 of the external wall keeps the thickness to a minimum.
With reference to
The U-shaped longitudinal portion extends between the front of the radome, at a second end 26 of the electrically conductive strip, and the base 2. In this embodiment, the second end 26 extends into the housing 20 and without being retained by an attachment means. Indeed, as the electrically conductive strip 22 is covered by the external wall 12, no means for attaching the second end 26 is required as it is not susceptible to being unstuck by the air flux.
The U-shaped longitudinal portion comprises a transverse leg 20a and two longitudinal legs 20b, 20c extending from the transverse leg 20a. Since the electrically conductive strip 22 is disposed in the U-shaped longitudinal portion, the dimensions of the U-shaped longitudinal portion are adapted to the dimensions of the electrically conductive strip 22. Incidentally, as the electrically conductive strip 22 is in contact with the inner surface 13 of the external wall, the length of the longitudinal legs 20b, 20c is substantially equal to the thickness of the electrically conductive strip 22.
As for the two hooking tabs 20d, they extend from the U-shaped longitudinal portion, giving the housing a general Ω shape. More specifically, each hooking tab 20d extends from the other end of the longitudinal legs 20b, 20c respectively which is not connected to the transverse leg 20a.
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 strip 22 is retained in the housing 20 which 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 structure 10 is perforated since this area is never in direct contact with lightning strikes.
In the embodiment shown in
In the example embodiment shown in
Whilst in the example embodiments of
With reference to
As in the first embodiment, the first end 24 of 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 in
The invention also relates to an aircraft comprising an antenna capable of transmitting and receiving a radio frequency signal and a radome 1 as previously described. The radome 1 allows 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).
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2009090 | Sep 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/074728 | 9/8/2021 | WO |
