Lightning-resistant fastener and mounting structure of lightning-resistant fastener

To provide a lightning-resistant fastener capable of assuring a sufficient lightning-resistant performance. A cap 30A has an elastically deformable part 50 continuous in the circumferential direction thereof. The elastically deformable part 50 has a smaller thickness than the other parts of the cap 30A in a circumferentially continuous area thereof. Since the cap 30A has the elastically deformable part 50, even if a surface 22b of a member 22 is inclined with respect to a plane perpendicular to the axis of a fastener main body 25, the cap 30A can be installed without forming a gap.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lightning-resistant fastener, which is used for an airframe of an aircraft, especially for a wind thereof, and a method of mounting a lightning-resistant fastener.

2. Description of the Related Art

A wing constituting an airframe of an aircraft is of a hollow construction, and a wing surface panel forming a wing surface is fixed to a structural member existing in the wing by a fastener member (fastener).

The fastener member fastens the wing to the structural member by inserting a pin-shaped fastener main body into through holes, which have been formed in both the wing and the member attached to the wing, from the outside of wing, and by fixing the front end portion of the fastener main body by using a fixture from the interior side of the wing.

The aircraft must make thoroughgoing provisions against lightning strikes. In the case where the wing surface panel and the fastener member are made of different materials, at the time of lightning strikes, an arc discharge (spark) is produced in the direction extending along the interface between the wing surface panel and the fastener member by an electric potential difference between the wing surface panel and the fastener member. Since a fuel tank is housed in the internal space of the wing, it is necessary to reliably suppress the production of arc discharge at the time of lightning strikes.

To meet such necessity, a structure has conventionally been proposed in which, as shown inFIG. 9, on the inside of a wing1, a cap6is installed in a state of being separate from a fastener main body4aof a fastener member4, which penetrates a first member2corresponding to the wing surface panel and a second member3installed within the wing, and a fixture4b, and an air-gap7filled with air is formed between the cap6and the fastener main body4a, the fixture4b(for example, refer to Japanese Patent Laid-Open No. 2-7398).

However, the technique descried in Japanese Patent Laid-Open No. 2-7398 does not provide a structure in which the cap6can be positioned with respect to the fastener member4, and the installation position of the cap6depends on the worker. Therefore, the center of the cap6and the center of the fastener member4may shift greatly. If in the air-gap7, a place where a gap between the fastener member4and the cap6is narrow is produced, the function (insulation properties) of the cap6decreases. In the worst case, if the cap6is installed in a state of being in contact with the fastener member4, the function itself of the cap6may be impaired greatly.

The cap6is installed on the second member3with an adhesive9as shown inFIG. 9A, or is outer-peripherally covered with a rubber (insulating material)10as shown inFIG. 9B. Therefore, in the installation site, the bonding work or the coating work of the rubber10is required, so that the work takes much time and labor. Needless to say, the interior of the wing1of aircraft has a narrow space, and the above-described work performed at a secluded position provides very poor workability. Moreover, since the fastener member4is provided at several thousands to several ten thousands places throughout the wing1, the deterioration in workability leads directly to the rise in cost.

Furthermore, the above-described work is what is called manual work, so that the work quality is easily varied depending on the worker, which also exerts an influence on the reliability.

To solve the problems, the inventors have already proposed a technique in which a fastener member has an engaging part formed in a portion projecting to the interior side of an airframe, a cap has an engaged part to be engaged with the engaging part of the fastener member in a central portion of the inner peripheral surface thereof, and the engaging part of the fastener member is engaged with the engaged part (see Japanese Patent Laid-Open No. 2010-254287).

However, according to the techniques described above, the axis of the fastener member is not always perpendicular to the inner peripheral surface of the wing1. For example, the second member3mounted on the inner peripheral surface of the wing1may be inclined with respect to the axis of the fastener member4as shown inFIG. 9. In such a case, when the cap6is engaged with the fastener member4, a gap occurs between an outer circumferential edge6aof the cap6and the second member3, and therefore, a sufficient lightning-resistant performance cannot be assured.

In addition, if the ambient temperature repeatedly varies significantly, the cap6may be loosened, and a gap may occur between the outer circumferential edge6aof the cap6and the second member3.

The present invention has been accomplished in view of the technical problems described above, and an object of the present invention is to provide a lightning-resistant fastener capable of assuring a sufficient lightning-resistant performance.

SUMMARY OF THE INVENTION

To attain the object, the present invention provides a lightning-resistant fastener comprising: a fastener member used for fastening a second member to a first member constituting an airframe of an aircraft, the fastener member being made of a conductive material; and a cap installed so as to cover the fastener member projecting to the interior side of the airframe, the cap being made of an insulating material, wherein the fastener member has an engaging part in a portion projecting to the interior side of the airframe, the cap has an engaged part to be engaged with the engaging part of the fastener member in a central portion of the inner peripheral surface thereof, the cap being installed to the fastener member with the engaged part being engaged with the engaging part of the fastener member, a tip end part of the cap opposite to the engaged part abutting against the second member, and a gap being provided between the fastener member and a portion of the cap other than the engaged part, and an elastically deformable part is provided to allow the cap to be elastically deformed in the direction to compress the cap between the engaged part and the tip end part abutting against the second member while the engaged part is engaged with the engaging part.

As the elastically deformable part, the cap may have a part continuous in the circumferential direction of the cap having a smaller thickness than another part formed between the engaged part and the tip end part or at the tip end part.

When the engaged part of the cap is engaged with the engaging part, the fastening force acts in the direction to compress the cap between the engaged part and the tip end part abutting against the second member. At this point, the elastically deformable part is elastically deformed. As a result, for example, even if the second member is inclined with respect to the axis of the fastener member, the cap can be deformed to conform to the inclination to come into intimate contact with the second member.

An annular seal member continuous in the circumferential direction of the cap may be provided on the abutment surface between the tip end part of the cap and the second member. In this case, the sealability at the abutment surface between the cap and the second member can be improved.

The present invention also provides a structure for mounting a lightning-resistant fastener comprising: a fastener member used for fastening a second member to a first member constituting an airframe of an aircraft, the fastener member being made of a conductive material; and a cap comprising an open end opening at one end and installed so as to cover the fastener member projecting to the interior side of the airframe, the cap being made of an insulating material, wherein a recess is formed in a surface of the second member, and the cap is installed with the open end being housed in the recess formed in the second member.

If the open end of the cap is housed in the recess of the second member in this way, even if an arc discharge occurs between the cap and the second member, the spark can be prevented from leaking to the outside from the recess.

The outer peripheral surface of the open end of the cap can have any shape. For example, the outer peripheral surface of the open end of the cap may have a polygonal cross section in the direction perpendicular to the axis of the fastener member, and the inner peripheral surface of the recess may include an opposing surface that is opposite to the outer peripheral surface of the open end having the polygonal cross section. In this case, the outer peripheral surface of the cap abuts against the opposing surface of the recess, so that rotation and loosening of the cap can be prevented.

Alternatively, the outer peripheral surface of the open end of the cap may have a circular cross section in the direction perpendicular to the axis of the fastener member, and the recess may have a circular shape, and the inner peripheral surface of the recess may include an opposing surface that is opposite to the outer peripheral surface of the open end.

Furthermore, an annular seal member continuous in the circumferential direction of the cap may be provided on the abutment surface between the tip end part of the cap and the second member.

A screw groove may be formed in the outer peripheral surface of the open end of the cap, a screw groove to be engaged with the screw groove of the open end may be formed in the inner peripheral surface of the recess, and the cap may be installed by screwing the open end of the cap into the recess.

Furthermore, a mark that indicates the amount of a sealant charged into the cap may be formed on the inner peripheral surface of the cap.

According to the present invention, a gap can be prevented from occurring between the cap and the second member to assure a sufficient lightning-resistant performance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail based on an embodiment shown in the accompanying drawings.

FIG. 1is a sectional view of a part of a wing constituting an airframe of an aircraft, to which a lightning-resistant fastener, a cap and a method of mounting the lightning-resistant fastener in accordance with the embodiment shown below are applied.

As shown inFIG. 1, a wing20comprises a wing panel (first member)21as the outer shell thereof. The wing panel21is, for example, made of CFRP (Carbon Fiber Reinforced Plastics), which is a composite material of a carbon fiber and a resin, or a metallic material such as an aluminum alloy. A structural member for reinforcement, a fuel tank, and various types of equipment, which are provided within the wing20, are fixed to the wing panel21via a member (second member)22such as a stay. The stay is made of a metallic material such as an aluminum alloy. The member22such as the stay is installed on the wing panel21by using a fastener member24.

The fastener member24comprises a pin-shaped fastener main body25, and a collar26mounted on the fastener main body25on the interior side of the wing20.

The fastener main body25and the collar26are generally made of a metallic material from the viewpoint of strength. The pin-shaped fastener main body25comprises a screw groove (engaging part)25aon the front end portion thereof. The rear end portion of the pin-shaped fastener main body25is formed into a head part25bin which the diameter increases from the front end portion side. This fastener main body25is inserted into holes21aand22a, which are formed penetratingly in the wing panel21and the member22, from the outside of the wing20. The front end portion of the pin-shaped fastener main body25is projected to the inside of the wing20in a state in which the head part25bin the rear end portion is abutted against the peripheral surface of the hole21a.

The collar26has a tubular shape, and the inner peripheral surface thereof comprises a screw groove engaging with the screw groove25aof the fastener main body25. This collar26is screwed onto the screw groove25aof the fastener main body25projecting to the inside of the wing20. Thereby, the wing panel21and the member22are held between the head part25bof the fastener main body25and the collar26, and thereby the member22is fixed to the wing panel21. Note that a washer (not shown) made of an insulating material such as polyimide is disposed between the collar26and the member22.

In this state, a front end part25cof the fastener main body25projects to the inner periphery side of the wing20from the collar26, and further a certain length of the screw groove25ais exposed to the inner periphery side of the wing20from the collar26.

In the internal space of the wing20, a cap30A is mounted on the fastener main body25, and the interior of the cap30A is filled with an insulating sealant34. The sealant34interposed between the inner peripheral surface of the cap30A and the fastener main body25and collar26further enhances the insulation properties between the cap30A and the fastener main body25.

The cap30A has a shape such that only the one end part (front end portion, opening end)30aside is open, and the inside diameter and the outside diameter thereof decrease gradually toward the other end part30bside. This cap is preferably made of an insulating resin such as PPS (polyphenylene sulfide resin), polyimide, PEEK (polyether ether ketone resin), and nylon resin.

On the inner peripheral surface on the other end part30bside (hereinafter, the inner peripheral surface is referred to as a bottom surface) of the cap30A, a bottomed hole (engaged part)32having a circular cross section is formed. The inner peripheral surface of the hole32comprises a screw groove (engaged part)32aengaged with the screw groove25aof the fastener main body25. This cap30A is configured so that the front end part25cof the fastener main body25is inserted into the hole32. At this time, the screw groove32aof the cap30A engages with the screw groove25aof the fastener main body25, whereby the cap30A can be positioned and fixed to the fastener main body25easily and reliably.

For this cap30A, the inside diameter of an inner peripheral surface35is set so that when the cap30A is installed on the fastener main body25, a predetermined gap is formed with respect to the fastener main body25, and the collar26.

The cap30A comprises a straight part36ahaving a fixed diameter formed on the one end part30aside thereof, a tapered part36bextending from the straight part36atoward the hole32by gradually decreasing the inside diameter thereof, a disk-shaped part36chaving a circular plate shape, and a top part36din which the hole32is formed.

The cap30A has an elastically deformable part50continuous in the circumferential direction thereof. The elastically deformable part50has a smaller thickness than the other parts of the cap30A in a circumferentially continuous area thereof. The elastically deformable part50may be formed in the disk-shaped part36cas shown inFIG. 1or in the tapered part36bas shown inFIG. 2, for example.

When the cap30A is installed on the fastener main body25for fastening the wing panel21and the member22together, the interior of the cap30A is beforehand filled with the uncured sealant34. To prevent the amount of the sealant34from being insufficient or excessive, a mark indicating the charge level of the sealant34is formed on the inner peripheral surface of the cap30A, for example.

For example, the mark may be an indicator line100A that indicates the charge level of the sealant34formed on the inner peripheral surface of the cap30A. Alternatively, the mark indicating the charge level of the sealant34may be an inflexion point100B of the cap30A, which is the boundary between the straight part36aand the tapered part36b.

In the internal space of the wing20, the cap30A is pushed against the fastener main body25projecting to the inside.

At this time, the sealant34filled in the cap30A overflows through the opening portion of the one end part30aof the cap30A. It is preferable that the sealant34overflow from the entire periphery of the cap30A so that the sealant34spreads uniformly to the entire zone in the cap30A.

When the cap30A is pushed against the fastener main body25increasingly, since the hole32is formed in the cap30A, the fastener main body25can be positioned reliably and easily at the center of the cap30A. Thereby, a phenomenon can be prevented that the cap30A and the fastener main body25shift from each other and the gap between the cap30A and the fastener main body25becomes narrow depending on the place, and also a phenomenon can be prevented that the fastener main body25comes into direct contact with the cap30A.

After the hole32of the cap30A has been pushed against the fastener main body25, the cap30A is turned to be screwed on the fastener main body25.

When the cap30A is screwed until the one end part30aof the cap30A is pushed against the member22, the screwing of the cap30A is finished. At this time, if the surface22bof the member22is inclined with respect to a plane perpendicular to the axis of the fastener main body25as shown inFIGS. 1B and 2B, the elastically deformable part50warps, so that the one end part30aof the cap30A abuts against the surface22bof the member22along the entire circumference thereof. In this way, a gap is prevented from being formed between the surface22bof the member22and the one end part30aof the cap30A.

In this state, the screw groove25aformed on the fastener main body25engages with the screw groove32aformed in the hole32of the cap30A, so that the cap30A is reliably and fixedly held to the fastener main body25. Also, if the filling sealant34is cured, this sealant34also achieves an effect of fixing the cap30A to the fastener main body25.

Thus, the fastener member24on which the cap30A is installed is a lightning-resistant fastener.

As described above, the cap30A comprises the hole32, and the screw groove32ais formed in the hole32, whereby the cap30A can be positioned and installed reliably and easily on the fastener main body25, and even after installation, the cap30A can be reliably prevented from coming off.

Also, if the cap30A has been screwed on the fastener main body25, the cure of the sealant34need not be waited, and the installation work of the cap30A can be performed rapidly.

Thereby, while the insulation properties are assured reliably, the workability is improved to reduce the manufacturing cost, and the cap30A can be installed with stable quality irrespective of workers.

Since the cap30A has the elastically deformable part50, even if the surface22bof the member22is inclined with respect to a plane perpendicular to the axis of the fastener main body25, the cap30A can be installed without forming a gap. In this way, a sufficient lightning-resistant performance is assured.

A second embodiment described below is basically the same as the first embodiment except for a cap30B of a different construction than the cap30A, and the other components are the same as those in the first embodiment. The following description will be primarily focused on the difference from the first embodiment described above, and descriptions of the common components will be omitted.

As shown inFIG. 3, the cap30B according to this embodiment differs from the cap30A according to the first embodiment in that the cap30B does not have the disk-shaped part36cand comprises the straight part36a, the tapered part36b, and the top part36d.

Such a cap30B has a stepped part51formed in the one end part30athereof on the inner periphery side, and the stepped part51has a smaller thickness t than the other parts of the cap30B and serves as the elastically deformable part50.

With such a construction, when the surface22bof the member22is inclined with respect to a plane perpendicular to the axis of the fastener main body25, the one end part30aof the cap30B, which serves as the elastically deformable part50, warps, so that the one end part30aof the cap30B abuts against the surface22bof the member22along the entire circumference thereof. In this way, a gap is prevented from being formed between the surface22bof the member22and the one end part30aof the cap30B. In this way, a sufficient lightning-resistant performance is assured.

A third embodiment described below is basically the same as the second embodiment except for the construction of the cap30B, and the other components are the same as those in the second embodiment. The following description will be primarily focused on the difference from the second embodiment described above, and descriptions of the common components will be omitted.

As shown inFIG. 4, as with the cap30B according to the second embodiment, the cap30C according to this embodiment comprises the straight part36a, the tapered part36b, and the top part36d. The cap30C further has the stepped part51formed in the one end part30athereof on the inner periphery side.

A ring-shaped seal member52made of a rubber-based material is provided in the stepped part51.

With such a construction, when the surface22bof the member22is inclined with respect to a plane perpendicular to the axis of the fastener main body25, the seal member52provided at the one end part30aof the cap30C, which serves as the elastically deformable part50, prevents a gap from being formed between the surface22bof the member22and the one end part30aof the cap30B.

Furthermore, the one end part30awarps, so that the one end part30aof the cap30B abuts against the surface22bof the member22along the entire circumference thereof. In this way, a gap is prevented from being formed between the surface22bof the member22and the one end part30aof the cap30B.

In this way, a sufficient lightning-resistant performance is assured.

The following description of a fourth embodiment will be primarily focused on differences from the first embodiment described above, and descriptions of the common components will be omitted.

As shown inFIGS. 5A and 5B, a cap30D according to this embodiment has an octagonal or other polygonal cross section in a plane perpendicular to the axis of the fastener main body25. The cap30D is the same as the cap30A according to the first embodiment described above in that the bottomed hole32having a circular cross section is formed in the bottom surface at the other end part30bside thereof. In the inner peripheral surface of the hole32, the screw groove32ato be engaged with the screw groove25aof the fastener main body25is formed. The engagement of the screw groove32aof the cap30D with the screw groove25aof the fastener main body25allows the cap30D to be positioned with respect to and fixed to the fastener main body25easily and with reliability.

The cap30D comprises a straight part37ahaving a fixed diameter dimension formed on the one end part30aside thereof, a tapered part37bextending from the straight part37atoward the hole32by gradually decreasing the inside diameter, and a top part37din which the hole32is formed.

In the surface22bof the member22, a recess60is formed at a part on which the cap30D is installed. The recess60has a fixing wall (an opposing surface)61that comes into contact with at least two of the sides of the straight part37ahaving the polygonal shape of the cap30D. According to this embodiment, the recess60has a rectangular shape, and the fixing wall61is in contact with four sides of the straight part37a.

The straight part37aof the cap30D is fitted into the recess60with the four sides being opposite to the fixing wall61in the vicinity thereof.

The cap30D is installed with the one end part30aof the cap30D fitted in the recess60as described below.

First, as shown inFIG. 6A, the fastener main body25and the collar26are fastened, and then, a plate70is set to cover the recess60. The plate70is sized to be larger than the area of the opening of the recess60and has a slit71opening in one side. The width of the opening of the slit71is larger than the diameter of the fastener main body25.

Then, as shown inFIG. 6B, the cap30D is temporarily installed on the fastener main body25. In this step, the screw groove32aof the cap30D is screwed onto the screw groove25aof the fastener main body25until the one end part30aabuts against the plate70. Then, the screw groove32aof the cap30D is further screwed to firmly press the one end part30aagainst the plate70. Then, the one end part30aof the cap30D is elastically deformed toward the other end part30b.

To increase the degree of the elastic deformation of the cap30D, the elastically deformable part50shown in the second and third embodiments may be provided.

In this state, the plate70is pulled out along the slit71. Then, as shown inFIG. 6C, the elastically deformed cap30D is relieved, and the one end part30ais restored to its original shape in the direction away from the other end part30b. As a result, the one end part30aof the cap30D enters the recess60to come into contact with the fixing wall61.

With such a construction, since the one end part30aof the cap30D is fitted in the recess60, even if an arc discharge occurs between the one end part30aof the cap30D and the surface22bof the member22(a bottom surface60aof the recess60), the fixing wall61of the recess60can prevent the arc from leaking to the outside.

In addition, the fixing wall61limits rotation of the cap30D, thereby preventing loosening of the cap30D.

In addition, in installation of the cap30D, the cap30D can be fastened with higher torque, since the cap30D is elastically deformed by the plate70.

In this way, a sufficient lightning-resistant performance is assured.

The following description of a fifth embodiment will be primarily focused on differences from the fourth embodiment described above, and descriptions of the common components will be omitted.

As shown inFIG. 7, a cap30E has a circular cross section in a plane perpendicular to the axis of the fastener main body25. The cap30E is the same as the cap30A according to the first embodiment described above in that the bottomed hole32having a circular cross section is formed in the bottom surface at the other end part30bside thereof, and the screw groove32ato be engaged with the screw groove25aof the fastener main body25is formed in the inner peripheral surface of the hole32. The engagement of the screw groove32aof the cap30D with the screw groove25aof the fastener main body25allows the cap30E to be positioned with respect to and fixed to the fastener main body25easily and with reliability.

The cap30E comprises a straight part38ahaving a fixed diameter dimension formed on the one end part30aside thereof, a tapered part38bextending from the straight part38atoward the hole32by gradually decreasing the inside diameter, and a top part38din which the hole32is formed.

In addition, a ring-shaped seal member80made of a rubber-based material is provided on the outer peripheral surface of the straight part38aof the cap30E.

In the surface22bof the member22, a recess65having an inside diameter approximately equal to the outside diameter of the straight part38aof the cap30E is formed at a part on which the cap30E is installed.

The straight part38aof the cap30E is fitted into the recess65, and the seal member80provided on the outer peripheral surface comes into contact with an inner periphery surface (an opposing surface)66of the recess65.

To install the cap30E with the one end part30afitted in the recess65, the fastener main body25and the collar26can be fastened, and then, the screw groove32aof the cap30E can be screwed onto the screw groove25aof the fastener main body25.

Then, when the one end part30aabuts against the plate70, the seal member80is in intimate contact with the inner peripheral surface66of the recess65.

With such a construction, since the one end part30aof the cap30E is fitted in the recess65, even if an arc discharge occurs between the one end part30aof the cap30E and the surface22bof the member22(a bottom surface65aof the recess65), the inner peripheral surface66of the recess65can prevent the arc from leaking to the outside.

In addition, the seal member80limits rotation of the cap30E, thereby preventing loosening of the cap30E.

In this way, a sufficient lightning-resistant performance is assured.

Although the seal member80is provided on the outer peripheral surface of the straight part38ain this embodiment, it is essential only that the seal member80is in intimate contact with the recess65. For example, the seal member80may be provided on a tip end surface38sof the straight part38so that the seal member80is in intimate contact with the bottom surface65aof the recess65and provides sealability.

The following description of a sixth embodiment will be primarily focused on differences from the fifth embodiment described above, and descriptions of the common components will be omitted.

As shown inFIG. 8, a cap30F has a circular cross section in a plane perpendicular to the axis of the fastener main body25and comprises a straight part39ahaving a fixed diameter dimension formed on the one end part30aside thereof, a tapered part39bwhose inside diameter gradually decreases toward the other end part30b, and a top part39d.

The cap30F differs from the cap30A according to the first embodiment described above in that the bottomed hole32having a circular cross section is not formed in the top part39don the other end part30bside. A screw groove90is formed in the outer peripheral surface of the straight part39aof the one end part30aof the cap30F according to this embodiment.

In the surface22bof the member22, a recess68having an inside diameter approximately equal to the outside diameter of the straight part39aof the cap30F is formed at a part on which the cap30F is installed. A screw groove69is formed in the inner peripheral surface of the recess68.

With such a construction, the cap30F is installed by screwing the screw groove90into the screw groove69of the recess68. Once the cap30F is installed, the straight part39ais fitted in the recess68.

To install the cap30F with the one end part30afitted in the recess68in this way, the fastener main body25and the collar26can be fastened, and then, the screw groove90can be screwed into the screw groove69of the recess68. The screw groove69of the recess68and the screw groove90of the cap30F are thereby engaged with each other.

With such a construction, since the one end part30aof the cap30F is fitted in the recess68, even if an arc discharge occurs between the one end part30aof the cap30F and the surface22bof the member22(the bottom surface of the recess68), the screw grooves engaged with each other can prevent the arc from leaking to the outside.

In addition, since the cap30F is fixed to the member22by the screw groove90formed in the one end part30aof the cap30F, there is no need to fasten the fastener main body25and the cap30F to each other. As a result, the fastener main body25can be shortened, and the cap30F can be downsized.

The components shown in the embodiments described above can be used in any appropriate combination.

Besides, the configurations described in the above embodiment can be selected or can be changed as appropriate to other configurations without departing from the gist of the present invention.