Patent Description:
Large passenger aircraft are typically struck by lightning once or twice a year, each lightning bolt striking with up to <NUM>,<NUM> amps of electrical current that seeks the path of least electrical resistance. Many modern passenger aircraft have exterior surfaces made from composite materials which have a very high electrical resistance. There is therefore a high probability of lightning attachment at any of the many metallic fasteners in the exterior surface, which have a much lower electrical resistance. In the wing, some of these fasteners pass through the outer wing skin into the fuel tank.

<FIG> is a side view of part of a fastener assembly passing through a panel <NUM>, which may be a composite or metallic panel. The assembly comprises a fastener comprising an externally threaded bolt <NUM>, an internally threaded nut <NUM>, and a washer <NUM>. In the event of a lightning strike hitting the panel <NUM> and attaching to the fastener, sparking, plasma or out-gassing may occur at the locations indicated by reference <NUM> in <FIG>.

<FIG> are side views of another fastener passing through the panel <NUM>, which may be a composite or metallic panel. The assembly comprises a blind rivet <NUM> comprising an axially extending shaft or mandrel <NUM>, a head of the shaft <NUM>, and a tubular collar <NUM> slidably fitted around the shaft <NUM>. The collar <NUM> abuts the head <NUM> at one end and has a flange 8a at the other end. During installation, the blind rivet <NUM> is slid through an aperture in the panel <NUM> in the direction of the arrow shown in <FIG> until the flange 8a abuts the panel <NUM>. The collar <NUM> is then held in position by the flange 8a against the panel <NUM>, and the shaft <NUM> is drawn in the opposite direction in the direction of the arrow shown in <FIG>. By drawing the shaft <NUM> towards the held flange 8a, the collar <NUM> is compressed and urged to deform. The collar <NUM> therefore splays outwardly and forms an expanded portion on the opposing side of the panel <NUM> to the flange 8a, therefore acting as a fastener, as shown in <FIG>. The protruding portion of the shaft <NUM> is removable.

In the event of a lightning strike hitting the panel <NUM> and attaching to the fastener, sparking or plasma may occur at the locations indicated by reference <NUM> in <FIG> at the interface of the collar <NUM> and shaft <NUM>, and the blind rivet <NUM> and face of the aperture.

With the above arrangements, the panel <NUM> may provide a fuel tank boundary and the fastener may therefore be immersed in fuel or fuel vapour rich gas. A lightning strike at the fastener may therefore provide sparking and hot gas ignition sources which could cause ignition of the fuel.

A known method of providing spark suppression is described in <CIT>. A volume of gas is enclosed by a cap around the fastener. The gas provides spark suppression for arcing that may occur between the composite structure and the metal fastener during any lightning strike. Another method is known from <CIT> and another cap is known from <CIT>.

According to an aspect of the invention, there is provided a method of locating a spark containment cap over an aperture in a structure as recited in claim <NUM>.

Further, optional, features and method steps are recited in each of claims <NUM> to <NUM>.

An aircraft <NUM> is shown in <FIG>. The aircraft <NUM> includes a fuselage <NUM>. Two wings <NUM> extend from the fuselage <NUM>. It will be appreciated that the fuselage <NUM> and wings <NUM> may take a variety of different planned formed shapes and profiles depending on the particular application. Fuel tanks <NUM> are formed in the fuselage <NUM> and wings <NUM>. One such fuel tank <NUM> is schematically shown in <FIG>. The fuel tanks <NUM> are formed by a structure or structures forming part of the aircraft <NUM>.

<FIG> show a joint <NUM> in stages of installation. Referring in particular to the installed joint <NUM> shown in <FIG>, the joint <NUM> comprises a structure <NUM> such as an aircraft skin panel 110a joined to another component, such as another panel 110b. A fastener <NUM> extends through the structure <NUM>. The structure <NUM> in this embodiment is a composite aircraft structural component, but may be a hybrid composite-metallic component. The fastener <NUM> extends through an aperture <NUM> in the structure <NUM>.

An end <NUM> of a fastener <NUM> protrudes from the structure <NUM>. The fastener <NUM> comprises a first fastening member <NUM> and a second fastening member <NUM>. The first and second fastening members <NUM>, <NUM> are engageable with each other to form the joint <NUM>. As shown in <FIG>, the first fastening member <NUM> is a nut and the second fastening member <NUM> is a bolt. However, it will be understood that the fastener <NUM> may take alternative configurations. The second fastening member <NUM> comprises an axially extending shaft <NUM> which passes through the structure <NUM>.

The nut, acting as first fastening member <NUM>, has a bore <NUM>. The nut <NUM> acts as a fastening collar. The bore <NUM> has an internal thread and the shaft has a corresponding external threaded section. The nut <NUM> is threadingly engageable on the shaft <NUM>. The nut threadingly engages with the shaft <NUM> at the end <NUM> of the fastener <NUM>. At another end of the fastener <NUM>, the second fastening member <NUM> has a head <NUM> at the end of the shaft <NUM>. The head <NUM> has a countersunk surface <NUM> for being received in a countersink <NUM> formed in the structure <NUM>.

A washer <NUM> is received between the nut and the structure <NUM>. The washer <NUM> has a spherical concave surface <NUM> which bears against a similarly shaped convex, underside, surface <NUM> of the nut, thus enabling the shaft <NUM> to extend at an acute angle to the surface <NUM> (rather than at a right-angle as in <FIG>).

The bore <NUM> extends through the nut between the underside surface <NUM> of the nut and a top surface <NUM>. The bore <NUM> defines a central longitudinal axis of the nut <NUM>.

The fastener <NUM> has a drive configuration <NUM>. The drive configuration <NUM> comprises features which enable the fastener <NUM> to be move from an unfastened condition to a fastened condition. The drive configuration <NUM> comprises a first drive feature <NUM> on the nut. A second drive feature <NUM> is on the second fastening member <NUM>. Drive features are features on which a force may be applied to move at least one member relative to another member. The drive features act to retain a first member in a position and to move another member relative to the first member.

The nut has a hexagonal profile arrangement acting as the first drive feature <NUM>. A side wall <NUM> of the nut has six drive faces. The drive wall <NUM> has a hexagonal arrangement. It will be understood that the nut <NUM> may have an alternative arrangement, such as a splined arrangement, forming the first drive feature <NUM>. For example, the nut <NUM> may comprise at least one of a differing number of side faces, a recess and a slot acting as the first drive feature <NUM> in which a corresponding engaging feature <NUM>, as will be described hereinafter, may be received. The engaging feature <NUM> is configured to act against the first drive feature <NUM> to apply a retaining torque force to prevent rotation of the nut <NUM>.

The nut has a first, upper, section <NUM> and a second, lower, section <NUM>. The underside surface <NUM> is on the second section <NUM>. The first drive feature <NUM> is on the first section <NUM>. The second section <NUM> is cylindrical. The diametrical width of the second section is greater than or equal to the width of the first section <NUM>. A chamfered section <NUM> is formed between the first and second sections <NUM>, <NUM>.

The diameter of the washer <NUM> is less than the diameter of the second section <NUM> of the nut.

The second fastening member <NUM> has a profiled recess <NUM> acting as the second drive feature <NUM>. The profiled recess <NUM> is configured to receive a tool (not shown) to apply a fastening torque to the second fastening member <NUM>.

A cap <NUM> encloses the end <NUM> of the fastener <NUM>. The cap <NUM> is a spark containment cap. The cap <NUM> has a cap body <NUM> with a domed outboard (upper) part <NUM> and a substantially cylindrical base <NUM>. The base <NUM> forms an annular side wall. The substantially cylindrical base <NUM> terminates at a rim <NUM> which surrounds an opening into a central air cavity <NUM>. The rim <NUM> lies in a plane so it can intimately engage with a planar surface of the structure <NUM> around its full circumference when the cap is fitted over the end <NUM> of the fastener <NUM> as shown. The cap <NUM> and fastener <NUM> together form a fastening system <NUM>.

Hooks <NUM> are formed at the lower, inboard, end of the cap body <NUM>. In the present embodiment the cap is formed with six hooks <NUM>, however the number of hooks may differ. The hooks <NUM> are received as a snap-fit with the nut and locate against the underside surface <NUM> of the nut to retain the nut in the air cavity <NUM> when the fastening system <NUM> is at least partially assembled. The hooks <NUM> act on the lower side of the nut and retain the nut irrespective of its orientation about its central axis. The nut, acting as the fastening collar, is held by the cap <NUM>. The hooks <NUM> hold the nut in the air cavity <NUM>. The hooks <NUM> restrict the nut from being drawn from the cap <NUM>. The hooks <NUM> act as a retention configuration.

The cap <NUM> has an engaging feature <NUM>. The engaging feature <NUM> is formed in the air cavity <NUM>. The engaging feature <NUM> is configured to engage with the nut <NUM>. The engaging feature <NUM> extends in the air cavity <NUM>. The engaging feature <NUM> comprises a shoulder <NUM> protruding in the air cavity <NUM>. The cap abuts the shoulder <NUM>. The cap body <NUM> and engaging feature <NUM> are integrally formed. The shoulder <NUM> protrudes from the annular side wall of the cap <NUM>. The shoulder <NUM> extends from the upper end of the cap. The engaging feature <NUM> is spaced from the rim <NUM> of the annular base <NUM>.

The engaging feature <NUM> comprises a locating face <NUM>. The locating face <NUM> is configured to substantially correspond to the profile of the first drive feature <NUM> of the nut. As such, in the present embodiment, the locating face <NUM> has a substantially hexagonal profile. The locating face <NUM> has a plurality of opposing locating surfaces. However, it will be understood that the locating face <NUM> may have a differing arrangement in dependence on the arrangement of the drive feature with which the engaging feature <NUM> is configured to engage. The locating face <NUM> extends over corners of the first drive feature <NUM>. In embodiments, the locating face <NUM> extends over at least one corner.

The engaging feature <NUM> encloses the first drive feature <NUM>. The nut is slide-fit or push-fit in the engaging feature <NUM>. The shoulder <NUM> has a lower edge <NUM>. The lower edge <NUM> of the shoulder <NUM> is configured to abut against the chamfered section <NUM> of the nut to aid alignment of the nut in the cap <NUM>.

Channels <NUM> are formed in the engaging feature <NUM> (refer to <FIG>). The channels <NUM> extend from the locating face <NUM>. In the present embodiment, the channels <NUM> extend parallel to a longitudinal axis of the cap body <NUM>. The channels <NUM> extend in the locating surfaces of the locating face <NUM>.

The engaging feature substantially corresponds with the first drive feature <NUM> of the nut. As described above, the engaging feature <NUM> is configured to engage a hexagonal drive feature of the nut. However, alternative arrangements are possible. The configuration of the engaging feature <NUM> may differ to correspond with an alternative fastener arrangement.

<FIG> illustrates an alternative embodiment. In <FIG>, the first drive feature <NUM> of the nut <NUM> is a bi-hex drive feature. The arrangement of the nut <NUM>, acting as the first fastening member, is otherwise generally the same as described above. The engaging feature <NUM> comprises a plurality of ridges <NUM> which conform with and are received by the bi-hex drive feature when the nut <NUM> is received in the air cavity <NUM>.

The cap body <NUM> is formed with six axially extending ribs <NUM>. The ribs <NUM> project inwardly into the air cavity <NUM>. The ribs <NUM> abut the cylindrical second section <NUM> as an interference fit. Although the ribs <NUM> are shown only in the embodiment shown in <FIG>, they may be present in other embodiments or may be omitted. The hooks <NUM> at the lower, inboard, end of the cap body <NUM> protrude from the ribs <NUM>.

Alternative drive features may be used, such as a spline drive feature.

<FIG> illustrates an alternative embodiment. In <FIG>, the engaging feature <NUM> extends proximate the rim <NUM> of the first drive feature <NUM> of the nut <NUM> is disposed at the lower end of the cap <NUM>. That is, proximate to the rim <NUM> of the annular base <NUM>. The first drive feature <NUM> of the nut is on the second, lower, section <NUM>. The first drive feature <NUM> extends to the underside surface <NUM>. Such an arrangement helps to maximise the volume of the available air space in the air cavity <NUM> of the cap <NUM>.

In each of the embodiments described above, an annular skirt <NUM> extends from an outboard (upper) end <NUM> where it meets the cap body to an inboard (lower) skirt rim <NUM> which lies substantially in the same plane as the rim <NUM> of the annular base <NUM>. Like the rim <NUM>, the skirt rim <NUM> also contacts the planar surface of the structure <NUM> around the full closed circumference of the skirt rim <NUM>.

An annular pocket <NUM> is provided between the skirt <NUM> and the base <NUM>. The annular pocket acts as an annular sealing volume. The pocket <NUM> extends from a closed outboard end <NUM> at the outboard end <NUM> of the skirt, to an open inboard end <NUM> at the skirt rim <NUM>. Due to the flared shape of the outboard part <NUM> of the skirt, the pocket <NUM> has a radial width which increases as it extends from its outboard end <NUM> to its inboard end <NUM>.

The skirt <NUM> has an injection channel <NUM>. The injection channel <NUM> is arranged to interconnect with a sealing material injection device to provide a flow of sealing material through the skirt via the injection channel <NUM> into the pocket <NUM>. A suitable sealing material is a polysulphide sealant such as Naftoseal (R) MC238B, MC238A, or MC780 available from Chemetall Group.

The skirt also has an outlet <NUM>. The outlet <NUM> is in fluid communication with the pocket <NUM> and is arranged to enable air to escape the pocket <NUM> through the skirt via the outlet as the sealing material flows from the injection channel <NUM> into the pocket <NUM>. When the pocket <NUM> is full, then the pressure in the pocket increases until it forces sealing material to escape the pocket through the skirt via the outlet <NUM>. When this flow of sealing material out of the outlet <NUM> is visually observed, the flow of sealing material from the sealing material injection device is stopped. In embodiments, a gap may be formed about at least part of the skirt rim <NUM> to act as the outlet.

Alternative sealant arrangements may be provided to those shown. For example, the pocket may be prefilled with sealing material, or one part such as the annular skirt may be movable relative to another part, for example the cap body.

Once sealing material <NUM> is provided in the pocket <NUM>, the sealing material <NUM> is then allowed to cure, leaving a cured sealing material in the pocket which secures the cap to the structure and forms a seal around the cavity <NUM>. The sealing material forms an annular bead around the periphery of the cap <NUM>, the bead of sealing material serving to seal the air cavity <NUM> in order to prevent escape of outgassing products, and to adhere the cap <NUM> to the structure <NUM>. The seal prevents the ingress of water or other contaminants into the cavity <NUM>, and also prevents plasma or other out-gassing products from exiting the cavity <NUM> in the event of a lightning strike.

All parts of the cap <NUM> are integrally formed by injection moulding or similar. A suitable material is a glass filled polyetherimide (PEI) resin such as Ultem <NUM> or Ultem <NUM>, available from SABIC Innovative Plastics Holding BV, or Nylon PA6, PA66 or PA12.

The fastening system <NUM> includes a locator <NUM> as shown in <FIG>. The locator <NUM> acts as a locating tool. The locator <NUM> is configured to locate the cap <NUM> over the aperture <NUM> in the structure <NUM>. The locator <NUM> acts as a locating tool. The locator <NUM> comprises a locating member 350a. The locating member 350a is configured to locate in the aperture <NUM> to align the cap <NUM> over the aperture <NUM>. The locator <NUM> is formed from a resilient material, such as an elastomer. The locator <NUM> has a neck portion <NUM>. The neck portion <NUM> forms the locating member 350a. The locating member 350a is a deformable member, and may form an elastomeric shaft. The neck portion <NUM> is elongate and extends from a locator head <NUM>. The locator head <NUM> acts as a cap connecting feature. The locator head <NUM> is configured to connect with the nut <NUM>, acting as the fastening collar, which is received by the cap <NUM>. The nut <NUM> acts as a connecting feature connecting the locator <NUM> with the cap <NUM>. The locator head <NUM> engages with the nut to form a releasable connection. The diameter of the neck portion <NUM> is less than the diameter of the head <NUM>. A head step <NUM> is formed between the neck portion <NUM> and the head <NUM>.

A handle portion <NUM> is formed at an opposing end to the neck portion <NUM> to the locator head <NUM>. The handle portion <NUM> extends from the neck portion <NUM>. A handle step <NUM> is formed between the neck portion <NUM> and the handle portion <NUM>. The diameter of the neck portion <NUM> is less than the diameter of the handle portion <NUM> in an undeformed state. In an alternative embodiment, as will be described below, the neck portion <NUM>, acting as the locating member 350a, has a diameter equal to or greater than that of the handle portion <NUM>. The diameter of the neck portion <NUM> corresponds to the diameter of the bore <NUM> of the nut <NUM>. The head <NUM> is insertable through the bore <NUM> of the nut <NUM>, and is deformable to expand to abut the nut top surface upon being urged through the bore <NUM>. The head portion <NUM> is sized to be receivable in the air cavity <NUM> of the cap <NUM>. The neck portion <NUM> is deformable in a longitudinal direction. When the locator <NUM> is drawn in a longitudinal direction, the diameter of the neck portion <NUM> contracts. Similarly, the diameter of the handle portion <NUM> contracts. The contraction of the neck portion <NUM> and handle portion <NUM> is configured to be sufficient to allow the neck portion <NUM> and handle portion <NUM> to be inserted through the aperture <NUM>.

The length of the neck portion <NUM> substantially corresponds to the height of the nut <NUM>, the washer <NUM> and the length of the aperture <NUM> through which the fastener <NUM> is configured to extend.

<FIG> illustrates an alternative arrangement, in which the annular sealing volume of the cap is alternatively formed. In <FIG>, the fastener <NUM> is generally the same as the fastener described above for <FIG>, however it will be understood that alternative fastener arrangements may be used. A cap <NUM> comprises a two-part cap body <NUM> having an inner cap member <NUM> and an outer cap member <NUM>. The inner cap member <NUM> is a generally thin-walled dome-shaped member, defining the air cavity <NUM> which encloses the end <NUM> of the fastener <NUM> protruding from the structure.

The inner cap member <NUM> comprises an annular base <NUM> which has a generally cylindrical outer surface, and a domed portion <NUM>. An outer diameter of the inner cap member <NUM> reduces so the domed portion <NUM> has a smaller outer diameter than the annular base <NUM>.

A rim <NUM> of the annular base <NUM> abuts the structure <NUM> to fully encapsulate the end <NUM> of the fastener <NUM> within the air cavity <NUM>. Hooks <NUM> provide a mechanical connection between the inner cap member <NUM> and the nut <NUM>.

The outer cap member <NUM> is also a generally thin-walled dome shaped member, and is shaped to fit over the inner cap member <NUM> so that an annular sealing volume <NUM> is defined therebetween. The outer cap member <NUM> is generally made up of an annular skirt <NUM> and a smaller diameter domed portion <NUM>. The annular skirt <NUM> has a flared lip <NUM> at its free edge. An injection channel <NUM> is provided in fluid engagement with the sealing volume. The injection channel is omitted in an arrangement, with the inner and outer cap members being movable relative to each other and uncured sealing material being compressible therebetween.

The annular sealing volume <NUM> is open at its lower face such that sealing material <NUM> can flow outwardly from the annular sealing volume <NUM> and into contact with the structure <NUM>. The sealing material then forms an annular bead around the periphery of the nut cap <NUM>, the bead of sealing material serving to seal the air cavity <NUM> in order to prevent escape of outgassing products, and to adhere the nut cap <NUM> to the structure <NUM>.

Referring now to <FIG>, installation of the fastening system <NUM> to form the joint <NUM> will now be described. During installation, the nut <NUM>, acting as the fastening collar, and the cap <NUM> are assembled. The nut <NUM> is retained in the cap <NUM>. When the nut <NUM> is received in the cap <NUM>, the engaging feature <NUM> abuts with the first drive feature <NUM>. The nut and cap <NUM> are assembled with the locator <NUM> and the washer <NUM> as shown in <FIG>. In the present arrangement, the locater <NUM> is fitted to the nut; by stretching the locator <NUM> and sliding the nut onto it, prior to the cap <NUM> being assembled.

The panels <NUM>10a, 110b are brought together and the aperture <NUM> and countersink <NUM> are formed. One of the panels 110a is then removed. As shown in <FIG>, the assembled nut, washer <NUM> and cap <NUM> are located over the aperture <NUM> in the structure <NUM>. The locator <NUM> locates the nut, washer <NUM> and cap <NUM>. The locator <NUM> is inserted through the aperture <NUM>. Due to the resilience of the locator <NUM>, the nut is drawn towards the structure <NUM>. The washer <NUM> is disposed therebetween. The cap <NUM> encloses the nut and washer <NUM> and one side of the aperture. The handle portion <NUM> of the locator <NUM> protrudes from an opposing side of the structure. The washer <NUM> may be omitted. The nut <NUM> is retained by the cap <NUM>. When the locator <NUM> acts on the nut <NUM> to draw the nut <NUM> towards the structure <NUM>, the cap is drawn towards the structure <NUM>. The nut <NUM> acts against the hooks <NUM> and is drawn in an axial direction by the action of the locator <NUM>.

To locate the cap <NUM> over the aperture <NUM> in the structure <NUM>, the assembled cap <NUM> and locating tool <NUM> are assembled with the panel 110b. An elongate guide (not shown) is inserted through the aperture <NUM>. The elongate guide extends from the handle portion <NUM>. The handle portion <NUM> is then drawn through the aperture <NUM> using the guide member. The nut <NUM> is drawn towards the structure <NUM> such that the cap <NUM> is drawn towards the structure <NUM>. The rim <NUM> locates against the surface of the structure <NUM> and is in abutment with the surface around its diameter. The neck portion <NUM> engages with the aperture <NUM> and the handle portion <NUM> is released so that the shaft part in the sealed cavity <NUM> is in tension. As such, the neck portion <NUM> acts as a drawing arrangement, arranged to draw the head <NUM> towards the structure <NUM>. The head <NUM> therefore biases the cap <NUM> against the structure <NUM>.

Pre-mixed sealing material <NUM> is then injected into the annular sealing volume <NUM>. When the annular sealing volume <NUM> is full it overflows, causing an evenly distributed flow of sealing material <NUM>. The sealing material <NUM> completely fills the annular sealing volume <NUM> until it flows into contact with the structure <NUM>.

The curable sealing material <NUM> is left to cure. On curing, it provides a strong adhesive bond between the cap <NUM> and structure <NUM>. The sealing material <NUM> may cure to handling strength (i.e. a degree suitable to provide sufficient strength to withstand knocks or similar from assembly workers) in approximately <NUM> minutes for epoxy-based adhesive sealing materials, one hour for polythioether sealants, or over four hours for polysulphide sealants.

During cure of the sealing material <NUM> (or at least until the sealing material is partially cured) the locator <NUM> is left in position. The locator <NUM> draws the nut and cap <NUM> against the surface of the structure <NUM>. Once the sealing material <NUM> has cured, or at least partially cured, the structure <NUM> may be further assembled with other structures, such that access to the side of the structure <NUM> with the cap <NUM> is restricted.

Once the sealing material <NUM> has fully cured, the locator <NUM> is withdrawn. The head <NUM> is deformable when a withdrawal force is exerted on the locator <NUM> from the underside of the panel 110b to release the head <NUM> from the nut <NUM> and draw the head through the aperture <NUM>. It will be understood that the locator <NUM> may be omitted in some arrangements. The deformity of the locator <NUM> provides for the locator <NUM> to be easily removed. The cap <NUM> is securely fixed with the structure, and the nut is securely engaged with the cap <NUM>. As such, a rigid formation is formed between the structure <NUM>, the cap <NUM> and the nut.

Upon removal of the locator <NUM>, the panels 110a, 110b are brought together, and the second fastening member <NUM> is inserted through the aperture <NUM> in the structure <NUM> as shown in <FIG>. The free end of the second fastening member <NUM> is brought into contact with the nut. The free end of the second fastening member <NUM> passes through the washer <NUM>. Upon contact with the nut, acting as the nut <NUM>, a drive torque is applied to the second fastening member <NUM> through means of the second drive feature <NUM>. The drive torque cause rotation of the bolt, acting as the second fastening member <NUM> relative to the nut <NUM>. The bolt engages with the nut, through threaded engagement. As a torque is applied through the fastener <NUM>, a reaction force acts on the nut <NUM>. The fixed cap <NUM> reacts against the nut <NUM> through the engaging feature <NUM> to prevent rotation of the nut <NUM>. As such a fastening torque may be applied to the fastener <NUM>.

The adhesion strength of the sealant adhering the cap <NUM> and the strength of engagement of the nut and cap <NUM> are configured to overcome the reaction forces exerted onto the nut in reaction to the locking torque when the second fastening member <NUM> is tightened. In embodiments, the nut has a locking feature (not shown). The reaction forces are configured to exceed the locking torque caused by the friction generated by the locking feature of the nut. As the fastener is tightened the clamping pressure exerted onto the structure <NUM> will overcome a significant portion of the reaction torque. With the above described arrangement, it is possible to mount a fastener and spark containment cap without the need to apply a manual fastening torque to both sides of the fastener.

In embodiments, a chemical locking feature, such as a curable adhesive, is applied between the first and second fastening members. This helps prevent the need for a mechanical locking feature to be provided and so minimises the reaction force applied to the cap upon fastening the fastener.

<FIG> show an alternative spark containment cap assembly system <NUM>. The spark containment cap assembly system <NUM> is used to form the joint <NUM>. The joint <NUM> comprises a structure <NUM> such as an aircraft skin panel 410a joined to another component, such as another panel 410b. The joint <NUM> includes a fastener <NUM> and a cap <NUM>. A locator <NUM> acts as a locating tool. The locator <NUM> acts to locate the cap <NUM> over an aperture <NUM> in the structure <NUM> during assembly of the joint <NUM>. A number of the features of the structure <NUM>, the fastener <NUM>, the cap <NUM> and the locator <NUM> correspond to features of components described in the above embodiments. As such, a detailed description of common features will be omitted below. In the embodiment described below, the fastener <NUM> does not engage with the cap <NUM> such that relative movement is restricted between the components. In embodiments, an end <NUM> of the fastener <NUM> is spaced from the cap <NUM>.

The end <NUM> of the fastener <NUM> protrudes from the structure <NUM>. The fastener <NUM> comprises a first fastening member <NUM> and a second fastening member <NUM>. The first and second fastening members <NUM>, <NUM> are engageable with each other to form the joint <NUM>. The fastener <NUM> is a blind fastener. As such, the fastener <NUM> can be inserted and fully installed in the aperture <NUM> from only one side of the structure <NUM>, "blind" to the opposite side of the structure <NUM>. As shown in the Figures, the fastener <NUM> is inserted from the side of the aperture <NUM> which has a countersink <NUM>. In embodiments, the fastener <NUM> is a blind rivet.

The cap <NUM> encloses the end <NUM> of the fastener <NUM> when the fastener <NUM> is engaged through the aperture <NUM>. The cap <NUM> is aligned with and encloses one end of the aperture <NUM>. The cap <NUM> has a cap body <NUM> with a domed outboard (upper) part <NUM> and a substantially cylindrical base <NUM>. The base <NUM> terminates at a rim <NUM>. The rim <NUM> surrounds an opening into a central air cavity <NUM>. The central air cavity <NUM> forms a sealed cavity upon assembly of the joint <NUM>.

An annular skirt <NUM> extends from an upper end junction with the cap body <NUM> to an inboard (lower) skirt rim <NUM> which lies substantially in the same plane as the rim <NUM> of the annular base <NUM>. An annular pocket <NUM> acting as an annular sealing volume is provided between the skirt <NUM> and the base <NUM>. The annular pocket <NUM> has an injection channel <NUM>. The annular pocket <NUM> has an outlet (not shown). A sealing material injection device <NUM> is used to inject a suitable sealing material into the annular pocket <NUM> as shown in <FIG>. The sealing material injected into the annular pocket <NUM> forms an annular bead of curable sealant material.

Alternative sealant arrangements may be provided to those shown. For example, the pocket may be pre-filled with sealing material, or one part such as the annular skirt may be moveable relative to another part, for example the cap body. The cap <NUM> may be a two part cap instead of the one part cap shown in the figures, with sealant being received between the two parts of the cap.

The cap <NUM> comprises a locating tool connecting feature <NUM>. The locating tool connecting feature <NUM> is configured to connect with the locator <NUM>. The locating tool connecting feature <NUM> is in the cavity <NUM>. The locating tool connecting feature <NUM> is formed by a wall of the cap body <NUM>. The locating tool connecting feature <NUM> is formed about a longitudinal axis of the cap <NUM>. The locating tool connecting feature <NUM> is at the domed end <NUM> of the cap <NUM>. Engaging ridges <NUM> form the locating tool connecting feature <NUM>. The engaging ridges <NUM> extend circumferentially at the closed end of the cavity <NUM>. The locating tool connecting feature <NUM> is at the distal end of the cap body <NUM> to the rim <NUM>. As such, the locating tool connecting feature <NUM> is configured to be spaced, and so not interfere, with the fastener <NUM> upon assembly of the joint <NUM>.

The locating tool connecting feature <NUM> may have different forms, and for example, may include one or more of an adhesive, a protrusion, such as a ridge, a head (as described above), a shoulder, a ridge and a recess.

The locator <NUM>, acting as the locating tool, is initially assembled with the cap <NUM> prior to bringing the cap <NUM> together with the structure <NUM>. As such, the cap <NUM> and locator <NUM> are pre-assembled.

The locator <NUM> comprises a cap connecting feature <NUM> and a locating member <NUM>. The cap connecting feature <NUM> is at one end of the locating member <NUM>. The locating member <NUM> is elongate. The locating member <NUM> is configured to be received through the aperture <NUM> in the structure <NUM>. In the present embodiment, the locating member <NUM> is a deformable member which may be manipulated into an extended elongated form to reduce the diameter of the locating member <NUM> when deformed to have a diameter which is less than the diameter of the aperture <NUM>. In an undeformed condition, the locating member <NUM> has a diameter which is greater than the diameter of the aperture <NUM> formed in the structure <NUM>. When assembled with the cap <NUM>, the locating member <NUM> of the locator <NUM> extends from the opening to the cavity <NUM>. The extension of the locating member <NUM> from the cavity <NUM> is greater than the length of the aperture <NUM> over which the cap <NUM> is to be located. The locator <NUM> is formed from a suitable material such as an elastomeric material.

The cap connecting feature <NUM> is configured to connect with the locating tool connecting feature <NUM> of the cap <NUM>. The cap connecting feature <NUM> connects directly with the cap <NUM>. The cap connecting feature <NUM> has a plurality of ridges <NUM>. The cap connecting feature <NUM> corresponds with the locating tool connecting feature <NUM>. In embodiments, the cap connecting feature <NUM> includes, for example, one or more of a recess, such as a channel, a shoulder, a rib, a helical thread, and a protrusion. The cap connecting feature <NUM> and the locating tool connecting feature <NUM> may together be a single feature such as a releasable adhesive. The releasable adhesive may be at the end of the locator <NUM>.

The locator <NUM> is releasable from the cap <NUM>. The locator <NUM> is releasable in response to a release force being exerted on the locator <NUM> to draw the locator <NUM> away from the cap <NUM>. That is, to draw the locator <NUM> out of the cavity <NUM>. The release force is configured to be greater than the deformation force required to deform the locating member <NUM>.

Assembly of the joint <NUM> will now be described. The cap <NUM> and locator <NUM> assembly is assembled as shown in <FIG>. The cap <NUM> is aligned with the aperture <NUM> in the structure <NUM> and the locating member <NUM> of the locator <NUM> is drawn through the aperture <NUM>. A guide member (not shown) may extend from the free end of the locator <NUM> which has a smaller diameter than the locating member <NUM> and is insertable through the aperture <NUM> to align the locating tool <NUM> with the aperture <NUM>, and aid the locating member <NUM> to be drawn through the aperture <NUM>.

By drawing the free end of the locating member <NUM> away from the cap <NUM>, the locating member <NUM>, acting as a deformable member, deforms such that the diameter of the locating member <NUM> decreases and is receivable through the aperture <NUM>. When the free end of the locating member <NUM> is drawn through the aperture <NUM>, the locating member <NUM> is further drawn through the aperture <NUM> to draw the cap <NUM> against the structure <NUM>. The rim <NUM> of the cap <NUM> locates against the structure <NUM> and the locator <NUM> retained by the cap <NUM> biases the cap <NUM> against the structure. When the free end of the locating member <NUM> is released, the section of the locating member <NUM>, acting as a deformable member, in the cavity <NUM> is retained in tension and so draws the cap <NUM> against the structure <NUM>.

The released free end of the locating member <NUM> is biased towards an undeformed state due to its resilience and so engages with the aperture <NUM> and the underside of the structure <NUM> to retain the cap <NUM> in position. The locating member <NUM> therefore acts as a drawing arrangement to draw the cap <NUM> against the structure <NUM>. The cap <NUM> is therefore biased against the structure <NUM>, with the rim <NUM> in abutment against a surface of the structure <NUM>. As the release force required to disengage the locating tool connecting feature and the cap connecting feature is greater than that required to deform the locating member <NUM>, the locator <NUM> is retained in connection with the cap <NUM>.

When the cap <NUM> is in the biased condition, uncured sealing material is injectable into the annular sealing volume <NUM>. The pressure of injecting sealing material into the annular sealing volume <NUM> as shown in <FIG> is counteracted by the biasing force applied by the locator <NUM>. As such, the rim <NUM> is retained in abutment with the structure <NUM>. Sealant therefore does not flow into the cavity <NUM>.

Once an annular bead of uncured sealing material is received by the cap <NUM>, the sealing material may be cured to affix the cam <NUM> to the structure <NUM> as shown in <FIG>.

Once the sealing material is cured, and the cap <NUM> is fixably adhered to the structure <NUM> by the sealing material, a withdrawal force is applied to the locator <NUM>. The free end of the locating member <NUM> is drawn away from the structure <NUM> in a direction to bias the locating member <NUM> to move through the aperture <NUM> and out of the cavity <NUM>. A withdrawal force greater than the connecting force between the cap <NUM> and the locator <NUM> is applied so that the cap connecting feature <NUM> disengages from the cap <NUM>. Such a condition is shown in <FIG>. The locator <NUM> may then be fully withdrawn from the cap <NUM> and structure <NUM>. The locator <NUM> may be discarded or re-used on another cap.

A sealed cavity is therefore formed between the cap <NUM> and the structure <NUM>. The joint <NUM> may then be fully assembled by inserting the blind fastener <NUM> through the aperture <NUM> from an opposing side of the structure <NUM> to the cap <NUM>. The blind fastener <NUM> is engaged to form the joint <NUM>. With such an arrangement, the joint <NUM> may be formed during final assembly with access to only one side of the structure <NUM>. By providing the locating tool connecting feature <NUM> at the distal end of the cap <NUM> it is possible to ensure that the cap does not interfere with the fastening of the fastener <NUM>.

In <FIG> another embodiment of the spark containment cap assembly system <NUM> is shown. The system <NUM> shown in <FIG> generally corresponds to the system <NUM> shown in <FIG>. As such, a detailed description will be omitted herein. The arrangement is generally the same and includes a cap <NUM>, a structure <NUM>, a fastener <NUM> and a locator <NUM>. The dimensions of the cap <NUM> and locator <NUM> differ from those shown in <FIG>; however the features of the cap <NUM> generally correspond to those of the cap <NUM>. The locator <NUM> differs in that a fastening collar <NUM> is utilised as a drawing arrangement to draw a locating member <NUM> through an aperture <NUM> in the structure <NUM> and to bias the cap <NUM> against the structure <NUM>. The cap <NUM> includes a rim <NUM> around an opening to an air cavity <NUM>. A locating tool connecting feature <NUM> is at a distal end of the cap <NUM> to the rim <NUM>. The locating tool connecting feature <NUM> may have differing arrangements as described above.

The locator <NUM>, acting as the locating tool, comprises the locating member <NUM> and the fastening collar <NUM>. The locating member <NUM> is elongate. A cap connecting feature <NUM> is at one end of the locating member <NUM>. The fastening collar <NUM> is at a distal end of the locating member <NUM> to the cap connecting feature <NUM>. The locating member <NUM> is a shaft with the cap connecting feature <NUM> connecting with the cap <NUM>. The locating member <NUM> protrudes from the cavity <NUM> of the cap <NUM>. The diameter of the locating member <NUM> is configured to be less than or equal to the diameter of the aperture <NUM> in the structure <NUM>.

The fastening collar <NUM> is movably engaged with the free end of the locating member <NUM>. The fastening collar <NUM> is a nut, such as a wing nut, which is threadingly engaged with the locating member <NUM>. The fastening collar <NUM> is removable from the locating member <NUM>. The fastening collar <NUM> acts as the drawing arrangement. In such an arrangement, the locating member may be rigid. As such, there is no need for a deformable member. However, it will be understood that embodiments may include the fastening collar and a deformable portion.

To assemble the joint, the assembled cap <NUM> and locator <NUM> are aligned with the aperture <NUM> in the structure <NUM>. The fastening collar <NUM> is absent from the locating member <NUM>. The distal end of the locating member <NUM> is inserted through the aperture <NUM>. The locating member <NUM> protrudes from the aperture on an opposing side to the cap <NUM>. The fastening collar <NUM> is releasably engaged with the locating member <NUM> and is further engaged to draw the locating member <NUM> in a direction through the aperture <NUM>. As such, the cap <NUM> is moved into abutment with the structure <NUM> over the aperture <NUM>. The fastening collar <NUM> is engaged until the rim <NUM> is biased against the structure <NUM>.

As described above, sealing material is then inserted into an annular sealing volume <NUM> of the cap <NUM> and cured. An annular bead of cured sealing material is then formed to affix the cap <NUM> to the structure <NUM>. A withdrawal force is then imparted on the locator <NUM> to disengage the locating member <NUM> from the cap <NUM>. The locating member <NUM> is then drawn through the aperture <NUM> to remove the locator <NUM>. The locator <NUM> is reuseable. As shown in <FIG>, the blind fastener <NUM> may then be inserted through the aperture <NUM> and engaged to form the joint.

Referring now to <FIG>, an alternative fastener will now be described. Description of this alternative fastener is provided for information only. <FIG> show a joint <NUM> in stages of installation. The joint <NUM> comprises a structure <NUM> such as an aircraft skin panel 610a joined to another component, such as another panel 610b. A fastener <NUM> extends through the structure <NUM>. The structure <NUM> in this embodiment is a composite aircraft structural component, but may be a hybrid composite-metallic component. The fastener <NUM> is inserted through an aperture <NUM> in the structure <NUM>. A countersink <NUM> is formed at one end of the aperture <NUM>. The fastener <NUM> is a rivet. In particular, the fastener <NUM> is a blind-rivet. That is, the fastener can be inserted and fully installed in the aperture <NUM> from only one side of the structure <NUM>, "blind" to the opposite side of the structure <NUM>. As shown in the Figures, the fastener <NUM> is inserted from the side of the aperture <NUM> having the countersink <NUM>.

The fastener <NUM> comprises a mandrel <NUM> and a sleeve <NUM>. The sleeve <NUM> is deformable about the mandrel <NUM> to form the joint <NUM>. The mandrel <NUM> is formed from a material with a higher rigidity than the sleeve <NUM>. For example, the mandrel <NUM> is formed from a steel or stainless steel, and the sleeve <NUM> is formed from monel or aluminium.

The mandrel <NUM> comprises an elongate stem <NUM>. A head <NUM> is at one end of the elongate stem <NUM>. The stem <NUM> and head <NUM> are integrally formed, or may be formed as separate but joined components. The stem <NUM> forms an axially extending shaft. The stem <NUM> has a sleeve engaging section <NUM> and a tool engaging section <NUM>. The tool engaging portion <NUM> is at an opposing end of the stem to the head <NUM>. A frangible joint is formed between the tool engaging section <NUM> and the sleeve engaging section <NUM>. The stem is configured so that the force required to break the frangible joint is greater than the force required to deform the sleeve <NUM>. The tool engaging section <NUM> has a ridged surface <NUM> to aid engagement with a drawing tool (not shown).

The elongate stem <NUM> has a tapered portion <NUM> tapering inwardly away from the head <NUM>. The sleeve engaging section <NUM> forms the tapered portion <NUM>. The tapered portion <NUM> is an external taper which tapers along the longitudinal length. The head <NUM> forms an abutment <NUM> against which the sleeve <NUM> abuts. The head <NUM> has a diameter equal to or less than the diameter of the aperture <NUM> through which it is receivable.

The sleeve <NUM> extending around the elongate stem <NUM>. The sleeve is slidable along the elongate stem <NUM> in an unfastened condition. The sleeve <NUM> has a countersink flange <NUM> at one end. The countersink flange <NUM> acts as a structure locating feature. That is, the countersink flange <NUM> is locatable against the structure <NUM> when the fastener <NUM> is received in the aperture <NUM> to restrict movement of the sleeve <NUM> in the longitudinal direction. The countersink flange <NUM> is configured to be received in the countersink <NUM>.

The sleeve <NUM> has a deformable section <NUM> at a free end <NUM> of the sleeve <NUM> from the countersink flange <NUM>. A collar section <NUM> is between the deformable section <NUM> and the end of the sleeve <NUM> with the countersink flange <NUM>. The sleeve <NUM> is cylindrical in its undeformed condition. The diameter of an external cylindrical surface <NUM> of the sleeve <NUM> is configured to correspond to the diameter of the aperture <NUM> in which the sleeve <NUM> is receivable. The length of the collar section <NUM> is configured to correspond to the length of the aperture <NUM>.

The sleeve <NUM> has an internal taper. An internal tapered surface <NUM> of the sleeve <NUM> is defined along the sleeve <NUM>. The internal tapered surface <NUM> in the present arrangement extends along the collar section <NUM>. The taper <NUM> of the internal tapered surface <NUM> corresponds to the taper of the tapered portion <NUM> of the stem <NUM>. The angle of taper of the internal tapered surface <NUM> conforms with the angle of taper of the tapered portion <NUM> of the stem <NUM>. The maximum diameter of the tapered portion <NUM> is greater than the internal diameter of the internal tapered surface <NUM> of the sleeve <NUM>.

The deformable section <NUM> of the sleeve <NUM> has an internal taper. The angle of internal taper of the deformable section <NUM> corresponds to the tapered portion <NUM> of the stem <NUM>. A step <NUM> is formed between the deformable section <NUM> and the collar section <NUM>.

Upon installation of the fastener <NUM>, the fastener <NUM> is inserted through the aperture <NUM> as shown in <FIG>. The fastener <NUM> is initially in the undeformed condition, with the taper <NUM> of the deformable section <NUM> locating against the tapered portion <NUM> of the stem <NUM>. The free end <NUM> of the sleeve <NUM> is spaced from the head <NUM>. When the fastener <NUM> is inserted, the countersink flange <NUM>, acting as the locating feature, locates in the countersink <NUM> as shown in <FIG>. The collar section <NUM> is therefore received in the aperture <NUM>. The deformable section <NUM> protrudes from the opposing side of the structure <NUM>. The collar section <NUM> is slide or push fitted into the aperture <NUM>. The sleeve <NUM> is free to slide along the stem <NUM>.

The sleeve <NUM> is held in position, and a tool (not shown) engages the tool engaging section <NUM> of the stem <NUM>. The mandrel <NUM> is drawn through the sleeve <NUM> in the direction of the arrow in <FIG>. The head <NUM> is moved towards the sleeve <NUM> and into contact with the free end <NUM>. A compressive force is therefore applied to the sleeve <NUM>. As the stem <NUM> is moved, the corresponding tapered faces of the sleeve <NUM> and stem <NUM> are brought together.

The compressive force exerted by the mandrel <NUM> causes the deformable section <NUM> to deform outwardly. That is the deformable section <NUM> buckles and collapses. The deformable section <NUM> forms a shoulder as shown in <FIG>. The sleeve <NUM> therefore has extended portions on either side of the structure <NUM>. As the stem <NUM> is drawn along its longitudinal axis, the tapered portion of the stem <NUM> moves into abutment with the internal tapered surface of the sleeve <NUM>. These two surfaces are brought into an interference fit. The longitudinal movement of the stem <NUM> relative to the sleeve <NUM> causes the stem to apply a radially acting force on the collar section <NUM> of the sleeve <NUM>.

The collar section <NUM> of the sleeve <NUM> is urged to distend outwardly. The collar section <NUM> is therefore urged into an interference fit with the stem <NUM>, and the action of the stem <NUM> on the collar section <NUM> urges the collar section into an interference fit with the side wall of the aperture <NUM>.

By forming an interference fit in the aperture <NUM>, and between the sleeve <NUM> and stem <NUM> it is possible to restrict the formation of any gaps or spaces in the joint <NUM> which may lead to the formation of a sparking or plasma formation.

The further longitudinal action of the tool on the mandrel causes the frangible joint to break, such that the tool engaging section <NUM> is removed from the remainder of the mandrel, as shown in <FIG>.

Claim 1:
A method of locating a spark containment cap (<NUM>, <NUM>, <NUM>, <NUM>) over an aperture (<NUM>, <NUM>, <NUM>) in a structure (<NUM>, <NUM>, <NUM>), the method comprising:
receiving a locating tool (<NUM>, <NUM>, <NUM>) through the aperture;
drawing part of the locating tool through the aperture to draw a spark containment cap at one end of the tool against the structure; characterized by
releasing the locating tool from the spark containment cap and withdrawing the locating tool from the aperture.