Patent Description:
The present disclosure relates generally to aircraft and, more particularly, to a fastening system for aircraft structures.

Aircraft employ different types of fasteners to couple two or more structural components. However, access to structural components can be limited, requiring personnel or mechanics to perform confined space work to install and/or torque a fastener of a fastening system.

<CIT> describes, in accordance with its abstract, an alignment tolerant fastening system for interconnecting first and second members having first and second bores therethrough, respectively. The fastening system may include a fastening member having a shank portion which is receivable within the bores of the first and second members, a nut member for engaging at least a distal portion of the fastener shank portion proximate the second member, and first and second washers, at least one of which includes a plurality of serrations, positionable within the first bore of the first member, about the shank portion of the fastener. More specifically, for purposes of accommodating a misalignment between the first and second bores, the inner wall of the first washer is slidably engagable with the fastener shank portion and the outer wall of the second washer is slidably engagable or interconnectable with the first bore wall which defines the first bore of the first member.

<CIT> describes, in accordance with its abstract, an assembly that includes an aircraft fuel tank a captive nut with an internal thread, a secondary structure and a fastener which secures the secondary structure to the fuel tank. The fastener has a shaft which passes through the secondary structure and has an external thread coupled to the internal thread of the captive nut. The fuel tank has a fuel tank element with a hole, and the captive nut has a sleeve which is located in the hole with an interference fit between an outer surface of the sleeve and an inner surface of the wall of the hole.

<CIT> describes, in accordance with its abstract, a fastening structure which can be processed with less variation in axial force caused by a fastening member. The fastening structure comprises: a fastening member having a screw thread to which a mating member is assembled and a cylindrical part protruding vertically from a bearing surface; and a fixing member in which an open hole where the cylindrical part is inserted in an axial direction is formed to pass, and at least the inner surface of the open hole has a low hardness as compared with the fastening member. The inner surface of the open hole has a pressing-in part into which the cylindrical part is pressed in, and a large diameter part which connects a contact surface of the fixing member with which the bearing surface is in contact to the pressing-in part and has an inner diameter large as compared with an outer diameter of a part of the cylindrical part which is pressed into the pressing-in part.

<CIT> describes, in accordance with its abstract, a fastener providing protection against damage to an aircraft resulting from lightning strikes includes an elongated shaft having a head disposed at an upper end thereof, one, the other, or both of the shaft and the head containing a circumferential groove disposed proximate an intersection of the shaft and the head, a lower surface of the head including a plurality of grooves extending radially outward from the circumferential groove and terminating at an outer periphery of the lower surface. A tubular sleeve is disposed concentrically about the shaft and has a plurality of through-slots disposed therein. Each through-slot has a lower end disposed above a lower end of the sleeve, and an upper end disposed in fluid communication with the circumferential groove, such that superheated gases and particles generated in interfaces between the fastener and the adjacent skin due to lightning strikes are vented harmlessly to the atmosphere through the channels and grooves.

<CIT> describes, in accordance with its abstract, a fastener assembly that comprises a stud bolt including a bolt portion and a weld end to be welded to a workpiece, and a nut member to be screwed into the stud bolt. The nut member screwed into the stud bolt before welding is formed out of an electrically conductive material to allow the welding current to flow through the nut member into the stud bolt and weld the nut member to the workpiece while connected to the stud bolt. Then an attachment member is disposed on top of the workpiece, and the attachment member is fastened to the workpiece when the nut member is turned in the fastening direction.

According to an aspect, a fastening system as described in claim <NUM> is provided. According to a further aspect, a method as describes in claim <NUM> is provided.

An example fastening system to couple a first structure and a second structure includes a fastener, a nutplate having a body defining an opening to receive the fastener, a flange extending from the body to engage an outer surface of the first structure, and a first sleeve protruding from the flange in a direction away from the body, the first sleeve to couple to a first bore formed in the first structure and prevent rotation of the nutplate relative to the first structure.

An example aircraft includes a wingbox defining a structure including one or more spar chords, stringers and ribs, a close-out panel to close the wingbox, and a fastener assembly to couple the close-out panel and the wingbox. The fastener assembly includes a nutplate having a body and a first sleeve extending away from the body in a direction along a longitudinal axis of the body, the first sleeve to be press-fit in a first bore of the structure to prevent rotation of the nutplate relative to the structure, the nutplate configured to prevent rotation of the nutplate about the longitudinal axis relative to the structure when the nutplate is coupled to the structure. The fastener assembly also includes a fastener to couple to the nutplate via a second bore formed in the close-out panel to couple the close-out panel and the structure.

An example method includes aligning a close-out panel of an aircraft with a structure of an aircraft, forming a bore through the close-out panel and the structure, removing the close-out panel from the structure after forming the bore, inserting a nutplate to a first portion of the bore formed in the structure, re-aligning the close-out panel with the structure, inserting a sleeve in a second portion of the bore formed in the close-out panel, inserting a fastener in the second portion of the bore formed in the close-out panel from an exterior surface of the close-out panel, and coupling the fastener to the nutplate via the second portion of the bore to secure the close-out panel to the structure.

Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this disclosure, stating that any part (e.g., a layer, film, area, or plate) is in any way positioned on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, means that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. Stating that any part is in contact with another part means that there is no intermediate part between the two parts.

Aircraft employ fastening systems or fasteners to secure a first structure (e.g., an aircraft wall, a cover panel, a close-out panel, a wing skin, etc.) and a second structure (e.g., a stringer, a spar chord, a rib of an aircraft frame, etc.). Known fastening systems include a nutplate used in combination with a threaded screw or bolt to secure the first structure (e.g., the close-out panel) and the second structure (e.g., a spar chord of the wingbox). However, during aircraft assembly, the assembly areas can become confined and limited, which increases manufacturing complexity. For example, a close-out panel, when coupled to a wingbox, reduces access to an area or cavity within the wingbox. Aircraft technicians often have to enter a cavity of the wingbox through an access opening (e.g., an access opening located at a bottom of the wing) to perform confined space work to install and/or torque fasteners of the close-out panel, install hydraulic system, install fuel systems, seal fuel tank, apply lightning strike protection sealant, cleaning, systems testing, etc. However, confined space fastener installation is particularly time-consuming because such fastener installation requires installation in the extremities of every single rib bay in the wing).

Some existing fastening systems (e.g., nutplates) can be configured to reduce confined space work conditions. For example, some known fastening systems employ secondary self-retention features (e.g., small diameter rivets) for securing the nutplate within an installation hole of a structure (e.g., a rib) to react a torque (e.g., restrict or reduce rotation) applied to the nutplate when threadably coupling a bolt to the nutplate. In some examples, such secondary self-retention features include rivets, pins or other features used to secure the nutplate after the nutplate is installed or coupled to a structure. However, such existing nutplates have not been used due to cost, weight, complexity and/or ineffectiveness of the secondary self-retention features. For example, small diameter rivets increase installation costs. Further, adding rivets increases direct lightning strike concerns by forming additional pathways to an interior of a wingbox, requiring addition of a sealant (e.g., cap seals) for lightning direct strike protection. Addition of such sealant after a fastening system is installed requires confined space work because mechanics or personnel need to access the fastening system (e.g., the nutplate and rivets) from within the wingbox (e.g., after installation of a closeout panel) to apply the sealant. Additionally, such known sealant significantly increases aircraft weight. In other examples, nutplates are coldworked as a secondary operation to radially expand the nutplate in an installation hole to achieve an interference fit. However, cold-working as a secondary operation increases manufacturing costs and reduces manufacturing efficiency. As such, aircraft do not employ existing fastening systems as they increase airplane weight, manufacturing complexity and/or costs.

Example fastening systems for aircraft disclosed herein facilitate installation in confined work spaces and provide lightning direct strike protection. Specifically, example fastening systems disclosed herein do not require aircraft mechanics to perform confined space work to install and/or torque a fastener. For example, fastening systems disclosed herein eliminate confined space work needed for a mechanic to enter a wingbox to install and/or torque a fastener of a close-out panel (e.g., a close-out panel of a carbon fuel-carrying primary structure wingbox). Additionally, fastening systems disclosed herein can employ a conductive coating as a finish applied to an exterior surface of the fastening system parts, thereby increasing conductivity where the parts contact and/or gap each other. Other features of the fastening systems disclosed herein (e.g., a dome-shaped nutplate, etc.), in combination with the conductive coating, do not require separate application of a sealant for lightning direct strike protection after installation of the fastening system to a structural assembly.

Example fastening systems disclosed herein employ a nutplate used in combination with a threaded bolt to secure a first structure (e.g., a spar chord of the wingbox) and a second structure (e.g., a close-out panel). An example nutplate disclosed herein includes a unitary or one-piece body. The nutplate includes an integral construction with a dome, a flange or shoulder, and a sleeve (e.g., a circumferential leg) extending from the dome. The sleeve provides an integral self-retention feature that prevents rotation of the nutplate about a longitudinal axis when coupled to an installation hole of a structure. In other words, no additional fasteners or secondary self-retention features such as rivets, pins, etc., are needed to enable the nutplate to react a torque (e.g., rotation) applied to the nutplate. To prevent rotation of the nutplate, the integral self-retention feature includes a sleeve that couples to an installation hole of a structure via an interference fit. Thus, the example fasteners disclosed herein eliminate the need for rivets or other self-retention features to retain the nutplate. Additionally, installation of the nutplate can be provided prior to the addition of a close-out panel, thereby eliminating personnel from having to access a cavity of a frame (e.g., a wingbox) to react a torque from a fastener after installation of the close-out panel. Instead, a mechanic can torque a fastener of the fastening system after the close-out panel is coupled to the frame from an exterior of the frame (e.g., without having personnel access a cavity of the frame) because the integral self-retention feature of the nutplate reacts a torque from the fastener and prevents rotation of the nutplate about its longitudinal axis when a fastener is coupled to the nutplate. Additionally, the fastening systems disclosed herein include a conductive coating to provide lightning direct strike protection that can be applied during fabrication of the fastening system. The combination of the conductive coating with the direct lightning strike protection features of the fastening system disclosed herein (e.g., domed nutplate, a groove for fuel isolation from fastener assembly, etc.) eliminates the need for application of a sealant after installation of the fastening system. The example fastening systems disclosed herein significantly reduce manufacturing costs and/or improve manufacturing efficiency by eliminating the need for confined space work and/or reduce aircraft weight and manufacturing costs associated with application of a sealant after installation of the fastening system.

<FIG> illustrates an example aircraft <NUM> in which the examples disclosed herein can be implemented. The aircraft <NUM> includes a fuselage <NUM> and wings <NUM>, <NUM> extending laterally outward from the fuselage <NUM>. Each of the wings <NUM>, <NUM> of the illustrated example supports an aircraft engine <NUM> via a pylon <NUM>. In the examples disclosed herein, a fastening system <NUM> (e.g., a fastener assembly) disclosed herein secures or couples airplane structures associated with the wings <NUM>, <NUM>. For example, the fastening system <NUM> of <FIG> couples a close-out panel <NUM> (e.g., a wing skin <NUM>) to the wing <NUM>. Only one fastening system <NUM> is shown in <FIG> for illustrative purposes. However, the wing <NUM> (e.g., the close-out panel <NUM>) can include a plurality of fastening systems <NUM> to attach the close-out panel <NUM> to the wing <NUM>. Although <FIG> illustrates that the fastening system <NUM> is used to couple the close-out panel <NUM> and the wing <NUM>, the fastening system <NUM> disclosed herein can be used to secure any other structures of the aircraft <NUM>. Further, the wing <NUM> is similar to the wing <NUM>. For example, the wing <NUM> also includes an example fastening system (e.g., the fastening system <NUM>). For brevity, the wing <NUM> is not discussed further herein. Additionally, the aircraft <NUM> of <FIG> is a commercial aircraft. However, the fastening system <NUM> disclosed herein can be employed with unmanned vehicles (e.g., drones), military vehicles, marine vehicles, automobiles, other structures, and/or any frame(s) or structure(s). Further, the fastening system <NUM> disclosed herein is not limited to aircraft-specific structures. In some examples, the fastening system <NUM> can be employed to couple any other type(s) of structure(s) or frame(s) (e.g., box frames, housing, etc.).

<FIG> is a perspective view of the example wing <NUM> of the example aircraft of <FIG> with an upper close-out panel and other components removed to show wing sub-structure. <FIG> is an enlarged, partial view of the example wing <NUM> of <FIG>. The close-out panel <NUM> is not shown in <FIG>. The first wing <NUM> has an example wingbox <NUM> that includes structural components <NUM> that support and/or shape the wing <NUM>. The structural components <NUM> include load-bearing components that are structured or configured to withstand shear and/or bending moments acting on the wing <NUM> during loading conditions (e.g., lift). For example, the wingbox <NUM> includes a plurality of ribs <NUM> extending in a spar chordwise direction. Additionally, the wingbox <NUM> includes a front spar 210a (e.g., adjacent a leading edge 211a of the wing <NUM>), a rear spar 210b (e.g., adjacent a trailing edge 211b of the wing <NUM>) and a plurality of stringers <NUM> extending in a spanwise direction. The ribs <NUM> maintain an aerodynamic profile of the wing <NUM> and can be spaced relative (e.g., equidistant) to one another (e.g., repeated at frequent or equidistant intervals to form a skeletal shape of the wing <NUM>). For example, the ribs <NUM> form part of a boundary of the wingbox <NUM> onto which the wing skin <NUM> (<FIG>) is attached and support the wing skin <NUM> to prevent the wing skin <NUM> from buckling. The ribs <NUM> attach to the front spar 210a and the rear spar 210b that extend across the length of the wing <NUM> in the spanwise direction (e.g., between a wing root and a wing tip) and provide strength to the wing <NUM> by counteracting torsion and upward bending forces when the wing <NUM> generates lift. The stringers <NUM> carry axial loads resulting from bending moments in the wing <NUM>. The wing <NUM> forms a cavity <NUM> that can be used to store fuel. To permit access to the cavity <NUM> of the wingbox <NUM>, the wing <NUM> includes one or more access openings <NUM>. For example, the access openings <NUM> allow mechanics and/or personnel to perform confined space work within the cavity <NUM> of the wing <NUM> after attachment or assembly of the close-out panel <NUM> to the wingbox <NUM>.

<FIG> is a perspective view of the example wing <NUM> of <FIG>. The wing <NUM> of <FIG> includes the close-out panel <NUM> secured to the wing <NUM> via the example fastening system <NUM>. <FIG> is a perspective, enlarged view of the example wing <NUM> of <FIG> shown without the close-out panel <NUM>. Referring to <FIG>, during assembly of the aircraft <NUM>, the close-out panel <NUM> (e.g., the wing skin <NUM>) is installed and fastened to the wingbox <NUM> via the fastening system <NUM> to form the wing <NUM> of <FIG>. To install the close-out panel <NUM> to the wingbox <NUM>, a rib <NUM> includes a first opening <NUM> (e.g., a through hole, a first bore) to receive the fastening system <NUM>. When coupled to the wing <NUM>, a fastener head <NUM> of the fastening system <NUM> is positioned along (e.g., exposed from) an exterior surface <NUM> (e.g., an outer or external surface) of the close-out panel <NUM> and other portions of the fastening system <NUM> are located within the cavity <NUM> of the wingbox <NUM>. In other words, only the fastener head <NUM> (e.g., a bolt head) of the fastening system <NUM> is exposed to the exterior surface <NUM> (e.g., an exterior) of the wing <NUM>. Additionally, as described in detail below, the fastening system <NUM> can be torqued (e.g., via the fastener head <NUM>) when the close-out panel <NUM> is attached to the wingbox <NUM> and without requiring personnel to access the cavity <NUM> via the access openings <NUM> (<FIG>). As noted above, the aircraft <NUM> includes a plurality of fastening systems <NUM> to secure the close-out panel <NUM> to the wingbox <NUM>. For example, to install the close-out panel <NUM> to the wingbox <NUM>, the ribs <NUM> include a plurality of openings <NUM> to receive respective ones of the fastening systems <NUM>. Thus, each of the openings <NUM> receives a respective one of the fastening systems <NUM> to couple the close-out panel <NUM> to the wingbox <NUM>. The fastening systems <NUM> are identical to the fastening system <NUM> and, for brevity, will not be further discussed. Although not shown, the close-out panel <NUM> can be secured to other aircraft structure(s) such as, for example, the front spar 210a, the rear spar 210b, the stringers <NUM>, and/or other frame members via the fastening system <NUM> and/or the fastening systems <NUM>.

<FIG> is a perspective view of the fastening system <NUM> of <FIG> and <FIG>, not according to the presently claimed invention, but useful for understanding aspects thereof. <FIG> is a side view of the fastening system <NUM> of <FIG>, <FIG> and <FIG>. The fastening system <NUM> can implement each of the fastening systems <NUM> of <FIG>. Referring to <FIG>, the fastening system <NUM> includes an example nutplate <NUM>, an example fastener sleeve <NUM> (e.g., a second sleeve), and an example fastener <NUM>. The nutplate <NUM> includes an example body <NUM> having an example nutplate flange <NUM> and a base sleeve <NUM> (e.g., a first sleeve). The base sleeve <NUM> provides an integral self-retention feature. The nutplate flange <NUM> extends radially from the body <NUM> and the base sleeve <NUM> extends in a direction (e.g., in a longitudinal direction) away from the body <NUM>. Additionally, the nutplate flange <NUM> includes an example groove <NUM> (e.g., an annular groove) between a peripheral edge of the nutplate flange <NUM> and the base sleeve <NUM>. Additionally, the body <NUM> of the nutplate <NUM> of the illustrated example has a dome-shape. However, in other examples, the nutplate <NUM> can have any other shape (e.g., a cylindrical shape, a rectangular shape, etc.). The body <NUM>, the nutplate flange <NUM>, and the base sleeve <NUM> of the illustrated example are integrally formed as a unitary piece or single structure.

When the fastening system <NUM> is assembled, the fastener sleeve <NUM> and the base sleeve <NUM> receive (e.g., slidably receive) the fastener <NUM> such that the fastener sleeve <NUM> and the base sleeve <NUM> surround (e.g., encase) at least a portion of the fastener <NUM>. Additionally, a first fastener sleeve edge 410a is spaced from a base sleeve edge 406a to form a gap <NUM>. Further, the fastener head <NUM> of the fastener <NUM> is surrounded by the fastener sleeve <NUM>. For example, the fastener head <NUM> is flush mounted relative to a second fastener sleeve edge 410b opposite the first fastener sleeve edge 410a. In some examples, the fastener head <NUM> can be recessed within the fastener sleeve <NUM> or may extend past (e.g., above or beyond) the second fastener sleeve edge 410b. Additionally, the fastening system <NUM> (e.g., the nutplate <NUM>, the fastener sleeve <NUM>, and the fastener <NUM>) includes a conductive coating (e.g., indium coating, a teflon coating, etc.). The conductive coating can be applied to the fastening system <NUM> prior to installation of the fastening system <NUM> to the wing <NUM>. Such a conductive coating, in combination with features of the fastening system disclosed herein (e.g., domed nutplate, etc.) eliminates any further sealant (e.g., a cap seal) otherwise needed to provide lightning strike protection. The fastener sleeve <NUM> is used in a countersunk fastener installation, such that the fastener head <NUM> is positioned within (e.g., countersunk relative to) and/or flush mounted relative the fastener sleeve <NUM>.

<FIG> is an exploded view of the example fastening system <NUM> of <FIG>, <FIG>, <FIG>, not according to the presently claimed invention, but useful for understanding aspects thereof. <FIG> is an exploded cross-sectional view of the fastening system <NUM> of <FIG>. Referring to <FIG> and <FIG>, the fastener <NUM> is a bolt. For example, the fastener <NUM> includes a threaded portion <NUM> and a non-threaded portion or shank <NUM>. The outer diameter <NUM> of the threaded portion <NUM> is smaller than the outer diameter <NUM> of the non-threaded portion or shank <NUM>. In some examples, a length of the non-threaded portion or shank <NUM> can be the same as a length corresponding to a stack-up thickness of the aircraft structures to be assembled. In some examples, the fastener <NUM> includes a thread relief <NUM> below the threaded portion <NUM> for a fastener thread rolling run-out.

The body <NUM> and the base sleeve <NUM> of the nutplate <NUM> define an opening <NUM> to receive the fastener <NUM>. Specifically, a portion of the opening <NUM> defined by the body <NUM> includes a threaded portion or internal threads <NUM> to receive the threads of the threaded portion <NUM> of the fastener <NUM> when the fastener <NUM> couples to the nutplate <NUM>. A portion of the opening <NUM> defined by the base sleeve <NUM> defines a non-threaded portion <NUM> (e.g., a smooth surface) to receive (e.g., slidably receive) the shank <NUM> of the fastener <NUM>. Thus, the internal threads <NUM> are positioned in the body <NUM> of the nutplate flange <NUM> and an inner surface <NUM> of the base sleeve <NUM> does not include internal threads. The opening <NUM> has an inner diameter 538a and the base sleeve <NUM> has an outer diameter 538b. The base sleeve <NUM> of the illustrated example has a cylindrical shape. However, in some examples, an outer shape or surface of the base sleeve <NUM> can be a square shape, a rectangular shape, and/or any other suitable shape (e.g., non-circular, elliptical, etc.).

The fastener sleeve <NUM> includes a top sleeve <NUM> and a bottom sleeve <NUM> that define an opening <NUM> (e.g., a through hole) to receive (e.g., slidably receive) the fastener <NUM> (e.g., the shank <NUM>). The top sleeve <NUM> has a cylindrical shape and the bottom sleeve <NUM> flares or tapers from the top sleeve <NUM> to define a conical. The top sleeve <NUM> has an inner diameter 512a and an outer diameter 512b. The bottom sleeve <NUM> has an inner diameter 512c that is greater than the inner diameter 512a of the top sleeve <NUM>. The bottom sleeve <NUM> has a shape that is complementary to the shape of the fastener head <NUM> to enable the fastener head <NUM> to be flushmounted with the fastener sleeve <NUM>.

<FIG> is a partial, cross-sectional side view of the fastening system <NUM> and the wing <NUM> of <FIG>. Specifically, the fastening system <NUM> is coupled to the rib <NUM> and the close-out panel <NUM> of <FIG>. To couple the rib <NUM> and the close-out panel <NUM>, the nutplate <NUM> is coupled to the first opening <NUM> (e.g., a through hole) of the rib <NUM>. The nutplate <NUM> can be coupled to the rib <NUM> prior to attachment of the close-out panel <NUM> to the rib <NUM>. To couple the nutplate to the rib <NUM>, the base sleeve <NUM> is inserted into at least a portion of the first opening <NUM> of the rib <NUM>. In particular, the base sleeve <NUM> is coupled to the first opening <NUM> via a press-fit connection or interference-fit connection to prevent rotation of the nutplate <NUM> relative to the rib <NUM> about a longitudinal axis <NUM> of the nutplate <NUM>. Thus, the base sleeve <NUM> provides a self-retention device that prevents rotation of the nutplate <NUM> relative to the longitudinal axis <NUM>. While the initial outer diameter 538b (<FIG>) can be larger than a diameter <NUM> of the first opening <NUM> of the rib <NUM> (e.g., by <NUM> to <NUM> inches), after interference fit installation, the outer diameter 538b (<FIG>) of the base sleeve <NUM> matches and/or is substantially equal to the diameter <NUM> of the first opening <NUM> of the rib <NUM>. However, when coupled to the first opening <NUM>, the outer diameter 538b (<FIG>) of the base sleeve <NUM> is substantially equal to (e.g., identical) a diameter <NUM> of the first opening <NUM>. When coupled to the rib <NUM>, the nutplate flange <NUM> engages a first surface <NUM> of the rib <NUM>. The first surface <NUM> of the rib <NUM> is opposite a second surface <NUM> of the rib <NUM> that engages an inner surface <NUM> of the close-out panel <NUM> (e.g., opposite the exterior surface <NUM> of the close-out panel <NUM>). Thus, the first surface <NUM> of the rib <NUM> does not engage the close-out panel <NUM>. In other words, the first surface <NUM> is oriented towards the access openings <NUM> (<FIG>) of the wingbox <NUM>. A seal <NUM> is positioned in the groove <NUM> of the nutplate <NUM> that engages the first surface <NUM> of the rib <NUM>. The seal <NUM> provides a tight seal between the first opening <NUM> of the rib <NUM> and the cavity <NUM> of the wingbox <NUM> when the nutplate <NUM> is coupled to the rib <NUM>. For example, the seal <NUM> provides a tight seal and provides spark containment to reduce or prevent sparks from entering the cavity <NUM> of the wingbox <NUM> via the first opening <NUM> from the exterior surface <NUM> during, for example, a lightning strike event (e.g., that occurs during flight). The dome-shape of the body <NUM> prevents fluid communication or pathways to the cavity <NUM>, providing additional lighting direct strike protection.

The fastener sleeve <NUM> couples to (e.g., inserts into) a second opening <NUM> (e.g., a through hole, a second bore) formed in the close-out panel <NUM>. Specifically, the fastener sleeve <NUM> is coupled to the second opening <NUM> from the exterior surface <NUM> of the close-out panel <NUM>. The second opening <NUM> aligns (e.g., coaxially aligns) with the first opening <NUM> of the rib <NUM>. Specifically, the first opening <NUM> and the second opening <NUM> form an installation hole <NUM> (e.g., aperture, bore, etc.) to receive the fastening system <NUM>. The first opening <NUM> and the second opening <NUM> of the illustrated example have substantially the same size diameters. Additionally, the fastener sleeve <NUM> couples to the second opening <NUM> via a clearance fit. For example, the outer diameter 512b of the top sleeve <NUM> is slightly less (e.g., one-tenth of an inch less) than a diameter of the second opening <NUM> (e.g., creating a transition fit). The fastener sleeve <NUM> enables load transfer between the close-out panel <NUM>, the rib <NUM>, the fastener <NUM> and/or the other structure(s) or structural components <NUM> of the wingbox <NUM>. The close-out panel <NUM> includes a countersink <NUM> to receive the bottom sleeve <NUM> of the fastener sleeve <NUM>. The bottom sleeve <NUM> of the illustrated example is flush mounted relative to the fastener head <NUM> when the fastener <NUM> is coupled to the second opening <NUM>.

In the illustrated example, when the fastener sleeve <NUM> couples to the close-out panel <NUM>, the top sleeve <NUM> at least partially extends into the first opening <NUM> of the first structure (e.g., rib <NUM>). However, the first fastener sleeve edge 410a and the base sleeve edge 406a form the gap <NUM>. The gap <NUM> enables insertion of the fastener sleeve <NUM> without causing the fastener sleeve <NUM> to engage the base sleeve edge 406a of the base sleeve <NUM> and push or move the base sleeve <NUM> out from the first opening <NUM> when the fastener sleeve <NUM> is inserted into the second opening <NUM>. Additionally, the gap <NUM> is small enough to maintain spark protection. In some examples, the gap <NUM> can include a liquid or gas sealant (e.g., a non-conductive poly-sulfide sealant) for enhanced lightning direct strike protection.

The fastener <NUM> is coupled to (e.g., inserted into) the installation hole <NUM> from the exterior surface <NUM> of the close-out panel <NUM>. For example, the fastener sleeve <NUM> and the base sleeve <NUM> receive (e.g., slidably receive) and guide the fastener <NUM> toward the nutplate <NUM>. For example, the smaller outer diameter of the threaded portion <NUM> allows insertion through both sleeves <NUM>, <NUM>. The fastener <NUM> threadably couples to the nutplate <NUM> via the threads of the threaded portion <NUM> of the fastener <NUM> and the internal threads <NUM> of the nutplate body <NUM>. As the fastener <NUM> is rotated about the longitudinal axis <NUM> to threadably couple to the nutplate <NUM> and fasten the close-out panel <NUM> and the rib <NUM>, the nutplate <NUM> is configured to prevent rotation about the longitudinal axis <NUM> relative to the rib <NUM>. For example, rotation of the fastener <NUM> about the longitudinal axis <NUM> imparts a torque to the nutplate <NUM>. The base sleeve <NUM>, via the press-fit connection with the first opening <NUM>, counteracts the torque applied by the fastener <NUM> and prevents rotation of the nutplate <NUM> about the longitudinal axis <NUM> as the fastener <NUM> threads to the nutplate <NUM>. Thus, the base sleeve <NUM> prevents rotation of the nutplate <NUM> when applying a torque to the fastener <NUM>. In this manner, the fastener <NUM> couples to the nutplate <NUM> from the exterior surface <NUM> of the close-out panel <NUM> without requiring a tool or personnel to access the cavity <NUM> (<FIG>) of the wingbox <NUM> via access openings <NUM> to react the torque applied to the nutplate <NUM> by the fastener <NUM>. Thus, the fastening system <NUM> permits a more efficient assembly process given that the nutplate <NUM> is configured to fix rotation about the longitudinal axis <NUM> without requiring a tool to prevent rotation of the nutplate <NUM> about the longitudinal axis <NUM> when coupling the fastener <NUM> to the nutplate <NUM>. Thus, the fastening system <NUM> disclosed herein significantly reduces manufacturing complexity, time, and costs.

Additionally, as noted above, the dome-shape of the nutplate 400provides lightning direct strike protection as compared to known nutplates that have multiple parts and thereby multiple points of contact and/or gapping between the parts that create(s) a sparking risk. Further, the one-piece structure provided by the nutplate <NUM> in combination with the seal <NUM> contains and isolates any internal sparking from entering the cavity <NUM> (e.g., a fuel tank environment in the wing <NUM>) via the installation hole <NUM> in the event of a direct lightning strike on the exterior surface <NUM> of the close-out panel <NUM>. For example, the one-piece structure provided by the nutplate <NUM> eliminates the need to provide any additional self-retention components such as rivets that form openings in the rib <NUM> and/or the nutplate <NUM> that would otherwise provide a pathway or entrance to the cavity <NUM> and pose a sparking risk. For example, as noted above, secondary self-retention features such as rivets require additional sealants to cover or seal the openings formed by addition of the secondary self-retention features after installation of a closeout panel. Also, the fastening system <NUM> is coated with a conductive coating (e.g., indium coating, etc.) to enhance lightning direct strike protection. As such, the fastening system <NUM> can provide a high-bandwidth path for extreme amounts of current (e.g., <NUM>,<NUM> - <NUM>,<NUM> amps) to flow with no discontinuities that may otherwise cause sparking. The seal <NUM> and the nutplate <NUM> provide a tight fluid seal to prevent fluid and/or sparks from entering the cavity <NUM> via the installation hole <NUM> during a direct lightning strike event.

<FIG>, <FIG> and <FIG> illustrate other example fastening systems <NUM>-<NUM> disclosed herein. Those components of the example fastening systems <NUM>-<NUM> that are substantially similar or identical to the components of the example fastening system <NUM> described above in connection with <FIG> and that have functions substantially similar or identical to the functions of those components will not be described in detail again below. Instead, the interested reader is referred to the above corresponding descriptions. To facilitate this process, similar reference numbers will be used for like structures.

<FIG> is a side view of the example fastener <NUM> not according to the presently claimed invention, but useful for understanding aspects thereof. Referring to <FIG>, the fastening system <NUM> of the illustrated example includes a nutplate <NUM>, a fastener <NUM> and a sleeve <NUM>. The sleeve <NUM> includes a body <NUM> having a cylindrical shape and a flange <NUM>. The body <NUM> has a first end oriented toward the nutplate <NUM> and a second end opposite the first end (e.g., toward a head <NUM> of the fastener <NUM>). The sleeve <NUM> includes an opening (e.g., a through hole) to receive the fastener <NUM>. When coupled to the sleeve <NUM>, a portion (e.g., a fastener head <NUM>) of the fastener protrudes from the sleeve <NUM> (e.g., from the second end). In other words, the portion of the fastener <NUM> is visible from an exterior of the fastening system <NUM> when the fastening system <NUM> is coupled to a structure. The flange <NUM> can provide a seat (e.g., a washed) for the fastener head <NUM>. Such a fastener sleeve <NUM> can be used in applications where a closeout panel is not exposed to air streams. For example, the fastener system <NUM> can be used in wingbox assemblies where a close-out panel is provided by or coupled to the front spar chord 210a or a rear spar chord 210b. In some such examples, the fastener head <NUM> protrudes from the fastener sleeve <NUM> and does not affect an airflow stream (e.g., a boundary layer or pattern of the airflow stream) during flight.

<FIG> is an exploded view of a fastening system <NUM> disclosed herein. <FIG> is an assembled, cross-sectional view of the example fastening system <NUM> of <FIG>. Referring to <FIG> and <FIG>, the example fastening system <NUM> includes a nutplate <NUM>, a fastener sleeve <NUM>, and a fastener <NUM>. Similar to the nutplate <NUM> above, the nutplate <NUM> includes a domed body <NUM>, a flange <NUM>, a base sleeve <NUM> and an annular groove <NUM> to receive a seal (e.g., the seal <NUM>). In addition, the nutplate <NUM> of the illustrated example includes an opening <NUM> (e.g., a pin hole or relief opening). The opening <NUM> forms a relief hole and is provided in an upper area of a body <NUM> of the nutplate <NUM>. The opening <NUM> fluidly couple the opening <NUM> of the nutplate body <NUM> and an exterior surface <NUM> of the nutplate body <NUM>. For example, a sealant (e.g., a non-conductive poly-sulfide sealant) can be applied to the fastener <NUM> and/or the fastener sleeve <NUM> during installation with the nutplate <NUM>. Excess sealant in the opening <NUM> can flow through the relief hole (e.g., opening <NUM>). In some instances, sealant remaining in the opening <NUM> can cure (e.g. solidify) to fluidly seal the opening <NUM> of the nutplate <NUM> from the exterior (e.g., the exterior surface <NUM>).

<FIG> is a method <NUM> of coupling the structures (e.g., close-out panel <NUM> and the rib <NUM>) via the fastening system <NUM>. At block <NUM>, a first structure is aligned with a second structure. For example, referring to <FIG>, the close-out panel <NUM> is aligned with the rib <NUM>. At block <NUM>, an installation hole is formed through the aligned structures. For example, the installation hole <NUM> is formed through the close-out panel <NUM> and the rib <NUM> (e.g., the first opening <NUM> of the rib <NUM> and the second opening <NUM> of the close-out panel <NUM> are formed simultaneously when the close-out panel <NUM> is aligned with the rib <NUM>). In some examples, the first opening <NUM> is formed through the rib <NUM> and the second opening <NUM> is formed in the close-out panel <NUM> separately (e.g., prior to aligning or attaching the close-out panel to the rib <NUM>). In some examples, the first opening <NUM> is preformed with the fabrication of the rib <NUM> and the second opening <NUM> is preformed with the fabrication of the close-out panel <NUM>. At block <NUM>, the first structure is removed from the second structure. For example, in the example of <FIG>, the close-out panel <NUM> is removed or separated from the rib <NUM>. At block <NUM>, the nutplate <NUM> is press-fit into the installation hole. For example, the nutplate <NUM> is press-fit into the first opening <NUM> of the rib <NUM>. For example, the base sleeve <NUM> of the nutplate <NUM> couples to the first opening <NUM> via an interference fit sufficient to prevent rotation of the body <NUM> of the nutplate <NUM> about the longitudinal axis <NUM> relative to the rib <NUM>. At block <NUM>, the first structure is realigned with the second structure. For example, in the example of <FIG>, the closeout panel <NUM> is repositioned on the rib <NUM> and the first and second openings <NUM> and <NUM> are aligned (e.g. coaxially aligned) to provide or define the installation hole <NUM>. At block <NUM>, the fastener sleeve <NUM> is inserted into the installation hole. For example, the fastener sleeve <NUM> is inserted into the second opening <NUM> of the close-out panel <NUM>. Specifically, the fastener sleeve <NUM> is inserted into the second opening <NUM> from the exterior surface <NUM> of the close-out panel <NUM>. At block <NUM>, the fastener <NUM> is inserted into the installation hole <NUM>. Referring to <FIG>, the fastener <NUM> is inserted into the installation hole <NUM> via the opening of <NUM> the fastener sleeve <NUM> and the opening <NUM> of the base sleeve <NUM>. At block <NUM>, the fastener is coupled (e.g., torqued) to the nutplate <NUM> to secure or fasten first structure and the second structure. In the example of <FIG>, the fastener <NUM> threadably couples to the nutplate <NUM> to secure or fasten the close-out panel <NUM> and the rib <NUM>. Specifically, the fastener <NUM> rotates relative to the nutplate <NUM>, and the base sleeve <NUM> reacts a torque of the fastener <NUM> by preventing rotation of the body <NUM> relative to the fastener <NUM> and/or the rib <NUM> about the longitudinal axis <NUM>. As noted above, the press-fit connection between the nutplate <NUM> and the rib <NUM> eliminates confined space work that would otherwise need to be performed by an aircraft mechanic to counteract the torque of the fastener <NUM> as the fastener <NUM> couples to the nutplate <NUM>.

Claim 1:
A fastening system (<NUM>) to couple a first structure (<NUM>) and a second structure (<NUM>), the fastening system including:
a fastener (<NUM>);
a nutplate (<NUM>) having:
a body (<NUM>) defining an opening (<NUM>) to receive the fastener, wherein the body of the nutplate is dome-shaped and comprises a further opening (<NUM>) that forms a relief hole which is provided in an upper area of the body (<NUM>);
a flange (<NUM>) extending from the body to engage an outer surface (<NUM>) of the first structure; and
a first sleeve (<NUM>) protruding from the flange in a direction away from the body, the first sleeve to couple to a first bore (<NUM>) formed in the first structure and prevent rotation of the nutplate relative to the first structure.