Fastening system for aircraft structures

Abstract

The invention relates to a fastening system for aircraft structures. A fastening system is disclosed that couples a first aircraft structure and a second aircraft structure. The fastening system includes a fastener, a nut plate 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 that protrudes from the flange in a direction away from the body, the first sleeve being coupled to a first bore formed in the first structure and preventing rotation of the nut plate relative to the first structure.

Description

[0001] Cross-references to related applications

[0002] This patent claims the benefit of U.S. Provisional Patent Application No. 63 / 047,723, filed July 2, 2020, entitled “FASTENING SYSTEM FOR AIRCRAFTSTRUCTURES”, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates generally to aircraft, and more specifically, to fastening systems for aircraft structures. Background Technology

[0004] Aircraft employ different types of fasteners to couple two or more structural components. However, access to the structural components may be limited, requiring personnel or mechanics to perform confined space work to install and / or twist the fasteners of the fastening system. Summary of the Invention

[0005] An example fastening system coupling a first structure and a second structure includes a fastener, a nut plate, a flange, and a first sleeve. The nut plate has a defined opening to receive a body of the fastener. The flange extends from the body to engage an outer surface of the first structure. The first sleeve projects from the flange in a direction away from the body. The first sleeve is coupled to a first bore formed in the first structure and prevents rotation of the nut plate relative to the first structure.

[0006] An example aircraft includes: a wing box defining a structure comprising one or more spar chords, stringers, and ribs; a closing panel for closing the wing box; and a fastener assembly coupling the closing panel and the wing box. The fastener assembly includes a nut plate 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 is press-fitted into a first bore in the structure to prevent rotation of the nut plate relative to the structure. The nut plate is configured to prevent rotation about the longitudinal axis relative to the structure when coupled to the structure. The fastener assembly also includes a fastener coupled to the nut plate via a second bore formed in the closing panel to couple the closing panel and the structure.

[0007] An example method includes aligning a closure panel of an aircraft with a structure of the aircraft, forming a bore through the closure panel and the structure, removing the closure panel from the structure after forming the bore, inserting a nut plate into a first portion of the bore formed in the structure, re-aligning the closure panel and the structure, inserting a sleeve into a second portion of the bore formed in the closure panel, inserting a fastener from an exterior surface of the closure panel into the second portion of the bore formed in the closure panel, and coupling the fastener to the nut plate via the second portion of the bore to secure the closure panel to the structure. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 is a perspective view of an example aircraft in which aspects of the present disclosure can be implemented.

[0009] Figure 2A is a perspective view of an example wing with upper closure panels and other components removed to show Figure 1 wing substructure of the example aircraft of

[0010] Figure 2B is an enlarged partial perspective view of the example wing of Figure 2A

[0011] Figure 3A is a perspective enlarged view of the example wing of Figure 2B closure panels secured to the example wing via the example fastening system disclosed herein.

[0012] Figure 3B is a perspective view of the example wing of Figure 3A with closure panels removed.

[0013] Figure 4A is an assembled perspective view of the example fastening system disclosed herein.

[0014] Figure 4B is an assembled front view of the example fastening system of Figure 4A

[0015] is an exploded view of the example fastening system of Figure 5A Figure 4A is an exploded sectional view of the example fastening system of

[0016] Figure 5B Figure 5A is a sectional view of the example fastening system of

[0017] Figure 6 is a perspective view of the example wing of Figure 1 and 3A -3B coupled to Figure 4A and​​​4B an assembled cross-sectional view of the example fastening system of

[0018] Figure 7 an assembled front view of another example fastening system disclosed herein.

[0019] Figure 8A an exploded view of another fastening system disclosed herein.

[0020] Figure 8B is Figure 8A an assembled cross-sectional view of the example fastening system of

[0021] Figure 9 is an example method of assembling a first structure and a second structure of an example wing using Figures 4A-4B , 5A-5B, 7, and 8A-8B.

[0022] Whenever possible, the same reference designators will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this disclosure, a statement that any part (e.g., a layer, film, region, or plate) is positioned on (e.g., positioned on, located on, disposed on, or formed on) another part signifies that the referenced part is in contact with the other part, or the referenced part is above the other part with one or more intermediate parts positioned in between the referenced part and the other part. A statement that any part is in contact with another part signifies that there are no intermediate parts between the two parts. DETAILED DESCRIPTION

[0023] Aircraft employ fastening systems or fasteners to secure a first structure (e.g., an aircraft wall, a cover panel, a closure 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 nut plate in combination with a threaded screw or bolt to secure the first structure (e.g., a closure panel) and the second structure (e.g., a spar chord of a wing box). However, during aircraft assembly, the assembly area can become restricted and limited, which increases manufacturing complexity. For example, a closure panel reduces access to an area or cavity within a wing box when coupled to the wing box. Aircraft technicians often have to enter the cavity of the wing box through an access opening (e.g., an access opening located at the bottom of the wing) to perform confined space work to install and / or torque fasteners of the closure panel, install hydraulic systems, install fuel systems, seal fuel tanks, apply lightning strike protection sealant, clean, system testing, etc. However, confined space fastener installation is particularly time consuming because such fastener installation is required in the end of each individual rib bay installed in the wing.

[0024] Some existing fastening systems (e.g., nut plates) can be configured to reduce confined space working conditions. For example, some known fastening systems employ a secondary self-retaining feature (e.g., a small diameter rivet) for securing a nut plate within a mounting hole of a structure (e.g., a rib) to react torque applied to the nut plate (e.g., limit or reduce rotation) when a bolt is threadably coupled to the nut plate. In some examples, such secondary self-retaining features include a rivet, pin, or other feature for securing the nut plate after the nut plate is installed or coupled to the structure. However, such existing nut plates have not been used due to the cost, weight, complexity, and / or inefficiency of the secondary self-retaining feature. For example, the small diameter rivet increases installation costs. Additionally, adding the rivet increases the direct lightning strike issue due to forming an additional path to the interior of the wing box, requiring the addition of a sealant (e.g., a cap seal) for direct lightning strike protection. Adding such a sealant after the fastening system is installed requires confined space work as a mechanic or personnel needs to access the fastening system (e.g., the nut plate and rivet) from within the wing box (e.g., after installing a closure panel) to apply the sealant. Additionally, such known sealants significantly increase the weight of the aircraft. In other examples, the nut plate is cold worked as a secondary operation to radially expand the nut plate in the mounting hole to implement an interference fit. However, cold working as a secondary operation increases manufacturing costs and decreases manufacturing efficiency. As a result, aircraft do not employ existing fastening systems because they increase the weight, manufacturing complexity, and / or cost of the aircraft.

[0025] Example fastening systems for aircraft disclosed herein facilitate installation in confined working spaces and provide direct lightning strike protection. Specifically, example fastening systems disclosed herein do not require aircraft mechanics to perform confined space work to install and / or torque fasteners. For example, fastening systems disclosed herein eliminate the confined space work required for mechanics to access a wing box to install and / or torque fasteners of a closure panel (e.g., a closure panel of a main structural wing box that carries carbon fuel). Additionally, fastening systems disclosed herein can employ a conductive coating as a finish applied to exterior surfaces of fastening system parts, thereby increasing conductivity in the event the parts contact each other and / or break apart. Other features of fastening systems disclosed herein (e.g., a dome nut plate, etc.) in combination with the conductive coating do not require a sealant to be separately applied for direct lightning strike protection after the fastening system is installed to a structural component.

[0026] The example fastening systems disclosed herein employ a nut plate in combination with a bolt to secure a first structure (e.g., a spar of a wing box) and a second structure (e.g., a closure panel). The example nut plates disclosed herein include a monolithic or one-piece body. The nut plate includes an integral structure having a dome, a flange or shoulder, and a sleeve (e.g., a circumferential leg) extending from the dome. The sleeve provides an integral self- retaining feature that prevents the nut plate from rotating about a longitudinal axis when coupled to a mounting hole of the structure. In other words, no additional fasteners or auxiliary self-retaining features (such as a rivet, pin, etc.) are needed to enable the nut plate to react against torque (e.g., rotation) applied to the nut plate. To prevent rotation of the nut plate, the integral self-retaining feature includes the sleeve that is coupled to the mounting hole of the structure via an interference fit. Accordingly, the example fasteners disclosed herein eliminate the need for a rivet or other self-retaining feature to retain the nut plate. Additionally, installation of the nut plate can be provided prior to the addition of the closure panel, thereby eliminating the need for personnel to access a cavity of the frame (e.g., wing box) after installation of the closure panel to react against torque from the fastener. Rather, a mechanic can torque the fastener of the fastening system (e.g., without personnel accessing the cavity of the frame) after the closure panel is coupled to the frame from the exterior of the frame because the integral self-retaining feature of the nut plate reacts against torque from the fastener and prevents the nut plate from rotating about its longitudinal axis when the fastener is coupled to the nut plate. Additionally, the fastening systems disclosed herein include a conductive coating to provide direct lightning strike protection that can be applied during manufacture of the fastening system. The combination of the conductive coating with the direct lightning strike protection features of the fastening systems disclosed herein (e.g., the domed nut plate, the groove for fuel isolation from the fastener assembly, etc.) eliminates the need to apply 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 reducing aircraft weight and manufacturing costs associated with applying a sealant after installation of the fastening system.

[0027] Figure 1 An example aircraft 100 in which examples disclosed herein can be implemented is illustrated. The aircraft 100 includes a fuselage 104 and wings 102, 103 extending laterally outward from the fuselage 104. Each of the wings 102, 103 of the illustrated example supports an aircraft engine 106 via a pylon 108. In examples disclosed herein, a fastening system 110 (e.g., a fastener assembly) disclosed herein secures or couples aircraft structures associated with the wings 102, 103. For example, Figure 1 The fastening system 110 of the illustrated example couples a closure panel 112 (e.g., a wing skin 114) to the wing 102. For illustrative purposes, Figure 1Only one fastening system 110 is shown. However, the wing 102 (e.g., the closure panel 112) can include multiple fastening systems 110 to attach the closure panel 112 to the wing 102. Although Figure 1 The fastening system 110 is illustrated for coupling the closure panel 112 and the wing 102, the fastening system 110 disclosed herein can be used to secure any other structure of the aircraft 100. Further, the wing 103 is similar to the wing 102. For example, the wing 103 also includes an example fastening system (e.g., the fastening system 110). For brevity, the wing 103 is not discussed further herein. Additionally, Figure 1 The aircraft 100 is a commercial aircraft. However, the fastening system 110 disclosed herein can be used with unmanned vehicles (e.g., drones), military vehicles, maritime vehicles, automobiles, other structures, and / or any frame(s) or structure(s). Further, the fastening system 110 disclosed herein is not limited to aircraft-specific structures. In some examples, the fastening system 110 can be used to couple any other type of structure(s) or frame(s) (e.g., box-like frames, enclosures, etc.).

[0028] Figure 2A is Figure 1 A perspective view of an example wing 102 of an example aircraft, where an upper closure panel and other components are removed to show the wing substructure. Figure 2B is Figure 2A A close-up view of the example wing 102 of the example aircraft. The closure panel 112 is not shown in Figure 2A and 2BA first wing 102 is shown. The first wing 102 has an example wing box 200 that includes structural components 201 that support and / or shape the wing 102. The structural components 201 include load bearing components that are configured or arranged to withstand shear and / or bending moments acting on the wing 102 during a load condition (e.g., lift). For example, the wing box 200 includes a plurality of ribs 205 that extend in a chordwise direction. Additionally, the wing box 200 includes a front spar 210a (e.g., proximate to a leading edge 211a of the wing 102), a rear spar 210b (e.g., proximate to a trailing edge 211b of the wing 102), and a plurality of stringers 215 that extend in a spanwise direction. The ribs 205 maintain an aerodynamic profile of the wing 102 and can be spaced apart relative to one another (e.g., equidistantly) (e.g., repeating at frequent or equidistant intervals to form a skeletal shape of the wing 102). For example, the ribs 205 form a portion of a boundary of the wing box 200 to which a wing skin 114 (FIG. 1) is attached, and support the wing skin 114 to prevent the wing skin 114 from buckling. The ribs 205 are attached to the front spar 210a and the rear spar 210b, which extend across a length of the wing 102 in the spanwise direction (e.g., between a wing root and a wing tip) and provide strength to the wing 102 by countering torsion and upward bending when the wing 102 generates lift. The stringers 215 carry axial loads resulting from bending moments in the wing 102. The wing 102 forms a cavity 212 that can be used to store fuel. To allow access to the cavity 212 of the wing box 200, the wing 102 includes one or more access openings 220. For example, the access openings 220 allow a mechanic and / or personnel to perform confined space work within the cavity 212 of the wing 102 after attaching or assembling the closure panel 112 to the wing box 200.

[0029] Figure 3A is Figure 1 a perspective view of an example wing 102. Figure 3A The wing 102 of Figure 3B is shown without the closure panel 112 Figure 3A a perspective zoomed-in view of the example wing 102 of Figure 3A and Figure 3B During assembly of the aircraft 100, the closure panel 112 (e.g., wing skin 114) is installed and fastened to the wing box 200 via the fastening system 110 to form Figure 1of the wing 102. To install the closure panel 112 to the wing box 200, the rib 302 includes a first opening 304 (e.g., a through-hole, a first bore) to receive the fastening system 110. When coupled to the wing 102, the fastener head 313 of the fastening system 110 is positioned (e.g., exposed from) along an exterior surface 314 (e.g., an outer surface or an exterior surface) of the closure panel 112, and other portions of the fastening system 110 are located within the cavity 212 of the wing box 200. In other words, only the fastener head 313 (e.g., a bolt head) of the fastening system 110 is exposed to the exterior surface 314 (e.g., the exterior) of the wing 102. Additionally, as described in detail below, the fastening system 110 can be torqued (e.g., via the fastener head 313) when the closure panel 112 is attached to the wing box 200 without requiring a person to access the cavity 212 via the access opening 220. Figure 2A and 2B As described above, the aircraft 100 includes multiple fastening systems 306 to secure the closure panel 112 to the wing box 200. For example, to install the closure panel 112 to the wing box 200, the rib 205 includes multiple openings 308 to receive respective ones of the fastening systems 306. Accordingly, each of the openings 308 receives a respective one of the fastening systems 306 to couple the closure panel 112 to the wing box 200. The fastening systems 306 are identical to the fastening system 110, and for brevity, will not be discussed further. Although not shown, the closure panel 112 can be secured to other aircraft structure(s), such as the front spar 210a, the rear spar 210b, the stringer 215, and / or other frame members via the fastening system 110 and / or the fastening systems 306.

[0030] Figure 4A is a perspective view of the fastening system 110 of Figure 1 and 3A is a perspective view of the fastening system 110 of Figure 4B is a perspective view of the fastening system 110 of Figure 1 , 3A and 4A. The fastening system 110 can implement each of the fastening systems 306 of Figure 3B Referring to Figure 4A and 4BThe fastening system 110 includes an example nut plate 400, an example fastener sleeve 410 (e.g., a second sleeve), and an example fastener 420. The nut plate 400 includes an example body 402 having an example nut plate flange 404 and a base sleeve 406 (e.g., a first sleeve). The base sleeve 406 provides an integral self- retention feature. The nut plate flange 404 extends radially from the body 402, and the base sleeve 406 extends in a direction away from the body 402 (e.g., in a longitudinal direction). Additionally, the nut plate flange 404 includes an example groove 440 (e.g., an annular groove) between a peripheral edge of the nut plate flange 404 and the base sleeve 406. Additionally, the body 402 of the illustrated example nut plate 400 has a round top shape. However, in other examples, the nut plate 400 can have any other shape (e.g., a cylindrical shape, a rectangular shape, etc.). The body 402, the nut plate flange 404, and the base sleeve 406 of the illustrated example are integrally formed as a unitary piece or a single structure.

[0031] When the fastening system 110 is assembled, the fastener sleeve 410 and the base sleeve 406 receive (e.g., slidably receive) the fastener 420 such that the fastener sleeve 410 and the base sleeve 406 encircle (e.g., surround) at least a portion of the fastener 420. Additionally, the first fastener sleeve edge 410a is spaced apart from the base sleeve edge 406a to form the gap 430. Additionally, the fastener head 313 of the fastener 420 is encircled by the fastener sleeve 410. For example, the fastener head 313 is flush mounted relative to the second fastener sleeve edge 410b opposite the first fastener sleeve edge 410a. In some examples, the fastener head 313 can be recessed within the fastener sleeve 410, or can extend past (e.g., beyond or over) the second fastener sleeve edge 410b. Additionally, the fastening system 110 (e.g., the nut plate 400, the fastener sleeve 410, and the fastener 420) includes a conductive coating (e.g., an indium coating, a Teflon coating, etc.). The conductive coating can be applied to the fastening system 110 prior to installation of the fastening system 110 to the wing 102. Such a conductive coating, in combination with the features of the fastening system disclosed herein (e.g., the round top nut plate, etc.), eliminates any additional sealant (e.g., a cap seal) needed to provide lightning strike protection. The fastener sleeve 410 is used for countersunk fastener installation such that the fastener head 313 is positioned within (e.g., countersunk relative to) and / or flush mounted relative to the fastener sleeve 410.

[0032] Figure 5A is Figure 1 , 3B , 4A and 4B are exploded views of example fastening systems 110. Figure 5B is Figure 5AAnatomical view of the fastening system 110. (Reference) Figure 5A and 5B Fastener 420 is a bolt. For example, fastener 420 includes a threaded portion 526 and a non-threaded portion or shank 522. The outer diameter 540 of the threaded portion 526 is smaller than the outer diameter 542 of the non-threaded portion or shank 522. In some examples, the length of the non-threaded portion or shank 522 may be the same as the length corresponding to the stack thickness of the aircraft structure to be assembled. In some examples, fastener 420 includes a threaded relief 524 below the threaded portion 526 for fastener thread roll-out.

[0033] The body 402 of the nut plate 400 and the base sleeve 406 define an opening 510 for receiving a fastener 420. Specifically, a portion of the opening 510 defined by the body 402 includes a threaded portion or internal thread 530 to receive the threads of the threaded portion 526 of the fastener 420 when the fastener 420 is coupled to the nut plate 400. A portion of the opening 510 defined by the base sleeve 406 defines a non-threaded portion 531 (e.g., a smooth surface) to receive (e.g., slidably receive) the shank 522 of the fastener 420. Thus, the internal thread 530 is positioned in the body 402 of the nut plate flange 404, and the inner surface 533 of the base sleeve 406 does not include the internal thread. The opening 510 has an inner diameter 538a, and the base sleeve 406 has an outer diameter 538b. The base sleeve 406 in the illustrated example has a cylindrical shape. However, in some examples, the outer shape or surface of the base sleeve 406 may be square, rectangular and / or any other suitable shape (e.g., non-circular, elliptical, etc.).

[0034] Fastener sleeve 410 includes a top sleeve 512 and a bottom sleeve 514, which define an opening 505 (e.g., a through hole) to receive (e.g., slidably receive) a fastener 420 (e.g., a shank 522). The top sleeve 512 has a cylindrical shape, and the bottom sleeve 514 opens from the top sleeve 512 or tapers to define a conical shape. The top sleeve 512 has an inner diameter 512a and an outer diameter 512b. The inner diameter 512c of the bottom sleeve 514 is larger than the inner diameter 512a of the top sleeve 512. The bottom sleeve 514 has a shape complementary to the shape of the fastener head 313, such that the fastener head 313 can be flush-mounted with the fastener sleeve 410.

[0035] Figure 6 yes Figure 3B A partial cross-sectional side view of the fastening system 110 and the wing 102. Specifically, the fastening system 110 is coupled to... Figure 3Brib 302 and the closure panel 112. To couple the rib 302 and the closure panel 112, the nut plate 400 is coupled to the first opening 304 (e.g., a through-hole) of the rib 302. The nut plate 400 can be coupled to the rib 302 prior to attaching the closure panel 112 to the rib 302. To couple the nut plate to the rib 302, the base sleeve 406 is inserted into at least a portion of the first opening 304 of the rib 302. In particular, the base sleeve 406 is coupled to the first opening 304 via a press-fit connection or an interference-fit connection to prevent rotation of the nut plate 400 relative to the rib 302 about the longitudinal axis 602 of the nut plate 400. Thus, the base sleeve 406 provides a self-retaining device that prevents rotation of the nut plate 400 relative to the longitudinal axis 602. While the initial outer diameter 538b( Figure 5B ) of the base sleeve 406 can be greater than a diameter 620 (e.g., 0.0010 to 0.0040 inches) of the first opening 304 of the rib 302, the outer diameter 538b( Figure 5B ) of the base sleeve 406 matches and / or is substantially equal to the diameter 620 of the first opening 304 of the rib 302 after the interference-fit installation. However, the outer diameter 538b( Figure 5B ) of the base sleeve 406 is substantially equal to (e.g., the same) the diameter 620 of the first opening 304 when coupled to the first opening 304. The nut plate flange 404 engages the first surface 612 of the rib 302 when coupled to the rib 302. The first surface 612 of the rib 302 is opposite the second surface 614 of the rib 302 that engages the inner surface 616 of the closure panel 112 (e.g., opposite the outer surface 314 of the closure panel 112). Thus, the first surface 612 of the rib 302 does not engage the closure panel 112. In other words, the first surface 612 is oriented toward the access opening 220( Figure 2A ) of the wing box 200. The seal 604 is positioned in the groove 440 of the nut plate 400 that engages the first surface 612 of the rib 302. The seal 604 provides a tight seal between the first opening 304 of the rib 302 and the cavity 212 of the wing box 200 when the nut plate 400 is coupled to the rib 302. For example, the seal 604 provides a tight seal and provides spark suppression to reduce or prevent a spark from entering the cavity 212 of the wing box 200 from the outer surface 314 via the first opening 304 during, for example, a lightning strike event (e.g., that occurs during flight). The dome shape of the body 402 prevents fluid communication or a path to the cavity 212, thereby providing additional direct lightning strike protection.

[0036] The fastener sleeve 410 is coupled to (e.g., inserted into) a second opening 618 (e.g., a through-hole, a second bore) formed in the closure panel 112. In particular, the fastener sleeve 410 is coupled to the second opening 618 from the exterior surface 314 of the closure panel 112. The second opening 618 is aligned with (e.g., coaxially aligned with) the first opening 304 of the rib 302. In particular, the first opening 304 and the second opening 618 form a mounting hole 619 (e.g., an aperture, a bore, etc.) to receive the fastening system 110. The first opening 304 and the second opening 618 of the illustrated example have substantially the same size diameter. Additionally, the fastener sleeve 410 is coupled to the second opening 618 via a clearance fit. For example, the outer diameter 512b of the top sleeve 512 is slightly smaller (e.g., one-tenth of an inch) than the diameter of the second opening 618 (e.g., creating an interference fit). The fastener sleeve 410 enables load to be transferred between the closure panel 112, the rib 302, the fastener 420, and / or other structure or structural component(s) 201 of the wing box 200. The closure panel 112 includes a counterbore 622 to receive the bottom sleeve 514 of the fastener sleeve 410. The bottom sleeve 514 of the illustrated example is flush mounted relative to the fastener head 313 when the fastener 420 is coupled to the second opening 618.

[0037] In the illustrated example, the top sleeve 512 extends at least partially into the first opening 304 of the first structure (e.g., the rib 302) when the fastener sleeve 410 is coupled to the closure panel 112. However, the first fastener sleeve edge 410a and the base sleeve edge 406a form a gap 430. The gap 430 enables the fastener sleeve 410 to be inserted when the fastener sleeve 410 is inserted into the second opening 618 without causing the fastener sleeve 410 to engage the base sleeve edge 406a of the base sleeve 406 and push or dislodge the base sleeve 406 from the first opening 304. Additionally, the gap 430 is small enough to maintain spark protection. In some examples, the gap 430 can include a liquid or gas sealant (e.g., a non-conductive polysulfide sealant) for enhancing direct lightning strike protection.

[0038] The fastener 420 is coupled to (e.g., inserted from) the exterior surface 314 of the closure panel 112 to the mounting hole 619. For example, the fastener sleeve 410 and the base sleeve 406 receive (e.g., slidably receive) the fastener 420 and direct the fastener 420 toward the nut plate 400. For example, the smaller outer diameter of the threaded portion 526 allows insertion through both sleeves 406, 410. The fastener 420 is threadably coupled to the nut plate 400 via the threads of the threaded portion 526 of the fastener 420 and the internal threads 530 of the nut plate body 402. When the fastener 420 is rotated about the longitudinal axis 602 to threadably couple to the nut plate 400 and fasten the closure panel 112 and the rib 302, the nut plate 400 is configured to prevent rotation about the longitudinal axis 602 relative to the rib 302. For example, rotation of the fastener 420 about the longitudinal axis 602 applies a torque to the nut plate 400. The base sleeve 406 counteracts the torque applied by the fastener 420 via a press fit connection with the first opening 304 and prevents the nut plate 400 from rotating about the longitudinal axis 602 as the fastener 420 is threaded to the nut plate 400. Thus, the base sleeve 406 prevents rotation of the nut plate 400 when a torque is applied to the fastener 420. In this manner, the fastener 420 is coupled to the nut plate 400 from the exterior surface 314 of the closure panel 112 without requiring a tool or personnel to access the cavity 212 of the wingbox 200 (FIG. 2A) via the access opening 220 to react against the torque applied to the nut plate 400 by the fastener 420. Thus, the fastening system 110 allows for a more efficient assembly process given that the nut plate 400 is configured to fix rotation about the longitudinal axis 602 without requiring a tool to prevent rotation of the nut plate 400 about the longitudinal axis 602 when the fastener 420 is coupled to the nut plate 400. Thus, the fastening system 110 disclosed herein significantly reduces manufacturing complexity, time, and cost.

[0039] Additionally, as noted above, the dome shape of the nut plate 400 provides direct lightning strike protection as compared to known nut plates having multiple parts and thereby multiple points of contact and / or gaps between parts that create a spark risk. Additionally, the single piece construction provided by the nut plate 400 in combination with the seal 604 contains and isolates any internal spark from entering the cavity 212 (e.g., the fuel tank environment in the wing 102) via the mounting hole 619 in the event of a direct lightning strike on the exterior surface 314 of the closure panel 112. For example, the single piece construction provided by the nut plate 400 eliminates the need to provide any additional self-retaining components, such as rivets that form openings in the ribs 302 and / or the nut plate 400 that would otherwise lead to a path or entryway into the cavity 212 and create a spark risk. For example, as noted above, auxiliary self-retaining features such as rivets require additional sealant to cover or seal the openings formed by the addition of the auxiliary self-retaining features after the closure panel is installed. Moreover, the fastening system 110 is coated with a conductive coating (e.g., an indium coating, etc.) to improve direct lightning strike protection. Thus, the fastening system 110 can provide a high bandwidth path for extreme amounts of current (e.g., 40,000-200,000 amps) to flow without discontinuities that could otherwise cause a spark. The seal 604 and the nut plate 400 provide a tight fluid seal to prevent fluids and / or sparks from entering the cavity 212 via the mounting hole 619 during a direct lightning strike event.

[0040] Figure 7 , Figure 8A , Figure 8B and Figure 9 FIGS. 7-9 illustrate other example fastening systems 700-900 disclosed herein. Those components of the example fastening systems 700-900 that are substantially similar or identical to those of the example fastening system 110 described above in connection with Figures 1-6 will not be described in detail below. Instead, the interested reader can refer to the corresponding descriptions above. To facilitate this process, like reference numerals will be used for like structures.

[0041] Figure 7 is a side view of an example fastener 700. Reference is made to Figure 7The illustrated example fastening system 700 includes the nut plate 400, a fastener 702, and a sleeve 704. The sleeve 704 includes a body 706 having a cylindrical shape and a flange 708. The body 706 has a first end oriented toward the nut plate 400 and a second end opposite the first end (e.g., toward the head 745 of the fastener 702). The sleeve 704 includes an opening (e.g., a through hole) to receive the fastener 702. When coupled to the sleeve 704, a portion of the fastener (e.g., the fastener head 745) protrudes from the sleeve 704 (e.g., from the second end). In other words, when the fastening system 700 is coupled to a structure, the portion of the fastener 702 is visible from outside of the fastening system 700. The flange 708 can provide a seat (e.g., a wash seat) for the fastener head 745. Such a fastener sleeve 704 can be used in applications where a closure panel is not exposed to air flow. For example, the fastener system 700 can be used in a wing box assembly where a closure panel is provided by or coupled to a front spar chord 210a or a rear spar chord 210b. In some such examples, the fastener head 745 protrudes from the fastener sleeve 704 and does not affect an air flow stream (e.g., a boundary layer or pattern of the air flow stream) during flight.

[0042] Figure 8A is an exploded view of another fastening system 800 disclosed herein. Figure 8B is an assembled cross-sectional view of the example fastening system 800 of Figure 8A . With reference to Figure 8A and 8B , the example fastening system 800 includes a nut plate 802, a fastener sleeve 410, and a fastener 420. Similar to the nut plate 400 described above, the nut plate 802 includes a dome-shaped body 810, a flange 404, a base sleeve 406, and an annular groove 440 to receive a seal (e.g., the seal 604). Additionally, the illustrated example nut plate 802 includes an opening 806 (e.g., a pin hole or a cutout opening). The opening 806 forms a cutout hole and is provided in an upper region of the body 810 of the nut plate 802. The opening 806 fluidly couples the opening 510 of the nut plate body 810 and an exterior surface 812 of the nut plate body 810. For example, a sealant (e.g., a non-conductive polysulfide sealant) can be applied to the fastener 420 and / or the fastener sleeve 410 during installation of the nut plate 802. Excess sealant in the opening 510 can flow through the cutout hole (e.g., the opening 806). In some cases, the sealant remaining in the opening 806 can cure (e.g., solidify) to fluidly seal the opening 510 of the nut plate 802 from the exterior (e.g., the exterior surface 812).

[0043] Figure 9is a method 900 of coupling structures (e.g., a closure panel 112 and a rib 302) via a fastening system 110. At block 902, a first structure is aligned with a second structure. For example, referring to Figure 6 , the closure panel 112 is aligned with the rib 302. At block 904, a mounting hole is formed through the aligned structures. For example, the mounting hole 619 is formed through the closure panel 112 and the rib 302 (e.g., the first opening 304 of the rib 302 and the second opening 618 of the closure panel 112 are formed simultaneously when the closure panel 112 is aligned with the rib 302). In some examples, the first opening 304 is formed through the rib 302, and the second opening 618 is formed separately in the closure panel 112 (e.g., prior to aligning or attaching the closure panel to the rib 302). In some examples, the first opening 304 is preformed with the manufacture of the rib 302, and the second opening 618 is preformed with the manufacture of the closure panel 112. At block 906, the first structure is removed from the second structure. For example, in the example of Figure 6 , the closure panel 112 is removed or separated from the rib 302. At block 908, the nut plate 400 is press-fit into the mounting hole. For example, the nut plate 400 is press-fit into the first opening 304 of the rib 302. For example, the base sleeve 406 of the nut plate 400 is coupled to the first opening 304 via an interference fit sufficient to prevent the body 402 of the nut plate 400 from rotating about the longitudinal axis 602 relative to the rib 302. At block 910, the first structure is realigned with the second structure. For example, in the example of Figure 6 , the closure panel 112 is repositioned on the rib 302, and the first opening 304 and the second opening 618 are aligned (e.g., coaxially aligned) to provide or define the mounting hole 619. At block 912, the fastener sleeve 410 is inserted into the mounting hole. For example, the fastener sleeve 410 is inserted into the second opening 618 of the closure panel 112. In particular, the fastener sleeve 410 is inserted into the second opening 618 from the exterior surface 314 of the closure panel 112. At block 914, the fastener 420 is inserted into the mounting hole 619. Referring to Figure 6 , the fastener 420 is inserted into the mounting hole 619 via the opening 505 of the fastener sleeve 410 and the opening 510 of the base sleeve 406. At block 916, the fastener is coupled (e.g., twisted) to the nut plate 400 to secure or fasten the first structure and the second structure. In Figure 6In the example of FIG. 4, fastener 420 is threadably coupled to nut plate 400 to secure or fasten closure panel 112 and rib 302. Specifically, fastener 420 is rotated relative to nut plate 400, and base sleeve 406 reacts the torque of fastener 420 by preventing rotation of body 402 relative to fastener 420 and / or rib 302 about longitudinal axis 602. As described above, the press-fit connection between nut plate 400 and rib 302 eliminates the confined space work that would otherwise need to be performed by an aircraft mechanic to counteract the torque of fastener 420 when fastener 420 is coupled to nut plate 400.

[0044] An example fastening system for an aircraft structure is disclosed herein. Further examples and combinations thereof include the following:

[0045] Clause 1. A fastening system coupling a first structure and a second structure, the fastening system comprising a fastener, a nut plate, a flange, and a first sleeve, the nut plate having a body defining an opening to receive the fastener, the flange extending from the body to engage an outer surface of the first structure, the first sleeve protruding from the flange in a direction away from the body, the first sleeve being coupled to a first bore formed in the first structure and preventing rotation of the nut plate relative to the first structure.

[0046] Clause 2. The system of Clause 1, further comprising a second sleeve insertable into a second bore formed in the second structure.

[0047] Clause 3. The system of Clause 2, wherein the second sleeve is coupled to the second bore via a clearance fit.

[0048] Clause 4. The system of Clause 3, wherein the first end of the first sleeve is spaced apart from the second end of the second sleeve to define a clearance when the first sleeve is coupled to the first bore and the second sleeve is coupled to the second bore.

[0049] Clause 5. The system of Clause 2, wherein a first end of the first sleeve is oriented toward a second end of the second sleeve when the first sleeve is coupled to the first bore and the second sleeve is coupled to the second bore.

[0050] Clause 6. The system of Clause 5, wherein the second end of the second sleeve extends at least partially in the first bore of the first structure when the second sleeve is coupled to the second bore of the second structure.

[0051] Clause 7. The system of clause 2, wherein the first sleeve has a first outer diameter, and the second sleeve has a second outer diameter, wherein the first outer diameter is substantially equal to the second outer diameter when the first sleeve is positioned in the first bore and the second sleeve is positioned in the second bore.

[0052] Clause 8. The system of clause 7, wherein the first sleeve defines a first inner diameter, and the second sleeve defines a second inner diameter, wherein the first inner diameter is substantially equal to the second inner diameter when the first sleeve is positioned in the first bore and the second sleeve is positioned in the second bore.

[0053] Clause 9. The system of clause 1, wherein the body of the nut plate is dome-shaped.

[0054] Clause 10. The system of clause 1, wherein a first outer diameter of the first sleeve is greater than a first inner diameter of the first bore prior to the first sleeve being coupled to the first bore.

[0055] Clause 11. The system of clause 10, wherein the first sleeve is coupled to the first bore via a press fit connection to prevent rotation of the nut plate relative to the first structure.

[0056] Clause 12. An aircraft comprising a wing box defining a structure including one or more spar chords, stringers, and ribs, a closure panel closing the wing box, and a fastener assembly coupling the closure panel and the wing box, the fastener assembly comprising a nut plate 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 being press fit in a first bore of the structure to prevent rotation of the nut plate relative to the structure, the nut plate being configured to prevent rotation of the nut plate relative to the structure about the longitudinal axis when the nut plate is coupled to the structure, a fastener being coupled to the nut plate via a second bore formed in the closure panel to couple the closure panel and the structure.

[0057] Clause 13. The aircraft of clause 12, wherein the nut plate has a first sleeve extending from the body in a direction along the longitudinal axis, the first sleeve being press fit in the first bore to prevent rotation of the nut plate relative to the structure.

[0058] Clause 14. The aircraft of clause 12, wherein the fastener is threadably coupled to the nut plate.

[0059] Clause 15. The aircraft of clause 12, further comprising a second sleeve positioned in the second bore prior to coupling the fastener to the nut plate.

[0060] Clause 16. The aircraft of clause 15, wherein the first sleeve is integrally formed with a body of the nut plate.

[0061] Clause 17. A method comprising aligning a closure panel of an aircraft with a structure of the aircraft, forming a bore through the closure panel and the structure, removing the closure panel from the structure after forming the bore, inserting a nut plate into a first portion of the bore formed in the structure, inserting a sleeve into a second portion of the bore formed in the closure panel, inserting a fastener from an exterior surface of the closure panel into the second portion of the bore formed in the closure panel, and coupling the fastener to the nut plate via the second portion of the bore to secure the closure panel to the structure.

[0062] Clause 18. The method of clause 17, further comprising applying torque to the fastener via an exterior surface of the closure panel.

[0063] Clause 19. The method of clause 17, wherein inserting the nut plate into the first portion of the bore comprises press-fitting the nut plate in the first portion of the bore.

[0064] Clause 20. The method of clause 19, wherein press-fitting the nut plate comprises press-fitting a second sleeve of the nut plate in the first portion of the bore.

[0065] While certain example methods, apparatus and articles of manufacture have been described herein, the scope of coverage of this disclosure is not limited thereto. On the contrary, this disclosure covers all methods, apparatus and articles of manufacture falling within the scope of the claims.

Claims

1. A fastening system coupling a first structure and a second structure, the fastening system comprising: a fastener; a nut plate having: a body defining an opening to receive the fastener, wherein the body of the nut plate is dome-shaped and includes a clearance hole in an upper region of the body of the nut plate and the opening has internal threads to threadably receive a threaded portion of the fastener; a flange extending from the body to engage an outer surface of the first structure; a first sleeve protruding from the flange in a direction away from the body, the first sleeve being coupled to a first bore formed in the first structure and preventing rotation of the nut plate relative to the first structure, and wherein the flange includes a groove between a peripheral edge of the flange and the first sleeve, a sealant being located in the groove; and a second sleeve insertable into a second bore formed in the second structure, wherein a first end of the first sleeve and a second end of the second sleeve opposite the first end of the first sleeve define a gap to enable the first end of the first sleeve to be spaced apart from the second end of the second sleeve when the first sleeve is coupled to the first bore and the second sleeve is coupled to the second bore, the gap enabling the first sleeve to be inserted into the first bore and the second sleeve to be inserted into the second bore without contacting between the first sleeve and the second sleeve.

2. The system of claim 1, wherein the second sleeve is coupled to the second bore via a clearance fit.

3. The system of claim 1, wherein the second end of the second sleeve extends at least partially in the first bore of the first structure when the second sleeve is coupled to the second bore of the second structure.

4. The system of claim 1, wherein the first sleeve has a first outer diameter and the second sleeve has a second outer diameter, wherein the first outer diameter is substantially equal to the second outer diameter when the first sleeve is positioned in the first bore and the second sleeve is positioned in the second bore.

5. The system of claim 4, wherein the first sleeve defines a first inner diameter and the second sleeve defines a second inner diameter, wherein the first inner diameter is substantially equal to the second inner diameter when the first sleeve is positioned in the first bore and the second sleeve is positioned in the second bore.

6. The system of claim 1, wherein the first sleeve has a first outer diameter that is greater than a first inner diameter of the first bore prior to the first sleeve being coupled to the first bore.

7. The system of claim 6, wherein the first sleeve is coupled to the first bore via a press fit connection to prevent rotation of the nut plate relative to the first structure.

8. An aircraft comprising: a wing box defining a structure including one or more spars, stringers, and ribs; a closure panel closing the wing box; and a fastening system coupling the closure panel to the wing box, the fastening system comprising: a fastener; a nut plate having: a body defining an opening to receive the fastener, wherein the body of the nut plate is dome-shaped and includes a clearance hole in an upper region of the body of the nut plate and the opening has internal threads to threadably receive a threaded portion of the fastener; a flange extending from the body to engage an outer surface of the closure panel; a first sleeve protruding from the flange in a direction away from the body, the first sleeve being coupled to a first bore formed in the closure panel and preventing rotation of the nut plate relative to the closure panel, and wherein the flange includes a groove between a peripheral edge of the flange and the first sleeve, a sealant being located in the groove; and a second sleeve insertable into a second bore formed in the wing box, wherein a first end of the first sleeve and a second end of the second sleeve opposite the first end of the first sleeve define a gap to enable the first end of the first sleeve to be spaced apart from the second end of the second sleeve when the first sleeve is coupled to the first bore and the second sleeve is coupled to the second bore, the gap enabling the first sleeve to be inserted into the first bore and the second sleeve to be inserted into the second bore without contacting between the first sleeve and the second sleeve. a fastener assembly coupling the closure panel and the wing box, the fastener assembly comprising: a nut plate having: a body defining an opening to receive the fastener, wherein the body of the nut plate is dome shaped and includes a clearance hole in an upper region of the body of the nut plate and the opening has internal threads to threadably receive a threaded portion of the fastener; a flange extending from the body to engage an outer surface of the wing box; a first sleeve extending away from the body in a direction along a longitudinal axis of the body, the first sleeve press fit in a first bore of the wing box to prevent rotation of the nut plate relative to the wing box, the nut plate configured to prevent rotation of the nut plate relative to the wing box about the longitudinal axis when the nut plate is coupled to the wing box; a second sleeve insertable into a second bore formed in the closure panel, wherein a first end of the first sleeve and a second end of the second sleeve opposite the first end of the first sleeve define a gap to enable the first end of the first sleeve to be spaced apart from the second end of the second sleeve when the first sleeve is coupled to the first bore and the second sleeve is coupled to the second bore, the gap enabling the first sleeve to be inserted into the first bore and the second sleeve to be inserted into the second bore without contact between the first sleeve and the second sleeve; and a fastener coupled to the nut plate via the second bore formed in the closure panel to couple the closure panel and the wing box.

9. The aircraft of claim 8, wherein the second sleeve is positioned in the second bore prior to coupling the fastener to the nut plate.

10. The aircraft of claim 9, wherein the first sleeve is integrally formed with the body of the nut plate.

11. A method for securing a closure panel of an aircraft to a structure of the aircraft, comprising: aligning the closure panel of the aircraft with the structure of the aircraft; forming a bore through the closure panel and the structure; removing the closure panel from the structure after forming the bore; press fitting a nut plate having a first sleeve to a first portion of the bore formed in the structure; realigning the closure panel of the aircraft with the structure of the aircraft; press fitting a second sleeve in a second portion of the bore formed in the closure panel; inserting a fastener from an exterior surface of the closure panel into the second portion of the bore formed in the closure panel, and coupling the fastener to the nut plate via the second portion of the bore to secure the closure panel to the structure, wherein the nut plate includes a body defining an opening to receive the fastener, wherein the body of the nut plate is dome shaped and includes a clearance hole in an upper region of the body of the nut plate, and wherein the first sleeve is press fit in the first bore of the wing box to prevent rotation of the nut plate relative to the wing box, the nut plate configured to prevent rotation of the nut plate relative to the wing box about the longitudinal axis when the nut plate is coupled to the wing box. wherein a first end of the first sleeve and a second end of the second sleeve opposite the first end of the first sleeve define a gap to enable the first end of the first sleeve to be spaced apart from the second end of the second sleeve when the first sleeve is coupled to the first bore and the second sleeve is coupled to the second bore, the gap enabling the first sleeve to be inserted into the first portion of the first bore and the second sleeve to be inserted into the second portion of the second bore without contact between the first sleeve and the second sleeve.

12. The method of claim 11, further comprising applying torque to the fastener via an exterior surface of the closure panel.

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