Patent Description:
One issue faced by aerospace vehicle manufacturers is providing lightning protection for the aerospace vehicles when in flight. This is particularly an issue for carbon-fiber (or other composite) aerospace vehicle components. Often, aerospace vehicle wings, which typically contain fuel tanks, are of particular concern and metal fasteners used on the wings should be electrically isolated to prevent ignition hazards from lightning and the like.

The issue of electrical isolation is further complicated when the fasteners need to be removable for safety and maintenance inspections and the like. This is further complicated when the wing is thin (e.g., for hyper-sonic aerospace vehicles) and access to the fasteners is difficult or otherwise inconvenient. Typical solutions to these and other issues for wings include adding access panels or the like to allow inspection, removal, and replacement of fasteners or other parts. However, access panels add to the overall weight and drag of the wing structure which is, typically, undesirable.

Other solutions include using fasteners inserted from an accessible side of the aerospace vehicle component that crimp on an inaccessible side to connect the parts. However, such fasteners are not easily removable without destroying the fastener and requiring, if possible, re-insertion of new fasteners. Other drawbacks, inconveniences, inefficiencies, and issues also exist with current systems and methods.

<CIT>, in accordance with its abstract, states: Fasteners are inserted into a stack of members and terminated with parts having at least one of a dry dielectric coating and a dry dielectric seal at select locations to protect against electromagnetic effects (EME).

<CIT>, in accordance with its abstract, states: A structural assembly including a first member having an external side and an internal side, the first member defining a first member through-bore, a second member having an external side and an internal side, the second member defining a second member through-bore aligned with the first member through-bore, and a mechanical fastening system including a bushing at least partially received in the first member through-bore, the bushing defining a bushing through-bore and including a flange, wherein the flange is positioned in a gap between the internal side of the first member and the external side of the second member, a nut plate connected to the internal side of the second member, the nut plate defining a clearance bore aligned with the second member through-bore and the bushing through-bore, the nut plate including a nut, and a bolt extending through the bushing through-bore and into threaded engagement with the nut.

<CIT>, in accordance with its abstract, states: A lightning resistant composite structure, particularly for aircraft, in which a composite skin panel, for example of carbon fibre, is attached to an inner composite structure by one or more lightning resistant fastener assemblies. The fastener assembly comprises a nut and bolt, the bolt being in good conductive contact with a conductive sleeve engaging the skin panel and a non-conductive sleeve engaging the inner structure. The nut is contained within a capped nut assembly located to the undersurface of the inner structure. The non-conductive sleeve and the capped nut assembly isolate the inner structure from the effects of lightning strike, the conductive sleeve providing a high quality conductive interface between the bolt and the skin panel. By this means adverse penetration of lightning current into the inner structure is prevented.

<CIT>, in accordance with its abstract, states: The present disclosure relates to inserts for use with sandwich panels, such as composite panels, and related methods. Presently disclosed inserts may include a retention feature and/or an anti-rotation feature that may be configured to retain the insert in place within a bore formed in the sandwich panel. In this manner, presently disclosed inserts may be secured without the use of adhesive compounds, which may increase efficiency and/or reduce costs in manufacturing apparatus that include one or more sandwich panels having one or more inserts placed therein. Presently disclosed methods of installing an insert into a sandwich panel may include rotating the insert with respect to the sandwich panel as the insert is installed, such that a portion of the insert may be positioned under the skin of the sandwich panel (e.g., a portion of the insert may be positioned between the skin and the core of the sandwich panel).

According to the present disclosure, a fastening system, a method for assembling and a method for manufacturing as defined in the independent claims are provided. Further embodiments of the claimed invention are defined in the dependent claims. Although the claimed invention is only defined by the claims, the below embodiments, examples, and aspects are present for aiding in understanding the background and advantages of the claimed invention.

Disclosed embodiments address the above-noted, and other, drawbacks, inconveniences, and inefficiencies, of current systems and methods. Accordingly, disclosed embodiments include a fastening system for aerospace vehicles including a dielectric nut retainer strip formed of dielectric material having at least one fastener thru hole and at least one cap receiver portion, an anti-rotation nut retainer portion integrally formed in the dielectric nut retainer adjacent to the at least one fastener thru hole, a cap configured to mate with the at least one cap receiver portion, a fastener, and an anti-rotation nut configured to fit in the anti-rotation nut retainer portion and couple with the fastener. In further disclosed embodiments the cap may be a dielectric material. In still further disclosed embodiments the fastener is covered in a conductive coating.

Disclosed embodiments also include a stiffening member formed in the dielectric nut retainer strip, and a substructure fastener portion on the dielectric nut retainer strip configured to engage at least a portion of an aerospace vehicle substructure. In further disclosed embodiments, the substructure fastener portion is configured to engage a portion of a substructure that is interior to an aerospace vehicle wing. In still further disclosed embodiments the fastener is insertable from outside the aerospace vehicle wing into the at least one fastener thru hole of the dielectric nut retainer strip.

In some disclosed embodiments the conductive coating may be indium paste. In some disclosed embodiments the conductive coating may be a conductive sleeve.

Disclosed embodiments include a dielectric nut retainer system including a dielectric nut retainer strip having at least two fastener thru holes, an integrally formed nut retention pocket adjacent to each of the fastener thru holes, at least two caps formed at each of the fastener thru holes on an opposite side from the nut retention pocket, and a dielectric nut retainer strip attachment hole that enables attachment of the dielectric nut retainer strip to a structural element. Disclosed embodiments also include at least one anti-rotation nut configured to engage the nut retention pocket. In some disclosed embodiments the dielectric nut retainer system includes at least one fastener comprising a conductive coating and configured to be insertable into the one or more fastener thru holes.

Disclosed embodiments include a method for assembling an aerospace vehicle wing, the method including inserting at least one nut in at least one nut retention pocket formed on a dielectric nut retainer strip, attaching the dielectric nut retainer strip to a wing substructure over a fastener hole, applying at least one cap to the dielectric nut retainer strip over the at least one nut in the at least one nut retention pocket, locating a wing skin over the fastener hole, inserting a fastener through the wing skin into the fastener hole, and fastening the fastener to the at least one nut.

In some disclosed embodiments the method for assembling an aerospace vehicle wing, after applying at least one cap to the dielectric nut retainer strip, may also include applying a conductive coating to the fastener hole and the at least one nut. In some disclosed embodiments the conductive coating may be indium paste. In some disclosed embodiments the method may include coating the fastener with a conductive coating. In some disclosed embodiments the conductive coating may be indium paste.

Disclosed embodiments include a method of manufacturing a dielectric nut retainer strip, the method including forming a strip of dielectric material with a first side comprising at least two cap receiver portions configured to accept a cap, and forming an anti-rotation nut retainer portion in a second side of the strip of dielectric material at a location opposite of each of the at least two cap receiver portions. Some disclosed embodiments may also include forming a substructure engagement portion configured to engage a substructure of an aerospace vehicle. Some disclosed embodiments may also include forming a stiffening member on at least one edge of the strip of dielectric material.

Disclosed embodiment also include a fastening system for aerospace vehicles including a dielectric carrier strip having at least two fastener thru holes, one or more nut plates configured to align over the fastener thru holes and further having nut plate fasteners to attach the nut plates to the dielectric carrier strip, and metallic domes configured to align over the fastener thru holes and couple with a fastener. Further disclosed embodiments may include the metallic dome being integrally formed on the one or more nut plates.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the intention is to cover all modifications and alternatives falling within the scope of the invention as defined by the appended claims.

It should be understood that, as used herein, the terms "vertical," "horizontal," "lateral," "upper," "lower," "left," "right," "inner," "outer," etc., can refer to relative directions or positions of features in the disclosed devices and/or assemblies shown in the Figures. For example, "upper" or "uppermost" can refer to a feature positioned closer to the top of a page than another feature. These terms, however, should be construed broadly to include devices and/or assemblies having other orientations, such as inverted or inclined orientations where top/bottom, over/under, above/below, up/down, and left/right can be interchanged depending on the orientation.

It should also be understood that, as used herein, "aerospace vehicle" refers to any vehicle capable of flight in the air, space, or combinations thereof, and includes airplanes, spacecraft, manned vehicles, unmanned vehicles, remotely piloted vehicles, military vehicles, commercial vehicles, and the like.

<FIG> is a schematic overview of a typical basic fastening system <NUM> for aerospace vehicles in accordance with disclosed embodiments. As shown a first component <NUM> may be fastened to a second component <NUM>. First component <NUM> may be a metallic or composite substructure component (e.g., a wing spar, or the like) of an aerospace vehicle. Second component <NUM> may, likewise, be a metallic or composite component (e.g., a wing or fuselage skin, or the like). First component <NUM> may have a fastener thru hole 16A bored or otherwise formed in it, and second component <NUM> may have a corresponding fastener thru hole 16B bored or otherwise formed in it. One or more of the fastener thru holes 16A-B may also have a countersink portion 16C to accommodate the fastener <NUM> head. A nut plate <NUM> is inserted into one of the fastener thru holes (e.g., fastener thru hole 16A) and swaged to hold a nut <NUM> in place for coupling with fastener <NUM>.

In embodiments where electromagnetic effect (EME) considerations are needed (e.g., inside or around a fuel tank) fastener <NUM> may be covered in a conductive coating, such as an indium coated Torx head fastener, a fastener wrapped in a conductive sleeve, or the like. Likewise, a metallic (or other) dome <NUM> may be crimped onto the nut plate <NUM> and appropriately coated with EME paste or other sealants.

<FIG> is a cross-sectional view of an assembled fastening system <NUM> in accordance with disclosed embodiments. As shown, a wing skin <NUM> is fastened to a spar <NUM> inside or near a fuel tank (not shown). As also shown, a fuel sealant <NUM>, such as PR-<NUM> Class B Low Weight fuel tank sealant made by PPG Industries, Inc. , or the like, may be applied over metal dome <NUM> to inhibit fuel leakage. Additionally, a cap sealant <NUM>, such as TROGAMID®, or the like, may be applied over the fuel sealant <NUM>. Additional, or fewer, sealants may be applied as desired in accordance with the location, environment, intended use, and the like, for the fastened components.

<FIG> is an isometric view of a dielectric nut retainer strip <NUM> in accordance with disclosed embodiments. As shown, embodiment of dielectric nut retainer strip <NUM> may include fastener thru holes <NUM>. In some embodiments dielectric nut retainer strip <NUM> may be a crystallizable polyamide, such as TROGAMID®, or the like. Other dielectric materials may also be used. The dielectric nut retainer strip <NUM> may be machined, molded, extruded, additively manufactured (e.g., 3D-printed), or the like, to form the generally strip shape shown in <FIG>.

Embodiments of dielectric nut retainer strip <NUM> include a cap receiver portion <NUM> that is configured to mate with a cap <NUM> (not shown in <FIG>) as disclosed below. Mating of cap <NUM> and cap receiver portion <NUM> may be accomplished in any suitable fashion, such as a threaded fit, a snap fit, adhesive fit, or the like.

Embodiments of dielectric nut retainer strip <NUM> may also include one or more stiffening members <NUM> which may be ribs, walls, or the like, that contribute to the structural integrity of the dielectric nut retainer strip <NUM>. Embodiments of dielectric nut retainer strip <NUM> may also include one or more substructure fastener portions <NUM> that enable fastening of the dielectric nut retainer strip <NUM> to an aerospace vehicle substructure, such as a wing spar, or the like. Embodiments of substructure fastener portions <NUM> may be rivet hole, fastener (e.g., screws or bolts) holes, snap-fit portions, rails, or the like. As shown in <FIG>, substructure fastener portion <NUM> is a fastener thru hole.

<FIG> is a schematic, partial bottom-side view of a dielectric nut retainer strip <NUM> in accordance with disclosed embodiments. Embodiments of dielectric nut retainer strip <NUM> may include nut retainer anti-rotation features 44A on the back, or front, side of the dielectric nut retainer strip <NUM>. For example, as shown in <FIG>, a <NUM>-point star shape may be used to retain a nut <NUM> and hinder rotation of the nut <NUM> when retained and when a fastener <NUM> is being threaded into the nut <NUM>. Other shapes, orientations, sizes, and the like, may also be used for anti-rotation features 44A.

<FIG> is a schematic, exploded, partial bottom-side view of a dielectric nut retainer strip <NUM> illustrating nut <NUM> anti-rotation features 44A-B in accordance with disclosed embodiments. As illustrated, nut <NUM> will have the corresponding anti-rotation features 44B to mate with the anti-rotation features 44A on the dielectric nut retainer strip <NUM>. As noted, other shapes, orientations, sizes, and the like, may also be used for anti-rotation features 44A-B.

<FIG> is a schematic, isometric, bottom-side view of a dielectric nut retainer strip <NUM> with nuts <NUM> retained in place in accordance with disclosed embodiments. As shown, one or more nuts <NUM> may be secured into dielectric nut retainer strip <NUM> by snap-fit, threading, adhesive, or the like.

<FIG> is an isometric, partial view of an aerospace vehicle component (e.g., wing spar <NUM>) with a dielectric nut retainer strip <NUM> and nuts <NUM> installed in place in accordance with disclose embodiments. The view in <FIG> shows a bottom view of the spar <NUM> flange, the surface <NUM> indicated in <FIG> is where the second component (e.g., wing skin <NUM>) is mounted as shown in <FIG>. Dielectric nut retainer strip <NUM> may be installed on the component (e.g., wing spar <NUM>) in any appropriate manner, such as, for example, inserting a fastener (not shown) into substructure fastener portions <NUM>, adhering the strip <NUM>, sliding or otherwise engaging a lip or rib (e.g., stiffening members <NUM>) into a reciprocally shaped portion on the component, or the like.

<FIG> is a view of the dielectric nut retainer strip <NUM> of <FIG> showing caps <NUM> installed in accordance with disclosed embodiments. As shown, caps <NUM> mate with corresponding cap receiver portions <NUM> on the dielectric nut retainer strip <NUM>. Mating of the caps <NUM> and cap receiver portions <NUM> may be accomplished in any suitable fashion. For example, caps <NUM> may snap-fit into cap receiver portions <NUM>, may thread into place, may be adhesively secured, or the like. Embodiments of caps <NUM> may include caps made of dielectric material (e.g., TROGAMID®, or the like). Sealants (e.g., fuel sealants <NUM>, cap sealants <NUM>, or the like) may also be applied over the caps <NUM>.

<FIG> is an exploded, isometric, partial view of a wing skin <NUM> installation on one or more wing spars <NUM> in accordance with disclosed embodiments. As shown a wing skin <NUM> having fastener thru holes 16B with a countersink 16C bored, or otherwise formed, therein may be mounted on the mounting surface <NUM> of one or more wing spars <NUM>. Mounting surface <NUM> includes fastener thru holes 16A that align with fastener thru holes 16B and fastener thru hole <NUM> in the dielectric nut retainer strip <NUM>. Fasteners <NUM> (not shown in <FIG>) may be inserted from the wing skin <NUM> outer side into fastener thru hole 16B and 16A and torqued to a desired amount into nut <NUM> on dielectric nut retainer strip <NUM>. Additional sealants, adhesives, or the like, may also be used. <FIG> is a cross sectional view of an assembled wing skin fastening system <NUM> in accordance with disclosed embodiments.

<FIG> is an isometric, partial, bottom-side view of a dielectric nut retainer strip <NUM> in accordance with disclosed embodiments. As shown, embodiments of dielectric nut retainer strip <NUM> may include integrally formed caps 48A and anti-rotation features 44A. In some embodiments dielectric nut retainer strip <NUM> may be a crystallizable polyamide, such as TROGAMID®, or the like. Other dielectric materials may also be used. The dielectric nut retainer strip <NUM> may be machined, molded, extruded, additively manufactured (e.g., 3D-printed), or the like, to form the generally strip shape shown in <FIG>.

<FIG> is an isometric, exploded, partial, top side vide of the dielectric nut retainer strip <NUM> of <FIG>. As shown, one or more nuts <NUM> having corresponding, or reciprocal, anti-rotation features 44B may be installed in the integral dielectric caps 48A. As disclosed herein, sealants, adhesives, or the like, may also be used during installation. As also shown, dielectric nut retainer strip <NUM> may include a substructure fastener portion 42A, such as an edge, rib, lip, or the like, configured to engage a corresponding, or reciprocal, fastener portion 42B as shown in <FIG>.

<FIG> is an isometric, partial view of a fastening system <NUM> in accordance with disclosed embodiments. As shown, embodiments of the disclosed fastening system <NUM> may include a dielectric carrier strip 34A that is formed of dielectric material such as a crystallizable polyamide, such as TROGAMID®, Fiberglas®, other composites, or the like. Embodiments of dielectric carrier strip 34A may include one or more substructure fastener portions <NUM> to attach dielectric carrier strip 34A to a first aerospace vehicle component, such as a wing spar <NUM>, or the like. As also shown, dielectric carrier strip 34A includes one or more fastener thru holes <NUM>. In these embodiments, one or more nut plates <NUM> are fastened to the dielectric carrier strip 34A using nut plate fasteners <NUM> (e.g., a rivet, bolt, screw, adhesive, or the like) over each of the fastener thru holes <NUM>. Nut plate <NUM> may include an integral, or attachable, metallic dome <NUM>, or the like.

<FIG> is a schematic, cross-sectional view of a fastening system <NUM> of <FIG> in accordance with disclosed embodiments. As shown sealants <NUM>, <NUM> or other adhesive layers may be applied over nut plate <NUM>, nut plate fasteners <NUM>, or in between spar <NUM> and dielectric carrier strip 34A as desired.

<FIG> is a schematic flow chart illustrating methods of assembly <NUM> in accordance with disclosed embodiments. Optional or embodiment-dependent steps are shown in dashed lines. As shown, methods of assembling generally may initiate with locating, at <NUM>, a wing skin <NUM> (or other aerospace vehicle component) in place over the wing spars <NUM> (or other substructure components). At <NUM> thru holes (e.g., 16A-B) may be drilled, reamed, or otherwise formed, through the structural component parts. As indicated at <NUM>, the component parts may then be removed and deburred or otherwise cleaned up for assembly. For embodiments where a dielectric carrier strip 34A is to be used (e.g., <FIG>), at <NUM> the carrier strip 34A may be fastened to one of the components being assembled (e.g., wing spar <NUM>). The assembly method <NUM> then diverges depending upon which embodiment is being assembled.

As shown at <NUM>, for embodiments employing a nut plate <NUM>, or dielectric nut plate retainer strip <NUM>, the nut plate (e.g., <NUM>, <NUM>) may be positioned over fastener thru holes (e.g., 16A-B) and secured in place as disclosed herein. For embodiments that employ a swage nut plate (e.g., <FIG>), the nut plate <NUM> may be swaged into place as indicated at <NUM>. As indicated at <NUM>, a fastener thru hole (e.g., 16A-B, <NUM>) may be reamed, drilled, or otherwise formed through the complete assembly stack up. For embodiments that use a metallic dome <NUM>, it may be applied as indicated at <NUM>.

For embodiments that employ a riveted, or otherwise fastened, nut plate <NUM> (e.g., <FIG>) assembly may include, at <NUM>, drilling, or otherwise forming, in a dielectric nut retainer strip 34A to include through holes (e.g., matching those at step <NUM>) and nut plate fastener <NUM> holes. At <NUM> the nut plate <NUM> (some embodiments including a metallic dome <NUM>) may be riveted, or otherwise secured, to the dielectric nut plate retainer strip 34A. At <NUM> the dielectric nut plate retainer strip 34A may be attached to the structural component (e.g., wing spar <NUM>).

As indicated at <NUM>, a fuel sealant (e.g., sealant <NUM>) and an EME paste (e.g., sealant <NUM>) may be applied to the metallic dome <NUM>, cap <NUM>, or integrally formed cap 48A as desired for the particular embodiment being assembled. Additional fuel, or other sealants, may be applied as indicated at <NUM>. As indicated at <NUM> an EME paste (e.g., indium paste) may be applied to the cap (e.g., <NUM>, <NUM>, 48A) as desired. As indicated at <NUM>, additional fuel sealants (e.g., sealant <NUM>) may be applied to the relevant components. As indicated at <NUM> additional EME paste (e.g., indium or the like) may be applied to wing skin hole (e.g., 16B) and nut plate <NUM>, dielectric nut retainer strip <NUM>, or dielectric carrier strip 34A, as applicable. At <NUM> the wing skin <NUM> (or other component) is located in its final position, any additional sealants (e.g., <NUM>, <NUM>) are applied to fastener <NUM>, and the fastener <NUM> is torqued to the proper amount to complete the assembly <NUM>.

<FIG> is a schematic flow chart illustrating methods of assembly <NUM> in accordance with disclosed embodiments. For these embodiments, at <NUM> one or more nuts <NUM> with anti-rotation features 44B are inserted into the corresponding anti-rotation features 44A on a dielectric nut retainer strip <NUM>. At <NUM> the dielectric nut retainer strip <NUM> is located at the fastener thru holes (e.g., <FIG>, thru holes 16A) of the first component and aligned. At <NUM> the dielectric nut retainer strip <NUM> is fastened to the first component (e.g., wing spar <NUM>) using the substructure fastener portions <NUM> (or 42A-B). For embodiments without an integrally formed cap (e.g. 48A), caps (e.g., <NUM>) may be installed as indicated at <NUM>. At <NUM> any sealants or EME pastes (e.g., <NUM>, <NUM>) that are needed may be applied. At <NUM> the second component (e.g., wing skin <NUM>) may be located in final position and the fastener thru holes aligned (e.g., 16A-B). At <NUM> any additional or final sealants or EME pastes (e.g., <NUM>, <NUM>) may be applied to the fastener thru holes or other parts of the second component. At <NUM> the fasteners <NUM> may be inserted and torqued into the nuts <NUM> to specifications. Other embodiments, ordering of steps, additional steps, or the like, may be dictated by the particular embodiment, location, intended use, environment, or the like, as would be apparent to those of ordinary skill in the art having the benefit of this disclosure.

Claim 1:
A fastening system for aerospace vehicles comprising:
a dielectric nut retainer strip (<NUM>) formed of dielectric material comprising at least two fastener thru holes (<NUM>) and at least two cap receiver portions (<NUM>);
the dielectric nut retainer strip being attachable to a substructure of the aerospace vehicle;
at least two anti-rotation nut retainer portions (<NUM>) integrally formed in the dielectric nut retainer strip (<NUM>) adjacent to the at least two fastener thru holes;
at least two caps (<NUM>) configured to mate with the at least two cap receiver portions (<NUM>);
at least two fasteners (<NUM>); and
at least two anti-rotation nuts (<NUM>) configured to fit in the anti-rotation nut retainer portions and couple with the fasteners.