Patent Publication Number: US-11643224-B2

Title: Assembly line fabrication and assembly of aircraft wings

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/115,054, filed Nov. 18, 2020, and entitled “The disclosure relates to the field of aircraft, and in particular, to fabrication and assembly of aircraft wings;” which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The disclosure relates to the field of aircraft, and in particular, to fabrication and assembly of aircraft wings. 
     BACKGROUND 
     An airframe defines the mechanical structure of an aircraft. Airframes are made of multiple components that provide desired structural properties. For example, a portion of an airframe for a wing of an aircraft may include components that are mechanically coupled together (e.g., via co-bonding, co-curing, or fasteners) in accordance with design parameters. In particular, a wing assembly generally includes upper and lower wing panels, each of which include a wing skin stabilized by a series of stringers, that together sandwich a support structure consisting of forward and rear spars that extend along the span of the wing panels, and that are connected together by a series of parallel ribs that each extend chordwise across the wing panels. As presently practiced, components of an airframe are fabricated and assembled in predefined cells on a factory floor. For example, components may be laid-up, cured, or otherwise fabricated at one cell, and then may be transported in their entirety to a new cell where work is performed. 
     While the fabrication processes discussed above are reliable, they encounter delays when work at a specific portion of a component is completed more slowly than expected. For example, if a particular portion of a wing takes longer than expected to be laid-up or fastened together, then the entire wing assembly remains at the cell until all of the work that has been delayed is completed. Furthermore, after a component has been moved, a great deal of time is spent cataloging the configuration of the component. This time is not value-added time. Furthermore, frequent moves between cells add a substantial amount of time that is not value-added. That is, each movement of a component between cells (and hence, each cell used in the fabrication process) requires setup time, and this setup time should be minimized to enhance efficiency. Current designs utilize automated optical inspection techniques and/or probes to inspect position of parts along six degrees of freedom across their dimensions, but these are particularly time-consuming and expensive processes. 
     Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues. 
     SUMMARY 
     Embodiments described herein provide for enhanced systems and techniques that facilitate fabrication and assembly of aircraft wings via an assembly line. According to these embodiments, large components such as wing panels are transported in pulses or moved continuously. Discrete work stations disposed along the assembly line perform various work tasks on the component (e.g., during pauses between pulses or while the component is moved continuously). As discussed in greater detail below, the embodiments herein focus on assembling a wing assembly by following the progress of a wing panel, to which other components (for example, ribs, and spars, and then another wing panel) are gradually installed, through an assembly line. In some embodiments, indexing features, for indexing the component (e.g., a wing panel) to one or more of the work stations, are formed into the component. In embodiments in which the component is a wing panel, indexing features are formed into a manufacturing excess region of the wing panel that will eventually be trimmed off, as part of the forming of the wing panel. The wing panel may be indexed to a work station by means of these indexing features. In some embodiments, work stations are disposed in close enough proximity to each other such that a wing panel, due to its size, may encounter multiple work stations simultaneously. For example, an assembly line may include a sequence of stations arranged in a process direction so that a forward portion of the wing panel first encounters an inspection station (such as a non-destructive inspection, or NDI, station), then a cut-out station, and then a rib install station, as it is moved in the process direction. These stations may be disposed closely enough to each other so that when, for example, a forward portion encounters the rib install station, a middle portion of the wing panel encounters the cut-out station, and a rearward portion encounters the NDI station, such that two or more of the stations, or all three, may perform work tasks on the portion of the same wing panel that is within the purview of the respective station, such as at the same time or overlapping in time. This assembly technique provides a technical benefit by integrating transportation processes into assembly processes, and by reducing the amount of work to be performed on a large component each time the component is moved. 
     Some embodiments are methods for inspecting a wing panel, in which the methods include: advancing the wing panel in a process direction through a Non-Destructive Inspection (NDI) station having one or more inspection heads, and inspecting a portion of the wing panel with one or more inspection heads at the NDI station. Some methods further include suspending the wing panel beneath a strongback, for example prior to advancing the wing panel through the NDI station, such that the wing panel remains suspended beneath the strongback during advancement through the NDI station and inspection at the NDI station. In some of such methods, suspending the wing panel includes affixing vacuum couplers of the strongback to a surface of the wing panel. Some methods further include enforcing a predetermined contour to the wing panel, such as during advancement and/or NDI inspection of the wing panel. Some methods further include indexing the wing panel to the NDI station. 
     Some embodiments are methods for inspecting a wing panel, in which the methods include: receiving a wing panel at a Non-Destructive Inspection (NDI) station having one or more inspection heads, and inspecting a portion of the wing panel with one or more inspection heads at the NDI station during movement of the wing panel through the NDI station. In some methods, inspecting is performed during pulsed or continuous movement of the wing panel through the NDI station. 
     Some embodiments are non-transitory computer readable media embodying instructions which, when executed by a processor, are operable for performing the methods briefly mentioned above. 
     Some embodiments are systems for inspecting a wing panel, in which the systems include: a track; a strongback configured to suspend a wing panel beneath it, and to advance along the track in a process direction; and a Non-Destructive Imaging (NDI) station disposed at the track and that is configured to inspect the wing panel while the wing panel is suspended beneath the strongback. In some systems, the strongback is configured to enforce a predetermined contour onto the wing panel by means of adjustable-length pogos that include vacuum couplers. Some systems further include a controller configured to perform various actions, such as selectively retracting one or more vacuum couplers to allow NDI inspection of the wing panel, detecting out-of-tolerance conditions at the wing panel based on input from the NDI station, reporting out-of-tolerance conditions for rework, controlling operation of inspection heads of the NDI station, controlling advancement of the wing panel in the process direction, and relating input from the NDI station relating to locations on the wing panel. In some systems, the NDI station is configured to index with the wing panel and/or the strongback suspending the wing panel. 
     Other illustrative embodiments (e.g., methods, computer-readable media, systems, and so forth, relating to the foregoing embodiments) may be described below. The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the present disclosure are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
         FIG.  1    is a block diagram of a layup system that applies indexing features to a manufacturing excess of a preform that will be hardened into a composite part in an illustrative embodiment. 
         FIG.  2 A  illustrates a layup mandrel awaiting layup in an illustrative embodiment. 
         FIG.  2 B  illustrates a layup mandrel covered by a composite part in an illustrative embodiment. 
         FIG.  3    is a flowchart illustrating a method for applying indexing features to a manufacturing excess of a preform that will be hardened into a composite part in an illustrative embodiment. 
         FIG.  4    depicts takt timing for feeder lines for a composite part in an illustrative embodiment. 
         FIGS.  5 A- 5 F  are diagrams of an assembly line for a wing in an illustrative embodiment. 
         FIG.  5 G  is a diagram of an alternative configuration of an assembly line for a wing in an illustrative embodiment. 
         FIG.  6    is a flowchart illustrating a method of enforcing a contour onto a wing panel in an illustrative embodiment. 
         FIGS.  7  and  8    are flowcharts illustrating methods of non-destructive inspection of a wing panel in an illustrative embodiment. 
         FIG.  9    is a flowchart illustrating a method of installing ribs and spars to a wing panel in an illustrative embodiment. 
         FIG.  10    is a flowchart illustrating a further method of enforcing a contour onto a wing panel in an illustrative embodiment. 
         FIGS.  11 A- 11 D  illustrate installation of a rib at an upper wing panel in an illustrative embodiment. 
         FIG.  12    is a flowchart illustrating a method of affixing a rib to an upper wing panel in an illustrative embodiment. 
         FIGS.  13 - 15    are flowcharts illustrating methods of installing ribs and spars to an upper wing panel in an illustrative embodiment. 
         FIGS.  16 A- 16 C  are diagrams illustrating automated installation of shims between ribs and wing panels in illustrative embodiments. 
         FIGS.  17 A- 17 C  illustrate further views of a robot arm performing automated inspection and shim installation between ribs and wing panels in illustrative embodiments. 
         FIG.  18    is a flowchart illustrating a method of shim installation using a robot arm in an illustrative embodiment. 
         FIG.  19    is a perspective view of an aircraft that includes a fully assembled wing in an illustrative embodiment. 
         FIG.  20    is a block diagram of various components and systems discussed herein in an illustrative embodiment. 
         FIG.  21    broadly illustrates control components of a production system that performs ultrasonic inspection in an illustrative embodiment. 
         FIG.  22    depicts an assembly line in an illustrative embodiment. 
         FIG.  23    is a flow diagram of aircraft production and service methodology in an illustrative embodiment. 
         FIG.  24    is a block diagram of an aircraft in an illustrative embodiment. 
     
    
    
     DESCRIPTION 
     The figures and the following description provide specific illustrative embodiments of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within the scope of the disclosure. Furthermore, any examples described herein are intended to aid in understanding the principles of the disclosure, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the disclosure is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
     For convenience, the description is presented as a sequence of operations that may occur in the production of a wing for an aircraft, as it is assembled on an assembly line from constituent parts. In particular, the description begins with the formation of a wing panel from a preform, and proceeds through various operations performed on the wing panel, including the addition of structural components such as ribs and spars to the wing panel (which may be an upper wing panel), and joining another wing panel (such as a lower wing panel) to form a wing assembly. The term “wing assembly” is used herein generally to refer to a wing panel to which one or more major structural components, e.g. ribs and spars, has been affixed or installed, and may thus include a complete wing. However, as the description refers mainly to the formation of a wing panel and the addition of major structural components thereto, and not necessarily to the inclusion of cabling and mechanical and electrical systems that are typically also incorporated into a completed wing. Not all operations, processes, steps, and other actions described herein necessarily take place in all of the embodiments (e.g., embodiments of wing assemblies, embodiments of structural components thereof, embodiments of methods relating to the assembly thereof, etc.) described herein, or in other embodiments that are consistent with this disclosure. Further, the operations described, or certain actions included therein, may take place in a different order than as discussed, may take place at the same time or overlapping in time with other actions, may represent alternative operations for different wing panels (such as an upper wing panel as opposed to a lower wing panel, etc.), and so forth. 
     The wings and wing assemblies described herein may comprise metal parts and/or composite parts. Composite parts, such as carbon fiber reinforced polymer (CFRP) parts, are initially laid-up in multiple layers that together are referred to as a preform. Individual fibers within each layer of the preform are aligned parallel with each other, but different layers exhibit different fiber orientations in order to increase the strength of the resulting composite part along different dimensions. The preform includes a viscous resin that solidifies in order to harden the preform into a composite part (e.g., for use in an aircraft). Carbon fiber that has been impregnated with an uncured thermoset resin or a thermoplastic resin is referred to as “prepreg.” Other types of carbon fiber include “dry fiber” which has not been impregnated with thermoset resin but may include a tackifier or binder. Dry fiber is infused with resin prior to curing. For thermoset resins, the hardening is a one-way process referred to as curing, while for thermoplastic resins, the resin reaches a viscous form if it is re-heated. 
       FIG.  1    is a schematic diagram of an illustrative layup system  100  that applies indexing features to a manufacturing excess of a preform that will be hardened into a composite part in an illustrative embodiment. In prior systems, manufacturing excess for a composite part—that is, material that is beyond the intended final dimensions or boundaries (e.g., the final perimeter) of the composite part—is trimmed immediately after demolding. For example, this may include placing a wing panel into a dedicated cell, scanning the wing panel to characterize it, and then trimming the wing panel (e.g., with a cutter) along the perimeter of the part until final perimeter dimensions are accomplished. Similar processes are applied when trimming manufacturing excess for a fuselage. As will be described in greater detail herein, layup system  100  is unique in that it utilizes material that is traditionally immediately trimmed from a composite part after demolding. In particular, various indexing features are formed into the manufacturing excess of the preform, which can then be used to index (e.g. position, orient, identify, etc.) the hardened composite part for further operations, such as at one or more stations in an assembly line or other manufacturing process. Layup system  100  comprises any system, device, or component operable to apply indexing features to a preform which will be hardened into a composite part. In this embodiment, layup system  100  includes a layup mandrel  110  (e.g., a rigid metal mandrel) that defines a contour  112  (e.g., a curved, flat, or otherwise shaped contour) for a preform that will be hardened into a composite part, such as a wing panel. A preform  200  is shown to be disposed on the layup mandrel. 
     As can also be seen with reference to  FIGS.  2 A and  2 B , which show an isometric view of a simplified version of layup mandrel  110 , the mandrel has surface features  114 , such as indents, protrusions, ridges, grooves, notches, through-holes, blind holes, dams, etc. Like contour  112 , which imparts a corresponding contour to the preform, surface features  114  are capable of being used to directly place corresponding indexing features, shown at  210 , onto the preform. Others accommodate trimming of manufacturing excess at the layup mandrel  110 , or drilling of a composite part hardened at the layup mandrel  110 . In other words, the surface features  114  alter the shape of the preform  200  on a localized basis to place the indexing features  210  into the preform and/or hardened composite part, with the various types of surface features  114  offering different ways of forming the indexing features into the composite part. One way is in laying up the preform over a surface feature (e.g., a protrusion, which forms a corresponding indent in the preform that becomes part of the composite part after hardening); another way is by machining (e.g., by drilling) an indexing feature (e.g., a through-hole) into the composite part post-hardening. For example, in  FIG.  1   , surface features  114  are shown to include recesses  118  that are filled with potting compound and finished to a surface contour to complement the contour  112 , so that indexing features such as through-holes may be drilled into the composite part hardened from the preform  200  prior to de-molding the part from the mandrel  110 , with overshoot during the drilling operation removing some of the potting compound rather than damaging the surface of the layup mandrel. The surface features  114  are used to shape, or enforce, indexing features onto (and/or into) a preform  200  laid-up onto the layup mandrel  110 . 
     Overshoot during machining, such as drilling or trimming, at the layup mandrel  110  after hardening necessitates rework of the potted surface(s) prior to the next use of the layup mandrel  110 . The preform  200  is laid-up onto the layup mandrel  110  over the contour  112  and surface features  114 . 
     As shown in  FIG.  1    and as is also visible in  FIG.  2 A , which shows layup mandrel  110  awaiting a layup, the layup mandrel includes a layup region  120  for preform  200 , which includes contour  112 , and which is surrounded by a manufacturing excess region  122 , within which are disposed surface features  114 . Correspondingly, preform  200  is shown in  FIG.  1    to extend past a final trim boundary or final perimeter  202  for the resulting composite part. The region of the preform that extends beyond the final perimeter  202  is the manufacturing excess, indicated at  204 , which is defined by a manufacturing excess edge  206 . Accordingly, surface features  114  are positioned to complementarily form indexing features  210  in preform  200 . More particularly, the surface features  114  that are disposed in the manufacturing excess region  122  form indexing features  210  in the manufacturing excess  204  of preform  200  before hardening which, as noted above, may be utilized for indexing after the preform  200  has hardened into composite part  250 . Although the curve of contour  112 , which is shown as a shallow, concave surface, is shown to extend on layup mandrel  110  beyond the final perimeter  202  of the resulting composite part, this is not required to all embodiments, as the contour  112  is only required for the portion of the resulting composite part that is within the final perimeter  202 . Also, while a concave layup mandrel  110  is illustrated, layup mandrels of any suitable shape may be utilized. For example, convex layup mandrels, and layup mandrels that define complex curvatures, are also possible. Also, while an outer mold line layup mandrel  110  is illustrated, inner mold line layup mandrels may be utilized in another embodiment. 
     While  FIG.  2 A  shows layup mandrel  110  awaiting a layup,  FIG.  2 B  shows a composite part, indicated at  250 , which has been hardened from a preform  200 , awaiting demolding from layup mandrel  110 . Indexing features  210  of preform  200  have become indexing features  210  of composite part  250 . 
     In some embodiments, the surface features  114  are separated from neighboring surface features by a predefined distance (e.g., several inches, several feet, etc.), such as to create evenly spaced indexing features  210  at/on/in the preform  200  and resulting composite part  250 . In another embodiment, the surface features  114  are unevenly spaced from each other. The positions and/or predefined distance(s) between indexing features may depend, in part, on factors such as the arrangement of work stations on an assembly line. 
     Positions of the surface features  114  in the layup mandrel  110  are precisely toleranced (e.g., to a thousandth of an inch), and hence the positions of corresponding indexing features  210  at the preform  200  are also consequently known to a precise tolerance, even after the preform  200  has been hardened into composite part  250  and demolded from layup mandrel  110 . Thereafter, the indexing features  210  may be utilized by stations in an assembly line in order to orient and position the resulting composite part in a desired manner so that work may be performed upon the composite part. Furthermore, because the layup mandrel  110  is re-usable, there is no need for a separate process of applying indexing features to preforms. Performing this process at a layup mandrel that is within tolerance results in indexing features that are also within tolerance. Recesses  118 , also referred to as potting areas, are filled with a potting compound and placed to accommodate machining overshoot from a machining operation such as drilling operation to install indexing features (e.g. through-holes) after hardening into composite part  250  has been completed, as noted above, and refilled and/or resurfaced as necessary after machining and de-molding in order to prepare for the next preform. 
     Some embodiments include installing readable identifying means (shown generally at  126  in  FIG.  1   ) in the preform, such as a Radio Frequency Identifier (RFID) chip. In such embodiments, one or more RFID chips are coupled, attached, or embedded into the manufacturing excess  204  of a preform  200 . Readable identifying means such as an RFID chip can facilitate the indexing process by reporting information that characterizes aspects of the resulting composite part to which it is coupled. For example, an RFID chip can provide instructions to a work station regarding the portion of the structure within the purview of the particular work station. One or multiple RFID chips can provide instructions to one work station or multiple work stations, and there is no need for a one to one relationship of one RFID chip to one work station. In another example, the RFID chips report a type of structure/wing, including right or left, or upper or lower, or even model number, to the work station. 
     Further, although not shown in the drawings, one or more other readable identifying means  126  may be provided to preform  200 , or to the composite part  250  formed therefrom, as part of the forming process, in addition to or instead of an RFID chip. For example, a bar code or other indicia, which may be scanned or read by a suitable reader by one or more work stations in an assembly line, may be inscribed or applied to the preform or resulting composite part, prior to de-molding. For the sake of this disclosure, all references herein to a particular type of readable identifying means  126  (such as an RFID chip, or a bar code) (and depictions thereof, in the drawings) are intended to broadly encompass any such readable identifying means. 
     The layup system shown in  FIG.  1    further includes a cutter  130  having a blade  132  (e.g., a reciprocating or circular blade) and an actuator  134  that drives the blade  132  to cut portions of a composite part that are proximate to guides  116 , which are shown in the form of adjoining grooves that encompass the manufacturing excess region  122 , in the layup mandrel  110 . That is, the guide  116  seats the cutter  130  and/or defines a path for cutter  130 . Moreover, as shown in  FIG.  1   , the guide  116  may be filled with potting compound to accommodate a blade of the cutter (and refilled after use, similar to recessed areas  118 ). As shown in  FIG.  2 B , for example, in which the grooves that collectively form guide  116  are shown for clarity as a rectangular perimeter, composite part  250  is shown to include a portion  252  that is within layup region  120 , as well as a portion  254  in the manufacturing excess region  122  that is conformed to surface features  114 . A flash edge  256  of surplus material is shown in  FIG.  2 B  to extend beyond the manufacturing excess region  122 . The cutting operation, which is performed prior to demolding of the composite part  250  from the layup mandrel  110 , removes flash edge  256  to define a manufacturing excess edge  206 , and leaves a sufficient amount of manufacturing excess  204  to include indexing features  210  for use by stations in an assembly line. The rough cut provides a consistent edge, i.e. manufacturing excess edge  206 , to the part during the manufacturing process, prior to trimming the edge to a final perimeter, i.e. final perimeter  202 . This is desirable in contrast to working upon a part without a fixed consistent perimeter with respect to a manufacturing excess. Operations of the cutter  130  are managed by controller  140 . Controller  140  may be implemented, for example, as custom circuitry, as a hardware processor executing programmed instructions, or some combination thereof. 
     Illustrative details of the operation of layup system  100  will be discussed with regard to  FIG.  3    and method  300  shown therein. Assume, for this embodiment, that layup mandrel  110  has been cleaned and returned to the start of an assembly line after a composite part has been demolded from the layup mandrel  110 . Thus, layup mandrel  110  awaits layup of a preform, such as preform  200 , for a next composite part  250 . 
       FIG.  3    is a flowchart illustrating a method  300  for applying indexing features to a manufacturing excess  204  of a preform  200  that will be hardened into composite part  250  in an illustrative embodiment. The steps of method  300  are described with reference to components of layup system  100  shown in  FIGS.  1 ,  2 A, and  2 B , but those skilled in the art will appreciate that method  300  may be performed in other systems. As is the case with all of the methods illustrated and described in this disclosure, the steps shown in the flowchart described herein are neither all inclusive nor exclusive. Furthermore, the flowcharts herein (such as in  FIG.  3   ) illustrate only a specific embodiment of a particular method (such as method  300 ), it will be understood that other embodiments of methods consistent with and encompassed by this disclosure include a fewer or greater number of steps than as shown, include steps performed in a different order than as shown in, and/or contain other (e.g., additional, fewer, and/or alternative) actions than as depicted. Further, as will become clear from the disclosure, as the various methods shown and discussed herein relate to several different operations and sequences that may be performed as a wing panel is formed and assembled into a wing assembly, methods in accordance with this disclosure may combine or otherwise include various steps and operations of two or more of various illustrated methods. Also, although reference numbers for components described above are used in the description of this method  300 , it will be understood that the method (as well as other methods described herein) is applicable to components that may have different configurations than as illustrated and described above. 
     Focusing on method  300 , in step  302 , a preform  200  is laid-up onto the layup mandrel  110 , such as onto a layup region  120 , as well as onto a portion of the layup mandrel  110  that is located beyond final trim boundaries (i.e., the final perimeter  202 ) of the composite part  250 , such as a manufacturing excess region  122 . Manufacturing excess region  122  of the layup mandrel  110  includes surface features  114  configured to complementarily form indexing features  210  in the preform  200 . The layup mandrel  110 , in at least the layup region, defines a contour  112  for a composite part, and the preform  200  includes a manufacturing excess  204  that extends beyond the final perimeter for the composite part. Layup may be performed as the layup mandrel  110  itself is pulsed or moved continuously through an assembly line, and may include the synchronized operation of multiple lamination machines at once (e.g., during continuous motion of the layup mandrel, during pauses between movements of the layup mandrel, etc.). During layup, multiple plies of unidirectional fiber reinforced material are applied sequentially to build the preform  200  at a desired size and strength. The layup process extends the preform  200  beyond final trim (e.g. assembly-size) boundaries (e.g. beyond a final perimeter  202 ), which means that a portion of the preform  200  extends over surface features  114 . In this embodiment, the preform  200  is a preform for a wing panel  550  with multiple layers/plies. 
     In step  304 , the preform  200  is conformed to surface features  114  at the layup mandrel  110  that are located beyond the final trim boundaries of the composite part  250  and that complementarily form/enforce features into the preform  200  that will be hardened into indexing features  210 . In one embodiment, this comprises consolidating the preform  200  by vacuum bagging the preform and applying consolidation pressure. In further embodiments, tows of fiber-reinforced material applied during layup in step  302  are compressed by a roller or other device to conform the preform  200  to the surface features  114 . 
     In the illustrative method, steps  302  and  304  are usually performed in a clean room environment, to minimize the possibility of foreign object debris and other contaminants from contacting the preform  200 , such as during layup. The layup mandrel  110  is then moved to an autoclave, which hardens the preform  200  into a composite part  250  via the application of heat and/or pressure. In step  306 , the preform  200  is hardened into a composite part  250  that includes indexing features  210  complementarily formed therein, in that the indexing features  210  are complementary to the surface features  114 , and are disposed at the surface features  114 . During hardening, the preform  200  may be heated to a curing temperature for a thermoset resin within the preform  200 , or the preform  200  may be heated to a melting temperature of a thermoplastic resin and then cooled until the thermoplastic resin solidifies. This results in the resulting composite part  250  having indexing features  210  disposed at the surface features  114  on the layup mandrel  110 . 
     In further embodiments, additional indexing features  210  are added by milling or drilling the manufacturing excess, such as by installing holes, notches, channels, and/or grooves that remove material from the manufacturing excess. In still further embodiments, additional indexing features  210  such as pins, clips, rings, etc. are utilized and/or installed. 
     Some embodiments include installing readable identifying means  126  (such as an RFID chip, a bar code, and so forth) to the manufacturing excess  204 , either of the preform  200  or of the composite part  250 . Phrased another way, RFID chip and/or other readable identifying means  126  are placed in manufacturing excess  204  either prior or subsequent to hardening the preform into the composite part  250 . 
     In step  308 , material is removed (e.g., cut or otherwise separated) from the composite part  250  while retaining a manufacturing excess  204  that includes the indexing features  210 . The cutting operation of step  308  creates a consistent perimeter/border of manufacturing excess  122 . In one embodiment, this comprises operating a cutter  130  along guides  116  in order to cut away a resin flash (or flash edge  256 ) or other border of the composite part  250 , resulting in a manufacturing excess edge  206 . In one embodiment, trimming off flash edge  256  of the composite part is  250  performed prior to demolding the resulting composite part  250  from the layup mandrel  110 . The composite part  250  retains manufacturing excess  204  having indexing features  210  that will be used for indexing the composite part as it is worked upon by work stations in an assembly line. The composite part  250  may also include indexing features  210  in areas that will be trimmed off to accommodate, for example, wing access doors or other portions of a wing panel, and/or manufacturing excess beyond a wing panel final perimeter. A final perimeter  202  can then be achieved by trimming off the remaining manufacturing excess later in the process. That is, one or more of the indexing features may be subject to removal to accommodate the addition of one or more components during assembly. For example, work stations can be designed to trim out manufacturing excess or portions thereof, install components such as ribs or spars, join components such as wing panels together, etc. In further embodiments, additional indexing features  210 , such as holes, notches, channels, grooves, and so forth, are installed into/formed at the composite part  250  via drilling, milling, or other operations. In a further embodiment, removing material from the composite part  250  comprises installing such additional indexing features  210 . 
     In step  310 , after removing material, such as separating flash edge  256  and/or placing indexing one or more indexing features  210 , from the composite part  250 , the composite part is demolded from the layup mandrel  110 . The composite part  250  then proceeds (not shown) to an assembly line for further fabrication and assembly, while the layup mandrel  110  returns for cleaning and receiving another preform for a composite part. In one embodiment, the layup mandrel  110  is also reworked (e.g., refilled with potting compound to restore layup contour  112  as needed after drilling or cutting overshoot into potted areas of recesses  118  prior to demold, repaired, etc.) and transported to start a layup start location, such as on a wing panel layup line. 
     The method may then continue. For example, and as described in greater detail herein, the resulting composite part  250  may be indexed to a work station in an assembly line via the indexing features  210 , and work may be performed on the composite part at the work station while the composite part is indexed to the work station. In some embodiments, the composite part  250  is suspended or otherwise conveyed through the assembly line by a shuttle, such as a strongback. The composite part  250  may be indexed to the shuttle, such as by means of a corresponding indexing unit on a strongback. The strongback may in turn index to a work station, in which case the composite part may be said to be indexed to the work station via the strongback. In any case, the indexing characterizes to a work station at least a portion of the composite part  250  (and/or the strongback) within the purview of the work station. In further embodiments, multiple indexing features interact with multiple work stations and/or with the strongback. The indexing may occur for one or more work stations, until eventually the manufacturing excess  204  is trimmed from the composite part  250  (e.g., after indexing features located in the manufacturing excess are no longer being used for assembly). After trimming, the composite part  250  has its final perimeter  202 , and the indexing features  210  in the manufacturing excess have been removed. The composite part  250  is then integrated into a wing assembly of an aircraft. 
     Method  300  provides a substantial advantage over prior techniques, because it enables indexing features  210  to be installed into a composite part  250  during layup, by reference to surface features  114  on a mandrel  110  that has been precisely toleranced. This eliminates the need for the preform  200  to be precisely measured in order to install indexing features  210 , because the indexing features are already placed at precisely known locations by virtue of the placement of the surface features and placement relative to the layup mandrel  110 . The precision of the layup mandrel  110  and layup processes is therefore leveraged to avoid the need for downstream contour scanning and indexing. The precision of the layup mandrel  110  is therefore extended/leveraged beyond just layup processes to include post hardening processes such as trimming, milling or drilling to add indexing features prior to the demold of the composite part  250 . Therefore the accuracy relationship of multiple surface features  114  and correspondingly formed indexing features  210  placed into the composite part  250  by using the layup mandrel  110  is carried along as the composite part advances, which may enable fabrication processing steps to occur simultaneously on the same part. 
     An example diagram showing how different feeder lines and assembly or layup lines can be coordinated in an assembly line for assembling, for example, a wing assembly, is shown in  FIG.  4   .  FIG.  4    is a flow diagram illustrating an example of a schema, shown as schema  480  for feeder lines  490  and assembly/layup lines  491 , in an illustrative embodiment. Schema  480  provides a detailed example flow diagram for wing fabrication pertaining to feeder lines and takt times. All of the feeder lines, from layup material feeder lines through join operations for integrating wings to fuselage sections, are depicted, for a particular embodiment. In addition, each step indicated by an arrow is performed according to a desired takt time based upon the takt time of the component that it feeds into. 
     In this embodiment, each feeder line is designated with a different reference number  490  (e.g.,  490 - 1 ,  490 - 2 , etc.), and each assembly or layup line is designated with a different reference number  491  (e.g.,  491 - 1 ,  491 - 2 , etc.). More specifically, a feeder line  490 - 1  provides layup material to a wing panel layup line  491 - 1 . A feeder line  490 - 2  provides layup material to a spar layup line  491 - 5 . A feeder line  490 - 3  provides layup material to a rib layup line  491 - 3 , and a feeder line  490 - 4  provides layup material to a stringer layup line  491 - 2 . Also, layup lines feed into other layup lines. Rib layup line  491 - 3  feeds into a rib post-fabrication line  491 - 7 , wing panel layup line  491 - 1  feeds into a wing stringer placement line  491 - 4 , and spar layup line  491 - 5  feeds into a spar post-fabrication line  491 - 6 . 
     Each feeder line is shown to have a takt time that facilitates fabrication of the component that it fabricates. The takt times between feeder lines and the assembly lines that they feed are synchronized to provide just in time (“JIT”) delivery of components to the respective work station  520 , or work stations  520 , that use those components (e.g., as consumable goods, as inputs to a product being manufactured, etc.). The resulting component moves along assembly line  500  with work stations  520  and is also progressed at a takt time. Each of the feeder line  490 - 1  through  490 - 9  and or lines  491 - 1  through  491 - 9  takt times can be the same, or some may be the same, or all can be different. Each feeder line  490 - 1  through  490 - 9  progresses at a common takt for that particular line. 
     The takt time for each feeder line may be dependent upon a desired production rate for an assembly line that the feeder line feeds. For example, if ribs are attached at a rate of one per hour and are attached by two hundred fasteners, then two hundred fasteners should be supplied to a rib install station per hour by a feeder line, resulting in a fastener takt time of three and one third fasteners per minute. 
     In this embodiment, for example, rib layup line  491 - 3  progresses at a takt7 time and feeds into rib post-fabrication line  491 - 7 . Wing panel layup line  491 - 1  progresses at a takt3 time and feeds into wing stringer placement line  491 - 4 . Spar layup line  491 - 5  progresses at a takt5 time and feeds into spar post-fabrication line  491 - 6 . 
     The rib post-fabrication line  491 - 7  progresses at a takt6 time, wing stringer placement line  491 - 4  progresses at a takt2 time, and spar post-fabrication line  491 - 6  progresses at a takt4 time. All feed into a wing assembly line  491 - 8 , which progresses at a takt1 time and also receives access port covers from access port cover feeder line  490 - 5 , receives miscellaneous materials from miscellaneous material feeder line  490 - 6 , receives fasteners from fastener feeder line  490 - 7 , and receives sealant from sealant feeder line  490 - 8 . The wing panel  550  is hardened in the autoclave in line  490 - 10 . The composite part  250  is then trimmed and (in some embodiments) indexing features  210  are added prior to separation from mandrel  110 , for example in a demolding station, in line  490 - 11 . Trimmed excess material is removed from the wing assembly line  491 - 8  via down chute  490 - 9 . After fabrication is completed for a wing, line  491 - 9  moves the wing towards a fuselage for joining. Each of the various lines discussed above may provide material and/or a component just in time to the line that it feeds, at whatever rate may be desired. The takt time of the downstream line may or may not be equal to the line or lines feeding it. Each line may have a unique takt time. 
     Any of the assembly lines, including feeder lines, can operate as micro pulse, full pulse, and/or continuous lines with the fabrication process proceeding from left to right (relative to schema  480 ), with the various takt times synchronized for JIT delivery of components and/or materials at the next line downstream. As used herein, a “pulse” refers to advancement of a component in a process direction through an assembly line followed by a pause. A component can be “micro pulsed” (a term that herein refers to advancement of a component in the process direction by a distance that is less than its length) or can be “full pulsed” (advancement of a component by a distance equal to or more than its length). As a part of pulsed fabrication, components in an assembly line are pulsed synchronously, and multiple work stations can perform work on different portions of the components during the same pauses between pulses, or during the pulses themselves. Phrased another way, the stations each perform work on a portion of the wing panel at the same time, such that each station performs work on a different portion during a pause in advancement of the wing panel along the track. 
     This parallel processing significantly increases work density within the factory. The takt for each of the micro pulsed or fully pulsed components can be the same or different, or a defined fraction of a takt time for another assembly line that receives the component. For example, a takt time at feeder line  490 - 2  for layup material for a spar may be different for a takt time at feeder line  490 - 1  for layup material for a wing panel, which may be different for a takt time for sealant provided via sealant feeder line  490 - 8 . In one embodiment, the takt time is constant for each illustrated segment. 
     As noted above, the individual feeder lines discussed herein may be pulsed or continuously operated. Pulsed lines may implement micro pulses, wherein the components being fabricated are advanced by less than their length before receiving work from a work station during a pause, or may be full pulsed, wherein the components are advanced by an amount equal to their length. Furthermore, the various components (e.g., wing assemblies, wing panels, ribs, spars, etc.) can be fabricated from composite parts, or via additive or subtractive manufacturing techniques for metals. For example, in one embodiment, ribs are fabricated via subtractive manufacturing of metal components at rib post-fabrication line  491 - 7 , while wing panels are fabricated as composite parts (e.g., a preform) at wing panel layup line  491 - 1 . 
     Various aspects of the schema illustrated in  FIG.  4    and described above may be implemented in any fabrication setting, for example on a factory floor and/or in an assembly line for a wing, such as to coordinate the timing of assembly, movement (e.g., pulsed and/or continuous), and/or delivery of components and supplies, and/or other operations, on a JIT basis, or otherwise. Concordantly, the illustrative embodiments of an assembly line, such as the assembly line  500  depicted in  FIGS.  5 A- 5 F  and described below corresponds to assembly line  491 - 8 . However, other assembly lines and manufacturing processes consistent with this disclosure, may implement such a schema, or any aspects thereof, even if not specifically mentioned in the description of the embodiments. 
       FIGS.  5 A- 5 F  depict various aspects of an example assembly line  500  for a wing in an illustrative embodiment. The assembly line  500  may be utilized to perform work upon wing panels, such as a wing panel  550 , fabricated via the techniques and systems provided above in  FIGS.  1 - 4   . The description of  FIGS.  5 A- 5 F , as well as of the structures, components, and operations illustrated therein, are provided with respect to a wing panel, but are applicable to any composite part. The wing panel  550  is somewhat generically described, and may be an upper or lower, or right or left, wing panel. Where operations or features specific to a certain type of wing panel  550  are described (e.g., an upper wing panel), the wing panel will be indicated as such. The assembly line  500 , a top view of which is shown schematically in  FIG.  5 A , includes a track  510 , along which a shuttle, shown in the form of a group of three strongbacks  540 , travels in a process direction  541  (e.g., in a pulsed fashion from station-to-station, or continuously). The track  510  comprises one or more rails, rollers, or other elements that facilitate motion (e.g., rolling or sliding) of the shuttle along the track  510 . The track  510  is capable of being mounted to a floor, suspended from above, etc., depending on the specific environment in which it is used. In the illustrated embodiment, the track  510  is disposed above the various stations, and the shuttle (strongbacks  540 ) carries the wing panel  550  in the process direction. In particular, as can be seen in  FIG.  5 D , a strongback  540  is shown to include adapters  543 , which mate with track  510  and enable locomotion via the track  510 . For example, the adapters  543  may drive a strongback  540  along the track  510 , or may enable the track  510  to drive a strongback  540 . Either way, this configuration is intended to broadly encompass any suitable manner of structure designed to convey the wing panel  550  in a process direction  541 . In further embodiments, the track  510  includes a chain drive, motorized cart, or other powered system (not shown) that is capable of moving the strongback  540  in the process direction  541 . 
     One or more strongbacks  540  advance a wing panel  550  through a variety of work stations, generally designated at  520 , that perform work on the wing panel  550 . In  FIG.  5 A , three strongbacks  540  cooperate to carry a single wing panel  550 . However, a greater or fewer number of strongbacks  540  may be used, as suitable. For convenience, the term “strongback” herein refers generally to a single structure that is configured to extend over a transverse section of a wing panel  550 , such as a chordwise section, although for convenience the term may be used herein to refer generally to a shuttle that includes a plurality of such structures. When two or more strongbacks  540  cooperate to carry a component such as a wing panel  550 , they may be coupled to each other (not shown) in a manner that maintains their constant relative position, so that only one strongback  540  is driven along the track  510 . In such a manner, wing panels  550  of different lengths may be carried through assembly line  500 , such as by coupling a suitable number of strongbacks  540  together in order to support the entire length of the wing panel  550 . 
     In some embodiments, indexing features of the wing panel  550 , such as located in the manufacturing excess, may be used to index the wing panel  550  with the strongback  540  that supports it. In the view in  FIG.  5 B , which corresponds with view arrows “ 5 B” in  FIG.  5 A , strongback  540  is shown to include an indexing unit  542 , which is configured to interface with corresponding indexing features installed in a manufacturing excess  554  of the wing panel  550  (which may correspond to manufacturing excess  204  of a preform  200  that was hardened into wing panel  550 , per the fabrication process described above). In the illustrated embodiment, the indexing unit  542  physically couples with an indexing feature, in that the indexing unit  542  is shown to include a head  549  that is received within indexing features  210 - 1 , which is shown as a through-hole. Although only one indexing unit  542  is shown in  FIG.  5 B , each strongback  540  may include any suitable number of indexing units, each of which may be configured to couple with an indexing feature  210  of the wing panel  550 , such as to initially align, and/or maintain alignment of, the strongback with the wing panel. Like the indexing features  210 , the indexing units  542  may take any suitable configuration, and may include coupling means other than to enable a mechanical coupling, such as magnets, and so forth. The indexing units may be configured to couple with a variety of different indexing features  210 , or indexing features that may vary in location from one wing panel  550  to another, for example to enable the strongback  540  to couple with different wing panels, as needed. 
     In  FIG.  5 A , the work stations  520  of assembly line  500 , are shown to include a non-destructive inspection or NDI station  524 , a cut-out station  526 , a rib install station  528 , and a spar install station  530 . These work stations, as well as the operations performed at each, as well as other illustrative work stations, are discussed in greater detail below. Other embodiments may include different work stations than those shown, work stations disposed in a different order, multiples of one or more types of work station, and so forth. For example, in some embodiments, a fastener sealing station is utilized to seal the wing, and work stations are also included for installing electrical components, electrical equipment, and/or fuel tank related systems. 
     As can be seen in  FIG.  5 A  and more clearly in  FIG.  5 B , during work at the various work stations  520  such as NDI station  524 , the wing panel  550  remains suspended beneath strongback  540  by carriers  545  (e.g., independently adjustable components such as telescoping carriers, also referred to herein as pogos) that include vacuum couplers  548 , which apply a removable vacuum connection to the wing panel in order to affix to the wing panel underneath the strongback  540 ). The view in  FIG.  5 B  shows four carriers  545 , three of which are shown to have their vacuum couplers  548  positioned against the upper surface  574  of the wing panel  550 , and one of which is shown to be in a shortened configuration so that its vacuum coupler  548  is spaced from the upper surface of the wing panel. Referring briefly to  FIG.  5 A  shows that a different number of carriers  545  are used for each of the three strongbacks  540  that collectively support wing panel  550 , with the carriers linearly disposed along the width of the wing panel. However, any number and/or configuration of carriers  545  may be used. The carriers  545  are aligned to each contact the wing panel  550  at a predefined location and height on the wing panel  550 . Each carrier is rigid, once set to a desired length. Accordingly, the carriers  545 , or more particularly the alignment of the carriers  545  relative to each other and their lengths relative to the wing panel  550 , may be arranged to impart forces which are transferred through the wing panel  550 , and enforce a desired contour  544  into the wing panel  550 . Thus, the strongback  540  suspends the wing panel  550  beneath it while enforcing a contour  544  onto the wing panel. This contour  544  may be that imparted to the wing panel by layup mandrel  110  (e.g., contour  112  as shown in  FIG.  1   ), or a different contour required for a specific application. Thus, while the strongback  540  advances along the track  510  in a process direction  541 , the contour  544  is enforced by holding each carrier  545  at a desired height, which forces a geometry at the wing panel  550  that corresponds with the contour  544 . 
     The attachment mechanism shown in the illustrated embodiment, as can be seen in  FIG.  5 B , is one in which carriers  545  engage with an upper surface  574  of the wing panel  550 , to form a vacuum grip between the vacuum couplers  548  of the carriers and the wing panel  550 . The length of the carriers  545  is controlled by actuators  546 , such as hydraulic or pneumatic actuators, or linear actuators. For example, one of carriers  545  is shown to be in the process of being shortened, as indicated by arrow  1000 . The carriers  545  may have their length adjusted, for example, before a vacuum attachment is formed (for example, in order to facilitate initial alignment for the vacuum couplers  548 ), and/or after vacuum attachment is formed (in order to bend the wing panel  550  into a desired shape and/or enforce a desired contour upon the wing panel). In some embodiments, actuators  546  are controlled via controller  620 . 
     Although the shape of the wing panel  550 , including the contour and curvature thereof, is determined during layup and hardening, contour enforcement and adjustment may be desired after the wing panel has been demolded. Contour enforcement, ensures that the wing panel  550  maintains a desired shape and does not assume an undesirable contour, such as from sagging under its own weight. In some embodiments, the contour enforced by strongback  540  and carriers  545  facilitates installation of ribs and spars onto the wing panels, such as by ensuring proper alignment between the component and the portion(s) of the wing panel to which the component is to be installed. Specifically, the carriers  545  enforce both chordwise and spanwise contours to a desired level of tolerance. In one embodiment (not shown), the carriers  545  are capable of moving relative to the strongback to predefined positions, in order to enforce contours for a variety of wing shapes. Moreover, the “upper surface”  574  to which carriers  545  attach, may be the exterior surface of a wing panel  550  that is oriented “right side up” relative to strongback  540 , or may be the interior surface of a wing panel that is inverted, according to whichever orientation is preferable for contour enforcement (and/or other operations as the wing panel  550  proceeds through the assembly line  500 ). 
     During the discussion of assembly line  500  and the operations performed by the various stations  520 , intermittent references will be made to various flowcharts presented in the drawings (e.g.,  FIGS.  6 - 10   ) that illustrate methods in accordance with the components and operations illustrated in  FIGS.  5 A- 5 G . For example,  FIG.  6    is a flowchart illustrating a method  800  of carrying a wing panel  550  in an illustrative embodiment. According to method  800 , step  802  includes aligning a strongback  540  over a wing panel  550 . In some embodiments, this comprises driving a strongback  540  along the track  510  until it is positioned over a desired and/or predetermined transverse portion of the wing panel  550 , such as a chordwise portion. In some embodiments, this comprises driving multiple strongbacks  540  until they are each positioned over different desired and/or predetermined transverse (e.g., chordwise) portions of the wing panel  550 . In one example, one strongback  540  may be moved along the track  510  until it is positioned over a different portion of the wing panel  550  than another strongback  540  that remains stationary. In some embodiments, aligning the strongback  540  is performed by, or includes, indexing the strongback  540  to the wing panel  550 . In some of such embodiments, this indexing is done by coupling the strongback  540  with one or more indexing features of the wing panel  550 , such as by physically coupling an indexing unit  542  of the strongback  540  with a corresponding indexing feature  210  of the wing panel  550 . Indexing the strongback  540  with the wing panel  550  in this manner may maintain the strongback and the wing panel in proper alignment, such as throughout the subsequent actions of the method. 
     Step  804  includes forming a vacuum attachment between an upper surface  574  of the wing panel  550  and vacuum couplers  548  of pogos  545  extending beneath the strongback  540 , thereby coupling the pogos  545  to the upper surface  574  of the wing panel  550 . In one embodiment, this comprises extending each of the pogos  545  until vacuum couplers  548  of the pogos physically contact the upper surface  574  of the wing panel  550 . In a further embodiment, the pogos are attached systematically from the middle of the wing panel  550  (e.g., chordwise or spanwise) and then moved outward, attached systematically starting with the pogo that is at a most out-of-contour location on the wing panel, or attached all at once, and so forth. 
     As described in greater detail below, the positions of the pogos  545  along the surface of the wing panel  550  may be determined by a variety of factors, one of which is the manner in which the pogos, and the stress and/or strain forces imparted thereby, can cooperate in different possible configurations to enforce the predetermined contour to the wing panel. There are, however, other competing factors. As one example, as detailed below, inspection of the wing panel  550 , such as via non-destructive inspection (NDI) scanning may require an NDI inspection head to be positioned at, or moved over, one or more specific locations on the wing panel  550 . Because the pogos can be selectively retracted, this can be accommodated either by temporarily retracting a pogo  545  to allow NDI inspection of the location on the wing panel  550  to which the vacuum coupler  548  is coupled, or by initially attaching the pogos to the wing panel only at locations that will not interfere with NDI inspection. As another example, attachment of ribs and spars to the lower surface  576  (e.g., an interior surface) of wing panel  550  may involve fastening operations (e.g. drilling) to occur at corresponding locations on the upper surface  574  of the wing panel. As such, the positions of the pogos  545  may be located so as not to interfere with such operations. Accordingly, the positions of the pogos  545  may optimize some or all of these (and/or other) considerations. 
     The coupling applied is the result of drawing a vacuum between the vacuum coupler  548  and the wing panel  550 , and more specifically a surface thereof, such as upper surface  574 . The amount of vacuum force applied over a portion of the wing panel  550  is sufficient to grip and hold the wing panel, and is also enough to flex the wing panel and hold it according to a desired contour  544 . Specifically, the volume between the carrier  545  and the wing panel  550  is evacuated to a pressure that permits the atmospheric pressure around the vacuum coupler  548  to cause the carrier  545  to removably adhere to the wing panel  550 . The vacuum remains applied via the carriers  545  during transport, including during pulses and pauses. 
     Step  806  includes adjusting lengths of the pogos  545  to enforce a predetermined contour onto the wing panel  550 . That is, after the vacuum attachment is formed, the length of the pogos  545  is adjusted (e.g., via pressure, actuators, etc.) to conform wing panel  550  with a desired contour  544 . In the illustrated embodiment, the pogos  545  are independently adjustable. That is, depending on a position of each pogo  545  along the length and width of the wing panel  550  (e.g., as determined via manual or laser-assisted processes), and depending on the desired contour, the pogo is adjusted to a desired length. If the wing panel  550  is already in conformance with the desired contour, then no adjustment or only minor adjustment to the length of one or more pogos  545  may be performed. Alternatively, if the wing panel  550  is not in conformance with the desired contour (e.g., not within tolerance), then adjusting the length of the pogos  545  bends or contours the wing panel (e.g., by applying a desired amount and direction of strain) in order to hold the wing panel in a desired shape. 
     In some embodiments, scanning is performed to determine an initial wing panel contour. It is possible that no changes in the contour need to be enforced if a wing panel  550  is already at a desired (e.g. predetermined) contour initially, either across the entire wing panel or one or more portions thereof. In some of such embodiments, adjustments to the length of each pogo  545  (i.e., longer or shorter) relative to the strongback  540 , push and/or pull the wing panel  550  into a desired contour. Adjustments to the length of each pogo  545  is based at least in part by a determination of the extent to which the wing panel  550  is out of alignment with the desired contour. That is, the length of some of the pogos  545  may require adjustment, whereas the length of others of the pogos  545  may not (e.g., if only some of the sections of the wing panel  550  are not aligned with the predetermined contour). The location of the vacuum couplers  548  of the pogos  545  are precisely located relative to the upper surface  574  of the wing panel  550  to ensure that when the pogos are at the desired length, the contour enforced by the pogos corresponds with expectations. 
     The length of the pogos  545  may be adjusted on the fly (e.g., by adjusting air logic applied to a pneumatic actuator controlling length, adjusting a hydraulic actuator controlling length, etc.) to align the pogos for establishing a vacuum attachment in a first phase (e.g., step  804 ), and then enforcing a contour in a second phase (e.g., step  806 ). This facilitates length adjustment during initial attachment because if the pogos  545  are set rigidly to a particular length based on an expected shape of the wing panel  550 , then the vacuum couplers  548  may not be able to form a vacuum attachment if the wing panel is out of contour (i.e., because the pogos are too long or short). 
     In some embodiments, scanning is performed to determine whether the wing panel  550  is in the predetermined contour. This may be done while the length of the pogos  545  are being adjusted, or after all of the pogos have been adjusted. 
     The method may then continue, for example to advance the wing panel  550  while the contour is enforced, such as by moving the strongback  540  along track  510  in a process direction  541 , and/or performing work on the wing panel while the contour is enforced, such as at the various stations  520 . In embodiments in which scanning is performed, the method may include contour scanning during or after work operations are performed, for example to ensure that the wing panel  550  remains in the desired contour—or, in other words, that the wing panel has not become out of alignment with the predetermined contour as a result of the work operations. 
     Returning to  FIG.  5 A , stations  520  disposed along the track  510  perform work on the wing panel  550 , and may all operate at the same time (or at overlapping times) as each other, or synchronized with one or more others, to perform different tasks at different sections of the wing panel  550  (e.g., in the wing root section  577 , mid length section  578 , wing tip section  579 , etc.). In this embodiment, NDI station  524  inspects the wing panel  550  for out-of-tolerance conditions (e.g., internal voids, foreign object debris or FOD, edge delamination or inconsistency, etc.), cut-out station  526  cuts access ports into the wing panel  550  (e.g. in manufacturing excess  554 ), rib install station  528  mounts ribs to the wing panel  550 , and spar install station  530  installs spars to the wing panel  550 . 
     In this embodiment, as will be explained in greater detail below, ribs are attached to the wing panel  550  during micro pulse advancement. This can comprise multiple work stations operating on each rib at once, or multiple work stations each operating on different ribs during the same period of time. The spars are later attached while the wing panel  550  is retained at a full pulse work station  520 . However, depending on the embodiment, the spars are attached before the ribs, or could be installed in a full- or micro-pulse process. The ribs are attached to the wing panel  550  and spar using either micro pulsed or full pulse assembly. Alternatively, the wing panel  550  is lowered into position over ribs which are then attached, and spars are pulsed to the wing panel  550 . 
     In one embodiment, the rib and spar installation processes are performed by providing ribs and spar segments in a JIT manner from parallel feeder lines, such as by means of feeder lines similar to continuous rib feeder line  491 - 7  and continuous spar feeder line  491 - 5 , respectively, as shown in schema  480  in  FIG.  4   . Feeder lines are individually shown in  FIG.  5 A  with a different reference number  570  (e.g.,  570 - 1 ,  570 - 2 , etc.). These feeder lines may be the same as, similar to, or different from, the various feeder lines  490  shown in schema  480 , in terms of the materials or components provided, the takt time according to which the feeder line provides materials or components, etc. In one embodiment, several spar segments may be coupled, e.g. end-to-end, to form a spar. In further embodiments, there are several rib install stations along with one or more fastener sealing stations and a plurality of spar install stations. Another embodiment has each spar comprising three segments that are spliced together at the ends of a rib. 
     The stations  520  are disposed along the track  510  and may be separated by less than the length of wing panel  550  or even a portion thereof. In one embodiment, such an arrangement enables multiple stations, such as NDI station  524 , cut-out station  526 , and rib install station  528 , to perform work on the wing panel  550  simultaneously or overlapping in time. In further embodiments, the stations are distanced and/or otherwise configured such that only one work station at a time performs work on the wing panel  550 . 
     As discussed in further detail herein, after proceeding through the work stations  520  shown in  FIG.  5 A , the wing panel  550  (which may be an upper wing panel, to which ribs and spars may be installed) enters a panel join stage, shown as panel join station  599  in  FIG.  5 F , that attaches another wing panel (which may be a lower wing panel) to form a completed section of airframe (e.g. a wing assembly) for a wing. The panel join stage operates alone (e.g., by itself on the entirety of the wing, without other stations operating) after a wing panel  550  halts at the panel join station  599  for fastening. In one embodiment, the pausing of the wing panel  550  at the panel join station  599  lasts while other wing panels are pulsed through the work stations, until the other wing panels have advanced by at least their entire length. 
     In the illustrated embodiment, feeder lines  570 - 1  through  570 - 6  correspond, at least in part, to feeder lines  491 - 7 ,  491 - 4 , and  491 - 5 . Feeder lines  570 - 1  through  570 - 6  provide resources and components on a just in time (JIT) basis to the various work stations  520  discussed above, and their operations are controlled and/or synchronized by controller  560  (or additional controllers  560 ) according to a desired takt time. In one embodiment, feeder line  570 - 1  corresponds at least in part to access port cover feeder line  490 - 5 , and provides newly fabricated access hole covers to cut-out station  526 . Feeder line  570 - 2  provides fasteners to cut-out station  526 . Feeder line  570 - 3  provides fasteners to spar install station  530 . Feeder line  570 - 4  provides sealant to spar install station  530 . Feeder line  570 - 5  provides fasteners to rib install station  528 , and feeder line  570 - 6  provides sealant to rib install station  528 . In further embodiments, additional/other feeder lines provide newly fabricated ribs, fasteners, and sealant spars, lower panels, etc. to various work stations. 
     In one embodiment, an upper wing panel proceeds through the work stations  520  shown in  FIG.  5 A , and is followed by a lower wing panel. As briefly noted above, the lower wing panel does not receive ribs or spars (i.e., because these components are already installed to the upper wing panel). As will become clear, cut-out stations, such as cut-out station  526 , perform a majority of the work on the lower wing panel, while a majority of work on the upper wing panel consists of installing ribs and spars. 
     Each station  520  in the assembly line  500  is designed to physically couple, to image, and/or to otherwise interact with an indexing feature  210  in the wing panel  550 , or with a strongback  540  that is itself physically coupled with an indexing feature  210 . The indexing features  210  are placed at desired locations along the wing panel  550 . In some embodiments, the indexing features are aligned along the wing panel  550 . In some embodiments, the indexing features are not aligned. In some embodiments, the indexing features are equally spaced, and in some embodiments, the indexing features are not equally spaced. In some embodiments, the number of indexing features is equal to the number of work stations in the assembly line. In some embodiments, there can be more or fewer indexing features  210  than work stations at the assembly line. The indexing features  210  are disposed in a manufacturing excess  554  of the wing panel  550 , which is trimmed away prior to a wing being assembled into an airframe for a fuselage. 
     In this embodiment, each of the stations  520  in the assembly line  500  inserts into, grasps, fits, or aligns to an indexing feature  210 . In addition to (or instead of) a physical (e.g. mechanical) coupling, indexing in some embodiments may be facilitated or accompanied by reading an RFID chip and/or other readable identifying means  126  (e.g., a bar code, etc.) on the wing panel. An illustrative example of a physical coupling is shown in  FIG.  5 B , which shows a section of the wing panel  550  within NDI station  524 . Among the various structural components of NDI station  524  is an upper NDI unit  602 , which includes an upper frame  614 . Upper frame  614  is shown to include an indexing unit  622 . In a manner similar to that described above with indexing unit  542  of strongback  540 , indexing unit  622  of the NDI station  524  physically couples with an indexing feature of the wing panel  550 , specifically by means of a head  624  that is received in indexing feature  210 - 2  located in a manufacturing excess  554 , with indexing feature  210 - 2  shown as a through-hole. Again, although only one indexing unit  622  is shown in  FIG.  5 B , each work station  520  may include any suitable number of indexing units  622 , each of which may be configured to couple with an indexing feature of the wing panel  550 , such as to initially align, and/or maintain alignment of, the wing panel with the work station. Like the indexing features, the indexing units  622  may take any suitable configuration, and may include coupling means other than to enable a mechanical coupling, such as magnets, and so forth. The indexing units may be configured to couple with a variety of different indexing features, or indexing features that may vary in location from one wing panel to another, for example to enable the work station(s) to couple with different wing panels, as needed. 
     In the illustrated embodiment, indexing feature  210 - 1  of the wing panel  550  is shown to be coupled to an indexing unit  542  of the strongback  540 , whereas indexing feature  210 - 2  is shown to be coupled to an indexing unit  622  of the NDI station  524 . This is intended to illustrate example indexing configurations for the sake of explanation, rather than to indicate that indexing a wing panel by means of a physical coupling to both the strongback and the work station is required to all embodiments. In some embodiments, one or more work stations index with a strongback supporting the wing panel instead of directly indexing with the wing panel. In some embodiments, one or more work stations index with the wing panel  550  instead of with a strongback  540 . In some embodiments, work stations index with both the wing panel and a strongback. In any of these embodiments, the strongback may also index with the wing panel. 
     When an RFID chip (or other readable identifying means) is used, for example in addition to or as an alternative to another type of indexing feature, an RFID scanner (or suitable reader) may couple to provide indexing when brought into communication at a work station. In further embodiments, the strongback  540  itself physically couples with the indexing features  210 , RFID chip, and/or hard stops or other features to index the strongback  540  to the work stations. During assembly, the strongback  540  is coupled with/mounted for movement along track  510 , and is pulsed (e.g., micro pulsed by less than a length of the wing panel  550 , according to a takt that may or may not be commonly shared with other assembly lines). In one embodiment, a limiting factor on takt is the amount of time a portion of the wing panel  550  spends within the purview of a particular work station, plus the pulse time. This time can be adjusted by changing the work scope of the particular work station, or adding additional work stations to do the same work (such as multiple rib install stations  528  as opposed to only one), and so forth. The pulses discussed herein may be implemented as a distance at least equal to the shortest distance between indexing features  210  (e.g., a pitch distance between ribs, or “rib pitch,” or a multiple or a fraction of a rib pitch, etc.) or full length or a fraction length of the wing panel  550 . In embodiments where pitch distance between ribs, and/or rib pitch, is used for pulse length, that can be used to establish a micro pulse length. The wing panel  550  can be continuously moved, and indexed to the work stations  520 . Once indexed, work is then performed by the work stations  520 . Whenever the indexing features  210  (and/or RFID chip) and the strongback  540  are mated or otherwise in communication, the strongback  540  is indexed to one or more of the work stations  520 , and the location of the wing panel  550  is indexed to a location in a coordinate space shared by the track  510  and known to the work stations. In a further embodiment, indexing also includes conveying a 3D characterization of structure, such as of contour  544 , within the purview of the work station. For example, an RFID chip or other readable identifying means  126  (e.g. a bar code) can convey information indicating a geometry of the composite part being worked upon. 
     In one embodiment, indexing is performed at least according to a wing panel  550  carried upon a strongback  540  that moves along a track  510  comprising a rail system located above the work stations  520 . The rail system could be coupled to a gantry or a structure above the work stations such as a ceiling or to the floor such as embedded within the floor, bolted to the floor, etc., or may be coupled to another portion of the factory. The wing panel  550  has been fabricated on a layup mandrel  110  according to precise dimensions as discussed above. Because the layup mandrel  110  has finely toleranced surface features, and because the preform  200  for the wing panel  550  was laid-up over and conformed to those surface features, the wing panel  550  includes indexing features  210  that are precisely located in a manufacturing excess  554 . Thus, once the wing panel  550  is indexed and suspended under the strongback  540  and advanced to a work station  520 , the 3D position and rotation of the wing panel  550 , including the contour  544 , is conveyed by indexing and is precisely known at the work station  520 . Indexing may thus remove the need, for example, for a full scan via probes or robust optical technology at each work station  520 . This information is provided to the work station  520 , as needed, as part of the indexing, for example, via information provided by an RFID chip. This allows one line to work in series on different parts for an aircraft, for example right and left upper and lower wing panels, or even on different parts (e.g., wing panels) for different aircraft models. Thus, the characteristics of the wing panel  550  within the purview of the work station  520  is conveyed to the work station as part of each pulse or micro pulse. As a wing panel has more variation from pulse location to pulse location than a fuselage panel, manufacturing excess at the wing panel may include a larger number of surface features to facilitate indexing. 
     Because of the precise indexing performed, the positions of the tools at each work station  520  relative to the wing panel  550 , when indexed to the work station, are precisely known. In some embodiments, the wing panel  550  is locked into place at the work station  520 . The 3D position and orientation of the wing panel is then established or indexed into any Numerical Control (NC) programming, or manual or automated system in use at the work station. Therefore, no setup time or scanning may be needed after each movement (e.g., pulse and/or micro pulse) of the wing panel. Furthermore, structure added to or removed from the wing panel  550  in the prior work station  520  may be added to whatever wing panel model or representation is within the system, without the need to scan the wing panel for changes. 
     The operations of the work stations  520  are managed by a controller, generally indicated in  FIG.  5 A  as controller  560 . In one embodiment, controller  560  determines a progress of the strongback  540  along the track  510  (e.g., based on input from a technician), and uses this input to manage the operations of the work stations in accordance with instructions stored in an NC program. Controller  560  may be implemented, for example, as custom circuitry, as a hardware processor executing programmed instructions, or some combination thereof. 
     The following paragraphs discuss the operations of the various work stations  520  shown in  FIG.  5 A . As shown in  FIG.  5 A , in assembly line  500 , three work stations  520 —specifically, NDI station  524 , cut-out station  526 , and rib install station  528 —are disposed along track  510  in close enough proximity so that a wing panel  550  may encounter all three work stations as it progresses in process direction  541 . More specifically, given the span-wise  590  length of wing panels  550  from leading edge to trailing edge (e.g., a wing tip to a wing root, as oriented in the illustrated embodiment), different portions of a wing panel may proceed through two or more different work stations  520  at the same time. For example, wing panel  550  is shown positioned such that a trailing portion of the wing panel, shown as wing root section  577 , encounters NDI station  524  at the same time that a leading portion, shown as a wing tip section  579 , encounters rib install station  528 , and a middle portion, shown as mid length section  578 , encounters cut-out station  526 . As such, one, or two, or all three of these work stations  520  may perform operations on the respective portion(s) of wing panel  550  at the same time, or overlapping in time. In some embodiments, not all of these operations are necessarily performed at the same time, even though portions of the wing panel  550  are positioned in each work station  520 . In one embodiment, NDI is performed at NDI station  524  as portions of the wing panel  550  are pulsed through the work station. Thus, NDI occurs within NDI station  524  on only that portion of the wing panel  550  within the work station at any one time. 
       FIG.  5 B  is a front view of NDI station  524  (and, as noted above, corresponds with view arrows “ 5 B” in  FIG.  5 A ), which is shown in the process of inspecting a wing panel  550 , with wing panel  550  shown in cross section, in the illustrative embodiment.  FIG.  5 B  illustrates inspection techniques and systems that may be implemented, for example, prior to installation of ribs and spars onto the wing panel.  FIG.  5 B  depicts a strongback  540  that suspends a wing panel  550  beneath it. The NDI station  524  is disposed at the track  510 , and inspects the wing panel  550  while the wing panel  550  is suspended beneath the strongback  540 . 
     The NDI station  524  shown in  FIG.  5 B  includes an upper NDI unit  602  and a lower NDI unit  604 . Upper NDI unit  602  includes supports  612  and a frame  614  that carry one or more NDI inspection heads  606 , shown as upper NDI inspection head  608 , which is configured to move relative to wing panel  550  and inspect the upper surface  574  thereof. Lower NDI unit  604  of NDI station  524  is also shown to include a frame  618  and supports  616  that carry additional NDI inspection heads  606 , shown as lower NDI inspection heads  610 , in a manner than allows the inspection heads to inspect the lower surface  576  of the wing panel  550 . For simplicity, NDI inspection heads  606  are also referred to as “inspection heads,” or simply “heads.” Inspection heads  606  may be mobile—that is, they may be configured to move relative to the upper NDI unit  602 , the lower NDI unit  604 , and/or the wing panel  550 , or they may instead be stationary or fixed. For example, in the illustrated embodiment, upper inspection head  608  is shown, via directional arrow  1002 , to be in the process of moving relative to the upper surface  574  of wing panel  550 , as enabled by a track and/or a drive or any suitable mechanism (not shown) of the upper NDI unit  602 . Some or all of lower inspection heads  610  may also be mobile, in which case they may be independently moveable, configured to move in unison as an array, and so forth, or they may be stationary. Further embodiments may include any number or configuration of inspection heads other than as shown in  FIG.  5 B . Mobile inspection heads may be used for surface inspection during pauses between advancements or other movements of the wing panel  550  relative to the NDI station  524 , such as by individually traversing distinct areal portions of a surface of wing panel  550 . Fixed inspection heads may be used for surface inspection as the wing panel  550  pulses or otherwise moves relative to the NDI station  524 . For efficiency, the arrangement of inspection heads  606  relative to NDI station  524 , and/or to the position(s) of the wing panel  550  as it advances through the work station  520 , may be one that disposes the inspection heads at locations of interest, for example at locations where out of tolerance conditions are more likely to be found, such as those for which inspection of prior wing panels and/or analysis of prior wing panels indicates a need or desire for inspection, and are not placed where there is less need for inspection. Other arrangements of inspection heads may be used as desired or needed for a particular application. Some embodiments may include upper and lower inspection heads disposed in pairs, on either side of the wing panel  550 , such as to carry out through-transmission inspection techniques. In some embodiments, inspection heads  606  are disposed to inspect an entire surface, or surfaces, of the wing panel  550 . For example, in a further embodiment, fixed NDI inspection heads are placed such that the inspection occurs during the pulse, and the inspection heads are disposed in order to cover the entire surface without the need for head movement. This set up can be employed on both the upper and lower surfaces and can be implemented with less complexity than systems which utilize mobile heads. The inspection heads  606  discussed herein may comprise ultrasonic transducers that transmit ultrasonic energy through the wing panel  550  in order to characterize internal features of the wing panel. The operations of the inspection heads  606  (e.g., both the upper inspection heads  608  and lower inspection heads  610 ) are managed by a controller, shown at  620 , which operates an NC program to coordinate the actions of the inspection heads to facilitate scanning of the wing panel  550  in a pulse-echo or through-transmission mode. Controller  620  may interface with, and be distinct from, controller  560 . In some embodiments, controller  560  may provide the aforementioned functions of controller  620 . 
     As noted above, NDI station  524  is shown in the illustrated embodiment to be physically indexed to the wing panel  550  by means of indexing unit  622  of the NDI station, the head  624  of which is received within indexing feature  210 - 2  of the wing panel  550 . 
     Strongback  540  includes telescoping or adjustable-length carriers or pogos  545  which include vacuum couplers  548  configured to removeably attach to upper surface  574  of the wing panel  550 —forming a vacuum grip between the vacuum couplers  548  and the wing panel  550 . As noted above, the length of the carriers  545 , such as to impart or enforce a contour to wing panel  550 , is controlled by actuators  546 , such as hydraulic or pneumatic actuators, or linear actuators. Controller  620  may coordinate the control of actuators  546 . In some embodiments, controller  620  coordinates control of actuators  546  with the operation of NDI station  524 , such as to allow inspection of the wing panel  550  in a manner that avoids or accommodates vacuum couplers  548  coupled to the wing surface. In one such embodiment, the controller  620  directs the strongback  540  to selectively retract one or more of the vacuum couplers  548  by shortening corresponding carriers  545  to allow inspection head  608  of the NDI station  524  to inspect portions of the upper surface  574  of the wing panel  550  (such as portion  582 ) to which vacuum couplers  630  had been attached. This is shown in  FIG.  5 B  with the coordinated shortening of one of carriers  545  to retract its vacuum coupler  548  from portion  582 , indicated by directional arrow  1000 , with the movement of upper inspection head  608  toward portion  582 , as indicated by directional arrow  1002 . When the NDI inspection of, for example, portion  582  is completed, the corresponding carrier  545  is extended such that its vacuum coupler  548  is again vacuum connected to the upper surface  574  of the wing panel  550 . In a similar manner, other portions of the upper surface  574  of wing panel  550  that are obscured by a vacuum coupler  548  may be systematically inspected. Of course, such a configuration is not required to all embodiments. For example, in further embodiments, the inspection heads  606  are routed around the carriers  545  and vacuum couplers  548 , which are not retracted during NDI inspection. In further embodiments, the contour of wing panels  550  vary from type of wing panel, or of wing panel for different models, and the carriers  545  are therefore extended to different positions/extensions depending on the contour of the wing panel. 
     In further embodiments where a strongback  540  is used, inspecting locations on the wing panel  550  that contact the strongback (e.g., by means of pogos  545  and vacuum couplers  548 ) via NDI is performed prior to suspending the wing panel beneath the strongback. 
       FIG.  7    is a flowchart illustrating an embodiment of method of inspecting a wing panel, designated as method  820 . Method  820  progresses in a series of steps that include actions described with reference to the components and structure shown in  FIG.  5 B , as well as in  FIGS.  1 - 4  and  5 A . Method  820  is shown to begin with step  822 , which includes suspending a wing panel  550  beneath a shuttle, such as strongbacks  540 . In one embodiment as discussed above, suction is applied via the retractable vacuum couplers  548  to hold the wing panel  550  in position and to enforce a desired contour  544  onto the wing panel  550 . Specifically, the vacuum coupling of a vacuum coupler  548  along with the inflexibility of the strongback  540  and the extendability of pogos  545  allows contour enforcement to be performed on the wing panel  550 . The pogos  545  are removably coupled to the wing panel  550  in order to manipulate it into a desired contour. 
     Step  824  includes advancing the wing panel  550  in a process direction through an NDI station  524  via the shuttle. In embodiments in which the shuttle is a strongback  540 , this includes driving the strongback  540  along a track  510  as described above for earlier methods, and may be performed via pulsed or continuous movement techniques. In embodiments in which the shuttle takes another form, e.g. a cart, an Autonomous Guided Vehicle (AGV), and so forth, this step comprises driving the shuttle along a rail or appropriate pathway. 
     Step  826  includes inspecting the wing panel  550  via the NDI station  524  while the wing panel  550  is suspended beneath the strongback  540 . In one embodiment, this includes performing pulse-echo techniques (e.g., via one or more individual inspection heads  606 ), or through-transmission techniques (e.g., via pairs of inspection heads  606  arranged on either surface of the wing panel  550 ). These arrangements detect differences in timing from expected values as ultrasonic energy travels through the thickness of the wing panel  550 . This may comprise operating an array of inspection heads  606  at the NDI station  524  at once. Detected differences in timing are analyzed by the controller  620  to determine whether or not an out-of-tolerance condition exists that necessitates rework of the wing panel  550 . Rework may be accomplished at a dedicated work station downstream of the NDI station  524 . That is, controller  620  detects out-of-tolerance conditions at the wing panel  550  based on input from the NDI station  524 , and reports the out-of-tolerance conditions for rework (e.g., via a notification provided to a technician). In a further embodiment, the controller  620  controls the NDI station  524 , and controls advancement of the wing panel  550  in the process direction, and relates input from the NDI station to locations on the wing panel  550 . 
     As noted above, in some embodiments, inspection involves selectively retracting one or more vacuum couplers  548 , such as by the strongback  540 , as one or more inspection heads  606  inspects a surface of the wing panel, such as to allow inspection of the corresponding portions of the surface otherwise obsctructed by the vacuum couplers. In further embodiments inspection is performed by arranging carriers  545  and/or otherwise placing vacuum couplers  548  at locations on the surfaces of wing panel  550  where NDI inspection is not required, by inspecting locations on the wing panel that contact the strongback  540 —such as the aforementioned portions to which the vacuum couplers  548  connect—via NDI prior to suspending the wing panel beneath the strongback, and/or by operating an array of inspection heads  606  to enable an entirety of inspection to be performed without requiring single inspection heads to be moved, and so forth. 
     As also noted above, the NDI station  524  may include NDI inspection heads  606  that are mobile, or fixed, or a combination thereof. In some embodiments, the method includes disposing at least some of the inspection heads at locations of interest, such as those for which prior inspection and/or analysis indicates a need or desire for inspection. In some embodiments, the inspection heads are located in order to enable the inspection of the entirety of a desired portion of the wing panel  550  (such as one or more entire portions thereof, or the entire wing panel). In some embodiments in which the NDI inspection heads are fixed, advancing the wing panel  550  includes advancing the wing panel past the fixed inspection heads as they inspect the portion of the wing panel. In such embodiments, it may be said that step  824  and step  826  take place at the same time, or overlap in time. In some embodiments in which the NDI inspection heads are mobile, advancing the wing panel  550  includes advancing the wing panel past the mobile inspection heads. In some of such embodiments, such as those in which advancing the wing panel  550  includes pulsing the wing panel in a process direction, the inspection is performed during pauses between the pulses and/or during the pulses. In some embodiments that include an array of inspection heads, the method includes moving the inspection heads relative to the wing panel  550  while operating the array. In any of these manners, the NDI station  524  inspects a portion of the wing panel  550  at a time, as it is advanced through the NDI station. 
     The position of the wing panel  550  relative to the NDI station  524 , in some embodiments, is monitored by indexing the wing panel to the NDI station, such as by means of various indexing features and/or RFID chips, as noted above. In some embodiments, the indexing of the wing panel to the work station, either directly or via a strongback supporting the wing panel, conveys information about the wing panel to the NDI station controller, which in turn may direct NDI inspection of the wing panel based at least in part on this information. In some embodiments in which the indexing features are located in a manufacturing excess of the wing panel, the manufacturing excess is typically not inspected. 
     In some embodiments, the method continues with additional steps that are not shown in  FIG.  7   . For example, the method may continue by advancing the wing panel to the next work station (e.g., a cut-out station such as cut-out station  526 , and so forth). In embodiments in which the wing panel is suspended beneath a strongback, such a method may advance the wing panel to the next work station while the wing panel remains suspended beneath the strongback. Some embodiments utilize multiple NDI stations for inspection, and some embodiments utilize the NDI station (or more than one NDI station) for NDI inspection of additional components. For example, in some of such embodiments, an NDI station scans stiffener flanges while scanning the wing panel, and additional NDI stations scan stringers attached to the wing panel. 
     Above, it is noted that in some embodiments, NDI inspection is performed as the wing panel is advanced past NDI inspection heads. This may be done regardless of the manner of conveyance of the wing panel (e.g., via a strongback or otherwise).  FIG.  8    further depicts a method  840  of inspecting a wing panel  550  in an illustrative embodiment. According to  FIG.  8   , step  842  includes receiving a wing panel  550  at an NDI station  524 . Step  844  includes inspecting a portion of the wing panel  550  via the NDI station  524  during movement of the wing panel through the NDI station. The wing panel may be pulsed or advanced continuously through the NDI station, with inspection taking place during movement of the wing panel through the NDI station. As with method  820 , in method  840 , the NDI station may include mobile and/or fixed NDI inspection heads. In one embodiment the wing panel remains suspended beneath the strongback while the wing panel is at the NDI station. In a further embodiment, mobile inspection heads of the NDI station individually traverse distinct areal portions of the wing panel via mobile inspection heads of the NDI station. In this manner, inspection includes moving inspection heads relative to the wing panel while operating the array of inspection heads at NDI station. 
     Returning to  FIG.  5 A , mid-length section  578  of wing panel  550  is shown to be within cut-out station  526 . Broadly, cut-out station  526  is configured to remove material from wing panel  550 , for example within manufacturing excess  554  or otherwise. In some embodiments, cut-out station  526  cuts out one or more regions of wing panel  550 , for example to install an opening such as an access port that will be utilized in a work station downstream, such as to provide access to the interior volume between wing panels after they have been joined together at a join station. Although not necessary to all embodiments, such access ports are typically installed in lower wing panels, as opposed to upper wing panels. As will become clear herein from the discussion relating to shimming operations (e.g., as shown and described with respect to  FIGS.  16 A- 16 C and  17 A- 17 C ), in some embodiments, a lower wing panel is provided with several access ports that provide access to bays between adjacent ribs, for example to facilitate shim installation by a robot arm. Thus, in such embodiments, cut-out station  526  may perform more work operations on a lower wing panel than on an upper wing panel. In either case, cut-out station  526  may install access port covers and/or doors into the wing panel  550 , along with edge sealing, painting, and performing fastener drilling and installation, as suitable for the wing panel. In some embodiments, edge trimming of the manufacturing excess, and trimming of an access port, are performed at different work stations. 
     The terms “upper surface” and “lower surface” of wing panel  550  are used herein for convenience to indicate the relative orientations of the opposing surfaces of the wing panel as it is suspended below the strongback  540 , in the illustrated embodiment. However, as will become clear herein, additional components (such as ribs and spars) may be installed to the lower surface  576  of wing panel  550  as the upper surface  574  thereof continues to be held by vacuum couplers  548  of pogos  545 , to produce a wing assembly  600 . As such, the surface indicated in  FIGS.  5 A- 5 G  as lower surface  576  of the wing panel  550  becomes what may be thought of as an interior surface of a wing assembly  600 , whereas the surface indicated as upper surface  574  of the wing panel  550  becomes what may be thought of as an exterior surface of a wing assembly  600 . Accordingly, the terms “upper surface” and “lower surface” are not to be construed in a limiting sense. 
       FIG.  5 C  corresponds with the top view of assembly line  500  shown in  FIG.  5 A , but showing the strongback  540  as having advanced in the process direction  541  so that the wing root section  577  of wing panel  550  is within rib install station  528 . Some aspects of  FIG.  5 A  (e.g., various feeder lines, and so forth) are not shown in  FIG.  5 C , for simplicity.  FIG.  5 D  shows a simplified side view corresponding with view arrows “5D” of  FIG.  5 C , with some components that are visible in  FIG.  5 C  omitted to better illustrate the ongoing construction/progress of the wing panel  550  into a wing assembly  600 . As noted above, rib install station  528  affixes (that is, temporarily and/or permanently installs) ribs  572 . Ribs  572  are shown in these views in simplified form for ease of explanation, although they are often more complex in configuration and appearance, as described in greater detail in sections below. 
       FIG.  5 C  also shows, in spar install station  530 , that spars  580  have advanced from feeder lines (not shown) to the station  530 . As noted above, the supply of spars  580  to the spar install station  530  may be coordinated as just-in-time delivery for installation to a wing panel. Accordingly,  FIG.  5 C  may show a state of assembly line  500  just before wing panel  550  is moved to spar installation station  530  for installation of the spars  580 , which have just been supplied to the station. 
       FIG.  5 C  further illustrates the use of a mobile station  552  (also called a “follower”), which is configured to couple to the wing panel  550  and strongback  540  and perform work (such as trimming, installing fasteners, applying sealant, etc.) by traveling across the wing panel  550 , for example along a mobile station track  551  that may be removably installed onto the wing panel  550 . Although not required to all embodiments, mobile station  552  may perform the work during pulses (e.g., micro pulses), pauses (e.g., between micro pulses), or continuous motion of the wing panel  550  as it progresses through the assembly line  500 . Depending on design, the mobile station  552  can “ride along” with (or “follow”) the wing panel  550  for multiple pulses across multiple work stations  520 , and can operate independently of the other work stations of the assembly line  500 . During this process, the location and dimension of gaps (e.g. spacing) between strongbacks  540  enable placement of the mobile station track  551  and/or mobile station  552 . In further embodiments, chutes and other complementary elements are disposed at the factory such that mobile station  552  passes over or though these elements during fabrication processes. Mobile station  552  may be removed along a return line, shown in  FIG.  5 C  at  547 , and sent, e.g. in a direction opposite the process direction  541  (e.g., upstream in assembly line  500 ) to be installed on a next wing panel as desired. In further embodiments, one or more of strongbacks  540  form a “smart bridge” by dynamically moving relative to the wing panel  550 , in order to provide greater access to the wing panel  550  by the mobile station  552 . 
     As noted above,  FIG.  5 D  is a simplified side view of a portion of assembly line  500 , showing wing panel  550  with attached ribs  572  being transported along track  510  while suspended below a set of three strongbacks  540 . As briefly noted above, one or more adapters  543  may facilitate the movement of strongbacks  540  along the track  510 . The ribs  572  are attached to a lower surface  576  of the wing panel  550  at a suitable angle, indicated as angle θ. As will be explained below, in some embodiments, ribs  572  are aligned vertically and raised into position for attachment to the lower surface  576  of the wing panel  550  (or, more specifically, an upper wing panel). As such, the wing panel may be suspended below the strongback(s) at an angle that corresponds to and/or facilitates the rib installation at angle θ. This is shown in  FIG.  5 D  with the wing panel  550  tilted slightly upward from the wing root section  577  to the wing tip section  579 . 
       FIG.  5 D  also provides another view of an illustrative configuration of pogos  545  and vacuum couplers  548 . In the illustrated embodiment, the vacuum couplers  548  are capable of angular deflection relative to the pogos  545  and strongback  540 . The angular deflection may be facilitated by a universal type joint, either at the point at which vacuum coupler  548  is coupled to the pogo  545  and/or at the point at which the pogo  545  is coupled to the strongback  540 . The angular deflection may accommodate coupling to wing panel  550  during contour changes in the wing panel, to suspend the wing panel at a desired angle (as shown), and so forth. Owing to the angular flexibility of the vacuum couplers, by adjusting the pogos to appropriate lengths, the wing panel may be suspended at any desired angle. In further embodiments, otherwise-configured carriers  545  grip an upper surface  574  of the wing panel  550  (e.g., via clamping, interference fits, etc.). As explained in detail above, a desired contour can be enforced by adjusting the pogos  545  to predetermined lengths, which correspond with a desired vertical loft of the contour at each of multiple chordwise and spanwise locations. 
     As noted above, several factors may determine the positions of pogos  545 , and their respective vacuum couplers  548 , relative to the upper surface  574  of the wing panel  550 , such as to enforce a contour to wing panel  550 . In some embodiments, one factor is the manner in which ribs and spars are attached to the wing panel. For example, the pogos  545  and vacuum couplers  548  may be placed so that the positions of the vacuum couplers  548  on the upper surface  574  are spaced away from the corresponding positions on the lower surface  576  of the wing panel where ribs  572  will be attached to the wing panel (as in the view shown in  FIG.  5 D ). This may be done, for example, to allow fabrication access to the rib  572  install area, and can facilitate either manual or automated drill and fastener installation connecting ribs to wing panels. 
     In  FIG.  5 D , one rib  572  is shown attached to the portion of wing panel  550  that is within rib install station  528 . Other ribs  572 , which are shown attached to the portions of wing panel  550  that have advanced past rib install station  528 , were installed when those portions were within rib install station  528 . Although four are shown, the number of ribs  572  may be, and often are, greater in an actual wing assembly  600 . The wing panels, ribs, spars, and other components shown in  FIG.  5 D  and the other drawings are for illustration purposes only and are not necessarily to scale or contour. For example, ribs  572  are shown in simplified, schematic form in this series of drawings. Later drawings, such as  FIGS.  11 A- 11 D  and  FIGS.  17 A- 17 C , show illustrative ribs in greater detail. The rib configuration or number of ribs  572  of an actual wing assembly  600  may vary from that depicted herein. 
       FIG.  5 E , a top view of assembly line  500  corresponding to those in  FIGS.  5 A and  5 C , illustrates the wing panel  550  having been transported via strongbacks  540  to spar install station  530 , wherein spars  580  are attached (e.g., as part of a full-pulse process). In this embodiment, the spars  580  are installed after the ribs  572 , but in some embodiments the ribs  572  are installed prior to the spars  580 . Also,  FIG.  5 E  shows each spar, generally indicated at  580 , as having been assembled from a number of individual spar segments, each separately indicated as  580 - 1  through  580 - 7  (however, unless specifically indicated otherwise, reference number  580  is used herein to refer to spars, as well as spar segments or spar sections). Spar install station  530  may receive preassembled spars  580 , or individual spar segments or sections (e.g.,  580 - 1  through  580 - 7 ) that are assembled at the spar install station, or both, from one or more feeder lines  570  (a representative one of which is shown in  FIG.  5 E ). In embodiments in which spar segments are provided to spar install station  530 , the spar segments may be assembled to each other prior to installation to the wing panel, for example to form a partial or whole spar that is then installed to the wing panel, and/or the spar segments may be installed as spar segments to the wing panel, forming a spar as they are separately installed. Additional components such as fasteners, sealant, and so forth are also supplied to spar install station  530  to facilitate installation. After installation, the strongbacks  540  transport the wing panel  550  back to track  510 , and the wing panel  550  is further transported to receive additional work. In the illustrated embodiment, the strongbacks  540  progress to spar install station  530  in any suitable manner, such as a redirect track (not shown) configured to allow movement to spar install station  530  in direction  1004 . After installation, the strongbacks may either progress in direction  1006  back to track  510  via the same redirect track, for example for further progress along track  510  (e.g. toward a panel join station), or are directed to another track, or progress along a track other than track  510 . Another embodiment has spar install station  530  disposed along track  510  so that advancement of a strongback  540  in the process direction brings a wing panel into, through, and out of the station. 
     The illustrated configuration is an example of a configuration that may allow a work station  520 , such as spar install station  530 , to be selectively bypassed. As noted above, in some embodiments, ribs and spars are attached only to upper wing panels, and not to lower wing panels. In such embodiments, efficiency in transporting and/or performing work on wing panels may be achieved in a configuration that may allow one or more work stations  520  to be selectively bypassed, such as with upper wing panels being advanced into the spar install station  530 , but with lower wing panels being advanced past the station. In some of such embodiments, the lower wing panels may instead be directed to a work station configured for work specifically on lower wing panels, and not on upper wing panels, such as a work station that cuts access ports into the lower wing panel (for example, a work station such as cut-out station  526 ). In these embodiments, additional spars and/or spar segments are then fed to spar install station  530  for attachment to a next wing panel  550  traveling along the track  510 . 
       FIG.  5 F  illustrates an embodiment wherein, after work is complete at spar install station  530 , wing panel  550  has been moved in direction  1006  back to track  510 , and is ready to be advanced (in a pulsed or continuous fashion) in a process direction  541  along track  510  to further work stations  520 , shown as a rib-to-spar attach station  598 , and a panel join station  599 , at which a lower wing panel may be joined to an upper wing panel to which ribs and spars have been attached. This operation results in a wing assembly  600  awaiting installation of, for example, further components, and/or electrical and other systems. 
     In  FIG.  5 F , rib-to-spar attach station  598  is shown to be disposed on track  510 , whereas panel join station  599  is shown to be disposed off track  510 , requiring movement of the wing panel  550  in direction  1008  to the panel join station  599 . This may represent a configuration in which only upper wing panels proceed along this portion of the assembly line  500 , with lower wing panels having been redirected to another track (not shown) or station, for example, by bypassing spar install station  530  and rib-to-spar attach station  598 , and instead being delivered to panel join station  599  to await joining to an upper wing panel. Or, a lower wing panel may simply be transported through rib-to-spar attach station  598  without any work operations performed on it, thus effectively bypassing it. Or, in some embodiments, one or more work stations  520  may be configured to have multiple purposes, for example to perform certain work operations on, for example, upper wing panels, and other work operations on lower wing panels. Such configurations are within the scope of this disclosure. 
     In accordance with the concepts, components, systems, and apparatus discussed above relative to  FIGS.  5 A- 5 F , it is evident that other embodiments of an assembly line  500  that are consistent with this disclosure may take other configurations than those specifically illustrated and described. For example, some embodiments may produce a wing assembly using a different order of operations of joining wing panels, ribs, and spars, and thus may include some or all of the various work stations  520  in a different order, or include work stations other than those shown, or multiples of work stations  520 , or work stations that perform some or all of the functions of work stations  520  in addition to other tasks, and so forth. In some of such embodiments, instead of spars and ribs being individually installed to a wing panel (such as an upper wing panel), as in the illustrated embodiments of assembly line  500 , spars and ribs may instead be attached to each other, to form a ladder-like structure (with the spars as the “rails” of the ladder and the ribs forming the “rungs” thereof), which is then installed to a wing panel. Accordingly, such embodiments may include one or more work stations that assemble spars to ribs (to which may be supplied ribs, spars or spar sections, and fasteners, from appropriate feeder lines), and one or more work stations that install the rib-and-spar structure to the wing panel, and/or install the rib-and-spar structure between an upper wing panel and a lower wing panel. As with the illustrated embodiment of assembly line  500 , the various components and structures supplied to the aforementioned work stations may be configured for JIT delivery to the appropriate work station. 
     An example of this is shown in  FIG.  5 G , which shows an alternative configuration of an assembly line, indicated as assembly line  500 ′.  FIG.  5 G  generally corresponds with the top view of assembly line  500  shown in  FIGS.  5 C and  5 E . However, whereas the assembly line configuration shown in  FIGS.  5 C and  5 E  includes a rib install station  528  and spar install station  530 , at which ribs  572  and spars  580 , respectively, are individually and separately installed to wing panel  550 , the assembly line  500 ′ shown in  FIG.  5 G  instead is shown to include different work stations  520 ; specifically, a support structure assembly station  532 , and a support structure install station  534 . Support structure assembly station  530  is supplied with ribs  572  and spars  580 , and fastening and/or sealing supplies, from one or more feeder lines  570  (a representative one of which is shown in  FIG.  5 G ). For example, feeder lines corresponding to  491 - 6  and  491 - 7 , as shown in  FIG.  4   , may provide spars and ribs, respectively, just in time and in the desired order to support structure assembly station  532  for assembly into a ladder-like support structure indicated at  588 . Spars  580  may be preassembled or complete prior to provision to support structure assembly station  532 , or may be provided thereto in the form of separate spar segments or sections (not individually shown) for assembly with ribs  572  into support structure  588 . 
     When assembled, support structure  588  is transported (e.g., laterally) into support structure install station  534 , as indicated by arrow  1014 , and installed to wing panel  550 . A cart or other manner of shuttle may transport the support structure  588 , which may then be raised upward to the wing panel for installation. Alternatively or additionally, the wing panel may be lowered to the support structure  588 . Although not shown in the view of  FIG.  5 G , fasteners and other supplies may be provided to support structure install station  534  together with the support structure, or separately via one or more feeder or supply lines. As such,  FIG.  5 G  may show a state of assembly line  500 ′ just before a completely assembled support structure  588  is delivered to support structure install station  534  for installation to a waiting wing panel  550 . The movement of wing panel  550 , via strongback  540  along track  510 , may be coordinated with the provision of an assembled support structure  588 , so that both the wing panel  550  and the support structure  588  are delivered to support structure install station  534  at the same time, or one or the other may be provided just-in-time for installation, and so forth. 
     The wing panel  550 , with a support structure  588  of ribs  572  and spars  580  installed thereto, may proceed to a panel join station (such as panel join station  599  shown in  FIG.  5 F ) so that another wing panel, such as a lower wing panel, may be installed to the assembly. The alternative configuration discussed above with respect to  FIG.  5 G  may offer advantages over the configuration shown in assembly line  500 , for example by not involving transporting a wing panel laterally relative to track  510  in order for spar installation to take place (as shown in FIG.  5 E), or by achieving efficiency in installing ribs and spars together rather than separately, and so forth. 
     With reference to the various components of and concepts and operations embodied in, assembly line  500  presented in  FIGS.  5 A- 5 G  and described above,  FIG.  9    is a flowchart illustrating a method  860  of fabricating a wing via an assembly line, such as assembly line  500 , in an illustrative embodiment. In step  862 , a wing panel  550  is suspended beneath a shuttle, such as strongback  540 , that enforces a contour  544  onto the wing panel  550 . For example, in one embodiment the carriers  545  are affixed to the wing panel  550  via vacuum couplers  548 , and are vertically positioned to enforce the contour. As described above, in some embodiments, suspending the wing panel  550  includes indexing the strongback  540  with the wing panel. The indexing may be a physical coupling (e.g., physically attaching to, or otherwise establishing a link with) between the strongback  540  and one or more indexing features installed in the wing panel  550 , for example in a manufacturing excess of the wing panel  550 . Additionally or alternatively, the indexing feature may consist of or include readable identifying means, such as an RFID chip/tag or a bar code, and indexing includes reading the id identifying means with a suitable reader, such as an RFID reader, a scanner or bar code reader, and so forth (not shown). 
     In step  864 , the wing panel  550  is advanced in a process direction, such as process direction  541 , through at least one work station  520  (and usually multiple work stations  520 ) in an assembly line  500  via the strongback  540  while the contour  544  (e.g., as defined by upper surface  574  of  FIG.  5 B ) is enforced. For example, the strongback  540  may be advanced along the track  510  while vacuum couplers  548  of the carriers  545  to the wing panel  550  are disposed at vertical positions that correspond with the contour  544 . As noted above, enforcing a desired contour may be performed by aligning carriers  545  that each contact the wing panel at a predefined location on the wing panel, and during this process, the wing panel  550  may advance through an NDI station such as NDI station  524 , which performs NDI on the wing panel. During pauses between pulses, or during continuous motion, the wing panel  550  is indexed to the various work stations  520 . This can be performed by indexing the work stations  520  to the indexing features  210  of the wing panel  550  itself, such as described above with respect to indexing the strongback  540  to the wing panel, or by indexing the work stations  520  to indexing features of the strongbacks  540  carrying the wing panel  550 . 
     In step  866 , structural components such as ribs  572  and spars  580  are installed into the wing panel  550  while the contour  544  is enforced (by the combination of strongback  540 , carriers  545 , and vacuum couplers). This may comprise co-bonding and/or fastening the ribs  572  and spars  580  to the wing panel  550  while the wing panel  550  remains suspended from the strongback  540 . Or, it may involve assembling ribs  572  and spars  580  into a support structure  588 , which is then installed to the wing panel  550  while the wing panel remains suspended from the strongback. In one embodiment, advancing the wing panel  550  comprises pulsing (e.g., by full-pulse, or micro pulse) the wing panel in a process direction, and installation of ribs  572  and spars  580  is performed during pauses between the pulses. In a further embodiment, advancing the wing panel  550  comprises continuously moving the wing panel in a process direction, and installation of ribs  572  and spars  580  is performed while the wing panel continuously moves. 
     Although not specifically shown in  FIG.  9   , in some embodiments, method  860  further includes additional operating work stations  520  arranged along the process direction to perform a variety of different work operations, such as installing ribs and/or spars, joining ribs and/or spars to each other and/or to the wing panel, performing rework, inspecting the wing panel, cutting/installing access ports, and so forth. In some embodiments, multiple work stations  520  are provided to perform the same type of operation. 
     Method  860  may provide one or more technical benefits over prior techniques, for example because it enables a wing panel  550 , or a portion thereof, to remain indexed to each of the work stations  520  in a fabrication environment, even as the wing panel is transported through multiple work stations  520  for receiving work. That is, the wing panel  550  remains indexed to the strongbacks  540  during transport, which means that the work stations  520  can rapidly index themselves to the strongbacks  540 , the wing panels  550 , or both. Furthermore, the technique of suspending the wing panel  550  beneath a strongback  540  enables greater and more ergonomic access and inspection of the wing panel  550  during assembly processes (e.g., by technicians). 
       FIG.  10    is a flowchart depicting a method  880  of enforcing a contour onto a wing panel in an illustrative embodiment. According to method  880 , step  882  includes locating a wing panel for an aircraft beneath a strongback. As described in detail above, this step may involve moving a wing panel  550  underneath a strongback  540  that is configured to extend over a transverse section of the wing panel, indexing the wing panel to the strongback via indexing features (e.g., physical indexing features and/or readable identifying means) of the wing panel, hard stops, visual techniques, and/or other processes. Step  884  includes engaging pogos of the strongback to an upper surface of the wing panel in positions that are distinct from positions (e.g., corresponding positions on the lower surface of the wing panel) that correspond to where structural components, such as ribs and spars, will be attached to the wing panel. As noted above, this is performed to allow fabrication access to the rib or spar install area, for example to facilitate manual or automated drilling, fastener installation, and so forth, to allow ribs and spars to be installed to wing panels. The ribs may be made from metallic materials or composites. If the rib is made from aluminum, then one or more layers of fiberglass or other material are placed at an intersection between the aluminum and the carbon fiber. This can be accomplished via fiberglass isolation plies along with sealant at the wing panel in areas where the ribs will be placed (sometimes referred to as the “rib land area”). In one embodiment, this comprises physically engaging the pogos to the upper surface, and activating vacuum systems that apply suction via the pogos to the wing panel. 
     Step  886  includes controlling a length of the pogos to enforce a contour on the wing panel while the wing panel is suspended beneath the strongback. The pogos are independently adjustable. In one embodiment, controlling the length of the pogos is performed by setting the pogos to a predetermined length, while in further embodiments, this comprises operating actuators or air pressure to enforce specific lengths on each pogo. When the pogos are all set to their desired lengths, the wing panel is held in conformance with a desired contour at which ribs can be installed, provided the vacuum couplers of the respective pogos are located properly for the particular wing panel. 
     As noted above, in some embodiments, scanning is performed to determine an initial wing panel contour. It is possible that no changes in the contour need to be enforced if the wing panel is already at a desired contour. In such circumstances, a retention force applied by each pogo may be less than in circumstances where a contour of the wing panel is actively enforced by the pogos. Adjustments to the length of each pogo (i.e., longer or shorter) relative to the strongback, e.g. to push and/or pull the wing panel into a desired contour, is determined by design parameters for the wing panel. The locations of the vacuum couplers of the pogos are precisely located relative to the upper surface of the wing panel to ensure that when the pogos are at the desired length, the contour enforced by the pogos corresponds with expectations. 
     As noted above, in  FIGS.  5 A- 5 G , which show various aspects of assembly line  500  (or  500 ′) for a wing assembly, including the operations that take place as a wing panel  550  proceeds through a variety of work stations  520  disposed along the assembly line, many systems, operations, and components (e.g., ribs  572 ) are shown in simplified form and/or schematically, for ease of explanation.  FIGS.  11 A- 11 D  illustrate, in greater detail, the installation of additional components to wing panel  550  in the production of a wing assembly  600 . In particular,  FIGS.  11 A- 11 D  show the installation of a rib  572  to wing panel  550 , which in the embodiment shown is an upper wing panel  550 - 1 , at rib install station  528 . As such, wing panel  550  may be referred to in the following section as “upper wing panel  550 - 1 ,” or simply as “wing panel  550 - 1 ,” for convenience. The term “wing assembly” refers to the structure produced when wing components such as wing panels, ribs, and/or spars, are assembled together. As described in detail below,  FIG.  11 A  shows a rib  572  being moved into position beneath upper wing panel  550 - 1  by means of a shuttle, and  FIGS.  11 B and  11 C  show the rib being lifted upwards toward the lower surface of the upper wing panel for installation thereto.  FIG.  11 D  shows a resulting wing assembly  600 , with the rib  572  installed to the wing panel  550 - 1 , and with a pair of spars  580  installed at either end of the rib  572 . 
     The view shown in  FIGS.  11 A and  11 B  correspond generally with that of view arrow “ 11 ” in  FIG.  5 C , and show wing panel  550 - 1 , in a chordwise sectional view, suspended beneath a strongback  540  by means of pogos  545  that are coupled with the upper surface  574  of the wing panel via vacuum couplers  548 , in accordance with the explanation provided above. Wing panel  550 - 1 , or at least the cross-sectional portion shown in  FIG.  11 A , is disposed within rib install station  528 . As detailed in the discussion above, the wing panel  550 - 1  may be indexed to the work station  520 , either directly or via one or more of the strongbacks  540  supporting it. Wing panel  550 - 1  is shown to have several stringers  640  installed to its lower surface  576 , which are shown to have a T-shaped cross-section. While six stringers  640  are shown, a greater or fewer number of stringers may be used for a particular upper wing panel and/or rib  572 , and/or for a particular position along the spanwise length of the wing panel. In the context of an assembly line, such as assembly line  500  shown in  FIGS.  5 A- 5 F  (and/or assembly line  500 ′ shown in FIG.  5 G), stringers  640  may have been installed prior to rib installation, such as at any point upstream of the rib install station  528 , or provided during the initial fabrication of the upper wing panel from a preform. 
     Although a number of rib configurations are possible and within the scope of this disclosure, rib  572  in  FIGS.  11 A- 11 D  is shown as an elongate, solid structure including a web  646  that is reinforced—that is, held in contour—by a stiffener  648  (e.g., a beam or bracket that enforces a contour onto the rib prior to affixing the rib to the wing panel  550 ). The top and bottom edges of the rib  572  are shaped to follow the respective contours of the wing panels to which the rib  572  are to be installed, and are provided with a number of openings or “mouse holes”  650  that are sized and positioned to accommodate, for example, stringers  640 , as well as cables and other structure that may be installed (not shown). Web  646  also includes a number of access holes  652  that are located inward from the edges of the rib, for similar purposes. 
     In  FIG.  11 A , the rib  572  is advanced into position, and in one embodiment enters the rib install station  528  from a feeder line (indicated at  570 ), which may be a rib feeder line (such as rib feeder line  491 - 7 ), that supplies the ribs  572  to rib install station  528  in a just-in-time or JIT timing scheme. More specifically, in  FIG.  11 A , the rib  572  is held at a vertical orientation while being transported via a shuttle  700  (e.g., a manual cart or an automated cart propelled on rails, an Autonomous Guided Vehicle (AGV), etc.). The rib  572 , as discussed above, may be fed via a just in time feeder line to the shuttle  700 , and may be moved during a pause between pulses to enter the rib install station  528 . In the configuration shown, shuttle  700  advances perpendicular to a process direction of the wing panel  550 . The shuttle  700  is shown to be driven by wheels  702  (e.g., motorized wheels) across floor  710 , but may alternatively be disposed on rails, or a track, and so forth. The wheels  702  drive the chassis  708 , which translates the chassis  708  horizontally/laterally in direction  1008 , and thus transports the rib  572  to a position/location directly underneath the wing panel  550 . The shuttle  700  may include indexing features (not shown) to facilitate indexing of the cart relative to the rib install station  528 , to assure proper positioning of the shuttle relative to the rib install station prior to advancing into position beneath the wing panel  550 , and/or of the shuttle (and thus the rib) relative to the upper wing panel  550 - 1  when the shuttle is advanced into position. Such indexing features may take the form of cups and cones of a cup-and-cone indexing systems, hard stops, and/or other configurations. The chassis  708  holds one or more actuators  704 , as well as supports  706  that are affixed to the actuators  704 . Supports  706  are configured to cradle the rib  572  in vertical orientation. The actuators  704  (or other lifting apparatus) are configured to drive the supports  706  vertically, such as to lift the rib  572  vertically into contact with lower surface  576  of the wing panel  550 . 
       FIG.  11 B  shows the rib  572  after it has been driven vertically upward in direction  1010  to contact a lower surface  576  (e.g., onto a rib land area) of the upper wing panel  550 - 1 . The mouse holes  650  disposed along the upper edge of the rib  572  can now more clearly be seen to be sized and positioned to accommodate stringers  640 . The clearance between the rib  572  and the stringers  640  at the mouse holes  650  may be greater or less than as shown. The rib  572  is held at a desired orientation and position by supports  706 , during the coupling to the wing panel. Although the disclosure has in the prior discussion used the term “installation,” this term may encompass a temporary or a permanent attachment. Thus, when the rib  572  is first brought into contact with the wing panel, the coupling may be temporary, e.g., by clamping and/or tacking the rib  572  in place, or permanent, such as by the use of temporary or permanent fasteners (e.g., via automated or manual drill and fastener installation techniques, before and/or after removal of the shuttle  700 ), or the rib  572  can be permanently affixed while aligned with the upper wing panel  550 - 1 . In some embodiments, for example those described further below with reference to  FIGS.  16 A- 16 C  and  FIGS.  17 A- 17 C , shims may be installed to fill gaps at the rib to wing panel interface after the rib  572  has been temporarily fastened to the wing panel, but prior to permanent installation thereto. Either way, once coupled to the upper wing panel  550 - 1 , the coupling means hold the rib  572  at the desired position, so the shuttle  700  may be removed. 
     In other embodiments, one or more strongbacks  540  suspend the upper wing panel below via pogos  545  that form a vacuum attachment to the wing panel, and lower the wing panel into contact with the rib  572  by adjusting lengths of the pogos (and/or lowering the strongback  540 ), as opposed to the rib  572  being raised upward to the wing panel. Still other embodiments may employ a combination of movements of both rib  572 , and upper wing panel, in order to bring the two components into contact. In some embodiments, the rib  572  is installed subsequent to the installation of a spar or spar segment (not shown in this view), and the spar facilitates holding of a contour (e.g., a spanwise contour, while chordwise contour is held by the rib). Specifically, in such an embodiment, the spar  580  may prevent lateral (e.g. chordwise) shifting of the rib  572 , spanwise shifting of the ribs relative to each other, twisting of the ribs  572  and upper wing panel  550 - 1  about a spanwise  590  axis, and so forth. Further, in some embodiments, a support structure (such as support structure  588 ) is assembled from ribs and spars, which is then installed to the wing panel. Such embodiments may involve the use of multiple shuttles, and/or a differently configured shuttle, as compared to shuttle  700 , to transport and/or lift the support structure to the wing panel. 
       FIG.  11 C  corresponds with view arrows  11 C of  FIG.  11 B , and further illustrates the relationship between shuttle  700 , rib  572 , and upper wing panel  550 - 1 .  FIG.  11 C  further illustrates that in this embodiment, the upper wing panel  550 - 1 , and specifically the lower surface  576  thereof, includes an alignment feature  584  configured to align with a complementary alignment feature  586  at the rib  572 . The configuration of alignment features  584  and  586  may be any that achieves registration of the rib with the upper wing panel  550 - 1 , such as a cup-and-cone configuration, and so forth. There may be multiple corresponding pairs of indexing features for each rib. Furthermore, in some embodiments, alignment feature  584  is installed during fabrication of the upper wing panel  550 - 1  as an indexing feature  210 . These alignment features facilitates alignment of the rib  572  prior to fastening the rib  572  to the upper wing panel  550 - 1 . Thus, in one embodiment, lifting the rib  572  includes mating the rib  572  to an alignment feature  584  at the wing panel  550 . The ribs  572  are delivered as needed to the rib install station  528  in a just in time (JIT) manner from a parallel assembly line/feeder line. In this manner, different ribs are created in serial for placement in wing assembly  600  in a pulsed environment as needed. 
       FIG.  11 D  is an end view of a wing assembly  600  that includes a wing panel  550  (e.g., an upper wing panel  550 - 1 ) with attached ribs, of which the rib  572  is visible (i.e., rib  572  blocks the view of other ribs behind it). The upper wing panel  550 - 1  is transported along an assembly line in an illustrative embodiment; for example, via strongback  540 , which conveys the upper wing panel  550 - 1  (now part of wing assembly  600 ) along track  510 . Wing assembly  600  may be at least partially disposed within a rib install station  528 , such as shown in the view presented in  FIG.  5 C . In the embodiment shown in  FIG.  11 D , however, spars  580  are shown to be installed to either side/on either end of rib  572 ; as such, the wing assembly  600  may be at least partially disposed within a spar install station  530 , such as shown in the view presented in  FIG.  5 E , or a rib to spar attach station  598 , such as shown in the view of  FIG.  5 F , depending, for example, on the order in which the spars  580  and ribs  572  are installed. 
     In accordance with the components and operations discussed above,  FIG.  12    is a flowchart illustrating a method  900  of installing a rib into an upper wing panel in the production of a wing assembly in an illustrative embodiment. The description of the method will refer to components and concepts discussed above and shown in the drawings, but the method is applicable to a variety of settings. Step  902  includes suspending an upper wing panel  550 - 1  of an aircraft beneath a shuttle, such as strongback  540 . In accordance with many of the methods described above, this step may include (and/or be preceded by) demolding the upper wing panel  550 - 1  from a layup mandrel, indexing the upper wing panel to the strongback  540 , and/or coupling the wing panel with the strongback (such as via vacuum couplers  548  of pogos  545 ) to hold the upper wing panel while enforcing a contour onto it. 
     Step  904  includes translating the rib to a position underneath the upper wing panel. This step may be performed while the wing panel is paused between pulses through work stations. In some embodiments, this includes driving a shuttle (such as cart  700 , which may be a manually operated cart, an AGV, or otherwise-configured vehicle) that supports the rib into the desired position. The cart may be controlled according to an NC program, and may be positioned based on a track/rail system that enforces a desired orientation, or marks at the factory floor that indicate a desired position for placement, via radar or lidar, visual tracking, etc. In the illustrated embodiment, the position to which the rib is translated is directly beneath the location on the upper wing panel to which the rib will be installed. 
     Method  900  is shown to include a step  906  of orienting the rib  572  vertically upright. In some embodiments, after demolding, the rib  572  is assembled or otherwise worked on while in an upright position, such as on a jig or similar frame, and thus may not need to be oriented upright for installation (for example if moved directly from the jig to the cart  700  without changing its orientation). A jig may be used in order to place or enforce a desired contour, such as a flat contour, onto the rib. As noted above, a stiffener that runs the length of the rib is coupled to the rib after demolding to enforce a contour onto the rib. In some embodiments, the rib may be (or become) oriented in a direction other than a vertical orientation, such as during assembly or while being supplied to the rib install station, such that vertically upright orientation is needed prior to installation. In some embodiments, the orienting is performed by placing the rib  572  onto the cart  700 , where the rib is then held at the desired vertical orientation by supports  706 . Method  900  may, in some embodiments, include supplying ribs in a just in time (JIT) fashion, such as via a feeder line that is configured to have a suitable takt time for JIT delivery. 
     Although in the illustrated embodiment, the “orienting” step  906  is shown to follow the “translating” step  904 , this is not required to all embodiments. In some embodiments, the “orienting” step ( 906 ) is performed as a part of, or at least partially during, the “translating” step ( 904 ). In some embodiments, orienting is performed prior to translating (such as during loading the rib  572  onto the cart  700 ). 
     In step  908 , the rib  572  is placed into contact with the upper wing panel. As noted above, this may be performed lifting the rib vertically, such as by driving actuators  704  of the cart  700  to raise the rib  572  into contact with the lower surface  576  of the upper wing panel  550 - 1 . In some embodiments, this may be performed by lowering the upper wing panel, such as by means of pogos  545  of the strongback  540 , into contact with the rib. In some embodiments, a combination of lifting the rib and lowering the wing panel is performed, in order to bring the components into contact. In some embodiments, placing the rib  572  into contact with the upper wing panel  550 - 1  includes mating the rib to one or more indexing features of the wing panel (such as by coupling alignment features  584  and  586  as shown in  FIG.  11 C ). This may ensure final precise alignment of the rib  572  with the upper wing panel  550 - 1 . 
     As shown, for example, in  FIG.  5 D , the ribs  572  in some embodiments may be fastened to the wing panel  550 , or at least one or more portions of the lower surface thereof, at an angle, shown as installation angle θ. As such, in fabrication methods in which the rib  572  is oriented vertically, or in other words at an angle typically normal to a track  510  and/or floor surface  710 , and then lifted upward to the lower surface of the wing panel, installing the ribs at the desired installation angle θ relative to the wing panel may be facilitated by disposing the wing panel in a suitable orientation, e.g., by disposing the wing panel so that the lower surface thereof is canted at an angle that is complementary to the installation angle θ. This may be done during initially suspending the upper wing panel  550 - 1  beneath the strongback(s) in the suitable orientation, or the pogos may have their lengths adjusted prior to the rib installation procedure in a manner configured to change the orientation of the wing panel to one suitable for installation of the ribs. 
     In step  910 , the rib  572  is affixed to the upper wing panel  550 - 1  while the upper wing panel remains suspended from the strongback  540 . Affixing, as the term is used herein, encompasses temporarily holding the rib in position, such as by tack fastening, clamping, and/or other techniques, as well as permanently installing. In some embodiments, the rib  572  is held in position prior to permanent installation, such as to allow selective installation of shims into gaps, if any, at the rib to wing panel interface. In some embodiments, installing includes driving or otherwise installing fasteners through the upper wing panel  550 - 1  and the rib  572 . These operations may be performed via end effectors that install lockbolts, or by other means. In some embodiments, so as not to obstruct or interfere with fastening operations, vacuum attachment performed via vacuum couplers  548  located between or among, but in any case distinct from, rib install locations. Thus, in such embodiments, the vacuum couplers  548  are disposed on the wing panel  550  so that their locations do not interfere with operations such as tack fastening and/or permanent fastener installation of the rib  572 , performed by technicians or automation. 
     Steps  904  (translating the rib),  908  (placing the rib into contact with the wing panel), and  910  (affixing the rib to the wing panel) are all performed while the wing panel  550  is suspended, and/or while maintaining the rib  572  vertically upright. One or more, or all, of the steps of method  900  are performed at a rib install station. The method  900 , or a sequence of steps thereof, may be performed iteratively for a plurality of ribs  572  to be installed onto the same wing panel  550 . 
     Method  900  provides a technical benefit over prior systems and techniques, because it enables a contour to be enforced upon a wing panel  550 , and for ribs  572  to be rapidly installed into the wing panel while the contour remains enforced. By keeping the ribs vertically oriented throughout the installation process, method  900  can save labor and increase efficiency on the factory floor and/or on an assembly line. 
     In some embodiments, after at least one rib has been affixed (e.g., installed to upper wing panel  550 - 1 ), spars  580  are affixed to the ribs and to the wing panel, such as to close off the leading and trailing edge portions of the wing panels/ribs. In some of such embodiments, sections of spars are joined lengthwise to each other at a rib to make a spar, making the rib a part of the splice between spar segments. In some of such embodiments, spars  580  are affixed at a station downstream of a rib install station, such as a spar install station, such as spar install station  530  of assembly line  500  as shown in  FIGS.  5 E and  5 F . In one embodiment, a spar  580  consists of three spar sections, so there are two spar/rib splices. In some embodiments, spars  580  and ribs  572  are affixed simultaneously to a wing panel  550 , such as at two different stations and/or two different locations on the wing panel  550 . 
     The installation of the ribs and spars to the wing panel, and to each other, may include any suitable technique, including those disclosed herein. Some embodiments of the method  900  continue, such as with the joining of a lower wing panel to the ribs and spars installed to the upper wing panel. A more detailed explanation of one manner in which this is carried out is provided below with reference to  FIGS.  16 A- 16 C , which illustrate one manner of installing shims during the assembly of a wing assembly. 
     In some embodiments, there is a work station upstream of the spar install station where the wing panel is trimmed to final production dimensions (e.g., its final perimeter) and the indexing features in the manufacturing excess are removed (i.e., along with the manufacturing excess). This trimming is followed by sealing and painting, performed in a pulsed or continuous fashion. In some embodiments, trimming of the wing panel to its final perimeter (and/or sealing and painting) is performed after ribs and/or spars are installed. 
       FIG.  13    is a flowchart illustrating a method  920  of assembling a wing assembly in an illustrative embodiment, which involves components, concepts, and processes discussed in detail above, but which focuses on the aspect of the installation of ribs and spars to an upper wing panel while the wing panel is suspended beneath a shuttle. As such, step  922  includes suspending an upper wing panel  550  of an aircraft beneath a shuttle, such as a strongback (for example, strongback  540 ). Step  924  includes installing ribs  572  onto the upper wing panel  550 - 1 . Step  926  includes installing spars  580  onto the upper wing panel  550 - 1 . Step  928  includes fastening the spars  580  to the ribs  572 . Finally, step  930  includes joining a lower wing panel  550 - 2  to the spars  580  and ribs  572 . 
     As noted above, the joining of the various wing assembly components may occur in a different sequence than as shown in the illustrated embodiments. In some embodiments, one or more of the ribs are installed prior to the installation of the spars (or spar sections). In some embodiments, all of the ribs are installed prior to the installation of the spars (or spar sections). In some embodiments, ribs and spars are installed at the same time, or overlapping in time, for example in multiple work stations in an assembly line, and/or at multiple locations on the wing panel. 
     Further, in some embodiments, spars  580  (or spar sections) are joined to ribs  572  prior to affixing the ribs to a wing panel (such as upper wing panel  550 - 1 ), to produce a wing assembly having a horizontal, open ladder-like structure such as support structure  588  (best seen in  FIG.  5 G ), to which the upper and lower wing panels  550  are then installed.  FIG.  14    is a flowchart illustrating a further method  940  of assembling a wing assembly in such an embodiment. The embodiment includes joining of spars  580  to ribs  572  in step  942 . An upper wing panel  550  is then joined to the spars  580  and ribs  572 —or one side of the support structure  588 —in step  944 . This process may involve suspending the upper wing panel  550 - 1  beneath a shuttle, such as a strongback, as in other example methods, and raising the support structure  588  of joined ribs and spars into position to affix it to the upper wing panel. In some of such embodiments, all of the ribs and spars are fastened together prior to joining with an upper wing panel; in others of such embodiments, further ribs and/or spars, or spar sections, are attached to the wing assembly after the support structure  588  is joined with the upper wing panel. A lower wing panel is finally joined to the opposite side of the support structure  588  of the joined spars  580  and ribs  572  to complete the wing assembly, in step  946 . 
     As noted above, in some configurations of an assembly line for a wing assembly, various work stations may be arranged in a manner that facilitates performing several operations on a wing panel at the same time, or overlapping in time, as the wing panel is moved in a process direction along the assembly line.  FIG.  5 A , for example, shows a configuration in which different sections of the same wing panel  550  are positioned within multiple work stations  520 ; in particular, NDI station  524 , cut-out station  526 , and rib install station  528 . In other embodiments, further work stations  520  such as spar install station  530  ( FIG.  5 E ), support structure assembly station  532  and/or install station  534  ( FIG.  5 G ), as well as a rib-to-spar attach station  598  and/or a panel join station  599  (see  FIG.  5 F ) may also be so arranged. 
       FIG.  15    is a flowchart illustrating aspects of multiple operations being performed to a wing panel at the same time, or overlapping in time, and shows a method  960  of assembling a wing, or wing assembly, such as by installing a rib and spar to an upper wing panel, in an illustrative embodiment. Step  962  includes suspending an upper wing panel  550 - 1  of an aircraft beneath a shuttle, such as a strongback (for example, strongback  540 ). Step  964  includes installing one or more ribs  572  and one or more spars  580  (or sections of spars  580 ) to the upper wing panel  550  via stations  520  disposed at the upper wing panel, at the same time or at least overlapping in time, while the upper wing panel remains suspended. Step  966  includes pulsing the upper wing panel in a process direction through the work stations  520 . In some embodiments, additional work stations  520  also perform operations on the wing panel during these operations, including installing access ports (at a cut-out station), attaching ribs to spars (at a rib-to-spar attach station), and so forth. In a further embodiment, the work stations install ribs and spars during pauses between pulses of the upper wing panel. In a further embodiment, the method further includes affixing a lower wing panel to rib(s) and spar(s) installed to the upper wing panel. 
     Various aspects of wing assembly, such as rib and spar installation to a wing panel, may involve installation of shims between the wing panel and one or more ribs and/or spars, for example if any gaps between the various components exceed a certain size, such as a shimming tolerance threshold. Shim installation may be performed, for example, after ribs and spars have been clamped and/or tacked into place, but before the ribs and spars have been fastened together in the assembly line  500  of  FIG.  5 A , before or after a lower wing panel has been attached. The shims fill gaps between the various components (e.g., between a rib and the upper or lower wing panel, between a spar and the upper or lower wing panel, between a rib and a spar, and so forth), once the components have been located to each other and tacked/clamped into place. 
       FIGS.  16 A and  16 B  are diagrams illustrating automated installation of shims between ribs and wing panels in illustrative embodiments, specifically by means of an end effector of a robot arm that may be detachably coupled to the stiffener of each rib. In more detail, as shown in both  FIGS.  16 A and  16 B , a wing assembly  600  is suspended below a strongback (not shown) by means of adjustable-length pogos  545  that include vacuum couplers  548  that are coupled to the upper surface  574  of a wing panel  550  of the wing assembly.  FIG.  16 A  shows an embodiment in which the wing assembly  600  includes one wing panel  550 , in the form of an upper wing panel (indicated at  550 - 1 ), whereas  FIG.  16 B  shows an embodiment in which the wing assembly  600  also includes a second wing panel  550  in the form of a lower wing panel (indicated at  550 - 2 ). The wing assembly  600  is shown to have a number of ribs  572  affixed to the lower surface  576  of the upper wing panel  550 - 1 . 
     In some embodiments, there may be one or more gaps between coupled components of a wing assembly  600 , such as between a rib  572  and the surface of the wing panel to which it is installed, between a spar  580  and a wing panel  550 , between a rib  572  and a spar  580 , and so forth. If a gap is determined to exceed a certain size, in that one or more dimensions of the gap (e.g., width, depth, length, etc.) exceeds a certain threshold, which is also referred to herein as a shimming tolerance threshold, then a shim of a suitable size and configuration is installed into the gap, to fill it. In the illustrated embodiment, this is done by a robot arm  750 , and more specifically by an end effector  752  of the robot arm. End effector  752  is shown in  FIG.  16 A  to include a grasping device  754  configured to hold a shim  756 , such as to install into a gap that has been determined to be a shim location (indicated as  758 ). In some embodiments, the end effector  752  includes components or devices for inspection (not shown), such as a camera, laser, ultrasonic device, probe or feeler gauge, and so forth, in order to scan or otherwise visually or physically detect or assess gaps along the joint between joined components, and further to make or enable the determination of whether a gap exceeds a shimming tolerance threshold and is thus a suitable location for installation of a shim  756  (i.e. a shim location  758 ). In some embodiments, the robot arm  750  includes multiple end effectors  752 , such as one for inspection and another for installation. 
     Although other configurations are possible, in  FIG.  16 A , robot arm  750  is shown as a kinematic chain of actuators  760  and rigid bodies  762  that extends from a carriage  764 . Carriage  764  is in turn mounted on stiffener  648  of the rib  572 . Stiffener  648  is also referred to herein as a “bracket.” In some embodiments, such as described above, the bracket  648  is installed to the rib  572  prior to installation of the rib to the wing panel  550 , to function as a stiffener, that is, to stabilize the rib and/or enforce a desired (e.g. flat) contour to the rib. As such, bracket  648  in some embodiments serves both as a stiffener and as a connection point for the robot arm. In further embodiments, the bracket  648  may additionally or alternatively serve as a general connection point for machinery or equipment used to move or otherwise handle the rib during fabrication and/or assembly operations. In some embodiments, the bracket is removably attached, e.g. with bolts or other like fasteners. As detailed further below, the coupling between the carriage  764  of the robot arm  750  and the bracket  648  of the rib  572  is a removable one, so that the robot arm may be coupled and de-coupled from the bracket via a detachably mounting the carriage  764  on the bracket. Further, in the illustrated embodiment, the coupling is such that the carriage  764  is independently movable along the length of the bracket, such as to facilitate the robot arm to access gaps and/or shim locations  758  along the length of the rib  572 . 
     The robot arm  750  may be moved (e.g. relocated) from one bracket to another, such as by being decoupled from a first bracket and then coupled to a second one, to operate in different locations along the wing assembly  600 . In the embodiment shown in  FIG.  16 A , this is done by means a cart  770 . Cart  770  includes a set of wheels  772  mounted to and configured to support a cart body  774  relative to a surface, such as a floor surface. One or more wheels  772  may be motorized or otherwise driven. Cart body  774  in turn supports a telescopic lift  776 , which is configured to engage, and raise or lower, carriage  764 . As such, cart  770  is configured to position the carriage  764  for coupling to bracket  648 , or to move the carriage after it is de-coupled from the bracket of a first rib  572  to a position in which it may be coupled to a bracket of a second rib, and so forth, such as by a combination of raising or lowering the lift  776  and moving the position of the cart body relative to a floor surface (and/or rib  572 ) by means of wheels  772 . 
     As depicted, cart  770  also includes a controller  778 , which may partially or completely control the movements of cart body  774  and/or lift  776 , and/or the coupling/decoupling of carriage  764  relative to a bracket of a rib  572 . Controller  778  may, in whole or in part, control the operations of robot arm  750  and its end effector  752 . In some embodiments, robot arm  750  is operated in accordance with an NC program by controller  778  to visually inspect a location between the rib  572  and the wing panel  550 , in order to determine whether shims  756  will be used, and what size of shims will be used, and/or to install the shims. In other embodiments, some or all of these movements are remotely controlled, such as by an operator, or by a floor controller (not shown). Thus, it can be understood that  FIG.  16 A  illustrates multiple operations. For example, cart  770  and lift  776  are shown to cooperate to position carriage  764  in contact with bracket  648  of a rib  572 . Also, robot arm  750 , which extends from carriage  764 , is shown to have its end effector  752  holding a shim  756  for installation into shim location  758 . The various components of the cart  770  and robot arm  750  are shown in simplified, partially schematic form, for ease of explanation. Cabling and wiring, such as to provide power to the robot arm  750  and/or cart  770  from an external or integrated power source (not shown), and so forth, are not illustrated in this view. 
       FIG.  16 A  also shows a shim feeder line schematically represented at  780 , which, in the illustrated embodiment, is configured to supply shims  756  for installation by robot arm  750 . In some embodiments, shim feeder line  780  is configured to dynamically fabricate shims  756  for installation, such as responsive to signals or communications provided by an operator and/or controller  778 , based on input received from an end effector  752  configured to measure or otherwise assess each gap that is encountered during an analysis. 
     As such, it can be seen that an example operation of automatic shim installation for a wing assembly may proceed by assessing each of a sequence of locations in a wing assembly, such as each of a series of locations in which, for example, prior analysis indicates that a shim location  758  exists (or may exist), or the entirety of each of the joints between components that are joined together, and so forth. In one example, the carriage  764  of the robot arm  750  is sequentially coupled with the bracket  648  of each of several ribs  572  installed to a wing panel  550 , to perform detection and analysis of each gap, and/or shim installation for each shim location  758 , in the space bounded by one or two adjacent ribs  572 . This space is also referred to as a bay  790 . As noted above, in such an example, the carriage  764  may move along the bracket  648  to allow inspection and/or installation of the entire length of the rib  572 , or at least the sides of the ribs (or rib) that define the bay in which the robot arm  750  is mounted. In the embodiment shown in  FIG.  16 A , five ribs  572  (also individually indicated as  572 - 1 ,  572 - 2 ,  572 - 3 ,  572 - 4 , and  572 - 5 ), are shown installed to upper wing panel  550 - 1 , forming six bays  790  (which are only individually indicated, as  790 - 1 ,  790 - 2 ,  790 - 3 ,  790 - 4 ,  790 - 5 , and  790 - 6 ). Carriage  764  is shown coupled to the bracket  648  of rib  572 - 4 , allowing end effector  752  of robot arm  750  to inspect and/or install shims  756  not only to the side of rib  572 - 4  to which the bracket  648  is installed, but also to one side of the next adjacent rib (that is, rib  572 - 3 ), and any other location accessible in bay  790 - 4 . Accordingly, by coupling the carriage  764  of the robot arm  750  to the bracket  648  of each rib  572 , shim installation may be performed in each bay  790 - 1 ,  790 - 2 , etc. In a bay in which there is not a bracket  648  to which carriage  764  may be coupled, such as bay  790 - 6  in  FIG.  16 A , gap inspection and/or shim installation may be performed by moving the robot arm  750  by means of the cart body  774  and telescopic lift  776 . In other embodiments, additional brackets may be installed in order to allow inspection and/or shim installation solely by means of a bracket-mounted robot arm  750 . There may be more or fewer ribs (and correspondingly more or fewer bays) in different wing assemblies. In some embodiments, the robot arm  750  is coupled with a bracket  648  of a rib  572  prior to the rib being placed against the wing panel. 
     In some cases, a shim location  758  may be detected and/or assessed from both sides of a rib  572 , in which case shim installation may be performed from whichever side enables a more efficient operation. In some embodiments, multiple robot arms are simultaneously deployed on the same wing assembly, which (among other benefits) may facilitate efficient shim installation in shim locations that may be fillable from either side. In some of such embodiments, a single cart may facilitate the positioning (and re-positioning) of each of multiple robot arms, such as by lifting a carriage of a first robot arm into place for mounting on a first bracket, then disengaging from the carriage to leave the robot arm on the first bracket, then moving to engage a carriage of a second robot arm, such as to move it into place for mounting on a second bracket (e.g., in a different bay), and so forth. 
     In  FIG.  16 B , as noted above, wing assembly  600  is shown to also include lower wing panel  550 - 2 . Also, the telescopic lift  776  is shown to extend through an access port  792  in the lower wing panel  550 - 2  in order to access the bracket  648 , such as to couple (or de-couple) carriage  764  to (or from) the bracket. Access port  792  may have been installed at an upstream work station  520 , such as cut-out station  526  as shown in  FIG.  5 A . Access port  792  is sized to allow insertion and subsequent removal of robot arm  750  (including carriage  764 ). To minimize the size of access port  792 , robot arm  750  may be extended, or folded, or otherwise aligned into a configuration having a minimal cross-section for insertion and withdrawal through the access port. Alternatively, robot arm  750  may be sized and/or configured specifically to fit through a predetermined access port size. Lower wing panel  550 - 2  is shown to include several access ports  792 , one for each bay, to allow a robot arm  750  to be inserted and then coupled in order to perform inspection and/or shim installation in each bay. In one embodiment, the sides of the two ribs that define a bay are inspected and/or shimmed by the robot arm  750  while it is disposed within that bay, which reduces the number of times that the robot arm  750  is aligned with the access port  792  for insertion or removal. 
     In some embodiments,  FIGS.  16 A and  16 B  depict two phases of a sequential operation, in which installation of shims  756  (e.g., upper shims) to shim locations  758  between ribs  572  and the lower surface of the upper wing panel  550 - 1  is first performed (as shown in  FIG.  16 A ), followed by installation of the lower wing panel  550 - 2  to the wing assembly  600 , followed by installation of shims (e.g. lower shims) to shim locations between ribs  572  and the upper surface  574  of the lower wing panel  550 - 2  (as shown in  FIG.  16 B ). In other words, in such embodiments, the lower wing panel  550 - 2  is installed after the upper shims are installed. In other embodiments,  FIGS.  16 A and  16 B  depict alternative operations—for example,  FIG.  16 A  may represent the first stage of the sequential operation described above, whereas  FIG.  16 B  may represent an operation in which lower wing panel  550 - 2  is installed to the wing assembly  600  before installation of any (upper or lower) shims  756 . In either case, the robot arm  750  may be moved from bay to bay along the length of the wing assembly by means of the cart  770  in order to perform shim installation in each bay. As described above, in some embodiments, multiple robot arms are deployed for shim location detection and/or analysis, and/or shim installation, in more than one bay, at the same time. 
       FIG.  16 C  depicts a view of a rib  572  to which the carriage  764  of robot arm  750  is installed—specifically, rib  572 - 4  as shown in  FIG.  16 A —and thus corresponds with view arrows  16 C of  FIG.  16 A . However, the components illustrated in  FIG.  16 C  are applicable to any rib  572  in the illustrated embodiment. Only carriage  764  of the robot arm is shown in  FIG.  16 C , for clarity, and components of the strongback (e.g. pogos and vacuum couplers) are also not shown in this view.  FIG.  16 C  provides a view of an illustrative example configuration of bracket or stiffener  648 , which is shown to be installed against the web  646  of the rib  572 . More specifically, the bracket  648  is shown to be mated with indexing features at the rib  572 , which are generically shown as indexing features  794 . The indexing features may facilitate alignment of the bracket  648  with the rib  572  during installation thereto, and may take any suitable form, such as through-holes in web  646  that are configured to receive fasteners such as bolts.  FIG.  16 C  further illustrates that the bracket  648  comprises a rack  796  having teeth  798  to which the carriage  764  is clamped or otherwise removably attached. The carriage  764  is configured to utilize the teeth  798  to translate back and forth along the bracket  648  in a controllable and indexed manner (e.g., via a driven mechanism that engages the teeth, such as a pinion, a worm gear, and so forth). The position of the robot arm may thus be indexed with respect to a rib, such as the rib to which the carriage of the robot arm is coupled, based on a position of the bracket  648  (or relative to the bracket  648 ), and a position of the carriage  764  along the bracket  648 . Although not required to all embodiments, bracket  648  in  FIG.  16 C  is also shown to include a centering feature  654  that may facilitate indexing, such as by enabling more rapid determination the position of the carriage to a known reference point. 
     In one embodiment, the carriage  764  is operable to drive the robot arm (not shown) along the bracket  648  via a rack-and-pinion system in which the teeth  798  form the rack. Other embodiments of bracket  648  and/or carriage  764  have a different configuration to enable movement of carriage  764  along the bracket. In the illustrated embodiment, the carriage  764  is also capable of rotation, as shown by arrow  1012 , in order to enhance movement of, and access by, the robot arm. 
       FIG.  16 C  also shows a representative pair of spars  580  installed to the upper wing panel  550 - 1 , at either end of the rib  572 . The spars  580  are illustrated in a simplified form and thus are not shown to include, for example, specialized upper and lower cap shapes that facilitate fastener connections to a wing panel. Teeth  798  are shown to extend sufficiently toward the ends of the bracket  648 , which in this embodiment is coterminous with the rib  572  to which it is installed, to allow the carriage  764  to move close enough to the spars so that gap assessment and/or shim installation by the robot arm may be performed at the joint(s) between the spar and the wing panel(s), and/or at the joint between the spar and the rib. In further embodiments, the bracket  648  facilitates track mounting of a collar and/or nut installer. This may be particularly beneficial in circumstances where a lower wing panel is already installed and access is only available through access ports. Also, although the rib  572  and wing panel  550  are not shown to accurate scale or dimension,  FIG.  16 C  shows that a number of gaps exist between the rib  572  and the lower surface  576  of the upper wing panel  550 - 1 , such as at representative shim location  758 . 
     As noted above, in some embodiments, the robot arm  750  performs operations in addition to shim installation, such as detection and/or inspection of gaps to facilitate the identification of shim locations  758 . In some embodiments, the robot arm performs additional operations including sealing, sealant inspection, fastener installation, collar or nut installation on fasteners, collar or nut installation inspection, and so forth. The robot arm  750  may perform such operations via a selection of interchangeable end effectors  752  (which, for example, may be exchanged while the carriage  764  of the robot arm  750  is coupled to the bracket  648 , such as via an access port  792 ), or performed with multi-functional end effectors  752 , or with multiple robot arms  750  that can each be installed and left in place on a bracket, in some cases with more than one such robot arm coupled to a bracket. The robot arm  750  may be operated automatically or remotely via a floor-based controller that enables a technician to operate the robot arm (e.g., via remote control). After completing its work, a robot arm  750  can be re-attached to the cart  770  and removed. 
       FIGS.  17 A- 17 C  are perspective views of robot arms  750  each operating to inspect gaps, install shims  756  in shim locations  758 , install sealant or collars/nuts, and so forth, in a bay  790  disposed between two ribs  572  and bounded on one side by a spar  580  of an example wing assembly  600 . In the embodiments depicted in these drawings, a technician sets up, operates, and maintains the robot arm  750 , after placement of the carriage  764  of the robot arm on a bracket  648  via a cart (not shown). For simplicity, the following discussion assumes that the robot arm  750  operates in the same bay  790 , between the same two ribs  572  (individually numbered as  572 - 1  and  572 - 2 ), in each of this series of drawings. In  FIG.  17 A , the robot arm  750  is mounted on a bracket  648  installed against rib  572 - 1 , and operates its end effector  752  to inspect ribs  572  placed against an upper wing panel  550 , and specifically a location between rib  572 - 2  and the surface of the wing panel  550  against which it is positioned. Based on the inspection, the robot arm  750  will selectively install shims  756  at shim locations  758  within the bay. In  FIG.  17 B , the carriage  764  of the robot arm  750  has progressed along the bracket  648  to a position closer to the end of the bracket as compared to its position in  FIG.  17 A , and is shown using its end effector  752  to inspect a location near the bottom of rib  572 - 2 . In  FIG.  17 C , the robot arm  750  has used its end effector  752  to place a shim (not shown) at a shim location  758  above bracket  648 , where rib  572 - 1  is affixed to upper wing panel  550 . With the shim in place, fasteners may be installed through the upper wing panel  550  and the rib  572 - 1  to secure the wing panel to the rib, or at least the portions thereof that are local to the shim, with the shim in place. In some embodiments, a shim is fastened in place by means of one or more fasteners; in some embodiments, a shim is instead held in place in a friction fit due to the fastening of the rib to the wing panel. 
     With the aforementioned components and concepts in mind,  FIG.  18    is a flowchart illustrating a method  920  for operating a robot arm (such as robot arm  750 ) to perform tasks related to wing assembly (such as in a wing assembly  600 ) in an illustrative embodiment. Step  922  includes mounting a bracket  648  to a rib  572 . In some embodiments, this is done prior to holding or placing the rib against a wing panel  550 , such as after demolding the rib and during (or after) other preparation of the rib for installation to the wing panel. In some embodiments, this is done after holding or placing the rib against the wing panel. Mounting the bracket  648  may be facilitated by aligning the bracket with indexing features of the rib  572  (e.g., complementary cup-and-cone features, through-holes for receiving bolts, and so forth). Once mounted, the bracket  648  enforces a desired contour, such as a flat contour, onto the rib  572 . In some embodiments, the bracket is removably mounted. 
     After the bracket  648  has been mounted to the rib  572 , step  924  includes coupling a robot arm  750  to the bracket. In some embodiments, this is performed by detachably mounting a carriage  764  on the bracket. In some of such embodiments, a wheeled cart  770  that is outfitted with a telescopic lift  776  configured to support the carriage is deployed, for example for moving the carriage into a suitable orientation and/or position for mounting on the bracket. The coupling of the robot arm  750  to the bracket  648  may be accomplished via clamping, suction, magnets, mechanical alignment with a track on the bracket, and so forth. In some embodiments, the coupling is configured to allow the robot arm  750  to move relative to the bracket  648 , such as by means of a carriage  764  configured for movement along the bracket. In some of such embodiments, the bracket includes teeth that facilitate a rack and pinion system with the carriage. With the carriage  764  and/or the robot arm  750  coupled to the bracket  648 , a location of the robot arm  750  within the reference system of the wing assembly  600  (e.g., relative to one or more components of the wing assembly, such as a wing panel, or a rib, or a bracket mounted to the rib, or a spar, and so forth) is known. In that sense, coupling the robot arm  750  to the bracket  648  may include indexing the position of the robot arm relative to the bracket. 
     Once coupled, in step  926 , the robot arm  750  is operated to install one or more shims between the rib and the wing panel, at the rib to wing panel interface (i.e. while the robot arm is coupled to the bracket  648 , via the carriage  764 ). As explained above, this may include moving the robot arm  750  (e.g., by driving the carriage  764 ) along a length of the bracket  648 , in order to align the robot arm  750  with shim locations at the rib, and/or move the robot arm within range of additional shim locations. 
     In some embodiments of the method  920 , the robot arm is operated, via a suitably configured end effector, to inspect the rib to wing panel interface, such as to detect, inspect, and/or measure gaps between the components. In some of such embodiments, the result of a measurement is communicated, e.g. to a technician or a controller, to determine whether a particular gap exceeds a shimming tolerance threshold, which may represent an out of tolerance condition, and thus is considered to be a shim location (into which a shim is installed). In some of such embodiments, the result of a measurement is used to select a suitable shim to be installed, e.g., by size, dimension, taper, or other characteristic, to rectify the out of tolerance condition. 
     Shims  756  may be supplied via a shim feeder line in any suitable manner. For example, a selection of shims (e.g. of differing tapers and/or sizes, etc.) may be stocked in a bin accessible to the robot arm. In some embodiments, a new shim is dynamically fabricated, or a pre-fabricated shim is adjusted (e.g., trimmed), such as based on inspection and/or measurement of the gap, and then delivered for insertion into the shim location  758  and provided just in time for placement. 
     After the shim  756  has been installed, the method may further include retracting the robot arm  750 , and moving the carriage  764  to a new location along the bracket  648  for further shim installation and/or other operations. If shim  756  installation into shim locations  758  accessible from the bracket  648  is complete, then the carriage  764  may be decoupled from the bracket, and moved to a new location (such as to the bracket of another rib). In some embodiments, this is facilitated with a wheeled cart outfitted with a telescopic lift. In some embodiments, this involves removing the robot arm  750  through an access gap, such as in a lower wing panel  550 - 2 . 
     As can be appreciated with respect to the description above of  FIGS.  16 A through  17 C , method  900  may be employed in a wing assembly  600  that includes a variety of components and configurations. For example, although described in the context of an embodiment in which one rib is held against a wing panel, the method may be employed iteratively in a wing assembly that includes multiple ribs held against the wing panel. In other words, once steps  922 ,  924 , and  926  are performed to install shims in shim locations between a first rib and a wing panel, the steps may be repeated to install shims to shim locations between a second rib and the wing panel. Method  900  may further be employed in a wing assembly  600  in which multiple ribs  572  are held at their upper edges against a wing panel, such as an upper wing panel  550 - 1 , and in which another wing panel, such as a lower wing panel  550 - 2 , is held against the opposite (or lower) edges of the ribs. In such a configuration, the lower wing panel  550 - 2  may be added to the wing assembly prior to, or between, shim installation operations. In one example, the method includes performing steps  922 ,  924 , and  926  first for upper shim locations between the ribs and the upper wing panel, followed by the addition of the lower wing panel to the wing assembly, followed by performing steps  922 ,  924 , and  926  for lower shim locations between the ribs and the lower wing panel. As noted above, subsequent to shim installation between a rib and a wing panel, the rib may be fastened (e.g. installed) to the wing panel. In another example, the method includes performing shim installation on both upper and lower shim locations, for example in a configuration in which the lower wing panel has already been placed. In either of these examples, the method includes repositioning the robot arm, for example to couple the carriage to the brackets of different ribs, by moving (e.g. withdrawing and inserting) the robot arm through access gaps in a wing panel, such as in the lower wing panel. 
     Turning now to  FIG.  19   , an illustration of a representative aircraft  1200  is depicted in which an illustrative embodiment of a wing panel and/or a wing assembly produced in accordance with aspects of the present disclosure may be implemented. In other words, aircraft  1200  is an example of an aircraft which can be formed using composite parts, wing panels, and/or wing assemblies produced according to one or more aspects of: the illustrative fabrication methods shown in  FIG.  1    and  FIGS.  2 A and  2 B ; the illustrative schema shown in  FIG.  4   ; the illustrative assembly line  500  shown in  FIGS.  5 A- 5 F ; the illustrative rib and spar installation techniques shown in  11 A- 11 D; the illustrative shim installation techniques shown in  FIGS.  16 A- 16 C  and  FIGS.  17 A- 17 C ; one or more of the methods shown in the remaining drawings; and/or any of the aforementioned as discussed above. In this illustrative example, aircraft  1200  has wings  1202  attached to and extending to either side of a fuselage  1204 . Aircraft  1200  includes an engine  1206  attached to each wing  1202 . Disposed at the rear end of fuselage  1204  is tail section  1208 , which includes an opposed pair of horizontal stabilizers  1210  and a vertical stabilizer  1212 . Wings  1202  are formed of an upper wing panel  550  and a lower wing panel (not shown) joined together, with an assembly of ribs and spars (not shown) at least partially forming the interior structure thereof. 
       FIG.  20    is a block diagram of various components and systems (or stages) discussed herein in an illustrative embodiment. Specifically,  FIG.  20    depicts a factory  1300  that includes a first assembly line  1310  in a clean room environment indicated at  1312 , and a second assembly line  1314  in a non-clean room environment  1316 . A boundary (e.g., one or more walls or enclosures), represented at  1318 , separate the clean room  1312  and non-clean room  1316  environments. At layup  1320 , indexing features (such as indexing features  210 ) are integrated into a laminate  1322  (such as preform  200 ) for a wing panel. The laminate  1322  is hardened at an autoclave  1324  into a composite part  1326 . In accordance with the embodiments herein, the composite part  1326  is a wing panel (e.g., wing panel  550 ), and more specifically an upper wing panel, but factory  1300  may be configured to fabricate, process, and otherwise do work upon composite parts that take the form of other aircraft components in addition to a wing panel. The composite part  1326  is then transitioned to the assembly line  1314 , which in the illustrated embodiment is shown to progress the composite part  1326  in a process direction  1328  through various systems and stages specific to those appropriate for an upper wing panel. For example, at the assembly line  1314 , a trimming stage  1330  removes excess material and/or installs additional indexing features into the composite part  1326 . At demolding  1332 , the composite part  1326  is demolded (e.g., removed from a layup mandrel), after which a contour is enforced onto the composite part  1326  via contour enforcement  1334 , in which the composite part  1326  is affixed to a shuttle  1336  (such as one or more strongbacks  540 ) that includes carriers  1338  (e.g., adjustable-length pogos  545  that include vacuum couplers  548 ). The shuttle  1336 , such as via the carriers  1338 , enforce a contour onto the composite part  1326  as the composite part is advanced along the assembly line  1314 . Ribs and spars are installed onto the composite part  1326  as it is progressed through rib installation  1340  and spar installation  1342 . Inspection of the rib and spar assembly, and shim installation, is performed by a robot arm  1344 , as needed. A lower wing panel  1346  is then attached to form a wing assembly (e.g., wing assembly  600 ). The various systems and stages described with regard to factory  1300  may incorporate or be in the form of the various work stations  520  discussed above. Moreover, not all of the work stations  520  described above are specifically shown in  FIG.  20   , for simplicity, although the assembly line  1314  may include such stations as one or more NDI stations  524 , cut out stations  526 , and so forth. Other operations described above with respect to  FIG.  20    may incorporate or be in the form of one or more of the feeder, layup, or assembly lines shown in schema  480  and shown in  FIG.  4   ; for example, trimming  1330  and demolding  1332  may take place in a demolding operation  490 - 11 . 
     Attention is now directed to  FIG.  21   , which broadly illustrates control components of a production system that performs (e.g. continuously) lamination and/or ultrasonic inspection in an illustrative embodiment. A controller  1400  coordinates and controls operation of laminators  1420  and movement of one or more mobile platforms  1470  along a moving line  1460  having a powertrain  1462 . The controller  1400  may comprise a processor  1410  which is coupled with a memory  1412  that stores programs  1414 . In one example, the mobile platforms  1470  are driven along a moving line  1460  that is driven continuously by the powertrain  1462 , which is controlled by the controller  1400 . In this example, the mobile platform  1470  includes utility connections  1472  which may include electrical, pneumatic and/or hydraulic quick disconnects that couple the mobile platform  1470  with externally sourced utilities  1440 . In other examples, as previously mentioned, the mobile platforms  2470  may comprise, e.g., mandrels and/or other tools, parts, supplies, and so forth, on automated conveyances such as Automated Guided Vehicles (AGVs) that include on board utilities, as well as a GPS/autoguidance system  1474 . In still further examples, the movement of the mobile platforms  1470  is controlled using laser trackers  1450 . Position and/or motion sensors  1430  coupled with the controller  1400  are used to determine the position of the mobile platforms  1470  as well as the powertrain  1462 . 
       FIG.  22    depicts a view of an assembly line  1500  in an illustrative embodiment (e.g., of a continuous assembly line), in terms of a progression of work zones  1502  arranged along a moving line and configured to perform a variety of operations. The work zones include a work zone for tool preparation  1510  involving cleaning of, or application of coatings and/or potting compound to, or repairs to, a tool  1504  (e.g., layup mandrel  110 ), following which the tool  1504  is transported on a platform  1506  to additional work zones  1502 . The additional work zones include a work zone for material application  1520  (e.g., where lamination operations are performed) in order to form a preform  1522  (such as preform  200 ). The preform  1522  may then be delivered via the assembly line  1500  to downstream work zones, including a work zone for debulking  1530  and, a work zone for compaction  1540 , and a work zone for molding  1550 . Debulking and/or compacting the preform  1522  may comprise vacuum compaction performed via a vacuum bag  1532 . Molding the preform  1522  may be performed via precure forming, and/or via a combination of molding between the tool  1504  and a caul plate  1542 . 
     The preform  1522  is further moved to work zone for hardening  1560  the preform  1522  into a composite part  1564  (e.g., composite part  250 , which may be in the form of a wing panel  550 ), such as at an autoclave  1562 , a work zone for trimming  1570  (e.g., via cutters  1572 ) the composite part  1564 , a work zone for inspection  1580  (e.g., via an NDI machine  1582 ) of the composite part  1564 , a work zone for rework  1590 , and/or a work zone for surface treatment  1595 . 
     In one embodiment, the trimming process may involve mass trimming of the preform  1522  before it is hardened, followed by more specific trimming after the composite part  1564  has been formed. Inspection of the composite part  1564  may include visual inspection as well as inspection using NDI (nondestructive inspection) equipment. Although reworking the composite part  1564  along the assembly line  500  is possible, in many cases the composite part  1564  may not require rework. The composite part  1564  then proceeds in process direction  541  through assembly line  500 . 
     EXAMPLES 
     In the following examples, additional processes, systems, and methods are described in the context of a fabrication and assembly system for wings for aircraft. 
     Referring more particularly to the drawings, embodiments of the disclosure may be described in the context of aircraft manufacturing and service in method  1600  as shown in  FIG.  23    and an aircraft  1602  as shown in  FIG.  24   . During pre-production, method  1600  may include specification and design  1604  of the aircraft  1602  and material procurement  1606 . During production, component and subassembly manufacturing  1608  and system integration  1610  of the aircraft  1602  takes place. Thereafter, the aircraft  1602  may go through certification and delivery  1612  in order to be placed in service  1614 . While in service by a customer, the aircraft  1602  is scheduled for routine work in maintenance and service  1616  (which may also include modification, reconfiguration, refurbishment, and so on). Apparatus and methods embodied herein may be employed during any one or more suitable stages of the production and service described in method  1600  (e.g., specification and design  1604 , material procurement  1606 , component and subassembly manufacturing  1608 , system integration  1610 , certification and delivery  1612 , service  1614 , maintenance and service  1616 ) and/or any suitable component of aircraft  1602  (e.g., airframe  1618 , systems  1620 , interior  1622 , propulsion system  1624 , electrical system  1626 , hydraulic system  1628 , environmental  1630 ). 
     Each of the processes of method  1600  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG.  24   , the aircraft  1602  produced by method  1600  may include an airframe  1618  with a plurality of systems  1620  and an interior  1622 . Examples of systems  1620  include one or more of a propulsion system  1624 , an electrical system  1626 , a hydraulic system  1628 , and an environmental system  1630 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry. 
     As already mentioned above, apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service described in method  1600 . For example, components or subassemblies corresponding to component and subassembly manufacturing  1608  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  1602  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the subassembly manufacturing  1608  and system integration  1610 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  1602 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  1602  is in service, for example and without limitation during the maintenance and service  1616 . Thus, the invention may be used in any stages discussed herein, or any combination thereof, such as specification and design  1604 , material procurement  1606 , component and subassembly manufacturing  1608 , system integration  1610 , certification and delivery  1612 , service  1614 , maintenance and service  1616 ) and/or any suitable component of aircraft  1602  (e.g., airframe  1618 , systems  1620 , interior  1622 , propulsion system  1624 , electrical system  1626 , hydraulic system  1628 , and/or environmental  1630 . 
     In one embodiment, a part comprises a portion of airframe  1618 , and is manufactured during component and subassembly manufacturing  1608 . The part may then be assembled into an aircraft in system integration  1610 , and then be utilized in service  1614  until wear renders the part unusable. Then, in maintenance and service  1616 , the part may be discarded and replaced with a newly manufactured part. Inventive components and methods may be utilized throughout component and subassembly manufacturing  1608  in order to manufacture new parts. 
     Any of the various control elements (e.g., electrical or electronic components) shown in the figures or described herein may be implemented as hardware, a processor implementing software, a processor implementing firmware, or some combination of these. For example, an element may be implemented as dedicated hardware. Dedicated hardware elements may be referred to as “processors”, “controllers”, or some similar terminology. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, a network processor, application specific integrated circuit (ASIC) or other circuitry, field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), non-volatile storage, logic, or some other physical hardware component or module. 
     Also, a control element may be implemented as instructions executable by a processor or a computer to perform the functions of the element. Some examples of instructions are software, program code, and firmware. The instructions are operational when executed by the processor to direct the processor to perform the functions of the element. The instructions may be stored on storage devices that are readable by the processor. Some examples of the storage devices are digital or solid-state memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. 
     Although specific embodiments are described herein, the scope of the disclosure is not limited to those specific embodiments. The scope of the disclosure is defined by the following claims and any equivalents thereof.