Abstract:
A stringer having a stringer end trim that reduces pull-off forces in a stringer connection structure, including a stringer body; a stringer free edge provided on said stringer body; and a stringer end trim having at least one curvature provided in the stringer free edge forming the stringer connection structure.

Description:
TECHNICAL FIELD 
     The disclosure generally relates to composite stringers suitable for aerospace applications. More particularly, the disclosure relates to a composite stringer end trim which has one or multiple radii and is suitable for reducing stress and strain concentrations in a composite wing stringer web. 
     BACKGROUND 
     In modern commercial aircraft, high compression loads may be transitioned from an outer wing skin panel through a side-of-body (SOB) rib to an inner wing skin panel. On an aircraft with composite wings, composite stringers are commonly bonded to the composite wing skin panel. A large portion of the loads may be carried through stringers that are bonded to the wing skin panels. The inner and outer wing skin panels and stringers may be bolted to splice plates which are provided on the SOB or by some other suitable means to transfer loads between the wing skin panels. The offset of the splice plates relative to the centroid load path of the wing skin panels may induce a bending moment at the ends of the wing panels that is reacted as a pull-off load in the web of the stringer. The pull-off load may occur at the end of the stringer, where resistance to stress and strain concentrations may be needed. In metallic structure, this is less problematic due to the material system(s) isotropic properties with respect to in and out of plane loading. In composite structure, the out of plane loads act on the weaker laminate interface resulting in delamination of composites. In a typical composite skin/stringer design, stringers are co-bonded onto the skin panel. This configuration may create a situation where a large induced moment is applied along the skin/stringer bond line at the stringer free edge creating pull off forces. The intent of this trim is to reduce localized stress concentrations at the free edge of the stringer. 
     In structures in which the end of the composite wing stringer web which is attached to the SOB rib is solid from the stringer cap to the stringer base flange, the load path through the stringer end may impart undesired stress and strain to the cap and base flange of the stringer. 
     Accordingly, it would be advantageous to have an apparatus and method which takes into account one or more of the issues discussed above, as well as possibly other issues. 
     SUMMARY 
     A stringer end trim as disclosed will reduce the bending and axial stiffness at the stringer ends to essentially “un-load” the stringer ends. Furthermore, the end trim may distribute the load across a larger area and along the stringer trim cutout edge. As a result, pull-off force resistance capability and localized strain concentration resistance are both important characteristics of stringer end trim design. To minimize strain concentrations in the trim, a constantly varying radius may be the most effective way to reduce these strain concentrations along the cutout. In order to reduce the pull-off in a way that would meet the structural requirements of a given joint, additional considerations are necessary. It was determined that adding a transition between two constantly varying radii may provide additional capability by adding effective material to the stringer for bending stiffness enhancement while also minimizing strain concentration along the stringer trim. 
     In situations where the joint attachment is through both the base flange and cap flange of the composite stringer, a multiple radius trim may be the preferable method. The intent of this trim is to reduce localized stress and strain at the free edge by reducing the bending and axial stiffness near the SOB joint. Incorporating an end trim serves to distribute the load, and thus the stress and strain, in the composite structure near the SOB joint. In cases where such a trim is not practical due to spatial constraints, edge margin considerations, etc., a single variable radius trim may be preferred. 
     In cases where an attachment is preferred only via skin or stringer attachments through one flange of the stringer, a longer half ellipse/continuously varying radius trim is preferred for reducing stress and strain concentrations. In this instance, the stringer is trimmed back such that load is distributed away from the stringer end (especially the unfastened stringer flange) and into the stringer web, stringer fastened flange, fitting, and skin as much as is practical. The intent of this trim is to trim as much stringer away as is practical without compromising the Centroid alignment, moment capability, or axial stiffness of the joint. 
     The disclosure is generally directed to a stringer having a stringer end trim that reduces pull-off forces in a stringer connection structure, including a stringer body; a stringer free edge provided on said stringer body; and a stringer end trim having at least one curvature provided in the stringer free edge forming the stringer connection structure. 
     The disclosure is also directed to a stringer which has one or multiple radii and is suitable for reducing stress and strain concentrations in a composite wing stringer web. The radius or radii may drive loads from the stringer cap and stringer base flange into the radii to reduce stress and strain at the cap and base flange and along fixed edges of the stringer. An illustrative embodiment of the stringer includes a stringer body, a stringer free edge provided on the stringer body and a stringer end trim having at least one radius provided in the stringer free edge. 
     The disclosure is further generally directed to a wing-to-body structure or wing/fairing attachments on aerospace products (such as vertical and horizontal airplane stabilizers, wing/fin to body structure or aircraft, rockets and missiles, for example and without limitation). An illustrative embodiment of the wing-to-body structure includes a side of body rib, a stringer having a stringer body carried by the side of body rib, a stringer free edge provided on the stringer body and a stringer end trim having at least one radius provided in the stringer free edge and a wing skin panel carried by the side of body rib and the stringer. 
     The disclosure is further generally directed to a method for tailored reduction of stress concentrations within the free end of a stringer. An illustrative embodiment of the method includes providing a stringer having a stringer free end and providing at least one radius in the stringer free end. 
     In some embodiments, the stringer may include a laminated composite stringer body having a first stringer flange, a second stringer flange and a stringer web extending between the first stringer flange and the second stringer flange; a stringer free edge provided on the stringer web; and a double radius stringer end trim provided in the stringer free edge and having a first parabolic and continuously-varying edge radius, a second parabolic and continuously-varying edge radius and a convex transition radius joining the first edge radius and the second edge radius. 
     In some embodiments, the wing-to-body structure may include a side of body rib; a stringer having a laminated composite stringer body carried by the side of body rib and including a first stringer flange, a second stringer flange, a stringer web extending between the first stringer flange and the second stringer flange, a stringer free edge provided on the stringer web and a double radius stringer end trim provided in the stringer free edge and having a first parabolic and continuously-varying edge radius, a second parabolic and continuously-varying edge radius and a convex transition radius joining the first edge radius and the second edge radius; a wing skin panel carried by the side of body rib and the first stringer flange of the stringer; and a stringer cap fitting carried by the second stringer flange of the stringer. 
     In some embodiments, the method for tailored reduction of stress concentrations within the free end of a stringer may include providing a stringer having a laminated composite stringer body including a first stringer flange, a second stringer flange and a stringer web extending between the first stringer flange and the second stringer flange with a stringer free end on the stringer web; trimming a double radius stringer end trim having a first parabolic and continuously-varying radius, a second parabolic and continuously-varying radius and a convex transition radius joining the first radius and the second radius in the stringer free end; providing a wing-to-body structure having a side-of-body rib and a wing skin panel carried by the side-of-body rib; and assembling the stringer into the wing-to-body structure by joining the stringer body of the stringer to the side-of-body rib and the wing skin panel. With attachments that include a stringer cap and base flange attachment, a “Double Grodzinski” or double radius stringer end trim configuration may be used. For attachments that include stringer attachments through only one stringer flange, a single radius stringer end trim configuration may be preferred. 
     The disclosure is further generally directed to a method for reducing peel loading in a stringer of a wing to body structure. An illustrative embodiment of the method includes providing a stringer having a stringer free end and providing at least one radius in the stringer free end. 
    
    
     
       BRIEF DESCRIPTION OF THE ILLUSTRATIONS 
         FIG. 1  is an illustration of a side view of a stringer with a double radius stringer end trim provided in the stringer. 
         FIG. 1A  is a side view of a double Grodzinski radius which is suitable for implementation of the double radius stringer end trim. 
         FIG. 2  is an illustration of a perspective view of a wing to body structure having a stringer with a double radius stringer end trim. 
         FIG. 3  is an illustration of a sectional view of a wing to body structure having a pair of stringers with a double radius stringer end trim attached to a side of body (SOB) rib. 
         FIG. 4  is an illustration of a side view of a stringer with a single radius stringer end trim. 
         FIG. 5  is an illustration of a sectional view of a wing to body structure having a pair of stringers with a single radius stringer end trim attached to a side of body (SOB) rib. 
         FIG. 6  is a graph which illustrates load optimization of a stringer with a double radius stringer end trim in which normalized pull-off running load (Y-axis) is plotted vs. free edge onset capability (X-axis). 
         FIG. 7  is a graph which illustrates pull-off running load (lb/in) comparisons between stringers with different end trims. 
         FIG. 8  is a graph which illustrates running load comparisons between stringers with a double radius stringer end trim and stringers with a single radius stringer end trim. 
         FIG. 9  is a graph which illustrates pull-off running load comparisons between baseline stringers with a single radius stringer end trim (˜375 lbs/in) and stringers with a double radius stringer end trim with pull-off running load (˜150 lbs/in) plotted as a function of distance in inches from the free edge of the stringer. 
         FIG. 10  is an illustration of a flow diagram which illustrates a method for the tailored reduction of stress concentrations within the free end of a composite lamina assembled stringer. 
         FIG. 11  is an illustration of a flow diagram which illustrates a method for a tailored reduction of stress concentration in a stringer runout. 
         FIG. 11A  is an illustration of a flow diagram which illustrates a method of reducing peel loading in a stringer of a wing to body structure. 
         FIG. 12  is an illustration of a flow diagram of an aircraft production and service methodology. 
         FIG. 13  is an illustration of a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to practice the disclosure and are not intended to limit the scope of the appended claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     Referring initially to  FIGS. 1-3  of the drawings, an illustrative embodiment of a stringer with a double radius stringer end trim, hereinafter stringer, is generally indicated by reference numeral  2  in  FIG. 1 . As shown in  FIGS. 2 and 3 , in some embodiments the stringer  2  may be part of a wing-to-body structure  1  in an aerospace or other application in which it is desired to reduce stress and strain concentrations in a free edge  8  of the stringer  2 . In some embodiments, the free edge  8  may be curved as shown in  FIG. 1 . The stringer  2  may include a stringer body  9  which may be a composite material having a stringer base flange  3 , a stringer cap flange  4  and a stringer web  5  extending between the stringer base flange  3  and the stringer cap flange  4 . The stringer base  3  may be a laminated composite material having composite laminates  3   a . The stringer base flange  3 , the stringer cap  4  and/or the stringer web  5  may be a laminated composite material having composite laminates  4   a . The stringer  2  may have any of various cross-sectional configurations including a J-configuration, a Z-configuration, a T-configuration or a hat configuration, for example and without limitation. 
     The stringer body  9  of the stringer  2  may have a stringer free edge  8 . A double radius stringer end trim  7  may be provided in the stringer free edge  8 . As shown in  FIG. 1A , the double radius stringer end trim  7  may be a double Grodzinski radius  80  which is a double radius configuration having a first continuously varying radius  81 , a transition radius  82  extending from the first continuously varying radius  81  and a second continuously varying radius  83  extending from the transition radius  82 . As illustrated in  FIG. 1 , the double radius stringer end trim  7  may include a generally concave first edge radius  10 , a generally concave second edge radius  14  and a generally convex transition radius  12  which joins the first edge radius  10  and the second edge radius  14 . The first edge radius  10 , the transition radius  12  and the second edge radius  14  may have continuously-varying radii  16   a - 16   c , respectively. In some embodiments, the first edge radius  10  and the second edge radius  14  may each have a generally parabolic shape, as shown. The transition radius  12  may provide a smooth transitional contour between the first edge radius  10  and the second edge radius  14 . The first edge radius  10 , the second edge radius  14  and the transition radius  12  of the double radius stringer end trim  7  may be cut, formed and/or otherwise fabricated in the stringer free edge  8  according to the knowledge of those skilled in the art. 
     As shown in  FIGS. 2 and 3 , the stringer  2  may be part of a wing-to-body structure  1  which may include a side of body (SOB) splice plate  22 . The SOB splice plate  22  may be metallic, composite material and/or other material which is suitable for the purpose. The stringer  2  may be bonded and/or otherwise attached to a wing skin panel  18  which is attached to the SOB splice plate  22  with the stringer free edge  8  of the stringer  2  generally adjacent to the SOB splice plate  22 . The stringer  2  and the wing skin panel  18  may be bolted (not shown) and/or otherwise attached to the SOB splice plate  22 . As shown in  FIG. 2 , in some embodiments a stringer cap fitting  24  may be provided on the stringer cap  4  of the stringer  2 . 
     As shown in  FIG. 3 , in aerospace or other applications, compression loads  20  may be applied to the wing skin panel  18  and the stringer  2 . The compression loads  20  may be transferred from the wing skin panel  18  and the stringer  2  to the SOB splice plate  22 . The compression loads  20  may induce a bending moment  26  in the ends  18   a  of the wing skin panel  18  and the stringer  2 . The bending moment  26  may be reacted as a pull-off load  27  which may also be known as peel load in the stringer web  5  of the stringer  2 . The double radius stringer end trim  7  may reduce the absolute magnitude of the pull-off load  27  which results from the bending moment  26  at the stringer free edge  8 . The double radius stringer end trim  7  may additionally minimize edge-of-trim strains  30  throughout the stringer free edge  8 . As illustrated in  FIG. 2 , the double radius stringer end trim  7  may drive the load path  38  from the stringer base flange  3  and the stringer cap  4  into the double radius stringer end trim  7 . This may reduce stress and strain concentrations  30  along the stringer base flange  3  and the stringer cap  4  thus reducing the possibility of stringer being pulled off the skin. 
     Referring next to  FIGS. 4 and 5 , a stringer with a single radius stringer end trim, hereinafter stringer, is generally indicated by reference numeral  2   a . A single radius stringer end trim  28  may be provided in the stringer free edge  108  of the stringer body  109  of the stringer  2   a . The single radius stringer end trim  28  may have a single edge radius  29  which may have a continuously-varying radius  16 . As shown in  FIG. 4 , in some embodiments the single edge radius  29  of the single radius stringer end trim  28  may extend through the stringer cap flange  104  of the stringer  2   a . In some embodiments, the single edge radius  29  may have a generally parabolic shape, as shown. The single radius stringer end trim  28  may be cut, formed and/or otherwise fabricated in the stringer free edge  108  according to the knowledge of those skilled in the art. The stringer  2   a  may have any of various cross-sectional configurations including a J-configuration, a Z-configuration, a T-configuration or a hat configuration, for example and without limitation. 
     As shown in  FIG. 5 , the stringer  2   a  may be part of a wing-to-body structure  1   a  which may include a side of body (SOB) slice plate  122 . The stringer  2   a  may be bonded and/or otherwise attached to a wing skin panel  118  which may be attached to the SOB splice plate  122  with the stringer free edge  108  of the stringer  2   a  generally adjacent to the SOB splice plate  122 . The stringer  2   a  and the wing skin panel  118  may be bolted and/or otherwise attached to the SOB splice plate  122 . The stringer  2   a  with single radius stringer end trim  128  may be used in applications in which structure  118  such as the wing skin panel  118  is provided on only one side  106  of the stringer  2   a . In that case, a stringer cap fitting  124  ( FIG. 2 ) may be omitted from the opposite side  106   a  of the stringer  2 . 
     Application of the stringer  2   a  may be as was heretofore described with respect to the stringer  2  in  FIGS. 2 and 3 . Accordingly, in aerospace or other applications, compression loads  120  applied to the wing skin panel  118  may be transferred from the wing skin panel  118  to the stringer  2   a  through the SOB slice plate  122 . A bending moment  126  may be reacted as a pull-off load  127  in the stringer web  5  of the stringer  2   a . The single radius stringer end trim  128  may reduce the absolute magnitude of the pull-off load  127  which results from the bending moment  126  at the stringer free edge  108 . The single radius stringer end trim  128  may additionally minimize edge-of-trim strains  130  throughout the stringer free edge  108 . As illustrated in  FIG. 4 , the single radius stringer end trim  28  may drive the load path  39  from the stringer base flange  103  and the stringer cap  104  into the single radius stringer end trim  28 . This may reduce stress and strain concentrations  130  along the stringer base flange  103  and the stringer cap  104  and thus reducing pull-off loads. 
     Referring next to  FIG. 6 , a graph  32  which illustrates load optimization of a stringer  2  ( FIG. 1 ) with a double radius stringer end trim  7  is shown. In the graph  32 , free edge onset capability of the stringer  2  is plotted along the X-axis  33  and normalized running load  27  ( FIGS. 3 ,  5 ) for each value of free edge onset capability is plotted along the Y-axis  34 . The optimization direction  35  is shown as a straight line  35 . A normalized running load  27  of 1.0 corresponds to a free edge onset capability  33  of 100% of structural loading requirements. Points  36  on the graph  32  illustrate various optimized and non-optimized embodiments of the stringer  2  with double radius stringer end trim  7 . 
     Pull-off load  127  was resulted from the tensional load transferred from stringer web  5  to the stringer flange  103 . The proposed stringer end trim  128  will provides a gradual transition, which redistributes the tensional load in a longer transition path and resulted in a lower pull-off running load  127 . In addition, the end trim  128  will move the maximum pull-off load away from the free edge  108  to the location where a delamination arrestment and prevention mechanism could be implemented. The end trim utilizes the existing configuration to distribute the maximum load through a double shear fastener location (not shown) rather than directly onto a skin/stringer bond line (not shown). The usage of one radius or double radii curves depended on the cross-sectional configuration of the stringer including the fastener pattern. Generally, a double radius has proven to be optimal/preferred over a single radius for configurations where both sides of the stringer (cap &amp; base flange) are bolted. 
     Utilizing the Grodzinski curves, associated with the desired load transfer mechanism within the design configuration envelope, resulted in the proposed end trim  128  configuration. Furthermore, the Double Grodzinski has a transition radius  16   b  ( FIG. 1 ) which provides additional bending capability into the stringer  2  by increasing the stringer stiffness. This feature allows more of the load to transfer into the stringer  2  and away from the base flange  103  thus providing additional pull-off capability due to the slightly lower load through the base flange/skin fastener locations. 
     Referring next to  FIG. 7 , a graph  40  which illustrates running load (lb/in)  27  ( FIG. 3 ) comparisons between stringers  2   a  ( FIG. 3 ) with and without end trims  28  is shown. Distance to the stringer free edge  8  (in inches) is plotted along the X-axis  41  and the running load (lb/in)  27  applied to the stringer  2   a  is plotted along the Y-axis  42 . The maximum running load  43  at the stringer free edge  8  is 5400 lb/in. A fastener position  45  is 2˜3 inches from the stringer free edge  8 . The low peak running load  27  ( FIG. 3 ) at the stringer free edge  8  and located within the fastener influence range 44 is about 1000 lb/in. The data shown in this comparison was based on a heavy gage stringer configuration. 
     Referring next to  FIG. 8 , a graph  50  which illustrates peak running load comparisons between stringers  2  ( FIG. 1 ) with a double radius stringer end trim  7  and stringers  2   a  ( FIG. 4 ) with a single radius stringer end trim  28  is shown. Distance to the stringer free edge  8  (in inches) is plotted along the X-axis  51  and the running load (lb/in)  27  applied to the stringer  2 ,  2   a  is plotted along the Y-axis  52 . The peak running load  53  for the single radius stringer end trim  28  of the stringer  2   a  is about 2,400 lbs/in. The peak running load  54  for the double radius stringer end trim  7  of the stringer  2  is about 1,800 lbs/in. This corresponds to a 33% reduction in the peak pull off load  27  ( FIG. 3 ). 
     Referring next to  FIG. 9 , a graph  60  which illustrates running load  27  comparisons for a light gage stringer configuration between a stringer  2  with a single radius end trim  7  and test stringers  2  with a double radius stringer end trim  7  is shown. The distance in inches from the free edge  8  of the stringers  2  is plotted on the X-axis  61 . The running load  27  in lbs/in applied to the stringer  2  is plotted on the Y-axis  62 . A first stringer with a single radius end trim  63  had a maximum running load  27  of ˜375 lbs/in. A second stringer with a single radius end trim  65  had a maximum running load  27  of ˜460 lbs/in. The first stringer with a double radius trim  64  had a maximum running load  27  of ˜150 lbs/in. The second stringer with a double radius trim  66  had a maximum running load  27  of ˜160 lbs/in. Compared to the first stringer with a single radius trim  63  and the second stringer with a single radius trim  65 , the first stringer with a double radius trim  64  and the second stringer with a double radius trim  66  both had a lower running load  27 . The end trim helps both static load situation and dynamic load situation. The effectiveness was assessed and covered both static load condition as well as dynamic load condition (fatigue). 
     Referring next to  FIG. 10 , a flow diagram  1100  which illustrates a method for the tailored reduction of stress concentrations within the stringer free end  8  of a composite lamina assembled stringer  2  is shown. In block  1102 , a stringer  2  having a laminated composite stringer body  9  including stringer flanges  3 ,  4  and a stringer web  5  extending between the stringer flanges  3 ,  4  and with a stringer free end  8  on the stringer web  5  is provided. In block  1104 , a double radius stringer end trim  7  having first  10  and second  14  parabolic and continuously-varying radii and a smooth, convex transition radius  12  joining the first  10  and second  14  radii is trimmed in the stringer free end  8 . In block  1106 , a wing-to-body structure  1  having a side-of-body rib  22  and a wing skin panel  18  provided on the side-of-body rib  22  is provided. In block  1108 , the stringer  2  may be assembled into the wing-to-body structure  1  by joining the stringer body  9  of the stringer  2  to the side-of-body rib  22  and the wing skin panel  18 . 
     Referring next to  FIG. 11 , a flow diagram  1200  which illustrates a method for the tailored reduction of stress concentrations within the stringer free end  8  of a composite lamina assembled stringer  2   a  is shown. In block  1202 , a stringer  2   a  having a laminated composite stringer body  9  including stringer flanges  3 ,  4  and a stringer web  5  extending between the stringer flanges  3 ,  4  and with a stringer free end  8  on the stringer web  5  is provided. In block  1204 , a single radius stringer end trim  28  having a parabolic and continuously-varying single edge radius is trimmed in the stringer free end  8 . In block  1206 , a wing-to-body structure  1   a  having a side-of-body splice plate  22  and a wing skin panel  18  provided on the side-of-body splice plate  22  is provided. In block  1208 , the stringer  2   a  may be assembled into the wing-to-body structure  1   a  by joining the stringer body  9  of the stringer  2   a  to the side-of-body splice plate  22  and the wing skin panel  18 . 
     Referring next to  FIG. 11A , a flow diagram  1100   a  which illustrates a method of reducing peel loading in a stringer of a wing to body structure is shown. In block  1102   a , a stringer  2  having a laminated composite stringer body  9  including stringer flanges  3 ,  4  and a stringer web  5  extending between the stringer flanges  3 ,  4  and with a stringer free end  8  on the stringer web  5  is provided. In block  1104   a  and  1105   a , a single radius stringer end trim  28  having a parabolic and continuously-varying single edge radius is trimmed in the stringer free end  8  or a double radius stringer end trim  7  having first  10  and second  14  parabolic and continuously-varying radii and a smooth, convex transition radius  12  joining the first  10  and second  14  radii is trimmed in the stringer free end  8 . In block  1106   a , a wing-to-body structure  1  having a side-of-body rib  22  and a wing skin panel  18  provided on the side-of-body rib  22  is provided. In block  1108   a , the stringer  2  may be assembled into the wing-to-body structure  1  by joining the stringer body  9  of the stringer  2  to the side-of-body rib  22  and the wing skin panel  18 . 
     Referring next to  FIGS. 12 and 13 , embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method  78  as shown in  FIG. 12  and an aircraft  94  as shown in  FIG. 13 . During pre-production, exemplary method  78  may include specification and design  85  of the aircraft  94  and material procurement  87 . During production, component and subassembly manufacturing  84  and system integration  86  of the aircraft  94  takes place. Thereafter, the aircraft  94  may go through certification and delivery  88  in order to be placed in service  90 . While in service by a customer, the aircraft  94  may be scheduled for routine maintenance and service  92  (which may also include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  78  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. 13 , the aircraft  94  produced by exemplary method  78  may include an airframe  98  with a plurality of systems  96  and an interior  100 . Examples of high-level systems  96  include one or more of a propulsion system  102 , an electrical system  132 , a hydraulic system  134 , and an environmental system  136 . 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. 
     The apparatus embodied herein may be employed during any one or more of the stages of the production and service method  78 . For example, components or subassemblies corresponding to production process  84  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  94  is in service. Also one or more apparatus embodiments may be utilized during the production stages  84  and  86 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  94 . Similarly, one or more apparatus embodiments may be utilized while the aircraft  94  is in service, for example and without limitation, to maintenance and service  92 . 
     Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.