Abstract:
A central wing box for an aircraft, including a top panel, a bottom panel, a front spar, a rear spar, and at least one secondary rib. A secondary rib includes two stiffeners, a first stiffener extending adjacent to the top panel and to one of the front spar and the rear spar, and a second stiffener extending adjacent to the bottom panel and to the other of the front spar and the rear spar. A reduced number of components can be employed, thereby simplifying the construction of the central wing box of an aircraft, particularly the installation of the secondary ribs.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to French Patent Application FR 15 58205 filed Sep. 4, 2015, the entire disclosure of which is incorporated by reference herein. 
       TECHNICAL FIELD 
       [0002]    The disclosure herein relates to a rib for the central wing box of an aircraft, and more particularly to an internal rib referred to as a secondary rib. 
       BACKGROUND 
       [0003]    In  FIG. 1 , the structure of an aircraft comprises a fuselage  101  and a wing structure  102  which are joined together by a central box  103  referred to as the central wing box of the aircraft. The central wing box  103  notably withstands loading applied in flight to the wings of the aircraft. 
         [0004]    The central wing box  103 , and two frames  104  between which it is positioned, are depicted in  FIG. 1  in heavy line. An orthonormal frame of reference in which: the axis Ox corresponds to the longitudinal axis of the aircraft, which axis extends from the tail cone to the nose cone of the aircraft; the axis Oy corresponds to the transverse axis of the aircraft, making with the axis Ox a plane that is horizontal when the aircraft is standing on a horizontal surface; and the axis Oz corresponds to the heightwise axis of the aircraft, corresponding to the vertical when the aircraft is standing on a horizontal surface, is also depicted. 
         [0005]      FIG. 2  illustrates a detailed view of one example of a central wing box  103  oriented in space in the same way as in  FIG. 1 . The central wing box  103  in particular comprises: a top panel  1031 , or extrados panel, extending substantially in a plane parallel to the plane (xOy), but slightly inclined and curved relative to this plane; a bottom panel, or intrados panel, extending under the top panel, substantially parallel thereto (not visible in  FIG. 2 ); a front spar  1033 , extending in a plane parallel to the plane (yOz); and a rear spar, extending behind the front spar, parallel thereto (not visible in  FIG. 2 ). 
         [0006]    These four components together form a volume referred to as the “volume of interest”. In general, this volume is closed laterally by two ribs referred to as end ribs, which extend one on each side of the aircraft in planes substantially parallel to the plane (xOz). In  FIG. 2 , only the left-hand end rib  1035  is visible. Extending inside the volume of interest are ribs, referred to as secondary ribs or internal ribs. The internal ribs extend in planes substantially parallel to the plane (xOz) or, in other words, in planes substantially orthogonal to the top and bottom panels and to the front and rear spars. The internal ribs extend parallel to any end ribs there might be. The internal ribs form reinforcing components to strengthen the wing box  103 . 
         [0007]    Other elements of  FIG. 2  will be described further herein. 
         [0008]      FIG. 3  schematically illustrates one embodiment of a secondary rib  200  according to the prior art, viewed in a plane parallel to the plane (xOz). The secondary rib  200  comprises a vertical post  201 , which extends along the axis (Oz), adjacent to the front spar and outside of the volume of interest as defined hereinabove. The vertical post  201  is also visible in  FIG. 2 . A rib flange  202  extends adjacent to the bottom panel  1032 , inside the volume of interest, whereas an on-box beam  203  extends adjacent to the top panel  1031  and outside the volume of interest (see also  FIG. 2 ). The on-box beam  203  extends adjacent to the top panel  1031  on one side, and to a horizontal plane on the other. Rod fittings  204  project into the volume of interest and from the on-box beam. Each rod fitting  204  has two openings, each accepting a rod  205 . The two rods connected to the same rod fitting extend obliquely to the rib flange  202 , delineating a triangle shape therewith. A secondary rib  200  according to the prior art has, for example, six rods.  FIG. 3  also depicts floor links  206  which provide the connection between the secondary rib and the floor in the aircraft. These links all have more or less the same length along the axis (Oz). A second vertical post may extend adjacent to the rear spar. 
         [0009]    One disadvantage with the secondary ribs  200  according to the prior art is that they are complicated to install, particularly the rods  205 . 
         [0010]    One objective of the present disclosure is to allow a simplification of the installation of the internal or secondary ribs of an aircraft central wing box. 
       SUMMARY 
       [0011]    This objective is achieved with a central wing box for an aircraft, comprising a top panel, a bottom panel, a front spar, a rear spar, and at least one rib referred to as an internal rib, in which each internal rib comprises two pieces referred to as stiffeners arranged inside a volume delimited by the top panel, the bottom panel, the front spar, and the rear spar, a first stiffener extending adjacent to the top panel and to one of the front spar and the rear spar, and a second stiffener extending adjacent to the bottom panel and to the other of the front spar and the rear spar. 
         [0012]    The wing box according to the disclosure herein comprises internal ribs that have an alternative structure to the one proposed in the prior art. This alternative structure makes it possible to dispense with the rods extending inside the volume of interest as defined in the introduction. Without these rods, installing the internal ribs is greatly simplified. 
         [0013]    Preferably, at least one stiffener comprises: a first leg extending along adjacent to the top or bottom panel; a second leg extending along adjacent to the front or rear spar, a first end of the first leg and a first end of the second leg being joined together; and a reinforcing element extending from the first leg to the second leg. 
         [0014]    The reinforcing element may extend from a second end of the second leg to a support region of the first leg, the support region being situated some distance from the ends of the first leg. 
         [0015]    As an alternative, the reinforcing element may extend from a support region of the second leg to a support region of the first leg, each support region being situated some distance from the ends of the corresponding leg. 
         [0016]    A stiffener may comprise a through-opening extending between the reinforcing element, the first leg and the second leg. 
         [0017]    As an alternative, a region of a stiffener, situated between the reinforcing element, the first leg and the second leg, may be solid and of mechanical strength lower than that of the reinforcing element. 
         [0018]    Advantageously, the second ends of the first and second legs of each stiffener of the same internal rib are superposed in pairs. 
         [0019]    Preferably, second ends of the first and second legs of each stiffener of the same internal rib are joined together in pairs. 
         [0020]    At least one stiffener may comprise a series of cavities, distributed along the first leg and designed to accommodate stiffeners of the bottom or top panel to which the first leg is adjacent. 
         [0021]    The disclosure herein also relates to a method of installing an internal rib of a central wing box according to the disclosure herein, comprising the following steps: installing the first stiffener adjacent to the top panel and to one of the front spar and the rear spar; and installing the second stiffener adjacent to the bottom panel and to the other of the front spar and the rear spar. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The present disclosure will be better understood from reading the description of exemplary embodiments given purely by way of entirely non-limiting example and with reference to the attached drawings in which: 
           [0023]      FIG. 1  is a schematic perspective illustration of an aircraft and notably of the central wing box of the aircraft; 
           [0024]      FIG. 2  is a perspective illustration of one example of an aircraft wing box according to the prior art; 
           [0025]      FIG. 3  is a face-on illustration of an internal rib according to the prior art; 
           [0026]      FIG. 4  is a schematic face-on illustration of a first embodiment of an internal rib according to the disclosure herein; 
           [0027]      FIG. 5  illustrates a first alternative form of the embodiment depicted in  FIG. 4 ; 
           [0028]      FIG. 6  is an exploded view of the internal rib depicted in  FIG. 5 ; 
           [0029]      FIG. 7  illustrates a second alternative form of the embodiment depicted in  FIG. 4 ; 
           [0030]      FIG. 8  is a view in cross section illustrating a detail of the internal rib depicted in  FIG. 7 ; and 
           [0031]      FIG. 9  illustrates a detail of a second embodiment of an internal rib according to the disclosure herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    The central wing box according to the disclosure herein corresponds more or less to a central wing box according to the prior art, in which at least one internal rib according to the prior art is replaced by an internal rib according to the disclosure herein. Preferably, each internal rib according to the prior art is replaced by a respective internal rib according to the disclosure herein. 
         [0033]      FIG. 4  schematically illustrates a first embodiment of an internal rib  400  according to the disclosure herein. 
         [0034]    The internal rib  400  extends in a plane parallel to the plane (xOz). When end ribs are present, the internal rib  400  extends in a plane parallel to the plane of the end ribs. The internal rib is made up chiefly of two stiffeners  410 A and  410 B, both situated entirely inside the useful volume as defined in the introduction. 
         [0035]    A first stiffener  410 A extends adjacent to the top panel  1031  and to the front spar  1033 . It extends along the entire extent of the respective profiles of the top panel  1031  and of the front spar  1033 , inside the central wing box. These profiles are defined by the intersection of the top panel  1031  and, respectively, of the front spar  1033 , with a plane parallel to the plane (xOz) passing through the first stiffener  410 A. According to an alternative form that has not been depicted, the first stiffener  410 A does not extend along the entire extent of the profiles, but nevertheless does extend over more than three quarters of this extent. 
         [0036]    A second stiffener  410 B extends adjacent to the bottom panel  1032  and to the rear spar  1034 . It extends along the entire extent of the respective profiles of the bottom panel  1032  and of the rear spar  1034 , inside the central wing box. These profiles are defined by the intersection of the bottom panel  1032  or, respectively, of the rear spar  1034 , with a plane parallel to the plane (xOz) passing through the second stiffener  410 B. According to an alternative form that has not been depicted, the second stiffener  410 B does not extend over the entire extent of the profiles, but does nevertheless extend over more than three quarters of this extent. 
         [0037]    The internal rib is made in just two pieces, each being attached to a spar and to a panel. These two components together provide optimum support for the panels to prevent phenomena of buckling. They contribute to the rigidity of the central wing box. 
         [0038]    Installing an internal rib then simply comprises or consists of positioning and securing each of the two stiffeners. 
         [0039]    Each stiffener is formed as a single piece at the time that it is installed in the central wing box. 
         [0040]    The assembly according to the prior art, comprising the rib flange, the on-box beam, the at least one vertical post, the rod fittings and the series of several rods according to the prior art, is replaced by two stiffeners situated inside the useful volume defined in the introduction. Assembling the internal rib is thus greatly simplified. 
         [0041]    The entirety of the internal rib lies inside the volume of interest defined in the introduction, and this likewise makes assembly easier. 
         [0042]    The disclosure herein offers the advantage of not requiring modifications to the overall structure of the central wing box of the aircraft, notably to the bottom and top panels, the front and rear spars and, where present, the end ribs. 
         [0043]    Constructing the rib as two components allows it to be fitted accurately to each central wing box, it being possible for this box to exhibit dimensions that differ slightly from one individual example to another depending on the manufacturing and positioning tolerances acceptable therefor. Fitting involves only a very limited number of elements. The positions of the first and second stiffener are simply adjusted. 
         [0044]    The internal rib according to the disclosure herein has a mechanical strength suited to the model of aircraft for which it is intended, preferably at least equivalent to that of the corresponding internal rib of the prior art. In particular, it is able to absorb all of the following:
       pressure loading, parallel to the axis (Oz), exerted notably as a result of the difference in pressure between the central wing box and the cabin;   loading on the front spar, caused by the aviation fuel upon impact with the ground; and   loading referred to as “positive gust” loading, corresponding to significant flexing of the wings of the aircraft relative to the fuselage.       
 
         [0048]    The internal rib according to the disclosure herein no longer comprises a series of rods, but simply comprises two substantially planar components extending parallel to the plane (xOz). 
         [0049]    In the prior art, there is a certain tolerance on the positioning of the holes in the rod fittings, intended to accommodate the pivot about which one end of the rod pivots. The slight differences that may exist, from one individual example of wing box to another, need to be taken into consideration when mounting the rods. In particular, the spacing between the two pivots about which each rod pivots needs to be measured and the rod needs then to be customized for length. According to the disclosure herein, these rods are dispensed with, making it possible to dispense with this customization with regard to length. The mounting of the internal rib is therefore greatly simplified. 
         [0050]    The first stiffener  410 A, as illustrated in  FIG. 4 , will now be described in greater detail. This is a rigid component made up of two legs and a reinforcing element. 
         [0051]    A first leg  411 A extends adjacent to the top panel  1031 . The first leg  411 A follows the profile of the top panel  1031 , this profile being defined by the intersection between this top panel and a plane parallel to the plane (xOz) passing through the first leg  411 A. 
         [0052]    A second leg  412 A extends adjacent to the front spar  1033 . The second leg  412 A follows the profile of the front spar  1033 , this profile being defined by the intersection between this front spar and a plane parallel to the plane (xOz) passing through the second leg  412 A. 
         [0053]    The first and second legs each preferably have a planar shape, extending in a plane parallel to the plane (xOz). The first and second legs have reduced widths in this plane. 
         [0054]    The first leg  411 A and the second leg  412 A are joined together at their respective first ends  4111 A,  4121 A, at the corner formed between the top panel  1031  and the front spar  1033 . 
         [0055]    In order to strengthen the assembly formed by these two legs, a reinforcing element  413 A extends between them, connected on one side to the first leg  411 A and on the other to the second leg  412 A. The reinforcing element extends in the plane of the first and second legs  411 A,  412 A. It extends obliquely relative to the first and second legs  411 A,  412 A. It has a planar shape, parallel to the plane (xOz), of width preferably less than or equal to the mean width of the first and second legs. 
         [0056]    In the example illustrated in  FIG. 4 , the reinforcing element  413 A extends from the second end  4122 A of the second leg to a support region  4113 A of the first leg. The second end  4122 A of the second leg is the opposite end of the second leg to the first end  4121 A as defined hereinabove. 
         [0057]    The support region  4113 A is situated some distance from the ends of the first leg  410 A. The distance between the center of the support region and the ends  411 A,  412 A of the first leg, along the profile of the top panel  1031 , is, for example, greater than 10% or even 20% of the length of the first leg. 
         [0058]    The support region  4113 A is, for example, adjacent to the second fifth of the profile of the top panel  1031  (the panel to which the first leg  411 A is adjacent). This profile is measured from the intersection of this top panel with the front spar (the spar to which the second leg  412 A is adjacent), to the intersection of this top panel with the rear spar. This is a panel profile, inside the central wing box. This profile is defined by the intersection between the top panel and the plane parallel to the plane (xOz) passing through the first leg  411 A. This profile does not necessarily extend in a straight line. The length of the profile does not denote its dimension along (Ox) but its extent inside the wing box and in the plane parallel to (xOz). 
         [0059]    Thus, considering a profile of length 1=L, with 1=0 at the intersection with the front spar  1033 , the support region extends from 1=L/5=L*0.2 to 1=2L/5=L*0.4. As an alternative, the support region is situated in the second third of the profile. According to another alternative form, the support region is situated in the second quarter of the profile. 
         [0060]    In other words, the reinforcing element  413 A may extend from the second end  4122 A of the second branch to a support region  4113 A of the first leg, the support region being adjacent to the second fifth of the profile of the corresponding bottom or top panel, the profile being defined in a plane parallel to the internal ribs and passing through the first leg, and a length of the profile being measured from its intersection with the front or rear spar to which the second leg is adjacent. 
         [0061]    According to an alternative form that has not been depicted, the reinforcing element extends from a support region of the second leg to a support region of the first leg, each support region being situated some distance from the ends of the corresponding leg. The distance between the center of a support region and the ends of the corresponding leg, along the profile of the top panel or, respectively, the bottom panel, is for example greater than 10% or even 20% of the length of the leg. 
         [0062]    Configuring the stiffener as two legs and a reinforcing element between them makes it possible to limit its bulk, for the same mechanical strength. 
         [0063]    The positioning of the reinforcing element described hereinabove, and the siting of the support region offer optimum mechanical strength and optimum transmission of load, whether the load is oriented along (Oz) or along (Ox). 
         [0064]    In the example depicted in  FIG. 4 , the space situated between the first and second legs  411 A,  412 A and the reinforcing element  413 A is a simple through-opening  414 A, or in other words a hole. As an alternative, this space may be solid. When this space is solid, it may have mechanical strength lower than that of the reinforcing element, for example more than two times lower. In practice, this lower mechanical strength may manifest itself in a smaller thickness along the axis (Oy). 
         [0065]    The second stiffener  410 B has the same structure as the first stiffener  410 A. Whereas the first stiffener  410 A extends along the top panel  1031  and the front spar  1033 , the second stiffener  410 B extends along the bottom panel  1032  and the rear spar  1034 . The second stiffener  410 B has a first leg  411 B adjacent to the bottom panel  1032 , a second leg  412 B adjacent to the rear spar  1034 , and a reinforcing element  413 B between the two. 
         [0066]    The two stiffeners extend, more or less symmetrically, inside the volume of interest defined in the introduction. The degree of superposition between the second stiffener and the symmetry with the first stiffener is greater than or equal to 90%, or even 95%. 
         [0067]    In the example depicted in  FIG. 4 , the first and second stiffener  410 A,  410 B are superposed, at the two corners formed respectively between the top panel  1031  and the rear spar  1034 , and between the bottom panel  1032  and the front spar  1033 . In particular, the second end  4112 A of the first leg  411 A (on the opposite side to its first end  4111 A) is superposed with the second end  4122 B of the second leg  412 B, and the second end  4112 B of the first leg  411 B is superposed with the second end  4122 A of the second leg  412 A. 
         [0068]    Because the on-box beam illustrated in  FIG. 3  has been dispensed with, the floor links  406 , which provide the connection between the internal rib and the floor of the aircraft have variable lengths, along the profile of the top panel. For example, the ratio between the longest link and the shortest link is greater than 1.5. 
         [0069]    At least one stiffener may be made up of metal plates that have been machined, or deformed by stamping, pressing or forging. In addition or as an alternative, at least one stiffener may be made up of several metal beams fixed together. 
         [0070]      FIG. 5  illustrates, in a perspective view, one particular alternative form  500  of the internal rib illustrated in  FIG. 4 .  FIG. 5  again shows the two stiffeners  510 A,  510 B each comprising a first leg  511 A,  511 B respectively, a second leg  512 A,  512 B respectively, and a reinforcing element  513 A,  513 B respectively. 
         [0071]    The stiffeners are each made from at least one machined metal plate. In particular, various elements are cut from a metal plate and assembled with one another. 
         [0072]    As an alternative, the stiffeners are each made by deforming at least one metal plate. The deformation may be obtained by stamping, pressing or forging. 
         [0073]    As an alternative, the stiffeners are each produced by assembling metal beams joined together by welding and/or nuts and bolts. 
         [0074]    The first leg, the second leg and the reinforcing element may be produced separately, and these three pieces are then joined together, before being installed inside the volume of interest of the central wing box of the aircraft. 
         [0075]    Each stiffener has, at certain points, shapes that provide rigidity, for example turned-over edges referred to as “flanged edges”. 
         [0076]    The first and second stiffeners  510 A,  510 B are superposed at two points, as described with reference to  FIG. 4 . They are fixed together at the regions of superposition, for example using rivets. In the example depicted in  FIG. 5 , the second ends of each leg of the two stiffeners each have a series of bores  507  to accept rivets, for example between three and nine bores. 
         [0077]    According to an alternative form which has not been depicted, the second ends of the legs of the stiffeners are fixed together in pairs without being superposed. They are then fixed together indirectly at two points, for example using two intermediate components each one positioned at one of these two points. 
         [0078]      FIG. 6  corresponds to  FIG. 5 , this time depicted in exploded view.  FIG. 6  notably shows that each second end of each leg of the stiffeners has nine bores, distributed in a square mesh arrangement and together forming a three by three square of bores. 
         [0079]    In  FIG. 5 , the internal rib  500  is depicted as being set in between the top panel  1031 , the bottom panel  1032 , the front spar  1033  and the rear spar  1034 .  FIG. 6  depicts the internal rib  500  on its own.  FIG. 6  shows cavities  508  distributed along each first leg  511 A and  511 B respectively, these cavities being able to accommodate stiffeners  509  of the top panel and bottom panel respectively. In other words, the profile of the first leg  511 A (or  511 B respectively) in a plane parallel to the plane (xOz) and on the side of the top (or respectively bottom) panel has a series of cavities  508 . The stiffeners  509  are bars which extend from the top or, respectively, bottom, panel. These each fit into a cavity  508  and collaborate therewith to contribute to holding the internal rib in position relative to the top or, respectively, the bottom, panel. 
         [0080]    In the example illustrated in  FIGS. 5 and 6 , the front and rear spars also have stiffeners which fit into corresponding cavities of the second legs  512 A and  512 B in order further to improve the retention of the internal rib in position. 
         [0081]    At least one stiffener may be made of a composite material with a thermosetting or thermoplastic matrix. 
         [0082]      FIG. 7  illustrates a second alternative form  700  of an internal rib as depicted schematically in  FIG. 4 .  FIG. 7  again shows the two stiffeners  710 A,  710 B each comprising a first leg  711 A,  711 B respectively, a second leg  712 A,  712 B respectively, and a reinforcing element  713 A,  713 B respectively. The internal rib has been depicted as being installed, between the top and bottom panels and between the front and rear spars. It is notably possible to see the stiffeners  709  of each of these elements, set into corresponding cavities of the two stiffeners  710 A,  710 B. 
         [0083]    Each stiffener  710 A,  710 B is made of carbon fiber reinforced resin (or CFRP which stands for carbon fiber reinforced polymer). Such a resin is a composite material with a thermosetting matrix, making it possible to manufacture components of low mass. Each stiffener may be produced by injection molding or by infusion (for example liquid resin infusion). 
         [0084]    As an alternative, each stiffener is made of a composite material with a thermoplastic matrix containing fibers, notably made of carbon fiber. Such a component is produced by injection molding or by infusion. According to an advantageous alternative form, each stiffening component is produced by stamping. Stamping makes large variations in the thickness of the same mechanical component possible. 
         [0085]    Embodiments in composite material offers a wide variety of possible shapes. 
         [0086]      FIG. 8  illustrates a view in cross section of the stiffener  710 B, on a plane parallel to the plane (yOz) passing through the axis AA′. 
         [0087]    The first leg  711 B is planar, parallel to the plane (xOz). It has a thickness at the center (along Oy) denoted e, and a height (along Oz) denoted H, with the ratio H/e greater than or equal to 10, or even 20. 
         [0088]    The first leg  711 B has thicker edges, one of them extending from the side of the bottom panel, and the other on the opposite side of the first leg. For example, the thickness of the first leg at these edges is at least twice its thickness at the center e. 
         [0089]    On the side adjacent to the panel, the stiffener has a T-shaped cross section, the horizontal bar of the T being adjacent to the panel. The H/L ratio between the height H and the length L of the horizontal bar of the T (along Oy) is approximately 2, for example between 1.5 and 3. 
         [0090]    A person skilled in the art will easily know how to calculate the details for the sizing of a stiffener, notably using finite element calculation software. 
         [0091]      FIG. 8  depicts a first leg formed of a central piece  81 , a lower reinforcement  82  and an upper reinforcement  83 . The central piece  81  has a thickness e. The lower reinforcement  82  surrounds a lower region of the central component to increase the thickness of the first leg  711 B on the side of the bottom panel and form the horizontal bar of the T as defined hereinabove. The upper reinforcement  83  surrounds an upper region of the central component to increase the thickness of the first leg  711 B on the opposite side to the bottom panel. 
         [0092]      FIG. 9  illustrates a detail of a second embodiment of an internal rib according to the disclosure herein.  FIG. 9  in particular illustrates a second stiffener  810 B. The shape of this second stiffener  810 B differs from the shape of the second stiffener illustrated notably in  FIG. 7  in that the region  880  situated between the first and second legs  811 B,  812 B and the reinforcing element  813 B is solid. It may nevertheless have a mechanical strength lower than that of the reinforcing element. 
         [0093]    The stiffener  810 B is formed for example from CFRP and produced by stamping. 
         [0094]    The second stiffener  810 B, once installed, is adjacent to the bottom panel and to the front spar. A first stiffener is therefore adjacent to the top panel and to the rear spar. A person skilled in the art will know how to vary the disclosure herein in numerous ways, notably form alternative forms of the embodiments presented with reference to  FIGS. 4 through 8 , in which the first stiffener is adjacent to the top panel and to the rear spar and the second stiffener is adjacent to the bottom panel and to the front spar. 
         [0095]    While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a”, “an” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.