Abstract:
Disclosed are structures and features of a space frame aircraft. In particular, this disclosure relates to bracing for a space frame aircraft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application, under 35 U.S.C. §119, claims the benefit of U.S. Provisional Patent Application Ser. No. 62/365,266 filed on Jul. 21, 2016, and entitled “Space Frame Aircraft Structures,” the contents of which is hereby incorporated by reference herein. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    This disclosure relates generally to structures and features of a space frame aircraft. In particular, this disclosure relates to bracing for a space frame aircraft. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Space frame aircraft are known. For example, U.S. Pat. No. 7,891,608, titled “Space Frame Fuselage Structure And Related Methods,” discloses embodiments of space frame aircraft and is hereby incorporated by reference in its entirety. In general, space frame aircraft may be used for, among other things, carrying cargo in one or more containers, such as an International Organization for Standardization (“ISO”) shipping container.  FIGS. 1-2  are schematic examples of portions of a space frame aircraft carrying a plurality of ISO containers. 
         [0004]    In various configurations throughout this disclosure, a fuselage structure may accommodate inter-modal containers conforming to ISO specification 1496. ISO specification 1496 describes a family of inter-modal containers. Containers conforming to the foregoing specification have been commonly accepted throughout the world for surface vehicle use, e.g., to transport cargo on large ships, trucks and trains. A related specification, ISO specification 8323, describes an air-compatible, lightweight container. Throughout this disclosure all of the family of containers meeting either specification are collectively referred to as “ISO containers.” 
         [0005]    Typically, a space frame fuselage structure of the aircraft may include a plurality of nodes and a plurality of elements connecting the nodes to form a space frame in which to carry cargo. As disclosed in U.S. Pat. No. 7,891,608, a space frame may generally include longitudinal elements (e.g., longerons), lateral elements, vertical elements, or other elements that are joined together at nodes. Diagonal elements (also referred to herein as trusses, braces, or bracing) may also be included and connected between nodes. 
         [0006]    One implementation of a fuselage space frame is indicated generally in  FIG. 1  by reference number  20 . The space frame  20  has a front, rear, and right and left sides indicated generally by reference numbers  22 ,  24 ,  26  and  28  respectively. The space frame  20  includes a plurality of longitudinal elements  30 , lateral elements  32  and vertical elements  34  joined at a plurality of nodes  36 . A plurality of diagonal elements  40  are connected between some of the nodes  36 . Also included, though not shown on  FIG. 1 , may be a number of pins or mechanisms that support ISO containers  68 . In some embodiments, the pins or support mechanisms for the ISO containers  68  may be slightly displaced relative to the space frame  20  structural nodes  36  to allow for a more simple integration of the support mechanisms in the space frame structure  20 . This offset feature may result in some amount of bending moment being sustained by the longitudinal members  30 . For the purposes of this disclosure, the locations of the support pins will be shown as being coincident with the structural nodes  36 . In some places on the figures, some nodes  36  are depicted with a larger dot which represents the nodes  36  that are connected or close to the pins that carry the ISO containers  68 , and are thus places where loads (mostly vertical) are introduced into the truss. Both the depiction of coincident location of pins and nodes, and differing size dots, are for simplicity and are inconsequential to the concepts of the current disclosure. 
         [0007]    The space frame fuselage structure  20  is included in a space frame aircraft  44  parts of which are shown schematically in  FIG. 2 . External struts  48  (shown in phantom) may optionally be used to link wings  52  of the aircraft  44  with a portion  54  of the fuselage in the vicinity of landing gear  55 . In this disclosure, the terms “wing” and “wings” may be used interchangeably. Other portions of the space frame  20  include a cargo hold  56  and an aft fuselage portion  60 . Of course, other features of aircraft  44  are also possible. 
         [0008]    The cargo hold  56  is configured to hold one or more ISO containers  68  in one or more generally rectangular bays  72  defined by one or more decks  76   a,    76   b,  a plurality of longitudinal columns  80 , and a plurality of transverse rows  84 . For example, as shown in  FIG. 1 , a two-high stack or block  88  of 20-foot long ISO containers are in the left-most row  84  in the third 20-foot long column  80  of a deck  76   a  of the space frame  20 . It should be noted that a space frame  20  may have rows  84  of different lengths. For example, as shown in  FIG. 1 , the space frame  20  has four rows  84 : two outer rows and two center rows which are longer than the outer rows by the length of two bays  72 . Other row  84  configurations are also possible. Likewise, columns  80  may be of differing widths and sizes. 
         [0009]    It also should be noted that the term “deck” as used herein does not necessarily denote the presence of a “floor” on which one may walk. In the  FIG. 1  embodiment, the decks  76   a,    76   b  do not include floor surfaces (except, e.g., for such surface areas as may be provided by longitudinal and lateral elements  30  and  32 .) Rather, “deck” refers to a level of the aircraft  44  that supports the cargo containers  68  from below. Thus, e.g., in the aircraft  44  of  FIG. 1 , the deck  76   a  is an upper deck on which the containers  68  are supported above a lower deck  76   b . Likewise in  FIG. 1 , the space frame  20  is open at the front end  22  to permit full-width loading of the cargo hold  56  as further described below. Other configurations are possible. It should be noted that the open nature of the space frame allows it to typically be non-pressurized during flight. 
         [0010]    The word “bay” has two meanings in this document. The first meaning is the open volume within the fuselage for carrying cargo—the “cargo bay.” The second meaning refers to the approximately rectangular shape formed by coplanar, approximately orthogonal primary space frame elements. Typically, in order to be structurally efficient, the diagonals  40  for a space frame  20  should be triangularized. One way to provide triangularization is to add diagonals  40  in some or all of the rectangular bays  72 , as depicted in  FIG. 3 . For a general load condition, diagonals  40  must be capable of carrying tension or compression. The direction of the diagonals  40 L,  40 R in each rectangular bay  72  can be in either direction as shown in  FIG. 4 . Although various arrangements may be heavier or lighter than other arrangements, they will all work structurally. If so called X-bracing is utilized as shown in  FIG. 5 , the diagonals  40  can be designed to carry only tension, and not compression. This arrangement has the advantage that the diagonals  40  need not be designed for buckling, which allows for a much more slender diagonal  40 . The disadvantage is that there are twice as many diagonals  40 , and the behavior is non-linear if some diagonals buckle, and thus, more involved to analyze. 
         [0011]    Using diagonals  40  with this basic space frame  20  as shown in  FIGS. 3-4  results in very long diagonals  40 —approximately twenty-three feet for a conventional, ISO container  68  compatible, rectangular bay  72 . These long diagonals  40  become heavy due to their need to resist buckling. Another disadvantage to the geometry illustrated in  FIGS. 3-5  is that the angle the diagonals  40  make with the longitudinal elements  30  is smaller than desired. Because of this small angle, the forces in the diagonals  40  are larger than they would be if the angle were larger. Other drawbacks also exist. 
       SUMMARY 
       [0012]    Accordingly, the disclosed systems and methods address the above noted drawbacks and issues with existing systems and methods. Disclosed embodiments include systems and methods for bracing a space frame  20 . 
         [0013]    Disclosed embodiments include a space frame for an aircraft including a bay sized to hold an ISO container and further including a first vertical element having a first end and a second end, a first longitudinal element having a length, a first node coupling the first end of the first vertical element to the first longitudinal element, a second node positioned along the first longitudinal element at a location that is a fraction of the first longitudinal element length, and a first brace extending from the second end of the first vertical element to the second node. In some embodiments, the location of the second node may be a location that is substantially half, one-third, or one-quarter of the length of the first longitudinal element. 
         [0014]    Disclosed embodiments also include a second longitudinal element connected at a third node to the second end of the first vertical element, and a second brace extending between the second node and the second longitudinal element. In some embodiments, a second brace extends between the second end of the first vertical element to the first longitudinal element. In some embodiments, a second brace extends between the second node and the first vertical element. In some embodiments, a second brace extends between the first brace and the first vertical element. In some embodiments, a second brace extends between the first brace and the first longitudinal element. In some embodiments, the second brace is a tree structure. In some embodiments, the first longitudinal element is curved. 
         [0015]    Disclosed embodiments also include a space frame cargo hold including a lower deck including a first transverse row of substantially rectangular bays and a second transverse row of substantially rectangular bays, an upper deck, above the lower deck, and including a first transverse row of substantially rectangular bays and a second transverse row of substantially rectangular bays, wherein each substantially rectangular bay is sized to hold an ISO container and includes a longitudinal element having a length and a vertical element, a first node connecting a juncture of the longitudinal element with the vertical element, a second node positioned along the longitudinal element at a location that is a fraction of the length of the longitudinal element, and a first brace extending from the vertical element to the second node. In some embodiments, the location of the second node is a location that is substantially half, one-third, or one-quarter of the length of the first longitudinal element. 
         [0016]    In some embodiments, the substantially rectangular bay further includes a second brace extending between the first brace and the vertical element. In some embodiments, a second brace extends between the first brace and the longitudinal element. In some embodiments, the second brace comprises a tree structure. Other embodiments and modifications are also disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of a space frame aircraft fuselage in accordance with embodiments of the disclosure. 
           [0018]      FIG. 2  is a schematic side view of a space frame aircraft in accordance with embodiments of the disclosure. 
           [0019]      FIG. 3  is a schematic side view of exemplary bracing in accordance with embodiments of the disclosure. 
           [0020]      FIG. 4  is a schematic side view of exemplary bracing in accordance with embodiments of the disclosure. 
           [0021]      FIG. 5  is a schematic side view of exemplary X-bracing in accordance with embodiments of the disclosure. 
           [0022]      FIG. 6  is a schematic illustration of bracing with additional nodes in accordance with embodiments of the disclosure. 
           [0023]      FIG. 7  is a schematic illustration of bracing with additional nodes in accordance with embodiments of the disclosure. 
           [0024]      FIG. 8  is a schematic illustration of bracing with additional nodes in accordance with embodiments of the disclosure. 
           [0025]      FIG. 9  is a schematic illustration showing bracing for mixed-length bays in accordance with embodiments of the disclosure. 
           [0026]      FIG. 10  is a schematic illustration of additional bracing to divide the upper and lower longitudinal members into shorter lengths in accordance with embodiments of the disclosure. 
           [0027]      FIG. 11  is a schematic illustration showing additional bracing supporting the center longitudinal element in accordance with embodiments of the disclosure. 
           [0028]      FIG. 12  is a schematic illustration showing the division of the center longitudinal element into segments in accordance with embodiments of the disclosure. 
           [0029]      FIG. 13  is a schematic illustration showing bracing of vertical elements at one or more locations along their length in accordance with embodiments of the disclosure. 
           [0030]      FIG. 14  is a schematic illustration showing combination bracing for longitudinal elements or vertical elements in accordance with embodiments of the disclosure. 
           [0031]      FIG. 15  is a schematic illustration showing combination bracing for longitudinal elements or vertical elements in accordance with embodiments of the disclosure. 
           [0032]      FIG. 16  is a schematic illustration showing bracing tree structures in accordance with embodiments of the disclosure. 
           [0033]      FIG. 17  is a schematic illustration showing no-compression, exterior bracing with curved longitudinal and vertical elements in accordance with embodiments of the disclosure. 
           [0034]      FIG. 18A  and  FIG. 18B  are schematic illustrations showing details of a curved longitudinal member in accordance with embodiments of the disclosure. 
       
    
    
       [0035]    While the disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0036]    It should be noted that, although implementations are described with reference to ISO containers  68  and/or reference to containers having specific dimensions, the disclosure is not so limited. The disclosure may be implemented in relation to many different types and/or sizes of containers. 
         [0037]    As noted above, the diagonals  40  for a space frame  20  presents several issues. One solution to the above-noted, and other, issues is to provide additional nodes  36   b  at substantially the midpoint between the original nodes  36   a  for each longitudinal element  30  as illustrated on  FIG. 6 . In this manner, the member lengths for the diagonals  40  can be greatly reduced. 
         [0038]    In addition, the lengths of the longerons or longitudinal elements  30  in this arrangement are one-half those in the previous arrangement (e.g., compare  FIG. 3 , longitudinal elements approximately twenty feet, and  FIG. 6  longitudinal elements approximately ten feet). Since the buckling load of a member in compression varies as the square of the length, this reduced length of the longitudinal elements  30  is advantageous. 
         [0039]    Further, the lengths of the diagonals  40  in  FIG. 6  are also greatly reduced to about sixty-five percent of their original twenty-three foot length shown in  FIG. 3 . This reduction in length for the diagonals  40  is also advantageous for the same reason as it is for the longitudinal elements  30 . 
         [0040]    In addition, the angle of the diagonals  40  in  FIG. 6  is also improved over those in  FIG. 3 , which reduces the loads in the diagonals  40 . These improvements result in a lighter-weight structure  20 , which makes the single diagonal  40  in the configuration of  FIG. 6  more favorable compared to the bracing arrangement in  FIG. 3 . 
         [0041]    As shown in  FIG. 7 , additional nodes  36   c  may be provided substantially at the one-third distance between the original nodes  36   a  for each longitudinal member  30 . As discussed above, the longitudinal member  30  lengths are further reduced. This arrangement also has an improved angle for the diagonals  40 , which can result in a lower weight structure  20 . Another advantage of this arrangement is that the skin panels attached to such a frame span much less distance and are, therefore, lighter. The size of such panels may be that each panel spans from one truss vertical member  34  to another, or they may span across multiple vertical members  34 . 
         [0042]    This approach can be extended as shown in  FIG. 8 . Additional nodes  36   d  are provided substantially at the one-fourth the distance between the original nodes  36   a  for each longitudinal member  30  and the lengths are further reduced. Likewise, the angle of the diagonals  40  is improved. 
         [0043]      FIG. 9  is an embodiment showing diagonals  40  for mixed-length bays  72 . For example, it may be advantageous in some embodiments for the fractional module spacing to be larger near the mid-length  90  of the fuselage where the shear forces are larger near the wing and main landing gear attachments, and smaller near the ends  92  of the fuselage where the shear loads may be smaller. This is because larger shear forces will necessitate members with larger cross sectional areas, which will naturally be able to have greater lengths for the same value of axial load. For example, the ends  92  of the fuselage may implement nodes  36   d  at one-third distance between the original nodes  36   a  and mid-length  90  of the fuselage may implement nodes  36   b  at one-half the distance between the original nodes  36   a.  Other combinations of spacing are also possible. 
         [0044]    In some embodiments, additional bracing  40   b  may also be introduced in addition to the diagonals  40   a  to further divide the buckling length for various members. As used herein, a truss diagonal such as  40   a  carries shear loads that travel through the truss, by virtue of their being attached to nodes  36  where longerons  30 , columns  34 , and diagonal members  40  intersect. In contrast, “bracing” (like member  40   b ) are present for the purpose of providing support to another member to improve its buckling length. For example,  FIG. 10  depicts additional bracing  40   b  along with the diagonals  40   a  to divide the upper  30   a  and lower  30   b  longitudinal members into two lengths each. These additional braces  40   b  carry either tension or compression. 
         [0045]    In some embodiments, additional bracing  40   b  may also be introduced to support the central longeron or longitudinal elements  30 . For example,  FIG. 11  depicts the additional bracing  40   b  and diagonals  40   a  supporting the center longitudinal element  30 . Since there is bracing  40   b  on both the upper and lower side of the longitudinal element  30 , this bracing  40   b  need be capable of carrying only tension to adequately provide resistance to buckling for the longitudinal element  30 . This arrangement is advantageous because the bracing  40   b  need not be designed for buckling. 
         [0046]    The bracing  40   b  need not be limited to dividing the longitudinal elements  30  into two segments. For example,  FIG. 12  illustrates the division of the center longitudinal element  30   a,    30   b,  and  30   c  into two, three, or four segments, respectively. The number of divisions can be specified for each longitudinal element  30  depending on, among other things, the loading requirements. For the same reasons as discussed above, more lightly-loaded longitudinal elements  30  may benefit from more bracing  40   b  locations compared to more heavily-loaded longitudinal elements  30 , which may require less bracing  40   b  locations. Other configurations are also possible. 
         [0047]    Likewise, columns or vertical elements  34  may be braced also.  FIG. 13  is an example of diagonals  40   a  and bracing  40   b  showing how vertical elements  34  may be braced at one or more locations along their length. For example, the bracing  40   b  for the interior vertical elements  34   a  need carry only tension, while the diagonals  40   a  and bracing  40   b  for the exterior vertical elements  34   b  may take both tension and compression. 
         [0048]    The diagonals  40   a  and bracing  40   b  arrangements depicted in  FIGS. 10-13  can be combined in any combination for any longitudinal element  30  or vertical element  34 , as shown in  FIG. 14 . Instead of having the large amount of overlap of diagonals  40   a  and bracing  40   b  shown in  FIG. 14 , it may be advantageous in some embodiments to arrange the bracing  40   b  as shown in  FIG. 15 . As in both  FIGS. 14 and 15 , some diagonals  40   a  can carry both tension and compression, while other bracing members  40   b  may carry only tension because they are arranged in pairs to brace the interior members ( 30 ,  34 ). The variety of the arrangement with some members ( 30 ,  34 ) braced with either one, two, or three diagonals and bracing members ( 40   a,    40   b ) is intended to show the flexibility available to the structural designer. An actual structure may be much more uniform. Also, the number of diagonals and bracing members ( 40   a,    40   b ) for a given member ( 30 ,  34 ) need not be limited to three. 
         [0049]    In some embodiments, instead of arranging the tension/compression diagonals and bracing members ( 40   a,    40   b ) such that they all originate from the intersection of the X-bracing for a given longitudinal element  30  or vertical element  34 , they may be arranged in a “tree” structure  33  as shown in  FIG. 16 . The trunk of the tree  33  that connects to the center node of the X-bracing can be a more substantial cross section, which better resists buckling. 
         [0050]      FIGS. 6-16  have illustrated the bracing concepts discussed in this disclosure by using the vertical elements  34  and longitudinal elements  30  in the XZ (longitudinal-vertical) plane. However, this concept is also applicable to the XY (longitudinal-lateral) plane using longitudinal elements  30  and lateral elements  32 . Similarly, the disclosed concepts can be applied to YZ bracing as well. However, in some embodiments, bracing  40   b  at the forward and aft ends  92  of the ISO container-carrying portion of the space frame  20  may not need as much bracing since they are relatively heavily loaded. Other bracing configurations are also possible. 
         [0051]    In some embodiments, it may be advantageous to implement bracing that does not need to sustain compression loads for the longitudinal  30 , vertical  34 , or lateral  32  members that are “exterior” members of the space frame  20 . For example, diagonal  40   a  in  FIGS. 15-16  is an example of exterior member bracing. 
         [0052]    One embodiment of no-compression, exterior bracing is to construct the longitudinal  30   c  and vertical  34   c  elements such that they are curved, as shown in  FIG. 17 . The curvature of the exterior longitudinal  30   c  or vertical  34   c  members may be very slight, and in  FIG. 17  the curvature is exaggerated for illustrative purposes. 
         [0053]    The concept is illustrated in  FIG. 18 , which is a diagram showing one longitudinal member  30   c  in closer detail. The upper portion of  FIG. 18  shows that the curved longitudinal member  30   c  will tend to buckle in a direction away from the center of curvature, but not towards the center of curvature. Thus, to prevent buckling of such a longitudinal member  30   c,  the diagonals and bracing  40   a,    40   b  need only be capable of resisting tension forces, because the longitudinal member  30   c  will not tend to buckle in a direction that would put the diagonals and bracing  40   a,    40   b  into compression. The longitudinal member  30   c  is designed to have enough curvature to preclude buckling in the undesirable direction, but not so much curvature as to induce significant beam-longitudinal bending moments in the longitudinal member. 
         [0054]    Although various embodiments have been shown and described, the present disclosure is not so limited and will be understood to include all such modifications and variations are would be apparent to one skilled in the art.