Patent Publication Number: US-11649042-B2

Title: Collapsible spar mandrel

Description:
STATEMENT OF FEDERAL SUPPORT 
     This invention was made with government support under W911W6-19-9-0005 awarded by the US Army. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     Exemplary embodiments of the invention generally relate to a hollow composite member for a rotary wing aircraft, and more particularly, to the process and apparatus used to manufacture the composite rotor blades of a rotary wing aircraft. 
     Rotor blades typically include a spar that extends from the root of the rotor blade to its tip. The spar is a major structural element of the rotor blade that provides the blade with the structural strength needed to carry high operational loads. The typical rotor blade spar is a long tubular structure around which the rest of the blade is formed. The spar tube has an elliptical cross-section that is formed to provide a forward or leading edge and rearward or trailing edge. In order to provide optimum aerodynamic performance, many spar tubes include a slight twist about the longitudinal axis. Typical twists in the spar provide rotations of the elliptical cross-section of up to 10 degrees and more from the root of the rotor blade to its tip. 
     The typical composite spar is fabricated by applying an uncured composite material to the surface of a long cylindrical mold or mandrel that is shaped to provide the interior surface of the spar tube. After the composite material is applied to the mandrel, it is compacted and cured at an elevated temperature to provide the final spar structure. A problem associated with making composite spars revolves around how to fabricate a mandrel with specific exterior surface contours, and that is removable from a cavity of the spar. The length of the mold and the variations in the elliptical cross-section of the spar, as well as any twist in the spar, make it very difficult to remove the mandrel after the spar has cured. 
     BRIEF DESCRIPTION 
     According to an embodiment, a method of assembling a mandrel includes assembling a plurality of members via interlocking features arranged at opposing edges of each member of the plurality of members to form a compartment, the assembled members having a collective outer surface that conforms to an inner surface of the spar. A support member is inserted into the compartment formed radially inward from the assembled members, the support member making contact with a portion of each member of the plurality of members. 
     In addition to one or more of the features described above or below, or as an alternative, each interlocking feature comprises a respective tongue portion and groove portion. 
     In addition to one or more of the features described above or below, or as an alternative, assembling the plurality of members includes inserting a respective tongue portion of each member of the plurality of members into a respective groove portion of another member of the plurality of members. 
     In addition to one or more of the features described above or below, or as an alternative, the support member includes a plurality of vanes extending radially outwardly from a center of the support member. 
     In addition to one or more of the features described above or below, or as an alternative, the support member has a number of vanes equal to a number of members of the plurality of members. 
     In addition to one or more of the features described above or below, or as an alternative, inserting the support member into the compartment includes sliding a respective edge of each vane into a respective groove of each member of the plurality of members. 
     In addition to one or more of the features described above or below, or as an alternative, the method further includes coupling a first sub-member to a second sub-member to form a member of the plurality of members. 
     In addition to one or more of the features described above or below, or as an alternative, the method further includes inserting the assembled mandrel into a spar cavity of an uncured spar. Then removing, in response to the spar being cured, the support member from the compartment. Then removing, upon removal of the support member, the assembled mandrel from the spar cavity. 
     In addition to one or more of the features described above or below, or as an alternative, removing the support member includes sliding the support member out of the assembled mandrel. 
     In addition to one or more of the features described above or below, or as an alternative, the method further includes applying a pressure to an outer surface of the uncured spar while the mandrel is inserted in the spar cavity. 
     In addition to one or more of the features described above or below, or as an alternative, removing the assembled mandrel includes sliding a single member of the plurality of members out of the spar cavity prior to removing a balance of the plurality of members. 
     In addition to one or more of the features described above or below, or as an alternative, each member of the plurality of members is fabricated through an additive manufacturing process. 
     In addition to one or more of the features described above or below, or as an alternative, the method further includes generating a computer-model of the surface of the spar, determining a number of members of the plurality of members on the computer-model, defining a model member for each of the determined number of members, and additively manufacturing each of the members according to the defined model member. 
     In addition to one or more of the features described above or below, or as an alternative, a first member of the plurality of members has a surface profile that conforms to a leading edge surface of the spar; and a second member of the plurality of members has a surface profile that conforms to a trailing edge surface of the spar. 
     According to another embodiment, a mandrel assembly includes a first member having a first surface contour that conforms to a first portion of the spar surface, the first member including respective interlocking features at opposing edges, a second member having a first surface contour that conforms to a second portion of the spar surface, the second member including respective interlocking features at opposing edges, a third member having a first surface contour that conforms to a third portion of the spar surface, the third member including respective interlocking features at opposing edges to interlock with the respective interlocking features of the first and second members, a fourth member having a first surface contour that conforms to a balance of the spar surface, the fourth member including respective interlocking features at opposing edges to interlock with the respective interlocking features of the first and second members, and a support member having a plurality of vanes that extend outwardly, each vane having an end insertable into a respective groove of each of the first member, second member, third member, and fourth member, whereby the interlocking features are configured to interconnect the first through fourth members to permit the mandrel to remain assembled without the support member. 
     In addition to one or more of the features described above or below, or as an alternative, the interlocking features include a respective tongue portion and groove portion. 
     In addition to one or more of the features described above or below, or as an alternative, the support member further includes a planar base having a contour matching a contour of the compartment. 
     In addition to one or more of the features described above or below, or as an alternative, the support member includes four vanes. 
     In addition to one or more of the features described above or below, or as an alternative, the four vanes are arranged in a cross pattern. 
     In addition to one or more of the features described above or below, or as an alternative, the first surface contour of the first member conforms to a surface contour of a leading edge of a spar. 
     In addition to one or more of the features described above or below, or as an alternative, the first surface contour of the second member conforms to a surface contour of a trailing edge of a spar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an exploded view of a mandrel according to an embodiment of the invention; 
         FIG.  2    is a cross-sectional view of a mandrel according to an embodiment of the invention; 
         FIG.  3    is a cross-sectional view of a mandrel member interfacing with another mandrel member according to an embodiment of the invention; 
         FIG.  4    is a perspective view of a rotor blade assembly of a rotor system of the rotary wing aircraft of  FIG.  7   ; 
         FIG.  5    is a cross-sectional view of the rotor blade assembly of  FIG.  4    taken at line A-A; 
         FIG.  6    is a schematic diagram of a method of constructing a mandrel according to another embodiment of the invention; and 
         FIG.  7    is a perspective view of an example of a rotary wing aircraft; 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     Referring to  FIG.  1 - 3   , a mandrel  100  is shown. As seen, a plurality of members may be assembled to form a mandrel that has a shape that conforms to an exterior surface of a spar  302 . As illustrated, the mandrel  100  includes an upper member  102  that has an exterior surface  104  shaped to form a portion of an upper surface of the spar  302 . The upper member  102  further includes an interior surface  164  defining a first portion of an open compartment  154 . The upper member  102  is configured to be arranged adjacent to a leading edge member  106  that has an exterior surface  108  shaped to form a portion of a leading edge surface of the spar  302 . The leading edge member  106  further includes an interior surface  166  defining a second portion of the open compartment  154 . A first side  110  of the upper member  102  is configured to interface with an adjacent side  112  of the leading edge member  106 . The leading edge member  106  is configured to be arranged adjacent to a lower member  114  that has an exterior surface  116  shaped to form a portion of a lower surface of the spar  302 . The lower member  114  further includes an interior surface  168  defining a third portion of the open compartment  154 . A first side  118  of the leading edge member  106  is configured to interface with an adjacent side  120  of the lower member  114 . The lower member  114  is configured to be arranged adjacent to a trailing edge member  122  that has an exterior surface  124  shaped to form a portion of a trailing edge surface of the spar  302 . The trailing edge member  122  further includes an interior surface  170  defining a balance of the open compartment  154 . A first side  126  of the lower member  114  is configured to interface with an adjacent side  128  of the trailing edge member  122 . A first side  130  of the trailing edge member  122  is configured to interface with an adjacent side  132  of the upper member  102 . 
       FIG.  3    illustrates an exemplary coupling between an interlocking feature of the upper member  102  and an interlocking feature of the trailing edge member  122 . A first side  130  of the trailing edge member  122  is arranged opposite to the adjacent side  132  of the upper member  102  such that the first side  130  is flush with the adjacent side  132 . The adjacent side  132  of the upper member  102  includes a first surface  134  that extends at an angle from the exterior surface  104  of the upper member  102  toward an interior surface  164  of the upper member  102  and ends at a groove portion  138 . The groove portion  138  is connected at one end to the first surface  134  and to a tongue portion  140  at an opposite end. The cross-sectional contours of the groove portion  138  and the adjacent tongue portion  140  form an s-shaped pattern. The tongue portion  140  is connected at one end to the groove portion  138  and is connected to a second surface  142  at an opposite end. The second surface  142  extends from the opposite end of the tongue portion  140  to the interior surface  164  of the upper member  102 . 
     The first side  130  of the trailing edge member  122  includes a first surface  144  that extends at an angle from the exterior surface  124  of the trailing edge member  122  toward the interior surface  170  of the trailing edge member  122  and ends at a tongue portion  148 . The tongue portion  148  is connected at one end to the first surface  144  and to a groove portion  150  at an opposite end. The cross-sectional contours of the tongue portion  148  and the adjacent groove portion  150  form an s-shaped pattern similar to the s-shaped pattern of the groove portion  138  and the adjacent tongue portion  140  of the upper member  102 . The groove portion  150  is connected at one end to the tongue portion  148  and is connected to a second surface  146  at an opposite end. The second surface  146  extends from the opposite end of the groove portion  150  to the interior surface  170  of the trailing edge member  122 . 
     As seen in  FIG.  3   , the tongue portion  148  of the trailing edge member  122  rests against the groove portion  138  of the upper member  102  when the tongue portion  148  of the trailing edge member  122  is fully inserted into the groove portion  138  of the upper member  102 . Additionally, the tongue portion  140  of the upper member  102  is arranged against the groove portion  150  of the trailing edge member  122  when the tongue portion  140  of the upper member  102  is fully inserted into the groove portion  150  of the trailing edge member  122 . It is appreciated that while  FIG.  3    only illustrates an interlocking of the upper member  102  and trailing edge member  122  the above-described s-shaped interconnect may be applied to any of the mandrel members  102   106   114   122 . As assembled, the upper member  102  interlocks with the leading edge member  106  and the trailing edge member  122 . The leading edge member  106  interlocks with the upper member  102  and the lower member  114 . The lower member  114  interlocks with the leading edge member  106  and the trailing edge member  122 . The trailing edge member  122  interlocks with the upper member  102  and the lower member  114 . As assembled, the mandrel members  102   106   114   122  require no external support in order to remain in an assembled position. While shown with a particular number and shape of members, it is understood that the number and shape of the components is not specifically limited to the shown numbers and shapes. 
     As seen in  FIGS.  1  and  2   , a support member  152  is configured to be arranged inward from the open compartment  154  defined by an assembled upper member  102 , leading edge member  106 , lower member  114  and trailing edge member  122 . An exemplary embodiment of the support member  152  is illustrated in  FIGS.  1  and  2   . The support member  152  includes a first vane  156 , a second vane  158 , a third vane  160 , and a fourth vane  162 . The first vane  156  extends radially outwardly toward a first groove  176  of the upper member  102 . The second vane  158  extends radially outwardly toward a second groove  178  of the leading edge member  106 . The third vane  160  extends radially outwardly toward a third groove  180  of the lower member  114 . The fourth vane  162  extends radially outwardly toward a fourth groove  182  of the trailing edge member  122 . Each vane  156   158   160   162  extends from a base  172  to a tip  174  along a longitudinal axis L of the support member  152 . A surface contour of each groove  176   178   180   182  complements a surface of a tip of each vane  156   158   160   162 . Each groove  176   178   180   182  extends from the base  172  to the tip  174  along the longitudinal axis L, such that the support member  152  is slidable into and out of the mandrel  100  along the grooves  176   178   180   182 . The base  172  may include a generally planar structure connected at a proximal end of the support member  152 . A contour  136  of the base  172  may conform to a contour of an opening the open compartment  154  at the proximal end. The tip  174  may also include a generally planar structure connected at a distal end of the support member  152 . A contour of the tip  174  may conform to a contour of an opening the open compartment  154  at the distal end. As the support member  152  is inserted into the mandrel, it provides structural support for the mandrel  100 . It is appreciated that although the Figures illustrate four mandrel members  102   106   114   122  and a support member  152  that includes four vanes  156   158   160   162 , a mandrel  100  may be comprised of two or more members that may be assembled to form the mandrel  100 . Furthermore, a number of vanes of the support member  152  may be based on a number of mandrel members or a desired level of structural support for the mandrel  100 . 
     In some other embodiments, each mandrel member  102   106   114   122  is further divided into sub-members at a point along the longitudinal axis L. As illustrated  FIG.  1   , the upper member  102  may further be sub-divided into a distal member  184  and a proximal member  186 . The distal member  184  may be coupled to the proximal member  186  at any point along the longitudinal axis L. The coupling may be similar to the coupling between a vane  156   158   160   162  of the support member  152  and a mandrel member  102   106   114   122 , the interaction between mandrel members  102   106   114   122 , or other appropriate interaction permissible to allow a plurality of sub-members to be assembled into a member  102   106   114   122 . It should be appreciated that each mandrel member  102   106   114   122  may be subdivided into two or more sub-members, for example, a member can be further subdivided into three members such as a central member flanked on each side by a distal member and a proximal member. 
     The mandrel members  102   106   114   122  and their respective interfaces provide a means to remove the mandrel  100  upon completion of the spar lay-up. The support member  152  may be removed from the mandrel  100  by sliding the support member  152  out of the open compartment  154 . Upon removal of the support member  152 , the mandrel members  102   106   114   122  may be removed individually from the spar cavity  308 . 
     Referring now to the exemplary rotor blade assembly  300  illustrated in  FIGS.  4  and  5   , a generally hollow, tubular spar  302  configured to couple to the rotor hub  20  at an inboard end  304  extends over at least a portion of the length of the rotor blade assembly  22 . In one embodiment, the spar  302  may extend to the blade tip  306  of the rotor blade assembly  22 . The cross-section of the spar  302  may vary in size and shape over the length of the spar  302  depending on the contour of the rotor blade assembly  22 . Such changes can include reduced cross-sectional area, twists as a function of length, and/or turns to accommodate a swept portion of a blade. The spar  302 , as shown in  FIG.  4   , includes a plurality of interior surfaces that define an interior spar cavity  308 . The interior surfaces include an interior leading edge surface  310 , an interior trailing edge surface  312 , an interior upper surface  314 , and an interior lower surface  316 . Both the interior upper and lower surfaces  314 ,  316  extend opposite one another between the interior leading and trailing edge surfaces  310 ,  312 . While shown with a tip  306  having a swept geometry, it is understood that the tip  306  need not have a swept geometry in all embodiments of the invention. 
     Referring to  FIG.  6   , a method  600  of assembling a mandrel  100  is shown. At block  602 , each of the individual mandrel members  102   106   114   122  are formed. The number of mandrel members  102   106   114   122  may be based in part on an interior surface of the spar, or other appropriate consideration. The mandrel members  102   106   114   122  may be formed using various fabrication techniques. 
     In an exemplary embodiment, the mandrel members  102   106   114   122  are formed through additive manufacturing. Additive manufacturing may be utilized to fabricate three-dimensional (3D) mandrel members by adding layer-upon-layer of material until an individual mandrel member is formed. Additive manufacturing utilizes three-dimensional modeling (e.g., computer-aided design (CAD)) software, computer-controlled additive-manufacturing equipment, and raw materials in powder or liquid form. The modeling may be used to determine an optimal surface contour of a spar, and an optimal number of members. Additive manufacturing further includes a wide variety of technologies and incorporates a wide variety of techniques, for example, laser freeform manufacturing (LFM), laser deposition (LD), direct metal deposition (DMD), laser metal deposition, laser additive manufacturing, laser engineered net shaping (LENS), stereolithography (SLA), selective laser sintering (SLS), fused deposition modeling (FDM), multi-jet modeling (MJM), three-dimensional printing, rapid prototyping, direct digital manufacturing, layered manufacturing, and additive fabrication. Each member can respectively be defined by a respective model, prior to manufacturing. Each member can be additively manufactured separately. By applying computer modeling techniques and additive manufacturing, the members may be fabricated to conform to any desirable spar dimensions and to replace a member during a spar fabrication process as needed. 
     At block  604 , the individual members  102   106   114   122  are coupled together to form the mandrel  100 . For example, an upper member  102  may be coupled to a leading edge member  106 . The leading edge member  106  may be coupled to a lower member  114 . The lower member  114  may be arranged such that an inner surface of the lower member  114  faces an inner surface of the upper member  102 . Furthermore, the lower member  114  may be coupled to a trailing edge member  122 , and the trailing edge member  122  may be coupled back to the upper member  102 . The trailing edge member  122  may be arranged such that an inner surface of the trailing edge member  122  faces an inner surface of the leading edge member  106 . 
     At block  606 , a support member  152  is inserted into the assembled mandrel. The support member, the upper member  102 , leading edge member  106 , lower member  114 , and trailing edge member  122  may be configured to permit the support member  152  to slide into the assembled mandrel  100 . For example, the support member  152  may include a plurality of vanes  156   158   160   162  and the assembled mandrel  100  may have a plurality of grooves  176   178   180   182 . Each groove  176   178   180   182  may be arranged to receive a respective vane  156   158   160   162 . The vanes  156   158   160   162  of the support member  152  may come into contact with the grooves  176   178   180   182  of the mandrel  100 , such that the support member  152  adds to a resistive force created when an external force is applied to an exterior surface of the mandrel  100 . At block  608 , the assembled mandrel  100  is inserted into a cavity of an uncured spar. An external force is applied to the spar, causing the external surface contour of the spar to conform to the external surface contour of the mandrel. The mandrel  100  may then be removed after the spar is cured by reversing the process. 
       FIG.  7    schematically illustrates a rotary-wing aircraft  10  having a main rotor system  12 . The aircraft  10  includes an airframe  14  having an extending tail  16 , which mounts a tail rotor system  18  as an anti-torque system. The main rotor assembly  12  is driven about an axis of rotation A through a main gearbox (illustrated schematically at T) by one or more engines E. The main rotor system  12  includes a rotor hub  20  having a plurality of rotor blade assemblies  22  mounted to and projecting radially outwardly therefrom. Although a particular helicopter configuration is illustrated and described in the disclosed non-limiting embodiment, other configurations and/or machines, such as high speed compound rotary wing aircraft with supplemental translational thrust systems, dual contra-rotating coaxial rotor system aircraft, turboprops, tilt-rotors, and tilt-wing aircraft, will also benefit from the present invention. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.