Abstract:
A fastening system with a rotatable fastener that may secure an aircraft store to an aircraft and may rotate to reduce a drag coefficient of the aircraft store. Reducing the drag coefficient of the aircraft store may increase fuel efficiency of the aircraft store by requiring less energy to propel the aircraft store at a given speed or acceleration. 
     The rotatable fastener allows the aircraft store to attach to the aircraft and to possess a low drag coefficient once the aircraft store is deployed. The rotatable fastener member may be configured to conform to attachment interface standards, such as Standardization Agreement (“STANAG”) 3842 or any other suitable aircraft store attachment interface standard.

Description:
GOVERNMENT LICENSE RIGHTS 
       [0001]    This invention was made with Government support under contract number FA8650-15-C-8301, awarded by the Department of Defense. The Government has certain rights in the invention. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates generally to expendable aircraft stores, and more particularly to a retracting hooks assembly for securing expendable aircraft stores to an aircraft. 
       BACKGROUND 
       [0003]    Missiles are typically attached to an aircraft by a pair of hooks that must withstand large forces based on the weight of the missile and the motion of the aircraft. While the aircraft flies, takes-off, or lands, the aircraft may expose the missile to multiple g-forces, which can multiply the amount of stress experienced by the hooks to maintain the attachment of the missile to the aircraft. 
         [0004]    To withstand the large amount of stress, the hooks are typically fixed to the missile. Thus when the missile is launched from the aircraft the hooks often remain protruding outward from an outer skin of the missile. 
         [0005]    Some missiles have utilized linearly retractable hooks instead of hooks fixed to the missile. The linearly retractable hooks require a large amount of space and weight within the missile to withstand the large amount of stress endured by the hooks while the aircraft operates. 
       SUMMARY OF INVENTION 
       [0006]    A fastening system with a rotatable fastener is used to secure an aircraft store to an aircraft and may rotate to reduce a drag coefficient of the aircraft store. Reducing the drag coefficient of the aircraft store may increase fuel efficiency of the aircraft store by requiring less energy to propel the aircraft store at a given speed or acceleration. 
         [0007]    The rotatable fastener allows the aircraft store to attach to the aircraft and to possess a low drag coefficient once the aircraft store is deployed. The rotatable fastener member may be configured to conform to attachment interface standards, such as Standardization Agreement (“STANAG”) 3842 or any other suitable aircraft store attachment interface standard. 
         [0008]    The rotatable fastener also may require less space and weight compared with previously known linearly retractable hooks. The space and weight savings may provide fuel efficiencies when transporting the fastening system, and may provide fuel efficiencies when deploying the aircraft store that includes the fastening system. 
         [0009]    In an embodiment, the rotatable fastener member includes a leg to form an L-shape that allows the rotatable fastener to distribute stress more efficiently compared to previously known linearly retractable hooks. Distributing the stress allows the rotatable fastener to withstand large stresses caused by operation of the aircraft while maintaining a size and weight compared to known linearly retractable hooks. 
         [0010]    In another embodiment the fastening system includes one or more double actuators for locking, unlocking, and actuating the rotatable fastener. The fastening system may include a second rotatable fastener that is locked and unlocked by a first double actuator and actuated by a second double actuator. The first rotatable fastener may be locked and unlocked by the second double actuator and may be actuated by the first double actuator. 
         [0011]    According to one aspect of the invention, a fastening system for securing an expendable aircraft store to an aircraft, may include a housing that forms part of the expendable aircraft store, the housing extending along a longitudinal axis, a first fastener rotatably connected to the housing, wherein the first fastener is rotatable about a first fastening axis, and a second fastener rotatably connected to the housing opposite the first fastener relative to the longitudinal axis of the housing, wherein the second fastener is rotatable about a second fastening axis, and wherein the second fastener is rotatable about a portion of the second fastening axis that is laterally offset from the longitudinal axis opposite the first fastening axis, wherein each fastener includes an engagement section for securing the respective fastener to a mechanical interface of the aircraft, each engagement section being radially outward of the respective fastening axis, and wherein each fastener is rotatable from an open position, where the respective engagement section is engageable with the mechanical interface of the aircraft, to a closed position that reduces a drag coefficient of the fastening system compared to the open position. 
         [0012]    Each fastener may include a leg for distributing load when the respective fastener is in the open position. 
         [0013]    The housing may include a longitudinally-extending support with a leg-bearing surface for distributing load received from each leg when the respective fastener is open. 
         [0014]    The bearing surface may include an adjustable-leg-bearing surface for adjusting the open position of the first fastener or the second fastener. 
         [0015]    The housing may include a closed-position adjuster for adjusting the closed position of the first fastener or the second fastener. 
         [0016]    The fasteners may rotate about a load-bearing pin that is radially fixed to the housing. 
         [0017]    When the fasteners are in the open position the fasteners may be positively locked open, or when the fasteners are in the closed position the fasteners may be positively locked closed. 
         [0018]    The fastening system may include an actuator assembly operably connected to each fastener. 
         [0019]    The actuator assembly may include a pneumatic actuator operably connected to at least one of the fasteners. 
         [0020]    An expendable aircraft store may include the fastening system. Rotating each fastener from the open position to the closed position may reduce a drag coefficient of the expendable vehicle store compared to the open position. 
         [0021]    The expendable aircraft store may be a missile. 
         [0022]    An aircraft may include a mechanical interface connected to the fasteners of the fastening system of the expendable aircraft store. 
         [0023]    An aircraft may include the expendable aircraft store. The fastening system may include an actuator assembly operably connected to each fastener to positively lock the fasteners in the open position, to close the fasteners, to open the fasteners, or to positively lock the fasteners in the closed position, wherein the actuator assembly includes a pneumatic actuator, wherein the housing includes a closed-position adjuster for adjusting the closed position of the first fastener or the second fastener, wherein the fasteners rotate about a load bearing pin that is radially fixed to the housing, wherein when the fasteners are in the open position the fasteners are positively locked open, or when the fasteners are in the closed position the fasteners are positively locked closed. 
         [0024]    The fasteners may be configured to secure to a mechanical interface that is in conformance with STANAG 3842. 
         [0025]    According to another aspect of the invention, a method of operating a fastening system for securing an expendable aircraft store to an aircraft, may include providing a housing that forms part of the expendable aircraft store, the housing extending along a longitudinal axis, rotating a first fastener about a first fastening axis, wherein the first fastener is rotatably connected to the housing, and rotating a second fastener about a second fastening axis that is laterally offset from the first fastening axis relative to the longitudinal axis, wherein the first fastener is rotatably connected to the housing, wherein each fastener includes an engagement section for securing the respective fastener to a mechanical interface of the aircraft, each engagement section being radially outward of the respective fastening axis, and wherein each fastener is rotatable from an open position, where the respective engagement section is engageable with a mechanical interface of the aircraft, to a closed position that reduces a drag coefficient of the fastening system compared to the open position. 
         [0026]    The method may include rotating each fastener from the open position to the closed position, thereby reducing the drag coefficient of the fastening system. 
         [0027]    The method may include actuating an actuator assembly that is operably connected to each fastener to positively lock the fasteners in the open position, to close the fasteners, to open the fasteners, or to positively lock the fasteners in the closed position. 
         [0028]    The method may include launching the expendable aircraft store, and rotating the fasteners of the launched expendable aircraft store to the closed position, thereby reducing the drag coefficient of the expendable aircraft store. 
         [0029]    The method may include adjusting a bearing surface of the housing to adjust the open position of the first fastener or the second fastener, wherein a vertical distance of the bearing surface from the first fastening axis or the second fastening axis is adjusted. 
         [0030]    The method may include adjusting a closed-position adjuster of the housing to adjust the closed position of the first fastener or the second fastener. 
         [0031]    The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is an oblique view of an exemplary aircraft with an exemplary expendable aircraft store including an exemplary fastening system. 
           [0033]      FIG. 2  is an oblique view of the fastening system of  FIG. 1  in a locked-open state and including fasteners in an open position. 
           [0034]      FIG. 3  is an oblique view of the fastening system of  FIG. 2  with a cover removed to illustrate internal components of the fastening system in the locked-open state. 
           [0035]      FIG. 4  is an exploded perspective view of the fastening system of  FIG. 2 . 
           [0036]      FIG. 5  is an oblique view of a valve member of the fastening system of  FIG. 4 . 
           [0037]      FIG. 6  is a cross-sectional view taken along line  6 - 6  of the fastening system of  FIG. 3  and a mechanical interface of the aircraft of  FIG. 1 . 
           [0038]      FIG. 7  is cross-sectional view of the fastening system of  FIG. 6  in an unlocked-open state. 
           [0039]      FIG. 8  is cross-sectional view of the fastening system of  FIG. 6  in an unlocked-partially-open state. 
           [0040]      FIG. 9  is cross-sectional view of the fastening system of  FIG. 6  in a further unlocked-partially-open state. 
           [0041]      FIG. 10  is cross-sectional view of the fastening system of  FIG. 6  in a locked-closed state. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    The principles of this present application have particular application to fastening expendable aircraft stores to an aircraft until launch from the aircraft, such as launching a missile from an airplane, and thus will be described below chiefly in this context. It will be appreciated that principles of this invention may be applicable to other stores where it is desirable to reduce a drag coefficient of the store upon detachment of the other store from a vehicle. 
         [0043]    Referring now to the drawings and initially to  FIG. 1 , an exemplary aircraft is designated generally by reference numeral  20 . The aircraft  20  can be provided with an expendable aircraft store detachably attached to a portion of the aircraft  20 . For example, the expendable aircraft store may be a missile  22  or an unmanned aerial vehicle (“drone”) (not shown). Each missile  22  may be detachably attached to a wing of the aircraft  20  to be deployable while the aircraft is airborne. Each missile  22  may include an exemplary fastening system  24  for detachably attaching the missile  22  from the wing of the aircraft  20 . 
         [0044]      FIG. 2  illustrates one of the fastening systems  24  in a locked-open state. The fastening system  24  may include a housing  26 , which may extend along a longitudinal axis Y, and may include fasteners  28  and  30  (e.g., hooks) that are rotatably connected to the housing  26 . The housing  26  and the fasteners  28  and  30  may have reflectional symmetry across a YZ-plane defined by the longitudinal axis Y and a vertical axis Z. 
         [0045]    The housing  26  may include a main body  32 , a longitudinally-extending support  34 , a longitudinally-extending flange  36 , and a cover  38  longitudinally opposite the main body  32 . The longitudinally-extending support  34  and the longitudinally-extending flange  36  may connect to a longitudinally-inner surface  40  of the main body  32  and a longitudinally-inner surface  42  of the cover  38  to define an inner cavity  44  to allow rotation of the fasteners  28  and  30 . 
         [0046]    The longitudinally-extending support  34 , the main body  32 , and the cover  38  may define the inner cavity  44 . 
         [0047]    The inner cavity  42  may have a longitudinal length at least equal to or greater than a longitudinal length of each fastener  28  or  30  to allow the fasteners  28  or  30  to rotate without interference by the longitudinally-inner facing surfaces  40  and  42  of the main body  32  and the cover  38 , respectively. 
         [0048]    The longitudinally-extending support  34  and the main body  32  may be one-piece to form a portion of the housing  26 . In an embodiment, the longitudinally-extending support and the cover may be one-piece to form a portion of the housing. 
         [0049]    The housing  26  of the fastening system  24  may be integrated as part of the missile  22  (shown in  FIG. 1 ) in any suitable manner. For example, the housing  26  may form part of a housing of the missile  22 . Counter-bored holes  46  may receive securing members, such as bolts (not shown), to fix the fastening system  24  to a support structure (not shown) or skin of the missile  22 . Alternatively, the housing may be fixed to the housing of the missile  22  with another method of fixing, such as bolting, welding, and/or clamping. 
         [0050]    The fasteners  28  and  30  are illustrated in an open position. The fasteners  28  and  30  may each include a body  60  or  62  with an engagement section  64  or  66  for securing the missile  22  to the aircraft  20 . The engagement section  64  or  66  may be disposed at a radially outward end of a radially-extending portion  68  or  70  of the corresponding body  60  or  62 . 
         [0051]    The engagement section  64  or  66  may include a protrusion  72  or  74  for engaging a concave surface  76  or  78  (shown in  FIG. 6 ) of a mechanical interface  80  of the aircraft  20  when the fastener is open. The concave surface  76  or  78  may be longitudinally and vertically aligned with the corresponding protrusion  72  or  74  to receive the corresponding protrusion  72  or  74  (as shown in  FIG. 6 ). 
         [0052]    The engagement section  64  or  66  may engage the longitudinally-extending support  34  when the corresponding fastener  28  or  30  is closed. For example, each lateral side of the longitudinally-extending support  34  may include a recess—defined by a concave surface  82  or  84  of the longitudinal extending support  34 —for receiving the corresponding fastener  28  or  30  when the fastener  28  or  30  rotates to the closed position. The engagement section  64  or  66  of the fastener  28  or  30  may have a longitudinal length equal to or less than the longitudinal length of the concave surface  82  or  84  and may be longitudinally aligned with the concave surface  82  or  84  to allow the recess to receive the protrusion  72  or  74  of the engagement section  64  or  66 . 
         [0053]    For example, the concave surface  82  or  84  may be radially spaced from the corresponding fastening axis F 1  or F 2  a distance that is equal to the distance the engagement section  64  or  66  is radially spaced from the corresponding fastening axis F 1  or F 2 . In an embodiment, the engagement section of the fastener includes a recess for receiving a protrusion of the aircraft and/or a protrusion of the longitudinally-extending support. The recess of the fastener may be radially spaced from the corresponding fastener axis F 1  or F 2  a distance that is equal to the distance that the corresponding protrusion is radially spaced from the fastener axis F 1  or F 2 . 
         [0054]    Turning now to  FIG. 3 , the fastening system  24  may include fastener pins  86  and  88  to rotatably attach each fastener  28  or  30  to the housing  26 , and an actuator assembly  90  that may be axially fixed to the housing  36  by a pair of center blocks  92  that may be axially and rotatably fixed to the housing  26 . 
         [0055]    The body  60  or  62  of the fasteners  28  and  30  may include a through hole  94  or  96  for receiving each corresponding fastener pin  86  or  88 . The through hole  94  may define the first fastening axis F 1  and the through hole  96  may define the second fastening axis F 2 . The first fastening axis F 1  may be laterally offset from the longitudinal axis Y and parallel with the longitudinal axis Y. The distance of the lateral offset may be equal to or greater than a distance that the engagement section  64  is radially offset from the first fastening axis F 1 . 
         [0056]    The second fastening axis F 2  may be laterally offset from the longitudinal axis Y, opposite the first fastening axis F 1 , and parallel with the longitudinal axis Y. The distance of the lateral offset may be equal to or greater than a distance that the engagement section  66  is radially offset from the second fastening axis F 2 . 
         [0057]    The fastener pins  86  and  88  may be load bearing and extend concentrically with the corresponding fastening axis F 1  or F 2  from the main body  32  to the cover  38  (shown in  FIG. 1 ) to allow the fasteners  28  and  30  to rotate and to radially fix the fasteners  28  and  30  to the housing  26 . For example, the fastener pin  86  may allow the fastener  28  to rotate about a portion of the first fastening axis F 1  and the fastener pin  88  may allow the fastener to rotate about a portion of the second fastening axis F 2 . 
         [0058]    The body  60  or  62  of the fasteners  28  or  20  may be L-shaped to distribute load from the radially-extending portion  68  or  70  and to limit the open position of the fasteners  28  or  30 . The body  60  or  62  may include a leg  100  or  102  with a support-bearing surface  104  or  106  to form the L-shape. For example, the leg  100  or  102  may extend radially outward from a pivot portion of the body  60  or  62  to form an oblique angle θ with the radially-extending portion  68  or  70  (shown more clearly in  FIG. 6 ). The angle θ may be anywhere from 60° to 90°. In an embodiment angle θ is anywhere from 60° to 130°, anywhere from 75° to 110°. 
         [0059]    The L-shaped body allows the fastener  28  and  30  to distribute a portion of the stress from the radially-extending portion  68  or  70  to the support-bearing surface  104  or  106  of the leg  100  or  102  when the corresponding fastener  28  or  30  is in the open position. The support-bearing surface  104  or  106  of the leg  100  or  102  may transfer a portion of the stress to a leg-bearing surface  108  or  110  of the longitudinally-extending support  34 , which may transfer a portion of the stress to the housing  26 . Transferring stress through the support-bearing surface  104  or  106  may reduce stress experienced by the corresponding fastener pin  86  or  88 . 
         [0060]    The support-bearing surface  104  or  106  and the leg-bearing surface  108  or  110  may limit the amount the corresponding fastener  28  or  30  can rotate from the open position to the closed position. Engaging the support-bearing surface  104  or  106  with the leg-bearing surface  108  or  110  may prevent further opening rotation of the corresponding fastener. 
         [0061]    An outer surface  112  or  114  of the corresponding radially-extending portion  68  or  70  may have a profile that matches adjacent portions of the housing  26  or a skin (shown schematically in  FIG. 1 ) of the missile  22 . The outer surface  112  or  114  may be any suitable shape to reduce the drag coefficient of the fastening system  24  and/or the missile  22 . 
         [0062]    Referring briefly to  FIG. 6 , when the fastener  28  or  30  is closed the outer surface  112  or  114  may be contiguous with a radially-outward-facing surface  116  of the housing  26  or a radially-outward-facing surface of the skin of the missile  22 . The outer surface  112  or  114  may have a profile that is contiguous with the radially-outward-facing surface  116  of the housing  26  or the skin along an XZ-plane. The outer surface  112  or  114  may have a profile that is contiguous with the housing  26  or the skin along the longitudinal axis Y, as illustrated in  FIG. 10 . 
         [0063]    Turning back to  FIG. 3 , the actuator assembly  90  may be operably coupled to both fasteners  28  or  30  to open, to close, to positively lock open, and/or to positively lock closed the fasteners  28  or  30 , as discussed in more detail below in the discussion of  FIG. 4 . 
         [0064]    The housing  26  may include a closed-position adjuster  118  for adjusting the closed position of the fastener  28 . The closed-position adjuster may be disposed within a laterally-extending portion  120 —of the longitudinally-extending support  34 —that receives the radially-extending portion  68  of the fastener  28 . For example, the closed-position adjuster  118  may include a threaded hole in the laterally-extending portion  120  and a set screw that engages with the threaded hole. Rotation of the set screw while engaged with the threaded hole may adjust a distance that the set screw protrudes from the portion of the longitudinally-extending support  34  to adjust the amount the radially-extending portion  68  may rotate to reach the closed position. 
         [0065]    Adjusting the rotation of the radially-extending portion  68  may adjust the drag coefficient of the fastening system  24  by adjusting the position of the outer surface  112  of the radially-extending portion  68  when the fastener  28  is closed, as discussed in more detail below in the discussion of  FIG. 10 . 
         [0066]    A closed-position adjuster  122  (shown in  FIG. 6 ) may be disposed within a laterally-extending portion  124  of the longitudinally-extending support  34  for adjusting the closed position of the second fastener  30 . The closed-position adjuster  122  may be the same as the above described closed-position adjuster  118 , except mirrored across the XY-plane. 
         [0067]    Turning to  FIG. 4 , the fastening system  24  may include a control system  150  operably coupled to the actuator assembly  90  to lock and actuate the fasteners  28  and  30 . The control system  150  may include a pressure source  152  that is operably coupled to a controller  154  for controlling the actuator assembly  90  via the pressure source  152  and an actuator pivot  156 . 
         [0068]    The controller  154  may be configured to operate the pressure source  152  to pneumatically actuate the actuator assembly  90 . For example, the controller  154  may be any suitable computer or electronic processor that is able to control or instruct the pressure source  152 . 
         [0069]    The pressure source  152  may be any suitable device able to provide fluid pressure to the actuator pivot  156 . For example, the pressure source may be a pressurized air reservoir. In an embodiment, the pressure source is another source of mechanical force, such as an electromechanical actuator, or another suitable device operably coupled to the actuator assembly. 
         [0070]    The actuator assembly  90  may include the actuator pivot  156 , a pair of double actuators  158  and  160  that are each operably connected to both fasteners  28  and  30  and rotatable about the actuator pivot  156 . The actuator pivot  156  may have a fluid passage  162  (partially shown in  FIG. 5 ) at an end  164  operably coupled to the pressure source  152 . 
         [0071]    Each double actuator  158  or  160  may include a body  166  or  168 , a closing piston  170  or  172  axially movable within a blind hole  174  or  176  in the body  166  or  168 , and a locking piston  178  or  180  axially moveable within a locking-piston through hole  182  or  184  in the body  166  or  168 . 
         [0072]    The closing piston  170  or  172  may have an end  186  or  188  that is operably coupled to the corresponding fastener  28  or  30 . Each end  186  or  188  may be rotatably coupled to the opposite fastener  28  or  30  that the corresponding locking piston  178  or  180  engages. The end  186  or  188  may be rotatably coupled at a position that creates a rotational moment about the corresponding fastening axis F 1  or F 2  when the closing piston  170  or  172  extends from the body  166  or  168 . 
         [0073]    For example, a pin  190  or  192  may extend parallel to the corresponding fastening axis F 1  or F 2  through each lateral recess  194  or  196  and through each end  186  or  188  to rotatably couple the ends  186  and  188  to the fasteners  28  or  30  at location vertically opposite the engagement section  64  or  66  relative to the corresponding fastening axis F 1  or F 2 . 
         [0074]    Each end  186  or  188  may be disposed within the lateral recess  194  or  196  of the fastener  28  or  30  to provide space for the fastener  28  or  30  to rotate without interference from the closing piston  170  or  172 . Each lateral recess  194  or  196  may be longitudinally offset from one another based on a longitudinal width of each double actuator  158  or  160  and the distance each double actuator  158  or  160  is longitudinally spaced from the other. 
         [0075]    Each body  166  or  168  of the double actuators  158  or  160  may include a through hole  210  or  212  that is concentric with the longitudinal axis Y for receiving the actuator pivot  156 . Each body  166  or  168  may be rotatably connected to the actuator pivot  156  (as shown in detail in  FIGS. 6-10 ). 
         [0076]    The actuator pivot  156  may include a longitudinally-extending nipple  214  for fluidly connecting each body  166  or  168  to the pressure source  152 . For example, the longitudinally-extending nipple  214  may include a portion of the fluid passage  162  (shown in  FIG. 5 ) that is fluidly connected to the pressure source and may have a sealed longitudinal end to prevent fluid flow longitudinally through the entire nipple  214 . For example, the fluid passage  162  may extend longitudinally from the longitudinal end  164  that may be operably connectable to the pressure source  152 —to a first radial-through-hole  216 —that is longitudinally offset from the longitudinal end  164 —for providing pressurized fluid to the blind hole  176  and the locking-piston through hole  184  within the body  168 . The fluid passage  162  may extend longitudinally from the first radial-through-hole  216  to a second radial-through-hole  218  that is longitudinally offset from the longitudinal end  164  and longitudinally beyond the first radial-through-hole  216  for engaging the blind hole  174  and the locking-piston through hole  182  within the body  166 . 
         [0077]    The actuator pivot  156  may seal either longitudinal side of each radial-through-hole  216  or  218  against a radially inward facing surface of each body that defines each through hole  210  or  212 . For example, the actuator pivot  156  may include sealing members (not shown) circumscribing a portion of the longitudinally-extending nipple  214  on both longitudinal sides of each radial-through-hole  216  and  218 . The sealing members (not shown) may be placed within each circumscribing groove  220  that is longitudinally spaced on either side of each radial-through-hole  216  and  218 . The sealing members may be o-rings or any other suitable sealing member. 
         [0078]    The longitudinally-extending nipple  214  may be longitudinally aligned with and longitudinally fixed to each body  166  or  168  of the actuator assembly  90 . For example, the longitudinally-extending nipple  214  may include a retaining-ring groove  222  or  224  proximate each end of the longitudinally-extending nipple  214 , as shown more clearly in  FIG. 5 . Each retaining ring  226  or  228  may engage a longitudinally-facing surface of each center block  92  to limit longitudinal movement of the longitudinally-extending nipple  214  in a first-longitudinal direction and/or a second-longitudinal direction opposite the first-longitudinal direction. 
         [0079]    Limiting the longitudinal movement allows the longitudinally-extending nipple  214  to longitudinally align each radial-through-hole  216  or  218  with the corresponding body  166  or  168  to provide pressurized fluid to each body  166  or  168 . 
         [0080]    The actuator pivot  156  may provide pressurized fluid, such as air, to each body  166  or  168  to retract the locking piston  178  or  180  and to extend the closing piston  172  or  174 , as discussed in more detail below in the discussion of  FIG. 6 . Alternatively, the actuator pivot  156  may remove pressurized fluid from each body  166  or  168  to retract the closing piston  172  or  174  (e.g., to open the corresponding fastener) and to extend the locking piston  178  or  180 . 
         [0081]    Each locking piston  178  or  180  may include a moveable end with a leg-locking-surface  230  or  232  for engaging a lock-bearing surface  234  or  236  (shown more clearly in  FIG. 6 ) of the corresponding leg  100  or  102  to prevent inward rotation of the corresponding fastener  28  or  30 . For example, the leg-locking surface  230  or  232  may engage the lock-bearing surface  234  or  236  when the fastener  28  or  30  is open and the lock-bearing surface  234  or  236  faces in a direction opposite the leg-bearing surface  230  or  232 . Fixing the locking piston  178  or  180  in the extended position while the leg-locking surface  230  or  232  engages the lock-bearing surface  234  or  236  may prevent inward rotation of the fastener  28  or  30  about the respective fastening axis F 1  or F 2  to lock each fastener  28  or  30  in the open position. 
         [0082]    The longitudinally-extending support  34  may include an adjustable-leg-bearing surface  240  for adjusting the open position of the fastener  28  or  30  and/or for distributing load received from each leg  100  or  102  when the fastener  28  or  30  is open. For example, a shim plate  242  may form the leg-bearing surface  108  or  110 . The shim plate  242  may be fixed to the longitudinally-extending support  34  to engage the legs  100  and  102 . The shim plate  242  may have any suitable vertical depth for attaining the desired open position of the fastener  28  or  30 , or the shim plate  242  may include multiple shim plates  242  of varying vertical depths to adjust the open position of the fastener  28  or  30 . 
         [0083]    The shim plate  242  may be fixed by securing members, such as bolts  244  that extend through vertical holes in the longitudinally-extending support  34  and the shim plate  34  and nuts  246  that fix the bolts  244  to the longitudinally-extending support  34 . 
         [0084]    When the fastener  28  or  30  is in the open position, the leg-bearing surface  108  or  110  may distribute load received from each leg  100  or  102  to the housing  26 . For example, the leg-bearing surface  108  or  110  may be fixed to the main body  32  and the cover  38  of the housing  26 . The longitudinally-extending support  34  and the main body  32  may be one-piece, except for the shim  242 . 
         [0085]    The cover  38  may be vertically and laterally fixed to the longitudinally-extending support  34  by a plurality of pins  248 ,  250 ,  252 ,  254 , and  256  that are vertically and laterally fixed to the main body  32 . The plurality of pins  248 - 256  may extend longitudinally beyond the longitudinally-extending flange  36  of the main body  32  to engage with longitudinally extending holes in the cover  38 . 
         [0086]    The cover  38  may be longitudinally fixed to the main body  32  by any suitable device. For example, a longitudinally fixed surface may abut a longitudinally outward facing surface  258  of the cover  38  and a longitudinally outward facing surface  260  of the main body  32 , as illustrated schematically in  FIG. 1 . In an embodiment, the cover and the main body are each fixed to a support structure of the missile. In another embodiment, the cover and the main body are bolted together and/or clamped together. 
         [0087]    The pin  256  may be a center-block pin that may extend longitudinally through the center blocks  92  to the cover  38  to rotatably fix the center blocks  92  to the housing  26 . 
         [0088]    Turning to  FIGS. 6-10 , the body  166  of the double actuator  158  may include a fluid passage  270  and a resilient member  272  biasing the locking piston  178 . The fluid passage  270  may fluidly connect the blind hole  174  and the locking-piston through hole  182  to the through hole  210 . For example, the fluid passage  270  may be a blind hole that extends radially through a portion of the blind hole  174  and through a portion of the locking-piston through hole  182 . 
         [0089]    A sealing member  274  may prevent fluid within the blind hole  174  or the locking-piston through hole  182  from flowing out of the fluid passage  270 . The sealing member  274  may be a set screw that is threadably coupled to the body  166  to prevent fluidly flow out of the fluid passage  270 . 
         [0090]    The resilient member  272  may bias the locking piston  178  to laterally toward the fastener  30  to engage the leg-locking surface  230  with the lock-bearing surface  236  of the fastener  30 . The resilient member  272  may abut a longitudinally-extending pin  276  and a radially-outward protrusion  278  of the locking piston to laterally bias the leg-locking surface  230  toward the lock-bearing surface  236 . 
         [0091]    The resilient member  272  may be any suitable biasing device, such as a spring in a compressed state that abuts the longitudinally extending pin  276  and the radially-outward protrusion  278 . 
         [0092]    The longitudinally-extending pin  276  may be fixed to the body  166 . For example, the longitudinally-extending pin  276  may be press-fit into a through hole of the body  166  at an end of the through hole  182  that is opposite the leg-locking surface  230 . 
         [0093]    The locking piston  178  may be sealingly connected to the body  166 . For example, the radially-outward protrusion  278  may include a sealing member  280 , such as an o-ring, for sealing against a radially-inner-facing surface of the body  166  that defines a portion of the through-hole  182  to prevent fluid flow between the radially-outward protrusion  278  and the body  166 . The body  166  may include a sealing member  282 , such as an o-ring, for sealing against a radially-outer-facing surface the locking piston  178  disposed between the radially-outward protrusion  278  and the leg-locking surface  230 . 
         [0094]    The closing piston  170  may be sealingly connected to the body  166 . For example, the closing piston  170  may include a sealing member  284 , such as an o-ring, for sealing against a radially-inner-facing surface of the body  166  that defines a portion of the blind hole  174 . 
         [0095]    The double actuator  160  may be the same as the double actuator  158  and oriented in reverse to unlock the fastener  28  and to rotate the fastener  30  when the fasteners  28  and  30  are disconnected from the mechanical interface  80 , which may be referred to below as a store fastener  80  below. 
         [0096]    When the fasteners  28  and  30  are in the open position, the store fastener  80  may be coupled to the fasteners  28  and  30 . The store fastener  80  and the fasteners  28  and  30  may conform to a mechanical interface standard, such as STANAG 3842. For example, the protrusions  72  and  74  of the engagement sections  64  and  66  may engage with the laterally-opposite-facing concave surface  76  and  78  of the store fastener  80 . In an embodiment, the engagement sections engage with protrusions of the store fastener. 
         [0097]    The fasteners  28  and  30  may remain attached to the store fastener  80  during take-off, flight, and/or landing of the aircraft  20 , until the missile  22  is launched. While the aircraft  20  operates, the fasteners  28  and  30  may experience thousands of pounds of load, such as when the aircraft  20  suddenly changes direction or accelerates in speed. The support-bearing surface  104  or  106  of the leg  100  or  102  may transfer a portion of the resulting stress that is perpendicular to the corresponding fastener axis F 1  or F 2  to the leg-bearing surface  108  or  110 . The leg-bearing surface  108  or  110  may distribute a portion of the stress to the main body  32  and the cover  38  (shown in  FIGS. 2 and 4 ). 
         [0098]    The leg-bearing surface  108  or  110  may be adjusted, as mentioned above regarding  FIG. 4 , the adjustable-leg-bearing surface  240  may be adjusted to modify the vertical distance between the adjustable-leg-bearing surface  240  and the fastening axis F 1  or F 2 . Modifying the vertical distance adjusts the open position of the fastener  28  or  30 . For example, decreasing the vertical distance may restrict the open position, which may provide laterally tighter engagement between the fasteners  28  and  30  and the store fastener  80 . Increasing the vertical distance may increase the open position, which may provide laterally looser engagement between the fasteners  28  and  30  and the store fastener  80 . 
         [0099]    The drag coefficient of the fastening system  24  may be highest when the fasteners are in the open position. The aerodynamic drag may be a function of speed of the missile  22 , launch/release conditions such as speed and altitude, shape and size of the missile  22 , and shape and size of other features such as strakes or fixed wings protruding from the missile  22 . For example, the missile  22  (shown in  FIG. 1 ) may have an aerodynamic drag when the fasteners  28  and  30  are open that is reduced by anywhere from 5%-25% when the fasteners  28  and  30  are closed. 
         [0100]    Once the missile is launched, the controller  154  (shown in  FIG. 4 ) may instruct the pressure source  152  (shown in  FIG. 4 ) to provide pressurized fluid to the fluid passage  162  of the actuator pivot  156  to provide the pressurized fluid to each fluid passage  270  to pressurize the locking piston  178  and  180  and the closing piston  170  and  172 . Once pressurized, the locking piston  178  and  180  may retract to unlock the corresponding fastener  28  or  30 , thereby allowing the fastener  28  or  30  to rotate to reduce the drag coefficient. 
         [0101]    As shown in  FIG. 7 , once the fastener  28  or  30  is unlocked and free to rotate to the closed position, the corresponding closing piston  170  or  172  may extend to rotate the corresponding fastener  28  or  30  toward the closed position. 
         [0102]    As shown in  FIG. 8 , once the closing piston  170  begins to extend, the fastener  28  may begin to rotate inward about the corresponding fastener axis F 1 . As the closing piston  170  extends, the closing piston  170  rotates about the pin  190 , which may rotate about the corresponding fastening axis F 1 . As the pin  190  rotates about the fastening axis F 1 , the corresponding body  166  of the double actuator  158  may rotate about the longitudinal axis Y to allow the end  186  of the closing piston  170  to follow the pin  190 . 
         [0103]    Operation of the double actuator  160  may be the same as the operation of the double actuator  158  to unlock the fastener  28  and/or to rotate the fastener  30 . For example, each double actuator  28  and  30  may perform the same operations described above simultaneously. 
         [0104]    As shown in  FIGS. 9 and 10 , the closing piston  170  or  172  may continue to extend until the fastener  28  or  30  reaches the closed position. The fastener  28  or  30  may be in the closed position when the fastener  28  or  30  engages the longitudinally-extending support  34 . For example, the fastener  28  or  30  may engage the closed-position adjuster  118  or  122 , which may prevent further inward rotation of the fastener  28  or  30 . 
         [0105]    The closed-position adjuster  118  or  122  may be extended or retracted to modify the closed position of the corresponding fastener  28  or  30 , as mentioned above regarding  FIG. 3 . Extending the closed-position adjuster  118  or  122  may restrict how much the fastener  28  or  30  can rotate inwardly to the closed position. Retracting the closed-position adjuster  118  or  122  may increase how much the fastener  28  or  30  can rotate inwardly to the closed position. If the outer surface  112  or  114  of the fastener  28  or  30  is protruding from and not contiguous with the housing  26  or the skin (shown schematically in  FIG. 1 ), the closed-position adjuster  118  or  122  may be retracted until the corresponding outer surface  112  or  114  is contiguous when in the closed position. If the outer surface  112  or  114  of the fastener  28  or  30  is receded from and not contiguous with the housing  26  or the skin, the closed-position adjuster  118  or  122  may be extended until the outer surface  112  or  114  is contiguous when in the closed position. 
         [0106]    As the fasteners  28  or  30  rotate to the closed position, the drag coefficient of the fastening system  24  or the missile  22  (shown in  FIG. 1 ) may be reduced. Once the fasteners  28  or  30  are in the closed position, as shown in  FIG. 10 , the drag coefficient may be lower than any other position of the fasteners  28  or  30  between the open and closed positions. 
         [0107]    The drag coefficient Ca may be a function of the perimeter length of the cross-sectional profile of the fastening system  24  shown in  FIGS. 6-10 . Closing each fastener  28  or  30  may reduce perimeter length of cross-sectional profile of the fastening system  24 , thereby reducing a drag coefficient of the fastening system. For example, the perimeter length of the cross-sectional profile of the fastening system  24  when the fasteners  28  or  30  are closed may be anywhere from 60% to 95% of the perimeter when the fasteners  28  or  30  are open. 
         [0108]    The actuator assembly  90  may actuate the fasteners  28  or  30  in reverse to the above described operation described in reference to  FIGS. 6-10 . For example, pressure from the pressure source  152  may be lowered to allow the closing piston  170  or  172  to retract. Retracting the closing piston  170  or  172  may allow the corresponding fastener  28  or  30  to rotate to the open position. Once the fastener  28  or  30  is in the open position, the locking piston  178  or  180  may extend to lock the fastener  28  or  30  in the open position. 
         [0109]    Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.