Abstract:
Self-aligning retractable strut stabilization assemblies that are ground engageable in use are provided to stabilize a vehicle, e.g., a cargo aircraft during loading/unloading operations. The strut stabilization assembly may be on-board equipment associated with an aircraft that may be actuated (e.g., via on-board hydraulic and/or electric actuation systems) by the aircraft operator so as to stabilize the aircraft during certain ground operations, e.g., cargo and/or personnel loading/unloading operations. A laterally separated pair of centering mechanisms are attached to the main strut and define a zero-spring bias load state corresponding to an aligned condition of the main strut. Displacement of the main strut out of the aligned condition responsively causes at least one centering mechanism to exert a spring-biased load in an opposite direction of the displacement causing the at least one centering mechanism to return to the zero-spring bias load state thereby returning the main strut to the aligned condition thereof.

Description:
FIELD 
       [0001]    The embodiments disclosed herein relate generally to retractable aircraft stabilization struts for stabilizing an aircraft fuselage, e.g., at either the tail or the front of the fuselage, during ground-based loading/unloading operations. 
       BACKGROUND 
       [0002]    Cargo aircraft typically have a center of gravity (CG) that is typically forward of the main landing gear. There may thus be a tendency during loading/unloading applications for those aircraft equipped with rear cargo ramps for the aircraft to shift about the main landing gear assembly which in turn raises the aircraft nose. In extreme situations, aircraft shifting during loading/unloading could cause a severe tail strike damaging the airframe and/or exposing personnel to injury hazard. For these reasons, it is advisable for cargo aircraft to include additional tail ground-stabilization aft of the main landing gear during loading/unloading operations. 
         [0003]    A variety of aircraft tail stabilization assemblies are generally known. For example, tail stabilization assemblies are known which are positionally fixed and consist of a fixed support that is typically associated with ground-based equipment manually placed under the aircraft. As can be appreciated such fixed stabilization assemblies require the pre-positioning of the ground based equipment as well as a substantial time to install thereby prolonging the loading/unloading operation, each being an obvious disadvantage if the cargo aircraft is being loaded/unloaded in an active combat zone. 
         [0004]    On-board stabilization systems which may be mechanically or manually operated are also known. For example telescopic strut stabilization systems are know that usually employ on-board hydraulic and/or electric actuators. Telescopic strut stabilization systems typically include a main strut and a retraction actuator as the same component. 
         [0005]    An on-board tail jack assembly is also known from U.S. Pat. No. 4,593,871, the entire content of which is expressly incorporated hereinto by reference, which includes a manually activated hydraulic jack system and a strut that may be operatively fixed to the jack system. The operator may thus extend/retract the strut as may be needed to stabilize the tail. However, when not in use, the strut must be physically disconnected from the jack and stored remotely (e.g., as part of the tail stairwell). 
         [0006]    Retractable strut stabilization systems are also know which employ hydraulic and/or electric actuators so as to be capable of deployment between a stowed condition within a strut bay of the aircraft fuselage and an extended condition whereby the strut stabilizes the aircraft tail. Such retractable stabilization systems will typically be equipped with a strut door which can be manually operated or actuated by a mechanism linked to the stabilizer or by a dedicated door actuator. 
         [0007]    Retractable strut stabilization systems however are problematic to operate in the event that the strut is not aligned with the strut bay during retraction. That is, when a retractable strut stabilization system is deployed during an aircraft loading/unloading operation, side loads can be experienced which can cause the strut to become off-centered or misaligned with the strut bay. If the strut is then attempted to be retracted into the strut bay while off-centered or misaligned, it could become jammed thereby precluding operation of the aircraft. 
         [0008]    What has been needed in the art, therefore, are retractable strut assemblies that have a self-aligning mechanism to address the problems associated with the strut being off-centered or misaligned as a result of the aircraft loading/unloading operations. As such, a self-alignable retractable strut assembly would provide a measure of safety and reliability for the cargo aircraft operations. It is towards fulfilling such needs that the embodiments of the invention herein are directed. 
       SUMMARY 
       [0009]    The embodiments disclosed herein are generally directed toward self-aligning retractable strut stabilization assemblies that are ground engagement in use to stabilize a vehicle, e.g., a cargo aircraft during loading/unloading operations. In certain embodiments, the strut stabilization assembly will be on-board equipment associated with an aircraft that may be actuated (e.g., via on-board hydraulic and/or electric actuation systems) by the aircraft operator so as to stabilize the aircraft during certain ground operations, e.g., cargo and/or personnel loading/unloading operations. 
         [0010]    According to some embodiments, therefore, an aircraft is provided with an on-board self-aligning strut stabilization assembly which is moveable between a retractable position wherein the strut stabilization assembly is housed within a strut bay of the aircraft, and an extended position wherein the strut stabilization assembly is in ground-engaging contact to stabilize an aft portion of the aircraft. The strut stabilization assembly will advantageously include a main strut pivotally connected to supporting structure of the aircraft for pivotal movements between the extended and retracted positions thereof, a strut extension member operatively associated with the main strut for movements between a retracted state and a ground-engaging extended state, an actuator operatively connected to the main strut for moving the main strut and the strut extension member operatively associated therewith between the extended and retracted positions, and a pair of laterally separated double-acting spring-biased centering mechanisms each having one end pivotally attached to the supporting structure of the aircraft and an opposite end attached to the main strut. 
         [0011]    In preferred embodiments, the centering mechanisms will each define a zero-spring bias load state corresponding to an aligned condition of the main strut such that a displacement of the main strut out of the aligned condition responsively causes at least one centering mechanism to exert a spring-biased load in an opposite direction of the displacement causing the at least one centering mechanism to return to the zero-spring bias load state thereby returning the main strut to the aligned condition thereof. The centering mechanisms may comprise extendible extension posts having a terminal end pivotally attached to the supporting structure of the aircraft. 
         [0012]    The strut extension member may be telescopically received within the main strut for reciprocal rectilinear movements between the retracted and ground-engaging states thereof. A ground-engageable foot pad may advantageously be connected to a terminal end of the strut extension member. 
         [0013]    A main strut door may operatively be connected to the main strut for covering the strut assembly when stowed in the strut bay. A main strut door linkage may be provided to operatively link the main strut door to the main strut so as to cause the main strut door to move from between opened and closed states in response to the main strut being pivotally moved between the extended and retracted positions thereof. A secondary strut door may also be provided in which case a linkage yoke operatively mechanically links the secondary strut door the main strut door so that the main and second strut doors are slaved to one another for movements between opened and closed states thereof. 
         [0014]    These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof. 
     
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
         [0015]    The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which: 
           [0016]      FIG. 1  is a partial side elevational view of a cargo aircraft which includes a retractable self-aligning stabilization strut assembly in accordance with an embodiment of the invention; 
           [0017]      FIG. 2  is a detailed perspective view of the retractable self-aligning stabilization strut assembly in accordance with an embodiment of the invention shown in a retracted position; 
           [0018]      FIG. 3  is detailed perspective view of the self-aligning stabilization strut assembly in accordance with an embodiment of the invention shown in an extended position; 
           [0019]      FIGS. 4-7  show an operational sequence whereby the self-aligning stabilization strut assembly is retracted from its extended operational position ( FIG. 4 ) and into a retracted position whereby the strut assembly is housed within the strut bay ( FIG. 7 ); 
           [0020]      FIGS. 8-10  are aft-facing elevational views of the kinematic ranges of motion for the self-aligning strut assembly in accordance with an embodiment of the invention that may occur during lateral displacements of the aircraft; 
           [0021]      FIGS. 11-13  are lateral-facing elevational views of the kinematic ranges of motion for the self-aligning strut assembly in accordance with an embodiment of the invention that may occur during longitudinal (forward and aft) displacements of the aircraft; 
           [0022]      FIG. 14  is a detailed view of the freedoms of motion for the strut stabilization assembly and associated centering mechanism; and 
           [0023]      FIGS. 15-18  are end views of the self-aligning strut assembly in accordance with an embodiment of the invention showing self-alignment when retracted. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Accompanying  FIG. 1  depicts a cargo aircraft  10  in which an embodiment of a self-aligning stabilization strut assembly  20  according to the invention may operationally be employed. The exemplary cargo aircraft  10  includes a fuselage  10 - 1  having an aft main cargo ramp  10 - 2  which is shown in an opened condition to allow cargo to be physically loaded into the cargo space  10 - 1  a within the fuselage  10 - 1 . 
         [0025]    The stabilization strut assembly  20  is pivotally moveable into and out of a strut bay  10 - 4  within the fuselage  10 - 1  of the aircraft  10  by way of suitable hydraulic and/or electric actuators (see, e.g., actuator  30  depicted, for example, in  FIGS. 2 and 3 ). For example, as is depicted in solid line in  FIG. 1 , the stabilization strut assembly  20  is shown as being in an extended and operational position aft of the aircraft main landing gear assembly  10 - 3  in engagement with the ground surface GS to thereby stabilize the aft portion of the aircraft fuselage  10 - 1  when cargo is loaded/unloaded via the ramp  10 - 2  when opened. When the cargo loading/unloading operation is complete, however, the cargo ramp  10 - 2  may be closed and the strut assembly  20  pivotally moved (arrow A 1 ) into a retracted position within the strut bay  10 - 4  of the fuselage  10 - 1  as shown in dashed line in  FIG. 1 . Conversely, in preparation for a loading/unloading operation, the stabilization strut assembly  20  may be pivotally moved (arrow A 1 ) from its stowed position within the strut bay  10 - 4  and into an operative ground-engaging position as will be described in greater detail below. 
         [0026]    Accompanying  FIGS. 2 and 3  depict the self-aligning strut stabilization assembly  20  disembodied from the aircraft  10  in its retracted and extended positions, respectively. The strut stabilization assembly is generally comprised of main strut  22  which includes a strut extension member  24  which in the embodiment depicted is telescopically received within the main strut  22  and thereby reciprocally rectilinearly extendible (e.g., via suitable hydraulic and/or electrical actuation (not shown)) between a retracted state as shown in  FIG. 2  and an extended ground-engaging state as shown in  FIG. 3 . The terminal end of the strut extension member  24  includes a foot pad  26  that is adapted to engage the ground surface GS when the strut extension member  24  is in its extended condition as shown in  FIG. 3  to provide load transmission from main strut  22  to the ground surface GS. 
         [0027]    The upper end of the main strut  22  is pivotally connected to supporting structure  10 - 5  of the aircraft fuselage  10 - 1  by a pivot pin assembly  28 . A hydraulically or electrically activated actuator  30  is pivotally connected at one end to a support boss  10 - 5 a of the supporting structure  10 - 5  and includes an extensible actuator piston  30 - 1  connected pivotally at its terminal end to a connection lug  22 - 1  associated with the main strut  22 . 
         [0028]    The strut assembly  22  is also provided with main and secondary strut doors  32 ,  34 , respectively. The main strut door  32  includes a pair of laterally separated main door hinges  32   a,    32   b.  The second strut door  34  is supported by a support bracket  34   b  which is connected to the fuselage  10 - 1  of the aircraft  10  by pivot pints  34   a - 1 . A door linkage yoke  36  pivotally interconnects the main door hinges  32   a,    32   b  to the secondary door support bracket  34   a.  A strut door linkage arm  38  is pivotally connected at one end to the main strut  22  and at an opposite end thereof to the main door  32  so as to operatively link the main strut  22  to the main door  32 . Movement of the main strut  22  between its retracted and extended positions will therefore responsively cause the main strut door to be moved between its closed and opened conditions by virtue of the interconnection therebetween provided by the linkage arm  38 . The mechanical linkage between the main strut door  32  and the secondary strut door  34  provided by way of the door linkage yoke  36  will concurrently cause the secondary strut door  34  to be moved between its closed and opened positions. 
         [0029]    The strut assembly  20  also includes a laterally separated pair of spring-biased centering mechanisms  40 ,  42  each having an extension post  40 - 1 ,  42 - 1  being journally connected at its terminal end  40   a,    42   a  to a proximal end of the main door hinges  32   a,    32   b.  The mechanisms  40 ,  42  are also journally connected at an end opposite to the ends  40   a,    42   a  to the lateral connection lobes  40   b,    42   b  of the main strut  22 , respectively. (Only connection lobe  40   b  is visible in  FIG. 3 , but see for example  FIGS. 8-11 .) Each of the centering mechanisms  40 ,  42  houses a double-acting spring cartridge (not shown) having a nominal length corresponding to a centered position both laterally and longitudinally relative to the longitudinal axis of the aircraft fuselage  10 . When the strut assembly  20  is in a longitudinally and vertically aligned (centered) position, therefore, each of the centering mechanisms will define a nominal length whereby a zero-spring bias load is presented. Lateral and/or longitudinal movements of the main strut  22  (e.g., that may occur during loading/unloading operations of the aircraft  10  when the strut extension  24  is in engagement with the ground surface GS) will cause extension and/or retraction the extension posts  40 - 1  and/or  42 - 1  which in turn responsively changes the nominal length of at least one of the double acting spring cartridges associated with the centering mechanisms  40  and/or  42 , respectively. This change in the nominal spring length will thereby in turn cause a spring-bias load to be generated in an opposite direction that encourages the extension posts  40 - 1  and/or  42 - 1  to return to their nominal or centered zero-spring bias load state. 
         [0030]    Accompanying  FIGS. 4-7  depict an operational sequence to retract the strut assembly  20  into the strut bay  10 - 4  of the aircraft fuselage  10 - 1 . When in the extended position as shown in  FIG. 4 , the strut extension member  24  will need to initially be retracted by operation of on-board hydraullically electrically activated actuation systems (not shown) operatively associated with the main strut  22 . The retracted state of the strut extension member  24  relative to the main strut  22  is depicted in  FIG. 5 . Thereafter, actuation of the actuator  30  associated with the main strut  22  will therefore cause the actuator arm  30 - 1  to retract thereby responsively causing the main strut  22  to be pivotally moved about the pivot pin assembly  28 . Pivotal movement of the main strut  22  about the pivot pin assembly  28  also responsively cause the main and secondary strut doors  32 ,  34 , respectively, to follow due to the mechanically slaved linkage thereby provided by the main strut door linkage yoke  36  and main strut door linkage arm  38 . An intermediate state of the strut retraction is depicted in  FIG. 6 . Continued retraction of the main strut  22  will therefore cause it to be fully housed within the strut bay  10 - 4  whereby the main and secondary strut doors  32 ,  34 , respectively are flush with the exterior skin of the fuselage  10 - 1 . Such a fully retracted state of the strut assembly  20  is depicted in  FIG. 7 . As can be appreciated, when in the retracted position as shown in  FIG. 7 , actuation of the actuator  30  will therefore cause the actuator arm  30 - 1  to extend thereby responsively causing the main strut  22  to be pivotally moved about the pivot pin assembly  28  into the extended position as shown in  FIG. 4 , i.e., in an operational sequence opposite to that depicted sequentially by  FIGS. 4-7 . 
         [0031]      FIGS. 8-10  are aft-facing elevational views of the kinematic ranges of motion for the self-aligning strut assembly  20  that may occur during lateral displacements of the aircraft, it being appreciated that  FIG. 9  shows the assembly  20  in a longitudinally aligned (centered) state.  FIGS. 11-13  on the other hand are lateral-facing elevational views of the kinematic ranges of motion for the self-aligning strut assembly  20  that may occur during longitudinal (forward and aft) displacements of the aircraft, it being appreciated that  FIG. 12  shows the assembly  20  in a vertically aligned (centered) state. It will be noted that the journal connections of the actuator  30  and centering mechanisms  40 ,  42  have sufficient play so as to allow predetermined degrees of misalignment relative to the aircraft&#39;s longitudinal and vertical axes. Such angular misalignments that are permitted by any of the journal connections of the actuator  30  and centering mechanisms  40 ,  42  are also depicted by the dashed lines of  FIG. 14 , whereby the solid lines thereof depict the assembly  20  in a longitudinally and vertically aligned state. 
         [0032]    Accompanying  FIGS. 15-18  depict an end view of the strut assembly  20  showing how the centering mechanisms  40 ,  42  serve to physically return the main strut  22  to its aligned (centered) state to allow full retraction thereof into the strut bay  10 - 4  of the fuselage  10 - 1 . 
         [0033]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.