Abstract:
A method of controlling mixing of a flow exiting a downstream end of a primary nozzle associated with a jet engine. The method may involve coupling a shape memory alloy (SMA) element to a mixing structure disposed at the downstream edge of the primary nozzle. An electrical signal may be applied to the SMA element to heat the SMA element and induce a phase change in the SMA element. The phase change may cause an axial length of the SMA element to constrict, to cause movement of the mixing structure into a path of the flow exiting the primary nozzle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 12/568,195, filed Sep. 28, 2009 (now U.S. Pat. No. ______), which is a divisional of U.S. application Ser. No. 12/025,872, filed Feb. 5, 2008 (now U.S. Pat. No. 7,644,575), which claims the benefit of U.S. application Ser. No. 10/988,287, filed Nov. 12, 2004 (now U.S. Pat. No. 7,340,883). The disclosure of each of the above applications is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to structures that are adapted to change shape or position for operational purposes. More particularly, the present disclosure relates to structures configured to alter shape or position without the use of electric or hydraulic actuators to pivotally rotate hinged components. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    There is a growing desire in the design of various structures to have structures that can change shape or position without the use of bulky mechanical devices. For example, in mobile platform design, e.g. aircraft, automobiles, trains and ships, to have structures that can change shape or position while the mobile platform is in operation. Such shape or positional changes are often desirable to meet fluctuating aerodynamic needs throughout the duration of mobile platform&#39;s travel. Typically, such dynamic shaping is performed through specific control structures such as flaps, spoilers, ailerons, elevators, rudders, etc. These structures are normally rigid structures that are hinged and pivotally actuated utilizing complex kinematic mechanisms driven by bulky electric or hydraulic actuators. Typically, such kinematic mechanisms and actuators are located either on an exterior surface of the structure or within internal cavities of the structure. 
         [0004]    However, it is often desirable to dynamically alter the shape or position of structures that can not internally or externally accommodate such kinematic mechanisms and the actuators that drive them. For example, with present day jet aircraft, structures typically known in the industry as “chevrons” have been used to help in suppressing noise generated by a jet engine. The chevrons have traditionally been fixed (i.e., immovable), triangular, tab-like elements disposed along a trailing edge of a jet engine bypass and/or core nacelles such that they project into and interact with the exiting flow streams. Although the chevrons have been shown useful to attenuate noise, since they interact directly with the flow streams generated by the engine, the chevrons also generate drag and loss of thrust. Consequently, it would be desirable to have the chevrons deploy into the flow streams when noise reduction is a concern and then return or move to a non-deployed position when reduction of drag is a concern. Due to the aerodynamics necessities and extreme operational conditions associated with the engine nacelle and chevrons, kinematic mechanisms and the related actuators that would be needed to deploy the chevrons can not be located on external surfaces of the nacelle and chevrons. Furthermore, neither the nacelle structure nor the chevron structures provide adequate internal space to accommodate such kinematic mechanisms and actuators. 
       BRIEF SUMMARY 
       [0005]    In one aspect the present disclosure relates to a method of controlling mixing of a flow exiting a downstream end of a primary nozzle associated with a jet engine. The method may comprise coupling a shape memory alloy (SMA) element to a mixing structure disposed at the downstream edge of the primary nozzle. An electrical signal may be applied to the SMA element to heat the SMA element and induce a phase change in the SMA element. The phase change may cause an axial length of the SMA element to constrict, to cause movement of the mixing structure into a path of the flow exiting the primary nozzle. 
         [0006]    In another aspect the present disclosure relates to a method of controlling mixing of a flow exiting a downstream end of a primary nozzle associated with a jet engine. The method may comprise coupling a shape memory alloy (SMA) element to a mixing structure disposed at the downstream edge of said primary nozzle. A signal may be applied to the SMA element to that causes a phase change in the SMA element, thus changing its axial length. The change in axial length of the SMA element may be used to pivot the mixing structure into a path of the flow exiting the primary nozzle. 
         [0007]    In still another aspect the present disclosure relates to a method of controlling mixing of a flow exiting a downstream end of a primary nozzle associated with a jet engine. The method may comprise coupling a shape memory alloy (SMA) element to a mixing structure disposed at the downstream edge of said primary nozzle. A signal may be applied to the SMA element to that causes a phase change in the SMA element, thus changing a dimensional property of the SMA element. The change in dimensional property of the SMA element may be used to flex the mixing structure into a path of the flow exiting the primary nozzle. 
         [0008]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the various embodiments of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. Furthermore, the features, functions, and advantages of the present disclosure can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present disclosure will become more fully understood from the detailed description and accompanying drawings, wherein; 
           [0010]      FIG. 1  is a simplified side view of a nacelle for housing a jet engine of an aircraft, with the nacelle incorporating a plurality of appending structures of the present disclosure along a trailing circumferential lip portion of a secondary flow nozzle of the nacelle; 
           [0011]      FIG. 2  is an isometric view of a portion of a main body of the nacelle secondary nozzle shown in  FIG. 1 , having one of the plurality of appending structures attached to the lip portion, in accordance with various embodiments of the present disclosure; 
           [0012]      FIG. 3  is an isometric view of one of the plurality of appending structures shown in  FIG. 1 , having a section of an outer skin cut away to illustrate at least one actuator, in accordance with a various embodiment of the present disclosure; 
           [0013]      FIG. 4  is an isometric view of the actuator shown in  FIG. 3 ; 
           [0014]      FIG. 5  is an exploded view of the actuator shown in  FIG. 4 ; 
           [0015]      FIG. 6  is a partial view of the portion of the nacelle secondary nozzle main body and appending structure, as shown in  FIG. 2 , with an outer wall of the main body and an outer skin of the appending structure removed to illustrate an actuator guide, in accordance with various embodiments of the present disclosure; 
           [0016]      FIG. 7  is an illustration of various alternate embodiments of distal ends of the appending structure inner and outer skins, whereby the distal ends are joined utilizing an hinge device; and 
           [0017]      FIG. 8  is a simplified side view of the nacelle shown in  FIG. 1  in accordance with other embodiments of the present disclosure. 
       
    
    
       [0018]    Corresponding reference numerals indicate corresponding parts throughout the several views of drawings. 
       DETAILED DESCRIPTION 
       [0019]    The following description of the various embodiments is merely exemplary in nature and is in no way intended to limit the disclosure, its application or uses. Additionally, the advantages provided by the various embodiments, as described below, are exemplary in nature and not all embodiments provide the same advantages or the same degree of advantages. 
         [0020]      FIG. 1 , illustrates an exemplary structure  10 , shown as a jet engine nacelle, in accordance with various embodiments of the present disclosure. Although the structure  10  and associated features and components will be described herein with respect to a jet engine nacelle, it should be understood that the present disclosure is applicable to any structure configured to change shape, form or position, and that the specific references herein to the jet engine nacelle are merely exemplary. For example, the present disclosure could be applicable to environmental control system air flow structures, automotive fuel and drive chain structures, or control structures for mobile platforms, e.g. flaps, spoilers, ailerons, elevators and rudders. 
         [0021]    The nacelle  10  houses a jet engine  14  and includes a primary flow nozzle  18 , also referred to in the art as a core exhaust nozzle. The primary flow nozzle  18  channels an exhaust flow from a turbine (not shown) of the engine  14  out the aft end of the nacelle  10 . The nacelle  10  additionally includes a secondary flow nozzle  22 , also referred to in the art as a bypass fan exhaust nozzle, that directs the exhaust flow from an engine bypass fan (not shown) out of the aft end of the nacelle  10 . A plug  24  is disposed within the nacelle  10 . In various embodiments, the secondary flow nozzle  22  includes a main body  26  and a plurality of mixing appending structures  28  (hereinafter simply the “appending structures  28 ”). The appending structures  28  are deployable to extend from a circumferential lip area  30 , i.e. end portion, of the main body  26 . The appending structures  28 , commonly referred to in the art as “chevrons”, extend into a flow stream emitted from the secondary flow nozzle  22 , i.e. by-pass fan exhaust flow, to alter the exhaust flow. Therefore, the appending structures  28  may also be referred to herein as exhaust mixing structures and/or flow altering structures. By altering the exhaust flow, the appending structures  28  create an intermixing of the exhaust flow with the ambient air flowing adjacent the nacelle  10  and the appending structures  28 . The intermixing of the exhaust flow and the ambient air flow attenuates the noise generated by the engine  14 . 
         [0022]    Referring to  FIG. 2 , a portion of the nacelle secondary flow nozzle body  26  is illustrated having one of the appending structures  28  attached to the lip area  30  of the nacelle secondary flow nozzle body  26 . More specifically, each appending structure  28  includes an inner skin  34  and an outer skin  38 . Preferably, the appending structure outer skin is constructed of any metallic or composite material suitable for the construction of jet engine nacelles, such as aluminum or carbon fiber. The secondary flow nozzle main body  26  includes an inner wall  42  and an outer wall  46  separated by cavity or gap  50 . A proximal end  54  of the appending structure inner skin  34  is moveably positioned between the inner and outer body walls  42  and  46 , within the cavity  50 . A proximal end  58  of the appending structure outer skin  38  is fixedly coupled to the lip portion  30  of the body outer wall  46 . A distal end portion  62  of the appending structure inner skin  34  is joined to a distal end portion  66  of the appending structure outer skin  38 . The distal end portions  62  and  66  can be joined together using any suitable fastening means, such as screws, rivets, welding or diffusion bonding. 
         [0023]    Referring now to  FIGS. 3 and 4 , a plurality of actuators  70  are located within the cavity  50  and attached to the appending structures  28  and the main body  26  of the secondary flow nozzle  22 . Each appending structure  28  has at least one actuator  70 , preferably a plurality of actuators  70 , attached thereto. More specifically, each actuator  70  includes a fixed pulling bracket  74  affixed to an internal side, i.e. the side adjacent and facing the cavity  50 , of the main body inner wall  42 . The fixed pulling bracket can be fixedly attached to the interior side of the inner wall  42  using any suitable fastening means, for example rivets, by welding, or any other suitable securing means. 
         [0024]    Each actuator additionally includes a sliding pulling bracket  78  affixed to an internal side of a tab  82  extending from the proximal end  54  of the appending structure inner skin  34 . Accordingly, if more than one actuator  70  is affixed to each appending structure inner skin  34 , each inner skin  34  would include a plurality of tabs  82  such that each sliding bracket  78  is affixed to a separate independent tab  82 . 
         [0025]    Furthermore, each actuator  70  includes at least one shape memory alloy (SMA) tendon  86  connected to and extending between the fixed and sliding pulling brackets  74  and  78 . In various embodiments, each actuator includes a plurality of the SMA tendons  86 . The number of actuators  70  and SMA tendons  86  utilized is based on the particular application, e.g. a desired amount of appending structure upper skin deflection and a desired amount of force generated when the SMA tendons are activated. In various forms, the SMA tendons  86  are wires or cables constructed of any suitable SMA metal, for example, a nickel-titanium alloy such as a NITINOL® shape memory alloy. However, the SMA tendons  86  could have any form suitable such that when activated, i.e. heated, each SMA tendon  86  constricts in a one-dimensional direction along a longitudinal centerline, or axis, X ( FIG. 4 ) of the respective SMA tendon  86 . For example, the SMA tendons  86  could be long narrow flat strips of a SMA metal. 
         [0026]    Referring also now to  FIG. 5 , each SMA tendon  86  is coupled at a first end  90  to the fixed pulling bracket  74  and coupled at a second end  94  to the sliding pulling bracket  78 . As described above, each SMA tendon  86  is configured to one-dimensionally constrict along the longitudinal center line X when activated by heat. The constriction of the SMA tendon(s)  86  pulls the sliding pulling bracket(s)  78  and the appending structure inner skin  34 , connected to the sliding pulling bracket(s)  78 , toward the fixed pulling bracket(s)  74 . That is, the proximal end  54  of the appending structure inner skin  34  is pulled further into the cavity  50 . Since the inner and outer skins  34  and  38  of the appending structure  28  are joined or coupled together at their respective distal end portions  62  and  66 , when the inner skin  42  is pulled further into the cavity  50 , the outer skin  38  is caused to turn down or bend toward the nacelle primary flow nozzle  18 . Thus, the inner skin  34  slides into the cavity  50  and remains essentially flat. However, the outer skin  38  is fixed to the lip area  30  of the secondary flow nozzle  22  and therefore the distal end portion  66  of appending structure outer skin is pulled down causing the appending structure  28  to be deflected into the exhaust flow. That is, the constriction of the SMA tendon(s)  86  causes the appending structure  28  to deploy such that the appending structure  28  moves from a first position to a second position that projects into the exhaust flow from the secondary flow nozzle  22 . More specifically, the constriction of the SMA tendon(s)  86  causes the appending structure  28  to deploy by changing shape from a first form to a second form. When deployed, the appending structure  28  extends into the exhaust flow, thereby altering the exhaust flow and causing it to intermix with the ambient air flowing adjacent an external side of the outer wall  46 . 
         [0027]    Thus, when heated, the SMA tendons  86  constrict in a one-dimensional linear direction, thereby causing the appending structures  28  to extend (i.e., “be deployed”) at least partially into the exhaust gas flow path exiting from the secondary flow nozzle  22 . In various embodiments, all of the appending structures  28  are comprehensively controlled such that all the appending structures  28  are deployed, as described above, in a substantially simultaneously manner, at the substantially the same time. Thus, when the appending structures  28  are deployed, all the appending structures, as a whole, change into a peripherally constricted state. Alternatively, each appending structure  28  could be independently controlled such that appending structures  28  could be coordinated to be deployed independent of each other, at different times, and/or to varying degrees of deployment. That is, some appending structures  28  could be deployed further into the exhaust flow than other appending structures  28 . 
         [0028]    The SMA tendons  86  have a predetermined length when secured between the fixed and sliding pulling brackets  74  and  78 . When the SMA tendons  86  are not being heated, the modulus of elasticity of the appending structure outer skin  38  is greater than that of the SMA tendons  86 , thus causing the SMA tendons  86  to be held taut between the fixed and sliding pulling brackets  74  and  78 . This may also be referred to as the “martensitic” state of the SMA tendons  86  (i.e., the “cold” state). As described above, the SMA tendons  86  are activated by heat. 
         [0029]    When the SMA tendons  86  experience heat the modulus of elasticity of the SMA tendons  86  increases significantly i.e., also known as its “austenitic” state. The increase in the modulus of elasticity causes the SMA tendons  86  to constrict, i.e. shorten in length, which in turn causes the appending structures  28  to deploy, i.e. bend or deform into the exhaust gas flow. In their heated condition, the modulus of elasticity of the SMA tendons  86  overcomes the modulus of elasticity of the appending structure outer skin  38 , thus causing the appending structures  28  to deploy. Once the heat source is removed, the modulus of elasticity of the outer skin  38  gradually overcomes the modulus of elasticity of the SMA tendons  86  as the SMA tendons  86  cool. This effectively “pulls” the SMA tendons  86  back to their original length and returns the appending structures  28  to their non-deployed position. Thus, in various embodiments, the outer skin  38  of each appending structure  28  acts as a biasing device, i.e. a ‘return spring’, to return each appending structure  28  to its non-deployed positions. It should be understood that the non-deployed position is when the appending structures are positioned adjacent the exhaust flow path and not being deformed by the constriction of the SMA tendons  86  to extend into the exhaust flow path. 
         [0030]    In one implementation, the appending structure outer skin  38  is constructed of a shape memory alloy such as NITINOL® shape memory alloy. An advantage of utilizing a super-elastic alloy is that it is extremely corrosion resistant and ideally suited for the harsh environment experienced adjacent the exhaust gas flow. Also, of significant importance is that it can accommodate the large amounts of strain required of the deformed shape. 
         [0031]    In various embodiments, the SMA tendons  86  are heated by connecting the SMA tendons  86  to a pair of electrical wires  98  that are connected to a controllable current source (not shown). To heat the SMA tendons  86  the current source is turned on such that current flows through the wires  98  to the SMA tendons  86 . The electrical resistance of the SMA tendons  86  causes the SMA tendons  86  to generate heat that in turn causes the modulus of elasticity of the SMA tendons  86  to increase significantly. As described above, the increase in the modulus of elasticity causes the SMA tendons  86  to constrict, and the appending structures  28  to deploy into the exhaust gas flow. When it is desired that the appending structures  28  no longer be deployed, the current source is turned off. This allows the SMA tendons  86  to cool so that the modulus of elasticity of the appending structures outer skins  38  gradually overcomes the modulus of elasticity of the SMA tendons  86 , thereby returning the appending structures  28  to their non-deployed positions. 
         [0032]    In various alternative embodiments, the SMA tendons  86  are heated using the exhaust gases from the secondary exhaust gas flow nozzle  22 . In actual operation, the heat provided by the exhaust gases emitted from the secondary flow nozzle  22  are typically sufficient in temperature (approximately 130 degrees Fahrenheit) to produce the needed constriction of the SMA tendons  86 . The actual degree of deformation may vary considerably depending upon the specific type of shape memory alloy used, as well as gauge or diameter of the SMA tendons  86 . In the exemplary embodiment, wherein the structure  10  is a jet engine nacelle, when the aircraft reaches its cruising altitude, the significant drop in ambient temperature effectively acts to cool the SMA tendons  86 . The cooling of the SMA tendons  86  allows the appending structure outer skin  38  to stretch the SMA tendons  86  back to their non-activated length and appending structures  28  to return to their non-deployed positions. 
         [0033]    Referring now specifically to  FIG. 5 , an exploded view of an actuator  70  is illustrated in accordance with various embodiments of the present disclosure. The fixed pulling bracket  74  includes a base  102  and a retainer  106  that fits within a reservoir  108  of the fixed pulling bracket base  102 . In various embodiments, the base  102  is constructed of a metal such as stainless steel. The retainer  106  is constructed of a polymer, such as acetal, to provide a layer of electrical insulation. Alternatively the retainer  106  is constructed of a ceramic material. The first end  90  of each SMA tendon  86  is retained by the retainer  106 . The first ends  90  can be retained in any suitable manner, for example the first ends  90  can be screwed, riveted, welded or otherwise bonded to the retainer  106 . In various embodiments, as illustrated in  FIG. 5 , a swaged fitting  110  is pressed onto the first end  90  of each SMA tendon  86 . The swaged fittings  110  are then retained, as illustrated, within the retainer  106 . Once the SMA tendons  86  are retained by the retainer  106  and the retainer  106  is placed within the reservoir  108 , a cover  112  is fastened to the base  102  using fasteners  114 . Preferably, the cover  112  is constructed of a polymer such as polyethylene, polypropylene or TEFLON®. The fasteners  114  can be any suitable fastener such as screws, rivets or nuts and bolts. 
         [0034]    Similarly, the sliding pulling bracket  78  includes a base  118  and a retainer  122  that fits within a reservoir  126  of the sliding pulling bracket base  118 . In various embodiments, the base  118  is constructed of a metal such as stainless steel. The retainer  122  is constructed of a polymer, such as acetal, to provide a layer of electrical insulation. The second end  94  of each SMA tendon  86  is retained by the retainer  122 . The second ends  94  can be retained in any suitable manner, for example the second ends  94  can be screwed, riveted, welded or otherwise bonded to the retainer  122 . In various embodiments, as illustrated in  FIG. 5 , a swaged fitting  128  is pressed onto the second end  94  of each SMA tendon  86 . The swaged fittings  128  are then retained, as illustrated, within the retainer  122 . Once the SMA tendons  86  are retained by the retainer  122  and the retainer  122  is placed within the reservoir  126 , a cover  130  is fastened to the base  118  using fasteners  134 . Preferably, the cover  130  is constructed of a polymer such as polyethylene, polypropylene or TEFLON®. The fasteners  134  can be any suitable fastener such as screws, rivets or nuts and bolts. 
         [0035]    Additionally, in the embodiment wherein the SMA tendons  86  are heated utilizing an electrical current source, one of the wires  98  is connected to the first end of one SMA tendon  86  and the other wire  98  is connected to the first end of a separate SMA tendon  86  within the same actuator  70 . The two SMA tendons  86  connected to the wires  98 , and any other SMA tendons  86  within the same actuator  70 , are electrically coupled together using jumpers  138 . Therefore, current provided by the current source will travel through each SMA tendon  86  included in the actuator  70 , and thereby activate each SMA tendon  86  as described above. In the case where an actuator  70  included only one SMA tendon  86 , one of the wires  98  would be connected to the first end  90  of the SMA tendon  86  and the other wire  98  would be connected to the opposing second end  94  of the SMA tendon  86 . 
         [0036]    Referring now to  FIG. 6 , a partial view of the portion of the nacelle secondary nozzle main body  26  and appending structures  28 , as shown in  FIG. 2 , is illustrated with the outer wall  46  of the main body  26  and the outer skin  38  of the appending structure  28  removed. An actuator guide plate  142  is affixed to the main body inner wall  42  using any suitable fastening means, such as screws, rivets, welding or diffusion bonding. The actuator guide plate  142  includes guide channels  146  that are adapted to guide the sliding pulling bracket  78  when the SMA tendons  86  are activated. The actuators  70  are positioned and fitted within the guide channels  146  and in a ‘slip-fit’ manner. This allows the sliding pulling brackets  78  to slide toward the fixed pulling brackets  74  while guiding the movement of sliding pulling brackets  78  such that the appending structure inner skin  34  is moved toward the fixed pulling brackets in a substantially straight line. Therefore, the sliding pulling brackets  78  are not allowed to vary their movement and the appending structures  28  are deployed with accuracy and consistency. 
         [0037]      FIG. 7  illustrates the appending structure  28  inner and outer skins  34  and  38  joined at the respective distal portions  62  and  66  using a hinge device  150 . As described above, the distal end portions  62  and  66  of the appending structure inner and outer skins  34  and  38  are joined together. Therefore, when the actuators  70  are activated, the inner skin  34  is pulled further into the cavity  50  causing the outer skin  38  to turn down or bend, more particularly, causing the appending structure  28  to deploy. In various embodiments the distal portions  62  and  66  are hingedly coupled via the hinge device  150 . The hinge device  150  can be any suitable hinged device that pivots along a line Y that is substantially parallel to an aft edge  152 , shown in  FIG. 2 , of the nacelle secondary nozzle main body  22 . 
         [0038]    Referring to  FIG. 8 , in further description of the exemplary embodiment wherein the structure  10  is a jet engine nacelle, another preferred embodiment will be described wherein the primary flow nozzle  18  includes a plurality of appending structures  154 . The appending structures  154  extend from a lip area  158  of the primary flow nozzle  18 . SMA actuators (not shown) that are substantially identical to the SMA actuators  70  described above, are attached to the appending structures  154  in the same manner as described above with reference to the nacelle secondary nozzle  22 . Therefore, the appending structures  154  and associated SMA actuators and SMA tendons (not shown) that are utilized to deploy the appending structures  154 , are essentially the same in form and function as the appending structures  154  and associated SMA actuators  70  and SMA tendons  86 , described above with reference to  FIGS. 1-7 . 
         [0039]    However, the appending structures  154  deploy to increase the mixing of core exhausts, i.e. turbine exhaust, with the ambient air and/or by-pass fan exhaust. Accordingly, the appending structures  154  are constructed of a high temperature material, such as titanium. Thus, although the above description of the present disclosure with respect to appending structures  28  will not be repeated with reference to appending structures  154 , it should be understood that appending structures  154  are deployed utilizing SMA actuators and tendons in essentially the identical manner as described above with reference to appending structures  28 . Furthermore, it should be understood that  FIGS. 1-7  and the related description set forth above can be used to describe the present disclosure with reference to both appending structures  28  and  154 , with the understanding that the appending structures  154  are associated with the primary flow nozzle  18  while the appending structures  28  are associated with the secondary flow nozzle  22 . 
         [0040]    The various embodiments described herein thus provide a structure that includes a body having a first wall and a second wall, at least one appending structure extending from an end of the body. At least one SMA actuator is positioned between the first and second walls. The SMA actuator includes first end coupled to a portion of the body and a second end coupled to a portion of the appending structure. At least one SMA tendon is connected to and extends between the first and second ends of the SMA actuator. The SMA tendon(s) is/are adapted to controllably constrict when activated by heat to cause the appending structure to move from a first position or form to a second position or form. Therefore, the shape or position of the appending structure is dynamically altered without complex kinematic mechanisms or the use of bulky actuators that occupy excessive space and add considerable costs and weight. 
         [0041]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.