Patent Publication Number: US-10766608-B2

Title: Aircraft landing gear having a retract actuator, aircraft including the same, and related methods

Description:
FIELD 
     The present disclosure relates to aircraft landing gear having a retract actuator, aircraft including the same, and related methods. 
     BACKGROUND 
     Aircraft with one or more of large engine fan diameters, long fuselages, long wings, and specialized under-aircraft payloads, for example, may require a tall landing gear structure to provide ground clearance to the engine and sufficient clearance to the tail during take-off. While the aircraft is in flight, the landing gear structures generally are stored within corresponding wheel wells in the fuselage of the aircraft. Integrating larger landing gear structures into the aircraft may impose expensive design constraints on the aircraft and also may add weight, which in turn requires greater fuel consumption by the aircraft. 
     Landing gear structures on aircraft generally employ an oleo strut shock absorber, in which a piston compresses a volume that includes both a compressible gas and a substantially incompressible liquid. The volume includes two chambers separated by an orifice through which the liquid flows, such that the overall structure provides both resilient shock absorption and dampening of the oscillation of the oleo strut shock absorber. Typically, such landing gear structures include a main fitting (e.g., an outer tube), a piston (e.g., an inner tube), and a sliding tube cylinder, thus involving three tubes/cylinders. A landing gear structure that includes an oleo strut shock absorber may be compressed into a retracted configuration for stowage in the wheel well during flight. However, achieving the retracted configuration may require compressing the compressible gas to an undesirably high pressure. Additionally, such landing gear structures tend to be heavy and complex, thus creating potential disadvantages from aircraft economy, maintenance, and manufacture standpoints. 
     SUMMARY 
     Aircraft landing gear structures according to the present disclosure include a strut assembly and a retract actuator. The strut assembly includes a lower tubular housing operatively coupled to an upper tubular housing such that the lower tubular housing is longitudinally translatable with respect to the upper tubular housing as the strut assembly transitions between an extended configuration, a compressed configuration, and a retracted configuration. The strut assembly also includes a shrink mechanism configured to selectively transition the strut assembly to the retracted configuration. The retract actuator is configured to selectively transition the strut assembly between the extended configuration and the retracted configuration by actuating the shrink mechanism, and is further configured to retract the aircraft landing gear structure into the aircraft for stowage during flight via a retraction mechanism. In this manner, aircraft landing gear structures according to the present disclosure may have a single actuator (e.g., the retract actuator) that effectuates both shrinking the strut assembly to the retracted configuration and retracting the aircraft landing gear structure into the aircraft during flight, as opposed to prior art assemblies that include separate actuators for such functions. 
     Related methods include providing the aircraft landing gear structure according to the present disclosure and/or an aircraft including the same, shrinking the strut assembly to the retracted configuration, and retracting the aircraft landing gear into the aircraft for stowage during flight. In presently disclosed methods, shrinking the strut assembly to the retracted configuration and retracting the aircraft landing gear structure are both performed via the retract actuator, which actuates both the shrink mechanism and the retraction mechanism, thereby both shrinking and retracting the aircraft landing gear structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an example aircraft. 
         FIG. 2  is a schematic black-box diagram representing examples of aircraft landing gear structures according to the present disclosure. 
         FIG. 3  is a schematic elevation view representing examples of aircraft landing gear structures according to the present disclosure. 
         FIG. 4  is an elevation, partial cut-away view of an example of an aircraft landing gear structure according to the present disclosure, in a compressed configuration. 
         FIG. 5  is an elevation, partial cut-away view of the aircraft landing gear structure of  FIG. 4 , in an extended configuration. 
         FIG. 6  is an elevation, partial cut-away view of the aircraft landing gear structure of  FIG. 4 , in a retracted configuration. 
         FIG. 7  is a close-up, perspective, partial cut-away view of a portion of an example of an aircraft landing gear structure according to the present disclosure, in an extended configuration. 
         FIG. 8  is a close-up, perspective, partial cut-away view of a portion of an example of an aircraft landing gear structure according to the present disclosure, in a compressed configuration. 
         FIG. 9  is an elevation view of an example of an aircraft landing gear structure according to the present disclosure. 
         FIG. 10  is a perspective view of an example of a retract actuator for an aircraft landing gear structure according to the present disclosure, in a ground configuration. 
         FIG. 11  is a perspective view of the retract actuator of  FIG. 10 , in a stowed configuration. 
         FIG. 12  is a flowchart schematically representing methods of retracting a strut assembly for stowing aircraft landing gear, according to the present disclosure. 
         FIG. 13  is a flowchart schematically representing aircraft production and service methodology. 
         FIG. 14  is a block diagram schematically representing an aircraft. 
     
    
    
     DESCRIPTION 
     Generally, in the figures, elements that are likely to be included in a given example are illustrated in solid lines, while elements that are optional to a given example are illustrated in broken lines. However, elements that are illustrated in solid lines are not essential to all examples of the present disclosure, and an element shown in solid lines may be omitted from a particular example without departing from the scope of the present disclosure. 
       FIG. 1  is an illustration of an example aircraft  10  that includes strut assemblies  100  according to the present disclosure. Aircraft  10  generally may be utilized to transport persons and/or cargo. As illustrated in  FIG. 1 , aircraft  10  generally includes a fuselage  12  and a wing assembly  14  operatively coupled to fuselage  12 . Fuselage  12  and/or wing assembly  14  define one or more wheel wells  16  (and/or landing gear storage bays and/or wheel storage bays) operatively coupled to and/or configured to receive a corresponding landing gear structure  18 . Landing gear structure  18  may include a wheel assembly  20  operatively coupled to fuselage  12  and/or wing assembly  14  via strut assembly  100  and/or a lever assembly  21 . In some examples of aircraft  10 , the volume of the wheel wells  16  may be minimized so as to maximize the volume available in the fuselage for accommodating passengers, cargo, and structural components, as well as to optimize the aerodynamic properties of the aircraft  10 . 
       FIGS. 2-3  are schematic views of illustrative, non-exclusive examples of strut assemblies  100  and aircraft landing gear structures  18  according to the present disclosure. Strut assemblies  100  may form a portion of landing gear structure  18  (also referred to herein as aircraft landing gear structure  18 ), which generally also include wheel assembly  20 , lever assembly  21 , and a shrink mechanism  22 . Strut assembly  100  is configured to vary in length (e.g., along a longitudinal axis  24  indicated in  FIG. 3 ) such that strut assembly  100  is configured to transition between a compressed configuration, an extended configuration, and a retracted configuration. In the compressed configuration, strut assembly  100  has a compressed length responsive to a compressive force exerted on strut assembly  100  (e.g., when strut assembly  100  is fully weighted by an aircraft, such as aircraft  10 ). In the extended configuration, strut assembly  100  has an extended length (e.g., when strut assembly  100  is not weighted by the aircraft). And in the retracted configuration (e.g., for stowage of aircraft landing gear structure  18  within an aircraft wheel well (e.g., wheel well  16 )), strut assembly  100  has a retracted length that is less than the extended length, to facilitate stowage of aircraft landing gear structure  18  during flight. 
     While the compressive force from the weight of the aircraft when the aircraft is on the ground causes strut assembly  100  to transition to the compressed configuration, and removing the compressive force causes strut assembly  100  to transition to the extended configuration, shrink mechanism  22  is configured to transition strut assembly  100  from the extended configuration to the retracted configuration (which may also be referred to as a shrink configuration). The compressed length and the retracted length are less than the extended length, and all are defined along longitudinal axis  24  of strut assembly  100 . Because the length of strut assembly  100  is configured to be shortened (or “shrink”) after take-off (e.g., when no compressive force from the weight of the aircraft is present), strut assemblies  100  and/or landing gear structures  18  may be configured such that aircraft  10  can accommodate a longer landing gear structure  18  without increasing the size of wheel well  16 . 
     As shown in  FIG. 3 , strut assembly  100  includes an upper tubular housing  26  and a lower tubular housing  28  operatively coupled to upper tubular housing  26  such that lower tubular housing  28  is configured to be longitudinally translated (e.g., moved along longitudinal axis  24 , indicated by arrow  30 ) relative to upper tubular housing  26 . Lower tubular housing  28  is configured to be translated between a compressed position when strut assembly  100  is in the compressed configuration and an extended position when strut assembly  100  is in the extended configuration. Lower tubular housing  28  is further configured to be selectively and longitudinally translated to a retracted position when strut assembly  100  is in the retracted configuration. Upper tubular housing  26  may be coupled to an airframe of the aircraft. 
     Shrink mechanism  22  is at least partially contained within upper tubular housing  26  and/or lower tubular housing  28  and is configured to selectively and longitudinally translate lower tubular housing  28  with respect to upper tubular housing  26 , thereby selectively transitioning strut assembly  100  between the extended configuration and the retracted configuration. In some examples, shrink mechanism  22  is entirely positioned within upper tubular housing  26  and/or lower tubular housing  28 , in contrast to prior art mechanisms that are external to the strut assembly. In some examples, shrink mechanism  22  is a mechanical (e.g., physical) link between components of strut assembly  100 , as opposed to a hydraulic or pneumatic shrink mechanism. Additionally or alternatively, in some examples, strut assembly  100  is configured such that activation of (also referred to as “actuation of”) shrink mechanism  22  by a retract actuator  32  also causes raising and/or tilting of wheel assembly  20  with respect to upper tubular housing  26 , via a truck beam  34  and a forward link  36  of lever assembly  21 . Additionally or alternatively, in some examples, strut assembly  100  is configured such that actuation of retract actuator  32  is configured to both shrink strut assembly  100  (e.g., shorten the length of strut assembly  100 , thereby transitioning strut assembly  100  to the retracted configuration) and also retract strut assembly  100  into a wheel well of the aircraft. Aircraft landing gear structures  18  according to the present disclosure may include just one of these features, may include any combination of two of these features, or may include all three of these features. Each of these concepts will be explained in further detail below. 
     Turning first to examples of strut assembly  100  with a mechanical shrink mechanism  22 , strut assembly  100  may include an upper bulkhead  38  supported by upper tubular housing  26 , and configured to be selectively and longitudinally translated with respect to upper tubular housing  26  between a lower position and an upper position. Upper bulkhead  38  is in the lower position when strut assembly  100  is in the compressed configuration and the extended configuration, and upper bulkhead  38  is in the upper position when strut assembly  100  is in the retracted configuration. Strut assembly  100  may also include a lower bulkhead  40  fixed with respect to and supported by lower tubular housing  28 , wherein a pressure chamber  42  may be formed between upper bulkhead  38  and lower bulkhead  40 , within upper tubular housing  26  and lower tubular housing  28 . Shrink mechanism  22  may include upper bulkhead  38 . For example, translation of upper bulkhead  38  to the upper position may mechanically cause translation of lower tubular housing  28  to the retracted position, by virtue of a mechanical (e.g., physical) link between upper bulkhead  38  and lower tubular housing  28 . In some examples, translation of upper bulkhead  38  to the upper position mechanically causes longitudinal translation of a third tubular member  44  and a third tubular member stop  46  while third tubular member stop  46  is in contact with an inner tube stop  48  fixed within lower tubular housing  28 , thereby causing translation of inner tube stop  48  and lower tubular housing  28  with respect to upper tubular housing  26  until lower tubular housing  28  is in the retracted position. 
     In examples of strut assembly  100  where activation of shrink mechanism  22  also causes raising and/or tilting of wheel assembly  20  with respect to upper tubular housing  26 , wheel assembly  20  is operatively coupled to strut assembly  100  via lever assembly  21  (e.g., truck beam  34  and forward link  36 ). For example, forward link  36  is pivotally coupled to upper tubular housing  26  via a first link pivot joint  50 , in some examples. Forward link  36  also includes a second link pivot joint  52  to pivotally couple forward link  36  to truck beam  34 . Truck beam  34  is further pivotally coupled to lower tubular housing  28  in these examples, such as by a middle pivot joint  54 , and truck beam  34  is pivotally coupled with respect to a wheel hub  56  of wheel assembly  20 . For example, truck beam  34  may be pivotally coupled to wheel hub  56 , to an axle  55  of wheel assembly  20 , and/or to any other component of wheel assembly  20 . Wheel assembly  20  may thus be operatively coupled to upper tubular housing  26  and/or lower tubular housing  28  of strut assembly  100  via forward link  36  (e.g., via first link pivot joint  50  coupling forward link  36  to upper tubular housing  26 ) and truck beam  34  (e.g., via middle pivot joint  54  coupling truck beam  34  to lower tubular housing  28 ). As used herein, two components are said to be ‘pivotally coupled’ to one another when those components are movably coupled with respect to one another, such that the components are pivotable with respect to one another and also coupled together. 
     In this manner, truck beam  34  may be coupled with respect to strut assembly  100  such that longitudinal translation of lower tubular housing  28  with respect to upper tubular housing  26  causes pivoting of forward link  36  and truck beam  34  with respect to one another. In other words, in some aircraft landing gear structures  18  according to the present disclosure, when strut assembly  100  is transitioned to the retracted configuration (e.g., shrunk) and lower tubular housing  28  is translated longitudinally with respect to upper tubular housing  26 , at least a portion of truck beam  34  is also longitudinally translated with respect to upper tubular housing  26  by virtue of being coupled to lower tubular housing  28 . This translation of truck beam  34  and lower tubular housing  28  with respect to upper tubular housing  26  thus causes pivoting of truck beam  34  with respect to forward link  36  such that a pivot angle  60  between the two changes as strut assembly  100  is transitioned between configurations. Such pivoting of truck beam  34  with respect to forward link  36  causes raising and/or tilting of wheel assembly  20 , thereby reducing the overall length of aircraft landing gear structure  18  for stowage during flight (e.g., retraction). 
     In examples of strut assembly  100  where retract actuator  32  both shrinks strut assembly  100  (e.g., transitions strut assembly  100  from the expanded configuration to the retracted configuration, shortening the overall length of strut assembly  100 ) and retracts strut assembly  100  into the aircraft for stowage during flight (e.g., rotates strut assembly  100  into wheel wells of the aircraft for flight), retract actuator  32  may be mechanically linked (which may also be referred to as physically linked, or “slaved”) to shrink mechanism  22 , such that actuation of retract actuator  32  to retract strut assembly  100  also causes activation of shrink mechanism  22  to transition strut assembly  100  to the retracted configuration. In other examples, strut assembly  100  may include retract actuator  32  to retract aircraft landing gear structure  18  into the aircraft, and a separate shrink actuator  33  configured to activate shrink mechanism  22  and shrink strut assembly  100 . Some examples include a retraction mechanism  166  that acts in conjunction with retract actuator  32  to retract aircraft landing gear structure  18 . 
     In some examples, shrink mechanism  22  is positioned at least partially within upper tubular housing  26  and/or lower tubular housing  28 , such that it is at least partially shielded from the environment outside strut assembly  100 . As compared to prior landing gear structures with external mechanisms for shrinking the strut assembly and/or raising the wheels, presently disclosed aircraft landing gear structures  18  may be simpler and/or more resistant to fatigue, damage, and/or wear. Shrink mechanism  22  includes a locking link assembly  106  in some examples. 
     In some examples, strut assembly  100  has an extended pressure within pressure chamber  42  when strut assembly  100  is in the extended configuration and in the retracted configuration, and a compressed pressure within pressure chamber  42  when strut assembly  100  is in the compressed configuration. The compressed pressure is greater than the extended pressure, such as due to compression of a strut gas within pressure chamber  42 . In some examples, a retracted pressure within pressure chamber  42  when strut assembly  100  is in the retracted configuration is substantially equal to the extended pressure (e.g., there is substantially no compression of strut fluids or gases within pressure chamber  42  when strut assembly  100  is transitioned to the retracted configuration). Furthermore, in these examples, pressure chamber  42  has a first internal volume when strut assembly  100  is in the extended configuration and in the retracted configuration, and a second internal volume when strut assembly  100  is in the compressed configuration, wherein the first internal volume is greater than the second internal volume. 
     In some examples, strut assembly  100  also includes a metering pin  62  coupled to or integrally formed with lower bulkhead  40  such that it extends longitudinally from lower bulkhead  40  towards upper bulkhead  38 , and such that it is configured to be received through an orifice  64  formed in an orifice plate  66  of an orifice support tube  45  (which is an example of third tubular member  44 ). Metering pin  62  is configured to be translated longitudinally through and with respect to orifice  64 , as strut assembly  100  is transitioned between the extended configuration and the compressed configuration. In examples where strut assembly  100  is an oleo strut assembly (which may also be referred to as a gas-oil strut assembly), pressure chamber  42  contains a strut fluid (e.g., a strut oil) and/or a strut gas between upper bulkhead  38  and lower bulkhead  40 , such that metering pin  62  meters or controls the flow of the strut fluid through orifice  64  as strut assembly  100  transitions between configurations. In these examples, orifice plate  66  and metering pin  62  are positioned within pressure chamber  42 . 
     While  FIG. 3  and examples described herein illustrate upper tubular housing  26  as an outer tubular housing, and lower tubular housing  28  as an inner tubular housing (e.g., lower tubular housing  28  is longitudinally translated within, or adjacent an inner surface  86  of, upper tubular housing  26 ), it is also within the scope of the present disclosure for the housings to be arranged in the reverse, such that lower tubular housing  28  is the outer tubular housing, and upper tubular housing  26  is the inner tubular housing, such that lower tubular housing  28  would longitudinally translate outside of, or adjacent an outer wall  87  of, upper tubular housing  26 . 
     In some examples, strut assembly  100  includes a recoil chamber  58  and a recoil valve  59  positioned between pressure chamber  42  and recoil chamber  58 . For example, one or more recoil chambers  58  may be defined between upper tubular housing  26  and lower tubular housing  28 . Recoil valve  59  may be configured to regulate flow of a strut liquid between pressure chamber  42  and recoil chamber  58  when strut assembly  100  transitions between the compressed configuration and the extended configuration. Additionally or alternatively, recoil valve  59  may be configured to selectively prevent flow of a strut liquid between pressure chamber  42  and recoil chamber  58  when strut assembly  100  transitions between the retracted configuration and the extended configuration. 
     Turning now to  FIGS. 4-11 , illustrative non-exclusive examples of aircraft landing gear structures  18  are illustrated. Where appropriate, the reference numerals from the schematic illustrations of  FIGS. 2-3  are used to designate corresponding parts in  FIGS. 4-11 ; however, the examples of  FIGS. 4-11  are non-exclusive and do not limit aircraft landing gear structures  18  to the illustrated embodiments. That is, aircraft landing gear structures  18  are not limited to the specific embodiments of the illustrated  FIGS. 4-11  and may incorporate any number of the various aspects, configurations, characteristics, properties, etc. of aircraft landing gear structures  18  that are illustrated in and discussed with reference to the schematic representations of  FIGS. 2-3  and/or the embodiments of  FIGS. 4-11 , as well as variations thereof, without requiring the inclusion of all such aspects, configurations, characteristics, properties, etc. For the purpose of brevity, each previously discussed component, part, portion, aspect, region, etc. or variants thereof may not be discussed, illustrated, and/or labeled again with respect to each embodiment or schematic illustration, however, it is within the scope of the present disclosure that the previously discussed features, variants, etc. may be utilized with other embodiments. 
       FIGS. 4-6  illustrate aircraft landing gear structure  70  (which is an example of aircraft landing gear structure  18 ) in the compressed configuration ( FIG. 4 ), extended configuration ( FIG. 5 ), and retracted configuration ( FIG. 6 ). Aircraft landing gear structure  70  includes a mechanical (rather than pneumatic or hydraulic) shrink mechanism  23  (which is an example of shrink mechanism  22 ) that is configured to transition (e.g., shrink) strut assembly  71  (which is an example of strut assembly  100 ) from the extended configuration to the retracted configuration. Again, aircraft landing gear structure  70  is in the compressed configuration of  FIG. 4  when weighted by the aircraft (e.g., when the aircraft is on the ground), and in the extended configuration of  FIG. 5  when the weight is removed (e.g., when the aircraft is in the air). In the compressed configuration, which may be a statically compressed configuration, a majority of lower tubular housing  28  is positioned within upper tubular housing  26 , with a majority of metering pin  62  positioned within orifice support tube  45 , and a majority of orifice support tube  45  positioned within lower tubular housing  28 . In the extended configuration, lower tubular housing  28  is longitudinally translated such that it is partially outside of (e.g., below and not contained within) upper tubular housing  26 , a majority of metering pin  62  is outside of (e.g., below, and not contained within) orifice support tube  45 , and a majority of orifice support tube  45  is not contained within lower tubular housing  28 . 
     Strut assembly  71  or aircraft landing gear structure  70  includes upper bulkhead  38  supported by upper tubular housing  26 , and configured to be selectively and longitudinally translated with respect to upper tubular housing  26  between a lower position ( FIGS. 4 and 5 ) and an upper position ( FIG. 6 ). Upper bulkhead  38  is in the lower position when strut assembly  71  is in the compressed configuration and the extended configuration, and upper bulkhead  38  is in the upper position when strut assembly  71  is in the retracted configuration. Translation of upper bulkhead  38  to the upper position mechanically causes translation of lower tubular housing  28  to the retracted position, by virtue of a mechanical (e.g., physical) link between upper bulkhead  38  and lower tubular housing  28 . In this manner, shrink mechanism  23  includes upper bulkhead  38 . 
     More specifically, translation of upper bulkhead  38  to the upper position mechanically causes longitudinal translation of orifice support tube  45  (or other third tubular member  44 ) and an orifice plate flange  47  (which is an example of third tubular member stop  46 ) while orifice plate flange  47  contacts and causes longitudinal translation of inner tube stop  48  fixed within lower tubular housing  28 . Pulling up on inner tube stop  48  by orifice plate flange  47  (or other third tubular member stop  46 ) thereby causes translation of lower tubular housing  28  with respect to upper tubular housing  26  until lower tubular housing  28  is in the retracted position shown in  FIG. 6 .  FIG. 7  illustrates a close-up view of a portion of aircraft landing gear structure  70  in the extended position of  FIG. 5 , more clearly illustrating upper bulkhead  38  in the lower position, with orifice plate flange  47  in contact with inner tube stop  48  of lower tubular housing  28 . When upper bulkhead  38  is moved to the upper position of  FIG. 6 , such translation of upper bulkhead  38  with respect to upper tubular housing  26  causes corresponding translation of orifice support tube  45  and orifice plate flange  47  (because both are fixed to upper bulkhead  38 ) with respect to upper tubular housing  26 . Because of the positioning of orifice plate flange  47  below inner tube stop  48 , and because inner tube stop  48  is fixed with respect to lower tubular housing  28 , when orifice plate flange  47  is translated upwards (e.g., in the direction of upper bulkhead  38 ), it pulls up on an underside  68  of inner tube stop  48 , thereby pulling up on lower tubular housing  28  and causing longitudinal translation of lower tubular housing  28  with respect to upper tubular housing  26 . Such longitudinal translation of lower tubular housing  28  moves it further inside upper tubular housing  26  (though in other examples, the arrangement may be reversed such that upper tubular housing  26  is partially within lower tubular housing  28 , rather than vice versa, as shown), thereby reducing the overall height of strut assembly  71  (e.g., shrinking strut assembly  71 ), and transitioning strut assembly  71  to the retracted configuration shown in  FIG. 6 . Inner tube stop  48  may also be configured to limit longitudinal translation of lower tubular housing  28  with respect to upper tubular housing  26 , such as by preventing complete separation of upper tubular housing  26  from lower tubular housing  28  as strut assembly  71  extends to the extended configuration. 
     In the compressed configuration of  FIG. 4  strut assembly  71  has a compressed length  72 , in the extended configuration of  FIG. 5  strut assembly  71  has an extended length  74 , and in the retracted configuration of  FIG. 6  strut assembly  71  has a retracted length  76 . Compressed length  72  and retracted length  76  are less than extended length  74 . In some examples, compressed length  72  is less than retracted length  76 , though in other examples, compressed length  72  and retracted length  76  may be approximately equal to one another, or retracted length  76  may even be less than compressed length  72 . In some examples, extended length  74  is 1.1-1.5 times greater than retracted length  76 . Additionally or alternatively, a difference between extended length  74  and retracted length  76  may be in a range of 0-5 inches, 5-10 inches, 5-15 inches, 10-25 inches, 10-20 inches, 10-15 inches, 15-25 inches, 15-20 inches, and/or 20-25 inches. 
     In this example, strut assembly  71  also includes lower bulkhead  40  fixed with respect to and supported by lower tubular housing  28 , such that a pressure chamber  42  is formed between upper bulkhead  38  and lower bulkhead  40 , and within upper tubular housing  26  and lower tubular housing  28 . Pressure chamber  42  generally contains a strut fluid and/or strut gas, such as in examples where strut assembly  71  is an oleo strut assembly. For example, upper bulkhead  38  forms a gas seal  82  within upper tubular housing  26 , thereby substantially preventing the strut fluid and/or strut gas from exiting pressure chamber  42  at upper bulkhead  38 . Gas seal  82  may be a dynamic gas seal (e.g., is moveable, as upper bulkhead  38  moves between the upper position and the lower position) formed between an outer surface  84  of upper bulkhead  38  and inner surface  86  of upper tubular housing  26 . 
     Orifice plate  66  (best seen in  FIG. 7 ) and metering pin  62  are positioned within pressure chamber  42  such that as strut assembly  71  is transitioned between the compressed configuration and the extended configuration, strut fluid may pass through orifice  64  of orifice plate  66 , with metering pin  62  limiting the speed at which the fluid flows through orifice  64 . In some examples, a mass of strut gas within pressure chamber  42  has a compressed pressure when strut assembly  71  is in the compressed configuration, an extended pressure when strut assembly  71  is in the extended configuration, and a retracted pressure when strut assembly  71  is in the retracted configuration. Generally, the compressed pressure is greater than the extended pressure and the retracted pressure. Strut assembly  71  is configured to transition between the compressed configuration, the extended configuration, and the retracted configuration without the use of sensors or feedback data, in some examples. 
     Third tubular member  44  (e.g., orifice support tube  45 ) extends longitudinally from a first end region  78  to a second end region  80 , with third tubular member  44  being coupled to upper bulkhead  38  within first end region  78 , such that third tubular member  44  is fixed with respect to upper bulkhead  38 . Third tubular member  44  is substantially cylindrical in some examples, though other shapes are also within the scope of the present disclosure. As best seen in  FIG. 7 , third tubular member  44  may include a plurality of bores  88  formed therethrough, from an outer support tube wall  90  to an inner support tube wall  92 . Inner support tube wall  92  defines an interior volume  94  of third tubular member  44 , through which strut fluid and/or strut gas may flow as it passes through bores  88  and orifice  64  as strut assembly  71  is transitioned between configurations. Bores  88  may be formed through the wall of third tubular member  44  such that each respective bore has a respective bore axis  96  that is orthogonal to longitudinal axis  24  in some examples. The plane of orifice  64  intersects longitudinal axis  24  in some examples. Third tubular member  44  is generally substantially rigid, such that orifice plate  66  and third tubular member stop  46  (e.g., orifice plate flange  47 ) are fixed with respect to first end region  78  of third tubular member  44 , and therefore with respect to upper bulkhead  38  (though third tubular member stop  46  may be positioned and/or fixed within second end region  80  of third tubular member  44 ). Orifice plate  66  and third tubular member stop  46  are generally fixed with respect to one another, such that third tubular member  44 , orifice plate  66 , and third tubular member stop  46  move together as a unit when upper bulkhead  38  moves between the upper position and the lower position, thereby causing translation of third tubular member  44  with respect to upper tubular housing  26 . 
     Third tubular member  44 , orifice plate  66 , and third tubular member stop  46  may be integrally formed with one another in some examples, or may be individual components coupled together. For example, and as best seen in  FIG. 7 , an inner surface  98  of orifice plate flange  47  may be coupled to outer support tube wall  90 . An outer surface  101  of orifice plate flange  47  may engage lower tubular housing  28  (e.g., an inner wall  102  of lower tubular housing  28 ). Inner tube stop  48  is coupled to inner wall  102  of lower tubular housing  28  in this example, in an upper end region  104  of lower tubular housing  28 , such that orifice plate flange  47  and inner tube stop  48  are engaged with one another when lower tubular housing  28  is maximally extended with respect to upper tubular housing  26  (e.g., in the extended configuration of  FIG. 5 ). 
     Second end region  80  of third tubular member  44  is positioned within lower tubular housing  28  in the example of  FIGS. 4-7 , with lower tubular housing  28  being longitudinally translated with respect to third tubular member  44  as strut assembly  71  transitions between the compressed configuration ( FIG. 4 ) and the extended configuration ( FIG. 5 ). In the compressed configuration of  FIG. 4 , the majority of third tubular member  44  is positioned within lower tubular housing  28 , whereas, in the extended configuration of  FIG. 5 , the majority of third tubular member  44  is positioned outside of (e.g., above) lower tubular housing  28  and within upper tubular housing  26 , though second end region  80  remains within lower tubular housing  28  even in the extended configuration. 
     In some examples, and as shown in  FIGS. 4-6 , shrink mechanism  23  may include locking link assembly  106 . Locking link assembly  106  includes an upper link  108  and a lower link  110  pivotally coupled to one another, in some examples. Lower link  110  is pivotally coupled to upper bulkhead  38  in the example shown in  FIGS. 4-6 . Locking link assembly  106  is configured to transition between a lengthened configuration and a shortened configuration. Locking link assembly  106  is in the lengthened configuration when strut assembly  71  is in the compressed configuration ( FIG. 4 ) and the extended configuration ( FIG. 5 ), and locking link assembly  106  is in the shortened configuration when strut assembly  71  is in the retracted configuration ( FIG. 6 ). 
     Locking link assembly  106  may be a bistable mechanism, such that it has two stable positions of upper link  108  and lower link  110  relative to one another. For example, in the lengthened configuration ( FIGS. 4-5 ), upper link  108  and lower link  110  may be held over-center, as shown. In the shortened configuration ( FIG. 6 ), upper link  108  and lower link  110  are not held over-center, but instead are pivoted with respect to one another such that the overall length of locking link assembly  106  is reduced in the shortened configuration as compared to the lengthened configuration. Additionally, transitioning locking link assembly  106  to the shortened configuration longitudinally translates (e.g., raises) lower link  110  with respect to upper tubular housing  26 . In the lengthened configuration, locking link assembly  106  is configured to withstand forces from the weight of the aircraft that are transferred to locking link assembly  106  via lower tubular housing  28 , lower bulkhead  40 , and upper bulkhead  38 , such that locking link assembly  106  remains in the lengthened configuration when strut assembly  71  is in the compressed configuration ( FIG. 4 ). Put another way, when strut assembly  71  is in the compressed configuration and locking link assembly  106  is in the lengthened configuration, locking link assembly  106  may be configured to prevent longitudinal translation of upper bulkhead  38  away from lower bulkhead  40 , such that upper bulkhead  38  is substantially fixed in place with respect to upper tubular housing  26  and lower bulkhead  40  when strut assembly  71  is in the compressed configuration of  FIG. 4 . 
     Because locking link assembly  106  is coupled to upper bulkhead  38  via lower link  110  in this example, transitioning locking link assembly  106  to the shortened configuration ( FIG. 6 ) causes longitudinal translation of upper bulkhead  38  with respect to upper tubular housing  26  such that upper bulkhead  38  is moved to its upper position as lower link  110  is longitudinally translated (e.g., raised) with respect to upper tubular housing  26 . In one example, transitioning locking link assembly  106  to the shortened configuration results in longitudinal translation of lower link  110  by a first distance, as well as a corresponding longitudinal translation of lower tubular housing  28  by a second distance. First distance and second distance may be substantially equal to one another in some examples. 
     Shrink mechanism  23  may be actuated, or engaged, by a retract actuator (e.g., retract actuator  32 ), examples of which are illustrated in  FIGS. 9-11 , or by a separate shrink actuator  33  ( FIG. 2 ). For example, and as best seen in  FIGS. 10-11 , upper link  108  of locking link assembly  106  may be coupled to retract actuator  32  (or shrink actuator  33 ) such that selectively actuating retract actuator  32  (or shrink actuator  33 ) transitions locking link assembly  106  between the lengthened configuration and the shortened configuration (thereby selectively shrinking strut assembly  71  via shrink mechanism  23 ). In other examples, lower link  110  of locking link assembly  106  may be coupled to retract actuator  32  (or shrink actuator  33 ) such that selectively actuating retract actuator  32  (or shrink actuator  33 ) transitions locking link assembly  106  between the lengthened configuration and the shortened configuration. 
     Upper link  108  is pivotally coupled to a fixed structure of the aircraft, in some examples, such as via an upper pin  116 . An apex pin  118  pivotally couples upper link  108  to lower link  110 , and a lower pin  120  pivotally couples lower link  110  to strut assembly  71  (e.g., to upper bulkhead  38 ) in some examples. In other examples, upper link  108  and lower link  110  may be coupled via other mechanisms, and/or locking link assembly  106  may be coupled to upper bulkhead  38  via other mechanisms. Additionally or alternatively, locking link assembly  106  may include additional links, connections, and/or components. 
     Some strut assemblies  100  (e.g., strut assembly  71 ) may include bearings between upper tubular housing  26  and lower tubular housing  28 , such as upper bearings  122  (best seen in  FIG. 7 ) and lower bearings  124  (best seen in  FIG. 5 ). Upper bearings  122  and lower bearings  124  may radially separate upper tubular housing  26  from lower tubular housing  28 , as well as facilitate longitudinal translations of lower tubular housing  28  with respect to upper tubular housing  26  (e.g., when strut assembly  100  transitions between the extended configuration and the compressed configuration, or between the extended configuration and the retracted configuration). In some examples, upper bearings  122  and lower bearings  124  are longitudinally spaced apart, such that recoil chamber  58  is defined there between. 
     As best seen in  FIG. 8 , which is a partial close-up of strut assembly  71  in the compressed configuration as seen in  FIG. 4 , strut assembly  71  may include a shelf  126  for positioning and restricting longitudinal movement of lower bulkhead  40  with respect to lower tubular housing  28 . For example, shelf  126  may be configured to engage an underside portion  128  of lower bulkhead  40 , where underside portion  128  is opposite an upper portion  130  of lower bulkhead  40  that faces upper bulkhead  38 . In this manner, lower bulkhead  40  may be substantially fixed with respect to lower tubular housing  28 , whether strut assembly  71  is in the extended configuration, the compressed configuration, or the retracted configuration. 
     Returning to  FIGS. 4-6 , presently disclosed aircraft landing gear structures  18  may include a respective lever assembly  21  operatively coupled to strut assembly  100 , and further operatively coupled to wheel assembly  20 , such as via axle  55 . Lower tubular housing  28  is directly coupled to wheel assembly  20  and/or to lever assembly  21  in some examples. In other examples, lower tubular housing  28  is operatively coupled to wheel assembly  20  and/or to lever assembly  21  via one or more intermediate members (e.g., truck beam  34 ). 
     In the example of aircraft landing gear structure  70 , forward link  36  is pivotally coupled to upper tubular housing  26  via first link pivot joint  50 , and pivotally coupled to truck beam  34  via second link pivot joint  52 . Truck beam  34  is further coupled to lower tubular housing  28  and coupled with respect to wheel hub  56  (e.g., truck beam  34  may be coupled to wheel hub  56 , to axle  55  of wheel assembly  20 , and/or to another component of wheel assembly  20 ). In this manner, truck beam  34  is coupled with respect to strut assembly  71  such that longitudinal translation of lower tubular housing  28  with respect to upper tubular housing  26  causes pivoting of forward link  36  and truck beam  34  with respect to one another. For example, forward link  36  and truck beam  34  are arranged differently with respect to one another when strut assembly  71  is in the compressed configuration ( FIG. 4 ) than when strut assembly  71  is in the extended configuration ( FIG. 5 ) or retracted configuration ( FIG. 6 ). For example, as shown, pivot angle  60  is acute when strut assembly  71  is in the compressed configuration, and obtuse when strut assembly  71  is in the extended configuration. This is not meant to be limiting as to the arrangement between truck beam  34  and forward link  36  (e.g., all examples of strut assembly  100  or aircraft landing gear structure  18  need not have this arrangement), but rather is meant to describe an example of forward link  36  and truck beam  34  pivoting with respect to one another as strut assembly  71  transitions between configurations. 
     Shrink mechanism  23  (which may including locking link assembly  106  and upper bulkhead  38  mechanically coupled to lower tubular housing  28 , as described above, or may be a different mechanism) is configured to selectively and longitudinally translate lower tubular housing  28  with respect to upper tubular housing  26 , which, in this example, causes pivoting of forward link  36  with respect to truck beam  34 . In other words, in this example, shrinking strut assembly  71  (e.g., longitudinally moving lower tubular housing  28  with respect to upper tubular housing  26  to the retracted configuration of  FIG. 6 ) also causes lever assembly  21  to raise and/or tilt wheel hub  56 . 
     In this example, middle pivot joint  54  (which pivotally couples truck beam  34  to lower tubular housing  28 ) is longitudinally translated with respect to upper tubular housing  26  when lower tubular housing  28  is longitudinally translated with respect to upper tubular housing  26 . Truck beam  34  is pivotally coupled to second link pivot joint  52  of forward link  36 , such as via a truck pivot point  132 , which may be positioned within a forward end region  134  of truck beam  34 . Truck beam  34  is pivotally coupled with respect to wheel hub  56  within an aft end region  136  in some examples, where aft end region  136  is opposite forward end region  134 . Middle pivot joint  54  is positioned between aft end region  136  and forward end region  134  of truck beam  34  in this example. Similarly, first link pivot joint  50  may be positioned within a first end region  138  of forward link  36  and second link pivot joint  52  may be positioned within a second end region  140  of forward link  36 , though other arrangements are also within the scope of the present disclosure. 
     For purposes of describing the relative motion of forward link  36  and truck beam  34 , pivot angle  60  may be defined at the intersection of a first line  142  and a second line  144  (illustrated in  FIG. 4 ), with the vertex of pivot angle  60  opening towards lower tubular housing  28 , as indicated in the figures. First line  142  intersects the center points of first link pivot joint  50  and second link pivot joint  52 , and second line  144  intersects the center points of truck pivot point  132  and axle  55 . Lever assembly  21  is configured such that longitudinal translation of lower tubular housing  28  with respect to upper tubular housing  26  causes pivot angle  60  to change (e.g., increase or decrease, depending on whether strut assembly  71  is being shortened or lengthened). When pivot angle  60  is reduced (e.g., when strut assembly  71  is shortened, such as via shrink mechanism  23  or other shrink mechanism  22 ), forward link  36  and truck beam  34  are tilted, by virtue of their connection with upper tubular housing  26  and lower tubular housing  28 , respectively. In these cases, longitudinal translation of lower tubular housing  28  with respect to upper tubular housing  26  causes a greater respective longitudinal translation of aft end region  136  of truck beam  34  with respect to upper tubular housing  26  (e.g., due to tilting of lever assembly  21 ). For example, longitudinal translation of aft end region  136  with respect to upper tubular housing  26  may be at least 1.25 times greater, at least 1.5 times greater, at least 1.75 times greater, at least 2 times greater, at least 2.5 times greater, at least 3 times greater, and/or at least 5 times greater than the corresponding respective longitudinal translation of lower tubular housing  28  with respect to upper tubular housing  26 , depending on the specific configuration of various particular examples. Put another way, a shortening length, defined by the difference between an overall length  146  of aircraft landing gear structure  70  in the extended configuration ( FIG. 5 ) and an overall length  147  of aircraft landing gear structure  70  in the retracted configuration ( FIG. 6 ), may be greater than the difference between extended length  74  of strut assembly  71  in the extended configuration and retracted length  76  of strut assembly  71  in the retracted configuration. 
     Lower tubular housing  28  may include one or more lower tubular housing forks  148  extending from lower tubular housing  28 . Lower tubular housing forks  148  may be angled towards a front end of the aircraft such that truck beam  34  does not contact upper tubular housing  26  in any of the configurations of strut assembly  71 . Truck beam  34  may be pivotally coupled to lower tubular housing forks  148 , such as via middle pivot joint  54 , though in other examples truck beam  34  may be pivotally coupled to another part of lower tubular housing  28 . In some examples, lower tubular housing forks  148  may be pivotally coupled to a brake rod  150  that is pivotally coupled with respect to wheel hub  56  and/or a brake housing. Lever assembly  21  may be referred to as being “semi-levered” in some examples. Wheel assembly  20  is shown as a single axle wheel assembly, though other examples may include additional axles  55  and/or wheels/wheel hubs  56 . 
     While strut assembly  71  is illustrated with lever assembly  21  according to the present disclosure in  FIGS. 4-6 , in other examples of aircraft landing gear structures different types of lever assemblies containing more or fewer links may be combined with a strut assembly according to the present disclosure (e.g., strut assembly  100  having shrink mechanism  22  and/or shrink mechanism  23 ). 
     Turning now to  FIGS. 9-11 , aircraft landing gear structure  152  (which is an example of aircraft landing gear structure  18 ) includes a strut assembly  154 , lever assembly  21 , and retract actuator  32 , which also serves as shrink actuator  33 . Strut assembly  154  may be any strut assembly, such as strut assembly  100 , strut assembly  71 , or a different strut assembly. Additionally or alternatively, aircraft landing gear structure  152  may include any assembly (e.g., lever assembly  21 , or a different assembly) to couple strut assembly  154  to wheel assembly  20 . 
     Retract actuator  32  is configured to transition strut assembly  154  between the extended configuration and the retracted configuration. Additionally, retract actuator  32  is configured to retract aircraft landing gear structure  152  into the aircraft for stowage during flight. In this manner, a single actuator (e.g., retract actuator  32 ) is configured to both shrink strut assembly  154  and also retract aircraft landing gear structure  152 , as compared to prior art landing gear structures, which utilize separate actuators for these two different functions. 
     In the example of aircraft landing gear structure  152 , retract actuator  32  is slaved to a shrink mechanism (e.g., shrink mechanism  22 ) that is configured to shrink strut assembly  154  from an extended configuration to a retracted configuration, such that shrink mechanism  22  and retract actuator  32  are mechanically linked. In other words, actuation of retract actuator  32  causes actuation of shrink mechanism  22  directly via a physical link between the two. Additionally, actuation of retract actuator  32  causes truck beam  34  of lever assembly  21  to tilt with respect to strut assembly  154 , thereby raising wheel hub  56  of aircraft landing gear structure  152  with respect to upper tubular housing  26  of strut assembly  154 . 
       FIGS. 10-11  illustrate a close-up, partial cut-away view of retract actuator  32  coupled to a shrink mechanism  22  that includes a locking link assembly  106 , though in other examples retract actuator  32  may be mechanically linked to a different shrink mechanism  22 . Retract actuator  32  is configured to transition between a stowed configuration ( FIG. 11 ), in which aircraft landing gear structure  152  is retracted into the aircraft for stowage, and a ground configuration ( FIG. 10 ), in which aircraft landing gear structure  152  is positioned outside a wheel well of the aircraft. In the example of  FIGS. 10-11 , a drive link  156  couples locking link assembly  106  to retract actuator  32  via a retraction mechanism  166 . In some examples, upper link  108  of locking link assembly  106  is coupled to retraction mechanism  166 . Additionally or alternatively, lower link  110  of locking link assembly  106  is coupled to retraction mechanism  166  in some examples. In the example of  FIGS. 10-11 , drive link  156  couples retraction mechanism  166  to upper link  108  (though drive link  156  may be additionally or alternatively coupled to lower link  110 , or to another component of shrink mechanism  22 , in other examples). In this manner, actuation of retract actuator  32  transitions it between the stowed configuration and the ground configuration, and moves drive link  156  with respect to the aircraft and/or with respect to the upper tubular housing (e.g., upper tubular housing  26 , though the same is not shown in  FIGS. 10-11 , for clarity), thereby causing locking link assembly  106  to transition from the lengthened configuration ( FIG. 10 ) to the shortened configuration ( FIG. 11 ). Such shortening of locking link assembly  106  raises upper bulkhead  38  and shrinks the strut assembly (e.g., strut assembly  154 ). 
     As shown in  FIGS. 10-11 , upper link  108  may be pivotally coupled to a fixed structure  158  of the aircraft (though the remainder of the aircraft is not shown, for clarity), such as via upper pin  116 . Apex pin  118  pivotally couples upper link  108  and lower link  110  together in aircraft landing gear structure  152 , and lower pin  120  pivotally couples lower link  110  to upper bulkhead  38  of strut assembly  154 . In some examples, drive link  156  is coupled to locking link assembly  106  adjacent apex pin  118 , as shown, though other arrangements and positions are also within the scope of the present disclosure. Drive link  156  may include a first drive link end region  160  and a second drive link end region  162  opposite first drive link end region  160 . In some examples, drive link  156  is pivotally coupled to retraction mechanism  166  within first drive link end region  160 , and is pivotally coupled to locking link assembly  106  (e.g., lower link  110 ) within second drive link end region  162 . 
     Retraction mechanism  166  pivots about a retraction axis  164  in some examples, as it transitions between the stowed configuration and the ground configuration. Such pivoting about retraction axis  164  causes translation of drive link  156  with respect to retraction axis  164 . Such translation of drive link  156  actuates shrink mechanism  22 , thereby transitioning strut assembly  154  to the retracted configuration. In this manner, retract actuator  32  causes retraction of aircraft landing gear structure  152  into the aircraft via retraction mechanism  166 . In some examples, pivoting retraction mechanism  166  about retraction axis  164  (e.g., transitioning retract actuator  32  to the stowed configuration) is caused by extension of retract actuator  32 . Retraction mechanism  166  may be coupled to strut assembly  154  and/or to the aircraft itself, either directly or via one or more linking members. For example, one end region  168  of retraction mechanism  166  may be coupled to upper tubular housing  26 , while an opposing end region  170  of retraction mechanism  166  may be coupled to retract actuator  32 . Retraction axis  164  may be transverse to longitudinal axis  24  (shown in  FIG. 10 ) of strut assembly  154 , in some examples. In some examples, retraction mechanism  166  includes a walking beam. Retract actuator  32  and/or retraction mechanism  166  may include any suitable type of actuator or mechanism, such as a hydraulic actuator, a bell/crank, or any other suitable type of actuator or mechanism. 
       FIG. 12  schematically provides a flowchart that represents illustrative, non-exclusive examples of methods  200  for retracting a strut assembly (e.g., strut assembly  100 ) and/or aircraft landing gear structure (e.g., aircraft landing gear structure  18 ) into an aircraft (e.g., aircraft  10 ) for stowage during flight, according to the present disclosure. In  FIG. 12 , some steps are illustrated in dashed boxes indicating that such steps may be optional or may correspond to an optional version of a method according to the present disclosure. That said, not all methods according to the present disclosure are required to include the steps illustrated in solid boxes. The methods and steps illustrated in  FIG. 12  are not limiting and other methods and steps are within the scope of the present disclosure, including methods having greater than or fewer than the number of steps illustrated, as understood from the discussions herein. 
     Methods  200  generally include providing the aircraft and/or aircraft landing gear structure at  202 , shrinking the strut assembly of the aircraft landing gear structure at  204 , and retracting the aircraft landing gear structure at  206 . Providing the aircraft and/or aircraft landing gear structure at  202  may include providing any of the aircraft landing gear structures having any of the strut assemblies disclosed herein. Such strut assemblies and/or aircraft landing gear structures may be installed in existing aircraft (e.g. the aircraft may be retrofitted), or may be provided for use within an aircraft at the time of manufacturing. Presently disclosed strut assemblies and aircraft landing gear structures including the same may be provided separately from the aircraft in which they are to be used, or may be provided together with the aircraft. Providing the aircraft at  202  may include providing an aircraft with a plurality of strut assemblies and/or aircraft landing gear structures, and/or may include providing a plurality of strut assemblies and/or aircraft landing gear structures for use within an aircraft. 
     Shrinking the strut assembly at  204  generally includes reducing an overall length of the strut assembly, such as by transitioning the strut assembly from the extended configuration to the retracted configuration. In some examples, shrinking the strut assembly at  204  includes longitudinally translating an upper bulkhead (e.g., upper bulkhead  38 ) from a lower position to an upper position at  208 , such that longitudinally translating the upper bulkhead mechanically causes translation of a lower tubular housing (e.g., lower tubular housing  28 ) of the strut assembly with respect to an upper tubular housing (e.g., upper tubular housing  26 ) of the strut assembly, thus placing the strut assembly in the retracted configuration. In some specific examples, translating the upper bulkhead at  208  mechanically causes longitudinal translation of a third tubular member (e.g., third tubular member  44 , which may be orifice support tube  45 , in some examples) and a corresponding third tubular member stop (e.g., third tubular member stop  46 , which may be orifice plate flange  47 , in some examples) while the third tubular member stop contacts and causes longitudinal translation of an inner tube stop (e.g., inner tube stop  48 ) of the lower tubular housing, thereby causing translation of the lower tubular housing to the retracted position. Generally, the shrinking the strut assembly at  204  (e.g., the translating the upper bulkhead at  208 ) is performed after takeoff of the aircraft (e.g., once the aircraft is in flight) at  218 . 
     Retracting the aircraft landing gear structure at  206  generally includes retracting and stowing the aircraft landing gear structure within the aircraft during flight, such as within a wheel well of the aircraft, within a landing gear storage bay within the aircraft, and/or within a wheel storage bay within the aircraft. Retracting the aircraft landing gear structure at  206  may be performed by a retract actuator (e.g., retract actuator  32 ). In some methods  200 , the retract actuator also actuates a shrink mechanism (e.g., shrink mechanism  22 ) that performs the shrinking the strut assembly at  204 . In some examples, shrinking the strut assembly at  204  includes actuating a shrink actuator (e.g., shrink actuator  33 , which may be the same actuator as retract actuator  32 , in some examples) at  210 , thereby actuating a shrink mechanism at  212  to shrink the strut assembly. 
     Retracting the aircraft landing gear structure at  206  may be performed after the shrinking the strut assembly at  204  in some examples, or may be performed substantially simultaneously (e.g., concurrently) with the shrinking the strut assembly at  204 . In some examples, the shrinking the strut assembly at  204  and the retracting the aircraft landing gear structure at  206  may be initiated at the same time or by the same process, mechanism, or actuator, though the shrinking the strut assembly may be completed before the retracting the aircraft landing gear structure is completed, in some examples. Retracting the aircraft landing gear structure at  206  may include rotating the retract actuator about a retraction axis (e.g., retraction axis  164 ) in some methods. 
     In some examples, shrinking the strut assembly at  204  involves longitudinally translating the lower tubular housing of the strut assembly with respect to the upper tubular housing and pivoting a forward link of a lever assembly (e.g., forward link  36  of lever assembly  21 ) with respect to a truck beam (e.g., truck beam  34 ) of the lever assembly. In this manner, shrinking the strut assembly at  204  may include tilting the truck beam at  214  and/or raising the truck beam with respect to the upper tubular housing, at  216 . Tilting the truck beam at  214  and raising the truck beam at  216  generally also result in raising a wheel of a wheel assembly (e.g., wheel hub  56  of wheel assembly  20 ) along with the truck beam. 
     Some methods  200  including locking a locking link assembly (e.g., locking link assembly  106 ) in a lengthened configuration at  220 , which may retain the upper bulkhead of the strut assembly in its lower position both when the strut assembly is in the extended configuration and in the compressed configuration. Before shrinking the strut assembly at  204  (or substantially simultaneously therewith), the locking link assembly may be unlocked at  222  and transitioned to its shortened configuration, thereby translating the upper bulkhead to its upper position to move the strut assembly to the retracted configuration. In some methods  200 , unlocking the locking link assembly  222  may be part of the shrinking the strut assembly at  204 . 
     Methods  200  may include mechanically linking the shrink mechanism to the retract actuator at  224 , such that the shrink mechanism is mechanically slaved to the retract actuator, and such that actuation of the retract actuator causes actuation of the shrink mechanism. 
     Turning now to  FIGS. 13-14 , embodiments of the present disclosure may be described in the context of an aircraft manufacturing and service method  500  as shown in  FIG. 13  and an aircraft  10  as shown in  FIG. 14 . During pre-production, exemplary method  500  may include specification and design  504  of the aircraft  10  and material procurement  506 . During production, component and subassembly manufacturing  508  and system integration  510  of the aircraft  10  takes place. Thereafter, the aircraft  10  may go through certification and delivery  512  in order to be placed in service  514 . While in service, the aircraft  10  is scheduled for routine maintenance and service  516  (which may also include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  500  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 14 , the aircraft  10  produced by exemplary method  500  may include an airframe  518  with a plurality of systems  520  and an interior  522 . Examples of high-level systems  520  include one or more of a propulsion system  524 , an electrical system  526 , a hydraulic system  528 , and an environmental system  530 . Any number of other systems also may be included. Although an aerospace example is shown, the principles of the inventions disclosed herein may be applied to other industries, such as the automotive industry. 
     Apparatus and methods disclosed herein may be employed during any one or more of the stages of the production and service method  500 . For example, components or subassemblies corresponding to production process  508  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  10  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  508  and  510 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  10 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  10  is in service, for example and without limitation, to maintenance and service  516 . 
     As used herein, the terms “adapted” and “configured” mean that the element, component, or other subject matter is designed and/or intended to perform a given function. Thus, the use of the terms “adapted” and “configured” should not be construed to mean that a given element, component, or other subject matter is simply “capable of” performing a given function but that the element, component, and/or other subject matter is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the function. It is also within the scope of the present disclosure that elements, components, and/or other recited subject matter that is recited as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa. Similarly, subject matter that is recited as being configured to perform a particular function may additionally or alternatively be described as being operative to perform that function. 
     As used herein, the terms “selective” and “selectively,” when modifying an action, movement, configuration, or other activity of one or more components or characteristics of an apparatus, mean that the specific action, movement, configuration, or other activity is a direct or indirect result of user manipulation of an aspect of, or one or more components of, the apparatus. 
     The various disclosed elements of apparatuses and steps of methods disclosed herein are not required to all apparatuses and methods according to the present disclosure, and the present disclosure includes all novel and non-obvious combinations and subcombinations of the various elements and steps disclosed herein. Moreover, one or more of the various elements and steps disclosed herein may define independent inventive subject matter that is separate and apart from the whole of a disclosed apparatus or method. Accordingly, such inventive subject matter is not required to be associated with the specific apparatuses and methods that are expressly disclosed herein, and such inventive subject matter may find utility in apparatuses and/or methods that are not expressly disclosed herein.