(19)
(11)EP 3 135 582 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
26.06.2019 Bulletin 2019/26

(21)Application number: 16184274.5

(22)Date of filing:  16.08.2016
(51)International Patent Classification (IPC): 
B64C 25/52(2006.01)

(54)

THREE-POSITION AIRCRAFT TAIL SKID MECHANISM AND METHOD OF ACTUATION

DREIPOSITIONS-FLUGZEUGSCHWANZSPORNMECHANISMUS UND VERFAHREN ZUR BETÄTIGUNG

MÉCANISME DE PATIN DE QUEUE POUR AÉRONEF À TROIS POSITIONS ET PROCÉDÉ D'ACTIONNEMENT


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 24.08.2015 US 201514834369

(43)Date of publication of application:
01.03.2017 Bulletin 2017/09

(73)Proprietor: The Boeing Company
Chicago, IL 60606-2016 (US)

(72)Inventor:
  • MELLOR, Mitchell L. R.
    Chicago, IL 60606-2016 (US)

(74)Representative: Boult Wade Tennant LLP 
5th Floor, Salisbury Square House 8, Salisbury Square
London EC4Y 8AP
London EC4Y 8AP (GB)


(56)References cited: : 
EP-A1- 2 636 595
US-B2- 6 845 944
EP-A2- 0 319 051
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    BACKGROUND


    1. Technical Field:



    [0001] This disclosure relates to aircraft tail skids in general, and in particular, to a three-position aircraft tail skid mechanism and methods for actuating it.

    2. Related Art:



    [0002] A "tail strike" occurs when the tail of a tricycle-gear aircraft strikes the ground during takeoff or landing. Although many tail strikes occur during the "rotation" phase of a takeoff, i.e., a maneuver in which the pilot raises the nose of the aircraft and lowers its tail to achieve a liftoff of the aircraft from the runway, some tail strikes occur during the "flare" phase of a landing, i.e., a maneuver in which the pilot raises the nose of the aircraft and lowers its tail to slow the aircraft and/or decrease its rate of descent toward the runway. Tail strikes are often due to pilot error, as well as to the presence of gusty winds or wind shear.

    [0003] Tail skids are often provided on tricycle-gear aircraft to prevent or reduce damage to the aircraft in the event of a tail strike. These can range from structures that are fixed to a lower surface of the tail portion of an aircraft's fuselage, to structures that employ a mechanism to move between a deployed position for takeoff or landing operations and a more streamlined, retracted configuration for cruise operation.

    [0004] Tail skid mechanisms that utilize the same position for takeoff and landing can result in a penalty in that, during a takeoff, they limit downward rotation of the tail to that which is safely allowable for a landing, which may be less than that safely allowable for a takeoff. This results in the use of unnecessarily higher rotation (VR) and liftoff (VLO) speeds during a takeoff, and hence, unnecessarily longer takeoff runs and the need for longer runways.

    [0005] Accordingly, there is a need for aircraft tail skids that, while effectively preventing or reducing tail strike damage to a host aircraft, can be selectably deployed to and locked in one of three different positions relative to the aircraft, viz., a stowed position, a takeoff position, and a landing position, and that also minimize the number, size and types of the components needed to implement and actuate the mechanism.

    [0006] US-B-6845944 discloses multi-positional tail skid assemblies and methods for their use. In one embodiment, a multi-positional tail skid assembly includes a skid member and a skid deployment system operably connected to the skid member. The skid member can include a first portion attachable to an aft portion of a fuselage and a second portion movable relative to the aft portion of the fuselage. The second portion can support a skid surface configured to contact a surface of a runway. The skid deployment system can be configured to move the skid surface between first and second positions. When the skid surface is in the first position, the skid surface is closer to the aft portion of the fuselage than when the skid surface is in the second position.

    [0007] EP-A-2636595 discloses a method and apparatus for positioning a tail skid assembly for a maximum rotation angle for an aircraft may be provided. A determination may be made as to whether the tail skid assembly is to be deployed for takeoff or landing. A set of parameters may be identified based on a determination of whether the tail skid assembly is to be deployed for takeoff or landing. A desired maximum rotation angle for the aircraft may be identified using the set of parameters. The tail skid assembly may be deployed to allow the desired maximum rotation angle for the aircraft.

    SUMMARY



    [0008] The present disclosure provides a system according to claim 1.

    [0009] The present disclosure further provides a method according to claim 8.

    [0010] In accordance with the present disclosure, example embodiments of aircraft tail skid mechanisms are provided, together with methods for actuating them, that effectively prevent or reduce tail strike damage to a host aircraft, that can be selectably deployed to and locked in one of three different positions relative to the aircraft, viz., a stow position, a landing position, and a takeoff position intermediate the stow and landing positions, and that minimize the number, size and types of components need to implement and deploy the mechanisms.

    [0011] The present invention discloses a system comprising an aircraft having a fuselage with a tail portion and a tail skid disposed in an opening of the tail portion. The tail skid comprises a ground contact shoe and a mechanism configured to selectably move the ground contact shoe between respective ones of a stow position disposed within the opening, a landing position disposed below the opening, and a takeoff position disposed below the opening and above the landing position.

    [0012] The present invention further discloses a method for protecting an aircraft against tail strike damage comprises providing a tail skid disposed in an opening of a tail portion of the aircraft. The tail skid comprises an elongated shock absorber having a ground contact shoe disposed at a lower end thereof. The ground contact shoe is moveable between re-spective ones of a stow position disposed within the opening, a landing position disposed below the opening, and a takeoff position disposed below the opening and above the landing position. Before a takeoff or a landing, the ground contact shoe is moved to a corresponding one of the takeoff or landing positions such that, in the event of an over-rotation of the aircraft during a takeoff, or an over-flaring of the aircraft during a landing, the ground contact shoe makes contact with the ground and the shock absorber absorbs the shock of, or a portion of the kinetic energy associated with, the contact and thereby prevents tail strike damage to the aircraft.

    [0013] In another example embodiment, a tail skid mechanism comprises upper and lower vertical links, each having opposite upper and lower ends, and front and rear horizontal links, each having opposite front and rear ends. The upper end of the upper vertical link is coupled to a first attach pin for conjoint rotation therewith. The upper end of the lower vertical link is coupled to the lower end of the upper vertical link for rotation relative thereto. An over-center locking mechanism extends between the upper and lower vertical links and is configured to prevent lateral movement of the hinge past a locked position in which the upper and lower vertical links are disposed generally collinear with each other, and to permit unlocking movement of the hinge relative to the locked position. The front end of the front horizontal link is coupled to a second attach pin for conjoint rotation therewith. The front end of the rear horizontal link is coupled to the rear end of the front horizontal link for rotational movement relative thereto, and such that a hinge is defined between the front and rear horizontal links. The rear end of the rear horizontal link is coupled to the lower end of the lower vertical link for rotation relative thereto. An over-center locking mechanism extends between the front and rear horizontal links and is configured to prevent downward movement of the hinge past a locked position in which the front and rear horizontal links are disposed generally collinear with each other, and to permit unlocking upward movement of the hinge relative to the locked position. The upper end of the shock absorber is coupled to the lower end of the lower vertical link and the rear end of the rear horizontal link for rotation relative thereto. A lever arm has a front end coupled to a third attach pin for rotation relative thereto and an opposite rear end coupled to the lower end of the shock absorber for rotation relative thereto. A ground contact shoe is disposed on the rear end of the lever arm. According to the disclosure of the present invention, first and second crank arms are respectively fixed to opposite first and second ends of the first attach pin for conjoint rotation therewith, and a third crank arm is fixed to a first end of the second attach pin for conjoint rotation therewith. A stow actuator has a first end coupled to an outer end of the first crank arm for rotation relative thereto and a opposite second end coupled to an outer end of the third crank arm for rotation relative thereto. A takeoff/landing actuator has a first end coupled to an outer end of the second crank arm for rotation relative thereto, and an opposite second end coupled to an end of the second attach pin opposite to the first end thereof for rotation relative thereto.

    [0014] The scope of the invention is defined by the claims, which are incorporated into this section by reference. A better understanding of the tail skid mechanisms and methods of actuating them of the present disclosure, as well as an appreciation of the above and additional advantages thereof, will be afforded to those of skill in the art by a consideration of the following detailed description of one or more example embodiments thereof. In this description, reference is made to the various views of the appended sheets of drawings, which are briefly described below, and within which like reference numerals are used to identify like ones of the elements illustrated therein.

    [0015] The disclosure further describes a tail skid mechanism, comprising: an upper vertical link having opposite upper and lower ends, the upper end being coupled to a first attach pin for conjoint rotation therewith; a lower vertical link having opposite upper and lower ends, the upper end being coupled to the lower end of the upper vertical link for rotation relative thereto and defining a first hinge between the upper and lower vertical links; a front horizontal link having opposite front end and rear ends, the front end being coupled to a second attach pin for conjoint rotation therewith; a rear horizontal link having opposite front and rear ends, the front end being coupled to the rear end of the front horizontal link for rotational movement relative thereto and defining a second hinge between the front and rear horizontal links, the rear end being coupled to the lower end of the lower vertical link for rotation relative thereto; a first over-center locking mechanism extending between the upper and lower vertical links and configured to prevent aft movement of the first hinge past a locked position in which the upper and lower horizontal links are disposed generally collinear with each other and to permit unlocking forward movement of the first hinge relative to the locked position; a second over-center locking mechanism extending between the front and rear horizontal links and configured to prevent downward movement of the second hinge past a locked position in which the front and rear horizontal links are disposed generally collinear with each other, and to permit unlocking upward movement of the hinge relative to the locked position; a shock strut cartridge having opposite upper and lower ends, the upper end being coupled to respective ones of the lower end of the lower vertical link and the rear end of the rear horizontal link for rotation relative thereto; a lever arm having opposite front and rear ends, the front end being coupled to a third attach pin for rotation relative thereto and the rear end being coupled to the lower end of the shock strut cartridge for rotation relative thereto; a ground contact shoe disposed on the rear end of the lever arm; first and second crank arms respectively fixed to opposite first and second ends of the first attach pin for conjoint rotation therewith; a third crank arm fixed to a first end of the second attach pin for conjoint rotation therewith; a stow actuator having opposite first and second ends, the first end being coupled to an outer end of the first crank arm for rotation relative thereto, the second end being coupled to an outer end of the third crank arm for rotation relative thereto; and a takeoff/landing actuator having opposite first and second ends, the first end being coupled to an outer end of the second crank arm for rotation relative thereto, and the second end being coupled to an end of the second attach pin opposite to the first end thereof for rotation relative thereto.

    [0016] Preferably, the first, second and third crank arms are configured and arranged such that: when each of the stow and takeoff/landing actuators is disposed in an extended state, the ground contact shoe is disposed in a landing position; when each of the stow and takeoff/landing actuators is disposed in a retracted state, the ground contact shoe is disposed in a stow position; and when the stow actuator is disposed in an extended state and the takeoff/landing actuator is disposed in a retracted state, the ground contact shoe is disposed in a takeoff position that is located between the landing position and the stow position.

    [0017] Preferably, the first, second and third crank arms are configured and arranged such that: when the ground contact shoe is disposed in the landing position, simultaneous extension of the stow actuator and retraction of the takeoff/landing actuator causes the ground contact shoe to move from the landing position to the takeoff position; when the ground contact shoe is disposed in the takeoff position, simultaneous retraction of the stow actuator and extension of the takeoff/landing actuator causes the ground contact shoe to move from the takeoff position to the landing position; when the ground contact shoe is disposed in the takeoff position, simultaneous retraction of the stow actuator and the takeoff/landing actuator causes the ground contact shoe to move from the takeoff position to the stow position; and when the ground contact shoe is disposed in the stow position, simultaneous extension of the stow actuator and the takeoff/landing actuator causes the ground contact shoe to move from the stow position to the landing position.

    [0018] Preferably, the first, second and third crank arms are configured and arranged such that: when the ground contact shoe is disposed in the landing position, simultaneous extension of the stow actuator and retraction of the takeoff/landing actuator causes the takeoff/landing actuator to control the rotation of the vertical links in opposition to the stow actuator.

    [0019] Preferably, the first, second and third crank arms are configured and arranged such that: when the ground contact shoe is disposed in the takeoff position, simultaneous retraction of the stow actuator and the takeoff/landing actuator causes the over-center locking mechanism to unlock and then re-lock; and when the ground contact shoe is disposed in the stow position, simultaneous extension of the stow actuator and the takeoff/landing actuator causes the over-center locking mechanism to unlock and then re-lock.

    [0020] Preferably, the tail skid mechanism further comprises a pair of stops respectively disposed on a rear surface of the upper vertical link and a rear surface of the lower vertical link and configured to prevent folding of the upper vertical link past a first selected acute angle relative to the lower vertical link.

    BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS



    [0021] 

    Figs. 1A and 1B are front-and-left-side perspective views of two prior art, two-position tail skid mechanisms, both shown disposed in a landing position;

    Figs. 2A and 2B are a front-and-right-side perspective view, and a front-and-left-side perspective view, respectively, of an example embodiment of a three-position tail skid mechanism in accordance with the present disclosure, shown disposed in a landing position;

    Figs. 3A and 3B are partial left-side and right-side elevation views, respectively, of an upper portion of the tail skid mechanism, showing a configuration and arrangement of a pair of actuators and a trio of actuator crank arms thereof;

    Fig. 4 is an enlarged partial left-side elevation view of the upper portion of the tail skid mechanism, showing a configuration and arrangement of a pair of actuators and a pair of crank arms thereof;

    Figs. 5A, 5B and 5C are partial front-and-left-side perspective views of the exam-pie three-position tail skid mechanism of Figs. 2A and 2B, shown mounted within an opening in a tail portion of an aircraft fuselage structure and disposed in a stow position, a landing position, and a takeoff position, respectively;

    Figs. 6A, 6B and 6C are front-and-right-side perspective views of the example tail skid mechanism, in which adjacent aircraft structure has been omitted for clarity, and shown disposed in the stow, landing and takeoff positions, respectively;

    Figs. 7A - 7D are successive partial-front-and-left-side elevation views of the up-per portion of the tail skid mechanism, shown moving from the landing position to the takeoff position;

    Figs. 8A - 8D are successive partial-front-and-right-side elevation views of the upper portion of the tail skid mechanism, shown moving from the takeoff position to the stow position; and

    Figs. 9A and 9B are a table and a graphic respectively summarizing the states and changes in state of a stow (S) actuator and a takeoff/landing (TOL) actuator of the tail skid mechanism during movement of the tail skid between the stow, landing and takeoff positions.


    DETAILED DESCRIPTION



    [0022] The present disclosure presents embodiments of aircraft tail skid mechanisms and methods for actuating them that effectively prevent or reduce tail strike damage to a host aircraft, that can be selectably deployed to and locked in one of three different positions relative to the aircraft, and that minimize the number, size and types of components need to implement and deploy the mechanisms.

    [0023] Figs. 1A and 1B are front-and-left-side perspective views of two prior art, two-position tail skid mechanisms 10A and 10B, both shown disposed in a landing position. As can be seen in Figs. 1A and 1B, each of the two prior art mechanisms 10A and 10B incorporate several elements that are substantially similar to each other, including three "attach pins" 12, 14, and 16 that are each pinned within surrounding aircraft structure 18 (not shown in Fig. 1B) and to which various ones of the links of the mechanisms are respectively coupled for movement relative to the structure 18, i.e., between a "stow" position (not illustrated) and an extended or "landing/takeoff' position, as illustrated in the figures.

    [0024] Both prior art tail skid mechanisms 10A and 10B comprise a single vertical link 40 and an over-center locking mechanism that includes front and rear horizontal links 22 and 24 that are coupled to each other at a hinge 25. As illustrated in the figures, the shock absorber 42 has an upper half 20 and a lower half 26, and has an upper end coupled to the attach pin 41 for conjoint rotation therewith. The front end of the front horizontal link 22 is coupled to the attach pin 14 for conjoint rotation therewith. A pair of crank arms 28 and 30 are respectively coupled to corresponding outer ends of the attach pins 12 and 14 for respectively conjoint rotation therewith. Each of the conventional tail skid mechanisms 10A and 10B includes a single actuator 32, e.g., a hydraulic or electromechanical actuator, having opposite ends respectively coupled to an outer end of one of the crank arms 28 or 30, such that extension or retraction of the actuator 32 causes a corresponding rotation or counter-rotation of the crank arms 28 and 30, and hence, of the corresponding links 40 and 22.

    [0025] A lever arm 34 has a front end coupled to the attach pin 16 for rotation relative thereto, and an opposite rear end coupled to a lower end of the shock absorber 42 for rotation relative thereto. A ground contact shoe 36, e.g., a pad of a hard, abrasion-resistant material, is disposed on the rear end of the lever arm 34 at its juncture with the lower end of the shock absorber 42, such that forces imparted to the ground contact shoe 36 by the runway during a takeoff or landing act along a line passing through the center of the shock absorber 42 and vertical link 40.

    [0026] As illustrated in Figs. 1A and 1B, the over-center locking mechanism comprises a rigid finger 38 that extends rearwardly from the front horizontal link 22 and into a corresponding notch in the upper surface of the rear horizontal link 24. The rigid finger 38 prevents downward movement of the hinge 25 located between the front and rear horizontal links 22 and 24 past a locked position in which the hinge 25 is disposed a small distance below the line of action between the pin 14 and the pin 41 and the front and rear horizontal links 22 and 24 are disposed generally collinear with each other, but permits an unlocking upward movement of the hinge 25 relative to the locked position.

    [0027] Thus, when the actuator 32 is extended, the vertical link 40 is extended downward to a fully extended landing/takeoff position, such that the vertical link 40 and the two horizontal links 22 and 24, along with the airplane structure 18 form a rigid, triangular structure that fixes the location of the pin 41. The shock absorber 42, the lever arm 34, the pin 41 and the airplane structure 18 form a second rigid triangular structure that fixes the location of the ground contact shoe 36 in the landing/takeoff position illustrated in the figures. Retraction of the actuator 32 causes the front horizontal link 22 to rotate counterclockwise relative to the airplane structure 18, which causes the hinge 25 to rise upwardly, thereby unlocking the over-center locking mechanism and allowing the front and rear horizontal links 22 and 24 to fold together about the hinge 25. This movement raises the vertical link 40, and hence, the ground contact shoe 36, upward to a fully retracted, or stow position (not illustrated).

    [0028] While the foregoing, prior art, two-position tail skid mechanisms 10A and 10B provide satisfactory performance, they are incapable of effecting a three-position, over-center locking configuration, i.e. one in which the ground contact shoe 36 is moved between a fully retracted position or stow position, a fully extended or landing position, and an intermediate or takeoff position, and thus, impose a penalty on the takeoff performance of the associated aircraft discussed above. However, as described in detail below, it has been discovered that a three-position tail skid mechanism 100 which locks in each of a stow, landing and takeoff position, can be confected by, among other things, replacing the single vertical link 40 with two vertical links and by adding a second actuator, which can be identical to the first actuator 32 in terms of length, stroke and power. The two vertical links can lock in two positions and thereby effectively achieve two different lengths. The second actuator can attach to crank arms that attach to the same attach pins as the first actuator 32, but in so doing, achieve a second, locked, partially extended or takeoff position not achievable in the prior art mechanisms 10A or 10B.

    [0029] Figs. 2A and 2B are a front-and-right-side perspective view, and a front-and-left-side perspective view, respectively, of an example embodiment of a three-position tail skid mechanism 100 in accordance with the present disclosure, shown disposed in a landing position. As illustrated in Figs. 2A and 2B, the example tail skid mechanism 100 includes several elements similar to those of the prior art tail skid mechanisms 10A and 10B discussed above, including an upper vertical link 102 having opposite upper and lower ends, the upper end being coupled to a first attach pin 104 for conjoint rotation therewith, and a lower vertical link 106 having opposite upper and lower ends, the upper end being coupled to the lower end of the upper vertical link 102 for rotation relative thereto.

    [0030] A front horizontal link 108 has opposite front end and rear ends, the front end being coupled to a second attach pin 110 for conjoint rotation therewith. A rear horizontal link 112 has opposite front and rear ends, the front end being coupled to the rear end of the front horizontal link 108 for rotational movement relative thereto and, as in the prior art mechanisms 10A and 10B described above, defining a hinge 114 between the front and rear horizontal links. The rear end of the rear horizontal link 112 is coupled to the lower end of the lower vertical link 106 for rotation relative thereto.

    [0031] As in the prior art mechanisms 10A and 10B of Figs. 1A and 1B, an over-center locking mechanism is disposed between the front and rear horizontal links 108 and 112 and is configured to prevent downward movement of the hinge 114 past a locked position in which the hinge 114 is located a small distance below the line of action between the pin 110 and the pin or node 130, as illustrated in, e.g., Figs. 2A and 2B, and to permit unlocking upward movement of the hinge 114 relative to the locked position, as illustrated in, e.g., Figs. 8C and 8D. As illustrated in the latter figures, the over-center locking mechanism can comprise a rigid finger 116 that extends from the first horizontal link 108 and into a corresponding notch 118 in an upper surface of the second horizontal link 112.

    [0032] As illustrated in, e.g., Figs. 2A and 2B, the example mechanism 100 further includes a shock absorber 140 having opposite upper and lower end portions 120 and 122. The upper end of the shock absorber 140 is coupled to respective ones of both the lower end of the lower vertical link 106 and the rear end of the rear horizontal link 112 for rotation relative thereto, and defines a node 130, discussed in more detail below, thereat. As in the prior art mechanisms 10A and 10B discussed above, the lower portion 122 of the shock absorber 140 can comprise a "crush cartridge," i.e., a cylinder of a crushable material, e.g., an aluminum honeycomb or other shock-absorbing material, that is configured to absorb the shock of an impact, and then be discarded and replaced after one or more uses. The shock absorber 140 can also comprise a hydraulic cylinder that is configured to absorb the shock of an impact and then be reused.

    [0033] In a manner similar to the prior art mechanisms 10A and 10B discussed above, the example mechanism 100 includes a lever arm 124 having opposite front and rear ends. The front end is coupled to a third attach pin 126 for rotation relative thereto, and the rear end is coupled to the lower end of the shock absorber 140 for rotation relative thereto. A ground contact shoe 128 is disposed on the rear end of the lever arm 124.

    [0034] As those of some skill will recognize, the lever arm 124, the shock absorber 140 and the ground shoe 128 can be considered together as a "follower mechanism," in that the respective positions of these elements are substantially determined by the position of the pin or node 130 defined by the juncture of the lower end of the lower vertical link 106 and the rear end of the rear horizontal link 112. Accordingly, an understanding of the motion of the former elements, and in particular, that of the ground contact shoe 128, can be obtained from an understanding of the selectably controlled movement of the elements located above the node 130 necessary to obtain that movement, as is discussed in more detail below.

    [0035] Figs. 3A and 3B are partial left-side and right-side elevation views, respectively, of the upper portion of the tail skid mechanism 100, shown in the landing position and illustrating the configuration and arrangement of a pair of actuators 132 and 134 and a trio of actuator crank arms 136, 138 and 140 thereof, and Fig. 4 is an enlarged partial left-side elevation view of the upper portion of the tail skid mechanism 100, also shown in the landing position and illustrating the configuration and arrangement of the actuators 132 and 134 and two of the crank arms 136 and 138 thereof. As illustrated in these figures, the example tail skid mechanism 100 includes first and second crank arms 136 and 138 respectively fixed to opposite first and second ends of the first attach pin 104 for conjoint rotation therewith, and a third crank arm 140 fixed to a first end of the second attach pin 110.

    [0036] The first actuator 132, referred to herein as a "stow" (S) actuator," has a first end coupled to an outer end of the first crank arm 136 for rotation relative thereto, and an opposite second end coupled to an outer end of the third crank arm 140 for rotation relative thereto. The second actuator 134, referred to herein as a takeoff/landing (TOL) actuator, has a first end coupled to an outer end of the second crank arm 138 for rotation relative thereto, and an opposite second end coupled to an end of the second attach pin 110 opposite to the first end thereof.

    [0037] As illustrated in Figs. 3A and 4, the TOL actuator 134 is rotatably attached about the centerline of the second attach pin 110, and therefore, cannot apply any turning moment to the front horizontal link 108, which is coupled to the second attach pin 110 for conjoint rotation. However, the opposite end of the TOL actuator 134 is rotatably attached to the outer end of the second crank arm 138, and can therefore apply a turning moment to the first attach pin 104, and hence, the upper vertical link 102, which is coupled to the first attach pin 104 for conjoint rotation. As illustrated in Figs. 3B and 4, the opposite ends of the S actuator 132 are rotatably coupled to the first and second attach pins 104 and 110 through the first and third crank arms 136 and 140, and accordingly, can exert a turning moment on both attach pins 104 and 110, and hence, on both the upper vertical link 102 and the front horizontal link 108.

    [0038] As illustrated in Fig. 4, the respective centerlines 142 and 144 of the S and TOL actuators 132 and 134 pass through ends of respective ones of two imaginary moment arms 146 and 148 that extend perpendicular to respective ones of the centerlines 142 and 144 and through the long axis of the first attachment pin 104. The respective lengths of these two moment arms 146 and 148 are a function of the respective lengths and relative angular positions of the first and second crank arms 136 and 138. These can be configured such that, for example, when each of the S and TOL actuators 132 and 134 is disposed in an extended state, such as illustrated in Figs. 3A, 3B and 4, the node 130, and hence, the ground contact shoe 128, is disposed in a landing, i.e., an extended, position. In this position, the TOL actuator 134 has a greater mechanical advantage than the S actuator 132. Therefore, a "retract" command applied to the TOL actuator 134 will cause the upper vertical link 102 to rotate clockwise relative to the attach pin 104, as indicated by the arrow 150 in Fig. 4, moving the node 130, and hence, the ground contact shoe 128, from the landing position illustrated in Fig. 4 to the takeoff position illustrated in, e.g., Fig. 6C.

    [0039] An "extend" command is simultaneously applied to the S actuator 132. Since the TOL actuator 134 at this position has a mechanical advantage over the S actuator 132, the S actuator 132 is compressed by the TOL actuator 134. The stow actuator extend force acts on the crank 140, causing a downward moment of the forward link 108, thus preventing the over-center locking mechanism between the front and rear horizontal links 108 and 112 from unlocking.

    [0040] In general, the configuration and arrangement of the two actuators 132 and 134 and the three crank arms 136, 138 and 140 is pre-configured such that one of the two actuators 132 or 134 is always provided with a mechanical advantage over the other actuator, depending on the position of the mechanism 100, thereby enabling two actuators 132 and 134 of substantially identical length, stroke and output force to be used effectively within the same tail skid mechanism 100. Additionally, stop features 156 and 158 can create an over-center locking mechanism between the upper and lower vertical links 102 and 106 and can be configured to prevent lateral movement of the hinge 114 past a locked position in which the upper and lower vertical links 102 and 106 are disposed generally collinear with each other, and to permit un-locking movement of the hinge 114 relative to the locked position such that, in the locked position, the upper and lower vertical links 102 and 106 can react compression loads applied by the shock absorber 140 without relative rotation between the upper and lower vertical links 102 and 106. Also, as illustrated in, e.g., Fig. 4, a first pair of abutting surfaces or "knuckles"152 and 154 can be respectively disposed on a rear surface of the upper vertical link 104 and a rear surface of the lower vertical link 106 and configured so as to prevent a rearward rotation of the upper vertical link 102 past a first selected angle relative to the lower vertical link 106 when they are engaged with each other, such that the upper and lower vertical links 102 and 106 can react compression loads applied by the shock absorber 140 without relative rotation between upper and lower vertical links 102 and 106 as illustrated in, e.g., Fig. 6C. And, as illustrated in, e.g., Fig. 6A, showing the mechanism in the stow, or fully retracted position, a second pair of knuckles 156 and 158 can similarly be respectively disposed on a lower surface of the upper vertical link 102 and an upper surface of the lower vertical link 106 and configured to prevent forward rotation of the upper vertical link 102 past a second selected angle relative to the lower vertical link 106, as illustrated in, e.g., Figs. 8A and 8B.

    [0041] Figs. 5A, 5B and 5C are partial front-and-left-side perspective views of the example three-position tail skid mechanism 100, shown mounted within an opening 160 in a tail portion of an aircraft fuselage structure 162 and disposed in a stow position, a landing position, and a takeoff position, respectively, and Figs. 6A, 6B and 6C are front-and-right-side perspective views of the example tail skid mechanism 100, in which the adjacent aircraft structure 162 has been omitted for clarity, and likewise shown disposed in the stow, landing and takeoff positions, respectively.

    [0042] An understanding of the way in which the example tail skid mechanism 100 is actuated into respective ones of the three positions by the S and TOL actuators 132 and 134 can be obtained from a consideration of Figs. 9A and 9B, wherein Figs. 9A and 9B are a table and a graphic respectively summarizing the states and changes in state of the S actuator 132 and the TOL actuator 134 during movement of the ground contact shoe 128 between respective ones of the stow, landing and takeoff positions.

    [0043] Thus, as indicated in Fig. 9A, when each of the S and TOL actuators 132 and 134 is disposed in a retracted state, the ground contact shoe 128 is disposed in the stow position, as illustrated in Figs. 5A and 6A. In the particular example embodiment illustrated in the figures, the upper vertical link 102 is disposed at a maximum rearward angle of about 162 degrees relative to the vertical, and the S and TOL actuators 132 and 134 are retracted to their minimum lengths. As illustrated in Fig. 5A, in this state, the tail skid mechanism 100 is fully retracted within the opening 160 in the fuselage of the aircraft, and in some embodiments, the lever arm 124 of the mechanism 100 can be configured to act as a closure for the opening 160 for purposes of streamlining, i.e., to reducing aerodynamic drag of the mechanism 100 during flight.

    [0044] As further indicated in Fig. 9A, when each of the S and TOL actuators 132 and 134 is disposed in an extended state, the upper vertical link 102 is disposed at an angle of about 0 degrees relative to the vertical, and the ground contact shoe 128 is disposed in its lowest or most extended position, i.e. the landing position, as illustrated in Figs. 5B and 6B. The upper vertical link 102 is disposed at an angle of about 47 degrees relative to the vertical when the ground contact shoe 128 is disposed in the takeoff position, located between the landing position and the stow position, as illustrated in Figs. 5C and 6C.

    [0045] As illustrated in Fig. 9B, the ground contact shoe 128 of the mechanism 100 is moved between the stow, landing and takeoff positions by inputting commands, i.e., "extend" and/or "retract" commands, to respective ones of the S and TOL actuators 132 and 134. Thus, when the ground contact shoe 128 is disposed in the landing position, retraction of the TOL actuator 134 causes the ground contact shoe 128 to move from the landing position to the takeoff position. When the ground contact shoe 128 is disposed in the takeoff position, simultaneous extension of the S and TOL actuators 132 and 134 causes the ground contact shoe 128 to move from the takeoff position to the landing position. When the ground contact shoe 128 is disposed in the takeoff position, simultaneous retraction of the S actuator 132 and the TOL actuator 134 causes the ground contact shoe 128 to move from the takeoff position to the stow position, and when the ground contact shoe 128 is disposed in the stow position, simultaneous extension of the S actuator 132 and the TOL actuator 134 causes the ground contact shoe 128 to move from the stow position to the landing position.

    [0046] As those of some skill will appreciate from an examination of Fig. 9B, the operation of the example tail skid mechanism 100 is not fully "reversible," i.e., is "unidirectional" in operation for some of the transitions between positions. Thus, as illustrated in Fig. 9B, the transitions between the takeoff position and the stow position is unidirectional. That is, while the mechanism 100 can move directly from the takeoff position to the stow position by commanding both of the S and TOL actuators 132 and 134 to retract, the mechanism 100 cannot move directly from the stow position to the takeoff position by simply reversing the foregoing procedure.

    [0047] The consequences of the foregoing are that 1) the mechanism 100 cannot transition directly from the stow position to the takeoff position, but must first pass through the landing position, and 2) the mechanism 100 can transition reversibly between the landing and takeoff positions.

    [0048] In sum, the S and TOL actuators 132 and 134, together with the first, second and third crank arms 136 138 and 140, are configured and arranged such that, when the ground contact shoe 128 is disposed in the landing position, simultaneous extension of the S actuator 132 and retraction of the TOL actuator 134 causes the S actuator 132 to be back-driven by the TOL actuator 134, and the upper and lower vertical links 102 and 106 to unlock from the over-center locking position and move to a compressed or folded position in which the stops 152 and 154 contact each other, causing the ground contact shoe 128 to move to the takeoff position. When the ground contact shoe 128 is disposed in the takeoff position, simultaneous retraction of the S actuator 132 and the TOL actuator 134 causes the over-center locking mechanism between the horizontal links 108 and 112 to unlock and then re-lock in the stow position. When the ground contact shoe 128 is disposed in the stow position, simultaneous extension of the S and TOL actuators 132 and 134 causes the S actuator 132 to unlock the horizontal links 108 and 112, the TOL actuator 134 causes the vertical links 102 and 106 to rotate clockwise about the attach pin 104 and then unfold into the over-center locking position. Continued extension of the S actuator 132 causes the horizontal links 108 and 112 to re-lock. As discussed above, in the direct transition from the landing position to the takeoff position, or vice-versa, no unlocking or relocking of the horizontal over-center locking mechanism between the horizontal links 108 and 112 occurs.

    [0049] A better understanding of the foregoing operations can be obtained from a consideration of Figs. 7A - 7D, which are successive partial-front-and-left-side elevation views of the upper portion of the tail skid mechanism 100 in moving from the landing position to the takeoff position, and from Figs. 8A - 8D, which are successive partial-front-and-right-side elevation views of the upper portion of the tail skid mechanism 100 moving from the takeoff position to the stow position.

    [0050] Thus, in Fig. 7A, showing the upper portion of the mechanism 100 disposed in the most-extended, i.e., landing position, the upper vertical link 102 is disposed over the lower vertical link 106 at about 0 degrees relative to the vertical, with the front pair of opposing knuckles 156 and 158 on respective ones of the lower and upper surfaces of the two vertical links 102 and 106 disposed in abutment with each other, and with the knuckles 152 and 154 on respective ones of the rear surfaces spaced apart from each other. The front and rear horizontal links 108 and 112 are disposed collinear with each other, i.e., in the over-center locked state, thereby defining one of the legs of a generally triangular structure of the type discussed above in connection with the prior art tail skid mechanisms 10A and 10B, the other two legs of which consist of the aircraft fuselage structure 162 and the two vertical members 102 and 106 locked in the over-center locking state.

    [0051] As discussed above, when the S actuator 132 is commanded to extend and the TOL actuator 134 is simultaneously commanded to retract, the extension of the S actuator 132 prevents the over-center locking mechanism between the two horizontal links 108 and 112 from unlocking, thus allowing the upper vertical link 102 to rotate clockwise relative to the pin 104 in the direction of the arrow 150. This, in turn, causes the pair of upper and lower knuckles 156 and 158 to separate and move away from each other, and the pair of rear knuckles 152 and 154 to move toward each other, as seen in Figs. 7B and 7C.

    [0052] As further illustrated in Figs. 7B and 7C, continued rotation of the upper vertical link 102 relative to the pin 104 ultimately results in the pair of knuckles 156 and 158 continuing to spread further apart, while the pair of knuckles 152 and 154 rotate into abutment with each other, as illustrated in Fig. 7D, with the upper vertical link 102 disposed at an angular position of about 47 degrees relative to the vertical. This results in the formation of a new triangular locking structure, consisting of the over-center horizontal links 108, 112, aircraft fuselage structure 162, and the folded position of the upper and lower vertical links 102 and 106, in which the two knuckles 152 and 154 are disposed in contact with each other. This position is substantially shorter than the over-center locked position of the two vertical links 102 and 106 when disposed in the landing position of Fig. 7A. As above, this folding of the vertical links 102 and 106 results in an upward movement of the node 130, and hence, the ground contact shoe 128, i.e., to the landing position. It may be noted that, in the foregoing transition, it was unnecessary to unlock the over-center locking mechanism between the two horizontal links 108 and 112.

    [0053] The case is not the same for either the transition from the stow position to the landing positon, or, as illustrated in Figs. 8A - 8D, the transition from the takeoff position to the stow position. Thus, in Fig. 8A, the upper end portion of the mechanism is shown disposed in the takeoff position, with the rear knuckles 152 and 154 disposed in abutment with each other, as discussed above in connection with Fig. 7D. As discussed above in connection with Figs. 9A and 9B, if the S and TOL actuators 132 and 134 are then both commanded to retract, the front horizontal link 108 is rotated clockwise relative to the pin 110, causing the over-center locking finger 116 to rotate out of engagement with the corresponding notch 118 in the rear horizontal member 112, thereby unlocking the over-center locking mechanism and causing the two horizontal members 108 and 112 to rotate or fold together about the hinge 114 between them.

    [0054] As illustrated in Figs. 8B and 8C, this unlocking enables the upper and lower vertical links 102 and 106 to rotate as a fixed unit rearwardly about the pin or node 130. The knuckles 152 and 156 may or may not be disposed in abutment with each other.

    [0055] As illustrated in Figs. 8C and 8D, the crank arms 136 and 140 are oriented such that retraction of the S actuator 132 initially causes the forward horizontal link 108 to rotate clockwise with respect to the pin 110 when moving from the takeoff position to the stow position. However, the favorable angular clocking and length of the crank arm 136 over the crank arm 140 changes the line of action for the S actuator 132 as the links 104 and 108 rotate. As illustrated in Fig 8D, the angular clocking of crank 140 at or near the stow position causes the link 108 to reverse direction and rotate counterclockwise, causing the over-center locking mechanism between the horizontal links 108 and 112 to re-lock in the generally collinear, over-center position, with the upper vertical link rotated rearwardly at an angle of about 162 degrees relative to the vertical. Thus, a new triangular locking structure is defined, comprising the over-center locked horizontal links 108 and 112, the aircraft fuselage structure 162, and the abutting, generally collinear knuckles 152 and 154 of the vertical links 102 and 106. As may be seen in a comparison of Figs. 8A, i.e., the takeoff position, and 8D, i.e., the stow position, the node 130 at the upper end of the shock strut cartridge 120 moves from a position disposed below the actuators 132 and 134 to a position disposed well above them. A similar unlocking and re-locking of the over-center locking mechanism and resulting re-definition of the triangular over-center locking structure occurs during the transition from the stow position, shown in Figs. 5A and 6A, to the takeoff position, shown in Figs. 5B and 6B.

    [0056] As those of some skill in this art will understand, since large modern aircraft are equipped with a plurality of sensors that automatically sense the state of various components of the aircraft, it is relatively easy to automate much of the actuation of the example tail skid mechanism 100 and thereby free the pilot of having to remember to do so. In particular, many large commercial aircraft have sensors that detect, among other things, when the landing gear of the aircraft is deployed, and if so, whether the landing gear is bearing the weight of the aircraft, such as when the aircraft is disposed on the ground, i.e., on a runway or tarmac. Accordingly, an automatic control system can easily be confected for the example tail skid mechanism 100 which senses whether the landing gear of the aircraft is deployed, and if so, whether the landing gear is bearing the weight of the aircraft. If the automatic control system senses that the landing gear is not deployed, the system can automatically move the ground contact shoe 128 to the stow position. If the control system senses that the landing gear is deployed but is not bearing the weight of the aircraft, the system can automatically move the ground contact shoe 128 to the landing position, and if the system senses the landing gear is deployed and is bearing the weight of the aircraft, the control system can automatically move the ground contact shoe 128 to the takeoff position.


    Claims

    1. A system, comprising:

    an aircraft having a fuselage (162) with a tail portion; and

    a tail skid (100) disposed in an opening (160) of the tail portion, the tail skid (100) comprising:
    a ground contact shoe (128); and

    a mechanism configured to selectably move the ground contact shoe (128) between respective ones of a stow position disposed within the opening (160), a landing position disposed below the opening (160), and a takeoff position different than the stow and landing positions;

    wherein the mechanism comprises:

    first and second attach pins (104, 110) respectively pinioned within a structure of the aircraft for rotation relative thereto;

    a linkage comprising two pairs of links (102, 106; 108, 112) coupled between the first and second attach pins (104, 110) and defining a node (130) at a middle of the linkage; and

    an actuating device (132, 134) configured to selectably rotate respective ones of the first and second attach pins (104, 110) in such a way as to move the node (130) between positions respectively corresponding to the stow, landing and takeoff positions, wherein the actuating device comprises:

    first and second crank arms (136, 138) respectively fixed to opposite first and second ends of the first attach pin (104) for conjoint rotation;

    a third crank arm (140) fixed to a first end of the second attach pin (110) for conjoint rotation; and

    first and second actuators (132, 134), each having opposite ends, wherein:

    a first end of the first actuator (132) is coupled to an outer end of the first crank arm (136) for relative rotation,

    a second end of the first actuator (132) is coupled to an outer end of the third crank arm (140) for relative rotation,

    a first end of the second actuator (134) is coupled to an outer end of the second crank arm (138) for relative rotation, and

    a second end of the second actuator (134) is coupled to an end of the second attach pin (110) opposite to the first end thereof for relative rotation.


     
    2. The system of claim 1, wherein the mechanism further comprises:

    an elongated shock absorber (140) having opposite ends (120, 122), a first end (120) being coupled to the node (130) for relative rotation; and

    a lever arm (124) having opposite ends, a first end being coupled to a third attach pin (126) for relative rotation and a second end being coupled to a second end (122) of the shock absorber (140) for relative rotation, wherein

    the ground contact shoe (128) is disposed on the second end of the lever arm (124).


     
    3. The system of claim 2, wherein the shock absorber (140) compresses to absorb energy.
     
    4. The system of any preceding claim, wherein the linkage comprises:

    first and second vertical links (102, 106), each having opposite ends, wherein

    an upper end of the upper vertical link (102) is coupled to the first attach pin (104) for conjoint rotation therewith,

    an upper end of the second vertical link (106) is coupled to a lower end of the first vertical link (102) for rotation relative thereto; and

    first and second horizontal links (108, 112), each having opposite ends, wherein

    a front end of the first horizontal link (108) is coupled to the second attach pin (110) for conjoint rotation therewith,

    a front end of the second horizontal link (112) is coupled to a rear end of the first horizontal link (108) for rotation relative thereto, and

    a rear end of the second horizontal link (112) is coupled to a lower end of the second vertical link (106) for rotation relative thereto at the node (130).


     
    5. The system of any preceding claim, further comprising a dual over-center locking mechanism for locking the ground contact shoe (128) in each of the stow, landing and takeoff positions.
     
    6. The system of claim 5, wherein the dual over-center locking mechanism comprises:

    a first over-center mechanism that contains a first horizontal stop (116) feature disposed on a first horizontal link (108) and a second horizontal stop feature (118) disposed on a second horizontal link (112),

    the first and second horizontal stop features (116, 118) being configured to prevent downward movement of a hinge (114) defined between the first and second horizontal links (108, 112) when the two horizontal stop features (116, 118) are disposed in contact with each other and past a locked position in which the hinge (114) is disposed below a load line extending between two horizontal link attach points and to permit unlocking upward movement of the hinge (114) relative to the locked position; and

    a second over-center mechanism that contains a first vertical stop feature (156) disposed on a first vertical link (102) and a second vertical stop feature (158) disposed on a second vertical link (106),

    the first and second vertical stop features (156, 158) being configured to prevent lateral movement aft of a hinge defined between the first and second vertical links (102, 106) when the two stop features (156, 158) are in contact with each other and past a locked position in which the hinge is disposed aft of a load line extending between the two horizontal link attach points and to permit unlocking forward movement of the hinge relative to the locked position.


     
    7. The system of claim 5 or claim 6, further comprising a mechanism for unlocking then re-locking the over-center locking mechanism when
    the ground contact shoe (128) is moved from the takeoff position to the stow position, and
    the ground contact shoe (128) is moved from the stow position to the landing position.
     
    8. A method for protecting an aircraft against tail strike damage, the method comprising:

    providing a tail skid (100) disposed in an opening (160) of a tail portion of the aircraft, the tail skid (100) comprising an elongated shock absorber (140) having a ground contact shoe (128) disposed at a lower end (122) thereof, the ground contact shoe (128) being moveable between respective ones of a stow position disposed within the opening (160), a landing position disposed below the opening (160), and a takeoff position disposed at a position different than the stow and the landing positions; and

    moving the ground contact shoe (128) to the takeoff position before a takeoff such that, in an over-rotation of the aircraft during the takeoff, the ground contact shoe (128) makes contact with a ground surface and the shock absorber (140) absorbs a shock of the contact to reduce tail strike damage to the aircraft;

    wherein the mechanism comprises:

    first and second attach pins (104, 110) respectively pinioned within a structure of the aircraft for rotation relative thereto;

    a linkage comprising two pairs of links (102, 106; 108, 112) coupled between the first and second attach pins (104, 110) and defining a node (130) at a middle of the linkage; and

    an actuating device (132, 134) configured to selectably rotate respective ones of the first and second attach pins (104, 110) in such a way as to move the node (130) between positions respectively corresponding to the stow, landing and takeoff positions, wherein the actuating device comprises:

    first and second crank arms (136, 138) respectively fixed to opposite first and second ends of the first attach pin (104) for conjoint rotation;

    a third crank arm (140) fixed to a first end of the second attach pin (110) for conjoint rotation; and

    first and second actuators (132, 134), each having opposite ends, wherein:

    a first end of the first actuator (132) is coupled to an outer end of the first crank arm (136) for relative rotation,

    a second end of the first actuator (132) is coupled to an outer end of the third crank arm (140) for relative rotation,

    a first end of the second actuator (134) is coupled to an outer end of the second crank arm (138) for relative rotation, and

    a second end of the second actuator (134) is coupled to an end of the second attach pin (110) opposite to the first end thereof for relative rotation.


     
    9. The method of claim 8, further comprising:
    moving the ground contact shoe (128) to the landing position before a landing such that, in an over-flaring of the aircraft during the landing, the ground contact shoe (128) makes contact with the ground surface and the shock absorber (140) absorbs a shock of the contact to reduce tail strike damage to the aircraft.
     
    10. The method of claim 8 or claim 9, further comprising:

    sensing whether a landing gear of the aircraft is deployed;

    sensing whether the landing gear is bearing a weight of the aircraft;

    moving the ground contact shoe (128) to the stow position if the landing gear is not deployed;

    moving the ground contact shoe (128) to the landing position if the landing gear is deployed and is not bearing the weight of the aircraft; and

    moving the ground contact shoe (128) to the takeoff position if the landing gear is deployed and is bearing the weight of the aircraft.


     


    Ansprüche

    1. System, umfassend:

    ein Flugzeug mit einem Rumpf (162) mit einem Heckabschnitt; und

    einen Hecksporn (100), der in einer Öffnung (160) des Heckabschnitts angeordnet ist, wobei der Hecksporn (100) umfasst:

    einen Bodenkontaktschuh (128); und

    einen Mechanismus, der konfiguriert ist, um den Bodenkontaktschuh (128) wahlweise zwischen einer innerhalb der Öffnung (160) angeordneten Stauposition, einer unterhalb der Öffnung (160) angeordneten Landeposition und einer von der Stau- und Landeposition verschiedenen Startposition zu bewegen;

    wobei der Mechanismus umfasst:

    erste und zweite Befestigungsbolzen (104, 110), die jeweils innerhalb einer Struktur des Flugzeugs zur Drehung in Bezug auf diese verzahnt sind;

    eine Verbindung, die zwei Paare von Gliedern (102, 106; 108, 112) umfasst, die zwischen dem ersten und dem zweiten Befestigungsbolzen (104, 110) gekoppelt sind und einen Knoten (130) in einer Mitte der Verbindung definieren; und

    eine Betätigungsvorrichtung (132, 134), die konfiguriert ist, um die jeweiligen der ersten und zweiten Befestigungsbolzen (104, 110) selektiv so zu drehen, dass der Knoten (130) zwischen Positionen bewegt wird, die jeweils der Stau-, Lande- und Startposition entsprechen,

    wobei die Betätigungsvorrichtung umfasst:

    einen ersten und einen zweiten Kurbelarme (136, 138), die jeweils an gegenüberliegenden ersten und zweiten Enden des ersten Befestigungsbolzens (104) zur gemeinsamen Drehung befestigt sind;

    einen dritten Kurbelarm (140), der an einem ersten Ende des zweiten Befestigungsbolzens (110) zur gemeinsamen Drehung befestigt ist; und

    ein erstes und ein zweites Stellglieder (132, 134), die jeweils entgegengesetzte Enden aufweisen, wobei:

    ein erstes Ende des ersten Stellglieds (132) mit einem äußeren Ende des ersten Kurbelarms (136) zur relativen Drehung gekoppelt ist,

    ein zweites Ende des ersten Stellglieds (132) mit einem äußeren Ende des dritten Kurbelarms (140) zur relativen Drehung gekoppelt ist,

    ein erstes Ende des zweiten Stellglieds (134) mit einem äußeren Ende des zweiten Kurbelarms (138) zur relativen Drehung gekoppelt ist, und

    ein zweites Ende des zweiten Stellglieds (134) mit einem Ende des zweiten Befestigungsbolzens (110), das dem ersten Ende desselben gegenüberliegt, zur relativen Drehung gekoppelt ist.


     
    2. System nach Anspruch 1, bei dem der Mechanismus ferner umfasst:

    einen langgestreckten Stoßdämpfer (140) mit entgegengesetzten Enden (120, 122), wobei ein erstes Ende (120) mit dem Knoten (130) zur relativen Drehung gekoppelt ist; und

    einen Hebelarm (124) mit entgegengesetzten Enden, wobei ein erstes Ende mit einem dritten Befestigungsbolzen (126) zur relativen Drehung und ein zweites Ende mit einem zweiten Ende (122) des Stoßdämpfers (140) zur relativen Drehung gekoppelt ist, wobei der Bodenkontaktschuh (128) am zweiten Ende des Hebelarms (124) angeordnet ist.


     
    3. System nach Anspruch 2, bei dem der Stoßdämpfer (140) komprimiert wird, um Energie zu absorbieren.
     
    4. System nach einem beliebigen der vorhergehenden Ansprüche, bei dem die Verbindung umfasst:

    ein erstes und ein zweites vertikales Glied (102, 106), die jeweils entgegengesetzte Enden aufweisen, wobei

    ein oberes Ende des oberen vertikalen Gliedes (102) mit dem ersten Befestigungsstift (104) zur gemeinsamen Drehung damit gekoppelt ist,

    ein oberes Ende des zweiten vertikalen Gliedes (106) mit einem unteren Ende des ersten vertikalen Gliedes (102) zur Drehung relativ dazu gekoppelt ist; und

    ein erstes und ein zweites horizontales Glied (108, 112), die jeweils entgegengesetzte Enden aufweisen, wobei

    ein vorderes Ende des ersten horizontalen Gliedes (108) mit dem zweiten Befestigungsbolzen (110) zur gemeinsamen Drehung damit gekoppelt ist,

    ein vorderes Ende des zweiten horizontalen Gliedes (112) mit einem hinteren Ende des ersten horizontalen Gliedes (108) zur Drehung in Bezug auf dieses gekoppelt ist, und

    ein hinteres Ende des zweiten horizontalen Gliedes (112) mit einem unteren Ende des zweiten vertikalen Gliedes (106) zur Drehung relativ dazu am Knoten (130) gekoppelt ist.


     
    5. System nach einem der vorhergehenden Ansprüche, ferner mit einem doppelten überzentrischen Verriegelungsmechanismus zum Verriegeln des Bodenkontaktschuhs (128) in jeder der Stau-, Lande- und Startpositionen.
     
    6. System nach Anspruch 5, bei dem der doppelte überzentrische Verriegelungsmechanismus umfasst:

    einen ersten überzentrischen Mechanismus, der ein erstes horizontales Anschlagelement (116), das auf einem ersten horizontalen Glied (108) angeordnet ist, und ein zweites horizontales Anschlagelement (118), das auf einem zweiten horizontalen Glied (112) angeordnet ist, enthält,

    wobei das erste und das zweite horizontale Anschlagelement (116, 118) konfiguriert sind, um eine Abwärtsbewegung eines Scharniers (114) zu verhindern, das zwischen dem ersten und dem zweiten horizontalen Glied (108, 112) definiert ist, wenn die beiden horizontalen Anschlagelemente (116, 118) in Kontakt miteinander und hinter einer verriegelten Position angeordnet sind, in der das Scharnier (114) unterhalb einer Lastlinie angeordnet ist, die sich zwischen zwei Horizontalglied-Befestigungspunkten erstreckt, und um eine entriegelnde Aufwärtsbewegung des Scharniers (114) in Bezug auf die verriegelte Position zu ermöglichen; und

    einen zweiten überzentrischen Mechanismus, der ein erstes vertikales Anschlagselement (156), das an einem ersten vertikalen Glied (102) angeordnet ist, und ein zweites vertikales Anschlagselement (158), das an einem zweiten vertikalen Glied (106) angeordnet ist, enthält,

    wobei das erste und das zweite vertikale Anschlagelement (156, 158) konfiguriert sind, um eine Seitwärtsbewegung nach hinten eines Scharniers zu verhindern, das zwischen dem ersten und dem zweiten vertikalen Glied (102, 106) definiert ist, wenn die beiden Anschlagelemente (156, 158) in Kontakt miteinander und hinter einer verriegelten Position stehen, in der das Scharnier hinter einer Lastlinie angeordnet ist, die sich zwischen den zwei Horizontalglied-Befestigungspunkten erstreckt, und um eine Vorwärtsbewegung des Scharniers in Bezug auf die verriegelte Position zu ermöglichen.


     
    7. System nach Anspruch 5 oder Anspruch 6, ferner mit einem Mechanismus zum Entriegeln und Wiederverriegeln des überzentrischen Verriegelungsmechanismus,

    wenn der Bodenkontaktschuh (128) aus der Startposition in die Stauposition bewegt wird, und

    wenn der Bodenkontaktschuh (128) aus der Stauposition in die Landeposition bewegt wird.


     
    8. Verfahren zum Schutz eines Flugzeugs vor Heckaufprallschäden, wobei das Verfahren umfasst:

    Bereitstellen eines Hecksporns (100), der in einer Öffnung (160) eines Heckabschnitts des Flugzeugs angeordnet ist, wobei der Hecksporn (100) einen langgestreckten Stoßdämpfer (140) mit einem Bodenkontaktschuh (128) umfasst, der an seinem unteren Ende (122) angeordnet ist, wobei der Bodenkontaktschuh (128) zwischen einer innerhalb der Öffnung (160) angeordneten Stauposition, einer unterhalb der Öffnung (160) angeordneten Landeposition und einer an einer anderen Position als der Stau- und der Landeposition angeordneten Startposition beweglich ist; und

    Bewegen des Bodenkontaktschuhs (128) in die Startposition vor einem Start, so dass der Bodenkontaktschuh (128) bei einer Überdrehung des Flugzeugs während des Starts mit einer Bodenoberfläche in Kontakt kommt und der Stoßdämpfer (140) einen Kontaktstoß absorbiert, um Heckaufprallschäden am Flugzeug zu reduzieren;

    wobei der Mechanismus umfasst:

    erste und zweite Befestigungsbolzen (104, 110), die jeweils innerhalb einer Struktur des Flugzeugs zur Drehung in Bezug auf diese verzahnt sind;

    eine Verbindung, die zwei Paare von Gliedern (102, 106; 108, 112) umfasst, die zwischen dem ersten und dem zweiten Befestigungsbolzen (104, 110) gekoppelt sind und einen Knoten (130) in einer Mitte der Verbindung definieren; und

    eine Betätigungsvorrichtung (132, 134), die konfiguriert ist, um die jeweiligen der ersten und zweiten Befestigungsbolzen (104, 110) selektiv so zu drehen, dass der Knoten (130) zwischen Positionen bewegt wird, die jeweils der Stau-, Lande- und Startposition entsprechen,

    wobei die Betätigungsvorrichtung umfasst:

    einen ersten und einen zweiten Kurbelarm (136, 138), die jeweils an gegenüberliegenden ersten und zweiten Enden des ersten Befestigungsbolzens (104) zur gemeinsamen Drehung befestigt sind;

    einen dritten Kurbelarm (140), der an einem ersten Ende des zweiten Befestigungsbolzens (110) zur gemeinsamen Drehung befestigt ist; und

    ein erstes und ein zweites Stellglied (132, 134), die jeweils entgegengesetzte Enden aufweisen, wobei:

    ein erstes Ende des ersten Stellglieds (132) mit einem äußeren Ende des ersten Kurbelarms (136) zur relativen Drehung gekoppelt ist,

    ein zweites Ende des ersten Stellglieds (132) mit einem äußeren Ende des dritten Kurbelarms (140) zur relativen Drehung gekoppelt ist,

    ein erstes Ende des zweiten Stellglieds (134) mit einem äußeren Ende des zweiten Kurbelarms (138) zur relativen Drehung gekoppelt ist, und

    ein zweites Ende des zweiten Stellglieds (134) mit einem Ende des zweiten Befestigungsbolzens (110) gekoppelt ist, das dem ersten Ende desselben zur relativen Drehung gegenüberliegt.


     
    9. Verfahren nach Anspruch 8, ferner umfassend:
    Bewegen des Bodenkontaktschuhs (128) in die Landeposition vor einer Landung, so dass der Bodenkontaktschuh (128) bei einem übermäßigen Aufrichten des Flugzeugs während der Landung mit der Bodenoberfläche in Kontakt kommt und der Stoßdämpfer (140) einen Kontaktstoß absorbiert, um die Heckaufprallschäden am Flugzeug zu reduzieren.
     
    10. Verfahren nach Anspruch 8 oder Anspruch 9, ferner umfassend:

    Erfassen, ob ein Fahrwerk des Flugzeugs ausgefahren ist;

    Erfassen, ob das Fahrwerk ein Gewicht des Flugzeugs trägt;

    Bewegen des Bodenkontaktschuhs (128) in die Stauposition, wenn das Fahrwerk nicht ausgefahren ist;

    Bewegen des Bodenkontaktschuhs (128) in die Landeposition, wenn das Fahrwerk ausgefahren ist und das Gewicht des Flugzeugs nicht trägt; und

    Bewegen des Bodenkontaktschuhs (128) in die Startposition, wenn das Fahrwerk ausgefahren ist und das Gewicht des Flugzeugs trägt.


     


    Revendications

    1. Système comprenant :

    un aéronef ayant un fuselage (162) avec une partie de queue ; et

    un sabot de queue (100) disposé dans une ouverture (160) de la partie de queue, le sabot de queue (100) comprenant :

    un patin de contact avec le sol (128) ; et

    un mécanisme configuré pour déplacer sélectivement le patin de contact avec le sol (128) entre des positions respectives parmi une position rentrée disposée dans l'ouverture (160), une position d'atterrissage disposée au-dessous de l'ouverture (160), et une position de décollage différente des positions rentrée et d'atterrissage ;

    dans lequel le mécanisme comprend :

    des première et deuxième broches de fixation (104, 110) respectivement fixées par pignon dans une structure de l'aéronef pour la rotation par rapport à cette dernière ;

    une tringlerie comprenant deux paires de liaisons (102, 106 ; 108, 112) couplées entre les première et deuxième broches de fixation (104, 110) et définissant un noeud (130) au milieu de la tringlerie ; et

    un dispositif d'actionnement (132, 134) configuré pour faire tourner sélectivement des broches respectives des première et deuxième broches de fixation (104, 110) afin de déplacer le noeud (130) entre des positions correspondant respectivement aux positions rentrée, d'atterrissage et de décollage, dans lequel le dispositif d'actionnement comprend :

    des premier et deuxième bras de manivelle (136, 138) respectivement fixés aux première et seconde extrémités opposées de la première broche de fixation (104) pour la rotation conjointe ;

    un troisième bras de manivelle (140) fixé sur une première extrémité de la deuxième broche de fixation (110) pour la rotation conjointe ; et

    des premier et second actionneurs (132, 134), ayant chacun des extrémités opposées, dans lequel :

    une première extrémité du premier actionneur (132) est couplée à une extrémité externe du premier bras de manivelle (136) pour la rotation relative,

    une seconde extrémité du premier actionneur (132) est couplée à une extrémité externe du troisième bras de manivelle (140) pour la rotation relative,

    une première extrémité du second actionneur (134) est couplée à une extrémité externe du deuxième bras de manivelle (138) pour la rotation relative, et

    une seconde extrémité du second actionneur (134) est couplée à une extrémité de la deuxième broche de fixation (110) opposée à sa première extrémité pour la rotation relative.


     
    2. Système selon la revendication 1, dans lequel le mécanisme comprend en outre :

    un amortisseur allongé (140) ayant des extrémités opposées (120, 122), une première extrémité (120) étant couplée au noeud (130) pour la rotation relative ; et

    un bras de levier (124) ayant des extrémités opposées, une première extrémité étant couplée à une troisième broche de fixation (126) pour la rotation relative et une seconde extrémité couplée à une seconde extrémité (122) de l'amortisseur (140) pour la rotation relative, dans lequel :
    le patin de contact avec le sol (128) est disposé sur la seconde extrémité du bras de levier (124).


     
    3. Système selon la revendication 2, dans lequel l'amortisseur (140) effectue un mouvement de compression pour absorber l'énergie.
     
    4. Système selon l'une quelconque des revendications précédentes, dans lequel la tringlerie comprend :

    des première et seconde liaisons verticales (102, 106), ayant chacune des extrémités opposées, dans lequel :

    une extrémité supérieure de la liaison verticale supérieure (102) est couplée à la première broche de fixation (104) pour la rotation conjointe avec cette dernière,

    une extrémité supérieure de la seconde liaison verticale (106) est couplée à une extrémité inférieure de la première liaison verticale (102) pour la rotation relative par rapport à cette dernière ; et

    des première et seconde liaisons horizontales (108, 112), ayant chacune des extrémités opposées, dans lequel :

    une extrémité avant de la première liaison horizontale (108) est couplée à la deuxième broche de fixation (110) pour la rotation conjointe avec cette dernière,

    une extrémité avant de la seconde liaison horizontale (112) est couplée à une extrémité arrière de la première liaison horizontale (108) pour la rotation relative par rapport à cette dernière, et

    une extrémité arrière de la seconde liaison horizontale (112) est couplée à une extrémité inférieure de la seconde liaison verticale (106) pour la rotation par rapport à cette dernière au niveau du noeud (130).


     
    5. Système selon l'une quelconque des revendications précédentes, comprenant en outre un double mécanisme de blocage décentré pour bloquer le patin de contact avec le sol (128) dans chacune parmi les positions rentrée, d'atterrissage et de décollage.
     
    6. Système selon la revendication 5, dans lequel le double mécanisme de blocage décentré comprend :

    un premier mécanisme décentré qui contient une première caractéristique de butée horizontale (116) disposée sur une première liaison horizontale (108) et une seconde caractéristique de butée horizontale (118) disposée sur une seconde liaison horizontale (112),

    les première et seconde caractéristiques de butée horizontales (116, 118) étant configurées pour empêcher le mouvement descendant d'une charnière (114) définie entre les première et seconde liaisons horizontales (108, 112) lorsque les deux caractéristiques de butée horizontales (116, 118) sont disposées en contact entre elles et au-delà d'une position bloquée dans laquelle la charnière (114) est disposée au-dessous d'une ligne de charge s'étendant entre deux points de fixation de liaison horizontale et pour permettre le déblocage du mouvement ascendant de la charnière (114) par rapport à la position bloquée ; et

    un second mécanisme décentré qui contient une première caractéristique de butée verticale (156) disposée sur une première liaison verticale (102) et une seconde caractéristique de butée verticale (158) disposée sur une seconde liaison verticale (106),

    les première et seconde caractéristiques de butée verticales (156, 158) étant configurées pour empêcher le mouvement latéral à l'arrière d'une charnière définie entre les première et seconde liaisons verticales (102, 106) lorsque les deux caractéristiques de butée (156, 158) sont en contact entre elles et au-delà d'une position bloquée dans laquelle la charnière est disposée à l'arrière d'une ligne de charge s'étendant entre les deux points de fixation de liaison horizontale et pour permettre le déblocage du mouvement vers l'avant de la charnière par rapport à la position bloquée.


     
    7. Système selon la revendication 5 ou la revendication 6, comprenant en outre un mécanisme pour débloquer, ensuite bloquer à nouveau le mécanisme de blocage décentré, lorsque :

    le patin de contact avec le sol (128) passe de la position de décollage à la position rentrée, et

    le patin de contact avec le sol (128) passe de la position rentrée à la position d'atterrissage.


     
    8. Procédé pour protéger un aéronef contre l'endommagement de la queue provoqué par un impact, le procédé comprenant les étapes consistant à :

    prévoir un sabot de queue (100) disposé dans une ouverture (160) d'une partie de queue de l'aéronef, le sabot de queue (100) comprenant un amortisseur allongé (140) ayant un patin de contact avec le sol (128) disposé au niveau de son extrémité inférieure (122), le patin de contact avec le sol (128) étant mobile entre des positions respectives parmi une position rentrée disposée à l'intérieur de l'ouverture (160), une position d'atterrissage disposée au-dessous de l'ouverture (160) et une position de décollage disposée dans une position différente des positions rentrée et d'atterrissage ; et

    déplacer le patin de contact avec le sol (128) dans la position de décollage avant un décollage, de sorte que, lors d'une rotation excessive de l'aéronef pendant le décollage, le patin de contact avec le sol (128) établit le contact avec une surface de sol et l'amortisseur (140) absorbe un choc du contact afin de réduire l'endommagement de la queue provoqué par un impact, pour l'aéronef ;

    dans lequel le mécanisme comprend :

    des première et deuxième broches de fixation (104, 110) respectivement fixées par pignon dans une structure de l'aéronef pour la rotation par rapport à cette dernière ;

    une tringlerie comprenant deux paires de liaisons (102, 106 ; 108, 112) couplées entre les première et deuxième broches de fixation (104, 110) et définissant un noeud (130) au milieu de la liaison ; et

    un dispositif d'actionnement (132, 134) configuré pour faire sélectivement tourner les broches respectives des première et deuxième broches de fixation (104, 110) afin de déplacer le noeud (130) entre des positions correspondant respectivement aux positions rentrée, d'atterrissage et de décollage, dans lequel le dispositif d'actionnement comprend :

    des premier et deuxième bras de manivelle (136, 138) respectivement fixés sur les première et seconde extrémités de la première broche de fixation (104) pour la rotation conjointe ;

    un troisième bras de manivelle (140) fixé à une première extrémité de la deuxième broche de fixation (110) pour la rotation conjointe ; et

    des premier et second actionneurs (132, 134), ayant chacun des extrémités opposées, dans lequel :

    une première extrémité du premier actionneur (132) est couplée à une extrémité externe du premier bras de manivelle (136) pour la rotation relative,

    une seconde extrémité du premier actionneur (132) est couplée à une extrémité externe du troisième bras de manivelle (140) pour la rotation relative,

    une première extrémité du second actionneur (134) est couplée à une extrémité externe du deuxième bras de manivelle (138) pour la rotation relative, et

    une seconde extrémité du second actionneur (134) est couplée à une extrémité de la deuxième broche de fixation (110) opposée à sa première extrémité pour la rotation relative.


     
    9. Procédé selon la revendication 8, comprenant en outre l'étape consistant à :
    faire passer le patin de contact avec le sol (128) dans la position d'atterrissage avant un atterrissage de sorte que, lors d'un évasement excessif de l'aéronef pendant l'atterrissage, le patin de contact avec le sol (128) établit le contact avec la surface de sol et l'amortisseur (140) absorbe un choc du contact afin de réduire l'endommagement de la queue provoqué par un impact, pour l'aéronef.
     
    10. Procédé selon la revendication 8 ou la revendication 9, comprenant en outre les étapes consistant à :

    détecter si un train d'atterrissage de l'aéronef est déployé ;

    détecter si le train d'atterrissage supporte le poids de l'aéronef ;

    faire passer le patin de contact avec le sol (128) dans la position rentrée si le train d'atterrissage n'est pas déployé ;

    faire passer le patin de contact avec le sol (128) dans la position d'atterrissage si le train d'atterrissage est déployé et ne supporte pas le poids de l'aéronef ; et

    faire passer le patin de contact avec le sol (128) dans la position de décollage si le train d'atterrissage est déployé et supporte le poids de l'avion.


     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description