PIVOTING LANDING GEAR PROVIDED WITH AN IMMOBILIZATION SYSTEM

A landing gear provided with a stand and a pivoting assembly carrying a contact member and able to rotate about a pivot axis in relation to the stand. An immobilization system comprises a movable pin and a passage provided in a base secured to the pivoting assembly. An elastic locking system tends to push the pin into the passage in a locked mode. An elastic unlocking system is configured to move the pin out of the passage when activation of an unlocked mode is commanded by a control, the elastic unlocking system being calibrated to allow the pin to be extracted from the passage only when there is a shearing force less than a threshold between the base and the pin.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of FR 23 07363 filed on Jul. 10, 2023, the disclosure of which is incorporated in its entirety by reference herein.

TECHINICAL FIELD

The present disclosure relates to a pivoting landing gear provided with an immobilization system.

BACKGROUND

A landing gear of an aircraft, for example a rotorcraft or a helicopter, may comprise at least one pivoting landing gear. Such a pivoting landing gear may comprise an assembly carrying at least one ground contact member and able to pivot through 360 degrees about a pivot axis in order to facilitate the movement of the aircraft on the ground. The term “ground” refers hereinafter to any surface on which an aircraft can land, such as the surface of the Earth, the roof of a building, the deck of a ship, etc.

For example, a tricycle-gear rotorcraft may comprise two main landing gears and one auxiliary landing gear each comprising at least one wheel. The two main landing gears are not able to pivot. However, the auxiliary landing gear is able to pivot in order to ensure the maneuverability of the aircraft on the ground. When on the ground, the wheel or wheels of the auxiliary landing gear are free to pivot about a pivot axis that is separate from the axis or axes of rotation of the wheels. On a helicopter provided with a yaw angle control system, for example of the type comprising a rear rotor, turning can be undertaken on the ground by controlling the thrust exerted by this yaw angle control system. The yaw angle control system generates a moment on an airframe of the aircraft carried by the landing gears, and this moment automatically pivots the auxiliary landing gear to orientate the aircraft in the required direction.

However, such a pivoting landing gear is conventionally provided with an immobilization system. On command, the immobilization system locks the pivoting landing gear in a position that causes the aircraft to move in a straight line. Indeed, it is necessary to pivotally lock the auxiliary landing gear during a running landing with engine failure, or when landing the aircraft on a slope or on the deck of a ship or equivalent.

A known immobilization system comprises a pin capable of entering a bore of a base secured to the pivoting assembly of a pivoting landing gear. The immobilization system also comprises an elastic connecting rod linked to the pin and to a control. The control may comprise a handle linked to the elastic connecting rod by a non-elastic link.

In order to place the immobilization system in an unlocked mode, the control is maneuvered by an operator to position the elastic connecting rod in a first position. The locking pin is then outside the bore. As a result, the pivoting assembly is free to pivot about a pivot axis.

In order to lock the pivoting landing gear, the control is maneuvered by an operator to position the elastic connecting rod in a second position, bringing it closer to the bore.

If the pin is in line with the bore, this pin enters the bore. The immobilization system is then in a locked phase of a locked mode. The pivoting assembly is then no longer free to pivot through 360 degrees about the pivot axis.

If the pin is not in line with the bore, the pin comes to abut against the base. The elastic connecting rod is compressed and tends to push the pin towards the base. The immobilization system is then in an armed phase of the locked mode. The pivoting assembly is temporarily free to pivot about the pivot axis. As soon as the pin reaches the bore, the elastic connecting rod expands and pushes the pin into this bore. Therefore, the immobilization system switches automatically into the locked phase of the locked mode.

Another known immobilization system comprises a pin that is able to move not in translation but in rotation.

Such locking systems are useful. However, when the pivoting assembly is in the locked phase and tends to pivot, the base exerts a shearing force on the locking pin. Depending on the intensity of this force and the friction coefficient between the pin and the base, unlocking may not be possible. In particular, when the yaw angle control system generates significant transverse thrust, the shearing force can be significant. However, if a pilot forces and manages to move the control to place the immobilization system in the unlocked mode, the aircraft may suddenly be destabilized.

Document U.S. Pat. No. 3,375,999 A describes a releasable locking mechanism for a pivoting wheel. This mechanism comprises a projection that can be accommodated in a notch between two locking arms. The wheel is locked at rest and unlocked when the force exceeds a threshold. Therefore, this system is not designed to deal with the present problem.

Document WO2010115893 A1 discloses a system comprising a friction member for exerting a frictional force between two components. The system comprises control means for varying the pre-load exerted by the pressing member on the friction member.

Document EP 662906 B1 describes a means for rotationally locking a landing gear provided with a locking pin assembly.

Document CN104210654 A describes a wheel lock indicator comprising a pin that is able to move in translation in relation to a housing and is automatically held in position by means of a return spring.

Document U.S. Pat. No. 2,502,522 A describes a landing gear provided with a stand and a pivoting assembly carrying a contact member. The landing gear has an immobilization system that comprises a pin and a passage provided in the stand. Moreover, an elastic system comprises two springs. A first spring is arranged between an upper plate secured to the pivoting assembly and a collar secured to the pin, whereas a second spring is arranged between a lower plate secured to the pivoting assembly and the collar.

Document U.S. Pat. No. 2,384,054 A describes a retractable landing gear provided with a system comprising a cable passing around a pulley to join a centering pin.

Document GB 970425 A describes a landing gear provided with a latch that can be engaged in openings of a fork carrying a wheel.

SUMMARY

An object of the present disclosure is thus to propose a landing gear provided with an innovative immobilization system for limiting the risks of sudden destabilization.

The disclosure thus relates to a landing gear provided with a stand and a pivoting assembly carrying a contact member that is configured to be in contact with the ground, said pivoting assembly being able to rotate about a pivot axis in relation to the stand, said landing gear having an immobilization system comprising a movable pin and a control configured to request the application of a locked mode or an unlocked mode, the immobilization system comprising a passage provided in a base secured to the pivoting assembly, the pin being outside said passage in an unlocked phase of the unlocked mode, the pin being able to move in said passage in azimuth relative to the pivot axis in a locked phase of the locked mode, the immobilization system having an elastic locking system tending to push/pushing the pin into the passage in the locked mode, the pin being pushed in the locked mode, by the elastic locking system, either against the base during an armed phase of the locked mode as long as the pin does not enter the passage, or into the passage as soon as the pin is in line with the passage in the locked phase.

The immobilization system comprises an elastic unlocking system configured to move said pin out of the passage when activation of the unlocked mode is commanded by the control, the elastic unlocking system being calibrated to allow the pin to be extracted from the passage only when there is a shearing force less than a threshold between the base and the pin.

The immobilization system is thus configured to immobilize said pivoting assembly within a predetermined range of positions in relation to the stand during a locked phase of a locked mode and to authorize unlimited pivoting of the pivoting assembly in relation to the stand during an unlocked phase of an unlocked mode.

The expression “immobilization system configured to immobilize said pivoting assembly within a predetermined range of positions in relation to the stand during a locked phase of a locked mode” means that the pivoting assembly can pivot only within the space in azimuth, in relation to the pivot axis, between the stand and the pin when the pin is in the passage. Indeed, the passage has, with reference to the pivot axis, a dimension along an arc of a circle that is greater than a dimension of the pin. Therefore, the pin can easily enter the passage, but the base has limited freedom of movement in azimuth. Depending on the position of the pin in the passage, the base exerts or does not exert a shearing force on the pin.

The expression “the pin being able to move in said passage in azimuth relative to the pivot axis” means that there is always a gap separating the pin from the base along an of a circle centered on the pivot axis. This gap gives the base freedom of movement in relation to the pin, when the pin is in the passage, limited to the predetermined range of positions, for example of the order of 0.5 degrees. On an aircraft, this angle may depend on the longitudinal distance between fixed landing gears of the aircraft and the landing gear that has the pivoting assembly of the disclosure.

In addition to the armed, locked and unlocked phases of the prior art, the elastic unlocking system makes it possible to create a disarmed phase when switching from the locked mode to the unlocked mode.

If the base exerts a shearing force less than the threshold on the pin, the pin moves directly out of passage, the immobilization system switching directly to the unlocked phase. The pivoting assembly is free to pivot about the pivot axis, at least over 180 degrees, for example, or indeed over 360 degrees.

If the base exerts a shearing force greater than or equal to the threshold on the pin, for example if there is a rear rotor generating a significant yaw moment on an airframe of the aircraft, the switch from the locked mode to the unlocked mode causes the elastic unlocking system to compress. The immobilization system switches to a disarmed phase of the unlocked mode. This elastic unlocking system is calibrated such that it is not able to expand in these conditions. In other words, the stiffness along the compression/expansion axis of the elastic unlocking system is chosen to ensure a switch to the unlocked phase in the desired conditions. As soon as the shearing force drops below the threshold, following a slight pivoting of the pivoting assembly, the elastic unlocking system expands and automatically expels the pin from the passage to reach the unlocked phase.

Therefore, the elastic unlocking system prevents unlocking when there is a significant shearing force, that is synonymous on a helicopter of a significant moment exerted on the airframe. This elastic unlocking system helps prevent sudden movement when activation of the unlocked mode is commanded by a pilot. This means that the landing gear can only be unlocked in specific operational situations. If there is a high shearing force, unlocking is prohibited, even if it is commanded by the pilot. The pilot can therefore command unlocking regardless of the shear stress on the pin. Unlocking will only take effect when the force applied to this pin drops below a predetermined force threshold. The pivoting landing gear according to the disclosure therefore helps optimize safety.

The landing gear according to the disclosure may have one or more of the following features, taken individually or in combination.

According to a first alternative, the pin may be able to move in translation in relation to the base along a translation axis, for example parallel to the pivot axis.

The first alternative is therefore applicable to a system comprising a pin that is able to move in translation.

For example, the immobilization system may comprise a hollow support that extends towards the base along the translation axis from an end wall to an open end, the open end being arranged between the end wall and the base, the pin comprising a head secured to a locking rod, the head being located in the hollow support and the locking rod emerging through the open end of the hollow support at least in the locked phase, the elastic locking system being arranged between the end wall and the head.

The support guides the translational movement of the head, and consequently of the pin. The stand may also guide the translational movement of the pin.

The elastic locking system can thus be compressed when switching from the unlocked mode to the locked mode when the pin is not in line with the passage. The immobilization system is then in an armed phase, the elastic locking system being ready to expand to push the pin into the passage.

The elastic locking system may possibly comprise a locking spring with a coil fastened to the end wall.

According to a first variant of the first alternative, the support may be able to move in translation in relation to the stand, said control being connected to the support.

During the switch from the unlocked mode to the locked mode, the support switches from a first position to a second position. If the pin is not in line with the passage, the support compresses the elastic locking system during a possible armed phase. The pin is then pressed against the support. As soon as the pin is positioned in line with the passage, the elastic locking system expands to switch automatically to the locked phase as soon as possible.

During the switch from the locked mode to the unlocked mode, the support switches from the second position to the first position. If the base exerts a shearing force greater than or equal to the threshold on the pin, the pin remains in place and the support compresses the elastic unlocking system during a possible disarmed phase. As soon as the shearing force on the pin drops below the threshold, the elastic unlocking system expands to switch automatically to the unlocked phase.

The first variant of the first alternative can therefore be relatively simple and easy to implement.

The elastic unlocking system may possibly be arranged between the head and an inner shoulder of the support, the locking rod passing through the inner shoulder, the inner shoulder being situated between the head and the base.

The elastic unlocking system may possibly comprise an unlocking spring with a coil fastened to the inner shoulder.

According to a second variant of the first alternative, the support may be stationary in relation to the stand, the pin comprising an entry rod secured to the head and passing through the end wall of the support.

For example, the entry rod extends from the head to a top secured to a hollow tube, said control comprising a cable that extends up to a plate that is able to move in translation in the hollow tube, passing through a wall of the tube, the elastic unlocking system being arranged between said wall and said plate.

Furthermore, the stiffness of the elastic unlocking system along the translation axis may be greater than the stiffness of the elastic locking system along the translation axis. Therefore, the elastic unlocking system expands when the pin is released by the base.

The second variant of the first alternative may also be relatively simple and easy to implement.

Furthermore, the stiffness of the elastic unlocking system along the translation axis may be greater than the stiffness of the elastic locking system along the translation axis, in particular but not only according to the second variant of the first alternative. Therefore, the elastic unlocking system expands when the pin is released by the base.

According to a second alternative, the pin has not a degree of translation freedom but a degree of rotational freedom in relation to the stand.

For example, the pin may be carried by a lever pivotally connected to the stand, the elastic locking system being arranged between the stand and the lever, the control comprising a cable connected to a panel that is able to move in translation in a guide, the guide being connected to the lever, the elastic unlocking system being arranged between the panel and a partition of the guide through which the cable passes.

Regardless of the alternative, the contact member may comprise a wheel that is able to rotate about a wheel axis in relation to the pivoting assembly, said wheel axis being distinct from the pivot axis. The wheel axis and the pivot axis are also not parallel.

According to another object, a rotorcraft may comprise at least one pivoting landing gear according to the disclosure.

The disclosure also relates to the method that is implemented, i.e., a method for locking and unlocking a landing gear provided with a stand and a pivoting assembly carrying a contact member that is configured to be in contact with the ground, said pivoting assembly being able to rotate about a pivot axis in relation to the stand, said landing gear having an immobilization system configured to immobilize said pivoting assembly within a predetermined range of positions in relation to the stand during a locked phase of a locked mode and to authorize unlimited pivoting of the pivoting assembly in relation to the stand during an unlocked phase of an unlocked mode, the immobilization system comprising a movable pin and a control configured to request the application of the locked mode or the unlocked mode, the immobilization system comprising a passage provided in a stand secured to said pivoting assembly, the pin being outside said passage in the unlocked phase, the pin being able to move in said passage in azimuth relative to the pivot axis in the locked phase.

This method comprises:when the immobilization system is in the unlocked mode, activating said control in order to switch to the locked mode, then: (i) if the pin is in line with the passage, moving the pin into the passage; and (ii) if the pin is not in line with the passage, pressing the pin against the base with an elastic locking system and moving the pin into the passage as soon as the pin comes into line with the passage; andwhen the immobilization system is in the locked mode, activating said control in order to switch to the unlocked mode, then, if the pin is in the passage and in contact with the base, compressing an elastic unlocking system, and: (i) keeping the pin in the passage as long as the pin is subject to a shearing force greater than or equal to a threshold, the immobilization system being in a disarmed phase; and (ii) as soon as the pin is subject to a shearing force less than the threshold, expansion of the elastic unlocking system and ejecting the pin out of the passage under the effect of said expansion in order to switch to an unlocked phase.

DETAILED DESCRIPTION

Elements that are present in more than one of the figures are given the same references in each of them.

FIG.1shows a rotorcraft1according to the disclosure. This rotorcraft1comprises an airframe2possibly carrying at least one rotor and a yaw control system. In this case, the rotorcraft1shown comprises a main rotor4and a rear rotor5acting as a yaw control system.

Furthermore, the airframe2rests on a landing system6comprising, for example, at least one landing gear, i.e., two main landing gears7and an auxiliary landing gear8in this example.

This rotorcraft1comprises, in particular, at least one pivoting landing gear10, i.e., the auxiliary landing gear8in this example.

In reference toFIG.2, when the yaw control system exerts lateral thrust F1, the pivoting landing gear10rotates on the ground about a pivot axis AXP in order to modify the orientation of the rotorcraft1.

The landing gear10therefore comprises an immobilization system to keep the pivoting landing gear10substantially aligned along the axis of forward movement of the rotorcraft1, under certain conditions.

FIG.3shows an embodiment of a pivoting landing gear10according to the disclosure. Irrespective of the embodiment, the landing gear10is provided with a stand11, connected to the airframe2, and a pivoting assembly12that can pivot about a pivot axis AXP in relation to the stand11. The pivoting assembly12carries at least one contact member15that is configured to be in contact with the ground100. For example, a contact member15comprises a skid and/or a wheel150that is able to rotate about a wheel axis AXROT in relation to the pivoting assembly12.

By way of illustration,FIG.3shows an example of a stand11and a pivoting assembly12, but other embodiments of the pivoting assembly12may be envisaged. In particular, the stand11may be fixed or retractable without going beyond the ambit of the disclosure. According to the example shown, the pivoting assembly12may comprise a cylinder13that is able to rotate about the pivot axis in relation to the stand11. Moreover, the pivoting assembly12comprises a damper14carried by the cylinder13and housed at least partially in this cylinder13, this damper14possibly being provided with a device referred to as an anti-shimmy device. Furthermore, scissors16are hinged to the cylinder13and to the damper14. At least one contact member15may be carried by the scissors16or the damper14, for example.

Irrespective of the embodiment of the pivoting assembly12and the stand11, the landing gear10comprises an immobilization system20configured to: (i) immobilize the pivoting assembly12within a predetermined restricted range of positions in relation to the stand11during a locked phase of a locked mode; and to (ii) authorize unlimited pivoting of the pivoting assembly12in relation to the stand11during an unlocked phase of an unlocked mode.

FIG.3shows a first version of a first alternative shown in more detail inFIGS.4to6, but other embodiments can be seen inFIGS.7to15.

Irrespective of the embodiment, the immobilization system20comprises a pin25that is able to move in relation to the pivoting assembly12and a control30configured to request the application of the locked mode or the unlocked mode. Each mode may comprise two phases that are explained below. For example, this control30may comprise at least one cable33that is able to move in translation, at least one bellcrank, etc. The term “cable” denotes an elongate link that is, for example, non-elastic and/or is advantageously housed in a protective sheath.

The immobilization system20further comprises a passage22provided in a base21that is secured to the pivoting assembly12. For example, the base21forms a one-piece component with the cylinder13according toFIG.3.

Therefore, the pin25is outside the passage22during an unlocked phase of the unlocked mode, so as to give the pivoting assembly12total freedom of movement in rotation about the pivot axis AXP.

Conversely, the pin25is arranged in the passage22during the locked phase of the locked mode shown inFIG.3, so as to prevent the pivoting assembly12from rotating about the pivot axis AXP. The freedom of movement in rotation of the pivoting assembly about the pivot axis AXP is then restricted to an operating clearance. The pin25is then able to move slightly in the passage22in azimuth relative to the pivot axis AXP.

Furthermore, the immobilization system20has an elastic locking system40, that is activated indirectly by the control30during the locked mode, to tend to push the pin25into the passage22in this locked mode. Starting from the unlocked mode, the method of the disclosure thus comprises activating the control30in order to switch to the locked mode, then, if the pin25is in line with the passage22, moving the pin25into the passage22to reach the locked phase. If the pin25is not in line with the passage22, the elastic locking system40presses the pin25against the base21during an armed phase, then moves the pin25into the passage22as soon as the pin25comes into line with the passage22.

Moreover, the immobilization system20comprises an elastic unlocking system50that is activated indirectly by the control30during the unlocked mode, in order to make the pin25exit the passage22and thus release the pivoting assembly12. The elastic unlocking system50is configured to allow the pin25to be extracted from the passage22only when there is a shearing force less than a threshold between the base21and the pin25. Starting from the locked mode, the method of the disclosure thus comprises activating the control30in order to switch to the unlocked mode, then, if the pin25is in the passage22and in contact with the base21, compressing an elastic unlocking system50during a disarmed phase. The pin25is kept in the passage22as long as this pin25is subject to a shearing force greater than or equal to a threshold. However, as soon as the pin25is subject to a shearing force less than the threshold, the elastic unlocking system50expands and ejects the pin25out of the passage22in order to switch to an unlocked phase.

According to the first alternative ofFIGS.3to10, the pin25is able to move in translation in relation to the base21along a translation axis AXT, for example parallel to the pivot axis AXP. The passage22can then be a bore in the base21.

The immobilization system20therefore comprises a hollow support60. This support60comprises a tubular guide that extends towards the base21, along the translation axis AXT, from an end wall61of this support60to an open end62of this support60. As a result, the open end62is located, along the translation axis AXT, between the end wall61and the base21.

The pin25then extends partially into the support60, at least during the locked phase. Irrespective of the variant of the first alternative, the pin25comprises a head26that slides in the support60, being guided by the tubular guide. Moreover, the pin25comprises a locking rod27secured to the head, and therefore connected to the head. This locking rod27emerges through the open end62of the support60, at least during the locked phase, so as to be able to enter the passage22in the base21. For safety, the locking rod27may comprise a weak-link region270. The locking rod27may also be guided by a guide secured to the base.

In these conditions, the elastic locking system40is arranged between the end wall61and the head26. The elastic locking system40may possibly be fastened to the end wall61. For example, the elastic locking system40may comprise an elastic block or a locking spring41having a coil42fastened to the end wall61in a conventional manner.

According to the first variant of the first alternative ofFIG.3, the support60is able to move in translation in relation to the base21along the translation axis AXT. For example, the support60slides in a guide secured to the stand11.

The control30is connected to the support60in order to move this support from a first position POS1requesting the application of the unlocked mode to a second position POS2requesting the application of the locked mode. For example, the control30comprises a handle31or an equivalent, or indeed a linear actuator or the like, linked by a cable33to the support60and, for example, to the end wall61. The cable33can slide in a rigid sheath32.

Furthermore, the elastic unlocking system50is arranged between the head26and an inner shoulder63of the support60. The inner shoulder63is situated between the head26and the base21. The locking rod27passes through this inner shoulder63and the elastic unlocking system50. For example, the elastic unlocking system50is fastened to the inner shoulder63, or comprises an elastic block or an unlocking spring51having a coil52fastened to the inner shoulder63.

FIGS.3to6illustrate the operation of the first variant of the first alternative.

In the locked phase ofFIG.3, the support60is pushed into the second position POS2by the control30. The pin25is arranged partially inside the passage22. The elastic locking system40and the elastic unlocking system50are slightly compressed in order to hold the pin25in position, i.e., to prevent the pin25from moving in translation relative to the support60under the effect of vibrations, for example.

In reference toFIG.4, a pilot can operate the control30in order to switch to the unlocked mode. The support60is moved to the first position POS1by being moved away from the base21in the direction shown by the arrow F2. A distance DIS between the end wall61and the base21increases. The elastic locking system40is then at rest, being neither compressed nor extended. The elastic locking system40possibly no longer touches the pin25, this elastic locking system40being carried by the end wall61.

If the pivoting assembly12is slightly out of axial alignment, the base21bears against the pin25, as shown in FIG.4. The base21exerts a shearing force on the pin25. If there is a shearing force greater than or equal to a threshold between the base21and the pin25, the pin25does not move. The translational movement of the support60then compresses the elastic unlocking system50. This elastic unlocking system50is calibrated so as not to cause the pin25to move in translation in these conditions. Indeed, the elastic unlocking system50is calibrated to allow the pin25to be extracted from the passage22only when there is a shearing force less than this threshold between the base21and the pin25. The immobilization system20is then in an innovative disarmed phase. For example, the elastic unlocking system50is defined to prevent unlocking when the lateral thrust F1is 20% greater than the thrust threshold enabling the pivoting assembly to pivot about the pivot axis AXP when this pivoting assembly is not pivotally locked.

In reference toFIG.5, as soon as the shearing force between the base21and the pin25drops below the threshold, the elastic unlocking system50expands. With the support60rendered immobile by the control30, the elastic unlocking system50exerts a force on the pin25to make it exit the passage22. The immobilization system20is then in an unlocked phase.

Depending on the relative position of the pin25and the base21when the unlocked mode is activated, the immobilization system20can switch directly from the locked phase to the unlocked phase.

From this point, a pilot can operate the control30in order to switch to the locked mode. The support60is moved to the second position POS2by being moved towards the base21in the direction shown by the arrow F3inFIG.6. The distance DIS between the end wall and the base21decreases.

If the pin25is aligned with the passage22, the immobilization system20can switch to the locked phase ofFIG.3. If this is not the case, and in reference toFIG.6, the pin25comes into contact with the base21. The translational movement of the support60then compresses the elastic locking system40. In contrast, the elastic unlocking system50is at rest, being neither compressed nor extended. The elastic unlocking system50possibly no longer touches the pin25, this elastic unlocking system50being retained by the inner shoulder63. The immobilization system20is then in an armed phase enabling it to automatically enter the locked phase when the pin25is in line with the passage22.

FIGS.7to10show a second variant of the first alternative. In reference toFIG.7, the support60is now stationary in relation to the stand11, for example being secured to the stand11.

In addition to the head26and the locking rod27referred to above, the pin25comprises an entry rod28that is also secured to the head26, i.e., connected to the head. The locking rod27and the entry rod28are situated to either side of the head26along the translation axis AXT. The entry rod28also passes through the end wall61so as to extend partially out of the support60.

The entry rod28therefore cooperates with the control30and the elastic unlocking system50. This entry rod28may comprise a top29carrying a tube70. The control30may comprise a cable33that passes through a wall of the tube to reach a plate71that is guided in translation in the tube70. The cable33may be linked to a handle, or to an output shaft35of an actuator34controlled by a human-machine interface, for example.

The elastic unlocking system50may be arranged between said wall72and the plate71. The elastic unlocking system50may comprise a spring or an equivalent, such as an elastic block, for example, made from elastomer, for example. The stiffness of the elastic unlocking system50along the translation axis AXT may be greater than the stiffness of the elastic locking system40along the translation axis.

In the locked phase ofFIG.7, the cable33is moved towards the base21or released. The plate71is then arranged as close as possible to the base21in a locked position POS3. The elastic locking system40and the elastic unlocking system50are possibly slightly compressed in order to hold the pin25, i.e., to prevent the pin25from moving unduly under the effect of vibrations, for example.

In reference toFIG.8, a pilot can operate the control30in order to switch to the unlocked mode. The plate71moves upwards to the unlocked position POS4. If the pivoting assembly12is slightly out of axial alignment, the base21bears against the pin25. The base21exerts a shearing force on the pin25. If there is a shearing force greater than or equal to a threshold between the base21and the pin25, the pin25does not move. The translational movement of the plate71then compresses the elastic unlocking system50. The immobilization system20is then in an innovative disarmed phase.

In reference toFIG.9, as soon as the shearing force between the base21and the pin25drops below the threshold, the elastic unlocking system50expands and exerts a force on the pin25to make it exit the passage22. The immobilization system20is then in an unlocked phase.

Depending on the relative position of the pin25and the base21when the unlocked mode is activated, the immobilization system20can switch directly from the locked phase to the unlocked phase.

From this point, a pilot can operate the control30in order to switch to the locked mode. The plate71is moved to the position locked POS3by being moved towards the base21.

If the pin25is aligned with the passage22, the immobilization system20can switch to the locked phase ofFIG.7. If this is not the case, and in reference toFIG.10, the pin25comes into contact with the base21. The translational movement of the pin25relative to the support60then compresses the elastic locking system40. In contrast, the elastic unlocking system50is at rest, being neither compressed nor extended, the cable33possibly being able to be braced. The immobilization system20is then in the armed phase.

FIGS.11to15show a second alternative comprising a pin25that is able to rotate in relation to the base, in particular. In reference toFIG.12, the pin25can enter the passage22formed by a radial notch in the base21.

According toFIG.11, the pin25is carried by a lever75pivotally connected to the stand11. The elastic locking system40is then arranged between the stand11and the lever75.

Moreover, the control30comprises a cable33connected to a panel76that is able to move in translation in a guide77. The elastic unlocking system50is arranged between the panel76and a partition78of the guide77through which the cable33passes. The cable33may be linked to a handle as in the example shown, or to an actuator, for example, possibly via one or more bellcranks.

The guide77is then secured to the lever75.

In the locked phase ofFIG.11, the cable33is pulled by the lever75or released. The panel76is then arranged as close as possible to the lever75in a locked position POS5. The elastic locking system40and the elastic unlocking system50are possibly slightly compressed. The lever75pivots to position the pin25in the passage22.

In reference toFIG.13, a pilot can operate the control30in order to switch to the unlocked mode. The panel76is moved to the unlocked position POS6. If the pivoting assembly12is slightly out of axial alignment, the base21bears against the pin25. The translational movement of the panel76then compresses the elastic unlocking system50. The immobilization system20is then in an innovative disarmed phase.

In reference toFIG.14, as soon as the shearing force between the base21and the pin25drops below the threshold, the elastic unlocking system50expands and exerts a force on the guide77that pivots the lever75, making the pin25exit the passage22. The immobilization system20is then in an unlocked phase.

From this point, a pilot can operate the control30in order to switch to the locked mode. The panel76is controlled to be moved once more to the position locked POS5. If the pin25is aligned with the passage22, the immobilization system20can switch to the locked phase ofFIG.11. If this is not the case, the pin25comes into contact with the base21. The lever75then compresses the elastic locking system40. The immobilization system20is then in the armed phase shown inFIG.15.

Naturally, the present disclosure is subject to numerous variations as regards its implementation. Although several embodiments are described above, it should readily be understood that it is not conceivable to identify exhaustively all the possible embodiments. It is naturally possible to replace a described means with equivalent means without going beyond the ambit of the present disclosure.