Assembly for an aircraft

Abstract

An assembly for maintaining a pitch angle of a flight control surface of an aircraft is disclosed. The assembly includes a shaft including a thread and defining an axis of the shaft; and a nut. The nut includes: a housing; a barrel located in the housing and including threads for engaging with the threads of the shaft; and at least one locking element, the at least one locking element being located in the housing. The housing includes a radially inner cam surface adjacent the locking element. The barrel is configured to rotate relative to the housing when the threads of the barrel engage with and rotate with the threads of the shaft, thereby moving the locking element along the cam surface from a disengaged position, in which the locking element is spaced from the threads of the shaft, to an engaged position, in which the locking element is wedged between the threads of the shaft and the housing, as a result, relative rotation between the shaft and the housing is prevented.

Description

Technical Field

[0001] The present disclosure relates to an assembly for maintaining the pitch angle of a flight control surface of an aircraft, and preferably a trimmable horizontal stabilizer of an aircraft, and more particularly to a secondary nut for use with such an assembly. Background Art

[0002] Horizontal stabilizers are used on aircraft to maintain the longitudinal balance (or trim) of the aircraft in flight. Trimmable horizontal stabilizers allow the pitch angle of the horizontal stabilizer to be adjusted and are widely used in the aviation industry. They effectively change or maintain the pitch angle of the aircraft during flight and help maintain a stable flight altitude. Trimmable horizontal stabilizers also help reduce the drag applied by the tail section of the aircraft.

[0003] The pitch angle of the trimmable horizontal stabilizer can be adjusted using at least one actuator, referred to as a trimmable horizontal stabilizer actuator ("HSTA") or a trimmable horizontal stabilizer actuator ("THSA"). The actuator is located in the fuselage or body of the aircraft, or in the tail section of a T-tail configuration. The actuator is part of a mechanism that includes a generally vertically disposed threaded shaft and a nut that engages the shaft and the trimmable horizontal stabilizer. Each trimmable horizontal stabilizer extends into the fuselage of the aircraft (e.g., through a slot in the fuselage) to attach to a nut of the actuator. The trimmable horizontal stabilizer may also be rotatably connected to the fuselage via a hinge connection. In operation, the actuator rotates the shaft, which causes the nut to translate vertically along the shaft, thereby pivoting the trimmable horizontal stabilizer about the hinge connection to adjust the pitch angle of the trimmable horizontal stabilizer.

[0004] Since the horizontal stabilizer is integral to maintaining the balance of the aircraft, it is important to still provide a structural link between the shaft and the trimmable horizontal stabilizer in the event of failure of the primary load path (provided by the primary nut). The structural link may be provided by a secondary nut (providing a secondary load path) that engages the shaft in the event of failure of the primary load path (e.g., in the event of a primary nut breaking).

[0005] In known arrangements, the secondary nut can engage or lock onto the shaft by creating a friction torque between the threads of the nut and the threads of the screw shaft (e.g., using a clamp mechanism). In such arrangements, the friction torque depends on factors such as the axial load applied to the nut by the horizontal stabilizer, which axial load depends on external forces applied to the horizontal stabilizer, and the friction torque may rely on other components such as a spring box to apply friction. Such arrangements rely on a certain amount of load applied to the horizontal stabilizer in order to trigger the locking mechanism and offset the drive motor torque. This can be problematic when the actuator is not significantly loaded, such as during cruise. Other known arrangements rely on sensors to sense when the primary load path fails to trigger engagement of the secondary nut with the shaft. However, such arrangements are complex and rely on the proper operation of the computer systems and sensors involved.

[0006] The present invention aims to improve the mechanism by which the secondary nut engages the shaft, making the mechanism more reliable and less dependent on the aerodynamic loads applied to the horizontal stabilizer. It should also be noted that although the present invention is presented in connection with a trimmable horizontal stabilizer, it can be used in connection with other control surfaces such as aircraft flaps or aircraft slats. Summary of the invention

[0007] According to one aspect of the invention, there is provided an assembly for maintaining the pitch angle of a flight control surface of an aircraft, the flight control surface being preferably a trimmable horizontal stabilizer, the assembly comprising: a shaft including threads and defining an axis of the shaft; and a nut including: a housing; a barrel located in the housing and including threads for engaging with threads of the shaft; and at least one locking element located in the housing, wherein the housing comprises a radially inner cam surface adjacent to the locking element, and the barrel is configured to rotate relative to the housing when the threads of the barrel engage with the threads of the shaft and rotate with the threads of the shaft, thereby moving the locking element along the cam surface from a disengaged position to an engaged position, in which the locking element is spaced apart from the threads of the shaft, and in which the locking element is wedged between the threads of the shaft and the housing, thereby preventing relative rotation between the shaft and the housing, and optionally increasing the drive torque to a level sufficient to stop an actuator configured to rotate the shaft. Such a nut provides a more reliable locking mechanism than known arrangements. This is at least in part because the operation of the locking mechanism depends on the torque applied by the actuator, rather than the force applied by the flight control surface. The locking mechanism is particularly strong because the friction locking the nut in place increases as the torque applied by the actuator increases (even if the aerodynamic forces applied to the flight control surface are small). The locking mechanism is also completely mechanical and does not rely on any sensors or actions by the aircraft's pilot or computer systems, further increasing its reliability.

[0008] According to another aspect of the present invention, there is provided a nut for maintaining the pitch angle of a flight control surface (and preferably a trimmable horizontal stabilizer) of an aircraft, the nut comprising: a housing; a barrel located in the housing, the barrel having a thread; and a locking element, wherein the locking element is configured to move from a disengaged position to an engaged position when the thread of the barrel engages with the thread of a shaft, wherein in the engaged position, the locking element is wedged between the thread of the shaft and the housing.

[0009] According to another aspect of the present invention, there is provided an assembly for maintaining the pitch angle of a flight control surface, the flight control surface preferably being a trimmable horizontal stabilizer, the assembly comprising: a shaft, the shaft comprising threads and defining an axis of the shaft; and a nut, the nut comprising: a housing, wherein the nut housing is configured to be connected to the flight control surface, for example, by a universal joint; a barrel, the barrel being located in the housing and comprising threads for engaging with the threads of the shaft; and at least one locking element, the at least one locking element being located in the housing, wherein the housing comprises a radially inner cam surface adjacent to the locking element, and the barrel being configured to rotate relative to the housing when the threads of the barrel engage with the threads of the shaft and rotate with the threads of the shaft, thereby moving the locking element along the cam surface from a disengaged position to an engaged position, wherein the disengaged position is spaced apart from the threads of the shaft, and wherein the engaged position is wedged between the threads of the shaft and the housing, thereby preventing relative rotation between the shaft and the housing, and optionally increasing the drive torque to a level sufficient to stop the actuator. The actuator may be configured to rotate the shaft. Such a nut provides a more reliable locking mechanism than known arrangements. This is at least in part because the operation of the locking mechanism depends on the torque applied by the actuator, rather than the force applied by the flight control surface. The locking mechanism is particularly strong because the friction locking the nut in place increases as the torque applied by the actuator increases (even if the aerodynamic forces applied to the flight control surface are small). The locking mechanism is also completely mechanical and does not rely on any sensors or actions by the aircraft's pilot or computer systems, further increasing its reliability.

[0010] The shaft base including the non-rotating portion of the actuator may be configured to be connected to the fuselage, such as by a universal joint, so that when the shaft rotates relative to the nut, the nut moves vertically relative to the fuselage to change the pitch angle of the flight control surface.

[0011] The following optional features may apply to any of the above aspects:

[0012] The barrel may include at least one radial opening, and the opening may be in the form of at least one slit. The at least one locking element may be located in the at least one radial opening. The slit may be configured to allow the locking element to radially translate to an engagement position from a disengaged position relative to the barrel so that the locking element is driven to rotate by the barrel when the barrel rotates. This provides a robust and reliable device for transferring movement between the barrels to the at least one locking element.

[0013] The cam surface may comprise an indentation formed in a radially inner surface of the housing adjacent the locking element such that when the cartridge is rotated relative to the housing, the roller is urged radially inwardly towards the threads of the shaft.

[0014] The indentation may be formed by a concave surface. The specific shape of the indentation may vary and may be optimised to ensure a self-locking function as described below. This provides a simple and effective means for moving the locking element into an engaged position in a controlled manner.

[0015] The indentation may include three concavities, the central concavity of which is deeper than the two adjacent concavities. This particular shape is advantageous because the nut can remain locked when the torque applied by the actuator is released. This feature also helps to reduce the risk of chatter during operation because any play between the nut and the shaft can be eliminated by this feature.

[0016] The locking element may be a roller. This allows the locking element to roll easily along the cam surface. A roller means that the locking element will move in a particular direction when rotated, allowing it to effectively translate along the cam surface.

[0017] The assembly may further comprise at least one biasing member configured to bias the locking element towards the cam surface. This helps ensure that the locking element will effectively travel along the cam surface during the locking step, and also helps avoid contact between the at least one locking element and the threads of the shaft when the threads of the barrel are disengaged from the threads of the shaft (i.e. outside the locking step). This helps avoid unnecessary wear of the at least one locking element.

[0018] The assembly may also include a plurality of locking elements distributed circumferentially around the barrel. The plurality of locking elements may include two rows of locking elements. The at least one biasing member may engage with a continuous locking element. The plurality of locking elements helps provide a robust and reliable assembly even under high load conditions because the plurality of locking elements will distribute the applied torque over a larger surface area.

[0019] The at least one biasing member may comprise a leaf spring. A leaf spring is particularly suitable for this purpose as it is simple to produce and will effectively maintain a constant distance between the locking elements so as to bias the locking elements outwardly towards the cam surface. The leaf spring is also easy to produce and fit between the locking elements.

[0020] The threads of the barrel may be ACME threads.

[0021] The assembly may include at least one bearing axially located between the barrel and the housing. In such an arrangement, the axial end of the barrel may include a series of blind holes, and the at least one bearing (e.g., a ball bearing) is disposed in a corresponding blind hole. The assembly may preferably include at least two axial bearings, each axial bearing being located on two opposite axial sides of the barrel.

[0022] The cam surface can be shaped so that the locking element can move from the disengaged position to the engaged position as the barrel rotates in two opposite rotational directions. This allows the nut to be effective regardless of the direction of torque applied to the shaft by the actuator. This eliminates the need for more than one secondary nut in the assembly.

[0023] According to another aspect of the present invention, there is provided a component for changing and maintaining the pitch angle of a flight control surface of an aircraft, the component comprising a component for maintaining the pitch angle of a flight control surface of an aircraft according to any one of the above items, wherein the nut is a secondary nut, and the component comprises a main nut threadedly engaged with a shaft and an actuator, the actuator being configured to rotate the shaft or the main nut so that the shaft and the nut translate relative to each other when the actuator rotates, and the secondary nut being configured to engage with the shaft of the component when the main nut fails. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Various embodiments will now be described, by way of example only, and with reference to the accompanying drawings, in which:

[0025] Figure 1 A schematic diagram showing an assembly for changing and maintaining the pitch angle of a trimmable horizontal stabilizer when installed on an aircraft;

[0026] Figure 2 A cross-sectional view showing a secondary nut, a portion of a primary nut and a portion of a shaft of an assembly for maintaining a pitch angle of a trimmable horizontal stabilizer according to the present invention;

[0027] Figure 3 Shows Figure 2 A perspective view of the barrel and locking element of the secondary nut is shown;

[0028] Figure 4 Shows Figure 2 A cross-sectional view of the secondary nut and shaft shown;

[0029] Figure 5 Shows Figure 2 A close-up cross-sectional view of a portion of a secondary nut and shaft is shown, the secondary nut having a housing providing an indentation having a concave profile;

[0030] Figure 6 A close-up cross-sectional view of a portion of another embodiment of a secondary nut and shaft is shown, the secondary nut providing indentations having a wavy profile; and

[0031] Figure 7 A close-up cross-sectional view of a portion of another set of nuts with a compression spring between locking elements is shown. DETAILED DESCRIPTION

[0032] First reference Figure 1 , an assembly 3 for changing and maintaining the pitch angle of a trimmable horizontal stabilizer 7 of an aircraft is shown. The assembly 3 comprises a shaft 6, a primary nut 4 (preferably a ball nut) and a secondary nut 2. The primary nut 4 comprises a thread (not shown) which engages with a thread 32 of the shaft 6, preferably via a plurality of ball members (not shown). The shaft 6 may extend generally vertically and may be connected at its upper or lower end to an actuator 9, preferably an electric or hydraulic actuator, which is configured to rotate the shaft 6, preferably via a gear assembly (not shown). The shaft base 5 is connected to an upper support universal joint (not shown), which in turn is pivotally fixed at a fixed position to a part of a rudder section, a fuselage section or a tail section (more generally, a reference structure) of the aircraft.

[0033] The trimmable horizontal stabilizer 7 may be pivotally connected via a pivot structure 15, which is fixed to a rudder section or a fuselage tail section (not shown) of the aircraft. The front end of the trimmable horizontal stabilizer 7 may in turn be pivotally connected to a drive universal joint (not shown), which in turn is pivotally connected to the main nut 4.

[0034] To selectively set the position of the trimmable horizontal stabilizer 7, the pilot, by operating the internal control unit, will control the actuator 9 to rotate the shaft 6, which will move the main nut 4 along the shaft 6 to pivot the front end of the trimmable horizontal stabilizer 7. The actuator 9 can be rotated in two opposite directions to move the main nut 4 up or down relative to the aircraft, and thereby the trimmable horizontal stabilizer 7 can be rotated to the desired position. When this happens, the assembly 3 can pivot at the fixed support universal joint and pivot at the movable drive universal joint to accommodate the angular arc displacement of the front end of the trimmable horizontal stabilizer 7.

[0035] Figure 2 A cross-sectional view of an assembly 1 for maintaining the pitch angle of a trimmable horizontal stabilizer according to the invention is shown. Figure 2 The assembly 1 shown may form part of an assembly 3 for changing and maintaining Figure 1 The pitch angle of the horizontal stabilizer 7 can be trimmed as shown.

[0036] The assembly 1 comprises a secondary nut 2, a primary nut 4 (a portion of which is shown) and a shaft 6 (a portion of which is also shown). The section is taken through the central or longitudinal axis 8 of the shaft 6.

[0037] As mentioned above, the actuators for the trimmable horizontal stabilizer are typically located in the fuselage or body of the aircraft and in the tail section thereof. The actuator 9 may be an electric motor or a hydraulic actuator and is part of a mechanism for changing the pitch angle of the trimmable horizontal stabilizer. The description provided below assumes that there is a trimmable horizontal stabilizer having two sides, each side extending laterally out of opposite sides of the fuselage, but it should be understood that the same assembly can be used to change the pitch angle of any flight control surface, such as any suitable number (e.g., two) of stabilizers.

[0038] The actuator 9 is configured to rotate the shaft 6, which can be arranged generally vertically. The shaft base including the non-rotating portion of the actuator can be configured to be connected to the fuselage, for example, by a universal joint. The portion of the trimmable horizontal stabilizer 7 that extends through the fuselage (not shown) is connected to the nut of the assembly, for example, by a universal joint. In normal operation, the trimmable horizontal stabilizer is attached to the main nut of the actuator, for example, by a universal joint, to provide a main load path between the trimmable horizontal stabilizer and the mechanism. The trimmable horizontal stabilizer is also pivotally connected to the fuselage via a hinge connection. In such operation, the main nut engages with the shaft 6, and the actuator is configured to rotate the shaft 6, which causes the main nut to translate vertically along the shaft 6, thereby pivoting the trimmable horizontal stabilizer around the hinge connection to adjust the pitch angle of the trimmable horizontal stabilizer. In other embodiments, the shaft and actuator can be configured to move more than the trimmable horizontal stabilizer, for example, the shaft and actuator can be configured to rotate two horizontal trimmable actuators.

[0039] Figure 2 The secondary nut 2 is shown engaged with the shaft 6. As described below, the secondary nut 2 is configured to engage with the shaft 6 using a locking mechanism in the event of failure of the primary nut. The secondary nut 2 includes a trunnion 10 for connecting to a connecting element of the trimmable horizontal stabilizer, such as a strut, so that the trimmable horizontal stabilizer can pivot relative to the nut and translate with it. In other embodiments, the trimmable horizontal stabilizer can be directly connected to the nut and the strut may not be present.

[0040] The secondary nut 2 includes a housing 12 and a barrel 14 disposed in the housing. The barrel 14 has a series of circumferentially spaced slots 16 for receiving a plurality of locking elements 18 in the form of rollers. The housing 12 can be configured to be connected to a trimmable horizontal stabilizer. Such a connection can be provided by at least one trunnion of the housing 12. The connection between the housing 12 and the trimmable horizontal stabilizer prevents the housing from rotating about the axis 6.

[0041] Figure 3 A perspective view of a barrel 14 and rollers 18 is shown. Each slot 16 extends through the entire thickness of the barrel 14 (thickness defined in the radial direction). Each roller 18 is disposed in a corresponding slot 16 so that the roller 18 can rotate about its axis and translate radially relative to the barrel 14. Each roller 18 can be retained in a corresponding slot 16 without being rigidly attached to the barrel 14 to allow the roller 18 to rotate about its axis and translate radially relative to the barrel 14. In the embodiment shown, there are two rows of axially spaced rollers 18, with eight rollers 18 in each row. However, the exact number is not important, and in other embodiments, there may be more or fewer rows of rollers, or more or fewer numbers of rollers in each row. For example, there may be a single row of rollers, or more than two rows of rollers.

[0042] Figures 3 to 6 Leaf springs 20 are shown placed between successive rollers. Each leaf spring 20 may be retained in a corresponding cavity 22 in the outer surface 24 of the barrel 14. The leaf springs 20 are configured to hold the barrel in place in the housing via the rollers and to radially hold the rollers 18 in place. In this position, there is a gap 48 between the rollers and the threads 32 of the shaft 6. This helps to hold the rollers 18 in their corresponding slots 16 in the barrel 14 to prevent contact between the rollers 18 and the shaft 6 during normal operation (i.e., the primary load path that has not failed) and to provide stability to the structure. Leaf springs 20 are not required. For example, in other embodiments, such as Figure 7 As shown, the roller 18 may be held circumferentially in position using a compression spring 26 or any other resilient element or preloading device suitable for applying a load to the roller in a radially outer direction of the drum.

[0043] Another function of placing a spring (e.g., a leaf spring) between the rollers 18 is to hold the drum 14 in position relative to the housing 16. This is because the spring acts to push the rollers 18 radially outward so that they contact the radially inner surface of the housing 16, thereby creating friction and preventing the drum 14 from rotating in normal operation (i.e., outside of the locking step).

[0044] Although springs are advantageous because they firmly hold rollers 18 in radial position and help maintain gap 48, springs are not necessary and may not exist in other embodiments. In such embodiments, rollers 18 may be loosely held in corresponding slots 16.

[0045] Figure 3The radial inner surface 28 of the barrel 14 is shown, which includes threads 30. The threads 30 of the barrel 14 are configured to engage with threads 32 of the shaft 6. The threads 30 of the barrel 14 include raised portions 29, which together follow a spiral path. The raised portions 29 are separated by slots 16 at circumferential positions. A channel 31 is formed between the raised portions 29, which also follows a spiral path. The threads 32 of the shaft 6 and the threads 30 of the barrel 14 can each be in the form of an ACME thread.

[0046] like Figure 2 and Figure 3 As shown, the barrel 14 is disposed in the radially inner portion of the housing 12. Each axial end 34, 36 of the barrel 14 has a corresponding thrust bearing 13. In this embodiment, each thrust bearing 13 includes a series of blind holes 38 located on each axial end 34, 36 of the barrel 14 for receiving a corresponding ball bearing 40. However, the thrust bearings can be of any suitable configuration, for example, the thrust bearings can include tapered rollers instead of ball bearings, or the series of blind holes 38 can be replaced by cylindrical slots for receiving ball bearings. Figure 2 As shown, the barrel 14 extends axially between the axial surface 11 of the housing 12 at one end and the cap 42 at the other end to prevent the barrel 14 from moving axially. The cap 42 may be present to ensure that a seal is provided in the secondary nut 2 to prevent lubricant leakage. However, the cap 42 is not required, and in other embodiments, for example, the barrel 14 may be axially held in place by another surface of the housing 12.

[0047] Figure 4 A cross-sectional view of the secondary nut 2 and the shaft 6 is shown, the section being taken perpendicular to the longitudinal axis 8 of the shaft 6, and Figure 5 A close-up view (in the same cross section) of the secondary nut 2 and a portion of the shaft 6 is shown.

[0048] like Figures 4 to 7 As shown, the radially inner portion 45 of the housing 12 has a cam surface 43 that includes a plurality of indentations 44, each indentation 44 being adjacent to a respective roller 18. Figure 5 As shown, when the secondary nut 2 is in the disengaged or unlocked position (i.e. during normal operation where the primary nut provides a load path), each roller 18 will be located at its deepest position, and in this case, in the central portion 46 of the indentation 44. This means that there is a gap 48 between the roller and the threads 32 of the shaft 6.

[0049] Thus, in normal operation, when the primary load path / primary nut is active, the primary nut holds the secondary nut 2 in position such that the threads 30 of the secondary nut 2 do not engage with the threads 32 of the shaft 6. In this position, the threads 30 of the secondary nut 2 are spaced apart from the threads 32 of the shaft 6 such that the threads 30 of the secondary nut 2 do not contact with the threads 32 of the shaft 6. This spacing is possible, for example, because the helical raised portion 29 of the threads 30 of the secondary nut 2 has a smaller axial width than the helical channel 33 of the threads 32 of the shaft 6, so that the helical raised portion 29 of the threads 30 can be retained in the channel 33 with axial clearance on either side of the raised portion 20. In such a position, the secondary nut 2 is in an unlocked position, and since the secondary nut 2 is connected to the primary nut, the secondary nut will translate axially during operation of the actuator without the need for the secondary nut 2 to engage with the threads 32 of the shaft 6. This avoids unnecessary wear of the secondary nut 2 during normal operation.

[0050] When the primary load path fails, the threads 32 of the shaft 6 engage the threads 30 of the barrel 14 of the secondary nut 2. Failure of the primary nut 4 may occur for a variety of reasons, such as failure of the trunnion of the primary nut 4, or failure of the bolts of the primary nut 4.

[0051] The assembly 1 is configured such that upon failure of the primary nut 4, the primary nut 4 no longer holds the secondary nut 2 in place, such that the threads 30 of the secondary nut 2 are not engaged with the threads 32 of the shaft 6. This may occur, for example, due to a pin (e.g., a shear pin) connecting the primary nut 4 to the secondary nut 2 breaking upon failure of the primary nut 4. Once the connection between the primary nut 4 and the secondary nut 2 is broken, the secondary nut 2 may be axially displaced such that the threads 30 of the secondary nut 2 are engaged with the threads 32 of the shaft 6. For example, an axially facing surface of the threads 30 of the secondary nut 2 may contact a corresponding axially facing surface of the threads 32 of the shaft 6.

[0052] Once the primary load path fails, the threads 32 of the shaft 6 engage with the threads 30 of the barrel 14. Due to this engagement, when the shaft 6 is rotated by the actuator, the friction between the threads 32 of the shaft 6 and the threads 30 of the barrel 14 causes the barrel 14 to rotate relative to the housing 12 and the cap 42 (if present). The bearings 40 at the axial ends 34, 36 of the barrel 14 are configured to allow the barrel 14 to rotate relative to the housing 12 and the cap 42. The bearings 40 are not required, for example, there can be sliding contact between the barrel 14 and the housing 12 and the cap 42 instead of the bearings 40. For example, the sliding contact between the barrel 14 and the housing 12 and the cap 42 can be provided by anti-friction rings (e.g., PTFE, ceramic), self-lubricating rings, or anti-friction coatings applied to the barrel and / or housing interface surfaces.

[0053] As the drum 14 rotates relative to the housing 12, each roller 18 moves along its corresponding indentation 44 (see Figure 5) runs circumferentially. The profile of the indentation 44 is shaped so that when the roller 18 moves circumferentially, the roller 18 is pushed radially inwardly toward the thread 32 of the shaft 6. This reduces the gap 48 between the roller and the thread 32 of the shaft 6, which will continue to exist until the roller 18 contacts the thread 32 of the shaft 6.

[0054] In the locked position, the roller 18 is wedged between the radial inner surface of the housing 12 (at the periphery of the indentation 44) and the threads 32 of the shaft 6. This creates friction between the roller, the barrel 14 and the housing 12, and prevents the barrel 14 from rotating relative to the housing 12. In this way, the secondary nut 2 is in the locked position. In the locked position, the barrel 14 is prevented from rotating relative to the housing 12. Under both the primary load path condition and the secondary load path condition, the housing is prevented from rotating about the shaft 2 due to the connection of the housing 12 to the trimmed horizontal stabilizer. Under the secondary load path condition (when the primary load path fails), the trimmed horizontal stabilizer is prevented from rotating because the secondary nut 2 is in the locked position and is prevented from translating along the shaft 6. This is because the roller 18 is wedged between the threads 32 of the shaft 6 and the housing 12, thereby preventing both rotation of the shaft 6 and translation of the secondary nut 2.

[0055] Means may also be provided for monitoring the device and informing the pilot that the primary load path has failed and / or the secondary load path has engaged. These means may detect if the primary load path has failed by detecting a stall of the motor. Once a failure of the primary load path is detected, the actuator may be instructed to maintain the torque applied by the motor. This may help the secondary nut 2 to move into a locked position. This feature is also useful for reducing the risk of chattering, as it may eliminate any play between the secondary nut 2 and the shaft 6.

[0056] The indentations 44 extend along the length of the roller in the axial direction. Figures 4 to 7 As shown, the indentation 44 is generally concave.

[0057] In specific embodiments, more specific cross-sectional shapes can be provided. For example, Figure 6 As shown, the indentation 44 can have a wavy cross-section 49. In this arrangement, the cross-section includes three concave surfaces with peaks defined between each concave surface. In such an arrangement, the central concave surface is deeper than the two adjacent concave surfaces so as to provide an integral indentation 44. In normal operation, the roller 18 can be seated in the central concave surface. When the secondary nut 2 is then moved to a locked configuration, the roller 18 can move through one of the peaks into one of the shallower concave surfaces. This particular shape is advantageous because the secondary nut 2 can remain locked when the torque applied by the actuator is released. This feature can also be used to reduce the risk of vibration when operating through the secondary load path because it can eliminate any play between the secondary nut 2 and the shaft 6.

[0058] Locking elements 18 in the form of rollers (which are cylindrical) are advantageous because they can easily roll in the circumferential direction while providing sufficient surface contact due to their length, allowing them to withstand high loads. However, the use of cylindrical rollers is not necessary, and alternative locking elements configured in the same manner, such as spherical locking elements, can be provided. In the case of spherical locking elements, the locking elements can be assembled in a plurality of radially extending circular openings formed in the barrel, which can be arranged circumferentially or axially offset from each other. Another possibility is to assemble a plurality of spherical locking elements in contact with each other in an elongated slot formed in the barrel in a manner similar to the slots presented in the embodiment with rollers. Even if not optimal, non-rolling locking elements, such as preload pads, can also be considered, which use the same principles as described above for rollers or spherical locking elements.

[0059] The secondary nut 2 of the present invention provides a more reliable locking mechanism than known arrangements. This is at least in part because the operation of the locking mechanism can only be triggered by rotation of the shaft and is therefore dependent on the torque applied by the actuator and not on the axial force applied by the horizontal stabilizer. The locking mechanism is particularly strong because the friction force locking the secondary nut 2 in place increases as the torque applied by the actuator increases (even if the aerodynamic forces applied to the horizontal stabilizer are small). In addition, the locking mechanism is bidirectional in that it can operate in both rotational directions of the shaft 6, regardless of the axial load applied to the nut. The locking mechanism is also completely mechanical and does not rely on any sensors or actions performed by the aircraft's pilot or computer system, further increasing its reliability.

[0060] Although an arrangement having a trimmable horizontal stabilizer connected to a primary nut and a secondary nut has been described, the benefits of the secondary nut described above can equally apply to an arrangement having a trimmable horizontal stabilizer connected to an axle base (rather than to a primary nut and a secondary nut), for example, by a universal joint, the axle base including a non-rotating portion of the axle actuator. In such an arrangement, the primary and secondary nuts remain stationary relative to the aircraft fuselage, and when the actuator rotates the axle, the axle moves vertically relative to the primary and secondary nuts. The trimmable horizontal stabilizer is attached to the axle base, and when the axle rotates, the trimmable horizontal stabilizer will move vertically relative to the primary and secondary nuts to change the pitch angle of the stabilizer. In such an arrangement, if the primary nut fails, the secondary nut will engage the axle in the same manner as described above.

[0061] In yet another embodiment, the primary nut may be rotatably driven by an actuator, and the shaft is configured to translate relative to the primary nut and secondary nuts when the primary nut rotates. In this case, the nut base including the non-rotating portion of the nut actuator is connected to the trimmable horizontal stabilizer and the shaft is connected to the aircraft fuselage in a manner similar to the first presented arrangement, or the shaft is connected to the trimmable horizontal stabilizer and the nut base including the non-rotating portion of the nut actuator is connected to a stationary component of the aircraft (e.g., the fuselage).

[0062] Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the present invention as set forth in the following claims.

Claims

1. An assembly for maintaining a flight control surface of an aircraft, preferably maintaining a pitch angle of a trimmable horizontal stabilizer, the assembly comprising: a shaft including threads and defining a shaft axis; as well as A nut, comprising: case; a barrel located in the housing and including threads for engaging the threads of the shaft; and at least one locking element, the at least one locking element being located in the housing, wherein: The housing includes a radially inner cam surface adjacent the locking element, and The barrel is configured to rotate relative to the housing when the threads of the barrel engage with the threads of the shaft and rotate as the threads of the shaft rotate, thereby causing the locking element to move along the cam surface from a disengaged position, in which the locking element is spaced apart from the threads of the shaft, to an engaged position, in which the locking element is wedged between the threads of the shaft and the housing, thereby preventing relative rotation between the shaft and the housing.

2. The assembly of claim 1, wherein the barrel comprises at least one radial opening, optionally at least one slot, and the at least one locking element is located in the at least one radial opening.

3. The assembly of claim 1 or 2, wherein the slot is configured to allow radial translation of the locking element relative to the barrel from the disengaged position to the engaged position.

4. An assembly according to any preceding claim, wherein the cam surface comprises an indentation formed in a radially inner surface of the housing adjacent the locking element so that when the barrel is rotated relative to the housing, the locking element is urged radially inwardly towards the threads of the shaft. The assembly of claim 4 , wherein the indentation is formed by a concave surface.

6. The assembly of claim 4, wherein the indentation comprises three concavities, a central concavity among the concavities being deeper than two adjacent concavities.

7. An assembly according to any preceding claim, wherein the locking element is a roller.

8. An assembly according to any preceding claim, further comprising at least one biasing member configured to bias the locking element towards the cam surface.

9. An assembly according to any preceding claim, comprising a plurality of locking elements distributed circumferentially around the barrel.

10. An assembly according to claim 9, comprising two rows of locking elements.

11. An assembly according to claim 9 or 10 when appended to claim 8, wherein the at least one biasing member engages with a continuous locking element.

12. The assembly of claim 11, the at least one biasing member comprising a leaf spring.

13. An assembly according to any preceding claim, comprising at least one bearing located axially between the barrel and the housing, optionally wherein the axial end of the barrel comprises a series of blind holes, the at least one bearing being a spherical bearing and each of the at least one bearing being disposed in a respective blind hole.

14. An assembly according to any preceding claim, wherein the cam surface is shaped so that the locking element can move from the disengaged position to the engaged position as the cartridge is rotated in two opposite rotational directions.

15. An assembly for changing and maintaining the pitch angle of a flight control surface of an aircraft, the assembly comprising: An assembly for maintaining the pitch angle of a flight control surface of an aircraft according to any preceding claim, wherein the nut is a secondary nut; a main nut, the main nut being engaged with the threads of the shaft; as well as An actuator is configured to rotate the shaft or the primary nut so that the shaft and the primary nut translate relative to each other when the actuator rotates, and the secondary nut is configured to engage the shaft of the assembly when the primary nut fails.

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