Rotary actuator for an aircraft

Abstract

A rotary actuator 40 for a folding aircraft wing having a plurality of hinge elements 42, 44 arranged along a length of a hinge axis 46, each comprising a circumferential body portion (43, 45 figure 2

Description

FIELD OF THE INVENTION This invention relates to rotary actuators for aircraft, in particular geared rotary actuators for providing a powered hinge for a folding wing tip of an aircraft wing. Such a rotary actuator may also be used for any movable surface or structure of an aircraft, such as flight control surfaces, which can be moved relative to a fixed part of the aircraft. BACKGROUND TO THE INVENTION Aircraft wings may be provided with a folding wing tip part or outer wing structure, for example such that the wing tip may be retracted to reduce the span of the aircraft wings on the ground, or for movement in flight for example to change the wing shape and / or the aerodynamic characteristics of the wing. Such folding wing tips are generally required to be lockable or latchable in place, either whilst in flight or whilst on the ground. Many different aircraft, including military and commercial aircraft, having a folding wing section or tip make use of a geared rotary actuator (GRA) or 'power hinge' as part of the joint mechanism positioned between a fixed part of the wing and a movable or folding part. These take the form of a hinge mechanism having multiple sections or 'slices' along the length of a hinge axis, which each comprise a fixed hinge element attachable to the fixed part of the wing, and a movable hinge element attachable to the movable part of the wing. The fixed and movable hinge elements may be arranged alternately along the length of the hinge axis. The elements may each be provided with a connector such as flange extending from the element for mounting to the respective wing structure, for example using bolts. Rotary movement of the movable elements relative to the fixed elements about the hinge axis provides relative movement between the movable and fixed wing sections. The GRA is commonly arranged along a hinge line which extends generally chord-wise between the fixed wing part and the movable wing part. Where the wing is relatively thin with a relatively long chord, such as for many military aircraft, a suitable GRA can generally be accommodated within the wing profile. However, where the wing has a shorter chord to thickness ratio, or for high aspect ratio wings with a long span and relatively short chord, such as in the case of a commercial aircraft wing, the shape of the GRA (being essentially rectangular in longitudinal cross-section) is not well suited to accommodation within the wing profile. This means that a GRA of a suitable size, which may have associated equipment, may extend beyond the wing profile, necessitating the use of a fairing on the outside of the wing to cover any protruding parts. A fairing will involve additional cost and will also likely increase drag. This is inefficient aerodynamically and in terms of material use and cost. This invention aims to alleviate this issue. SUMMARY OF THE INVENTION According to the present invention, there is provided a rotary actuator for a folding aircraft wing, the actuator having a plurality of hinge elements arranged along a length of a hinge axis, the hinge elements each comprising a circumferential body portion and a connector portion, the hinge elements comprising a plurality of fixed elements for attachment to a fixed wing part by means of the connector portion, and a plurality of movable hinge elements for attachment to a movable wing part by means of the connector portion, wherein the circumferential body portion of at least one of the hinge elements has an outer radial size which is different from the outer radial size of the circumferential body portion of at least one other of the hinge elements, such that the axial cross-sectional size of the actuator varies along the length of the hinge axis. This allows the axial cross-sectional size of the actuator to be matched more closely to the wing profile, and thus may improve the ease of integration of a multi-element GRA into a short chord commercial aircraft wing. The provision of a multi-slice GRA with a cross section which varies along its length may allow it to be housed in a smaller space, and be tailored to the wing profile. Such tighter packaging of the actuator has drag (and therefore fuel-burn) benefits, as the requirement for a fairing may be reduced or eliminated. Indeed, the actuator may itself provide an outer aerodynamic surface of the wing. The manufacture of any fairing is an additional cost, which can also be reduced if the size of the fairing is reduced. Conveniently, the connector of the or each fixed hinge element extends radially in a first direction and the connector of the or each movable hinge element extends radially in a second direction, the actuator being operable to vary the angular spacing between the first and second directions, in order to provide movement of the movable wing part in use. For example, the connector of each hinge element may comprise at least one flange extending from the circumferential body portion, the or each flange being bounded by at least one edge extending tangentially from the body portion. This is convenient for attachment to the wing section, since the edge may extend substantially parallel with a surface of the wing section. Preferably, the axial cross-section of the actuator has a substantially curved profile along the length of the actuator. For example, the outer radial size of the body portion of at least one hinge element positioned at or adjacent one or both ends of the actuator is smaller than the outer radial size of the body portion of at least one adjacent hinge element positioned towards the centre of the actuator. This allows the shape of the actuator to be more sympathetic with the shape of the wing profile. In particular, the diameters may be tailored to reduce the volume at one end of the actuator, which may be used at the front of the wing profile. The fixed hinge elements and the moveable hinge elements are preferably arranged alternately along the hinge axis. The number of hinge elements may be selected according to design requirements. Optionally, at least one of the actuator elements comprises at least one other element arranged along the hinge axis which is not a hinge element. For example, the at least one other element comprises at least one of a latching element for latching and locking the actuator against rotation, and a power interface arranged to transfer power across the actuator elements. Thus the hinge elements may be axially spaced apart. The actuator may comprise a drive shaft arranged to be operated by a motor, the drive shaft being arranged to cause movement of the movable elements relative to the fixed elements. The drive shaft may comprise a sun gear shaft, the actuator comprising a plurality of planetary gear shafts arranged between the sun gear shaft and the hinge elements. The hinge elements may each comprise a ring gear arranged to engage the planetary gears, the ring gear being arranged on an inner surface of the circumferential body portion of each hinge element. Thus the invention also provides an aircraft wing comprising a fixed part and a movable part, and a rotary actuator as defined above, the actuator being arranged between the fixed part and the movable part and being arranged to cause relative movement of the movable part with respect to the fixed part. For example, the fixed part may be a main body of the wing, and the movable part may be a folding wing tip. The outer radial sizes of body portions of the hinge elements may be arranged such that the axial cross-sectional size of the actuator has a shape arranged to fit closely with the profile of at least one of the upper and lower surfaces of the wing. In particular, the axial cross-sectional size of the actuator may be arranged to fit closely with the profile of the upper surface of the wing. This allows minimal if any fairing on the upper surface of the wing, which is more important aerodynamically than the lower surface of the wing. The invention may also provide an aircraft comprising an actuator as defined above, or a wing as defined above. Input rotation can be provided to the actuator by a drive means such as a motor (not shown) that drives an input shaft. This causes rotation of the gears of the actuator which results in relative rotary movement between the first and second sections. BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made by way of example to the accompanying drawings, in which: Figure 1 is a perspective view of a conventional geared rotary actuator according to the prior art; Figure 2 is a schematic perspective view of an actuator according to an embodiment positioned in a wing section; Figure 3 is a side view of the actuator of Figure 2; Figure 4 is an end view of the actuator of Figure 2; Figure 5 is a plan view of the actuator of Figure 2; and Figures 6A and 6B are front views of an aircraft having folding wingtips. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS. Referring to Figure 1, a conventional geared rotary actuator 2 comprises a plurality of hinge elements comprising a plurality of relatively fixed elements 4 and a plurality of relatively movable elements 6. These are arranged alternately along a hinge axis 8. The elements 4, 6 each have a generally circular inner body portion 10, 12. Flanges 16, 14 extend radially outwardly from one edge of each body portion 10,12, with the flanges 16 extending from the fixed elements 4 radially in one direction and the flanges 14 extending from the movable elements 6 radially in an opposing direction. In this example, each element 4, 6 has a pair of attachment flanges 16, 14 for securing to a structure within the aircraft wing. Referring to the fixed element 4, each of the pair of flanges 16 is substantially planar and includes a pair of lobes 22 each provided with an aperture 24 for receiving a bolt. In this way, the fixed elements 4 can each be secured to a structure within a fixed part of the wing. In a similar manner, each movable element 6 has a pair of flanges 14 which are also planar having a pair of lobes 18 having apertures 20 for receiving a bolt. In this way, the movable elements 6 can each be secured to a structure within a movable part of the wing, such as a folding wing tip. The elements 4, 6 each have a flattened profile 26, 28 along opposing sides corresponding to the upper and lower edges of the actuator. In association with the upper and lower edge surfaces of the flanges 14,16, these provide a surface which sits within or adjacent the upper and lower profile of the wing, and can be shaped to correspond with the wing surfaces. A sun gear 30 extends along the inside of the actuator, and operates planetary gears 32 for meshing with gear teeth provided on an inner surface of the body 12 of each of the movable elements to provide relative movement between the fixed and movable elements 6. The sun gear 30 is connected to a power drive unit for turning the sun gear to actuate the hinge, and latching or locking features may also be provided to retain the hinge in a required position; for example folded or in-line. Various arrangements exist for the layout of the GRA, power drive units and latching and locking features. In use, the actuator is mounted chordwise within the wing profile, along a hinge line extending across the wing profile, between a fixed part of the wing and a movable part such as a wing tip. However, the shape of the actuator is not well suited to a wing profile with a relatively high thickness to chord ratio. This is because the actuator is substantially rectangular in longitudinal cross-section, whereas the wing profile or aerofoil shape has a thickness which varies significantly from the leading to the trailing edge of the wing. Figure 2 shows a wing profile or aerofoil 34 typical of a commercial aircraft. It can be seen that a conventional actuator with constant longitudinal cross section fitted within such a wing profile would have to have a relatively small radial size, leading to considerable space above and below the upper and lower surfaces thereof where the thickness of the wing is larger, in order to be accommodated in those parts of the wing profile at the leading and trailing edges 36, 38, which are thinner. This is an inefficient use of space, and would also lead to the power of such an actuator being correspondingly compromised. If a larger actuator is used, the actuator would extend outside of the wing profile at least in some areas. This leads to a requirement for a fairing structure protruding from the wing, which is undesirable in terms of cost and aerodynamic efficiency. Referring also to Figure 3, the actuator 40 has elements of varying radial sizes in order to mitigate this issue. The actuator 40 has a plurality of fixed hinge elements 42, in this example numbering six, and a plurality of movable hinge elements 44, in this example numbering five (shown hatched in opposite directions for clarity). The fixed and movable hinge elements 42, 44 are arranged alternately along a longitudinal hinge axis 46 of the actuator 40, and are separated by other elements in the form of bearing elements 48. As can also be seen in Figures 4 and 5, in a similar manner to the actuator shown in Figure 1, the hinge elements 42, 44 each comprise a circumferential body portion 43, 45 having a substantially circular axial cross-sectional shape. The body portions 43, 45 each form a ring gear, with gear teeth (not shown) provided on an inner surface thereof in a known manner and as described above in relation to Figure 1. Since the radial size or diameter of the body portions may vary, as described in more detail below, each ring gear may have a different number of gear teeth compared to the ring gear of an adjacent body portion, as required. Substantially circular bearing parts 48 are substantially aligned with circumferential body portions 43, 45 and separate the elements 42, 44. The fixed elements 42 each have at least one flange 50 extending radially in a first direction from one side of the body portion for attachment to, for example, a structure provided on a fixed wing part. The movable elements 44 each have a flange 52 extending in a second direction for attachment to a structure on a movable wing part. In the position of the actuator shown in the drawings, being an aligned position of the hinge, which corresponds to a position in which the fixed and movable parts of the wing are aligned with each other, the second direction is opposed to the first direction. The flanges 50, 52 are substantially planar, extending along an axial plane, and have upper and lower edges 51, 53 which have a flattened profile. The flattened edges extending in a substantially tangential direction from the circular body portion 43,45 of each element, so as to form a substantially smooth planar upper edge surface of each element. This is convenient for fitting within the profile of the upper and lower surfaces of the wing, and attaching to the wing structure. Whilst not shown in Figures 2 to 5, the actuator 40 may be operable in a conventional manner as described above in relation to Figure 1. Thus the ring gear of each of the hinge elements 42, 44 may be operated by planet gears surrounding a sun gear shaft extending along the hinge axis 46. The sun gear shaft may be operated by at least one power unit 62, 68 provided at one or both ends of the actuator having an input shaft for connection to the sun gear shaft, in a known manner. The power unit or units 62, 68 can also include a braking function. Whilst two power units can be provided for redundancy of the joint articulation, alternatively there may be a single power unit at one end of the actuator, and a latching and locking unit at the other end, or a combination thereof. In more detail, as can also be seen from Figure 3, the actuator comprises a first slice 54 having a relatively small diameter a, a second slice 56 having a relatively larger diameter b, a third slice 58 having a still larger diameter c, and a fourth slice 60 having a smaller diameter d similar to that of the second part. The diameter of each slice corresponds to the outer radial size of the circumferential body portions of the hinge elements. Thus it can be seen that the actuator 40 has a substantially 'curved' profile which is more similar to the envelope of the wing profile 34 than a conventional rotary actuator of substantially rectangular profile. In particular, the volume of the actuator may be reduced at the front of the wing profile 34. Although the actuator 40 is shown in the drawings oversized compared to this particular wing profile 34, it can be seen that the diameters of the actuator elements can be adjusted more closely to match the curvature of the wing upper surface 33, lower surface 35, or both surfaces. This can lead to a more sympathetic fairing shape, should a fairing be required. In this example the first, second and fourth parts 54, 56, 60 each comprises one movable element 544, 564, 604, arranged between two fixed elements 546a, 546b, 566a, 566b, 606a, 606b. The third and largest part 58 comprises two movable elements 584 arranged between three fixed elements 586a, 586b. The fixed elements at the end of each section 54-60 which borders another section have a smaller width. These elements may optionally each be attached to the fixed element at the end of the adjacent section, depending on operational requirements, effectively providing a single fixed element with a compound thickness. For example, the first fixed element 546a at a first end of the first section 54 has a first thickness a, and a width which is around half of that of the full width of the first movable element 544 in the first section 54. The second fixed element 546b at a second end of the first section 54 also has a first thickness a, and a first width, and is attached to a third fixed element 566a at a first end of the second section 56, which also has a first width and has a second thickness b. The second and third fixed elements 546b, 566a therefore form a compound fixed element together having a full width which is similar to the full width of each movable element. Bearings 48 provided between each fixed and movable element also have diameters corresponding to the thickness a, b, c, d, of each section 54, 56, 58, 60. Other components can be included in the actuator in addition to or instead of the bearings, either between the elements or at one or both ends of the actuator. For example, a latching or locking mechanism for latching or locking the joint in position may be provided, and / or an interface to transfer power across the joint may be included in the actuator. Referring to Figures 6A and 6B, the actuator may be used for actuating a folding wingtip of an aircraft 80. The wings 82 of the aircraft 80 may comprise a fixed part 84 forming a main body of the wing 82, and a movable part 86 forming a wingtip. A rotary actuator 88 may be positioned along a hinge line which extends substantially chord-wise, between the fixed part 84 of the wing 82 and the wingtip 86. As can be seen from Figure 6A, the wingtip 86 may have a folded position in which it extends an angle to the main body 84 of the wing, commonly extending upwardly. As shown in Figure 6B, the wingtip 86 also has an extended position in which it extends substantially in line with the main body 84 of the wing 82. The rotary actuator 88 may be operated to move the wingtip 86 between these two positions, for example so as to reduce the wingspan of the aircraft 80 when on the ground and / or to change the aerodynamic characteristics of the wings 82 in flight. The actuator of the invention is not restricted to use for a folding wing tip, but may also be used for any movable surface or structure of an aircraft, such as flight control surfaces, which can be moved relative to a fixed part of the aircraft.

Claims

1. A rotary actuator for a folding aircraft wing, the actuator having a plurality of hinge elements arranged along a length of a hinge axis, the hinge elements each comprising a circumferential body portion and a connector portion, the hinge elements comprising a plurality of fixed elements for attachment to a fixed wing part by means of the connector portion, and a plurality of movable hinge elements for attachment to a movable wing part by means of the connector portion, wherein the circumferential body portion of at least one of the hinge elements has an outer radial size which is different from the outer radial size of the circumferential body portion of at least one other of the hinge elements, such that the axial cross-sectional size of the actuator varies along the length of the hinge axis.

2. An actuator as claimed in claim 1, wherein the connector of the or each fixed hinge element extends radially in a first direction and the connector of the or each movable hinge element extends radially in a second direction, the actuator being operable to vary the angular spacing between the first and second directions.

3. An actuator as claimed in claim 1 or 2, wherein the connector of each hinge element comprises at least one flange extending from the circumferential body portion, the or each flange being bounded by at least one edge extending in a substantially tangential direction from the body portion.

4. An actuator as claimed in claim 1, 2 or 3, wherein the axial cross-section of the actuator has a substantially curved profile along the length of the actuator.

5. An actuator as claimed in claim 4, wherein the outer radial size of the body portion of at least one hinge element positioned at or adjacent one or both ends of the actuator is smaller than the outer radial size of the body portion of at least one adjacent hinge element positioned towards the centre of the actuator.

6. An actuator as claimed in any preceding claim, wherein the fixed hinge elements and the moveable hinge elements are arranged alternately along the hinge axis.

7. An actuator as claimed in any preceding claim, wherein at least one of the actuator elements comprises at least one other element arranged along the hinge axis which is not a hinge element.

8. An actuator as claimed in claim 7, wherein the at least one other element comprises at least one of a latching element for latching and locking the actuator against rotation, and a power interface arranged to transfer power across the actuator elements.

9. An actuator as claimed in any preceding claim, comprising a drive shaft arranged to be operated by a motor, the drive shaft being arranged to cause movement of the movable elements relative to the fixed elements.

10. An actuator as claimed in claim 9, wherein the drive shaft comprises a sun gear shaft, the actuator comprising a plurality of planetary gear shafts arranged between the sun gear shaft and the hinge elements.

11. An actuator as claimed in claim 10, wherein the hinge elements each comprise a ring gear arranged to engage the planetary gears, the ring gear being arranged on an inner surface of the circumferential body portion of each hinge element.

12. An aircraft wing comprising a fixed part and a movable part, and a rotary actuator as claimed in any preceding claim, the actuator being arranged between the fixed part and the movable part and being arranged to cause relative movement of the movable part with respect to the fixed part.

13. An aircraft wing as claimed in claim 12, wherein the fixed part is a main body of the wing and the moveable part is a folding wing tip, the outer radial sizes of body portions of the hinge elements being arranged such that the axial cross-sectional size of theactuator has a shape arranged to fit closely with the profile of at least one of the upper and lower surfaces of the wing.

14. An aircraft wing as claimed in claim 13, wherein the axial cross-sectional size of the5 actuator is arranged to fit closely with the profile of the upper surface of the wing.

15. An aircraft comprising an actuator as claimed in any one of claims 1 to 11, or a wing as claimed in claim 12, 13 or 14.1013

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