There is provided an aerofoil comprising an inboard section, a tip section moveable between a flying configuration and a parked configuration, a hinge shaft mounted at a compound angle in the inboard section, a fixed gear mounted concentrically on the hinge shaft and a drive gear coupled to the tip section and configured to mesh with the fixed gear, wherein a rotation of the drive gear against the fixed gear causes the tip section to rotate about the hinge shaft between the flying configuration and the parked configuration.

This application is the U.S. national phase of International Application No. PCT/GB2010/051760 filed 19 Oct. 2010 which designated the U.S. and claims priority to GB 0919019.0 filed 30 Oct. 2009, the entire contents of each of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to an aerofoil. Particularly, but not exclusively, the invention relates to an aerofoil comprising a rotary hinge unit to allow movement of a portion of the aerofoil between flying and parked configurations, and a rotary clamping unit to lock the aerofoil in the flying configuration.

BACKGROUND TO THE INVENTION

It is well understood that the fuel efficiency and aerodynamic performance of an aircraft is dependent on wingspan. It is therefore important to ensure that all aircraft are manufactured with their optimum wingspan.

For passenger aircraft, a limit on wingspan is set by the physical characteristics of gates at airport terminals. Such gates have historically accommodated aircraft with a maximum wingspan of thirty-six meters, meaning that aircraft with wingspans exceeding the thirty-six meter limit are generally unable to taxi to the gate. This makes larger wingspan aircraft much less practical than the smaller aircraft currently in use.

Modification of airport terminals to accommodate larger wingspan aircraft would be both expensive and disruptive. It would also necessarily lead to a corresponding reduction in the number of aircraft which could be accommodated simultaneously at the terminal, and therefore a reduction in overall airport capacity. As such, another solution must be found in order to improve the practicality of larger wingspan aircraft.

One proposal has been to provide large wingspan aircraft with a “piano-hinge” at the tip end of the wing, allowing the wing tip to be folded upwards from a horizontal configuration to a vertical configuration upon landing. This is shown inFIG. 1. In the vertical configuration, the wingspan of the aircraft is reduced so that the aircraft can access restricted size terminal gates.

However, it will be appreciated that the proposed piano-type hinge requires a significant amount of torque to be exerted in order to lift the wing tip out of the horizontal configuration. Providing such a large torque requires the wing to be equipped with a high-torque lifting means. High-torque lifting means of this type are heavy, and therefore their inclusion undesirably adds significant weight to both the wing and the aircraft. Furthermore, because the torque required to lift the wing tip rapidly reduces as the tip moves towards the vertical configuration, the high-torque capability of the lifting means is wasted for all but the initial phase of the lift. This proposal is therefore both extremely inefficient and heavy.

Whilst the vertical configuration of the wing described above may provide the potential for a large wingspan aircraft to access a restricted size airport gate, it is obviously crucial that the wing does not enter the vertical configuration when the aircraft is in flight. Previous folding wing designs have addressed this issue by employing a simple “shot-bolt” clamp to lock the wing tip in the horizontal configuration. It will be appreciated that a small amount of clearance is required in such “shot bolt” clamps in order to allow the shot bolt to slide freely when the clamp is to be engaged/disengaged. This clearance allows a small amount of play within the clamp which, although relatively small in the clamp itself, can translate to a relatively large movement at the tip of the wing due to the distance between the tip and the clamp. This can cause the wing tip to flutter during flight, which is extremely undesirable.

The natural vibration of the wing during flight causes the components of the clamps to wear relatively quickly, especially if the wing tip has begun to flutter. This increases the amount of play within the clamp. As the wear becomes significant, large and potentially dangerous wing tip movements are observed during flight meaning that, in order to maintain aircraft safety, it is necessary to replace the clamp on a frequent basis.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided an aerofoil comprising an inboard section, a tip section moveable between a flying configuration and a parked configuration, a hinge shaft mounted at a compound angle in the inboard section, a fixed gear mounted concentrically on the hinge shaft, and a drive gear coupled to the tip section and configured to mesh with the fixed gear, wherein a rotation of the drive gear against the fixed gear causes the tip section to rotate about the hinge shaft between the flying configuration and the parked configuration.

The aerofoil may further comprise a free gear mounted concentrically on the hinge shaft and configured to mesh with the drive gear.

The free gear may comprise a reaction gear configured to balance cantilever loads exerted by the drive gear.

The fixed gear, drive gear and free gear may respectively comprise first, second and third bevel gears.

The hinge shaft may be mounted on an inner frame in the inboard section.

The drive gear may be mounted on a drive shaft extending from the tip section to the hinge shaft.

The drive gear may be coupled to a driving means mounted in the tip section, the driving means being configured to rotate the drive gear against the fixed gear.

An upper end of the hinge shaft may be tilted from a vertical axis in both a longitudinal and a chordal direction to create the compound angle.

The upper end of the hinge shaft may be tilted towards the tip section in the longitudinal direction and towards a trailing edge of the aerofoil in the chordal direction.

A rotation of the tip section between the flying configuration and the parked configuration may comprise a rotation of substantially ninety degrees about both a chordal axis of the aerofoil and a longitudinal axis of the aerofoil.

According to a second aspect of the invention, there is provided an aerofoil comprising an inboard section, a tip section moveable between a flying configuration and a parked configuration, a hinge shaft mounted at a compound angle in the inboard section, a drive gear mounted concentrically on the hinge shaft and a fixed gear coupled to the tip section and configured to mesh with the drive gear, wherein rotation of the drive gear against the fixed gear causes the tip section to rotate about the hinge shaft between the flying configuration and the parked configuration.

According to a third aspect of the invention, there is provided an aerofoil comprising an inboard section, a tip section moveable between a flying configuration and a parked configuration and a clamp unit configured to lock the tip section in the flying configuration, the clamp unit comprising a ramped slot and a clamp head configured to move along the slot until a frictional engagement corresponding to a locked configuration of the clamp unit is reached.

The clamp unit may further comprise an actuator configured to move the slot with respect to the clamp head until the frictional engagement between the slot and clamp head causes a predetermined torque limit of the actuator to be reached.

The clamp unit may comprise an actuator configured to move the clamp head with respect to the slot until the frictional engagement between the slot and the clamp head causes a predetermined torque limit of the actuator to be reached.

The slot may comprise an arcuate slot formed in a rotatably mounted plate, and the actuator may be configured to rotate the plate with respect to the clamp head to enter the locked configuration of the clamp unit.

The clamp head may have a T-shaped cross section and the slot may have a T-shaped cross-section configured to accommodate the clamp head.

The slot may comprise an entrance hole having a diameter larger than a maximum diameter of the clamp head to allow the clamp head to enter the slot.

The clamp unit may further comprise a bolt means, configured to block the entrance hole to prevent disengagement of the clamp head and the slot.

The clamp unit may further comprise a ratchet configured to prevent disengagement of the clamp head and the slot.

The ratchet may be configured to allow the slot to rotate with respect to the clamp head in a locking direction, whilst preventing the slot from rotating with respect to the clamp head in an unlocking direction.

The ratchet may be configured to allow the slot to rotate with respect to the clamp head such that the entrance hole moves away from the clamp head, whilst preventing the slot from rotating with respect to the clamp head such that the entrance hole moves towards the clamp head.

The ratchet may be released to allow disengagement of the clamp head and the slot, thereby allowing the aerofoil to enter the parked configuration.

The aerofoil may comprise a transparent window in a skin of the aerofoil to allow ground crew to inspect the relative positions of the clamp head and the slot in the locked configuration of the clamp unit.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the invention will now be described with reference toFIGS. 2 to 26of the accompanying Figures.

Referring toFIG. 2, an aerofoil100may consist of an aircraft wing100for use on an aircraft such as a jet airliner. The aircraft wing100comprises an inboard section200, which includes a root210for securing the wing100to a fuselage of an aircraft. The wing100also comprises a tip section300, which is located at the outer end of the wing100and may comprise one or more ailerons at its trailing edge.FIG. 2shows the wing100in a flying configuration, in which the inboard section200and the tip section300are aligned in substantially the same geometric plane.

The inboard section200and the tip section300are coupled together at a hinge unit400, which is configured to allow movement of the tip section300between the flying configuration and a parked configuration in which the wingspan of the aircraft is reduced. An example of a transitional position between the flying configuration and the parked configuration of the wing100is shown inFIG. 3. The parked configuration of the wing100is shown inFIG. 4. The transition between the flying configuration and the parked configuration of the wing100may involve a dual rotational movement, in which the tip section300of the wing100rotates substantially 90 degrees through two perpendicular axes of rotation. The geometric plane of the tip section300in the parked configuration may be substantially ninety degrees to the fixed geometric plane of the inboard section200.

As is shown inFIGS. 2 to 4, a first aspect of a transition from the flying configuration to the parked configuration may be a rotation of a longitudinal axis XT, which runs lengthways along the tip section300, through ninety degrees. This may involve a transition from an orientation substantially parallel to a fixed longitudinal axis XI(seeFIG. 16) of the inboard section200to an orientation substantially parallel to a longitudinal axis along the length of the fuselage of the aircraft.

A second aspect of the transition from the flying configuration to the parked configuration may be a rotation of a chordal axis YT, which runs across the width of the tip section300, through ninety degrees. This may involve a transition from an orientation substantially parallel to the longitudinal axis of the fuselage of the aircraft to an orientation substantially perpendicular to both the longitudinal axis of the fuselage and the longitudinal axis XIof the inboard section200of the wing100. The longitudinal axis XTand chordal axis YTof the tip section300may be substantially horizontal and vertical respectively when the wing100is in the parked configuration.

It will be appreciated that the movement of the tip section300from the flying configuration shown inFIG. 2to the parked configuration shown inFIG. 4significantly reduces the wingspan of the aircraft. This may enable a large wingspan aircraft to be accommodated at a size restricted airport gate.

Referring toFIGS. 5 to 10, the hinge unit400may comprise an inner frame410which is immovably fixed in position relative to the inboard section200of the wing100. For example, the inner frame410may be securely mounted inside an outer end portion of the inboard section200at the inboard section's outer end face. This may be achieved by securing the inner frame410to heavy structures within the inboard section200of the wing100, such as front and rear spars (not shown). Optionally, a bridging spar (not shown) may extend transversely between the front and rear spars and the inner frame410may be secured to the bridging spar at a desired location. The inner frame410may comprise a fixed-position J-shaped or U-shaped primary structure411, which is oriented in the inboard section of the wing100such that it presents an open end towards the tip section300. This is illustrated inFIG. 11.

A hinge shaft420may be connected across the open end of the primary structure411and fixed in position such that it cannot rotate with respect to either the primary structure411or the inboard section200of the wing100. For example, the hinge shaft420may be securely mounted to the ends of first and second arms412,413of the U-shaped primary structure411. The hinge shaft420may be equipped with a free gear430and a fixed gear440, which are respectively rotatable and non-rotatable with respect to the hinge shaft420. The free gear430may alternatively be referred to as a reaction gear430, as will be explained below. Each of the gears430,440may be concentrically aligned with the axis of the hinge shaft420and mounted at a fixed position such that neither gear430,440is free to slide axially along the hinge shaft420.

The free gear430and fixed gear440may respectively comprise first and second bevel gears430,440, which are substantially equivalent in size with corresponding helical/spiral, involute tooth profiles. The gears430,440may be concentrically aligned with one another on the hinge shaft420. The gears430,440may also oppose each other, such that the tooth profile of the first bevel gear430faces that of the second bevel gear440along the axis of the hinge shaft420. A gap may be provided between the mounted positions of the first and second bevel gears430,440to allow the gears430,440to simultaneously mesh with a driving gear460, as is described in more detail below. A cross-sectional shape of the gap may be a flat-bottomed “V” or conical shape, in which the sloping sides of the “V” are formed by the first and second bevel gears430,440and the flat base of the “V” is formed by a circumferential surface of the hinge shaft420. This is clearly shown inFIG. 10.

The free bevel gear430may be mounted on a lower portion of the hinge shaft420(i.e. closer to the underside of the wing100), and may be freely rotatable with respect to both the hinge shaft420and the inboard section200of the wing100. The fixed bevel gear440may be mounted on an upper portion of the hinge shaft420(i.e. closer to the upper face of the wing100), and fixed in position such that it cannot freely rotate with respect to either the hinge shaft420or the inboard section200of the wing100. In an alternative configuration, the roles of the lower and upper bevel gears may be switched, such that the upper bevel gear is freely rotatable with respect to the hinge shaft210and the lower bevel gear is not.

The hinge unit400may further comprise an outer frame450which is immovably fixed in position relative to the tip section300of the wing100. For example, as shown inFIG. 11, the outer frame450may be securely mounted inside an inner end portion of the tip section300of the wing100at the tip section's inner end face. The outer frame450may comprise a secondary U-shaped structure451oriented in the wing100such that it presents an open end toward the inner frame410. The distance between the ends of first and second arms453,454of the secondary structure451may be less than the distance between the ends of the first and second arms412,413of the primary structure411described above.

As shown inFIGS. 5 to 10, the ends of the arms453,454of the secondary structure451may be coupled to the hinge shaft420such that the hinge shaft420forms an axis about which the secondary structure451and outer frame450can rotate with respect to the inner frame410and inboard section200of the wing100. For example, the coupling between the secondary structure451and the hinge shaft420may be facilitated by ring sections452at the end of each of the arms453,454of the secondary structure451. The hinge unit400may be assembled such that the hinge shaft420passes through each of the ring sections452before being secured to the open ends of the arms412,413of the primary structure411of the inner frame410, thereby securing the inner frame410and the outer frame450together. The outer diameter of the hinge shaft420may be less than the inner diameter of the ring sections452to allow the inner and outer frames410,450to move with respect to one another about the axis of the hinge shaft420. The hinge shaft420therefore provides a hinge line about which the tip section300of the wing100can move with respect to the inboard section200of the wing100.

Referring again toFIGS. 5 to 10, the hinge unit400may further comprise a drive gear460inserted into the gap between the free gear430and the fixed gear440described above. The drive gear460may be configured to mesh with the free and fixed gears430,440to allow it to exert a driving force against the tooth profile of both of the free and fixed gears430,440. For example, as clearly shown inFIGS. 5,7and10, the drive gear460may comprise a third bevel gear460having a helical/spiral involute tooth profile substantially matching the tooth profile of the free gear430and fixed gear440. The cross-sectional shape of the bevel drive gear460may correspond to the cross sectional shape of the gap between the free and fixed gears430,440on the hinge shaft420. This allows the teeth of the drive gear460to fully engage with the teeth of the free gear430and fixed gear440.

The drive gear460may be securely mounted on an end of a drive shaft470such that the drive shaft470and the drive gear460cannot be rotated with respect to each other. The drive shaft470and drive gear460are, however, free to rotate with respect to the outer frame450and therefore also the tip section300of the wing100in which the outer frame450is immovably mounted. As shown inFIG. 5, the drive shaft may pass through a guide hole455in the secondary structure451to locate the drive shaft470on the outer frame450and ensure that the drive gear460meshes with the free gear430and fixed gear440on the hinge shaft420. The drive shaft470may be coupled to a driving means480via a drive train490to cause rotation of the drive shaft470with respect to the outer frame450. The driving means480may comprise a rotary actuator480, consisting for example of a hydraulically or electrically driven stepper unit.

The driving means480may be securely mounted in the tip section300of the wing100, for example on the outer frame450, and coupled to the drive train490to supply a driving force through the drive train490to the drive shaft470. The drive train490may comprise, for example, first and second meshing spur gears491,492having helical/spiral, involute tooth profiles. The first of the spur gears491may be directly coupled to the driving means480, and the second of the spur gears492may be directly coupled to the drive shaft470. Alternatively, as shown inFIGS. 5 to 10, the first spur gear491may be coupled to the driving means480through meshing contact with a third spur gear493which is directly coupled to the driving means480. The third spur gear may have a helical/spiral, involute tooth profile as with the first and second spur gears491,492. Referring again toFIGS. 5 to 10, the drive train490may be directly coupled to a rear of the outer frame450such that it is securely mounted inside the tip section300of the wing100.

In an exemplary operation, rotation of a hydraulic actuator480or an electric stepper motor480in the tip section300of the wing100causes a corresponding rotation of the first spur gear491through a direct drive connection. The rotation of the first spur gear491causes the driving force originating from the stepper unit480to be exerted by the teeth of the first spur gear491against the teeth of the second spur gear492, thereby causing a corresponding rotation of the second spur gear492. The rotation of the second spur gear492leads to rotation of the drive shaft470through a direct drive connection between the second spur gear492and the drive shaft470, and thereby also causing rotation of the drive gear460at the end of the shaft470.

As discussed above, the drive gear460meshes between the free and fixed gears430,440. Rotation of the drive gear460therefore exerts a driving force against the teeth of both the free gear430and fixed gear440, causing the free gear430to rotate on the hinge shaft420and the drive gear460to climb around the fixed gear440. This movement is shown by the arrows inFIG. 12. As the drive gear460rotates and climbs around the fixed gear440on the hinge shaft420, the coupling between the drive shaft470and the outer frame450at the guide hole455causes the outer frame450to follow the drive gear460around the axis of the hinge shaft420on the inner frame410. Since the outer frame450is securely mounted to the tip section300of the wing100, rotation of the drive gear460also causes the tip section300of the wing100to rotate around the axis of the hinge shaft420.

The free gear430supports the reaction load exerted by the drive gear460as it rotates around the hinge shaft420, and thereby resists the bending load applied to the cantilevered drive shaft470as the tip section300rotates.

The rotational movement of the outer frame450around the axis of the hinge shaft420is shown inFIGS. 5 to 10. For example, inFIG. 5the hinge unit400is shown in a closed position corresponding to the position shown inFIG. 11whereas, inFIG. 6, the hinge unit400is shown in an open position in which the outer frame450has been rotated around the axis of the hinge shaft420. The closed position of the hinge unit400corresponds to the flying configuration of the wing100shown inFIG. 2, and the open position of the hinge unit400corresponds to the parked configuration of the wing100shown inFIG. 4. It will be appreciated that movement of the hinge unit400between the closed and open positions causes a transition of the wing100from the flying configuration to the parked configuration.

FIGS. 7 and 8respectively show the hinge unit400in the closed and open positions described above from a different angle to the view shown inFIGS. 5and6. A further view of the closed and open positions is provided inFIGS. 9 and 10respectively. The wing100itself is not shown inFIGS. 5 to 10for the purposes of clearly representing the components of the hinge unit400. However, the hinge unit400is shown together with the wing100inFIGS. 13 to 15, which show the wing100in the flying configuration (closed position of hinge unit400), an intermediate configuration and the parked configuration (open position of hinge unit400) respectively.

It will be appreciated that, in an alternative configuration, the roles of the positions of the drive gear and fixed gear could be switched. More specifically, the drive gear may be provided concentrically on the hinge shaft420in the position of the fixed gear shown inFIGS. 5 to 12and the fixed gear may be coupled to the end of the shaft470in the tip section300in the position of the drive gear shown inFIGS. 5 to 12.

The hinge shaft420may be oriented at a compound angle within the inboard section200of the wing100to facilitate the dual rotation of the wing tip300described above. The angle of the hinge shaft420is referred to below using a Cartesian coordinate system comprising a longitudinal axis XIalong the length of the inboard section200of the wing100, a chordal axis YIacross the width of the inboard section200of the wing100and a vertical axis ZIthrough the depth of the inboard section200of the wing100. These axes are shown inFIG. 16. Starting from a position parallel with the vertical axis ZI, the hinge shaft420may be tilted in both the longitudinal XIand chordal YIdirections to provide a compound angle hinge line comprising a longitudinal tilt element and a chordal tilt element. This is described below in relation toFIG. 11. The compound angle of the hinge shaft420is described below with respect to the vertical axis ZIof the inboard section. Starting from a vertical position, the top end of the hinge shaft420closest to the upper edge of the wing100is tilted with respect to the bottom end of the shaft420both towards the trailing edge110of the wing100(chordal tilt element) and towards the tip of the wing100(longitudinal tilt element). The primary structure411may be tilted towards the trailing edge110of the wing100at the same angle. This is shown inFIGS. 5 to 12.

A corresponding tilt to that described above for the primary structure411may also apply to the orientation of the secondary structure451with respect to the longitudinal, chordal and vertical axes XT, YTand ZTof the tip section300of the wing100. The precise orientation of the hinge shaft420, the primary structure411and the secondary structure451in the wing100may be configured in dependence of the exact desired rotational movement of the tip section300.

The compound angle configuration of the hinge shaft420and secondary structure451described above ensures that the torque required to move the tip section300of the wing100between the flying configuration and the parked configuration is relatively constant over the transition. The very high torque level actuator required to perform the initial phase of lifting a piano-type hinged tip is not necessary. Instead, a less powerful, lighter and more compact driving means480can be used, which operates close to its optimum torque level over the entire movement between the flying and parked configurations of the wing100. The load on the driving means480can be reduced by reducing the gearing in the drive train490. Additionally or alternatively, the load on the driving means480can be reduced by reducing the gearing at the drive gear460or at the free and fixed gears430,440. This may allow further weight and size reductions at the driving means480.

Separation of the inboard and tip sections200,300of the wing100may be facilitated by the abutting faces of the inboard and tip sections200,300being angled appropriately. For example, at the trailing edge of the wing100, the abutting faces of the inboard and tip sections200,300of the wing100may meet each other at an angle which is approximately ninety degrees to the longitudinal tilt element of the hinge shaft420. At the leading edge of the wing100, the abutting faces of the inboard and tip sections200,300of the wing100may meet each other at an angle which is approximately equal to the chordal tilt element of the hinge shaft420. Therefore, the angle at which the abutting faces meet each other at the leading edge of the wing100may differ from the angle at which the abutting faces meet each other at the trailing edge of the wing100. As is shown byFIG. 17, in this configuration, the separation line S between the inboard and tip sections200,300may extend in a curve across the upper and lower surfaces of the wing100. A significant portion of the separation line may extend across the upper and lower faces of the wing at an acute angle with respect to the chordal axes YIand YT. The separation line S may also extend across the leading and trailing faces of the wing100at an acute angle with respect to the vertical axes ZIand ZT.

The wing100may further comprise a clamp unit500comprising an engaging means510and a receiving means520configured to accommodate the engaging means to clamp the wing100in the flying configuration. Referring toFIGS. 18 to 26, the engaging means510may comprise a catch510secured to the inboard section200of the wing100. The catch510may have an approximately T-shaped cross-section with a head511facing towards the tip section300of the wing100and a stem512extending away from the head511towards the root210of the inboard section200of the wing100. The catch510may, for example, comprise a “mushroom” shaped catch. The head511of the catch510may be referred to as the clamp head511.

The receiving means520of the clamp unit500may comprise a substantially circular plate520secured to the tip section300of the wing100, comprising an arcuate slot521configured to engage with the head511of the catch510in order to provide a lock between the catch510and the plate520. The arcuate slot521may have an approximately T-shaped cross-section substantially matching the T-shaped cross-section of the catch510, such that the catch510cannot be freely removed from the slot521when the two are locked together. More specifically, as is shown inFIGS. 22,23and26, the profile of the slot521may wrap around the profile of the head511of the catch510when the two are engaged to prevent the head511from being removed from the slot521.

Referring toFIGS. 18 and 20an entrance hole522may be provided at one end of the slot521in order to allow the head511of the catch510to enter and exit the slot521. The diameter of the entrance hole522is greater than the diameter of the head511of the catch510, such that the catch510may freely enter and exit the slot521through the entrance hole522. This is shown inFIGS. 18 to 21. The diameter of the entrance hole522may be large enough to allow the head511of the catch510to enter the hole522even when the head511and the hole522are not in perfect axial alignment. This may allow the head511of the catch510to enter/exit the entrance hole522as the tip section300of the wing100rotates towards/away from the inboard section200, into and out of the flying configuration.

Referring toFIG. 22, the slot521may comprise a narrower section524configured to accommodate the stem512of the catch510, and a wider section525configured to accommodate the head511of the catch510. The wider section525may be directly beneath the narrower section524. More specifically, the narrower section524may extend into the plate520directly away from an engagement face526of the plate520. The narrower section524may have a substantially constant width over the length of the slot521, which substantially matches the diameter of the stem512of the catch510. However, a sufficient amount of clearance may be provided to allow the stem512to slide along the path of the arcuate slot521. The depth D1of the narrower section524may vary over the length of the slot521. More specifically, the shallowest part of the narrower section524may be directly adjacent the entrance hole522and the deepest part of the narrower section524may be at the opposite end of the slot521. The depth D1of the narrower section524may increase substantially linearly as the slot521extends away from the entrance hole522. For example, the depth D1of the narrower section may increase by between 3 mm and 5 mm over the length of the slot521. This may cause the wider section525of the slot521to ramped, such that it spirals deeper into the plate520as the slot521extends away from the entrance hole522. This is explained in more detail below.

The wider section525of the slot521may lie directly beneath the narrower section524such that the stem512of the catch510can extend through the narrower section524and the head511of the catch510can be secured in the wider section525of the slot521. As with the narrower section524, the width of the wider section525may be substantially constant over the length of the slot521. However, unlike the narrower section, the specific depth D2(not shown in Figures) of the wider section525of the slot521may also be substantially constant over the length of the slot521. The depth D2may, for example, be substantially equal to the depth of the head511of the catch510, although a small amount of clearance should be provided to allow the catch510to move in the slot521.

More specifically, a front face (not shown in Figures) of the wider section525of the slot521(closest to the engagement face526of the plate520) may be substantially parallel to a rear face527of the wider section525of the slot521(furthest from the engagement face of the plate520). Therefore, the distance between the front face of the wider section525and the engagement face526of the plate520varies directly with the depth D1of the narrower section524of the slot521. Similarly, the distance between the rear face527of the wider section525and the engagement face526of the plate520varies directly with the depth D1of the narrower section524of the slot521, remaining substantially parallel with the front face of the wider section525. This causes the distances between both front and rear faces of the wider section525of the slot521and the engagement face526of the plate520to increase as the slot521extends away from the entrance hole522. The wider section525thus ramps away from the engagement face526, spiraling deeper into the plate520as the slot521extends away from the entrance hole522in a manner corresponding to the increasing depth D1of the narrower section524.

The width of the wider section524of the slot521adjacent the entrance hole522may be greater than the corresponding width of the head511of the catch510such that head511can slide along the arcuate slot521away from the entrance hole522. However, only a small clearance need be provided.

In one example, the plate520is a rotary plate coupled to a concentric spur gear523at the rear of the plate520. A driving means such as an actuator530may comprise a driving spur gear580configured to mesh with the spur gear523at the rear of the plate520. The driving means530may be configured to drive a rotation of the plate520via the spur gear523, such that the plate520rotates with respect to both the tip section300of the wing100and the catch510to lock the tip section300and inboard section200of the wing100together in the flying configuration. It should be noted that the spur gears discussed above could be replaced with spiral/helical tooth form gears or worm drive tooth form gears. More specifically, in an exemplary operation, the plate520may be mounted in the tip section300of the wing100such that the entrance hole522is aligned with the head511of the catch510in the inboard section200when the wing100is in the flying configuration. In this configuration, the head511of the catch510may enter the entrance hole522in the slot521automatically upon the wing100entering the flying configuration. The actuator530may then drive a rotation of the plate520with respect to the catch510such that the head511of the catch510slides into the wider section525of the slot521to provide a locked configuration between the tip section300and inboard section200of the wing100. The plate520may be rotated by the actuator530until the frictional contact between the deepening front face of the wider section525of the slot521and the head511of the fixed-position catch510causes a torque limit of the actuator530to be reached.

More specifically, as the plate520rotates, the ramped front face of the wider section of the slot521moves away from the fixed position of the catch510due to the fact that the front face of the wider section of the slot521is not parallel to the engagement face of the plate520. As the front face of the wider section525of the slot521ramps away from the fixed position catch510, the plate520may effectively pull the head511of the catch510against the front face of the wider section525of the slot521, thereby increasing the amount of torque that is required to continue to rotate the plate520. Once the torque limit of the actuator530is reached, the plate520ceases to rotate and the clamp unit500is locked.

As shown inFIGS. 18 to 26, a ratchet550may be provided to prevent the plate520from rotating in the opposite direction thus ensuring that the catch510does not undesirably disengage from the slot521. The ratchet550may comprise a ratchet arm551comprising a first set of ratchet teeth552. The teeth552on the ratchet arm551may engage with a second set of ratchet teeth553on a circumferential surface of the plate520. The ratchet550may allow the plate520to rotate in a locking direction, whilst preventing the plate520from rotating in an unlocking direction unless the first and second sets of teeth552,553are disengaged. This is shown inFIGS. 18 to 23. The teeth552of the ratchet arm551may be held against the teeth553on the circumferential surface of the plate520by resilient means560such as a coil spring560. Disengagement of the first and second set of teeth552,553may be facilitated by a ratchet release actuator570, comprising an actuator arm571configured to force the ratchet arm551against the spring560. When sufficient force is supplied by the release actuator570, the spring560compresses and the teeth552on the ratchet arm551are lifted away from the teeth553on the plate520.

Once the ratchet550is disengaged, the actuator530may drive a rotation of the plate520in the unlocking direction, thereby allowing the catch510to disengage from the slot521and the tip section300of the wing100to rotate out of the flying configuration.

The torque limited actuator530ensures that wear on the head511of the catch510caused by frictional contact with the front surface of the wider section of the slot521does not affect the secure connection between the plate520and the clamp510when the clamp unit500is in the locked configuration. For example, should the depth of the head511be reduced by wear, the frictional engagement between the front face of the wider section of the slot521and the catch head511will be reduced thereby allowing the torque-limited rotary actuator530to further rotate the plate520until the torque limit of the actuator530is reached again. Rotation of the plate520effectively causes the head511of the catch510to moves further around the slot521, as is shown inFIGS. 22 and 23and26. The actuator530will always continue to rotate the plate520until its torque limit is reached, thereby always providing a securely locked configuration of the clamp unit500.

This aspect of the clamp unit500ensures that a fully locked configuration is maintained in the flying configuration of the wing100even when the head511of the catch510is subject to a significant amount of wear. A transparent window may be provided in the skin of the wing100to allow ground crew to inspect the position of the catch510with respect to the slot521when the clamp unit500is in the locked configuration. When the position of the catch510in the locked configuration approaches the end of the slot521, the catch head511should be replaced.

In the locked configuration, a shot bolt540may enter the entrance hole522to ensure that there is no possibility of the head511of the clamp510becoming aligned with the entrance hole522to allow the plate520and the clamp510to disengage. The shot bolt540is clearly shown inFIGS. 18,22,23and25.FIGS. 18 and 22illustrate an unextended state of the shot bolt540, andFIG. 23illustrates the shot bolt540as being extended into the entrance hole in a “fail-safe” configuration. Both of the shot bolt540and the ratchet550may be disengaged upon landing of the aircraft, thereby allowing the plate520to rotate with respect to the catch510to disengage the clamp unit500and thereby allow the wing100to move to the parked configuration.

For increased safety, disengagement of both of the bolt540and ratchet550may be dependent upon the aircraft being on the ground. For example, a sensor may be configured to detect when a force is provided against the landing gear of the aircraft by the ground. Disengagement of the bolt540and ratchet550may be dependent upon the force experienced by the landing gear being greater than a predetermined threshold, which may be substantially equal to the weight of the aircraft, to ensure that the wing100cannot move to the parked configuration when the aircraft is in flight.

The wing100may comprise a plurality of the clamp units500described above. For example, a clamp unit500of the type described above may be provided at the abutting faces of the inboard and tip sections200,300of the wing100, proximate each of the leading and trailing edges of the wing100. The hinge unit400may be provided between them. This is shown inFIGS. 13,14and15.

In the example described above, the plate520is described as being rotated by an actuator530with respect to a fixed-position catch/clamp head511. It will be appreciated, however, than in an alternative configuration s suitable actuator could be used to drive the catch/clamp head511around the path of the slot521in the plate520. In this alternative configuration, the plate520may be secured in a fixed-position such that it is not able to rotate.

It will be appreciated that the aerofoil100described above could be used on any type of aircraft, including military aircraft, helicopters and gliders. Furthermore, although the examples discussed above describe a fixed gear on the hinge shaft and a drive gear in the tip section, it will be understood that the invention could alternatively employ a drive gear on the hinge shaft and fixed gear in the tip section.