WO2017108053A1

WO2017108053A1 - Lifting apparatus for a wind turbine blade

Info

Publication number: WO2017108053A1
Application number: PCT/DK2016/050448
Authority: WO
Inventors: Michael Kastrup; Senthil MURUGESH
Original assignee: Vestas Wind Systems A/S
Priority date: 2015-12-23
Filing date: 2016-12-20
Publication date: 2017-06-29

Abstract

A lifting apparatus (10) for a wind turbine blade (2), said apparatus comprising a cradle (12) for carrying a said blade, and a lifting yoke (14) which is cooperable with a crane, in use, to lift the cradle. The lifting yoke is mounted to the cradle and is moveable in a lengthwise direction relative to the cradle to permit adjustment of the orientation of the cradle when the yoke is suspended from a lifting point associated therewith. Said apparatus is particularly relevant for lifting and manoeuvring wind turbine blades which are particularly large and heavy and difficult to move between sites. It is one benefit of the invention that the orientation of the blade when carried in the cradle can be controlled conveniently, safely and reliably by adjusting the position of the yoke relative to the cradle.

Description

LIFTING APPARATUS FOR A

WIND TURBINE BLADE

Technical field

The invention relates to a lifting apparatus for a wind turbine blade.

Background to the invention The transport of wind turbine blades for wind farm applications is a complex process, especially because of the scale of the blades which have to be manoeuvred safely and efficiently. Typically, larger wind turbine blades can extend up to and can even exceed 70m in length and weigh in excess of 100 tonnes. The transport of such blades safely and efficiently is therefore a challenge.

Wind turbine blades are often transported between sites in a stacked arrangement but lifting the devices onto and off of the stack is awkward as it requires very careful control of the positioning of the blade. Likewise, lifting the blades for mounting to a rotor hub is an awkward process. Due to the elongate nature of the blades, it is a particular problem to manoeuvre the blades safely without them toppling and causing damage to the surroundings and to the blades themselves. Unless manoeuvring of the blades is well controlled, there may be risks posed to operating personnel.

Lifting apparatus for larger wind turbine blades is known, but has limitations. EP2589795 describes a lifting apparatus for wind turbine blades, comprising a main frame for carrying the rotor blade and a sub-frame which carries ropes with which it can be fixed to a lifting crane hook. The main frame is suspended from the sub-frame by means of two tilt wires and two pitch wires which allow the tilt and pitch, respectively, of the blade to be adjusted.

Winches serve to wind and unwind the tilt wires so that they are either coiled or uncoiled, so that the tilt angle of the rotor blade can be varied appropriately. The tension in the pitch wires determines the position of the centre of gravity of the rotor blade as it is manoeuvred, and this tension can also be adjusted.

Whilst the system permits some flexibility one problem is that the blade is lifted and manoeuvred in a vertical orientation, with its heavier end adopting a lower position relative to the lighter 'top' end. This is not always desirable for stacking purposes for transit. The winch

l system can also be difficult to control accurately as it requires adjustment of four wires to ensure the blade adopts exactly the correct alignment. There remains considerable scope for error in achieving the exact tilt and alignment that is required.

DE 102009005632 describes a similar system in which a hanging wire between the main frame (yoke) and the crane is adjusted to adjust the blade centre of gravity, vertically, in relation to the lifting crane. Similar limitations exist for this system as described previously due to the reliance on wire adjustment to adjust the blade centre of gravity. With this arrangement, accurate, safe and convenient control of the blades is therefore not readily achieved.

It is an object of the present invention to provide a lifting apparatus for an elongate object such as a wind turbine blade which aims to address or at least reduce at least one of the aforementioned problems.

Summary of the invention

According to a first aspect of the invention there is provided a lifting apparatus for a wind turbine blade, said apparatus comprising a cradle for carrying a said blade, and a lifting yoke which is co-operable with a crane, in use, to lift the cradle. The lifting yoke is mounted to the cradle and is moveable in a lengthwise direction relative to the cradle to permit adjustment of the orientation of the cradle when the yoke is suspended from a lifting point associated therewith.

In another aspect, the invention may be expressed as a method of lifting a wind turbine blade using a lifting apparatus comprising a cradle for carrying the blade, and a lifting yoke movably coupled to the cradle, wherein the method comprises: mounting the blade in the cradle; using the yoke to lift the cradle; moving the yoke in a lengthwise direction relative to the cradle so as to adjust the orientation of the blade and the cradle relative to a lifting point associated with the yoke.

The invention is particularly relevant for lifting and manoeuvring wind turbine blades which are particularly large and heavy and difficult to move between sites. It is one benefit of the invention that the orientation of the blade when carried in the cradle can be controlled conveniently, safely and reliably by adjusting the position of the yoke relative to the cradle. In order to fine tune the orientation of the blade so that it is carried substantially horizontally, the yoke may be moved relative to the cradle so as to align a combined centre of gravity defined by the blade and cradle with the lifting point of the yoke.

The cradle may be configured for lifting a said blade so that a longitudinal axis of said blade is generally parallel to a lengthwise extent of said cradle.

In order to guide the movement of the yoke relative to the cradle, the yoke may be in the form of a movably carriage that moves along a track defined by the cradle. The track may be configured such that it extends in a lengthwise direction of the cradle, for example as a pair of parallel rails that are aligned with a major axis of the cradle.

The yoke may be movable by way of an adjustment drive, which may be provided by a hydraulic or electric actuator for example. Although the adjustment drive may be controlled locally, for example at a console located on the cradle, in some embodiments the adjustment drive may be controlled remotely, for example by way of a control handset equipped with suitable radio communications equipment.

In order to connect the yoke to a lifting line of a crane, the yoke may include a connection arrangement. The connection arrangement may be in the form of a sling or harness in one example, in which the sling may comprise flexible or rigid members. In one alternative, the connection arrangement may comprise a removable spreader that is connectable to a lifting line of a crane and which can be locked onto or removed from the main structure of the yoke.

The cradle may include a gripper for holding a blade securely therein. The gripper may include at least one gripper portion, but in one embodiment includes two gripper portions spaced along the lengthwise extent of the cradle. Accordingly, the gripper portions grip the blade at longitudinally-spaced gripping locations which provides a secure mounting arrangement for the blade.

The at least one first gripper portion may include a first gripper member that is opposed to a second gripper member. One or other of the gripper members may be movable so that the gripper members act like a pair of jaws arranged to releasably grip a blade that is moved into the space between the jaws. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that matter.

Brief description of the drawings

In order for the invention to be more fully understood, it will now be described by way of example only with reference to the following drawings, in which:

Figures 1 a to 1 d are a series of side views of a wind turbine blade being lifted using a lifting apparatus in accordance with an embodiment of the invention;

Figure 2 is a perspective view of one implementation of a lifting apparatus according to an embodiment of the invention;

Figure 3 is a perspective view of an upper region of the lifting apparatus shown in Figure 2;

Figures 4a and 4b are side views of the lifting apparatus shown in Figure 2; and

Figure 5 is a perspective view of a lifting apparatus according to another embodiment of the invention.

Detailed description of embodiments of the invention

Referring initially to Figure 1 a, a wind turbine blade 2 is shown. The wind turbine blade 2 in this example is suitable for a horizontal-axis wind turbine (HAWT). However, the skilled person will be aware of alternative blade designs suitable for alternative wind turbine installations and embodiments of the invention are equally applicable to these alternative blade designs.

As is typical, the blade 2 is elongate and has an aerodynamic outer profile that extends in a spanwise, or lengthwise, direction between a root end 4 and a tip end 6. The design of the blade 2 is such that the root end 4 is heavier than the tip end and therefore, the blade 2 defines a centre of gravity, as determined by the design specification, which is located closer to the root end of the blade than the tip end.

However, the true centre of gravity of the blade may not exactly coincide with the centre of gravity as predicted by the design specification. Any modifications made to the blade, for example, the incorporation of functional equipment such as lightning conductors, heating devices and the like may affect the precise spanwise location of the blade centre of gravity. Furthermore, if the blade is damaged or heavily worn from use then the true centre of gravity may diverge from the expected centre of gravity based on the design specification. Therefore, there may be an uncertainty in the precise spanwise position of the centre of gravity of the blade.

As discussed above by way of background, the blade may require lifting, for example in order to arrange the blade within a stack for transporting between sites, to install the blade onto the hub of a wind turbine generator, or for servicing or repair. To achieve this, the blade may be mounted in a lifting apparatus 10, as shown schematically in Figure 1 b.

The lifting apparatus 10 may comprise a main frame or 'cradle' 12, to which is attached a crane interface assembly, or lifting yoke 14. The cradle 12 is configured to carry the blade 2 and is arranged to embrace a spanwise section of the blade. The cradle 12 therefore includes an appropriate gripping arrangement 22, hereinafter 'gripper' (not shown in Figures 1 b-1 d, but shown in Figure 2), for supporting and securing the blade, as will be described in more detail later. For certain operations, the blade 2 may preferably be lifted in the horizontal orientation shown in the figure and therefore, the blade is mounted in the cradle such that the lifting apparatus is generally vertically aligned with the location of the centre of gravity of the blade as defined by the design specification of the blade. According to this type of lifting orientation, it is appropriate for the cradle 12 to have a longitudinal extent, along a longitudinal or major axis L, which extends parallel or approximately parallel to the longitudinal extent of a blade 2 supported therein. Advantageously, and according to an aspect of the invention, the yoke 14 is movably mounted to the cradle 12, preferably to the top of the cradle 12. The yoke 14 may comprise a main frame which is attached or attachable to a crane lifting wire 16 at a lifting point 18 to enable lifting of the blade 2 within the cradle 12. As such, the yoke is cooperable with a crane (not shown). Since the yoke 14 is movable in translation along at least a portion of the longitudinal extent of the cradle 12, the location of the lifting point 18 can be adjusted in relation to the cradle 12 and, in use, the blade 2. The relevant parameter to consider is the position of the centre of gravity of the combination of the blade and the cradle, which is defined when the blade is mounted in the cradle. This combined centre of gravity is shown in Figures 1 b-d as 'G'. Movement of the lifting yoke 14, in particular in a direction parallel to the lengthwise extent of the blade 2 and of the cradle 12, allows the precise location of the combined centre of gravity G to be adjusted in a blade spanwise direction relative to the yoke 14. This may permit the blade to be lifted and manoeuvred safely in a preferred orientation, as will now be described.

As discussed above, the blade 2 may be mounted in the cradle 12 such that the weight of the blade 2 is distributed evenly to either side of the lifting apparatus 10. In this embodiment, if the combined centre of gravity G of the cradle 12 and the blade 2 are aligned centrally with respect to the yoke 14, that is to say in line vertically with the lifting point 18, then this will enable the blade 2 to be lifted so that it remains generally horizontal, i.e. level with the ground. However, in some circumstances, the true centre of gravity of the blade may not exactly coincide with the centre of gravity of the blade as modelled by the design process. This might be, for example, where internal components of the blade may have shifted position, or where the external surface finish of the blade has eroded in certain locations.

For at least the reasons outlined above, the lifting apparatus 10 may not be optimally balanced with respect to the lifting point 18 of the yoke 14. In this example, the combined centre of gravity G is not vertically aligned with the effective lifting point 18 when the blade is horizontal, as can be seen in Figure 1 b, but instead is displaced slightly to the left hand side, in the orientation of the Figures. Therefore, when the lifting apparatus 10 is lifted by the crane lifting line 16, the weight of the blade and cradle will exert a moment about the effective lifting point 18. This causes the lifting apparatus 10 to tilt or list and the blade within the cradle tilts until the combined centre of gravity is vertically aligned with the lifting point, exerting zero moment, as shown in Figure 1 c. As can be seen, the blade 2 is therefore not level when it is lifted, but instead is tilted to one side. However, since the yoke 14 is movable in relation to the cradle 12, the position of the lifting point in relation to the combined centre of gravity can be altered, adjusted, modified or shifted. Expressed another way, the weight distribution of the blade 2 and cradle 12 can be adjusted with respect to the yoke and, more specifically, the effective lifting point thereof.

As shown in Figure 1 d, the yoke 14 may be moved longitudinally along the cradle until the lifting apparatus 10 is balanced with the blade in the horizontal orientation. That is, the position of the yoke 14 may be adjusted such that the combined centre of gravity G is vertically aligned with the effective lifting point 18 when the blade is horizontal. Thus, the lifting apparatus 10 of this embodiment of the invention allows the blade 2 to be lifted and manoeuvred in the horizontal orientation.

It may also be desirable to lift the blade 2 in another orientation, for example at a specific tilt angle. The skilled person will appreciate that the above-described principle is equally applicable in these circumstances as the lifting apparatus permits precise control over the orientation of the cradle load, i.e. the blade.

As described above, the spanwise positioning of the blade 2 within the cradle 12 of the lifting apparatus 10 provides coarse control of the longitudinal lifting angle of the blade. The movement of the yoke 14 in relation to the cradle 12 provides fine control of the lifting angle of the blade 2 and offers a solution for dealing with uncertainty in the spanwise position of the true centre of gravity of the blade.

Having described the operating principle of the lifting apparatus 10, an example of an implementation of a suitable lifting apparatus will now be described with reference to Figures 2 to 4. Where appropriate, the same reference numerals will be used to refer to parts and features that have already been referred to above.

Figure 2 shows a perspective view of the lifting apparatus 10 according to one embodiment of the invention. In this embodiment, the cradle 12 may generally have the shape of a three dimensional rectangular main frame 20 or 'parallelepiped' defined by a network of structural members, beams, or structures. The main frame 20 may be an approximate C-shape in cross section as defined by first and second main structural components 21 at either end of the main frame 20. Each of the structural components 21 may comprise an upright spine member 21 a to which may be coupled upper and lower transverse members 21 b, 21 c. Advantageously, a trellis-like network of minor structural members 23 may extend between each of the main structural components 21 . An important function of the main frame 20 is to provide sufficient structural rigidity and strength to support a blade gripper 22 and the movably-mounted yoke 14.

The main frame 20 may define a mounting region 24 within which a blade is carried in the cradle. The mounting region 24 may be defined by the mouth of the C-shaped form of the main frame 20. As such, one side of the main frame 20 may be free from structural members, presenting an open area which provides an access opening 25 to the mounting region 24. The access opening 25 is shown in Figure 2 and also on Figures 4a and 4b. The blade is retained in position within the mounting region 24 by the gripper 22 that is supported by the main frame 20. As will now be described, the gripper 22 provides an adjustable gripping aperture to receive and grip a blade so as to hold it securely in the cradle.

In the illustrated embodiment, the gripper 22 may comprise two gripper portions 30, one gripper portion positioned at either end of the main frame 20. In effect, each gripper portion 30 acts like a set of jaws which are operable between an open state in order to receive a portion of a blade and a closed state in which the gripper portions 30 clamp onto the blade to hold it securely in position. Since there are two gripper portions 30 spaced apart from each other in the cradle 12 in a longitudinal direction, they serve to grip the blade 2 at respective spanwise stations spaced along the length of the blade received in the cradle 12.

As can be seen in Figures 4a and 4b, in this embodiment, each gripper portion 30 may comprise a first or 'lower' gripper member 32 and a second or 'upper' gripper member 34.

The first and second gripper members 32,34 may be shaped to define gripping surfaces that complement the aerodynamic surface of the blade so that the gripping action of the gripper 30 does not damage the blade surface. The blade contact surfaces may be defined by a compliant material, such as a high density foam or rubber, to allow the gripper members 32,34 to conform to the profile of a blade at different spanwise positions, or to accept blades of differing designs.

The upper and lower gripper members 32,34 of each gripper portion 30 may be opposed to one another and configured so that the opposed gripper members 32,34 can adjust the space between them. For example, one gripper member may be movable relative to the other gripper member. Movement may be achieved by way of a hydraulic ram, for example. In this embodiment, the lower gripper member 32 is mounted to the main frame in a fixed position, whereas the upper gripper member 34 is movably mounted to the main frame 20. With reference to Figure 2, the upper gripper members 34 may be mounted to the main frame 20 by a hydraulically operated arm 38.

Thus, the movement of the gripper members 32,34, specifically the upper gripper member 34, allows the gripper 22 to receive and then clamp a blade, with the retracted and gripping positions of the gripper members 32,34 corresponding respectively to the open and closed states of the gripper 22.

In order to mount a blade within the main frame 20, the gripper 22 is configured in a partially open state, with the upper gripper members 34 in partially retracted position. This is the position shown in Figures 2, 4a and 4b. The blade is placed within the gripper 22 so as to rest on the upper surfaces of the lower gripper members 32. The upper gripper members 34 are then moved towards the gripping position, reducing the size of the gripping aperture, in order to close the gripper 22 thereby clamping the blade in place in the main frame 20.

It will be appreciated that the process of closing the gripper may be controlled and regulated in various ways. For example, one or both of the gripper members 32,34 may include pressure sensors (not shown) so that movement can be stopped when the output of the pressure sensors exceeds a predetermined threshold, indicating that the blade is sufficiently compressed between the gripper portions. Alternatively, the gripper members 32,34 may be configured to move to a predefined gripping position, determined based on the known geometry of the blade that is to be gripped. In other embodiments, the movement of the upper gripper members 34 may be controlled manually by an operative.

In order to assist in manoeuvring a blade into the main frame, bumpers or fenders may be provided on the forward facing parts of the main frame 20 at points where the blade may be likely to contact. In the illustrated embodiment, rotatable fenders 40 are mounted to the forward ends of the lower gripper members 32 and a further rotatable fender 42 is located on the forward-most point of the main frame 20 at the upper end of the access opening 25.

Static fenders may also be provided to protect the vulnerable blade surface from parts of the main frame. For example, in the illustrated embodiment, a static fender 43 is provided towards one end of the main frame 20. The static fender 43 has an elongated form and is positioned with an inclined orientation to guard against the blade coming into contact with upper regions of the main frame 20 as the blade is manoeuvred into the access opening.

Returning to Figures 2 and 3, the yoke 14 of the lifting apparatus 10 is shown movably mounted to the main frame 20. In this example, the yoke 14 comprises a movable trolley, truck or carriage 44, and a connection arrangement 46 for connecting to a lifting hook of a crane, for example. The main structural shape of the yoke may be provided by two transverse structural members 48 that may be in the form of I-beams spaced in the longitudinal direction of the cradle 12. A yoke frame 50 may be constructed between said structural members 48.

The yoke 14 may be movable along a track 52. Here, the track 52 is defined by structural beams 54 of the main frame 20. The structural beams 54 may be I-beams that extend across an upper part of the main frame 20 in the longitudinal direction of the frame. The structural beams 54 may be parallel to one another so that the yoke moves smoothly between the beams. In effect, therefore, the structural beams 54 define a pair of parallel rails.

The yoke 14 is mounted to the track 52 and, under the action of an adjustment drive, is able to be moved along the track 52 in a controlled manner. Therefore, the longitudinal position of the yoke 14 in relation to the cradle 12 is adjustable and permits adjustment of the orientation of the cradle 12 when the yoke 14 is suspended from a lifting line, as described above.

The yoke 14 may generally sit between in the track 52 so that it is between the rails 54. However, the yoke 14 may be supported on the rails 54 at each of its four corners by respective rolling arrangements or bogies 60. Referring to the inset panel in Figure 3, each bogie 60 may comprise one or more respective rollers 62 that engage with a respective rail 54 so as to allow the bogie 60 to roll smoothly along it.

Various means may be provided to drive the yoke along the track 52. For example the adjustment drive may be integrated into the bogies 60 by way of electric or hydraulic actuators configured to drive the bogies 60 directly. In one option, and as is shown in the illustrated embodiment, the adjustment drive may be configured as a hydraulic actuator or ram 64 is operable to drive the yoke 14 along the track 52. End stops 68 may be provided on the track to limit extreme movement of the yoke 14 on the track 53, for example in the case of malfunction of the adjustment drive.

It should be appreciated that the illustrated embodiment includes by way of example various parts that are hydraulically driven. For example the upper gripper members 34 are powered by hydraulic arms 38, and the adjustment drive may also be hydraulically powered. Usefully, the main frame 20 may therefore include hydraulic power pack 70. The hydraulic power pack 70 may be integrated onto the main frame 20 of the cradle 12 and include all necessary components for example hydraulic fluid accumulator, fluid reservoir, hydraulic pump and control equipment/console, to operate the hydraulic consumers of the cradle 12. In one embodiment, the hydraulic power pack 70 may be controlled from a suitable hydraulic control centre 72 provided remotely from the lifting apparatus. The control centre 72 may also be used to convey useful information about the lifting apparatus to an operative. For example the control centre may be provided with a suitable display screen which provides the user with information about the angle of inclination of the cradle 12.

The connection arrangement 46 provides a suitable structure defining an effective lifting point to allow the yoke to be connected to a lifting line suspended from a crane (not shown). Referring more specifically to Figure 3, in this embodiment the connection arrangement 46 is a sling or harness structure defined by a network of rigid bar members or rods 76 that extend from the four corners of the yoke 14 to a high central point or apex 78. The sling structure therefore can be considered to have the shape of a square-based pyramid. The apex 78 provides the effective lifting point for the yoke 14 onto which a crane hook may be attached. Although in the illustrated embodiment the sling structure comprises bar-like members 76, embodiments are also envisaged in which the bar-like members 76 are flexible, for example as might be provided by steel cable or ribbon.

From the above discussion it will be appreciated that the cradle 12 may be lifted by the yoke 14 and that a blade 2 may be received into the access opening 25 at the front of the cradle 12. Although the cradle 12 would be in a static position when resting on the ground, it may be desirable to control the orientation and attitude of the cradle 12 as it is lifted. For this purpose, the cradle 12 may be provided with one or more guide handles 80. The guide handles 80 may be formed of suitably strong material to enable them to be grasped, handled, pushed or pulled by end-manipulators of hydraulic arms or crane cables for example. In the illustrated embodiment, two guide handles 80 are provided which are tubular in form, for example steel tubes, and which are mounted to respective rear corners of the main frame 20. The guide handles 80 may extend away from the main frame 20 in a sideways direction and are angled towards the access opening 25.

The skilled person would understand that modifications could be made to the specific embodiments described above without departing from the aspects of the invention, as defined by the claims. Some variants on the specific embodiments have been mentioned above; others will now be described.

In the embodiment illustrated above, the yoke 14 included a pyramid-like connection arrangement which serves to couple the structure of the yoke to a lifting line at a single point. However, this is just one way in which the yoke could be coupled to a lifting line. Another option is shown in Figure 5. In this embodiment, the yoke 14 includes a coupling 100 which is configured to lockingly engage with a removable spreader bar 102. The spreader bar 102 is elongate in form and includes appropriate lifting points 104 on either end thereof which serve to attach to a lifting line 106 of a crane. It should be appreciated that the illustrated lifting points 104 are only given by way of example and that the spreader bar 102 may be provided with lifting points in other locations.

Claims

1 . Lifting apparatus for a wind turbine blade, said apparatus comprising: a cradle for carrying a said blade, and a lifting yoke which is cooperable with a crane, in use, to lift the cradle, wherein the lifting yoke is mounted to the cradle and is moveable in a lengthwise direction relative to the cradle to permit adjustment of the orientation of the cradle when the yoke is suspended from a lifting point associated therewith.

2. The lifting apparatus of claim 1 , wherein said cradle has a lengthwise extent and wherein said cradle is configured for lifting a said blade with a longitudinal axis of said blade generally parallel to the lengthwise extent of said cradle.

3. The lifting apparatus of claims 1 or 2, wherein the yoke is a movable carriage that moves along a track defined by the cradle.

4. The lifting apparatus of claim 3, wherein the track extends in a lengthwise direction of the cradle.

5. The lifting apparatus of claims 2 or 3, wherein the yoke is moved along the track by an adjustment drive.

6. The lifting apparatus of claim 5, wherein the adjustment drive includes a hydraulic actuator.

7. The lifting apparatus of claim 5, wherein the adjustment drive includes an electric actuator.

8. The lifting apparatus of any of claims 5 to 8, wherein the adjustment drive is controlled remotely.

9. The lifting apparatus of any of claims 1 to 8, wherein the yoke includes a connection arrangement for connecting to a lifting line.

10. The lifting apparatus of claim 9, wherein the connection arrangement is a sling coupled to the yoke.

1 1 . The lifting apparatus of claim 10, wherein the connection arrangement is a spreader that is removably coupled to the yoke.

12. The lifting apparatus of any of claims 1 to 1 1 , wherein the cradle comprises a gripper for holding the blade securely in the cradle.

13. The lifting apparatus of claim 12, wherein the gripper comprises at least a first gripper portion.

14. The lifting apparatus of claim 13, wherein the first gripper portion includes a first gripper member that is opposed to a second gripper member.

15. The lifting apparatus of claim 14 wherein at least one of the gripper members is movable with respect to the other gripper member.

16. The lifting apparatus of any of claims 13 to 15, wherein the gripper comprises a second gripper portion, wherein the first and second gripper portions are spaced from each other in the cradle at respective longitudinal blade gripping stations.

17. A method of lifting a wind turbine blade using a lifting apparatus comprising a cradle for carrying the blade, and a lifting yoke movably coupled to the cradle, wherein the method comprises: mounting the blade in the cradle; using the yoke to lift the cradle; moving the yoke in a lengthwise direction relative to the cradle so as to adjust the orientation of the blade and the cradle relative to a lifting point associated with the yoke.

18. The method of claim 17, wherein the yoke is moved relative to the cradle so as to align a combined centre of gravity defined by the blade and cradle with the lifting point of the yoke.

19. The method of claims 17 or 18, wherein the yoke is moved along a track defined on an upper portion of the cradle.