WO2017071719A1

WO2017071719A1 - Blade lifting method and apparatus

Info

Publication number: WO2017071719A1
Application number: PCT/DK2016/050348
Authority: WO
Inventors: Alessio D'alesio
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2015-10-30
Filing date: 2016-10-28
Publication date: 2017-05-04
Anticipated expiration: 2018-04-30

Abstract

In a blade lifting method and apparatus, the apparatus comprises a lifting bar to be fitted within the hollow, root portion of a wind turbine blade and a lifting connector to be suspended from a crane and passed through a hole in the blade root to engage with the lifting bar. The root end of a wind turbine blade may thereby be supported during lifting by an external lifting means such as a crane. Support pads may be fitted to the lifting bar ends or to the inside of the blade root. These provide a point of engagement between the lifting bar and the internal surface of the blade root. A hole in a blade root may be positioned such that, in a predefined lifting orientation of the blade, the hole lies vertically above the centre of gravity of the blade, or the sectional centre of gravity at the lifting point. The blade root lifting apparatus and method are suitable for both the construction or disassembly of a wind turbine.

Description

BLADE LIFTING METHOD AND APPARATUS

This invention relates to a blade lifting method and apparatus. In particular, the invention relates to lifting a wind turbine blade safely when constructing or disassembling a wind turbine, and to methods and apparatus for doing the same.

A wind turbine hub, to which the wind turbine blades are connected, rotates as the wind applies lift to the blades. The rotation of the hub is coupled to a gearbox and generator in order to convert the rotational motion into electrical energy. Due to the size of the blades and hub, it is often necessary in wind turbine construction, transport, and handling, to first position the hub at the nacelle, on top of the wind turbine tower and subsequently to lift the wind turbine blades up to the hub where they can be connected. Although some blades may be preinstalled and connected to the hub to form a rotor prior to positioning it at the nacelle, it is not always practical to lift the entire rotor assembly in one manoeuvre due to its prohibitively large size. It is also necessary when disassembling a wind turbine or when servicing blades, to lift the blades down from the hub after they have been disconnected.

Modern wind turbines are designed with increasingly high towers in order to access higher wind speeds, thereby maximising the energy they can extract from the wind. At higher altitude the wind is also less prone to turbulence due to the increased distance from the ground. However, as the height of the wind turbine tower increases it becomes harder to lift the wind turbine blades safely for connection or disconnection to or from the hub. In addition to the increased lifting height, wind turbines having higher towers also typically have longer blades with greater mass. This further impacts upon the safety of lifting the blade. Furthermore, larger blades are more susceptible to the effects of wind during a lifting manoeuvre, making it harder still to lift them safely.

In WO 2012/062352 A1 , a wind turbine blade is lifted by positioning a first sling around a root end and a second sling around a tip end. Each of the slings is suspended from a lifting beam, connectable to a crane. A similar lifting arrangement for a wind turbine blade is disclosed in DE 20 2010 003 033 U1 . Here, a sling is used to support the tip region and a cable is wrapped around the root region. The cable and sling are connected to a boom-type yoke for lifting. Therefore, in known lifting arrangements, a sling or strap may be wrapped one or more times around the wind turbine blade close to the root, where the blade has an approximately round profile, and another sling extending around the blade may be used to support the blade closer to the tip, where the profile is flatter. Therefore two lifting locations are provided along the span of the blade, one, at the root, being inboard of the blade's centre of gravity, with the other, at the mid- or tip-portion being outboard of the blade's centre of gravity. These lifting slings may be suspended from respective ends of a boom- type yoke which in some cases may, for example, be a T'-yoke. The yoke is then secured to a crane by means of further cables to allow the assembly to be lifted.

A sling or strap wrapped around the root can be difficult to remove safely once the blade is secured to a hub because it requires a technician to access the outside of the blade root, when it is up the tower, in order to release the sling. It is also very difficult to attach and wrap such a sling or strap safely to the root when the blade is secured to the hub, prior to dismantling of a wind turbine. Again, typically, an installation engineer must emerge to the outside of the hub, mount the blade on the outside and manually attach the sling by wrapping it round the blade root. The safety concerns for an engineer who must work outside of the nacelle to handle the sling at a blade installed on the hub are considerable. In addition, it can be difficult to accurately position the wrapped sling with regard to the desired blade orientation during lifting. The need to correct or adjust the blade orientation for lifting, after attachment of the sling, or during lifting, can necessitate a drive device capable of pulling on the sling, while it is suspended from the yoke. Hence, the use of a sling around the blade root, as well as being labour intensive, this poses a number of practical and safety challenges.

It has been suggested, for example in US2014/0127025, to lift a blade by means of three fixing units inside the blade, distributed around and close to the blade's centre of gravity. The blade is suspended from three such fixings via respective slings, each attached to a fixing through a respective hole in the blade upper shell surface. The slings can be attached to the fixings by technicians inside the blade. Although this method does not require the use of a sling around the blade root, it imposes the load of the blade's full weight locally around the blade's centre of gravity because, in effect, the blade has only one, local lifting area with three holes arranged close together. Moreover, the blade shell is thinner in blade regions outboard of the root, so that there remain some structural advantages from using the root as a lifting location. In addition, when a blade is lifted or lowered using a single lifting location, that lifting location can have the undesirable effect of acting as a pivot about which the blade can rock, making the blade more difficult to control while it is suspended, because it is more prone to being blown or nudged away from its intended lifting orientation. Long tag lines need to be used to maintain the blade in its desired orientation, but these can be less effective or unusable at considerable heights. Moreover, still in the arrangement per US2014/0127025, the fixings remain inside the blade after its installation and during turbine operation. This adds weight to the blade and raises the question whether or not the fixings are structurally sound before re-use when dismantling a blade for servicing or replacement.

Therefore, there is a need to provide an improved blade lifting method and apparatus, to enable a wind turbine blade to be lifted or lowered safely during the construction or disassembly of a wind turbine and addressing shortcomings of known arrangements.

SUMMARY OF THE INVENTION

In a blade lifting method and apparatus according to aspects of the invention, the apparatus comprises a lifting bar to be removably fitted within the hollow, root portion of a wind turbine blade and a lifting connector to be suspended from a lifting apparatus and removably passed through a hole in the blade root to engage with the lifting bar. The root end of a wind turbine blade may thereby be supported during lifting by an external lifting means such as a crane. Support pads may be fitted to the lifting bar ends or to the inside of the blade root. These provide a point of engagement between the ends of the lifting bar and the internal surface of the blade root. The invention thereby provides a simple means for reliably lifting or lowering a blade at its root end without ordinarily requiring access to the outside of the blade. Moreover, the lifting gear fixed inside the blade is minimised, even while the blade root is lifted from within. The invention is defined in the appended independent claims to which reference is made. Further, optional advantageous features are defined in the dependent claims.

In a first aspect, the invention comprises a method of lifting a wind turbine blade by means of a lifting yoke which may be a boom type lifting yoke, said blade having a shell extending longitudinally from a root region to a tip region and a lifting hole positioned at a lifting location in the blade root region; the method including suspending the blade from a lifting yoke at a root region and at a mid- or tip-region thereof, the method additionally including: passing a first end of a lifting connector through the lifting hole to an interior root region within the blade shell; providing within the interior root region of said shell a lifting bar having a first end region and a second end region spaced from each other; connecting, within said shell, said first end of said lifting connector to said lifting bar, such that said lifting connector engages with said lifting bar at or near a middle portion thereof between its first and second end regions; bringing said lifting bar into supporting contact with the inside surface of the interior root region of said shell at respective first and second portions of the inside surface of the interior root region of said shell; and lifting the blade using the lifting bar and the lifting connector connected to the boom type lifting yoke preferably at a root end of the lifting yoke.

Accordingly, the wind turbine blade is lifted without the need to wrap a sling or strap around the root portion of the blade, whilst providing improved support of the blade structure. The lifting connector and lifting bar can be safely installed and/or removed by an engineer working within the blade root, thereby improving safety during the lift. During use, the lifting connector extends externally of the blade and internally of it. Preferably, the said lifting location and the said hole may be located spanwise inboard of the blade's main internal structural spar or shear web structure. Thereby, the lifting bar can be positioned inside the blade shell at its root region without being obstructed by or interacting with the blade internal structural reinforcement such as the blade main spar or main web (or main webs, as the case may be). For the avoidance of doubt, according to the method of the invention, the mid- or tip-region of the blade at which the outboard lifting location is located, lies outboard of the centre of gravity of the blade. Similarly, a root region of the blade at which the inboard lifting location is located, lies inboard of the centre of gravity of the blade.

Preferably, the lifting bar is brought into supporting contact with inside surface portions of the interior root region of the shell at respective first and second shell wall portions which are spaced from each other e.g. at diametrically opposite sides of the lifting hole.

Preferably, the lifting according to the invention is carried out such that the root end of the blade is supported via only a single lifting hole in the root region.

The method preferably additionally comprises disengaging, when lifting the blade is completed, e.g. after attachment of the blade to a wind turbine rotor hub, said lifting bar from the lifting connector, and retracting said lifting connector through the lifting hole. The lifting apparatus can therefore be safely and efficiently dismantled after the lift is completed.

The method may additionally comprise removing the lifting bar from the blade shell once lifting the blade is completed. The lifting apparatus can therefore be safely and efficiently dismantled after the lift is completed. Moreover, the lifting apparatus thereby does not remain inside the blade during use. This can be of particular significance for heavy load- bearing elements, which may themselves add considerable weight to be blade thereby reducing its efficiency. The problem of potentially disruptive or dangerous deterioration of internally fixed lifting elements during operation of the blade may thereby also be avoided.

Preferably, prior to the lifting of the blade, the blade is positioned at a predetermined lifting orientation with respect to the lifting connector. To this end, the lifting apparatus may be fitted to the blade in the predetermined lifting orientation, thereby avoiding any tendency for the blade orientation to shift as the lift progresses. In this context, the lifting orientation is to be understood to be the aspect which the blade presents with respect to the horizontal. By way of example, a blade's positional orientation, or aspect, may be defined by the angle of the blade's longitudinal axis with respect to the horizontal, and by the angle of the axis of the maximum chord with respect to the horizontal. Alternatively or additionally, a blade's positional orientation may be defined in relation to any other reference point and may in particular be determined in the form of respective angles between a reference line or plane and the blade's longitudinal axis and its maximum chord axis. The blade's longitudinal axis may also be known as the blade axis. In the present context, a lifting connector may be suspended from a crane prior to and during a blade lifting or lowering operation. As such, a positional orientation of the blade may be determined in relation to the suspended lifting connector. It may be of importance that the blade orientation is more or less constant prior to and during lifting and also upon release of the lifting connector from the lifting bar. Therefore, preferably, throughout the lifting of the blade, the blade is maintained in the predetermined lifting orientation with respect to the lifting connector. This further improves the safety during the lift and avoids damaging the blade. This may in particular be achieved in that a hole in a blade root may be positioned such that, in a predefined lifting orientation of the blade, the hole lies vertically above the centre of gravity of the blade, or the sectional centre of gravity at the lifting point.

Preferably, the lifting is carried out using only a single lifting hole in the root region of the blade shell. The use of only a single lifting hole in the blade root avoids additional damage to the structure of the blade. In this context, the hole may be located in a part of the root region which lies inboard of the main internal structural elements of the blade, such as its main spar or its main web/webs. The terms inboard and outboard are intended to designate relative proximity to or distance from the centre of rotation of the blade when positioned on a rotor hub. When applied to a lifting location along the blade, the terms outboard and inboard may refer to positions outboard or inboard relative to the blade centre of gravity.

In preferred aspects, the method may include positioning the lifting bar within the root region of the shell in a substantially horizontal orientation, and/or in an orientation which is substantially perpendicular to the lifting connector. The blade is therefore adequately and evenly supported by the lifting apparatus during the lift.

Preferably, each of the said first and second end regions of the lifting bar may be engageable with at least one support pad for providing supporting contact with the inside surface of the interior root region of the blade shell. The support pads enable a large contact area to be established between the lifting bar and the blade shell, thereby improving the degree of support for the blade during the lift whilst avoiding damaging the shell. Preferably a support pad is arranged at each end of said lifting bar and carried thereon. Alternatively, one or more support pads may be arranged on the inside surface of said blade root region for engagement with said lifting bar prior to and during lifting. A support pad at one end of said lifting bar may comprise a single support pad or it may be a composite support pad, made up from multiple pads all at a same end of said lifting bar. The larger surface area of the support pads may reduce the local stress and strain in the blade shell in its root region.

Still preferably, the support pads may have a complementary shape to the inside surface of the interior root region of the blade shell. The support pads therefore readily engage with the blade shell or with the lifting bar, providing improved support during the lift. In aspects the support pads may exhibit a gripping high-friction surface to mitigate against slippage at the blade shell internal surface during use. Preferably the support pads are made from resilient material which recovers its shape after use. The material may preferably be or may comprise an elastomeric material. In aspects of the method, the connecting step may comprise locking the lifting connector to the lifting bar. This may be achieved by any suitable means, using fixing elements or locking elements and connecting elements of sufficient strength to carry the weight of the root end of the blade without rupturing. In particular, the method may include passing the first end of the lifting connector through an aperture in the lifting bar, and then locking the lifting connector to the lifting bar preventing accidental disengagement thereof. By way of example, the said locking may be effected by passing a locking pin through an aperture at said first end of said lifting connector. The lifting connector is preferably configured such that it is of narrow enough dimensions to pass through the lifting hole whilst still being securable to the lifting bar. Optionally, the lifting bar and lifting connector may exhibit one or more holes, apertures or eyes, allowing one of these to be threaded through the other, or allowing the two to be connected by a connecting piece such as a shackle.

In still further aspects according to the method of the invention, and in order to support the outboard end of the blade during lifting or lowering, the said step of suspending said blade from the boom type lifting yoke at a said body or tip region thereof may include passing a lifting sling externally around said blade at or nearby said mid- or tip-region thereof. An outboard lifting sling may additionally comprise a rigid or semi-rigid cradle for positioning under the lower surface of the blade being lifted and capable of more evenly distributing the lifting force at the outboard lifting location than by use of a strap-type sling alone which tends to focus the lifting force at the blade edges. In embodiments, a rigid cradle may run beneath the blade mid- or tip-region, connected at a leading and trailing edge portion thereof to two lifting straps, each of which may run up to a hook or connecting piece at the yoke, in particular at a tip end of the yoke.

In a further aspect, the step of suspending the blade at its body or tip region may include passing a first end of an elongate lifting sling externally around a longitudinally extending internal structural support member of the blade through two pairs of holes arranged adjacent the internal structural support member. In this context, each pair of holes may be provided in a respective suction or pressure side of the blade shell and with a respective one of each said pair of holes at a leading and at a trailing edge side of said internal structural support member. In this context a longitudinally extending internal structural support member of the blade may be a main spar, a main shear web or a pair of main shear webs. It is not excluded that there may be more than a pair of shear webs around which the lifting sling may pass, e.g. three or more, but these constructions are less likely. In this way, a first end of a lifting sling may be passed through a hole at the uppermost blade shell surface, through the inside of the blade, past one side of its structural reinforcing elements and out through the lowermost shell surface, and then around the outside of the blade along the lowermost outer blade shell surface underneath the blade structural support, around and then up through a further hole in the lowermost blade shell surface, at an opposite side of the structural reinforcement member(s), upwards through the inside of the blade along the opposite side of the structural reinforcement member(s) before passing it out through another hole at the uppermost blade shell surface, from where it may be passed to a lifting link. This threading process may in particular be carried out while a second end of said lifting sling is connected or connectable to a suspended lifting link. By way of example, this procedure may be carried out by personnel positioned inside the blade and on either side of the main structural support member(s), one or more of whom may be equipped with a grabbing stick for pulling an end of the lifting sling in through a hole or for pushing an end of the lifting sling out to the outside and possibly up to a lifting link. In this way, a positive connection can be achieved between the lifting sling and the blade, even more so than by using a purely external sling. This may further reduce the risk of slippage of the blade from a purely externally positioned lifting sling. It should be noted, of course, that this procedure and other procedures requiring personnel to be inside the blade at a region outboard of the centre of gravity may only be performed in larger blades where there is preferably a minimum of fifty centimetres of internal clearance space between the uppermost and lowermost blade shell surfaces. In a still further aspect, the lifting sling may comprise a first length and a second length and the method may include joining together, inside the blade shell, the first and second lengths of the sling at a bridge section thereof at a location adjacent the longitudinally extending internal structural support member. The bridge section of the first and second sling lengths may be connected by a longitudinal pin or by shackles or by a combination of these. Other fixing elements may also be contemplated provided these have the requisite strength to carry the blade weight at its mid- or tip-region without rupturing. According to this aspect, it may be advantageous for the first and second sling lengths to be of different effective lengths between their respective lifting link connection end, which may be called a tack end, and their bridge section end. In this way, for example, a bridge section end of a first length of said sling may be lowered from a lifting link to which its tack end is attached, though a hole in the shell uppermost surface and threaded through the blade around the internal support members and back up into the inside of the blade, while a second, shorter length of the lifting sling, also suspended by its tack end from a lifting link, may be passed only through the other of a pair of holes in the uppermost shell surface. In this way, the respective different effective lengths of the first and second sling lengths allows their respective bridge section ends to meet adjacent one side of the blade's main internal structural members.

In a second aspect, the invention comprises a lifting apparatus for lifting a wind turbine blade, which blade has a shell extending longitudinally from a root region to a tip region and a lifting hole positioned at a lifting location in the root region of the blade, the lifting apparatus comprising: a lifting connector for passing through the lifting hole to an interior root region of the blade shell; a lifting bar having a first end region and a second end region spaced apart from each other, for providing supporting contact with respective first and second portions of the inside surface of the interior root region of said shell; and an engagement portion provided between the first and second end regions of the lifting bar, for engaging with a first end of the lifting connector. The lifting apparatus according to this aspect is, in particular, connectable to a boom type lifting yoke.

Accordingly, the apparatus can be used to lift a wind turbine blade without the need to wrap a sling or strap around the root portion of the blade, whilst providing improved support of the blade structure. The lifting connector and lifting bar can be safely installed and/or removed by an engineer working within the blade root, thereby improving safety during the lift. A further advantage of removing the lifting bar after lifting or lowering the blade resides in that neither the lifting bar nor its connection to the blade shell inner surfaces are subject to deterioration during use of the blade. Some prior art lifting elements are known to be left in the blade during the blade's service life, to be later used during lowering the blade e.g. for servicing or repair after possibly prolonged use. In these cases, there may be a risk that such lifting elements or their connection to the blade may have deteriorated over time and as a result of wear, to the extent that their use may be dangerous or impossible. The removal of the lifting gear after use avoids this problem.

The first end of the lifting connector may be provided with an engagement member for engaging with the engagement portion of the lifting bar. The lifting connector can therefore be secured to the lifting bar prior to lifting, and the apparatus can be easily dismantled after lifting.

The apparatus may comprise a sling or strap for suspending the body or tip region of the blade from a boom type lifting yoke. The wind turbine blade is thereby additionally supported at a second lifting location, outboard of the blade centre of gravity. When used in connection with a rigid or semi-rigid mid- or tip-cradle, this arrangement may enable the position and orientation of the blade to be controlled and possibly adjusted during the lifting or lowering manoeuvre.

In embodiments, the lifting connector may comprise a cable, cord, chain, rod, pole or bar or combinations of these. The lifting connector can preferably be passed easily through a lifting hole in the blade shell to engage with the lifting bar. Preferably, the first and second end regions of the lifting bar may have support pads for providing supporting contact with the inside surface of the interior root region of the blade shell. The support pads enable a large contact area to be established between the lifting bar and the blade shell, thereby improving the degree of support for the blade during the lift.

At least part of the support pads for providing supporting contact with the inside surface of the interior root region of the blade shell may be made of a resilient, flexible material. The material therefore does not damage the interior of the blade shell when providing supporting contact.

The support pads may have a complementary shape to the inside surface of the interior of a blade root region. The support pads therefore readily engage with the blade shell, providing improved support during the lift.

BRIEF DESCRIPTION OF THE DRAWINGS

Some features of the invention and various aspects and implementations thereof will now be described, by way of example only, and with reference to the accompanying schematic drawings, in which:

Figure 1 shows a simplified, three-dimensional view of a wind turbine blade; Figure 2 shows a simplified end elevation view of a wind turbine blade;

Figure 3 shows a schematic, not-to scale, simplified cross-sectional view of a root and transition region of a wind turbine blade to be lifted according to aspects of the invention; Figures 4a and 4b show schematic views of a lifting apparatus according to aspects of the invention;

Figure 5 shows a schematic three-dimensional view of a wind turbine blade ready for lifting or during lifting with a blade root lifting apparatus, according to aspects of the invention; Figure 6 illustrates aspects of a blade lifting tool used in the construction of a wind turbine and the lifting of a wind turbine blade using the tool, according to aspects of the invention;

Figure 7 shows a schematic end view of a wind turbine blade fitted with a blade root lifting apparatus, with the blade being lifted in a certain orientation, according to aspects of the invention;

Figure 8 shows a schematic end view of a wind turbine blade fitted with a blade root lifting apparatus, with the blade being lifted in a different orientation, according to aspects of the invention;

Figure 9 shows a schematic end view of a wind turbine blade illustrating the disassembly of a blade root lifting apparatus; Figure 10 shows schematically an alternative lifting method according to aspects of the invention;

Figs. 1 1 a-b show schematically further features of the alternative lifting method per Fig. 10; Figure 12 shows details according to the embodiments of Figs. 10, 1 1 a and 1 1 b.

DETAILED DESCRIPTION

Figure 1 shows a simplified, schematic, not-to scale, three-dimensional view of a wind turbine blade 108. The blade 108 exterior is defined by a shell which extends spanwise between a root portion 1 10 and a tip 1 1 1 and chordwise between a leading edge 210 and a trailing edge 212. Arrow 202 indicates an approximate chordwise direction, while arrow 204 indicates a spanwise direction, corresponding to the length direction of the blade. The chordwise direction 202 lies substantially perpendicular to the spanwise direction 204 and is defined by a straight line extending between the leading and trailing edges 201 , 212. A thickness direction of the blade 206 typically extends perpendicular to both the chordwise 202 and spanwise 204 directions, at any given spanwise location along the blade 108. It will be appreciated that the chordwise direction 202 varies along the blade length, mainly to accommodate for greater blade operating speeds near the tip 1 1 1 than near the root 1 10. Consequently, also the thickness direction 206 can vary along with the progressively shifting chordwise direction 202. The approximate location of the blade's centre of gravity is indicated by arrow 125. A windward or suction side of the shell is separated in a thickness direction 206 from a leeward or pressure side of the blade shell. A maximum chord axis (not shown) runs from the leading edge 210 to the trailing edge 212 at the spanwise location exhibiting the greatest chord length.

The blade 108 terminates at a most inboard end of its root 1 10 in a pitch bearing ring face 222 for connection with a corresponding bearing ring on a rotor hub 106. The connection may be made by means of stud bolts securely fixed into holes 224 formed in the blade shell wall at its root 1 10, where the blade shell may be thickest, and secured through holes in a corresponding bearing ring at the rotor hub 106. Outboard of the blade root 1 10 is a root transition region which extends to a so-called shoulder where the chordwise dimension of the blade increases significantly in relation to the root diameter dimension. The maximum chord dimension of a blade typically lies nearby its shoulder and slightly outboard thereof. The blade centre of gravity typically also lies outboard of its shoulder. The blade centre of gravity may be very approximately at a quarter of the blade spanwise dimension from the root. Hence, the blade root 1 10 lies inboard of its shoulder and inboard of a root transition region.

The blade shell defines the aerodynamic shape of the blade 108 and is typically internally structurally reinforced and supported by a longitudinally extending main reinforcing structure such as a spar or shear web (not shown in Fig. 1 ) which extends in a thickness direction 206 between a blade suction or a blade pressure surface and in a spanwise direction 204 from a blade root region to a tip region 219 or tip 1 1 1 . In some cases a main shear web may comprise a pair of mainly co-extensive shear webs arranged side-by side. It is not excluded that the main shear web may comprise more than two shear webs. In general, the main reinforcing structure extends longitudinally along the internal length of the blade 108, bridging the greatest internal thickness dimension along the blade. In Fig. 1 , respective blade shell surfaces are indicated as an upper shell surface 216 and a blade lower shell surface 218, either of which may be at a leeward or windward face of the blade, depending which way up it is oriented. The internal reinforcing structure supports the shell and transmits operating or environmental loads on the entire length of the blade 108 during operation to its root 1 10. The internal reinforcing structure also ensures and maintains a spacing or separation in a thickness direction between the opposing pressure and suction surfaces of the shell which thereby improves the blade stiffness. Moving outboard from the pitch bearing face 222, the blade root portion 1 10 is followed by a blade root region and then a blade root transition region towards the blade shoulder 230. Thereafter, the blade mid-region 217 is followed by the blade tip-region 219 which runs to the tip 1 1 1 .

The cross-section of the blade 108 changes and evolves from the round root portion 1 10 towards the slender aerofoil-shaped tip 1 1 1 . First, in the root transition region, the blade widens in a chordwise direction and tapers down gradually in a thickness direction to the shoulder 230. The blade becomes progressively flatter, i.e. shallower in the thickness direction and shorter in a chordwise direction towards the mid-region 217. From the mid- region 217 through the tip-region 219 to the very tip 1 1 1 of the blade span, the blade becomes progressively more flat, exhibiting a recognisable aerofoil-shaped cross-section. The length of the chord also decreases towards the tip 1 1 1 . In larger blades, perhaps having a length 50m or 60m and above, the internal thickness dimension inside a blade in its mid-region 217 can be greater than 50cm, sometimes 1 .5m or 2m or more. An internal root dimension may easily exceed 2m, perhaps even reaching 4m or more.

The blade 108 is typically made from lightweight laminated composite materials such as fibre-glass in a resin matrix. Additional reinforcing materials may be used in certain regions while lightweight spacer materials such as foam and balsa wood may be used in places to improve stiffness without adding weight. In the view depicted in Figure 1 , the blade is shown at an orientation corresponding approximately to a horizontal longitudinal axis and horizontal maximum chord axis. This may correspond approximately to a desired lifting orientation for horizontal type lifting operations or for horizontal type blade-to-hub attachment operations.

In use, the blades 108 are connected to a hub 106 to form a rotor. When the blades 108 are pitched into the wind, air passes over the leading edge 210 towards the trailing edge 212 and beyond, creating lift as a result of the blade's aerofoil shape. The rotor is connected via its hub 106 to a rotating shaft which drives a generator (not shown) in the nacelle 104.

Figure 2 shows a side elevation view of the root 1 10 of a wind turbine blade 108. A chordwise direction 202 is shown perpendicular to a thickness direction 206. The leading 210 and trailing 212 edges are also shown. The chordwise 202, thickness 206 and spanwise 204 directions may intersect at and along a central longitudinal axis 304. It should be noted that Figure 2, and all of the other figures herein depicting wind turbine blades, show a generalised shape which is used schematically. As will be known to the skilled person, the actual profile of a wind turbine blade may differ from that shown in the figures in order to optimise the performance of the wind turbine.

The view in Figure 2 depicts the blade 108 looking in a spanwise direction towards the root 1 10. Pitch-bearing ring face 222 has a circular cross-section, and comprises holes 224 extending part-way into the thickness of the blade shell at the root 1 10. For e.g. a 60m blade, a typical diameter for the root portion 1 10 will be, in one example, 3m. The holes 224 are used to receive stud-bolts 406 for connection to a pitch-bearing ring at the hub.

Figure 3 shows a cross-section in a spanwise direction through the root region in more detail. A blade shell internal surface 404 extends on the inside of the shell. The bearing ring face 222 comprises holes into which stud-bolts 406 are fixed, housed inside the wall thickness of the blade 108 at its root 1 10. These are used to connect the blade 108 to the hub 106.

An internal blade main longitudinal reinforcing structure 414 is shown, extending in a thickness direction 206 of the blade, between internal wall surfaces 404 at a respective suction side and pressure side of the blade. In Fig. 3, this main internal reinforcing structure is shown by way of example as a shear web although a spar or pair of shear webs or other configuration may be envisaged. The blade root portion 1 10 is free of the main reinforcing structure 414. In the case of one or more shear webs, these typically end somewhat short of the blade root portion 1 10, while in the case of a main spar, this typically blends into the root portion walls at the blade root 1 10. In the case illustrated, a webbing boundary begins at a spanwise position 416 along the blade, separated from the bearing face 222 by the extent of the blade root. For the purposes of the present disclosure, the blade root 1 10 is considered to extend inboard along a spanwise direction 204 away from the most inboard edge 416 of the blade reinforcement member 414. In accordance with aspects of the present invention, the blade root 1 10 is provided with a lifting hole 606. The hole 606 is arranged further inboard of the most inboard extent of the main internal reinforcing structure 414. By way of example, it may be desirable to locate the lifting hole 606, at an approximate distance within 2m or within 1 .5m or within 1 m from the most inboard end of the root portion 1 10. This enables the lifting hole to be formed in the blade laminate whilst being clear of the stud-bolt receiving holes 224 and the blade internal structural reinforcement 414. With reference to Figs. 4a and 4b, blade root lifting apparatus 600 comprises a lifting connector 604 and a lifting bar 610. The lifting connector 604 has a longitudinal extension between a first end 6041 and a second end 6042. The lifting connector 604 is illustrated in part in Fig. 4a and in part in Fig. 4b. A first end 6041 of the lifting connector 604 is configured to pass through a lifting hole 606 formed through the wall of a blade 108, in particular at its root 1 10. The second end 6042 of the lifting connector 604 is configured to be positioned outside a blade 108, and is configured to be connectable to a lifting apparatus such as a lifting yoke 1 14 (shown in part in Fig. 4a), crane, and/or other lifting equipment, capable of applying a lifting force to the lifting connector 604. The first end 6041 of the lifting connector 604 is connectable to a lifting bar 610, as shown in Figs. 5-8. To that end, the lifting connector may be provided with a lifting surface 650 such as an aperture or hole, as shown in Fig. 4b or any other lifting surface which may include a flange, bracket, shoulder, recess, keyway or other engagement surface.

The lifting bar 601 has a longitudinal extent including two ends 616, 618. The ends 616, 618 of the lifting bar provide a lifting connection between a blade 108 and the lifting apparatus 600. In particular, the weight of a blade, at its root 1 10 may rest on the ends 616, 618 of the lifting bar 610, preferably additionally via respective pressure pads 612, 622 fixed either to the inside of the blade 108 e.g. at an inside surface 404 thereof, or fixed to the lifting bar 610. In some embodiments, the end regions 616, 618 of the lifting bar 610 may be adapted to be seated within pressure pads 612, 622 provided fixed to the interior surface 404 of the blade root 1 10. Alternatively, as in the example illustrated in Fig. 4b, each end 616, 618 of the lifting bar 610 may be provided with a respective support pad 612, 622 fixed thereto or removably fixed thereto. The two ends 616, 618 are spaced apart at opposite ends of a middle portion 615 to which a lifting connection can be made together with the lifting connector 604. A fixing element 608 may be provided for securing the lifting connector 604 and the lifting bar in mutual engagement. The fixing element 608 may be fixed at a position along the lifting bar 610 or it may be movable. Fig. 4b shows the fixing element 608 in the form of a shackle. Other devices may be used for this purpose according to preferences or to circumstances, such as a locking pin, snap-shackle, socket, strap or cable or other suitable fixing means such as a shoulder, recess or keyway. In embodiments, there may be more than one fixing element 608 spaced along the lifting bar 610. These may be fixed at the lifting bar 610 or movably arranged therealong, preferably at selectable, lockable positions. In the example of Fig. 4b, a selectively movable or fixed retainer 640 may be included to maintain the fixing element 608 in a predetermined position along the length of the middle portion 615 of the lifting bar 610. Optionally (not shown) the position of the retainer 640 may be moved and set at selectable positions along the length extent of the middle portion 615 of the lifting bar 610. Thereby, optionally, the lifting connection between the lifting connector 604 and the lifting bar 610 may be selectably moved to any desired position along the length of the lifting bar 610. Hence, if desired, in relation to Fig. 4b, the lifting connection between the lifting bar 610 and the lifting connector 604 may be further towards one or other extremity of the lifting bar 610. On the other hand, in embodiments, it is not excluded that the fixing element 608 may be located at the mid-point of the lifting bar 610. On the other hand, it need not be positioned equidistant between the two lifting bar ends 616, 618, although this may be desirable in certain embodiments. A mark can be made on the lifting bar 610 to indicate to an engineer where the fixing element 608 should be located, and/or where lifting connector 604 should be connected to the lifting bar 610 by any other means. This assists the engineer in fitting the lifting apparatus 600 accurately, with the correct alignment.

Each support pad 612, 622 may comprise a plate, for example a rigid or steel plate, connectable to an end 616, 618 of the lifting bar 610. Padding may be provided in association with the plate to prevent damage to the blade 108 when the apparatus is used. In some embodiments, the support pads 612, 622 comprise a resilient, flexible material. The pads 612, 622 may have a rubber coating, for example a 10mm or 5mm or other thickness standard friction coating. In use, each of the pads 612, 622 engages with the inside 404 of a blade 108 at its root portion 1 10.

Optionally, in some embodiments, a support pad 612, 622 may be provided in the form of multiple sub-pads such that each end of the lifting bar 610 may co-operate with a support pad 612, 622 in the form of multiple sub-pads. In particular, each end 616 or 618 may be provided with more than one connection to a sub-pad of a support pad 612, 622 for contacting the blade interior surface 404. Hence, each support pad 612, 622 may comprise multiple pads fixed to each end 616, 618 of the lifting bar 610, or the inside wall 404 of the blade may be provided with a support pad 612, 622 fixed to it in the form of a set of sub-pads into which each end 616, 618 of an appropriately configured lifting bar 610 may be seated. According to this embodiment, the ends 616 or 618 of the lifting bar 610 may be forked, possibly with two, three, for our more tines, and with each tine co-operating with a sub-pad of a support pad 612, 622. Preferably, in embodiments in which a blade comprises support pads 612, 622 fixed to its inside wall 404, these are arranged at diametrically opposing sides of a blade root lifting hole 606, thereby providing lifting support between the lifting bar 610 and the blade 108 on either side of the lifting hole 606.

According to aspects of the invention, at a root end lifting location, the number of points at which the blade 108 is lifted using the lifting apparatus of the invention for example by means of the support pads 612, 622 is greater than the number of lifting holes 606. This allows a single lifting hole 606 to give rise to a large blade lifting support or contact area within the interior of the blade root portion, particularly if the support pads 612, 622 have a large area of contact with the blade shell. As the support pads 612, 622 are provided spaced apart from each other and away from the lifting hole 606, improved structural stability during the lift is achieved.

Figures 5 and 6 illustrate simplified, schematic, not-to scale aspects of a blade lifting arrangement used in the construction of a wind turbine in accordance with aspects of the present invention. With reference to Fig. 6, a wind turbine 100 comprises a tower 102, on top of which a nacelle 104 is located. Attached to one end of nacelle 104 is a hub 106. Wind turbine blades 108 are secured to the hub 106, and in operation the aerodynamic lift applied to blades 108 by the wind results in a rotation of hub 106, which in turn drives the wind turbine's generator.

In general, and according to aspects of the invention, a blade 108 may be lifted at two lifting locations respectively spanwise inboard and outboard of the blade's centre of gravity. In particular, a blade 108 may be lifted at a first lifting location inboard of the blade centre of gravity 125 and at a second lifting location outboard of the centre of gravity 125. As already mentioned, blade 108 comprises a root portion 1 10 and a blade tip 1 1 1 . As mentioned, root portion 1 10 is typically circular or round when viewed in a chordwise cross- section and terminates in a circular pitch-bearing face 222. The whole root region and the root 1 10 provide structural strength where loading on the blade 108 will be highest, namely at its connection to the hub 106. The approximate location of the blade's centre of gravity 125 is indicated. According to aspects of the invention, a blade 108 may be lifted or lowered by means of a longitudinally extending yoke 1 14 from which it may be suspended. In particular, according to aspects of the invention, it may be lifted at a first location at its root 1 10 and inboard of the blade centre of gravity 125, and at a second location at or nearby a mid- 217 or tip- region 219. The second lifting location may in particular lie outboard of the blade centre of gravity 125. For this purpose, the yoke 1 14 may be a boom type yoke, as shown, having a longitudinal extent extending between an inboard end 1 13 and an outboard end 1 15. The illustrated yoke 1 14 is a boom-type yoke. The yoke 1 14 may have a beam construction. The yoke may be suspended from a crane cable 122 via a hook or shackle or any appropriate fitting (not shown). Optionally, a wire or cable 120 may extend between the lifting yoke 1 14 and the crane cable 122. Optionally, the yoke 1 14 may be suspended from a crane wire 122 at an inboard end 1 13 and at an outboard end 1 15. The yoke 1 14 may additionally comprise a spreader bar 1 17, in particular at or near its outboard end 1 15, thereby making it "T" shaped. Such a yoke may be referred to as a T-yoke'. The yoke 1 14 allows the blade 108 to be lifted e.g. from the ground up to a position suitable for connection to a hub 106, or alternatively allows the blade 108, having been disconnected from the hub 106, to be lowered e.g. to the ground, e.g. during disassembly of the wind turbine or for blade service or replacement.

According to aspects of the invention, a lifting connector 604 may be attached to an inboard end 1 13 of the yoke 1 14 and suspended therefrom. A first end 6041 of the lifting connector 604 may be lowered from outside and above the blade root 1 10 through a hole 606 in the blade shell to the inside of the blade shell at its root 1 10. All the while, the lifting connector 604 may be secured at its second end 6042 to the lifting yoke 1 14.

Further outboard along the blade 108, towards the blade tip 1 1 1 , a sling 1 18, connected to outboard end 1 15 of said yoke 1 14 may pass beneath the blade 108 thereby supporting it at a second lifting location. The illustrated sling 1 18 in Fig. 5 is suspended at both ends from a spreader bar 1 17 of a T-yoke. In the illustration of Fig. 6, the lifting sling 1 18 additionally comprises a resilient or rigid cradle 1 16 which provides more evenly distributed support from the sling 1 18 to the blade 108 at the second lifting location.

As shown in Fig. 5, the lifting bar 610 adopts a lifting support position inside the blade root 1 10. Its angular position corresponds to a horizontal or approximately horizontal position. Similarly, the lifting connector 604 adopts an approximately vertical or vertical orientation. It may be noted that in the lifting operations shown in both Figs. 5 and 6, the blade 108 maintains a predetermined lifting orientation which, advantageously, may correspond to a hub attachment orientation of the blade 108.

For reasons of stability, controllability and damage avoidance during lifting, it is desirable to minimise the blade's rotational moment when suspended at its lifting locations. In particular, it is desirable to minimise the rotational moment about the spanwise axis of the blade. In some embodiments, this can be achieved by ensuring that - during lifting - the centre of gravity of the blade 125, or its sectional centre of gravity 620 at any spanwise location, is positioned vertically below the lifting hole 606. The asymmetric distribution of mass resulting from the "bulge" at the blade trailing edge tends to draw the position of the centre of gravity 125 of the blade 108, or the sectional centre of gravity 620, away from the blade axis 304. In some embodiments, during lifting or prior to lifting, the lifting connector 604, the lifting hole 606, and the centre of gravity 125 of the blade or sectional centre of gravity indicated by cross 620 are all aligned in a vertical direction, as illustrated by the dashed line 632 in Figure 7. Minimising the rotational moment about the point of lifting means that the lifting forces applied to the blade wall 404 at the blade root lifting location and the reaction forces due to gravity at that location are rotationally neutral. The risk of damage to the blade 108 for example by chafing of the lifting connector 604 within it is reduced. The exact position of the lifting hole can be calculated using computer models and specific data relating to the relevant blade design and construction. The blade root lifting apparatus 600 can be fitted into the root 1 10 while the blade 108 is secured on the ground or while it is attached to the hub 106. Lifting bar 610 is positioned in the blade root by an installation engineer, and lifting connector 604 is inserted into lifting hole 606 and connected to the lifting bar 610. Lifting hole 606 may be formed at the installation site, for example by drilling in the blade laminate, or may be pre-formed at the manufacturing facility. If the lifting hole 606 is formed at the installation site, the position of the lifting hole may be marked on the blade laminate during the manufacture of the blade, to allow the lifting hole 606 to be accurately positioned when it is formed. The lifting bar 610 and the support pads 612, 622 within which it is seated are positioned such that support pads 612, 622 abut the interior surface 404 of the blade, and the fixing element 608 is used to connect one end of the vertical support 604 to the lifting bar 610. The blade 108 can be marked to show the positions at which the support pads 612, 622 should contact the interior surface of the blade laminate. These can then be pre-positioned on the blade interior wall 404 or they can be pre-fitted to the lifting bar 610. The blade root lifting apparatus 600 can be fitted by an engineer who can access the root portion 206 either directly if the blade 108 is located on the ground and about to be lifted up the hub 106, or via the nacelle 104 and hub 106 if the blade 108 is connected to the hub and about to be lifted down to the ground. The engineer may use the marks on the blade 108 to assist in fitting the lifting apparatus 600 with the correct alignment. Once the fixing element 608 is secured between one end 6041 of the lifting connector 604 and the lifting bar 610, the other end 6042 of the lifting connector 604 can be lifted e.g. by a crane. The lifting force applied to the lifting connector 604 is transferred via the fixing element 608 and lifting bar 610 to the support pads 612, 622 and thence to the blade root 1 10. The lifting bar 610 is therefore brought into supporting contact with first and second portions of the inside surface of the blade root 1 10. This then causes the blade 108 to be lifted upwards.

The lifting connector 604 could be a tubular bar, for example a scaffolding bar. In alternative embodiments the lifting connector 604 could be one or more cables, for example flexible steel cables, or one or more cords, chains, rods, poles, and/or bars.

Lifting bar 610 could be any bar, for example, a tubular bar, for example a scaffolding bar. In alternative embodiments the lifting bar 610 comprises an I-beam, with a hook provided for connecting to the lifting connector 604. In further alternative embodiments, the lifting bar 610 may comprise an eye or aperture through which an end of the lifting connector 604 can pass. A fixing element 608 in the form of a locking pin may be passed through an engagement surface 650 in a first end 6041 of the lifting connector. Such an engagement surface 650 may in this embodiment comprise a hole. A suitable locking hole may be substantially perpendicular to the length axis of the lifting connector 604. This has the advantage that the lifting connector 604 can remain as narrow as possible, thereby ensuring it can easily fit through the lifting hole 606 and avoiding the need for lifting hole 606 to be excessively large. In some embodiments, a locking pin may be connected to the lifting bar 610 by means of a flexible line, cable or chain. This ensures that the locking pin is attached to the lifting bar 610, even when it is not being used to lock the lifting connector 604 and lifting bar 610 together. This prevents the locking pin from becoming lost, particularly when the blade root lifting apparatus 600 is being used at height.

In the figures the lifting bar 610 is shown as substantially perpendicular to the lifting connector 604. In other embodiments this need not be the case and the support pads 612, 622 need not be level with one another. Thus a first support pad 612 may be positioned above a second support pad 622.

In some embodiments, fixing element 608 may comprise a releasable bracket or set of bolts to secure the lifting connector 604 to the lifting bar 610. A scaffolding-type connection may be suitable. Alternatively, the fixing element could be articulated to allow the lifting bar 610 to rotate with respect to the lifting connector 604. In other embodiments the connector 608 may be a flexible cable, for example a steel cable, wrapped around or engaged with the lifting bar 610 and lifting connector 604. The fixing element 608 may be integral to either the lifting bar 610 or lifting connector 604. In embodiments in which the lifting connector 604 is a cable, the connector 608 may be part of the same cable. The diameter of the lifting hole 606 will depend on the diameter of the lifting connector 604, and must be of large enough diameter to allow at least one end of the lifting connector 604 to pass through the lifting hole 606. In embodiments, a lifting hole may be configured as a spanwise extending slot, to accommodate some longitudinal tilting of the blade 108 during a lift. In some embodiments, the edges of the lifting hole 606 or slot may be protected by a ring or other fixing to avoid the lifting connector coming into direct contact with the blade laminate and causing damage.

It is important when lifting a wind turbine blade to do so in a stable and secure manner. This may require consideration of the position of the centre of gravity of the whole or a part of the blade 108 in relation to the lifting location or lifting locations. It is often desirable to maintain the local centre of gravity vertically below a relevant lifting point(s) in order to minimise the rotational moment exerted by the force of gravity on the blade during lifting. In this context, it may be appropriate to consider the "localised" centre of gravity close to each lifting location. Thus, a lifting hole can advantageously be positioned such that the

"localised" centre of gravity of the blade close to the lifting point is below that lifting hole 606. Such a localised centre of gravity can be determined by considering the sectional centre of gravity, defined as the centre of gravity of the cross-section of the blade at a given spanwise position. Figures 7 and 8 illustrate schematically and not to scale, cross sections of a blade 108 at its root 1 10 taken along line A-A in Fig. 3. A root lifting apparatus 600, according to an embodiment of the present invention is shown fitted in position inside the blade root 1 10 and contacting its internal surfaces 404. In the example of Fig. 7, lifting orientation has a maximum chord direction, shown as line 202, in an approximately horizontal orientation and the longitudinal axis also lies approximately horizontal. By way of example, it may be decided to take the maximum chord line 222 as a reference chord for designating or defining a blade lifting orientation. For reasons of expediency and for creating certainty during blade attachment, it may be decided to select a blade lifting orientation for which the reference angle, between the maximum chord 222 and the vertical, is approximately 90 degrees to the vertical. At the same time, also by way of example, it may be chosen to lift the blade with its main axis 304 lying horizontal or near horizontal. In this case, the lifting hole 606 in the blade root needs to be located at a chosen position on the blade shell along an axis normal to both the chord direction 222 and to the blade axis 304. This is illustrated in Fig. 7. With this arrangement of the hole 606, and with the blade 108 positioned prior to lifting in a horizontal arrangement of the maximum chord 222 and of the blade axis 304, the blade orientation will remain the same before and during lifting, when lifted using the lifting apparatus 600, using the method described herein. Note that the support pads 612, 622 may be correspondingly pre-positioned at the blade interior walls 404 such that the lifting bar 610 can readily be seated in the correct lifting position without experimentation.

Alternatively, the blade interior walls 404 can be pre-marked with a first and a second support point indication at those positions where the ends 616, 618 of the lifting bar 610, preferably with fitted support pads 612, 622 are positionable for lifting.

Figure 8 illustrates the blade root lifting apparatus 600 being used to lift a blade when a non-horizontal lifting orientation of the reference chord 222 is desired. Much of the above description of Figure 7 is also relevant here and will not be repeated. However, in Figure 8 the blade 108 is to be lifted with the reference chord (maximum chord direction 202) inclined at a non-orthogonal angle to the vertical direction. Compared to Figure 7, the position of the centre of gravity of the blade or the sectional centre of gravity is located at the same place within the blade 108, indicated by cross 620, but because of the different orientation of the blade 108 the position of the lifting hole 606, chosen so as to be - for the illustrated lifting orientation - vertically above the centre of gravity or sectional centre of gravity 620, is at a different place on the blade shell surface. Preferably, the position of the lifting hole 606 in the blade shell is chosen so as to be on the zero turning moment lifting axis for the particular blade orientation.

A variety of factors may be important in choosing the lifting orientation of the blade 108. This may include the pitch angle at which the blade 108 is to be connected to the hub 106, for example. As it is generally difficult to rotate the blade 108 during the lift, the blade may be lifted in a predetermined orientation with respect to the lifting yoke matching that required at the end point of the lift. The blade 108 may also be positioned in the

predetermined orientation with respect to the lifting yoke prior to lifting.

Figure 9 illustrates the disassembly of the blade root lifting apparatus 600 after the blade 108 has been lifted into position. Once the blade 108 has been lifted into position or lowered, the blade root lifting apparatus 600 is removed by detaching the lifting connector 604 from the lifting bar 610, by releasing the fixing element 608. The lifting connector 604 is then lifted out of the lifting hole 606, in the direction of the arrow 1000. This lifting may be undertaken by the same crane or lifting apparatus that was used to lift the entire blade 108 or by other manual or powered means. Either before or after the removal of the lifting connector 604 from the blade 108, the lifting bar 610 is removed from the blade 108 altogether. This may be undertaken by an engineer in the root portion 206 releasing the connector 608 and moving the lifting bar downwards in the direction of arrow 1002. In some embodiments, the lifting bar 610 may be disengaged from the support pads 612, 622 prior to removing the lifting bar 610 from the blade walls 404. The support pads may remain within the blade 108 or these may optionally be removed separately from the lifting bar 610 or together with it.

In alternative embodiments, the lifting bar 610 and support pads 612, 622 are removed first from the inside wall 404 and the lifting connector 604 is moved downwards, in the direction of arrow 1002, into the root section 1 10 where, like the lifting bar 610, it is also removed by an engineer inside the root section 1 10. This is only possible if the lifting connector 604 is sufficiently flexible or short to allow it to fit within the root section 1 10.

The lifting hole 606 that remains in blade 108 can be sealed when the lift is completed. In some embodiments, the hole 606 is filled in with blade laminate, a plastic plug, sigmaflex, or flexible sealer. This can be drilled out easily if the lifting hole 606 is needed again for future lifting.

In other embodiments, the lifting bar 610 is extendable so that it can fit across different widths of the root section 206 of the blade 108. This also enables the blade root lifting apparatus 600 to be compatible with blade roots of various different sizes.

In other embodiments, the support pads 612, 622 may be replaceable as they become worn down through use. In further embodiments, and in connection with a root lifting method and apparatus described herein, a lifting sling 1 18 may be passed partly through the inside of a blade 108 at an outboard lifting location relative to the centre of gravity 125, namely at a mid- or tip- region of the blade 108. The lifting sling 1 18 may be suspended from a lifting yoke 1 14 at its outboard end 1 15 for lifting the body portion of the blade 108. This is illustrated in various ways in Figs. 10 or 1 1 a-1 1 b and in Fig. 12, in which figures many details already described above have been left out only for simplicity. Preferably, with the blade axis 304 lying approximately horizontal, and with a chordwise direction also generally approximately horizontal, the blade 108, beyond its root end 1 10, may present a generally uppermost and a lowermost aerofoil surface. A free end of a sling 1 18 may be passed from the outside of a blade 108 through a hole 906, 908 in an uppermost blade surface and thereafter through the inside of the blade 108 before being passed out through a further hole 1006, 1008 in the lowermost blade surface, following which it may be passed back into the blade though a further hole 1006, 1008 in the lowermost surface, through the inside of the blade 108 and back out through a second hole 906, 908 in the uppermost blade surface. Thereafter, the sling 1 18 may be suspended from a lifting arrangement such as a yoke 1 14, in particular at an outboard end 1 15 thereof. The blade 108 may thus be lifted at an outboard lifting location using the sling 1 18. Optionally the holes 906, 908 in the uppermost surface may be a pair of holes while the holes 1006, 1008 in the lowermost surface may be a second pair of holes. The yoke 1 14 is shown as a beam-type yoke in Fig. 10 although any suitable yoke may be used with equivalent function. Preferably, each one of a pair of uppermost surface holes 906, 908 is provided at an opposite side of a blade main reinforcing member 414, with a first hole 906 at a leading edge 210 side of the main supporting member 414 and a second hole 908 at its trailing edge 212 side. Preferably, each one of a pair of lowermost surface holes 1006, 1008 is provided at an opposite side of a blade main reinforcing member 414, with a first hole 1006 at a leading edge 210 side of the main supporting member 414 and a second hole 1008 at its trailing edge side 212. These holes may equally be described as a pair of leading edge holes 906, 1006, each on a respective upper and lower blade surface, and pair of trailing edge holes 908, 1008, each on a respective upper and lower blade surface. The holes 906, 908, 1006, 1008 may be in the form of spanwise extending slots. The lifting sling 1 18 may be shaped as a wide strap, having a considerable width dimension in relation to its thickness to thereby more evenly distribute the lifting loads at the outboard lifting location. The sling 1 18 may be threaded into position and installed for lifting by a technician operating inside the body of the blade 108. Some basic tools may be needed for drawing the ends of the sling 1 18 through the respective holes 906, 1006, 1008, 908.

The main internal reinforcing structure in the blade 108 may be in the form of a spar (Fig. 1 1 a) or a single shear web (Fig. 1 1 b) or a double shear web or other suitable structure. Preferably, the lifting sling 1 18 passes through the inside of the blade 108 but always outside the main reinforcing structure 414. In a variant (see Fig. 12 or Fig. 1 1 b), the lifting sling may comprise a first length 1 18a and a second length 1 18b. Each length 1 18a, 1 18b may have a suspension end 128a, 128b (or tack end), for connection to a lifting device and a bridge end 138a, 138b for connection to each other via a bridging link 460. In use, the bridging ends 138a, 138b may be connected together inside the blade 108, at a leading edge side or at a trailing edge side relative to a main reinforcement member 414, for example by means of a bridging link 460. Preferably, a first length 1 18a has a longer effective length dimension than a second length 1 18b. This ensures that their respective bridging ends 138a, 138b meet at one side of the main reinforcement ember 414 when the sling lengths 1 18a, 1 18b are respectively threaded into a lifting position inside and outside the blade 108. Preferably, the first sling length 1 18a passes through the blade down through an uppermost surface and a lowermost surface at one side of a main reinforcement member 414 and back again up through the lowermost blade surface at an opposite side of the main reinforcement member 414 and inside the blade 108. Conversely, a second length 1 18b may simply pass down through an uppermost blade surface such that its bridging end 138b is located inside the blade at the same side of the main reinforcement member 414 as the bridging end 138a of the first length. This is illustrated by way of example at Fig. 1 1 b. This embodiment avoids the need to feed a free end of the sling 1 18 back up to a lifting arrangement after threading through the blade 108. It also allows disengagement of a lifting sling 1 18 without removing a tack end thereof from a lifting arrangement.

It is envisaged that features from any of the embodiments described herein may be combined together, at least to the extent that it is not prohibited by the laws of physics or otherwise manifestly impossible, and similarly that the steps of the methods described herein may be likewise be combined together or performed in a different order to that described. For the avoidance of doubt, the term "lifting" may include the act or operation of lowering, especially a blade 108. The mid-region of a blade may alternatively be referred to as a body region. A blade leeward side may be known as a pressure side. A blade windward side may be known as a suction side. A blade shell typically comprises a suction and a pressure side or a suction and a pressure surface. References to a shell may be references to the physical wall of a blade. Where a part is referred to in the singular "a", it may not necessarily be excluded that multiple such parts may be envisaged unless expressly excluded using the word "single" or "only one" or the like. Various modifications to the example embodiments described above are possible without departing from the scope of the following claims.

Claims

1 . A method of lifting a wind turbine blade by means of a lifting yoke, said blade having a shell extending longitudinally from a root region to a tip region and a lifting hole positioned at a lifting location in the blade root region;

the method including suspending the blade from a lifting yoke at respective lifting locations in a root region and at a mid- or tip-region thereof, the method additionally including:

passing a first end of a lifting connector through said lifting hole to an interior root region of the blade shell;

providing within the interior root region of said shell a lifting bar having a first end region and a second end region spaced from each other;

connecting, within said shell, said first end of said lifting connector to said lifting bar, such that said lifting connector engages with said lifting bar at a portion thereof between its first and second end regions;

bringing respective first and second end regions of said lifting bar into supporting contact with the inside surface of the interior root region of said shell at respective first and second points within said shell; and

lifting the blade using the lifting bar in said root region of said blade, and using said lifting connector connected at a second end thereof to said lifting yoke;

the method further comprising disengaging, when lifting the blade is completed, said lifting bar from the lifting connector, retracting said lifting connector out through said lifting hole and removing said lifting bar from within the blade shell.

2. The method of any preceding claim, including positioning said lifting bar within said root region of said shell in a substantially horizontal orientation.

3. The method of any preceding claim, wherein the connecting step comprises locking the lifting connector to the lifting bar.

4. The method according to any preceding claim, wherein said step of suspending said blade mid- or tip-region from the lifting yoke includes supporting a lifting sling from an outboard end of said yoke and passing said lifting sling externally around said blade at or nearby said mid- or tip-region thereof.

5. The method according to any preceding claim 1 -3, wherein said step of suspending said mid- or tip-region of said blade from said lifting yoke includes passing an elongate lifting sling internally through said blade shell and externally around a longitudinally extending internal structural support member of said blade.

6. The method according to claim 5, further including passing said lifting sling through two pairs of holes arranged adjacent said internal structural support member wherein each pair of holes is provided in a respective suction or pressure side of said blade shell and with a respective one hole of each of said pair of holes being provided at a leading and at a trailing edge side of said internal structural support member.

7. The method according to claim 6, including joining together, inside said blade shell, a first and a second length of said sling at a bridge section thereof at a location adjacent said longitudinally extending internal structural support member.

8. The method of any preceding claim, further including selecting a desired lifting orientation of said blade; determining for said lifting orientation, the reference angle between a blade reference chord and the vertical axis; providing a hole in the blade shell root at a point which lies vertically above the blade's centre of rotation at its root when the blade reference chord is at its reference angle.

9. The method of any preceding claim, wherein prior to the lifting of the blade, the blade is positioned in a predetermined lifting orientation with respect to the lifting connector.

10. A lifting apparatus configured for lifting a wind turbine blade, said blade having a shell extending longitudinally from a root region to a tip region and a lifting hole positioned at a lifting point in the root region of the blade, the lifting apparatus comprising:

a lifting connector having a first end configured for passing through said lifting hole to an interior root region of the blade shell;

a lifting bar having a first end region and a second end region spaced apart from each other, for providing supporting contact with respective first and second portions of the inside surface of the interior root region of said shell; and

an engagement portion provided between the first and second end regions of the lifting bar, for engaging with said first end of said lifting connector; said lifting connector being connectable at a second end to a lifting yoke externally of said blade to thereby suspend, together with said lifting bar, said root portion of said blade from said yoke.

1 1 . The lifting apparatus of claim 10, wherein the first end of the lifting connector is provided with an engagement member for engaging with the engagement portion of the lifting bar.

12. The lifting apparatus of claims 10 or 1 1 , additionally comprising a sling or strap configured for suspending the mid- or tip-region of the blade from a lifting yoke.

13. The lifting apparatus of any of claims 10 to 12, additionally comprising support pads configured for providing supporting contact between the inside surface of the interior root region of the blade shell and said first and second end regions of the lifting bar.

14. The lifting apparatus of claim 13, wherein at least part of said support pads comprises a resilient, flexible material.

15. The lifting apparatus of claim 13 or 14, wherein the support pads have a complementary shape to the inside surface of the interior of a blade root region.