Patent Publication Number: US-2012027595-A1

Title: Pitchable winglet for a wind turbine rotor blade

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to wind turbines and, more particularly, a wind turbine rotor blade having a pitchable winglet. 
     BACKGROUND OF THE INVENTION 
     Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from the wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid. 
     To ensure that wind power remains a viable energy source, efforts have been made to increase energy outputs by modifying the size and capacity of wind turbines. One such modification has been to increase the length and surface area of the rotor blades. However, the magnitude of deflection forces and loading of a rotor blade is generally a function of blade length, along with wind speed, turbine operating states, blade stiffness, and other variables. This increased loading not only produces fatigue on the rotor blades and other wind turbine components but may also increase the risk of a sudden catastrophic failure of the rotor blades, for example when excess loading causes deflection of a blade resulting in a tower strike. 
     To reduce the effective length of a rotor blade without significantly impacting its performance, it is known to include a wingtip device, such as winglet, at the tip of each rotor blade. However, even with the shortened effective length that can be achieved using a winglet, loads acting on a rotor blade, particularly in high speed wind conditions, may still cause the blade to deflect significantly towards the tower. Moreover, due to its orientation on the rotor blade as well as its aerodynamic profile, a winglet generates lift forces that cause bending moments to be applied at the tip of the rotor blade. These bending moments result in an increase in the amount of blade deflection, which, in some instances, may further decrease the amount of clearance between the rotor blade and the wind turbine tower. 
     Accordingly, a rotor blade having a pitchable winglet that permits the loads exerted by the winglet on the blade to be adjusted and/or controlled would be welcomed in the technology. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect, the present subject matter discloses a rotor blade for a wind turbine. The rotor blade may include a blade root, a blade tip and a body. The body may include a base portion extending from the blade root and a winglet extending from the base portion to the blade tip. Additionally, at least a portion of the winglet may be configured to be pitched independent of the base portion. 
     In another aspect, the present subject matter discloses a rotor blade for a wind turbine. The rotor blade may include a blade root, a blade tip and a body. The body may include a base portion extending from the blade root and a winglet extending from the base portion to the blade tip, wherein at least a portion of the winglet may be configured to be pitched independent of the base portion. In addition, the winglet may be further configured to pivot relative to the base portion between an in-line position and a winglet position. 
     In a further aspect, the present subject matter discloses a wind turbine. The wind turbine may generally include a plurality of rotor blades. Each rotor blade may include a blade root, a blade tip and a body. The body may include a base portion extending from the blade root and a winglet extending from the base portion to the blade tip. Additionally, at least a portion of the winglet may be configured to be pitched independent of the base portion. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  illustrates a perspective view of one embodiment of a wind turbine; 
         FIG. 2  illustrates a perspective view of one embodiment a rotor blade having a pitchable winglet; 
         FIG. 3  illustrates a partial, side view of the rotor blade shown in  FIG. 2 , particularly illustrating a side view of the pitchable winglet; 
         FIG. 4  illustrates a cross-sectional view of the winglet shown in  FIG. 3  taken along line  4 - 4 ; 
         FIG. 5  illustrates a partial, side view of an embodiment of a rotor blade having a pitchable and pivotable winglet, particularly illustrating the winglet in a winglet position; 
         FIG. 6  illustrates another partial, side view of the rotor blade shown in  FIG. 5 , particularly illustrating the winglet after it has been moved from the winglet position to an in-line position; 
         FIG. 7  illustrates a partial, side view of another embodiment of a rotor blade having a pitchable and pivotable winglet; 
         FIG. 8  illustrates a spanwise view of the rotor blade shown in  FIG. 7 , particularly illustrating a spanwise view of the winglet taken about line  8 - 8 ; and, 
         FIG. 9  illustrates a cross-sectional view of the winglet shown in  FIG. 8  taken along line  9 - 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     In general, the present subject matter is directed to a rotor blade having a pitchable winglet in order to control the loads exerted on the rotor blade by the winglet. Specifically, the winglet may be configured to be actively pitched in order to control the lift forces generated by the winglet in a manner that minimizes blade deflection towards the tower of a wind turbine. For example, when a rotor blade includes a pressure side winglet, the winglet may be pitched so that the lift force generated by the winglet produces a lift vector directed in an inboard direction, thereby producing a bending moment on the rotor blade that tends to bow or flex the blade away from the tower. Moreover, the disclosed winglet may be used to improve the aerodynamic efficiency of a rotor blade and/or to increase the amount of energy captured by a rotor blade. 
     It should be appreciated that, by reducing blade deflection towards the tower, numerous advantages may be provided to a wind turbine. For example, reduced blade deflection may allow for a lighter rotor blade to be utilized, thereby increasing the overall performance of the wind turbine. In addition, reduced blade deflection may result in decreased fatigue loading on the rotor blades, thereby reducing damage to the blades and increasing their operating life. Moreover, due to the increased tower clearance, suction side winglets may be utilized without significantly increasing the likelihood of a tower strike. 
     It should also be appreciated that, in several embodiments, the disclosed winglet may be pivotally connected to the remainder of the blade such that the winglet is movable between an in-line position, wherein the winglet is aligned with the pitch axis of the rotor blade, and a winglet position, wherein the winglet is angled relative to the pitch axis of the rotor blade. By configuring the winglet in this manner, the effective length of the rotor blade may be adjusted depending on the operating conditions of the wind turbine. For example, in low load conditions wherein blade deflection is relatively small, the winglet may be moved to the in-line position to increase the effective length of the rotor blade, thereby increasing its ability to capture energy from the wind. However, in high load conditions, the winglet may be moved to the winglet position to reduce the effective length of the rotor blade, thereby reducing the amount of deflection occurring due to the increased loads. 
     Referring now to the drawings,  FIG. 1  illustrates perspective view of one embodiment of a wind turbine  10 . As shown, the wind turbine  10  includes a tower  12  extending from a support surface  14 , a nacelle  16  mounted on the tower  12 , and a rotor  18  coupled to the nacelle  16 . The rotor  18  includes a rotatable hub  20  and at least one rotor blade  22  coupled to and extending outwardly from the hub  20 . For example, in the illustrated embodiment, the rotor  18  includes three rotor blades  22 . However, in an alternative embodiment, the rotor  18  may include more or less than three rotor blades  22 . 
     Additionally, the wind turbine  10  may also include a turbine control system or turbine controller  24  centralized within the nacelle  16 . However, it should be appreciated that the turbine controller  24  may be disposed at any location on or in the wind turbine  10 , at any location on the support surface  14  or generally at any other location. The controller  24  may generally be configured to control the various operating modes (e.g., start-up or shut-down sequences) and/or the components of the wind turbine  10 . For example, the controller  24  may be configured to adjust a pitch angle or blade pitch of each of the rotor blades  22  (i.e., an angle that determines a perspective of the rotor blades  22  with respect to the direction  26  of the wind) in order to control the loads acting on and/or the power generated by the wind turbine  10  by adjusting an angular position of at least one of the rotor blades  22  relative to the wind. For instance, the controller  24  may control the blade pitch of the rotor blades  22  about their pitch axes  28 , either individually or simultaneously, by controlling a suitable pitch adjustment mechanism  30  housed within the nacelle  16 . 
     It should be appreciated that the turbine controller  24  may generally comprise a computer or any other suitable processing unit. Thus, in several embodiments, the turbine controller  24  may include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions. As used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) of the turbine controller  24  may generally comprise memory element(s) including, but are not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the turbine controller  24  to perform various functions including, but not limited to, transmitting suitable control signals to the disclosed pitch adjustment mechanisms and the like. In addition, the controller  24  may also include various input/output channels for receiving inputs from sensors and/or other measurement devices and for sending control signals to various components of the wind turbine  10 . 
     Referring still to  FIG. 1 , as shown, each rotor blade  22  generally includes a pressure side winglet  32 . However, in alternative embodiments, each rotor blade  22  may include a suction side winglet. As is generally understood, winglets  32  may be used to improve the overall efficiency and performance of a wind turbine  10 . For example, each winglet  32  may generally define an aerodynamic profile similar to the aerodynamic profile defined by the remainder of the rotor blade  22 . As such, the winglets  32  may generate lift forces as the rotor blades  22  rotate about the rotor  18 . However, depending on the orientation of each winglet  32  relative to the direction  26  of the wind, the magnitude and direction of the lift vector produced by the winglet  32  may vary significantly, which may, in turn, vary the loads that the winglet  32  exerts on the rotor blade  22 , both on average and in extreme loading conditions. For example, as shown in  FIG. 1 , when the winglet  32  generates a lift vector  34  that is directed in a substantially inboard direction (e.g., in a direction generally towards the hub  20 ), a bending moment  36  may be applied by the winglet  32  that tends to flex or bow the rotor blade  22  away from the tower. Similarly, when the winglet  32  generates a lift vector  38  that is directed in a substantially outboard direction (i.e., in a direction generally away the hub  20 ), a bending moment  40  may be applied by the winglet  32  that tends to flex or bow the rotor blade  22  towards the tower. As such, winglet lift vectors  34  directed in the outboard direction tend to decrease the amount of tower clearance  42  defined between the rotor blade  22  and the tower  12 , thereby increasing the likelihood of a tower strike. 
     It should be appreciated that, in embodiments in which each rotor blade  22  includes a suction side winglet, the bending moments  36 ,  38  generated by such winglets may be reversed. For example, lift vectors  38  generated by suction side winglets that are directed in the outboard direction will tend to flex or bow the rotor blade  22  away from the tower  12 . Similarly, lift vectors  34  generated by suction side winglets that are directed in the inboard direction will tend to flex or bow the rotor blade  22  towards the tower  12 . 
     Referring now to  FIGS. 2-4 , various views of one embodiment of a rotor blade  100  having a pitchable winglet  102  is illustrated in accordance with aspects of the present subject matter. Specifically,  FIG. 2  illustrates a perspective view of the rotor blade  100 .  FIG. 3  illustrates a partial, side view of the rotor blade  100 , particularly illustrating a side view of the winglet  102 . Additionally,  FIG. 4  illustrates cross-sectional view of the winglet  102  taken along line  4 - 4 . 
     As shown, the rotor blade  100  generally includes a blade root  104  configured for mounting the rotor blade  100  to the rotor hub  20  of the wind turbine  10  ( FIG. 1 ) and a blade tip  106  disposed opposite the blade root  104 . A body  108  of the rotor blade  100  may generally extend from the blade root  104  to the blade tip  106  and may serve as the outer shell of the rotor blade  100 . As is generally understood, the body  108  may define an aerodynamic profile, such as by defining a symmetrical or cambered airfoil-shaped cross-section, to enable the rotor blade  100  to capture kinetic energy from the wind using known aerodynamic principles. As such, the body  108  may generally include a pressure side  110  and a suction side  112  extending between a leading edge  114  and a trailing edge  116 . Additionally, the rotor blade  100  may have a span  118  defining the total length of the blade  100  between the blade root  104  and the blade tip  106  and a chord  120  defining the total length of the body  108  between the leading edge  114  and the trailing edge  116 . As is generally understood, the chord  120  may vary in length with respect to the span  118  as the rotor blade  100  extends between the blade root  104  to the blade tip  106 . 
     The body  108  of the rotor blade  100  may generally include a base portion  122  and a pitchable winglet  102  extending from the base portion  122 . In particular, the base portion  122  may generally extend outwardly from the blade root  104  and may comprise the main airfoil section of the rotor blade  100 . The winglet  102  may generally be configured as a wingtip device for improving the aerodynamic efficiency of the rotor blade  100  and, thus, may extend between the base portion  122  and the blade tip  106 . As shown in the illustrated embodiment, the winglet  102  comprises a pressure side winglet. However, in alternative embodiments, the winglet  102  may comprise a suction side winglet. 
     It should be appreciated that, in several embodiments, the winglet  102  may be manufactured as a separate component from the base portion  122  and, thus, may be configured to be coupled to the base portion  122  using any suitable means and/or method known in the art (e.g., by using suitable fasteners, adhesives and like). For example, as shown in  FIGS. 2 and 3 , a blade joint  124  may be defined at the interface between the winglet  102  and the base portion  122  generally corresponding to the point of coupling of such components. Alternatively, the winglet  102  and the base portion  122  may be formed integrally as a single component. For instance, in one embodiment, the entire body  108  (including the winglet  102  and the base portion  122 ) may be initially cast together in a common mold. 
     Referring still to  FIGS. 2-4 , the rotor blade  100  may also include a pitch adjustment mechanism  126  disposed within the body  108  that is separate from the pitch adjustment mechanism  30  ( FIG. 1 ) adapted to rotate the entire rotor blade  100  about its pitch axis  128 . In general, the pitch adjustment mechanism  126  may be configured to pitch the winglet  102  relative to and/or independent from the base portion  122  of the body  108 . Specifically, in several embodiments, the pitch adjustment mechanism  126  may be configured to rotate at least a portion of the winglet  122  about a winglet pitch axis  130  oriented at an angle  132  relative to the pitch axis  128  of the rotor blade  100 . For example, as particularly shown in  FIG. 3 , the angle  132  defined between the winglet pitch axis  130  and the blade pitch axis  128  may be equal to about 90 degrees. However, in alternative embodiments, the angle  132  may be less then 90 degrees or greater than 90 degrees. 
     In general, the pitch adjustment mechanism  126  may comprise any suitable device and/or combination of devices known in the art that may be configured to pitch at least a portion of the winglet  102  about its pitch axis  130 . For example, as particularly shown in  FIG. 3 , the pitch adjustment mechanism  126  may, in one embodiment, comprise a motor  134  (e.g., an electric motor) coupled to a portion of the winglet  102 . In such an embodiment, the motor  134  may be directly coupled to winglet  102  (e.g., by directly coupling the output shaft of the motor  134  to a portion of the winglet  102 ) or the motor  134  may be indirectly coupled to the winglet  102  (e.g., by coupling the motor  134  to a portion of the winglet  102  through a gearbox, any suitable linkage or coupling and/or any other suitable component). In other embodiments, the pitch adjustment mechanism  126  may comprise any other suitable rotational motion device and/or arrangement. For instance, the pitch adjustment mechanism  126  may comprise other gear driven devices, belt and pulley arrangements, ball and socket arrangements and the like. In even further embodiments, the pitch adjustment mechanism  126  may comprise one or more suitable actuators whose output(s) may be converted into rotational motion through suitable linkages and/or couplings. For instance, the pitch adjustment mechanism  126  may comprise a linear actuator (e.g., a pneumatic or hydraulic cylinder, a electro-mechanical actuator, a solenoid actuated device and/or the like) coupled to the winglet  102  through suitable linkages and/or couplings. 
     As indicated above, in several embodiments, the pitch adjustment mechanism  126  may only be configured to pitch a portion of the winglet  102  about the winglet pitch axis  120 . For example, as shown in  FIG. 3 , in one embodiment, the winglet  102  may include a first, fixed portion  136  rigidly coupled to the base portion  122  at the blade joint  124  and a second, rotatable portion  138  extending outwardly from the fixed portion  136  towards the blade tip  106 . In such an embodiment, the rotatable portion  138  may generally be configured to be rotated about the winglet pitch axis  130  at a pitch joint  140  defined at the interface between the fixed portion  136  and the rotatable portion  136 . For example, as shown in the illustrated embodiment, the pitch adjustment mechanism  126  may be coupled to the rotatable portion  138  at or adjacent to the pitch joint  140  to permit the rotatable portion  138  to be pitched relative to the fixed portion  136 . 
     It should be appreciated that, in alternative embodiments, the entire winglet  102  may be configured to be pitched relative to the base portion  122  of the rotor blade  100 . For example, the pitch adjustment mechanism  126  may be coupled to the winglet  102  at or adjacent to the blade joint  124  such that the winglet  102  may be pitched relative to the base portion  122  at such joint  124 . 
     By configuring at least a portion of the winglet  102  to be pitchable independent of the base portion  122 , the orientation of the winglet  102  relative to the direction  26  of the wind may be actively adjusted in order to control the loads exerted by the winglet  102  on the rotor blade  100 . For example, as particularly shown in  FIG. 4 , rotation of the winglet  102  about its pitch axis  130  may alter the orientation of the leading edge  114  of the winglet  102  relative to the wind direction  26 , thereby adjusting the aerodynamic performance of the winglet  102 . Thus, in several embodiments, the winglet  102  may be pitched in a manner that minimizes deflection of the rotor blade  100  towards the wind turbine tower  12  ( FIG. 1 ), thereby decreasing the likelihood of a tower strike occurring. For example, when a pressure side winglet  102  is included on the rotor blade  100 , it may be desirable to pitch the winglet  102  in a manner that causes the lift vector  34  ( FIG. 1 ) generated by the winglet  102  to be directed in the inboard direction, thereby producing a bending moment  36  ( FIG. 1 ) at the blade tip  106  that tends to bow the rotor blade  100  away from the tower  12 . In such an embodiment, it should be appreciated that the winglet  102  may be pitched so that the lift vector  34  is continuously directed in the inboard direction (e.g., by continuously pitching the winglet  102  around the entire rotational path of the blade  100  in order to maintain the lift vector  34  directed in the inboard direction) or the winglet  102  may be pitched so that the lift vector  34  is only directed in the inboard direction at particular rotor positions (e.g., by actively pitching the winglet  102  so that the lift vector  34  is directed in the inboard direction as the rotor blade  100  passes the tower  12 ). 
     It should be appreciated that, in several embodiments, the winglet  102  may be actively pitched using the turbine controller  24  described above. For example, the pitch adjustment mechanism  126  may be communicatively coupled to the turbine controller  24  (e.g., via a wired or wireless connection) so that suitable control signals may be transmitted from the controller  24  to the pitch adjustment mechanism  126  in adjust the pitch of the winglet  102 . In such embodiments, it should be appreciated that the turbine controller  24  may be configured to receive any manner of input from various sensors  142  disposed on and/or within the rotor blade  100  or at any other suitable location on, within and/or around the wind turbine  10  that are configured to monitor various operating conditions of the rotor blade  100  and/or the wind turbine  10 . For example, the sensors  142  may be configured to sense, detect and/or measure operating conditions such as, but not limited to, loads acting on the rotor blade  100 , the orientation of the winglet  102  relative to the direction  26  of the wind, the amount of tower clearance  42  present, wind conditions (e.g., wind speed and direction), and the like and then transmit suitable signals to the turbine controller  24  corresponding to the operating condition(s) being monitored. The turbine controller  24  may then be configured to analyze such operating conditions and determine when and/or to what extent to pitch each winglet  102  about its pitch axis  130  in order to control the loads generated by each winglet  102  and/or to optimize the overall efficiency and/or performance of the rotor blade  100 . 
     Referring now to  FIGS. 5 and 6 , a partial view of another embodiment of a rotor blade  200  is illustrated in accordance with aspect of the present subject matter. In general, the illustrated rotor blade  200  may be configured similarly to the rotor blade  100  described above. For example, the rotor blade  200  may include a body  208  having a base portion  222  extending from a blade root  104  ( FIG. 2 ) and a pitchable winglet  202  extending from the base portion  222  towards a blade tip  206 . In addition, the rotor blade  200  may include a pitch adjustment mechanism  226  configured to pitch a rotatable portion  238  of the winglet  202  about a winglet pitch axis  230 . As such, the orientation of the winglet  202  relative to the direction  26  of wind ( FIG. 4 ) may be adjusted independent of the base portion  222 . 
     However, unlike the embodiment described above, in addition to being pitchable, the winglet  202  may also be configured to be movable from a winglet position (shown in  FIG. 5 ), wherein the winglet pitch axis  230  is oriented at an angle relative to the blade pitch axis  228 , to an in-line position (shown in  FIG. 6 ) wherein the winglet pitch axis  230  is generally aligned with the blade pitch axis  228 . Specifically, the rotor blade  200  may include an actuating mechanism  250  provided at any suitable location within the base portion  222  for moving the winglet  202  between the winglet and in-line positions. For example, as shown in the illustrated embodiment, the actuating mechanism  250  may comprise a piston  252  coupled to the winglet  202  by a suitable linkage and/or coupling  254 . However, in alternative embodiments, the actuating mechanism  250  may generally comprise any the suitable active control mechanism that is configured to receive control signals from the turbine controller  24  in order to retract and/or deploy the winglet  202 . For instance, the actuating mechanism  250  may comprise an electric motor, a pneumatic or hydraulic cylinder, a electro-mechanical actuator, a solenoid actuated device and/or the like. In further embodiments, the actuating mechanism  250  may also include a passive component, such as a spring, or other biasing member that may be configured to bias the winglet  202  to either of the in-line or winglet positions. In such an embodiment, an active device, such as a motor, piston, or the like, may then be used to move the winglet  202  in the respective opposite direction against the bias force of the spring or other biasing member. 
     It should also be appreciated that the actuating mechanism  250  may be configured to variably actuate the winglet  202  to any suitable winglet position. For example, as shown in  FIG. 5 , the winglet  202  has been actuated to a position at which the winglet pitch axis  230  is generally disposed at a 90 degree angle relative to the blade pitch axis  228 . However, in alternative embodiments, the actuating mechanism  250  may be configured to actuate the winglet  202  such that the angle defined between the winglet pitch axis  230  and the blade pitch axis  228  is less than 90 degrees or greater than 90 degrees. 
     In addition, unlike the fixed portion  136  of the winglet  100  described above with reference to  FIG. 3 , the illustrated winglet  200  may include a pivoting portion  236  configured to be pivotally coupled to the base portion  222  of the rotor blade  200  to permit the winglet  200  to be pivoted between the winglet and in-line positions. Specifically, as shown in the illustrated embodiment, the pivoting portion  236  may be configured to extend generally between a pitch joint  240  defined at the interface between the rotating portion  238  and the pivoting portion  236  and an end  256  of the base portion  222  when the winglet  202  is in the winglet position. However, when the winglet  202  is moved to the in-line position, the pivoting portion  236  may be configured to deployed within or otherwise pivot into the base portion  222 . For instance, in several embodiments, the pivoting portion  236  may comprise a rigid or semi-rigid, arcuate shaped member that is configured to swing into the base portion  222  when the winglet  202  is moved to the in-line position and swing out of the base portion  222  when the winglet  202  is moved to the winglet position. In an alternative embodiment, the pivoting portion  236  may be compressible so as to fit within the base portion  222  in the in-line position, but may assume its arcuate or extended shape upon deployment to the winglet position. For instance, the pivoting portion  236  may be formed from any suitable pliable, conformable and/or elastic material (e.g., a canvas or other suitable sheet material, a pleated material, a collapsible material, and so forth) so that the pivoting portion  236  is capable of being folded or otherwise reduced in size into deployed or stowed position within the base portion  222  and/or the winglet  202  when the winglet  202  is moved to the in-line position. 
     It should be appreciated that the pivoting portion  236  of the winglet  202  may generally be pivotally coupled to the base portion  222  using any means known in the art. For example, as shown in the illustrated embodiment, the pivoting portion  230  may be coupled to the base portion  222  with a hinge joint  258  defined by any suitable hinge structure, such as a mechanical hinge, a living hinge, and so forth. 
     Referring now to  FIGS. 7-9 , various views of a further embodiment of a rotor blade  300  having a pitchable winglet  302  are illustrated in accordance with aspects of the present subject matter. Specifically,  FIG. 7  illustrates a partial, side view of the rotor blade  300 , particularly illustrating a side view of the winglet  302 .  FIG. 8  illustrates a partial, spanwise view of the rotor blade  300  looking from the hub  18  of the wind turbine  10  ( FIG. 1 ), particularly illustrating a spanwise view of the winglet  302  taken along line  8 - 8 . Additionally,  FIG. 9  illustrates a cross-sectional view of the winglet  302  taken along line  9 - 9 . 
     In general, the illustrated rotor blade  300  may be configured similarly to the rotor blades  100 ,  200  described above with reference to  FIGS. 2-6 . For example, the rotor blade  300  may include a body  308  having a base portion  322  extending from a blade root  104  ( FIG. 2 ) and a pitchable winglet  302  extending from the base portion  322  towards a blade tip  306 . In addition, the rotor blade  300  may include a pitch adjustment mechanism  326  configured to pitch a at least a portion of the winglet  302  about a winglet pitch axis  330 . As such, the orientation of the winglet  302  relative to the direction  26  of wind may be adjusted independent of the base portion  322 . 
     However, unlike the embodiments described above, the illustrated pitch adjustment mechanism  326  may be configured to control the pitch of the winglet  302  by flexing or otherwise deforming the winglet  302  along its length. Specifically, in several embodiments, at least a portion of the winglet  302  may be formed from a flexible and/or deformable material that is capable of being flexed and/or deformed by the pitch adjustment mechanism  326 . For example, as shown in  FIG. 7 , in one embodiment, the winglet  302  may be configured as a flexible sleeve  360  having a first end  362  coupled to the base portion  322  at the blade joint  324  and a second end  364  terminating at the blade tip  306 . In such an embodiment, the flexible sleeve  360  may be formed from any suitable material that is capable of maintaining the winglet&#39;s aerodynamic profile (e.g., an airfoil shaped cross-section) when in an unstressed state, but may be flexed and/or deformed when a force is applied to it. For instance, the flexible sleeve  360  may be formed from various suitable polymer materials, rubber materials and/or the like. 
     Additionally, the pitch adjustment mechanism  326  may generally comprise any suitable device and/or combination devices that are configured to flex and/or deform the winglet  302  in order to adjust the winglet&#39;s orientation relative to the wind. For example, as shown in the illustrated embodiment, the pitch adjustment mechanism  326  may include a first rod  366  extending adjacent to and/or being coupled to the leading edge  314  of the winglet  302  and a second rod  368  extending adjacent to and/or being coupled to the trailing edge  316  of the winglet  302 . In addition, the pitch adjustment mechanism  326  may include one or more actuators  370 ,  372  configured to actuate the rods  366 ,  368  in one or more directions. For example, as particularly shown in  FIG. 8 , the pitch adjustment mechanism  326  may include a first actuator  370  coupled to the first rod  366  and a second actuator  372  coupled to the second rod  368 . Each actuator  370 ,  372  may generally be configured to actuate its respective rod  366 ,  368  (e.g., by rotating each rod  366 ,  368  about an actuation point  374  ( FIG. 7 )) in order to flex and/or deform at least a portion of the winglet  302  is along its length. 
     By actuating one or both of the rods  366 ,  368 , the orientation of the winglet  302  relative to the direction  36  of the wind may be adjusted. For example, as shown in  FIG. 9 , by actuating the first and second rods  366 ,  368  in opposite directions (e.g., by rotating the rods  366 ,  368  in opposite directions about the actuation point  374 ), the winglet  302  may be twisted, flexed and/or deformed along its length, thereby altering positions of the leading and trailing edges  314 ,  316  of the winglet  302  relative to the wind and adjusting the pitch of the winglet  302  about the pitch axis  330 . In another embodiment, only one of the rods  366 ,  368  may be actuated within the winglet  302  in order to adjust the position of the leading edge  314  or the trailing edge  316  relative to the direction  36  of the wind. 
     It should be appreciated that the first and second rods  366 ,  368  may generally comprise any suitable elongated members that have sufficient stiffness and/or rigidity to permit the winglet  302  to be flexed and/or deformed when the rods  366 ,  368  are actuated. For example, the rods  366 ,  368  may be formed from various rigid and/or semi-rigid materials, such as one or more metal materials, hard plastic materials and the like. Additionally, it should be appreciated that the actuators  370 ,  372  may generally comprise any suitable device and/or combination of devices that may be configured to actuate the rods  366 ,  368  in one or more directions. For example, the actuators  370 ,  372  may comprise motors, electro-mechanical actuators, solenoid actuated devices, pneumatic or hydraulic cylinders and the like. Moreover, in several embodiments, the pitch adjustment mechanism  326  may only include a single rod, such as by including a single rod extending adjacent to or being coupled to the leading edge  314  or trailing edge  316 . Similarly, the pitch adjustment mechanism  326  need not include both a first actuator  370  and a second actuator  372 . For example, in one embodiment, a single actuator may be coupled to the first and second rods  366 ,  368  and may be configured to actuate the rods  366 ,  368  simultaneously and/or individually. 
     It should also be appreciated that, in alternative embodiments, the pitch adjustment mechanism  326  may include any other suitable components and/or may have any other suitable arrangement that permits it to function as described herein. For example, the pitch adjustment mechanism  326  may simply comprise one or more linear actuators configured to flex and/or otherwise deform a portion of the winglet  302 . 
     In addition, as particularly shown in  FIG. 7 , in several embodiments, the winglet  302  may also be configured to be moved from a winglet position, wherein the winglet pitch axis  330  is oriented at an angle relative to the blade pitch axis  328 , to an in-line position (indicated by the dashed lines  376 ), wherein the winglet pitch axis  330  is generally aligned with the blade pitch axis  328 . In particular, the flexible and/or deformable nature of the material used to form the winglet  302  may allow the winglet  302  to be flexed and/or deformed in a manner that brings the winglet  302  into alignment with the base portion  322  of the rotor blade  300 . Thus, as shown in the illustrated embodiment, the actuators  370 ,  372  of the pitch adjustment mechanism  326  may be configured to rotate the rods  366 ,  368  approximately 90 degrees about the actuation point  374 , thereby aligning the winglet  302  with the pitch axis  328  of the rotor blade  300 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.