WO2014039636A1

WO2014039636A1 - Multicant winglets

Info

Publication number: WO2014039636A1
Application number: PCT/US2013/058203
Authority: WO
Inventors: James David COLLING; John Stephenson NEEL; York Nelson ZENTNER
Original assignee: V Cirrus Winglet Group, Llc
Priority date: 2012-09-05
Filing date: 2013-09-05
Publication date: 2014-03-13
Also published as: US20140064979A1

Abstract

A multicant winglet has a first blade section having a leading and a trailing edge, a first lowermost edge and a first uppermost edge, and a first central plane defined by the edges, and a second blade section having a leading and a trailing edge, a second lowermost edge and a second uppermost edge, and a second central plane defined by the edges. The first central plane is canted from vertical by a first cant angle, and the second central plane is canted from vertical by a second cant angle, the first cant angle unequal to the second cant angle.

Description

MULTICANT WINGLETS

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Patent Application (PPA) 61/696,984 filed on September 5, 2012. All disclosure of the PPA is incorporated at least by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the technical area of wing and winglet design and function, and pertains more particularly to multicant winglets.

2. Description of Related Art

There is a need for increased efficiency in wing and winglet performance due to increasing cost of energy and concern for carbon emissions into the environment. In some applications, such as racing of aircraft, automobiles and boats, obtaining maximum speed with the available power is critical. Obtaining greater fluid dynamic efficiency of lifting surfaces such as for aircraft wings and wind turbine blades can reduce the required energy for flight or the volume and velocity of wind required to rotate wind turbine blades. For hydrodynamic foils, such as in the use of "America Cup" type sailing catamarans, greater fluid dynamic efficiency of lifting surfaces will allow a hull to be lifted off a water surface at a lower velocity and with better control, thus reducing drag and obtaining higher velocity.

Winglets are installed on many aircraft in current art, and are typically composed of a winglet blade set at a single overall cant angle. Some winglet designs have a continuous transition from the primary lifting surface / wing and the "winglet" which acts in turn more like an upwardly curved wing extension rather than a separate winglet. The present inventors have discovered, and teach in the following specification, improvements in winglet design that have beneficial effects on performance. BRIEF SUMMARY OF THE INVENTION In one embodiment of the invention a multicant winglet is provided, comprising a first blade section having a leading and a trailing edge, a first lowermost edge and a first uppermost edge, and a first central plane defined by the edges, and a second blade section having a leading and a trailing edge, a second lowermost edge and a second uppermost edge, and a second central plane defined by the edges. The first central plane is canted from vertical by a first cant angle, and the second central plane is canted from vertical by a second cant angle, the first cant angle unequal to the second cant angle.

In one embodiment the multicant winglet has more than two blade sections canted at different angles from vertical. Also in one embodiment the first blade section is a base or lower section having a base dimension between the leading and the trailing edges at the lowermost edge, and the leading and trailing edges converge to a second dimension less than the base dimension at the first uppermost edge. Still in one embodiment

dimension between the leading and the trailing edges of the second blade section at its lowermost edge is equal to the second dimension at the uppermost edge of the first blade section, and the leading and trailing edges of the second blade section converge further to the uppermost edge of the second blade section.

Further in one embodiment the uppermost edge of the second blade section is a straight edge, and further comprising a tip section having a lowermost edge equal in dimension to the uppermost edge of the second blade section, and wherein the leading and trailing edges of the tip section converge and join in a curved uppermost edge.

Also in one embodiment the tip section has a cant angle from vertical different than those of the first and the second blade sections. In another embodiment the cant angle from vertical is greatest for the first blade section, next greatest for the second blade section, and least for the tip section. In one embodiment the cant angle for the tip section is zero. In some embodiments the second central plane of the second blade section is rotated in a horizontal plane by a toe angle from the first central plane of the first blade section. Also in some embodiments the tip section is rotated in a horizontal plane by a toe angle from the second central plane of the second blade section.

In some embodiments the leading edges of the first and the second blade sections are swept back at a backswept angle from the position at the first lowermost edge of the first blade section, and in some cases the backsweep angle is between 25 and forty degrees inclusive.

In another aspect of the invention a lifting assembly is provided comprising a primary lifting element having a leading and a trailing edge and a central plane defined by the edges, a multicant winglet comprising a first blade section having a leading and a trailing edge, a first lowermost edge and a first uppermost edge, and a first central plane defined by the edges, and a second blade section having a leading and a trailing edge, a second lowermost edge and a second uppermost edge, and a second central plane defined by the edges, wherein the first central plane is canted from vertical by a first cant angle, and the second central plane is canted from vertical by a second cant angle, the first cant angle unequal to the second cant angle, and a contoured transition section having a first interface with a shape for joining to a cross section of the primary lifting element and a second interface with a shape for joining to a cross section of the first blade section of the multicant winglet, the contour of the transition section shaped such that the sections are joined to present the multicant winglet blades at their first and second cant angles.

In one embodiment the multicant winglet in the assembly comprises more than two blade sections canted at different angles from vertical. Also in one embodiment the first blade section of the multicant winglet is a base or lower section having a base dimension between the leading and the trailing edges at the lowermost edge, and the leading and trailing edges converge to a second dimension less than the base dimension at the first uppermost edge. Also in some embodiments dimension between the leading and the trailing edges of the second blade section of the multicant winglet at its lowermost edge is equal to the second dimension at the uppermost edge of the first blade section, and the leading and trailing edges of the second blade section converge further to the uppermost edge of the second blade section. In one embodiment the uppermost edge of the second blade section is a straight edge, and the assembly further comprises a tip section having a lowermost edge equal in dimension to the uppermost edge of the second blade section, and wherein the leading and trailing edges of the tip section converge and join in a curved uppermost edge.

In some embodiments the tip section has a cant angle from vertical different than those of the first and the second blade sections. Also in some embodiments the cant angle from vertical is greatest for the first blade section, next greatest for the second blade section, and least for the tip section. In one embodiment the cant angle for the tip section is zero.

In some embodiments of the assembly the second central plane of the second blade section is rotated in a horizontal plane by a toe angle from the first central plane of the first blade section. Also in some embodiments the tip section is rotated in a horizontal plane by a toe angle from the second central plane of the second blade section. The leading edges of the first and the second blade sections may be swept back at a backsweep angle from the position at the first lowermost edge of the first blade section. The backsweep angle may be between 25 and forty degrees inclusive.

In one embodiment the first interface of the transition section with the primary lifting element comprises a mechanism enabling the toe angle of the multicant winglet to be adjusted.

Also in one embodiment transition section comprises a plurality of openings connected to one or both of a pump and a suction mechanism, whereby air or other gaseous medium may be drawn in or pumped out through the openings. Also in one embodiment the assembly comprises one or more boundary layer trip strips applied to surfaces of one or more sections, tripping laminar flow to turbulent flow. The assembly may further comprise a mechanism providing vibration to sections of the winglet, the vibration changing patterns of laminar and turbulent flow. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Fig. la illustrates use of multicant winglets according to an embodiment of the present invention on aircraft.

Fig. lb illustrates a multicant winglet on the end of a wind turbine blade in an embodiment of the invention.

Fig. lc illustrates a multicant winglet at the end of a hydrofoil from a hull of a racing watercraft in an embodiment of the invention.

Fig. 2a is a side elevation view of a multicant winglet joined to a lifting element 201.

Fig. 2b is a view of the winglet of Fig. 2a at 90 degrees from the view of Fig 2a in an embodiment of the invention.

Figs. 3a, 3b and 3c illustrate a typical winglet, a Blended winglet and an Elliptical winglet.

Fig. 4 illustrates airflow conditions over a wing with a multicant winglet in an embodiment of the invention.

Fig. 5 is an elevation view of a multicant winglet joined to a wing in an embodiment of the invention.

Fig. 6 illustrates position of a winglet blade leading edge relative to lifting surface leading edge in an embodiment of the invention.

Fig. 7 is a plan view downward onto a wing and a multicant winglet illustrating tip inflow in an embodiment of the invention.

Fig. 8 illustrates a multicant winglet blade joined to a wing, and swept back in an embodiment of the invention.

Fig. 9 is a perspective view of a wing joined by a transition section to a multicant winglet in an embodiment of the invention.

Fig. 10a, b and c illustrate the proper position of the leading edge of the winglet blade with respect to the primary lifting surface in an embodiment of the invention.

Fig. 11 is a downward perspective view of a wing joined by a transition region to a multicant winglet in an embodiment of the invention. Fig. 12 is a side elevation view of a wing joined to a multicant winglet by a contoured transition section, to illustrate boundary layer control in an embodiment of the invention.

Fig. 13 is an elevation view of an assembly for placing LED lighting for navigation, strobe or recognition purpose at or near the tip of a multicant winglet blade in an embodiment of the invention.

Fig. 14 illustrates several wing planforms to which multicant winglets may be added in embodiments of the invention.

Fig. 15 illustrates an aircraft with two wings to which multicant winglets may be applied in an embodiment of the invention.

Fig. 16 illustrates by heavy boundary lines an exemplary region of cavitation from a hydrofoil without multicant winglets.

DETAILED DESCRIPTION OF THE INVENTION

A multicant winglet is a wing-like device which is canted outboard from vertical orientation comprising a lifting surface with multiple, (1 or more), dihedral angle breaks on the winglet blade lifting surface. The lifting surface of the winglet is attachable to a primary fluid dynamic lifting surface, such as an aircraft wing, wind turbine blade, or hydrofoil surface, having an airfoil or hydrofoil cross section with an upper and lower wing surfaces. In a critical departure from the typical winglet design approaches, the winglet blade has defined cant angle breaks, which may be dihedral or polyhedral. Inclusion of these cant angle breaks reduces shed vortex strength by breaking up the trailing vortices into multiple smaller vortices along the trailing edge of the winglet blade at each cant angle break at the multicant winglet blade tip and at the contoured section which transitions the primary lifting surface to the winglet blade. By having multiple cant angles on the winglet, the design may be better optimized by the use of winglet blade twist, wash-out or wash-in, best for the particular winglet cant angle and height above the fluid dynamic lifting surface. This also allows for having a greater winglet cant angle, measured from vertical, at the base of the winglet, and less cant angle, more vertical, higher up from the lifting surface. By having multiple cant angles along the winglet, the overall loads at the tip of the lifting surface can be reduced by reducing the area of the winglet planform section with the higher cant angle, thus reducing the vertical load in this section.

Further, in a departure from other winglet designs, such as the "blended winglet" or "elliptic winglet", the multicant winglet leading edge is set back from the primary lifting surface leading edge such that the leading edge is not a continuous blend from the wing to the winglet. This is due to the fact that the lifting surface tip vortex starts to form at the lifting surface leading edge. By setting back the winglet blade leading edge, the tip vortex is allowed to form at the wing tip and flow to the low pressure side of the winglet blade root and contoured section. The strength of the tip vortex is used to provide an induced tip inflow which is stronger and at a greater angle at the root and less strength and angle at the top of the winglet blade. For this reason, the winglet blade is swept back such that the induced inflow continues to provide an induced angle of attack at the top of the winglet blade as the inflow continues downstream. The upper section of the winglet blade is generally washed- in (twisted inboard) in order to maintain a consistent angle of attack from the root to the tip of the winglet blade.

The shape of the contoured section from the lifting surface to the winglet blade can be defined by a Non-uniform rational B-spline (NURBS) curve fit from the lifting surface airfoil to the winglet blade airfoil. The shape of the contoured section is defined by the toe out angle, height of the winglet blade root and the distance out from the lifting surface to the winglet blade root. These dimensions may be changed depending on the wing loading and Reynolds number. Guidelines for the design of the contoured section of the winglet are provided in the text of this patent.

The toe angle of the winglet blade root is set based on design parameters such as the winglet blade lift curve slope, induced inflow and the required performance aspects. The winglet toe angle is generally fixed but having the ability to adjust this angle can greatly benefit the overall performance of the winglet and to assist in fine adjustment during installation.

The use of boundary layer control such as fluid suction or blowing, acoustics or boundary layer turbulators, can be utilized to further improve efficiency as-well-as the capability of having the winglet toe angle be adjustable on ground or in flight either passively or actively to optimize the winglet for different conditions such as climb, cruise, velocity and fluid density.

The present invention includes an option to have navigation, strobe and/or recognition lighting embedded in a tip or other portion of a winglet blade to further reduce parasitic drag.

On a multicant winglet, the leading edge of the winglet is set back a distance from the primary lifting surface. In this manner, the tip vortex of the primary lifting surface is allowed to form which provides the required inflow at the winglet root leading edge and contoured transition region such that the winglet will produce an induced angle of attack due to the inflow caused by the tip vortex. This induced angle of attack will in turn produce a forward component of the lift vector, thus reducing the induced drag as well as producing additional lift at the end of the wing, reducing the required wing angle of attack, further reducing drag. On a multicant winglet in embodiments of the invention, the tip vortices are further split into multiple smaller and weaker vortices at each winglet cant angle dihedral break and at the winglet blade tip as opposed to a strong vortex which has been simply moved from the wingtip to the winglet tip in the case of conventional blended or elliptic type winglets or in the case of a wing tip extension.

The toe angle of a winglet is critical and depends on different aspects of operation as well as the winglet cant angle. For aircraft, the winglet toe out angle can be set depending of what flight characteristics are required. This toe angle can be set by rotating (twisting) the winglet blade to a different angle at each cant angle break. In addition, having the capability to adjust the toe angle, either passively by ground adjustment or actively in flight, the winglet can be adjusted for optimal performance. This capability can provide greater efficiency and installation adjustability.

The use of boundary layer control may also be used to help in flow attachment during some operational conditions. The boundary layer may be controlled by means of suction or blow holes in the surface of the winglet blade and/or the contoured transition section of the winglet. The use of boundary layer trip strips or the use of acoustic vibration may be used to effect boundary layer transition from laminar to turbulent and the eliminate boundary separation bubbles which may occur during high lift / high angle of attack conditions. Multicant winglets in embodiments of this invention may also include a unique feature in that the navigation and strobe lighting are embedded into the tip of the winglet blades to further reduce drag, have greater visibility to other aircraft for collision avoidance and to give a unique appearance.

Fig. la illustrates use of multicant winglets according to an embodiment of the present invention on aircraft. Element 101 is a multicant winglet at an end of an aircraft wing 102. Fig. lb illustrates a multicant winglet 104 on the end of a wind turbine blade 103. Fig. lc illustrates a multicant winglet 106 at the end of a hydrofoil 105 from a hull of a racing watercraft 107.

On aircraft, as shown in Fig. la, addition of multicant winglets improves fuel efficiency, increases cruise speed and has an added benefit of lowering stall speed, thus reducing takeoff and landing distance, increasing climb rate and allowing for a higher gross weight. Multicant winglets, because of their design characteristics, help to prevent wingtip stall and thus improve flight safety at low speeds by improving aileron control and helping to prevent spins.

For wind turbine blades, as illustrated in Fig. lb, the addition of multicant winglets allows rotation of the turbine at lower wind speeds and has the added benefit of reduce aeroacoustic noise.

On high performance boats such as "Americas Cup" type racing catamarans, as illustrated in Fig. lc, use of multicant winglets on the keels, centerboards and foils allow the hull to be lifted out of the water at lower speeds and provides more stable control at higher speeds, as-well-as reducing onset of cavitation at the tip of the hydrofoil blade. These features reduce drag and allow for greater velocity.

Fig. 2a is a side elevation view of a multicant winglet 200 joined to a lifting element 201, such as an aircraft wing or wind turbine blade. Fig. 2b is a view of winglet 200 at 90 degrees from the view of Fig 2a, as shown by arrow 2b in Fig. 2a. Winglet 200 in this example has a transition portion 202 at an interface to the lifting element, and two blade portions 203 and 204, oriented at different angles from vertical as illustrated by angles φΐ and cp2 in Fig. 2b. Portions 203 and 204 join at dihedral angle break 205. Height "h" of the winglet is typically at least one chord length of the primary lifting surface tip. A wing or other lifting surface such as 201 may be considered to have a central plane defined by edges of the wing, the plane lying horizontal. Similarly, any blade portion of a winglet joined to the lifting element will also have a central plane defined by the edges of the winglet. Central planes are considered in this discussion because the outside surfaces of a wing or winglet will typically have some curvature. The central plane of a wing or other lifting element, lying horizontal, is oriented 90 degrees from vertical. As a convention in this specification the cant angle of a winglet blade section is measured from vertical, and for higher accuracy should be measured to the central plane, although measuring to the substantial plane of one or the other outside surface will show but a very small difference.

Figs. 3a, 3b and 3c illustrate a typical winglet 301, a Blended winglet 302 and an Elliptical winglet 303. In a critical departure from usual winglet design

approaches, the winglet blade of the multicant winglet in embodiments of this invention has defined cant angle breaks (203 in Figs. 2a and 2b) which may be dihedral or polyhedral. Use of cant angle breaks reduces shed vortex strength by breaking up trailing vortices into multiple smaller vortices.

Fig. 4 illustrates airflow conditions over a wing 401 with a multicant winglet 402 in an embodiment of the invention. Vortices are shown along the trailing edge of the multicant winglet at cant angle break 403, as well as along the inboard surface of contoured section 404 and winglet tip 405. The vortex at the base of the winglet tends to improve the pressure gradient which in turn promotes an increase in laminar boundary layer on the upper surface of primary lifting surface 401. Line 406 represents transition between laminar flow in the boundary layer, and turbulent flow over the trailing portion of the wing. A sharp transition between the cant angles at 403 produces a more defined shed vortex at the cant angle break.

Fig. 5 is an elevation view of a multicant winglet 501 joined to a wing 502 in an embodiment of the invention, illustrating changes in toe angle as well as cant angle. Winglet 501 in this example has three changes in toe angle, one at location 503, a second at location 504, and a third at location 505.

Portions 506 and 507 of winglet 501 have different cant angles with vertical.

The different portions may also have different toe angles, which is the angle of the surface of a portion of the winglet measured in a horizontal plane relative to a reference. The reference may be the toe angle of a connection portion of the winglet. Portion 506, for example, has a toe angle of λΐ, portion 507 has a toe angle of λ2, and tip 508 has a toe angle of λ3. The toe angle can be a toe-in, where the plane edge of the subject portion may be rotated such that the leading edge rotates toward the wing, or toe out, away from the wing.

By having multiple cant angles on the winglet the toe angle of the wing blade may be better optimized for the cant angle. For example, the lower winglet blade may be set at a single toe out angle at the root 503 and at the first break 504, whereas the winglet blade above the first cant angle break can be rotated in from the lower toe out angle) to reduce the toe out angle higher up on the winglet.

Fig. 6 illustrates position of the winglet blade 601 leading edge relative to lifting surface leading edge 602, and this is critical for optimal performance. In a departure from conventional winglet designs, such as one that is blended 302, or an elliptic winglet 303 (see Fig. 3), the multicant winglet leading edge 601 in this example is set back from the lifting surface leading edge 602 by 40% of the wing dimension, such that the leading edge is not a continuous in-line blend from the lifting surface leading edge to the winglet leading edge. This is due to the fact that the lifting surface tip vortex starts to form at the wing leading edge 602. By setting back the winglet leading edge, the tip vortex is allowed to form at the wing tip and flow to the low pressure side of the winglet root and contoured section 60. For best results, the winglet blade should be positioned between 25 and 50 percent back from the lifting surface leading edge.

Fig. 7 is a plan view downward onto a wing 701 and a multicant winglet 702 illustrating tip inflow, induced by strength of the tip vortex, which is greater at the root and less at the top of the winglet blade.

Fig. 8 illustrates a multicant winglet blade 801 joined to a wing 802, and swept back, such that the blade remains in the influence of the induced inflow from root to tip, as shown in Fig. 7. The amount of winglet blade sweep depends on the strength of the induced inflow which is in turn depends on wing loading, aspect ratio, and Reynolds number. Typical winglet blade sweep is in the range of 25 to 45 degrees.

Fig. 9 is a perspective view of a wing 901 joined by a transition section 903 to a multicant winglet 902 in an embodiment of the invention. The transition is a contoured section from the primary lifting surface to the winglet blade, and is quite important to maintain proper inflow and flow attachment to the winglet blade. This shape in various embodiments may be defined by a Non-uniform rational B-spline (NURBS) curve fit from the primary lifting surface foil 901 to the winglet blade foil 902. The curves should match the chordwise percent positions between

airfoils/hydrofoils. The NURBS curve fit is a mathematical model commonly used in computer graphics for generating and representing curves and surfaces. The shape of the contoured section is defined by the toe out angle a, height of the winglet blade root, the distance d out from the primary lifting surface to the winglet blade root, and the distance of the winglet blade leading edge from the lifting surface leading edge. These dimensions may be changed depending on the wing loading, Reynolds number and the shape and type of lifting surface.

Fig. 10a, b and c illustrate the proper position of the leading edge of the winglet blade with respect to the primary lifting surface, which is critical for optimum performance. If the winglet leading edge is too far forward as in Fig. 10a, the vortex induced inflow will not have a chance to fully develop and the winglet will perform more like a tip extension, as shown in Fig. 10b, by moving the tip vortex to the end of the winglet. If the winglet is set back further than 50 percent of the lifting surface tip chord, as in Fig. 10c, the winglet will be in the region of a fully developed tip vortex thus stalling the winglet root, as shown at the tip of the winglet. The multicant aspect in embodiments of this of this invention still applies even when a contoured section is not used and/or the winglet blade leading edge is not set back from the lifting surface leading edge as described above.

In general, the multicant winglets are designed to be a passive system which is optimized for a particular application. However, performance in some embodiments may be further enhanced by an ability to adjust the root toe angle of the multicant winglet blade. Fig. 11 is a downward perspective view of a wing 1105 joined by a transition region 1104 to a multicant winglet 1101 comprising two regions 1102 an 1103 joined at angle break 1108. In this embodiment winglet 1101, including transition region 1104, is joined to wing 1105 by a mechanical interface in which a planar portion of the wing lies adjacent and coplanar with a planar portion of the transition region, and the two planar portions are joined by a pivot 1106, which allows the winglet toe angle to be changed within at least a small arc. In this example a pushrod or jackscrew may be remotely controlled to control the toe angle. It will be apparent to the skilled artisan that the interface and mechanism to adjust the toe angle may be accomplished in a variety of ways.

Adjusting the toe angle is advantageous for changes in operational conditions such as climb, cruise and glide path for aircraft and for changes in velocity and fluid density (Reynolds number) in other applications. On aircraft, greater toe out angles improve climb where-as lower toe out angles will improve cruise speed. The toe angle can be adjusted on the ground or actively in operation by changing the length of the pushrod or by the repositioning of the pushrod. For a jack screw arrangement, adjustments can be made by use of a screw driver type tool to rotate the jack screw. The adjustment may also be made by the use of servos to either move the push rod or the rotate the jack screw. In order to reduce drag at the junction of the lifting surface and the contoured section of a toe angle adjustable winglet, the outer surface skins will be allowed to slide within such that there is minimal gap produced.

Fig. 12 is a side elevation view of a wing 1201 joined to a multicant winglet 1202 by a contoured transition section 1203, to illustrate boundary layer control. In this example turbulator trip tape is applied one or both sides of the winglet to trip the boundary layer from laminar to turbulent flow to prevent formation of separation bubbles or laminar flow separation on the winglet blade or contoured section.

Boundary layer control, especially in the contoured section of the winglet, can be utilized to further improve winglet performance by preventing flow separation at high angle of attack of the lifting surface, such as during climb in an aircraft.

In this example openings 1205 connect to pumping and suction mechanisms for ingesting air or blowing air over the surface of transition section 1203 as a means of boundary layer control. Acoustic vibration can also be used to trip the entire winglet surface to a turbulent boundary layer to promote flow attachment at speeds near stall or during high lift conditions.

Fig. 13 is an elevation view of an assembly for placing LED lighting for navigation, strobe or recognition purpose at or near the tip of a multicant winglet blade to further reduce parasitic drag. The assembly comprises a clear lens 1301 covering LEDs and a structural back frame which encloses LED lighting circuit boards 1303. The back frame may be either molded into the winglet blade or may be a separate component which is attachable to the end of the winglet blade.

Aircraft Applications

Multicant winglets according to various embodiments of the present invention can be used on aircraft which include but are not limited to airplanes and sailplanes. Multicant winglets may be added to existing aircraft wings which were originally not designed for the use of winglets. Fig. 14 illustrates several wing planforms to which multicant winglets may be added. These planforms include, but are not limited to, straight 1401, tapered 1402, swept 1403, multi taper 1404, elliptic 1405, crescent

1406, or any other type of wing planform. Multicant winglets may also be included in the original design of new aircraft. They may also be added to any lifting surface for aircraft with multiple lifting surfaces, such as on tandem wing or multi surface aircraft. Fig. 15 illustrates an aircraft 1501 with two wings. Multicant winglets may be used on both of the wings of aircraft 1501 illustrated in Fig. 15.

Even though the multicant winglet in embodiments of this invention pertains to the definition of the contoured section and the multicant feature of the winglet blade, they can also be added to the end on wing tip extensions. Wind Turbine Applications

For wind turbine blades, addition of multicant winglets allows the rotation of the turbine at proper RPM at lower wind speeds. Typically, multicant winglets on turbine blades will be a passive system. However, the same features as those described above for aircraft can be implemented in design. An additional benefit of multicant winglets on wind turbines is reduction of aerodynamic generated noise.

Hydrofoils and High Performance Yachts

On high performance watercraft, such as "America's Cup" type racing catamarans, the use of multicant winglets on the keels and/or centerboards allows the hull to be lifted out of the water at lower speeds and provides more stable control at higher speeds. The use of multicant winglets helps to prevent cavitation. Fig. 16 illustrates by heavier boundary lines an exemplary region of such cavitation from a hydrofoil 1601 without multicant winglets. Reduced cavitation with multicant winglets on the hydrofoil is due to more efficient spanwise loading and more favorable pressure gradient on the upper surface at the primary lifting surface tip.

The design features of multicant winglets helps to reduce wing tip load and wing root bending moment as compared to more conventional winglet designs, including "blended" and elliptical winglets. This is due to reduced winglet blade surface area in the lower section of the winglet blade. Because of leading edge setback used to induce inflow at the winglet root, the multicant winglet produces greater performance gains with reduced winglet blade surface area and has a smaller winglet root chord length as opposed to winglets which blend the wing and winglet together or compared to wingtip extensions alone. Multicant winglet design covers design of the contoured transition from the lifting surface to the winglet, the multicant aspect of the invention and the use of design features such as adjustable toe angle, boundary layer control and integrated winglet tip lights all in an effort to reduce the drag, to increase efficiency and to increase safety. However, wing extensions may be included with the installation of multicant winglets.

It will be apparent to the skilled person that the examples provided above to describe the features and advantages of multicant winglets in various embodiments may be altered in a variety of ways without departing from the scope of the invention, which is limited only by the scope of the claims below.

Claims

1. A multicant winglet comprising:

a first blade section having a leading and a trailing edge, a first lowermost edge and a first uppermost edge, and a first central plane defined by the edges; and a second blade section having a leading and a trailing edge, a second lowermost edge and a second uppermost edge, and a second central plane defined by the edges;

wherein the first central plane is canted from vertical by a first cant angle, and the second central plane is canted from vertical by a second cant angle, the first cant angle unequal to the second cant angle.

2. The multicant winglet of claim 1 comprising more than two blade sections canted at different angles from vertical.

3. The multicant winglet of claim 1 wherein the first blade section is a base or lower section having a base dimension between the leading and the trailing edges at the lowermost edge, and the leading and trailing edges converge to a second dimension less than the base dimension at the first uppermost edge.

4. The multicant winglet of claim 3 wherein dimension between the leading and the trailing edges of the second blade section at its lowermost edge is equal to the second dimension at the uppermost edge of the first blade section, and the leading and trailing edges of the second blade section converge further to the uppermost edge of the second blade section.

5. The multicant winglet of claim 1 wherein the uppermost edge of the second blade section is a straight edge, and further comprising a tip section having a lowermost edge equal in dimension to the uppermost edge of the second blade section, and wherein the leading and trailing edges of the tip section converge and join in a curved uppermost edge.

6. The multicant winglet of claim 5 wherein the tip section has a cant angle from vertical different than those of the first and the second blade sections.

7. The multicant winglet of claim 6 wherein the cant angle from vertical is greatest for the first blade section, next greatest for the second blade section, and least for the tip section.

8. The multicant winglet of claim 7 wherein the cant angle for the tip section is zero.

9. The multicant winglet of claim 1 wherein the second central plane of the second blade section is rotated in a horizontal plane by a toe angle from the first central plane of the first blade section.

10. The multicant winglet of claim 5 wherein the tip section is rotated in a horizontal plane by a toe angle from the second central plane of the second blade section.

11. The multicant winglet of claim 1 wherein the leading edges of the first and the second blade sections are swept back at a backswept angle from the position at the first lowermost edge of the first blade section.

12. The multicant winglet of claim 11 wherein the backsweep angle is between 25 and forty degrees inclusive.

13. A lifting assembly comprising:

a primary lifting element having a leading and a trailing edge and a central plane defined by the edges;

a multicant winglet comprising a first blade section having a leading and a trailing edge, a first lowermost edge and a first uppermost edge, and a first central plane defined by the edges, and a second blade section having a leading and a trailing edge, a second lowermost edge and a second uppermost edge, and a second central plane defined by the edges, wherein the first central plane is canted from vertical by a first cant angle, and the second central plane is canted from vertical by a second cant angle, the first cant angle unequal to the second cant angle; and

a contoured transition section having a first interface with a shape for joining to a cross section of the primary lifting element and a second interface with a shape for joining to a cross section of the first blade section of the multicant winglet, the contour of the transition section shaped such that the sections are joined to present the multicant winglet blades at their first and second cant angles.

14. The lifting assembly of claim 13 wherein the multicant winglet comprises more than two blade sections canted at different angles from vertical.

15. The lifting assembly of claim 13 wherein the first blade section of the multicant winglet is a base or lower section having a base dimension between the leading and the trailing edges at the lowermost edge, and the leading and trailing edges converge to a second dimension less than the base dimension at the first uppermost edge.

16. The lifting assembly of claim 15 wherein dimension between the leading and the trailing edges of the second blade section of the multicant winglet at its lowermost edge is equal to the second dimension at the uppermost edge of the first blade section, and the leading and trailing edges of the second blade section converge further to the uppermost edge of the second blade section.

17. The lifting assembly of claim 13 wherein the uppermost edge of the second blade section is a straight edge, and further comprising a tip section having a lowermost edge equal in dimension to the uppermost edge of the second blade section, and wherein the leading and trailing edges of the tip section converge and join in a curved uppermost edge.

18. The lifting assembly of claim 17 wherein the tip section has a cant angle from vertical different than those of the first and the second blade sections.

19. The lifting assembly of claim 18 wherein the cant angle from vertical is greatest for the first blade section, next greatest for the second blade section, and least for the tip section.

20. The lifting assembly of claim 19 wherein the cant angle for the tip section is zero degrees from vertical.

21. The lifting assembly of claim 13 wherein the second central plane of the second blade section is rotated in a horizontal plane by a toe angle from the first central plane of the first blade section.

22. The lifting assembly of claim 17 wherein the tip section is rotated in a horizontal plane by a toe angle from the second central plane of the second blade section.

23. The lifting assembly of claim 13 wherein the leading edges of the first and the second blade sections are swept back at a backsweep angle from the position at the first lowermost edge of the first blade section.

24. The lifting assembly of claim 23 wherein the backsweep angle is between twenty- five and forty degrees inclusive.

25. The lifting assembly of claim 13 wherein the first interface of the transition section with the primary lifting element comprises a mechanism enabling the toe angle of the multicant winglet to be adjusted.

26. The lifting assembly of claim 13 wherein the transition section comprises a plurality of openings connected to one or both of a pump and a suction mechanism, whereby air or other gaseous medium may be drawn in or pumped out through the openings.

27. The multicant winglet of claim 1 further comprising one or more boundary layer trip strips applied to surfaces of one or more sections, tripping laminar flow to turbulent flow.

28. The multicant winglet of claim 1 further comprising a mechanism providing vibration to sections of the winglet, the vibration changing patterns of laminar and turbulent flow.