Aircraft winglet system

Abstract

Winglet system for an aircraft. The present invention provides a winglet system for an aircraft wing, the winglet system comprising: an attachment end for attachment to a main wing of the aircraft; an upper winglet; and a lower winglet. The upper winglet and the lower winglet are staggered from each other along a chord of the attachment end and also overlap each other. The spanwise profile of the lower winglet has a midpoint, wherein the slope of the spanwise profile at points outboard of the midpoint is more upwardly inclined than the slope of the spanwise profile at the midpoint. The configuration of the winglet system can provide benefits such as reducing bending moments and reducing adverse interference between winglets while controlling ground clearance.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 954,752, filed December 30, 2019, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to aircraft and, more particularly, to winglets for aircraft. Background Art

[0004] Winglets are wingtip extensions known to increase lift and reduce lift-induced drag on fixed-wing aircraft wings. For example, winglets can improve the wing's long-range or high-speed cruise performance, helping to increase the aircraft's range, and can help improve climb gradients and / or reduce climb thrust. Winglets can also enhance the aircraft's visual appearance.

[0005] Because winglets are typically lift-generating surfaces, they induce bending moments in the wing to which they are attached. This requires that the wing's structure be designed to withstand these bending moments. Consequently, adding a winglet to a wing places a weight burden on both the winglet itself and the heavier wing structure, which must be constructed to withstand the bending moments induced by the winglet. Summary of the Invention

[0006] In one aspect, the present disclosure describes a wing for an aircraft. The wing includes:

[0007] a main wing including a main wingtip; and

[0008] A winglet system is attached to the main wingtip, the winglet system comprising:

[0009] an upper winglet having an upper winglet tip outboard of the main wingtip; and

[0010] a lower winglet having a lower winglet tip outboard of the main wingtip, the upper winglet tip of the upper winglet being arranged higher relative to the main wingtip than the lower winglet tip of the lower winglet;

[0011] in:

[0012] The upper winglet and the lower winglet are staggered along the chord of the main wingtip;

[0013] The upper winglet and the lower winglet overlap each other along the chord of the main wingtip; and

[0014] The lower winglet has a spanwise profile extending along a leading edge thereof having a midpoint, and a slope of the spanwise profile at points outboard of the midpoint is more upwardly inclined than the slope of the spanwise profile at the midpoint.

[0015] A point on the spanwise profile outboard of the midpoint may be closer to the lower winglet tip than the midpoint.

[0016] The point on the spanwise profile outboard of the midpoint may be substantially at the lower winglet tip.

[0017] The upper and lower winglets may extend upwardly relative to the main wingtip.

[0018] The upper winglet may extend upwardly relative to the main wingtip, and the lower winglet may extend downwardly relative to the main wingtip.

[0019] The spanwise profile of the lower winglet may include a lower winglet inflection. The lower winglet inflection may be arranged between a proximal portion of the spanwise profile of the lower winglet, closer to the main wingtip, and a distal portion of the spanwise profile, further away from the main wingtip. The proximal portion of the spanwise profile may be shorter than the distal portion of the spanwise profile.

[0020] In some embodiments, at least a majority of the distal portion of the spanwise profile may be recessed relative to the space between the upper and lower winglets when viewed along the chord of the main wingtip.

[0021] In some embodiments, at least a majority of the distal portion of the spanwise profile may be curved when viewed along the chord of the main wingtip.

[0022] The lower winglet tip may be oriented upward.

[0023] The engagement angle between the upper and lower winglets may be between 60 degrees and 90 degrees when viewed along the chord of the main wingtip.

[0024] The engagement angle between the upper and lower winglets may be greater than 45 degrees and up to 150 degrees when viewed along the chord of the main wingtip.

[0025] The root chord length of the lower winglet may be between 55% and 80% of the chord length of the main wingtip.

[0026] The wing root chord length of the upper winglet may be between 55% and 80% of the chord length of the main wing tip.

[0027] The overlap of the root chords of the upper winglet and the lower winglet may be between 10% and 60% of the chord length of the main wingtip.

[0028] The leading edge of the lower winglet may be arranged forward of the leading edge of the upper winglet relative to the chord of the main wingtip.

[0029] The leading edge of the upper winglet may be arranged forward of the leading edge of the lower winglet relative to the chord of the main wingtip.

[0030] The overlapping portion between the upper winglet and the lower winglet may extend from a junction of the upper winglet and the lower winglet to a tip of the lower winglet.

[0031] The spanwise profile of the upper winglet extending along the leading edge of the upper winglet may be tangentially discontinuous with the leading edge of the main wing when viewed along the chord of the main wingtip.

[0032] The spanwise profile of the upper winglet may have a first upper winglet bend. The spanwise profile of the upper winglet may have a second upper winglet bend.

[0033] The lower winglet may be swept back relative to the chord of the main wingtip. The upper winglet may be swept back relative to the chord of the main wingtip.

[0034] The upper winglet tip may be arranged outboard of the lower winglet tip.

[0035] Embodiments may include combinations of the above features.

[0036] In another aspect, the present disclosure describes a winglet system for an aircraft wing. The winglet system includes:

[0037] an attachment end for attachment to a main wing of the aircraft and defining an airfoil section having a chord;

[0038] Upper winglets; and

[0039] Lower winglet, wherein, in the operating orientation of the winglet system:

[0040] The upper winglet has an upper winglet tip outboard of the attachment end;

[0041] The lower winglet has a lower winglet tip outboard of the attachment end;

[0042] an upper winglet tip of the upper winglet being arranged higher relative to the attachment end than a lower winglet tip of the lower winglet;

[0043] The upper winglet and the lower winglet are staggered along the chord of the attachment end;

[0044] The upper and lower winglets overlap each other along a chord of the attachment ends; and

[0045] The spanwise profile of the lower winglet extending along the leading edge of the lower winglet has a midpoint, and the slope of the spanwise profile at points outboard of the midpoint is more upwardly inclined than the slope of the spanwise profile at the midpoint.

[0046] Both the upper and lower winglets may extend upwardly relative to the attachment end.

[0047] The upper winglet may extend upward relative to the attachment end, and the lower winglet may extend downward relative to the attachment end.

[0048] Embodiments may include combinations of the above features.

[0049] In a further aspect, the present disclosure describes an aircraft comprising:

[0050] body;

[0051] one or more engines for propelling the aircraft, the one or more engines being mounted to the fuselage; and

[0052] a first wing and a second wing disposed on opposite sides of the fuselage, said first and second wings each comprising:

[0053] a main wing including a main wingtip; and

[0054] A winglet system is attached to the main wingtip, the winglet system comprising:

[0055] an upper winglet having an upper winglet tip outboard of the main wingtip; and a lower winglet having a lower winglet tip outboard of the main wingtip;

[0056] in:

[0057] The upper winglet tip of the upper winglet is arranged to be higher than the lower winglet tip of the lower winglet relative to the main wingtip;

[0058] The upper winglet and the lower winglet are staggered along the chord of the main wingtip;

[0059] The upper winglet and the lower winglet overlap each other along the chord of the main wingtip; and

[0060] The spanwise profile of the lower winglet extending along the leading edge of the lower winglet has a midpoint, and the slope of the spanwise profile at points outboard of the midpoint is more upwardly inclined than the slope of the spanwise profile at the midpoint.

[0061] The upper and lower winglets may extend upwardly relative to the main wingtip.

[0062] The upper winglet may extend upwardly relative to the attachment end, and the lower winglet may extend downwardly relative to the main wingtip.

[0063] The aircraft may be devoid of any engines mounted on the first and second wings for propelling the aircraft.

[0064] Embodiments may include combinations of the above features.

[0065] In a further aspect, the present disclosure describes an aircraft including the winglet system described herein.

[0066] Further details of these and other aspects of the subject matter of the present application will be apparent from the detailed description included below and in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Reference will now be made to the accompanying drawings, in which:

[0068] Figure 1 and Figure 2 is a perspective view of an exemplary aircraft including the winglet system described herein;

[0069] Figure 3 It's on the ground Figure 1 Front view of the aircraft;

[0070] Figure 4 and Figure 5 yes Figure 1 an enlarged perspective view of an exemplary left winglet system of an aircraft;

[0071] Figure 6 yes Figure 4 A side view of the winglet system;

[0072] Figure 7 yes Figure 4 Front view of the winglet system;

[0073] Figure 8 yes Figure 4 Rear view of the winglet system;

[0074] Figure 9 yes Figure 4 Top view of the winglet system;

[0075] Figure 10 yes Figure 4 Bottom view of the winglet system;

[0076] Figure 11 yes Figure 1 an enlarged perspective view of another exemplary left winglet system of an aircraft;

[0077] Figure 12 yes Figure 11 Top view of the winglet system;

[0078] Figure 13 yes Figure 11 Front view of the winglet system;

[0079] Figure 14 yes Figure 1 an enlarged perspective view of another exemplary left winglet system of an aircraft;

[0080] Figure 15 yes Figure 14 Top view of the winglet system;

[0081] Figure 16 yes Figure 14 Front view of the winglet system;

[0082] Figure 17 Is in a superimposed arrangement Figure 4 、 Figure 11 and Figure 14 Front view of the winglet system;

[0083] Figure 18 yes Figure 1 an enlarged perspective view of another exemplary left winglet system of an aircraft;

[0084] Figure 19 yes Figure 18 Top view of the winglet system;

[0085] Figure 20 yes Figure 18 Front view of the winglet system;

[0086] Figure 21 yes Figure 1 an enlarged perspective view of another exemplary left winglet system of an aircraft;

[0087] Figure 22 yes Figure 21 A top view of the winglet system; and

[0088] Figure 23 yes Figure 21 Front view of the winglet system. DETAILED DESCRIPTION

[0089] The winglet system described herein includes an upper winglet and a lower winglet intended to be attached to the same main wingtip of an aircraft wing. In some embodiments, the dual winglet system described herein can induce a reduced bending moment on the main wingtip compared to a single larger winglet providing similar performance benefits.

[0090] In some embodiments, the spanwise profile of the lower winglet can be configured to allow the lower winglet to have sufficient span without excessively sacrificing wingtip ground clearance. The configuration of the lower winglet can provide increased ground clearance, thereby reducing the risk of the lower winglet striking the ground when the aircraft is operating near or on the ground, such as during takeoff and landing. The configuration of the lower winglet is particularly advantageous for business jets with engines mounted on the fuselage and relatively low wings. However, it should be understood that the winglet system described herein can also be used on other types of aircraft, including aircraft with engines mounted on the wing.

[0091] As used herein, the term "substantially" may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related.

[0092] Various aspects of the various embodiments are described with reference to the accompanying drawings.

[0093] Figure 1 and Figure 2 is a perspective view of an exemplary aircraft 10 including two winglet systems 12 as described herein. The aircraft 10 can be any type of manned or unmanned aircraft (e.g., drone), such as corporate, private, commercial, and passenger aircraft. For example, the aircraft 10 can be a (e.g., ultra-long-range) business jet, a narrow-body twin-engine jetliner, or a turboprop aircraft. The aircraft 10 can be a fixed-wing aircraft. The winglet system 12 can be used on different types of aircraft, but can provide significant benefits for long-range fixed-wing aircraft that travel relatively close to the speed of sound (e.g., Mach 0.8-0.95) and have fuselage-mounted engines (rather than wing-mounted engines).

[0094] The aircraft 10 may include two opposed wings 14 extending on opposite sides of a fuselage 16. The wings 14 may each include one or more movable flight control surfaces 15. The aircraft 10 may include one or more engines 18 for propelling the aircraft 10, and a tail 20. The engines 18 may be mounted to the rear of the fuselage 16 via corresponding pylons 22. In some embodiments, the aircraft 10 may not have any engines mounted on the wings 14. Alternatively, the aircraft 10 may have one or more engines mounted on the wings 14 (e.g., on the underside). The fuselage 16 may have a longitudinal axis LA that may substantially correspond to the roll axis of the aircraft 10. Figure 1 and Figure 2 Forward (FWD) and aft (AFT) directions are labeled in FIG. 1 , both generally referring to opposite directions along the longitudinal axis LA of the fuselage 16 .

[0095] Each wing 14 includes a main wing 24 and a winglet system 12. The main wing 24 may include an inboard main wing root 26 for mounting to the fuselage 16 via, for example, a suitable wing box; and an opposing outboard main wing tip 28. The main wing 24 may have a leading edge 29. The winglet system 12 is attached to the main wing tip 28. The winglet system 12 includes an upper winglet 30A extending upward relative to the main wing tip 28; and a lower winglet 30B extending downward relative to the main wing tip 28.

[0096] Figure 3 is a front elevational view of the aircraft 10 when stationary on the ground G. Figure 3 The ground clearance CL is indicated between the opposing lower winglets 30B and the ground G. On aircraft having fuselage-mounted engines 18 and / or no engines mounted below the wings 14, the wings 14 may be arranged low relative to the ground G. Thus, for such aircraft configurations, as explained below, the winglet system 12 may be configured to avoid unduly sacrificing ground clearance CL, thereby avoiding unduly increasing the risk of wingtip collisions when the aircraft 10 is operating near or over the ground G.

[0097] Figure 4 and Figure 5 1 is an enlarged perspective view of the left winglet system 12 of the aircraft 10. The right winglet system 12 can be a mirror image of the left winglet 12. The winglet system 12 can include an optional blended portion 32 that provides a relatively smooth and curved transition between the main wingtip 28 and the corresponding upper winglet 30A and lower winglet 30B. The blended portion 32 can be configured to provide desired flow conditions near the main wingtip 28. The upper winglet 30A and the lower winglet 30B each extend directly from the main wingtip 28 via the blended portion 32, as opposed to one (e.g., smaller) winglet extending from the other (e.g., larger) winglet.

[0098] The main wing 24 may be a lift-generating surface, and the main wing tip 28 may have an airfoil-shaped cross-section having a Figure 5 . The attachment end 36 of the winglet system 12 may be shaped to substantially match the shape of the main wingtip 28. For example, the attachment end 36 may have a similar or substantially the same airfoil cross-section as the main wingtip 28. Thus, the chord 34 may be shared between the main wingtip 28 and the attachment end 36 of the winglet system 12.

[0099] The upper winglet 30A and the lower winglet 30B may be staggered along the chord 34 of the main wingtip 28 such that the lower winglet 30B is disposed forward of the upper winglet 30A. However, it should be understood that as discussed below with respect to Figures 18 to 20 As explained, instead, the lower winglet 30B can be positioned rearward of the upper winglet 30A. In some embodiments, the staggered configuration of the upper and lower winglets 30A, 30B can be advantageous by reducing adverse interference between the upper and lower winglets 30A, 30B. Depending on the specific geometry of the winglet system 12, the staggered configuration can, for example, reduce the amount of influence that airflow over the upper side of the lower winglet 30B may have on airflow over the lower side of the upper winglet 30A. Specifically, the acceleration of flow over the upper surface of the lower winglet 30B can cause adverse interference with the upper winglet 30A, which can result in increased drag.

[0100] It should be understood that the components of the winglet system 12 may have some flexibility and may deflect during use. Apart from such deflection, the winglet system 12 may have a substantially fixed geometry, wherein the positions of the upper winglet 30A and the lower winglet 30B may not be selectively adjusted.

[0101] As follows about Figure 9 To explain further, the upper winglet 30A and the lower winglet 30B may overlap one another along the chord 34 . Figure 4 An overlap area 38 is shown overlapping the lower winglet 30B. Since the light source is arranged vertically above the winglet system 12 and directed downward, the overlap area 38 may represent a shadow cast by the upper winglet 30A onto the lower winglet 30B.

[0102] Figure 6 is a side view of the winglet system 12 . Figure 6 The winglet tip 40A of the upper winglet 30A and the winglet tip 40B of the lower winglet 30B are shown, respectively. One or both of the upper winglet 30A and the lower winglet 30B can be lift-generating surfaces and can have cross-sections that are airfoil-shaped and asymmetric about their chords. Thus, one or both of the upper winglet 30A and the lower winglet 30B can have corresponding suction (e.g., upper) and pressure (e.g., lower) sides.

[0103] The winglet system 12 can be made of similar or identical materials as the main wing 24 using known or other manufacturing methods. In various embodiments, the outer skin of the winglet system 12 can be made of a (e.g., aluminum-based) metal material or a fiber-reinforced composite material (such as carbon fiber reinforced polymer). The winglet system 12 can include an internal framework that supports the outer skin and structurally connects the winglet system 12 to the main wing 24.

[0104] Figure 7 and Figure 8 are respective front and rear views of the winglet system 12 . Figure 7 The vantage point in the diagram is substantially along the chordwise direction of the main wing tip 28 (i.e., along the Figure 5 chord 34 shown in FIG).

[0105] Even though the lower winglet 30A can extend below the main wingtip 28, the bending of the lower winglet 30B can be used to control the downward extension of the downward wingtip 30B due to wingtip impact considerations. Figure 730B. The inflection point IP1 may correspond to a location along the spanwise profile 42 where the spanwise profile 42 changes from convex to concave. The inflection point IP1 may be disposed between a proximal portion 42A of the spanwise profile 42 proximal to the main wingtip 28 and a distal portion 42B of the spanwise profile 42 distal to the main wingtip 28. At least a portion of the proximal portion 42A of the spanwise profile 42 may be convex relative to the space 44 between the upper winglet 30A and the lower winglet 30B. In some embodiments, at least a majority of the proximal portion 42A of the spanwise profile 42 may be convex relative to the space 44. In some embodiments, substantially the entire proximal portion 42A of the spanwise profile 42 may be convex relative to the space 44. Conversely, at least a portion of the distal portion 42B of the spanwise profile 42 may be recessed relative to the space 44 between the upper winglet 30A and the lower winglet 30B. In some embodiments, at least a majority of the distal portion 42B of the spanwise profile 42 may be recessed relative to the space 44. In some embodiments, substantially all of the distal portion 42B of the spanwise profile 42 may be recessed relative to the space 44.

[0106] In some embodiments, at least a substantial portion of the distal portion 42B of the spanwise profile 42 may be curved when viewed along the chord 34 of the main wingtip 28, such as Figure 7 In some embodiments, the proximal portion 42A of the spanwise profile 42 can be substantially completely curved when viewed along the chord 34 of the main wingtip 28. In some embodiments, at least a majority of the distal portion 42B of the spanwise profile 42 can be curved when viewed along the chord 34 of the main wingtip 28. Figure 7 In some embodiments, the distal portion 42B of the spanwise profile 42 may be substantially completely curved when viewed along the chord 34 of the main wingtip 28 .

[0107] Inflection point IP1 may be positioned closer to the main wingtip 28 than to the wingtip 40B of the lower winglet 30B. Thus, the curve length of the proximal portion 42A of the spanwise profile 42 may be shorter than the curve length of the distal portion 42B of the spanwise profile 42. In some embodiments, the distal portion 42B of the spanwise profile 42 may be two or more times the length of the proximal portion 42A of the spanwise profile 42. In some embodiments, the distal portion 42B of the spanwise profile 42 may be three or more times the length of the proximal portion 42A of the spanwise profile 42. In some embodiments, the distal portion 42B of the spanwise profile 42 may be four or more times the length of the proximal portion 42A of the spanwise profile 42. In some embodiments, the distal portion 42B of the spanwise profile 42 may be two to five times the length of the proximal portion 42A of the spanwise profile 42.

[0108] When the chord 34 (see Figure 5 ), the spanwise profile 42 may be tangentially continuous with the leading edge 29 of the main wing 24. The spanwise profile of the upper winglet 30A, which extends along a leading edge 46A of the upper winglet 30A and outwardly projects toward the main wingtip 28, may be tangentially continuous with the leading edge 29 of the main wing 24 when viewed along the chord 34 of the main wingtip 28.

[0109] Figure 7 Shows that it can be Figure 3 , and the horizontal axis H is parallel to the ground G shown in FIG. With respect to the horizontal axis H, the wingtip 40B of the lower winglet 30B may be oriented upward in some embodiments. The terms "upward" and "downward" as used herein are intended to encompass "partially upward" and "partially downward," respectively, and are not intended to be limited to a purely vertical orientation. Thus, Figure 7 The angle α1 shown in FIG can be positive. In some embodiments, the angle α1 can be approximately 10 degrees. However, it should be understood that in some embodiments, the angle α1 can be negative. In some embodiments, the angle α1 can be between +10 and -10 degrees with respect to the horizontal axis H. In some embodiments, the angle α1 can be between +20 and -20 degrees with respect to the horizontal axis H. In some embodiments, the angle α1 can be approximately zero.

[0110] Figure 7 Also shown is a vertical axis V that may be perpendicular to the horizontal axis H. Relative to the vertical axis V, the wingtip 40A of the upper winglet 30A may be arranged higher than the wingtip 40B of the lower winglet 30B. In some embodiments, the wingtip 40A of the upper winglet 30A may be arranged outboard or inboard of the wingtip 40B of the lower winglet 30B. In some embodiments, the wingtip 40A of the upper winglet 30A may be substantially vertically aligned with the wingtip 40B of the lower winglet 30B.

[0111] The configuration of the winglet system 12 may allow for a relatively large engagement angle α2 between the upper winglet 30A and the lower winglet 30B, as viewed along the chord 34 of the main wingtip 28. Figure 7 . The upper winglet 30A and the lower winglet 30B may extend in a diverging manner away from the attachment end 36. The main wing 24 defines a wing plane that passes through a chord 34 of the main wing 24 and one or more chords disposed inboard of the chord 34. The upper winglet 30A may extend upward from the wing plane, and the lower winglet 30B may extend downward from the wing plane.

[0112] A relatively large engagement angle α2, combined with the staggering of the upper and lower winglets 30A, 30B, can reduce the likelihood of adverse interference between the upper and lower winglets 30A, 30B (which could act as a source of drag), by reducing the amount that airflow over the upper side of the lower winglet 30B could affect airflow over the lower side of the upper winglet 30A. In some embodiments, the engagement angle α2 can be between 60 and 90 degrees. In some embodiments, the engagement angle α2 can be greater than 45 degrees and up to 120 degrees.

[0113] The bend provided in the lower winglet 30B also allows for a relatively large engagement angle α2 while also reducing the downward extension of the lower winglet 30B toward the ground G (e.g., Figure 3 The concave curvature of the distal portion 42B of the spanwise profile 42 can allow for a longer lower winglet 30B and a larger engagement angle α2 while limiting the downward extension of the lower winglet 30B (see, for example, Figure 3 In comparison, a lower winglet with a completely linear spanwise profile 42 and similar span and ground clearance would result in a smaller engagement angle α2.

[0114] The dual winglet configuration of the winglet system 12 can induce less bending moment in the main wing 24 than a single larger winglet providing similar performance benefits. In some cases, a larger winglet will produce a greater drag reduction. However, disadvantages associated with increased winglet size include increased loads and bending moments on the main wing from root to tip, which means a heavier wing structure. This increased weight may offset some of the benefits provided by a single larger winglet. Figure 7 In the example shown in , the moment M caused by the lift generated by the upper winglet 30A and the lower winglet 30B about a reference point O during flight can be expressed as M=F1*D1+F2*D2, where F1 is the resultant force generated by the upper winglet 30A, D1 is the distance between the location where force F1 is applied and the reference point O, F2 is the resultant force generated by the lower winglet 30B, and D2 is the distance between the location where force F2 is applied and the reference point O. Compared to a single, larger winglet providing similar performance benefits, it is believed that in some circumstances, the twin winglet system 12 will induce a lower total moment M than a single, larger winglet. Specifically, a single, larger force applied over a larger distance on a single, larger winglet will provide a larger moment M than two smaller forces F1 and F2 applied at two shorter distances D1 and D2, respectively. In other words, for a given moment M caused by a single, larger winglet, the twin winglet system 12 can provide a greater performance benefit for the same moment M.

[0115] refer to Figure 7The spanwise profile 42 may have a midpoint MP disposed at or near the middle of the spanwise profile 42. The midpoint MP may be disposed along the spanwise profile 42 midway between the attachment end 36 and the wingtip 40B of the lower winglet 30B. For example, the midpoint MP may be disposed between the inboard and outboard portions of the spanwise profile 42 having substantially equal curvilinear lengths. The spanwise profile 42 may have a slope M1 at the midpoint MP. In various embodiments, the slope M1 may be negative (i.e., sloped downward), zero, or positive (i.e., sloped upward) relative to the vertical axis V.

[0116] The spanwise profile 42 may have a slope M2 at an outboard point OP1 disposed outboard of the midpoint MP. The slope M2 at the outboard point OP1 may be greater than the slope M1 at the midpoint MP. In other words, the slope M2 may be more upwardly inclined than the slope M1. In various embodiments, the slope M2 may be negative (i.e., downwardly inclined), zero, or positive (i.e., upwardly inclined) relative to the vertical axis V. The outboard point OP1 may be disposed closer to the wingtip 40B of the lower winglet 30B than the midpoint MP along the spanwise profile 42.

[0117] The spanwise profile 42 may have a slope M3 at an outboard point OP2 disposed outboard of the midpoint MP. The slope M3 at the outboard point OP2 may be greater than the slope M1 at the midpoint MP. The slope M3 at the outboard point OP2 may also be greater than the slope M2 at the outboard point OP1. In other words, the slope M3 may be more upwardly inclined than the slopes M1 and M2. In various embodiments, the slope M3 may be negative (i.e., downwardly inclined), zero, or positive (i.e., upwardly inclined) relative to the vertical axis V. The outboard point OP2 may be disposed substantially at the wingtip 40B of the lower winglet 30B. The outboard point OP2 may be disposed at the outboard end of the spanwise profile 42. The more upward orientation of the outboard portion (e.g., including the wingtip 40B) of the lower winglet 30B relative to the midportion or inboard portion of the lower winglet 30B may facilitate greater ground clearance.

[0118] Figure 9 and Figure 101 and 2 are top and bottom views of the winglet system 12, respectively. In various embodiments, the upper winglet 30A and the lower winglet 30B can be similar in size in terms of wetted area (i.e., surface area that interacts with ambient air), root chord length, and span. In some embodiments, the wetted area of ​​the upper winglet 30A can be substantially equal to the wetted area of ​​the lower winglet 30B. In some embodiments, the wetted area of ​​the lower winglet 30B can be between 50% and 120% of the wetted area of ​​the upper winglet 30B. The similar dimensions of the upper winglet 30A and the lower winglet 30B can provide a relatively uniform load distribution (i.e., good load balancing) between the upper winglet 30A and the lower winglet 30B. In some embodiments, the lower winglet 30B can have a smaller wetted area than the upper winglet 30A. In some embodiments, the lower winglet 30B can have a larger wetted area than the upper winglet 30A.

[0119] The wing root chord length C1 of the upper winglet 30A and the wing root chord length C2 of the lower winglet 30B can be expressed as a percentage of the wing tip chord length C3. Figure 9 , the root chord length C1 may be illustrated by extending (e.g., extrapolating) the leading edge 46A of the upper winglet 30A to the main wingtip 28 so that the root chord length C1 may extend from the trailing edge of the main wingtip 28 to the intersection of the extension line 50A and the chord 34 of the main wingtip 28. Similarly, the root chord length C2 may be illustrated by extending (e.g., extrapolating) the trailing edge 48B of the lower winglet 30B to the main wingtip 28 so that the root chord length C2 may extend from the leading edge 29 of the main wingtip 28 to the intersection of the extension line 50B and the chord 34 of the main wingtip 28. The root chords of the upper winglet 30A and the lower winglet 30B defined above may be coaxial with the chord 34 of the main wingtip 28.

[0120] From an aerodynamic perspective, reducing the winglet root chord can be offset by increasing the winglet inclination angle so that the net winglet lift remains constant. This generally provides a drag reduction while reducing the winglet's wetted area and, therefore, also reducing frictional drag. However, from a structural perspective, this trade-off is limited because the winglet becomes so thin that the internal space is insufficient for an efficient structural arrangement. In various embodiments, the root chord lengths C1 and C2 can each be greater than 50% but less than 100% of the chord length C3 of the chord 34 of the main wingtip 28 to provide an overlap region 38. In some embodiments, the root chord length C1 can be between 55% and 80% of the chord length C3. In some embodiments, the root chord length C2 can be between 55% and 80% of the chord length C3.

[0121] In various embodiments, the amount of overlap OL between the wing root chord length C1 and the wing root chord length C2 may be between 10% and 60% of the chord length C3 of the chord 34 of the main wingtip 28. In some embodiments, the staggered arrangement of the upper winglet 30A and the lower winglet 30B, combined with the relatively small amount of overlap OL, may reduce the risk of adverse interference between the lower winglet 30B and the upper winglet 30A at and near the junction between the lower winglet 30B and the upper winglet 30A, as explained above.

[0122] The staggered arrangement of the upper winglet 30A and the lower winglet 30B may be such that the leading edge 46B of the lower winglet 30B is disposed forward of the leading edge 46A of the upper winglet 30A relative to the chord 34 of the main wingtip 28. Similarly, the staggered arrangement of the upper winglet 30A and the lower winglet 30B may be such that the trailing edge 48B of the lower winglet 30B is disposed forward of the trailing edge 48A of the upper winglet 30A relative to the chord 34 of the main wingtip 28.

[0123] In some embodiments, the leading edge 46B and / or the trailing edge 48B of the lower winglet 30B outboard of the blended portion 32 may be curved or straight in top and bottom views, such as Figure 9 and Figure 10 Thus, in top view, the leading edge 46B of the lower winglet 30B may not be continuously curved with the leading edge 29 of the main wingtip 28. Similarly, in some embodiments, the leading edge 46A and / or trailing edge 48A of the upper winglet 30B outboard of the blended portion 32 may be curved or straight in top or bottom view, such as Figure 9 and Figure 10 Thus, in top view, the trailing edge 48A of the upper winglet 30A may not be continuously curved with the trailing edge of the main wingtip 28 .

[0124] like Figure 9 and Figure 10 As shown in FIG, the lower winglet 30B may be swept back. The upper winglet 30A may also be swept back. In some embodiments, the transition between the upward portion 30A and the attachment end 36 of the winglet system 12 may define a rounded protrusion 52 as an appendage that extends in a rearward direction beyond the trailing edge 48A of the upper winglet 30A.

[0125] Figures 11 to 13 Another exemplary left winglet system 112 that may be suitable for aircraft 10 is shown. Figure 11 is an enlarged perspective view of the winglet system 112 . Figure 12 and Figure 13146A and 146B are top views and front views of the winglet system 112, respectively. The description of the elements of the winglet system 112 that correspond to the elements of the winglet system 12 described above will not be repeated. Elements of the winglet system 112 that correspond to elements of the winglet system 12 are identified by reference numerals increased by 100. The winglet system 112 may include an upper winglet 130A, a wingtip 140A of the upper winglet 130A, a lower winglet 130B, a wingtip 140B of the lower winglet 130B, a fusion portion 132 of the winglet system 112, and an attachment end 136. The upper winglet 130A may have a leading edge 146A, and the lower winglet 130B may have a leading edge 146B. The upper winglet 130A and the lower winglet 130B may be aligned along the chord 34 of the main wingtip 28 (see Figure 5 ) overlap each other to provide an overlapping region 138, as shown Figure 11 As shown in .

[0126] The winglet system 112 may provide similar benefits as explained above with respect to the winglet system 12. However, with reference to Figure 13 , the configuration of the winglet system 112 may allow for a greater engagement angle α2. The lower winglet 130B of the winglet system 112 may be substantially identical to the lower winglet 30B of the winglet system 12. At the junction of the upper winglet 130A and the blended portion 132, there may be a discontinuity in the curvature of the upper winglet 130A relative to the main wing 24, thereby allowing the upper winglet 130A to extend from the blended portion 132 at a greater engagement angle α2, so as to further reduce the risk of adverse interference between the lower winglet 130B and the upper winglet 130A. When the chord 34 (see FIG. 34 ) along the main wing 28 is substantially the same as the lower winglet 30B of the winglet system 12, the curvature of the upper winglet 130A relative to the main wing 24 may be substantially the same as the lower winglet 30B of the winglet system 12. Figure 5 ) when viewed from above, the extension of the upper winglet 130A from the blended portion 132 may not be tangential to the main wing 24, as shown in FIG. Figure 13 In other words, the spanwise profile of the upper winglet 130A extending along the leading edge 146A of the upper winglet 130A may be tangentially discontinuous with the leading edge 29 of the main wing 24 when viewed along the chord 34 of the main wingtip 28 .

[0127] The upper winglet 130A may have an inflection point IP2 (e.g., Figure 13 ). Inflection point IP2 may correspond to a location along leading edge 146A where the curvature of upper winglet 130A changes from convex to concave. In some embodiments, at least a portion of leading edge 146A inboard of inflection point IP2 may be convex relative to space 44 between upper winglet 130A and lower winglet 130B. Conversely, at least a portion of leading edge 146A outboard of inflection point IP2 may be concave relative to space 44 between upper winglet 130A and lower winglet 130B. Inflection point IP2 may be positioned closer to main wingtip 28 than to wingtip 140A of upper winglet 130A.

[0128] In some embodiments of the winglet system 112, the engagement angle α2 may be between 60 degrees and 90 degrees. In some embodiments of the winglet system 112, the engagement angle α2 may be greater than 45 degrees and up to 150 degrees.

[0129] Figures 14 to 16 Another exemplary left winglet system 212 that may be suitable for aircraft 10 is shown. Figure 14 is an enlarged perspective view of the winglet system 212 . Figure 15 and Figure 16 2 and 3. They are a top view and a front view of the winglet system 212, respectively. The description of the elements of the winglet system 212 corresponding to the elements of the winglet system 12 described above will not be repeated. The elements of the winglet system 212 corresponding to the elements of the winglet system 12 are identified using reference numerals increased by 200. The winglet system 212 may include an upper winglet 230A, a wingtip 240A of the upper winglet 230A, a lower winglet 230B, a wingtip 240B of the lower winglet 230B, a fusion portion 232 of the winglet system 212, and an attachment end 236. The upper winglet 230A may have a leading edge 246A, and the lower winglet 230B may have a leading edge 246B. The upper winglet 230A and the lower winglet 230B may be along the chord 34 of the main wingtip 28 (see Figure 5 ) overlap each other to provide an overlapping area 238, as shown Figure 14 As shown in .

[0130] The winglet system 212 may provide similar benefits as explained above with respect to the winglet system 12. Similar to the winglet system 112, the winglet system 212 may also allow for a greater engagement angle α2 to be achieved. The lower winglet 230B of the winglet system 212 may be substantially identical to the lower winglet 30B of the winglet system 12. At the junction of the upper winglet 230A and the blended portion 232, there may be a discontinuity in the curvature of the upper winglet 230A relative to the main wing 24, thereby allowing the upper winglet 230A to extend from the blended portion 232 at a greater engagement angle α2, so as to further reduce the risk of adverse interference between the lower winglet 230B and the upper winglet 230A. When the chord 34 (see FIG. 2 ) along the main wing 28 is substantially the same as the chord 34 (see FIG. 2 ), the winglet 230B may be substantially the same as the winglet 30B of the winglet system 12. Figure 5 ), the spanwise profile of the upper winglet 230A extending along the leading edge 246A of the upper winglet 230A may be tangentially discontinuous with the leading edge 29 of the main wing 24.

[0131] The upper winglet 230A may have inflection points IP2 and IP3 along the leading edge 246A of the upper winglet 230A (e.g., Figure 16). Inflection points IP2 and IP3 may correspond to locations along leading edge 246A where the curvature of upper winglet 230A changes from convex to concave, and vice versa. In some embodiments: at least a portion of leading edge 246A inboard of inflection point IP2 may be convex relative to space 44 between upper winglet 230A and lower winglet 230B; at least a portion of leading edge 246A between inflection points IP2 and IP3 may be concave relative to space 44; and at least a portion of leading edge 246A outboard of inflection point IP3 may be convex relative to space 44. Inflection point IP2 may be positioned closer to main wingtip 28 than to wingtip 240A of upper winglet 230A. Inflection point IP3 may be positioned closer to wingtip 240A of upper winglet 230A than to main wingtip 28. Inflection points IP2 and / or IP3 may be incorporated into the upper winglet 230A to adjust the span of the winglet 212 and / or potentially adjust the amount of bending moment induced by the winglet 212 .

[0132] In some embodiments of the winglet system 212, the engagement angle α2 may be between 60 degrees and 90 degrees. In some embodiments of the winglet system 212, the engagement angle α2 may be greater than 45 degrees and up to 150 degrees.

[0133] Figure 17 is the chord 34 along the main wing tip 28 in a stacked arrangement (see Figure 5 ) is a front view of the winglet systems 12, 112, and 212. The winglet systems 12, 112, and 212 are shown with identical lower winglets 30B, 130B, 230B. The configuration of the upper winglets 130A and 230A may allow for a greater engagement angle α2 than the configuration of the upper winglet 30.

[0134] Figures 18 to 20 Another exemplary left winglet system 312 that may be suitable for aircraft 10 is shown. Figure 18 is an enlarged perspective view of the winglet system 312 . Figure 19 and Figure 20 3 and 4. FIG. 3 is a top view and a front view of winglet system 312, respectively. The description of the elements of winglet system 312 corresponding to the elements of winglet system 12 described above will not be repeated. Elements of winglet system 312 corresponding to elements of winglet system 12 are identified using reference numerals incremented by 300. Winglet system 312 may include an upper winglet 330A, a wingtip 340A of upper winglet 330A, a lower winglet 330B, a wingtip 340B of lower winglet 330B, a blended portion 332 of winglet system 312, and an attachment end 336. Upper winglet 330A may have a leading edge 346A, and lower winglet 330B may have a leading edge 346B.

[0135] The upper winglet 330A and the lower winglet 330B may be arranged along the chord 34 of the main wingtip 28 (see FIG. Figure 5) overlap each other to provide an overlapping area 338, as shown Figure 18 In some embodiments, such an overlapping region 338 may extend from the junction of the upper winglet 330A and the lower winglet 330B to the wingtip 340B of the lower winglet 330B.

[0136] The winglet system 312 can provide similar benefits as explained above with respect to the winglet systems 12, 112, and 212. The winglet system 312 illustrates that the lower winglet 330B can be arranged behind the upper winglet 330A relative to the chord 34 of the main wingtip 28, and the upper winglet 330A can be arranged forward of the lower winglet 330B. Thus, the leading edge 346A of the upper winglet 330A can be arranged forward of the leading edge 346B of the lower winglet 330B relative to the chord 34 of the main wingtip 28.

[0137] Figures 18 to 20 The upper winglet 330A is shown to be similar to the upper winglet 30A and the lower winglet 330B is shown to be similar to the lower winglet 30B. However, it should be understood that Figures 18 to 20 The positioning of the upper winglet 330A and the lower winglet 330B shown in FIG. 5 may be applied to any of the winglet systems 12 , 112 , and 212 described herein.

[0138] refer to Figure 20 The spanwise profile of the upper winglet 330A extending along the leading edge 346A of the upper winglet 330A may be tangentially continuous with the leading edge 29 of the main wing 24 when viewed along the chord 34 of the main wingtip 28 .

[0139] Figures 21 to 23 Another exemplary left winglet system 412 that may be suitable for aircraft 10 is shown. Figure 21 is an enlarged perspective view of the winglet system 412 . Figure 22 and Figure 23 4 and 5. are top and front views, respectively, of the winglet system 412. Figure 23 The viewpoint in the diagram is substantially along the chordwise direction of the main wing tip 28 (i.e., along Figure 5 chord 34 shown in FIG. ). The description of the elements of winglet system 412 corresponding to the elements of winglet system 12 described above is not repeated. Elements of winglet system 412 corresponding to elements of winglet system 12 are identified using reference numerals incremented by 400. Winglet system 412 may include an upper winglet 430A, a wingtip 440A of upper winglet 430A, a lower winglet 430B, a wingtip 440B of lower winglet 430B, a blended portion 432 of winglet system 412, and an attachment end 436. Upper winglet 430A may have a leading edge 446A, and lower winglet 430B may have a leading edge 446B. Wingtip 440A of upper winglet 430A may be arranged higher than wingtip 440B of lower winglet 430B.

[0140] The upper winglet 430A and the lower winglet 430B may be arranged along the chord 34 of the main wingtip 28 (see FIG. Figure 5 ) overlap each other to provide an overlapping region 438, as shown Figure 21 In some embodiments, such an overlapping region 438 may extend from the junction of the upper winglet 430A and the lower winglet 430B to the wingtip 440B of the lower winglet 430B.

[0141] The winglet system 412 can provide similar benefits as explained above with respect to the winglet systems 12, 112, 212, and 312. The upper winglet 430A and the lower winglet 430B can be staggered along the chord 34 of the main wingtip 28. The winglet system 412 shows that the lower winglet 430B can be arranged forward of the upper winglet 430A relative to the chord 34 of the main wingtip 28, and the upper winglet 430A can be arranged behind the lower winglet 430B. Thus, the leading edge 446B of the lower winglet 430B can be arranged forward of the leading edge 446A of the upper winglet 430A relative to the chord 34 of the main wingtip 28. Alternatively, the lower winglet 430B can be arranged behind the upper winglet 430A relative to the chord 34 of the main wingtip 28, and the upper winglet 430A can be arranged forward of the lower winglet 430B.

[0142] refer to Figure 23 A spanwise profile 442 of the lower winglet 430B extending along a leading edge 446B of the lower winglet 430B may be tangentially continuous with the leading edge 29 of the main wing 24 when viewed along the chord 34 of the main wingtip 28 .

[0143] Both the upper winglet 430A and the lower winglet 430B may extend upward relative to the main wingtip 28 and relative to the leading edge 29 of the main wing 24. The wingtip 440B of the lower winglet 430B may be arranged to be clear of the ground G (e.g., Figure 3 In some embodiments, when the Figure 23 When viewed from the viewpoint of FIG, at least a majority of the leading edge 446B of the lower winglet 430B may be recessed relative to the space 44 between the upper winglet 430A and the lower winglet 430B.

[0144] With respect to the longitudinal axis LA of the fuselage 16 (e.g. Figure 1 ) and the wingtip 440A of the upper winglet 430A may be laterally disposed outboard or inboard of the wingtip 440B of the lower winglet 430B relative to the main wingtip 28. In some embodiments, the wingtip 440B of the lower winglet 430B may be substantially vertically aligned with the wingtip 440A of the upper winglet 430A.

[0145] refer to Figure 23The spanwise profile 442 can have a midpoint MP disposed at or near the middle of the spanwise profile 442. The midpoint MP can be disposed midway along the spanwise profile 442 between the attachment end 436 of the lower winglet 430B and the wingtip 440B. For example, the midpoint MP can be disposed between the inboard and outboard portions of the spanwise profile 442 having substantially the same curve length. The spanwise profile 442 can have a slope M1 at the midpoint MP. In various embodiments, the slope M1 can be negative (i.e., sloped downward), zero, or positive (i.e., sloped upward) relative to the vertical axis V.

[0146] The spanwise profile 442 may have a slope M2 at an outboard point OP1 disposed outboard of the midpoint MP. The slope M2 at the outboard point OP1 may be greater than the slope M1 at the midpoint MP. In other words, the slope M2 may be more upwardly inclined than the slope M1. In various embodiments, the slope M2 may be negative (i.e., downwardly inclined), zero, or positive (i.e., upwardly inclined) relative to the vertical axis V. The outboard point OP1 may be disposed along the spanwise profile 442 closer to the wingtip 440B of the lower winglet 430B than to the midpoint MP.

[0147] The spanwise profile 442 may have a slope M3 at an outboard point OP2 disposed outboard of the midpoint MP. The slope M3 at the outboard point OP2 may be greater than the slope M1 at the midpoint MP. The slope M3 at the outboard point OP2 may also be greater than the slope M2 at the outboard point OP1. In other words, the slope M3 may be more upwardly inclined than the slopes M1 and M2. In various embodiments, the slope M3 may be negative (i.e., downwardly inclined), zero, or positive (i.e., upwardly inclined) relative to the vertical axis V. The outboard point OP2 may be disposed substantially at the wingtip 440B of the lower winglet 430B. The outboard point OP2 may be disposed at the outboard end of the spanwise profile 442. The more upward orientation of the outboard portion (e.g., including the wingtip 440B) of the lower winglet 430B relative to the midportion or inboard portion of the lower winglet 430B may facilitate greater ground clearance.

[0148] The foregoing description is merely exemplary, and those skilled in the art will recognize that changes may be made to the described embodiments without departing from the scope of the invention disclosed. The present disclosure may be embodied in other specific forms without departing from the subject matter of the claims. The present disclosure is intended to cover and encompass all suitable changes in technology. Modifications that fall within the scope of the present invention will be apparent to those skilled in the art upon review of the present disclosure, and such modifications are intended to fall within the appended claims. Furthermore, the scope of the claims should not be limited to the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the entire specification.

Claims

1. A wing for an aircraft, comprising: a main wing, the main wing including a main wing tip; and A winglet system is attached to the main wingtip, the winglet system comprising: an upper winglet having an upper winglet tip outboard of the main wingtip; and a lowermost winglet having a lowermost winglet tip outside the main wingtip, an upper winglet tip of the upper winglet being arranged higher relative to the main wingtip than the lowermost winglet tip of the lowermost winglet; in: The upper winglet and the lowermost winglet overlap each other along the chord of the main wingtip; The upper winglet and the lowermost winglet both extend upward relative to the main wingtip; The upper winglet and the lowermost winglet each extend directly relative to the main wingtip; the spanwise profile of the lowermost winglet extending along a leading edge of the lowermost winglet having a midpoint, the slope of the spanwise profile at all points outboard of the midpoint closer to the tip of the lowermost winglet than the midpoint being more upwardly inclined than the slope of the spanwise profile at the midpoint, such that the lowermost winglet curves upwardly at points outboard of the midpoint; The leading edge of the lowermost winglet is staggered relative to the leading edge of the upper winglet along the chordwise direction of the main wingtip.

2. The wing according to claim 1, wherein: The spanwise profile of the lowermost winglet has a lowermost winglet bend.

3. The wing according to claim 2, wherein: The lowermost winglet bend is arranged between a proximal portion of the spanwise profile of the lowermost winglet proximal to the main wingtip and a distal portion of the spanwise profile; and The proximal portion of the spanwise profile is shorter than the distal portion of the spanwise profile.

4. The wing according to claim 3, wherein: When viewed along a chord of the main wingtip, at least a majority of the distal portion of the spanwise profile is recessed relative to a space between the upper winglet and the lowermost winglet.

5. The wing according to claim 3, wherein: When viewed along a chord of the main wingtip, at least a majority of the distal portion of the spanwise profile is curved.

6. The wing according to any one of claims 1 to 5, wherein: The lowermost winglet tip is directed upward.

7. The wing according to any one of claims 1 to 5, wherein: The engagement angle between the upper winglet and the lowermost winglet is between 60 degrees and 90 degrees when viewed along the chord of the main wingtip.

8. The wing according to any one of claims 1 to 5, wherein: The engagement angle between the upper winglet and the lowermost winglet when viewed along the chord of the main wingtip is greater than 45 degrees and is up to 150 degrees.

9. The wing according to any one of claims 1 to 5, wherein: The root chord length of the lowermost winglet is between 55% and 80% of the chord length of the main wingtip.

10. The wing according to any one of claims 1 to 5, wherein: The root chord length of the upper winglet is between 55% and 80% of the chord length of the main wingtip.

11. The wing according to any one of claims 1 to 5, wherein: The overlap of the root chords of the upper winglet and the lowermost winglet is between 10% and 20% of the length of the chord of the main wingtip.

12. The wing according to any one of claims 1 to 5, wherein: The leading edge of the lowermost winglet is arranged forward of the leading edge of the upper winglet relative to the chord of the main wingtip.

13. The wing according to any one of claims 1 to 5, wherein: The leading edge of the upper winglet is arranged forward of the leading edge of the lowermost winglet relative to the chord of the main wingtip.

14. The wing according to claim 13, wherein: The overlapping portion between the upper winglet and the lowermost winglet extends from a junction of the upper winglet and the lowermost winglet to a tip of the lowermost winglet.

15. The wing according to any one of claims 1 to 5, wherein: When viewed along the chord of the main wingtip, a spanwise profile of the upper winglet extending along the leading edge of the upper winglet is tangentially discontinuous with the leading edge of the main wing.

16. The wing according to any one of claims 1 to 5, wherein: The spanwise profile of the upper winglet has a first upper winglet bend.

17. The wing according to claim 16, wherein: The spanwise profile of the upper winglet has a second upper winglet bend.

18. The wing according to any one of claims 1 to 5, wherein: The lowermost winglet is swept back relative to a chord of the main wingtip.

19. The wing according to any one of claims 1 to 5, wherein: The upper winglet is swept relative to the chord of the main wingtip.

20. The wing according to any one of claims 1 to 5, wherein The upper winglet tip is arranged outboard of the lowermost winglet tip.

21. A wing according to any one of claims 1 to 5, wherein: The upper winglet and the lowermost winglet each extend directly from the main wingtip via a blended portion.

22. An aircraft comprising a wing according to any one of claims 1 to 21.

23. A winglet system for an aircraft wing, the winglet system comprising: an attachment end for attachment to a main wing of an aircraft, the attachment end defining an airfoil cross-section having a chord; upper winglet; and The lowermost winglet, wherein, when said attachment end is attached to the main wing of the aircraft: the upper winglet having an upper winglet tip outboard of the attachment end; The lowermost winglet has a lowermost winglet tip outboard of the attachment end; the upper winglet and the lowermost winglet each extending directly relative to the attachment end; an upper winglet tip of the upper winglet being arranged higher relative to the attachment end than a lowermost winglet tip of the lowermost winglet; the upper winglet and the lowermost winglet overlapping each other along a chord of the attachment end; The upper winglet and the lowermost winglet both extend upward relative to the main wingtip; a spanwise profile of the lowermost winglet extending along a leading edge of the lowermost winglet having a midpoint, the slope of the spanwise profile at all points outboard of the midpoint closer to the tip of the lowermost winglet than the midpoint being more upwardly inclined than the slope of the spanwise profile at the midpoint, such that the lowermost winglet curves upwardly at points outboard of the midpoint; The leading edge of the lowermost winglet is offset relative to the leading edge of the upper winglet in a chordwise direction of the attachment end.

24. An aircraft comprising: body; one or more engines for propelling the aircraft and mounted to the fuselage; and a first wing and a second wing, the first wing and the second wing being arranged on opposite sides of the fuselage, the first wing and the second wing each comprising: a main wing, the main wing including a main wingtip; and A winglet system is attached to the main wingtip, the winglet system comprising: an upper winglet having an upper winglet tip outboard of the main wingtip; and a lowermost winglet having a lowermost winglet tip outboard of the main wing tip; in: The upper winglet tip of the upper winglet is arranged to be higher relative to the main wingtip than the lowermost winglet tip of the lowermost winglet; The upper winglet and the lowermost winglet overlap each other along the chord of the main wingtip; The upper winglet and the lowermost winglet both extend upward relative to the main wingtip; The upper winglet and the lowermost winglet each extend directly relative to the main wingtip; a spanwise profile of the lowermost winglet extending along a leading edge of the lowermost winglet having a midpoint, the slope of the spanwise profile at all points outboard of the midpoint closer to the tip of the lowermost winglet than the midpoint being more upwardly inclined than the slope of the spanwise profile at the midpoint, such that the lowermost winglet curves upwardly at points outboard of the midpoint; The leading edge of the lowermost winglet is staggered relative to the leading edge of the upper winglet along the chordwise direction of the main wingtip.

25. The aircraft of claim 24, wherein: The aircraft does not have any engines mounted on the first wing and the second wing for propelling the aircraft.

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