ELLIPTICAL WING TIP AND METHOD OF FABRICATING SAME

Abstract

A wingtip of a lifting surface of an aeronautical vehicle, the lifting surface having a span, a leading edge, a trailing edge, an upper surface and a lower surface, the wingtip being in a range of five percent to fifteen percent of an end portion of the span of the lifting surface, the wingtip including: an elliptical shape between the leading and trailing edges, the elliptical shape tapering in a direction towards an outer edge of the wing tip, wherein the tapering occurs in a plurality of geometric parameters of the lifting surface including spanwise chord distribution between the leading and trailing edges, spanwise mean camber distribution between the leading including and trailing edges, spanwise maximum thickness between the upper and lower surfaces, and spanwise twist of a mean average of the spanwise chord distribution of the wingtip.

Claims

1. A wingtip of an airfoil of an aircraft, the airfoil having a span, a leading edge, a trailing edge, an upper surface and a lower surface, the wingtip being in a range of five percent to fifteen percent of an end portion of the span of the airfoil, the wingtip comprising: an elliptical shape between the leading and trailing edges, the elliptical shape tapering in a direction towards an outer edge of the wing tip, wherein the tapering of the wingtip occurs in four geometric parameters including spanwise chord distribution between the leading and trailing edges, spanwise mean camber distribution between the leading and trailing edges, spanwise maximum thickness between the upper and lower surfaces, and spanwise twist of a mean average of the spanwise chord distribution of the wingtip; and wherein the chord length is tapered in a range of 0.45 to 0.50 of the initial chord at 100% span, the mean camber distribution tapers to zero at 100% span, a thickness to chord ratio tapers to less than one percent at 100% span, and twist of a mean chord distribution of the span of the wingtip is in a range of negative one degree and negative three degrees at 100% span relative to the innermost airfoil of the wingtip in a direction of a positive lift axis.

2. A wingtip of a lifting surface of an aeronautical vehicle, the lifting surface having a span, a leading edge, a trailing edge, an upper surface and a lower surface, the wingtip being in a range of five percent to fifteen percent of an end portion of the span of the lifting surface, the wingtip comprising: an elliptical shape between the leading and trailing edges, the elliptical shape tapering in a direction towards an outer edge of the wing tip, wherein the tapering occurs in a plurality of geometric parameters of the lifting surface including spanwise chord distribution between the leading and trailing edges, spanwise mean camber distribution between the leading and trailing edges, spanwise maximum thickness between the upper and lower surfaces, and spanwise twist of a mean average of the spanwise chord distribution of the wingtip.

3. The wingtip of claim 2, wherein the trailing edge of the lifting surface is constant.

4. The wingtip of claim 3, wherein the chord length is tapered in a range of 0.35 to 0.60 of the initial chord at 100% span.

5. The wingtip of claim 3, wherein the chord length is tapered in a range of 0.45 to 0.50 of the initial chord at 100% span.

6. The wingtip of claim 2, wherein the trailing edge of the lifting surface is tapered.

7. The wingtip of claim 6, wherein the chord length is tapered in a range of 0.35 to 0.60 of the initial chord at 100% span.

8. The wingtip of claim 6, wherein the chord length is tapered in a range of 0.45 to 0.50 of the initial chord at 100% span.

9. The wingtip of claim 2, wherein the mean camber distribution tapers to zero at 100% span.

10. The wingtip of claim 2, wherein a thickness to chord ratio tapers to less than one percent at 100% span.

11. The wingtip of claim 2, wherein the spanwise twist of a mean average of the spanwise chord distribution of the wingtip is in a range of negative one degree and negative three degrees at 100% span relative to the innermost airfoil of the wingtip in a direction of a positive lift axis.

12. The wingtip of claim 2 which is configured for installation on one of a BOEING model 737 NG-700, 737 NG-800, and 737 NG-900 aircraft.

13. The wingtip of claim 2 which is configured for installation on one of a BOEING model 737 MAX-7, 737 MAX-8, 737 MAX-9, and 737 MAX-10 aircraft.

14. The wingtip of claim 2 which is configured for installation on a main wing of an aircraft.

15. The wingtip of claim 2 which is configured for installation on a horizontal stabilizer of an aircraft.

16. The wingtip of claim 2 which is configured for installation on a canard of an aircraft.

17. The wingtip of claim 2 which is configured for installation on rotor blade of a helicopter.

18. The wingtip of claim 2 which is configured for installation on a blade of a propeller.

19. A method of fabricating wingtip of a lifting surface of an aeronautical vehicle, the lifting surface including a span, and an elliptical shape defined by a leading edge, a trailing edge, an upper surface and a lower surface, the method comprising the steps of: determining an outer portion of the lifting surface forming the wingtip; tapering the elliptical shape of the wingtip in a direction towards a distal end of the wingtip, said tapering including: tapering spanwise chord distribution between the leading and trailing edges, tapering spanwise mean camber distribution between the leading and trailing edges, tapering spanwise maximum thickness between the upper and lower surfaces, tapering spanwise twist of a mean average of the spanwise chord distribution of the wingtip; and forming the lifting surface with the elliptical tapered wingtip.

20. The method of claim 20, wherein the step of determining an outer portion of the lifting surface forming the wingtip comprises determining a proximal end and the distal end of the wingtip, wherein the proximal end being located at an outer five percent to fifteen percent of the span of the lifting surface.

21. The method of claim 20, further comprising maintaining the trailing edge of the lifting surface constant.

22. The method of claim 22, further comprising tapering the chord length in a range of 0.35 to 0.60 of the initial chord at 100% span.

23. The method of claim 22, further comprising tapering the chord length in a range of 0.45 to 0.50 of the initial chord at 100% span.

24. The method of claim 20, further comprising tapering the trailing edge of the lifting surface.

25. The method of claim 25, further comprising tapering the chord length in a range of 0.35 to 0.60 of the initial chord at 100% span.

26. The method of claim 25, further comprising tapering the chord length in a range of 0.45 to 0.50 of the initial chord at 100% span.

27. The method of claim 20, further comprising tapering the mean camber distribution to zero at 100% span.

28. The method of claim 20, further comprising tapering a thickness to chord ratio to less than one percent at 100% span.

29. The method of claim 20, further comprising tapering twist of a mean chord distribution of the span of the wingtip is in a range of negative one degree and negative three degrees at 100% span relative to the innermost airfoil of the wingtip in a direction of a positive lift axis.

30. The method of claim 20, further comprising configuring the lifting surface with the tapered wingtip for installation on one of a BOEING model 737 NG-700, 737 NG-800, and 737 NG-900 aircraft.

31. The method of claim 20, further comprising configuring the lifting surface with the tapered wingtip for installation on one of a BOEING model 737 MAX-7, 737 MAX-8, 737 MAX-9, and 737 MAX-10 aircraft.

32. The method of claim 20, further comprising configuring the lifting surface with the tapered wingtip for installation on a main wing of an aircraft.

33. The method of claim 20, further comprising configuring the lifting surface with the tapered wingtip for installation on a horizontal stabilizer of an aircraft.

34. The method of claim 20, further comprising configuring the lifting surface with the tapered wingtip for installation on a canard of an aircraft.

35. The method of claim 20, further comprising configuring the lifting surface with the tapered wingtip for installation on rotor blade of a helicopter.

36. The method of claim 20, further comprising configuring the lifting surface with the tapered wingtip for installation on a blade of a propeller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 depicts a top plan view of a right side horizontal stabilizer of a swept wing jet transport aircraft and illustrating an elliptical wingtip in accordance with the present invention;

[0028] FIG. 2 depicts a right side elevation view of the elliptical wing tip of FIG. 1 as viewed from a perspective of the trailing edge of the swept horizontal stabilizer;

[0029] FIG. 3 depicts a right side elevation view of the elliptical wing tip of the swept horizontal stabilizer of FIG. 1;

[0030] FIG. 4 depicts an exploded view of a first airfoil of the wingtip of FIG. 2 illustrating its chord line, mean camber line and maximum thickness;

[0031] FIG. 5 depicts a top, rear, right-side perspective view of the swept horizontal stabilizer and illustrating sectional views of the elliptical shape of the wing tip of FIG. 1;

[0032] FIG. 6 depicts a top, front, right-side perspective view of the swept horizontal stabilizer and illustrating the sectional views of the elliptical shape of the wing tip of FIG. 4;

[0033] FIG. 7 is a flow diagram of a method for fabricating a lifting surface of the present invention for an aeronautical vehicle;

[0034] FIG. 8A (prior art) and FIG. 8B are graphical images of a bottom, right-side view of wingtip of a wing of an aircraft without and with the elliptical shaped wingtip, respectively, and comparatively displaying computer simulations of high and low velocity surface air flow and turbulence over the wing and wingtip of the aircraft with and without the elliptical wingtip;

[0035] FIG. 9A (prior art) and FIG. 9B are graphical images of an enlarged, bottom, right-side view of wingtip of a wing of an aircraft of FIGS. 7A and 7B without and with the elliptical shaped wingtip, respectively, and comparatively displaying computer simulations of high and low velocity surface air flow and turbulence over the wing and wingtip of the aircraft with and without the elliptical wingtip; and

[0036] FIG. 10A (prior art) and FIG. 10B are graphical images of a top, right-side view of wingtip of a wing of an aircraft without and with the elliptical shaped wingtip, respectively, and comparatively displaying computer simulations of high and low velocity surface air flow and turbulence over the wing and wingtip of the aircraft with and without the elliptical wingtip;

[0037] To further facilitate an understanding of the invention, the same reference numerals have been used, when appropriate, to designate the same or similar elements that are common to the figures. Further, unless otherwise indicated, the features shown in the figures are not drawn to scale, but are shown for illustrative purposes only.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention is directed to an elliptical shaped wingtip of a wing of an aircraft. In one embodiment, the elliptical wingtip preferably tapers at the outer five to fifteen percent of the combined wing surface and wingtip system. The elliptical tapering is provided across four geometric design parameters of the wing including chord distribution, mean camber distribution, wing thickness, and twist. The combined elliptical tapering across all four geometric parameters provides the advantageous effects of the elliptical wingtip that exceeds the prior art wingtip designs.

[0039] In particular, the elliptical wingtip has numerous effects on the wing surface. For example, the shape of the elliptical wingtip moves the initiation of the wingtip vortex to the most aft and outboard point on the wingtip. This is evidenced by straight streamlines at the 99% to 100% span area of the combined wing and wingtip, as discussed below with respect to FIGS. 8A-10B. This outer and aft-most positioning of the wingtip vortex leads to lower induced drag, while also producing less lift on the wingtip than observed on prior art wing/wingtip designs.

[0040] Referring to FIG. 1, a bottom view of a horizontal stabilizer 110 of an aircraft 100 is illustratively shown. The elliptical wingtip 120 is illustratively shown and discussed with respect to a horizontal stabilizer of an aircraft, but is not considered limiting. For example, the elliptical shape can be similarly provided on an aircraft wing, lifting stabilizer, lifting canard, helicopter rotor blade, winglet and other lifting surfaces. The horizontal stabilizer is attached to the fuselage 101 of the aircraft 100 and extends outwardly in a well-known manner. The horizontal stabilizer includes a leading edge 112, a trailing edge 114 and terminates at a wingtip 120 having an elliptical shape of the present invention. The wingtip includes the outer 5% to 15% of the combined span of the wing surface. The elliptical wingtip portion can be represented by a plurality of local airfoils or cross-sections 122, for example, nine cross-sections 122-1 through 122-9 as illustratively shown in FIG. 1. The elliptical taper of the airfoils 122 can best be seen in FIGS. 2-4.

[0041] Referring now to FIGS. 2 and 3, the elliptical taper of the wingtip cross sections is illustratively shown. FIG. 2 depicts a side elevation view of the horizontal stabilizer 110, while FIG. 3 depicts an elevation view parallel to the trailing edge 114 of the horizontal stabilizer 110. The nine airfoils illustrate the diminishing curvature of the leading edge 112 of the elliptical wingtip with respect to the trailing edge 114 which is substantially linear, i.e., constant. Referring to FIG. 2, the first airfoil 122-1 defines the largest elliptical profile and the outermost airfoil 122-9 defines he smallest elliptical profile. The second through eighth elliptical profiles 122-2 through 122-9 are evenly spaced and define the leading edge curvature between the first and last airfoils 122-1, 122-9. The lower surface 124 of the wingtip 110 tapers upwardly in a lateral direction from the first airfoil 122-1 to the last airfoil 122-9, as best seen in FIG. 5. Similarly, the upper surface 126 of the wingtip 110 tapers downwardly in the lateral direction from the first airfoil 122-1 to the last airfoil 122-9, as best seen in FIG. 6.

[0042] Referring to FIG. 4, a cross-sectional view of the first airfoil 122-1 of the tapered wingtip 110 is shown. It is well-known that an elliptic curve over a two dimensional field of quantities x and y consists of all the points that satisfy the following equation: 1=(x.sup.2/a.sup.2)+(y.sup.2/b.sup.2), where a is the elliptical radius on the x axis and b is the elliptical radius on the y axis and the curve does not have any singular points, i.e., no cusps or self-intersections.

[0043] The cross-sectional view illustrates the chord 130-1 and the mean camber line 132-1, both of which extend between the leading edge 112-1 and trailing edge 114-1 of the illustrative cross-section 122-1. The maximum thickness 134-1 of the wingtip at the cross-section 122-1 is also illustrated. Each of the other illustrative airfoils 122-2 through 122-9 have similar, but tapered characteristics, as shown in the elevation views of FIGS. 2 and 3 and the perspective top right-side views of FIGS. 5 and 6.

[0044] FIG. 7 is a flow diagram of a method 700 for fabricating a lifting surface of the present invention for an aeronautical vehicle. The method 700 starts at step 701, where the type of lifting surface is identified. For example, the lifting surface can be a wing, horizontal stabilizer, vertical stabilizer, or canard of an aircraft, or a blade of a helicopter or propeller, among other lifting surfaces. The method 700 then proceeds to step 702, where an outer portion of the lifting surface which forms the wingtip is determined. In one embodiment, the outer five percent to fifteen percent of the lifting surface forms the wingtip, although such percentages are not considered limiting.

[0045] At step 704, tapering of the elliptical shape of the wingtip in a direction towards a distal end of the wingtip is performed. The tapering includes tapering spanwise chord distribution between the leading and trailing edges, tapering spanwise mean camber distribution between the leading and trailing edges, tapering spanwise maximum thickness between the upper and lower surfaces, and tapering spanwise twist of a mean average of the spanwise chord distribution of the wingtip.

[0046] At step 706, the lifting surface with the elliptical tapered wingtip is formed by fabricating the wingtip from well-known materials such as fiberglass, carbon fiber, Kevlar, VECTRAN or other aerospace grade reinforcing fibers and plastics. The lifting surface can also be fabricated from metals such as aluminum, steel, stainless steel, titanium, or other aerospace grade metals, or a combination of composite and metal materials. Processes for fabricating the lifting surface can include molding, machining, additive manufacturing, or combination of these practices. Once the fabrication process of fabricating the lifting surface with the tapered wingtip of the present invention is completed, the lifting surface can be attached as a kit to older aircraft, or incorporated into the fuselageas part of a new aircraft design. Alternatively, the tapered wingtip 110 can be fabricated separately from the lifting surface and attached thereon in a well-known manner. The method 700 then proceeds to step 799, where the method 800 ends.

[0047] A comparison with respect to air flow at the wingtip of a wing of a horizontal stabilizer 110 with and without the tapered elliptical wingtip 120 of the present invention installed on an aircraft 100 can best be seen in the graphic images of FIGS. 8A-10B.

[0048] Referring now to FIGS. 8A-10B, representations of various views of screen shots of computer-simulated aircraft to illustrate comparative effects on airflow with and without the tapered elliptical wing tip 120 of the present invention mounted on the horizontal stabilizer 110 of an aircraft 100 are illustratively shown. FIGS. 8A and 9A are bottom, right-side views and FIG. 10A is a top right-side view of an unmodified horizontal stabilizer 110 without the tapered elliptical wing tip 120 of the present invention. FIGS. 8B and 9B are top, right-side views and FIG. 10B is a top, right-side view of the same horizontal stabilizer 110 being modified with the tapered elliptical wing tip 120. The drawings were taken from color-coded computer simulations which were configured and performed by the inventors using the well-known NASA Common Resource Model (CRM) from the 5th AIAA Drag Prediction Workshop, although such simulation program is not considered limiting. The simulations conducted were from an industry standard model of a 767/777/A330/A350 class aircraft. The CRM is used throughout the industry in wind tunnel and computational fluid dynamics (CFD) work to develop an understanding of drag and how to predict it. High surface pressure areas are illustrated by darker shading, as compared to low surface pressure areas which are illustrated by lighter shading at specific areas of the aircraft.

[0049] Referring to FIGS. 8A, 9A and 10A, during flight of the aircraft 100, the illustrative horizontal stabilizer 110 with the non-tapered wing tip induces wingtip vortices as illustrated by the concentration of curved streamlines as illustrated by arrow A. The horizontal stabilizer of a conventional commercial aircraft is designed to generate negative lift for purposes of stability. More specifically, the air above the horizontal stabilizer 110, which is at a high pressure/low velocity along the upper surface 124 of the wingtip 110, flows downwardly at the outermost end portion 123 of the wingtip 110 to the low pressure/high velocity lower surface 126 of the wingtip 110 in the form of a trailing or lift-induced vortex, as illustratively shown by the plurality of curved arrows identified by arrow B. The initiation of the wingtip vortex occurs at the outboard 5% of the leading edge of the combined horizontal stabilizer 110 and wingtip 120 (See arrow A of FIGS. 8A, 9A and 10A).

[0050] By contrast and referring to FIGS. 8B, 9B and 10B, the shape of the tapered elliptical wingtip 120 moves the initiation of the wingtip vortex to the most aft, outboard point on the wingtip 120, as illustrated by the plurality of arrows C. This is further evidenced by straight streamlines at the 99% to 100% span area of the combined wing and wingtip, as illustrated by arrow D. This outer and aft-most positioning of the wingtip vortex leads to lower induced drag, while the wingtip producing less lift on the wingtip than other designs provides for lower wing bending.

[0051] The inboard shift of the spanwise lift distribution leads to a lower bending moment on the wing structure. For a given lift condition, the reduction in bending moment increases the structural margin of the wing. The lower bending moment may allow an increase in the maximum gross weight capability of the aircraft with changes limited to the fuselage and landing gear systems. The design of the elliptical wingtip reducing lift at the wingtip also leads to a decrease in load on the OEM wingtip fasteners for retrofit applications. The existing fasteners, nut plates, and wingtip attachment can be retained in many cases. If needed, any additional structure required is far less than that required for other prior art wingtip devices.

[0052] Due to the increased inboard lift efficiency caused by the elliptical wingtip, the flight angle of, for example, the horizontal stabilizer will be reduced by approximately 0.2 degrees. Both manual and auto trim systems can accommodate this change without alteration to any indicator or control system. This difference in trim alpha will be nearly imperceptible to a flight crew.

[0053] Although an embodiment of the tapered elliptical wingtip 120 on a horizontal stabilizer 110 has been shown and described herein for mounting on an aircraft, such as the BOEING 737 model airframes (e.g., 737 NG-700 and the 737 MAX-7 airframes), such wingtip and airframe are described for illustrative purposes only, as a person of ordinary skill in the art will appreciate that the method 700 and tapered elliptical wingtip 120 of the present invention can be provided for any other aircraft or aeronautical vehicle having a lifting surface 110.

[0054] It is well known that each aircraft wing 102 (left and right, symmetrical about the long axis of the aircraft) generates a separate downwash sheet. The downwash sheets are virtually independent of each other due to the lateral separation created by the fuselage 101. The unique effect of the tapered elliptical wingtip 120 of the present invention is the more efficient extension of the left and right downwash sheets at the outermost edge of the wingtips and with greater lift distribution towards the inboard portion of the wings.

[0055] Another advantage is that the present tapered elliptical wingtip 120 can be implemented after the wing designs have been frozen or are already in production. For a newly designed aircraft, the tapered elliptical wingtip 120 can be iterative and be optimized with regard to the other components. A person of ordinary skill in the art will appreciate that other embodiments of the tapered elliptical wingtip 120 can be formed and positioned in a similar manner described above for various aircraft models.

[0056] While the foregoing is directed to embodiments of the present invention, other and further embodiments and advantages of the invention can be envisioned by those of ordinary skill in the art based on this description without departing from the basic scope of the invention, which is to be determined by the claims that follow.