Slotted natural laminar flow airfoil

Abstract

An aircraft capable of transonic flight is equipped with a slotted airfoil to significantly improve the cruise performance during flight. The aircraft includes a plurality of slotted airfoils uniquely configured to maximize natural laminar flow across the aircraft wings. In addition to reduced wing drag, the unique configuration minimizes shocks at various conditions over the course of a flight. Each slotted airfoil includes a fore element, an after element, and a slot disposed between the fore element and aft element. The aft element is maneuverable relative to the fore element. The slot is configured to promote a substantially constant air flow field onto the aft element during all flight angles of attack.

Description

SLOTTED NATURAL LAMINAR FLOW AIRFOILSPECIFICATIONBACKGROUND1. Field of the Invention

[0001] The present application relates to aircraft design. In particular, the present application relates to an airfoil configuration for optimizing efficiency of airflow across an aircraft during flight.2. Description of Related Art

[0002] Generally, a central focus of aircraft design is to achieve a substantially efficient aerodynamic configuration, while also following proper guidelines and regulations provided by any relevant governing bodies. One such goal of aerodynamic efficiency is to obtain laminar flow of air around the surface of the aircraft.

[0003] Laminar flow is the orderly layered flow of air over the surface of aircraft parts that greatly reduces the drag on such surfaces while in flight. In contrast, turbulent flow occurs when this orderly flow is disrupted. Laminar flow occurs in a boundary layer of fluid / air in the immediate vicinity of a surface, the boundary layer being formed by the fluid / air flowing along the surface.

[0004] Laminar flow can be achieved in two different ways, actively and naturally. Active laminar flow can be achieved through the addition of energy into the boundary layer, while natural laminar flow can be achieved by utilizing the surface geometry which maintains a favorable pressure gradient and therefore creating a laminar boundary layer over the surface.

[0005] Current aircraft designs utilize various shapes of wing airfoils, depending on the desired performance of the aircraft. While the common wing succeeds in providing proper lift for the aircraft, there is often turbulent flow across a significant portion of the wing,SpecificationAttorney Docket No. 1832JW-62999-PCTwhich reduces the efficiency of the aircraft. Although standard aircraft designs utilize varying shapes, the wing airfoils are generally a single-element configuration.

[0006] Although the aforementioned aircraft system designs represent great strides in the field of aviation technology, many shortcomings remain.Specification Attorney Docket No. 1832JW-62999-PCTDESCRIPTION OF THE DRAWINGS

[0007] The novel features believed characteristic of the invention are set forth in the appended claims. However, the invention itself, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein:Figure 1 is a side view of an example slotted airfoil shape;Figure 2 is a top and bottom view of aircraft wings with a slotted airfoil according to a preferred embodiment of the present application;Figure 3 is a top view illustrating multiple sections of an aircraft wing;Figure 4A is a graphical depiction of the cross-section of a wing root airfoil according to the preferred embodiment of the present application;Figure 4B is a graphical depiction of the cross-section of a side of body airfoil according to the preferred embodiment of the present application;Figure 4C is a graphical depiction of the cross-section of a kink airfoil according to the preferred embodiment of the present application;Figure 4D is a graphical depiction of the cross-section of an aileron root airfoil according to the preferred embodiment of the present application;Figure 4E is a graphical depiction of the cross-section of a winglet root airfoil according to the preferred embodiment of the present application;Figure 5 is a cross-sectional view of a wing with various aft elements according to the preferred embodiment of the present application;Figure 6 is a cross-sectional view of a wing with various aft elements and the associated hinge lines according to the preferred embodiment of the present application;SpecificationAttorney Docket No. 1832JW-62999-PCTFigure 7 is a top view of an aircraft wing geometry according to an alternative embodiment of the present application.While the assembly of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present application as defined by the appended claims.SpecificationAttorney Docket No. 1832JW-62999-PCTDETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0008] Illustrative embodiments of a slotted natural laminar flow airfoil according to the present application are provided below. It will of course be appreciated that in the development of any actual embodiment, numerous implementation-specific decisions will be made to achieve the developer’s specific goals, such as compliance with assembly- related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0009] Many different aircraft are designed to operate at transonic air speeds. A transonic airspeed is a speed within a certain range in which there are regions of both subsonic and supersonic airflow across the object. The present application utilizes a slotted airfoil on a transonic aircraft wing in order to greatly improve the cruise performance of the aircraft by lowering the wing drag. Such application can be utilized in a variety of aircraft, including private jets, commercial airliners, military aircraft, and a variety of other aircraft. In addition to reducing the wing drag, the slotted airfoils may provide an improvement in maximum lift of the aircraft while protecting against certain undesired characteristics of the aircraft while at maximum lift. For example, certain bad stall characteristics may be eliminated, or at least significantly reduced.

[0010] Referring now to Figure 1 in the drawings, an exemplary slotted airfoil is illustrated. Airfoil 100 includes two primary elements, a fore element 101 and an aft element 103. There is a small gap 105, or slot, in between the fore element 101 and the aft element 103. The gap 105 preferably exists at all times; however, the gap may change in width at various times, dependent on possible movement of the aft element 103 with respect to the fore element 101. A substantial benefit of a two-element, slotted airfoil is that each element may be uniquely configured to promote large amounts of laminar flow, as opposed to a single-element airfoil being much less maneuverable in shape and configuration. The promotion of larger amounts of laminar flow and reduction of turbulent flow is key to minimizing drag.SpecificationAttorney Docket No. 1832J -62999-PCT

[0011] Referring now also to Figure 2 in the drawings, multiple views depicting areas of flow over wings of an aircraft are illustrated. The left half of Figure 2 illustrates bottom portion 201 , while the right half of Figure 2 illustrates top portion 203. Bottom portion 201 represents the underside of an aircraft and top portion 203 represents the top surface of an aircraft. Both bottom portion 201 and top portion 203 have a fore element 205 and at least one aft element 207. The bottom portion 201 and the top portion 203 are coupled to fuselage 209. Figure 2 best illustrates the areas of laminar and turbulent flow over the aircraft wings. The areas configured for laminar flow are indicated by the dark black areas, while the areas configured for turbulent flow are indicated by the lighter grey areas. It should be appreciated that alternative embodiments of the present application may have flow areas that are not exactly shaped and sized as depicted in Figure 2. For example, some aircraft with two-element, slotted airfoils may have alternatively shaped and sized wings, such that the exact areas of laminar and turbulent flow do not perfectly match the depiction presented herein.

[0012] The aft element 207 is preferably configured such that laminar flow occurs over a majority of the lower surface, as shown on bottom portion 201. Meanwhile, turbulent flow mostly only occurs on the upper surface of the aft element 207, as shown on top portion 203. The preferred design choices presented herein make the wing design very efficient with low drag, while maintaining safety for the range of any mission segments.

[0013] The aft element 207 is preferably positioned closely behind the fore element 205. This positioning results in a slot between the two elements. The slot configuration results in a jet of air onto the top surface of the aft element 207. The resulting flow field around the aft element 207 remains nearly constant for all angles of attack for the airfoil. As such, the aft element 207 is protected from flow separations that generally occur with traditional single-element airfoils. At least a significant reduction of these flow separations leads to potential safety improvements with the unique configuration of the present application. The slot and aft element 207 may also be configured to allow a hinged movement downward of the trailing edge of the aft element 207 in order to increase lift at a given angle of attack, thus essentially functioning as a flap. Similarly, movement of the aftSpecificationAttorney Docket No. 1832JW-62999-PCTelement 207 may also be utilized to function as an aileron by deflecting a portion of the trailing edge up or down.

[0014] The transonic, natural-laminar flow airfoils of the present application have preferably been designed such that a large amount of laminar flow occurs on both the upper and lower surfaces of the fore element, while also minimizing shocks at typical climb, cruise, and descent conditions. Such configuration of the airfoils allows for lower drag to be achieved than is possible for a traditional, single-element airfoil.

[0015] The preferred embodiment of the present application utilizes a series of airfoils designed using multiple flight conditions that may be experienced during climb, cruise, and descent segments of a typical flight mission. The multi-point airfoil design configuration provides a robust performance across the flight envelope.

[0016] Referring now also to Figure 3 in the drawings, a top view of a portion of an aircraft wing is illustrated according to a preferred embodiment of the present application. Aircraft 300 includes fuselage 302, fore element 301 , and aft elements 303. The fore element 301 and aft elements 303 extend horizontally from the fuselage 302. There are preferably three different portions of the aft elements 303, being an inboard flap, an outboard flap, and an aileron. Some embodiments of the present application may utilize a winglet on the end of the wing opposing the fuselage attachment end.

[0017] Figure 3 best illustrates five different slotted natural laminar flow airfoils. Under the preferred embodiment of the present application, the aircraft includes a centerline airfoil 305, a side of body airfoil 307, a kink airfoil 309, an aileron root airfoil 311 , and a winglet root airfoil 313. Each of the five slotted natural laminar flow airfoils are utilized for the transonic wing loft, with spanwise cross-sections taken as shown in Figure 3. Each of the cross-sections are defined in the streamwise direction, but rotated to the dihedral angle, that is equivalent to the wing reference ZX plane. From the five defined airfoil locations, the airfoils are then blended using a linear interpolation. The planform, i.e. root, kink, and tip chords, kink spanwise location, leading edge sweep, span and flap, aileron and winglet definition are selected to achieve desired cruise wing loading, takeoff, and landing performance and control power.SpecificationAttorney Docket No. 1832JW-62999-PCT

[0018] Referring now also to Figures 4A-4E in the drawings, various cross-sectional depictions of the airfoils are shown according to a preferred embodiment of the present application. Each of Figures 4A-4E illustrate a non-dimensional airfoil cross-section with fore element 401 and aft element 403. It should be noted that the winglet does not employ a slotted natural laminar flow airfoil. Figure 4A illustrates a cross-sectional view of centerline airfoil 305. Figure 4B illustrates a cross-sectional view of side of body airfoil 307. Figure 4C illustrates a cross-sectional view of kink airfoil 309. Figure 4D illustrates a cross-sectional view of aileron root airfoil 311 . Figure 4E illustrates a cross-sectional view of winglet root airfoil 313.

[0019] Referring now also to Figures 5 and 6 in the drawings, multiple cross-sectional views of a slotted natural laminar flow airfoil are illustrated according to a preferred embodiment of the present application. Figure 5 illustrates an airfoil with a fore element 501 and an aft element 503. Aft element 503 is shown in three different possible positions depending upon the desired aircraft behavior. Position 503a is for the aft element in a cruise position, which has the lowest drag. Position 503b has the aft element with its trailing edge in an upward position, while position 503c has the trailing edge in a downward position. To arrive at such positions, aft element 503 rotates around a hinge point 505.

[0020] Figure 6 provides a zoomed in view of the rotatable aft element. Similar to Figure 5, Figure 6 includes a fore element 601 and aft element 603. Aft element 603 is shown in three different positions: 603a (cruise position), 603b (trailing edge up), and 603c (trailing edge down). Hinge point 605 is where the aft element preferably rotates about. The upper surface of the aft element has a leading edge with a circular contour that is centered at the hinge point 605. The arrow extending from hinge point 605 represents the radius of the aft element’s circular contour. The fore element has a trailing edge with a cove shape, configured in a substantially circular design. The cove shape has a radius centered at point 607, which is preferably positioned slightly forward of hinge point 605. The radius of the cove shape is represented by the arrow extending from point 607. With such configuration, a slot is formed that is slightly converging all the way to its exit. Because of the transonic flow, the slot helps to prevent a shock from forming and causing chokedSpecificationAttorney Docket No. 1832JW-62999-PCTairflow. The illustrated trailing edge thickness is provided as an example due to specific manufacturing conditions. It should be appreciated that alternative embodiments may utilize alternative thicknesses dependent upon various desires and conditions.

[0021] Referring now also to Figure 7 in the drawings, a pair of overlaid wing geometries are illustrated from a top view according to an embodiment of the present application. Wing system 700 is best configured for coupling to an aircraft fuselage. As is standard with aircraft, there should be a wing system 700 extending horizontally from each side of the fuselage. Wing system 700 preferably includes a new wing geometry 701 in place of a standard wing geometry 703. Wing geometry 701 has a chord that is larger than that of geometry 703 by approximately 8.5 percent. Further, the leading-edge sweep of geometry 701 includes an additional 3.5 degrees of angle compared to the geometry 703. It should be appreciated that alternative embodiments may include various wing geometries that are of different offsets from the standard, beyond the 8.5 percent chord size difference and the 3.5-degree leading-edge sweep angle difference, and that those exact differences are present in a preferred embodiment, but are not required for all embodiments of the present application.

[0022] Changes in both chord size and leading-edge sweep angles can provide unique advantages in operation of an aircraft. Providing a larger chord and an increased leadingedge sweep angle, in combination with the features described above, result in a reduction in cruise drag and an increase in cruise speed, respectively. As such, the efficiency of standard flight operation is increased. It should be appreciated that such wing geometry changes may be used in conjunction with the slotted airfoils described herein, or with other more standard aircraft wing configurations.

[0023] It is apparent that a system with significant advantages has been described and illustrated. The particular embodiments disclosed above are illustrative only, as the embodiments may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. It is therefore evident that the particular embodiments disclosed above may be altered or modified, and all such variations are considered within the scope and spirit of the application. Accordingly, theSpecificationAttorney Docket No, 1832J -62999-PCTprotection sought herein is as set forth in the description. Although the present embodiments are shown above, they are not limited to just these embodiments, but are amenable to various changes and modifications without departing from the spirit thereof.SpecificationAttorney Docket No. 1832JW-62999-PCT

Claims

What is claimed is:1 . A slotted airfoil for a wing of an aircraft, comprising: a fore element; an aft element disposed behind the fore element; and a slot disposed between the fore element and the aft element; wherein at least the aft element is maneuverable relative to the fore element; and wherein the slot is configured to promote a substantially constant airflow field onto the aft element for all flight angles of attack of the aircraft.

2. The slotted airfoil according to claim 1 , wherein the maneuverability of the aft element is a hinged movement of a trailing edge of the aft element in order to alter lift of the aircraft.

3. The slotted airfoil according to claim 2, wherein the trailing edge is manipulated downward to increase lift.

4. The slotted airfoil according to claim 2, wherein the trailing edge is manipulated downward to decrease lift.

5. The slotted airfoil according to claim 1 , wherein the fore element comprises: a fore top surface; and a fore bottom surface; and wherein the aft element comprises: an aft top surface; and an aft bottom surface; wherein natural laminar flow occurs over a substantial portion of at least the fore top surface, the fore bottom surface, and the aft bottom surface.

6. The slotted airfoil according to claim 1 , wherein the slot is configured to slightly converge from its point of air entry to its point of air exit.SpecificationAttorney Docket No. 1832JW-62999-PCT7. An aircraft wing, comprising: a fore element; an aft element; a slot disposed between the fore element and the aft element; and a plurality of airfoil configurations; wherein the slot is configured to promote increased natural laminar flow over a substantial portion of the aircraft wing during at least a significant portion of the phases of flight.

8. The aircraft wing according to claim 7, wherein the plurality of airfoil configurations comprise: a centerline airfoil; a side of body airfoil; a kink airfoil; an aileron root airfoil; and a winglet root airfoil.

9. The aircraft wing according to claim 7, wherein the plurality of airfoil configurations are blended using a linear interpolation.

10. The aircraft wing according to claim 7, wherein the aircraft wing shape is selected to achieve desired wing loading, takeoff and landing performance, and control power.11 . The aircraft wing according to claim 7, further comprising: a wing chord having an increased size relative to a standard aircraft wing geometry; and a wing leading edge sweep having an increased angle relative to a standard aircraft wing.SpecificationAttorney Docket No. 1832JW-62999-PCT12. The aircraft wing according to claim 11 , wherein the wing chord is 8.5 percent larger than the standard aircraft wing geometry.

13. The aircraft wing according to claim 11 , wherein the wing leading edge sweep is increased by 3.5 degrees relative to the standard aircraft wing.

14. The aircraft wing according to claim 7, wherein the fore element comprises: a fore top surface; and a fore bottom surface; and wherein the aft element comprises: an aft top surface; and an aft bottom surface; wherein natural laminar flow occurs over a substantial portion of at least the fore top surface, the fore bottom surface, and the aft bottom surface.

15. The aircraft wing according to claim 7, wherein the aft element is maneuverable relative to the fore element.

16. The aircraft wing according to claim 15, wherein the maneuverability of the aft element is a hinged movement of a trailing edge of the aft element in order to alter lift of the aircraft.

17. The aircraft wing according to claim 16, wherein the trailing edge is manipulated downward to increase lift.

18. The aircraft wing according to claim 16, wherein the trailing edge is manipulated downward to decrease lift.SpecificationAttorney Docket No. 1832JW-62999-PCT

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