WO2002020350A2

WO2002020350A2 - Method of providing an aircraft wing with an airfoil for low speed flight

Info

Publication number: WO2002020350A2
Application number: PCT/US2001/028224
Authority: WO
Inventors: Norbert A. Weisend, Jr.
Original assignee: Goodrich Corporation
Priority date: 2000-09-07
Filing date: 2001-09-07
Publication date: 2002-03-14
Also published as: WO2002020350A3

Abstract

A method of altering the aerodynamic characteristics of the wings (14) of an aircraft (12). For low speed flight, a first wall portion (46) is expanded to provide an airfoil geometry for low speed flight (e.g., high camber, blunt leading edge) and a second wall portion (48) is maintained (e.g., suction is applied to a corresponding chamber) so that it follows a concave path. For high speed flight, the wall portions (46, 48) are retracted to provide the airfoil geometry for high speed flight (e.g., low camber, sharp leading edge).

Description

METHOD OF PROVIDING AN AIRCRAFT WING WITH AN AIRFOIL FOR LOW SPEED FLIGHT

FIELD OF THE INVENTION This invention relates generally as indicated to a method of providing an aircraft wing with an airfoil geometry for low speed flight and, more particularly, to a method of controlling pressures within an inflatable panel installed on the wing to achieve a lift-enhancing airfoil geometry.

BACKGROUND OF THE INVENTION Flight requires the overcoming of two forces - drag and weight. Weight, which is gravitational force acting on the aircraft, is overcome primarily through lift. Lift is provided by producing a low pressure area over the wing and a high pressure area under the wing. The low pressure area is produced by air traveling faster over the top of the wing than under wing whereby the increase in air velocity results in a decrease in air pressure. The high pressure area under the wing acts to push the wings and aircraft upward.

Drag, which is the resulting force due to the resistance of air striking the aircraft's surface, is overcome primarily through thrust. Thrust is provided by, for example, jet engines which push the aircraft in the forward direction. Accordingly, the less drag an aircraft is subjected to, the faster it may travel with the same amount of thrust-producing capacity.

The wings of an aircraft are consequently designed to provide sufficient lift and to minimize drag. An important component in this design is the airfoil geometry of the wing. When evaluating airfoil geometry, a straight chord line may be drawn from the leading edge to the trailing edge of the airfoil thereby conceptually dividing the airfoil into a topside and an underside. A mean camber line may be drawn by plotting the points halfway between the topside and the underside of the airfoil. The camber, that is the maximum distance between the chord line and the mean camber line, represents the curvature of the air foil and a high camber corresponds to a high curvature.

A high camber allows an aircraft to operate at lower take-off and landing speeds and thus operate on runways of reduced distances. Also, a greater chord length often translates into a greater lift-enhancing surface area. Further, a relatively blunt leading edge will ensure that the air will flow smoothly over the airfoil's top side during low speeds. (At low speeds, sharp leading edges tend to "slice" the air causing it to separate from the airfoil's topside and swirl turbulently whereby the smooth flow causing the velocity increase does not occur.) In contrast, during high speed flight, a low camber, less chord length, and sharp leading edges translate into less drag and faster speeds for a given thrust-producing capacity.

Accordingly, it is often desirable to provide an aircraft wing with an airfoil geometry for low speed flight (i.e., take-off and landing) and another airfoil geometry for high speed flight. U.S. Patent No. 2,937,826 to Johnson discloses an airfoil shape-altering panel for this purpose. The panel comprises a top margin positioned on the topside of the wing, a bottom margin positioned on the underside of the wing, and an outer wall extending therebetween. The wall comprises a first expandable wall portion extending between the panel's top margin to the airfoil's under side and a second stretchable wall portion extending between a bottom end of the first wall portion to the bottom margin.

For low speed flight, a first chamber of the Johnson panel is inflated so that the first wall portion extends outward from the wing's leading edge and its underside in a non-parallel shape which increases the camber, blunts the curve of the leading edge, and increases the chord length. When the first chamber is inflated to expand the first wall portion, the second chamber is stretched so that the second wall portion is in a substantially straight path between the bottom end of the inflated first wall portion to the panel's bottom margin. For high speed flight, the chambers of the Johnson panel are deflated so that the first wall portion and the second wall portion lie flat against the wing thereby closely conforming to the low camber and sharp leading edge of the wing.

SUMMARY OF THE INVENTION The present invention provides an improved method of using an airfoil shape-altering panel, such as the Johnson panel, to produce an improved airfoil geometry for low speed flight. In this method, the second wall portion (i.e., the wall portion extending from the bottom of the first expandable wall portion to the bottom margin of the panel) is maintained in a concave, rather than straight, path. This concave profile of the second wall portion is believed to enhance the lift capacity of the wing, reduce non-stall speed, and thereby allow the use of even shorter runway distances. More particularly, the method of the present invention provides an aircraft wing with an airfoil geometry for low speed flight and another airfoil geometry for high speed flight. In this method, a panel is installed to the wing having a first expandable wall portion and a second expandable wall portion extending from a bottom end of the first wall portion to a bottom margin of the panel. The first wall portion is expanded (e.g., pressure is applied to a corresponding chamber) so that it is positioned to provide the airfoil geometry for low speed flight. When the first wall portion is expanded, the second wall portion is maintained (e.g., suction is provided to a corresponding chamber) in a concave path relative to a line between the bottom end of the first wall portion and the bottom margin of the panel.

These and other features of the invention are fully described and particularly pointed out in the claims. The following description and annexed drawings set forth in detail a certain illustrative embodiment of the invention, this embodiment being indicative of but one of the various ways in which the principles of the invention may be employed.

DRAWINGS Figure 1 is a schematic perspective view of an aircraft having an airfoil shape altering panel used in the method of the present invention installed on each of its wings. Figure 2 is a cross-sectional view of one of the wings with the panel being shown in a retracted condition for high speed flight.

Figure 3 is a cross-sectional view of one of the wings with the panel being shown in an expanded condition for low speed flight.

DETAILED DESCRIPTION Referring now to the drawings, and initially to Figure 1 , panels 10 used in the method of the present invention are shown installed on an aircraft 12, and more particularly the aircraft's wings 14. The wings 14 each have a topside 16, an underside 18, and leading edge 20 therebetween. In the illustrated aircraft 12, the wings 14 are characterized by a low camber and a sharp thin leading edge.

Referring now to Figures 2 and 3, the panel 10 is shown in a retracted condition for high speed flight (Figure 2) and is shown in an expanded condition for low speed flight, such as during take-off and landing (Figure 3). This results in two different airfoil geometries being created depending on whether the aircraft 12 is to be operated at a high speed or at a low speed. The airfoil shown in Figure 2 closely conforms to the airfoil of the wing 14 and has a low camber, a sharp leading edge 32, and a chord line 34. The airfoil shown in Figure 3 has a high camber, a blunt leading edge 32', and a chord line 34' of increased length.

The panel 10 comprises a top margin 40 positioned on the airfoil's topside 16, a bottom margin 42 positioned on the airfoil's underside 18, an outer wall 44 extending therebetween. The outer wall 44 includes connected expandable wall portions 46 and 48. An upper fairing 50 forms a transition from the top margin 40 to the top of the expandable wall portion 46 and a lower fairing 52 forms a transition from the bottom margin 42 to the bottom of the expandable wall portion 48. The panel 10 additionally comprises internal walls which form, in conjunction with the expandable wall portion 46, a first chamber 54, and which form, in conjunction with the expandable wall portion 48, a second chamber 56. (See Figure 3.) A tubular fitting 60 communicating with the first chamber 54 and a tubular fitting 62 communicating with the second chamber 56 are mounted on the panel 10. During operation of the aircraft 12, the fittings 60 and 62 are connected to a pressure/suction source (not shown) so that the shape of the chambers 54 and 56 may be selectively controlled during flight.

In the illustrated embodiment, the wall portions 46 and 48, the fairings 50 and 52, and the chambers 54 and 56 are part of a carcass 64 made of an elastic material (e.g., a natural rubber composition). The inner surface of the carcass 64 is bonded to an inextensible fabric base 66 (e.g., a square woven nylon fabric with a rubberized coating) which is cemented to the wing 14. The outer surface of the carcass 64 is bonded to an extensible fabric base 68 (e.g., woven tricot nylon fabric with a neoprene coating). This results in the inner surface of the carcass 64 being essentially unstretchable but its outer surface being able to expand/retract to transform the airfoil geometry. Further details of the construction of the illustrated panel 10 is set forth in U.S. Patent No. 2,937,826 to Johnson, the entire disclosure of which is hereby incorporated by reference. For example, the panel 10 may include reinforcing tapes, ridged venting strips, and/or a nylon reinforcement layer.

To place the panel 10 in the expanded condition shown in Figure 3, the chamber 54 is inflated by providing, for example, air up to about fifteen psi. The inflated chamber 54 takes on a "fat comma" shape best described by referring to the drawings. In this inflated form, the expandable wall portion 46 forms an outwardly extending curved path having a large radius and a downwardly offset positioning relative to the wing's leading edge 20. Specifically, this path starts from a point just slightly above the wing's leading edge 20 and extends downwardly to the wing's underside 18. Only a minor part of the inflated chamber 54 is positioned adjacent the wing's leading edge 20 whereby the major change in airfoil geometry occurs therebelow. In any event, the positioning of the wall portion 46 when the chamber 54 is inflated results in an airfoil geometry having a less sharply curved, or blunt, leading edge 32', a longer chord line 34', and a higher camber.

When the chamber 54 is inflated, the second expandable wall portion 48 is pulled outwardly by the first wall portion 46. According to the present invention, the second chamber 56 is maintained at a vacuum so that it follows the concave path shown in Figure 3. By maintaining the wall portion 48 in this concave path, the downward and rearward distension of the inflatable chamber 54 is accomplished and there is also a smooth transition from the bottom end of the first wall portion 46 to the lower fairing 52. Without this vacuum, the second wall portion 48 would follow a straight path (see e.g., Figure 5 in U.S. Patent No. 2,987,826 to Johnson). The concave profile of the second wall portion 48 is believed to decrease the non-stall speed of the aircraft when compared to the prior art straight wall profile, thereby allowing even lower takeoff and landing speeds and thus even shorter runways.

To return the panel 10 to the retracted condition shown in Figure 2, suction is applied to deflate the chambers 54 and 56 whereby the panel 10 elastically returns to close conformance with the leading edge geometry of the wing 14. If necessary, suction may continue to be applied throughout high speed flight to ensure that the panel 10 remains flush against the wing 14.

Thus, during take-off of the aircraft 12, the first wall portion 46 of each panel 10 would be expanded (e.g., by applying pressure to the chamber 54) to provide the lift-enhancing airfoil geometry and the second wall portion 48 would be maintained (e.g., by applying suction to the chamber 56) in its concave path. Once take-off is completed, and the aircraft 12 is ready for high speed flight, the wall portions 46 and 48 are returned to their non-expanded condition (e.g., by applying suction to the chambers 54 and 56). The first wall portion 46 may be again expanded and the second wall portion 48 maintained in its concave path for landing of the aircraft 12.

One may now appreciate that the method of the present invention may be used to provide an improved airfoil geometry for low speed flight which enhances the lift capacity, reduces non-stall speed, and allows the use of shorter runway distances. Although the invention has been shown and described with respect to a certain preferred embodiment, equivalent and obvious alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification. The present invention includes all such alterations and modifications and is limited only by the scope of the following claims.

Claims

1. A method of providing an aircraft wing (14) with an airfoil geometry for low speed flight and another airfoil geometry for high speed flight, said method comprising the steps of: installing a panel (10) to the wing (14) having a first expandable wall portion (46) and a second expandable wall portion (48) extending from a bottom end of the first wall portion (46) to a bottom margin (42) of the panel (10); expanding the first wall portion (46) so that it is positioned to provide the airfoil geometry for low speed flight; maintaining the second wall portion (48) in a concave path relative to a line between the bottom end of the first wall portion (46) and the bottom margin (42) the panel when the first wall portion (46) is expanded; and retracting the first wall portion (46) and the second wall portion (48) to provide the airfoil geometry for high speed flight.

2. A method of altering the aerodynamic characteristics of the wings

(14) of an aircraft (12), said method comprising the steps of: installing, to each wing (14) of the aircraft (12), a panel (10) having expandable wall portions (46, 48) for providing the wing (14) with an airfoil geometry for low speed flight and another airfoil geometry for high speed flight; expanding a first wall portion (46) of each of the panels (10) so that it is positioned to provide the airfoil geometry for low speed flight; maintaining, when the first wall portions (46) are expanded, a second wall portion (48) of each of the panels (10) so that it is positioned in a concave path relative to a line between a bottom end of the respective first wall portion (46) and a bottom margin (42) of the respective panel (10); and retracting the first wall portion (46) and the second wall portion (48) to provide the airfoil geometry for high speed flight.

3. A method as set forth in the preceding claim, wherein the wings (14) each have a certain airfoil geometry before the panel (10) is installed and wherein said step of retracting the first wall portions (46) and the second wall portions (48) positions them flush against the wing (14) whereby the airfoil geometry for high speed flight closely conforms to the wing airfoil geometry.

4. A method as set forth in either of the two preceding claims, wherein the wings each have a low camber and a sharp leading edge.

5. A method as set forth in any of the three preceding claims, wherein the airfoil geometry for low speed flight has a high camber and a blunt leading edge.

6. A method of using an inflatable airfoil shape-altering panel (10) installed on a wing (14) of an aircraft (12), the panel (10) including a top margin (40) positioned on the topside of the wing (14), a bottom margin (42) positioned on the underside of the wing (10), and an outer wall (44) extending therebetween; the wall (44) including a first wall portion (46) extending between the top margin (40) to the wing's underside and a second wall portion (48) extending between a bottom end of the first wall portion (46) to the bottom margin (42); the first and second wall portions (46, 48) lying substantially flush against the wing (14) when the panel (10) is in a retracted condition thereby providing an airfoil geometry for high speed flight, the first wall portion (46) being expandable to extend outward from the wing's leading edge (32) and its underside in a non-parallel shape thereby providing an airfoil geometry for low speed flight; said method comprising the steps of: expanding the first wall portion (46); and maintaining the second wall portion (48), while the first wall portion (46) is expanded, in a concave path relative to a line from the bottom end of the first wall portion (46) to the panel's bottom margin (42).

7. A method as set forth in any of the preceding claims, wherein said panel (10) includes a chamber (56) which is at least partially defined by the second wall portion (48) and wherein said maintaining step comprises controlling the pressure within this chamber (56).

8. A method as set forth in the preceding claim, wherein said pressure-controlling step comprises applying a suction to the chamber.

5 9. A method as set forth in either of the two preceding claims, wherein the panel (10) includes a first chamber (54) which is at least partially defined by the first wall portion (46) and wherein said expanding step comprises controlling the pressure within the first chamber (54).

10. A method as set forth in the preceding claim, wherein said o pressure-controlling step comprises inflating the first chamber (54).

11. A method as set forth in either of the two preceding claims, wherein said panel (10) includes a second chamber (56) which is at least partially defined by the second wall portion (48) and wherein said maintaining step comprises controlling the pressure within the second chamber (56).

5 12. A method as set forth in the preceding claim, wherein said pressure-controlling step comprises applying a suction to the second chamber (56).

13. A method as set forth in any of claims 9-12, wherein said retracting step comprises controlling the pressure within the first chamber (54) and the o second chamber (56).

14. A method as set forth in the preceding claim, wherein said pressure-controlling step comprises applying a suction to the first chamber (54) and the second chamber (56).

15. A method as set forth in any of the preceding claims, wherein the airfoil geometry for low speed flight has a higher camber than the airfoil geometry for high speed flight.

16. A method as set forth in any of the preceding claims, wherein the airfoil geometry for low speed flight has a longer chord line than the airfoil geometry for high speed flight.

17. A method as set forth in any of the preceding claims, wherein the airfoil geometry for low speed flight has a less sharp leading edge than the airfoil geometry for high speed flight.

18. A method as set forth in any of the preceding claims, wherein said expanding and maintaining steps are performed during take-off of the aircraft (12).

19. A method as set forth in any of the preceding claims, wherein said expanding and maintaining steps are performed during landing of the aircraft (12).