Abstract:
A small secondary leading edge device, called a compound Krueger vane, works in parallel with a primary device (e.g., a Krueger flap) to delay flow separation on an aircraft wing. The compound Krueger vane is deployed behind a gapped Krueger flap to turn flow ahead of the wing attachment region on the underside of the wing. The compound Krueger vane turns flow that moves forward from the wing lower surface attachment region toward the leading edge of the wing, thereby delaying flow separation on the aircraft wing.

Description:
BACKGROUND 
     This disclosure generally relates to high-lift leading edge flaps for the wings of an aircraft, and more particularly to a Krueger leading edge flap having at least a stowed position for high-speed cruise operation and a forwardly extended position in which the forward edge of the Krueger flap forms an aerodynamic slot with the leading edge of the aircraft wing for takeoff and landing. 
     Modern aircraft often use a variety of high-lift leading and trailing edge devices to improve high-angle of attack performance during various phases of flight, including takeoff and landing. Existing leading edge devices include leading edge slats and Krueger flaps. 
     Current leading edge slats generally have a stowed position in which the slat forms a portion of the leading edge of the wing, and one or more deployed positions in which the slat extends forward and down to increase the camber and/or planform area of the wing. The stowed position is generally associated with low drag at low angles of attack and can be suitable for cruise and other low angle of attack operations. The extended position(s) is/are generally associated with improved airflow characteristics over the aircraft&#39;s wing at higher angles of attack. Typical leading edge slat designs include arrangements in which the leading edge device retracts in an aft direction to form the leading edge of the wing when stowed. 
     Krueger flaps have generally the same function as leading edge slats, but rather than retracting aft to form the leading edge of the cruise wing, Krueger flaps are hinged, and typically fold into the lower surface of the wing when stowed. When deployed, Krueger flaps extend forward from the under surface of the wing, increasing the wing camber and maximum coefficient of lift. 
     In the case of a typical Krueger flap, a slot or gap is created between the flap and the wing as the flap is extended forward. During certain operating conditions, air can flow through this slot to energize the airflow over the upper surface of the wing, and improve overall airflow characteristics over the wing. 
     For some airplane applications, such as extended laminar flow or high cruising speeds, it may be advantageous to design a wing with a small leading edge radius. A small leading edge radius can cause premature flow separation (stall) on the wing surface, even when a Krueger flap is present. This has unfavorable consequences in aerodynamics, since flow separation can significantly decrease lift and increase drag of the wing. 
     Existing leading edge devices turn the air flow as it moves aft. Turning the aft-moving flow before it reaches the wing leading edge is a necessary condition for delaying stall of a sharp-nosed wing, but it may not be sufficient. This is particularly true if the leading edge device must be positioned high relative to the wing leading edge, as is required for some configurations. 
     SUMMARY 
     The leading edge device disclosed hereinafter is designed to mitigate the effect of a small leading edge radius on an aircraft wing. This leading edge device may be embodied in many different ways. In accordance with the embodiments disclosed hereinafter, the device comprises a small secondary leading edge device that works in parallel with a primary device (e.g., a Krueger flap) to delay flow separation at the leading edge of an aircraft wing. More specifically, a compound Krueger vane is deployed behind a gapped Krueger flap to turn flow ahead of the wing attachment region on the underside of the wing. The attachment region is the vicinity around the attachment line; the streamline which divides the flow that travels across the upper and lower wing surfaces. Traditional leading edge devices turn streamwise flow to the upper wing surface as it moves aft (toward the trailing edge of the wing). The compound Krueger vane turns flow that moves forward from the wing lower surface attachment region toward the leading edge of the wing, thereby delaying flow separation at the leading edge of the aircraft wing. 
     One aspect of the disclosed subject matter is an aircraft comprising: a wing having a leading edge including a leading edge spanwise section formed by an upper surface and a lower surface; a leading edge flap coupled to the wing, the flap being disposed generally parallel to and forward of the leading edge spanwise section of the wing; and a vane coupled to the wing, the vane being disposed generally parallel to and under the leading edge spanwise section of the wing, wherein the vane is closer to the leading edge of the wing than the flap is. 
     Another aspect of the disclosed subject matter is a leading edge assembly for an airplane wing having upper and lower surfaces that meet at a leading edge, the assembly comprising: a leading edge flap coupled to the wing, the flap being disposed generally parallel to and forward of a leading edge of a spanwise section of the wing; and a vane coupled to the wing, the vane being disposed generally parallel to and under the leading edge of the spanwise section of the wing, wherein the vane is closer to the leading edge of the wing than the flap is. 
     A further aspect of the disclosed subject matter is a method of directing air flow relative to a leading edge of a wing, the method comprising: (a) moving a leading edge flap from a stowed position to a deployed position, the flap being disposed generally parallel to and forward of a leading edge of a spanwise section of the wing when in its deployed position and forming part of a lower surface of the spanwise section of the wing when in its stowed position; and (b) moving a vane from a stowed position to a deployed position, the vane being disposed generally parallel to and under the leading edge of the spanwise section of the wing when in its deployed position and being disposed inside the wing in its stowed position, wherein the vane is closer to the leading edge of the wing than the leading edge flap is when the flap and the vane are in their respective deployed positions. 
     Yet another aspect of the disclosed subject matter is an aircraft wing comprising: a leading edge and first and second leading edge airfoil-shaped bodies spaced apart from each other and relative to the leading edge along a direction away from the wing, wherein the first and second leading edge airfoil-shaped bodies in combination are configured and positioned relative to the leading edge to direct airflow from a position under the leading edge to a position in front of the leading edge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments will be hereinafter described with reference to drawings for the purpose of illustrating the foregoing and other aspects of the disclosed subject matter. 
         FIG. 1  is a diagram showing a plan view of an airplane having wings equipped with Krueger flaps. 
         FIG. 2  is a diagram showing simulated air flow past a leading edge of a wing of an airplane at a high angle of attack, which leading edge is equipped with a Krueger flap. The Krueger flap is shown in a deployed position where a slot or gap is formed between the forward edge of the flap and the leading edge of the wing. 
         FIG. 3  is a diagram showing stowed, deployed, and intermediate positions of a secondary vane (referred to hereinafter as a “compound Krueger vane”) in accordance with one embodiment, which vane is disposed between the Krueger flap and the wing leading edge when the Krueger flap and compound Krueger vane are in their deployed positions. 
         FIG. 4  is a diagram showing simulated air flow past the leading edge of the wing depicted in  FIG. 3  at a high angle of attack. 
         FIG. 5  is a block diagram showing components of a computer-controlled system for coordinated actuation of a Krueger flap and a compound Krueger vane in accordance with one embodiment. 
     
    
    
     Reference will hereinafter be made to the drawings in which similar elements in different drawings bear the same reference numerals. 
     DETAILED DESCRIPTION 
     Although embodiments are disclosed in detail below, various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the subject matter disclosed herein. In addition, many modifications may be made to adapt a particular situation to the teachings without departing from the essential scope thereof. Therefore it is intended that the claims not be limited to the particular embodiments disclosed hereinafter. 
     Well-known apparatus, such as linking mechanisms, will not be shown or described in detail below. Descriptions of known Krueger flaps and associated linking mechanisms can be found, for example, in U.S. Pat. Nos. 7,578,484 and 5,158,252, both assigned to the present assignee. U.S. Pat. No. 7,578,484 discloses a Krueger flap comprising a rigid fixed-shape leading edge panel and a rigid fixed-shape bullnose pivotably coupled thereto, whereas U.S. Pat. No. 5,158,252 discloses a variable camber Krueger flap. The difference between rigid Krueger flaps and variable camber Krueger flaps occurs after those devices deploy from the stowed position. The panel of a variable camber Krueger flap flexes; the panel on a rigid Krueger flap does not. The compound Krueger vane disclosed herein is not limited in its application to any particular type of Krueger flap or to any particular shape of the Krueger flap. 
       FIG. 1  is a plan view of an airplane  2  comprising a fuselage  4 , a pair of wings  6 , an empennage  8 , and wing-mounted engines  10 . The leading edges  12  of the wings  6  are equipped with a multiplicity of leading edge assemblies  14  (indicated by dashed lines). Each leading edge assembly  14  comprises a Krueger flap and an associated set of linking mechanisms (not shown in  FIG. 1 ). In conventional manner, Krueger flaps can be deployed to improve high-angle of attack performance during takeoff and landing. When in the stowed position, the Krueger flaps are disposed beneath the wing leading edge  12  and define a portion of the lower skin surface of the wing. Upon actuation, the Krueger flaps move from a stowed position within the wing envelope through any desired rotational angle to a fully deployed position. Krueger flaps can be made from metal, composites, or both. The Krueger flaps may include thin panels, hollow-core structures, matrix composite structures, or solid sections. 
     The results of a computational flow simulation are shown in  FIG. 2 . The curved shape in the center of  FIG. 2  represents a leading edge  12  of a Krueger flap-equipped wing  6 . The curved element in front of the wing leading edge  12  represents a deployed Krueger flap  20 . The streamlines with spaced arrowheads represent the paths and directions of air flowing relative to the deployed Krueger flap  20  and the wing leading edge  12  of an aircraft flying at a high angle of attack. When the Krueger flap  20  is in the deployed position shown in  FIG. 2 , an opening  28  is formed in the wing lower surface  17  and a slot or gap  24  is formed between the trailing edge  22  of the flap  20  and the leading edge  12  of the wing  6 . In this deployed position, flap  20  is disposed generally parallel to and forward of a leading edge  12  of a spanwise section of the wing  6 . In its stowed position, the flap  20  forms a part of the lower surface  17  of the same spanwise section of the wing  6 . Streamline  18  generally indicates the boundary of air flowing in the aft direction underneath the wing. 
     The Krueger flap  20  depicted in  FIG. 2  is configured to provide enhanced high-lift characteristics for wing  6 . The wing  6  can be configured to cruise at high subsonic Mach numbers representative of typical commercial transport airliners. The wing  6  comprises an upper surface  16 , a lower surface  17 , and a leading edge  12  that is faired smoothly into both the upper surface  16  and the lower surface. When the Krueger flap  20  is in its stowed position, a portion of the flap  20  will seal the opening  28  to provide for a generally continuous, aerodynamically smooth lower surface  17 . When the Krueger flap  20  is deployed, as shown in  FIG. 2 , the opening  28  is exposed and the slot  24  is formed. 
     The simulation whose results are depicted in  FIG. 2  was based on certain assumptions, including that the leading edge radius is small relative to the chord length of the simulated wing and that the aircraft is flying at a high angle of attack. The simulation results indicate that under such conditions, flow separation (indicated by arrow FS) can occur starting at the leading edge  12  and continuing along the upper surface  16  of wing  6 . When the air flow separates from the upper surface  16 , the air closest to the upper surface  16  flows in a forward direction relative to the wing. 
     To delay the flow separation depicted in  FIG. 2 , a secondary leading edge device can be installed aft of the Krueger flap  20 . In this regard, the secondary leading device or Krueger vane  30 , described in more detail below, is deployed proximal to the leading edge  12  of the wing  6  relative to the Krueger flap  20  that is deployed distal to the leading edge  12  of wing  6  when compared to the Krueger vane  30 . 
     In accordance with one embodiment partly depicted in  FIG. 3 , the secondary leading edge device comprises a compound Krueger vane  30  attached to an arm  32  that is pivotably coupled to wing  6 . Each vane  30  is pivotable between stowed and deployed positions respectively represented by dashed lines and dash-dotted lines in  FIG. 3 . Intermediate angular positions of the compound Krueger vane  30  are shown by thin dashed lines. In accordance with other embodiments, the compound Krueger vane  30  could be actuated by a relatively more complicated mechanism, such as a scissor-type linkage. Alternatively, the compound Krueger vane  30  may be attached to the linkages being used to extend the main leading edge device. 
     The compound Krueger vane  30  may have the cross-sectional shape and be positioned as depicted in  FIG. 3 . However, the shape of the compound Krueger vane  30  may vary depending on the application, much like the shape of conventional leading edge devices. A variety of shapes could provide the intended function. In the present case, the intended function is to delay flow separation on the wing upper surface  16 , for example, under the conditions which were simulated to produce  FIG. 2 . 
       FIG. 3  also depicts a Krueger flap  20  having a well-known structure comprising a leading edge panel  42  and a bullnose  44  that is pivotably connected (not shown in  FIG. 3 ) to the leading edge panel  42 . The bullnose  44  is folded inward when the Krueger flap  20  is stowed. The leading edge panel  42  is depicted as the flexed panel of a variable-camber Krueger flap, but Krueger panels can also be rigid. A panel support structure can be positioned to support the streamwise flow surface and maintain its shape. Accordingly, the streamwise flow surface may undergo small deflections due to aerodynamic loading. The bullnose  44  can also include a generally rigid, fixed-shape flow surface. 
     The Krueger flap  20  is shown in its fully deployed position A in  FIG. 3 . In this position, the leading edge panel  42  of the Krueger flap  20  is positioned forward of and forms a gap  24  with the wing leading edge  12 . The bullnose  44  of Krueger flap  20  is positioned under the leading edge panel  42 . In this configuration, the Krueger flap  20  turns the air flow before it reaches the leading edge of the wing  6 , which allows the wing  6  to operate efficiently at high angles of attack. Such angles of attack may be encountered during approach, landing, and takeoff. 
     Still referring to  FIG. 3 , each compound Krueger vane  30  is disposed generally parallel to and under a spanwise section of the leading edge  12  of wing  6  when in its deployed position B and is disposed inside the wing envelope in its stowed position C. When the flap  20  and vane  30  are in their respective deployed positions (A and B as shown in  FIG. 3 ), the vane  30  is considered closer or proximal to leading edge  12  than is the flap  20 , which is positioned distal to the leading edge  12  when compared to the vane  30 . The vane  30  comprises an outer aerodynamic surface  31  that faces flap  20  and an inner aerodynamic surface  33  that faces the wing  6  when the flap  20  and vane  30  are both deployed. The inner aerodynamic surface  33  of the vane  30  turns air flow that moves forward from a flow attachment region, generally shown as region R in  FIG. 4 , toward the leading edge  12  of wing  6  when Krueger flap  20  and vane  30  are in their respective deployed positions during flight at a high angle of attack. 
     The simulation results depicted in  FIG. 4  were based on the same conditions assumed for the simulation results depicted in  FIG. 2 , except that the effect of a compound Krueger vane  30  was also taken into account. The simulation results shown in  FIG. 4  indicate that under similar conditions, the compound Krueger vane delays flow separation at the leading edge  12  of the wing  6 . More specifically, the addition of the compound Krueger vane  30  produces attached flow on the wing upper surface  16  as opposed to the flow separation FS depicted in  FIG. 2 . 
     Referring to  FIG. 5 , each Krueger flap  20  is coupled to a wing by means of a suitable flap linking mechanism  36  having a flap stowed configuration and a flap deployed configuration. The flap linking mechanism  36  can be reconfigured in response to the application of a driving force by a flap actuator  38 , which has at least two operational modes. In one mode, the flap actuator  38  causes the flap linking mechanism  36  to extend from the flap stowed position to the flap deployed position, thereby causing the Krueger flap to deploy to a position whereat a slot or gap is formed between the forward edge of the Krueger flap and the leading edge of the wing. In another mode, the flap actuator  38  causes the flap linking mechanism  36  to retract from the flap deployed configuration to the flap stowed configuration. 
     The structural details of the link mechanism for deploying the Krueger flaps are not shown in the drawings. Many link mechanisms for Krueger flaps are known. The configuration of the link mechanism will depend on the desired flap position relative to the wing leading edge when each Krueger flap is deployed. When each Krueger flap is stowed, it is received within a respective leading edge cavity. The leading edge cavity also houses the Krueger flap link mechanism (not shown). The link mechanism can be powered by any number of known actuator arrangements, and can be coupled to multiple (two or more) link mechanisms spaced along a spanwise section of the wing. Each Krueger flap arranged along a wing leading edge may be deployed by actuation of a respective set of two or more linking mechanisms. 
     Still referring to  FIG. 5 , each compound Krueger vane  30  is coupled to a wing by means of a vane linking mechanism  32  having a vane stowed position and a vane deployed position. The vane linking mechanism  32  can extend in response to the application of a driving force by a vane actuator  34 , which also has two operational modes. In one mode, the vane actuator  34  causes the vane linking mechanism  32  to extend from the vane stowed position to the vane deployed position, thereby causing the compound Krueger vane  30  to deploy to a position whereat a small gap is formed between the forward edge of the compound Krueger vane  30  and the leading edge  12  of the wing  6 . In another mode, the vane actuator  34  causes the vane linking mechanism  32  to retract from the vane deployed position to the vane stowed position. In the example depicted in  FIG. 3 , the vane pivots from a vane stowed angular position to a vane deployed angular position. 
     Methods and systems for controlling the actuation of Krueger flaps are well known. In accordance with the embodiment disclosed herein, a controller  40  controls the operation of vane actuator  34  and flap actuator  38  by transmitting electrical control signals along respective signaling channels, such as electrical cables, optical fibers, or other means, from controller  40  to actuators  34  and  38 . The flap and vane actuators may comprise pneumatic or hydraulic cylinders having associated mechanical means for converting the linear movement of the piston into a force that drives rotation of the flap or vane linking mechanism. Alternatively, the flap and vane may be driven by rotary actuators or electric motors. 
     The controller  40  may comprise a computer programmed to execute routines or a non-programmable electronic device. The controller  40  can be activated by the pilot or it can be preprogrammed according to flight conditions. The controller can be embodied in a special-purpose computer or a data processor that is specifically programmed, configured or constructed to perform computer-executable routines for flap and vane actuation. In particular, the controller  40  may be part of the flight control system. 
     The controller  40  can independently control the operation of the vane actuator  34  and the flap actuator  38  to produce the deployed configuration depicted in  FIG. 3 . Accordingly, the controller  40  can be programmed to first actuate the deployment of flap  20  and then actuate the deployment of vane  30 . Alternatively, controller  40  can be programmed to cause the flap  20  and vane  30  to deploy concurrently. In accordance with a further alternative (not shown), the vane linking mechanism  32  and the flap linking mechanism  36  could be mechanically coupled to a common actuator (not shown) which actuates the mechanisms in tandem. 
     While the disclosed subject matter has been described with reference to various embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the intended scope. In addition, many modifications may be made to adapt a particular situation to the teachings without departing from the essential scope thereof. Therefore it is intended that the claims not be limited to the particular embodiments disclosed. 
     The method claims set forth hereinafter should not be construed to require that all steps of the method be performed in alphabetical order or in the order in which they are recited. In particular, the method claims should be construed to encompass two operations being performed concurrently or in sequence.