Abstract:
According to an embodiment disclosed herein, a gurney flap assembly includes an actuator, and a flexible body attaching to the actuator, the body having a downwardly depending flap for moving into and out of an airstream in a pressure side of a wing, wherein the flexible body flexes in reaction to motion of the actuator. This increases the lift force of the rotor blade, wing or aerofoil blade.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to European Application No. 11250481.6, filed Apr. 12, 2011. 
       BACKGROUND 
       [0002]    This application relates to Gurney flaps and more particularly to active Gurney flaps. 
         [0003]    A Gurney flap is a small flat tab projecting from a trailing edge area of a wing. Typically the Gurney flap is set at a right angle to the pressure side surface of the airfoil, and projects up to 2% of the wing chord. The chord wise position is typically between 0.9 chord to the extreme trailing edge when measured from the leading edge. This trailing edge will improve airfoil lift. 
         [0004]    The Gurney flap operates by increasing pressure on the pressure side of the wing that increases the lift force and may be used in auto racing, helicopter rotors, horizontal stabilizers, and high drag aircraft that take advantage of the resultant lift force. 
         [0005]    The Gurney flap typically increases the drag coefficient, especially at low angles of attack, although for thick airfoils, a reduction in drag has been reported. A net benefit in overall lift to drag ratio is possible if the flap is sized appropriately based on the boundary layer thickness. 
       SUMMARY 
       [0006]    According to an embodiment disclosed herein, a gurney flap assembly includes an actuator, and a flexible body attaching to the actuator, the body having a downwardly depending flap for moving into and out of an airstream on the pressure side of a wing, wherein the flexible body flexes in reaction to motion of the actuator. 
         [0007]    According to a further embodiment disclosed herein, a gurney flap assembly for a rotary wing aircraft has a wing having a pressure side, a suction side, a trailing edge and a hollow portion between the pressure side and the suction side. The hollow portion is adjacent the trailing edge of the wing. An actuator is disposed within the hollow portion of the wing. The actuator attaches to a flexible body that is shown attached to the pressure side of the wing but would also perform the necessary task if attached to the suction side. The flexible body flexes in response to the actuator to move a downwardly depending flap into and out of an airstream in the pressure side. 
         [0008]    According to a still further embodiment disclosed herein, a method for controlling performance of a rotary-winged aircraft, has the steps of providing a wing having a pressure side and a suction side, disposing an actuator in the wing, flexing a flexible body that is attached to the pressure side to move a downwardly depending flap into and out of an airstream in a pressure side of a wing in response to motion of the actuator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0010]      FIG. 1  shows an example helicopter. 
           [0011]      FIG. 2  shows an embodiment of a rotary wing of the helicopter of  FIG. 1 . 
           [0012]      FIG. 3  shows a sectional view of the aircraft wing of  FIG. 2  partially in phantom and the Gurney flap assembly. 
           [0013]      FIG. 4  shows a side view of  FIG. 3  in a retracted position. 
           [0014]      FIG. 5  shows a deployed view of the Gurney flap of  FIG. 4  side. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  schematically illustrates an example of a rotary-wing aircraft  10  having a main rotor system  12 . The aircraft  10  includes an airframe  14  having an extending tail  16  which mounts a tail rotor system  18 , such as an anti-torque system. The main rotor assembly  12  is driven about an axis of rotation A through a main gearbox (illustrated schematically at T) by one or more engines E. The main rotor system  12  includes a multiple of rotor blade assemblies  20  mounted to a rotor hub H. Although a particular helicopter configuration is illustrated and described in the disclosed non-limiting embodiment, other configurations and/or machines, such as high speed compound rotary wing aircraft with supplemental translational thrust systems, dual contra-rotating, coaxial rotor system aircraft, turbo-props, tilt-rotors and tilt-wing aircraft, may also benefit from the present invention. 
         [0016]    Referring to  FIG. 2 , each rotor blade assembly  20  of the rotor assembly  12  generally includes a root section  22 , an intermediate section  24 , a tip section  26  and a tip cap  28 . Each rotor blade section  22 ,  24 ,  26 ,  28  may define particular airfoil geometries to particularly tailor the rotor blade aerodynamics to the velocity increase along the rotor blade span. The rotor blade tip section  26  may include an anhedral form though any angled and non-angled forms such as cathedral, gull, bent, and other non-straight forms will benefit from the present invention. 
         [0017]    The rotor blade sections  22 - 28  define a span R of the main rotor blade assembly  20  between the axis of rotation A and a distal end  30  of the tip cap  28  such that any radial station may be expressed as a percentage in terms of a blade radius x/R. The rotor blade assembly  20  defines a longitudinal feathering axis P between a leading edge  32  and a trailing edge  34 . The distance between the leading edge  32  and the trailing edge  34  defines a main element chord length C. 
         [0018]    Referring now to  FIG. 3 , a perspective view of a Gurney flap assembly  50  is shown. The helicopter wing  75  has a pressure side  85 , a suction side  80 , a support beam or spar  90 , deposed between the pressure side  85  and the suction side  80 , a leading edge  92  and a trailing edge  95 . 
         [0019]    The Gurney flap assembly  50  is disposed between the pressure side  85  and the suction side  80  aft of the support beam  90  and has an actuator  100 , a controller  105 , an actuator output  110 , such as a piston rod that is reciprocated by the actuator  100 . The controller  105  can be located in close proximity to the actuator  100  or located remotely from the actuator  100 . The actuator output  110  has an eye end assembly item  111  that fits within ears  113  of a yolk assembly  115  and is anchored thereto by a pin  114  that passes through the ears  113  and the eye end assembly item  111 . The actuator  100  can be mounted span wise by the addition of a suitable bell crane mechanism (not shown). 
         [0020]    The yolk assembly  115  has a pair of angled arms  120 , a central support  125  that extends from the ears  113  through the angled arms  120  and attaches to a perpendicularly disposed bottom support  130 . As shown in this embodiment, the bottom support  130  has three sets of bosses  140  through which a pin  145  grips a protrusion  135  of a Gurney flap  150 . 
         [0021]    The Gurney flap  150  has a flexible body  155  having a forward edge  157  that attaches to the pressure side  85  of the wing  75  as will be discussed infra. The flexible body  155  has a flap  160  extending downwardly from a trailing edge  161  thereof in close proximity of the trailing edge  95 . The Gurney flap  150  is disposed in a rectangular cut-out or slot  163  of the pressure side  85 . A brush seal  170 , or the like, is disposed at either side of the extending flap  160  to minimize a passage of debris into a chamber  171  between the pressure side  85  and the suction side  80  (see  FIGS. 4 ,  5 ). Such debris might damage the actuator  100  or the controller  105  or the Gurney flap assembly  50 . Though shown on a pressure side of a wing, the flaps may also attach to other areas of the wing including the suction side. 
         [0022]    Referring now to  FIG. 4 , a side view of the Gurney flap assembly of  FIG. 3  is shown in a retracted position. In this position, the actuator output  110  is retracted thereby pulling the eye end assembly item  111  forward thereby pulling the Gurney flap  150  upwardly into the wing  75  such that the Gurney flap assembly  50  pulls its flap edge  160  out of the air stream that travels along the pressure side  85  of the wing  75  in a stowed position. The forward edge  157  of the flexible body  155  is attached to the inner surface of the pressure side  85  by adhesive or other appropriate means such as riveting or the like. While the actuator  100  moves the actuator output  110  linearly, the yoke assembly  115  translates this motion into a rotary motion of the flexible body  155  about its forward edge  157  attachment with the pressure side of the wing  75 . This rotary motion causes the flap to move in and out of deployment in the cut out  163 . 
         [0023]    Referring to  FIG. 5  and  FIG. 3 , an activated position (e.g., deployed position), the actuator  100  pushes the yolk assembly  115  aft thereby urging the legs  120  and the support  125  forward and downward to push the flap edge  160  into the air stream through a slot along the trailing edge  95  of the wing  75 . 
         [0024]    A first position sensor  195  is placed schematically around the actuator output  110  that informs the controller  105  as to the position of the flap  160  via the Gurney flap assembly  50 . In addition, a second optional sensor  190 , which communicates with the controller  105 , is placed in close proximity to the edge  195  of the Gurney flap  150 . The second sensor  190  allows the controller to fine tune the position of the Gurney flap  150  should the wing  75  encounter excessive bending or other moments and the second sensor  190  provides a degree of redundancy should it or the first sensor  195  fail. The first and second sensors  195 ,  190  in conjunction with the controller  105  permit the aircraft  10  to rapidly modulate the position of the flap  160  to allow the helicopter wing  75  to provide a desired or even magnified mode of operation. The actuator  100  is designed to provide sinusoidal operation or full stowing/deployment with steady holding states between movements. For instance, if control is collective, a deployed flap  160  may allow a wing  75  to provide more lift relative to a wing without a deployed flap  160  and a stowed flap has minimal effect on the functionality of the wing  75 . If control is cyclic, the actuator  100 , at the behest of the controller  105 , may modulate the flap  160  inwardly and outwardly to match the cyclic action required of the wing  75  and may even magnify the action of the wing  75  by providing more lift if the flap  160  is deployed. The controller  105  may compare signals from the first sensor  195  and the second sensor  190  to test whether the flap  160  is actually in a desired position and may reset the yoke assembly  150  to place the flap  160  in a desired position. Similarly, a second controller  305  in the aircraft  10  (see  FIG. 1 .) may compare the output of controller  105  with the expected performance of the wing  75  or the aircraft  10  and direct the controller  105  to position the yoke assembly  115  to position the flap  160  so that required performance is met. 
         [0025]    The flexible body  150  and the flap  160  are made out of a flexible material such as a thin metal or a composite or the like. The flap  160  stiffness may be enhanced by the addition of local reinforcing. The thin metal or other composite is freely bendable to allow the actuator  100  to move the Gurney flap without producing distortions or undulations into the surface of the wing  75 . 
         [0026]    The assembly can be used in helicopter rotor blade primary control and higher harmonic applications. Also, multiple gurney flaps assemblies can be incorporated into rotor blade span to provide redundancy. 
         [0027]    The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.