Abstract:
A method and apparatus is provided, including an actuator system that may be connected to a wing frame for controlling an active element. The actuator system may include sliding elements movable along an axis parallel to the span-wise axis of the wing. The sliding elements may be connected to fixed elements and a crank element, the crank element generally comprising a beam element and a pivot element. The beam element may be offset from the pivot element so that the crank element is rotatable about the pivot element with a negative stiffness under an external force that tends to pull the sliding elements away from the fixed elements.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates in general to the field of heavier-than-air aircraft, and more particularly to a method and apparatus for actively manipulating aerodynamic surfaces. 
       DESCRIPTION OF THE PRIOR ART 
       [0002]    Emerging and future generations of rotary-wing and tilt-rotor aircraft have active elements on the blade or wing, such as trailing edge flaps and leading edge droops, which can provide a number of enhancements over passive designs. For example, active elements can be used for vibration reduction, noise reduction, and performance improvements. Actuator systems are needed to operate active elements, but actuator systems also add weight and complexity to the aircraft. Accordingly, the design of powerful, light-weight actuator systems presents significant challenges to engineers and manufacturers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The features believed characteristic and novel of a method and apparatus (collectively, a system) for active manipulation of aerodynamic surfaces are set forth in the appended claims. However, the system, 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: 
           [0004]      FIG. 1  is a perspective view of an example embodiment of a helicopter according to the present specification; 
           [0005]      FIG. 2  is a partial top view of an example embodiment of a helicopter having an active blade element and actuator system according to the present specification; 
           [0006]      FIG. 3  is a simple top-view schematic of an example embodiment of an actuator system according to the present specification having a span-wise orientation and a parallel configuration of linear actuators in a rotor blade; 
           [0007]      FIG. 4  is a simple side-view schematic of an example embodiment of an actuator system according to the present specification having a span-wise orientation and a parallel configuration of linear actuators in a rotor blade; 
           [0008]      FIG. 5  is a cut-away view of an example embodiment of a linear motor actuator according to the present specification; 
           [0009]      FIG. 6  is a simple top-view schematic of another example embodiment of an actuator system according to the present specification having a span-wise orientation and a serial configuration of linear actuators in a rotor blade; and 
           [0010]      FIG. 7  is a perspective view of another example embodiment of an actuator system according to the present specification having a span-wise orientation and a parallel configuration of linear actuators in a rotor blade. 
       
    
    
       [0011]    While the system and apparatus for active manipulation of aerodynamic forces is susceptible to various modifications and alternative forms, the novel features thereof are shown and described below through specific example embodiments. It should be understood, however, that the description herein of specific example embodiments is not intended to limit the system or apparatus to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims. 
       DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    Illustrative embodiments of the novel system are described below. In the interest of clarity, not all features of such embodiments may be described. It should be appreciated that in the development of any such system, numerous implementation-specific decisions must be made to achieve specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it should be appreciated that such decisions 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. 
         [0013]    Reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the system is depicted in the attached drawings. However, as should be recognized by those skilled in the art, the elements, members, components, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the example embodiments described herein may be oriented in any desired direction. 
         [0014]    Referring to the appended drawings,  FIG. 1  is a perspective view of an example embodiment of a helicopter  10  according to the present specification. In general, helicopter  10  has a fuselage  12  and a main rotor assembly  14 , which includes main rotor blades  16   a - c  and a main rotor shaft  18 . Helicopter  10  may also include a tail rotor assembly  20 , which generally includes tail rotor blades  22  and a tail rotor shaft  24 . Main rotor blades  16   a - c  may rotate about a longitudinal axis  26  of main rotor shaft  18 . 
         [0015]    Tail rotor blades may rotate about a longitudinal axis  28  of tail rotor shaft  24 . Also illustrated in  FIG. 1  are flaps  32   a - b  and actuator systems  36   a - b  on main rotor blades  16   a - b,  respectively. Not visible in  FIG. 1  are flap  32   c  and actuator system  36   c  on main rotor blade  16   c.    
         [0016]      FIG. 2  is a partial top view of helicopter  10 , including main rotor blade  16   a , connected to a hub  30  on main rotor shaft  18 . In the example embodiment of helicopter  10 , main rotor blade  16   a  may include additional active elements that may be used to manipulate aerodynamic surfaces, such as flap  32   a.  Flap  32   a  in the example embodiment of helicopter  10  is placed outboard along the trailing edge  34   a,  but may be placed in other positions according to particular design criteria. And while flap  32   a  is illustrated and described herein as a distinct component of main rotor blade  16   a,  it may also be any movable or flexible portion of main rotor blade  16   a.  An example embodiment of actuator system  36   a  is also depicted in the cut-away section  FIG. 2 , generally oriented parallel to a span-wise axis  17   a  of main rotor blade  16   a.  During operation, main rotor blade  16   a  may rotate about hub  30 , while actuator system manipulates flap  32   a.  The rotation causes a number of reactive forces, including lift and centrifugal forces (CF). 
         [0017]      FIG. 3  is a simple top-view schematic of actuator system  36   a  in main rotor blade  16   a.  Actuator system  36   a  may include linear actuators  38   a - b . Each linear actuator  38   a - b  typically includes a fixed or stationary element, such as stators  40   a - b , and a moving or sliding element, such as sliders  42   a - b . Stators  40   a - b  in the example embodiment are rigidly connected to the frame of main rotor blade  16   a,  and they may be identical elements or may have distinct properties for certain applications. Likewise, sliders  42   a - b  may be identical or have distinct properties for certain applications. Linear actuators  38   a - b  each has an elongated shape with a lengthwise axis  39   a - b  that is generally oriented parallel with span-wise axis  17   a  of main rotor blade  16   a.  In the example embodiment of  FIG. 3 , linear actuators  38   a - b  are also generally oriented parallel to each other along the span of main rotor blade  16   a.  Such a span-wise orientation is generally preferable to other orientations as it generally provides larger space in the blade for larger, more powerful motors with longer strokes, and better mass placement. 
         [0018]    In actuator system  36   a,  a crank  44  is connected to sliders  42   a - b . Crank  44  includes a beam element  46 , a pivot element  48 , and an arm element  50 . Examples of pivot element  48  include a conventional bearing with rolling elements, an elastomeric element, a sleeve bushing, or a structural flexure. Pivot element  48  may be positioned coincident with beam element  46 , or may be offset a distance L relative to beam element  46 , as shown in  FIG. 3 . By adjusting distance L, the large centrifugal force acting on sliders  42   a - b  may be used advantageously to create a negative stiffness spring effect, wherein the negative spring constant, k, is proportional to the centrifugal force CF, distance L, and angular displacement θ(−k=CF*L*sin(θ)/θ). The negative spring effect may counteract aerodynamic forces and reduce actuator power requirements, thereby also potentially reducing the mass of actuator system  36   a.  Arm element  50  may be rigidly attached to beam element  46 , or beam element  46  and arm element may  50  be fabricated as a single element. 
         [0019]      FIG. 4  is a simple side-view schematic of actuator system  36   a.  Stators  40   a - b  are preferably placed within the frame of main rotor blade  16   a  in parallel. Connecting rod  52  connects actuator system  36   a  to flap  32   a  through crank  44  (see  FIG. 3 ) and sliders  42   a - b  (see  FIG. 3 ). Flap  32   a  may rotate about an axis  33  in response to force from connecting rod  52 . Alternate positions of flap  32   a  as it rotates about axis  33  are illustrated in phantom as flaps  32   a - 1  and  32   a - 2 . 
         [0020]      FIG. 5  is a cut-away view of an example embodiment of a linear actuator  60 . In this embodiment, linear actuator  60  is an electromagnetic linear motor having a fixed element, stator  62 , having electric coils, and an elongated, high-power permanent magnetic slider  64 . The slider  64  moves and converts electrical power to useful work. The motion, position, and retention of slider  64  are controlled with electromagnetic force generated with the electric coils of stator  62 . Such an actuator may provide benefits in certain applications where high bandwidth and large stroke with a small footprint are desirable. For example, an electromagnetic motor such as linear actuator  60  may be advantageous in a helicopter rotor blade where vibrations and noise are counteracted with relatively small flap deflections at high frequency, but performance is enhanced with larger deflections at a lower frequency. 
         [0021]    During rotation of main rotor blade  16   a,  the centrifugal forces are carried across beam element  46  and reacted by pivot  48 , effectively canceling the tendency of sliders  42   a - b  to sling outward because of the centrifugal forces. Crank  44  is similar to a common bell crank, and as it rotates it converts the span-wise motion of sliders  42   a - b  into chord-wise motion that may be used to manipulate an active element, such as flap  32   a,  which is connected to arm element  50  through a connecting rod  52  or similar linkage. 
         [0022]    In operation, sliders  42   a - b  are actuated such that each reciprocates generally parallel to axis  17   a  and slider  42   a  moves opposite to slider  42   b.  Thus, as slider  42   a  moves in the outboard direction of main rotor blade  16   a,  slider  42   b  moves inboard. And as slider  42   a  moves outboard and slider  42   b  moves inboard, crank  44  rotates about pivot element  48 , causing arm element  50  to advance toward trailing edge  34   a  of main rotor blade  16   a.  The movement of arm element  50  toward trailing edge  34   a  in turn causes connecting rod  52  to act on flap  32   a,  which may rotate about axis  33  to position  32   a - 1 . 
         [0023]    Conversely, as slider  42   a  moves inboard and slider  42   b  moves outboard, crank  44  rotates in the opposite direction about pivot element  48 , causing arm element  50  to retreat from trailing edge  34   a.  The movement of arm element  50  away from trailing edge  34   b  in turn causes connecting rod  52  to act on flap  32   a,  which may rotate about axis  33  to another position, such as  32   a - 2 . 
         [0024]      FIG. 6  is a simple top-view schematic of another example embodiment of an actuator system  70  in a main rotor blade  72  according to the present specification. Actuator system  70  may include linear actuators  74   a - b . Each linear actuator  74   a - b  typically includes a fixed or stationary element, such as stators  76   a - b , and a moving element or sliding element, such as sliders  78   a - b . Stators  76   a - b  in the example embodiment are rigidly connected to the frame of main rotor blade  72 , and they may be identical elements or may have distinct properties for certain applications. Likewise, sliders  78   a - b  may be identical or have distinct properties for certain applications. Linear actuators  74   a - b  each has an elongated shape with a lengthwise axis  75   a - b  that is generally oriented parallel with span-wise axis  73  of main rotor blade  72 . In contrast to linear actuators  38   a - b  in  FIG. 3 , linear actuators  74   a - b  are generally oriented in series along the span of main rotor blade  72 . 
         [0025]    In actuator system  70 , a crank  80  is connected to sliders  78   a - b . Crank  80  includes a beam element  82 , a pivot element  84 , and an arm element  86 . Extension elements  79   a - b  may be used to connect sliders  78   a - b  to beam element  82 . Examples of pivot element  84  include a conventional bearing with rolling elements, an elastomeric element, a sleeve bushing, or a structural flexure. Pivot element  84  may be positioned coincident with beam element  82 , or may be positioned a distance L relative to beam element  82 , as shown in  FIG. 6 . By adjusting distance L, the large centrifugal force acting on sliders  78   a - b  may be used advantageously to create a negative stiffness spring effect, wherein the negative spring constant, k, is proportional to the centrifugal force CF, distance L, and angular displacement θ(−k=CF*L*sin(θ)/θ). The negative spring effect may counteract aerodynamic forces and reduce actuator power requirements, thereby also potentially reducing the mass of actuator system  70 . Arm element  86  may be rigidly attached to beam element  82 , or beam element  82  and arm element  86  may be fabricated as a single element. 
         [0026]    During rotation of main rotor blade  72 , the centrifugal forces are carried across beam element  82  and reacted by pivot element  84 , effectively canceling the tendency of sliders  78   a - b  to sling outward because of the centrifugal forces. Crank  80  is similar to a common bell crank, and as it rotates it converts the span-wise motion of sliders  78   a - b  into chord-wise motion that may be used to manipulate an active element, such as flap  88 , which is connected to arm element  86  through a connecting rod  90  or similar linkage. 
         [0027]    In operation, sliders  78   a - b  are actuated such that each reciprocates generally parallel to axis  73  and slider  78   a  moves opposite to slider  78   b.  Thus, as slider  78   a  moves in the outboard direction of main rotor blade  72 , slider  78   b  moves inboard. And as slider  78   a  moves outboard and slider  78   b  moves inboard, crank  80  rotates about pivot element  84 , causing arm element  86  to advance toward trailing edge  92  of main rotor blade  72 . The movement of arm element  86  toward trailing edge  92  in turn causes connecting rod  90  to act on flap  88 , which may rotate about axis  89 . 
         [0028]    Conversely, as slider  78   a  moves inboard and slider  78   b  moves outboard, crank  80  rotates in the opposite direction about pivot element  84 , causing arm element  86  to retreat from trailing edge  92 . The movement of arm element  86  away from trailing edge  92  in turn causes connecting rod  90  to act on flap  88 , which may rotate about axis  89 . 
         [0029]      FIG. 7  is a perspective view of another example embodiment of an actuator system  100  in a main rotor blade  102  according to the present specification. Actuator system  100  may include linear actuators  104   a - b . Each linear actuator  104   a - b  typically includes a fixed or stationary element and a moving or sliding element, such as sliders  106   a - b . The fixed element may be rigidly connected to the frame of main rotor blade  102 , and they may be identical elements or may have distinct properties for certain applications. Likewise, sliders  106   a - b  may be identical or have distinct properties for certain applications. Linear actuators  104   a - b  each has an elongated shape with a lengthwise axis that is generally oriented parallel with a span-wise axis of main rotor blade  102 . In the example embodiment of  FIG. 7 , linear actuators  102   a - b  are also generally oriented parallel to each other along the span of main rotor blade  16   a.  Such a span-wise orientation is generally preferable to other orientations as it generally provides larger space in the blade for larger, more powerful motors with longer strokes, and better mass placement. 
         [0030]    In actuator system  100 , tension belts  108   a - b  may be connected to sliders  106   a - b , respectively. Tension belts  108   a - b  are routed around pivot elements  110   a - b , respectively, and then fastened to an active element  112 , such as a flap. 
         [0031]    In operation, sliders  106   a - b  are actuated such that each reciprocates generally parallel to the span-wise axis of main rotor blade  102  and slider  106   a  moves opposite to slider  106   b.  Thus, as slider  106   a  moves in the outboard direction of main rotor blade  102 , slider  106   b  moves inboard. And as slider  106   a  moves outboard and slider  106   b  moves inboard, tension belt  108   b  is pulled inboard about pivot element  110   b,  causing active element  112  to rotate. Conversely, as slider  106   a  moves inboard and slider  106   b  moves outboard, tension belt  108   a  is pulled inboard about pivot element  110   a,  causing active element  112  to rotate in the opposite direction. 
         [0032]    Alternatively or additionally, an actuator system may include hydraulic, piezoelectric, or electromechanical components. For example, a linear actuator may have a fixed element such as a hydraulic cylinder and a moving element such as a hydraulic ram. 
         [0033]    The system and apparatus described herein provides significant advantages, including: (1) reducing or eliminating the adverse effects of centrifugal forces on linear actuators in a span-wise orientation; (2) more powerful motors; (3) longer stroke and greater bandwidth than other systems; and (4) improved mass distribution characteristics. 
         [0034]    Certain example embodiments have been shown in the drawings and described above, but variations in these embodiments will be apparent to those skilled in the art. The principles disclosed herein are readily applicable to a variety of aircraft, including many types of rotary wing, tilt-rotor, and fixed wing aircraft, as well as a variety of other active wing elements, including leading edge droops. The preceding description is for illustration purposes only, and the claims below should not be construed as limited to the specific embodiments shown and described.