Abstract:
A tiltrotor aircraft having a wing and a rotatable pylon carried by the wing is disclosed. The pylon is secured to a pylon support spindle that extends into the wing. A link connects a radial portion of the pylon support spindle to a radial portion of a rotary actuator, such that the pylon support spindle is rotated as the actuator is rotated.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to tiltrotor aircraft. In particular, the present invention relates to compact pylon-conversion actuation system for a tiltrotor aircraft.  
       DESCRIPTION OF THE PRIOR ART  
       [0002]     Tiltrotor aircraft are hybrids between traditional helicopters and traditional propeller driven aircraft. Typical tiltrotor aircraft have rotor systems that are capable of articulating relative to the aircraft fuselage. This articulating portion is referred to as a nacelle. Tiltrotor aircraft are capable of converting from a helicopter mode, in which the aircraft can take-off, hover, and land like a helicopter; to an airplane mode, in which the aircraft can fly forward like a fixed-wing airplane.  
         [0003]     The design of tiltrotor aircraft poses unique problems not associated with either helicopters or propeller driven aircraft. In particular, the tiltrotor assemblies must be articulated between helicopter mode and airplane mode. To convert between helicopter mode and airplane mode the nacelle must rotate relative to the fuselage.  
         [0004]     It is known in the art to use linear actuators, such as screw jacks or hydraulic jacks, to rotate the nacelle about a rotation point relative to the fuselage. Linear actuators tend to be bulky and extend outside the envelope of the wing or nacelle requiring fairings that extend beyond the preferred aerodynamic shape of the wing or nacelle. Another disadvantage when using linear actuators is that very high torque is required at the extremes of the systems movement. Most linear actuators have constant torque throughout the range of motion, but are arranged so that they have the least mechanical advantage at the extremes of the range of motion. Therefore, the linear actuator is larger than it needs to be for the majority of the range of motion so that it can be of sufficient size at the extremes.  
         [0005]     Although there have been significant developments in the area of tiltrotor conversion actuation systems, considerable shortcomings remain.  
       SUMMARY OF THE INVENTION  
       [0006]     There is a need for tiltrotor pylon-conversion actuation system that can provide the necessary torque at the extremes of the range of motion while also being compact.  
         [0007]     Therefore, it is an object of the present invention to provide a tiltrotor pylon-conversion actuation system that can provide the necessary torque at the extremes of the range of motion while also being compact.  
         [0008]     This object is achieved by providing a rotary actuator and link assembly to rotate the pylon, or nacelle, over the limited range of motion needed to convert a tiltrotor aircraft from airplane mode to helicopter mode, and vice versa. The pylon rotates about a pylon support spindle while a rotary actuator drives an actuator spindle parallel to the pylon support spindle. The pylon support spindle is connected to the actuator spindle by a solid link. The difference in diameter of the spindles provides an increase in torque at the extremes of the range of motion and the solid link provides a limit on the range of motion.  
         [0009]     The present invention provides significant advantages, including: (1) providing a compact drive system that can be housed completely within the wing structure; (2) increased mechanical advantage at the extremes of the range of motion to match that closely match the needs of the application; (3) a rigid limit on the range of motion to prevent over-extension under severe conditions; and (4) rigid support to hold the pylon in whatever position the system has moved the pylon into.  
         [0010]     Additional objectives, features, and advantages will be apparent in the written description that follows.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     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:  
         [0012]      FIG. 1  is a perspective view of a tiltrotor aircraft in airplane mode;  
         [0013]      FIG. 2  is a perspective view of a tiltrotor aircraft in helicopter mode;  
         [0014]      FIG. 3  is a partial cutaway view of the end of a left wing of a tiltrotor aircraft incorporating an embodiment of a pylon-conversion actuation system according to the present invention, system being shown in conversion mode;  
         [0015]      FIG. 4  is an enlarged cutaway view of the actuation system of  FIG. 3  in conversion mode;  
         [0016]      FIG. 5  is an enlarged cutaway view of the actuation system of  FIG. 3  in airplane mode;  
         [0017]      FIG. 6  is an enlarged cutaway view of the actuation system of  FIG. 3  in conversion mode;  
         [0018]      FIG. 7  is an enlarged cutaway view of the actuation system of  FIG. 3  in helicopter mode;  
         [0019]      FIG. 8A  is a schematic view of the system linkage as shown in  FIG. 5 , in airplane mode;  
         [0020]      FIG. 8B  is a schematic view of the system linkage as shown in  FIG. 6 , in conversion mode;  
         [0021]      FIG. 8C  is a schematic view of the system linkage as shown in  FIG. 7 , in helicopter mode; and  
         [0022]      FIG. 9  is a graph of the torque advantage of the actuation system of  FIG. 3 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]     The present invention represents the discovery that a specific actuator system may be used to provide several benefits in rotating the pylon of a tiltrotor aircraft from airplane mode to helicopter mode. The actuator system according to the present invention is particularly useful in applications in which a compact system is needed to maintain the aerodynamic shape of the wing and pylon.  
         [0024]     Referring to  FIG. 1  of the drawings, a tiltrotor aircraft  11  is shown in airplane mode. In particular, aircraft  11  shown in  FIG. 1  is an unmanned aerial vehicle (UAV), as opposed to manned vehicles, and therefore has no provision for onboard human pilots. The invention is not limited to UAVs and may be used on manned vehicles as well. Aircraft  11  has a fuselage  13  with wings  15  extending from the fuselage  13 . At the ends of wings  15  are pylons  17 , which rotate on the ends of wings  15  through a range of from about 90° of rotation up to about 100° of rotation. In a UAV such as aircraft  11 , pylons  17  provide a rotatable support for rotors  19 , and the engine used to power rotors  19  is located within the fuselage. In larger tiltrotor aircraft, such as a manned tiltrotor, engines may be located in pylons  17 . When configured in airplane mode the plane of each rotor  19  is generally vertical and each pylon  17  is generally horizontal. While aircraft  11  is shown with pylons located at the ends of wings  15 , other configurations may be used, such as a configuration in which the pylons are rotatably connected to the fuselage.  
         [0025]     Referring now to  FIG. 2  of the drawings, tiltrotor aircraft  11  is shown in helicopter mode. In helicopter mode the plane of each rotor  19  is generally horizontal and each pylon  17  is generally vertical.  
         [0026]     Referring now to  FIG. 3  of the drawings, the pylon end of a left wing  15  is shown in partial cutaway view. Wing  15  is shown with pylon-conversion actuation system  21  exposed, and pylon  17  is shown in phantom. Pylon  17  is in conversion mode, in other words, between helicopter mode and airplane mode.  
         [0027]     Referring now to  FIG. 4  of the drawings, the pylon end of left wing  15  of  FIG. 3  is shown in cutaway view with actuation system  21  in conversion mode. Wing  15  is structurally comprised of skin  23  (shown in  FIGS. 5 through 7 ) and structural ribs  25  (partially removed in  FIG. 4  for clarity). Pylon support spindle  27  extends from the end of wing  15  through two ribs  25 . Where the support spindle  27  passes through ribs  25  bearing housings  29  support spindle  27  and allow for axial rotation of spindle  27  about spindle axis  31 . Spindle bracket  33  is on the outer circumference of support spindle  27  and provides a spindle connection point  35  for link  37 . Link  37  is pivotally mounted to spindle bracket  33  at spindle connection point  35 . Link  37  is a rigid, curved member, the curve allowing for a slight increase in range of motion than would be available if a straight member was used. A taller bracket  33  would allow use of a straighter link  37  at the cost of compactness.  
         [0028]     Link  37  is pivotally mounted to bracket  33  at one end of link  37  with the opposite end of link  37  being pivotally mounted to rotary actuator  39  at actuator connection point  41 . Rotary actuator  39  is supported by actuator bearings  43  on either side of rotary actuator  39 . Actuator bearings  43  are supported by actuator support  45  (partially sectioned in  FIG. 4 ). Actuator support  45  and actuator bearings  43  support rotary actuator  39  and allow rotary actuator  39  to rotate about actuator axis  47 , which is parallel to spindle axis  31 . Rotary actuator  39  is driven by electric actuator drive  49  to rotate about actuator axis  47 , though a wide variety of types of actuator drives  49  may be used, including drives  49  using hydraulic power or electric motors.  
         [0029]     Referring now to  FIG. 5  of the drawings, the pylon end of left wing  15  is shown in cutaway view with actuation system  21  in airplane mode and actuator drive  49  removed. Input shaft  51  is shown extending from rotary actuator  39  through rib  25  to connect with actuator drive  49  (not shown in  FIG. 5 ). Actuator drive  49  applies torque to input shaft  51 , which is connected to rotary actuator  39  through a gear-reduction system (not shown), such as a planetary-gear system. This gear system multiplies the amount of output torque from actuator drive  49  and permits use of a smaller, lower-torque actuator drive  49 . For example, a gear system may provide for a 50:1 ratio of revolutions of shaft  51  to revolutions of rotary actuator  39 .  
         [0030]     In the embodiment shown input shaft  51  extends through the last rib  25  of wing  15  towards pylon  17 . This allows the actuator drive  49  to be easily accessed when pylon  17  is removed. Alternatively, input shaft  51  may extend into wing  15 , away from pylon  17 , allowing actuator drive  49  to be accessed by removing a portion of skin  23 .  
         [0031]     Continuing with  FIG. 5  of the drawings, the actuation system  21  is shown in airplane mode. Rotary actuator  39  is rotated forward (counter-clockwise as shown from the end of left wing  15 ) such that link  37  is generally adjacent the circumference of spindle  27  and spindle  27  is rotated forward such that pylon  17  is in airplane mode.  
         [0032]     Referring now to  FIG. 6  of the drawings, a cutaway view of the pylon end of left wing  15  shows actuation system  21  in conversion mode, which is any position between the airplane mode and helicopter mode positions. In order to move from the airplane mode shown in  FIG. 5  to the conversion mode shown in  FIG. 6 , actuator drive  49  applies a torque to input shaft  51  to rotate rotary actuator  39  backward (clockwise as shown from the end of left wing  15 ) about actuator axis  47 . This puts link  37  in tension and thereby creates a torque on pylon support spindle  27 , rotating pylon support spindle  27  backward (clockwise as shown from the end of left wing  15 ) about spindle axis  31  to put pylon  17  into conversion mode.  
         [0033]     Referring now to  FIG. 7  of the drawings, a cutaway view of the pylon end of left wing  15  shows actuation system  21  in helicopter mode. In order to move from the conversion mode shown in  FIG. 6  to the helicopter mode shown in  FIG. 7 , actuator drive  49  applies a torque to input shaft  51  to rotate rotary actuator  39  further backward (clockwise as shown from the end of left wing  15 ) about actuator axis  47 . This puts link  37  in tension and thereby creates a torque on pylon support spindle  27  to rotate the pylon support spindle  27  further backward (clockwise as shown from the end of left wing  15 ) about spindle axis  31  to put pylon  17  into helicopter mode.  
         [0034]     Referring now to  FIGS. 8A, 8B , and  8 C of the drawings, each is a schematic of the linkage of pylon-conversion actuation system  21 . The schematics are in the plane normal to spindle axis  31  and actuator axis  47 , spindle axis  31  and actuator axis  47  being parallel, as described above. Therefore, spindle axis  31  and actuator axis  47  are represented as points in  FIGS. 8A, 8B , and  8 C. Also, spindle connection point  35  and actuator connection point  41  are shown as points at either end of link  37  as described above. Rotary actuator  39  rotates about actuator axis  47  and pylon support spindle  27  rotates about spindle axis  31 . Actuator connection point  41  rotates about actuator axis  47  and spindle connection point  35  rotates about spindle axis  31 . Link  37  maintains a fixed distance between spindle connection point  35  and actuator connection point  41 , thereby causing spindle connection point to rotate in reaction to the rotation of actuator connection point  41 , as shown in  FIG. 8A, 8B , and  8 C.  
         [0035]      FIG. 8A  is a schematic of the linkage of actuation system  21  in airplane mode. Rotary actuator  39  is rotated counter-clockwise until link  37  has pushed pylon support spindle  27  to rotate counter-clockwise into airplane mode.  
         [0036]      FIG. 8B  is a schematic of the linkage of actuation system  21  in conversion mode. Rotary actuator  39  is rotating and link  37  is causing spindle  27  to rotate in the same direction as rotary actuator  39 . As compared to  FIG. 8A , rotary actuator  49  has rotated clockwise, thereby causing spindle  27  to rotate clockwise toward helicopter mode. As compared to  FIG. 8C , rotary actuator  49  has rotated counter-clockwise, thereby causing spindle  27  to rotate counter-clockwise toward airplane mode.  
         [0037]      FIG. 8C  is a schematic of the linkage of actuation system  21  in conversion mode. Rotary actuator  39  is rotated clockwise until link  37  has pulled pylon support spindle  27  to rotate clockwise into helicopter mode.  
         [0038]     It is important to note that all of the detail drawings of pylon-conversion actuation system  21  have been of actuation system  21  as deployed on left wing  15  of aircraft  11 . It is to be understood that actuation system  21  is equally adapted for placement on right wing  15  of aircraft  11  and that actuation system  21  on right wing  15  would be a mirror image of actuation system  21  on left wing  15 , and the direction of rotation needed to move actuation system  21  between the various modes would be the opposite of that discussed herein.  
         [0039]     Referring now to  FIG. 9  of the drawings, the graph shows a torque ratio curve  53  for the embodiment shown in  FIGS. 3 through 8 C. The torque ratio curve  53  is plotted with the torque ratio on the y-axis  55  and the conversion angle on the x-axis  57 . The torque ratio is the torque applied to pylon support spindle  27  divided by the torque applied to rotary actuator  39 . Therefore, a torque ratio value greater than 1.0 indicates a positive mechanical advantage in the system. The conversion angle is the relative position of pylon support spindle  27 . A conversion angle of “0” indicates that pylon  17  is in airplane mode, whereas a conversion angle of “90” indicates that pylon  17  is in helicopter mode. Torque ratio curve  53  clearly shows that the above embodiment provides a mechanical advantage over the full range of motion, and this advantage is related to the ratio of the larger diameter of pylon support spindle  27  to the smaller diameter of actuator spindle  39 . More importantly, the torque ratio increases at the extremes of the range of motion, i.e., near 0 degrees and near 90 degrees, and this increase in torque ratio shows an increase in mechanical advantage where it is needed most.  
         [0040]     As described above, pylons  17  may be rotatably attached to aircraft  11  at locations other than at the ends of wings  15 . For example, a pylon may be attached to the fuselage or may be located in an inboard portion of wing  15 . Also, while link  37  is shown as a rigid, rod-like member, other types of linking means, such as a belt or chain, may be used to link rotary actuator  39  to pylon support spindle  27 .  
         [0041]     It is apparent that an invention with significant advantages has been described and illustrated. Although the present invention is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.