Patent Publication Number: US-2020301463-A1

Title: Cyclic stick support and friction adjustment

Description:
BACKGROUND 
     A rotorcraft may include one or more rotor systems. One example of a rotor system is a main rotor system on the rotorcraft. A main rotor system may generate aerodynamic lift to support the weight of the rotorcraft in flight and may generate thrust to counteract aerodynamic drag and move the rotorcraft in forward flight. Another example of a rotorcraft rotor system is a tail rotor system. A tail rotor system may generate thrust in the same direction as the main rotor system&#39;s rotation to counter the torque effect created by the main rotor system and to keep the rotorcraft&#39;s fuselage aligned in a desired direction. 
     Rotorcraft have flight control systems that allow pilots to control the main and tail rotor systems. Flight control systems comprise a collection of mechanical linkages and equipment connecting cockpit controls, such as a collective, a cyclic, and rudder pedals, to flight control surfaces that allow a rotorcraft to be flown with precision and reliability. For example, the rotorcraft flight control system controls operation (e.g. pitch) of the rotor blades through a swash plate component. The rotorcraft&#39;s flight control system is critical to flight safety. 
     SUMMARY 
     Embodiments are directed to a flight control device comprising a grip, a stick associated with the grip, and a gimbal. The gimbal comprises a spherical bearing coupled to the stick, a first plate having a first hole configured to receive a top portion of the spherical bearing, and a second plate having a second hole configured to receive a bottom portion of the spherical bearing, wherein the first plate and the second plate are configured to move relative to each other to apply a variable force against the spherical bearing. The first hole further comprises a first inner surface, and the second hole comprises a second inner surface. The variable force against the spherical bearing may be applied by mechanical interaction between the first and second inner surfaces and a surface of the spherical bearing. 
     The flight control device further comprises a clamping device coupled to the first plate and the second plate, wherein the clamping device is configured to move the first plate and the second plate relative to each other. The clamping device may comprise a knob portion configured to receive a bolt portion. The knob is positioned to apply a force against the first plate, and the bolt portion is positioned to apply a force against the second plate. Turning the knob portion in a first direction reduces a distance between the first plate and the second plate. Turning the knob portion in a second direction opposite the first direction increases the distance between the first plate and the second plate. The clamping device may be selected from a mechanical clamp, an electronic motor, and a hydraulic actuator. 
     The first plate and the second plate may be configured to remain in a generally parallel relationship as they move relative to each other. Alternatively, a first end of the first plate and a first end of the second plate may be configured to remain at a fixed distance from each other, and a second end of the first plate and a second end of the second plate may be configured to move relative to each other to apply a variable force against the spherical bearing. 
     The flight control device may further comprise a lever coupled to the spherical bearing at a position opposite to the stick. The lever may be configured to be coupled to a flight control linkage. The flight control device may further comprise a cyclic stop coupled to the second plate, and a bump stop coupled to the spherical bearing and the lever, wherein the cyclic stop and the bump stop are configured to limit a range of motion of the spherical bearing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  depicts a rotorcraft according to an example embodiment. 
         FIG. 2  depicts an example embodiment of a flight control device, such as a cyclic control assembly. 
         FIG. 3A  depicts an example prior art cyclic stick support with a friction adjustment. 
         FIG. 3B  is a cross-section view of the prior art cyclic stick support shown in  FIG. 3A . 
         FIG. 4A  depicts an example cyclic stick support with improved friction adjustment according to one embodiment. 
         FIG. 4B  is a cross-section view of the cyclic stick support shown in  FIG. 4A . 
         FIG. 5A  depicts an example cyclic stick support with improved friction adjustment according to an alternative embodiment. 
         FIG. 5B  is a side view of the cyclic stick support shown in  FIG. 5A . 
     
    
    
     While the system of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the system 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 present application as defined by the appended claims. 
     DETAILED DESCRIPTION 
     Illustrative embodiments of the system of the present application are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort 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. 
     In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of 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 device described herein may be oriented in any desired direction. 
       FIG. 1  depicts a rotorcraft  100  according to an example embodiment. Rotorcraft  100  features a rotor system  110 , blades  120 , a fuselage  130 , a landing gear  140 , and an empennage  150 . Rotor system  110  couples torque from an engine (not shown) to blades  120  and causes the blades  120  to rotate. Rotor system  110  may include a flight control system for selectively controlling the pitch of each blade  120  in order to selectively control direction, thrust, and lift of rotorcraft  100 . Fuselage  130  represents the body of rotorcraft  100  and may be coupled to rotor system  110  such that rotor system  110  and blades  120  may move fuselage  130  through the air. Landing gear  140  supports rotorcraft  100  when rotorcraft  100  is landing and/or when rotorcraft  100  is at rest on the ground. Empennage  150  represents the tail section of the aircraft and features components of a rotor system and blades  160 . Blades  160  may provide thrust in the same direction as the rotation of blades  120  to counter the torque effect created by rotor system  110  and blades  120 . The teachings of certain embodiments relating to rotor systems as described herein may apply to rotor system  110  and/or other rotor systems, such as other tilt rotor and helicopter rotor systems. It should also be appreciated that teachings from rotorcraft  100  may apply to aircraft other than rotorcraft, such as airplanes and unmanned aircraft, to name a few examples. 
     A pilot may manipulate one or more pilot flight control devices in order to achieve controlled aerodynamic flight. Inputs provided by the pilot to the pilot flight control devices may be transmitted mechanically and/or electronically (e.g., via a fly-by-wire flight control system) to flight control systems. Flight control systems may represent devices operable to change the flight characteristics of the aircraft. Examples of flight control systems on rotorcraft  100  may include the control system operable to change the positions (e.g., pitch) of blades  120  and blades  160 . 
     Rotorcraft  100  may feature at least three sets of pilot flight control devices: a collective control assembly, a cyclic control assembly, and a pedal assembly. Although examples discussed herein describe pilot flight controls such as cyclic control assemblies, collective control assemblies, and pedal assemblies, teachings of certain embodiments recognize that other pilot flight controls may be used. For example, in some embodiments, a tiltrotor aircraft may include a power control device, and a thrust control device. 
     In general, cyclic pilot flight controls may allow a pilot to impart cyclic motions on blades  120 . Cyclic motions in blades  120  may cause rotorcraft  100  to tilt in a direction specified by the pilot. For tilting forward and back (pitch) and/or tilting sideways (roll), the angle of attack or pitch of blades  120  may be altered cyclically during rotation, creating different amounts of lift at different points in the cycle. 
     Collective pilot flight controls may allow a pilot to impart collective motions on blades  120 . Collective motions in blades  120  may change the overall lift produced by blades  120 . For increasing or decreasing overall lift in blades  120 , the angle of attack or pitch for all blades  120  may be collectively altered by equal amounts at the same time resulting in ascents, descents, acceleration, and deceleration. 
     Anti-torque pilot flight controls may allow a pilot to change the amount of anti-torque force applied to rotorcraft  100 . As explained above, blades  160  may provide thrust in the same direction as the rotation of blades  120  to counter the torque effect created by rotor system  110  and blades  120 . Anti-torque pilot flight controls may change the amount of anti-torque force applied to change the heading of rotorcraft  100 . For example, providing anti-torque force greater than the torque effect created by rotor system  110  and blades  120  may cause rotorcraft  100  to rotate in a first direction, whereas providing anti-torque force less than the torque effect created by rotor system  110  and blades  120  may cause rotorcraft  100  to rotate in an opposite direction. In some embodiments, anti-torque pilot flight controls may change the amount of anti-torque force applied by changing the pitch of blades  160 , increasing or reducing the thrust produced by blades  160  and causing the nose of rotorcraft  100  to yaw in the direction of the applied pedal. In some embodiments, rotorcraft  100  may include additional or different anti-torque devices, such as a rudder or a NOTAR (no tail rotor) anti-torque device, and the anti-torque flight controls may change the amount of force provided by these additional or different anti-torque devices. 
       FIG. 2  depicts an example embodiment of a flight control device  200 , such as a cyclic control assembly. Flight control device  200  may feature a grip  210 , stick  220 , and gimbal assembly  230 . The gimbal assembly  230  may be mounted on the floor  240  of an aircraft, such as a rotorcraft. Gimbal assembly  230  couples the flight control device  200  to one or more flight control linkage  250  through a lever  255 . Flight control linkage  250  is coupled to flight control devices (not shown), such as a rotorcraft swashplate or aircraft flight control surfaces. Gimbal assembly  230  allows a pilot or other operator to move flight control device  200  so that it rotates around a pitch axis  260  and/or a roll axis  270 . Such movement of flight control device  200  then is transferred to the flight control surfaces through lever  255  and flight control linkage  250 . For example, in a rotorcraft, movement of flight control device  200  translates all the way up to motion at the rotor system, which changes the attitude and direction of the rotorcraft. 
     The gimbal assembly  230  has a first function to hold that flight control device  200  in place and to act as the rotation point for the device. The secondary purpose of gimbal assembly  230  is to control friction in the system, which appears to an operator as “stiffness” associated with moving grip  210  and stick  220 . A friction knob  280  may be configured such that twisting friction knob  280  applies friction to gimbal assembly  230  so that movement of flight control device  200  requires more force. In one embodiment, clockwise movement around axis  290  increases the friction applied by gimbal assembly  230  to flight control device  200 , while turning friction knob  280  counter-clockwise around axis  290  decreases the friction applied by gimbal assembly  230 . Therefore, when the friction applied by gimbal assembly  230  is increased, grip  210  may become harder to move; and when the friction applied by gimbal assembly  230  is decreased, grip  210  may become easier to move. 
     There may be several reasons why an adjustment of the friction by gimbal assembly  230  is preferable. For example, a pilot of rotorcraft  100  ( FIG. 1 ) may desire to have the stiffness of flight control device  200  increased while rotorcraft  100  is hovering. This friction allows the pilot to release flight control device  200  during flight without concern that vibration or other movement of rotorcraft  100  will cause the flight control device  200  to move on its own, which would translate to movement of the rotor system or flight controls. It may also be preferable to increase the stiffness of flight control device  200  when certain components of rotorcraft  100  are being replaced or repaired. 
       FIG. 3A  depicts an example prior art cyclic stick support  300  with friction adjustment.  FIG. 3B  is a cross-section view of the prior art cyclic stick support  300  shown in  FIG. 3A . A flight control stick coupling  310  is attached to the top of spherical bearing  320 . Flight control stick coupling  310  is adapted to receive a flight control stick  220  and grip  210  assembly ( FIG. 2 ). Lever  330  is coupled to the bottom of spherical bearing  320 . Lever  330  may be coupled to one or more flight control linkages (not shown). Spherical bearing  320  is mounted in a bearing housing  340 . The bearing housing  340  is mounted in base  350 , which may be mounted on or under a rotorcraft floor or deck, for example. When flight control stick coupling  310  is rotated around spherical bearing  320 , such movement is transferred to flight control linkages via lever  330 . A cyclic stop  355  limits the range of motion of the flight control stick. 
     Friction is applied to cyclic stick support  300  using friction knob  360 . Friction knob  360  has a stem  361  with a threaded portion  362 . End portion  363  of stem  361  abuts plate  364  and prevents stem  361  from being removed from cyclic stick support  300  when friction knob  360  is moved. Friction wedge  365  is treaded to match threaded portion  362 . When friction knob  360  is turned, stem  361  and threaded portion  362  also turn. The rotating threads on portion  362  cause wedge  365  to move upward or downward depending on which direction knob  360  is turned. Friction wedge  365  has a sloped surface  366  that pushes against a sloped surface  321  of bearing wedge  322 . As friction wedge  365  is moved upward, sloped surface  366  moves against sloped surface  321 , which causes bearing wedge  322  to move to the right in  FIG. 3  toward bearing housing  340 . This causes surface  323  of bearing wedge  322  to press against bearing housing  340  which creates a pinching force between bearing housing  340  and spherical bearing  320  at regions  341  and  342 . The pinching force creates friction that limits movement of cyclic stick support  300 . 
     Even though the configuration of cyclic stick support  300  has its advantages, such as limiting the movement of flight control stick coupling  310 , it may also have some potential disadvantages. One potential disadvantage may be local “stiff” spots due to the mechanical system. For example, because bearing housing  340  applies force against spherical bearing  320  only at regions  341  and  342  to create friction, this may effectively create an axis  370  that spherical bearing  320  can more freely rotate around. Therefore, friction created in this manner is uneven, with the friction in the longitudinal stick direction always higher than in the lateral direction. Moreover, this configuration may be ineffective at holding a minimum friction setting, and a maximum friction setting may not be high enough. Because there can be potential disadvantages to using the friction system illustrated in  FIGS. 3A and 3b  to adjust the stiffness of a flight control device, there is a need for an improved flight control device which allows the stiffness to be more evenly distributed. 
       FIG. 4A  depicts an example cyclic stick support  400  with improved friction adjustment according to one embodiment.  FIG. 4B  is a cross-section view of the cyclic stick support  400  shown in  FIG. 4A . Flight control stick coupling  410  is attached to the top of spherical bearing  420 . Lever  430  is coupled to the bottom of spherical bearing  420 . Lever  430  may be coupled to one or more flight control linkages (not shown). Spherical bearing  420  is mounted between a top plate  440  and a bottom plate  450 . The top plate  440  may be mounted on or under a rotorcraft floor or deck, for example. Top plate  440  has a hole  441  that is adapted to fit around the upper surface of spherical bearing  420 . Similarly, bottom plate  450  has a hole  451  that is adapted to fit around the lower surface of spherical bearing  420 . The top surface of spherical bearing  420  is held in place by inner wall  442  of hole  441 , and the lower surface of spherical bearing  420  is held in place by inner wall  452  of hole  451  and may rotate in all directions. When flight control stick coupling  410  is rotated around spherical bearing  420 , such movement is transferred to flight control linkages via lever  430 . 
     Friction is applied to cyclic stick support  400  using friction knob  460 . Friction knob  460  has a stem  461  with a threaded portion  462 . End portion  463  of stem  461  abuts plate  464  and prevents stem  461  from being removed from cyclic stick support  400  when friction knob  460  is moved. Plate  465  is threaded to match threaded portion  462 . When friction knob  460  is turned, stem  461  and threaded portion  462  also turn. The rotating threads on portion  462  cause plate  465  to move upward or downward depending on which direction knob  460  is turned. When friction knob  460  is turned to move plate  465  upward, then plate  465  causes end  453  of bottom plate  450  to also move upward toward end  443  of top plate  440 . Spacer  470  holds end  444  of top plate  440  at a fixed distance from the corresponding end  454  of bottom plate  450 . When end  453  of bottom plate  450  moves upward due to tightening of friction knob  460 , the gap  421  between bottom plate  450  and top plate  440  is reduced. This movement also causes the inner walls  442 ,  452  of holes  441 ,  451  in top plate  440  and bottom plate  450 , respectively, to clamp against spherical bearing  420  thereby creating friction. 
     The friction generated using the system illustrated in  FIGS. 4A and 4B  is fairly even in all directions because the inner walls  442 ,  452  of the holes  441 ,  451 , respectively, encircle spherical bearing  420  and provide an even distribution of force around spherical bearing  420 . The friction provided in cyclic stick support  400  is capable of generating a higher maximum friction compared to existing systems since more surface area touches spherical bearing  420  to apply friction force. Additionally, cyclic stick support  400  may hold a minimum friction setting better than existing systems. 
     Although a threaded knob  460  and bolt  462  are used to move the plates  440  and  450  closer together or farther apart in the example illustrated in  FIGS. 4A and 4B , it will be understood that any other appropriate mechanical, electrical, or hydraulic device may be used to move plates  440  and  450 . For example, a mechanical clamp, electric motor, or hydraulic actuator may be used to move plates  440  and  450  so that inner walls  442 ,  452  of holes  441 ,  451 , respectively, may provide an evenly distributed, variable friction force against spherical bearing  420 . Moreover, although  FIGS. 4A and 4B  illustrate a single clamping system (i.e., components  460 - 464 ) to move plates  440  and  450 , it will be understood that in other embodiments, multiple devices may be used to position plates  440  and  450  and to adjust the distance therebetween. 
     Plates  440  and  450  may be configured to remain in a generally parallel arrangement in some embodiments. For example, plates  440  and  450  may move on rails, pins, or guides, such as bolts  462  and  471 , so that the plates maintain a parallel relationship as the distance between plates  440  and  450  changes. Alternatively, plates  440  and  450  may hinge or pivot around a fixed point, such as spacer  470 , when a clamping force is applied so that the distance between one end  443 ,  453  of each plate varies as the other end  444 ,  454  of each plate maintains a constant distance. In other embodiments, springs may be used in cyclic stick support  400  to push plates  440  and  450  apart in opposition to the clamping force applied by clamping system  460 - 464 . For example, springs may be provided at location  472  and/or in place of spacer  470  to provide a force opposite to clamping system  460 - 464  so that plates  440  and  450  move quickly and freely as friction is applied or reduced. 
     In various configurations, either plate  440  or plate  450  may be considered to be in a fixed location, such as attached to the floor or deck of a rotorcraft cockpit. For example, if plate  440  is attached to the cockpit floor, then clamping system  460 - 464  would have the effect of pulling plate  450  upward to increase friction forces on spherical bearing  420 . Alternatively, if plate  450  is attached to the cockpit floor, then clamping system  460 - 464  would have the effect of pulling plate  450  downward to increase friction forces on spherical bearing  420 . 
     Cyclic stick support  400  further comprises a cyclic stop  480  coupled to plate  450 . Cyclic stop  480  may be an annular ring having a hollow center region defined by an inner wall  481 . A spherical bump stop  482  is coupled to the spherical bearing  420  and lever  430 . Cyclic stop  480  may limit the movement of cyclic stick support  400 . When bump stop  482  hits inner wall  481  due to movement of spherical bearing  420 , the inner wall  481  and bump stop  482  prevent spherical bearing  420  from further movement in that direction. This effectively limits the degree of freedom and range of motion available to a stick attached to flight control stick coupling  410  and/or to flight control linkages attached to lever  430 . 
       FIG. 5A  depicts an example cyclic stick support  500  with improved friction adjustment according to an alternative embodiment.  FIG. 5B  is a side view of the cyclic stick support  500  shown in  FIG. 5A . Flight control stick coupling  510  is attached to the top of spherical bearing  520 . Lever  530  is coupled to the bottom of spherical bearing  520 . Lever  530  may be coupled to one or more flight control linkages (not shown). Spherical bearing  520  is mounted in bearing housing ring  540 , which is part of a base plate  550 . The base plate  550  may be mounted on or under a rotorcraft floor or deck, for example. Bearing housing ring  540  is adapted to hold spherical bearing  520  bearing in place while allowing spherical bearing  520  to rotate in all directions. When flight control stick coupling  510  is rotated around spherical bearing  520 , such movement is transferred to flight control linkages via lever  530 . 
     Friction is applied to cyclic stick support  500  by adjusting a clamping force applied by bearing housing ring  540  to spherical bearing  520 . Bearing housing ring  540  does not form a complete circle but has a gap  541  that is defined by edges  542  and  543 . The inner diameter of bearing housing ring  540  can be reduced by closing gap  541 —i.e., by moving edges  542  and  543  closer together. Reducing the inner diameter of bearing housing ring  540  would assert a clamping force on spherical bearing  520  thereby increasing the friction in cyclic stick support  500 . Conversely, the inner diameter of bearing housing ring  540  can be increased by opening gap  541 —i.e., by moving edges  542  and  543  farther apart. Increasing the inner diameter of bearing housing ring  540  reduces the clamping force on spherical bearing  520  thereby reducing friction. 
     In one embodiment, friction is applied using friction knob  560 . Friction knob  560  has a stem  561  that passes through lugs  544  and  545  on bearing housing ring  540 . Lugs  544  and  545  may be any bump, spur, tab, or projection that allow friction knob  560  and stem  561  to be connected to bearing housing ring  540 . Lugs  544  and  545  may be integral components of bearing housing ring  540  or may be separate attachments to bearing housing ring  540 . In one embodiment, lug  544  is threaded and lug  545  is unthreaded. In other embodiments, either lug  544  or lug  545  may be threaded. Jam nut  562  is attached to stem  561  at a point adjacent to lug  544 . Nut  563  is attached to stem  561  at a point adjacent to lug  545 . 
     Friction is controlled by turning knob  560 , which causes lugs  544  and  545  to move toward each other or apart from each other. Movement of lugs  544  and  545  cause corresponding movement of edges  542  and  543  of bearing housing ring  540 . The direction and degree to which lugs  544  and  545  move in response to turning knob  560  is determined by the direction and pitch of the threads in lug  544 . In one embodiment, the threads are configured so that clockwise movement of knob  560  moves lugs  544  and  545  closer together. In this configuration, nut  563  presses up against unthreaded lug  545  causing the bearing housing ring clamp to close. Jam nut  562  on lug  544  may set a maximum amount that the bearing housing ring clamp can open, which also sets a minimum friction. As lugs  544  and  545  move together, the inner diameter of bearing housing ring  540  decreases, which applies a clamping force on spherical bearing  520  thereby generating friction. 
     The friction generated using the system illustrated in  FIGS. 5A and 5B  is even in all directions because the bearing housing ring  540  encircles spherical bearing  520  and provides an even distribution of force around spherical bearing  520 . The friction provided in cyclic stick support  500  is capable of generating a higher maximum friction compared to existing systems since more surface area touches spherical bearing  520  to apply friction force. Additionally, cyclic stick support  500  may hold a minimum friction setting better than existing systems. 
     Although a knob  560  and threaded lug  544  are used to adjust gap  541  and to move edges  542  and  543  relative to each other in the example illustrated in  FIGS. 5A and 5B , it will be understood that any other appropriate mechanical, electrical, or hydraulic device may be used to adjust gap  541 . For example, a mechanical clamp, electric motor, or hydraulic actuator may be used to adjust gap  541  and to move edges  542  and  543  relative to each other so that bearing housing ring  540  may provide an evenly distributed, variable friction force against spherical bearing  520 . Moreover, although  FIGS. 5A and 5B  illustrate a system using lugs  545  and  544  to adjust gap  541 , it will be understood that in other embodiments the clamping device may be attached directly to bearing housing ring  540 . 
     In one embodiment, a flight control device comprises a grip, a stick associated with the grip, and a gimbal. The gimbal comprising a spherical bearing coupled to the stick, a first plate having a first hole configured to receive a top portion of the spherical bearing, and a second plate having a second hole configured to receive a bottom portion of the spherical bearing. The first plate and the second plate are configured to move relative to each other to apply a variable force against the spherical bearing. The first hole further comprises a first inner surface, and the second hole comprises a second inner surface. The variable force against the spherical bearing is applied by mechanical interaction between the first and second inner surfaces and a surface of the spherical bearing. 
     The flight control device may further comprise a clamping device coupled to the first plate and the second plate. The clamping device is configured to move the first plate and the second plate relative to each other. The clamping device may comprise a knob portion configured to receive a bolt portion, wherein the knob is positioned to apply a force against the first plate and the bolt portion is positioned to apply a force against the second plate, and wherein turning the knob portion in a first direction reduces a distance between the first plate and the second plate. Turning the knob portion in a second direction opposite the first direction increases the distance between the first plate and the second plate. The clamping device may be selected from a mechanical clamp, an electronic motor, and a hydraulic actuator. 
     The first plate and the second plate may be configured to remain in a generally parallel relationship as they move relative to each other. 
     In a further embodiment, a first end of the first plate and a first end of the second plate are configured to remain at a fixed distance from each other. A second end of the first plate and a second end of the second plate are configured to move relative to each other to apply a variable force against the spherical bearing. 
     The flight control device may further comprise a lever coupled to the spherical bearing at a position opposite to the stick. The lever may be configured to be coupled to a flight control linkage. A cyclic stop may be coupled to the second plate. A bump stop may be coupled to the spherical bearing and the lever, wherein the cyclic stop and the bump stop are configured to limit a range of motion of the spherical bearing. 
     In another embodiment, a flight control stick support comprises a spherical bearing coupled to a flight control stick, a first plate having a first hole configured to receive a top portion of the spherical bearing, a second plate having a second hole configured to receive a bottom portion of the spherical bearing, and a clamping device configured to move the first plate relative to and the second plate to apply a variable force against the spherical bearing. 
     The first hole may comprise a first inner surface, and the second hole may comprise a second inner surface. The variable force against the spherical bearing is applied by mechanical interaction between the first and second inner surfaces and a surface of the spherical bearing. 
     The clamping device may be configured to apply a variable amount of stiffness to the flight control stick. 
     The clamping device may comprise a knob portion configured to receive a bolt portion, wherein the knob is positioned to apply a force against the first plate and the bolt portion is positioned to apply a force against the second plate, and wherein turning the knob portion in a first direction reduces a distance between the first plate and the second plate. Turning the knob portion in a second direction opposite the first direction increases the distance between the first plate and the second plate. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.