Patent Publication Number: US-8973864-B2

Title: Independent blade control system with hydraulic cyclic control

Description:
TECHNICAL FIELD 
     This invention relates generally to rotorcraft blade control, and more particularly, to an independent blade control system with hydraulic cyclic control. 
     BACKGROUND 
     A rotorcraft may include one or more rotor systems. One example of a rotorcraft rotor system is a main rotor system. A main rotor system may generate aerodynamic lift to support the weight of the rotorcraft in flight and 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. A rotor system may include one or more devices to rotate, deflect, and/or adjust rotor blades. 
     SUMMARY 
     Particular embodiments of the present disclosure may provide one or more technical advantages. A technical advantage of one embodiment may include the capability to implement independent blade control on a rotor system. A technical advantage of one embodiment may include the capability to provide a reliable independent blade control system without the need for redundant electrical or mechanical systems, condition monitoring systems, or secondary load paths. A technical advantage of one embodiment may include the capability to control an independent blade control system mechanically. A technical advantage of one embodiment may include the capability to conserve power in an independent blade control system. 
     Certain embodiments of the present disclosure may include some, all, or none of the above advantages. One or more other technical advantages may be readily apparent to those skilled in the art from the figures, descriptions, and claims included herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To provide a more complete understanding of the present invention and the features and advantages thereof, reference is made to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a rotorcraft according to one example configuration; 
         FIG. 2  shows the rotor system and blades  120  of  FIG. 1  according to one example configuration; 
         FIG. 3A  shows the motion of the blades of  FIG. 1  for a frequency of one oscillation per revolution; 
         FIG. 3B  shows the motion of the blades of  FIG. 1  for a frequency of three oscillations per revolution; 
         FIG. 3C  shows the motion of the blades of  FIG. 1  for a frequency of five oscillations per revolution; 
         FIGS. 4A-4D  shows the motions of the blades of  FIG. 1  for a frequency of four oscillations per revolution; 
         FIG. 5A  shows the motion of the blades of  FIG. 1  for a frequency of two oscillations per revolution; 
         FIG. 5B  shows the motion of the blades of  FIG. 1  for a frequency of six oscillations per revolution; 
         FIGS. 6A and 6B  show an example hydraulic actuation system; 
         FIGS. 7A and 7B  show another example hydraulic actuation; 
         FIGS. 8A and 8B  show yet another example hydraulic actuation system; 
         FIGS. 8C and 8D  show an example hydraulic actuation system having two cams; 
         FIG. 9A  shows yet another example hydraulic actuation system according to one embodiment; 
         FIG. 9B  shows the sum of each sinusoidal oscillation pattern generated by the example hydraulic actuation system of  FIG. 9A ; 
         FIGS. 10A-10S  show a radial fluid device and the frequencies of blade motions produced during operation of the radial fluid device according to one example embodiment; 
         FIGS. 11A-11K  show an alternative embodiment of the radial fluid device of  FIGS. 10A-10S  and the frequencies of blade motions produced during operation of this alternative embodiment; 
         FIGS. 12A-12E  show an individual blade control (IBC) system featuring the radial fluid device of  FIGS. 10A-10S  according to one example embodiment; 
         FIGS. 13A-13K  and  13 M show a radial fluid device and the frequencies of blade motions produced during operation of the radial fluid device according to another example embodiment; 
         FIG. 13L  show an alternative embodiment of the radial fluid device of  FIGS. 13A-13K  and  13 M; 
         FIGS. 14A-14C  show an IBC system featuring the radial fluid device of  FIGS. 13A-13J  and  13 M according to one example embodiment; 
         FIGS. 15A-15F  show the blade actuators of the IBC system of  FIGS. 14A-14C  according to one example embodiment; 
         FIG. 16A  shows two of the blade actuators of  FIGS. 15A-15F  coupled in series according to one example embodiment; 
         FIG. 16B  shows three of the blade actuators of  FIGS. 15A-15F  coupled in series according to one example embodiment; 
         FIG. 17A  shows an IBC system featuring three of the radial fluid devices of  FIGS. 13A-13J  and  13 M and four sets of the coupled blade actuators of  FIG. 16B  according to one example embodiment; and 
         FIG. 17B  shows an IBC system featuring two of the radial fluid devices of  FIGS. 13A-13J  and  13 M and four sets of the coupled blade actuators of  FIG. 16A  according to one example embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Rotor Systems 
       FIG. 1  shows a rotorcraft  100  according to one example configuration. Rotorcraft  100  features a rotor system  110 , blades  120 , a fuselage  130 , a landing gear  140 , and an empennage  150 . Rotor system  110  may rotate blades  120 . Rotor system  110  may include a 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  110  and blades  120 ′. Blades  120 ′ may provide thrust in the same direction as the rotation of blades  120  so as to counter the torque effect created by rotor system  110  and blades  120 . Teachings of certain embodiments relating to rotor systems 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. 
       FIG. 2  shows rotor system  110  and blades  120  of  FIG. 1  according to one example configuration. In the example configuration of  FIG. 2 , rotor system  110  features a power train  112 , a hub  114 , a swashplate  116 , and pitch links  118 . In some examples, rotor system  110  may include more or fewer components. For example,  FIG. 2  does not show components such as a gearbox, a swash plate, drive links, drive levers, and other components that may be incorporated. 
     Power train  112  features a power source  112   a  and a drive shaft  112   b . Power source  112   a , drive shaft  112   b , and hub  114  are mechanical components for transmitting torque and/or rotation. Power train  112  may include a variety of components, including an engine, a transmission, and differentials. In operation, drive shaft  112   b  receives torque or rotational energy from power source  112   a  and rotates hub  114 . Rotation of rotor hub  114  causes blades  120  to rotate about drive shaft  112   b.    
     Swashplate  116  translates rotorcraft flight control input into motion of blades  120 . Because blades  120  are typically spinning when the rotorcraft is in flight, swashplate  116  may transmit flight control input from the non-rotating fuselage to the hub  114 , blades  120 , and/or components coupling hub  114  to blades  120  (e.g., grips and pitch horns). References in this description to coupling between a pitch link and a hub may also include, but are not limited to, coupling between a pitch link and a blade or components coupling a hub to a blade. 
     In some examples, swashplate  116  may include a non-rotating swashplate ring  116   a  and a rotating swashplate ring  116   b . Non-rotating swashplate ring  116   a  does not rotate with drive shaft  112   b , whereas rotating swashplate ring  116   b  does rotate with drive shaft  112   b . In the example of  FIG. 2 , pitch links  118  connect rotating swashplate ring  116   b  to blades  120 . 
     In operation, according to one example embodiment, translating the non-rotating swashplate ring  116   a  along the axis of drive shaft  112   b  causes the pitch links  118  to move up or down. This changes the pitch angle of all blades  120  equally, increasing or decreasing the thrust of the rotor and causing the aircraft to ascend or descend. Tilting the non-rotating swashplate ring  116   a  causes the rotating swashplate  116   b  to tilt, moving the pitch links  118  up and down cyclically as they rotate with the drive shaft. This tilts the thrust vector of the rotor, causing rotorcraft  100  to translate horizontally following the direction the swashplate is tilted. 
     Independent Blade Control 
     Independent blade control (IBC) may refer to the ability to control motion of individual rotor system blades, such as blades  120   a - 120   d . For example, IBC may provide the ability to control harmonic motions of individual blades as the individual blades rotate. For discussion purposes, harmonic blade motions may be separated into three categories: harmonic cyclic motions, harmonic collective motions, and reactionless motions. These three categories do not define any particular mechanization to drive the blades. Rather, these categories may be defined by the characteristics of their oscillatory blade motions. 
     Harmonic cyclic motions may represent rotor blade sinusoidal motions similar to those that can be generated by application of oscillatory swashplate tilting inputs to the non-rotating half of the swashplate. In the example of  FIG. 2 , harmonic cyclic motions may be similar to the application of tilting inputs to non-rotating swashplate ring  116   a.    
     The frequency of harmonic cyclic motions may be expressed as specific multiple integers of rotor revolution frequency (e.g., revolutions per minute, or RPM). On a four-bladed rotor system such as rotor system  110 , the frequencies of harmonic cyclic oscillations are odd integer values (e.g., one blade oscillation per revolution, 3/rev, 5/rev, 7/rev, etc.). 
       FIGS. 3A-3C  show the motions of blades  120   a - 120   d  for frequencies of one, three, and five blade oscillations per revolution.  FIG. 3A  shows the motion of blades  120   a - 120   d  for a frequency of one oscillation per revolution. One blade oscillation per revolution may be accomplished, for example, by maintaining non-rotating swashplate ring  116   a  in a fixed, tilted position.  FIG. 3B  shows the motion of blades  120   a - 120   d  for a frequency of three oscillations per revolution.  FIG. 3C  shows the motion of blades  120   a - 120   d  for a frequency of five oscillations per revolution. 
     Harmonic collective motions move all blades sinusoidally in phase with each other. In the example of  FIG. 2 , harmonic collective motions may be similar to the application of axial inputs to non-rotating swashplate ring  116   a.    
     The frequency of harmonic collective motions may be expressed as specific multiple integers of rotor revolution frequency (e.g., RPM). In particular, the frequency of harmonic collective motions may be expressed as multiples of the number of blades on the rotor. On a four-bladed rotor system such as rotor system  110 , the frequencies of harmonic collective oscillations are 4/rev, 8/rev, etc.  FIGS. 4A-4D  shows the motions of blades  120   a - 120   d  for a frequency of 4/rev. As shown in  FIGS. 4A-4D , blades  120   a - 120   d  move uniformly sinusoidally in phase with each other. 
     Unlike harmonic cyclic and collective motions, reactionless motions cannot be replicated by or analogized to swashplate motions. For a four-bladed rotor system, the frequencies of reactionless motions are 2/rev and 6/rev, which cannot be achieved using the rotor system  110  of  FIG. 2 . Oscillation frequencies of 2/rev and 6/rev for a four-bladed rotor system results in adjacent blades having a 180 degree phase lag and opposite blades being in phase with each other.  FIG. 5A  shows the motions of blades  120   a - 120   d  for a frequency of 2/rev, and  FIG. 5B  shows the motions of blades  120   a - 120   d  for a frequency of 6/rev. Teachings of certain embodiments recognize that implementing reactionless controls may increase rotor system efficiency as well as reduce noise and vibration. 
     Thus, IBC may represent the ability to move rotor blades unconstrained from the cyclic and collective kinematic motion limitations imposed by conventional swashplate controls. Although IBC is not a prerequisite to implement cyclic and collective controls, it is a prerequisite to implement reactionless controls. 
     Teachings of certain embodiments recognize the ability to implement IBC on a rotor system. For discussion purposes, IBC systems may be separated into two categories: partial authority and full authority. Partial-authority IBC systems sum their higher harmonic and reactionless control motions with a swashplate providing fundamental blade motion for cyclic and collective control. Full-authority IBC systems provide for independent blade control through the full range of cyclic and collective motion. In some circumstances, partial-authority IBC systems may be preferable because the total summed amplitudes of higher harmonic and reactionless motions are typically a relatively small percentage of the total blade travel required for cyclic and collective control. Therefore, the failure mode effects of partial-authority IBC actuators are not as critical as with full-authority systems, allowing for lesser levels of reliability and redundancy. Full-authority IBC systems, on the other hand, may be preferable because they can allow for the elimination of the swashplate and thus elimination of certain drag and weight penalties. 
     Hydraulic Systems 
     Teachings of certain embodiments recognize the ability to implement IBC by hydraulically actuating the position of each rotor blade.  FIGS. 6A and 6B  show an example hydraulic actuation system  200 . Hydraulic actuation system  200  features a pump  210 , control valves  220  (e.g., electro-hydraulic valves), an actuator  230 , and a reservoir  240 . In operation, pump  210  provides hydraulic fluid to control valves  220 , which either provides into or releases fluid out of actuator  230 . Changing the volume of fluid in actuator  230  allows hydraulic actuation system  200  to either raise or lower load  250 . Control valves  220  may pass hydraulic fluid to reservoir  240 , which may provide hydraulic fluid to pump  210 , as needed. 
     In the example of  FIGS. 6A and 6B , hydraulic actuation system  200  is a constant-pressure system in that pump  210  provides a constant pressure of hydraulic fluid. In a constant-pressure hydraulic system, the power expended to move the actuator is independent of the applied load on the actuator because power is a function of product flow and system pressure. 
     Maximum actuator rate capacity is achieved when control valves  220  are commanded to their maximum orifice size, which is also the maximum operating efficiency condition of hydraulic actuation system  200 . Thus, the maximum operating efficiency condition occurs when load  250  is largest, as shown in  FIG. 6A . 
     When less than maximum actuator rate is required (such as when load  250 ′ is smaller, as shown in  FIG. 6B ), control valves  220  throttle down flow by reducing the orifice size and converting the unused power into waste heat. Power is converted to even more waste heat when commanding control valves  220  to move actuator  230  at less than maximum rate in the same direction as an aiding load. In addition to the power wasted throttling down the hydraulic flow going into actuator  230 , hydraulic fluid being pushed out the actuator  230  is also throttled by control valves  220  squandering potentially regenerative power and converting it into heat waste. 
     Adding a second set of actuators  230  for increased system reliability may magnify this power waste more than a simple factor of two. For redundancy, each control valve  220  would be independently capable of providing required power. This suggests that, when operating together, they both waste more than half the power they consume. Therefore the power wasted by adding a second set of control valves  220  may increase the power wasted and the heat generated by a factor of four. 
     By regulating the volume of fluid going in and out of a hydraulic actuator without throttling down flow, control valve power losses and the resulting waste heat generation may be reduced or eliminated.  FIGS. 7A and 7B  show an example hydraulic actuation system  300 . Hydraulic actuation system  300  features a pump  310  and an actuator  320 . Pump  310  is a reversible-flow hydraulic pump featuring a swashplate  312  that may be adjusted by control inputs  314 . In operation, pump  310  may move a load  330  by changing the position of swashplate  312 , which allows fluid to flow between the chambers of actuator  320 . Thus, swashplate  312  may provide control over both displacement and flow direction. 
     Unlike hydraulic actuation system  200 , hydraulic actuation system  300  may provide control of actuator position without the throttling power loss. However, application of this technology to IBC may be impractical due to performance, system complexity, weight, and control issues. In particular, the high relative inertia of swashplate  312  may not be able to provide the frequency response required for IBC. In addition, a four-bladed rotor with dual redundancy would require a system of at least eight pumps total because each actuator requires a dedicated pump for control. 
     Thus, although the power density and jam resistance of hydraulic actuation may make hydraulic actuation suitable for application to IBC, efficiency and inertia issues may make some hydraulic actuation systems impracticable. Teachings of certain embodiments, however, recognize the capability to actuate loads in an IBC system without the wasted energy associated with hydraulic actuation system  200  or the high inertia problems associated with hydraulic actuation system  300 . In particular, teachings of certain embodiments recognize the capability to efficiently and effectively actuate loads in an IBC system through the use of mechanically-programmed cams. 
       FIGS. 8A and 8B  show a hydraulic actuation system  400  according to one example embodiment. Hydraulic actuation system  400  features a cam  410  and piston assemblies  420  and  430 . Unlike hydraulic actuation system  200 , hydraulic actuation system  400  does not feature any control valves to limit flow volume. Rather, piston assemblies  420  and  430  are ported directly to one another. Thus, hydraulic actuation system  400  may not suffer from the energy losses associated with hydraulic actuation system  200 . In addition, unlike hydraulic actuation system  300 , hydraulic actuation system  400  does not feature a swashplate and thus may not be subject to the inertia problems associated with hydraulic actuation system  300 . 
     In operation, as shown in  FIG. 8A , cam  410  pushes down the piston of piston assembly  420 , which forces fluid into piston assembly  430 , thus raising load  440 . To lower load  440 , as shown in  FIG. 8B , cam  410  allows the piston of piston assembly  420  to pull up, which allows fluid to flow out of piston assembly  430 , thus lowering load  440 . Disregarding friction losses, raising or lowering load  440  may be 100% efficient regardless of the size of load  440 . 
     Teachings of certain embodiments recognize the ability to reduce the power required to move a cam  410  by balancing loads between two cams  410 , as shown in  FIGS. 8C and 8D . In this example, a cam shaft  450  joins two cams  410  together at 180 degrees out of phase. Disregarding leakage and friction losses, the sinusoidal raising and lowering of the cylinder loads would require no additional energy to sustain motion once a constant speed of cam shaft  450  is achieved. 
     In addition, teachings of certain embodiments recognize the capability to program sinusoidal motion of a load by providing multiple cams of different shapes. As explained above with regard to the different categories of IBC motions, IBC motions may be expressed as specific integers of rotor revolutions (e.g., for a four-blade rotor system, 1 oscillation per revolution for cyclic motion, 2/rev for reactionless motion, 3/rev for cyclic motion, 4/rev for collective motion, 5/rev for cyclic motion, 6/rev for reactionless motion, etc.). Teachings of certain embodiments recognize the ability to program sinusoidal motion by providing a cam for each oscillation frequency and then hydraulically summing the outputs. 
       FIG. 9A  shows a hydraulic actuation system  500  according to one example embodiment. Hydraulic actuation system  500  features a cam assembly  510 , piston assemblies  520 , and an actuator  530  operable to move a load  540 . Each cam of cam assembly  510  is operable to oscillate a corresponding piston of piston assemblies  520  according to the sinusoidal oscillation patterns  560  shown in  FIG. 9A . 
     In the example of  FIG. 9A , cam assembly features six cams  511 - 516  coupled to a cam shaft  550 . Each cam  511 - 516  corresponds to a different oscillation frequency. Cam  511 , for example, is a single-lobed cam that oscillates piston  521  once per revolution of cam shaft  550 , as shown by sinusoidal oscillation pattern  561 . Cam  512  is a two-lobed cam that oscillates piston  522  twice per revolution of cam shaft  550 , as shown by sinusoidal oscillation pattern  562 . Cam  513  is a three-lobed cam that oscillates piston  523  three times per revolution of cam shaft  550 , as shown by sinusoidal oscillation pattern  563 . Cam  514  is a four-lobed cam that oscillates piston  524  four times per revolution of cam shaft  550 , as shown by sinusoidal oscillation pattern  564 . Cam  515  is a five-lobed cam that oscillates piston  525  five times per revolution of cam shaft  550 , as shown by sinusoidal oscillation pattern  565 . Cam  516  is a six-lobed cam that oscillates piston  526  six times per revolution of cam shaft  550 , as shown by sinusoidal oscillation pattern  566 . 
     A precise waveform may be generated by hydraulically summing the outputs from each piston assembly  520 . For example,  FIG. 9B  shows the sum of each sinusoidal oscillation pattern  560 . As shown in  FIG. 9B , the sum of each sinusoidal oscillation pattern  560  may result in a summed oscillation pattern  570  that is not sinusoidal. 
     With these concepts in mind, teachings of certain embodiments recognize the capability to implement IBC on a rotor system, as discussed in greater detail below. 
     Partial-Authority IBC 
       FIGS. 10A-10S  show a radial fluid device  600  according to one example embodiment. Teachings of certain embodiments recognize that radial fluid device  600  may generate sinusoidal waveform amplitude and synchronization displacement control to multiple actuators from a single unit. As will be explained in greater detail below, the shape and synchronization of these sinusoidal displacement changes may be defined by the corresponding volumetric sum of hydraulic fluid required to displace each IBC actuator to replicate desired cyclic harmonic, collective harmonic, and reactionless blade motions. In this manner, radial fluid device  600  may emulate the hydraulic summation capabilities of hydraulic actuation system  500 . In addition, teachings of certain embodiments recognize that radial fluid device  600  may emulate the power conservation and regeneration capabilities of hydraulic actuation system  400  by utilizing aiding actuator loads to drive radial fluid device  600  as a hydraulic motor. 
       FIG. 10A  shows a side view of radial fluid device  600 , and  FIG. 10B  shows a top view of radial fluid device  600 . Radial fluid device  600  features multiple stacked radial piston sections rotating together in conjunction with a common cylinder block  604  (not shown in  FIGS. 10A and 10B ). In the example of  FIGS. 10A-10S , radial fluid device  600  features stacked radial piston sections  620 - 660  and  620 ′- 660 ′ rotating together with shaft  602  and cylinder block  604 . 
     As will be shown in greater detail below, shaft  602  is coupled to cylinder block  604 . In some embodiments, shaft  602  is removably coupled to cylinder block  604 . For example, different shafts  602  may have different gear splines, and an installer may choose from among different shafts  602  for use with radial fluid device  600 . 
     Cylinder block  604  rotates within radial fluid device  600 . In the example of  FIGS. 10A-10S , the axis of rotation of cylinder block  604  is coaxial with shaft  602 . Bearings may separate cylinder block  604  from the non-rotating body of radial fluid device  600 . 
     Each pump section pair (e.g., sections  620  and  620 ′,  630  and  630 ′, etc.) is dedicated to generating the desired waveform for a specific frequency. In the example of  FIGS. 10A-10S , the pump section pairs are dedicated to generating desired waveforms for 2/rev through 6/rev. In this example, the fundamental cyclic motions (1/rev) are generated by a mechanical swashplate, such as swashplate  116  of  FIG. 2 . 
     Although the pump section pairs in radial fluid device  600  are dedicated to generating desired waveforms for 2/rev through 6/rev, teachings of certain embodiments recognize that other fluid devices may include pump sections dedicated to generating more, fewer, or different desired waveforms. For example, the performance benefits provided by some frequencies may be minimal, and the pump sections generating these frequencies would be eliminated. As one example, a variation of radial fluid device  600  may only feature pump sections dedicated to 2/rev (reactionless) and 4/rev (collective harmonic), with the fundamental cyclic motions (1/rev) generated by a mechanical swashplate. 
     Separate section frequencies from each pump section pair in radial fluid device  600  may be hydraulically summed together to generate a final desired waveform to each actuator, such as described above with regard to  FIG. 9B . In particular, as will be explained in greater detail below, manifold  670  transmits the hydraulically summed fluids from radial fluid device  600  to actuators corresponding to each blade in a rotor system. 
       FIG. 10C  shows a cross-section view of pump section  620  along the cross-section line indicated in  FIG. 10B . In operation, pump section  620  is operable to provide a hydraulic flow that results in reactionless blade motions (2/rev) by blades  120   a - 120   d , as shown in  FIG. 10D . In particular, as shown in  FIG. 10D , adjacent blades  120   a  and  120   b  are 180 degrees out of phase, and opposite blades  120   a  and  120   c  are in phase. In this manner, the motion of blades in  FIG. 10D  resembles the motion of blades in  FIG. 5A . As will be explained in greater detail below, teachings of certain embodiments recognize that using four equally-spaced radial pistons driven by an elliptical cam may allow the volume of fluid displaced by each piston to replicate the required 2/rev reactionless sinusoidal motion and blade synchronization. 
     In the example of  FIG. 10C , pump section  620  features four pistons  621   a - 621   d . Each piston  621   a - 621   d  is slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . As shown in greater detail below, each chamber  604   a - 604   d  represents a plurality of cylinders within cylinder block  604  that are in fluid communication. Each chamber  604   a - 604   d  may have an independent outlet port that exits radial fluid device  600  to control a different IBC actuator. 
     Pump section  620  also features a cam  622 . During operation, pistons  621   a - 621   d  stroke inwards and outwards depending on the distance between cam  622  and the axis of rotation of cylinder block  604 . For example, cam  622  is an elliptical cam having two lobes. As each piston  621   a - 621   d  moves from the transverse diameter of cam  622  towards the conjugate diameter of cam  622 , each piston  621   a - 621   d  will be pushed closer to the axis of rotation of cylinder block  604 . Likewise, as each piston  621   a - 621   d  moves from the conjugate diameter of cam  622  to the transverse diameter of cam  622 , each piston  621   a - 621   d  will be pushed away from the axis of rotation of cylinder block  604 . As a result, each piston  621   a - 621   d  reciprocates towards and away from the axis of rotation of cylinder block  604 . Each reciprocation towards and away from the axis of rotation thus includes two strokes: a down stroke and an up stroke. 
     In the example of  FIG. 10C , cam  622  is elliptical and thus has two lobes. The number of lobes indicates how many sinusoidal stroke motions a piston completes during one full rotation of cylinder block  604 . For example, each piston  621   a - 621   d  completes two sinusoidal stroke motions during one rotation of cylinder block  604 . The ability of pump section  620  to complete two sinusoidal stroke motions during one rotation corresponds to the two blade oscillations per revolution required for certain reactionless blade motions. 
     Rotating cam  622  may change when pistons  621   a - 621   d  begin their strokes. For example, rotating cam  622  changes the location of the transverse diameter of cam  622  and thus changes where each piston  621   a - 621   d  begins a down stroke. As will be explained in greater detail below, moving cam  622  relative to the corresponding cam  622 ′ of pump section  620 ′ may change the amount of time between when corresponding pistons of pump sections  620  and  620 ′ begin their downstrokes. Teachings of certain embodiments recognize that changing the amount of time between the downstrokes of corresponding pistons of pump sections  620  and  620 ′ may change the maximum accessible cylinder volume of chambers  604   a - 604   d  and therefore change how fluid flows in and out of radial fluid device  600 . 
     Cam gear  623 , drive gear  624 , and cam adjuster  625  may, in combination, adjust the position of cam  622 . Cam gear  623  is coupled to cams cam  622 . Drive gear  624  interact with the teeth of cam gear  623 . Cam adjuster  625  rotates drive gear  624  such that drive gear  624  rotates cam gear  623 . As stated above, moving cams  622  changes when pistons  621   a - 621   d  begin their strokes, and changing when pistons  621   a - 621   d  begin their strokes can change how fluid flows in and out of radial fluid device  600 . Thus, teachings of certain embodiments recognize the ability to change how fluid flows in and out of radial fluid device  600  by changing the position of cam adjuster  625 . 
     In the example of  FIG. 10C , cam gear  623  is a ring gear, drive gear  624  is a worm gear, and cam adjuster  625  is an electric motor. Teachings of certain embodiments recognize that an electric-driven worm gear may be particularly suitable for adjusting phase angle and amplitude for higher harmonics (e.g., 2/rev or greater) in an IBC system. In an IBC system, high-speed changes in phase angle and amplitude may not be required or even desired for higher harmonics. For example, slow changes in elliptical cam phase angle may provide time for failure modes to be identified and bypassed before undesirable blade motions are generated. In addition, a small-diameter worm gear running on a large-diameter ring gear may provide a high-gear reduction, thus reducing the torque of the electric motor required and providing irreversibility in the event of a motor failure. In the event an electric motor should fail, the oscillatory motion may be nullified by the still operating pump section (e.g., pump section  620 ′) by indexing it&#39;s cam to an opposing phase position. 
       FIGS. 10E ,  10 F, and  10 G show pump sections  620  and  620 ′ in operation with their cams  622  and  622 ′ in phase.  FIG. 10E  shows a cross-section view of pump section  620  along the cross-section line indicated in  FIG. 10A ,  FIG. 10F  shows a cross-section view of pump section  620 ′ along the cross-section line indicated in  FIG. 10A , and  FIG. 10G  shows the resulting blade angle for blade  120   a  that is produced by pump sections  620  and  620 ′. 
     In operation, pump section  620 , is operable to provide a hydraulic flow that results in reactionless blade motions (2/rev) by blades  120   a - 120   d . As shown in  FIG. 10F , pump section  620 ′ features pistons  621   a ′- 621   d ′, a cam  622 ′, a cam gear  623 ′, a drive gear  624 ′, and a cam adjuster  625 ′. Each piston  621   a ′- 621   d ′ is slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . In this manner, corresponding pistons  621   a  and  621   a ′ share chamber  604   a , corresponding pistons  621   b  and  621   b ′ share chamber  604   b , corresponding pistons  621   c  and  621   c ′ share chamber  604   c , and corresponding pistons  621   d  and  621   d ′ share chamber  604   d.    
     Cam  622 ′ is elliptical and thus has two lobes. Each piston  621   a ′- 621   d ′ completes two sinusoidal stroke motions during one rotation of cylinder block  604 . The ability of pump section  620 ′ to complete two sinusoidal stroke motions during one rotation corresponds to the two blade oscillations per revolution required for certain reactionless blade motions. 
     Cam gear  623 ′, drive gear  624 ′, and cam adjuster  625 ′ may, in combination, adjust the position of cam  622 ′. In some embodiments, the relative positions of cams  622  and  622 ′ may be adjusted independently. For example, cams  622  and  622 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  622  may not necessarily match the distance of rotation of  622 ′. 
       FIG. 10G  shows the resulting blade angle for blade  120   a  that is produced by pump sections  620  and  620 ′ when cams  622  and  622 ′ are in phase. In this example, both pump sections  620  and  620 ′ are in phase such that pistons  621   a  and  621   a ′ complete their upstrokes and begin their downstrokes at zero degrees and 180 degrees azimuth. In this configuration, the sum of the sinusoidal waves generated by pump sections  620  and  620 ′ is effectively double the contributing sinusoidal waves. 
       FIGS. 10H ,  10 I, and  10 J show pump sections  620  and  620 ′ in operation when their cams  622  and  622 ′ are 90 degrees out of phase.  FIG. 10E  shows a cross-section view of pump section  620  along the cross-section line indicated in  FIG. 10A ,  FIG. 10F  shows a cross-section view of pump section  620 ′ along the cross-section line indicated in  FIG. 10A , and  FIG. 10G  shows the resulting blade angle for blade  120   a  that is produced by pump sections  620  and  620 ′ when cams  622  and  622 ′ are 90 degrees out of phase. As shown in  FIG. 10H , cam  622  has been rotated 90 degrees relative to its position shown in  FIG. 10E . 
     In this example, both pump sections  620  and  620 ′ are 90 degrees out of phase such that pistons  621   a  and  621   a ′ complete their upstrokes and begin their downstrokes 90 degrees apart. In this configuration, the contributing sinusoidal waves generated by pump sections  620  and  620 ′ effectively cancel out. Thus, pump sections  620  and  620 ′ effectively have no impact on flow in or out of chamber  604   a  and therefore do not cause any reactionless motions by blade  120   a.    
     The examples of  FIGS. 10G and 10J  show how rotating cams  622  and  622 ′ in opposite directions relative to one another may change the effective flow volume of chamber  604   a  and thus change the amplitude of the total sinusoidal wave produced by the combination of pump sections  620  and  620 ′. Teachings of certain embodiments recognize the ability to change the phase of the total sinusoidal wave produced by the combination of pump sections  620  and  620 ′ in addition to changing the amplitude. In particular, rotating cams  622  and  622 ′ in the same direction may change when the total sinusoidal wave reaches peak amplitude without changing the magnitude of the peak amplitude. 
     In the example of  FIGS. 10C-10J , pump sections  620  and  620 ′ include two-lobed (elliptical) cams capable of generating certain reactionless blade motions. Teachings of certain embodiments recognize that radial fluid device  600  may also include additional pump sections capable of generating different blade motions. 
       FIG. 10K  shows a cross-section view of pump section  630  along the cross-section line indicated in  FIG. 10B . In operation, pump section  630  is operable to provide a hydraulic flow that results in cyclic blade motions (3/rev) by blades  120   a - 120   d , as shown in  FIG. 10L . In this manner, the motion of blades in  FIG. 10L  resembles the motion of blades in  FIG. 3B . 
     Radial fluid device  600  also includes a corresponding pump section  630 ′. Pump sections  630  and  630 ′ may operate together to generate cyclic blade motions (3/rev) similarly to how pump sections  620  and  620 ′ operate together to generate reactionless blade motions (2/rev). 
     As shown in  FIG. 10K , pump section  630  features pistons  631   a - 631   d , a cam  632 , a cam gear  633 , a drive gear  634 , and a cam adjuster  635 . Each piston  631   a - 631   d  is slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . Similarly, each piston  631   a ′- 631   d ′ of pump section  630 ′ is also slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . In this manner, corresponding pistons  631   a  and  631   a ′ share chamber  604   a , corresponding pistons  631   b  and  631   b ′ share chamber  604   b , corresponding pistons  631   c  and  631   c ′ share chamber  604   c , and corresponding pistons  631   d  and  631   d ′ share chamber  604   d . In addition, pistons  631   a  and  631   a ′, pistons  631   b  and  631   b ′, pistons  631   c  and  631   c ′, and pistons  631   d  and  631   d ′ share chambers with pistons of the other pump sections of radial fluid device  600 . 
     Cam  632  has three lobes. Each piston  631   a - 631   d  completes three sinusoidal stroke motions during one rotation of cylinder block  604 . The ability of pump section  630  to complete three sinusoidal stroke motions during one rotation corresponds to the three blade oscillations per revolution required for certain cyclic blade motions. 
     Cam gear  633 , drive gear  634 , and cam adjuster  635  may, in combination, adjust the position of cam  632 . In some embodiments, the relative positions of cams  632  and  632 ′ may be adjusted independently. For example, cams  632  and  632 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  632  may not necessarily match the distance of rotation of  632 ′. 
       FIG. 10M  shows a cross-section view of pump section  640  along the cross-section line indicated in  FIG. 10B . In operation, pump section  640  is operable to provide a hydraulic flow that results in collective blade motions (4/rev) by blades  120   a - 120   d , as shown in  FIG. 10N . In this manner, the motion of blades in  FIG. 10N  resembles the motion of blades in  FIGS. 4A-4D . 
     Radial fluid device  600  also includes a corresponding pump section  640 ′. Pump sections  640  and  640 ′ may operate together to generate collective blade motions (4/rev) similarly to how pump sections  620  and  620 ′ operate together to generate reactionless blade motions (2/rev). 
     As shown in  FIG. 10M , pump section  640  features pistons  641   a - 641   d , a cam  642 , a cam gear  643 , a drive gear  644 , and a cam adjuster  645 . Each piston  641   a - 641   d  is slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . Similarly, each piston  641   a ′- 641   d ′ of pump section  640 ′ is also slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . In this manner, corresponding pistons  641   a  and  641   a ′ share chamber  604   a , corresponding pistons  641   b  and  641   b ′ share chamber  604   b , corresponding pistons  641   c  and  641   c ′ share chamber  604   c , and corresponding pistons  641   d  and  641   d ′ share chamber  604   d . In addition, pistons  641   a  and  641   a ′, pistons  641   b  and  641   b ′, pistons  641   c  and  641   c ′, and pistons  641   d  and  641   d ′ share chambers with pistons of the other pump sections of radial fluid device  600 . 
     Cam  642  has four lobes. Each piston  641   a - 641   d  completes four sinusoidal stroke motions during one rotation of cylinder block  604 . The ability of pump section  640  to complete four sinusoidal stroke motions during one rotation corresponds to the four blade oscillations per revolution required for certain collective blade motions. 
     Cam gear  643 , drive gear  644 , and cam adjuster  645  may, in combination, adjust the position of cam  642 . In some embodiments, the relative positions of cams  642  and  642 ′ may be adjusted independently. For example, cams  642  and  642 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  642  may not necessarily match the distance of rotation of  642 ′. 
       FIG. 10O  shows a cross-section view of pump section  650  along the cross-section line indicated in  FIG. 10B . In operation, pump section  650  is operable to provide a hydraulic flow that results in cyclic blade motions (5/rev) by blades  120   a - 120   d , as shown in  FIG. 10P . In this manner, the motion of blades in  FIG. 10P  resembles the motion of blades in  FIG. 3C . 
     Radial fluid device  600  also includes a corresponding pump section  650 ′. Pump sections  650  and  650 ′ may operate together to generate cyclic blade motions (5/rev) similarly to how pump sections  620  and  620 ′ operate together to generate reactionless blade motions (2/rev). 
     As shown in  FIG. 10M , pump section  650  features pistons  651   a - 651   d , a cam  652 , a cam gear  653 , a drive gear  654 , and a cam adjuster  655 . Each piston  651   a - 651   d  is slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . Similarly, each piston  651   a ′- 651   d ′ of pump section  650 ′ is also slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . In this manner, corresponding pistons  651   a  and  651   a ′ share chamber  604   a , corresponding pistons  651   b  and  651   b ′ share chamber  604   b , corresponding pistons  651   c  and  651   c ′ share chamber  604   c , and corresponding pistons  651   d  and  651   d ′ share chamber  604   d . In addition, pistons  651   a  and  651   a ′, pistons  651   b  and  651   b ′, pistons  651   c  and  651   c ′, and pistons  651   d  and  651   d ′ share chambers with pistons of the other pump sections of radial fluid device  600 . 
     Cam  652  has five lobes. Each piston  651   a - 651   d  completes five sinusoidal stroke motions during one rotation of cylinder block  604 . The ability of pump section  630  to complete five sinusoidal stroke motions during one rotation corresponds to the five blade oscillations per revolution required for certain cyclic blade motions. 
     Cam gear  653 , drive gear  654 , and cam adjuster  655  may, in combination, adjust the position of cam  652 . In some embodiments, the relative positions of cams  652  and  652 ′ may be adjusted independently. For example, cams  652  and  652 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  652  may not necessarily match the distance of rotation of  652 ′. 
       FIG. 10Q  shows a cross-section view of pump section  660  along the cross-section line indicated in  FIG. 10B . In operation, pump section  660  is operable to provide a hydraulic flow that results in reactionless blade motions (6/rev) by blades  120   a - 120   d , as shown in  FIG. 10R . In this manner, the motion of blades in  FIG. 10R  resembles the motion of blades in  FIG. 5B . 
     Radial fluid device  600  also includes a corresponding pump section  660 ′. Pump sections  660  and  660 ′ may operate together to generate reactionless blade motions (6/rev) similarly to how pump sections  620  and  620 ′ operate together to generate reactionless blade motions (2/rev). 
     As shown in  FIG. 10M , pump section  660  features pistons  661   a - 661   d , a cam  662 , a cam gear  663 , a drive gear  664 , and a cam adjuster  665 . Each piston  661   a - 661   d  is slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . Similarly, each piston  661   a ′- 661   d ′ of pump section  660 ′ is also slidably received within a corresponding cylinder associated with chambers  604   a - 604   d . In this manner, corresponding pistons  661   a  and  661   a ′ share chamber  604   a , corresponding pistons  661   b  and  661   b ′ share chamber  604   b , corresponding pistons  661   c  and  661   c ′ share chamber  604   c , and corresponding pistons  661   d  and  661   d ′ share chamber  604   d . In addition, pistons  661   a  and  661   a ′, pistons  661   b  and  661   b ′, pistons  661   c  and  661   c ′, and pistons  661   d  and  661   d ′ share chambers with pistons of the other pump sections of radial fluid device  600 . 
     Cam  662  has six lobes. Each piston  661   a - 661   d  completes six sinusoidal stroke motions during one rotation of cylinder block  604 . The ability of pump section  660  to complete six sinusoidal stroke motions during one rotation corresponds to the six blade oscillations per revolution required for certain reactionless blade motions. 
     Cam gear  663 , drive gear  664 , and cam adjuster  665  may, in combination, adjust the position of cam  662 . In some embodiments, the relative positions of cams  662  and  662 ′ may be adjusted independently. For example, cams  662  and  662 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  662  may not necessarily match the distance of rotation of  662 ′. 
       FIG. 10S  shows a cross-section view of radial fluid device  600  along the cross-section line indicated in  FIG. 10B . As shown in  FIG. 10S , all pump sections generating frequencies 2/rev through 6/rev are situated about the same cylinder block  604 . In addition, all pump sections share the same chambers  604   a - 604   d . Each chamber  604   a - 604   d  is ported out of radial fluid device  600  through manifold  670 . Manifold  670  may enable fluid communication between each chamber  604   a - 604   d  and a corresponding actuator with rotor blades  120   a - 120   d  (e.g., fluid communication between chamber  604   a  and the actuator associated with rotor blade  120   a ). 
     Teachings of certain embodiments recognize that radial fluid device  600  may provide for IBC in a relatively compact space. For example, a 9000 pound helicopter featuring a four-bladed rotor system operating at 3000 PSI operating pressure may utilize a radial fluid device such as radial fluid device  600  that measures approximately 6 inches by 6 inches by 11 inches (not including the cam adjusters). In this example, pump sections  620  and  620 ′ may be sized to provide 20% of normal cyclic authority while all other frequencies may be sized to provide 10% of normal cyclic authority. 
     In some embodiments, cylinder block  604  may rotate at the same speed as drive shaft  112   b . Teachings of certain embodiments recognize that rotating cylinder block  604  at the same speed as drive shaft  112   b  may allow harmonic outputs from radial fluid device  600  to be synchronized with the rotor blades  120   a - 120   d  rotating about drive shaft  112   b . In the example of  FIG. 10S , an exterior power source rotates shaft  602  at the same speed as drive shaft  112   b , which causes cylinder block  604  to also rotate at the same speed. Teachings of certain embodiments recognize that radial fluid device  600  may be well suited to operate at the same speed as drive shaft  112   b . For example, helicopter hydraulic pumps in other settings may operate at approximately 5000 RPM and industrial radial pumps of similar displacements as radial fluid device  600  may operate at approximately 1500 RPM, whereas as rotor speeds are typically lower than these speeds (e.g., 400 to 500 RPM). 
     In the example of  FIGS. 10A-10S , radial fluid device  600  is configured to provide IBC in a four blade rotor system. Teachings of certain embodiments recognize, however, recognize that the concepts described with regard to radial fluid device  600  may be adapted to support IBC for rotor systems with more or fewer blades (e.g., two blades, three blades, five blades, six blades, seven blades, etc.) by adapting the arrangement of pistons, cams, and porting. For example,  FIGS. 11A-11K  shows a radial fluid device  700  configured to provide IBC in a five blade rotor system. 
       FIG. 11A  shows a top view of radial fluid device  700 . Radial fluid device  700  features multiple stacked radial piston sections rotating together in conjunction with a common cylinder block  6704  (not shown in  FIG. 10A ). In the example of  FIGS. 11A-11J , radial fluid device  700  features stacked radial piston sections  720 - 760  and  720 ′- 760 ′ rotating together with shaft  702  and cylinder block  704 . 
     As will be shown in greater detail below, shaft  702  is coupled to cylinder block  704 . In some embodiments, shaft  702  is removably coupled to cylinder block  704 . For example, different shafts  702  may have different gear splines, and an installer may choose from among different shafts  702  for use with radial fluid device  600 . 
     Cylinder block  704  rotates within radial fluid device  700 . In the example of  FIGS. 11A-11J , the axis of rotation of cylinder block  704  is coaxial with shaft  702 . Bearings may separate cylinder block  704  from the non-rotating body of radial fluid device  700 . 
     Each pump section pair (e.g., sections  720  and  720 ′,  730  and  730 ′, etc.) is dedicated to generating the desired waveform for a specific frequency. In the example of  FIGS. 11A-11J , the pump section pairs are dedicated to generating desired waveforms for 2/rev through 6/rev. In this example, the fundamental cyclic motions (1/rev) are generated by a mechanical swashplate, such as swashplate  116  of  FIG. 2 . 
     Although the pump section pairs in radial fluid device  700  are dedicated to generating desired waveforms for 2/rev through 6/rev, teachings of certain embodiments recognize that other fluid devices may include pump sections dedicated to generating more, fewer, or different desired waveforms. For example, the performance benefits provided by some frequencies may be minimal, and the pump sections generating these frequencies would be eliminated. As one example, a variation of radial fluid device  700  may only feature pump sections dedicated to 2/rev (reactionless) and 4/rev (collective harmonic), with the fundamental cyclic motions (1/rev) generated by a mechanical swashplate. 
     Separate section frequencies from each pump section pair in radial fluid device  700  may be hydraulically summed together to generate a final desired waveform to each actuator, such as described above with regard to  FIG. 9B . In particular, as will be explained in greater detail below, manifold  770  transmits the hydraulically summed fluids from radial fluid device  700  to actuators corresponding to each blade in a rotor system. 
     In this example embodiments, pump sections  730 - 760  and  730 ′- 760 ′ of radial fluid device  700  may operate in a similar manner to pump sections  630 - 660  and  630 ′- 660 ′ of radial fluid device  600 . For example,  FIG. 11B  shows a cross-section view of pump section  730  along the cross-section line indicated in  FIG. 11A . In operation, pump section  730  is operable to provide a hydraulic flow that results in cyclic blade motions (3/rev) by blades  120   a - 120   d , as shown in  FIG. 11C . In this manner, the motion of blades in  FIG. 11C  resembles the motion of blades in  FIG. 3B . 
     Radial fluid device  700  also includes a corresponding pump section  730 ′. Pump sections  730  and  730 ′ may operate together to generate cyclic blade motions (3/rev) similarly to how pump sections  730  and  730 ′ operate together to generate cyclic blade motions (3/rev). 
     As shown in  FIG. 11B , pump section  730  features pistons  731   a - 731   e , a cam  732 , a cam gear  733 , a drive gear  734 , and a cam adjuster  735 . Each piston  731   a - 731   e  is slidably received within a corresponding cylinder associated with chambers  704   a - 704   e . Similarly, each piston  731   a ′- 731   e ′ of pump section  730 ′ is also slidably received within a corresponding cylinder associated with chambers  704   a - 704   e . In this manner, corresponding pistons  731   a  and  731   a ′ share chamber  704   a , corresponding pistons  731   b  and  731   b ′ share chamber  704   b , corresponding pistons  731   c  and  731   c ′ share chamber  704   c , corresponding pistons  731   d  and  731   d ′ share chamber  704   d , and corresponding pistons  731   e  and  731   e ′ share chamber  704   e . In addition, pistons  731   a  and  731   a ′, pistons  731   b  and  731   b ′, pistons  731   c  and  731   c ′, pistons  731   dc  and  731   d ′, and pistons  731   e  and  731   e ′ share chambers with pistons of the other pump sections of radial fluid device  700 . 
     Cam gear  733 , drive gear  734 , and cam adjuster  735  may, in combination, adjust the position of cam  732 . In some embodiments, the relative positions of cams  732  and  732 ′ may be adjusted independently. For example, cams  732  and  732 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  732  may not necessarily match the distance of rotation of  732 ′. 
       FIG. 11D  shows a cross-section view of pump section  740  along the cross-section line indicated in  FIG. 11A . In operation, pump section  740  is operable to provide a hydraulic flow that results in collective blade motions (4/rev) by blades  120   a - 120   d , as shown in  FIG. 11E . In this manner, the motion of blades in  FIG. 11E  resembles the motion of blades in  FIGS. 4A-4D . 
     Radial fluid device  700  also includes a corresponding pump section  740 ′. Pump sections  740  and  740 ′ may operate together to generate collective blade motions (4/rev) similarly to how pump sections  640  and  640 ′ operate together to generate collective blade motions (4/rev). 
     As shown in  FIG. 11D , pump section  740  features pistons  741   a - 741   e , a cam  742 , a cam gear  743 , a drive gear  744 , and a cam adjuster  745 . Each piston  741   a - 741   e  is slidably received within a corresponding cylinder associated with chambers  704   a - 704   e . Similarly, each piston  741   a ′- 741   e ′ of pump section  740 ′ is also slidably received within a corresponding cylinder associated with chambers  704   a - 704   e . In this manner, corresponding pistons  741   a  and  741   a ′ share chamber  704   a , corresponding pistons  741   b  and  741   b ′ share chamber  704   b , corresponding pistons  741   c  and  741   c ′ share chamber  704   c , corresponding pistons  741   d  and  741   d ′ share chamber  704   d , and corresponding pistons  741   e  and  741   e ′ share chamber  704   e . In addition, pistons  741   a  and  741   a ′, pistons  741   b  and  741   b ′, pistons  741   c  and  741   c ′, pistons  741   d  and  741   d ′, and pistons  741   e  and  741   e ′ share chambers with pistons of the other pump sections of radial fluid device  700 . 
     Cam gear  743 , drive gear  744 , and cam adjuster  745  may, in combination, adjust the position of cam  742 . In some embodiments, the relative positions of cams  742  and  742 ′ may be adjusted independently. For example, cams  742  and  742 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  742  may not necessarily match the distance of rotation of  742 ′. 
       FIG. 11F  shows a cross-section view of pump section  750  along the cross-section line indicated in  FIG. 11A . In operation, pump section  750  is operable to provide a hydraulic flow that results in cyclic blade motions (5/rev) by blades  120   a - 120   d , as shown in  FIG. 11G . In this manner, the motion of blades in  FIG. 11G  resembles the motion of blades in  FIG. 3C . 
     Radial fluid device  700  also includes a corresponding pump section  750 ′. Pump sections  750  and  750 ′ may operate together to generate cyclic blade motions (5/rev) similarly to how pump sections  650  and  650 ′ operate together to generate cyclic blade motions (5/rev). 
     As shown in  FIG. 11F , pump section  750  features pistons  751   a - 751   e , a cam  752 , a cam gear  753 , a drive gear  754 , and a cam adjuster  755 . Each piston  751   a - 751   e  is slidably received within a corresponding cylinder associated with chambers  704   a - 704   e . Similarly, each piston  751   a ′- 751   e ′ of pump section  750 ′ is also slidably received within a corresponding cylinder associated with chambers  704   a - 704   e . In this manner, corresponding pistons  751   a  and  751   a ′ share chamber  704   a , corresponding pistons  751   b  and  751   b ′ share chamber  704   b , corresponding pistons  751   c  and  751   c ′ share chamber  704   c , corresponding pistons  751   d  and  751   d ′ share chamber  704   d , and corresponding pistons  751   e  and  751   e ′ share chamber  704   e . In addition, pistons  751   a  and  751   a ′, pistons  751   b  and  751   b ′, pistons  751   c  and  751   c ′, pistons  751   d  and  751   d ′, and pistons  751   e  and  751   e ′ share chambers with pistons of the other pump sections of radial fluid device  700 . 
     Cam gear  753 , drive gear  754 , and cam adjuster  755  may, in combination, adjust the position of cam  752 . In some embodiments, the relative positions of cams  752  and  752 ′ may be adjusted independently. For example, cams  752  and  752 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  752  may not necessarily match the distance of rotation of  752 ′. 
       FIG. 11H  shows a cross-section view of pump section  760  along the cross-section line indicated in  FIG. 11A . In operation, pump section  760  is operable to provide a hydraulic flow that results in reactionless blade motions (6/rev) by blades  120   a - 120   d , as shown in  FIG. 11I . In this manner, the motion of blades in  FIG. 11I  resembles the motion of blades in  FIG. 5B . 
     Radial fluid device  700  also includes a corresponding pump section  760 ′. Pump sections  760  and  760 ′ may operate together to generate reactionless blade motions (6/rev) similarly to how pump sections  660  and  660 ′ operate together to generate reactionless blade motions (6/rev). 
     As shown in  FIG. 11H , pump section  760  features pistons  761   a - 761   e , a cam  762 , a cam gear  763 , a drive gear  764 , and a cam adjuster  765 . Each piston  761   a - 761   e  is slidably received within a corresponding cylinder associated with chambers  704   a - 704   e . Similarly, each piston  761   a ′- 761   e ′ of pump section  760 ′ is also slidably received within a corresponding cylinder associated with chambers  704   a - 704   e . In this manner, corresponding pistons  761   a  and  761   a ′ share chamber  704   a , corresponding pistons  761   b  and  761   b ′ share chamber  704   b , corresponding pistons  761   c  and  761   c ′ share chamber  704   c , corresponding pistons  761   d  and  761   d ′ share chamber  704   d , and corresponding pistons  761   e  and  761   e ′ share chamber  704   e . In addition, pistons  761   a  and  761   a ′, pistons  761   b  and  761   b ′, pistons  761   c  and  761   c ′, pistons  761   d  and  761   d ′, and pistons  761   e  and  761   e ′ share chambers with pistons of the other pump sections of radial fluid device  700 . 
     Cam gear  763 , drive gear  764 , and cam adjuster  765  may, in combination, adjust the position of cam  762 . In some embodiments, the relative positions of cams  762  and  762 ′ may be adjusted independently. For example, cams  762  and  762 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  762  may not necessarily match the distance of rotation of  762 ′. 
     In the examples of  FIGS. 11B-11I , each piston is ported sequentially to a corresponding blade actuator with the 72 degree radial spacing for the five-blade frequencies of 3/rev, 4/rev, 5/rev, and 6/rev. For 2/rev reactionless motion using an elliptical cam, however, teachings of certain embodiments recognize that piston ports may be crossed in pump section  720  for a five-bladed rotor system. In particular, cross-porting may allow fluid device  700  to use pistons with 72 degree spacing to generate blade motions of 144 degree spacing, which may satisfy requirements of 2/rev reactionless motions. 
       FIG. 11J  shows a cross-section view of pump section  720  along the cross-section line indicated in  FIG. 11A . In operation, pump section  720  is operable to provide a hydraulic flow that results in reactionless blade motions (2/rev) by blades  120   a - 120   d , as shown in  FIG. 11K . In this manner, the motion of blades in  FIG. 11K  resembles the motion of blades in  FIG. 5A . 
     Radial fluid device  700  also includes a corresponding pump section  720 ′. Pump sections  720  and  720 ′ may operate together to generate reactionless blade motions (2/rev) similarly to how pump sections  620  and  620 ′ operate together to generate reactionless blade motions (2/rev), except that the piston ports in pump section  720  are crossed for a five-bladed rotor system. 
     As shown in  FIG. 11J , pump section  720  features pistons  721   a - 721   e , a cam  722 , a cam gear  723 , a drive gear  724 , and a cam adjuster  725 . Each piston  721   a - 721   e  is slidably received within a cylinder associated with chambers  704   a - 704   e . However, unlike pump sections  730 - 760 , the correspondence between pistons  721   a - 721   e  and chambers  704   a - 704   e  is crossed for some pistons. In the example of  FIG. 11J , piston  721   a  is slidably received within a cylinder associated with chamber  704   a , piston  721   b  is slidably received within a cylinder associated with chamber  704   c , piston  721   c  is slidably received within a cylinder associated with chamber  704   e , piston  721   d  is slidably received within a cylinder associated with chamber  704   b , and piston  721   e  is slidably received within a cylinder associated with chamber  704   d . Similarly, piston  721   a ′ is slidably received within a cylinder associated with chamber  704   a , piston  721   b ′ is slidably received within a cylinder associated with chamber  704   c , piston  721   c ′ is slidably received within a cylinder associated with chamber  704   e , piston  721   d ′ is slidably received within a cylinder associated with chamber  704   b , and piston  721   e ′ is slidably received within a cylinder associated with chamber  704   d . In this manner, corresponding pistons  721   a  and  721   a ′ share chamber  704   a , corresponding pistons  721   b  and  721   b ′ share chamber  704   c , corresponding pistons  721   c  and  721   c ′ share chamber  704   e , corresponding pistons  721   d  and  721   d ′ share chamber  704   b , and corresponding pistons  721   e  and  721   e ′ share chamber  704   d . In addition, pistons  721   a  and  721   a ′, pistons  721   b  and  721   b ′, pistons  721   c  and  721   c ′, pistons  721   d  and  721   d ′, and pistons  721   e  and  721   e ′ share chambers with pistons of the other pump sections of radial fluid device  700 . 
     Cam gear  723 , drive gear  724 , and cam adjuster  725  may, in combination, adjust the position of cam  722 . In some embodiments, the relative positions of cams  722  and  722 ′ may be adjusted independently. For example, cams  722  and  722 ′ may be rotated in either the same direction or opposite directions, and the distance of rotation of cam  722  may not necessarily match the distance of rotation of  722 ′. 
     Implementing Partial-Authority IBC 
     As stated above, radial fluid device  600  may provide sinusoidal waveform amplitude and synchronization displacement control to multiple actuators for use in a partial-authority IBC system. For example, radial fluid device  600  may include pump section pairs dedicated to generating desired waveforms for 2/rev through 6/rev. In this example, the fundamental cyclic motions (1/rev) are generated by a mechanical swashplate, such as swashplate  116  of  FIG. 2 . As will be explained in greater detail below, teachings of certain embodiments recognize the capability to convert harmonic pressure changes in hydraulic fluid within radial fluid device  600  into movements of blades  120   a - 120   d.    
       FIG. 12A  shows an IBC system  800  according to one example embodiment. IBC system  800  is a partial-authority IBC system that features radial fluid device  600 , a hydraulic control manifold  810 , a hydraulic swivel  820 , four pitch link actuators  830   a - 830   d  (corresponding to rotor blades  120   a - 120   d ), a hydraulic pump  840 , a hydraulic reservoir  850 , and a heat exchanger  860 . 
     As shown in  FIGS. 12A-12E , IBC system  800  may include a variety of fluid lines that provide fluid communication between multiple components. For convenience, some of these fluid lines have been labeled “a,” “b,” “c,” “d,” “e,” or “f.” In these example embodiments, labels “a”-“d” correspond with chambers  604   a - 604   d  and blades  120   a - 120   d . For example, fluid line “a” may represent a fluid line in the path between chamber  604   a  and blade  120   a . Fluid line “e” may refer to system fluid, and fluid line “f” may refer to return fluid, both of which are described in greater detail below. 
     In operation, according to one example embodiment, radial fluid device  600  provides hydraulic fluid to hydraulic control manifold  810 . Hydraulic control manifold directs the fluid through hydraulic swivel  820 , which is configured to transfer the fluid flow from the fixed-frame portion of the rotorcraft to the rotating-frame portion of the rotorcraft. In one example embodiment, hydraulic swivel  820  provides the fluid up along the drive shaft to pitch link actuators  830   a - 830   d , which converts pressure changes in the supplied hydraulic fluid into movements of rotor blades  120   a - 120   d.    
     In addition to providing fluid from radial fluid device  600  to pitch link actuators  830   a - 830   d , IBC system  800  also provides system fluid from hydraulic pump  840  to pitch link actuators  830   a - 830   d . This system fluid represents a constant-pressure fluid supply. Teachings of certain embodiments recognize that the supply fluid may not necessarily stay constant, such as due to leakage or other effects that may change the pressure of the supply fluid. The supply fluid may be provided to pitch link actuators  830   a - 830   d  to provide a balance against the pressures of the hydraulic fluid from radial fluid device  600 . Excess fluid may also be accumulated through hydraulic control manifold  810  and hydraulic swivel  820 , passed through heat exchanger  860 , and stored in hydraulic reservoir  850  before being resupplied to hydraulic pump  840 . 
       FIG. 12B  shows hydraulic control manifold  810  according to one example embodiment. Hydraulic control manifold  810  features valves  812  and control ports  814 . 
     In operation, according to one example embodiment, hydraulic control manifold  810  receives fluid from chambers  604   a - 604   d  of radial fluid device  600  and communicates the fluid to valves  812  and control ports  814 . In this example embodiment, hydraulic control manifold  810  receives the fluid from chambers  604   a - 604   d  through manifold  670 , which rotates with cylinder block  604 . Manifold  670  includes ports for each chamber  604   a - 604   d . In addition, manifold  670  includes seals around each port for chambers  604   a - 604   d . Furthermore, manifold  670  includes return ports to accumulate leaking hydraulic fluid and return the accumulated hydraulic fluid to reservoir  850 . 
     Radial fluid device  600  may not include provisions for independently trimming pitch link actuator stroke position to equalize their lengths and maintain IBC operation about a center stroke. Accordingly, hydraulic control manifold  810  may include valves  812  operable to trim the position of each pitch link actuator  830   a - 830   d  and to compensate for leaking hydraulic fluid. In one example embodiment, valves  812  are three-way direct drive valves. 
     Valves  812  may add supply fluid to fluid lines a-d if the fluid pressure falls below a threshold. Alternatively, valves  812  may remove fluid from fluid lines a-d associated if the fluid pressure rises about a threshold. In one example embodiment, valves  812  receives measurements from position sensors associated with pitch link actuators  830   a - 830   d  and then adds fluid to or removes fluid from the fluid lines a-d based on the received measurements. The measurements from the position sensors may indicate, for example, the amount of fluid that has leaked from various fluid lines within IBC system  800 . As another example, the measurements from the position sensors may indicate whether fluid line pressure should be adjusted to trim the position of each pitch link actuators  830   a - 830   d.    
     In one example embodiment, valves  812  may adjust for drift and leakage in IBC system  800 , but valves  812  may not drive high-frequency changes in system pressure. Rather, high-frequency changes may be implemented by radial fluid device  600 . Teachings of certain embodiments recognize that only using valves for low-frequency changes in system pressure may reduce the necessary size of the valves and increase longevity of the valves. 
     Control ports  814  communicate fluid between hydraulic control manifold  810  and hydraulic swivel  820 . Teachings of certain embodiments recognize that control ports  814  may also terminate fluid flow in the event of some system failures. In the example of  FIG. 12B , each control port  814  is equipped with a solenoid bypass valve. In the event of a partial-authority system failure requiring isolation from the conventional flight control system, for example, IBC system  800  may remove power to the solenoid bypass valves associated with each control port  814 . In response, control ports  814  cut off pressure to their pressure relief/bypass valves, causing them to redirect system fluid to the hydraulic fluid return lines f that lead back to reservoir  850 . Redirecting system fluid prevents the system fluid from reaching the pitch link actuators  830   a - 830   d , which as will be explained in greater detail below, causes the pitch link actuators  830   a - 830   d  to lock at their center stroke position. 
       FIG. 12C  shows hydraulic swivel  820  according to one example embodiment. Hydraulic swivel  820  includes a rotating portion  822  and a stationary portion  824 . Rotating portion  822  includes ports  822   a - 822   d  that communicates fluid between pitch link actuators  830   a - 830   d  and non-rotating portion  824 . Rotating portion  822  also includes port  822   e , which communicates system fluid between pitch link actuators  830   a - 830   d  and non-rotating portion  824 . Rotating portion  822  includes port  822   f , which communicates return fluid between pitch link actuators  830   a - 830   d  and non-rotating portion  824 . 
     Rotating portion also includes rotary seals  823  between each port  822   a - 822   f . Teachings of certain embodiments recognize that providing both port  822   f  for return fluid and seals  823  may extend seal life and reduce or eliminate issues associated with nuisance leakage. 
     Rotating portion also includes wiring for communicating signals from pitch link actuators  830   a - 830   d  to the non-rotating portions of IBC system  800 . In one example embodiment, the wiring includes wires for each position sensor associated with the pitch link actuators  830   a - 830   d  plus three common wires providing excitation power. 
     Stationary portion  824  includes fluid lines  824   a - 824   d  that communicates fluid between ports  822   a - 822   d  and fluid lines a-d. Stationary portion  824  also includes fluid line  824   e , which communicates fluid between port  822   e  and fluid line e. Stationary portion  824  includes fluid line  824   f , which communicates fluid between port  822   f  and fluid line f. 
       FIG. 12D  shows pitch link actuator  830   a  according to one example embodiment. Pitch link actuator  830   a  is operable to change the position of blade  120   a  during operation of rotorcraft  100 . Similarly, pitch link actuators  830   b - 830   d  are operable change the positions of blades  120   b - 120   d , respectively. 
     In one example embodiment, pitch link actuator  830   a  may be coupled between hub  114  and swashplate  116  such that pitch link actuator  830   a  may change the distance between hub  114  and swashplate  116 . In this example, pitch link actuator  830   a  is coupled between hub  114  and swashplate  116  but not necessarily coupled to hub  114  and/or swashplate  116 . For example, pitch link actuator  830   a  may be coupled to other components in mechanical communication with hub  114  and/or swashplate  116 . In addition, pitch link actuator  830   a  may only change one measurement of a distance between hub  114  and swashplate  116 . For example, pitch link actuator  830   a  may change the distance between hub  114  and swashplate  116  proximate to pitch link actuator  830   a , whereas the distance between hub  114  and swashplate  116  proximate to pitch link actuator  830   b  may remain the same. 
     In the example of  FIG. 12D , pitch link actuator  830   a  includes a linear hydraulic actuator that includes a piston  832   a  that separates a control chamber  831   a  from a system chamber  833   a . Control chamber  831   a  receives fluid from line a. System chamber  833   a  receives controlled system fluid from line e. In operation, piston  832   a  moves in response to a pressure difference between fluid in control chamber  831   a  and fluid in system chamber  833   a.    
     In the example of  FIG. 12D , piston  832   a  is unbalanced. The piston area on the side of control chamber  831   a  is greater than the piston area on the side of system chamber  833   a . In this example, system fluid in system chamber  833   a  may prevent hydraulic cavitation from occurring by creating a constant-force, hydraulic-spring effect on piston  832   a.    
     Teachings of certain embodiments recognize that pitch link actuators  830   a - 830   d  may conserve hydraulic power during operation. For example, during higher-harmonic cyclic and reactionless motions, the total net flow used by pitch link actuators  830   a - 830   d  may be near zero due to the summed opposing sinusoidal flow demands canceling. For example, during reactionless motions, a downstroke by piston  832   a  may be offset by an upstroke by piston  832   b.    
     On the other hand, higher-harmonic collective motions may require significantly more fluid to move all blades sinusoidally in unison. In this example, pitch link actuators  830   a - 830   d  may push a large volume of fluid back into the remaining components of IBC system  800  or pull a large volume of fluid out of the remaining components of IBC system  800 . Teachings of certain embodiments recognize, however, that hydraulic accumulator may capture and recover this hydraulic energy on the rotor-frame side of IBC system  800 . In the example of  FIG. 12A , the hydraulic accumulator is connected to the system fluid line e. 
     In the example of  FIG. 12D , pitch link actuator  830   a  also includes a position sensor  834   a . Position sensor  834   a  may measure the displacement distance of piston  832   a . One example of position sensor  834   a  may include a linear variable differential transformer. Position sensor  834   a  may be used as part of a feedback control system. For example, the cams of radial fluid device  600  may be programmed so as to produce an expected displacement distance of piston  832   a . If position sensor  834   a  measures a displacement distance different from the expected displacement distance, one or more problems could be the cause. For example, IBC system  800  could be leaking fluid, which may change the pressure difference between fluid in chambers  831   a  and  833   a , which would change the displacement distance of piston  832   a . In response, IBC system  800  may take one or more corrective actions. As one example, the cams of radial fluid device  600  may be repositioned to achieve the expected displacement distance. As another example, valves  812  may add fluid to or remove fluid from the fluid lines (e.g., fluid lines a-e) to adjust the fluid pressures in pitch link actuator  830   a . In some embodiments, adjusting the cams of radial fluid device  600  may be more appropriate for making large changes in fluid pressure, whereas adjusting valves  812  may be more appropriate for smaller changes or trimming of fluid pressure. 
     In the example of  FIG. 12D , pitch link actuator  830   a  also includes a stroke lock  836   a . Stroke lock  836   a  may prevent piston  832   a  from moving in the event of system failure. As shown in  FIG. 12D , stroke lock  836   a  separates the system fluid from a spring. The spring provides an opposing force to the pressure from the system fluid. If, for example, the pressure from the system fluid is reduced or eliminated, force from the spring pushes the spring lock  836   a  towards piston  832   a  and prevents piston  832   a  from moving, as shown in  FIG. 12E . Such a scenario might occur, for example, if control port  814   e  prevents system fluid from reaching pitch link actuator  830   a.    
     Full-Authority IBC 
     The example radial fluid device  600 , described above, generates displacement changes to drive higher-harmonic motions (e.g., 2/rev through 6/rev) but does not necessarily generate fundamental cyclic motions (e.g., 1/rev). In some embodiments, it may be possible for radial fluid device  600  to provide fundamental cyclic motions by providing a single-lobed pump section similar to pump section  620 . In some circumstances, however, fundamental cyclic motions must be implemented more quickly than higher-harmonic motions because the pilot may steer the direction of the rotorcraft through fundamental cyclic motions. In these circumstances, the radial piston approach used by radial fluid device  600  to implement higher-harmonic motions may be too slow for fundamental cyclic motions. Thus, in some embodiments, the higher-harmonic approach described with regard to radial fluid device  600  may not be suitable for fundamental cyclic motions. 
     In some embodiments, it may also be possible to implement fundamental cyclic motions using the valves  812  of IBC system  800 . For example, valves  812  may be capable of changing fluid line pressures so as to implement fundamental cyclic motions on pitch link actuators  830   a - 830   d . As explained above, however, valves  812  may be more suitable for implementing small pressure changes, whereas fundamental cyclic motions may require large pressure changes in the fluid lines. Increasing the valve flow gain in valves  812  to implement these large pressure changes may increase the risk of hard-over failures. In addition, the power consumed and heat generated by valves  812  in this scenario may raise additional issues. 
     Teachings of certain embodiments recognize the capability to generate fundamental cyclic actuator motions quickly while still protecting against hard-over failures, conserving hydraulic power, and minimizing heat generation. Teachings of certain embodiments also recognize the capability to eliminate the mechanical rotor swashplate from a rotor system by hydraulically generating the fundamental cyclic motions. 
       FIGS. 13A-M  show a radial fluid device  900  according to one example embodiment.  FIG. 13A  shows a side view of radial fluid device  900 , and  FIG. 13B  shows a top view of radial fluid device  900 . Radial fluid device  900  features multiple stacked radial piston sections rotating together in conjunction with a common cylinder block  904  (not shown in  FIGS. 13A and 13B ). 
     In the example of  FIGS. 13A-13M , radial fluid device  900  features a fundamental cyclic pump  910  as well as stacked radial piston sections  920 - 960  and  920 ′- 960 ′ rotating together with shaft  902 , cylinder block  904 , and manifold  970 . Embodiments of stacked radial piston sections  920 - 960  and  920 ′- 960 ′ may resemble and operate similarly to stacked radial piston sections  620 - 660  and  620 ′- 660 ′. 
     As will be shown in greater detail below, shaft  902  is coupled to cylinder block  904 . In some embodiments, shaft  902  is removably coupled to cylinder block  904 . For example, different shafts  902  may have different gear splines, and an installer may choose from among different shafts  902  for use with radial fluid device  600 . 
     Cylinder block  904  rotates within radial fluid device  900 . In the example of  FIGS. 10A-10M , the axis of rotation of cylinder block  904  is coaxial with shaft  902 . Bearings may separate cylinder block  904  from the non-rotating body of radial fluid device  900 . 
     Fundamental cyclic pump  910  and each pump section pair (e.g., sections  920  and  920 ′,  930  and  930 ′, etc.) are dedicated to generating the desired waveform for a specific frequency. In the example of  FIGS. 13A-13M , fundamental cyclic pump  910  is dedicated to generating desired waveforms for fundamental cyclic motions (1/rev), and the pump section pairs are dedicated to generating desired waveforms for 2/rev through 6/rev. 
     Although the pump section pairs in radial fluid device  900  are dedicated to generating desired waveforms for 2/rev through 6/rev, teachings of certain embodiments recognize that other fluid devices may include pump sections dedicated to generating more, fewer, or different desired waveforms. For example, the performance benefits provided by some frequencies may be minimal, and the pump sections generating these frequencies would be eliminated. As one example, a variation of radial fluid device  900  may only feature pump sections dedicated to 2/rev (reactionless) and 4/rev (collective harmonic), with the fundamental cyclic motions (1/rev) generated by fundamental cyclic pump  910 . 
     Separate section frequencies from fundamental cyclic pump  910  and each pump section pair in radial fluid device  900  may be hydraulically summed together to generate a final desired waveform to each actuator, such as described above with regard to  FIG. 9B . In particular, as will be explained in greater detail below, manifold  970  transmits the hydraulically summed fluids from radial fluid device  900  to actuators corresponding to each blade in a rotor system. 
       FIG. 13C  shows a cross-section view of fundamental cyclic pump  910  along the cross-section line indicated in  FIG. 13B . Fundamental cyclic pump  910  features four pistons  911   a - 911   d . Each piston  911   a - 911   d  is slidably received within a corresponding cylinder associated with chambers  904   a - 904   d . Each chamber  904   a - 904   d  represents a plurality of cylinders within cylinder block  904  that are in fluid communication. Each chamber  904   a - 904   d  may have an independent outlet port that exits radial fluid device  900  to control a different IBC actuator. 
     Fundamental cyclic pump  910  also features cam  912 . During operation, pistons  911   a - 911   d  stroke inwards and outwards depending on the distance between cam  912  and the axis of rotation of cylinder block  904 . Each piston  911   a - 911   d  reciprocates towards and away from the axis of rotation of cylinder block  604 . Each reciprocation towards and away from the axis of rotation thus includes two strokes: a down stroke and an up stroke. 
     In the example of  FIG. 13C , cam  912  is a circular cam and has one lobe. The number of lobes indicates how many sinusoidal stroke motions a piston completes during one full rotation of cylinder block  904 . For example, each piston  911   a - 911   d  completes one sinusoidal stroke motion during one rotation of cylinder block  904 . The ability of fundamental cyclic pump  910  to complete one sinusoidal stroke motion during one rotation corresponds to the one blade oscillation per revolution required for fundamental cyclic motions. 
     Repositioning cam  912  may change the displacement distance for each piston  911   a - 911   d . In the example of  FIG. 13C , positioning pistons  913 ,  914 , and  915  may reposition cam  912 . In this example, positioning piston  913  is coupled to cam  912 , and positioning pistons  914  and  915  are coupled to a crank associated with cam  912 . 
     Cam  912  may be repositioned by varying the pressure in at least one of the cylinders associated with positioning pistons  913 ,  914 , and  915 . Positioning pistons  913 ,  914 , and  915  may allow cam  912  to be translated in two perpendicular axis, similar to swashplate lateral and longitudinal motions. The housing surrounding cam  912  may be dimensioned to provide stops limiting lateral and longitudinal cyclic travel. 
     In the example of  FIG. 13C , fluid in the cylinder associated with positioning piston  913  is maintained at a relatively constant system pressure, and fluid in the cylinders associated with positioning pistons  914  and  915  may be varied to reposition cam  912 . Positioning piston  913  may operate as a hydraulic spring to oppose the forces exerted by positioning pistons  914  and  915 . 
     In the example of  FIG. 13C , fundamental cyclic pump  910  includes position sensors  916  and  917 . Position sensors  916  and  917  may measure the displacement distance of positioning pistons  914  and  915 , respectively. One example of position sensor may include a linear variable differential transformer. 
     Valves  918  and  919  may provide fluid to the cylinders associated with positioning pistons  913 ,  914 , and/or  915 . In some embodiments, valves  918  and  919  may change the size of their orifices to vary the pressure of fluid in the cylinders associated with positioning pistons  914  and  95 . In one example embodiment, valves  918  and  919  are three-way direct drive valves. In some embodiments, valves  918  and  919  may be single coil or dual coil three-way valves. 
     In some circumstances, if cylinder block  904  is rotating (such as at rotor speed) and cam  912  is positioned concentric with the input shaft axis, pistons  911   a - 911   d  do not stroke. This scenario results in no fluid displacement control changes being sent to the IBC actuators for fundamental cyclic motions. 
     Translating cam  912  away from this concentric position, however, may result in fluid displacement control changes being sent to the IBC actuators for fundamental cyclic motions.  FIG. 13D , for example, shows how retracting positioning pistons  914  and  915  may reposition cam  912 . The example of  FIG. 13D  may correspond to a full-forward longitudinal cyclic position in some scenarios. Moving cam  912  as shown in  FIG. 13D  results in fundamental cyclic motions by each blade  120   a - 120   d , as shown in  FIG. 13E . 
     As another example,  FIG. 13F  shows how extending positioning pistons  914  and  915  may reposition cam  912 . The example of  FIG. 13F  may correspond to a full-aft cyclic position in some scenarios. Moving cam  912  as shown in  FIG. 13F  results in fundamental cyclic motions by each blade  120   a - 120   d , as shown in  FIG. 13G . Comparing the examples of  FIGS. 13E and 13G , blade  120   a  in  FIG. 13E  is 180 degrees out of phase with blade  120   a  in  FIG. 13G . 
     Fundamental cyclic pump  910  may also implement lateral cyclic motions as well as longitudinal cyclic motions.  FIG. 13H , for example, shows how retracting positioning piston  914  and extending  915  may reposition cam  912 . The example of  FIG. 13H  may correspond to a full-left lateral cyclic position in some scenarios. Moving cam  912  as shown in  FIG. 13H  results in fundamental cyclic motions by each blade  120   a - 120   d , as shown in  FIG. 13I . 
     As another example,  FIG. 13J  shows how extending positioning piston  914  and retracting positioning piston  915  may reposition cam  912 . The example of  FIG. 13J  may correspond to a full-right longitudinal position in some scenarios. Moving cam  912  as shown in  FIG. 13J  results in fundamental cyclic motions by each blade  120   a - 120   d , as shown in  FIG. 13K . Comparing the examples of  FIGS. 13I and 13K , blade  120   a  in  FIG. 13I  is 180 degrees out of phase with blade  120   a  in  FIG. 13K . Comparing the examples of  FIGS. 13E and 13I , blade  120   a  in  FIG. 13E  is 90 degrees out of phase with blade  120   a  in  FIG. 13I . 
     In the example of  FIGS. 13A-13K , fundamental cyclic pump  910  is configured to provide fundamental cyclic motions in a four blade rotor system. Teachings of certain embodiments recognize, however, recognize that the concepts described with regard to fundamental cyclic pump  910  may be adapted to support IBC for rotor systems with more or fewer blades (e.g., two blades, three blades, five blades, six blades, seven blades, etc.). 
     For example,  FIG. 13L  shows a fundamental cyclic pump  910 ′ configured to provide IBC in a five-blade rotor system. In this example, fundamental cyclic pump  910 ′ features five pistons  911   a ′- 911   e ′ corresponding to each blade in the five-blade rotor system. Fundamental cyclic pump  910 ′ also features a cam  912 ′, positioning pistons  913 ′- 915 ′, position sensors  916 ′ and  917 ′, and valves  918 ′ and  919 ′ that may operate in a similar manner to corresponding components in fundamental cyclic pump  910 . 
       FIG. 13M  shows a cross-section view of radial fluid device  900  along the cross-section line indicated in  FIG. 13B . As shown in  FIG. 13M , fundamental cyclic pump  910  and all pump sections generating frequencies 2/rev through 6/rev are situated about the same cylinder block  904 . In addition, fundamental cyclic pump  910  and all pump sections share the same chambers  904   a - 904   d . Each chamber  904   a - 904   d  is ported out of radial fluid device  900  through manifold  970 . Manifold  970  may enable fluid communication between each chamber  904   a - 904   d  and a corresponding actuator with rotor blades  120   a - 120   d  (e.g., fluid communication between chamber  904   a  and the actuator associated with rotor blade  120   a ). 
     In some embodiments, cylinder block  904  may rotate at the same speed as drive shaft  112   b . Teachings of certain embodiments recognize that rotating cylinder block  904  at the same speed as drive shaft  112   b  may allow harmonic outputs from radial fluid device  900  to be synchronized with the rotor blades  120   a - 120   d  rotating about drive shaft  112   b . In the example of  FIG. 13M , an exterior power source rotates shaft  902  at the same speed as drive shaft  112   b , which causes cylinder block  904  to also rotate at the same speed. 
     Implementing Full-Authority IBC 
     As stated above, radial fluid device  900  may provide sinusoidal waveform amplitude and synchronization displacement control to multiple actuators for use in a full-authority IBC system. For example, radial fluid device  900  may include a fundamental cyclic pump and pump section pairs dedicated to generating desired waveforms for 1/rev through 6/rev. In this example, the mechanical swashplate, such as swashplate  116  of  FIG. 2 , may be eliminated of the rotor system. As will be explained in greater detail below, teachings of certain embodiments recognize the capability to convert harmonic pressure changes in hydraulic fluid within radial fluid device  900  into movements of blades  120   a - 120   d.    
       FIG. 14A  shows an IBC system  1000  according to one example embodiment. IBC system  1000  is a full-authority IBC system that features radial fluid device  900 , a hydraulic control manifold  1100 , a hydraulic swivel  1200 , four blade actuators  1300   a - 1300   d  (corresponding to rotor blades  120   a - 120   d ), a hydraulic pump  1400 , a hydraulic reservoir  1500 , and a heat exchanger  1600 . 
     As shown in  FIGS. 14A-14C  and  15 A- 15 E, IBC system  1000  may include a variety of fluid lines that provide fluid communication between multiple components. For convenience, some of these fluid lines have been labeled “a,” “b,” “c,” “d,” “e,” or “f.” In these example embodiments, labels “a”-“d” correspond with chambers  904   a - 904   d  and blades  120   a - 120   d . For example, fluid line “a” may represent a fluid line in the path between chamber  904   a  and blade  120   a . Fluid line “e” may refer to system fluid, and fluid line “f” may refer to return fluid, both of which are described in greater detail below. 
     In operation, according to one example embodiment, radial fluid device  900  provides hydraulic fluid to hydraulic control manifold  1100 . Hydraulic control manifold directs the fluid through hydraulic swivel  1200 , which is configured to transfer the fluid flow from the fixed-frame portion of the rotorcraft to the rotating-frame portion of the rotorcraft. In one example embodiment, hydraulic swivel  1200  provides the fluid up along the drive shaft to blade actuators  1300   a - 1300   d , which converts pressure changes in the supplied hydraulic fluid into movements of rotor blades  120   a - 120   d.    
     In addition to providing fluid from radial fluid device  900  to blade actuators  1300   a - 1300   d , IBC system  1000  also provides system fluid from hydraulic pump  1400  to blade actuators  1300   a - 1300   d . This system fluid represents a constant-pressure fluid supply. Teachings of certain embodiments recognize that the supply fluid may not necessarily stay constant, such as due to leakage or other effects that may change the pressure of the supply fluid. The supply fluid may be provided to blade actuators  1300   a - 1300   d  to provide a balance against the pressures of the hydraulic fluid from radial fluid device  900 . Excess fluid may also be accumulated through hydraulic control manifold  1100  and hydraulic swivel  1200 , passed through heat exchanger  1600 , and stored in hydraulic reservoir  1500  before being resupplied to hydraulic pump  1400 . 
       FIG. 14B  shows hydraulic control manifold  1100  according to one example embodiment. Hydraulic control manifold  1100  features valves  1112  and control ports  1114 . 
     In operation, according to one example embodiment, hydraulic control manifold  1100  receives fluid from chambers  904   a - 904   d  of radial fluid device  900  and communicates the fluid to valves  1112  and control ports  1114 . In this example embodiment, hydraulic control manifold  1100  receives the fluid from chambers  904   a - 904   d  through manifold  970 , which rotates with cylinder block  904 . Manifold  970  includes ports for each chamber  904   a - 904   d . In addition, manifold  970  includes seals around each port for chambers  904   a - 904   d . Furthermore, manifold  970  includes return ports to accumulate leaking hydraulic fluid and return the accumulated hydraulic fluid to reservoir  1500 . 
     Radial fluid device  900  may not include provisions for independently trimming blade actuator stroke position to equalize their lengths and maintain IBC operation about a center stroke. Accordingly, hydraulic control manifold  1100  may include valves  1112  operable to trim the position of each blade actuator  1300   a - 1300   d  and to compensate for leaking hydraulic fluid. In one example embodiment, valves  1112  are three-way direct drive valves. 
     Valves  1112  may add supply fluid to fluid lines a-d if the fluid pressure falls below a threshold. Alternatively, valves  1112  may remove fluid from fluid lines a-d if the fluid pressure rises about a threshold. In one example embodiment, valves  1112  receives measurements from position sensors associated with blade actuators  1300   a - 1300   d  and then adds fluid to or removes fluid from fluid lines a-d based on the received measurements. The measurements from the position sensors may indicate, for example, the amount of fluid that has leaked from various fluid lines within IBC system  1000 . As another example, the measurements from the position sensors may indicate whether fluid line pressure should be adjusted to trim the position of each blade actuators  1300   a - 1300   d.    
     In one example embodiment, valves  1112  may adjust for drift and leakage in IBC system  1000 , but valves  1112  may not drive high-frequency changes in system pressure. Rather, high-frequency changes may be implemented by radial fluid device  900 . Teachings of certain embodiments recognize that only using valves for low-frequency changes in system pressure may reduce the necessary size of the valves and increase longevity of the valves. 
     Unlike partial-authority IBC system  800 , full-authority IBC system  1000  includes two valves  1112  for each rotor blade (e.g., two valves  1112   a  for rotor blade  120   a ). Teachings of certain embodiments recognize that multiple valves  1112  may be capable of providing fundamental collective input. In some embodiments, additional valves  1112  may add or remove fluid from the volume trapped between radial fluid device  900  and blade actuators  1300 . Because the high-frequency flow providing fundamental cyclic and IBC is controlled by radial fluid device  900 , valves  900  may be relatively low gain, thus minimizing the impact of a valve hard-over failure. 
     Even with a relatively low gain, a valve hard-over failure on a full-authority IBC actuator could create rotor instability if not bypassed quickly. Teachings of certain embodiments recognize that redundant systems may be appropriate for full-authority IBC systems because of the risks associated with removing the mechanical swashplate from the rotor system. Accordingly, the example full-authority IBC system  1000  includes redundant valves  1112  for each rotor blade. By incorporating two valves per IBC actuator, hard-over failures may be quickly bypassed by commanding the second valve in the opposite direction. 
     Control ports  1114  communicate fluid between hydraulic control manifold  1100  and hydraulic swivel  1200 . Teachings of certain embodiments recognize that control ports  1114  may also terminate fluid flow in the event of some system failures. In the example of  FIG. 14B , each control port  1114  is equipped with a solenoid bypass valve. In the event of a full-authority system failure requiring isolation from the conventional flight control system, for example, IBC system  1000  may remove power to the solenoid bypass valves associated with each control port  1114 . In response, control ports  1114  cut off pressure to their pressure relief/bypass valves, causing them to redirect system fluid to the hydraulic fluid return lines f that lead back to reservoir  1500 . 
     As will be explained in greater detail below with regard to  FIGS. 17A and 17B , two or more radial fluid devices  900  may operate in parallel. In this scenario, damaging control force fighting between IBC actuators may occur if the displacement control outputs are not correctly synchronized. Should pressure synchronization fail or a blade actuator be inadvertently bottomed on a stationary vane, for example, damaging control pressures and actuator loads can be induced. 
     Teachings of certain embodiments recognize the ability to provide position sensors for synchronizing operations between multiple radial fluid devices  900 . In some embodiments, position sensors may be provided on positioning pistons  913 - 915  which are discussed above with regards to  FIGS. 13A-13K ) and/or the higher-harmonic cams of each radial fluid device  900 . In these embodiments, however, the position sensors may not have the appropriate resolution to control force fights in a rigid system. Accordingly, teachings of certain embodiments recognize the capability to monitor control port pressure for each IBC actuator to control force fights between IBC actuators. In one example embodiment, each control port  1114  includes a position sensor  1116 . Position sensors  1116  may measure the displacement distance of the control valve associated with each control port  1114 . One example of position sensor may include a linear variable differential transformer. 
     In some embodiments, each control port  1114  may respond to changes in control port pressure by displacing its control valve proportionally to the pressure change. Each position sensor  1116  may measure the amount of displacement of each control valve. If control port pressure exceeds an allowable threshold, valves  1114  may port excess pressure to the return fluid system. Valves  1114  may isolate the system following a failure by applying electric power to the solenoids associated with valves  1114  and causing all control ports  1114  to port fluid to the return fluid system, effectively bypassing the entire system. 
       FIG. 14C  shows hydraulic swivel  1200  according to one example embodiment. Hydraulic swivel  1200  includes a rotating portion  1222  and a stationary portion  1224 . Rotating portion  1222  includes ports  1222   a - 1222   d  that communicates fluid between blade actuators  1300   a - 1300   d  and non-rotating portion  1224 . Rotating portion  1222  also includes port  1222   e , which communicates system fluid between blade actuators  1300   a - 1300   d  and non-rotating portion  1224 . Rotating portion  1222  includes port  1222   f , which communicates return fluid between blade actuators  1300   a - 1300   d  and non-rotating portion  1224 . 
     Rotating portion also includes rotary seals  1223  between each port  1222   a - 1222   f . Teachings of certain embodiments recognize that providing both port  1222   f  for return fluid and seals  1223  may extend seal life and reduce or eliminate issues associated with nuisance leakage. 
     Rotating portion also includes wiring for communicating signals from blade actuators  1300   a - 1300   d  to the non-rotating portions of IBC system  1000 . In one example embodiment, the wiring includes two wires for each position sensor associated with the blade actuators  1300   a - 1300   d  plus three common wires for each blade actuator providing excitation power. 
     Stationary portion  1224  includes fluid lines  1224   a - 1224   d  that communicates fluid between ports  1222   a - 1222   d  and fluid lines a-d. Stationary portion  1224  also includes fluid line  1224   e , which communicates fluid between port  1222   e  and fluid line e. Stationary portion  1224  includes fluid line  1224   f , which communicates fluid between port  1222   f  and fluid line f. 
       FIGS. 15A-15F  show blade actuator  1300   a  according to one example embodiment.  FIG. 15A  shows a top view of blade actuator  1300   a , and  FIG. 15B  shows a side view of blade actuator  1300   a . Blade actuator  1300   a  is operable to change the position of blade  120   a  during operation of rotorcraft  100 . Similarly, blade actuators  1300   b - 1300   d  are operable change the positions of blades  120   b - 120   d , respectively. 
     In the example of  FIGS. 15A-15F , blade actuator  1300   a  is a hydraulic rotary vane actuator. In some embodiments, a hydraulic rotary vane actuator may be powered at the root of each rotor blade. Teachings of certain embodiments recognize that vane actuators may have reduced leakage due to their dependency on a rotary seal, as compared to an equivalent-power linear hydraulic actuator with a sliding seal. In addition, a hydraulic vane actuator may also have a higher relative stiffness. 
     As shown in  FIGS. 15A and 15B , blade actuator  1300   a  may feature a shaft  1302  and a rotary seal  1304  disposed within one or more openings of a housing  1310 . As will be shown in greater detail below, shaft  1302  is coupled to a vane within housing  1310 . In some embodiments, different shafts  1302  may have different gear splines, and an installer may choose from among different shafts  1302  for use with different rotor blades. Rotary seal  1304  is positioned about shaft  1302  and separates the interior of housing  1310  from the exterior of housing  1310 . 
     In some embodiments, rotary seal  1304  is an elastomeric membrane seal. Teachings of certain embodiments recognize that an elastomeric membrane seal may be suitable in situations where shaft  1302  is limited to a certain range of motion. For example, an elastomeric seal may be coupled to shaft  1302  and may stretch as shaft  1302  rotates so long as shaft  1302  does not stretch the elastomeric seal past its elasticity limit. In some embodiments, angular travel of shaft  1302  may be limited to plus/minus 18 degrees of rotation. In these embodiments, the elastomeric membrane seal may stretch to absorb the plus/minus 18 degrees of rotation. In addition, as will be explained below with regard to  FIG. 15D , the elastomeric membrane seal may not be exposed to high pressures (e.g., return fluid pressure of approximately 100 pounds per square inch), thus limiting the axial hydraulic forces pushing against the seal. 
     In the example of  FIGS. 15A and 15B , housing  1310  includes multiple pieces connected together using bolts  1312 . Housing  1310  may also include connection points  1314  for securing blade actuator  1300   a  to the rotorcraft. 
       FIG. 15C  shows a cross-section view of blade actuator  1300   a  along the cross-section line indicated in  FIG. 15B . As seen in  FIG. 15C , blade actuator  1300   a  features stationary vanes  1320  and vane impeller  1330 . In this example, stationary vanes  1320  define three chambers, although other embodiments may define more or fewer chambers. Vane impeller  1330  includes three vane surfaces, each vane surface extending into a corresponding chamber between stationary vanes  1320 . Vane impeller  1330  is coupled to shaft  1302  such that rotation of vane impeller  1330  results in rotation of shaft  1302 . 
     Each chamber defined by stationary vanes  1320  includes two openings for communicating fluid into and out of the chamber. Within each chamber, the vane surface of vane impeller  1330  separates the two openings such that fluid from both openings may accumulate and pressurize on both sides of the vane surface. In operation, a difference in fluid pressure on opposite sides of a vane surface may cause the vane surface (and thus vane impeller  1330  as a whole) to rotate. 
     In the example of  FIG. 15C , each chamber includes variable-pressure control fluid  1322  on one side of a vane surface. In two chambers, return fluid  1324  is accumulated and ported out of blade actuator  1300 . In these two chambers, the pressure of the control fluid  1322  is expected to be greater than the pressure of the return fluid  1324 . In the third chamber, approximately-constant system fluid  1326  is provided opposite the variable-pressure control fluid  1324 . In this third chamber, the system fluid  1326  applies a constant source of hydraulic pressure to oppose pressure from the control fluid  1322  and create a hydraulic spring effect. In this example, the first two chambers, in combination, have twice the effective vane area as the third chamber, doubling the ability of the variable-pressure control fluid  1322  to move vane impeller  1330 . 
     In some circumstances, blade actuator  1300   a  may be subject to leakage. For example, leakage across rectangular vane surfaces in a rotary vane may be higher than in piston actuators in a cylinder. Accordingly, teachings of certain embodiments recognize that leaked fluid should be ported returned to the system rather than vented to the atmosphere. Teachings of certain embodiments also recognize the ability to use this leaked fluid to provide a continuous lubrication to support bearings in blade actuator  1300   a  and create low pressure areas behind rotary seals  1304 . 
       FIG. 15D  shows a cross-section view of blade actuator  1300   a  along the cross-section line indicated in  FIG. 15A . As shown in  FIG. 15D , support bearings  1340  may support rotation of shaft  1302  within blade actuator  1300   a . In this example, leaking fluid may lubricate support bearings  1340  and then be ported to the return fluid  1324 . In addition, teachings of certain embodiments recognize that providing return fluid  1324  behind rotary seal  1304  may prevent rotary seal  1304  from being subject to high hydraulic forces. 
       FIGS. 15E and 15F  show cross-section views of blade actuator  1300   a  along the cross-section line indicated in  FIG. 15B  during operation of blade actuator  1300   a . In the example of  FIG. 15E , hydraulic pressure of control fluid  1322  is greater than hydraulic pressure of system fluid  1326 , which forces vane impeller  1330  to rotate counter-clockwise by 18 degrees. In the example of  FIG. 15E , hydraulic pressure of control fluid  1322  is less than hydraulic pressure of system fluid  1326 , which forces vane impeller  1330  to rotate clockwise by 18 degrees. 
     In some embodiments, multiple blade actuators  1300  may be coupled together to operate in series. Teachings of certain embodiments recognize that providing multiple blade actuators  1300  per blade may provide redundancy and reduce catastrophic failure in the event a blade actuator fails. For example,  FIG. 16A  shows two blade actuators  1300   a  coupled together in series, and  FIG. 16B  shows three blade actuators  1300   a  coupled together in series. In each of these examples, coupling assemblies  1350  couple together shafts  1302   a  from different blade actuators  1300   a.    
       FIGS. 17A and 17B  show redundant IBC systems having multiple blade actuators  1300  coupled together in series. In  FIG. 17A , IBC system  2000  features three blade actuators  1300  coupled together in series for each rotary blade (e.g., rotor blade  120   a  is coupled to three blade actuators  1300   a ). IBC system  2000  also features three flight control computers (flight control computers  2100 ,  2200 , and  2300 ). Each flight control computer is in communication with a corresponding radial fluid device  900 . Each flight control computer/radial fluid device combination is operable to control one of the three blade actuators  1300  for each rotor blade, as shown in  FIG. 17A . 
     In operation, according to one example embodiment, flight control computers  2100 ,  2200 , and  2300  receive cyclic and collective instructions from input device  2050 . One example of input device  2050  may include a control stick accessible by a pilot. Each flight control computer  2100 ,  2200 , and  2300  programs a radial fluid device  900  to implement the cyclic and collective instructions. For example, each flight control computer may send signals indicating how the fundamental cyclic motion pistons and the higher-harmonic cams of each radial fluid device  900  should be positioned. 
     Each flight control computer  2100 ,  2200 , and  2300  may also receive measurements indicating whether blade actuators  1300  are fighting against one another. For example, each flight control computer may measure shaft rotation speeds, fluid pressures, and/or piston/valve displacements. In this example, a difference in these measurements between flight control computers  2100 ,  2200 , and  2300  may indicating that two or more blade actuators  1300  may be fighting each other. Thus, flight control computers  2100 ,  2200 , and  2300  may communicate with each other using cross-channel data links to share synchronization information. As one example, if two blade actuators  1300  are mechanically fighting, the two corresponding flight control computers may share information indicating that at least one of the flight control computers should adjust fluid line pressure within its portion of the IBC system. 
     In  FIG. 17B , IBC system  3000  features two blade actuators  1300  coupled together in series for each rotary blade (e.g., rotor blade  120   a  is coupled to two blade actuators  1300   a ). IBC system  3000  also features four flight control computers (flight control computers  3100 ,  3200 ,  3300 , and  3400 ). Unlike IBC system  2000 , two flight control computers are in communication with one corresponding radial fluid device  900 . In this example, each radial fluid device  900  is in communication with redundant flight control computers, allowing each radial fluid device  900  to continue powering blade actuators  1300  even if one flight control computer is disabled. 
     Teachings of certain embodiments recognize that IBC systems may include any number of blade actuators, flight control computers, and radial fluid devices. The numbering and configuration may depend, for example, on the safety requirements for a particular rotorcraft. 
     Modifications, additions, or omissions may be made to the systems and apparatuses described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. 
     Although several embodiments have been illustrated and described in detail, it will be recognized that substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the appended claims. 
     To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke paragraph 6 of 35 U.S.C. §112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.