Abstract:
A control surface drive system having a plurality of actuator assemblies are coupled to first and second supply lines and to a return line. The first and second supply lines are connected to a source of hydraulic fluid. At least one of the actuator assemblies has a hydraulic actuator movably connectable to an aircraft control surface. A flow control assembly is connected to the return line and to at least one of the first and second supply lines. A bypass line is in fluid communication with the first and second supply lines and positioned to recycle the hydraulic fluid from one of the first and second supply lines back into the other one of the first and second supply lines when the hydraulic actuator moves toward the first position. A computer controller operatively interconnects the plurality of actuator assemblies and the flow control assembly. It is emphasized that this abstract is provided to comply with the rules requiring an abstract. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims 37 C.F.R. §1.72(b)).

Description:
[0001]    This application is a divisional of U.S. patent application Ser. No. 12/409,460 filed Mar. 23, 2009, which is a divisional of U.S. patent application Ser. No. 10/959,629 filed Oct. 5, 2004, now U.S. Pat. No. 7,506,842. U.S. patent application Ser. No. 10/959,629 was a divisional of U.S. patent application Ser. No. 10/720,786, filed on Nov. 24, 2003, now U.S. Pat. No. 6,799,739, which is incorporated herein by reference to its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to drive systems for aircraft control surfaces, and more particularly to hydraulic drive systems for moving and controlling the aircraft control surfaces. 
       BACKGROUND 
       [0003]    All aircraft include movable control surfaces for directional control in flight. Such control surfaces can include ailerons for roll control, elevators for pitch control, and rudders for yaw control. In addition, most conventional jet transport aircraft typically include leading edge slats and trailing edge flaps on the wings. These devices can be used to generate high lift during takeoff and landing when the aircraft is traveling at relatively low air speeds. 
         [0004]    Federal aviation regulations (FARs) impose airworthiness standards on lift and drag devices for transport category aircraft. For example, FAR §25.697 requires that such devices (e.g., trailing edge flaps) must maintain selected positions (e.g., extended positions) without further attention by the pilot. This requirement applies at all times during flight. Thus, lift and drag devices must be able to maintain extended positions even in the unlikely event of a general failure of the aircraft&#39;s power system. 
         [0005]    Trailing edge flaps (“flaps”) on jet transport aircraft typically deploy aft of the wing and downward to increase wing area and camber. The flaps are typically powered by a drive system having a drive shaft that extends longitudinally inside the wing and is coupled to a central power drive unit. The drive shaft for each wing is connected by a system of gears to a series of ball screws and linear actuators distributed along the length of the wing adjacent to the flaps. Rotation of the drive shaft in a first direction causes the ball screws to rotate in a corresponding direction, thereby extending the flaps on the wing. Similarly, counter rotation of the drive shaft causes the ball screws to counter-rotate, thereby retracting the flaps. Flap drive systems are mechanically interconnected to provide wing-to-wing symmetry of the trailing edge flaps on both wings. Such wing-to-wing symmetry, or equivalent, is required by the current FARs. These conventional drive systems, however, can be very heavy and costly. 
         [0006]    Hydraulic drive systems with linear actuators have also been used for flap drive systems. For safety purposes, these hydraulic flap drive systems are typically designed to include built-in backup or redundant systems. Accordingly, the hydraulic flap drive systems are powered by two hydraulic systems and utilize twice as many linear actuators as are required to handle the system loads. The resulting hydraulic flap drive systems tend to weigh more and cost more than the drive systems using the drive shafts and gears. 
       SUMMARY 
       [0007]    A hydraulic actuator is controlled to move a control surface of an aircraft. The actuator moves the control surface towards a first position in response to fluid flow through a first supply line, and it moves the control surface towards a second position in response to fluid flow through a second supply line. The method comprises moving a blocking member to an open position to allow hydraulic fluid to move through the first and second supply lines; controlling fluid flow through the first and second supply lines to move the control surface between the first and second positions; moving the blocking member to a closed position to block hydraulic fluid from moving to and from the hydraulic actuator; and directing hydraulic fluid from the second supply line into the first supply line through a bypass line when the blocking member is closed to recycle at least a portion of the hydraulic fluid back into the first supply line. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a partially schematic, top isometric view of an aircraft having a control surface drive system configured in accordance with an embodiment of the invention. 
           [0009]      FIG. 2  is a schematic diagram of the control surface drive system of  FIG. 1 , which includes a plurality of actuator assemblies. 
           [0010]      FIG. 3  is an enlarged schematic view of one of the actuator assemblies of  FIG. 2 . 
           [0011]      FIG. 4  is a schematic view of another embodiment having a plurality of control surface drive systems shown coupled to a hydraulic fluid source and a common flight control computer. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The following disclosure describes drive systems for use with aircraft trailing edge flaps and other aircraft control surfaces. Certain specific details are set forth in the following description and in  FIGS. 1-4  to provide a thorough understanding of various embodiments of the invention. Other details describing the well-known structures and systems often associated with aircraft, and more specifically with aircraft control surface drive systems, are not set forth in the following description to avoid unnecessarily obscuring the description of the various embodiments of the invention. 
         [0013]    Many of the details, dimensions, and other specifications shown in the Figures are merely illustrative of particular embodiments of the invention. Accordingly, other embodiments can have other details, dimensions, and specifications without departing from the spirit or scope of the present invention. In addition, other embodiments of the invention may be practiced without several of the details described below. 
         [0014]      FIG. 1  is a partially schematic, top isometric view of an aircraft  100  having a control surface drive system  102  configured in accordance with an embodiment of the invention. In one aspect of this embodiment, the aircraft  100  includes a fuselage  104  and wings  106  (shown as first and second wings  106   a  and  106   b ) fixedly attached to the fuselage. Each wing  106  can include a number of movable control surfaces for controlling the aircraft  100  during flight. These control surfaces can include trailing edge flaps  108 , leading edge slats  110 , and ailerons  112 . The trailing edge flaps  108 , which are shown as an inboard flap  108   a  and an outboard flap  108   b , are used for generating increased lift during takeoff and landing of the aircraft  100 . 
         [0015]    In operation, the control surface drive system  102  can move the flaps  108  between a retracted position (shown by solid lines) and an extended position (shown by dashed lines). In the extended position, aerodynamic forces on the flaps  108  may be substantial. The control surface drive system  102 , in accordance with Federal Aviation Regulations, should be able to hold the flaps  108  in the extended position against the aerodynamic forces without any input by the pilot of the aircraft  100 , even in the event of a general power failure. Accordingly, the control surface drive system  102  can be configured to lock the flaps  108  in the extended position, the retracted position, or any intermediate position therebetween against the aerodynamic forces, as discussed in greater detail below. Although the foregoing discussion refers to the flaps  108  for purposes of illustration, the discussion is equally applicable to driving other control surfaces that function in a similar manner and are generally subject to the same functional requirements imposed on the flaps, such as the slats  110 . 
         [0016]      FIG. 2  is a schematic view of the control surface drive system  102  of  FIG. 1  configured in accordance with an embodiment of the invention. In one aspect of this embodiment, the control surface drive system  102  (“system  102 ”) includes a plurality of actuator assemblies  120  connected to the flaps  108 . In the illustrated embodiment, two actuator assemblies  120  are connected to the inboard flap  108   a  and two actuator assemblies are connected to the outboard flap  108   b  of each wing  106  ( FIG. 1 ). The actuator assemblies  120  are extendible and retractable to drive the flaps  108  between the extended and retracted positions in direct response to instructions from the pilot. 
         [0017]    The actuator assemblies  120  each include a hydraulic actuator  122  that has a head end  124  and a rod end  126 . The hydraulic actuator  122  is configured to receive high pressure hydraulic fluid in the head end  124  or rod end  126  to move the respective actuator assembly  120  between extended and retracted positions. The high-pressure hydraulic fluid is received from the aircraft&#39;s primary hydraulic system  128 , which also controls a variety of other hydraulically driven systems in the aircraft  100  ( FIG. 1 ). The primary hydraulic system  128  has a hydraulic fluid source  130  and a primary electrical power source  132 . 
         [0018]    The system  102  has two hydraulic supply lines  134  that connect to each actuator assembly  120 . The first supply line is referred to as an extend line  136  because it directs hydraulic fluid to the actuator assemblies  120  for movement of the flap  108  toward the extended position. The extend line  136  is coupled at one end to the hydraulic fluid source  130  and coupled at the other end to the head end  124  of each hydraulic actuator  122 . The second supply line is referred to as a retract line  138  because it directs hydraulic fluid to the actuator assemblies  120  for movement of the flap  108  toward the retracted position. The retract line  138  is coupled at one end to the hydraulic fluid source  130  and coupled at the other end to the rod end  126  of each hydraulic actuator  122 . 
         [0019]    In the illustrated embodiment, the system  102  is configured so each hydraulic actuator  122  is normally always pressurized toward the retracted position. A check valve  140  is connected to the retract line  138  to prevent backflow of hydraulic fluid to the hydraulic fluid source  130 . Another check valve  142  is connected to the extend line  136  to avoid backflow of the hydraulic fluid toward the hydraulic fluid source  130 . 
         [0020]    The system  102  also has a hydraulic fluid return line  144  coupled to each actuator assembly  122 . In the illustrated embodiment, the return line  144  is coupled at one end to the head end  124  of each hydraulic actuator  122  and is coupled at the other end to a system return  146  in the aircraft&#39;s primary hydraulic system  128 . The system return  146  is configured to return the hydraulic fluid back to the hydraulic fluid source  130 . Accordingly, when the hydraulic actuators  122  are moved toward the retracted position, hydraulic fluid is added to each actuator&#39;s rod end  126  and removed from the head end  124 . The removed hydraulic fluid is directed into the return line  144  to be recycled through the system return  146  back to the hydraulic fluid source  130 . 
         [0021]    In the illustrated embodiment, flow of the hydraulic fluid through the system  102  is controlled at least in part by a control valve module  148 . The control valve module  148  is connected to the extend line  136  and to the return line  144  to control the flow of hydraulic fluid to and from the head end  124  of each hydraulic actuator  122 . The control valve module  148  has a directional control valve  150  connected to the extend line  136  and the return line  144 . The directional control valve  150  is adjustable between a plurality of positions to direct hydraulic fluid flow through either the extend line  136  or the return line  144 . The directional control valve  150  is also movable to a neutral position that prevents the hydraulic fluid from flowing through both of the extend and return lines  136  and  144 , respectively. Accordingly, when the directional control valve  150  is in this neutral position, the hydraulic actuators  122  and the flaps  108  are securely held in a fixed position and resist the air loads exerted on the flaps. 
         [0022]    The control valve module  148  of the illustrated embodiment also includes a pair of solenoids  152  coupled to the extend and return lines  136  and  144 , respectively, and operatively connected to the directional control valve  150 . The solenoids  152  can be activated to facilitate the flow of hydraulic fluid through the directional control valve  150  for the desired movement of the hydraulic actuators  122  toward either the extended or retracted positions. While the illustrated embodiment utilizes a directional control valve  150  and solenoids  152  in the control valve module  148 , other valving configurations can be used in alternate embodiments to control the flow of the hydraulic fluid to and from the actuator assemblies  120 . 
         [0023]      FIG. 3  is an enlarged schematic view of one of the actuator assemblies  120  in the system  102  of  FIG. 2 . The illustrated actuator assembly  120  is representative of all of the actuator assemblies in the system  102  of the embodiment described above. The actuator assembly  120  has a valve mechanism  154  connected to the extend line  136 . The valve mechanism  154  is adjustable to control the flow of hydraulic fluid to and from the head end  124  of the hydraulic actuator  122 , thereby controlling the position and movement of the hydraulic actuator. The valve mechanism  154  is configured to modulate the flow to the head end  124  of each hydraulic actuator  122  to ensure that the entire system  102  ( FIG. 2 ) and the associated flaps  108  remain synchronized with the slowest-moving hydraulic actuator. Because the air loads on the actuator assemblies  120  during operation of the aircraft  100  ( FIG. 1 ) always tend to retract the hydraulic actuators  122 , the valve mechanisms  154  provide additional control of the flow of the hydraulic fluid against the aerodynamic forces exerted on the flaps  108 . For example, the valve mechanisms provide a “meter in” flow control for loads that work against the hydraulic actuators  122  and the associated flap  108 . During flap extension the valve mechanisms  154  also provide a “meter out” flow control for loads that aid the retracting movement of the hydraulic actuators  122  and the associated flap  108  during flap retraction. 
         [0024]    While the illustrated embodiment has the valve mechanism  154  connected to the extend line  136 , the valve mechanism can be connected to the retract line  138  in another embodiment. In addition, the valve mechanism  154  of the illustrated embodiment is a servovalve, although other valve mechanisms can be used in alternate embodiments to provide an actuator-position control device within each actuator assembly  120 . 
         [0025]    The actuator assembly  120  also includes a blocking valve  156  connected to the retract line  138  and to the extend line  136 . The blocking valve  156  is movable between an open position and a closed position. In the open position, the blocking valve  156  allows the hydraulic fluid to flow substantially freely through the retract line  138  and the extend line  136  during normal movement of the hydraulic actuator  122 . When a certain condition exists in the system  102 , such as during a loss of hydraulic pressure, the blocking valve  156  automatically moves to the closed position. In the closed position, the blocking valve  156  blocks all hydraulic fluid flow to and from the hydraulic actuator  122  through both of the extend and retract lines  136  and  138 , respectively. When the blocking valve  156  is in the closed position, the hydraulic actuator  122  is locked in place, thereby locking the associated flap  108  in a fixed position until the blocking valve is reopened. 
         [0026]    In the illustrated embodiment, the blocking valve  156  is a pressure-sensitive shutoff valve that is spring-biased toward the closed position. If hydraulic pressure drops below a threshold level in the retract line  138 , a spring  158  will automatically move the blocking valve  156  to the closed position, thereby locking the hydraulic actuator  122  in a fixed position. Accordingly, the actuator assemblies  120  with the blocking valves  156  provide a safety feature that will hold the associated flap  108  in a last-commanded position in the event of a system malfunction, even in response to the air loads on the flap. Although the illustrated embodiment utilizes a pressure-sensitive shutoff valve for the blocking valve  156 , alternate embodiments can use other valving configurations, such as a solenoid-controlled valve or other valving mechanism. 
         [0027]    The actuator assembly  120  also includes a position sensor  160  connected to the hydraulic actuator  122 . The position sensor  160  is configured to monitor the position and movement of each actuator  122 , which allows for indirect monitoring of the position and movement of each flap  108  to which each hydraulic actuator is connected. The position sensor  160  of the illustrated embodiment is a linear transducer, although other sensor devices can be used in alternate embodiments. In other embodiments, a position sensor can be applied to a flap  108 , which allows for indirect monitoring of the position and movement of the hydraulic actuator between the extended and retracted positions. 
         [0028]    In the illustrated embodiment, each position sensor  160  is operatively connected to a flight control computer  162  on the aircraft  100  ( FIG. 1 ). The flight control computer  162  monitors and compares the position and movement of each actuator assembly  120  and its associated flap  108  to ensure there is simultaneous and uniform movement of the flaps in response to a pilot&#39;s command. The flight control computer  162  is also operatively connected to the valve mechanism  154  in each actuator assembly  120 . The flight control computer  162  effectively modulates all of the valve mechanisms  154  to control synchronized movement of the actuator assemblies  120  and flaps  108 . 
         [0029]    Referring back to  FIG. 2 , the flight control computer  162  is also operatively connected to the control valve module  148 , and is configured to monitor and adjust the directional control valve  150  and the solenoids  152 . Accordingly, the flight control computer  162  controls the flow of hydraulic fluid to and from the head end  124  of the hydraulic actuators  122 , thereby controlling movement of the flaps  108  between the extended and retracted positions. When the actuator assemblies  120  have moved the flaps  108  to the correct position in response to a pilot&#39;s command, the flight control computer  162  can switch the directional control valve  150  to the neutral position and lock the actuator assemblies  120  in the commanded position. In addition, if the flight control computer  162  determines that the movement of the actuator assemblies  120  is not uniform or is abnormal, the flight control computer can activate the control valve module  148  to lock the actuator assemblies and flaps  108  in a fixed or last-commanded position. Therefore, the control valve module  148 , when in the neutral position, provides a backup blocking system to lock the actuator assemblies  120  and the flaps  108  in a fixed position, either in response to normal flight commands or in response to an abnormal condition. 
         [0030]    Referring again to  FIG. 2 , when the actuator assemblies  120  and flaps  108  are to be moved toward the retracted position, the control valve module  148  receives a signal from the flight control computer  162  to activate the retract solenoid  152   a . The retract solenoid  152   a  moves the directional control valve  150  to the retract position. High-pressure hydraulic fluid is directed through the retract line  138  and is added into the rod end  126  of each hydraulic actuator  122 . In the illustrated embodiment, actuator retraction is effected by simply coupling the head end  124  of the hydraulic actuator  122  to the system return  146  via the return line  144 . Accordingly, the head end  124  of each hydraulic actuator  122  is substantially unpressurized. The high-pressure hydraulic fluid at the rod end  126  of the hydraulic actuator  122  will cause the actuator assembly  120  to move toward the retracted position. As the hydraulic fluid is added into the rod end  126 , hydraulic fluid is forced out of the head end  124 . As the hydraulic fluid flows from the head end  124 , the directional control valve  150  directs the hydraulic fluid flow into the return line  144  and back toward the system return  146 . 
         [0031]    When the flaps  108  are to remain stationary in a position commanded by the pilot, the directional control valve  150  in the control valve module  148  remains in the neutral position. If an unintended positional change occurs to any of the actuator assemblies  120 , the flight control computer  162  activates the control surface drive system  102  to lock the hydraulic actuators  122  and the flaps  108  in the last-commanded position. The flight control computer  162  then provides a signal to the pilot annunciating the status of the flap configuration. Under current Federal Aviation Regulations, flap panel skews due to air loads are considered acceptable if annunciated to the pilot. 
         [0032]    To extend the actuator assemblies  120  toward the extended position, the flight control computer  162  activates the extend solenoid  152   b  and the directional control valve  150  is moved to the extend position. Movement of the hydraulic actuator  122  against an opposing load toward the extended position is caused by the pressure applied to the differential area between the head end  124  and the rod end  126  in the actuator  122 . Accordingly, high-pressure hydraulic fluid is ported from the extend line  136  into the head end  124  of each hydraulic actuator  122 . The flight control computer modulates actuator extension by controlling the pressurized hydraulic fluid to the head end  124  of the hydraulic actuator  122 . As the hydraulic fluid moves into the head end  124  and the actuators  122  move toward the extended position, hydraulic fluid is forced out of the rod end  126  back along the retract line  138 . 
         [0033]    In the illustrated embodiment, a bypass line  164  is coupled at one end to the retract line  138  and at the other end to the extend line  136 . The bypass line  164  is connected to a one-way check valve  166  that allows the hydraulic fluid to flow through the bypass line in only one direction, namely toward the extend line  136 . In the illustrated embodiment, the check valve  166  is a pressure-relief check valve, although other valve mechanisms can be used in alternate embodiments. 
         [0034]    When the hydraulic actuators  122  are moved toward the extended position, the hydraulic fluid from the rod end  126  moves back along the retract line  138  and into the bypass line  164 . The check valve  140  in the retract line  138  is positioned to allow the backflow of hydraulic fluid into the bypass line  164 , but the check valve prevents further backflow through the retract line toward the hydraulic fluid source  130 . In the illustrated embodiment, the check valve  142  is also provided in the supply lines  134  at a position upstream of the bypass line  164  to avoid backflow or back driving of hydraulic fluid to the hydraulic source  130 . 
         [0035]    The bypass line  164  directs the hydraulic fluid from the retract line  138  back into the extend line  136 , which carries the hydraulic fluid toward the head end  124  of the hydraulic actuator  122 . Accordingly, the bypass line  164  provides a bypass or “run around” circuit that allows local recycling of the hydraulic fluid volume for use by the actuator assemblies  120 . The system  102  does not provide a significant demand on the aircraft&#39;s primary hydraulic system  128 , and the primary hydraulic system only needs to provide enough hydraulic fluid to make up the difference between the volume in the head end  124  and the volume in the rod end  126  of the actuator assemblies  120 . Therefore, the system  102  requires a minimum amount of hydraulic fluid from the hydraulic fluid source  130 , which provides for a significant weight and cost savings for the aircraft  100  ( FIG. 1 ). 
         [0036]    The control surface drive system  102  illustrated in  FIG. 2  also includes a dedicated alternate mode power system  170  that can be used to temporarily operate the actuator assemblies  120  in the event that the primary hydraulic source  130  or power source  132  is unavailable. Accordingly, the power system  170  provides a dedicated backup power system within each control surface drive system  102  to drive the actuator assemblies  120  and the flaps  108 . In the illustrated embodiment, the power system  170  includes a hydraulic line  172  that defines a backup circuit connected to the retract line  138 . 
         [0037]    A pump  174  is connected to the hydraulic line  172  and is operatively connected to the flight control computer  162 . The pump  174  can be activated to pressurize and pump hydraulic fluid for operation of all actuator assemblies  120  in the system  102 . In the illustrated embodiment, the pump  174  is a self-contained, AC motor pump, although other dedicated pump mechanisms could be used in alternate embodiments. 
         [0038]    The alternate mode power system  170  also includes a check valve  176  connected to the hydraulic line  172  on one side of the pump  174 , and a valve assembly  178  connected to the hydraulic line  172  on the other side of the pump  174 . In the illustrated embodiment, the valve assembly  178  is a motor-operated shutoff valve operatively connected to the flight control computer  162 . The valve assembly  178  is movable between a normal, blocked mode and an activated mode. In the normal, blocked mode, the power system  170  is not activated and the valve assembly  178  blocks the hydraulic fluid from flowing through the hydraulic line  172 . In the activated mode, the valve assembly  178  is switched to allow the pump  174  to pump hydraulic fluid through the hydraulic line  172  to operate the actuator assemblies  120 . 
         [0039]    The power system  170  of the illustrated embodiment provides enough hydraulic power so the actuator assemblies  120  can be moved to position and retain the flaps  108  in a suitable landing configuration. The power system  170  can be configured in another embodiment to allow for full flap extension. In other alternate embodiments, the dedicated power system  170  can be configured for less than full movement of the actuator assemblies  120 , provided that the power system meets the requirements of pilot procedures or federal aviation regulations. 
         [0040]      FIG. 4  is a schematic view of an arrangement in accordance with another embodiment having a plurality of the control surface drive systems  102 . In this alternate embodiment, the system  102  has a left-side control surface drive system  102   a  (“left system  102   a ”) and a right-side control surface drive system  102   b  (“right system  102   b ”). Each of the left and right systems  102   a  and  102   b  is operatively connected to the aircraft&#39;s primary hydraulic system  128 . The left system  102   a  is connected to the aircraft&#39;s left wing  106   a  ( FIG. 1 ) and has four actuator assemblies  120 . Two of the actuator assemblies  120  are connected to the left inboard flap  108   a , and the other two actuator assemblies are connected to the left outboard flap  108   b.    
         [0041]    The right system  102   b  is connected to the aircraft&#39;s right wing  106   b  ( FIG. 1 ) and also has four actuator assemblies  120 , two connected to the right inboard flap  108   a  and two connected to the right outboard flap  108   b . The configuration and operation of each of the left and right systems  102   a  and  102   b  is substantially identical to the system  102  described above with reference to  FIG. 2 . In the illustrated embodiment, the left system  102   a  includes a control module  148  to service the left wing, and the right system  102   b  includes a different control module that services the right wing. In another embodiment, the left and right systems  102   a  and  102   b  can be connected to a single control module  148  that services both wings. In the illustrated embodiment, each of the left and right systems  102   a  and  102   b  provides a bypass circuit with the bypass line  164  and check valve  166 , as discussed above. Each of the left and right systems  102   a  and  102   b  also have a dedicated alternate-mode power system  170  for operation of the actuator assemblies  120  and the flaps  108  during operation of the aircraft  100  ( FIG. 1 ). 
         [0042]    Each of the left and right systems  102   a  and  102   b  are operatively connected to the single flight control computer  162 . The flight control computer  162  simultaneously monitors and controls both of the left and right systems  102   a  and  102   b . Accordingly, the flight control computer  162  ensures simultaneous and consistent operation of the flaps  108  on both left and right wings  106   a  and  106   b  during normal operation. The flight control computer  162  also provides the equivalent of a mechanical interconnection between the left and right systems  102   a  and  102   b , respectively, to provide wing-to-wing symmetry of the flaps  108  during operation of the aircraft  100  ( FIG. 1 ). 
         [0043]    In another embodiment, a single control surface drive system  102  substantially identical to the system described above can have eight actuator assemblies  120 , four of which are on each wing  106 . This single system  102  with the eight actuator assemblies  120  could be configured to simultaneously control the flaps on both wings  106 . In other alternate embodiments, a separate dedicated control surface drive system  102  could be provided to control each flap or other selected control surfaces. Accordingly, an aircraft  100  ( FIG. 1 ) with four flaps would have four separate control surface drive systems  102 . In this alternate embodiment, each control surface drive system  102  is operatively connected to, and controlled by, the flight control computer  158 . 
         [0044]    From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. As an example, one embodiment provides an actuator control system having actuator assemblies  120  with pneumatic actuators or other fluid-driven actuators coupled to a pressurized fluid system to drive and control the fluid-driven actuators. Accordingly, the invention is not limited except as by the appended claims.