RUDDER HYDRAULIC ACTUATION.pdf

GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL RUDDER HYDRAULIC ACTUATION — SYSTEM DESCRIPTION 1. General A. Description The rudder hydraulic actuators are powered by 3000 psi from the left and right hydraulic systems during normal operation. Hydraulic system pressure is ported from the rudder manifold...

GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL RUDDER HYDRAULIC ACTUATION — SYSTEM DESCRIPTION 1. General A. Description The rudder hydraulic actuators are powered by 3000 psi from the left and right hydraulic systems during normal operation. Hydraulic system pressure is ported from the rudder manifolds to the two rudder actuators to drive the rudder to its commanded location. See Figure 1. Hydraulic actuation is commanded by the Flight Control Computers (FCCs) or Backup Flight Control Unit (BFCU). The FCCs provide position signals to the Remote Electronic Units (REUs) and Motor Control Electronics (MCE) using Bidirectional ARINC 429 (BD429) digital data buses. The REUs process the signals to drive hydraulic manifold valves that initiate actuator movement to control the flight surface movement. If both FCCs fail, the BFCU provides position signals to the REUs using standard ARINC 429 (A429) digital data buses. The following three types of manifolds drive the actuators: EB HA EHSA The following two types of actuator systems are used: EHSA system - Upper actuator EBHA system - Lower actuator The EHSA system includes a hydraulic cylinder / piston assembly and a separate manifold. The EBHA system includes a hydraulic EHSA type part, mated with a local MCE controlled Integrated Motor Pump Assembly (IMPA) that drives the hydraulic cylinder / piston in electric backup state. The backup state is used if the aircraft hydraulic system fails and the adjacent EHSA is unavailable. NOTE: Hydraulic manifolds for EHSA type and EBHA type spoiler actuators are not interchangeable. The same REU fits all locations. The applicable REU software is selected by installation strapping for each location. The actuation system may operate in one of the following six states, depending on the possible system failures that may occur: TYPE OF CONTROL REU STATE DESCRIPTION Dual hydraulic EBHA active hydraulic state and EHSA active, both controlled by their REU; force fight alleviation in EBHA REU using EHSA pressure sensors. EHSA only EHSA in hydraulic state controlled by its REU, EBHA (inop) in damped bypass state. EBHA only EBHA active in hydraulic state controlled by its REU, EHSA (inop) in damped bypass state. EBHA electrical backup EBHA in electric state controlled by its REU / MCE, EHSA (inop) in damped bypass state. 27-23-00 Page 1 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL TYPE OF CONTROL STATE DESCRIPTION MCE MCE backup position control EBHA active in electric state is controlled by the MCE backup controller function, EHSA is in damped bypass state. No control Damped bypass EBHA and EHSA in damped bypass state (no REU / MCE control). 2. Component Location COMPONENT ATA QTY PER A/C LOCATION Rudder EHSA actuator 27-23-01 1 Vertical stabilizer rear beam Rudder EBHA actuator 27-23-03 1 Vertical stabilizer rear beam Rudder EHSA manifold 27-23-05 1 Vertical stabilizer rear beam Rudder EB manifold 27-23-07 1 Vertical stabilizer rear beam Rudder HA manifold 27-23-09 1 Vertical stabilizer rear beam 3. Component Details A. Rudder EHSA Actuator The upper rudder actuator is an EHSA. The rudder EHSA hydraulic actuator is a flange-mounted actuator that employs a toggle link to ensure freedom of motion while providing the hinge movement required to deflect the rudder during yaw functions. The actuator accepts hydraulic inputs from the adjacent rudder EHSA manifold and provides positional feedback to the rudder EHSA REU via a single channel main ram LVDT to close the control loop during all states of operation. The EHSA is controlled electrically by its REU and uses hydraulic power to move the control surface. The REU receives electrical power from a single circuit breaker on the right essential dc bus. The actuator receives hydraulic power from the aircraft left system. The REU is mounted directly to the EHSA manifold and the actuator is separate. The EHSA system consists of the following three separate components: REU Hydraulic actuator Hydraulic manifold The hydraulic actuator contains a single channel LVDT that provides position sensing information to the REU. There are no other electrical components in the actuator. The rudder EHSA has the following two states of operation: Active hydraulic (normal) Damped bypass (1) Active Hydraulic State In the EHSA active hydraulic (normal) state, the Mode Select Valve (MSV) is energized and allows hydraulic flow from the Electro-Hydraulic Servo Valve (EHSV) to the actuator. In the active hydraulic state, the REU energizes a normally open three-way MSV Solenoid Operated 27-23-00 Page 2 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL Valve (SOV) that moves the MSV into the active position. The active position connects the cylinder ports to the EHSV and disconnects the cylinder ports from the Variable Damping Orifice (VDO). In EHSA active hydraulic state, the REU uses the internal main ram LVDT signal to determine the main ram position. It then calculates the difference between the commanded ram position (from the FCC or the BFCU) and the actual ram position to generate an error signal. The REU applies an electrical command current to the first stage coils in the EHSV that is proportional to the error signal. The EHSV command current proportionally increases the flow orifice metering area between of the following: The supply pressure and one cylinder port The return pressure and the opposing cylinder port The polarity of the EHSV command current causes the ram to move in a direction that reduces the positional error signal until the error signal reaches zero. The polarity of the EHSV command current in effect determines which cylinder ports (extend or retract) get connected to supply and return pressures. (2) Damped Bypass State The EHSA system is placed in damped bypass state when the MSV is de-energized. The state is entered when there has been a failure in the REU or the aircraft hydraulic system. A damping force is placed on the actuator since it is no longer being actively controlled, but still needs to provide sufficient damping for flutter suppression. The associated EBHA actuator, is also actively controlling the same surface and will overcome the damping force of the EHSA actuator. In the EHSA damped bypass state, the actuator may be commanded to shut down through a solenoid valve driving the MSV. The REU de-energizes the three-way MSV SOV that moves the MSV so that the cylinder ports are disconnected from the EHSV and interconnected through the VDO. Upon loss of electrical or hydraulic power, the actuator MSV automatically reverts to the damped state. B. Rudder EBHA Actuator The lower rudder actuator is an EBHA. The rudder EBHA hydraulic actuator is a flange-mounted actuator. It employs a toggle link to ensure freedom of motion while providing the hinge movement required to deflect the rudder during yaw functions. The actuator accepts hydraulic inputs from the adjacent rudder HA manifold. The actuator provides positional feedback to the rudder REU and MCE using a dual-channel main ram LVDT to close the control loop during all states of operation. The EBHA system includes a hydraulic cylinder / piston assembly and two hydraulic manifolds (HA and EB). A separate hydraulic actuator is located between the EB and HA manifolds. The hydraulic actuator contains a two channel LVDT that provides position sensing information. One channel is connected to the REU and the other to the MCE. There are no other electrical components in the actuator. The EBHA system consists of the following five separate components: REU MCE Hydraulic actuator Electric backup manifold Hydraulic actuation manifold The REU receives electrical power from two separate circuit breakers, both located on the Uninterruptible Power Supply (UPS) 28 Vdc bus. Two circuit breakers are provided to allow 27-23-00 Page 3 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL separate wire routes from each breaker through the engine and APU rotor burst zones. The actuator receives hydraulic power from the aircraft right system. The EBHA is controlled electrically by its REU and uses hydraulic power to move the control surface. The MCE receives electrical power from a single 65 amp circuit breaker on the 28 Vdc EBHA bus. The MCE uses the power for its internal electronics and to power the IMPA. The EBHA has the following three states of operation: Active hydraulic (normal) Damped bypass Electrical backup (power select valve de-engerized) (1) Active Hydraulic State In the EBHA active hydraulic state, hydraulic pressure is from the aircraft system. The EHSV modulates the flow of fluid to provide the desired actuator movement. The Power Select Valve (PSV) controls the state between normal and electrical backup. In the normal energized position, the valve allows the EHSV modulated aircraft hydraulic pressure to move the actuator. The de-energized position allows pressure from the self-contained electrical backup hydraulic system to move the actuator. The EBHA active hydraulic state with normal hydraulic power provides closed loop positional control of the EBHA using the EHSV. When the EBHA is commanded into active state with normal hydraulic power, the REU and MCE energize a torque motor that positions the twoposition MSV into the active position. The active position connects the cylinder ports to the EHSV and disconnects the cylinder ports from the VDO. The REU and MCE also energize another torque motor that positions the two-position PSV into the position for normal hydraulic power. The PSV connects hydraulic system pressure to the EHSV and connects the EHSV extend and retract control ports to the ram using the MSV. (2) Damped Bypass State The EBHA damped bypass state provides for adequate dynamic damping to prevent surface flutter in the event of a loss of all hydraulic pressure or electrical power. The EBHA may be commanded into the damped bypass state. If there is a loss of electrical power or hydraulic pressure, the EBHA will default to the damped bypass state. If the EBHA is no longer being actively controlled, a damping force is placed on the actuator but it still provides sufficient damping for flutter suppression. The associated EHSA actuator, also actively controlling the rudder, will overcome the damping force of the EBHA actuator. (3) Electrical Backup State In the EBHA electrical backup state, the EHSV is bypassed and the starting, stopping and reversing of the IMPA modulates the flow of fluid to provide the desired actuator movement. The MSV controls entry into the damped bypass state. In the energized position the MSV allows hydraulic flow during either normal or electrical backup state. Electrical backup control of a surface is only used if both the EHSA and EBHA systems do not function in their normal hydraulic state. There will not be mixed operation in which an EHSA is operated in its normal hydraulic state and the EBHA is in electrical backup state. However, the electrical pump function is activated in a warm up state when there has been a hydraulic failure to the EBHA, even when the EHSA is still functioning normally. The warm up state circulates warm hydraulic fluid through the manifold and prevents it from becoming cold soaked. This insures the EBHA is ready to immediately control the surface in the event there is a subsequent failure to the EHSA that requires the electrical backup state to be engaged. 27-23-00 Page 4 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL In the EBHA electrical backup state, backup power provides closed loop positional control of the EBHA using the pump motor. When the EBHA is commanded into active state with electrical backup power, the REU and MCE energize a torque motor that positions the twoposition MSV into the active position. The active position connects the cylinder ports to the pump and disconnects the cylinder ports from the VDO. The REU and MCE de-energize the PSV torque motor, positioning the two-position PSV for backup hydraulic power. The PSV connects the pump extend and retract control ports to the ram via the MSV and blocks hydraulic system pressure from the EHSV. In the EBHA electrical backup state, positional control is provided by first comparing the commanded ram position to the actual ram position. The REU demodulates the main ram LVDT signal to determine the main ram position and calculates the difference between the commanded ram position and the actual ram position to generate the error signal. The REU then applies an electrical command current to the MCE and the MCE commands the electrical motor driving the pump that is proportional (within limits) to the error signal. The pump motor command current proportionally increases (within limits) the pump motor velocity. The polarity of the pump motor command determines which cylinder ports (extend or retract) get connected to the inlet and outlet ports of the pump. For proper closed loop control, the polarity of the pump motor command current causes the ram to move in a direction that reduces the positional error signal until the error signal reaches zero. C. Rudder EHSA Manifold The manifold servo valve is commanded by the REU and ports fluid accordingly to the extend or retract chambers of the associated actuator. The manifold output is open loop as all of the command computation is done within the REU. For maintenance purposes, the manifold contains a relief valve that may be manually driven. The REU is mounted on its associated hydraulic manifold. The REU processes FCC commands and initiates electrical commands to the MSV solenoid and the EHSV. The MSV and EHSV control the flow of hydraulic fluid that moves the actuator. The EHSA manifold includes the following components: SOV MSV VDO EHSV and position sensor Fluid pressure sensors Bidirectional relief valve Fluid filter Fluid reservoir Anticavitation check valves The REU controls the EHSV to port pressure to the cylinder. The cylinder delivers the force to move the surface. Sensors within the manifold provide status information back to the REU. These include the following sensors: EHSV position LVDT Hydraulic supply and return pressure sensors Compensator position LVDT The compensator is an LP spring-loaded accumulator that stores a small hydraulic fluid reserve. The retract and extend cylinder pressure sensors are located in the EHSA manifold, but they provide information only to the EBHA REU. The sensors monitor the hydraulic pressure on both extend and retract chambers of the hydraulic actuator. The EBHA REU monitors similar pressure 27-23-00 Page 5 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL information from the EBHA actuator and compares the two pressures to insure the two actuators are working together with no force fight issue between the two. Status information in the form of a discrete signal is passed from each REU to the other. This lets the associated REU know if the other is invalid and not actively controlling the surface. D. Rudder EB Manifold The rudder EB manifold contains the following components: EHSV SOV PSV IMPA Anticavitation check valves During all states of operation, the EB manifold is commanded by its electrical interface with the MCE and REU. During normal operation, aircraft hydraulic pressure is controlled by the EHSV to extend or retract the actuator. During the electrical backup state, the IMPA generates hydraulic pressure to extend or retract the actuator based on the direction of motor rotation. The REU processes FCC signals and initiates electrical commands to the PSV solenoid and EHSV in the EB manifold. Those components control the flow of hydraulic fluid that moves the actuator. Sensors within the manifold provide status information back to the REU. The EB manifold contains the following sensors: EHSV position LVDT Hydraulic supply and return pressure sensors Hydraulic temperature sensor The MCE is mounted directly to the EB manifold. Each MCE has its own 65 amp circuit breaker on the 28 Vdc EBHA bus. The MCE uses the power for its internal electronics and to power the IMPA. The MCE controls the operation of the IMPA. It receives motor position and velocity information from the motor resolver. The MCE knows the status of both the EBHA REU and the EHSA REU and receives a status discrete from each. If the EBHA REU is active and the EHSA REU is inactive, the EBHA REU issues the motor velocity commands to the MCE over the REU to MCE RS485 data bus. This data bus is referred to as the Motor Control Data Link (MCDL). The MCE passes its internal status monitors back to the REU using the MCDL. E. Rudder HA Manifold The rudder HA manifold contains the following components: SOV MSV VDO Bidirectional Relief Valve (BDRV) Anticavitation check valves Compensator Compensator position LVDT Retract and extend cylinder pressure sensors Return relief valve NOTE: The pressure sensors monitor hydraulic pressure on both extend and retract chambers of the hydraulic actuator. The REU is mounted directly to the HA manifold. The HA manifold receives electrical input from the REU. The REU processes FCC signals and initiates electrical commands to the MSV solenoid in the HA manifold. This controls the flow of hydraulic fluid from the manifold to the actuator. 27-23-00 Page 6 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL The BDRV interconnects the extend and retract chambers when the greater of the two chambers exceeds the compensator circuit pressure by more than a preset value. The BDRV limits the maximum load on the actuator, in addition to the maximum pressure in each chamber. The HA manifold interfaces hydraulically with the EB manifold to pressurize the extend / retract ports of the rudder actuator. The HA manifold features a manual override for the return relief valve. This allows maintenance personnel to move the rudder surface when required. 4. Controls and Indications A. Circuit Breakers The system is protected by the following circuit breakers: NOMENCLATURE PANEL LOCATION POWER SOURCE RUD EBHA PRI REER B1 UPS 28VDC RUD EBHA SEC REER B2 UPS 28VDC RUD HA REER B7 R ESS 28VDC RUD EBHA PWR N/A EBHA PDB (Tail Compartment) EBHA BUS 28VDC B. CAS Messages The CAS messages for the system are shown in the following table: MESSAGE COLOR MESSAGE DESCRIPTION Yaw Trim Auto Center Blue Yaw trim automatic centering feature is active. No action is needed if this is desired condition. Yaw Trim Nose Left Limit Blue Yaw trim has reached its capacity in nose left direction. Yaw Trim Nose Right Limit Blue Yaw trim has reached its capacity in nose right direction. Rudder Steering Fail Amber Rudder steering failed. Rudder Steering Off Amber Rudder steering is off. Rudder Single Actuator Amber Single rudder actuator failed.Notify maintenance for corrective action. Attempt FLT CTRL RESET. Rudder Fail Amber Both REUs failed or loss of rudder command. Continue flight within flight envelope limitations. Attempt FLT CTRL RESET. Yaw Authority Limit Amber Rudder approaching maximum displacement. Adjust flight condition as necessary. Yaw Damper Fail Amber Yaw damper has failed. Continue flight within flight envelope limitations. NOTE: The FCC status information required by the flightcrew is shown on the main displays as CAS messages and synoptic page data. 27-23-00 Page 7 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL 5. Operation A. Rudder Hydraulic Actuation Rudder hydraulic control is accomplished by the following two types of actuators: EHSA EBHA (1) EHSA Operating States An EHSA is controlled electrically by its REU and uses hydraulic power to move the control surface. The EHSA system consists of the following three separate components: REU Hydraulic manifold Hydraulic actuator The REU is mounted directly to the hydraulic manifold and receives electrical power from a single circuit breaker on the right essential dc bus. The REU receives surface position commands from the FCCs on two separate and independent BD429 data buses. One bus is from FCC 1 and the other from FCC 2. The REU processes the FCC signals and initiates electrical commands to the MSV solenoid and the EHSV. The MSV and EHSV control the flow of hydraulic fluid to move the actuator in the desired direction. Sensors within the manifold provide status information to the REU. These include the EHSV position LVDT, hydraulic supply and return pressure sensors and compensator position LVDT. The compensator is an LP spring-loaded accumulator that stores a small hydraulic fluid reserve. The retract and extend cylinder pressure sensors are also located in the EHSA manifold, but they provide information only to the EBHA REU. The sensors monitor the hydraulic pressure on both extend and retract chambers of the hydraulic actuator. The EBHA REU monitors similar pressure information from the EBHA actuator and compares the two pressures to insure the two actuators are working together with no force fight issue between the two. Status information in the form of a discrete signal is passed from each REU to the other. This lets the associated REU know if the other is invalid and not actively controlling the surface. The EHSA actuator is separate and receives hydraulic power from the aircraft left system. The hydraulic actuator contains a single channel LVDT that provides position sensing information to the REU. There are no other electrical components in the actuator. The EHSA has the following two states of operation: Active hydraulic (normal) Damped bypass In the EHSA active hydraulic state, the MSV is energized and allows hydraulic flow from the EHSV to the actuator. In the active hydraulic state, the REU energizes a normally open threeway MSV SOV that moves the MSV into the active position. The active position connects the cylinder ports to the EHSV and disconnects the cylinder ports from the VDO. In EHSA active hydraulic state, the REU uses the internal main ram LVDT signal to determine the main ram position and then calculates the difference between the commanded ram position (from the FCC or the BFCU) and the actual ram position to generate an error signal. The REU applies an electrical command current to the first stage coils in the EHSV that is proportional to the error signal. The EHSV command current proportionally increases the flow orifice metering area between supply pressure and one cylinder port along with the flow 27-23-00 Page 8 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL orifice metering area between return pressure and the opposing cylinder port. The polarity of the EHSV command current causes the ram to move in a direction that reduces the positional error signal until the error signal reaches zero. The polarity of the EHSV command current in effect determines which cylinder ports (extend or retract) get connected to supply and return pressures. The EHSA system is placed in damped bypass state when the MSV is de-energized. The state is entered when there has been a failure in the REU or the aircraft hydraulic system. A damping force is placed on the actuator since it is no longer being actively controlled, but still needs to provide sufficient damping for rudder flutter suppression. The associated EBHA actuator, is also actively controlling the same surface and will overcome the damping force of the EHSA actuator. In the EHSA damped bypass state, the actuator may be commanded to shut down through a solenoid valve driving the MSV. The REU de-energizes the three-way MSV SOV that moves the MSV so that the cylinder ports are disconnected from the EHSV and interconnected through the VDO. Upon loss of electrical or hydraulic power the actuator MSV automatically reverts to the damped state. (2) EBHA Operating States An EBHA is controlled electrically by its REU and uses hydraulic power to move the control surface. The EBHA system consists of the following five separate components: REU MCE Hydraulic actuator HA manifold EB manifold The REU is mounted directly to the HA hydraulic manifold and receives electrical power from two separate circuit breakers, both located on the UPS 28 Vdc bus. Two circuit breakers are provided to allow separate wire routing from each breaker through the engine and APU rotor burst zones. The EBHA REU receives surface position commands from the FCCs on two separate and independent BD429 data buses. One bus is from FCC 1 and the other from FCC 2. The REU processes the FCC signals and initiates electrical commands to the MSV solenoid in the HA manifold and the PSV solenoid and EHSV in the EB manifold. Those components control the flow of hydraulic fluid to move the actuator in the desired direction. If both the EBHA REU and EHSA REU are invalid, the MCE is capable of controlling the electrical motor and actuator on its own. In that condition, the MCE receives the surface command signals directly from FCC 2 on the MCE standard ARINC 429 bus. The MCE is mounted directly to the EB hydraulic manifold. Each MCE has its own 65 amp circuit breaker on the 28 Vdc EBHA bus. The MCE uses the power for its internal electronics and to power the IMPA. The MCE controls the operation of the backup electrical motor. It receives motor position and velocity information from the motor resolver. The MCE knows the validity of both the EBHA REU and the EHSA REU and receives a status discrete from each. If the EBHA REU is valid, then the REU issues the motor velocity commands to the MCE using the MCDL. The MCE passes its internal status monitors back to the REU over the MCDL. A separate actuator is located above the HA and EB manifolds and receives hydraulic power from the aircraft right system. The hydraulic actuator contains a two channel LVDT that 27-23-00 Page 9 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL provides position sensing information. One channel is connected to the REU and the other to the MCE. There are no other electrical components in the actuator. The EBHA has the following three states of operation: Active hydraulic (normal) Electrical backup Damped bypass (de-engerized) In the EBHA active hydraulic state, hydraulic pressure is from the aircraft system. The EHSV modulates the flow of fluid to provide the desired actuator movement. The PSV controls the state between normal and electrical backup. In the normal energized position, the valve allows the EHSV modulated aircraft hydraulic pressure to move the actuator. The de-energized position allows pressure from the self-contained electrical backup hydraulic system to move the actuator. The EBHA active hydraulic state with normal hydraulic power provides closed loop positional control of the EBHA, using the EHSV. When the EBHA is commanded into active state with normal hydraulic power, the REU and MCE energize a torque motor that positions the twoposition MSV into the active position. The active position connects the cylinder ports to the EHSV and disconnects the cylinder ports from the VDO. The REU and MCE also energize another torque motor that positions the two-position PSV into the position for normal hydraulic power. The PSV connects hydraulic system pressure to the EHSV and connects the EHSV extend and retract control ports to the ram via the MSV. In the EBHA electrical backup state the EHSV is bypassed and the starting, stopping and reversing of the IMPA modulates the flow of fluid to provide the desired actuator movement. The MSV controls entry into the damped bypass state. In the energized position the MSV allows hydraulic flow during either normal or electrical backup state. Electrical backup control of a surface is only used if both the EHSA and EBHA systems do not function in their normal hydraulic state. There will not be mixed operation where an EHSA is operated in its normal hydraulic state and the EBHA is in electrical backup state. However, the electrical pump function is activated in a warm up state when there has been a hydraulic failure to the EBHA, even when the EHSA is still functioning normally. The warm up state circulates warm hydraulic fluid through the manifold and prevents it from becoming cold soaked. This insures the EBHA is ready to immediately control the surface in the event there is a subsequent failure to the EHSA which requires the electrical backup state to be engaged. In the EBHA electrical backup state, backup power provides closed loop positional control of the EBHA, using the IMPA. When the EBHA is commanded into active state with electrical backup power, the REU and MCE energize a torque motor that positions the two-position MSV into the active position. The active position connects the cylinder ports to the pump and disconnects the cylinder ports from the VDO. The REU and MCE de-energize the PSV torque motor, positioning the two-position PSV for backup hydraulic power. The PSV connects the pump extend and retract control ports to the ram via the MSV and blocks hydraulic system pressure from the EHSV. In the EBHA electrical backup state, positional control is provided by first comparing the commanded ram position to the actual ram position. The REU demodulates the main ram LVDT signal to determine the main ram position and calculates the difference between the commanded ram position and the actual ram position to generate the error signal. The REU then applies an electrical command current to the MCE and the MCE commands the electrical motor driving the pump that is proportional (within limits) to the error signal. The pump motor command current proportionally increases (within limits) the pump motor velocity. The polarity of the pump motor command determines which cylinder ports (extend or retract) 27-23-00 Page 10 August 15/14 GULFSTREAM G650ER SYSTEM DESCRIPTION MANUAL get connected to the inlet and outlet ports of the pump. For proper closed loop control, the polarity of the pump motor command current causes the ram to move in a direction that reduces the positional error signal until the error signal reaches zero. The EBHA damped bypass state provides for adequate dynamic damping to prevent surface flutter in the event of a loss of all hydraulic pressure or electrical power. The EBHA may be commanded into the damped bypass state or the EBHA will default to the damped bypass state, if there is a loss of electrical power or hydraulic pressure. A damping force is placed on the actuator since it is no longer being actively controlled but still needs to provide sufficient damping for rudder flutter suppression. The associated EHSA actuator, also actively controlling the rudder, will overcome the damping force of the EBHA actuator. 27-23-00 Page 11 August 15/14