Recent Advances in Aerospace Actuation Systems and Components, May 30 - June 1, 2018, Toulouse, France
SPOILER AND FLAP ROTARY EM ACTUATION (REMA) IMPLEMENTATION ON A RECENTLY CERTIFIED BUSINESS JET
ZATLOFF, Errol Curtiss-Wright Sensors and Controls Actuation Group 201 Old Boiling Springs Road, Shelby, NC, USA Phone: +1-973-541-3742 Email: [email protected]
ABSTRACT A recently certified business jet makes use of REMA solutions for both spoiler and flap actuation. A feature of this aircraft is A recently certified business jet makes use of Rotary EMA its ability to land and take-off from short and unfinished (REMA) solutions for both spoiler and flap actuation. This runways, and the highly effective spoilers and flaps contribute paper will describe aspects of the Spoiler and Flap Actuation significantly to this capability. In the case of the spoilers, Subsystems and their development. This includes particulars individual REMAs are implemented for both multi-function of the subsystem functionalities and architectures, REMA and ground spoiler actuation. In the case of the flaps, mechanical configurations, controller design, control system distributed REMAs are implemented rather than a traditional implementation, component installation and integration, centrally powered system. The various REMA applications subsystem performance, and the use of computer simulation have distinct functional, safety and loading requirements, and modeling in the development process. the REMAs are configured and sized accordingly. Actuation Power and Control Modules (APCMs) are integrated with the REMAs; they provide power conditioning KEYWORDS and filtering, motor current and velocity loop closure, subsystem monitoring, BIT, and other functionalities. The Actuation, actuator, electromechanical, flight control, flap, REMAs together with the APCMs comprise the Spoiler and REMA, rotary, spoiler Flap Actuation Subsystems, which in turn are integrated within the aircraft flight control and monitoring system. I INTRODUCTION Electromechanical Actuation (EMA) for aircraft flight II SPOILER ACTUATION SUBSYSTEM controls continues to advance as new aircraft are developed. ARCHITECTURE In particular, secondary flight controls on business aircraft have been early adopters of EMA technology. Smaller The Spoiler Actuation Subsystem (SAS) architecture is shown business aircraft generally rely on mechanical flight controls in Figure 1. Each wing includes four spoiler surfaces rather than hydraulics, and so implementing fly-by-wire EMA comprising inboard and outboard ground spoilers (GS), and secondary flight control subsystems is a logical step when inboard and outboard multi-function spoilers (MFS). The GS improvements to performance capability are designed in to performs a lift dumping function and is deployed only upon new aircraft. landing. The MFS perform three different functions: While EMA flight controls often refer to linear actuation 1. Roll Assist – At reduced aircraft speeds, such as when configurations, the advantages of rotary EMA (REMA) the flaps are deployed, the MFS are activated to assist the solutions have made it a viable option and a preferred ailerons to provide roll control of the aircraft approach in some cases. Some advantages of REMAs include 2. Air Brake – In the event a rapid descent from cruise improved maintenance requirements and favorable wing altitude is required, the MFS can be deployed as air integration. brakes to decelerate the aircraft 3. Lift Dump – Upon landing, the MFS are deployed along with the GS to dump lift
Recent Advances in Aerospace Actuation Systems and Components, May 30 - June 1, 2018, Toulouse, France
A/C Power, Control, Monitoring
OUTBD APCM INBD APCM
Outboard MFS Inboard MFS Outboard GS Inboard GS Inboard GS Outboard GS Inboard MFS Outboard MFS
MFS_LOB MFS_LIB GS_LOB GS_LIB GS_RIB GS_ROB MFS_RIB MFS_ROB
Figure 1. Spoiler Actuation Subsystem
The subsystem includes two APCMs mounted remote from typical relevant aircraft elements and subsystems. It also the wings; they provide power conditioning, current and includes the position resolver electrical interfaces, and velocity loop implementation, and monitoring and BIT implementation of the digital compensation for outer position functionality for the actuation channels. To provide functional loop closure of the actuators. redundancy, the four inboard spoiler surfaces, one inboard MFS and one inboard GS per wing, interface with one APCM III FLAP ACTUATION SUBSYSTEM referred to as the Inboard APCM. Similarly, the four outboard ARCHITECTURE surfaces interface with one APCM, the Outboard APCM. In this manner, disabling of an individual APCM or its aircraft The Flap Actuation Subsystem (FAS) architecture is shown in interface allows usage of a single MFS and GS on each wing, Figure 2. An Inboard Flap (IBF) and Outboard Flap (OBF) thus retaining a level of functionality with half of the surfaces actuator drives each wing flap through a flap linkage available. arrangement. The Flap APCM is mounted remotely from the actuators, and the four flap actuators drive in a synchronized Splitting the surface types into inboard and outboard pairs also manner in response to individual position commands reduces the criticality of any single surface to experience a originating in the flight control computer. Flap angle is jammed condition and inability to be retracted. controlled and held within limits by the synchronicity of the In turn, the APCMs interface with the aircraft flight control output of the four actuators. computer. The flight control computer interfaces with the
A/C Power, Control, Monitoring
Flap APCM
LOB Flap LIB Flap RIB Flap ROB Flap
Flap_LH Flap_RH Figure 2. Flap Actuation Subsystem
Recent Advances in Aerospace Actuation Systems and Components, May 30 - June 1, 2018, Toulouse, France IV Spoiler Actuation Functionality and Rotary Geared Actuator (RGA) Actuator Configurations Position feedback resolver The primary architectural differences are the presence of the power-off holding brake in the MFS, and the presence of the The functional and safety requirements of the MFS and GS one-way no-back in the GS. When fully retracted during actuation differ, and this is reflected in the differences between flight, there is typically an airload acting on the spoiler surface the actuator configurations. External views of the spoiler tending to make it extend, or ‘upfloat’. In particular, the actuators are shown in Figure 3. ground spoilers are large surfaces to provide effective lift dumping upon landing, and the upfloating of a surface during flight is highly undesirable. The one-way no-back provides effective irreversibility in the extend direction, thereby not allowing the unpowered actuator to move in the extend direction and the surface to upfloat. If a ground spoiler surface is extended fully or partially when actuator power is lost for any reason, it is desirable that the surface be allowed to be backdriven by airloads to as low an angle as possible even at minimum temperatures of -65°C. This is accommodated by the one-way no-back, which allows the actuator to be reversible in the retract direction. Multifunction Spoiler (MFS) Actuator The multifunction spoiler has three functions as previously noted – roll-assist, air brake and lift dumping. It also experiences airloads tending to cause it to upfloat during flight, but it relies on the power-off brake to maintain retracted position rather than a no-back. All spoiler actuators operate in a position servo mode, and when the MFS is operated during flight in roll-assist or airbrake mode, static position is held by servo control action. Allowing the motor to ‘feel’ and respond to the applied airloads through the reversibility of the actuator improves the overall position control response of the system, and so the power-off brake is incorporated in the MFS rather than a no-back as in the GS. In the event a multifunction spoiler is extended fully or partially when actuator power is lost, but brake power is still available and applied to maintain release of the brake, it is Ground Spoiler (GS) Actuator desirable that the surface be allowed to be backdriven by Figure 3. External Views of MFS and GS Actuators airloads to as low an angle as possible, similar to a ground spoiler. The reversible design of the MFS actuator allows for Components making up both actuator types are noted below: this function. Table 1 contains some fundamental performance parameters of the MFS and GS actuators. MFS:
Brushless DC motor with commutation resolver, power-
off brake and temperature sensor Gearhead Slip Clutch
Rotary Geared Actuator (RGA) Position feedback resolver GS: Brushless DC motor with commutation resolver and temperature sensor Gearhead
Slip Clutch One-way no-back
Recent Advances in Aerospace Actuation Systems and Components, May 30 - June 1, 2018, Toulouse, France Table 1. Spoiler Actuation Parameters
It can be seen the maximum commanded output rates of the MFS and GS actuators are quite high. To achieve these high output speeds, the total gear reduction of the actuator is maintained to be relatively low, and so relatively low gearhead and RGA ratios are implemented. These low gear reductions in turn help to achieve the desired back driving capabilities of these actuators. As noted, the MFS and GS actuators incorporate slip clutches. The combination of operating speeds and torques result in kinetic energies for these actuators which, in the event of a jam condition within the actuator or downstream in the spoiler or its mechanism, would result in relatively high jam loads. The slip clutches limit the output jam loads to a safe level for the actuator and the aircraft. Inboard Flap (IBF) Actuator The output positions of the actuators are measured by resolvers. The resolver assemblies interface mechanically with the RGAs, and include a gearhead to reduce the output motion to be within the operating range of the resolver transducer in order to provide an absolute position measurement. The resolvers interface with the flight control computer for outer position loop closure and monitoring functions.
V FLAP ACTUATION FUNCTIONALITY AND ACTUATOR CONFIGURATIONS
The IBF and OBF actuators are functionally and architecturally similar to each other, though not identical. As Outboard Flap (OBF) Actuator is typical, flap inboard loads are significantly greater than Figure 4. External Views of IBF and OBF Actuators outboard loads, and the component sizing reflects this. Components making up both actuator types are noted below: IBF and OBF: Functional requirements for the flaps differ from those of the spoilers. For the flaps, it is critical that flap angle is maintained Brushless DC motor with commutation resolver, power- at all actuator stations whenever target detent positions are off brake and temperature sensor achieved (i.e. retracted, take-off, or land positions) or in the Gearhead event of a loss of power or system failure. Redundancy of this Two-way no-back position holding function is provided by the combination of Rotary Geared Actuator (RGA) the power-off brake and the no-back. Position feedback resolver Table 2 below contains some fundamental performance External views of the flap actuators are shown in Figure 4. parameters of the IBF and OBF actuators.
Recent Advances in Aerospace Actuation Systems and Components, May 30 - June 1, 2018, Toulouse, France Table 2. Flap Actuation Parameters
As shown, output speeds are significantly slower than for the spoiler actuators. For these actuators relatively high ratio gear reductions are used which allow for reasonably high speed motors to maintain small envelopes and minimize weight. Since the safety requirement is for the actuators to maintain position with no power applied under all conditions, they do not need to be designed to be readily backdriveable and so relatively high gear reductions are acceptable and consistent with the low output speeds required. The combination of speed and load result in lower kinetic energies than for the spoiler actuators, and analysis demonstrated that sufficient actuator compliance exists to Outboard Flap (OBF) Actuator maintain the jam loads to safe levels without the need for incorporating slip clutches. Figure 5. IBF and OBF Actuators As with the spoiler actuators, the output positions of the VI APCM FUNCTIONALITY AND actuators are measured by resolvers. The resolver assemblies similarly interface mechanically with the RGAs, and because FEATURES the output travel differs from those of the spoiler actuators, a The APCMs provide power conditioning and filtering, motor different gearhead reduction is used to reduce the output current and velocity loop closure, subsystem monitoring, BIT, motion to be within the operating range of the resolver and other functionalities. The Spoiler and Flap APCMs are transducer. The resolvers similarly interface with the flight functionally and architecturally very similar, and share many control computer for outer position loop closure and common subassemblies. The description below applies to monitoring functions. both, except where noted. The IBF and OBF actuators are also shown in the photos in A key design criterion and feature of the APCM is that it is not Figure 5. software based. It contains a PLD that implements the motor commutation logic based on the motor resolver to digital converter output. All other functionality is accomplished with discrete electronic hardware. The APCM is certified to DO- 254 requirements, Design Assurance Level (DAL) A. The major APCM functions are shown in the Functional Block Diagram of Figure 6, and listed below: Input Power Conditioning/EMI Filtering Boost Converter Regenerative Clamp Bias Power Supply Flap actuator control and drive electronics Inboard Flap (IBF) Actuator Monitoring Enable and Shutdown Function
Recent Advances in Aerospace Actuation Systems and Components, May 30 - June 1, 2018, Toulouse, France
28V_Act EMI Filtering, 28V_Act RTN Transient 28V_Elec Suppression, 48V 28V_Elec RTN DC-DC Conversion, Chassis GND Galvanical Isolation Boost Conversion SHUTDOWN SPEED LOOP CURRENT LOOP Current BRK PBIT CMD PLD Sensors MOTOR P + SPEED COMMAND P + - + - GATE I + MOTOR HED COMMUTATION DRIVER HED RGA
HED STOW COMMAND Resolver
CURRENT FDBK Analog Filtering and Scaling Circuitry Temp 28V_Elec Sensor
APCM BRAKE APCM TEMP Controlled Temperature CURRENT FEEDBACK Surface Monitoring SW
Resolver SPEED FEEDBACK To MOTOR SPEED Digital POSITION FEEDBACK Resolver RESOLVER FAIL DRIVE ENABLE BIT, Drive Temperature APCM READY Control & Monitoring, MOTOR TEMP Signal Temp Detection MOT OVERCURRENT Shutdown Conditioning BRIDGE VOLTAGE BRAKE DRIVE Figure 6. APCM Functional Block Diagram
Some particulars of these functions follow. Aircraft power extend the surface. Thirdly, in the case of the flaps, a brake provided is 28 Vdc, and it was determined early on that the PBIT current limit is implemented to support the brake output power levels, particularly for the spoilers, require high checking function on the ground prior to flight in order to motor currents, with associated implications regarding confirm the motor holding brakes are functioning and winding size and thermal considerations. In order to reduce providing the minimum required torque. The selection of the motor current levels, a boost converter was designed and applicable current limit during the various modes of operation implemented. This boosts the motor voltage to 50 Vdc, are done by the aircraft flight control computer. resulting in reasonable motor current levels that are more A number of BIT and Monitoring functions are accomplished commensurate with equipment sizing targets. within the APCM, including: Regenerative clamping is provided to prevent regenerated energy from being returned to the aircraft 28 Vdc power bus. Motor and Driver Bridge Current The regenerative clamps manage the regenerative energy due Bridge Voltage to aiding load conditions or dynamic braking of the actuators. Resolver Status They are optimized for the operating conditions of the spoilers Motor Temperature or flaps actuation channels in their respective APCMs. APCM Temperature Motor Velocity The servo-control implementation actuation is a typical three- Motor Current loop arrangement with an inner current control loop, an Internal Bias Supplies intermediate velocity control loop, and an outer position control loop. The current and velocity control loops are The status of each of the monitored functions is reported to the implemented within the APCM, while the outer position loop aircraft as analog or discrete signals. Some BIT functions is implemented in the aircraft flight control computer. The require particularly fast action, and for these the APCM can APCM velocity and current loop compensation is initiate shutdown of individual drive channels; these include accomplished in analog hardware circuitry. The APCM the Bridge Over-Current, Motor Over-Current, and Resolver receives velocity commands from the flight control computer Status BITs. as analog voltages, and the motor current reference results The Enable and Shutdown functions are important safety from the velocity and current loop compensation. The output features that are implemented within the APCM. The Enable of the current loop is a PWM duty cycle command that is signal is a regularly used input from the aircraft that enables processed by the PLD commutation logic to establish the the motor drive H-bridge when power is applied and the motor H-bridge gate drive sequencing to excite the appropriate APCM monitored functions are all within limits; a channel is phase windings with the target current level. enabled when all monitored functions are within limits and the Current limits are set in the velocity loop, where the current actuation system is ready to respond to velocity commands loop command is limited to the established levels for each from the aircraft. Until the system is enabled, motion of the actuator motor and enforced through the high bandwidth actuators cannot occur. current loop control response. A number of current limits are The Shutdown function is an additional feature that can available to support functionality under different operating disable the motor drive bridge in the event there are any safety modes. First, each channel includes a normal current limit that related abnormal conditions that demand immediate shutdown is established based on the peak current demand under the of the system by the aircraft monitoring processing unit. Being highest load conditions during normal operation. Second, in a critical safety feature, the design of its implementation in the case of the spoilers, a stowing current limit is implemented particular is a driver in the DAL of the APCM being Level A. to support the stowing function when retracting in order to preload the actuator into the stops; this is to preclude surface A view of the physical configuration of the APCM is shown deflection under the prevailing flight loads that tend to try to in Figure 7.
Recent Advances in Aerospace Actuation Systems and Components, May 30 - June 1, 2018, Toulouse, France
torque. The intermediate velocity loop is critical to provide system damping. Comparing the closed loop transfer function of the three-loop system with that of a two-loop topology without the velocity loop, the damping term in the second order response transfer function is provided by the inclusion of the intermediate velocity loop, and absent in the two-loop topology. As the position loop is implemented in the flight control computer, the APCM input is a velocity command. Though there is a velocity control loop, the speed of each actuator is actually controlled by the position commands being generated at the desired ramp rate. The position response will follow the commanded position ramp, effectively controlling the speed of the actuator and control surface. Tight control is important for all modes of operation, and particularly critical to ensure synchronous motion of the four flap actuators for smooth flap deployment, and synchronous motion of left and right wing MFS actuators to ensure symmetric spoiler deployment when used in Air Brake mode.
VIII MODEL BASED DESIGN AND VIRTUAL Figure 7. Spoiler and Flap APCM Configuration PROTOTYPING VII SPOILER AND FLAP ACTUATION As part of the development process, simulation models of the CONTROL LOOP IMPLEMENTATION actuation subsystems were developed. These proved essential to various aspects of the design, test and certification process. The three-loop servo-control implementation of the FAS and Some aspects of the models, their development, and use SAS is key to the performance of the spoiler and flap actuators follow. to position the control surfaces. As noted, there is an inner current control loop, an intermediate velocity control loop, and The simulation model platform was Matlab/Simulink. A top- an outer position control loop. The system requires high level view of the models is shown in Figure 8. current loop bandwidth to ensure tight control of the motor
Figure 8. Matlab/Simulink Model
Recent Advances in Aerospace Actuation Systems and Components, May 30 - June 1, 2018, Toulouse, France
The four major modules shown include: 1. Control Command Channel Model Position Command Generator Digital Position Control Loop Including Feedback Conditioning and Loop Compensation Stow Control (used only for the GS and MFS) Discrete Signals Generator for Enable and Brake Controls
2. APCM Model Analog Velocity Control Loop Including Feedback Conditioning and Loop Compensation Analog Current Control Loop Including Feedback Conditioning and Loop Compensation Motor Drive
3. Actuator Model Motor Model Gearhead Mechanical Model RGA Mechanical Model Position Sensor
4. Load Model Air Load vs. Position Stow Model Jam Model
Detailed predictive models of the slip clutches and no-backs were not included, however their mechanical characteristics such as inertia and stiffness, and their primary effects on the Figure 9a. Measured Results – IBF Extending at -55C load transfer through the actuator, were included. A significant challenge was to establish mechanical characteristics for all the component parts of the actuators. To this end, a test program was undertaken to perform such testing in order to define these parameters. It included testing at various component and subassembly levels, including motor only, motor with gearhead, and the complete actuator assembly. It included testing at low, room and high temperature. Test matrices were planned and followed in order to verify motor electrical and EM parameters such as motor Kt, Ke, R, L, and component mechanical parameters including efficiency, friction, and speed dependent drag. Together with component mechanical properties such as inertia and stiffness, this data was important in order to have accurate, representative models of the systems so they could be useful for predicting on-aircraft performance. An example showing measured and simulated performance for the IBF actuator operating at maximum airloads at -55C is shown in Figure 9.
Figure 9b. Simulated Results – IBF Extending and
Retracting at -55C
Recent Advances in Aerospace Actuation Systems and Components, May 30 - June 1, 2018, Toulouse, France The simulation models proved extremely useful for various IX AIRCRAFT INSTALLATION AND program aspects such as: MAINTENANCE BENEFITS Predicting on-aircraft performance Some benefits of employing REMAs for flight control Predicting highly dynamic characteristics such as actuation include the following. frequency response and jam loads Determining current, velocity and position loop 1. Installation/Integration compensation parameters Specifying and selecting system components The aspect ratio of rotary actuators is such that the longer axis Determining optimum current limits is typically along the axis of rotation, and orthogonal to the Designing test stands and equipment output motion. This allows for an installation that is aligned Planning tests and determining acceptance criteria along the span of the wing, rather than being aligned in the direction of the wing chord as is the case with linear actuators. Support of System Integration Lab and flight testing This provides more chord-wise space for the stroking of the actuators and their output mechanisms, and more clearance from fuel tanks and other elements located within the wing.
Figure 10 shows the orientation of the flap and spoiler REMAs as they are installed within the wing. They are seen to be roughly aligned in the span-wise direction, which is an
efficient arrangement particularly for thin wings. This is consistent with the widespread use of RGAs in high lift systems and military lead edge flap applications.
MFS
IBF
OBF GS
Figure 10 Flap and Spoiler REMA Orientation in Wing
2. Maintenance Because the rotary actuator maintains a constant internal volume as it operates, as opposed to a typical linear actuator, it is not constantly displacing and ingesting moist air. Sealing technology used in other rotary actuation applications can be employed effectively and result in removing the need for relubrication and scheduled maintenance for the lifetime of the aircraft.
CONCLUSION
Rotary EM actuation (REMA) has been implemented on a newly certified high performance business jet for spoiler and flap actuation. This includes multi-function and ground spoilers, and coordinated flap actuation using distributed inboard and outboard actuators. Advantages of REMAs for secondary flight controls includes their wing installation/integration and maintenance benefits. This demonstrates they can be considered a viable alternative to linear EM actuation for flight control applications.