Distributed and electrically synchronized EMA’s net for a new type of secondary Flight Control System

03/02/2015
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Distributed and electrically synchronized EMA’s net for a new type of secondary Flight Control System

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application/pdf Distributed and electrically synchronized EMA’s net for a new type of secondary Flight Control System Jean-claude Derrien, J. C. Minichetti, M. Gueniot
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Distributed and electrically synchronized EMA’s net for a new type of secondary Flight Control System

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Symposium More Electrical Aircraft, 2015, 4-5 February, Toulouse, France Distributed and electrically synchronized EMA’s net for a new type of secondary Flight Control System Jean-claude DERRIEN Sagem Défense Sécurité Division Avionique J.C. MINICHETTI / M. GUENIOT Sagem Défense Sécurité Division Avionique Keywords : Actuator, distributed architecture, electrical, flight controls systems, reliability, safety, synchronization and virtualization. Presentation Future aircraft programs will rely on always more increasing electrification of their systems. In the field of secondary actuation systems, the Avionics Division of Sagem R&T presents the progress of its research program ‘’Distributed Actuation System’’ (DAS). These new types of systems result two main investigations. At first, the innovative architectures with independent electrical synchronization of all surfaces, through the distributed control of Electro Mechanical Actuators (EMA). Then, the introduction of Centralized Power Drive Unit (PDU evolution with ‘more electric’ ) in the flaps architectures with synchronization. DAS modelizes in real time a Bizjet flaps architecture. Sagem is aiming to validate this concept on a generic bench, by testing the electric synchronization of the surfaces, as well as its possible failure and reconfiguration modes. The new methodological approach cope with complex Flight Control Systems (FCS) design and validation, thanks to a full virtualization concept. Architecture & model overview DAS architecture is composed of two High Lift Control Computers (HLCCs), interpreting the orders of the pilot and controlling directly independent EMAs through electrical wiring. The extension/retraction of each flap (2 independent surfaces per wing) are actuated by two EMAs that integrate their own motors and sensors. All surfaces are mechanically independent and their synchronization is fully electric. The system is performed by a Hardware In the Loop (HIL) bay, which simulates and controls all the equipments. It allows to inject components failures within the system. Figure 1 : Profile and failures management IHM Each HLCC is a segregated hardware resource associated to four EMAs. Their management is realized by COM/MON laws : the actuators commanded by “calculator COM” are monitored in “calculator MON” and vice versa. The high level functions implemented in the HLCC are the actuators control with braking strategy and the flap moving synchronization. The actuators control model computes the current command of the motor after a position and a speed control loops. The braking model actuates the opening or activation of the brake depending on the actuator position. The flap synchronization model controls the deployment / position of all the flaps in accordance to the slowest one. If an actuator jamming occurs, its twin and the symmetric flap do not move any longer. The other flaps remain controlled by the other HLCC. Several monitoring functions explore the failure mode states consumed by the HLCC, for each actuator. For exemple, the sensors monitoring checks that the sensors operate properly and that the motor and screw positions sensors give consistent values. Also, the breaking/jamming monitoring detects a breakdown or a jamming of the motor or the screw. At last, the synchronization monitoring checks the synchronization of all the actuators of the given HLCC. FCS complete modelization & validation The development of physical parts is based on more than 800 technical requirements. These iterations ensure the maturity of equipments and system specifications and an efficient correlation of the model with the physical parameters. The main outputs of this approach are the verification of the complete system (Real EMAs, real loads, HIL bay, cable length effects) after the integration of Simulink DAS model with HIL functionalities : fine tuning of position / speed / current loops of real EMAs, model synchronization with measurements on bench and Dspace Model upgrade. Figure 2 : Real time system test bench A real time system test bench has been manufactured to ensure an incremental and progressive verification of the anticipated performances and behaviour of the complete system, through a set of virtual models representing each equipment. It is organized around a digital data-processing platform, Symposium More Electrical Aircraft, 2015, 4-5 February, Toulouse, France encompassing the system’s integral model, thus securing the application of some scenarii onto this model, the piloting of ‘’virtualized prototyped elements’’ (identically to the physical and real ones), the acquisitions and signal processing of all inputs/outputs within the embedded computer. It is also possible to close the loop of the system onto an A/C model, which allows to analyse its behaviours and its performances, before a future development of associated equipments and their intégration. The test bench is used to perform a validation tests campaign. The procedure includes 94 sequences mainly focused on the functional or dysfunctional responses of the architecture. Also it consists in commanding a reference extension/retraction profile while setting failures of different types at different times, and observe the monitoring and reconfiguration functions. The failures can be generated are actuator jamming, excessive friction on mechanism, motor resolver power switch off, ball screw resolver power switch off, loss of the brake. The performance targets that have driven the functional design of the system are the transition time and velocity, the maxima surfaces asymmetry during extension or retraction, at final manual selected position, at retracted position, the difference between positions two actuators when they are the same active surface. Some results validation tests We can present some interesting results. Below the graphic post-processing shows the signals of the position loop and monitoring (HLCC). It gives the control lever position with the measured positions of the four actuators of the group. The control is framed by validation gauges, asymmetry signals, reconfiguration and shutdown thresholds. Figure 3 : Graphic post-processing On a nominal profile, the requirement for maximum asymmetry, stabilized values and position gauges are respected during this test. The measuring curves are superimposed for each pair of actuators. Deplacement times for different parts of the profile are compliant. Deployment times are identical to the pairs L1/L2 and R1/R2 which have similar kinematics. The pair L4/R4 (30% more length) has a little more time important that the pair L3 / R3. It is characterized by a rise in higher rated speed time. Other exemple with a jamming case on L1 at 20s. L2, R1 and R2 stop at the position where L1 is jammed. The symmetry requirement is respected. L3, L4, R3 and R4 keep on following the pilot orders to keep the resulting lift as close as possible to the target, in terms of performance expected by the pilot. Finaly, if the L1 speed is reduced by 40% (frictions) so L2, R1 and R2 adapt their speeds to keep synchronized with L1. L3, L4, R3 and R4 respect the nominal path, and finish transiting earlier than L1. On all configurations, the results confirm the functional validation of the DAS project and architectural choices. They provide a representation of model performance (TRL5). Electrification of embedded systems The classical centralized design using torque shafts and the other using an innovative distributed and electrically synchronized architecture. The existing high lift systems are mostly based on centralized hydraulic or electric power equipment which drives shafts located in the wings that transmit the power and movement to the surfaces actuators, with a full mechanical connection. This ensures the synchronized and symmetric positioning during the movement of the surfaces. Figure 4 : Mechanical centralized design Vs distributed architecture A distributed architecture offers multiple advantages, such as the possibility of not losing the totality of the flap function in case of breakdown on a surface (blocking of this last one and its symmetric: “Pair locking” and integrity preservation of the remaining surfaces), the introduction of advanced features like roll assist in cruise, optimization of trail and load alleviation, and significant gains of mass at aircraft level. Electrical equipment (in particular electromechanical ones) introduce new types of failure modes, like the electronics ones, mechanical jamming, effort limitation, non natural damping. In general these failure modes are quite different from what can be seen with hydraulic actuators. New flight controls functionalities are also being investigated. In both cases, Safety requirements are completely analyzed through each equipment FMEA’s and are simulated in real time. Simultaneously a high reliability must be targeted, in order to achieve stringent safety and availability goals, at system level. Conclusion We showed the definition/specification of the architecture of this innovative system, the safety/certification strategy studies associated with a new methodological concept and the modelling in real time concerning the new flaps surfaces control strategies. Moreover, the COM/MON laws facilitates to implement new types of algorithms with FCC’s interfaces or with smart actuators (active/active, active/stand-by, active/damped). The implementation in a HIL bay and the tests with physical actuators have the advantage to constantly challenge the model with the reality. DAS solves the main problems related to the electrically synchronized distributed actuation of the flaps system by introducing several innovations patented (N° WO2012117009) by Sagem. All system components within the complete architecture are modelized (sensors, computers, actuators…) using virtual integration and model based system engineering methods. With this powerful FCS system design tool, it is possible to simulate in real time the behaviour of any type of electrical wing (classical or innovative) or all types of « High Lift » system architectures within an EMA network (Flap, Slat, Minited...). The DAS project was aiming High-Lift Bizjet applications but the results will be re-used in future developments by SAFRAN/Sagem. New applications and research programs (Turboprop or larger civil aircraft) are foreseen in the frame of the more electric aircraft. The certification strategy of such innovative flight control system remains a challenge.