Neural Network Bias Compensator for Flight Control Actuators

The report discusses the design and operation of electro-hydraulic servo-valves, illustrates a basic contol implementation design for an electro-hydraulic servo-valve controlled hydraulic actuator [for aircraft flight control actuation] and provides a survey of the state of the art of flight control of aircraft using fly-by-wire (FBW) architecture. The electro-hydraulic servo-valve figures prominently in typical FBW implementations and is an essential part of a modern aircraft flight control system. The scope of this report represents a large area of research, presented at a general level, and serves as a general summary of technologies and considerations for modern aircraft control. Fly-by-wire provides many advantages over traditional forms of aircraft flight control, and it represents both the state of the art in this area and also the future of almost all civilian and military aircraft flight control. The architecture, characteristics and control design relating to electro-hydraulic servo-valve controlled actuators is discussed in the report. The application of such actuators to fly-by-wire implementation is discussed in some depth, and the process by which fly-by-wire systems are developed is discussed.

The report discusses the design and operation of electro-hydraulic servo-valves, illustrates a basic contol implementation design for an electro-hydraulic servo-valve controlled hydraulic actuator [for aircraft flight control actuation] and provides a survey of the state of the art of flight control of aircraft using fly-by-wire (FBW) architecture. The electro-hydraulic servo-valve figures prominently in typical FBW implementations and is an essential part of a modern aircraft flight control system. The scope of this report represents a large area of research, presented at a general level, and serves as a general summary of technologies and considerations for modern aircraft control. Fly-by-wire provides many advantages over traditional forms of aircraft flight control, and it represents both the state of the art in this area and also the future of almost all civilian and military aircraft flight control. The architecture, characteristics and control design relating to electro-hydraulic servo-valve controlled actuators is discussed in the report. The application of such actuators to fly-by-wire implementation is discussed in some depth, and the process by which fly-by-wire systems are developed is discussed.

Spherical joints, or rod-ends, are critical components employed in flight control systems to connect the actuator to the aerodynamic surface and to the airframe. As any mechanical component, rod-ends are subjected to a wide range of failure modes, which can cause catastrophic effects at the actuator level and hence at the aircraft level. Despite this criticality, they are often overlooked in studies concerning the definition of new Prognostics and Health Management systems for flight control actuators, mainly due to the lack of sensors to monitor their behavior. The definition of a physics-based model of the rod-ends is hence a required preliminary step to pursue the definition of novel Health Monitoring schemes able to detect the fault inception in these components and track their evolution in time up to failure conditions. In this paper, a model working under few simplifying assumptions is proposed, complete with a Finite-Difference Method solution for the behavior of the lubricating film. The proposed model is then applied to a pre-existing, experimentally validated model of the flight control actuators of an in-service, wide-body commercial aircraft in presence of excessive backlash. Comments on the rod-end model are presented and further work is laid out.

Aircraft maintenance is one of the most important cost items faced by the operators of air fleets and is a major contributor to the aircraft life cycle cost. An aircraft fly-by-wire flight control system has a total of primary flight control actuators ranging from 10 to 20 depending on the aircraft type, with a failure rate of 1/1000 flight-hours; therefore, a health monitoring system for primary flight control actuators, able to recognize an actuator degradation in its early stage could greatly contribute to optimize the maintenance operations, reduce the airplane downtime and prevent missions interruptions.This note presents the initial part of an ongoing research project aimed at developing a prognostic and health management system for fly-by-wire primary flight control actuators. A key feature of the project is to develop a PHM system for these actuators suitable for the flight control actuators of legacy airplanes, which are poised to operate for still a long time, and not only for those of new aircraft. The primary flight control actuators of fly-by-wire flight control systems of existing aircraft are electrohydraulic servoactuators with a typical configuration and complement of transducers, and there is no practical possibility of introducing additional sensors. For this reason, the research activity was directed towards the study of algorithms able to identify faults only by using the already available information of the servoactuators state variables.The implemented algorithms are a combination of mathematical and neural network based ones, and the identification of degradations was performed by the analysis of the response of the servoactuators to a sequence of selected stimuli provided in preflight or postflight. The servovalve current and the feedback position are processed by dedicated algorithms in order to obtain significant indicators of the servocatuator health condition. The values of the indicators obtained during the sequence of stimuli are analyzed in combination with those obtained in the past.This is performed by the neural network part of the algorithm which allows a reliable identification of presence and of type of a degradation.The results obtained from the initial part of the research activity are interesting and encouraging. Individual degradations of the servoactuator parameters have so far been addressed and the algorithms for identifying them have been developed. All that makes up the foundations of the future research activity which will be focused on analyzing the effects of simultaneous multiple degradations and to the estimation of the remaining useful life.

This paper presents a model-based approach to design aileron endurance test rig (ETR). ETR is a dynamic load simulator which simulates aerodynamic load on-ground for verifying and validating the design, performance and stability of aileron actuator. Aileron actuator is a servo-controlled linear hydraulic actuator used to control the movement of ailerons in aircraft. Aileron is one of the primary flight control surfaces which controls roll of the aircraft. In ETR, Aileron actuator acts as unit under test (UUT) while a double-acting linear hydraulic actuator produces a dynamic load with the help of high pressure fluid source and electro-hydraulic servo valve (EHSV). The design of the test rig depends on load and velocity requirements which vary widely over the whole flight envelop and depends on deflection of surface, angle of attack, aircraft speed and altitude. One of the critical factor in designing ETR is to accurately model the interaction between the UUT and load system. This paper presents a simple yet powerful approach of free body diagram to account the power flow between the two systems. Model-based approach allowed to simulate the complete test rig behavior identifying the values of the critical parameters prior to building it. A high fidelity, non-linear mathematical model of aileron ETR is developed, simulated and verified. An appropriate load actuator and its electro-hydraulic servo valve are chosen to meet load and velocity requirements. The minimum rig structure stiffness is determined to ensure the stability of the load control system. A velocity feed-forward-based load controller along with proportional-integral control is implemented and tuned to meet the load control performance satisfactorily. Finally, the developed model is validated against the experimental data from actual test rig.

Hardware-in-the-loop simulator for research on fault tolerant control of electrohydraulic actuators in a flight control application

The McDonnell Douglas F-15E dual-role fighter has the mission requirement for night, all weather penetration capability for the deep interdiction role. A govemment furnished Low Altitude Navigation and Brgeting InfraRed for Night (LANTIRN) system developed by Martin Marietta provides the low level, day or night Terrain Following (TF) penetration capability over all types of terrain. The LANTIRN Navigation pod consists of a Forward Looking InfraRed (FLIR) sensor and a Terrain Following Radar (TFR) which provide inlunder the weather Manual or Automatic TF capability when coupled with the aircraft's Automatic Flight Control System (AFCS). The FUR provides terrain imagery on the Heads Up Display and Multi-Purpose Displays in the crew stations. The TFR system provides vertical axis steering information to the flight crew and AFCS for terrain clearance. A 61 flight test program totalling 132.1 flight hours for evaluation and verification of proper integration of the NAV-FLIR and TFR system with the aircraft avionics, flight controls, and crew station displays was accomplished on the F-15E at Edwards Air Force Base, Califomia between 28 October 1987 and 13 December 1989. Overall results were favorable with areas for improvement noted in the autopilot steering modes and roll wings level logic. These improvements have been incorporated and successfully tested as part of the annual F-15E software update evaluation.

Simulation is an important tool in control system design. Real-time simulation of flight controllers for the GARTEUR designed RCAM challenge was previously conducted on the University of Toronto Institute for Aerospace Studies real-time systems simulator (RTSS). As a next step to the controller design and simulation problem, it was desired to test a controller in the flight training device (FTD), which presents a more complex and realistic aircraft model, as well as offering a different visual perspective. The FTD runs on a commercial simulation software package called FLSIM. This project consisted of transferring two controllers from the RTSS to a FLSIM module. In order to duplicate the RCAM landing approach, the trajectory generator was also transferred. All other systems, such as flight dynamics and control actuators, were modeled by FLSIM. Through this exercise, a procedure for transferring models from the RTSS to the FTD was developed. Furthermore, it was found that controllers developed in the RTSS function in the FTD environment, but require tuning to achieve optimal results due to the more complex operational environment.

Multiple model adaptive estimation (MMAE) is a method of estimating unknown system parameters by modeling different discrete parameter values in several filters that are run in parallel and compared. The parameters for this research are failure status conditions associated with flight control actuators and sensors on the LAMBDA unmanned research vehicle, an experimental aircraft. Six actuator failures and eight sensor failures are modeled, along with the fully functional aircraft, in fifteen elemental Kalman filters. These filters propagate and update their own aircraft state estimates in real time. A probability computation representing the likelihood of each elemental filter's match to the true condition of the aircraft is used to generate relative probabilities for each filter's hypothesis. The MMAE algorithm is extended for the identification of dual failures through the use of a hierarchical structure of filter banks. Aircraft state excitation is required for effective MMAE performance. Sinusoidal dither signals are applied to the command inputs of a flight control system which controls pitch rate, roll rate, and sideslip angle. >

<div class="section abstract"><div class="htmlview paragraph">A significant step is achieved on the flight control actuation system toward the more electrical aircraft through the Airbus A380, A400M and the A350 development phase ongoing. The A380/A400M/A350 features a mixed flight control actuation power source distribution, associating electrically powered actuators with conventional FlyByWire hydraulic servocontrols.</div><div class="htmlview paragraph">In the scope of the preparation of the future Airbus Aircraft, this paper presents the perspectives of the use of the EMA technologies for the flight control systems in the more electrical aircraft highlighting the main technical challenges need to treat: jamming susceptibility, “on board” maintenance reduction, Operational reliability increase, power electronics and power management optimization, and regarding the environmental constraints, the predicted performances; the benefits associated to the optimized utilization of on-board power sources.</div><div class="htmlview paragraph">On the 4<sup>th</sup> of January 2011, an aileron EMA was successful flown on Airbus A320 MSN1. It is an important step towards the EMA technology for flight control actuation system.</div></div>

The ability to conduct an automatic landing maneuver is a key requirement for many unmanned aerial vehicles. By the example of the novel SAGITTA Demonstrator UAV, an autoland algorithm is presented as a modular extension to an automatic flight guidance and control system. At the Institute of Flight System Dynamics of the Technical University of Munich, a procedural definition of the automatic landing has been elaborated and implemented as a finite state machine. Based on this, existing guidance and control modules of the auto flight system are utilized to perform the landing maneuver. Particular attention has been paid to the design of transition conditions of the state machine, as these guide the temporal sequence of the maneuver and must reflect the high uncertainties that prevail concerning the performance of a novel aircraft configuration and its systems. Simulation testing and verification results in combination with ground testing of SAGITTA present a proof of concept of the design and give an outlook to its application during SAGITTA's maiden flight.

This chapter introduces a number of the issues which must be addressed during the design and development of an automatic flight control system (AFCS). It does not make a comparison of potential system architectures nor does it suggest an optimum approach because each AFCS is different, depending upon the airframe and application. However, there is a common theme associated with an AFCS development programme that can be introduced and used to familiarise the reader with some of the concepts which must be addressed during the design evolution.

This article presents the results of the study of joint work of electro-hydraulic actuator with combined speed control of the output link and electro-hydraulic servovalve actuator, obtained using the method of mathematical modeling. It is shown that at joint work of the above mentioned heterogeneous electro-hydraulic actuators in a mode of summation of efforts on a uniform control surface, on the output links of actuators there is a force fighting that negatively affects a resource of a design and the quality of regulation of actuators at the area of a low input control signals. The article presents the results of mathematical modeling of the system of force equalization (FES) that was developed by the authors and shows the possibility of significant reduction of mutual power load in the actuators when including the above-mentioned force equalization system in the control loop. As the base of data to mathematical model were used a real characteristics of actuators.

Automatic flight control systems have become increasingly vital ever since the emergence of airplanes. Automatic systems are not subject to fatigue and emotions as compared to the human pilot. As such, the possibility of human errors in flight control is minimized. Current automatic Flight Control Systems are designed based on classical control theories using linear controllers that are complex and inefficient. Since an aircraft is naturally nonlinear in its behavior, it is intuitive to design a nonlinear controller that could cover a wide variety of possible `extreme' flight conditions. A novel controller utilizing the Nonlinear Energy Method was developed by Akmeliawati for the longitudinal dynamics of an aircraft, and has been proven to provide effective control and better performance when compared to an equivalent linear controller. The novel controller was designed using the Passivity-Based Control (PBC) technique. In this paper, a similar nonlinear controller was designed to direct the roll and yaw motion, which is part of the lateral dynamics of the aircraft. Simulations show that this PBC is able to stabilize both roll and yaw motion of the aircraft.

The number of operations incorporating E-VTOL aircrafts is increasing each year, and the optimization of the energy consumption of such vehicles is a major problem. In this paper, a small-scale ARCHER helicopter’s energy consumption is analyzed, wherein different flight conditions, main rotor revolutions, and flight control system settings are considered. The helicopter dynamic model was developed in the FLIGHTLAB environment and was then validated based on flight test data. The model used for the calculation of energy consumption was developed using the electric and dynamic characteristics of the main rotor, electric motor, and transmission system. The main part of this work concerns the analysis of electric energy consumption during the vehicle’s flight via the use of an automatic flight control system (AFCS) that ensures repeatable flight conditions. The AFCS was designed such that it includes both path and attitude control to provide hover and cruise control modes. The helicopter’s energy consumption was analyzed during different phases of flight, when executing maneuvers, and using different main rotor angular velocities to perform - a given task. The results show that the level of energy consumption significantly depends on the helicopter’s main rotor revolutions, flight speed, and the maneuvers performed. The proposed methodology can be used in prospective energy-efficient mission planning and UAV helicopter design.