Reconfigurable Flight Control Research Articles

Flight Control Reconfiguration in Oscillatory Failure Case Scenarios

A fault detection system together with a flight control reconfiguration algorithm is proposed to tackle the problem of oscillatory failure case scenarios in hydraulically actuated flight control loops. The fault detection system employs a set of residual filters designed using a model-based approach via command-input decoupling and free assignment of the filter dynamics via dynamic inversion. As underlying design model, an optimized, multi-model hydraulic actuator approximation covering the actuator dynamics together with stochastically distributed, uncertain parameters is derived. A flight control reconfiguration algorithm is presented which smoothly transitions the control law from its normal configuration to the alternate law after detection of a fault. The performance of the transition is analyzed using advanced linear time-varying analysis methods based on an extension of the well-known Bounded Real Lemma. The achieved detection and reconfiguration performance is verified via non-linear simulations.

Adaptive Neural Networks-Based Dynamic Inversion Applied to Reconfigurable Flight Control and Envelope Protection Under Icing Conditions

Aircraft icing can result in degradation of the aerodynamic characteristics and reduction of the control effectiveness, which would pose serious threats to flight safety. Reconfigurable flight control and envelope protection of iced aircraft have become an effective solution to ensure flight safety in icing encounters. In this study, the dynamic model of the iced aircraft was established, and high precision numerical simulation method and wind tunnel virtual flight experiment were applied to obtain the icing aerodynamic database. Furthermore, the reconfigurable flight control law was designed by using the adaptive neural networks based dynamic inversion (ANN-DI) control method. Simulation results demonstrate that the control method behaves well tracking performance and strong robustness in the presence of modeling errors and control surface damage. After that, an icing envelope protection system was designed based on control limiting strategy and the ANN-DI control was applied to calculate the control surface deflection limits based on the limit values of the key flight safety parameters. Finally, the designed icing envelope protection system has been verified through simulation in two autopilot modes under icing conditions. The simulation results obtained here show that the system could keep the key flight safety parameters such as the flight speed, the angle of attack (AOA), the side slip angle, and bank angle within the flight safe region under icing conditions. The method proposed in this study is expected to provide flight safety measures for in-flight icing.

THE RECONFIGURABLE FLIGHT CONTROL SYSTEM FOR RECOVERING STABILITY AND CONTROLLABILITY OF THE AIR-PLANE IN SPECIAL FLIGHT SITUATIONS

In this paper is given comparative analysis of the statistics adverse flight conditions in flight. Possibility of application of system methods parametric and structural reconfiguration in order to prevent the current flight situation in catastrophic is examined. In this paper, reconfigurable (active) flight control system for recovering stability and controllability of the aircraft when an unexpected problem (such as faults or failures to the actuators/sensors or structural damage) occurs during a flight is proposed.

Flight control reconfiguration of unmanned tiltrotor aircraft

The unmanned tiltrotor aircraft has many flying advantages, in the meantime it brings some new problems. In order to improve the flight stability of the UAV, the simulation of flight control law reconstruction was designed based on the multi-model adaptive control theory for actuator failure. Using the principle of small disturbance, the linear model of the UAV was established. Aiming at several typical actuator failures, the reconfigurable control strategy was designed. The classical PID control method was used to design the control law structure. Simulation results show that the proposed reconfiguration control strategy can be used in unmanned tiltrotor aircraft, which has good fault-tolerant effects and can significantly improve the safety of aircraft performance.

Adaptive LFT control of a civil aircraft with online frequency‐domain parameter estimation

SummaryThis paper describes the application of an indirect linear fractional transformation (LFT)–based state‐space adaptive control scheme to a transport aircraft, within the context of the European project REconfiguration of CONtrol in Flight for Integral Global Upset REcovery. The principle of the scheme is to design and validate off‐line a gain‐scheduled controller, depending on the plant parameters to be estimated, and to combine it online with a model estimator, so as to minimize the onboard computational time and complexity. A modal approach, very classical for the design of a flight control law, is used to directly synthesize the static output feedback LFT controller, depending on the control and stability derivatives, ie, the parameters of the linearized aerodynamic state‐space model to be estimated. Since the gain‐scheduled LFT controller online depends on the parameter estimates instead of the true values, its robustness to transient and asymptotic estimation errors needs to be assessed using μ and integral quadratic constraint analysis techniques. A primary concern being an online implementation, a fully recursive frequency‐domain estimation technique is proposed, with a low online computational burden and the capability to track time‐varying parameters. Full nonlinear simulations along a trajectory validate the good performance properties of the combined estimator and gain‐scheduled flight controller. To some extent, minimal guaranteed stability and performance properties of the adaptive scheme can be ensured by switching to a robust controller when the parameter estimates are not reliable enough, thus bypassing the Certainty Equivalence Principle.

Development and evaluation of an integral sliding mode fault‐tolerant control scheme on the RECONFIGURE benchmark

SummaryThis paper describes the development, application, and evaluation of a linear parameter‐varying integral sliding mode control allocation scheme to the Reconfiguration of Control in Flight for Integral Global Upset Recovery benchmark model to deal with an actuator failure/fault scenario. The proposed scheme has the capability to maintain close to nominal (fault free) load factor control performance in the face of elevator failures/faults by including a retrofitted integral sliding mode term and then rerouting (via control allocation) the augmented control signal to healthy elevators without reconfiguring the baseline controller. In order to mitigate any chattering appearing in the elevator demands, the retrofitted signal is based on a super‐twisting sliding mode structure. This produces a control signal that is continuous and does not have the discontinuous switching nature of traditional sliding mode schemes. The scheme is evaluated using an industrial Functional Engineering Simulator developed as part of the Reconfiguration of Control in Flight for Integral Global Upset Recovery project. Monte Carlo campaign results are shown to demonstrate the performance of the proposed scheme.

Reconfigurable Flight Control Design for the Complex Damaged Blended Wing Body Aircraft

Reconfigurable Flight Control Design for the Complex Damaged Blended Wing Body Aircraft

An overview of the FP7 RECONFIGURE project: industrial, scientific and technological objectives

This paper details the industrial challenges, goals and objectives of the European Framework 7th project termed “REconfiguration of CONtrol in Flight for Integral Global Upset REcovery” (RECONFIGURE). This project aims at investigating and developing advanced aircraft Guidance, Navigation and Control (GNC) technologies that facilitate the automated handling of off-nominal events and optimize the aircraft status and flight. These technologies will extend the operation of the current GNC functionalities that assist the pilot and optimize the aircraft performance. Thus, the aim is to provoke a change in aircraft transport towards: “Full-time, all-event availability of performance-enhancement electrical fly-by-wire”. Three key enablers have been identified for moving towards this new paradigm: Flight Parameter Estimation, Fault Detection and Diagnosis, and Fault Tolerant Control.

Reconfigurable control of an UAV against sensor/actuator failures

An active fault-tolerant flight control system against sensor/actuator failures for unmanned aerial vehicle (UAV) is proposed. In the case of sensor faults, the faulty sensor is isolated, and the Kalman filter (KF) that ignores the feedback from the faulty sensor, is built. If the fault is an actuator fault, the actuator fault isolation and identification are performed. For this purpose the partial loss and stuck faults in the actuators are isolated and identified by the two-stage KF. The parameters of the feedback controller are tuned by the control reconfiguration procedure. In the simulations, the longitudinal and lateral dynamics of the UAV model is considered, and reconfigurable flight control against sensor/actuator failures is implemented.

Development of the block diagram of aircraft control system in case of an emergency

The main causes of an in-flight emergency were analyzed. Statistics of air accidents, caused by bird strikes were examined, an increase in such air accidents was noted. The formulas of the aerodynamic coefficients, which included emergency coefficients were developed. These formulas are systems of differential equations of the aircraft longitudinal and lateral movement, which include coefficients that describe the impact of an emergency on the aircraft aerodynamic properties. Equations of the aircraft motion dynamics taking into account the impact of an emergency were also formulated. The development of these equations is needed to create an aircraft control system in case of an emergency and work out a stabilizing effect. Block diagram of the aircraft flight control reconfiguration system in case of an emergency was elaborated. Designing the flight control reconfiguration system will allow to prevent emergency development and follow the intended flight path. As a result of the study, the basic causes of the failures that lead to emergencies, including lightning strike damage, bird strike damage, drive power loss or sensor failures were revealed. Necessary characteristics, determination of which allows to use model predictive control were also singled out. These characteristics are forecast horizon length, constraints on the control signal, sampling increment. Using the reconfiguration system will allow to reduce the accident risk, improve the aircraft sustainability and controllability, increase overall flight safety.

Reconfigurable Control of Morphing Air Vehicle Based on Real-time Dynamic Modeling

This paper describes a reconfigurable flight control system for morphing air vehicles. The approach combines real-time physical model identification with Nonlinear Dynamic Inversion (NDI). It could solve the problem such as severe changes of aerodynamic characteristics or influences of atmospheric disturbances during the primary stage of flight, and fulfill the high robustness requirements of flight control systems. The aerodynamic characteristics are identified by the two step method which consists of a separate state estimation step and an aerodynamic coefficients identification step instead of the one step method. The two step method is based on iterated extended Kalman filter and fading memory least squares method which is easy to achieve on-line. The sensitivity of NDI to modeling errors is eliminated by making use of an on-line updated reference model of the air vehicle, then reconfigures for the changes in real time. Furthermore, the effectiveness and robustness of the designed flight controller has been validated by six Degree-of-freedom (DOF) nonlinear flight simulations with severe changes of aerodynamic characteristics on the morphing air vehicle and unknown atmospheric disturbances.

Adaptive neural observer‐based backstepping fault tolerant control for near space vehicle under control effector damage

In this study, a theoretical framework for reconfigurable flight control is developed and applied to near space vehicle (NSV) attitude dynamics. First, NSV reentry mode is described. Second, an adaptive neural network observer is proposed, which ensures asymptotic convergence of the state observer error to zero under control effector damage and uncertainty. Next, a reconfigurable command-filter backstepping controller is designed based on the adaptive neural network observer. The authors focus is on the accommodation of the control effector damage, uncertainty and resulting disturbances. It is shown that the presented new control design results in asymptotic convergence of the attitude tracking error to zero. Finally, simulation results are given to demonstrate the effectiveness and potential of the proposed fault tolerant control scheme.

Reconfigurable flight control based on nonlinear dynamic inversion and dynamic control allocation

Based on nonlinear dynamic inversion (NDI) and dynamic control allocation, a new reconfigurable flight control scheme is proposed for multi effector aircraft. Firstly, basic flight control law is designed by NDI method to produce desired moment command according to the given attitude angle command. Then, the moment command is optimally distributed into individual control surfaces with position and rate constraints by dynamic control allocation (DCA) algorithm. In the face of control surface faults, control reallocation is performed in the remained control surfaces to fulfil flight reconfiguration, and the basic flight control law need not to be redesigned. The reconfigurable flight control scheme is evaluated by a nonlinear six degree–of–freedom (DoF) aircraft model under jammed case and damaged case, respectively. Effectiveness of the reconfigurable flight control method is demonstrated by simulation results.

AIRBUS efforts towards advanced real-time Fault Diagnosis and Fault Tolerant Control

In this article the industrial goals and objectives of the European Framework 7th project termed “REconfiguration of CONtrol in Flight for Integral Global Upset Recovery (RECONFIGURE)” are presented. Commercial aircraft fault tolerant control (FTC) strategies in the flight control system (FCS) are based on fail-safe flight control law reconfiguration which relies on upstream hardware redundancy-based robust Fault Detection and Diagnosis (FDD). This industrial state-of-practice fits well in the current certification process but it also decreases the easiness of the piloting task as soon as the system level of degradation increases. Thus, the main goal of RECONFIGURE is to research and develop aircraft FDD and FTC technologies that facilitate the automated handling of off-nominal/abnormal events and optimize the aircraft status and flight. The article details the project description of work, from industrial benchmark (fault scenarios and aircraft model) up to industrial verification and validation (V&V) activities, via advanced FDD/FTC research and development. The expected results and perspectives are also presented.

Survey on nonlinear reconfigurable flight control

An overview on nonlinear reconfigurable flight control approaches that have been demonstrated in flight-test or highfidelity simulation is presented.Various approaches for reconfigurable flight control systems are considered,including nonlinear dynamic inversion,parameter identification and neural network technologies,backstepping and model predictive control approaches.The recent research work,flight tests,and potential strength and weakness of each approach are discussed objectively in order to give readers and researchers some reference.Finally,possible future directions and open problems in this area are addressed.

Analysis of partial wing damage on flying-wing unmanned air vehicle

This article investigates the effect of asymmetric wing damage on flight dynamic characteristics of a flying-wing single motor unmanned air vehicle. To construct a six degree-of-freedom model of the damaged aircraft, a flying-wing type unmanned aerial vehicle is designed, and the wind tunnel test for damaged configurations is performed to identify the change of aerodynamic coefficients. The changes of mass, center of gravity, and moment of inertia are also calculated for each damage configuration with CATIA. The changed trim states are calculated depending on the severity of damage, and the movements of poles in longitudinal/lateral-directional flight modes are examined to evaluate the change of the dynamic stability and performance. Numerical simulations and eigenvalue analyses are performed to investigate the altered flight dynamics. It is verified that an asymmetrically wing-damaged unmanned air vehicle shows a sluggish roll behavior with longitudinal instability, and the result of this study can be a cornerstone for the future research on reconfigurable flight controller design against aircraft damage.

Reconfigurable Flight Control Design for Combat Flying Wing with Multiple Control Surfaces

With control using redundant multiple control surface arrangement and large-deflection drag rudders, a combat flying wing has a higher probability for control surface failures. Therefore, its flight control system must be able to reconfigure after such failures. Considering three types of typical control surface failures (lock-in-place (LIP), loss-of-effectiveness (LOE) and float), flight control reconfiguration characteristic and capability of such aircraft types are analyzed. Because of the control surface redundancy, the aircraft using the dynamic inversion flight control law already has a control allocation block. In this paper, its flight control configuration during the above failures is achieved by modifying this block. It is shown that such a reconfigurable flight control design is valid, through numerical simulations of flight attitude control task. Results indicate that, in the circumstances of control surface failures with limited degree and the degradation of the flying quality level, a combat flying wing adopting this flight control reconfiguration approach based on control allocation could guarantee its flight safety and perform some flight combat missions.

Reconfigurable flight control for robust transient response

When a control surface fails during aircraft flying, reconfigurable control system with new configuration aims to use the other available control surfaces and attempts to preserve the design properties of the original system. Restoring transient response is particularly important when transition from damaged to healthy configuration takes place. In this article, a new design procedure for robust transient response of the reconfigured system is presented. A linear algebraic formulation for right eigenstructure assignment in state feedback format is derived. A system of linear equations for the controller is solved. Reconfigurable control using an F-18 model is illustrated.

Modular robust reconfigurable flight control system design for an overactuated aircraft

In this study a modular approach to the robust reconfigurable flight control system design for an overactuated aircraft is proposed. The structure of the proposed scheme consists of three parts: a backstepping controller module, a robust control allocator and an online actuator effectiveness estimator. Firstly, the backstepping control law is developed for the strict feedback form of an Aero-Data Model in Research Environment aircraft to produce the desired commands. Furthermore, a novel robust optimisation-based control allocation algorithm is proposed to distribute the commands among redundant actuators with the consideration of control effectiveness uncertainties. Lastly, the control effectiveness factors are introduced to denote the healthiness of the actuators, and the least trimming squares-based estimator is designed for online estimation of the actuator effectiveness. With the proposed scheme, good tracking performance, robustness and reconfigurable capability are achieved. Evaluation of the overall system is accomplished by numerical simulation with various conditions, including adverse scenarios where actuator failures occur. The results show the effectiveness of the proposed scheme.

Design and simulation of fault tolerant flight control based on a physical approach

This paper presents a study on fault tolerant flight control of a benchmark aircraft model, using a physical modular approach. Reconfiguring control is implemented by making use of adaptive nonlinear dynamic inversion for autopilot control. The weakness of classical nonlinear dynamic inversion, its sensitivity to modeling errors, is circumvented here by making use of a real-time identified physical model of the damaged aircraft. With help of the Boeing 747 benchmark simulation model, including the realistic component as well as the structural failure modes, it is possible to analyze the damage accommodation capabilities of the considered approach. In failure conditions, the damaged aircraft model is identified in real time by the two-step method and this model is applied subsequently to the model-based adaptive nonlinear dynamic inversion routine in a modular structure, which allows flight control reconfiguration on-line. Pseudo Control Hedging is included to guarantee that no unachievable reference commands are given to the system, which would otherwise result in control effector saturation. Various simulated reconfiguration test results are shown for damaged aircraft models. These results indicate satisfactory failure handling capabilities of this fault tolerant control setup, for component as well as structural failures.