Fault Tolerant Flight Control System Research Articles

Promoting the Maneuverability and Fault-Tolerant Control Capabilities of Dual-System/Hybrid VTOL UAVs

This paper presents an active fault-tolerant flight control system (FCS) design for the dual-system/hybrid VTOL UAV configuration that maximally exploits its inherent over-actuation abilities to provide higher levels of fault-tolerance and reliability compared to that of the other VTOL UAVs configurations up to this point. The significance of this study is to convert the main drawback of having the vertical rotors as dead weights during the cruise to a key advantage where all the UAV's controls are kept active during all the flight phases raising the UAV's fault-tolerance and maneuverability abilities. The FCS proposed elaborates on a new architecture for the hierarchical automatic control loops using the dynamic inversion control to design the trajectory tracking virtual commands and employing optimal dynamic control allocation to optimally resolve the controls redundancy. Regarding fault-tolerance, the presented FCS handles simultaneous failures and jamming of all the control surfaces during flight where the control commands to the healthy controls (vertical rotors) were automatically adapted such that the trimming and trajectory tracking were successfully maintained till the mission end. Additionally, this paper addresses for the first time the employment of the controls redundancy to enhance the VTOL UAV's maneuverability in fault-free cases, where we present a study of reducing the minimum turn radius of the UAV when the vertical rotors are employed with the control surfaces during the maneuver. A reduction of 38% in the coordinated steady-level minimum turn radius turn at 35 m/sec flight speed was achieved.

Flight Test Techniques - An Overview

Flight test techniques towards performance, handling qualities, stability and control are brought out. Hazardous flight conditions are covered. Instrumentation aspects are highlighted. Data reduction and some flight evaluation cases are addressed. Airframe structural performance under different conditions of flight test are explained. Fault tolerant flight control system testing is brought out. Features related to online development of restructurable and reconfigurable control laws are highlighted.

Recent advances in active fault tolerant flight control systems

The Flight Control System (FCS) is considered as the brain of an aerial vehicle. It is a mechanism through which pilot’s commands are transferred to the actuators of the aircraft control surfaces. In order to ensure safety and increase reliability of aerial vehicles, development of fault tolerant FCSs has been the focus of research community for past few decades. Fault tolerant ability enables an aircraft to maintain satisfactory performance even in the state of a fault. Fault Tolerant Control Systems (FTCS) are categorized as passive and active control systems. Passive FTCS are designed to mitigate the effects of certain known faults. These faults can be related to sensor failure, actuator failure, or system component failure. On the other hand, active FTCS contain a controller reconfiguration mechanism, whereby, they can adjust the controller input online to mitigate the effects of the faults. In this way, they can accommodate complicated and versatile faults as compared to their passive counterparts. This paper presents a review of significant research during last decade in active fault tolerant control with applications to FCSs. A review of state-of-the-art works in this domain has also been presented. Upon review, these state-of-the-art research interests have been categorized into respective categories. Furthermore, research works have been cataloged based on their technology readiness levels. Based on these reviews, future research directions have also been highlighted.

Fuzzy robust fault estimation scheme for fault tolerant flight control systems based on unknown input observer

Purpose The purpose of this study is to present a new integrated structure for a fault tolerant aircraft control system because fault diagnosis of flight control systems is extremely important in obtaining healthy flight. An approach to detect and isolate aircraft sensor faults is proposed, and a new integrated structure for a fault tolerant aircraft control system is presented. Design/methodology/approach As disturbance and sensor faults are mixed together in a flight control system, it is difficult to isolate any fault from the disturbance. This paper proposes a robust unknown input observer for state estimation and fault detection as well as isolation using fuzzy logic. Findings The dedicated observer scheme (DOS) and generalized observer scheme (GOS) are used for fault detection and isolation in an observer-based approach. Using the DOS, it has been shown through simulation that sensor fault detection and isolation can be made, but here the threshold value must be well chosen; if not, the faulty sensor cannot be correctly isolated. On the other hand, the GOS is more usable and flexible than the DOS and allows isolation of faults more correctly and for a fuzzy logic-based controller to be used to realize fault isolation completely. Originality/value The fuzzy logic approach applied to the flight control system adds an important key for sensor fault isolation because it reduces the effect of false alarms and allows the identification of different kinds of sensor faults. The proposed approach can be used for similar systems.

Aircraft flight control system fault tolerance under structural and parametric uncertainties

The concept of an intelligent hybrid aircraft fault-tolerant flight control system operating under complete parametric and structural uncertainty is considered. Fault tolerance in the proposed system is ensured through the efficient integration of model-based and model-free health monitoring and reconfiguring methods.

Pilot-in-the-loop simulation of simple adaptive fault-tolerant controller

A piloted simulator evaluation is an important step for making a Fault-Tolerant Flight Control (FTFC) system more practical and reliable. Especially, in the case of an adaptive technique, conformance of the adaptive controller to the human pilot's intended maneuver must be investigated carefully since the overall control performance will be changed by the additional loop closed by the pilot. In this paper, we present a pilot-in-the-loop simulation of Simple Adaptive Control (SAC) with a PID compensator. By SAC adjusting to the faulty aircraft dynamics, the proposed FTFC system reduces the pilot workload in emergency situations.

A Detail of Fault Tolerant Flight Control Techniques

Fault tolerant flight control (FTFC) system deals with the detection and diagnosis of faults and looks at the task of regaining control in the presence of the fault. Current modern aircraft are made highly complex for comfort or high performance. The study of improvement in safety, redundancy, and adapting the flight control laws after its occurrence of faults has fascinated the thoughtfulness of several investigators in the previous two decades. Overall illustration of different fault diagnosis and fault-tolerant flight control approaches involved are provided in this review paper.

Adaptive Closed-Loop Control Allocation-Based Fault Tolerant Flight Control for an Overactuated Aircraft

This paper discusses the adaptive control allocation based fault tolerant flight control problem for an overactuated aircraft in the presence of unknown uncertainties and actuator faults. Inspired by the feedback of control moments, an innovative adaptive closed-loop control allocation scheme with an estimator for the uncertainties is designed to tackle the distinct non-monotonic and the coupled nonlinearity caused by actuator failures or faults. Furthermore, since actuator faults will cause difficulty in modeling the aircraft dynamics precisely, an adaptive super twisting sliding mode controller is developed to track the reference trajectory. The convergence of the adaptive closed-loop control allocation and the stability of the fault tolerant flight control system is analyzed. Simulation results indicate the effectiveness and performance of the developed controller.

Robust Model Reference Fault Detection and Identification System for Fixed Wing Aircrafts

Fault Detection and Identification system (FDI) and Fault Tolerant Flight Control (FTFC) system are used to correct the faulty operation of an aircraft. Both FDIs and FTFCs have operational disadvantages due to their inherent limitation of fault source identification. This paper presents the design and implementation of a robust model reference fault detection and identification (MRFDI) system on a fixed-wing aircraft for identifying actuator fault, instrument fault and presence of any uncertainties. The proposed MRDFI fuses the real-time parameters and actuator feedback to combine the advantages of data driven and model reference FDI that makes robust fault estimation. The MRFDI system is implemented on a typical aircraft altitude hold autopilot simulation environment with a predefined fault scenario. The fault scenario includes a faulty elevator, a faulty skin-implantable sensor and wind gust as environmental uncertainty. The MRFDI performs logical analysis to detect fault using state-dependent real-time parameters and state-independent skin implantable sensor. This two-step fault detection method makes MRFDI robust to any type of fault identification. The results show that the MRFDI detects and distinguishes faults in actuator, instrument and any of the listed uncertainties thrown by the environment accurately.

Flight test of fault-tolerant flight control system using simple adaptive control with PID controller

PurposeThis paper aims to demonstrate the effectiveness of a fault-tolerant flight control method by using simple adaptive control (SAC) with PID controller.Design/methodology/approachNumerical simulations and flight tests are executed for pitch angle and roll angle control of research aircraft MuPAL-α under the following fault cases: sudden reduction in aileron effectiveness, sudden reduction in elevator effectiveness and loss of longitudinal static stability.FindingsThe simulations and flight tests reveal the effectiveness of the proposed SAC with PID controller as a fault-tolerant flight controller.Practical implicationsThis research includes implications for the development of vehicles’ robustness.Originality/valueThis study proposes novel SAC-based flight controller and actually demonstrates the effectiveness by flight test.

Design of a tolerant flight control system in response to multiple actuator control signal faults induced by cosmic rays

Due to continued miniaturization, semiconductor-based components used in high-performance digital microelectronics are becoming increasingly sensitive to cosmic rays and solar particle events. In the context of high-altitude flight control systems based on fly-by-wire techniques, this may produce sensor noise or affect actuator control signals. Although the consequences so far have been simply reductions in aircraft performance, catastrophic scenarios may be envisioned. In this article, we propose a novel architecture for a fault-tolerant flight control system able to detect and compensate for cosmic ray-induced multiple-bit upsets that affect actuator control signals in modern fly-by-wire avionics systems while assuming that the actuator itself remains healthy. A fault detection and diagnosis procedure was designed using a geometric approach combined with an extended multiple-model adaptive estimation technique. This procedure is able to process multiple faulty actuator-control signals and identify their parameters. The parameters thus obtained are then used with a reconfigurable sliding-mode control to compensate for such errors by mobilizing the remaining actuators’ healthy control signals. Lyapunov stability theory is used to analyze the closed-loop system stability. Simulation results using Matlab /Simulink showed the effectiveness of the proposed approach in the case of a system challenged with double faults.

Active Fault-Tolerant Control of UAV Dynamics against Sensor-Actuator Failures

AbstractIn this paper, an active fault-tolerant flight control system against sensor/actuator failures for unmanned aerial vehicles (UAVs) is proposed. First, an approach to detecting and isolating UAV sensor failures affecting the mean of the Kalman filter (KF) innovation sequence is proposed. Second, an adaptive two-stage linear Kalman filtering algorithm is used to isolate the sensor and actuator faults and to estimate the loss of control effectiveness and the magnitude of degree of stuck faults in a UAV model. Control effectiveness factors and stuck magnitudes are used to quantify the faults entering the UAV flight control system through actuators. In the case of a sensor fault, the faulty sensor is isolated, and the KF that ignores the feedback from the faulty sensor is built. If the fault is an actuator fault, then the actuator fault isolation and identification are performed using the adaptive two-stage KF. The parameters of the feedback controller are tuned by the control reconfiguration procedure...

Active fault-tolerant control strategy of large civil aircraft under elevator failures

Aircraft longitudinal control is the most important actuation system and its failures would lead to catastrophic accident of aircraft. This paper proposes an active fault-tolerant control (AFTC) strategy for civil aircraft with different numbers of faulty elevators. In order to improve the fault-tolerant flight control system performance and effective utilization of the control surface, trimmable horizontal stabilizer (THS) is considered to generate the extra pitch moment. A suitable switching mechanism with performance improvement coefficient is proposed to determine when it is worthwhile to utilize THS. Furthermore, AFTC strategy is detailed by using model following technique and the proposed THS switching mechanism. The basic fault-tolerant controller is designed to guarantee longitudinal control system stability and acceptable performance degradation under partial elevators failure. The proposed AFTC is applied to Boeing 747-200 numerical model and simulation results validate the effectiveness of the proposed AFTC approach.

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.

Flight Control: Challenges and Opportunities

摘要: 当前,飞行器控制的发展面临前所未有的机遇与挑战.基于对飞行器的发展趋势、新需求和新技术特征的分析,本文从飞行器新技术特征、信息化环境、无人系统自主性、高可靠可重构容错系统、飞控系统评估与确认五个方面研究和分析了飞行器控制面临的机遇与挑战.为了达到利用机遇和赢得挑战的目标,作者建议加强如下五个方面的研究: 加强面向飞行器新技术特征的飞行器控制概念、理论与方法研究; 加强面向信息化环境的控制、计算与通讯一体化,以及控制、决策与管理一体化的研究; 加强面向不确定性的无人系统高级别自主性的研究; 加强面向高可靠、高安全性的可重构容错飞控系统的研究; 加强面向高效、高可信度的飞控系统评估与确认方法的研究. 关键词: 飞行控制 / 飞行器新特征 / 信息化 / 容错系统 / 自主能力

Differential geometry based active fault tolerant control for aircraft

This work shows how to use a differential geometry tool to design a novel nonlinear active fault tolerant flight control system for aircraft. The proposed control scheme consists of two main subsystems: a controller, which is designed for the nominal plant, and a fault detection and diagnosis module, which provides fault estimation. A further feedback loop exploits the fault estimation to accommodate faults affecting the system. The estimate convergence and the stability of the active fault tolerant flight controller are theoretically proved. Finally, high fidelity simulations show the effectiveness of the scheme.

Recursive Actuator Fault Detection and Diagnosis for Emergency Landing of UASs

This paper presents a practical recursive fault detection and diagnosis (FDD) scheme for online identification of actuator faults for unmanned aerial systems (UASs) based on the unscented Kalman filtering (UKF) method. The proposed FDD algorithm aims to monitor health status of actuators and provide indication of actuator faults with reliability, offering necessary information for the design of fault-tolerant flight control systems to compensate for side-effects and improve fail-safe capability when actuator faults occur. The fault detection is conducted by designing separate UKFs to detect aileron and elevator faults using a nonlinear six degree-of-freedom (DOF) UAS model. The fault diagnosis is achieved by isolating true faults by using the Bayesian Classifier (BC) method together with a decision criterion to avoid false alarms. High-fidelity simulations with and without measurement noise are conducted with practical constraints considered for typical actuator fault scenarios, and the proposed FDD exhibits consistent effectiveness in identifying occurrence of actuator faults, verifying its suitability for integration into the design of fault-tolerant flight control systems for emergency landing of UASs.

Fault-Tolerant Control of a Unmanned Aerial Vehicle with Partial Wing Loss

Abstract This paper presents the design, implementation and flight testing of a fault-tolerant flight control system for an unmanned aerial vehicle that can accommodate partial wing loss. A dynamic model for the damaged unmanned aerial vehicle (UAV) is based on an asymmetric six degrees-of-freedom equations of motion model. The effect of partial wing loss on the aerodynamic coefficients, centre of mass location and moments of inertia are calculated as a function of percentage wing loss using vortice lattice techniques and computer assisted design software respectively. The model also accounts for changes in the aileron control authority due to partial control surface loss. The equilibrium manifold of the aircraft state is determined as a function of partial wing loss by solving the nonlinear differential equations with a sequential quadratic programming algorithm. A linear parameter-varying model is then obtained by linearising the nonlinear model over the range of equilibrium states. It is found that the trim state of the aircraft changes significantly over the range of percentage wing loss, but that the stability about the trim condition does not change drastically. An acceleration-based flight control system is designed and its robustness is analysed in terms of maximum variations in gain and phase margins. A flight test is performed where 20% of the wing is jettisoned in-flight. The experimental results show that the flight control system is able to stabilise the damaged aircraft and continue with normal waypoint navigation.

Nonlinear Actuator Fault Detection for Small-Scale UASs

This paper presents a recursive strategy for online detection of actuator faults on a unmanned aerial system (UAS) subjected to accidental actuator faults. The proposed detection algorithm aims to provide a UAS with the capability of identifying and determining characteristics of actuator faults, offering necessary flight information for the design of fault-tolerant mechanism to compensate for the resultant side-effect when faults occur. The proposed fault detection strategy consists of a bank of unscented Kalman filters (UKFs) with each one detecting a specific type of actuator faults and estimating corresponding velocity and attitude information. Performance of the proposed method is evaluated using a typical nonlinear UAS model and it is demonstrated in simulations that our method is able to detect representative faults with a sufficient accuracy and acceptable time delay, and can be applied to the design of fault-tolerant flight control systems of UASs.

Fault tolerant flight control system for the tilt-rotor UAV

A fault tolerant control scheme for actuator and sensor faults is proposed for a tilt-rotor unmanned aerial vehicle (UAV) system. The tilt-rotor UAV has a vertically take-off and landing (VTOL) capability like a helicopter during the take-off & landing while it could cruise with a high speed as a conventional airplane flight mode. A dual system in the flight control computer (FCC) and the sensor is proposed in this study. To achieve a high reliability, a fault tolerant flight control system is required for the case of actuator or sensor fault. For the actuator fault, the fault tolerant control scheme based on model error control synthesis is presented. A designed fault tolerant control scheme does not require system identification process and it provides an effective reconfigurability without fault detection and isolation (FDI) process. For the sensor fault, the fault tolerant federated Kalman filter is designed for the tilt-rotor UAV system. An FDI algorithm is applied to the federated Kalman filter in order to improve the accuracy of the state estimation even when the sensor fails. For a linearized six-degree-of-freedom linear model and nonlinear model of the tilt-rotor UAV, numerical simulation and process-in-the-loop simulation (PILS) are performed to demonstrate the performance of the proposed fault tolerant control scheme.