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The Flight Control System (FCS) is one of the most important systems in all modern aircraft. For such systems it is required to have robust Fault Detection Isolation and Reconfiguration (FDIR) functionalities with high detection performance. In this work we specifically consider the Oscillatory Failure Cases (OFC), which, if not mitigated, can cause additional structural loads for which the aircraft is not designed. A Sliding Mode Observer (SMO) based detection method is proposed for fast and consistent detection of these OFC faults. A benchmark of a generic aircraft FCS equipped with OFC simulation capabilities, as well as the presented solution for detection, have previously been presented within a competition at the 2020 IFAC World Congress. [ABSTRACT FROM AUTHOR]

Lightweight flexible aircraft suffers from unwanted oscillatory vibrations during aircraft manoeuvres. A recently developed distributed-delay signal (DZV) shaper is therefore proposed to be applied as a feedforward controller to alleviate the manoeuvre loads, as an alternative to traditional structural filters used routinely in this context. Structural filters are essentially linear low-pass filters with bandwidth below the significant flexible modes, applied to control signals generated either by the pilot's direct input or by the flight control system. It has been showed that if instead a properly tuned signal shaper is used, better performance can be achieved: first, the target modes are significantly attenuated while the responsiveness of the aircraft is less compromised and secondly, the oscillatory nature of the vibrations are reduced. The high fidelity simulation results on a full scaled dynamic model of a highly flexible blended wing–body (BWB) aircraft show that in comparison to traditional structural filters, signal shapers significantly reduce the wing root loading (forces and moments) which provides potential structural benefits. [ABSTRACT FROM AUTHOR]

A comprehensive autolanding design for a representative model of a twin-engined commercial aircraft is presented in this paper. To facilitate the design task and minimize control law switching, a cascaded control structure is selected which resembles integrator chains. Classical loopshaping and robust control techniques are used to design the individual control loops. The emphasis is on providing a complete and comprehensive qualitative design strategy. The control system’s ability to safely land the aircraft despite strong crosswind in a variety of possible scenarios is demonstrated in an industry-grade verification campaign. Nonlinear Monte Carlo simulations of the airliner model are used to assess the risk of unsafe landing conditions and provide insight into the performance characteristics and limitations of the proposed control system. [ABSTRACT FROM AUTHOR]

An adaptive neural guidance and control system is proposed in this paper for a generic fixed-wing aerial robot. Unlike most of the existing low-level control systems, which utilize a non-adaptive guidance loop, in this work both the guidance and control loops are trained using an efficient adaptive neural algorithm. A feedforward neural network is employed in each loop to identify uncertain dynamics, while an adaptive disturbance observer allows to compensate for both the external disturbances and estimation error of the neural network. This would lead to a resilient flight control system, and thus, the asymptotic stability of both the guidance and control loops can be theoretically ensured for a generic aerial robot subject to different types of nonparametric internal and external disturbances. Besides, to enhance the learning efficiency, a composite learning method is adopted in which the neural network and the disturbance observer are trained using a composite error function consisting of the tracking error and the estimation error of an introduced adaptive state observer. To the best of the authors' knowledge, this is the first completely adaptive integrated guidance and control system with guaranteed stability under parametric and nonparametric internal and external disturbances. The introduced control system is then applied to a simulation model of an electric aircraft that has been validated on the basis of real data and flight experiments. The obtained results indicate that the proposed approach could be considered a reliable guidance and control system for a generic fixed-wing aerial vehicle in the presence of actuator faults, unmodeled dynamics, external disturbances, and measurement noises. [ABSTRACT FROM AUTHOR]

The design of a high-performance guidance and control system for a small-scale helicopterUnmanned Aerial Vehicle (UAV), with an engine OFF flight condition (i.e. autorotation), is known to be a challenging task. It is the purpose of this paper to present a Trajectory Planning (TP) and Trajectory Tracking (TT) system, having onlinecomputational tractability. The presented Flight Control System (FCS) is anchored within the aggregated paradigms of differential flatness based optimal planning, and robust control based tracking. In particular the first real-time feasible, model-based TP and model-based TT, for a small-scale helicopter in autorotation is being demonstrated using a high-fidelity, high-order, nonlinear helicopter simulation. [ABSTRACT FROM AUTHOR]

Energy harvesting based on tethered kites benefits from exploiting higher wind speeds at higher altitudes. The setup considered in this paper is based on a pumping cycle. It generates energy by winching out at high tether forces, driving an electrical generator while flying crosswind. Then it winches in at a stationary neutral position, thus leaving a net amount of generated energy. The focus of this paper is put on the flight control design, which implements an accurate direction control towards target points and allows for a flight with an eight-down pattern. An extended overview on the control system approach, as well as details of each element of the flight controller, is presented. The control architecture is motivated by a simple, yet comprehensive model for the kite dynamics. In addition, winch strategies based on an optimization scheme are presented. In order to demonstrate the real world functionality of the presented algorithms, flight data from a fully automated pumping-cycle operation of a small-scale prototype are given. The setup is based on a 30 m 2 kite linked to a ground-based 50 kW electrical motor/generator by a single line. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Two different approaches for fault detection, the geometric and the detection filter based methods, are compared in the paper from practical aspects, using the linear parameter-varying (LPV) framework. Presenting two designs allows a comparison of global, system level, and local component level fault detection methods with special emphasis on their relevance to aircraft industry. Practical engineering design decisions are highlighted via applying them to a high-fidelity commercial aircraft problem. The successive steps of the design, including fault modeling, LPV model generation, and LPV FDI filter synthesis, including implementation aspects, are discussed. Results are presented according to the industrial assessment perspectives phrased within the EU ADDSAFE project. [ABSTRACT FROM AUTHOR]

The presented work is undertaken within the FP7-ADDSAFE (Advanced Fault Diagnosis for Sustainable Flight Guidance and Control) project, a European collaborative project that aims to propose new fault diagnosis techniques for AIRBUS aircraft that could significantly advance the aircraft performance, e.g. by optimizing the aircraft structural design (weight saving) or decreasing its environmental footprint (e.g. less fuel consumption and noise). The paper discusses the design of a model-based fault detection scheme for robust and early detection of faults in aircraft control surfaces servo-loop. The proposed strategy consists of two fault detectors: The first fault detector is based on a H − / H ∞ residual generator that maximizes sensitivity to any kind of control surface servo-loop faults whilst simultaneously minimizes the influence of unknown inputs. The second fault detector consists of a pure H ∞ residual generator that is sensitive to a restricted set of faults and robust to unknown inputs. By such a structured strategy, it is shown that it is possible to discriminate between different fault types occurring in the control surfaces servo-loop. Monte-Carlo campaigns from a highly representative simulator provided by AIRBUS as well as experimental results obtained on AIRBUS test facilities demonstrate the fault detection performance, robustness and viability of the proposed technique. [ABSTRACT FROM AUTHOR]

In this article a high-fidelity aircraft benchmark, developed by Airbus for advanced flight control related studies, is presented in relation to its evolution towards advanced fault diagnosis within a European 7th Framework Program project entitled "Advanced Fault Diagnosis for Sustainable Flight Guidance and Control (ADDSAFE)". This European project was established to study and facilitate the transfer of model-based fault detection and diagnosis methods from Academia to Industry. The importance of the project arose on the one hand, due to the representativeness of the benchmark, and on the other hand, the industrial benchmarking and validation of the developed designs. The results presented in this article represent a quantitative measure of the success of the project since five of the developed designs were successfully validated in Airbus Verification and Validation (V&V) set-ups, and are currently undergoing further tests towards a possible real aircraft implementation. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the implementation of a predictive control strategy for Unmanned Air Vehicles in the presence of bounded disturbances. The goal is to prove the feasibility of such a real-time optimization-based control design and to demonstrate its tracking capabilities for the nonlinear dynamics with respect to a reference trajectory which is pre-specified via differential flatness. In order to benefit from the computational advantages of the linear predictive control formulations, an off-line linearization strategy of the nonlinear model of the vehicle along the flat trajectory is employed. The proposed method exhibits effective performance validated through software-in-the-loop simulations and real flight tests on different Unmanned Aerial Vehicles (UAVs). [Copyright &y& Elsevier]

Abstract: Aircraft pitot-static probes are essential to airspeed and altitude measurements and safe flight. Measurement integrity is typically achieved via sensor hardware redundancy and a voting system. Hardware redundancy imposes a cost and payload penalty. This paper investigates an analytical alternative to hardware redundancy requiring a mathematical model of faulted and unfaulted pitot-static probes. The most common probe faults–debris, ice, or water blockages–are modeled using physical air data relationships and experimental wind tunnel data. These models are used with a linear model of the NASA GTM aircraft at one flight condition to design robust fault detection filters. Two linear filters are designed to detect faults, reject disturbances, and provide robustness to model errors. Performance is evaluated using experimentally derived fault models with nonlinear aircraft simulations that incorporate actuator uncertainty. [Copyright &y& Elsevier]

Abstract: Due to the inherent instabilities and nonlinearities of rotorcraft dynamics, its changing properties during flight and the engineering difficulties to predict its aerodynamics with high levels of fidelity, helicopter flight control requires the application of special strategies. These strategies must allow to cope with the nonlinearities of the system and assure robustness in the presence of inaccuracies and changes in configuration. In this paper, a novel approach based on an Incremental Nonlinear Dynamic Inversion is applied to simplify the design of helicopter flight controllers. With this strategy, by employing the feedback of acceleration measurements to avoid the need for information relative to any aerodynamic change, the control system does not need any model data that depends exclusively on its states, thus enhancing its robustness to model uncertainties. The overall control system is tested by simulating two tasks with distinct agility levels as described in the ADS-33 helicopter handling qualities standard. The analysis shows that the controller provides an efficient tracking of the commanded references. Furthermore, with the robustness properties verified within the range of inaccuracies expected to be found in reality, this novel method seems to be eligible for a potential practical implementation to helicopter vehicles. [Copyright &y& Elsevier]

Abstract: A novel fault detection and isolation (FDI) method using set-valued observers (SVOs), for uncertain linear parameter-varying (LPV) systems, is introduced. The proposed method relies on SVO-based model invalidation to discard models incompatible with measured data. When compared to the most common strategies in the literature, the suggested approach: (i) under suitable conditions, guarantees false alarms are avoided; (ii) unlike residual-based architectures, does not require the computation of thresholds to declare faults; (iii) has applicability to a wide class of plants. The performance of the proposed approach is assessed in simulation, using the full nonlinear model of a fixed-wing aircraft longitudinal dynamics. [Copyright &y& Elsevier]

Abstract: A method for oscillatory fault detection and isolation is presented and used to detect oscillatory failures of redundant aircraft sensors involved in the computation of flight control laws. The objective is to switch off the erroneous sensor and to compute a consolidated parameter using data from valid sensors, in order to eliminate any anomaly before propagation in the control loop. The benefit of the presented method is to improve the consolidation process with a fault detection and isolation approach when only few sources (less than three) are valid. Different techniques are compared to accurately detect any behavioral change of the sensor outputs. The approach is validated on a normalized real flight data set. [Copyright &y& Elsevier]

Abstract: This paper presents the design and implementation of a model predictive control (MPC) system to guide and control a chasing spacecraft during rendezvous with a passive target spacecraft in an elliptical or circular orbit, from the point of target detection all the way to capture. To achieve an efficient system design, the rendezvous manoeuvre has been partitioned into three main phases based on the range of operation, plus a collision-avoidance manoeuvre to be used in event of a fault. Each has its own associated MPC controller. Linear time-varying models are used to enable trajectory predictions in elliptical orbits, whilst a variable prediction horizon is used to achieve finite-time completion of manoeuvres, and a 1-norm cost on velocity change minimises propellant consumption. Constraints are imposed to ensure that trajectories do not collide with the target. A key feature of the design is the implementation of non-convex constraints as switched convex constraints, enabling the use of convex linear and quadratic programming. The system is implemented using commercial-off-the-shelf tools with deployment using automatic code generation in mind, and validated by closed-loop simulation. A significant reduction in total propellant consumption in comparison with a baseline benchmark solution is observed. [Copyright &y& Elsevier]

Abstract: Quadrotor helicopters continue to grow in popularity for unmanned aerial vehicle applications. However, accurate dynamic models for deriving controllers for moderate to high speeds have been lacking. This work presents theoretical models of quadrotor aerodynamics with non-zero free-stream velocities based on helicopter momentum and blade element theory, validated with static tests and flight data. Controllers are derived using these models and implemented on the Stanford Testbed of Autonomous Rotorcraft for Multi-Agent Control (STARMAC), demonstrating significant improvements over existing methods. The design of the STARMAC platform is described, and flight results are presented demonstrating improved accuracy over commercially available quadrotors. [Copyright &y& Elsevier]

Abstract: This paper deals with industrial practices and strategies for Fault Tolerant Control (FTC) and Fault Detection and Isolation (FDI) in civil aircraft by focusing mainly on a typical Airbus Electrical Flight Control System (EFCS). This system is designed to meet very stringent requirements in terms of safety, availability and reliability that characterized the system dependability. Fault tolerance is designed into the system by the use of stringent processes and rules, which are summarized in the paper. The strategy for monitoring (fault detection) of the system components, as a part of the design for fault tolerance, is also described in this paper. Real application examples and implementation methodology are outlined. Finally, future trends and challenges are presented. This paper is a full version of the invited plenary talk presented by the author on the 1st July 2009 at the 7th IFAC Symposium Safeprocess ''09, Barcelona. [Copyright &y& Elsevier]

Abstract: This paper describes a reconfiguring flight control algorithm for damaged aircraft based upon a modular approach. This approach combines real time physical model identification with adaptive nonlinear dynamic inversion (NDI). The sensitivity of NDI to modeling errors is eliminated here by making use of a real time identified model of the aircraft. In failure situations, the damaged aircraft model is identified by the two step method and this updated model is supplied to the model-based adaptive NDI routine, which reconfigures for the fault in real time. Reconfiguration test results for damaged aircraft models indicate good fault handling capabilities of this fault tolerant control set-up, for component as well as structural faults. [Copyright &y& Elsevier]

Abstract: Current practice for flight control validation relies heavily on linear analyses and nonlinear, high-fidelity simulations. This process would be enhanced by the addition of nonlinear analyses of the flight control system. This paper demonstrates the use of region of attraction estimation for studying nonlinear effects. A nonlinear polynomial model is constructed for the longitudinal dynamics of NASA''s Generic Transport Model aircraft. A polynomial model for the short period dynamics is obtained by decoupling this mode from the nonlinear longitudinal model. Polynomial optimization techniques are applied to estimate region of attractions around trim conditions. [Copyright &y& Elsevier]

Abstract: This paper focuses on failure detection in the electrical flight control system of Airbus aircraft. Fault tolerance is designed into the system by the use of stringent processes and rules, which are summarized below. Monitoring of the system components is part of this fault-tolerant design. This paper covers the particular case of oscillatory failure monitoring in the electrical flight control system. The main characteristics and consequences of these failures are presented. The detection of oscillatory failures on the A380 is considered, together with the concept of analytical redundancy to detect these failures. A nonlinear actuator model is used to generate a residual on which the failure is detected by oscillation counting. Real application and benefits of the overall method are also presented. The results are highly satisfactory and the overall method is currently implemented on A380 flight control computers. [ABSTRACT FROM AUTHOR]

Abstract: Statistics show that the landing accounts for the largest portion of all mishaps of unmanned aerial vehicles (UAVs) due to many difficulties including limited situational awareness of the external pilot and the limited maneuverability during the low speed flight before touchdown. In this paper, a vision-based automatic landing system using a dome-shaped airbag is proposed for small UAVs. Its isotropic shape allows airplanes to approach in any direction to avoid crosswind unlike net-assisted landing. The dome’s distinctive color improves the detection owing to its strong visual cue. Color- and shape-based detection vision algorithms are applied for robust detection under varying lighting conditions. Due to the insufficient accuracy of navigation sensors, a direct visual servoing is used for terminal guidance. The proposed algorithm is validated in a series of flight tests. [Copyright &y& Elsevier]

Abstract: This paper describes an autonomous guidance system based on receding horizon (RH) optimization. The system is integrated around a spatial, state-dependent cost-to-go (SVF) function that is computed as an approximation to the value function associated with the optimal trajectory planning problem. The function captures the critical interaction between the vehicle dynamics and environment, thereby resulting in tighter coupling between planning and control. The consistency achieved between the RH optimization and the SVF enables a more rigorous implementation of the RH framework to autonomous vehicle guidance. The paper describes the overall approach along flight experimental results obtained in an Interactive Guidance and Control Laboratory. [Copyright &y& Elsevier]

Abstract: Low-cost small unmanned aerial vehicles (UAVs) attracted researchers and developers around the world for use in both military and civilian applications. However, there are challenges in designing stable and robust flight controllers that handle the UAV model and environmental uncertainties. This paper focuses on the design and implementation of a roll-channel fractional order proportional integral () flight controller for a small fixed-wing UAV. Time domain system identification methods are used to obtain a simple auto-regressive with exogenous input (ARX) model of the UAV roll-channel. A new fractional order PI controller design method is introduced based on the identified simple model. The fractional order controller outperforms the optimized traditional integer order proportional integral derivative (PID) controller due to the fractional order introduced as a design parameter. The simulation results show the effectiveness of the proposed controller design strategy and the robustness of fractional order controller under conditions of wind gusts and payload variations. Further real flight test results are also provided to show the advantages of the proposed controller. [Copyright &y& Elsevier]

Abstract: This paper presents design and verification of an estimation and control system for a helicopter slung load system. The estimator provides position and velocity estimates of the slung load and is designed to augment existing navigation in autonomous helicopters. Sensor input is provided by a vision system on the helicopter that measures the position of the slung load. The controller is a combined feedforward and feedback scheme for simultaneous avoidance of swing excitation and active swing damping. Simulations and laboratory flight tests show the effectiveness of the combined control system, yielding significant load swing reduction compared to the baseline controller. [Copyright &y& Elsevier]

Abstract: This paper deals with the aerodynamic modeling of a ducted fan Vertical TakeOff and Landing (VTOL) Unmanned Aerial Vehicle (UAV) and the problem of attitude stabilization when the vehicle is remotely controlled by a human pilot in presence of crosswind. The main aerodynamic elements, which are inherent to the presence of the duct and explain the flight dynamics of this kind of vehicle, are first presented. Then, an attitude control is designed from a linearization of the dynamic model around the hovering flight equilibrium. As the vehicle is axis-symmetric, the pitch and the roll dynamics have a similar expression. For this reason, the presentation is focused on the design of the pitch controller. Similar results can be directly deduced for the roll. Experiments, led on the HoverEye platform designed by Bertin Technologies, show that the proposed attitude control is sufficient to open a large secure flight envelope. [Copyright &y& Elsevier]

Abstract: The area of research on probabilistic and randomized methods for analysis and design of uncertain systems is fairly recent and is focused both on algorithmic as well as theoretical developments. In this paper a framework for randomization-based control design is presented and applied to a Mini-UAV platform. The proposed approach makes use of random search and uncertainty randomization for controller synthesis and probabilistic robustness analysis. Several structured uncertain parameters, related to the plant and to the operating conditions, are taken into account to design a robust flight control system. A selection criterion, based on estimated probability and its degradation function, is proposed in order to match stability and performance metrics fulfillment. Computational issues associated to the specific application, integration of a priori domain knowledge and human designer interaction with automated design are also addressed. [Copyright &y& Elsevier]

Abstract: This paper describes a novel optimisation-based framework for analysing the robustness of advanced flight control laws for reusable launch vehicles. The proposed analysis methods are applied and tested on an industrial-standard simulation model of a reusable launch vehicle equipped with a full authority nonlinear dynamic inversion-based flight control law. The reliability, computational complexity and efficiency of the framework are evaluated against standard industrial approaches based on Monte Carlo simulation. The results of the study show that the proposed approach has the potential to significantly improve both the reliability and efficiency of the flight clearance process for future reusable launch vehicles. [Copyright &y& Elsevier]

Abstract: Based on a recent description of deadzone nonlinearities via local sector conditions, a new LMI characterization is proposed in this paper to compute static and full- or fixed-order anti-windup compensators for possibly open-loop unstable plants. The originality of this approach rests on the use of a specific performance criterion which is inspired by the framework. A significant part of the paper is then devoted to a challenging control problem which involves both magnitude and rate limitations. As an important point in this illustrative part, implementation and robustness issues of the anti-windup device are thoroughly discussed. [Copyright &y& Elsevier]

Abstract: In this paper, a novel hybrid optimisation algorithm is applied to the problem of analysing the robustness of a nonlinear flight control law in the presence of multiple variations in key aircraft parameters over continuous regions of the flight envelope. The analysis employs a typical nonlinear clearance criterion used by the European aerospace industry together with a simulation model of a high performance aircraft with a full authority control law which is gain scheduled over the flight envelope. The hybrid algorithm incorporates global (differential evolution) and local (sequential quadratic programming) optimisation algorithms to improve convergence properties and reduce computational overheads. The proposed approach is shown to have the potential to significantly improve both the reliability and efficiency of the industrial flight clearance process. [Copyright &y& Elsevier]

Abstract: A comparison between receding horizon control (RHC) approaches is presented for the longitudinal axis control of an F-16 aircraft. The results suggest that the flexibility provided by a scheduled RHC scheme based on flight condition-dependent linear prediction models is a necessary requirement for achieving good performance as opposed to a single LTI model-based method. The scheduled scheme offers an attractive alternative to a full nonlinear model-based RHC approach by trading off an acceptable degradation in performance to modest computational complexity and real-time implementability. [Copyright &y& Elsevier]

Abstract: The use of a linear design technique in combination with gain scheduling is the most common systematic approach to the design of nonlinear flight control laws. However, the selection of the operating points and the design of the interpolation scheme remains a time-consuming procedure. In order to reduce the design effort, an automated procedure has been developed and applied to the design of a longitudinal control law in a fly-by-wire flight control system. The number of operating points and their locations are determined automatically by using fuzzy clustering to capture characteristic patterns in the aerodynamic model throughout the flight envelope. This approach also directly provides the interpolation mechanism (membership functions) for the local flight control law parameters. The design procedure has been developed in close cooperation with airframe and control system manufacturers and was evaluated through pilot-in-the-loop flight simulator tests. Experienced test pilots could not detect any significant difference between the conventional flight control laws and those implemented with fuzzy gain scheduling, even though the latter used fewer operating points and was designed in an automated manner, as opposed to the conventional iterative manual procedure. [Copyright &y& Elsevier]

Abstract: Model predictive control (MPC) solves an optimization at every sampling instance to achieve commanded set points and control objectives subject to constraints on control inputs and system states. Such online optimization can incorporate many important factors to enable the control of systems subject to faults, changing dynamics, changing control objectives, failed control inputs and large disturbances. Reconfigurable flight control is one such application where the capabilities and flexibility of optimization-based control methods can be fully utilized and exploited. This paper presents formulations and experimental evaluations of various MPC schemes applied to a realistic full envelope non-linear model of a fighter aircraft. Investigations are carried out by exploring a variety of scenarios of fault and disturbance combinations along with modified and robust formulations of online constrained optimization. [Copyright &y& Elsevier]

A detailed description of a six-degree-of-freedom nonlinear flight simulation is presented and a method of generating the guidance commands for controlling the aircraft trajectory in three-dimensional space is proposed. Tracking errors are expressed in terms of zero effort miss vector, which is the expected miss distance at the future time between two flight vehicles, that is, one on the desired trajectory and the other on the actual trajectory. This zero effort miss vector is used to form a Lyapunov function. Then a set of guidance commands for the speed and flight direction control loops are selected in such a way that they will strictly decrease the Lyapunov function. Thus obtained guidance commands are incorporated into the existing flight control systems and tested with representative flight scenarios where the performance of trajectory tracking is considered to be important. [Copyright &y& Elsevier]

This paper presents a hierarchical flight control system for unmanned aerial vehicles. The proposed system executes high-level mission objectives by progressively substantiating them into machine-level commands. The acquired information from various sensors is propagated back to the higher layers for reactive decision making. Each vehicle is connected via standardized wireless communication protocol for scalable multi-agent coordination. The proposed system has been successfully implemented on a number of small helicopters and validated in various applications. Results from waypoint navigation, a probabilistic pursuit-evasion game and vision-based target tracking demonstrate the potential of the proposed approach toward intelligent flying robots. [Copyright &y& Elsevier]

This paper describes the design and flight-testing of a multivariable helicopter flight control system. The system consisted of separate longitudinal and lateral controllers, each designed using H-infinity optimization. The design was based on a low-order aircraft model. The system was successfully flight-tested on a fly-by-wire research helicopter. It was considerably simpler than other H-infinity controllers tested during the same research program. It also outperformed them in most respects, achieving bandwidths of 3.7 rad/s in roll, 2.5 rad/s in pitch and 1.5 rad/s in yaw, and virtually eliminating pitch–roll coupling. [Copyright &y& Elsevier]

A primary objective in the development of a navigation system is to test the effectiveness of its algorithms together with their capability of operating in real time. With this in mind a Virtual Laboratory capable of simulating the main features of general aviation aircraft navigational sensors together with their interface to the on-board computer has been developed. Some features regarding the DGPS ground segment have also been included in order to test the integrity of the algorithms that are part of the architecture conceived for the FODIAS. Realism in the simulated environment guarantees higher reliability of the performances obtainable in simulation, and confidence about the repeatability of results during real flight tests, drastically reducing the cost of development. [Copyright &y& Elsevier]

New research and developments on nonlinear logic-dynamic control and its applications to fault-tolerant motion control system of the maneuvering vehicle Ikar, developed by Russian State Research & Production Rocket-Space Center TsSKB-Progress and applied for the orbital placement of the Globalstar satellites, are presented. [Copyright &y& Elsevier]

The Infra-Red Imaging System-Tail/thrust-vector controlled (IRIS-T) missile is a next-generation short-range air-to-air missile currently developed by Germany, Greece, Italy, Norway, and Sweden. IRIS-T is characterized by an extreme maneuverability for close-in air-to-air combat. The corresponding highly nonlinear and rapidly time-varying dynamics constitute a significant challenge for the autopilot design. Robust control techniques are employed to design lateral and roll controllers taking into account uncertainties in aerodynamic coefficients and actuator bandwidth. The controllers are scheduled as a function of dynamic pressure using a conditioning/blending technique to achieve full flight envelope control capability. The performance and robustness characteristics of the autopilot are assessed in a nonlinear 6 degree-of-freedom simulation and in ground-launched flight tests of the operational missile. [Copyright &y& Elsevier]

The principles of construction and design features of inertial devices with gas-static support developed for using on booster rockets and space vehicles of different types are set up for the first time. The gyro-stabilized platform of space application created on their base and successfully tested at injection of the heavy telecommunication satellite “Horizon” into geostationary orbit in June 2000, is described. The capability of extension of the field of application of the created means of motion control is underlined. [Copyright &y& Elsevier]

Since the dynamics of the telemanipulator consisting of high reduction ratio joints is likely to be much slower than that of the master manipulator, the control inputs of the telemanipulator are frequently saturated resulting in poor position control performance and deteriorated stability. This paper proposes a bilateral control scheme for 2-DOF telemanipulators with control input saturation, which can improve the position tracking performance while effectively compensating for saturation. A series of experiments show that the proposed scheme provides an excellent position control performance regardless of saturation. [Copyright &y& Elsevier]

A study about how to design a control law that not only keeps following a reference attitude but also maintains attitude decoupling due to the vehicle manoeuvres has been performed. A control law was designed for a satellite launcher vehicle using eigenstructure assignment and optimal control method in order that the vehicle tracks a reference attitude and also to decouple the yaw response from roll and pitch manoeuvres and to decouple the pitch response from roll and yaw manoeuvres. It has been noticed that in order to achieve this objective it is necessary to use a linear coupled model to design the control law instead of the usual linear uncoupled model used to design the tracking control law. The design was based on a complete linear coupled model obtained from the complete vehicle non-linear model by linearisation at each trajectory point. A comparison of the system stability working with both control laws has also been performed. After all, the design was assessed with the vehicle time varying non-linear model showing a good performance and robustness. The used design method is explained and a case study for the Brazilian satellite launcher VLS is reported. By the end of the work some suggestions about how to implement this control law have also been studied. [Copyright &y& Elsevier]

We describe two schemes for scheduling an integrated flight and propulsion control system for an experimental vertical/short take-off and landing (V/STOL) aircraft concept in the acceleration from hover (0–120 kn) flight phase. Multivariable integrated flight and propulsion controllers are designed at several points over the V/STOL envelope and implemented as exact plant observers with state feedback. In the first scheduling scheme, the values of the state feedback and observer gain matrices are interpolated between the fixed-point designs as a function of aircraft speed. In the second approach, the control signals produced by the different fixed-point controllers are blended, allowing a significant reduction in the order of the scheduled controllers. Both scheduling schemes are shown in non-linear simulation to provide excellent handling qualities as the aircraft accelerates from the hover. [Copyright &y& Elsevier]

This paper describes the application of two frequency domain analysis tools, the structured singular value μ and the ν-gap metric, to the problem of evaluating the robustness properties of a multivariable integrated flight and propulsion control (IFPC) system for an experimental V/STOL aircraft configuration. Variations in aircraft parameters and dynamics over the V/STOL flight envelope are represented as linear fractional transformation (LFT) based parametric uncertainty descriptions, using a simple ‘black-box’ type modelling approach. Tight bounds on μ for the resulting high-order real parametric uncertainty model are computed by introducing small amounts of additional complex uncertainty, in order to analyse the stability robustness properties of the IFPC system. Stability and performance robustness of the IFPC system is also evaluated using the ν-gap metric. Results generated by both analysis tools are seen to be consistent, and to agree well with evaluation results obtained for the IFPC system in piloted simulation. [Copyright &y& Elsevier]

This paper solves an accurate fixed-time attitude and position control problems of a quadrotor UAV system. The aircraft system is subject to nonlinearities, parameter uncertainties, unmodeled dynamics, and external time-varying disturbances. To deal with the under-actuation problem of the quadrotor's dynamics, a hierarchical control structure with an inner–outer loop framework is adopted for the flight control system design. Robust nonlinear control strategies for attitude and position control are innovatively proposed based on a new continuous nonsingular terminal sliding mode control (CNTSMC) scheme. A full-order homogeneous terminal sliding surface is designed for the attitude and position states in such a way that the sliding motion is fixed-time stable independently of the system's initial condition. Hence, this contributes to enhancing the control system robustness. A disturbance observer-based control (DOBC) approach is developed to stabilize the inner rotational subsystem (attitude-loop). This compounded control structure integrates a finite-time observer (FTO) and the CNTSMC scheme. The FTO observer is incorporated into the control framework to cope with the strong perturbations. An output-feedback control approach is adopted for the outer translational subsystem (position-loop) to ensure a velocity-free control. In this context, the CNTSMC scheme is combined with a fixed-time extended state observer (FXESO) to achieve an active disturbance rejection control (ADRC) by estimating and canceling the lumped disturbances. Therefore, within the developed control approach including the robust CNTSMC scheme, DOBC, and ADRC strategies, robust and accurate trajectory tracking control can be achieved despite uncertainties and disturbances. Stability analysis of the closed-loop system is rigorously investigated by using the Lyapunov theorem, bi-limit homogeneous theory, and the notion of input-to-state stability (ISS). Extensive experimental tests under the influence of various disturbances are conducted to corroborate the theoretical findings. To this end, an effective model-based design (MBD) framework is established to implement the developed control algorithms in real autopilot hardware. Furthermore, processor-in-the-loop (PIL) experiments are also carried out within the MBD framework. A comparative study is made involving our control algorithms and other control strategies. Overall, the obtained results show that the synthesized control system yields performance improvement regarding fixed-time tracking stability featuring fast transient, strong robustness, and high steady-state precision. Besides, the chattering effect of regular linear sliding mode control (LSMC) is significantly alleviated. Moreover, unlike conventional TSMC, the control input shows no singularity. [Display omitted] • Asymptotic control methods have a slow convergence rate and less robustness. • Convergence time of finite-time control grows unboundedly along with the deviation of initial conditions from the equilibrium point. • CNTSMC control algorithm is adopted within DOBC and ADRC approaches to design a robust flight control system to achieve fast fixed-time stability for the quadrotor system despite multiple disturbances. • Experiments have been conducted on a real quadrotor aircraft. • Control system performance is improved compared to some existing robust controllers. [ABSTRACT FROM AUTHOR]

With the increasing use of quadrotors, the design of flight control systems has become particularly important. In this paper, a new robust flight control system consisted of an adaptive fuzzy terminal sliding mode controller, and two proportional-derivative (PD) controllers are proposed to stabilize a quadrotor and to track a pre-defined flight path in the presence of external disturbances and model uncertainties. The PD controllers determine the desired attitude of the quadrotor and terminal sliding mode control adjusts the rotation speed of rotors. The dynamics of the quadrotor and external disturbances are identified online by applying adaptive Mamdani fuzzy systems. Also, the control chattering is eliminated by defining a continuous terminal sliding mode. Two Kalman filters are also utilized to improve the estimation of the quadrotor attitude and position. The simulation results and real-time implementation of the proposed flight control system show the efficient performance of the control system during two flight scenarios of the quadrotor. • The flight control is evaluated through the simulated and real-time flight experiments. • The proposed method is robust to model uncertainties and external disturbances. • There is no need for a pre-identified model or physical parameters of the controlled quadrotor to implement the terminal sliding mode flight control. [ABSTRACT FROM AUTHOR]