Aircraft Longitudinal Dynamics Research Articles

Longitudinal Aerodynamic Parameter Estimation Using Neural Network and Gauss-Newton Method

A new parameter estimation method based upon Feed Forward Neural Network is proposed. The proposed method utilizes the universal mapping capability of Feed Forward Neural Network to develop flight dynamic model of aircraft. Gauss-Newton method is used to obtain values of aerodynamic parameters by minimizing a chosen error cost function. The method has then been validated using flight data pertaining to longitudinal dynamics of aircraft. Proof of match approach has been followed to verify the estimated model by the proposed method. The results obtained using the proposed method have also been compared with those obtained using wind tunnel tests, and Filter Error method. Unlike, most of the conventional methods, the proposed method does not require a priori description of the model. It also bypasses the requirement of solving the equations of motion. This feature may have special significance in handling flight data of an unstable aircraft.

Fault Diagnostics for Oscillatory Failure Case in Aircraft Elevator Servos

Oscillatory Failure Case (OFC) is a characteristic sinusoidal fault that propagates through control surfaces and actuator servo loops of commercial aircrafts that originates from spurious sensor measurements and actuator commands. The goal of this work is to detect such faults of unknown amplitudes and frequencies in the presence of turbulence. The fault detection scheme employs a graph-theoretic approach that uses a structural model of the aircraft's longitudinal dynamics and the servo actuators to determine residuals for OFC fault detection and isolation. A smooth controller reconfiguration strategy is proposed to switch between a nominal control law and a degraded alternate control law which utilizes sensor measurement feedback as well as virtual sensors from a digital model of longitudinal cruising dynamics without affecting the controller structure and feedback loops.

Two-time-scale robust output feedback control for aircraft longitudinal dynamics via sliding mode control and high-gain observer

This paper presents output feedback control for longitudinal dynamics of fixed-wing aircraft using singular perturbation techniques. The longitudinal dynamic model is separated into two timescales. A composite feedback control law based on sliding mode control (SMC) is designed for slow and fast subsystems to track the aerodynamic velocity and flight path angle references. Additionally, two separate high-gain observers (HGO) are designed for the slow and fast subsystems to estimate system states. The proposed technique not only simplifies the design but also is computationally efficient. Simulations are performed in MATLAB/Simulink environment with results demonstrating that the proposed output feedback control method robustly achieves trajectory tracking.

Robust fault-tolerant flight path angle control

Purpose The purpose of the paper is to design a nonlinear dynamic inversion (NDI) based robust fault-tolerant control (FTC) for aircraft longitudinal dynamics subject to system nonlinearities, aerodynamic parametric variations, external wind disturbances and fault/failure in actuator. Design/methodology/approach An uncertainty and disturbance estimator (UDE) technique is used to provide estimate of total disturbance enabling its rejection and thereby achieving robustness to the proposed NDI controller. As needed in the NDI design, the successive derivatives of the output are obtained through an UDE robustified observer making the design implementable. Further, a control allocation scheme consigns control command from primary actuator to the secondary one in the event of fault/failure in the primary actuator. Findings The robustness is achieved against the perturbations mentioned above in the presence of actuator fault/failure. Practical implications Lyapunov analysis proves practical stability of the controller–observer structure. The efficacy and superiority of the proposed design has been demonstrated through Monte-Carlo simulation. Originality/value Unlike in many FTC designs, robustness is provided against system nonlinearities, aerodynamic parametric variations, external wind disturbances and sinusoidal input disturbance using a single control law which caters for fault-free, as well as faulty actuator scenario.

Improved disturbance rejection control based on H∞ synthesis and equivalent-input-disturbance for aircraft longitudinal autopilot design

Disturbance rejection control has been developed over decades attracting wide interest and research attention. Aiming at providing a potential engineering application of disturbance rejection control to aircraft control system design following traditional frequency-domain methods, this paper presents an improved disturbance rejection control of two degrees of freedom based on [Formula: see text] synthesis and equivalent-input-disturbance for an aircraft longitudinal autopilot design. The mismatched disturbance is transformed as a “total disturbance” in the input channel for compensation through the establishment of an equivalent-input-disturbance system. The [Formula: see text] synthesis based on classical frequency-domain analysis is applied to a disturbance filter and a composite feedback controller design. In terms of the controller design, the system including the filter is considered as a whole in [Formula: see text] optimization process without separate design to guarantee the stability of the overall system. Furthermore, the proposed method is successfully implemented on the autopilot design by modeling nonlinear aircraft longitudinal dynamics as a linear equivalent-input-disturbance formulation of angle of attack. The simulation of tracking performance in comparison with existing renowned methods is conducted in the presence of aerodynamic uncertainties, gust disturbance, actuator characteristics and sensor noise. The results verify the effectiveness of the proposed method with excellent performance and practical prospects.

The Design of the Longitudinal Autopilot for the LSU-05 Unmanned Aerial Surveillance Vehicle

Longitudinal autopilot design for the LAPAN Surveillance Vehicle LSU-05 will be described in this paper. The LSU-05 is the most recent Unmanned Aerial Vehicle (UAV) project of the Aeronautics Technology Center (Pusat Teknologi Penerbangan – Pustekbang), LAPAN. This UAV is expected to be able to carry 30 kg of payload, four surveillance purposes. The longitudinal autopilot described in this paper consists of four modes, those are Pitch damper, Pitch Attitude Hold, Altitude Hold, and Speed Hold. The Autopilot of the UAV will be designed at four operating speeds, namely 15 m/s, 20 m/s, 25 m/s, and 30 m/. The Athena Vortex Lattice software is used to generate the aerodynamic model of the LSU-05. Non-linear longitudinal aircraft dynamics model is then developed in MATLAB/SIMULINK environment. Linearization of the non-linear model is performed using the linearization tool of SIMULINK. The controller is designed, based on the linear model of the aircraft in the state space form. A Proportional-Integral-Derivative (PID) controller structure is chosen, using root locus method to determine mainly the proportional (P) gain. Integral (I) and derivative (D) gain will only be used if the proportional gain can not achieve the desired target or if an overshoot / undershoot reduction is required. The overshoot/undershoot should not exceed 5% and settling time is less than 20 seconds. The controller designed is simulated using MATLAB and SIMULINK. Preliminary analysis of the controller performance shows that the controller can be used to stabilize the aircraft and to automatize the speed and altitude control throughout the considered speed range.

State Estimation for Landing Maneuver on High Performance Aircraft

State estimation methods are popular means for validating aerodynamic database on aircraft flight maneuver performance characteristics. In this work, the state estimation method during landing maneuver is explored for the first of its kind, using upper diagonal adaptive extended Kalman filter (UD-AEKF) with fuzzy based adaptive tunning of process noise matrix. The mathematical model for symmetrical landing maneuver consists of non-linear flight mechanics equation representing Aircraft longitudinal dynamics. The UD-AEKF algorithm is implemented in MATLAB environment and the states with bias is considered to be the initial conditions just prior to the flare. The measurement data is obtained from a non-linear 6 DOF pilot in loop simulation using FORTRAN. These simulated measurement data is additively mixed with process and measurement noises, which are used as an input for UD-AEKF. Then, the governing states that dictate the landing loads at the instant of touch down are compared. The method is verified using flight data wherein, the vertical acceleration at the aircraft center of gravity (CG) is compared. Two possible outcome of purely relying on the aircraft measured data is highlighted. It is observed that, with the implementation of adaptive fuzzy logic based extended Kalman filter tuned to adapt for aircraft landing dynamics, the methodology improves the data quality of the states that are sourced from noisy measurements.

Avionic Air Data Sensors Fault Detection and Isolation by means of Singular Perturbation and Geometric Approach.

Singular Perturbations represent an advantageous theory to deal with systems characterized by a two-time scale separation, such as the longitudinal dynamics of aircraft which are called phugoid and short period. In this work, the combination of the NonLinear Geometric Approach and the Singular Perturbations leads to an innovative Fault Detection and Isolation system dedicated to the isolation of faults affecting the air data system of a general aviation aircraft. The isolation capabilities, obtained by means of the approach proposed in this work, allow for the solution of a fault isolation problem otherwise not solvable by means of standard geometric techniques. Extensive Monte-Carlo simulations, exploiting a high fidelity aircraft simulator, show the effectiveness of the proposed Fault Detection and Isolation system.

Aircraft longitudinal decoupling based on a singular perturbation approach

Aircraft longitudinal dynamics is approximated by short-time mode and phugoid mode from experience. In this article, a rigorous mathematical method is provided based on the singular perturbation theory to deal with this decoupling problem. The longitudinal decoupling and singular perturbation are first introduced. The longitudinal equations are normalized and transformed into a canonical form to extract the perturbation coefficient. Thus, the entire dynamics model is partitioned into boundary-layer equations and slow equations according to singular perturbation theory, which presents a proof to the experience method. The simulation results show that the proposed decoupling approach is sufficiently excellent to approximate the underlying model both in time domain and frequency domain.

Trustable UAV for higher level control architectures

Future unmanned air vehicles (UAVs) are expected to operate under the supervision of higher level control architectures that give instructions to engage and direct the UAV to perform a certain task. These instructions allow the UAV to make decisions along any point of its trajectory and then modify its flight path by using a sequence of reconfigurable controllers at the decision points. Assume that the UAV is flying with a transient and with a steady state contributing to a flight control mode (FCM) such as an altitude hold, an ascent and a descent mode when only longitudinal aircraft dynamics is considered. At the time of a decision, if the UAV bifurcates from its original (or parent) FCM in an effort to acquire a new (or a child) FCM and comply with a higher level instruction, then the UAV is said to be trustable. Mathematically, at the time of bifurcation where controller reconfiguration takes place, trustable UAV with the child trajectory must originate from a region where the stability regions of the parent and child trajectories intersect. In this paper, a procedure to reconfigure such FCMs and their controllers that develop the trustable UAV are presented. A three degree of freedom UAV is considered to illustrate the trustable UAV.

Sufficient LMI conditions and Lyapunov redesign for the robust stability of a class of feedback linearized dynamical systems

The robust stability of a class of feedback linearizable minimum-phase nonlinear system, having parametric uncertainties, is investigated in this study. The system in new coordinates is represented to an equivalent formulation after the attempt of feedback linearization. Due to the parametric uncertainties the approximately linearized system entails a norm bounded input nonlinearity such that the equilibrium point condition in error dynamics can not be satisfied. Accordingly, to guarantee the regional asymptotic stability a control synthesis problem is proposed by means of sufficient Linear Matrix Inequalities (LMIs) together with an amended nonlinear control term, derived from the Lyapunov redesign method, which tackles zero steady-state error condition. The numerical examples of a general aviation aircraft's longitudinal dynamics and inverted pendulum are simulated to show the proficiency of the proposed control technique.

An Adaptive Dynamic Surface Controller for Ultralow Altitude Airdrop Flight Path Angle with Actuator Input Nonlinearity

In the process of ultralow altitude airdrop, many factors such as actuator input dead-zone, backlash, uncertain external atmospheric disturbance, and model unknown nonlinearity affect the precision of trajectory tracking. In response, a robust adaptive neural network dynamic surface controller is developed. As a result, the aircraft longitudinal dynamics with actuator input nonlinearity is derived; the unknown nonlinear model functions are approximated by means of the RBF neural network. Also, an adaption strategy is used to achieve robustness against model uncertainties. Finally, it has been proved that all the signals in the closed-loop system are bounded and the tracking error converges to a small residual set asymptotically. Simulation results demonstrate the perfect tracking performance and strong robustness of the proposed method, which is not only applicable to the actuator with input dead-zone but also suitable for the backlash nonlinearity. At the same time, it can effectively overcome the effects of dead-zone and the atmospheric disturbance on the system and ensure the fast track of the desired flight path angle instruction, which overthrows the assumption that system functions must be known.

Development of a Flight Simulation Test-Bed for a General Propeller-Driven Unmanned Aircraft

This paper presents the development of a flight simulator for a fixed-wing propeller-driven UAV. A new architecture for UAV low-level functional units is presented. The work involves modeling main low-level units of the UAV, which includes modeling of aircraft lateral and longitudinal dynamics and controlling of flight-path states holding. Key characteristics for aerodynamics and propulsion properties are calculated. A nested PID loops are used to provide a low-level control necessary for intelligent control and mission planning and execution. Simulation results are demonstrated in order to validate the effectiveness of the flight simulator and thereby providing an infrastructure low-level abstraction platform that can be used for various multi-level algorithms testing.

Modelling and adaptive backstepping control for TX-1570 UAV path tracking

The methodology to design an aircraft longitudinal path-tracking controller is shown in this paper. First a thorough modelling process which involves the estimation of the aerodynamic and propulsion system structure and parameters is carried out. Next, the Lyapunov based backstepping methodology is applied to design a non-linear controller for the aircraft longitudinal dynamics. The used procedure ensures the convergence of the system to a reference and the robustness in presence of modelling errors. The derived controller delivers manipulated inputs for a real plant and takes into account subsystem and model constraints. Finally, the performance of the controlled system to track a realistic path is demonstrated in front of parameter uncertainty, unmodelled dynamics and adverse initial conditions.

Chaotic Analysis and Control of Longitudinal Flight Dynamics

AbstractAircraft are considered to be sub‐stable within the flight envelope. This paper presents a chaotic analysis and two kinds of corresponding control methods of aircraft longitudinal flight dynamics. First, the chaotic behavior of the open loop longitudinal flight system is confirmed by the Poincaré section and the Lyapunov exponent. Studies have found that the flight envelope can be divided into a stable area and a sub‐stable area. The probability of instability caused by chaos exists in the sub‐stable area. The definition of the chaotic boundary is also given. Second, based on the chaotic analysis results and considering three different combinations of aircraft mass and elevator deflection, a linear feedback control (LFC) method is implemented to stabilize the chaotic boundary and enlarge the stable area. Third, taking system uncertainties into consideration, an adaptive backstepping sliding mode control (AB‐SMC) method is applied to the trajectory tracking problem of aircraft longitudinal motion, which is based on classic SMC, backstepping and dynamic surface methods. The numerical simulations are given, which can demonstrate the applicability of the proposed control methods.

Adaptive Control for Aircraft Longitudinal Dynamics with Thrust Saturation

An output-feedback control law is designed for the longitudinal flight dynamics of an aircraft. The proposed control law is designed using the adaptive backstepping method and does not require any knowledge of aircraft aerodynamics beyond well-known qualitative physical properties. The resulting feedback controller is able to follow given references in both airspeed and flight-path angle by actuating elevator deflections and aircraft engine thrust. Engine physical limits are incorporated into the design by using a Lyapunov function analysis that includes saturation, obtaining a novel hybrid adaptation law that guarantees closed-loop system stability. Simulation results show good performance of the feedback law and, in particular, demonstrate that the hybrid adaptation law improves the behavior of the closed-loop system when saturations are present. A degraded scenario (a sudden cargo displacement that renders the aircraft statically unstable) is also considered to show the adaptation capabilities of the control law. The simulations are carried out using a realistic aircraft model that is also developed in the paper.

Adaptive Fuzzy Observer-Based Active Fault-Tolerant Dynamic Surface Control for a Class of Nonlinear Systems With Actuator Faults

The problem of fault-tolerant dynamic surface control (DSC) for a class of uncertain nonlinear systems with actuator faults is discussed and an active fault-tolerant control (FTC) scheme is proposed. Using the DSC technique, a novel fault diagnostic algorithm is proposed, which removes the classical assumption that the time derivative of the output error should be known. Further, an accommodation scheme is proposed to compensate for both actuator time-varying gain and bias faults, and avoids the controller singularity. In addition, the proposed controller guarantees that all signals of the closed-loop system are semiglobally uniformly ultimately bounded, and converge to a small neighborhood of the origin. Finally, the effectiveness of the proposed FTC approach is demonstrated on a simulated aircraft longitudinal dynamics example.

Space-Indexed Control for Aircraft Vertical Guidance with Time Constraint

With the growth of civil aviation traffic capacity, safety and environmental considerations urge today for the development of guidance systems with improved accuracy for spatial and temporal trajectory tracking. This should induce increased practical capacity by allowing timely operations at minimum separation standards while at takeoff and landing and trajectory dispersion should be reduced, resulting in better controlled noise impacts on airport surrounding communities. Current civil aviation guidance systems operate with real-time corrective actions to maintain the aircraft trajectory as close as possible to a space-indexed planned trajectory while the flight management system copes indirectly with overfly time constraints. In this paper, the design of new longitudinal guidance laws is considered so that accurate vertical tracking is achieved while overfly time constraints are satisfied. Here, distance to land is adopted as the independent variable for the aircraft flight dynamics since it is today available onboard aircraft with acceptable accuracy. A representation of aircraft longitudinal guidance dynamics is developed according to this spatial variable, and a space-indexed nonlinear inverse control law is established to make the aircraft follow accurately a vertical profile and a desired airspeed. The desired airspeed is defined by an outer space-indexed control loop to make the aircraft overfly different waypoints according to a planned timetable. Numerical simulation experiments with different wind conditions for a transportation aircraft performing a descent approach for landing under this new guidance law are described. The resulting guidance performances are compared with those obtained from a classical time-based guidance control law.

Neural Adaptive Compensation Control for a Class of MIMO Uncertain Nonlinear Systems with Actuator Failures

A neural adaptive compensation control scheme for a class of multi-input multi-ouput (MIMO) uncertain nonlinear systems with actuator failures is proposed based on prescribed performance bound (PPB) transient performance which characterizes the convergence rate and maximum overshoot of the tracking error. RBF neural networks are used to approximate the error of plant model, the control law proposed can guarantee the asymptotic output tracking and closed-loop signal bounds. The control scheme is applied to a twin otter aircraft longitudinal nonlinear dynamics model in the presence of unknown failures. Simulation results demonstrate the effectiveness of the proposed method.

Adaptive fault‐tolerant backstepping control against actuator gain faults and its applications to an aircraft longitudinal motion dynamics

SUMMARYThe problem of fault‐tolerant control (FTC) for a class of uncertain nonlinear systems with actuator faults is discussed, and an observer‐based FTC scheme is proposed. Adaptive fuzzy observers are designed to provide a bank of residuals for fault detection and isolation. Using a backstepping approach, we proposed a novel fault diagnosis algorithm, which removes the classical assumption that the time derivative of the output error should be known. Further, an accommodation scheme is proposed to compensate for the effect of the fault, where it is not needed to know the bounds of the time derivative of the fault. The proposed controller guarantees that all signals of the closed‐loop system are semi‐globally uniformly ultimately bounded and converge to a small neighborhood of the origin by appropriately choosing designed parameters. In addition, a sufficient condition for the existence of an fault detection and isolation observer is derived using Lyapunov stability theory. Finally, a numerical example and a practical aircraft longitudinal motion dynamics are used to demonstrate the effectiveness of the proposed FTC approach. Copyright © 2013 John Wiley & Sons, Ltd.