Flight Simulation Results Research Articles

Adaptive Finite-Time Fault-Tolerant Control of Uncertain Systems With Input Saturation

In this article, an adaptive finite-time fault-tolerant control (FTC) strategy is proposed for state tracking of uncertain systems subject to actuator faults and input saturation. The actuator faults, which include multiplicative and time-varying additive modes, are allowed to be unknown. To deal with the coupling of the unknown model uncertainties and the actuator faults, an adaptive mechanism is designed based on a wisely chosen Lyapunov function. The proposed finite-time FTC scheme, with adaptive laws of uncertain parameters, guarantees the stability of the closed-loop system, and the practical finite-time state tracking property. Then, the algorithm is applied to a flight control system, simulation and comparison results demonstrate the effectiveness and advantages of the designed control scheme.

Robust Adaptive Control for Nonlinear Aircraft System with Uncertainties

Model reference adaptive control (MRAC) schemes are known as an effective method to deal with system uncertainties. High adaptive gains are usually needed in order to achieve fast adaptation. However, this leads to high-frequency oscillation in the control signal and may even make the system unstable. A robust adaptive control architecture was designed in this paper for nonlinear aircraft dynamics facing the challenges of input uncertainty, matched uncertainty, and unmatched uncertainty. By introducing a robust compensator to the MRAC framework, the high-frequency components in the control response were eliminated. The proposed control method was applied to the longitudinal-direction motion control of a nonlinear aircraft system. Flight simulation results demonstrated that the proposed robust adaptive method was able to achieve fast adaptation without high-frequency oscillations, and guaranteed transient performance.

Horizontal Stabilator Utilization for Post Swashplate Failure Operation on a UH-60 Black Hawk Helicopter

A flight simulation model for the UH-60 Black Hawk, based on Sikorsky's GenHel model, is modified to simulate a locked failure of a main rotor swashplate servo actuator, which is compensated by using the stabilator as a redundant control effector. Steady-state trim analysis is performed to demonstrate feasibility of trimmed flight in various conditions with different locked servo actuator positions for the forward, aft, and lateral actuators. A model-following, linear dynamic inversion controller is implemented and modified to account for locked actuator position. Postfailure, the controls are reconfigured to partially reallocate the control authority in the longitudinal axis from the main rotor longitudinal cyclic to the stabilator. This is done by manipulation of only the control allocation relating pilot stick inputs to servo actuator positions, whereas the feedback control gains and mechanical rigging between servo actuators and rotor pitch controls remain identical to the baseline. Flight simulation results demonstrate the ability of this reallocation to compensate for locked failure of the forward main rotor swashplate servo actuator, as well as the ability of the aircraft to decelerate from cruise at 120 kt to 50 kt, slower than the published safe rolling landing speed of 60 kt. A similar range of locked positions of the forward and aft actuators is demonstrated to be feasible for aircraft recovery using control of the stabilator. Feasibility of aircraft recovery for locked positions of the lateral servo actuator is also considered, as well as the effect of variation in gross weight, speed of actuator locking, and delays in fault detection and identification.

Design of Generalized Predictive Control for the Stabilizing Loop from a two-axis Gimbal Seeker, Considering Cross-Coupling in Between two Channels

In this research, Generalized Predictivecontrol (GPC) is proposed for the control of a stabilizing loop from a two axis gimbal seeker. In fact, there are some views about using GPC type controller which are two folds. First, it drives the stabilization loops that are made by a DC motor, Rate Gyro, inertia and cross coupling unit in between two channels using the predictive model type controller. Second, the theory is to excavate the results of flight simulation on the efficiency of two-axis gimbal seeker. The simulations, based on different scenarios, are valuated for the proficiency of the designed system considering the dynamic mass imbalance and the cross-coupling in between two channels and the flight simulation. The flight simulation results are explained the accuracy of the designed system with predictive control in opposite of conventional PI controller. For example, the simulation results in altitude of 2km show the suggested system in comparison with conventional PI controller improves miss-distance and flight time 11.98% and 1.5% respectively. Moreover, the suggested system in maximum control signal is 72.61%, minimum control signal is 1.55% and final time is 80.43% (control effort parameter), which is better than PI type controller.

Autonomous soaring using a simplified MPC approach

ABSTRACTThe need for efficient propulsion systems allied to increasingly more challenging fixed-wing UAV mission requirements has led to recent research on the autonomous thermal soaring field with promising results. As part of that effort, the feasibility and advantages of model predictive control (MPC)-based guidance and control algorithms capable of extracting energy from natural occurring updrafts have already been demonstrated numerically. However, given the nature of the dominant atmospheric phenomena and the amplitude of the required manoeuvres, a non-linear optimal control problem results. Depending on the adopted prediction horizon length, it may be of large order, leading to implementation and real-time operation difficulties. Knowing that, an alternative MPC-based autonomous thermal soaring controller is presented herein. It is designed to yield a simple and small non-linear programming problem to be solved online. In order to accomplish that, linear prediction schemes are employed to impose the differential constraints, thus no extra variables are added to the problem and only linear bound restrictions result. For capturing the governing non-linear effects during the climb phase, a simplified representation of the aircraft kinematics with quasi-steady corrections is used by the controller internal model. Flight simulation results using a 3 degree-of-freedom model subjected to a randomly generated time varying thermal environment show that the aircraft is able to locate and exploit updrafts, suggesting that the proposed algorithm is a feasible MPC strategy to be employed in a practical application.

Fluid–Structure–Jet Interaction Effects on High-Speed Vehicle Performance and Stability

This paper considers the performance and stability of high-speed vehicles due to 7changes in the vehicle configuration that introduce the interaction of multiple physics. A conventional vehicle model is developed as a reference configuration with a slender fuselage and aft control surfaces. From this baseline, different design characteristics are implemented to create successive vehicle models. The design trends under consideration are structural flexibility, attitude control jets, and removed control surfaces. The combination of these leads to a slender, flexible, cone–cylinder–flare structure with attitude control jets. The added flexibility introduces a coupled fluid–structure interaction, and the attitude control jets interact with external supersonic flow, which leads to a coupled fluid–structure–jet interaction. The complex multiphysics interaction is a nonlinear unsteady phenomenon that must be considered to simulate the vehicle response to various flight conditions and control inputs. This paper presents flight simulation results of multiple vehicle models with varying design characteristics to investigate the effect of multiphysics interactions on the system performance and stability.

Reentry attitude control for a reusable launch vehicle with aeroservoelastic model using type‐2 adaptive fuzzy sliding mode control

SummaryUsing a type‐2 adaptive fuzzy sliding mode control approach, a nonlinear reentry attitude control scheme is presented in this paper for a reusable launch vehicle (RLV) with aeroservoelastic model that assures reliable tracking of guidance commands. The mutual interactions between aerodynamics, structural dynamics, and the flight control system may lead to the aeroservoelasticity problem. Thus, based on the six‐degree‐of‐freedom geometry model of a RLV, the aeroservoelastic model is firstly established via hypothetical modal method and Galerkin method. Then, the overall attitude control strategy is carried out in two‐loop subsystem controller by using backstepping method. For each loop subsystem, a sliding mode controller is developed to assure tracking of guidance commands, and the interval type‐2 fuzzy logic systems combined with adaptive technique are employed to approximate the nonlinear parts to improve the reentry attitude tracking performance. Furthermore, the virtual control is introduced to the control strategy to attenuate the effect of control saltation. Theoretical analysis based on Lyapunov approach illustrates that the closed‐loop system under the designed control method is uniformly stable, and the attitude tracking error converges to a small neighborhood around origin. Finally, the six‐degree‐of‐freedom flight simulation results are provided to demonstrate the effectiveness of the proposed control scheme and aeroservoelastic characteristic of reentry RLV.

Modified immune network algorithm based on the Random Forest approach for the complex objects control

Nowadays application of the methods of artificial intelligence to create automated complex objects control systems in different application areas is topical. The article presents the developed modified algorithm based on artificial immune system, in which the Random Forest algorithm is used for data pre-processing and extraction of informative signs describing the behavior of a complex object of control. There are presented the results of aircraft flight simulation based on Ailerons database with the help of WEKA software and RStudio environment. There was made the comparative analysis of the modified immune network algorithm with different data pre-processing (based on the Random Forest and factor analysis).

Aircraft Flight Modeling During the Optimization of Gas Turbine Engine Working Process

The article describes a method for simulating the flight of the aircraft along a predetermined path, establishing a functional connection between the parameters of the working process of gas turbine engine and the efficiency criteria of the aircraft. This connection is necessary for solving the optimization tasks of the conceptual design stage of the engine according to the systems approach. Engine thrust level, in turn, influences the operation of aircraft, thus making accurate simulation of the aircraft behavior during flight necessary for obtaining the correct solution. The described mathematical model of aircraft flight provides the functional connection between the airframe characteristics, working process of gas turbine engines (propulsion system), ambient and flight conditions and flight profile features. This model provides accurate results of flight simulation and the resulting aircraft efficiency criteria, required for optimization of working process and control function of a gas turbine engine.

Comparison of GA and PSO approaches for the direct and LQR tuning of a multirotor PD controller

In the present paper different approaches for flight control stabilization tuning of a prototype of Unmanned Aerial Vehicle (UAV) are investigated. The mathematical model of a multirotor airframe is presented and its dynamical system is described by means of Newton-Euler equations for a rigid body. The proposed controller systems for the stabilization of the altitude and the attitude of the multirotor around its hovering configuration are based on Proportional Derivative (PD) regulator tuned by optimization techniques such as Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) or, for the linearized system, by means of Linear Quadratic Regulator (LQR). In this case, PSO and GA are applied to set entries of LQR scheme. Control flight simulation results have been compared in terms of minimization of work carried out by the control actions. Performed simulations pointed out that all approaches lead to zero the error of the position along gravity acceleration direction, stop the rotation of UAV around body axes and stabilize the multirotor. The direct PSO tuning of the PD parameters (PD-PSO) shows better results in terms of errors, performance and speed of convergence.

Robust roll autopilot design to reduce couplings of a tactical missile

The purpose of this work is to decrease coupling effects of a tactical missile by designing a robust autopilot for its roll channel. In tactical STT missiles due to control strategy, in order to execute acceleration commands, roll angular velocity should be kept close to zero. Generally, in the design of autopilot for many of tactical missiles the inter influences of channels is neglected. However, three channels of the missile impact each other in different ways including kinematic, inertia and aerodynamic couplings. Aerodynamic coupling is a dominant in roll channel dynamics appearing as induced and control cross coupling roll moments. In this paper first the coupling terms are modeled considering literature. Next, the system is linearized as input–output using models of induced and control cross coupling roll moments. Also, for increasing robustness of the autopilot against modeling errors, uncertainties, and external disturbances, an uncertainty and disturbance estimation (UDE) controller is used. To evaluate the performance of the designed controller, the results were compared with three controlling methods namely a PD controller based on simple dynamics model, a PD controller based on modified dynamics model and a robust controller based on the extended state observer (ESO). Flight simulation results revealed that if the approximate relationship of induced and control cross coupling roll moments are appropriately modeled, UDE control performance outperforms other methods and couplings between pitch and yaw channels are significantly decreased.

Assessment of Multiple Scattering in the Reflectance of Semiarid Shrublands

Multiple scattering within a mixed pixel results in a nonlinear effect on the measured spectra in remotely sensed imagery. This study provides a quantitative assessment of multiple scattering in the reflectance of semiarid shrublands and explores its relationship to the characteristics of shrubs (density and height) and imaging parameters (wavelength and viewing angles). Field measurements were conducted at the southern fringe of the Otindag Sandy Land in China. A Monte Carlo ray tracing model, the Forest LIGHT interaction model (FLIGHT), was applied to simulate the multiple scattering results. FLIGHT simulation results were first evaluated against field measurements and then compared with a Landsat-8 OLI image. Results show that: 1) the contribution of multiple scattering to the spectra of a scene increases linearly with the fractional cover of vegetation and crown height; 2) in general, multiple scattering has a stronger effect on the near-infrared (NIR) domain than on the visible bands; 3) shadows significantly strengthen the multiple scattering effect, specifically within the visible bands; and 4) 80 to 100% of the total multiple scattering is caused by the second-order scattering within the visible bands and 60% to 90% within the NIR band. This study helps to improve our understanding of the multiple scattering effect and to select between linear and nonlinear spectral unmixing models to solve the abundances of shrubs and soil in mixed pixels.

Nonlinear robust control for reusable launch vehicles in reentry phase based on time-varying high order sliding mode

This paper describes the design of nonlinear robust controller for reusable launch vehicles which is nonlinear, multivariable, strong coupling, and includes uncertain parameters. Firstly, the feasible guidance strategy is proposed to obtain the desired guidance commands. Then, the time-varying sliding mode manifold is designed through calculating a series of algebraic equations with fixed final states to make the system trajectories start on the manifold at the initial time. The global robustness is ensured via designing high order sliding mode attitude controller which forces the system trajectory to stay on the sliding mode manifold despite the model parameter uncertainties and external disturbances. Furthermore, in order to reduce control saltation, the virtual control is introduced into the control strategy. Finally, the six degree of freedom flight simulation results are provided to demonstrate the effectiveness of the integrated guidance and control strategy in tracking the guidance commands as well as achieving safe and stable reentry flight.

Trajectory linearization based output tracking control of an unmanned tandem helicopter with variance constraints

An output tracking control problem for an unmanned tandem rotor helicopter with variance constraints is investigated in this paper. A modified Trajectory Linearization Control (TLC) is proposed to stabilize a nonlinear continuous-time flight dynamics system of the tandem helicopter. The tracking controller structure of TLC is designed by using two-time-scale nonlinear dynamic inversion. The base control law of the translational and attitude loops is designed in a pseudo-inversion feedforward controller to deal with nonlinear features of the plant and a proportional integral controller to stabilize the linear slowly time-variant error system resulted from the nonlinear flight system. Furthermore, a feasible TLC strategy is designed to meet a performance index set including steady trajectory tracking error variance and desired Parallel D-spectrum (PD-) eigenvalues to achieve good flight quality. The Variance-constrained Trajectory Linearization Control (VCTLC) is designed to realize the desired steady tracking precision and agile capability. Flight simulation results show the VCTLC method is feasible and effective in attitude and altitude tracking.

A Criterion Based on Closed-loop Pilot-aircraft Systems for Predicting Flying Qualities

During the process of aircraft design, the mathematical model of pilot control behavior characteristics is always used to predict aircraft flying qualities (FQ). This is one of the important methods to avoid pilot-aircraft adverse coupling. In order to study the FQ criterion based on closed-loop pilot-aircraft systems, first, an experimental database is built, which includes 40 aircraft dynamics configurations and the corresponding flight simulation results. Second, the mathematical pilot models with a set of different aircraft configurations are obtained by this experimental database. Then, two FQ criteria, Neal-Smith criterion and Moscow Aviation Institute (MAI) criterion, are analyzed. And the relationship between the FQ level evaluated by actual pilot and the parameters of closed-loop pilot-aircraft systems is studied. Finally, an improved criterion of aircraft FQ is built based on the above two criteria. This new criterion is further used to predict FQ for four new aircraft dynamics configurations, and the prediction results verify its accuracy and practicability.

Applications of adaptive neural network control to an unmanned airship

This paper represents an application of a neural network-based adaptive control to the Stability and Control Augmentation System(SCAS) of an unmanned airship whose maneuvers consist of diverse flight phases at low speeds. The neural network (NN) based adaptive SCAS is based on the inversion of a linear model of the airship at a nominal operating point and the adaptation of neural networks to unmodeled dynamics, parameter variations, and uncertain environments. This paper also presents an evaluation of the adaptive SCAS with flight test results and simulation results. In this evaluation, an outer-loop control is used. The autopilot is designed using a classical PID control algorithm for trajectory line tracking and altitude hold modes. Moreover, the adaptive SCAS approach showed superiority over the classical PID design approach in terms of the gain tuning process during a flight test.

Investigation of the Flare Maneuver Using Optical Tau

Airline transport operations are carried out in a wide range of visual and instrument meteorological conditions. However, the pilot can choose to land the aircraft manually using the visual cues available for all but the most limiting of degraded visibilities. How this is achieved may seem rather obvious, but has challenged researchers for some time. Optical flow theory offers a solution: pilots detect motion from the surfaces over which they move. In a relatively recent incarnation, flow theory transforms motion into the temporal, time-to-contact parameter, tau. Research conducted at Liverpool has applied this theory to low-level helicopter flight. The present paper extends the application to the fixed-wing flare. Flight simulation results show that tau-guidance strategies exist for this maneuver. It is shown that, as expected from tau theory, the pilot-selected values of the rate of change of tau with time, tau-dot, and the tau-guide coupling constant, directly influence the acceptability of the touchdown rate achieved. Degraded visual environments are shown, under certain circumstances, to cause a breakdown in the tau relationships observed. Potential uses of these results are presented in terms of application to future pilot vision aids, which is the planned next stage of this work.

3406 高速飛行実証フェーズIIの数学モデルと飛行実験結果(S87-2 飛翔体のモデリングとシステム同定(2),S87 飛翔体のモデリングとシステム同定)

The High-Speed Flight Demonstration (HSFD) project is the latest in a series of flight experiments in a research program into reusable space transportation systems being conducted by JAXA. HSFD Phase II was a drop test from a stratospheric balloon to clarify the transonic aerodynamic characteristics of the HOPE-X configuration and to obtain data to validate wind tunnel tests and computational fluid dynamics (CFD) predictions. Since a phased flight experiment can not applied because of its launch method, it was necessary to establish a mathematical model as precise as possible and to conduct accurate flight simulation analysis beforehand. This paper describes the mathematical model of the experiment and the comparison between the results of flight simulation and the flight experiment.

A Multi-Objective Optimisation Approach to Robust Fault Diagnosis Using a Genetic Algorithm

To reduce false and missed alarm rates in fault detection, a number of performance indices are introduced into an observer-based residual generator design. Some performance indices are expressed in the frequency domain to take account of the frequency distributions of faults, noise and modelling uncertainties. All objectives are then reformulated into a set of inequality constraints on performance indices. The genetic algorithm is then used to search an optimal solution to satisfy these inequality constraints on performance indices. The approach developed is applied to a flight control system example and simulation results show that incipient faults can be detected reliably in the presence of modelling uncertainty.

Flight simulator fidelity assessment in a rotorcraft lateral translation maneuver

A model-based methodology for assessing flight simulator fidelity in closed-loop fashion is exercised in analyzing a rotorcraft low-altitude maneuver for which flight test and simulation results were available. The addition of a handling qualities sensitivity function to a previously developed model-based assessment criteria allows an analytical comparison of both performance and handling qualities between simulation and flight test. Model predictions regarding the existence of simulator fidelity problems are corroborated by experiment. The modeling approach is used to assess analytically the effects of modifying simulator characteristics on simulator fidelity.