Nonlinear Adaptive Control of Highly Maneuverable High Performance Aircraft


Book Description

This thesis presents an effective control design methodology using a one-step-ahead prediction adaptive control law and an adaptive control law based on a Lyapunov function. These control law were applied to a highly maneuverable high performance aircraft, in particular, a modified F/A-18. An adaptive controller is developed to maneuver an aircraft at a high angle of attack even if the aircraft is required to fly over a highly nonlinear flight regime. The adaptive controller presented in this thesis is based on linear, bilinear, and nonlinear prediction models with input constraints. It is shown that the linear, bilinear, and nonlinear adaptive controllers can be constructed to minimize the given cost function or Lyapunov function with respect to the control input at each step. The control is calculated such that the system follows the reference trajectory, and such that control signal remains within its constraints. From several simulation results, the nonlinear controller is controller is better than the linear controller. A nonlinear adaptive control law based on a Lyapunov function is designed such that control inputs are smoother than for the one-step-ahead prediction adaptive controller.




Nonlinear Stability and Control Study of Highly Maneuverable High Performance Aircraft, Phase 2


Book Description

This research should lead to the development of new nonlinear methodologies for the adaptive control and stability analysis of high angle-of-attack aircraft such as the F18 (HARV). The emphasis has been on nonlinear adaptive control, but associated model development, system identification, stability analysis and simulation is performed in some detail as well. Various models under investigation for different purposes are summarized in tabular form. Models and simulation for the longitudinal dynamics have been developed for all types except the nonlinear ordinary differential equation model. Briefly, studies completed indicate that nonlinear adaptive control can outperform linear adaptive control for rapid maneuvers with large changes in alpha. The transient responses are compared where the desired alpha varies from 5 degrees to 60 degrees to 30 degrees and back to 5 degrees in all about 16 sec. Here, the horizontal stabilator is the only control used with an assumed first-order linear actuator with a 1/30 sec time constant. Mohler, R. R. Unspecified Center...




Adaptive Model Reference Control of Highly Maneuverable High Performance Aircraft


Book Description

This thesis presents an adaptive model reference controller for a highly maneuverable high performance aircraft, in particular, a modified F18. An adaptive controller is developed to maneuver an aircraft at a high angle of attack. Thus, the aircraft is required to fly over a highly nonlinear flight regime. The adaptive controller presented in this thesis can be viewed as a combination of a linear and a nonlinear controller. Around a fixed flight condition the adaptive controller converges to a linear controller; however, the controller remains a nonlinear controller during maneuvers. The contributions of this thesis lie in two areas. The first area is in control. A successful application of linear adaptive control is presented for a highly nonlinear system. A new method is used to generate the reference trajectory. The reference model uses output feedback to improve the reference trajectory. It is shown that this improvement is necessary because of the control limitations. This work is also important to the control of highly maneuverable high performance aircraft. A successful adaptive controller has been developed to rapidly maneuver an aircraft to a high angle of attack. The main focus of this thesis is adaptive control.




Nonlinear Stability and Control Study of Highly Maneuverable High Performance Aircraft


Book Description

This project is intended to research and develop new nonlinear methodologies for the control and stability analysis of high-performance, high angle-of-attack aircraft such as HARV (F18). Past research (reported in our Phase 1, 2, and 3 progress reports) is summarized and more details of final Phase 3 research is provided. While research emphasis is on nonlinear control, other tasks such as associated model development, system identification, stability analysis, and simulation are performed in some detail as well. An overview of various models that were investigated for different purposes such as an approximate model reference for control adaptation, as well as another model for accurate rigid-body longitudinal motion is provided. Only a very cursory analysis was made relative to type 8 (flexible body dynamics). Standard nonlinear longitudinal airframe dynamics (type 7) with the available modified F18 stability derivatives, thrust vectoring, actuator dynamics, and control constraints are utilized for simulated flight evaluation of derived controller performance in all cases studied. Mohler, R. R. Unspecified Center ADAPTIVE CONTROL; AIRCRAFT PERFORMANCE; AIRCRAFT STABILITY; FLIGHT SIMULATION; HIGHLY MANEUVERABLE AIRCRAFT; NEURAL NETS; OPTIMAL CONTROL; ANGLE OF ATTACK; CONTROLLERS; F-18 AIRCRAFT; NONLINEAR FEEDBACK...




Nonlinear Control of High Performance Aircraft


Book Description

This thesis presents the design of various controllers for a highly maneuverable, high performance aircraft, namely the modified F-18. The aircraft was required to perform high angle-of-attack maneuvers, for which the aircraft behaves in as a highly nonlinear system. An adaptive PID controller was used to control the aircraft through these high angle-of-attack maneuvers. Several nonlinear controllers were then developed based on the adaptive PID control, and were tested for robustness. This thesis also looks at an improvement in the aircraft which may improve performance in high angle-of-attack maneuvers. The contributions of this thesis are in the areas of control, in general, and specifically in the area of aircraft control. Successful application of linear adaptive control and nonlinear control were presented. In the area of aircraft control, controllers were presented which produce good performance for high angle-of-attack maneuvers, while maintaining implementability. Also, some insight is gained into what aircraft changes could improve performance.







Adaptive Compensation of Nonlinear Actuators for Flight Control Applications


Book Description

This book provides a basic understanding of adaptive control and its applications in Flight control. It discusses the designing of an adaptive feedback control system and analyzes this for flight control of linear and nonlinear aircraft models using synthetic jet actuators. It also discusses control methodologies and the application of control techniques which will help practicing flight control and active flow control researchers. It also covers modelling and control designs which will also benefit researchers from the background of fluid mechanics and health management of actuation systems. The unique feature of this book is characterization of synthetic jet actuator nonlinearities over a wide range of angles of attack, an adaptive compensation scheme for such nonlinearities, and a systematic framework for feedback control of aircraft dynamics with synthetic jet actuators.




A Comparison of Intelligent, Adaptive, and Nonlinear Flight Control Laws


Book Description

This paper compares in simulation six different nonlinear control laws for multi-axis control of a high performance aircraft. The control law approaches are fuzzy logic control, backstepping adaptive control, variable structure control, and indirect adaptive versions of Model Predictive Control and Dynamic Inversion. In addition, a more conventional scheduled dynamic inversion control law is used as a baseline. In some of the cases, a stochastic genetic algorithm was used to optimize fixed parameters during design. The control laws are demonstrated on a 6 Degree-of-Freedom simulation with nonlinear aerodynamic and engine models, actuator models with position and rate saturations, and turbulence. Simulation results include a variety of single and multiple axis maneuvers in normal operation and with failures or damage. The specific failure and damage cases that are examined include single and multiple lost surfaces, actuator hardovers, and an oscillating stabilator case. There are also substantial differences between the control law design and simulation models, which are used to demonstrate some robustness aspects of the different control laws.




A Feasibility Study of Self-learning Adaptive Flight Control for High Performance Aircraft


Book Description

A study of the feasibility of a self-learning adaptive system for the flight control of high performance aircraft has been performed. A flight control system was developed for the investigation of the stability augmentation of the longitudinal axis of the F101B aircraft using self-learning adaptive control. The learning adaptive controller developed employs a three-loop concept. The innermost loop comprises a linear feedback control system in which a set of control gains is adjusted by a second (adaptive) loop employing a parameter identifier and a trainable function generator (automation). The automation provides the correct values of feedback gain in response to patterns derived from the identified aircraft parameters. The third loop (the learning loop) measures control system performance, and continually retrains the automation to improve the performance. Experiments were performed with a digital simulation of the aircraft and the learning adaptive control system. Results of the experiments indicate that learning adaptive control is feasible. However, a number of significant technical problems must be overcome prior to the use of such a control system in tactical aircraft. Studies of sensitivity must be performed to assess the effect of small perturbations in the identification parameters on system performance. Extended studies of property extraction from the identified parameters is required, and means for further simplifying the control structure is of importance in a real system. (Author).




Nonlinear Adaptive Flight Control with a Backstepping Design Approach


Book Description

This paper examines the use of adaptive backstepping for multi-axis control of a high performance aircraft. The control law is demonstrated on a 6 Degree-of-Freedom simulation with nonlinear aerodynamic and engine models, actuator models with saturation, and turbulence. Simulation results are demonstrated for large pitch-roll maneuvers, and for maneuvers with failure of the right stabilator. There are substantial differences between the control law design and simulation models, which are used to demonstrate some robustness aspects of this control law. Actuator saturation is shown to be a considerable problem for this type of controller. However, the flexibility of the backstepping design provides opportunities for improvement. In particular, the Lyapunov function is modified so that the growth of integrated error and the rate of change of parameter growth are both reduced when the surface commands are growing at a rate that will likely saturate the actuators. In addition, the deadzone technique from robust linear adaptive control is applied to improve robustness to turbulence.