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Title:Aircraft loss-of-control prevention via backup flight control law design and flight envelope protection
Author(s):Sun, Donglei
Director of Research:Hovakimyan, Naira
Doctoral Committee Chair(s):Hovakimyan, Naira
Doctoral Committee Member(s):Salapaka, Srinivasa M; Stipanovic, Dusan M; Voulgaris, Petros G
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
flight control
flight envelope protection
adaptive augmentation
Abstract:This dissertation seeks to tackle the aircraft loss-of-control problem by adaptive backup flight control law design and flight envelope protection for aircraft with physical damage. In the first part of the study, a backup lateral-directional flight control law for mid-sized transport aircraft with vertical-tail damage is proposed. In particular, the damage case scenarios considered in this work are characterized by a total loss of directional control via rudder, in addition to potential changes in the mass and aerodynamic properties of the aircraft. To compensate for the loss of rudder control, the proposed flight control law employs antisymmetric thrust and asymmetric spoiler deflection as directional control effectors. The design of the backup control law relies on a frequency-shaped approach that accounts for the slow dynamics of the aero-engines, and prevents excessive lift reduction resulting from continued large deflection of the aircraft's spoilers. In addition, the flight control law incorporates an L1 adaptive augmentation loop that is designed to restore prescribed flying qualities for a family of uncertain aircraft models with similar vertical-tail damage. Simulation results with NASA's Transport Class Model demonstrate that the developed backup flight control law is able to recover directional control authority and provide satisfactory flying and handling qualities of the impaired aircraft. In the second part of the study, command limiting control laws for flight envelope protection based on potential functions are presented. In particular, two flight envelope protection methods which are based on quadratic and exponential potential functions respectively are presented and analyzed. During the design process, first the flight envelope protection law is presented based on an n-th order linear model with stability analysis using Lyapunov stability theory. Then the methods are implemented to attitude protection of aircraft models augmented with rate control augmentation systems. Tuning parameters are introduced for better performance of the design with necessary theoretical analysis. Applications on bank-angle protection for NASA's Transport Class Model and pitch-angle protection for a high fidelity nonlinear unmanned aerial vehicle model are presented to verify the design. Simulation results indicate that the proposed methods can provide envelope protection effectively. Considering the existence of uncertainties, disturbances, and possible damages to the system, L1 adaptive augmentations for the flight envelope protection control laws are also proposed, which guarantees desired performance when uncertainties are present in the system dynamics. Finally, flight envelope protection method for two parameters is proposed based on quadratic potential functions. Protection law is designed for each parameter and then the minimum command of the two protection laws is passed to the system. Stability analysis of the closed-loop system with the envelope protection is analyzed using the circle criterion. Protection of both parameters in the steady-state is proved. Simulation examples of the proposed methods for the protection of the angle-of-attack and the pitch angle of a nonlinear unmanned aerial vehicle model are presented to justify the design.
Issue Date:2019-05-22
Rights Information:Copyright 2019 Donglei Sun
Date Available in IDEALS:2019-11-26
Date Deposited:2019-08

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