This book presents a novel approach to tackle the gust alleviation problem. Traditional approaches typically attempt to suppress the structural response at discrete points of the wing using only the conventional control surfaces (aileron, elevator, rudder), resulting in limited control authority, high-bandwidth actuator requirements, and necessity of gust field measurements ahead of the aircraft. In this book, the authors directly address the spanwise behavior of aerodynamic loads, as this is what should be primarily controlled. Because the gust loads are mainly caused by disturbances in the spanwise lift, the aim is at controlling the shape of the lift distribution profile along the span. Therefore, this distributed approach allows control of the loads at all points of the wing structure. Moreover, using modal decomposition concepts, the control surfaces can be designed to maximize controllability of the most relevant aerodynamic modes, which naturally results in lower actuator rate requirements.
In the work herein, the unsteady aerodynamics of a finite wing featuring multiple trailing edge flaps is modeled using the Unsteady Vortex Lattice Method (UVLM), yielding a linear, time-invariant, high-order state-space model. An Eigensystem Realization Algorithm (ERA) is applied for model-order reduction and modal identification, providing aerodynamic mode shapes and associated eigenvalues. By representing the system output (lift distribution) as a truncated superposition of aerodynamic mode shapes, a low-order MIMO modal representation is obtained, suitable for controller synthesis. This methodology is used to synthesize regulators, to suppress gust disturbances in lift distribution, and trackers, to dynamically follow any desired reference lift profile. A special observer structure decouples the gust input from the state estimation process and provides estimates for the gust amplitude along time, thus rendering the gust measurements ahead of the aircraft unnecessary.
Contents
Preface
Chapter 1: Introduction
Chapter 2: Unsteady Aerodynamic Modeling of a Multiflap Wing
Chapter 3: Review of Model Order Reduction Methods
Chapter 4: Modal Identification of Aerodynamic Systems
Chapter 5: Spatial Control of Spanwise Lift Distribution
Author(s): Joaquim Neto Dias, James E. Hubbard Jr.
Publisher: American Institute of Aeronautics and Astronautics
Year: 2020
Language: English
Pages: 203
City: Reston
Cover
Half Title
Title Page
Copyright Page
Contents
Preface
List of Tables
List of Figures
Acknowledgements
Chapter 1: Introduction
1.1 Motivation: The Quest for Increasingly Efficient Aircraft
1.2 Literature Review on Active Load Alleviation
1.3 Proposed Approach
1.4 Fundamental assumptions
1.5 Unique features of this book
1.6 Book Organization
Chapter 2: Unsteady Aerodynamic Modeling of a Multiflap Wing
2.1 Quasi-Steady Aerodynamic Model
2.2 Unsteady Lifting-Line Theory (ULLT)
2.3 Unsteady Vortex Lattice Method (UVLM)
2.4 Verification of Aerodynamic Models
2.5 Assumptions and Constraints
Chapter 3: Review of Model Order Reduction Methods
3.1 Introduction
3.2 Proper Orthogonal Decomposition: Fundamentals
3.3 Balanced Proper Orthogonal Decomposition
3.4 Eigensystem Realization Algorithm (ERA)
3.5 Example: Application to a Finite Element Model of a Cantilever Beam
3.6 Chapter Summary
Chapter 4: Modal Identification of Aerodynamic Systems
4.1 Modal Identification from UVLM
4.2 Limits in Identifiability
4.3 Modal Identification from ULLT
4.4 Physical Interpretation of Aerodynamic Modes
4.5 Effects of Varying Wing Planform on the Mode Shapes and Eigenvalues
4.6 Chapter Summary
Chapter 5: Spatial Control of Spanwise Lift Distribution
5.1 Model Output Expansion into Mode Shapes
5.2 Threshold for Model Truncation
5.3 Spatial-Temporal Controller Synthesis
5.4 Shape Control Problem
5.5 Gust Load Alleviation Problem
5.6 Gust Load Alleviation Problem with Gust Estimation
5.7 Chapter Summary
5.8 Future Developments of This Methodology
Appendix A
References
Index
Supporting Materials
