**Meet the editor**

Dr Thomas Lombaerts was born in 1980 in Brussels, Belgium. He graduated cum laude in 2004 as an aerospace engineer, specializing in flight control at the Faculty of Aerospace Engineering, Delft University of Technology in the Netherlands. In May 2010, he successfully defended his PhD research on Fault Tolerant Flight Control using a physical model approach at the same university.

Since September 2010, he has been a research fellow at the German Aerospace Center DLR in Munich. His research interests include aircraft state estimation and Kalman filtering, aerodynamic model identification, adaptive and nonlinear control, control allocation, handling qualities, and pilot workload analysis. In 2011, he won a Marie Curie International Outgoing Fellowship (IOF) from the European Union for the ADFLICO research project, involving the scientific partners NASA and DLR. Several conference and journal publications as well as book chapters about his research have been published in the past years.

Contents

**Preface VII** 

Chapter 2 **Quantitative Feedback** 

Chapter 3 **Gain Tuning of Flight Control** 

**Part 1 Literature Review and Theoretical Developments 1** 

**Theory and Its Application in UAV's Flight Control 37** 

**Laws for Satisfying Trajectory Tracking Requirements 71** 

Chapter 1 **Fundamentals of GNSS-Aided Inertial Navigation 3**  Ahmed Mohamed and Apostolos Mamatas

Xiaojun Xing and Dongli Yuan

Chapter 5 **Fault Tolerant Flight Control Techniques** 

Chapter 6 **Effects of Automatic Flight Control** 

Marilena D. Pavel

Chapter 7 **Tool-Based Design and** 

Urbano Tancredi and Federico Corraro

**Part 2 Adaptive and Fault Tolerant Flight Control 93** 

Youmin Zhang and Abbas Chamseddine

Chapter 4 **Adaptive Feedforward Control for Gust Loads Alleviation 95**  Jie Zeng, Raymond De Callafon and Martin J. Brenner

**with Application to a Quadrotor UAV Testbed 119** 

**System on Chinook Underslung Load Failures 151** 

**Evaluation of Resilient Flight Control Systems 185**  Hafid Smaili, Jan Breeman and Thomas Lombaerts

## Contents

## **Preface** XI


Preface

The history of flight control is inseparably linked to the history of aviation itself. Shortly after the German aviation pioneer Otto Lilienthal (1848-1896) left the ground for the first time in his self-made glider from Windmühlenberg (windmill hill) of Derwitz (Germany) in the summer of 1891, the problem of flight in a heavier-than-air vehicle created a new challenge, that of controlled flight. During his numerous experimental flights, Otto Lilienthal realized that leaving the ground was easier than staying in the air. For controlling his flights, he invented the first means of lateral stabilization using a vertical rudder. Following the first successful motorized flight of the Wright Brothers in 1903, the first artificially controlled flight was demonstrated in 1914 by Lawrence Sperry (1892-1923), the third son of the gyrocompass co-inventor Elmer Ambrose Sperry, by flying his Curtiss-C-2 airplane hands-free in front of a speechless crowd. This very first autopilot consisted of three gyroscopes and a magnetic compass both linked to the pneumatically operated flight control surfaces. The autopilot enabled stable flight by holding the pitch, roll and yaw attitudes constant, while maintaining the compass course. Since these early days, Sperry and many other engineers improved the concept of automatic stabilized flight further up to highly advanced automatic fly-by-wire flight control systems which can be found nowadays in military jets and civil airliners. Even today, many research efforts are made for the further development of these flight control systems in various aspects. Recent new developments in this field focus on a wealth of different aspects, such as nonlinear flight control, autonomous control of unmanned aircraft, formation flying, aeroservoelastic control, intelligent control, adaptive flight control, fault tolerant flight control, and many others. This book focuses on a selection of these key research areas.

This book consists of two major sections. The first section contains three chapters and focuses on a literature review and some recent theoretical developments in flight control systems. The second section discusses some concepts of adaptive and faulttolerant flight control systems. This topic has been receiving a lot of research attention from the scientific community lately. Each technique discussed in this book is

The first chapter is a literature survey providing a global overview perspective to the field of GPS-aided inertial navigation. The chapter discusses the topics of modeling,

illustrated by a relevant example.

sensor properties and estimation techniques.

## Preface

The history of flight control is inseparably linked to the history of aviation itself. Shortly after the German aviation pioneer Otto Lilienthal (1848-1896) left the ground for the first time in his self-made glider from Windmühlenberg (windmill hill) of Derwitz (Germany) in the summer of 1891, the problem of flight in a heavier-than-air vehicle created a new challenge, that of controlled flight. During his numerous experimental flights, Otto Lilienthal realized that leaving the ground was easier than staying in the air. For controlling his flights, he invented the first means of lateral stabilization using a vertical rudder. Following the first successful motorized flight of the Wright Brothers in 1903, the first artificially controlled flight was demonstrated in 1914 by Lawrence Sperry (1892-1923), the third son of the gyrocompass co-inventor Elmer Ambrose Sperry, by flying his Curtiss-C-2 airplane hands-free in front of a speechless crowd. This very first autopilot consisted of three gyroscopes and a magnetic compass both linked to the pneumatically operated flight control surfaces. The autopilot enabled stable flight by holding the pitch, roll and yaw attitudes constant, while maintaining the compass course. Since these early days, Sperry and many other engineers improved the concept of automatic stabilized flight further up to highly advanced automatic fly-by-wire flight control systems which can be found nowadays in military jets and civil airliners. Even today, many research efforts are made for the further development of these flight control systems in various aspects. Recent new developments in this field focus on a wealth of different aspects, such as nonlinear flight control, autonomous control of unmanned aircraft, formation flying, aeroservoelastic control, intelligent control, adaptive flight control, fault tolerant flight control, and many others. This book focuses on a selection of these key research areas.

This book consists of two major sections. The first section contains three chapters and focuses on a literature review and some recent theoretical developments in flight control systems. The second section discusses some concepts of adaptive and faulttolerant flight control systems. This topic has been receiving a lot of research attention from the scientific community lately. Each technique discussed in this book is illustrated by a relevant example.

The first chapter is a literature survey providing a global overview perspective to the field of GPS-aided inertial navigation. The chapter discusses the topics of modeling, sensor properties and estimation techniques.

## XII Preface

The second chapter discusses the concept of quantitative feedback theory. This frequency-based control technique makes use of the Nichols chart in order to achieve a desired robust design over a specified region of plant uncertainties. Desired timedomain responses are translated into frequency-domain tolerances, which lead to bounds (or constraints) on the loop transmission function. The design process is transparent, allowing a designer to see what trade-offs are necessary to achieve a desired performance level. As an example, QFT is applied for the lateral control of a UAV.

Preface IX

**Dr Ir Thomas Lombaerts**  German Aerospace Center DLR

Oberpfaffenhofen – Wessling

Germany

Institute of Robotics and Mechatronics Department of System Dynamics and Control

the black box data recovered from such an accident. This tool is freely available for the research community and can be used to develop new fault-tolerant flight control

I would like to express my sincere gratitude to all the authors for all the time and effort they spent contributing chapters of high quality to this book. I would like to thank the publisher, InTech, for taking the initiative to publish this book and for making this book Open Access, which guarantees a wide dissemination of the published results. I also wish to acknowledge the Publishing Process Manager Ms Martina Pecar-Durovic, for her indispensable technical and administrative assistance

algorithms.

while preparing and publishing this book.

The third chapter discusses the topic of gain tuning for flight control laws for an unmanned space re-entry vehicle technology demonstrator in order to satisfy trajectory tracking requirements. The method for gain tuning is based upon the Practical Stability criterion. This is a technique developed previously by the authors for analyzing the robustness of a given flight control law.

In the fourth chapter, the first of the second section, an adaptive feedforward control method is suggested for gust load alleviation. With the novel development of airborne Light Detection and Ranging (LIDAR) turbulence sensor available for the accurate measurement of the vertical gust velocity at considerable distances ahead of the aircraft, it becomes feasible to design an adaptive feedforward control algorithm to alleviate the structural loads induced by any turbulence and to extend the life of the structure. This proposed approach identifies in real time the flexible modes for parameter adjustment in the feedforward controller. This method is demonstrated on the F/A-18 active aeroelastic wing simulation model.

The fifth chapter provides an extensive overview of different fault-tolerant flight control techniques, including Gain-Scheduled PID control, Model Reference Adaptive Control, Sliding Mode Control, Backstepping Control, Model Predictive Control, and Flatness-based Trajectory Planning/Re-planning. At the end of the chapter, simulations and flight tests of a quadrotor UAV testbed are discussed.

The sixth chapter investigates the contributions that an automatic flight control system (AFCS) may provide to the recovery prospects of the Chinook tandem helicopter after a load failure scenario. An analysis is made as to how the advanced AFCS, implemented to improve the handling qualities characteristics of the helicopter, improves the CH-47 behavior during emergency situations such as failure scenarios of its suspended load. An example of such a failure scenario is when one of the load suspension cables snaps.

The seventh and last chapter describes a new high fidelity large transport aircraft simulation benchmark which has been developed as a tool-based design and evaluation platform for resilient flight control system design. The simulation model contains nonlinear kinematics and aircraft dynamics, and includes actuator and sensor properties. Moreover, the model includes an extensive list of failure modes, varying from stuck or faulty control surfaces to significant aerodynamic damage. An important failure mode is the engine separation scenario, which has been validated by means of the black box data recovered from such an accident. This tool is freely available for the research community and can be used to develop new fault-tolerant flight control algorithms.

VIII Preface

UAV.

The second chapter discusses the concept of quantitative feedback theory. This frequency-based control technique makes use of the Nichols chart in order to achieve a desired robust design over a specified region of plant uncertainties. Desired timedomain responses are translated into frequency-domain tolerances, which lead to bounds (or constraints) on the loop transmission function. The design process is transparent, allowing a designer to see what trade-offs are necessary to achieve a desired performance level. As an example, QFT is applied for the lateral control of a

The third chapter discusses the topic of gain tuning for flight control laws for an unmanned space re-entry vehicle technology demonstrator in order to satisfy trajectory tracking requirements. The method for gain tuning is based upon the Practical Stability criterion. This is a technique developed previously by the authors

In the fourth chapter, the first of the second section, an adaptive feedforward control method is suggested for gust load alleviation. With the novel development of airborne Light Detection and Ranging (LIDAR) turbulence sensor available for the accurate measurement of the vertical gust velocity at considerable distances ahead of the aircraft, it becomes feasible to design an adaptive feedforward control algorithm to alleviate the structural loads induced by any turbulence and to extend the life of the structure. This proposed approach identifies in real time the flexible modes for parameter adjustment in the feedforward controller. This method is demonstrated on

The fifth chapter provides an extensive overview of different fault-tolerant flight control techniques, including Gain-Scheduled PID control, Model Reference Adaptive Control, Sliding Mode Control, Backstepping Control, Model Predictive Control, and Flatness-based Trajectory Planning/Re-planning. At the end of the chapter, simulations

The sixth chapter investigates the contributions that an automatic flight control system (AFCS) may provide to the recovery prospects of the Chinook tandem helicopter after a load failure scenario. An analysis is made as to how the advanced AFCS, implemented to improve the handling qualities characteristics of the helicopter, improves the CH-47 behavior during emergency situations such as failure scenarios of its suspended load. An example of such a failure scenario is when one of the load

The seventh and last chapter describes a new high fidelity large transport aircraft simulation benchmark which has been developed as a tool-based design and evaluation platform for resilient flight control system design. The simulation model contains nonlinear kinematics and aircraft dynamics, and includes actuator and sensor properties. Moreover, the model includes an extensive list of failure modes, varying from stuck or faulty control surfaces to significant aerodynamic damage. An important failure mode is the engine separation scenario, which has been validated by means of

for analyzing the robustness of a given flight control law.

the F/A-18 active aeroelastic wing simulation model.

and flight tests of a quadrotor UAV testbed are discussed.

suspension cables snaps.

I would like to express my sincere gratitude to all the authors for all the time and effort they spent contributing chapters of high quality to this book. I would like to thank the publisher, InTech, for taking the initiative to publish this book and for making this book Open Access, which guarantees a wide dissemination of the published results. I also wish to acknowledge the Publishing Process Manager Ms Martina Pecar-Durovic, for her indispensable technical and administrative assistance while preparing and publishing this book.

## **Dr Ir Thomas Lombaerts**

German Aerospace Center DLR Institute of Robotics and Mechatronics Department of System Dynamics and Control Oberpfaffenhofen – Wessling Germany

**Part 1** 

**Literature Review and** 

**Theoretical Developments** 
