TABLE OF CONTENTS A basic understanding of the dynamic characteristics and available flight-data measurements for the aircraft under study is necessary as a starting point for system-identification studies. The system-identification analyst should be asking throughout, "Do the identified models make physical sense based on the known vehicle characteristics?"
The system-identification methods presented throughout this book make use of three example cases. We start with a simple example involving the simulation (using SIMULINK) of a simple inverted pendulum, stabilized with attitude and rate feedbacks. This example demonstrates the accuracy and interpretation of the methods and tools for known dynamic characteristics and perfect measurements. The basic inverted pendulum exhibits an aperiodic, unstable behavior, while the closed-loop system exhibits well-damped, second-order dynamics. This example is useful to demonstrate the ability to extract unstable bare-airframe characteristics from closed-loop data.
Two key examples that are developed as case studies throughout this book are based on flight-test data for the XV-15 tilt-rotor aircraft for hover and cruise conditions. We have specifically chosen to illustrate most of the system-identification methods and results using real flight data. Although identification studies based on synthesized data from simulations are useful for illustrating basic concepts, such studies do not expose the practical problems of aircraft system-identification applications for real-world flight data. The effects of measurement/process noise, multiple inputs, input correlation, piloting technique, high-order modes, and non-linearities can present considerable challenges. Many of these factors are present in the XV-15 flight data, thereby allowing the demonstration and discussion of the methods and guidelines presented...
