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The purpose of this book is to assist analysts, engineers, and students toward developing dynamic models, and analyzing the control of flight vehicles with various blended features comprising aircraft, launch vehicles, reentry vehicles, missiles and aircraft.
Graphical methods for analysing vehicle performance
Methods for trimming deflections of a vehicle that has multiple types of effectors
Presents a parameters used for speedily evaluating the performance, stability, and controllability of a new flight vehicle concept along a trajectory or with fixed flight conditions
Eric T. Falangas was a Lead Engineer/ Specialist and Project Manager at Boeing, Rockwell International and Aerospace Corporation in the fields of flight control design, spacecraft attitude control, vibration control and active vibration isolation, and other control and dynamics related projects. He received a BS in Electrical Engineering from the University of London and a MS in Control Systems from the University of Manchester Institute of Science and Technology. Eric has published several papers in magazines and conferences and was awarded 4 patents for developing active vibration control systems using piezo-electric actuator devices, and Flixan, which is a flight vehicle modelling and performance evaluation methodology, implemented in a Windows based program.
Autorentext
Eric T. Falangas was a Lead Engineer/ Specialist and Project Manager at Boeing, Rockwell International and Aerospace Corporation in the fields of flight control design, spacecraft attitude control, vibration control and active vibration isolation, and other control and dynamics related projects. He received a BS in Electrical Engineering from the University of London and a MS in Control Systems from the University of Manchester Institute of Science and Technology. Eric has published several papers in magazines and conferences and was awarded 4 patents for developing active vibration control systems using piezo-electric actuator devices, and Flixan, which is a flight vehicle modelling and performance evaluation methodology, implemented in a Windows based program.
Leseprobe
INTRODUCTION
The stability and performance of a flight vehicle can be analyzed from two distinct perspectives: static and dynamic. The static analysis is described in the second half of this book and it deals with the capability of the vehicle controls to balance the steady-state aerodynamic moments and forces and also having sufficient control authority to counteract the expected wind shear along a trajectory. Dynamic analysis evaluates the behavior of the closed-loop vehicle and control system together by using linear control analysis and requires dynamic models of the vehicle consisting of differential equations. In aerospace vehicle development, one of the central features is the simulation model of the vehicle dynamics. This model is a mathematical representation of its expected behavior and dynamic response to the control commands and to wind disturbances. This math model is used by the stability and control engineer to develop control laws that allow a human pilot or an autopilot to maneuver the vehicle and to perform its mission. It is necessary to understand the physics of how forces cause objects to move in order to be able to predict the resulting motion of a flight vehicle to excitations. This field of study is called "dynamics" and it examines the behavior of structures under the effects of external forces and torques. Equations of motion describe how the vehicle will move in response to applied forces. For example, simple equations describe how a rocket will accelerate when a constant thrust is provided by the rocket's engine. More difficult equations describe how the sloshing of propellant in a rocket's tank will cause the rocket's structure to vibrate or throw the rocket off course. Another type of modeling would be to predict, in a mathematical equation, how an aircraft will respond to hitting an updraft in the atmosphere, or how the aircraft will respond to the deflection of the control surfaces at different airspeeds. These equations are differential equations, in which the rate of change of some variables, called states, is described as being dependent upon inputs and other states. The set of mathematical equations that describe these motions are collectively called a math model or simulation model of the vehicle, and they can range in complexity from a single equation to a complex set of equations. Complex vehicle models are, for convenience, broken down into subsystems that deal with different sets of dynamics, such as vehicle, sensor, and actuator subsystems.
The dynamic behavior of flight vehicles, such as launch vehicles, re-entry vehicles, and high performance aircraft, is generally studied in two distinct phases. The first phase deals with orbital mechanics and flight trajectory optimization assuming that the vehicle can be perfectly steered. This analysis is usually referred to as "long period dynamics." The second study deals with variations of the vehicle from its flight trajectory and they have a relatively shorter period. The dynamic equations describe how a vehicle model will behave in response to a combination of applied forces and torques and they are expressed in two forms: (a) the nonlinear large-angle equations suitable for six-degrees-of-freedom (6-DOF) simulations and (b) the linearized equations that capture the shorter period dynamics and they describe small variations of the vehicle from its trim condition. Both types of equations are used by different groups of people for flight vehicle design to address different issues. The 6-DOF equations are used to simulate the nonlinear response of the vehicle to commands and to disturbances along the entire flight. The 6-DOF simulations, however, usually include only the rigid-body motion, they are complex because they contain a lot of operational details and logic, and they cannot be used for control design and stability analysis.
The linear models are used for modeling the short period
Inhalt
Preface xi
Acknowledgments xiii
Introduction 1
1 Description of the Dynamic Models 7
1.1 Aerodynamic Models, 8
1.2 Structural Flexibility, 9
1.3 Propellant Sloshing, 10
1.4 Dynamic Coupling between Vehicle, Actuators, and Control Effectors, 12
1.5 Control Issues, 13
1.6 Coordinate Axes, 15
Nomenclature, 16
2 Nonlinear Rigid-Body Equations Used in 6-DOF Simulations 19
2.1 Force and Acceleration Equations, 19
2.2 Moment and Angular Acceleration Equations, 21
2.3 Gravitational Forces, 22
2.4 Engine TVC Forces, 22
2.5 Aerodynamic Forces and Moments, 24
2.6 Propellant Sloshing Using the Pendulum Model, 28
2.7 Euler Angles, 29
2.8 Vehicle Altitude and Cross-Range Velocity Calculation, 30
2.9 Rates with Respect to the Stability Axes, 30
2.10 Turn Coordination, 31
2.11 Acceleration Sensed by an Accelerometer, 31
2.12 Vehicle Controlled with a System of Momentum Exchange Devices, 32
2.13 Spacecraft Controlled with Reaction Wheels Array, 33
2.14 Spacecraft Controlled with an Array of Single-Gimbal CMGs, 37
2.14.1 Math Model of a SGCMG Array, 38
2.14.2 Steering Logic for a Spacecraft with SGCMGs, 42
3 Linear Perturbation Equations Used in Control Analysis 47
3.1 Force and Acceleration Equations, 47
3.2 Linear Accelerations, 48
3.3 Moment and Angular Acceleration Equations, 50
3.4 Gravitational Forces, 51
3.5 Forces and Moments due to an Engine Pivoting and Throttling, 52
3.6 Aerodynamic Forces and Moments, 58
3.7 Modeling a Wind-Gust Disturbance, 70
3.8 Propellant Sloshing (SpringMass Analogy), 73
3.9 Structural Flexibility, 80
3.9.1 The Bending Equation, 85
3.10 Load Torques, 90
3.10.1 Load Torques at the Nozzle Gimbal, 91
3.10.2 Hinge Moments at the Control Surfaces, 93
3.11 …