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The importance of recognizing that each lower-order model used for rotorcraft parameter identification has a limited range of applicability is illustrated in some detail. Examples are given to illustrate the use of conditioning the test input signals and the potential of using multi-axis test inputs to enhance the parameter identifiability. The paper discusses the benefits and limitations of using frequency sweeps as flight-test input signals for identification of frequency response for rotorcraft and for the subsequent fitting of parametric transfer-function models. This paper demonstrates the major role played by analytical modeling and the understanding of the physics involved in the rotorcraft flight dynamics, particularly understanding the limit of lower-order models, in achieving successful rotorcraft parameter identification. (Author).
Identification Modeling and Characteristics of Miniature Rotorcraft introduces an approach to developing a simple and effective linear parameterized model of vehicle dynamics using the CIFERâ identification tool created by the Army/NASA Rotorcraft Division. It also presents the first application of the advanced control system optimization tool CONDUITâ to systematically and efficiently tune control laws for a model-scale UAV helicopter against multiple and competing dynamic response criteria. Identification Modeling and Characteristics of Miniature Rotorcraft presents the detailed account of how the theory was developed, the experimentation performed, and how the results were used. This book will serve as a basic and illustrative guide for all students that are interested in developing autonomous flying helicopters.
With the demand for more advanced fighter aircraft, relying on unstable flight mechanical characteristics to gain flight performance, more focus has been put on model-based system engineering to help with the design work. The flight control system design is one important part that relies on this modeling. Therefore, it has become more important to develop flight mechanical models that are highly accurate in the whole flight envelope. For today’s modern fighter aircraft, the basic flight mechanical characteristics change between linear and nonlinear as well as stable and unstable as an effect of the desired capability of advanced maneuvering at subsonic, transonic and supersonic speeds. This thesis combines the subject of system identification, which is the art of building mathematical models of dynamical systems based on measurements, with aeronautical engineering in order to find methods for identifying flight mechanical characteristics. Here, some challenging aeronautical identification problems, estimating model parameters from flight-testing, are treated. Two aspects are considered. The first is online identification during flight-testing with the intent to aid the engineers in the analysis process when looking at the flight mechanical characteristics. This will also ensure that enough information is available in the resulting test data for post-flight analysis. Here, a frequency domain method is used. An existing method has been developed further by including an Instrumental Variable approach to take care of noisy data including atmospheric turbulence and by a sensor-fusion step to handle varying excitation during an experiment. The method treats linear systems that can be both stable and unstable working under feedback control. An experiment has been performed on a radio-controlled demonstrator aircraft. For this, multisine input signals have been designed and the results show that it is possible to perform more time-efficient flight-testing compared with standard input signals. The other aspect is post-flight identification of nonlinear characteristics. Here the properties of a parameterized observer approach, using a prediction-error method, are investigated. This approach is compared with four other methods for some test cases. It is shown that this parameterized observer approach is the most robust one with respect to noise disturbances and initial offsets. Another attractive property is that no user parameters have to be tuned by the engineers in order to get the best performance. All methods in this thesis have been validated on simulated data where the system is known, and have also been tested on real flight test data. Both of the investigated approaches show promising results.
Twenty-nine papers and comments are contained in these Proceedings. Several discuss and compare results obtained with different parameter identification techniques applied to specific fighter aircraft at high angles of attack, subsonic and supersonic transports, VTOL and STOL aircraft, and helicopters. Special problem areas such as systems modelling with high internally-generated fluctuations, aircraft state estimation in non-steady flight and parameter identification for non-linear aerodynamic regimes are covered. The sessions at the Specialists' Meeting were titled mathematical models, instrumentation and filters, flight test techniques, analysis of flight test data, rotorcraft parameter identification and selected topics.
Identification of low order equivalent system dynamic models from flight test data was studied. Inputs were pilot control deflections, and outputs were aircraft responses, so the models characterized the total aircraft response including bare airframe and flight control system. Theoretical investigations were conducted and related to results found in the literature. Low order equivalent system modeling techniques using output error and equation error parameter estimation in the frequency domain were developed and validated on simulation data. It was found that some common difficulties encountered in identifying closed loop low order equivalent system models from flight test data could be overcome using the developed techniques. Implications for data requirements and experiment design were discussed. The developed methods were demonstrated using realistic simulation cases, then applied to closed loop flight test data from the NASA F-18 High Alpha Research Vehicle.Morelli, Eugene A.Langley Research CenterEXPERIMENT DESIGN; DYNAMIC MODELS; SYSTEM IDENTIFICATION; FLIGHT TESTS; DATA PROCESSING; FLIGHT CONTROL; DEFLECTION; AIRCRAFT PERFORMANCE; ERROR ANALYSIS; FLIGHT CHARACTERISTICS; FEEDBACK CONTROL
Flight Mechanics Modeling and Analysis comprehensively covers flight mechanics and flight dynamics using a systems approach. This book focuses on applied mathematics and control theory in its discussion of flight mechanics to build a strong foundation for solving design and control problems in the areas of flight simulation and flight data analysis. The second edition has been expanded to include two new chapters and coverage of aeroservoelastic topics and engineering mechanics, presenting more concepts of flight control and aircraft parameter estimation. This book is intended for senior undergraduate aerospace students taking Aircraft Mechanics, Flight Dynamics & Controls, and Flight Mechanics courses. It will also be of interest to research students and R&D project-scientists of the same disciplines. Including end-of-chapter exercises and illustrative examples with a MATLAB®-based approach, this book also includes a Solutions Manual and Figure Slides for adopting instructors. Features: • Covers flight mechanics, flight simulation, flight testing, flight control, and aeroservoelasticity. • Features artificial neural network- and fuzzy logic-based aspects in modeling and analysis of flight mechanics systems: aircraft parameter estimation and reconfiguration of control. • Focuses on a systems-based approach. • Includes two new chapters, numerical simulation examples with MATLAB®-based implementations, and end-of-chapter exercises. • Includes a Solutions Manual and Figure Slides for adopting instructors.
Progress made in joint NASA/Army research concerning rotorcraft flight-dynamics modeling, design methodologies for rotorcraft flight-control laws, and rotorcraft parameter identification is reviewed. Research into these interactive disciplines is needed to develop the analytical tools necessary to conduct flying qualities investigations using both the ground-based and in-flight simulators, and to permit an efficient means of performing flight test evaluation of rotorcraft flying qualities for specification compliance. The need for the research is particularly acute for rotorcraft because of their mathematical complexity, high order dynamic characteristics, and demanding mission requirements. The research in rotorcraft flight-dynamics modeling is pursued along two general directions: generic nonlinear models and nonlinear models for specific rotorcraft. In addition, linear models are generated that extend their utilization from 1-g flight to high-g maneuvers and expand their frequency range of validity for the design analysis of high-gain flight control systems. A variety of methods ranging from classical frequency-domain approaches to modern time-domain control methodology that are used in the design of rotorcraft flight control laws is reviewed. Also reviewed is a study conducted to investigate the design details associated with high-gain, digital flight control systems for combat rotorcraft. Parameter identification techniques developed for rotorcraft applications are reviewed. Chen, Robert T. N. and Lebacqz, J. Victor and Aiken, Edwin W. and Tischler, Mark B. Ames Research Center...