The rotor system is the primary source of vibratory forces on a helicopter. Vibratory forces result from the rotor system response to dynamic and aerodynamic loading. This thesis discusses sources of excitation, and investigates rotor system modeling methods. Computer models based on finite element and Mykiestad methods are developed and compared for the free and forced vibration cases of a nniform rotor blade. The modeling assumptions and the effects of non-iniform physical parameters are discussed. The Myklestad based computer model is expanded to include coupling effects isherent in modern rotor blades. This rotor modeling program is incorporated into the Dynamics section of the Joint Army/Navy Rotorcraft Analysis and Design (JANRAD) program currenfly used by the Naval Postgraduate School?s helicopter design course (AA43O6) for preliminary helicopter design and analysis. Computer programs are developed as tools to investigate the stabffity of a rotor system for the specfflc cases of rotor flapping and ground/air resonance. A rotor flapping stability model, based upon Floquet theory, provides a means of analyzing the effect of increasing advance ratio on the flapping stability of a rotor system. The ground/air resonance model uses a constant coefficient approximation of the rotor system to allow analysis of the effects of coupling between rotor lag motion and airframe motion.
Until recently, computer simulations of helicopter rotor dynamics have employed equations of motion that have been linearized or simplified. These modified equations of motion did not allow for the evaluation of nonlinear material properties in the rotor since higher order terms in the dynamics had been modified in the simplification process. With recent advances in both computer simulation hardware and symbolic mathematic manipulation software, the full nonlinear equations of motion may be utilized in helicopter rotor simulations. This dissertation reports on the use of the full nonlinear equations of motion in the analysis of rotor blade lead/lag motion and its effect on rotor hub and rigid body fulselage motion. Nonlinear modeling methods are implemented using Maple symbolic mathematic manipulation software and Matlab and Simulink computer simulation environments. Results are compared to the RAH- 66 Comanche Froude scale wind tunnel article and new methodologies evaluated in the search for a damperless rotor system that is free of ground and air resonance mechanical instabilities.
Rotor Blade vibratory stresses are of utmost importance in helicopter design. A modified Myklestad-Prohl method for rotating beams has been coded to assist in preliminary helicopter rotor blade design. The rotor blade dynamics program is part of the Joint Army/Navy Rotorcraft Analysis and Design (JANRAD) program which was developed to aid in the preliminary design and analysis of helicopter rotor performance, stability and control, and rotor dynamics. JANRAD is an interactive, user friendly program written in MATLAB version 4.0 programming language and has been used extensively in the Naval Postgraduate School's capstone helicopter design course (AA 4306). A sample case is run and results are discussed.
The book addresses computational methods for solving the problem of vibration, response, loads and stability of a helicopter rotor blade modeled as a rotating beam with flap or out-of-plane bending. The focus is on explaining the implementation of the finite element method in the space and time domain for the free vibration, aeroelastic response and stability problems. The use of Floquet analysis for the aeroelastic stability analysis of rotor blades is also shown. The contents of the book will be useful to researchers in aerodynamics and applied mechanics, and will also serve well professionals working in the aerospace industry.
Since the original publication of 'Bramwell's Helicopter Dynamics' in 1976, this book has become the definitive text on helicopter dynamics and a fundamental part of the study of the behaviour of helicopters. This new edition builds on the strengths of the original and hence the approach of the first edition is retained. The authors provide a comprehensive overview of helicopter aerodynamics, stability, control, structural dynamics, vibration, aeroelastic and aeromechanical stability. As such, Bramwell's Helicopter Dynamics is essential for all those in aeronautical engineering.THE single volume comprehensive guide for anyone working with helicopters Written by leading worldwide experts in the field
Modeling, Control and Coordination of Helicopter Systems provides a comprehensive treatment of helicopter systems, ranging from related nonlinear flight dynamic modeling and stability analysis to advanced control design for single helicopter systems, and also covers issues related to the coordination and formation control of multiple helicopter systems to achieve high performance tasks. Ensuring stability in helicopter flight is a challenging problem for nonlinear control design and development. This book is a valuable reference on modeling, control and coordination of helicopter systems,providing readers with practical solutions for the problems that still plague helicopter system design and implementation. Readers will gain a complete picture of helicopters at the systems level, as well as a better understanding of the technical intricacies involved.
The behaviour of helicopters is so complex that understanding the physical mechanisms at work in trim, stability and response, and thus the prediction of Flying Qualities, requires a framework of analytical and numerical modelling and simulation. Good Flying Qualities are vital for ensuring that mission performance is achievable with safety and, in the first edition of Helicopter Flight Dynamics, a comprehensive treatment of design criteria was presented. In this second edition, the author complements this with a new Chapter on Degraded Flying Qualities, drawing examples from flight in poor visibility, failure of control functions and encounters with severe atmospheric disturbances. Fully embracing the consequences of Degraded Flying Qualities during the design phase will contribute positively to safety. The accurate prediction and assessment of Flying Qualities draws on the modelling and simulation discipline on the one hand and testing methodologies on the other. Checking predictions in flight requires clearly defined ‘mission-task-elements’, derived from missions with realistic performance requirements. High fidelity simulations also form the basis for the design of stability and control augmentation systems, essential for conferring Level 1 Flying Qualities. The integrated description of flight dynamic modelling, simulation and flying qualities forms the subject of this book, which will be of interest to engineers in research laboratories and manufacturing industry, test pilots and flight test engineers, and as a reference for graduate and postgraduate students in aerospace engineering. The Author Gareth Padfield, a Fellow of the Royal Aeronautical Society, is the Bibby Professor of Aerospace Engineering at the University of Liverpool. He is an aeronautical engineer by training and has spent his career to date researching the theory and practice of flight for both fixed-wing aeroplanes and rotorcraft. During his years with the UK’s Royal Aircraft Establishment and Defence Evaluation and Research Agency, he conducted research into rotorcraft dynamics, handling qualities and flight control. His work has involved a mix of flight testing, creating and testing simulation models and developing analytic approximations to describe flight behaviour and handling qualities. Much of his research has been conducted in the context of international collaboration – with the Technical Co-operation Programme, AGARD and GARTEUR as well as more informal collaborations with industry, universities and research centres worldwide. He is very aware that many accomplishments, including this book, could not have been achieved without the global networking that aerospace research affords. During the last 8 years as an academic, the author has continued to develop his knowledge and understanding in flight dynamics, not only through research, but also through teaching the subject at undergraduate level; an experience that affords a new and deeper kind of learning that, hopefully, readers of this book will benefit from.
