CRANFIELD UNIVERSITY Brian P. Lee Pilot and Control System Modelling for Handling Qualities Analysis of Large Transport Aircraft School of Engineering Department of Aerospace Sciences Dynamics, Simulation, and Control Group PhD Thesis Academic Year: 2011 - 2012 Supervisor: M. V. Cook August, 2012 School of Engineering Department of Aerospace Sciences Dynamics, Simulation, and Control Group PhD Thesis Academic Year 2011 - 2012 Brian P. Lee Pilot and Control System Modelling for Handling Qualities Analysis of Large Transport Aircraft Supervisor: M. V. Cook August, 2012 © Cranfield University 2012. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. ABSTRACT The notion of airplane stability and control being a balancing act between stability and control has been around as long as aeronautics. The Wright brothers’ first successful flights were born of the debate, and were successful at least in part because they spent considerable time teaching themselves how to control their otherwise unstable airplane. This thesis covers four aspects of handling for large transport aircraft: large size and the accompanying low frequency dynamics, the way in which lifting surfaces and control system elements are modelled in flight dynamics analyses, the cockpit feel characteristics and details of how pilots interact with them, and the dynamic instability associated with Pilot Induced Oscillations. The dynamics associated with large transport aircraft are reviewed from the perspective of pilot-in-the-loop handling qualities, including the effects of relaxing static stability in pursuit of performance. Areas in which current design requirements are incomplete are highlighted. Issues with modelling of dynamic elements which are between the pilot’s fingers and the airplane response are illuminated and recommendations are made. Cockpit feel characteristics are examined in detail, in particular, the nonlinear elements of friction and breakout forces. Three piloted simulation experiments are described and the results reviewed. Each was very different in nature, and all were designed to evaluate linear and nonlinear elements of the cockpit feel characteristics from the pilot’s point of view. These included understanding the pilot’s ability to precisely control the manipulator itself, the pilot’s ability to command the flight path, and neuro-muscular modelling to gain a deeper understanding of the range of characteristics pilots can adapt to and why. Based on the data collected and analyzed, conclusions are drawn and recommendations are made. iii Finally, a novel and unique PIO prediction criterion is developed, which is based on control-theoretic constructs. This criterion identifies unique signatures in the dynamic response of the airplane to predict the onset of instability. Keywords: Stability and Control, Flight Dynamics, Flying Qualities, Pilot Induced Oscillation (PIO), iv DEDICATION To Jonathan, Alexander, and Rebekah I hope that in watching the process of producing this work you will have gained an appreciation for the importance of life-long learning. v ACKNOWLEDGEMENTS The pursuit of a PhD represents a significant endeavour in time invested, in level of attention, and both over a protracted period of time. In preparation for this endeavour, many contributory opinions were offered by various colleagues whose opinions deserve a great deal of respect. In particular, the late Dr. John McMasters observed that there are only three valid reasons to pursue a PhD, and John was adamant that this question should be addressed and answered prior to launching the requisite effort: • First, to prove to oneself that it can be done; rather like climbing a mountain. • Second, if the credential is required for some larger pursuit; like teaching at the university level in the US. • Third, if interest in a particular subject is so strong that pursuit of the PhD is the only legitimate way to justify the level of effort and depth of work. Even after having invested more than a third of a century studying how pilots interact with airplanes, it was clear that there is still much to learn. It was therefore in this third pursuit that the present work is continued. Having settled that question, it is recognized at the outset that no work of significance can be accomplished by one person alone, and this effort is no exception. A very special debt of gratitude is due to Mr. Michael Cook for sharing the fruits of his long and rich experience in flight dynamics and to his lovely wife, Helen for sharing him for this time. Mike’s depth of knowledge, his wisdom, and his unflappable demeanour have been a constant encouragement. Technical collaboration brings huge benefits to all participants as each shares talent, insight, experience, and occasional flashes of genius with the other. In this case a debt of gratitude is due to many professional colleagues around the world, who have contributed via direct collaboration, active encouragement, acting as a sounding board, or just being interested. The list is too long to try to enumerate without risking the embarrassment of inadvertently overlooking someone. Nevertheless, there is special appreciation for the late Dr. Victor vii Rodchenko, his successor Dr. Larisa Zaichik, and their colleagues at the Central Aero-Hydrodynamic Institute (TsAGI) of Russia. These extremely gifted individuals have served as a true inspiration. Appreciation is due also to Dr. Dale Hiltner for sharing both his insights and his frustrations during our development of the Dynamic Oversteer Criterion. Special insights and inspiration have been derived from long associations with John Hodgkinson, Dave Klyde, Dave Mitchell (all of the “Handling Qualities Daves”, really), Roger Hoh, and the late Robert Wattson. Any technical and academic endeavour requires extensive use of archival information. Thanks are due to the dedicated professional librarians, both at Cranfield and at the Boeing company for providing valuable assistance. I have never experienced university library staff so eager to offer such professional assistance as I found at Cranfield. In an industrial setting, the thoroughly professional staff of the Boeing library understand the special requirements of this kind of technical work and recognize the value to the company of providing technical staff with the best support in the world. Thanks also to the management of The Boeing Company for allowing the special privilege of studying this subject over this protracted period. Finally, very special thanks to Susan for her domestic contributions which were essential to the completion of this work. viii TABLE OF CONTENTS ABSTRACT ........................................................................................................ iii DEDICATION ..................................................................................................... v ACKNOWLEDGEMENTS.................................................................................. vii LIST OF FIGURES ............................................................................................. xi LIST OF TABLES ............................................................................................. xiii NOMENCLATURE ............................................................................................ xv 1 Introduction ................................................................................................. 1 1.1 The many elements of Handling Qualities. ............................................ 2 1.2 Open Loop / Closed Loop and Sometimes in Between ......................... 7 1.3 The Pilot’s Challenge ............................................................................ 8 1.4 Models and Frequencies of Interest ...................................................... 9 1.5 The Role of the Pilot ............................................................................ 11 1.6 Aims and Objectives of this work ........................................................ 12 1.7 Organization of the Thesis .................................................................. 13 2 Historical Context ...................................................................................... 17 3 Establishing the State of the Art ................................................................ 27 3.1 Flight Dynamics of Large Transport Aircraft ........................................ 28 3.1.1 Equations of Motion ...................................................................... 28 3.1.2 Reduced Order Forms .................................................................. 33 3.1.3 The Ubiquitous Second Order Problem ........................................ 34 3.2 Flight Dynamics Requirements ........................................................... 34 3.2.1 Philosophy for Requirements on Dynamics of Large Aircraft ........ 34 3.2.2 Civilian Requirements on Dynamics of Large Transport Airplanes 39 3.2.3 Military Requirements on Dynamics of Large Transport Aircraft ... 39 3.2.4 Summary of Requirements on Dynamics ..................................... 41 3.3 Effect of Airplane Size ......................................................................... 42 3.3.1 Effect of Airplane Size on Natural Frequencies ............................ 42 3.3.2 Effect of Airplane Size on Human Pilot Behaviour ........................ 43 3.3.3 Summary of Effect on Airplane Size ............................................. 45 3.4 Relaxed Static Stability .......................................................................