Airplane Performance on Grass Airfields Airplane Performance on Grass Airfields presents an experiment-based approach to analysis and flight testing of airfield performance on grass runways. It discusses improvements for operational efficiency and safety of these airfields. The book analyzes the interaction between the landing gear wheels and the surface of a grass runways during both takeoff and landing. Considering the ground performance of an aircraft on a grass runway, the book covers test methods and devices for measuring performance and introduces an information system for the surface condition of grass airfields: GARFIELD. The system is based on a tire–grass interaction model and uses digital soil maps, as well as current meteorological data obtained from a weather server. The book is intended for researchers and practicing engineers in the fields of aviation and aircraft safety and performance. Airplane Performance on Grass Airfields Jaroslaw A. Pytka First edition published 2023 by CRC Press 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487–2742 and by CRC Press 4 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN CRC Press is an imprint of Taylor & Francis Group, LLC © 2023 Jaroslaw A. Pytka Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. 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Description: First edition. | Boca Raton: CRC Press, [2023] | Includes bibliographical references and index. Identifiers: LCCN 2022053427 | ISBN 9781032320786 (hbk) | ISBN 9781032320809 (pbk) | ISBN 9781003312765 (ebk) Subjects: LCSH: Airplanes—Landing gear. | Private planes—Performance. | Airplanes—Takeoff. | Airplanes—Landing. | Runways (Aeronautics)—Testing. | Tires—Traction. Classification: LCC TL682 .P98 2023 | DDC 629.133/34—dc23/eng/20230109 LC record available at https://lccn.loc.gov/2022053427 ISBN: 978-1-032-32078-6 (hbk) ISBN: 978-1-032-32080-9 (pbk) ISBN: 978-1-003-31276-5 (ebk) DOI: 10.1201/9781003312765 Typeset in Times by Apex CoVantage, LLC Contents Preface ix Acknowledgments xi Author biography xiii 1 Introduction 1 1.1 Flying on grass airfields 1 1.2 Grass airfields around the world 2 1.3 Flying from grass airfields – major problems 3 1.4 Purpose and scope of the present work 3 1.5 Summary 4 References 4 2 Airfield performance of an airplane – the state-of the-art 7 2.1 Takeoff and landing 7 2.1.1 Takeoff and landing distance measurement 9 2.1.2 Takeoff and landing measurement with the use of GPS and IMU 10 2.1.3 Liftoff 11 2.1.4 Airplane stability during takeoff and landing ground roll 11 2.1.5 Touchdown 14 2.2 Factors having an effect on airfield performance 15 2.2.1 Effects of airplane design 15 2.2.1.1 Powerplant 16 2.2.1.2 Wing 16 2.2.1.3 Landing gear 17 2.2.2 A brief review of airplanes 17 2.2.2.1 The Wilga DRACO 18 2.2.2.2 The Scrappy airplane 20 2.2.3 Airplane certification tests for unpaved runway operation: the Pilatus PC-24 22 2.3 Effect of airfield conditions 26 2.3.1 Definitions 26 v vi Contents 2.3.2 Tire–runway interaction 27 2.3.2.1 Tire–runway friction coefficient 27 2.3.2.2 Methods for tire–runway friction measurements 27 2.3.2.3 Rolling resistance coefficient 29 2.3.2.4 Methods for rolling resistance measurement 32 2.3.3 Effect of wind 33 2.3.4 Effect of density altitude 33 2.4 Conclusion 34 References 35 3 Modeling of airfield performance of airplane on a grass runway 37 3.1 Introduction 37 3.2 Wheel–soil interaction modeling 38 3.3 Effect of soil deformation rate 39 3.4 Effect of vegetation 41 3.5 Effect of soil moisture 44 3.6 Synthesis of the model 45 3.6.1 Influence of the soil substrate of the grass runway 45 3.6.2 Determination of tractive forces 45 3.6.3 Modeling the influence of significant factors 46 3.6.3.1 Soil moisture content 46 3.6.3.2 Vegetation 46 3.6.3.3 Wind and density altitude 46 3.7 Concluding remarks 47 References 48 4 Methods 51 4.1 Grass runway surface characterization methods 51 4.1.1 Cone penetrometer – a classic terramechanical instrument 51 4.1.2 TDR – a handheld instrument for soil moisture measurements 53 4.1.3 Method for characterizing the biomass on the grass runway 53 4.2 Airplane performance measurement methods – ground testing 55 4.2.1 Wheel dynamometer for measurements of forces and moments acting on landing gear wheel 55 Contents vii 4.2.1.1 Introduction 55 4.2.1.2 Design and development of the wheel dynamometer system 57 4.2.1.3 Calibration of the sensor 60 4.2.1.4 Data acquisition and online transfer system 64 4.2.1.5 Certification of the sensor for ground and flight testing 64 4.2.2 Methods for determining the rolling resistance and braking friction 66 4.2.2.1 Tire–runway tester for the measurement of rolling resistance and braking friction 66 4.2.2.2 Pull test method 69 4.2.2.3 Instrumented vehicle method 72 4.3 Airplane performance measurement methods – flight testing 74 4.3.1 Flight test method for the determination of rolling resistance 74 4.3.2 Flight test method for the determination of ground reaction under landing gear wheel loading 77 4.3.3 Ground observer method for takeoff and landing ground distance measurement 80 4.3.4 Video camera method 81 4.3.5 Takeoff and landing measurements with the use of AI sensor 81 4.3.5.1 Introduction 81 4.3.5.2 Flight phases’ recognition by means of neural network 82 4.3.5.3 Neural network development 83 4.3.5.4 Instrumentation 84 4.3.5.5 Calibration of the method 86 4.3.5.6 Conclusion 90 4.3.6 Method for airplane stability during takeoff and landing ground roll 90 4.3.6.1 The test airplane and the method 90 4.3.6.2 Flight tests’ campaign 91 4.4 Conclusion 91 References 92 5 Results 95 5.1 Grass runway characterization 95 5.1.1 Cone Index 97 viii Contents 5.1.2 Rolling resistance of grass runway 99 5.1.3 Effect of soil moisture content upon rolling resistance and braking friction 101 5.2 Effect of speed on rolling resistance coefficient 102 5.3 Ground reaction determination under loading of airplane’s wheel at touchdown 104 5.3.1 Soil stress state under the airplane wheel on touchdown 104 5.3.2 Orientation of the inertial force and σ 107 1 5.3.3 Concluding remarks 108 5.4 Results from flight test measurements 108 5.4.1 Effect of soil strength 110 5.4.2 Effect of soil moisture 111 5.4.3 Effect of vegetation 112 5.4.4 Effect of wind and density altitude 114 5.4.5 Conclusions 116 5.5 Airplane stability during takeoff ground roll 116 5.5.1 Effect of short grass 117 5.5.2 Effect of tall grass 119 5.5.3 Conclusion 119 5.6 Summary 119 References 122 6 GARFIELD – an online information system on grassy airfields 125 6.1 Introduction 125 6.2 Motivation 126 6.3 GARFIELD system description 128 6.4 Methodology 129 6.4.1 Wheel–grass interaction modeling 129 6.4.2 GARFIELD software development 130 6.4.3 System validation 130 6.5 GRASSTAM – a notice on grass runway surface condition 130 6.5.1 Introduction 130 6.5.2 An idea of the GRASSTAM 131 6.5.3 Method of grass runway assessment 131 6.6 Conclusion 134 References 134 Index 137 Preface This book was written as a reference in a niche sub-discipline that combines two areas of knowledge and technology, namely aeronautical engineering and terramechanics. I set myself the task to develop a practical application of meth- ods known from terramechanics as well as new solutions in order to develop measuring devices and test procedures practically useful in the study of air- field performance of airplanes on a grass runway. Readers – aeronautical engi- neers, instrumentation design engineers, researchers, and graduate students as well as aviators – will find both the descriptions of devices and measurement methods as well as the results of tests that I carried out in real conditions, with airplanes, useful. I think that one of the most important advantages of this work are the results of the experiments, which can be both reference data and inspiration for the readers’ own research. I’ve tried to keep the text simple and concise throughout. I’ve assumed that the potential readers have a background knowledge of aeronautical engineering, elementary soil mechanics, electron- ics, and metrology. I express gratitude to several people, whose help was substantial. To Professor Zbigniew Pater, Rector of the Lublin University of Technology, who supported my research both good advice and financially; to Mr. Paweł Tomiło, my PhD student, who made some of my ideas a reality, in particular the design and construction of a measuring device with artificial intelligence; to pilots who carried out test aircraft flight tests, in particular to Mr. Krysztof Janusz from the Świdnik Aeroclub, for his excellent cooperation in the cockpit of the Koliber aircraft. Also, many thanks to my family members who helped with the research, in particular my eldest son Jan and his wife Kinga and my younger son Franciszek. Lublin, October 2022 ix