Introduction to Flight Testing. James W. Gregory
in order to fly the basic maneuvers described in this book. In fact, all of the procedures described herein are routine maneuvers that are encountered often in piloting practice. An interested reader can simply head to their nearest airport and work with a qualified, professional pilot (e.g., a certified flight instructor) to conduct the flights described here. In our educational contexts, we collaborate with flight instructors in the aviation programs at The Ohio State University and Western Michigan University to conduct flight tests for our students, but any flight instructor would be capable of performing these basic maneuvers.
We must be sure to emphasize that flying an aircraft involves elevated risk compared to other routine activities in daily life. It is critical for the pilot in command to always maintain positive control of the aircraft and to maintain flight within the performance envelope of the aircraft. All operating limitations of the Pilot's Operating Handbook, as well as all regulatory limitations and best practices for safety of flight, must be observed. Flights should be conducted with a minimum crew of two, where the pilot is solely focused on safe operation of the aircraft. Since precise flying is important for acquiring quality data, the pilot should be experienced – a pilot with a commercial license is likely a safe minimum standard for piloting credentials. The second crew member – the flight test engineer – should be dedicated to acquiring flight data and not have any responsibilities related to ensuring safe operation of flight. The flight test engineer is essentially a passenger for these flights, and all piloting authority and responsibility for the flight rest with the pilot in command. Chapter 6 of this book describes the principles of flight test safety and risk management, which form an essential foundation for the flight test profession. Fly safely!
While there are several other resources on flight testing already available, we saw a specific need for this textbook. Some of the existing resources are targeted toward flight testing professionals and may not be as accessible to the general student. Other resources have become dated, with the relatively recent rewrite of airworthiness certification standards for normal category airplanes (Title 14 of the U.S. Code of Federal Regulations, Part 23). In writing this book, we have sought to provide a modern and accessible resource for flight test educators and students, with several unique features that we hope will set it apart as a helpful and leading resource. Our primary audience is engineering students, with the goal of drawing connections between engineering practice and flight testing experience. We have provided guidelines on how to conduct each flight test, which will guide the reader in the flight test planning process. We have also included unique chapters on digital data acquisition and analysis techniques, uncertainty analysis, and unmanned aircraft flight testing. These are all modern topics that are not covered in the flight testing literature, but are now critical topics. And, with the proliferation of smartphones (repurposed as digital data acquisition devices in manned flight testing) and drones, the modern principles of flight testing are more accessible than ever.
The focus of our book is predominantly on light aircraft (small general aviation airplanes) and small unmanned aircraft. We have homed in on this subset of aviation since these aircraft are generally accessible to the public. While our focus is on light aircraft, the principles described here are equally applicable to all regimes of flight testing. This book provides an introduction, while other resources can be consulted for more advanced topics. The discussion here has been tailored to academic classroom instruction to convey the main principles of flight testing, rather than as a “field manual” for definitive best practices in all situations for flight testing. Having said that, we have made a reasonable effort to align the guidance provided here with accepted best practices. Also, we have decided to omit discussions of spin flight testing and flutter flight testing. These are significant and important topics in flight testing practice, but these are hazardous flight tests. We wish to encourage the reader to engage only with the safer dimensions of flight testing as an entry point.
Throughout this book, we'll predominantly use English units. This is primarily because aviation practice in North America has mostly converged on English units. For example, most air traffic control organizations around the world assign altitude in units of feet and airspeed in units of knots. While SI units are generally preferable in science and engineering environments, we'll generally work with the aviation standard. We view this choice as an educational opportunity for the reader to become acquainted with and proficient in multiple unit systems. There is clear pedagogical value in learning how to quickly convert between and track various units – we hope that students and professional engineers alike will become comfortable with all units and how to convert between them. Appendix B includes a range of unit conversion factors and discussion on best practices for handling units in aviation and engineering practice.
Furthermore, we have avoided embedding implied units into equations. This practice can be convenient for some cases when input and output units for a formula are well established and clearly documented – this can facilitate situations where rapid computations are needed without encumbering the analysis with unit conversions. However, in many cases this practice leads to confusion or ambiguity since the input and output units are seldom clearly documented or agreed upon. Another disadvantage of embedded units is that constants must be embedded in the formula, which have no basis on the physics. This can be confusing to a student who is exposed to theory for the first time. Finally, embedded units force the reader into one specific unit system. Our approach with equations that are unit‐agnostic will allow the reader to use either English or SI consistent units as desired. Thus, the assumption throughout this text (unless otherwise specified) is that equations are based on standard, consistent units.
To the reader – thank you for picking up this book. We are passionate about flight testing and are eager to share our deep interest in this domain with you. We hope that this book will be rewarding, enriching, and fascinating.
James W. GregoryColumbus, OhioTianshu LiuKalamazoo, Michigan
September 6, 2020
Acknowledgements
The authors are grateful for a wide array of colleagues, collaborators, and students who have shaped our thinking and provided input and feedback on this book.
JG would like to thank Profs. Stacy Weislogel and Gerald M. Gregorek, who as pioneers of educational flight testing in the 1970s were inspirations for this work. Prof. Hubert C. “Skip” Smith was also generous with ideas and resources along the way. The flight education department and colleagues in Aviation at The Ohio State University have been extremely helpful in providing tactical support over the years – D. Gelter, D. Hammon, B. Mann, S. Morgan, S. Pruchnicki, C. Roby, B. Strzempkowski, and S. Young. Special thanks go to Profs. Jeffrey Bons and Cliff Whitfield, who helped review significant portions of a near‐final version of the manuscript. (Any remaining errors or inaccuracies are solely the responsibility of the authors). Portions of this book were written in 2014–15 while JG was on sabbatical at the Technion in Israel; the support of Ohio State University and the Fulbright foundation is gratefully acknowledged.
JG also wishes to extend special thanks to Dr. Matt McCrink, who assisted with many of the flight tests presented in this book and coauthored the final chapter on UAV flight testing. He has been an instrumental sounding board and key partner throughout this project.
TL would like to thank M. Schulte, M. Mandziuk, S. Yurk, M. Grashik, S. Woodiga, P. Wewengkang, D. M. Salazar, and WMU's College of Aviation.
Numerous colleagues, including M. Abdulrahim, J. Baughn, K. Colvin, C. Cotting, K. Garman, B. Gray, C. Hall, J. Jacob, J. Kidd, K. Kolsti, J. Langelaan, B. Martos, N. Sarigul‐Klijn, R. Smith, J.P. Stewart, A. Suplisson, A. Tucker, J. Valasek, C. Walker, O. Yakimenko, and M. Yukish, helped influence the presentation of ideas in this book. The Flight Test Education Workshop, hosted by the USAF Test Pilot School, was a particularly helpful resource for materials and connections. A. Bertagnolli of Continental Aerospace Technologies (Continental Motors) and J. J. Frigge of Hartzell Propeller generously provided data and resources for the text. C. Daniloff, K. King, R. Heidersbach, H. Henley, K. King, N. Lachendro, H. Rice, H. Sakaue, B. Stirm, and R. Winiecki gracefully