The state of the art in aeronautical engineering has been continually accelerated by the development of advanced analysis and design tools. Used in the early design stages for aircraft and spacecraft, these methods have provided a fundamental understanding of physical phenomena and enabled designers to predict and analyze critical characteristics of new vehicles, including the capability to control or modify unsatisfactory behavior. For example, the relatively recent emergence and routine use of extremely powerful digital computer hardware and software has had a major impact on design capabilities and procedures. Sophisticated new airflow measurement and visualization systems permit the analyst to conduct micro- and macro-studies of properties within flow fields on and off the surfaces of models in advanced wind tunnels. Trade studies of the most efficient geometrical shapes for aircraft can be conducted with blazing speed within a broad scope of integrated technical disciplines, and the use of sophisticated piloted simulators in the vehicle development process permits the most important segment of operations-the human pilot-to make early assessments of the acceptability of the vehicle for its intended mission. Knowledgeable applications of these tools of the trade dramatically reduce risk and redesign, and increase the marketability and safety of new aerospace vehicles. Arguably, one of the more viable and valuable design tools since the advent of flight has been testing of subscale models. As used herein, the term "model" refers to a physical article used in experimental analyses of a larger full-scale vehicle. The reader is probably aware that many other forms of mathematical and computer-based models are also used in aerospace design; however, such topics are beyond the intended scope of this document. Model aircraft have always been a source of fascination, inspiration, and recreation for humans since the earliest days of flight. Within the scientific community, Leonardo da Vinci, George Cayley, and the Wright brothers are examples of early aviation pioneers who frequently used models during their scientific efforts to understand and develop flying machines. Progress in the technology associated with model testing in worldwide applications has firmly established model aircraft as a key element in new aerospace research and development programs. Models are now routinely used in many applications and roles, including aerodynamic data gathering in wind tunnel investigations for the analysis of full-scale aircraft designs, proof-of-concept demonstrators for radical aeronautical concepts, and problem-solving exercises for vehicles already in production. The most critical contributions of aerospace models are to provide confidence and risk reduction for new designs and to enhance the safety and efficiency of existing configurations. The objective of the material presented here is to provide the reader with an overview of some of the more interesting free-flight model testing techniques that have been developed and the role that the testing has played in fundamental and applied research, as well as in support of the development of some of the Nation's more important civil and military aerospace programs. The material also includes discussions of the development of the specialized facilities and equipment required for dynamic model tests.
About the Author: Joseph R. Chambers is an aviation consultant who lives in Yorktown, VA. He retired from the NASA Langley Research Center in 1998, after a 36-year career as a researcher and manager of military and civil aeronautics research activities. He began his career as a specialist in flight dynamics as a member of the staff of the Langley Full-Scale Tunnel, where he conducted research on a variety of aerospace vehicles, including V/STOL configurations, reentry vehicles, and fighter aircraft configurations. He later became the manager of research projects in the Full-Scale Tunnel, the 20-Foot Spin Tunnel, flight research at Langley, and piloted simulators. When he retired from NASA, he was manager of a group responsible for conducting systems analysis of the potential payoffs of advanced aircraft concepts and NASA research investments. Mr. Chambers is the author of over 50 NASA technical reports and publications, including NASA Special Publications SP-514, on airflow condensation patterns for aircraft; SP-2000-4519, on contributions of Langley to U.S. military aircraft of the 1990s; SP-2003-4529, on contributions of Langley to U.S. civil aircraft of the 1990s; and SP-2005-4539, on Langley research on advanced concepts for aeronautics. He has made presentations on research and development programs to audiences as diverse as the von Karman Institute in Belgium and the annual Experimental Aircraft Association (EAA) Fly-In at Oshkosh, WI. He has served as a representative of the United States on international committees and has given lectures in Japan, China, Australia, the United Kingdom, Canada, Italy, France, Germany, and Sweden. Mr. Chambers received several of NASA's highest awards, including the Exceptional Service Medal, the Outstanding Leadership Medal, and the Public Service Medal. He also received the Arthur Flemming Award in 1975 as one of the 10 Most Outstanding Civil Servants for his management of NASA stall/spin research for military and civil aircraft. He has a bachelor of science degree from the Georgia Institute of Technology and a master of science degree from the Virginia Polytechnic Institute and State University (Virginia Tech). He is coauthor of the recently released Radical Wings and Wind Tunnels by Specialty Press.