NASA RESEARCH RESULTS X-1s ith a Selected Bibliography 4 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION NASA SP-60 RESEARCH RESULTS X-15 With a Selected Bibliography By Wendell H. Stillwell AND SP CS AC TI E U A A D N M O I N R E I S A T L R A A T N I O O I Scientific and Technical Information Division N 1 9 6 5 T A N U.S.A. NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Washington, D.C. FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON, D.C., 20402-PRICE 55 CENTS Foreword N A PERIOD of a little more than sixty years since the first I flight of the Wright Brothers, man’s exploration of three-dimen- sional space above the surface of the Earth has extended beyond the atmosphere. Spectacular and exciting events in this dramatic quest have been well publicized. Behind these milestones of practical flight have been less publicized achievements in scientific research, making such progress possible. Although the X–15 has had its share of newsworthy milestones, its contributions to scientific research have been a more essential and more meaningful part of the program from its inception. This semi-technical summary of the X–15 program is directed toward the less publicized aspects of its achievements. The year 1964 marks the tenth anniversary of the inception of the X–15 flight-research program, the fifth year since the first X–15 flight. When the program was first approved, its objectives were clearly stated in terms of aerodynamic heating, speed, altitude, sta- bility-and-control research, and bioastronautics. Although these objectives have been essentially accomplished, it now appears that the three X–15’s may be flown for perhaps another five years, in a new role as test beds for fresh experiments utilizing the X–15 per- formance, which still offers more than twice the speed and three times the altitude capability of any other aircraft now in existence. Even though the program has been most successful in terms of achieving its planned objectives and is continuing to play an impor- tant role in aerospace research, many notable benefits have been of a different nature—more intangible and somewhat unforeseen at the time the X–15 program was approved. In the early years of our nation’s space program, which has been based to a large extent on the unmanned-missile technology that had been developed over the five years prior to Project Mercury, the X–15 has kept in proper perspective the role of the pilot in future manned space programs. It has pointed the way to simplified operational concepts that should iii X–15 RESEARCH RESULTS provide a high degree of redundancy and increased chance of suc- cess in these future missions. All of the people in industry and in government who have had to face the problems of design and of building the hardware and making it work have gained experience of great value to the more recent programs now reaching flight phase and to future aeronautical and space endeavors of this country. The X–15 program and Project Mercury have represented a par- allel, two-pronged approach to solving some of the problems of manned space flight. While Mercury was demonstrating man’s capability to function effectively in space, the X–15 was demon- strating man’s ability to control a high-performance vehicle in a near-space environment. At the same time, considerable new knowl- edge was obtained on the techniques and problems associated with lifting reentry. Already the lessons learned are being applied to our new manned space programs. The pilot is playing a much greater role in these programs. Certainly the problem of launching the lunar-excursion module from the surface of the Moon through the sole efforts of its two-man crew must appear more practical and feasible in the light of the repeated launchings of the X–15 through the efforts of its pilot and the launch operator on the carrier B–52 than would be the case if it were compared only with the elaborate launch proce- dures and large numbers of people, buried safely in blockhouses, that typify all other launch operations to date. Future space programs may well include a lifting reentry and a more conventional landing on Earth, in the fashion demonstrated by the X–15. Edwards, California PAUL F. BIKLE, Director November 1, 1964 NASA Flight Research Center iv Contents CHAPTER PAGE Foreword iii Chronology vi 1 The Role of the X–15 1 2 The First Hypersonic Airplane 9 3 Developing a Concept 17 4 Flight Research 33 5 Aerodynamic Characteristics of Supersonic- Hypersonic Flight 47 6 A Hypersonic Structure 59 7 The Dynamics of Flight 71 8 Man-Machine Integration 83 9 A Flying Laboratory 95 Bibliography 103 Index 117 Chronology June 1952 NACA Committee on February 1956 Reaction Motors, Aerodynamics recommends increase in Inc., awarded development contract research dealing with flight to Mach for XLR–99 rocket engine. 10 and to altitudes from 12 to 50 miles. December 1956 X–15 mock-up com- Also recommends that NACA endeavor pleted. to define problems associated with September 1957 Design configura- space flights at speeds up to the velocity tion set. Construction starts. of escape from Earth’s gravity. October 1958 Factory rollout of No. 1 July 1952 NACA Executive Com- airplane. mittee adopts recommendations of June 8, 1959 First glide flight, No. 1 Committee on Aerodynamics. airplane. September 1952 Preliminary stud- September 17, 1959 First powered ies of research on space flight and asso- flight, No. 2 airplane. ciated problems begun. November 15, 1960 First flight with February 1954 NACA Research XLR–99 engine. Airplane Projects panel meeting dis- February 7, 1961 Last flight with cusses need for a new research airplane interim rocket engine. to study hypersonic and space flight. March 7, 1961 First flight to Mach 4. March 1954 Laboratories request- June 23, 1961 First flight to Mach 5. ed to submit views on most important October 11, 1961 First flight above research objectives and design require- 200 000 ft. ments of a new research airplane. November 9, 1961 First flight to May 1954 NACA teams establish Mach 6. characteristics of a new research air- December 20, 1961 First flight of plane, which subsequently becomes the No. 3 airplane. X–15. July 17, 1962 First flight above July 1954 Proposal for new research 300 000 ft. airplane presented to the Air Force November 9, 1962 No. 2 airplane and Navy. damaged during emergency landing. December 1954 Memorandum of June 27, 1963 50th flight over Mach understanding for a “Joint Project for 4. a New High-Speed Research Airplane” January 28, 1964 100th flight in signed by representatives of the Air series. Force, Navy, and NACA. June 25, 1964 First flight of rebuilt December 1954 Invitations issued No. 2 airplane. by the Air Force to contractors to par- August 12, 1964 50th flight over ticipate in the X–15 design competi- Mach 5. tion. August 14, 1964 75th flight over September 1955 North American Mach 4. Aviation, Inc., selected to develop three October 15, 1964 50th flight by No. 1 X–15 research airplanes. airplane; 119th flight in program. vi C H A P T E R 1 The Role of the X–15 OT SINCE THE WRIGHT BROTHERS solved the basic Nproblems of sustained, controlled flight has there been such an assault upon our atmosphere as during the first years of the space age. Man extended and speeded up his travels within the vast ocean of air surrounding the Earth until he achieved flight outside its confines. This remarkable accomplishment was the culmination of a long history of effort to harness the force of that air so that he could explore the three-dimensional ocean of atmosphere in which he lives. That history had shown him that before he could explore his ethereal ocean, he must first explore the more restrictive world of aerodynamic forces. Knowledge about this world came as man developed theories and experimental techniques that helped him understand the complex reaction of air upon a vehicle moving through it. One of the earliest theories came from Leonardo da Vinci, who sought to explain the flight of birds. It was Sir Isaac Newton who, among his many achievements, first put a possible explanation for aerodynamic forces into mathematical form. Later, crude experiments began to pro- vide measurable answers to supplement the theories of airflow. Sometimes the theories failed to stand up in the light of experimental evidence. Often both theory and experiment gave incomplete answers. But man learned to apply this knowledge. Whenever enough theory was available to answer some questions and enough experi- mental evidence was at hand to answer others, he has advanced in flight, often past his full understanding of how he did it. While the Wright Brothers had learned many answers before their first flight, men were still trying to discover all the theories that explained it 2 X–15 RESEARCH RESULTS long after it was history. Every pioneering flight stimulated the building of other airplanes, and further theoretical and experimental studies. From all of these efforts has come the detailed under- standing of the aerodynamics of flight so necessary as the firm foun- dation upon which aviation progress has been built. Nowhere is the durability of this foundation more evident than in the most advanced airplane in the world, the X–15 rocket airplane. For the mathematical theory that Newton published in 1726—long discounted because it couldn’t be applied to airflow at low speeds— is now used to help understand the aerodynamic forces encountered by the X–15 at speeds of 4000 miles per hour.