© 1992 by the Smithsonian Institution
All rights reserved
Editor: Martha J. King
Designer: Janice Wheeler
Library of Congress Cataloging-in-Publication Data
Thompson, Milton O.
At the edge of space : the X-15 flight program / Milton O. Thompson
p. cm.
eISBN: 978-1-58834-386-4
1. X-15 (Rocket aircraft). 2. Airplanes—California—Edwards Air Force Base—Flight testing—History. I. Title.
TL789.8.U6X578 1992
629.134′53′0973—dc20
91-23701
British Library Cataloguing-in-Publication Data is available
The photographs appearing in this book are National Aeronautics and Space Administration and U.S. Air Force photographs from the archives of the Dryden Flight Research Facility and Air Force Flight Test Center. Smithsonian Books does not retain reproduction rights for these illustrations individually, or maintain a file of addresses for photo sources.
Publisher’s note: The description of otherwise undocumented personal incidents and the recollections of episodes and persons are entirely the author’s. Every effort has been made to verify details and ensure correctness; inaccuracy, if it occurs, is regretted.
v3.1_r1
Dedicated to my wife Therese,
who courageously supported my participation
in this program.
Take care of her, God.
Contents
Cover
Title Page
Copyright
Dedication
Foreword
Acknowledgments
Introduction: The Men
Flight 3-65-97
PART 1 THE INGREDIENTS
Chapter 1 The Machine
Chapter 2 The Operation
PART 2 THE PROGRAM
Chapter 3 Program Phases
Chapter 4 Demonstration Phase (1959–1962)
Chapter 5 In the Contrails of Giants (1962–1964)
Chapter 6 Trial by Fire and Water (1964–1968)
Chapter 7 Results and Unanticipated Problems
PART 3 TRIUMPH AND TRAGEDY
Chapter 8 Toward Mach 7—The X-15A-2
Chapter 9 Sometimes the Bull Wins
Chapter 10 The End
Author’s Note
Appendix 1 Flight Logs
Appendix 2 Pilot Statistics
Appendix 3 Aircraft Availability
Appendix 4 Typical X-15 Flight Plan
Photographs appear following this page and this page.
Foreword
From time to time in the world of flight, a flying machine is produced that has no commercial or military purpose. The 1903 Wright Flyer was such a machine. Indeed, many of the early flying machines were crafted just to investigate an idea or prove a concept. In an airplane, the proof is in the flying. Craft built to demonstrate a concept, or to pave the way for a commercial or military derivative, were termed “experimental.” In some countries, experimental airplanes were so licensed and prohibited from commercial activity.
World War II provided an enormous impetus for rapid aircraft development. Bombers needed more speed to reduce their chances of being shot down by enemy interceptors. Fighters needed more power to improve rate of climb and speed to permit them to intercept enemy bombers. Pilots of these new faster fighters soon noticed that their steeds sometimes became cantankerous in steep dives. At maximum speed, the aircraft buffeted and controls became sluggish and ineffective. These compressibility effects were believed to be the cause of a number of catastrophic accidents. When jet-powered fighters entered the scene late in the war, they could fly fast enough in level flight to encounter such difficulties and it became imperative to understand these and other phenomena associated with high-speed flight.
Aircraft designers depend on testing models in wind tunnels for predicting aircraft behavior. Wind tunnel results were generally reliable at speeds up to a Mach number of .75 (subsonic) and greater than 1.2 (supersonic). Airflow around an airplane, however, is characterized by wide variations in speed at various positions around it. Consequently, when an aircraft is flying near the speed of sound, some airflow around the craft is subsonic while the flow at other locations is supersonic. Wind tunnel testing was notoriously poor in this “transonic” region, partly because shock waves would form and be reflected off the tunnel walls onto the model, thus negating an accurate representation of the actual flow.
A number of researchers came to the conclusion that the best method for investigating this region was with a full-scale aircraft in actual flight. The U.S. Navy and the National Advisory Committee for Aeronautics (NACA) sponsored a turbojet-powered transonic research aircraft (the Douglas D-558-I), and the U.S. Army Air Force and the NACA sponsored a rocket-powered supersonic aircraft (the Bell XS-1). The Bell XS-1 became famous as the first manned aircraft to fly (in 1947) faster than sound. It was followed by a variety of other research aircraft: the Douglas X-3 (stubby, thin wing); the Northrop X-4 (tailless); the Bell X-5 (variable sweep wing); the Douglas D-558-II (swept wing, jet and/or rocket powered); and the Bell X-2 (swept wing, rocket powered). This stable of flying research tools made significant contributions to the understanding of the transonic and supersonic regimes and engendered wide support for the research airplane concept.
The German development of large rocket engines invited new advanced flight concepts. Among the most mind-boggling were the proposals of German scientists Eugene Sanger and Irene Bredt. They suggested the possibility of a rocket boosting a winged glider to very high speeds above the atmosphere. By skipping across the top of the atmosphere like a flat stone skipped across a pond, the glider could fly unpowered across the ocean!
Such heady ideas, whether practical or not, inspired substantial creative thinking on the possibilities of very high-speed flight. During the summer of 1952, the NACA Committee on Aerodynamics called for the NACA to increase its flight research at Mach numbers between four and ten and altitudes between twelve and fifty miles.
At about the same time, a number of proposals emerged for a piloted, rocket powered hypersonic (five or more times the speed of sound) research airplane. Max Hunter of Douglas Aircraft, Walter Dornberger of Bell Aircraft, and Hubert Drake and Robert Carman of the NACA generated preliminary designs. By the mid-1950s, enthusiasm had grown to the point where key policymaking groups at the NACA, the U.S. Air Force, and the U.S. Navy were supporting manned hypersonic flight. The X-1 and D-558-II rocket aircraft had been operated in a relatively successful manner over a number of years, and their launching from a “mother aircraft” was performed with confidence.
The problems would be substantial. It was well known that aircraft stability decreased as Mach number increased. The X-1A, flown by Chuck Yeager, went out of control at a Mach number of 2.44. The X-2, flown by Milburn Apt, similarly went out of control at a Mach number of 3.2. Unfortunately, both the X-2 and its pilot were lost. Clearly, finding a design configuration and developing techniques to maintain safe, controlled flight at high Mach number would be a major objective of any hypersonic airplane effort.
The second major challenge dealt with heating. When any object passes through air at high speed, the air molecules are heated, and the heat is transferred to the object. The effect is generally unnoticeable at subsonic speeds. At the speed of the Concorde supersonic transport, however, the passengers can easily feel the warming of the window panes. A craft at hypersonic speeds reaches temperatures at which aluminum would melt, and the temperature differences between different parts of the craft would create enormous stresses. A hypersonic airplane would require new materials, new fabricating techniques, and new methods for predicting the therma
lly induced stresses.
A rocket craft with hypersonic performance would have the ability to climb above the atmosphere where conventional control systems, airspeed indicators, and altimeters would not be functional. Clearly such a machine would need alternative instruments and methods of control.
These difficulties were not the reason why the hypersonic airplane was not built. They were, in fact, the very reason for its existence. Interest continued to grow, and the NACA conducted numerous studies during 1954 to refine the performance goals, configuration, and structural concepts. The results were encouraging. Inconel-X, a nickel-based alloy, could maintain structural strength to a temperature of 1,200° F. This would permit maximum Mach numbers of about 7. And a craft with a Mach number of 7 could reach altitudes well above 50 miles.
Late in 1954, the air force, navy, and the NACA agreed to go forward with the project, identified as the X-15, and established a joint committee responsible for its technical direction with Dr. Hugh Dryden of the NACA as chairman. The aeronautical industry was invited to compete on the program early in 1955. The companies who completed proposals were the Douglas Aircraft Company, the Bell Aircraft Company, the Republic Aviation Corporation, and the North American Aviation, Inc. After a tight competition, the contract was awarded to North American late in 1955.
The X-15 was to be capable of a speed of 6,600 feet per second and an altitude of 250,000 feet. It was to carry a pilot and a payload of 800 pounds of research instruments and recorders. At the time it seemed audacious. It had taken half a century for aircraft to reach Mach 2 and 80,000 feet. Now one new design would attempt to triple those achievements.
The X-15 would accomplish all its goals and more. In 199 flights over nearly a decade, it would become the most successful research airplane in history. But there is much more than numbers to that story.
Milt Thompson tells that “much more” in At the Edge of Space. And he is well qualified to spin the yarn. He was a participant in the program throughout the X-15’s career: as engineer, research scientist, and X-15 pilot. He brings vitality and vibrancy to a tale that bears retelling. He tells of the people, the triumphs, and the tragedies as observed from the inside of the project.
The X-15 no longer carves giant trajectories over southwestern deserts; no longer plunges earthward and slides to a stop on the dry lakebed at Edwards, California. The X-15 is long retired to museum status, a primitive pathfinder in the conquest of space. But history will record its legacy: a large ring of keys for unlocking the mysteries of future flight.
Neil A. Armstrong
Acknowledgments
This book was successfully completed primarily as a result of the moral support, encouragement and inspiration offered by Jack and June Kolf and their lovely daughter, Kathy. Their further assistance in the actual preparation and editing of the manuscript was an added bonus and an indication of the sincerity of their friendship. I cannot thank them enough for all the help that they provided.
I owe special thanks to Dick Hallion, my favorite author, who reviewed my first rough handwritten chapter and encouraged me to continue. His encouragement was crucial in convincing me that I could write a credible account of the flight program.
Paul Bikle read and reread several early versions of the book and provided many critical comments and recommendations. After several painstaking reviews, he finally began to like the book. Bob Rushworth and Neil Armstrong added their blessings. Johnny Armstrong, an X-15 flight planner, and Ed Saltzman, a research engineer, verified the authenticity of the book and offered suggestions for additional humor.
Tim Horton and Roy Bryant searched through their extensive personal accumulation of photos and other memorabilia to provide material that does not officially exist. Jim Young, the Air Force Flight Test Center Historian, loaned me his collection of X-15 photos for duplication. NASA Dryden provided additional photographic material, flight reports, and maps. Ted Ayers, Dryden’s deputy director, and Nancy Lovato, Dryden’s public affairs officer, provided good critiques.
And finally, my sons and daughter—Eric, Milt Jr., Peter, Kye, and Brett—as well as their spouses Dale, Cherri, and Gregg provided outstanding support and encouragement during the lengthy writing process. They were my cheering section. I am deeply indebted to them.
Introduction: The Men
The twelve X-15 pilots were a rather low-key bunch of pilots. None were celebrities or national heroes prior to being designated as X-15 pilots. They were known only in the flight test community. They were typical of the many highly capable but relatively unknown NACA and military test pilots who had been routinely testing airplanes since World War I. (The National Advisory Committee for Aeronautics [NACA] was the predecessor of NASA. The NACA was established by Congress in 1915 to conduct aeronautical research. When NASA was established in 1958, the NACA was used as the nucleus of the newly established space agency.) The X-15 pilots were all military or former military pilots. Five of them were combat pilots in World War II and three were combat pilots in Korea. They were all college graduates with engineering or physics degrees. Each of the career military pilots was a graduate of his respective test pilot school, while the NASA pilots were trained in-house. Five of the pilots were career USAF pilots, one was a career navy pilot, and five were NASA pilots. Crossfield was a contractor pilot for North American Aviation but also a former NACA pilot. Four of the pilots, (Crossfield, Walker, McKay, and Armstrong) had previous rocket airplane experience. Crossfield had the greatest number of rocket flights—eighty-one—followed by McKay with forty-eight, Walker with twenty-eight, and Armstrong with four. Ivan Kinchloe, the original prime USAF X-15 pilot, had rocket aircraft experience in the X-2, however, he was killed in an F-104 accident before the X-15 flew.
Based on this rocket airplane experience, NACA/NASA had a substantial advantage in experience going into the X-15 program, but it really was not evident in the relative performance of the pilots once they completed their checkout in the X-15. White and Rushworth were just as competent as Crossfield, Walker, and McKay. Forrest Petersen did not get a chance to demonstrate his full potential in the X-15 since he was recalled to squadron duty after only five flights. Although Neil Armstrong had only four rocket flights prior to his X-15 assignment, he was possibly the most technically capable of the early pilots, but he also left the program early, going on to Gemini, Apollo—and the history books. The later X-15 pilots performed as well as, or in some cases better than the original pilots. The biographies of the individual pilots prior to joining the X-15 program provide a little more information on their background. Some of my personal recollections of each pilot are included to provide some additional insight into their personalities and characters. The biographies are arranged chronologically according to involvement in the X-15 program.
A. SCOTT CROSSFIELD
Scott was a navy fighter pilot during World War II serving in the South Pacific. Following the war, he attended the University of Washington under the GI bill. He joined the naval air reserve unit at the Sand Point Naval Air Station and flew fighter aircraft on weekends while attending the university. He was a member of the navy acrobatic team flying FG-1D Corsairs at various exhibitions and airshows in the Pacific Northwest.
Scott graduated as an aeronautical engineer and went on to earn a master’s degree in aeronautics. He left Seattle in 1950 to work as a research pilot for the NACA at Edwards. As a research pilot, he flew almost all of the early research aircraft, including the X-1, X-4, X-5, XF-92, and D-558-I and -II, accumulating eighty-one rocket flights in the X-1s and the D-558-II aircraft. Scott left the NACA in the fall of 1955 to work for North American Aviation which had just been awarded the contract to design and build the X-15 aircraft. He was hired as a pilot and a design consultant for the X-15 program.
I have conflicting views of Scott’s role as an X-15 pilot. On the one hand, he did not participate in the high-speed exploratory flights of the aircraft. He flew the low-speed checkout and demonstration flights. In a sense,
he tested the race car prior to someone else actually driving the race. On the other hand, he was intimately involved in the design of the aircraft and contributed immensely to the success of the design, as a result of his extensive rocket airplane experience. The X-15 had some outstanding features which significantly enhanced the safety of flight operations. For example, it had very effective speed brakes. Good speed brakes are essential in an unpowered aircraft to adjust energy and ensure that a pilot gets to his intended destination. The more effective they are, the more precise the control of the energy and the more accurate the landing.
The X-15 had excellent landing characteristics for an unpowered aircraft. Once the main gear skids touched down, the nose of the aircraft came down and the aircraft stayed on the ground. There was absolutely no tendency for the aircraft to bounce back in the air. (Bouncing back in the air on an unpowered landing can spoil your whole day. You can run out of airspeed during the bounce and then stall and crash on the next impact.) The X-1s had this bad characteristic and many nose gears were busted as a result. The X-15 could be planted on the ground at almost any speed if we were high on energy and really wanted to set it down before running out of runway. It was also very stable during slideout due to the extreme aft mounted skids. The aircraft slid out straight without any tendency to weave or oscillate.
Scott was responsible for a number of other excellent operational and safety features built into the aircraft. Thus, one might give Scott credit for much of the success of the flight program. In Scott’s opinion, the high-speed exploratory flight program was somewhat superfluous since all of the serious potential problems had been addressed in the design and the contractor demonstration tests. The high-speed flight program simply validated the soundness of the design. I can empathize with Scott to some extent. I spent a couple of years supporting the development of the lifting bodies. I contributed to the design of every system in those vehicles. I spent hundreds of hours in the simulator assisting in the development of the flight control system. As the prime lifting body pilot, I greatly influenced the design of those vehicles. If someone else had made the first flight, I would very likely have felt that the first flight simply validated my design inputs. However, if unanticipated problems were encountered, it was a new ball game.
At the Edge of Space Page 1
