At the Edge of Space: The X-15 Flight Program

426 Pages·1992·14.98 MB·English

by  Milton O. Thompson

© 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: 978-1-58834386-4
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
1
PART THE INGREDIENTS
Chapter 1 The Machine
Chapter 2 The Operation
2
PART 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
3
PART 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 thermally 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.