Table Of ContentHypersonics Before
the Shuttle
A Concise History of the
X-15 Research Airplane
Dennis R. Jenkins
Monographs in Aerospace History
Number 18
June 2000
NASA Publication SP-2000-4518
National Aeronautics and Space Administration
NASA Office of Policy and Plans
NASA History Office
NASA Headquarters
Washington, D.C. 20546
The use of trademarks or names of manufacturers in this
monograph is for accurate reporting and does not constitute
an official endorsement, either expressed OTi mplied, of such
products or manufacturers by the National Aeronautics and
Space Administration.
Library of Congress Cataloging-in-Publication Data
Jenkins, Dennis R.
Hypersonics before the shuttle
A concise history of the X-15 research airplane / by Dennis R. Jenkins
p. cm. -- (Monographs in aerospace history ; no. 18) (NASA history series) (NASA
publication ; SP-2000.4518)
Includes index.
1. X-15 (Rocket aircraft)--History. I. Title. II. Series. III. Series: NASA history series
IV. NASA SP ; 2000.4518.
TL789.8.U6 X553 2000
629.133’38Gdc21
00.038683
Table of Contents
Preface Introduction and Author’s Comments ...................... 4
Chapter 1 The Genesis of a Research Airplane ....................... 7
Chapter 2 X-15 Design and Development ........................... .21
Chapter 3 The Flight Research Program ............................ 4s
Chapter 4 TheLegacyoftheX-15 ................................ 67
Appendix 1 Resolution Adopted by NACA Committee on Aerodynamics .... 85
Appendix 2 Signing the Memorandum of Understanding ................ 86
Appendix 3 Preliminary Outline Specification ......................... 92
Appendix 4 Surveying the Dry Lakes ............................... 102
Appendix 5 R&D Project Card-Project 1226 ......................... III
Appendix 6 X- I5 Flight Designation System .......................... 115
Appendix 7 Major Michael J. Adams Joins the Program ................. II6
Appendix 8 AsuonautWings ...................................... 117
Appendix 9 X-15 Program Flight Log ............................... I18
index .............................................. 122
One of the NE-52s
flies over the X-15-1
on Edwards Dry Lake
in September 1961.
(NASA photo
EC61 -0034)
Monographi in AerospaceH istory Number 18 ~ HyeersonicsB &e the Shuttle 3
Preface
Introduction andAuthor Comments
It is a beginning. Over forty-five years have fly 22 more X-15 tlights. Tragically, Major Dennis R. Jenkins is
elapsed since the X-15 was conceived; 40 Michael J. Adams would be killed on Flight an aerospace engi-
since it first flew. And 31 since the program 191, the only fatality of the program. neer who spent
ended. Although it is usually heralded as the almost 20 years on
most productive flight research program ever Unfortunately due to the absence of a subse- the Space Shuttle pro.
undertaken, no serious history has been quent hypersonic mission, aeronautical gram for various con-
assembled to capture its design, develop- applications of X-15 technology have been tractors, and has also
ment, operations, and lessons. This mono- few. Given the major advances in materials spent time on other
graph is the first step towards that history. and computer technology in the 30 years projects such as the
since the end of the flight research program, X-33 technology
Not that a great deal has not previously been it is unlikely that many of the actual hard- demonstrator.
written about the X-15, because it has. But ware lessons are still applicable. That being
most of it has been limited to specific aspects said, the lessons leaned from hypersonic He is also an author
of the program; pilot’s stories, experiments, modeling, simulation, and the insight gained who has writteno ver
lessons-learned, etc. But with the exception by being able to evaluate actual X- 15 flight 20 books on aero-
of Robert S. Houston’s history published by research against wind tunnel and predicted space history.
the Wright Air Development Center in 1958, results, greatly expanded the confidence of
and later included in the Air Force History researchers. This allowed the development of
Oftke’s Hypersonic Revolution, no one has Space Shuttle to proceed much smoother
attempted to tell the entire story. And the than would otherwise have been possible.
WADC history is taken entirely from the Air
Force perspective, with small mention of the In space, however, the X-15 contributed to
other contributors. both Apollo and Space Shuttle. It is interest-
ing to note that when the X-15 was con-
In 1954 the X-l series had just broken Mach ceived, there were many that believed its
2.5. The aircraft that would become the X-15 space-oriented aspects should be removed
was being designed to attain Mach 6, and to from the program since human space travel
fly at the edges of space. It would be accom- was postulated to be many decades in the
plished without the use of digital computers, future. Perhaps the major contribution was
video teleconferencing, the intemet, or email. the final elimination of a spray-on ablator as
It would, however, come at a terrible financial a possible thermal protection system for
cost--over 30 times the original estimate, Space Shuttle. This would likely have hap-
pened in any case as the ceramic tiles and
The X-15 would ultimately exceed all of its metal shingles were further developed, but
original performance goals. Instead of Mach the operational problems encountered with
6 and 250,000 feet, the program would the (admittedly brie0 experience on X-15A.2
record Mach 6.1 and 354,200 feet. And com- hastened the departure of the ablators.
pared against other research (and even oper-
ational) aircraft of the era, the X-15 was Many people assisted in the preparation of
remarkably safe. Several pilots would get this monograph. First and foremost are Betty
banged up; Jack McKay seriously so, Love, Dill Hunley, and Pete Merlin at the
although he would return from his injuries to DFRC History Off%x. Part of this project
4 HyperronicrA efuie rheS hut& - Mono~aphc in AerospnceH irtiq Number 1X
Preface lnrroducrion and Authori Comments
was assembling a detailed flight log (not part and lack Weher all provided excellent sup-
of this monograph), and Betty spent many port for the project. A. J. Lutz and Ray
long hours checking my data and researching Wagner at the San Diego Aerospace Museum
to till holes. 1 am terribly indebted to her. archives, Tony Landis, Brian Locke& Jay
Correspondence continues with several of Miller, and Terry Panopalis also provided
the program principals--John V. Becker, tremendous assistance to the project.
Scott Crossfield, Pete Knight, and William
Dana. Dr. Roger Launius and Steve Garber at Dennis R. Jenkins
the NASA History Office, and Dr. Richard Cape Canaveral, Florida
Hallion, Fred Johnsen, Diana Comelisse, Februuy 2000
With the XLR99
engine lagging behind
in its development
schedule, the X-15
program decided to
press ahead with ini-
tial flights using two
XLRl1 engines-the
same basic engine
that had powered the
Bell X-l on its first
supersonic flight. (San
Diego Aerospace
Museum Collection)
When the Reaction
Motors XLR99 engine
finally became avail-
able, the X-15 began
setting records that
would stand until the
advent of the Space
Shuttle. Unlike the
XLRI 1, which was
‘throttleable” by ignit-
ing different numbers
of thrust chambers,
the XLR99 was a truly
throttleable engine
that could tailor its
output for each specif-
ic mission. (San Diego,
Aerospace Museum
Collection)
Monqqaphz in AerospaceH istq Number 18 - HyperronicsB &e the Shuttle
Hydraulic lifts were
installed in the ramp
at the Flight Research
Center (now the
Dryden Flight
Research Center) to
lift the X-15 up to the
wing pylon on the
NB-52 mothership.
(Jay Miller Collection)
The early test flights
were conducted with a
long air data probe
protruding from the
nose of the X-15.
Notice the technician
manually retracting
the nose landing gear
on the X-15, some-
thing accomplished
after the research air-
plane was firmly con-
nected to the wing of
the NB-52 mothership.
(San Diego
Aerospace Museum
Collection)
chapter 1 The Gene~ixO fa ResearchA irplane
Chapter 1
The Genesis of a Research Airplane
It was not until the mid-1940s that it became whelming, but there was a growing body of
apparent to aerodynamic researchers in the opinion that it should be undertaken.
United States that it might be possible to build
a flight vehicle capable of hypersonic speeds. The first substantial official support for hyper-
Until that time, propulsion systems capable of sonic research came on 24 June 1952 when the
generating the thrust required for such vehi- NACA Committee on Aerodynamics passed a
cles had simply not been considered techni- resolution to “_. increase its program dealing
cally feasible. The large rocket engines that with the problems of unmanned and manned
had been developed in Germany during World flight in the upper stratosphere at altitudes
War II allowed concept studies to be initiated between 12 and 50 miles,’ and at Mach num-
with some hope of success. bers between 4 and 10.” This resolution was
ratified by the NACA Executive Committee
Nevertheless, in the immediate post-war peri- when it met the following month. A study
od, most researchers believed that hypersonic group consisting of Clinton E. Brown (chair-
flight was a domain for unmanned missiles. man), William J. O’Sullivan, Jr., and Charles
When an English translation of a technical H. Zimmerman was formed on 8 September
paper by German scientists Eugen Stiger and 1952 at the Langley’ Aeronautical Laboratory.
Irene Bredt was provided by the U.S. Navy’s This group endorsed the feasibility of hyper-
Bureau of Aeronautics (BuAer) in 1946, this sonic flight and identified stmchral heating as
preconception began to change. Expanding the single most important technological prob-
upon ideas conceived as early as 1928, Stinger lem remaining to be solved.
and Bredt had concluded during 1944 that a
rocket-powered hypersonic aircraft could be An October 1953 meeting of the Air Force’s
built with only minor advances in technology. Scientific Advisory Board (SAB) Aircraft
The concept of manned aircraft flying at Panel provided additional support for hyper-
hypersonic speeds was highly stimulating sonic research. Chairman Clarke Millikan
to researchers at the National Advisory released a statement declaring that the feasi-
Committee for Aeronautics (NACA).’ But bility of an advanced manned research aircraft
although there were numerous paper studies “should be looked into.” The panel member
exploring variations of the Stiger and Bredt from Langley, Robert R. Gihuth, played an
proposal in the late 194Os,n one bore fruit and important role in coordinating a consensus of
no hardware const~ction was undertaken at opinion between the SAB and the NACA.
that time. It was from this background, how-
ever, that the concept for a hypersonic Contrary to Slinger’s conclusions, by 1954 it
research airplane would emerge.’ was generally agreed within the NACA and
industly that the potential of hypersonic flight
At the time, there was no established need for could not be realized without major advances
a hypersonic aircraft, and it was assumed by in technology. In particular, the unprecedent-
many that no operational military’ 01 civil ed problems of aerodynamic heating and
requirement for hypersonic vehicles would be high-temperature stmctures appeared to be
forthcoming in the foreseeable future. ‘Ihe so formidable that they were viewed as
need for hypersonic research was not over- “buriers” to sustained hypersonic flight.
chapter 1
Fortunately, the successese njoyed by the sec- served to test preliminary design configura-
ond generation X-1s and other high-speed tions that led to the final hypersonic aircraft
research programs had increased political and configuration. Langley also organized a paral-
philosophical support for a more advanced lel exploratory program into materials and
research aircraft program. The large rocket stmctues optimized for hypersonic flight.
engines being developed by the long-range
missile (ICBM) programs were seen as a way Given this, it was not surprising that a team at
to provide power for a hypersonic research Langley was largely responsible for defining
vehicle. It was now agreed that manned the early requirements for the new research
hypersonic flight was feasible. Fortunately, at airplane. ‘Ihe members of the Langley team
the time there was less emphasis than now on included Maxim A. Faget in propulsion;
establishing operational requirements prior to Thomas A. Toll in configuration, stability, and
conducting basic research, and perhaps even control; Norris F. Dow in structllres and mate-
more fortunately, there were no large manned rials; and James B. Whitten in piloting. Au
space programs with which to compete for four fell under the direction of Becker. Besides
funding. The time was finally tight for launch- the almost mandatory elements of stability,
ing a hypersonic flight research program.” control, and piloting, a fourth objective was
outlined that would come to dominate virhu.-
The specific origins of the hypersonic ly every other aspect of the ai~rali’s design-
research program occurred during a meeting it would be optimized for research into the
of the NACA inter-laboratory Research r&ted fields of high-temperature aemdynam-
Airplane Panel held in Washington, DC, on 4. its and high-temperature structwes. Thus it
5 February 1954. The panel chairman, Hartley would become the first aircraft in which zero-
A. Soul& had directed NACA research air- thermo-structural considerations constituted
craft activities in the cooperative USAF- the primay research problem, as well as the
NACA program since 1946 and was well primary research objective.
versed in the politics and personalities
involved. The panel concluded that a wholly The preliminary specifications for the
new manned research vehicle was needed, research aircraft were surprisingly brief: only
and recommended that NACA Headquarters four pages of requirements, plus six addition-
request detailed goals and requirements for al pages of supporting data. A new sense of
such a vehicle from the research laboratories. urgency was present: “As the need for the
exploratory data is acute because of the rapid
In responding to the NACA Headquarters, all advance of the performance of service air-
of the NACA laboratories set up small ad hoc craft, the minimum practical and reliable air-
study groups during March 1954. Langley plane is required in order that the develop-
had been an island of hypersonic study since ment and construction time be kept to a mini-
the end of the war and chose to deal with the mum.“a In other versions of the requirements
problem in more depth than the other labora- this was made even more specific: “It shall be
tories. After the new I l-inch hypersonic wind possible to design and construct the airplane
tunnel at Langley became operational in 1947, within 3 years.“’ As John Becker subsequent-
a research group headed by Charles H. ly observed, “_. it was obviously impossible
McLellan was formed to conduct limited that the proposed aircraft be in any sense an
hypersonic research.’ This group, which optimum hypersonic configuration.”
reported to the Chief of the Langley Aero-
Physics Division, John V. Becker, provided In developing the general requirements, the
verification of newly developed hypersonic team developed a conceptual research aircraft
theories while investigating such important that served as a model for the eventual X-15.
phenomena as hypersonic shock-boundary- The aircraft they conceived was “. not pro-
layer interaction. The 11.inch tunnel later posed as a prototype of any of the particular
8 HypersonicrB e/oret he Shut& - Monographsi n AerorpaceH istory Numbei 18
chapter I
The first Sell X-2
(46-674) made its ini-
tial unpowered glide
flight on 5 August
1954. This aircraft
made a total of 17
flights before it was
lost on 27 September
1956. Its pilot, Air
Force Captain Milburn
Apt had flown to a
record speed 2,094
mph, thereby becom-
ing the first person to
exceed Mach 3.
(NASAIDFRC)
concepts in vogue in 1954 [but] rather as a primary problem associated with structural
general tool for manned hypersonic flight design, and where very little background
research, able to penetrate the new regime information existed. Hypersonic aerodynam-
briefly, safely, and without the burdens, ics was in its infancy in 1954. The few small
restrictions, and delays imposed by opera- hypersonic wind hmnels then in existence had
tional requirements other than research.” The been used almost exclusively for fluid
merits of this approach had been convincing- mechanics studies, and they were unable to
ly demonstrated by the successes of the X-l simulate either the high temperatures or the
and other dedicated research aircraft of the high Reynolds numbers of actual flight. It was
late 1940s and early 1950s.‘” generally believed that these wind tunnels did
not produce valid results when applied to a
Assuming that the new vehicle would be air full-scale aircraft. The proposed hypersonic
launched like the X- 1 and X-2, Langley estab- research airplane, it was assumed, would pro-
lished an aircraft size that could conveniently vide a bridge over the huge technological gap
be canied by a Convair B-36, the largest suit- that appeared to exist between laboratory
able aircraft available in the inventory. This experimentation and actual flight.”
translated to a gross weight of approximately
30,000 pounds, including IE,OtM pounds of One aspect of the Langley proposal caused
fuel and instrumentation.” A maximum speed considerable controversy. The Langley team
of 4,600 mph and an altitude potential of called for two distinct research flight profiles.
400,000 feet were envisioned, with the pilot The fust consisted of a variety of constant
subjected to approximately 4.5g (an accelera- angle-of-attack, constant altitude, and maneu-
tion equal to 4.5 times the force of gravity) at vering flights to investigate the aerodynamic
engine burnout.” and thermodynamic characteristics and limi-
tations of then-available technology. These
The proposed maximum speed was more than were the essential hypersonic research flights.
double that achieved by the X-2, and placed But the second flight profile was designed to
the aircraft in a region where heating was the explore some of the problems of manned
Monographsi n AerospaceH istory Number 18 - Hyperronicr Before the Shuttle 9
