THE HISTORY OF SPACEFLIGHT QUARTERLY

Volume 19, Number 22012OUEST

DEVELOPMENT OF THE

X-115 AT NACA LANGLEY

AERONAUTICAL LABORATORY

SUPER DYNA-SSOAR:

THE USAF DYNA-SSOAR

SYSTEM PROGRAM OFFICE

IN-HHOUSE PROPOSAL

JOHN TRIBE:

TALES OF A ROCKET ENGINEER

MY LIFE AS A NASAFLIGHT CONTROLLER

Mercury Apollo VIII Launch Control Operations

Gemini

Space Shuttle

FFeeaattuurreess

4 Chasing Theory to the Edge of Space:The Development of the X-115 at NACA Langley Aeronautical Laboratory

By Robert C. Moyer and Mary E. Gainer

34 My Life as a NASA Flight Controller By Cecil N. Bassham

45 Super Dyna-SSoar:The USAF Dyna-SSoar System Program Office In-HHouse Proposal

By David Stern

OOrraall HHiissttoorryy

19 John Tribe: Tales of a Rocket Engineer Interview by Joel Powell

ContentsVolume 19 • Number 2 2012

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MMoorree BBooookk RReevviieewwss

58 IInntteeggrraattiinngg WWoommeenn iinnttoo tthhee AAssttrroonnaauutt CCoorrppss::PPoolliittiiccss aanndd LLooggiissttiiccss aatt NNAASSAA,, 11997722-22000044Book by Amy E. FosterReview by Michael J. Neufeld

59 The Apollo Guidance Computer:Architecture and OperationBook by Frank O’BrienReview by Paul Ceruzzi

60 When Biospheres Collide:A History of NASA’s Planetary Protection ProgramsBook by Michael MeltzerReview by Lisa Westwood

61 Smoke Jumper, Moon Pilot: The Remarkable Life of Apollo 14 AstronautStuart RoosaBook by Willie G. MoseleyReview by Benjamin S. Zibit

62 Lights of Mankind:The Earth at Night As Seen from SpaceBook by L. Douglas KeeneyReview by Andrew K. Johnston

63 A Kansan Conquers the CosmosOr, “Spaced Out All My Life!”Book by Alan GlinesReview by Jim Remar

64 Into the Cosmos:Space Exploration and Soviet CultureEdited by James T. Andrews and Asif A. SiddiqiReview by Brian Frank

BBooookk RReevviieewwss

54 Turning Dust to Gold:Building a Future on the Moon and MarsBook by Haym BenaroyaReview by Harley Thronson

55 SpaceShipOne: An Illustrated HistoryBook by Dan LinehanReview by Scott Sacknoff

56 Selecting the Mercury Seven:The Search for America’s First AstronautsBook by Colin BurgessReview by Matthew H. Hersch

57 Beyond Pluto:Exploring the Outer Limits of the Solar SystemBook by John DaviesReview by Roger D. Launius

Front Cover Images

Mission control from the Mercury, Gemini, Apollo, andSpace Shuttle programs. Credit: NASA

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By Robert C. Moyer and Mary E. Gainer

Most aerospace enthusiasts, ifasked to identify the “home” of the X-15 research airplane on a map, wouldpoint to the high desert of California,where the operational phase of the X-15program took place. Images of thesleek black rocket-plane thunderingtoward the edge of the atmosphere athypersonic speeds above the Joshuatrees and dry lake runways of EdwardsAir Force Base are visually striking,and they tend to leave a lasting impres-sion. Edwards AFB and the NationalAeronautics and Space Administra-tion’s (NASA) Dryden Flight ResearchCenter, then known as the NationalAdvisory Committee for Aeronautics(NACA) High-Speed Flight Station(HSFS), are rightfully proud of theirrole in the setting of speed and altituderecords during the X-15 program.Nevertheless, the design concept thatbecame the X-15 was envisioned andrefined, not at Edwards and the HSFS,but at another NACA facility over 2,000miles to the east.

In the late 1940s and early 1950s,Langley Aeronautical Laboratory,known as the Langley MemorialAeronautical Laboratory prior to 1948,in Hampton, Virginia, was the only U.S.aeronautical research facility capable ofwind-tunnel tests at hypersonic speeds(“hypersonic” is defined as greater thanMach 5). Among Langley’s facilities,the crown jewel was the 11-InchHypersonic Tunnel, designed and builtby Langley personnel to test scale mod-els at speeds in excess of Mach 6. Afterusing their unique facility to determinethat hypersonic flight was feasible froman aerodynamic standpoint, the Langleyengineers who designed, built, andoperated the 11-Inch Tunnel then devel-oped a preliminary design for a hyper-

sonic aircraft, refined the concept, andworked with the Department of Defenseand industry on a rocket-powered flighttest vehicle that would be known as theX-15. Although the project would ulti-mately require the efforts of everyNACA/NASA aeronautical facility,Langley was the birthplace of the X-15,a vehicle that established design andoperational precedents that wereapplied to subsequent NASA vehicles,including the Space Shuttle.

Langley Research Center’s offi-cial involvement in what would beknown as the X-15 program began on10 July 1952, in the form of a memo-randum from NACA Headquarters toLangley titled “Research on SpaceFlight and Associated Problems.” Thememo informed the Langley director ofa 24 June 1952 resolution by theCommittee on Aerodynamics to“increase its program dealing withproblems of unmanned and mannedflight…at altitudes between 12 and 50miles, and at Mach numbers between 4and 10” and to “devote a modest effort”to flight above 50 miles and greaterthan Mach 10. The developments lead-ing to this resolution were also men-tioned, including a recommendationfrom Robert J. Woods of Bell Aircrafton 30 January 1952 and a letter fromthe Air Force in June 1952 suggestingthat hypersonic flight research beexplored. The memorandum concludedwith a request by author Milton B.Ames that Langley AeronauticalLaboratory “consider the research prob-lems related to outer atmosphere andspace flight in light of the foregoinginformation and resolution.”1

The interest in high-altitudehypersonic flight being shown byWoods and other employees at BellAircraft had already stimulated infor-mal research at Langley before theNACA resolution of 1952, although the

research in question focused more onissues of extreme altitude than hyper-sonic speeds. Under the direction ofDavid G. Stone, members of theStability and Control Branch ofLangley’s Pilotless Aircraft ResearchDivision (PARD) began a preliminarystudy of the feasibility of a manned air-craft capable of traveling into space. Ina report dated 21 May 1952, the studygroup established a practical definitionof “space” for research purposes (name-ly, the altitude at which there were “noaerodynamic effects” on the vehicle)and determined that “an altitude near300,000 feet (approximately 57 miles)may be considered equivalent to spaceas far as any aerodynamic effects areconcerned.” Based on this altitude,Stone’s group felt that a Bell X-2research aircraft would be “entirely fea-sible” if it were launched from a carrieraircraft and equipped with two JPL-4“Sargeant” solid-fuel rocket boosters.The report did caution, however, thatextrapolation of available flight dataindicated that “X-2 static directionalstability will be poor and the aerody-namic controls will be weak at Machnumbers greater than 2.0,” and recom-mended that wind tunnel tests at speedsbetween Mach 2 and Mach 4 be con-ducted to examine the problem morefully.2

The PARD study group addressedthe problem of controlling an aircraft ina region of flight where conventionalaerodynamic control surfaces were use-less and determined that low-thrustrockets mounted at the tail and wingtipscould be used to control aircraft attitudeabove 300,000 feet. The group exam-ined configurations involving bothswiveling and fixed thrusters beforedetermining that the fixed-thruster con-figuration was more fuel-efficient.Although the study’s findings didacknowledge that atmospheric re-entryvelocities would be “large,” the group

CCHASING TTHEORY TO THE EEDGE OF SSPACE::The Development of the X-115 at NACA

Langley Aeronautical Laboratory

was not expecting velocities above4,000 feet per second (around Mach 4).As a result, the group calculated thataerodynamic heating would only causean increase in aircraft surface tempera-ture around 300 degrees F and decidedthat excessive structural loading due toacceleration during the recovery por-tion of re-entry was the most significantdesign challenge.3

In response to the July 1952NACA memo, Langley Director HenryJ. E. Reid commissioned an additionalstudy group composed of three engi-neers from different divisions atLangley: Charles H. Zimmerman fromStability and Control, William J.O’Sullivan Jr. from PARD, and ClintonE. Brown from the CompressibilityResearch Division, who served aschairman for the group. Since hyper-sonic flight was identified as a goal inaddition to flight outside the atmos-phere, the group found that structuralheating rather than acceleration-induced structural loads was the pri-mary engineering problem. The Browngroup accepted the idea of using a mod-ified X-2 as a hypersonic research vehi-cle, but recommended several changesfrom Stone’s report. The most notice-able of these changes was the elimina-tion of strap-on boosters in favor of aninternal rocket engine powerful enoughto propel the vehicle at Mach 3.7. Dueto the perceived difficulties of solvingthe thermal heating problem at highervelocities, the Brown group recom-mended that exploration of speeds inexcess of Mach 4.5 should be conduct-ed by unmanned missiles.4

The decision by Langley man-agement to intentionally avoid special-ists in thermodynamics or hypersonicflight when choosing members for theBrown study group has puzzled histori-ans, especially in light of the fact thatsuch specialists were readily availableat Langley. Director Henry J. E. Reidand Assistant Director Floyd L.Thompson had taken this seeminglyunorthodox approach in the hope thatthe group members would offer innova-tive long-term suggestions withoutbeing constrained by the current state ofthe art in hypersonic research.

Unfortunately, this experiment in“thinking outside of the box” did notbear fruit. The Brown group’s conclu-sions, which were conservative andoffered little in the way of innovation,were particularly disappointing toAssistant Director Thompson, andwould prove to be of little use to theengineers and scientists who designedthe X-15.5

In February 1954, the NACAInterlaboratory Research AirplanePanel took another look at the hyper-sonic flight issue. As Langley engineerJohn Becker would later note, NACA“reached a definite conclusion: theexciting potentialities of rocket-boostedaircraft could not be realized withoutmajor advances in technology in allareas of aircraft design.”6 The Panelsuggested that instead of using a modi-fied X-2, NACA should “look into thepossibility of obtaining a new researchairplane having higher speed and alti-tude capabilities than present types.”On 9 March 1954, NACA headquartersin Washington requested that the threeNACA laboratories nationwide (Amesin California, Lewis in Ohio, andLangley in Virginia) as well as the

High-Speed Flight Research Station atEdwards Air Force Base consider theresearch objectives and design require-ments of such an airplane.7 All fourNACA research facilities establishedad-hoc committees in response to thisrequest.8

The engineers at LangleyAeronautical Laboratory had a signifi-cant advantage over the other NACAlaboratories in the area of hypersonicresearch equipment. The 11-InchHypersonic Tunnel, attributed to JohnV. Becker and his hypersonic researchprogram launched in 1945, was origi-nally so secret it was identified only bythe nondescript designator “Project506” until 1950, when technical reportsrevealed the nature of the wind-tunnelresearch taking place at Langley.9 Thetunnel allowed research to be conduct-ed at velocities up to Mach 6.86through a square aperture with sidesthat were 11 inches in length.10

Researchers at Langley began using the11-Inch Hypersonic Tunnel in 1947 toverify recently developed hypersonictheories and to discover previouslyunknown hypersonic airflow phenome-na such as shock-boundary layer inter-

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The Langley 11-Inch Hypersonic Tunnel and its founder, John V. Becker. Both Becker andthe 11-Inch Tunnel were instrumental in the development of the X-15. Credit: NASA

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action.11 The tunnel equipped Langleyengineers with the working knowledgeand experience necessary to address the1954 design request, and later served asthe primary aerodynamic research toolduring the development of the X-15.12

The Langley ad-hoc committeewas composed of four engineers fromdifferent areas of specialization: MaxA. Faget (propulsion), Thomas A. Toll(configuration, stability, and control),Norris F. Dow (structures and materi-als), and James B. Whitten (piloting).The group was chaired by John V.Becker, who had launched the hyper-sonic research program.13 The group’sprimary objectives, which were estab-lished by Langley Associate DirectorFloyd L. Thompson with the assistanceof John Stack, Robert Gilruth, andHartley A. Soulé, directed the group toexplore the feasibility of a research air-craft capable of at least Mach 5 veloci-ties and maximum altitudes “above thesensible atmosphere” in order toexplore alternate methods of attitudecontrol in flight regimes where conven-tional aerodynamic control surfacessuch as ailerons and rudders had virtu-ally no airflow to deflect.14 In a retro-spective lecture about the X-15 pro-gram, Becker explained that althoughthe idea of exploring hypersonic flightwas met with approval throughout theaeronautical research community, theidea of flying to the fringes of space“was viewed in 1954 with what can bestbe described as cautious tolerance” bythose outside of Langley who werefamiliar with the program.15

In addition to the formal objec-tives established for the Becker group,Floyd L. Thompson “provided a bit ofphilosophy” during a series of informaloffice chats with Becker that “stronglyinfluenced” the direction taken by thestudy group. Thompson pointed outthat “aero-thermal-structural considera-tions” created by air friction at hyper-sonic speeds would be the largest prob-lem to be overcome by the new design,and that Becker’s aim should be to“penetrate as deeply as possible into theregion of high-aerodynamic heatingand to seek fresh design approaches”

instead of “makeshift modifications toconventional designs.” At the sametime, however, Thompson cautionedthat the group should not “overreach theadvanced state of the art in materials,propulsion, launch techniques, etc.”16

There was a good reason for this seem-ing contradiction. Thompson wantedthe new aircraft to have “a procurementtime on the order of 3 years,” and sug-gested that Becker present his group’sfindings after an “intensive study” thatwould last only four weeks.17

Floyd L. Thompson’s suggestionof haste, both in the development of theinitial design concept and the produc-tion of the actual aircraft, was groundedin experience gained during his NACAtenure. The Bell X-2, predecessor tothe X-15 and the fastest experimentalaircraft at the time of Becker’s 1954study, had taken ten years to produce,which led some to complain that the X-2 was out of date before it began gener-ating flight test data.18 One of the mostoutspoken critics of the entire X-planesprogram was Clarence L. “Kelly”Johnson, the legendary designer of theLockheed U-2 reconnaissance aircraftand founder of the “Skunk Works” divi-sion at Lockheed. Never a man tomince words, Johnson declared thatmilitary aircraft with superior perform-ance had reached operational status andprovided flight data before similar X-planes had made their first flight.19

Later, when the NACA Committee onAerodynamics formally considered thequestion of whether to proceed withdevelopment of the X-15, Johnsonwould cast the only dissenting vote.20

Given the checkered past of the X-2 andthe resistance of Kelly Johnson, anynew X-plane would have to be builtquickly and correctly if it were going tobe built at all.

The Becker group took Floyd L.Thompson’s advice to heart. The feasi-bility study was divided into five majorareas, with each group member tacklingthe area that matched their specializa-tion: Faget examined launch andpropulsion; Dow worked on weights,materials and structures; Toll took con-figuration, stability, and control; andWhitten examined piloting issues.

Becker assigned trajectories and aero-dynamic heating, the most dauntingengineering problem, to himself.21 Thegroup took aircraft heating limitationsas the starting point from which the restof the design concept was developed. Amaximum skin temperature of 1,200degrees F could be sustained by manu-facturing the skin panels out of a high-temperature nickel-chromium alloyknown as Inconel X, which wouldendure with only a slight loss instrength and stiffness. With a maxi-mum sustainable skin temperature of1,200 degrees, the Becker group deter-mined that the aircraft could reachMach 6.3 if it were dropped from a B-52 carrier aircraft at 35,000 feet.22

Skin panels made of Inconel Xwould not solve all of the heating issuesthat would be encountered by the newdesign. Becker’s team determined thatthe lower surface of the aircraft wouldexperience considerably higher skintemperatures than the upper surface,and the resulting temperature differen-tial would change the camber (curva-ture) of the wing while at the same timecausing the wings to flex upward by asmuch as 12 to 14 inches. The internalstresses created by in-flight wing defor-mation would be relieved by an internalstructure of shear webs and trusses thatwould allow heat-related expansionwhile still providing structuralsupport.23

Although heating was the pri-mary engineering problem, it was by nomeans the only serious issue that theBecker group had to examine. ThomasToll’s examination of configuration,stability, and control for the new air-craft was driven by an incident that hadtaken place just a few months earlier.On 14 December 1953, as Air Force testpilot Chuck Yeager flew the Bell X-1Ato a maximum speed of Mach 2.44, theaircraft developed a series of lateraloscillations that steadily increased inseverity under powered flight andbecame much worse when power wascut. Yeager lost control of the aircraftfor a little over one minute, losing over50,000 feet of altitude and finallyrecovering control only after the X-1Ahad slowed to below Mach 1 and

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entered a spin from which a normalrecovery could be executed. This phe-nomenon of high-speed oscillationswould be encountered again in 1956 bythe X-2, killing pilot Milburn Apt dur-ing a flight that reached Mach 3.196and tragically validating the concernsexpressed by the Stone research groupat Langley in 1952.24

Examination of wind-tunnel datafrom the X-1A program revealed thatthe loss of stability at high speeds wascaused by a decrease in the effective-ness of the aircraft’s vertical stabilizer(tail) as airspeed increased duringsupersonic flight. The standard methodof increasing stabilizer effectivenesswas simple and direct—build a largerstabilizer. Toll’s research revealed thatif thin stabilizers such as those on theX-1A and X-2 were used, however, thestabilizer would have to be roughly thesame size as one of the aircraft’s wingsin order to be effective. Obviously, adifferent solution was needed. TheBecker study group approached severaldifferent research groups at Langleywith the problem and asked for theirsuggestions.25

A Langley aeronautical engineerin Becker’s line organization, namedCharles McLellan, provided a novelsolution. McLellan suggested discard-ing the thin stabilizer in favor of onewith a wedge-shaped cross section,with the point of the wedge directedtoward the nose of the aircraft. Testingin the 11-Inch Hypersonic Tunnel atLangley revealed that not only did awedge-shaped stabilizer not lose effec-tiveness at high Mach numbers like athin stabilizer, the effectiveness actuallyincreased with higher airspeeds.McLellan’s innovative solution ulti-mately resulted in a stable design andcreated one of the most visually distinc-tive features of the X-15 (McLellanwould also be awarded a $1,000 bonusfor his efforts.) In the Becker group’sreport, the suggested means of obtain-ing a wedge-shaped stabilizer was tostart with a thin stabilizer and add asplit-flap to the rear portion in order tocreate a variable wedge angle.26

With a solution for the stabilizers

in hand, Toll then examined the config-uration of the tail itself. A convention-al airplane tail, with horizontal stabiliz-ers behind the wings and a single verti-cal stabilizer extending above the fuse-lage, would create serious stability andcontrol issues. At high angles of attack,a single vertical stabilizer wouldbecome much less effective due to itsposition in the hypersonic wing-wake.Similarly, horizontal stabilizers in thesame geometric plane as the wingscould result in “undesirably largedownwash gradients” during levelflight at high speeds. The proposedsolution was a distinctive “X-tail” withfour stabilizers, each of which was ori-ented halfway between vertical and hor-izontal. Finally, Toll’s examination ofstability and control explored the prob-lem of controlling the aircraft outsidethe atmosphere. As the Stone researchgroup at PARD had suggested previous-ly, the Becker group’s report recom-mended the use of fixed hydrogen per-oxide thrusters at the wingtips andtail.27

The Becker study group present-ed their “research airplane study” toFloyd L. Thompson on 22 April 1954,just a little over a month after the origi-nal request for input from NACA

Headquarters. As John Becker laterexplained, “at this stage in the study, thevehicle concept itself was little morethan an object of about the right gener-al proportions and the right propulsivecharacteristics to achieve hypersonicperformance.” Although the vehicleconcept proposed by Becker’s team wasbased on sound engineering principlesand the best available data, the onlyway to refine the concept into a designthat could actually be built and flownwould be to answer “questions of feasi-bility…firmly on the basis of researchand analysis.” In 1954, there was onlyone facility in existence that could con-duct such research—the 11-InchHypersonic Tunnel at Langley.28

A team of aeronautical engineersconsisting of David Fetterman, Jim A.Penland, and Herbert Ridyard immedi-ately began working under the supervi-sion of Charles McLellan at the 11-InchHypersonic Tunnel to refine the Beckergroup’s concept.29 The team workedwith two scale models: a model of theairfoil (wing) design proposed by theBecker group and a model of the entireairplane that could test different tail andstabilizer configurations. Flow visuali-zation tests of the airfoil model at Mach6.86 revealed that the airflow behind

Langley engineer Charles McLellan at the Langley 11-Inch Hypersonic Tunnel.McLellan’s wedge stabilizer for the X-15 solved the problem of “intertia coupling” thatprevious X-planes had encountered at high velocities. Credit: NASA

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the wing (the “wing-wake”) consistedof distinct regions where dynamic pres-sure was either several times higher orlower than the dynamic pressure fromthe surrounding airflow. The 11-InchTunnel team learned from the airfoiltests that the lower two stabilizers of the“X-tail” should be located in a high-pressure region of the wing-wake whilethe upper two stabilizers should be in alow-pressure region, which resulted in asignificant difference in effectivenessbetween the upper and lower stabilizersthat increased as the aircraft’s speedincreased.30 Testing of the aircraftscale-model confirmed that the X-tailwould be unsuitable, and also con-firmed that the Becker group’s rejectionof a conventional tail configurationwith three stabilizers (two horizontaland one vertical) was correct. A “plus”tail configuration was also tested, butthe team discovered that at high anglesof attack the lower stabilizer penetratedinto an area of high pressure (making itmore effective) while the upper stabiliz-er did not. Consequently, a “stub-tail”configuration, with two horizontal sta-bilizers and a lower vertical stabilizerthat was much shorter than the upper,was tested in the 11-Inch Tunnel andfound to be the best solution.31 TheFetterman/Penland/Ridyard team co-authored four NACA ResearchMemoranda (RM) with their conclu-sions and supporting data from the 11-

Inch Tunnel tests, while their supervisorCharles McLellan published an addi-tional NACA RM describing hiswedge-tail stabilizer concept.32

While McLellan’s team workedto refine the Becker study group’s con-cept in the 11-Inch Hypersonic Tunnel,the Becker group’s 22 April 1954 find-ings were received favorably at NACAHeadquarters. The contents of the“Research Airplane Study” were incor-porated into a report titled “NACAViews Concerning a New ResearchAirplane,” which was presented atNACA Headquarters on 9 July 1954.Representatives from the Air Force andthe Navy were in attendance, as HartleySoulé and Walt Williams discussed thehistory of the NACA research airplaneprogram to date, followed by a briefingby John Becker and John Duberg (whostood in for Norris Dow) on the Beckergroup’s work at Langley. NACA’s pro-posal was largely given a favorablereception by the attendees. The Navyrepresentative, however, expressed adesire that operational military objec-tives be added to the purely research-related goals of the Becker study, aposition that was opposed by USAFrepresentative Clark Millikan. A NACAmemorandum the following month lentsupport to Millikan’s position by assert-ing that the limited availability ofstrategic elements that were used tomanufacture Inconel X meant that the

alloy was “obviously out of the ques-tion for airframe production in anyquantity.” The conference participantsreached an agreement that the Air Forceand Navy would review NACA’s pro-posal for a new research airplane, whileHugh Dryden worked on gettingapproval from the Department ofDefense.33

In the weeks following the July 9conference, members of the U.S. aero-nautical research community becameaware of the Langley concept for ahypersonic research airplane. Severalaircraft manufacturers sent representa-tives to Langley to learn more about theconcept, such as R. J. Woods of BellAircraft. Woods, whose 1952 recom-mendation to NACA had been theimpetus for the Becker study group’swork, became a firm supporter of theproject. NACA research advisorygroups including the Subcommittee onHigh Speed Aerodynamics, theCommittee on Aerodynamics, and theCommittee on Aircraft Construction,added their endorsements to the propos-al.34

NACA representatives held meet-ings with USAF and Navy representa-tives on 31 August 1954 and again on 8October, during which the three partiesagreed to conduct a joint program todevelop the new research airplane.Specifications suitable for presentationto contractors for the manufacture ofthe aircraft were also discussed. On 15October, a preliminary outline specifi-cation for a high-altitude, high-speedresearch airplane was adopted. Theoutline called for general specifications,including only two major performancerequirements—maximum speed of atleast 6,600 feet per second and maxi-mum altitude of at least 250,000 feet—in order to encourage innovation bymanufacturers while remaining true tothe Becker study. At the same time, theoutline stipulated the availability ofNACA facilities for “high Mach num-ber wind tunnel and structural develop-ment work” that would be “essential toestablish the final design of such aresearch airplane.” The outline alsoincluded a six-page appendix titled“Suggested Means of Meeting General

John Becker and Charles McLellan at the Langley 11-Inch Hypersonic Tunnel. Becker(left) developed the 11-Inch Tunnel and led the team that created the preliminary designfor the X-15. Credit: NASA

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Requirements” that was essentially asynopsis of the Becker study, includingengineering drawings of details, such asthe internal shear web and truss struc-ture developed by the Becker team.35

During this same period, intereston the part of NACA, the Air Force,and the Navy was codified by twoimportant legal documents that markedthe official beginning of the X-15 proj-ect. The first of these documents was aresolution adopted by the NACACommittee on Aerodynamics on 5October 1954 endorsing “the proposalof the immediate initiation of a projectto design and construct a research air-plane capable of achieving speeds ofthe order of Mach Number 7 and alti-tudes of several hundred thousandfeet.”36 A few weeks later on 9November 1954, the relationshipbetween the Air Force, the Navy, andNACA was formalized through aMemorandum of Understanding (MoU)that originated with the Air Force andwas circulated among all three partiesfor signatures. The MoU was a concisedocument, slightly over one page inlength, whose stated purpose was toimplement the recommendations stated

The Becker study group’s preliminary design for a hypersonic research aircraft. Note the“X-tail” (left) and the split-flap trailing edge that was used to create McLellan’s wedgestabilizer (bottom left). This drawing was completed by Jim A. Penland, an aeronauticalengineer at the 11-Inch Hypersonic Tunnel. Credit: NASA

The Langley 11-Inch Hypersonic Tunnel, originally referred to only as “Project 506,” gen-erated laminar airflow at Mach 6.86 and was the cornerstone of the X-15 program. Thetest section and other observation window are at the top of the steps. Credit: NASA

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in the 5 October 1954 NACA resolu-tion. Technical direction for theresearch airplane project was assignedto the NACA director, who would beadvised by a “research airplane com-mittee” composed of one member fromeach of the three parties. Financing ofthe design and construction of the air-craft would be shared by the Navy andthe Air Force, with the design and con-struction phase administered by the AirForce. Once the construction phase wascomplete, NACA would conduct flighttests and report the results. The manu-facturer of the aircraft would be deter-mined through a competitive biddingprocess, the basis of which would be“the characteristics determined by theconfiguration on which the NACA hasalready done much preliminary designwork.” The MoU was signed by allthree parties between 9 November and23 December 1954.37

On 30 December 1954, exactlyone week after Hugh Dryden providedthe final signature for the MoU onbehalf of NACA, the Air Force sent let-ters to Bell, Boeing, Chance-Vought,Convair, Douglas, Grumman,Lockheed, Martin, McDonnell, NorthAmerican, Northrop, and Republic,inviting them to submit bids. The letterinformed the companies that a bidders’conference would be held on 18January 1955 at Wright Field in Ohio,and asked that interested companiessend a representative after notifying theprocurement officer by 10 January.(NACA representatives were informedat the same conference that the projecthad been assigned the unclassified des-ignator of “Air Force Project 1226” andthe aircraft designation was X-15.) Ofthe twelve companies that were invited,nine chose to attend, and only four—Bell, Douglas, North American, andRepublic—submitted proposals by the9 May deadline. The attendees at thebidders’ conference had been providedwith refined specifications that retainedthe basic 6,600 fps velocity and250,000 foot altitude requirementsalong with additional requirementsincluding the allocation of 800 pounds,40 cubic feet, and 2.25 kilowatts forresearch instruments, and a 30-month

deadline for aircraft development andproduction. The attendees were alsoprovided with prerelease copies of theNACA reports detailing the researchthat had been conducted at Langleybased on the Becker study group’s con-cept, including the work done by theFetterman/Penland/Ridyard team in the11-Inch Hypersonic Tunnel. Evaluationgroups for NACA, the Air Force, andthe Navy were given copies of the pro-posals and instructed to submit theirresults by 22 June.38

As chairman of the NACA evalu-ation group, Hartley Soulé decided todivide technical evaluation dutiesamong the four major NACA laborato-ries, with some areas being assigned tomore than one facility: Ames andLangley shared all of the four evalua-tion criteria listed under “basic aerody-namic design” with the High-SpeedFlight Station at Edwards also sharingthe fourth (“loads criteria”). Ames,Langley, and HSFS also shared evalua-tion responsibilities for stability andcontrol. HSFS and Lewis sharedresponsibility for propulsion and mis-cellaneous systems. Only HSFS andLangley assumed sole responsibility,respectively, for any sections of thedesign evaluation criteria, with HSFSevaluating crew provisions, handlingand launching, and Langley evaluatingstructures.39 At the conclusion of theevaluation period, Langley engineersconsidered the North American propos-al to be the best design, followed byDouglas, with the Bell and Republicdesigns “about equal.”40 After theinput from the other NACA facilitieswas taken into account, the final NACAranking was (1) North American, (2)Douglas, (3) Bell, and (4) Republic.41

NACA, Air Force, and Navy evaluationteams met on 26-28 July 1955 at WrightField to discuss their findings, ultimate-ly selecting North American Aviation’sproposal as the winning design.42

There was one minor hitch in thisdecision—North American had devel-oped cold feet toward the X-15 project.On 23 August 1955, before the evalua-tion results were made known to thebidders, North American verballyinformed the Air Force that the compa-

ny wanted to withdraw from the compe-tition. Although the Air Force askedNorth American to reconsider, the com-pany sent a letter to the Air Force on 30August formally withdrawing from theX-15 program. The vice president ofNorth American later explained thatthis decision was made because thecompany had evaluated its positionafter winning two new military aircraftstudies and increasing activity on theYF-107 fighter project and had con-cluded that North American could nolonger meet a 30-month productiondeadline for the X-15. Unbeknownst toNorth American, the Research AirplaneCommittee had already recommendedan extension of the production scheduleof up to 18 months on 12 August. NorthAmerican felt that an 8-month exten-sion would be sufficient and retractedits letter of withdrawal after being noti-fied on 30 September 1955 that thecompany’s design had won the compe-tition.43

Although the North Americandesign closely resembled the conceptthat was proposed by the Becker teamand refined by Charles McLellan’sengineers in the 11-Inch HypersonicTunnel at Langley, the design team atNorth American added innovations oftheir own. The original X-15 designproposal from North American included“all moving” horizontal stabilizersbased on earlier Langley flight researchby Bob Gilruth, rather than the conven-tional arrangement of fixed stabilizerswith moving control surfaces attached.The X-15’s horizontal stabilizers couldalso rotate in either the same or oppo-site directions, controlling both pitchand roll. This “rolling tail” designallowed engineers to design the X-15’swings without ailerons, simplifying thestructural design of the wing. A wingwithout ailerons eliminated the need foraileron hinges that would protrudebelow the lower surface of the wing andcreate potentially disastrous multiplehypersonic shock waves. Another fea-ture of the North American design wasa “full-monocoque” fuselage in whichthe aircraft skin also served as the sidewalls of the fuel and oxidizer tanks forthe XLR-99 rocket engine that would

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power the aircraft. This design requiredside fairings for the fuel and oxidizerlines that ran from the tanks to theengine, creating flared fuselage sidesthat are a visually distinctive aspect ofthe X-15.44

Once the manufacturer’s prelimi-nary design was approved, NorthAmerican immediately accepted theoffer to use NACA facilities that hadbeen included in the original biddingspecifications. North American design-ed several different X-15 models fortesting at Ames and Langley, as well astheir own facilities. Before the first X-15 was rolled out of the NorthAmerican assembly plant in California,North American engineers and techni-cians built at least six different scalemodels, some with the direct assistanceof Langley personnel. Additionally,NACA engineers and fabricators builtseveral scale models in-house, includ-ing a free-flight model used in the FullScale Tunnel. Langley facilities testedX-15 models at speeds ranging from thesubsonic through Mach 1.15, 1.43, 3.0,4.0, up to a maximum, hypersonicvelocity of Mach 6.86. 45

One aspect of the North American

design that caused concern from theoutset among engineers at Langley wasthe fuselage side-fairings, whichextended forward to a point roughlyfour feet from the nose of the X-15.Testing in the 11-Inch HypersonicTunnel in March, 1956 revealed thatextending the side-fairings so far for-ward altered the aircraft’s center ofpressure (the aerodynamic equivalent ofcenter of gravity), causing “rathersevere pitch-up tendencies.” NorthAmerican sent a “dummy” fuselage toLangley for further testing in the 11-Inch Tunnel, which indicated that mov-ing the starting point of the side-fairingsfarther aft solved the problem. NorthAmerican modified the X-15 design bymoving the starting point of the fairingsabout eight feet rearward from thenose.46

The tail of the North Americandesign also was the focus of testing andmodification. The Becker team’s use ofsplit flaps to create Charles McLellan’swedge stabilizer for control at hyper-sonic speeds was noted and utilized bythe designers at North American, whodiscovered that the weight of the flapactuators changed the aircraft’s center

of gravity beyond design limits.47

North American’s response to this set-back was to design a solid 10-degreewedge for the upper and lower verticalstabilizers, with speed brakes thatopened vertically, clamshell-style, fromthe side-fairings on the fuselage.Testing at Langley revealed that thenew tail design “still did not providedirectional stability at maximum Machnumber and…the speed brakes on theside fairings were very ineffective inaddition to producing adverse effects onlongitudinal stability.”48

North American designersresponded by rotating the speed brakes90 degrees, placing them on the upperand lower vertical stabilizers and mak-ing them open horizontally instead ofvertically, but Langley engineers feltthat more improvements to the designwere needed. A “NACA tail” wasdeveloped as an alternative to the“North American tail.” The NACA tailhad roughly 55 square feet of surfacearea compared to about 75 square feetfor the North American tail. Althoughboth designs still had upper and lowervertical stabilizers, the NACA ratio wasroughly 60/40 between the length of the

Although the Langley 11-Inch Hypersonic tTnnel was displayed tovisitors in later years, its existence was originally disguised by thenon-designator “Project 506.” When technical reports revealed thatLangley engineers were conducting aeronautical testing at theunprecedented velocity of Mach 6.86, the existence of the tunnelwas acknowledged by NACA. Credit: NASA

Two models based on the Becker group’s design were tested—a scale model of the airfoil only (shown above) and a model ofthe entire airplane with interchangeable tail and stabilizer con-figurations. Credit: NASA

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upper and lower stabilizers versusabout 55/45 for the North Americandesign. As a result, the NACA designdid not extend so far below the fuselagethat it could strike the ground duringlanding (the North American solution tothis problem was to jettison a portion ofthe stabilizer just before landing.) Aninformal design competition of sortsdeveloped, as both designs were testedon a 1/50-scale model in the 11-InchHypersonic Tunnel at Mach 6.86 and inthe 9-Inch Supersonic Tunnel at Mach3. The Langley Stability ResearchDivision also analyzed both designs.North American and Langley engineersmet at Langley in early 1957 to reviewthe results, ultimately agreeing that thedata revealed the North American tail tobe the better design.49

X-15 models were tested inLangley wind tunnels of various sizesand speeds including the Full-ScaleTunnel, 8-Foot Transonic Tunnel, 4 x 4-Foot Supersonic Pressure Tunnel,Unitary Tunnel, 20-Foot Spin Tunnel,9-Inch Supersonic Tunnel, and the 11-Inch Hypersonic Tunnel, where theBecker team’s concept had originallybeen tested and refined. Although the11-Inch Hypersonic Tunnel may havebeen the heart of the X-15 program,Langley’s other wind-tunnel facilitiesconducted design tests at lower speeds,making their own vital contributions tothe program.

Free-flight tests in the Full-ScaleTunnel demonstrated that the low-speedstability and maneuvering characteris-

tics of the rolling-tail were satisfactory,which gave North American confidenceto proceed with the design.50 Outdoordrop models were used by Don Hewesand Jim Hassell to gain an understand-ing in stability and control.51 The aero-dynamic characteristics of the X-15 atthe critical moment of separation fromthe B-52 “mothership” were also inves-tigated by Langley engineers. Researchled by Joe Alford and Wayne McKinleyworking in both the High-Speed andLow-Speed 7 x 10-Foot Tunnels wascritical to launching the X-15 from theB-52 safely.52

There were several other Langleyresearch divisions that contributed tothe development of the X-15. NorthAmerican sent a wing assembly to theLangley Structures Research Divisionto test the structure under transient heat-ing conditions.53 PARD developed aplan to mount three full-size X-15 ver-tical stabilizers to a “Sargeant” rocketwith three Nike boosters as a way toinvestigate the stabilizer design’s sus-ceptibility to skin-panel flutter at hyper-sonic speeds (the test was cancelled dueto changes in the tail design.)54

Langley’s IBM 650 computer was usedto generate trajectory calculations thatwere then used by the StabilityResearch Division to conduct control-motion studies for hypersonic speedsand altitudes beyond the atmosphere,along with atmospheric re-entry condi-tions.55

The Langley Flight ResearchDivision built a longitudinal oscilla-

tions simulator “to determine how thepilot can function under the fluctuatingaccelerations likely to be encounteredat burnout or during re-entry,” and alsobuilt a five-degree-of-freedom analogsimulator with programmed velocity,Mach number, and dynamic pressure.The five-degree-of-freedom simulatorwas “flown” through the burnout phaseof high-altitude mission profiles to sim-ulated altitudes of 180,000 feet bypilots including Joe Walker of HSFSand Scott Crossfield of NorthAmerican, both of whom later flew theX-15. Pilots in the five-degree-of-free-dom simulator dealt with thrust mis-alignment and changing trim, aerody-namic coefficients, and dynamic pres-sure, with and without control dampingand with various speed-brake settings.The Langley Flight Research Divisionalso used a “pitch chair” to study oper-ation of the sidearm controller that wasused to operate the reaction-control sys-tem thrusters that controlled aircraftattitude outside of the atmosphere.56

The Instrumentation ResearchDivision (IRD) at Langley also con-tributed to X-15 development. Whenresearchers and engineers expressedconcern about the corrosive effects ofammonia (used as fuel for the XLR-99rocket engine), IRD engineers testedthermocouple wires, an airspeedrecorder, and other research instrumen-tation by subjecting them to a 50/50mixture of room air and ammonia, at 50percent humidity, for 360 hours toprove that the instrumentation couldwithstand ammonia exposure onboardthe X-15.57 The IRD also developedthe specifications for the X-15’s “stableplatform” inertial system.58

If any component of the X-15best represented Langley AeronauticalLaboratories as a whole, it was thepitot-pressure and flow-direction sen-sor, better known as the “ball nose” or“Q ball.” The ball nose was designed toreplace the conventional aircraft pitot-tube system that provided informationabout airflow speed and direction forthe flight instruments, but which wasnot adequate for hypersonic airflow.The heart of the ball nose was a sphereof Inconel X with four orifices that

Along with the scale model of the airfoil alone, this scale model of the Becker group’sdesign was tested in the Langley 11-Inch Hypersonic Tunnel. The model had an inter-changeable tail and stabilizer sections that could be used to test a wide variety of con-figurations. Credit: NASA

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were placed at equal distances from thecenter point of the nose. Servos keptthe sphere oriented so that pressuresfrom all orifices were equal, providinga way to sense both the pressure anddirection of the airflow. IRD developedthe instrumentation system, and thedesign was tested in the 11-InchHypersonic Tunnel. Later, the FlightResearch Center (formerly HSFS) atEdwards Air Force Base, California,developed a simple and direct methodto test the ability of the ball nose towithstand the heat and pressure ofhypersonic flight—the instrument wasplaced directly behind the engine of anF-100 Super Sabre with the afterburnerlit.59

The first flight of the X-15 tookplace on 8 June 1959, 44 months afterNorth American Aviation was informedthat they had been awarded the contractto build the aircraft. Floyd L.Thompson’s goal of a three-year pro-curement period had been missed byonly eight months, a vast improvementover the X-2. The X-15 exceeded near-ly every expectation envisioned in theBecker group’s original concept. ThreeX-15 aircraft were flown by 12 pilotsfor a combined total of 199 missionsover a 10-year period. At the end ofthat period, 11 pilots and two aircraftsurvived, an attrition rate that wasunfortunate but quite good for an exper-imental flight-test program neverthe-less. Flight milestones included a max-imum altitude of 354,200 feet during aflight by NACA/NASA pilot Joseph A.Walker on 22 August 1963 (over100,000 feet higher than the contractspecifications established by theNACA), and a maximum airspeed ofMach 6.70 (4,520 mph) established byMajor William J. “Pete” Knight, USAF,on 3 October 1967.60

Although the program did experi-ence a handful of less serious mishaps,the only X-15 fatality took place on 15November 1967, during the seventh X-15 flight of Major Michael J. Adams,USAF. As the aircraft approached amaximum altitude of 266,000 feet, itdrifted slightly off the correct heading,a condition that worsened when Adamsattempted a correction using the RCS

thrusters. As the aircraft traveledthrough a ballistic arc and began toreenter the atmosphere, neither Adamsnor his ground support team at Edwardsrealized that an initial yaw angle of 15degrees had increased to 90 degrees,and his aircraft was literally comingback into the atmosphere sideways. Atan altitude of 230,000 feet and a speedof Mach 5, Adams and X-15-3 enteredthe only hypersonic spin in the historyof human flight. Although the aircraftdid recover from the spin, the resultingaircraft gyrations created severe posi-tive and negative g-loads that incapaci-tated Adams and destroyed the aircraftat an altitude somewhere above 60,000feet.61

The accident review board foundseveral factors that contributed to thecrash including prior complaints of ver-tigo by Adams (not an uncommon con-

dition among pilots during X-15flights), a minor electrical disturbancein the adaptive flight-control systemcaused by one of the onboard scientificexperiments, and the inability of thesupport team at Edwards to monitor theaircraft attitude via telemetry. Theboard made five recommendations, thelast of which was perhaps the mosttelling: “X-15 aircraft when under bal-listic conditions should have adequateand redundant means of permitting thepilot to maintain the proper heading,and the primary attitude indicatorsshould not be changed from their con-ventional functions [italics mine].” TheX-15 primary attitude indicator includ-ed vertical and horizontal deviationneedles, identical in appearance toinstrument landing system (ILS)approach deviation needles in conven-tional aircraft. In the X-15, the functionof these needles could be changed by

Under the direction of Charles McLellan, 11-Inch Hypersonic Tunnel engineers JimPenland, Dave Fetterman, and Herbert Ridyard refined the Becker group’s design, eval-uating several different tail configurations. The original “X-tail” (top right) was aban-doned in favor of the “stub tail” configuration (center). Credit: NASA

Q U E S T 19:2 201214

pressing one of four switches, causingthe same set of indicator needles todirect a pilot to fly the precise attitudesrequired by an onboard experimentpackage, or fly the equally precise butvery different attitudes required to safe-ly reenter the atmosphere. In Adams’scase, the positions of four rather innocu-ous switches apparently caused his atti-tude indicator to direct him to fly anincorrect re-entry attitude that resultedin his death and the loss of his air-craft.62

The case could be made that theMike Adams X-15 crash represented thefirst in a series of “failures of imagina-tion” on the part of NASA, a phraseused by flight director Gene Kranz todescribe the circumstances that led tothe 1967 Apollo 1 fire that claimed thelives of astronauts “Gus” Grissom, EdWhite, and Roger Chaffee. The X-15program was instrumental in the begin-ning of many institutional traditions forthe fledgling National Aeronautics andSpace Administration, which absorbedNACA before the end of the X-15 pro-gram. Despite the Adams crash, mostof the traditions that resulted from theX-15 were not only positive but essen-

tial to the lofty goals that NASA wouldpursue in the years to come. Many keyX-15 personnel form a “who’s who” inAmerica’s human spaceflight program.Walt Williams, Max Faget, and GeraldTruszynski played key roles in thedevelopment of the X-15 program andlater made significant contributions asmanagers in the Mercury, Gemini, andApollo programs.63 Two X-15 pilotsblazed their own trails in the AstronautCorps—Neil Armstrong, who left oneof the most famous footprints in history,and Joe H. Engle, the only astronaut inthe history of the Space Shuttle programto fly an orbiter manually through re-entry all the way from Mach 25 totouchdown.64

Many operational solutions andprocedures that were pioneered anddeveloped by NACA and NASA duringthe X-15 flight test program were read-ily adopted by Project Mercury andbecame part of NASA human space-flight operations. The “High Range”tracking and telemetry network thatstretched across California and Nevadato support X-15 missions served as theprogenitor of similar networks that sup-ported spaceflight operations in the

1960s and 1970s. The practice of usingastronaut Capsule Communicators(CAPCOMs) to maintain voice commu-nication with fellow astronauts duringspace operations can be directly tracedto the use of X-15 pilots at the “NASA-1” console at Edwards to communicatewith other X-15 pilots during flightoperations. The extensive use ofground-based simulators to build pilotproficiency before and between X-15flights can also be seen as a direct influ-ence on astronaut training, as is evi-denced by the many spaceflight simula-tors at NASA facilities across the coun-try.65

Although plagued by cost over-runs and delays in the development ofthe XLR-99 engine, the X-15 programwas a phenomenal success. Amongmembers of the public who know of theprogram, the general impression of theX-15 is that of a truly “cosmic” aircraft,a technological wonder that wasdecades ahead of its time. The X-15was portrayed as a marvel of technolog-ical wizardry to an enamored Americanpublic in the early 1960s, a literal moviestar with top billing over contemporaryactors including Charles Bronson, MaryTyler Moore, and Jimmy Stewart.66

As is often the case, those whodesigned and built the X-15 had aslightly different perspective. JohnBecker observed that because of theemphasis on keeping the X-15’s designand procurement period as short as pos-sible, “it was obviously impossible thatthe proposed aircraft be in any sense anoptimum hypersonic configuration.”67

Becker asserted that instead the X-15was designed “as a general tool formanned hypersonic flight research, ableto penetrate the new regime briefly,safely, and without the burdens…imposed by operational requirementsother than research.”68 The X-15 wasa hypersonic workhorse whose briefforays into the realm of Mach 5+ veloc-ities and extra-atmospheric flightpushed the aircraft to its operationallimits. For an aircraft whose originaldevelopment constraints included ashort three-year procurement period andconfinement to state-of-the-art materi-als and construction techniques, the

This scale-model of North American’s initial design was tested in North American andNACA wind tunnels—note the conventional tail and fuselage side-tunnels that extend fartoward the aircraft nose. North American engineers would determine that the variablewedge-angle stabilizer created a weight issue and aeronautical testing by Langley engi-neers confirmed that the side-tunnels made the design less stable. Credit: NASA

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results were impressive. Those whodesigned and flew the X-15, whoseknowledge went far beyond the superfi-cial, understood the triumph of thedesign in light of its limitations. Formany X-15 project members, thatunderstanding was the basis of a loveaffair with the aircraft that lasts to thisday. As was often the case with glam-orous celebrities, the public’s percep-tion of the X-15 had little to do withreality. The aircraft’s true beauty lay,not in “effortless” performance, butrather in the ability to reliably do thejob for which it was designed, a job thatcould be done by no other aircraft in theworld.

About the AuthorsRobert C. Moyer received his B.A. inhistory from the University ofMaryland University College inDecember 2011 and is preparing tobegin work in Fall 2012 on a PhD in thehistory of science and technology. Heis currently working as an intern in theCultural Resources offices at NASALangley Research Center. When he isnot working on graduate school appli-cations, Robert enjoys kayaking on theChesapeake Bay and geocaching, ahobby that he describes as “the use ofmultimillion-dollar military satellitetechnology to find Tupperware hiddenin the woods.”

Mary E. Gainer has worked at theNASA Langley Research Center sinceMay 1998 and is currently the HistoricPreservation Officer for the Center.Prior to NASA, she taught geographyand geology at Valdosta StateUniversity in Georgia and worked forthe Environmental Office at MoodyAFB. Ms. Gainer’s degrees in biologyand geography are from Valdosta StateUniversity and the University of SouthFlorida where her emphasis was in GISand wetlands development. When notworking to preserve the history ofNASA Langley, Ms. Gainer enjoysfarming and restoring old houses.

Notes1 Milton B. Ames, Jr., Acting AssistantDirector for Research, Headquarters,National Advisory Committee forAerodynamics [henceforth: NACA], toHenry J. E. Reid, Director, LangleyAeronautical Laboratory [henceforth:LAL], 10 July 1952, Box 176, X-15 ProjectCorrespondence, May 1955—October1954, Entry 1—Project CorrespondenceFiles, 1918-1978, Records of the NationalAeronautics and Space Administration,Record Group 255 (RG 255), NationalArchives and Records Administration—Mid-Atlantic Region (Philadelphia) [hence-forth: Box 176, Entry 1, RG 255, NARA—Mid-Atlantic (PHL)].

2 David G. Stone, AeronauticalResearch Scientist, PARD, LAL, to Chief ofResearch, LAL, 21 May 1952, Box 176,Entry 1, RG 255, NARA—Mid-Atlantic(PHL).

3 Ibid.

4 Dennis R. Jenkins, X-15: Extendingthe Frontiers of Flight (Washington, DC: U.S. Government Printing Office, 2007), 20[henceforth: Jenkins, Extending].

5 John V. Becker, telephone conversa-tion with Robert C. Moyer, 12 February2012.

6 John V. Becker, “The X-15 Program inRetrospect,” (3rd Eugen Sänger MemorialLecture, Bonn, Germany, 5 December1968) [henceforth: Becker, “Retrospect”].

7 J. W. Crowley, Associate Director forResearch, Headquarters, NACA, toDirector, LAL, 9 March 1954, Box 176,Entry 1, RG 255, NARA—Mid-Atlantic(PHL)].

8 Jenkins, Extending, 24.

9 Jim A. Penland, interview by Laura T.Freeze, 28 June 2007, from “An OralHistory of the X-15 and Langley 11Hypersonic Wind Tunnel: RecordedInterviews with Mr. Jim A. Penland,”LARSS intern program, NASA LangleyResearch Center [henceforth: PenlandInterview, 28 June 2007].

10 Penland Interview, 21 June 2007.

11 John V. Becker, “The X-15 Project:Part 1—Origins and research back-ground,” Astronautics and AerospaceEngineering (February 1964): 54 [hence-forth: Becker, “Origins”].

12 Ibid., 55.

13 Ibid.

14 Staff Members of the LangleyResearch Center, “Conception andResearch Background of the X-15 Project”[ca. 1961], Jim A. Penland collection,

Scale model of the final X-15 configuration, mounted for testing in the Langley 11-InchHypersonic Tunnel. Project 506 would be used in every phase of the X-15’s develop-ment. Credit: NASA

Q U E S T 19:2 201216

NASA Langley Research Center, 8 [hence-forth: Langley Staff, “Conception”].

15 Becker, “Retrospect.”

16 Becker, “Origins,” 55; John V. Becker,telephone conversation with Robert C.Moyer, 11 August 2011.

17 “Conception,” 8.

18 Becker, “Origins,” 53.

19 Langley Staff, “Conception,” 6.

20 Jenkins, Extending, 55.

21 Langley Staff, “Conception,” 9.

22 John V. Becker et al., “ResearchAirplane Study” (working paper, LAL, 22April 1954), 8, 15, 18.

23 Ibid., 19.

24 Langley Staff, “Conception,” 11-12;Jay Miller, The X-Planes (Arlington, TX:Aerofax, 1988), 40-41, 43.

25 Langley Staff, “Conception,” 12.

26 Langley Staff, “Conception,” 12-12a;Becker et al., “Research Airplane Study,”12-13; Penland Interview, 8 June 2007;Charles H. McLellan, “A Method forIncreasing the Effectiveness of Stabilizing

Surfaces at High Mach Numbers” (NACARM L54F21, LAL, August 3, 1954), 11.

27 Becker et al., “Research AirplaneStudy,” 11-13.

28 Becker, “Origins,” 56.

29 Penland Interview, 8 June 2007.

30 Becker, “Origins,” 56-57.

31 Becker, “Origins,” 57.

32 The Fetterman/Penland/Ridyard doc-uments are NACA RM L54L03b, RML55A21a, RM L55C04, and RM L55F17,all published in 1955. The McLellan doc-ument is NACA RM L54F21, published in1954.

33 Langley Staff, “Conception,” 17-18;Jenkins, Extending, 36; Richard V. Rhode,Assistant Director for Research, NACA, toRobert R. Gilruth, LAL, 4 August 1954, Box176, Entry 1, RG 255, NARA—Mid-Atlantic(PHL).

34 Langley Staff, “Conception,” 19.

35 Langley Staff, “Conception,” 19-20;Henry J. E. Reid, Director, LAL, to head-quarters, NACA, 15 October 1994 (memo-randum with enclosure entitled

“Preliminary Outline Specification forHigh-Altitude, High-Speed ResearchAirplane,”) Box 176, Entry 1, RG 255,NARA—Mid-Atlantic (PHL).

36 Dennis R. Jenkins, HypersonicsBefore the Shuttle: A Concise History ofthe X-15 Research Airplane, no. 18 ofMonographs in Aerospace History(Washington, DC: NASA History Office,2000), 85 (photocopy of original resolu-tion.)

37 Ibid., 86-90 (photocopies of originalMoU and associated correspondence).

38 Jenkins, Extending, 59-60, 63; HenryJ. E. Reid, Director, LAL, to E. M. Scholes,North American Aviation, 24 March 1955,Box 176, Entry 1, RG 255, NARA—Mid-Atlantic (PHL).

39 Hartley A. Soulé, Research AirplaneProjects Leader, to Ames, Lewis, HSFS, 19May 1955, “Rules for NACA evaluation ofProject 1226 proposals,” Box 176, Entry 1,RG 255, NARA—Mid-Atlantic (PHL).

40 Henry J. E. Reid, Director, LAL, to NACAHeadquarters, 6 June 1955, “Langley ten-tative evaluation of X-15 airplane propos-als,” Box 176, Entry 1, RG 255, NARA—Mid-Atlantic (PHL).

41 Hartley A. Soulé, Research AirplaneProjects Leader, to NACA Headquarters,30 June 1955, “Summary of NACA evalu-ations of proposals on Project 1226,” Box176, Entry 1, RG 255, NARA—Mid-Atlantic(PHL).

42 Jenkins, Extending, 97-98.

43 Jenkins, Extending, 99-101.

44 Jenkins, Extending, 80-83; W. HewittPhillips, Journey in AeronauticalResearch: A Career at NASA LangleyResearch Center, no. 12 of Monographsin Space History (Washington, DC: NASAHistory Office, 1998), 53-55.

45 D.H. Mason, Staff Engineer,Engineering Data Section, North AmericanAviation, Inc., to Commander, Air MaterielCommand, Wright-Patterson AFB, OH[henceforth: Mason to Wright-PattersonAFB], “X-15 Research Aircraft SixthMonthly Progress Letter,” 8 June 1956,Box 175, Entry 1, RG 255, NARA—Mid-Atlantic (PHL); Mason to Wright-PattersonAFB, “X-15 Research Aircraft SeventhMonthly Progress Letter,” 12 July 1956,Box 175, Entry 1, RG 255, NARA—Mid-Atlantic (PHL); Mason to Wright-PattersonAFB, “X-15 Research Aircraft TwelfthMonthly Progress Letter,” 7 December1956, Box 174, Entry 1, RG 255, NARA—Mid-Atlantic (PHL); Hartley A. Soulé,

Although the 11-Inch Hypersonic Tunnel was the cornerstone of the X-15’s development,numerous other Langley wind tunnels were also involved. This Schlieren image is fromthe Langley 4x4 Foot Supersonic Pressure Tunnel. Credit: NASA

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Research Airplane Projects Leader,Langley Field, VA, to members of NACAResearch Airplane Projects Panel, “Project1226—Progress report for month of May1956,” 7 June 1956, Box 175, Entry 1, RG255, NARA—Mid-Atlantic (PHL); Soulé tomembers of NACA Research AirplaneProjects Panel, “Project 1226—Progressreport from 1 June 1956 to 9 July 1956,”July 18, 1956, Box 175, Entry 1, RG 255,NARA – Mid-Atlantic (PHL); Soulé to mem-bers of NACA Research Airplane ProjectsPanel, “Project 1226—Progress report formonths of January and February 1957,”19 March 1957, Box 174, Entry 1, RG255, NARA—Mid-Atlantic (PHL).

46 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226 –Progress report for month of March1956,” 10 April 1956, Box 175, Entry 1,RG 255, NARA—Mid-Atlantic (PHL); Souléto members of NACA Research AirplaneProjects Panel, “Project 1226—Progressreport for month of August 1956,” 18September 1956, Box 174, Entry 1, RG255, NARA—Mid-Atlantic (PHL).

47 Penland Interview, 8 June 2007.

48 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226—Progress report for months of Septemberand October 1956,” 15 November 1956,Box 174, Entry 1, RG 255, NARA—Mid-Atlantic (PHL).

49 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226—Progress report for months of Novemberand December 1956,” 17 January 1957,Box 174, Entry 1, RG 255, NARA—Mid-Atlantic (PHL); Soulé to members of NACAResearch Airplane Projects Panel, “Project1226—Progress report for months ofJanuary and February 1957,” 19 March1957, Box 174, Entry 1, RG 255, NARA—Mid-Atlantic (PHL).

50 Peter C. Boisseau, “Investigation ofthe Low-Speed Stability and ControlCharacteristics of a 1/7-Scale Model ofthe North American X-15 Airplane” (NACARM L57D09, LAL, 25 June 1957), 13-14.

51 Donald E. Hewes and James L.Hassell Jr., “Subsonic Flight Tests of a

1/7-Scale Radio-Controlled Model of theNorth American X-15 Airplane WithParticular Reference to High Angle-of-Attack Conditions” (NASA TM X-283, NASALangley Research Center, June 1960), 1.

X-15-2 is carried aloft by a B-52 in preparation for launch. After an air launch from 45,000 feet, the X-15 typically flew either an “alti-tude” mission that carried the aircraft outside the atmosphere on a ballistic arc or a “speed” mission at lower altitudes. Credit: NASA

The X-15 first flew in 1959, beginning anoperational career that spanned ten yearsand 199 flights. The aircraft set severalspeed and altitude records, some of whichstill stand today. Credit: Air Force

Q U E S T 19:2 201218

52 William J. Alford Jr. and Robert T.Taylor, “Aerodynamic Characteristics of theX-15/B-52 Combination,” a paper in“Research Airplane Committee Report onConference on the Progress of the X-15Project” (Los Angeles, CA, 28-30 July1958) 69-82.

53 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226—Progress report for months of Septemberand October 1956,” 15 November 1956,Box 174, Entry 1, RG 255, NARA—Mid-Atlantic (PHL).

54 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226—Progress report for month of March1956,” 10 April 1956, Box 175, Entry 1,

RG 255, NARA—Mid-Atlantic (PHL); Souléto members of NACA Research AirplaneProjects Panel, “Project 1226—Progressreport for months of November andDecember 1956,” 17 January 1957, Box174, Entry 1, RG 255, NARA—Mid-Atlantic(PHL); Soulé to members of NACAResearch Airplane Projects Panel, “Project1226—Progress report for months ofJanuary and February 1957,” 19 March1957, Box 174, Entry 1, RG 255, NARA—Mid-Atlantic (PHL).

55 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226—Progress report for March 1956,” 10 April1956, Box 175, Entry 1, RG 255, NARA—Mid-Atlantic (PHL); Soulé to members of

NACA Research Airplane Projects Panel,“Project 1226—Progress report for monthof April 1956,” 17 May 1956, Box 175,Entry 1, RG 255, NARA—Mid-Atlantic(PHL).

56 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226—Progress report for month of May 1956,” 7June 1956, Box 175, Entry 1, RG 255,NARA—Mid-Atlantic (PHL); Soulé to mem-bers of NACA Research Airplane ProjectsPanel, “Project 1226—Progress report formonth of August 1956,” 18 September1956, Box 174, Entry 1, RG 255, NARA—Mid-Atlantic (PHL); Soulé to members ofNACA Research Airplane Projects Panel,“Project 1226—Progress report formonths of September and October 1956,”15 November 1956, Box 174, Entry 1, RG255, NARA—Mid-Atlantic (PHL).

57 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226—Progress report for month of February1956,” 13 March 1956, Box 175, Entry 1,RG 255, NARA—Mid-Atlantic (PHL).

58 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226—Progress report from 1 June 1956 to 9July 1956,” 18 July 1956, Box 175, Entry1, RG 255, NARA—Mid-Atlantic (PHL).

59 Soulé to members of NACA ResearchAirplane Projects Panel, “Project 1226 –Progress report for months of Septemberand October 1956,” 15 November 1956,Box 174, Entry 1, RG 255, NARA—Mid-Atlantic (PHL); Jenkins, Extending, 161-163.

60 Jenkins, Extending, 603-658.

61 Donald R. Bellman et al.,“Investigation of the Crash of the X-15-3Aircraft on November 15, 1967”(NASA/USAF report, Edwards Air ForceBase, California, January 1968), 1.

62 Ibid., 2-3, 11-12, 16.

63 Jenkins, Hypersonics, 73-74.

64 NASA Johnson Space Center,“Astronaut Bio: Joe Henry Engle(06/2009)” http://www.jsc.nasa.gov/Bios/htmlbios/engle-jh.html (accessed 29September 2011).

65 Jenkins, Hypersonics, 72-73.

66 See the 1961 movie X-15,http://www.imdb.com/title/tt0055627/.

67 Jenkins, Extending, 35.

68 Becker, “Retrospect.” After earning astronaut wings in the X-15, Joe H. Engle (pictured here in front of X-15-2)joined the “conventional” astronaut corps. As commander of STS-2, Engle became the onlyastronaut in history to manually fly a Shuttle re-entry from start to finish. Credit: NASA