Transiting from Air to Space
The North American X-15


During the spring of 1952, the Committee on Aerodynamics of the National Advisory Committee for Aeronautics (NACA) recommended that several NACA laboratories begin studies of problems likely to be encountered in spaceflight and examine methods of exploring such problems. The NACA Executive Committee, which endorsed the recommendation, directed consideration of laboratory techniques, missiles, and manned aircraft.

Work along these lines progressed quietly for the next two years. Then, in February 1954, the NACA stepped up the pace, undertaking a more specific study to determine the extent to which an advanced research aircraft could contribute to the solution of problems earlier identified. Technical areas of concern at that time included high temperature structures, hypersonic aerodynamics, stability and control, and pilotage. An important requirement, specified at the outset of the work, was that "a period of only about three years be allowed for design and construction in order to provide the maximum possible lead time for application of the research results." Such a requirement precluded the development of new materials, new construction techniques, or improved launching practices. As one official subsequently observed, "it was obviously impossible that the proposed aircraft be in any sense an optimum hypersonic configuration."

NACA design engineers decided early that a relatively conventional airframe was essential to the resolution of low speed launch and landing difficulties. High speed requirements prompted the choice of a thick wedge tail to provide directional stability and a ventral tail to improve control at high angles of attack (where the upper vertical tail surface was immersed in low pressure flow fields generated by the wing and fuselage). Artificial damping seemed essential because of persistent uncertainties about the aerodynamic environment at extreme speeds and altitudes. Static stability for all flight conditions and the employment of hydrogen peroxide rockets for high altitude attitude control also became objectives of the tentative design. NACA materials experts decided that Inconel X offered the best heat sink structure and that heating problems in general would impose the use of a blunt wing leading edge. Assuming that air launch in the fashion of the X-1 and X-2 aircraft would be necessary, NACA established aircraft size as the largest that could conveniently be handled by B-36 or B-50 carriers. A maximum velocity of 6,800 feet per second, an altitude potential of 400,000 feet, and a gross weight of 30,000 pounds (18,000 pounds of fuel) completed the general proposal 1.

The studies that had prompted these recommendations of early 1954 were independently produced by the three NACA laboratory stations (Langley, Ames, and High Speed Flight Station). They induced NACA to adopt the official policy that a manned research airplane was essential for study of the problems earlier defined, that the construction of such an aircraft was wholly feasible, and that quick action should be taken to pursue the general objective. In June of 1954, therefore, the NACA contacted the Air Force and the Navy, asking that a special joint meeting be held to consider the need for a new research aircraft.

Wright Air Development Center (WADC), then having cognizance over system development, provided technical representation for the Air Force at the meeting - held in Washington on 9 July. Headquarters of the Air Research and Development Command (ARDC) and Headquarters, United States Air Force (USAF), sent policy representatives. In the course of the meeting it became apparent that neither the Air Force nor the Navy had been indifferent to the problems which had prompted NACA interest. The Air Force's Scientific Advisory Board had been urging the construction of a "super X-2" while the Navy's Bureau of Aeronautics had contracted for a feasibility study of a manned aircraft capable of reaching an altitude of 1,000,000 feet. The NACA proposal fell roughly between these extremes, being considerably less ambitious than the Navy program and substantially more advanced than the Air Force objective of the moment 2.

Both Navy and Air Force representatives viewed the NACA proposal with favor, though each had some reservations. At the close of the meeting, however, there was agreement that both services would study further the justification and objectives of the NACA program, and that NACA would take the initiative in securing project approval from the Department of Defense 3.

Three weeks later, on 29 July, Headquarters ARDC instructed WADC to submit technical comments on the proposal and to make time and cost estimates 4. Almost immediately, the WADC Power Plant Laboratory identified the principal shortcoming of the original "study" - the apparent lack of a suitable rocket engine. Initially and tentatively, NACA had suggested employing a modified Hermes A-1 power plant; the Power Plant Laboratory early in August pointed out that "no current rocket engines" entirely satisfied the NACA requirements, and urgently emphasized that the Hermes engine was not designed to be operated in close proximity to humans - that it usually was fired only when shielded by concrete walls. Other major objections to the Hermes engine lay in its relatively low level of development, in its limited design life (intended for missile use, it was not required to operate successfully more than once), and in the apparent difficulty of incorporating thrust variation provisions.

In the stead of the Hermes power plant, the laboratory suggested consideration of several engines originally designed for use in manned aircraft. Hesitating to make any positive recommendations in the absence of more specific data on the aircraft, however, WADC recommended only that the selection of an engine be postponed until propulsion requirements could be more adequately defined 5. WADC technical personnel who visited Langley on 9 August drew a firm distinction between engines intended for piloted aircraft and those designed for missiles; NACA immediately recognized the problem, but concluded that although program costs would go up, feasibility estimates would not be affected 6.

WADC's official reaction to the NACA proposal went to headquarters ARDC on August 13 a. The director of laboratories (Colonel V. R. Haugen) reported "unanimous" agreement among WADC participants that the proposal was technically feasible; excepting the engine situation, there was no occasion for adverse comment from WADC technical sources on the NACA-proposed solutions to major problems.

In one respect, however, the official letter from WADC to ARDC did not reflect unanimity of opinion. The comment forwarded by Colonel Haugen contained a cost estimate of $12,000,000 "distributed over three to four fiscal years" for two research aircraft, modification of a suitable carrier, and necessary government-furnished equipment 7. Mr. R. L. Schulz, technical director for aircraft in the WADC Directorate of Weapon Systems Operations, commented informally that although his directorate had concurred in the letter, the concurrence included a reservation about the estimated cost which the Fighter Aircraft Division reportedly furnished. Said Mr. Schulz, prophetically: "Remember the X-3, the X-5, [and] the X-2 overran 200%. This project won't get started for $12,000,000. 8"

On 13 September, Major General F. B. Wood, ARDC's Deputy Commander for Technical Operations, forwarded to Air Force headquarters an endorsement of the NACA position and its WADC support. Specifically, General Wood recommended that the Air Force "initiate a project to design, construct, and operate a new research aircraft similar to that suggested by NACA without delay." The aircraft, emphasized ARDC, should be considered a pure research vehicle and should not be programmed as a weapon system prototype. The research command estimated that about three and one-half years would be consumed in the design and fabrication process and forwarded WADC's cost estimate, broken down into specifics, without change. (Estimated costs included: $1,500,000 for design work; $9,500,000 for construction and development, including flight test demonstration; $650,000 for government furnished equipment, including engines, $300,000 for design studies and specifications; and $250,000 for modification of a carrier aircraft.) ARDC further suggested a preliminary design competition, assignment of "sole executive responsibility" to the Air Force, and eventual transfer of the resulting aircraft to NACA following a limited Air Force flight demonstration program 9.

Brigadier General B. S. Kelsey, Deputy Director of Research and Development in the office of the USAF Deputy Chief of Staff, Development, on 4 October 1954 expressed general agreement with the ARDC position, noting however that the Department of Defense had decided that the project would be a joint Navy-NACA-USAF effort managed by the Air Force and guided by a joint steering committee. A 1-B priority, $300,000 in FY55 funds, and directions to support the undertaking accompanied this explanation. Air Force headquarters further pointed out the necessity for funding a special flight test range as part of the project 10.

Formalization of the arrangements thus proposed required nearly eight weeks. On 5 October, the NACA Committee on Aerodynamics formally endorsed the proposal to build a Mach 7 research airplane to explore the fringes of space. 11 On 22 October a meeting of Navy, NACA, and Air Force representatives at Wright Field agreed on methods of originating and coordinating design requirements for an eventual competition. Additionally, the conferees settled on four development engines from which a power plant could be chosen by any interested airframe contractor. 12 Early in November the two services and NACA reached a general agreement on future operating procedures; a formal memorandum of understanding emerged from the office of Mr. Trevor Gardner (Special Assistant for Research and Development to the Secretary of the Air Force), and was forwarded for the signatures of the Assistant Secretary of the Navy for Air (Mr. J. H. Smith Jr.) and the Director of the NACA (Dr. H. L. Dryden). The process was effectively complete by 23 December. 13

The memorandum of understanding, which set a general pattern for the future management of the project, assigned technical direction of the program to the director, NACA, "with the advice and assistance of a Research Airplane Committee" .that included Navy and Air Force representatives. (General Kelsey became the Air Force member and Rear Admiral R. S. Hatcher the Navy member.) The Navy and the Air Force were to finance the undertaking and the Air Force was to administer its design and construction phases. The preliminary NACA design was to be the basis for solicited proposals for a design and construction contract. Upon acceptance of the airplane from the contractor, it was to become NACA property. The memorandum concluded with the statement: "Accomplishment of this project is a matter of national urgency." 14 Accompanying the memorandum, as a matter of course, was a secretarial-level Air Force concurrence in the establishment of a joint project to build the proposed research airplane. 15

In the meantime, notwithstanding the absence of formal agreements or procedure, Wright Field had been making arrangements for a design competition. By 15 November, individual laboratories had compiled specification data for inclusion in a letter of invitation to prospective contractors. Coordination with NACA and Navy organizations presented no great difficulty; by 30 November headquarters ARDC had approved plans to prepare official copies of competition data and had advised Wright Field that in about two weeks the Office of the Secretary of Defense probably would authorize distribution of the material. 16 Air Force headquarters scheduled a 13 December briefing for the Secretary of Defense and approved certain changes in the draft requirements. (USAF specified that air-launch was required, that a prone-pilot provision would not be acceptable, that unconventional design approaches would be sought, that instrumentation space was to be increased, that non-NACA facilities would be used for flight tests, and that references to costs in excess of $5,000,000 and to 1956 engine availability were to be eliminated from the invitation to bid.) 17

Advance notice of the forthcoming competition was informally given to prospective contractors early in December. In the last week of December, headquarters ARDC directed that the letter of invitation be dispatched as soon as the center received an official teletype authorizing such action. As prescribed by existing regulations, the letter was to be circulated by the Air Materiel Command (AMC), although that organization declined responsibility for selecting the recipients and held to the policy that the competition was exclusively an ARDC affair. 18

On 29 December the action teletype from Air Force headquarters arrived. 19 Rubber stamp dates completed the preparation process, and on 30 December AMC, over the signature of Colonel C. F. Damberg, Chief, Aircraft Division, sent invitation-to-bid letters to 12 prospective contractors (Bell, Boeing, Chance-Vought, Convair, Douglas, Grumman, Lockheed, Martin, McDonnell, North American, Northrop, and Republic). The document asked that interested concerns notify Wright Field by 10 January 1955 and plan to attend a special briefing on 18 January.

Attached to the letter were a general preliminary outline specification, an abstract of the NACA preliminary study, a discussion of power plant requirements and development levels, a list of data requirements, and a cost outline statement. Each bidder was required to satisfy various requirements thus set forth, except in the case of the NACA abstract which was presented as "representative of possible solutions." 20

Grumman, Lockheed, and Martin expressed slight interest in the competition and did not appear at the 18 January briefing. Subsequently, between that date and the 9 May deadline for the submission of proposals, Boeing, Chance-Vought, Convair, Grumman, McDonnell, and Northrop informed AMC that they would not participate. This left Bell, Douglas, North American and Republic as competitors.

Activity in the interim was varied. The contractors concentrated on the assembly of attractive proposals. In the course of this effort they had frequent recourse to the advisory services of both WADC and NACA. Concurrently, project officers (in the New Developments Office, Fighter Aircraft Division, Directorate of Weapon Systems Operations, which had been assigned full responsibility for the balance of the competition) attempted to refine an evaluation procedure acceptable to all concerned and sent supplemental data to the participating contractors. Of these tasks, the evaluation procedure loomed larger. Headquarters ARDC in early February emphasized the extreme importance of resolving all possible differences of opinion on the conduct of the technical evaluation; to this end, ARDC instructed that the ultimate recommendation reflect the opinion of NACA as well as that of WADC. Plans had been laid for submitting the evaluation rules to the Joint Steering Committee for approval. 21

Supplemental instructions to contractors reemphasized the urgency of the two and one-half year development period of the X-15. b The project office also relaxed very slightly the rigid limitations on engine selection, instructing competitors that "if ... an engine not on the approved list offers sufficient advantage, the airframe company may, together with the engine manufacturer, present justification for approval to the WSPO (Weapon System Project Office)." 22

The Power Plant Laboratory had originally listed the XLR81 and the XLR73, the XLR10 (and its variants - a compound XLR10 and a modification of the XLR30), and the NA-5400 (a North American engine in early development, still lacking a military designation) as engines that airframe competitors could use in their designs. Early in January, the laboratory had become concerned that the builders of engines other than those listed might protest the exclusion of their products. Consequently there emerged from the Liquid Rocket Section of the laboratory an explanation and justification of the engine selection process. It appeared that the engineers had confidence in the ability of the XLR81 and XLR73 to meet airplane requirements, had doubts about the suitability of the XLR25 (a Curtiss-Wright product), and held the thrust potential of the XLR8 and XLR11 (similar engines) in low repute. This for practical purposes exhausted the fund of Air Force-developed engines suitable for manned aircraft. Navy consultants had introduced the other two engines defined as acceptable in terms of the competition. 23

At about the time the industry briefing was held, the project office began seriously to consider sending copies of the bid invitation to "appropriate engine contractors." The Power Plant Laboratory discouraged unlimited distribution because of the possible compromise of proprietary data, but suggested that limited information be circulated and that inquiring contractors be informed what the Air Force had said about their own engines. 24 A course similar to this eventually was adopted; on 4 February each of the prospective engine contractors earlier identified (Reaction Motors, General Electric, North American, and Aerojet) was asked to submit a suitable engine development proposal. 25 Even earlier, certain of the engine contractors had been contacted for specific information about the engines originally listed as suitable for the X-15 program. 26 This information, relating to design and performance details, was distributed to all four prospective airframe contractors. 27 Data on the North American NA-5400 was scant, and the Reaction Motors XLR10 received a "not recommended" classification (at the suggestion of the engine contractor himself).

Progress in the completion of evaluation arrangements was less rapid than had originally been anticipated. A 1 March deadline established by ARDC early in February was later extended to 1 April, and the material itself did not leave Wright Field until 11 April. 28 Nevertheless, by that time the evaluation rules had been fully coordinated within WADC and with NACA.

The burden of the evaluation process fell on the project office, the WADC laboratories, and NACA - in that order. AMC and the Navy were to play subordinate - though still significant - roles. Four evaluation areas were specified: performance, technical design, development capability, and cost. 29

Headquarters ARDC forwarded the WADC evaluation plan to Air Force headquarters for approval and then advised WADC that the Research Airplane Committee planned to meet at Wright Field on 17 May to examine the submitted designs and to review evaluation arrangements. ARDC also suggested that commitments be obtained from the various engine contractors as early as possible so that the engine program would not adversely affect the selection of a winning airframe design. 30

On the appointed day, 9 May 1955, Bell, Douglas, North American, and Republic submitted their proposals to the project office. Two days later the technical data went to the several laboratories with a request that evaluation results be reported by 22 June. On 17 May the bidders made separate presentations to the Research Aircraft Committee and to a group of senior officials from WADC, ARDC, headquarters USAF, NACA, and the Air Force Flight Test Center. Later that day the Research Aircraft Committee confirmed previous arrangements for the evaluation procedure. Subsequently, both the Bureau of Aeronautics (Navy) and NACA independently accepted the resultant evaluation plan. Bureau of Aeronautics took pains. to insure that Navy and NACA consultants participated in the joint evaluation. 31 Later arrangements insured that engine evaluations, also coordinated with the Navy and the NACA, would be available by 12 July. 32

The final evaluation meeting, to consider the results of earlier examinations and comments, was scheduled for Wright Field on 25 July. In the interim, there was established a free interchange of preliminary opinion between Bureau of Aeronautics, NACA, and WADC laboratory and project office elements. 33 Notwithstanding this advance coordination, the evaluation results were delayed, first by the interference of higher priority work at WADC, later by a need for formal coordination with Bureau of Aeronautics. 34

By 5 August, the various portions of the evaluation had been completed and the evaluation report had identified North American's proposal as having considerably greater merit than any of the others. c On 12 August the Research Aircraft Committee accepted the findings. Preliminary moves to Confirm this decision and to award a design contract to North American hit a sudden snag, however, when on 23 August North American's local representative verbally notified the Fighter Aircraft Division that the firm was withdrawing its proposal because of the press of other work. 35 The immediate reaction of Wright Field was to inform everybody concerned that the evaluation results would have to be reexamined. (No contractors had yet been notified of the outcome.) On 30 August, the contractor officially and in writing confirmed his earlier announcement, citing inability to perform the work in the time allotted and recent awards in interceptor and fighter-bomber competitions plus a heavy F-107A workload as the motives. Within a week the project office (and the directorate) had decided that North American should be asked to reconsider the decision. But there was agreement that if the company held firm, Douglas would probably be ruled the competition winner, although the Douglas design (which employed magnesium instead of Inconel X) would require considerable modification before it satisfied NACA and USAF requirements. 36

During the middle weeks of September, both NACA and Air Force officials discussed with North American possible continuance of the contractor's X-15 activity. Dr. Dryden of NACA and Brigadier General H. M. Estes of the newly formed Directorate of Systems Management d had prominent roles in these negotiations. A presentation of the X-15 program at the Department of Defense level, on 14 September, induced a recommendation that the program be approved. Concurrently, however, two changes in philosophy appeared. First, the Army representative at the conference said flatly that the Army would oppose the project if it required special Department of Defense funds. This stand prompted an attempt to reduce program costs below earlier estimates. At the same time, it began to appear inevitable that the program would take more than the 30 months originally projected. On this basis, it seemed that North American might still be considered a competitor. The contractor's reluctance to proceed was frankly based on the thesis that the company could not devote sufficient effort to the X-15 project to permit its completion within the span of time initially provided. 37

On 20 and 21 September, contacts with Air Force headquarters confirmed earlier information that the Department of Defense had approved the project and North American's selection. But before any formal contract negotiations could be authorized, said the Department of Defense, a reduction in annual budget requirements would be necessary.

As these instructions reached Wright Field, General Estes was conferring with Mr. J. L. Atwood, North American's president. Mr. Atwood told the general that his company would reconsider its decision on the X-15 if the program were extended by eight months (to 38 months). Two days later, on 23 September, this offer was made officially. North American emphasized, however, that a program extension was essential to the company's accepting a contract. 38

On 27 September, Air Force headquarters agreed to this condition and canceled earlier instructions to negotiate a reduction in the contractor's fee. Information on the decision reached the center on 28 September; on the last day of that month, letters went to North American and to the unsuccessful bidders, officially advising them of the outcome of the competition. 39

Price negotiations followed. Wright Field project officers took the results of preliminary contact with North American (and with Reaction Motors, the prospective engine contractor) to a Pentagon meeting of 11 October. By that time the contractor's estimate of project cost had been reduced from $56,000,000 to $45,000,000 and the maximum annual funds requirement from $26,000,000 to $15,000,000. The USAF Directorate of Research and Development made a presentation of these figures to the Department of Defense Coordinating Committee on Piloted Aircraft on 19 October. The result was a committee decision to support the project. Shortly thereafter, the Department of Defense released the funds needed for the start of work. More meetings between NACA, project office, and North American personnel were held on 27-28 October, largely to define changes to the aircraft configuration originally submitted by the contractor. On 7 November, the AMC Directorate of Procurement and Production took the first steps toward issuance of a letter contract, by 9 November the principal clauses of that document had been composed, on 15 November it received the approval of the procurement directorate, on 18 November it was sent to North American, and on 8 December the contractor returned an executed copy. 40 At that point, about $2,600,000 was available to fund initial activity; a total contract cost of $39,000,000 was foreseen for design, development, three X-15 aircraft, and a flight demonstration program. 41

On 1 December 1955, a series of actions designed to produce an engine contract began. 42 A letter contract with Reaction Motors became effective on 14 February 1956. Its initial allocation of funds totaled $3,000,000, with an eventual expenditure of about $6,000,000 foreseen as necessary for the delivery of the first flight engine. 43

A definitive contract for North American was completed on 11 June 1956, superseding the letter contract and two intervening amendments. To that time, $5,315,000 had been committed to North American, in three increments, under the letter contract. (Essentially, North American had been given $2,715,000 more than the initial allocations.) The definitive contract of June contemplated the eventual expenditure of $40,263,709 plus a fee of $2,617,075. For this sum, the government was to receive three X-15 research aircraft and other specified items: a high speed and a low speed wind tunnel model program, a free-spin model, a full-size mockup, propulsion system tests and stands, flight tests, modification of a B-36 carrier, a flight handbook, a maintenance handbook, technical data, periodic reports of several types, ground handling dollies, spare parts ($100,000), and ground support equipment ($200,000). Exclusive of contract costs were fuel and oil, special test site facilities, and expenses incident to operation of a B-36 carrier. Delivery date for the aircraft and support equipment was to be 31 October 1958. 44

A final contract for the engine, the prime unit of government furnished equipment, was effective on 7 September 1956. Superseding the letter contract of February, it covered the expenditure of $10,160,030 plus a fee of $614,000. e For this sum, Reaction Motors agreed to deliver one engine, a mockup, reports, drawings, and tools. The engine described in the final contract was to have a maximum thrust of 50,000 pounds, to include provisions allowing for inflight thrust variation between 30 to 100 percent of maximum output, to be capable of 90 seconds operation at full thrust and 4 minutes 9 seconds at 30 percent thrust, to weigh 618 pounds (without fuel), and to have a specific impulse of 241 (pounds of 45 thrust per pound of fuel per second). 45

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