Transiting from Air to Space
The North American X-15


It might seem that a kind fate, after imposing the burdens involved in the development of the XLR99, would have permitted other phases of the X-15 program to proceed without hindrance. None of the other phases did present the problems posed by the engine, but difficulties continued to occur.

In early 1958, at the very height of the furor over the problems connected with the XLR99, a note of warning sounded for the auxiliary power unit (APU). North American had subcontracted the development of this important piece of equipment to the General Electric Company. On 26 March 1958 and again on 11 April 1958, General Electric notified North American of inability to meet the original specifications in the time available, and requested approval of new specifications. North American, with the concurrence of the X-15 project office, agreed to modify the requirements. The major changes involved an increase in weight from 40 to 48 pounds, an increase in start time from five to seven seconds, and a revision of the specific fuel consumption curves. In an effort to keep the fuel requirement as low as possible, North American asked General Electric to investigate the possibility of creating a derated auxiliary power unit. North American advised the project office that such a unit would reduce fuel consumption from 101 pounds per mission to 96 pounds and that the unit would still be capable of meeting the expected loads. General Electric was also fearful that an excessive amount of nitrogen might be necessary to overcome difficulties in cooling the upper turbine bearing of the power unit. 1

In late March and early May, Propulsion Laboratory and weapon system project office representatives visited the General Electric facilities at Malta, New York, and Lynn, Massachusetts, to review the auxiliary power unit development. The group found that testing was proceeding at a satisfactory pace, that the heating of the upper turbine bearing had been reduced by a change in one of the unit's seals, but that little progress had been made in reducing the amount of nitrogen required for cooling the unit. Nitrogen flow was running as much as 80 percent over that required by specifications. Although no tests had yet been performed, General Electric reported progress in the development of the derated unit requested by North American. 2

Actual tests of the derated unit began shortly after, and proved very encouraging. Bearing temperatures were held to about 300 degrees Fahrenheit with a nitrogen flow of only 12 pounds per hour. The predicted fuel economy of the derated unit was also established. 3 General Electric continued to alter the design in order to improve the cooling characteristics. A new inlet which permitted the introduction of the cooling nitrogen directly into the most troublesome bearing area alleviated the problem and reduced the nitrogen flow. Improvement was so substantial that them first production units were scheduled for shipment to North American in June. 4

Some difficulties continued to arise in the course of the testing which was carried on in the summer of 1958, but most of them proved amenable to correction or were traced to malfunctions of the testing equipment rather than to the unit itself. Starting times at low temperatures remained excessive, prompting investigations of the advisability of increasing the wattage of the hydrogen peroxide heater and of adding a wetting agent. 5 a The heater capacity was increased but the decision on the use of a wetting agent was postponed. 6

By the end of the summer of 1958, the auxiliary power unit seemed to have reached a more satisfactory state of development, an alternate machining method had effectively corrected undesirable stresses that had caused a turbine shaft failure, and satisfactory production units were ready for shipment. 7 The records of the project office thereafter failed to reveal any further concern with the auxiliary power unit until after the first captive flight in 1959. Those flights, unfortunately, did reveal some additional bearing problems and actually produced bearing failures. But investigation showed that the inflight failures had occurred because captive testing subjected the units to an abnormal operational sequence that would not be encountered during glide and powered flight. 8

During the course of the X-15 program, project personnel from time to time had some concern for the development of an escape system and a pressure suit. Of the many accessory tasks included in the X-15 program, these caused the most concern, probably because they seemed to offer the greatest threat to the total development schedule.

Although full-pressure suits had been studied during World War II, attempts to fabricate a practical garment had met with failure. The Air Force took renewed interest in pressure suits in 1954, for by then it had become obvious that the increasing performance of aircraft was going to necessitate such a garment. The first result of the renewed interest was the creation of a suit that was heavy, bulky and unwieldy. The garment had only limited mobility and various joints created painful pressure points. It was not until 1955 that the David Clark Company, utilizing a distorted-angle fabric, succeeded in producing a garment that held some promise of ultimate success. 9

As the Aero Medical Laboratory had met with only partial success in the design of a full-pressure suit at the time of the X-15 evaluation, there followed a certain amount of indecision as to the type of garment to be selected for the X-15 program. North American evidently had more confidence in the potential of full pressure suits than did the Air Force; in any event, the Plans Office of the Directorate of Research advised the Aero Medical Laboratory on 23 August 1955 that ”… the possibility and problems of utilizing a full-pressure suit” required further study. The same office felt that North American would require guidance in the field of pressure suits and that the Aero Medical Laboratory should determine whether a partial-pressure suit would be adequate for an aircraft with the proposed performance of the X-15. 10

Despite the reluctance of the Air Force to commit all effort to a full-pressure suit, North American's detail specifications of 2 March 1956 called for just such a garment – to be furnished by the contractor. 11 The company continued to proceed as though the matter had been entirely settled, issuing an equipment specification for an omni-environmental, full-pressure suit on 8 April 1956. 12 That the matter was not entirely settled, however, was evidenced by the fact that on 4 May 1956 the Aero Medical Laboratory advised the project office to forward details of partial-pressure suit equipment to North American for ”… engineering of installation of subject provisions in the X-15 aircraft.” 13

A positive step toward Air Force acceptance of a full pressure suit occurred during a conference held at North American's plant on 20–22 June 1956. A full-pressure suit developed by the Navy demonstrated during an inspection of the preliminary cockpit mockup, and although the Navy suit still had a number of deficiencies, the project office concluded that ”… the state-of-the-art on full pressure suits should permit the development of such a suit satisfactory for use in the X-15.” 14

On 12 July 1956, during a conference on the personal equipment of the X-15, representatives of the Aero Medical Laboratory reviewed the status of the laboratory's pressure suit development and indicated that the laboratory was willing to make any modifications necessitated by the requirements of the X-15 program. Mr. Crossfield, representing North American at the conference, had previously advocated a full-pressure suit and had taken the position that such a suit should be procured by his company rather than by the government. The reconciliation of divergent viewpoints at this pressure-suit conference influenced all subsequent government-contractor relationships, as the project officer was frequently faced with the necessity of reconciling the conflicting design philosophies of divergent personalities. The Aero Medical Laboratory's presentation at the conference convinced Crossfield that the laboratory could provide an adequate suit for the X-15 program. He insisted that the garment be designed specifically for the X-15 and that every effort be made to meet the laboratory's estimate schedule which called for an operational suit in the latter half of 1957. North American decided to take full advantage of the Aero Medical Laboratory's full-pressure suit, the laboratory agreed to work in close conjunction with the company in order to insure the suit would be suitable for the X-15, and the X-15 office accepted responsibility for providing funds to assist the laboratory's development program. Crossfield conceded that he could not commit North American to the change from a contractor furnished item to a government-furnished suit, but he added that he was in personal agreement with such a change and would so advise his company. 15 b

While the conference of 12 July settled the question of a full pressure garment as opposed to a partial-pressure suit and committed the Aero Medical Laboratory to the task of developing and supplying such a suit, the decision was not for realized for several months. North American's engineering change proposal which called for a government-furnished full pressure suit in lieu of contractor-furnished equipment was not issued until October 4, 1956, and it was not until 16 January 1957 that the AMC Directorate of Procurement and Production authorized the Air Force Plant Representative at North American to proceed with an official change in the contract. 16 North American's formal contract change request was not made until 8 February 1957. 17

Although an ”operational” suit had been promised for the latter half of 1957, progress was not as rapid as had been contemplated at the meeting in July 1956. The Aero Medical Laboratory did not have an opportunity to conduct major tests until the week of 14–18 October 1957, and those were of the first prototype suit. 18

The Aero Medical Laboratory specifications which described the X-15 suit in terms approximating its final configuration, was not issued until 1 January 1958. 19 On 10 April 1958, the laboratory advised the X-15 project office that the first suit, scheduled for Crossfield's use would be delivered on 1 June 1958. At the same time, the laboratory advised that the four suits scheduled for delivery during the summer were the only suits programmed in support of the X-15 project in fiscal year 1958. The laboratory was to receive other full-pressure suits, but the additional suits had been designed for service testing in operational aircraft and were not compatible with the X-15 cockpit. Aero Medical Laboratory specialists cautioned the project group that ”… funding for further X-15 suit procurement … during FY58 must of necessity be furnished by your office.” 20

The X-15 project office, faced with a scarcity of suits and funds, began to investigate the possibility of using a seat kit rather than a back kit for the X-15 suit. Such a change would permit the suits designed for service testing to be utilized by the X-15 pilots, would enable the pilots to try the suits in operational aircraft, and would eliminate the need to furnish each X-15 pilot with two suits--one for familiarization in operational aircraft and one for flight in the X-15. 21

The benefits to be derived from a program to make the X-15 and service test suits compatible would undoubtedly have been substantial, if such a program had been in effect from the beginning of the project. By May of 1958, however, the difficulties of obtaining compatibility outweighed the benefits. The X-15 project office continued to devote some thought to eventual compatibility, and the Aero Medical Laboratory actually carried out some preliminary design studies that were directed toward attainment of that goal. But despite these efforts, the suit utilized in the flight testing of 1959 was one that had been designed specifically for the X-15 and it was not suitable for use in operational aircraft. 22

On 3 May 1958, representatives of the Aero Medical Laboratory and North American met at the David Clark Company, Worcester, Massachusetts and decided to freeze the configuration of the X-15 suit. The decision proved to be somewhat premature, however.

Three months later, project personnel and contractor representatives, meeting c at the Aero Medical Laboratory, discovered that the final configuration of the suit was still indefinite and could not be ”frozen” until more data were on hand. The suit schedule had already been delayed about a month and it was apparent that further tests would be needed at once.

The lag in the suit schedule, and the possibility that there would be still further delays before adequate solutions were found for the remaining problems, created a new threat to the X-15 schedule. On 19 August 1958, the X-15 project office informed Colonel J. P. Stapp, the newly assigned chief of the Aero Medical Laboratory, that failure to produce an acceptable full pressure suit could result in a serious delay of the X-15 program. The project office suggested that a complete suit, including helmet and controller assembly, should be tested immediately. Colonel Stapp was also asked to press for a decision on a final configuration for the entire suit. Simultaneously, Colonel Stapp learned that the 8 August meeting had revealed a controversy in regard to the use of a face seal versus a neck seal in the suit assembly. He was asked to arrange tests of both types and to determine which was superior. The Aero Medical Laboratory was also asked to furnish a delivery schedule for the completed suits. 24

A meeting between the chiefs of the X-15 project office and the Aero Medical Laboratory, at the end of August, resulted in an agreement that a full discussion of the pressure suit program would take place on 8 September 1958. 25 The September meeting, in turn, produced agreement that a fully qualified pressure suit was essential to the X-15 program and that the Aero Medical Laboratory was responsible for meeting this requirement. The first suit would be needed by 1 January 1959, a second suit would be needed by 15 February 1959, and four additional suits had to be ready by 15 May 1959. A suit with a neck seal and with provision for electrical defogging (of the faceplate) was to be the basic configuration, but a suit incorporating a face seal was to be considered as a backup because that configuration was nearer to qualification testing. Both configurations were to be tested, and both were to be procured in a quantity which would insure delivery of the first two suits on schedule--no matter what configuration proved superior. Ordering the components for the four suits scheduled for May was to be postponed until one of the two configurations had been proved superior. All of the pilots were to be furnished suits without the defogging provisions as quickly as possible, such suits being necessary for evaluation and familiarization flights. 26 Three such suits were delivered by the first week in November. 27

Although at that point agreement and mutual understanding seemed to have encompassed all participants, such was not entirely the case. An Air Force inspection team that visited WADC as September became October to consider the X-15 project, found much to concern it in the pressure suit area. Inspectors reported the existence of ”a serious disagreement between the North American Aviation Corporation and the Aero Medical Laboratory regarding certain design philosophies of the MC-2 suit assembly.” 28 The reported disagreement was on the subject of a neck-seal versus a face-seal (actually an independently functioning oral-nasal mask inside the pressurized helmet), the Aero Medical Laboratory favoring the former and North American the latter. North American felt that the face seal could serve as an oxygen mask when the helmet face plate was raised and held that the pilot should be able to open his helmet. As the X-15 cockpit was pressurized by nitrogen, a pilot employing a suit with a neck-seal would be unable to raise the face plate, no matter what the emergency. Both North American and the X-15 project office had given some thought to pressurizing the cockpit with oxygen but this had not been done. At the time of the team's visit to Wright Air Development Center, the electrical defogging provisions for the face plate were not fully satisfactory and the plate itself had not yet been subjected to air blast tests. Still another area of disagreement had arisen over the laboratory's use of a fluid-filled ear cup in the helmet. North American advised the inspection team that the seal had failed during centrifuge tests and that a more satisfactory cup was needed.

In summary, the team listed inadequate testing of the regulator components, unqualified defogging provisions, the lack of a blast tested face plate, and the continuing controversy over the type of seal to be employed, as the major deficiencies of the pressure suit program. 29

Fortunately, pressure suit difficulties finally began to yield to the combined pressures of the project office, the Aero Medical Laboratory and the various contractors. The prototype helmet with electrical defogging provisions was delivered on 17 November 1958, and although the helmet was not completely satisfactory from an optical standpoint, it did pass the defogging tests. On 22 December, the helmet visor successfully withstood the wind blast tests, and by 16 January 1959, the Aero Medical Laboratory could report that the visor was ”fully qualified.” 30

Scott Crossfield, the North American pilot who was scheduled to make the first X-15 flights, received a new suit of the face-seal type on 17 December and, two days later, the suit successfully passed nitrogen contamination tests at the Aero Medical Laboratory. On 30 January 1959, the project office reported that the Aero Medical Laboratory had furnished general qualification and test information on a complete suit. The X-15 project officer attributed much of the credit for the successful and timely qualification of the full-pressure suit to the early and intensive efforts of Mr. Crossfield. 31

Apparently another minor crisis had been met and overcome. After the first captive flights there were complaints about the poor optical qualities of the helmet and the first months of 1959 witnessed attempts to find a snap-on visor that would provide a temporary ”fix.” 32

While not directly related to the pressure suit difficulties that threatened the over-all X-15 schedule, providing a means for successful escape from the aircraft, if that should become necessary, caused some concern during development. The type of escape system to be used in the X-15 had been the subject of debate at an early stage of the program; the decision to utilize the stable-seat, full-pressure-suit combination had been a compromise based largely on the fact that the ejection seat was lighter and offered fewer complications than the other alternatives.

As early as 8 February 1955, the Aero Medical Laboratory had recommended a capsular escape system, but the laboratory had also admitted that such a system would probably require extensive development. The second choice was a stable seat that incorporated limb retention features and one that would produce a minimum of deceleration. 33

During meetings held in October and November of 1955, it was agreed that North American would design an ejection seat for the X-15 and would also prepare a study justifying the use of such a system in preference to a capsule. North American was to incorporate head and limb restraints in the proposed seat. 34

Despite North American's plans to proceed with an ejection seat design, the Air Force was not convinced that such a seat was the best solution. At a specification meeting held at Wright Air Development Center on 2–3 May 1956, representatives of the X-15 project office and the Aero Medical Laboratory again pointed out the limitations of ejection seats. In the opinion of an NACA engineer who attended the meeting, the Air Force was still strongly in favor of a capsule – partly because of the additional safety a capsule system would offer and partly because the use of such a system in the X-15 would provide an opportunity for further developmental research. Despite this apparent preference for a capsule, the several participants finally agreed that because of the ”time factor, weight, ignorance about proper capsule design, and the safety features being built into the airplane structure itself, the X-15 was probably its own best capsule.” About the only result of the reluctance of the Air Force to endorse an ejection seat was another request that North American document the arguments for the seat. 35

By November 1956, North American's seat had completed a number of tests in the wind tunnel at Massachusetts Institute of Technology. The results were encouraging although the seat had a tendency to stabilize in one of several positions instead of in a single position. 36

The death of Captain Milburn G. Apt in the crash of the Bell X-2 in September 1956 renewed apprehension as to the adequacy of the X-15's escape system. Brigadier General Marvin C. Demler, ARDC's deputy commander for research and development, directed WADC to determine the best escape system for the X-15 and to conduct the study on an expedited basis. Evidently General Demler did not anticipate that the study would have any immediate effect on the design in progress, however, as he stated that the results of the study were to be incorporated in any ”future versions of the X-15.” 37

By early 1957, North American's seat development efforts had indicated that several benefits could be derived from a change in the seat catapult originally specified. The company pointed out that the substitution of a contractor-furnished ballistic type rocket (Talco Number 1057-2) for the government furnished type T-18 ejection seat originally specified would increase energy of the catapult from 35,000 to 45,000 pound-feet, reduce frictional losses during the period of guided travel, increase the low altitude escape ability, eliminate binding of the catapult tubes as the seat entered the airstream, eliminate the forward pitching moment of the original T-18 type and extend the deceleration period because of forward thrust component in the ballistic rocket type. 38 These arguments carried the day; the Air Force approved the change proposed by North American and the seat was equipped with the ballistic type rocket. 39

Sled tests of the ejection seat began early in 1958 at Edwards Air Force Base, California, with the preliminary tests concluded on 22 April. During the fourth and final run of the preliminary tests, a shock wave generator catapult exploded, the malfunction being attributed to the high air loads at the beginning of the extension sequence. The accident occurred at Mach 1.26 and at a pressure of 2,192 pounds per square foot. The seat, suit, and test dummy were all damaged beyond repair. 40 During a static firing on 24 April, the seat ejected successfully, but the post-ejection operation of the seat was a failure because a striker on the seat did not contact the striker plate on the seat frame. 41 A second static firing on May 14, 1958 was more satisfactory, but was not a complete success as the parachute and parachute lines wrapped around the seat. 42 Because of the high cost of sled runs, the X-15 project office advised North American to eliminate the planned incremental testing and to conduct the tests at just two pressure levels – 125 pounds per square foot and 1,500 pounds per square foot. The X-15 office felt that successful tests at these two levels would furnish adequate proof of seat reliability at intermediate pressures. 43

The first sled run of the second test series took place on 4 June 1958. It was made at the 125-pounds-per-square-foot level conducted and appeared satisfactory. 44 Three more sled runs were in June and July. The fourth test, which took place on 3 July revealed serious instability and North American decided to discontinue further testing until the cause of the instability could be determined. 45 A detailed analysis of the fourth test revealed that the seat would have to be considerably modified, and by the latter part of September, consideration was being given to the utilization of a Convair ”B” or ”industry” seat. As test data was incomplete for both the X-15 seat and the Convair seat, the Aero Medical Laboratory and the Aircraft Laboratory undertook only a preliminary evaluation. A final decision was to be reached after further sled tests of both seats. 46

North American's revised seat was ready for further tests and the postponed sled runs were resumed on 21 November. The revised seat included a trailing-boom modification, but the shock-wave generator that had been a part of the original design had been eliminated because the previous sled and wind tunnel tests had shown it to be unnecessary. 47 The redesigned seat functioned properly during the test of 21 November but the failure of a number of test-sled rockets reduced the scheduled 1,500 pounds per square foot pressure to about 800 pounds per square foot. 48 Two sled runs conducted in December were also marred by the failure of some of the test-sled rockets. 49

Sled tests scheduled for January 1959 were delayed because of the unavailability of seat rockets. As the X-15 was nearly ready for captive flight, the X-15 project office arranged for a meeting with Aircraft Laboratory personnel on January 12 and requested that the laboratory approve the ejection seat for captive and glide flights, even though the sled tests had not been completed. The Aircraft Laboratory verbally approved the use of the seat for such flights but only within a range between Mach 0.377 and Mach 0.72, and with dynamic pressures limited to those between 195 and 715 pounds conducted during per square foot. 50 (The only test that was January was a failure because the right-hand boom and right-hand fin both failed to deploy, with the result that the seat was highly unstable throughout most of the trajectory. The leg restraints of the seat failed during this same test, but this failure was attributed to the instability induced by the boom and fin malfunctions- The parachute functioned properly but did not open until just before the dummy reached the ground, too late to prevent a considerable amount of damage to the dummy.) 51

As a result of the January test, the booms were carefully rechecked and strengthened and the seat's gas system was pressure tested. 52 The final sled-test was conducted on 3 March 1959 with a dynamic pressure of about 1,600 pounds per square foot and at Mach 1.15; at conditions considerably in excess of requirements, it was by far the most successful test. The leg manacles broke during this test, but North American began an immediate program to correct this failure. 53

Additional sled tests and a parachute jump program were proposed in April of 1959, but project personnel decided that further extensive testing was unnecessary. The possibility of parachute tests was not eliminated but neither was there any definite decision to conduct such tests. 54

The third item in the X-15 program for which the Air Force retained direct responsibility (apart from the XLR99 rocket engine and the full-pressure suit) was the all-attitude inertial flight data system. Designers realized from the first that the X-15 s performance would necessitate a new means of determining altitude, speeds and aircraft attitude; the NACA had proposed a stable platform inertial integrating and attitude system as a means of meeting these needs. Unfortunately, not much thought seemed to have been given to the exact requirements of such a system or to the source from which it might be obtained.

An NACA report of meetings held at Wright Air Development Center and at North American in the fall of 1956 indicated that Wright Air Development Center agreed to furnish a stable platform. The NACA representative apparently assumed that the center had already developed a suitable platform, as his report stated that the instrument appeared to be a newly developed Bendix platform weighing only 28 pounds and occupying only one-half a cubic foot. 55

North American and the NACA were not as certain about the platform, for during a visit to North American's plant, Mr. Walter Williams, the chief of NACA's High Speed Flight Station, specifically asked that the question of who was to supply the stable platform be clarified. 56 It was not until 24 May 1956 that a meeting was held (at Langley) for the purpose of discussing the actual requirements for the proposed stable platform system. The May meeting was attended by representatives of North American Aviation, the NACA, the Eclipse-Pioneer Division of Bendix, and Wright Air Development Center. One of the center's representatives was Mr. M. L. Lipscomb of the Instrument Branch in the Flight Control Laboratory. Mr. Lipscomb was subsequently to play an important role in the selection and development of the system that was eventually procured. The attendance of Eclipse-Pioneer representatives indicated that Bendix was still being considered as the potential contractor. The consensus of those attending the meeting was that a suitable platform could be developed in twenty four months. North American presented the weight and size requirements for the system, and the NACA agreed that since the platform would provide research information, 40 pounds of the estimated 65 pound weight should be considered as a part of the allotted weight of the research instrumentation. 57

During the summer of 1956, Eclipse-Pioneer failed to display any further interest in providing the desired equipment and the Flight Control Laboratory invited the Sperry Gyroscope Company to submit proposals for a stable platform system. By August, Sperry had prepared the requested proposal, and on 4 October Sperry personnel participated in a briefing at Wright Air Development Center. 58

On 26 December 1956, Mr. Lipscomb asked the Air Materiel Command to start the procurement of eight all-attitude flight data systems. Two of the requested items were designated ”B” type and were to be utilized for research; six were to be assigned to the X-15 program and were designated type ”A.” The systems were described in detail in an accompanying exhibit, dated 12 December 1956. The laboratory recommended that the contract be given to the Sperry Gyroscope Company, estimating the cost at $1,030,000. 59 The request for a proposal from Sperry was not made until 6 February 1957. 60

Sperry replied on the 20th of the same month, and by 28 March the Flight Control Laboratory had evaluated and approved Sperry's proposals. In the meantime, however, the Air Materiel Command, the Flight Control Laboratory, the X-15 Weapon System Project Office, and Sperry had become involved in a controversy over a number of details. Some of the points at issue were the total amount of the contract, the amount of the fixed fee, the contractor's cost criteria, and the provisions for travel in connection with the proposed contract. By 11 April 1957, the contract negotiations seemed to have reached a deadlock, and the Air Materiel Command buyer notified the Flight Control Laboratory and the project office that he intended to solicit sources other than Sperry in an effort to secure the desired system at a reduced cost. The laboratory and the project office responded to this development by reiterating their reasons for considering Sperry to be the only contractor capable of producing the required system within the time period available. The laboratory's position was that Sperry was the only concern with experience in components, systems, and applications, and the project office emphasized that Sperry was the only supplier who could produce the equipment in time to meet the schedule of the X-15 program. 61

The Air Materiel Command still refused to concede the validity of the justifications for considering Sperry as a sole source and it was evident that the patience of all the parties concerned was rapidly being exhausted when the entire controversy was brought to a head on 22 April 1957. On that date, General Haugen, then director of development at Wright Air Development Center, advised the Air Materiel Command that ”sole source procurement from Sperry provides the only possibility of obtaining the specific equipment to meet the time schedule of the X-15 program.” General Haugen added that the importance of the X-15 program justified an award of the contract to Sperry ”at the earliest possible date.” 62 General Haugen's intervention proved the needed catalyst, for while negotiations continued, they were conducted only with the Sperry Gyroscope Company and a contract was ready for final negotiation by 26 April 1957. The cost-plus-fixed-fee contract, completed on 5 June 1957, provided an estimated cost of $1,213,518.06, with a fixed fee of $85,000. 63

By May 1958, the cost had risen to $2,498,518, and in June a further increase brought the cost to $2,741,375 and raised the fee to $102,000. No further increases took place during 1958, but several were permitted in early 1959. By mid-April 1959, costs had reached $3,234,188.87 and the fixed fee had risen to $119,888.56. 64

By April 1958, the Flight Control Laboratory and the X-15 project office had concluded that the scheduled delivery of the first Sperry unit in December of that year would not permit adequate testing to be performed prior to the first flights of the X-15. Consequently the several participants decided to install an interim gyroscopic system in the first two aircraft and to install the completed system in the third. 65

As the development of the stable-platform progressed, it became apparent that its weight had been seriously underestimated. The increase in weight was obvious by May 1958, when Sperry undertook a program of weight reduction which, unhappily, was not as successful as the Flight Control Laboratory and the project office had hoped. In August, the project office reported that the weight was then approximately 100 percent greater than had been originally anticipated. 66

As a result of the concern over the weight increase, the laboratory requested that Sperry be asked to justify the weight increase. 67 On 7 August 1958, the Air Materiel Command advised Sperry of the laboratory's desire for additional information on the company's weight reduction program and for a justification of the weight increases that had taken place. 68 Sperry's reply revealed that with a shock mount which would meet the vibration specification, the weight of the system had increased to 185.25 pounds and that with a less satisfactory but possibly adequate shock mount, the weight would be 165.25 pounds. Sperry stated that the company had been fully aware of the weight problem throughout the program and that it had ”… designed and developed an optimum system considering the present state of the art.” A number of detail changes that had been made in the effort to eliminate excess weight were also itemized. These included the substitution of aluminum for stainless steel whenever possible, the reduction of the thickness of cases and covers, the development of the less satisfactory but lighter shock mount, and a careful reduction of component weights whenever such reduction proved feasible. Sperry also pointed out that it had been necessary to include power supplies in the final design. Finally, Sperry had compared the X-15 system to similar systems made by other concerns and felt that the Sperry equipment was ”… lighter, more accurate, and required less total aircraft volume …” than any of the equipment to which it was compared. 69

Apparently Sperry's letter of justification was satisfactory, because project people thereafter accepted the fact that the system was overweight and was going to remain overweight.

By the end of November 1958, the two major system components, the stabilizer and the computer, had completed the individual tests and were ready to be tested as a complete system during the following month. The ground test equipment was also nearing completion and was scheduled for year-end delivery. The first system completed its acceptance test in December; the system and ground test cart were shipped to Edwards Air Force Base in mid-January 1959. 70 During the spring of 1959, the original plans to utilize the carrier B-52 as a test vehicle for the stable platform system were changed and arrangements made to test the equipment in a KC-97 that was already in use as a test aircraft in connection with the B-58 program. 71 The first test flights in the KC-97 were carried out in late April. 72 By June, North American had made a successful test installation of the Sperry system in the third X-15 and the stable-platform program seemed to be moving toward a successful conclusion with no major obstacles or difficulties foreseen. 73

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