Category X-15 EXTENDING THE FRONTIERS OF FLIGHT

Events took an unexpected twist on the afternoon of 23 August 1955 when the North American representative in Dayton verbally informed the WADC Project Office that his company wished to withdraw its proposal. Captain McCollough notified Hartley Soule, Air Force Headquarters, and BuAer of this decision, touching off a series of discussions concerning future actions. Within a week the Air Force asked North American to reconsider its decision. The Air Materiel Command recommended that Douglas be declared the winner if North American did not reconsider. The Research Airplane Committee, however, cautioned that the Douglas design would require considerable modification before it satisfied Air Force and NACA requirements. On 30 August, North American sent a letter to the Air Force formally withdrawing its proposal because sufficient resources were not available to complete the X-15 program within the 30-month schedule.-1159!

On 1 September Hugh Dryden informed Soule that he and General Kelsey had decided to continue the procurement, pending receipt of official notification from North American. The letter arrived sometime later in the week, and on 7 September, Soule contacted Dryden and recommended that the Research Airplane Committee consider the second-place bidder. Dryden responded that he wanted to reopen the competition rather than award the contract to Douglas.

Despite North American’s request to withdraw, the procurement process continued. A presentation to the Defense Air Technical Advisory Panel on 14 September presented the selection of North American for formal approval. Naturally, the Air Force recommended approval, but the Army representative to the panel flatly opposed the project if it required more Department of Defense funds than previously discussed. This prompted the Air Force to reduce project costs below earlier estimates. The panel was also concerned that the program could not be completed in 30 months, and concurred with the earlier Research Airplane Committee recommendation that the schedule be relaxed.1160!

By 21 September the Department of Defense had approved the selection of North American, with a caveat: a reduction in annual funding. The same week General Estes met with John Leland "Lee" Atwood, the president of North American, who announced that an extended schedule would allow North American to reconsider its position.-1161!

Two days later, the vice president and chief engineer for North American, Raymond H. Rice, explained that the company had decided to withdraw from the competition because it had recently won new bomber (WS-110A) and long-range interceptor (WS-202A) studies, and had increased activity relating to its ongoing YF-107 fighter program. Having undertaken these projects, North American said it would be unable to accommodate the fast engineering labor build-up that would be required to support the desired 30-month schedule. Rice went on to say that "due to the apparent interest that has subsequently been expressed in the North American design, the contractor [North American] wishes to extend two alternate courses which have been previously discussed with Air Force personnel. The engineering man-power work load schedule has been reviewed and the contractor wishes to point out that Project 1226 could be handled if it were permissible to extend the schedule…over an additional eight month period. In the event the above time extension is not acceptable and in the best interest of the project, the contractor is willing to release the proposal data to the Air Force at no cost."!162!

The approval granted by the Research Airplane Committee and the Defense Air Technical Advisory Panel to extend the schedule allowed North American to retract its previous decision to withdraw from the competition once the Air Force notified the company of its selection. Accordingly, on 30 September, Colonel Carl F. Damberg, chief of the Aircraft Division at Wright Field, formally notified North American that the company had won the X-15 competition. The company retracted its letter of withdrawal, and the Air Force thanked the other bidders for their participation. In the competitive environment that exists in the early 21st century, this course of events would undoubtedly lead to protests from the losing contractors, and possibly congressional investigations and court actions. However, as business was conducted in 1955, it was not considered cause for comment and the award went forward uncontested.!163!

Within North American, the program had also been the subject of discussions of which the government was probably unaware. The internal concerns were much the same as those related to the government, but they showed a marked divide between technical personnel and corporate management. Harrison Storms, who would be the chief engineer for the North American Los Angeles Division during the design of the X-15, remembers:!164!

My position at that time was that of manager of research and development for the Los Angles Division…. I was told that top corporate management wanted to reject the [X-15] program since it was small and they were concerned that too many of the top engineering personnel would be absorbed into the program and not be available for other projects that they considered more important to the future of the corporation. There was considerable objection to this position in the technical area. I was finally called into Mr. Rice’s office, the then chief engineer, and told that we could have the program on the condition that none of the problems were ever to be brought into his office. He further elaborated that it would be up to me to seek all the solutions and act as the top NAA representative for the program.

This was fine with me.

Funding was another issue, and on 5 October 1955 a meeting was held at Wright Field to discuss how to pay for the program. The Defense Coordinating Committee for Piloted Aircraft had tentatively allocated $30,000,000 to the program from the Department of Defense general contingency fund, with an expected burn rate of approximately $10,000,000 per year. The problem was that the new program estimate was $56,100,000, including a first-year expenditure of almost $26,000,000. The X-15 Project Office began to reduce expenditures by eliminating the static-test article (nobody was sure how to test it in any case), reducing the modifications to the B-36 carrier aircraft, and eliminating some previously required studies and evaluations. The agreed-upon eight-month extension also eased the peak annual expenditures somewhat. After some juggling, the revised cost estimates were $50,063,500-$38,742,500 for the airframes, $9,961,000 for the engine, and $1,360,000 for the new flight test range at Edwards. The peak expenditure ($16,600,000) would occur in the third year of the project.-1165

Contract negotiations followed. The Air Materiel Command took revised budget figures to a meeting on 11 October at the Pentagon. By that time, the reduced estimate was approximately $45,000,000 and the maximum annual expenditure was less than $15,000,000. The Air Force presented these figures to the Defense Coordinating Committee for Piloted Aircraft on 19 October. Support for the project was reconfirmed, although no additional funds were allocated. Nevertheless, the Department of Defense released funds to continue the procurement process.-1166!

The AMC Directorate of Procurement and Production drafted a $2,600,000 letter contract for North American on 7 November 1955. Higher headquarters approved the letter contract on 15 November, and North America returned a signed copy on 5 December. The detailed design and development of the hypersonic research airplane had been under way for just under a year at this point. Reaction Motors returned a signed copy of its $2,900,000 letter contract on 14 February

1956.H6Z1

At this point, the X-15 program budget was (in millions);!1681

There was still less than $30,000,000 available for the project, and an additional $16,000,000 needed to be found. In reality, this amount would become trivial as the project progressed.

The Air Force completed the definitive $5,315,000 contract for North American on 11 June 1956. The contract included three X-15 research airplanes, a full-scale mockup, various wind-tunnel models, propulsion system test articles, preliminary flight tests, and the modification of a B-36 carrier aircraft. The costs did not include government-furnished equipment, such as the engine, research instrumentation, fuel, and oil, or expenses to operate the B-36. The delivery date for the first X-15 was 31 October 1958.[1] [2] [3] [4] [5]™

All parties signed the final contract for the major piece of government-furnished equipment, the Reaction Motors engine, on 7 September 1956. The "propulsion subsystem" effort became Project 3116, which was carried on the books separately from the Project 1226 airframe. The final $10,160,030 contract, plus a fee of $614,000, required Reaction Motors to deliver one engine and a full-scale mockup. Amendments to the contract would cover the procurement of additional engines.-11719

Aircraft, 29 July 1954. In the files at the AFMC History Office; memorandum, E. C. Phillips, Chief, Operations Office, Power Plant Laboratory, to Director of Laboratories, WADC, subject: NACA Conference on 9 July 1954 on Research Aircraft-Propulsion System, 5 August 1954; letter,

Colonel Victor R. Haugen, Director of Laboratories, WADC, to Commander, ARDC, subject: new research aircraft, 13 August 1954. In the files at the ASD History Office; memorandum, J. W. Rogers, Liquid Propellant and Rocket Branch, Rocket Propulsion Division, Power Plant Laboratory, to Chief, Non-Rotating Engine Branch, Power Plant Laboratory, WADC, subject: conferences on 9 and 10 August 1954 on NACA Research Aircraft-Propulsion System, 11 August 1954. In the files at the AFMC History Office.

On 8 June, John Sloop at Lewis submitted the preliminary NACA engine results to Hartley Soule. The rankings were 1) XLR81, 2) XLR30, and 3) XLR73. Lewis also commented on various aspects of the airframe proposals, including propellant systems, engine installation, reaction controls, APUs, and fire extinguishing systems, although it drew no conclusions and did not rank the airframe competitors. The airframe manufacturers had concentrated on two of the possible engines: Bell and Republic opted for the Bell XLR81, while Douglas and North American used the Reaction Motors XLR30. Bell had also included an alternate design that used the XLR30 engine. Nobody had proposed using the Aerojet XLR73.[12]

The Power Plant Laboratory believed that minimum thrust was a critical factor. Reaction Motors indicated that its engine was infinitely variable between 30% and 100% thrust. The Bell engine, however, only had thrust settings of 8,000 and 14,500 lbf. However, since the Bell engine had to be used in multiples to provide sufficient thrust for the research airplane, this meant that the equivalent minimum thrust was 18% for the Bell design (which used three engines) and 14% for the Republic airplane (four engines). Initially, the engine evaluation set the desired lower thrust figure at 25%, resulting in a lower score for the Reaction Motors engine. The X-15 Project Office subsequently raised the lower throttle setting to 30%, and the evaluators then ranked the Reaction Motors engine as slightly better.-113

During the initial evaluation the Power Plant Laboratory found little difference between the Bell and Reaction Motors proposals except for the throttling limits, but the report left the impression that the Air Force favored the Bell design. Statements such as "the Bell engine would have potential tactical application for piloted aircraft use whereas no applications of the RMI engine are foreseen," and "in the event that the XLR73 development does not meet its objectives, the Bell engine would serve as a ‘backup’ in the Air Force inventory" made the laboratory’s feelings clear.-14 Of course, the idea that rocket engines potentially could be used in operational manned aircraft quickly waned as jet engines became more powerful, and this became a moot point.

The final meeting at Wright Field on 14-15 June finalized the ground rules for the engine evaluation. The engine companies attended the early portion of the meeting to present preliminary results from their proposals. The ground rules established by the Air Force, Navy, and NACA representatives included three major areas of consideration: 1) the development capability of the manufacturer, 2) the technical design (including the design approach and the research utility), and 3) the cost.13

On 24 June 1955, NACA Lewis issued a revised ranking of the engine competitors. From a technical perspective (not considering management and other factors), the Lewis rankings were now 1) XLR30, 2) XLR81, and 3) XLR73. The reason given for reversing the rankings of the XLR30 and XLR81 was a shift in the engine-evaluation ground rules. Previously researchers rated the XLR30 lower because of its unsatisfactory throttling limits, but new ground rules relaxed the requirements and elevated the engine’s ranking.

There still seemed to be some confusion over the engine-evaluation process, and yet another meeting at NACA Headquarters on 27 June attempted to ensure that everybody was on the same page. The meeting ended with an understanding that the engine evaluation should determine whether any of the engines was unsuitable for use in the airplane, or whether any engine was so clearly superior that it should be selected regardless of the choice of the winning airframe contractor. If neither of these conditions existed, then whichever engine the airframe contractor selected would be chosen. This was the same conclusion reached previously on 14-15 June, and all of the attendees appeared to be satisfied with the result.-1161

On 1 July, the HSFS sent its engine evaluation to Hartley Soule, ranking the power plants as 1) XLR30, 2) XLR73, and 3) XLR81. The transmittal letter, however, expressed concern about "the lack of development of all three of the proposed engines." Walt Williams again strongly recommended an interim engine for the initial flights of the new research airplane (he suggested the Reaction Motors LR8 based on previous HSFS experience). Since the early flights would be primarily concerned with proving the airworthiness of the airplane, they would not need the full power provided by the final engine. The HSFS believed that the development of the new engine would take longer than most expected, and using an interim engine would allow the flight-test program to begin at an earlier date. To minimize the hazards to personnel and instruments, researchers at the HSFS also recommended that Reaction Motors change the fuel for the XLR30 from anhydrous ammonia to gasoline or jet fuel.13

The Air Force evaluation group pointed out that using two fuels interchangeably in the Bell gas

generator systems would overly complicate the fuel system. The use of a separate system to meet the restart requirement was also expected to create safety and reliability problems. On the other hand, although the Reaction Motors engine was more orthodox than the Bell design, the company had not yet performed many tests on it, and the evaluators correctly predicted that it would have a difficult development. The evaluators noted that both engines would need substantial development being man-rated.-1181

A meeting at Wright Field on 6-7 July attempted to sort out the engine selection. De Beeler, John Sloop, and Arthur Vogeley represented the NACA, Oscar Bessio represented the Navy, and Joseph Rogers led the Air Force contingent. The representatives from the Power Plant Laboratory indicated a preference for the XLR73, with the XLR81 as their second choice, but the NACA participants argued that finishing the development of the Aerojet engine would consume a great deal of time. The Navy considered the XLR30 the best (not surprisingly, since it was a Navy engine), followed by the XLR81. The XLR73 was not considered worthy of further consideration because of unspecified "extremely difficult development problems."

The final evaluation report stated that none of the engines was clearly superior or deficient, and therefore the airframe contractor would select the most advantageous engine. The XLR73 was effectively eliminated from the competition since none of the airframe proposals used it, although the Power Plant Laboratory supported the continued development of the XLR73 for other uses.

The elimination of the XLR73 was ironic because, of the engines under consideration, only the Aerojet XLR73 was a fully funded development engine, and it was the only one that, theoretically at least, would not have entailed additional costs. The evaluators felt that the development timeline of the Bell engine better matched the program schedule by a small margin. The Bell cost estimate was $3,614,088 compared to $2,699,803 for Reaction Motors. Both were hopelessly optimistic.-191

In the last portion of the report, the Power Plant Laboratory presented its minority opinion justifying its choice of the XLR73 rocket engine, and the NACA included a recommendation to use an interim powerplant, specifically the Reaction Motors LR8-RM-8, for the initial X-15 flight program until the final powerplant was ready.191

Jack McKay conducted a short lake survey in late March 1961 to investigate possible launch lakes for the maximum speed flights. During this trip he visited Tonopah, Nevada, on 22 March to discuss communication requirements, refueling capabilities, and storage requirements. The officer in charge of the Tonopah site stated that F-104 proficiency flights would not be a problem. A 500-gallon fuel truck was available with 91-octane gasoline to refuel H-21 helicopters. The pilot would sign a Form 15, committing the AFFTC to reimburse Tonopah for the fuel. Storage facilities at the airport were limited to a small U. S. Navy installation that consisted of one small, corrugated-metal building leased to the Atomic Energy Commission for the storage of classified materials. However, a fenced area around the building appeared suitable for securing X-15 support equipment if necessary. The manager of the civilian airport informed McKay that 91- octane fuel was available for purchase from a 2,000-gallon fuel truck.-104-

McKay also visited Smith Ranch Lake, located 100 miles north-northwest of Mud Lake. The Air force initially acquired this site as a backup to Wah Wah Lake and removed a total of 25,000 acres from the public domain, although some privately owned land also existed on the southwest portion of the lakebed. A five-mile-long runway was marked on a heading of 025-205 degrees. McKay also investigated the use of Edwards Creek Valley Dry Lake, 26 miles northwest of Smith Ranch during the March 1961 trip, but took no further action.-105-

The increased performance of the "advanced X-15" (the X-15A-2) and its use of recoverable drop tanks necessitated that NASA and the AFFTC acquire rights to additional property. All of this land was in Nevada. Most of it was owned by the federal government, and a great deal of it was already out of the public domain.-106-

The X-15A-2 would use drop tanks on the high-speed flights, something that researchers had not anticipated for the original X-15 flight program. The X-15 jettisoned the tanks at approximately Mach 2.1 and 65,000 feet. After some free-fall, the parachutes opened at 15,000 feet and lowered the empty tanks to the ground. With the chutes deployed, the heavier tank had a descent rate of 25 feet per second (17 mph), while the lighter tank fell at 20 fps (14 mph). A helicopter recovered the tanks and placed them on flatbed trucks for the trips back to Edwards. Obviously, the program could not allow the tanks to fall onto civilians or their property. The possible impact areas for the tanks were quite large due to possible dispersions in the X-15 flight conditions at the time of tank jettison, as well as unknown wind effects.-107-

Despite its increased performance potential, the initial of the acceleration of X-15A-2 with full external tanks was considerably less than that of the standard X-15. This caused a reevaluation of the emergency lake coverage for flights with external tanks. Flight planners Robert G. Hoey and Johnny G. Armstrong used the AFFTC X-15A-2 hybrid simulator to conduct a parametric study of the glide capability of the aircraft for different engine burn times along the design profile to 100,000 feet. This study concluded that, of the originally selected launch points, only Mud Lake was suitable for flights using the external tanks. However, since Mud Lake was only 215 miles from Edwards, it was not suitable for the high-speed flights that required more distance. The use of Smith Ranch as a launch point was desirable, but unfortunately the distance between Smith Ranch and Mud Lake was too great for the glide capability of the airplane, and thus for a period of time X-15A-2 would have been without a suitable landing site. NASA wanted to find a usable lake between Smith Ranch and Mud Lake to fill the gap.

NASA conducted a new survey in May 1965 and again focused on Edwards Creek Valley Dry Lake, something that Jack McKay had mentioned as early as March 1961. This lake was 23 miles northwest of Smith Ranch; in a change of rules, there would be no plan to land at Edwards Creek, even in the event the engine failed to ignite immediately after launch. The lake did not provide the desired emergency coverage, but allowed a straight-in approach to Smith Ranch if an engine shutdown occurred at the worse possible time. In addition, if an emergency occurred at the time of tank ejection, the pilot could always land at Smith Ranch.-108

Johnny Armstrong carried out a further analysis of X-15A-2 flight profiles in early 1965 using the hybrid simulator. For instance, Armstrong studied the glide capability of the X-15A-2 by terminating engine thrust at different times along the Mach 8 profile. For X-15A-2 flights with external tanks, there were two critical points along the flight profile with regard to emergency landing sites. The first point was the decision to either to continue straight ahead to a forward landing site or initiate a turn to a landing site behind the airplane. The geographical location of potential emergency landing sites determined the length of this period. Second, the flight planners had to consider emergency lake coverage from the tank drop point. In all cases, it was desirable to arrive at the emergency landing lake at an altitude of 20,000 feet or greater.109

In his preliminary study the previous summer, Armstrong had concluded that launches from Mud Lake needed to be conducted from the east side of the lake because of external tank impact considerations, and this condition still held true. If a pilot was considering contingency landing sites, the critical time for a launch from Mud Lake was after 53 seconds of engine thrust; at that point it was possible to either continue forward to Grapevine Lake or turn around and land at Mud Lake. If the pilot elected to continue forward, he would arrive at Grapevine at an altitude of 43,000 feet. Returning to Mud Lake would result in an altitude of 11,000 feet (or 6,000 feet above Mud Lake).118

The simulations also showed that adequate emergency lake coverage was not available for a Smith Ranch launch. There was a period of 29-31 seconds (depending upon the exact launch point) during which the X-15 could not go forward or turn around and arrive at the emergency landing site at 20,000 feet altitude. Worse, there was a period of 4-7 seconds in which it was not even possible to arrive at the emergency lakes at 5,000 feet altitude. In other words, given that Mud Lake was at 5,000 feet altitude, the pilot could not even make a straight-in approach if the engine shut down during the critical time. Additionally, if the engine shut down during external tank separation, the X-15A-2 could not go forward to Mud Lake and would have to return to Smith Ranch, arriving with only 5,000 feet altitude.111

The use of Edwards Creek Valley as a launch lake allowed the pilot to attempt a straight-in approach at either Smith Ranch or Mud Lake if the engine shut down at a critical time. There was even a small period in which the pilot could elect to abort to either lake. Once the pilot jettisoned the tanks, he could turn the airplane back to Smith Ranch, arriving at 5,000 feet. Given this analysis, the program decided that X-15A-2 high-speed flights would proceed from either Mud Lake or Edwards Creek Valley. The tank recovery area for Mud Lake launches was entirely within Restricted Area R-4907 and posed only minor problems for securing use rights; however, the Air Force needed to acquire use rights for civilian property in the anticipated drop areas for Edwards Creek Valley (and Smith Ranch) launches.-1112!

based on two considerations: first, the airplane had slightly better gliding performance than anticipated, eliminating most of the gaps in emergency lake coverage from Smith Ranch; second, there had been some difficulties obtaining adequate external tank drop areas from Edwards Creek Valley. As it turned out, there never were any launches from Edwards Creek Valley since the X – 15A-2 program stopped at Mach 6.7 instead of proceeding to Mach 8. Of the four flights with external tanks, the program launched the first (with empty tanks) from Cuddeback, and the three flights with full tanks from Mud.113

Rogers Dry Lake was the designated landing site for all flights. Initially, the runways on Rogers were marked in typical fashion, showing left and right extremes, and thresholds on each end. A meeting of the original X-15 pilots on 19 October 1960 established a standard operational procedure for releasing the ventral stabilizer before landing. North American decided the pilots should jettison the ventral below 800 feet altitude and less than 300 knots to ensure recovery in a reusable condition. The pilots established that if the touchdown point on runway 18 (the most frequently used) was two miles from the north end, then the ideal jettison queue would be when the pilot passed over the railroad tracks located one mile from the end of the runway. The pilots asked Paul Bikle to request the AFFTC to mark all Rogers runways with chevron patterns one mile from each end (to indicate the ventral jettison point), and also two miles down each runway (to indicate the touchdown point). The program subsequently adopted these markings for most of the lakebed runways.-114

The markings on the lakebed were not paint, but a tar-like compound on top of the soil. The Air Force standardized the runways at 300 feet wide and at least 2 miles (often 3 miles) long. The tar strips outlining the edges of the runways were 8 feet wide. The width of the strips was critical because they provided a major visual reference for the pilot to judge his height (many of the lakebeds were completely smooth and provided no other reference). The chevron patterns were marked at the appropriate places on each lakebed with the same compound. The Air Force was responsible for keeping each of the active lakebeds marked, and laid new tar at least once per year after the rainy season. If the pilots complained the markings were not visible enough during the approaches practiced in the F-104s, the Air Force would re-mark the runway. As Milt Thompson remembered, "over the years, the thickness of the tar strips increased with each new marking until they exceeded 3 or 4 inches in height____________________ "1^115!

The FRC was primarily responsible for checking the lakebeds during the course of the flight program. As often as not, this involved landing the NASA DC-3 on the lakebed for a visual inspection (usually performed by Walter Whiteside riding a motorcycle). If the lakebed appeared damp, the pilot of the DC-3 would make a low pass and roll its wheels on the surface, making sure not to slow down enough to become stuck. He would then fly a slow pass and observe how far the wheels had sunk in the mud. If the DC-3 was not available, the pilots used a T-33 or whatever other airplane they could get, although obviously they could not carry the motorcycle in those instances. On at least one occasion, the pilots (Neil Armstrong and Chuck Yeager) became stuck in the mud when the lakebed turned out to be softer than they had anticipated.-116

The National Park Service declared Rogers Dry Lake a national historic landmark because of its role in the development of the nation’s space program. Since 1977, NASA has used the lakebed as a landing site for many Space Shuttle test and operational flights.-117!

Despite the time and effort spent on locating, acquiring, and marking many launch and intermediate lakes, none of the X-15 pilots had any real desire to land on any of them, although several did. The pilots considered a landing at the launch lake or an intermediate lake an emergency, while landing on Rogers Dry Lake was normal. Both were deadstick landings, so what

was the difference? Milt Thompson summed it up well in his book: "[Rogers] was where God intended man to land rocket airplanes. It was big. It had many different runways. It was hard. It had no obstructions on any of the many approach paths. It had all of the essential emergency equipment. It was territory that we were intimately familiar with and it had a lot of friendly people waiting there." In other words, it was home.-1118!

As it happened, John Stack had already considered other alternatives. The idea of a modern research airplane—one designed strictly to probe unknown flight regimes—came in a 1933 proposal by Stack. On his own initiative, Stack went through a preliminary analysis for "a hypothetical airplane which, however, is not beyond the limits of possibility" to fly well into the compressibility regime. Stack calculated that a small airplane using a 2,300-horsepower Rolls – Royce piston engine could obtain 566 mph in level flight—far beyond that of any airplane flying at the time. Ultimately, the NACA did not pursue the suggestion, and it would be another decade before the idea would come of age.-131

Ezra Kotcher at the Army Air Corps Engineering School at Wright Field made the next proposal for a high-speed research airplane. In 1939 Kotcher pointed out the unknown aspects of the transonic flight regime and the problems associated with the effects of compressibility. He further discussed the limitations of existing wind tunnels and advised that a full-scale flight research program would be an appropriate precaution. By early 1941 John Stack had confirmed that data from wind tunnels operating near Mach 1 were essentially worthless because of a choking problem in the test section. He again concluded that the only way to gather meaningful data near the speed of sound would be to build a vehicle that could fly in that regime. Again, no action resulted from either Kotcher’s or Stack’s suggestions and determining the effects of compressibility on airplanes remained a largely theoretical pursuit.-141

The real world intervened in November 1941 when Lockheed test pilot Ralph Virden died trying to pull a P-38 Lightning out of a high-speed dive that penetrated well into the compressibility regime. By 1942 the diving speed of the new generation of fighters exceeded the choking speed of the wind tunnels then in use. Researchers increasingly supported the idea of an instrumented airplane operating at high subsonic speeds. Those involved do not remember that any one individual specifically championed this idea, but John Stack soon became the chief Langley proponent.151

Interestingly, there was little interest within the NACA in flying through the sound barrier. It appeared that one of the early turbojet engines could push a small airplane to about Mach 0.9, but the only near-term way to go faster was to use a rocket engine—something that was considered too risky by the NACA.

A posed group portrait of early X-planes at the NACA High-Speed Flight Station in August 1953. Clockwise from the bottom are the Douglas D55-1, Douglas D-558-2, Northrop X-4, Convair XF-92A, and Bell X-5. This group represents a wide variety of research programs, and only the D558-2 was a true high-speed airplane. (NASA)

The Army, however, wanted a supersonic airplane and appeared willing to accept rocket propulsion. In fact, Ezra Kotcher had listed this as an option in his 1939 proposal, and it became increasingly obvious that a rocket engine represented the only hope for achieving supersonic speeds in level flight in the near future.-1161

Possible Navy interest in the undertaking also appeared during 1942-1944. However, significant differences of opinion came to the forefront during a 15 March 1944 meeting of Army, NACA, and Navy personnel. The NACA thought of the airplane as a facility for collecting high-subsonic speed aerodynamic data that were unobtainable in wind tunnels, while the Army thought it was a step toward achieving a supersonic combat aircraft. The Navy supported both views, wanting to dispel the myth of the impenetrable sound barrier, but was also interested in gathering meaningful high-speed data. Despite the NACA’s concerns, the Army soon announced its intention to develop a rocket-powered research airplane.-1171

As John Becker remembers, "The NACA continued to emphasize the assumed safety aspects and relatively long-duration data-gathering flights possible with a turbojet engine compared to the short flights of any reasonably sized rocket plane. Furthermore, the turbojet would have obvious applicability to future military aircraft while the rocket propulsion system might not. This apparently irreconcilable difference was easily resolved; the Army was putting up the money and they decided to do it their way.’1181

The beginning of supersonic flight research likely occurred when Robert J. Woods from Bell Aircraft met with Ezra Kotcher at Wright Field on 30 November 1944. After they discussed the basic specifications, Kotcher asked Woods if Bell was interested in designing and building the airplane. Woods said yes, and in late December Bell began contract negotiations with the Army to build the rocket-powered XS-1 research airplane.-119

Melvin N. Gough, the chief test pilot at Langley, dismissed the rocket-plane concept: "No NACA pilot will ever be permitted to fly an airplane powered by a damned firecracker." When it became clear in early 1944 that the Army was going to insist on rocket propulsion, John Stack began lobbying the Navy to procure the type of airplane the NACA wanted. The Navy was more receptive to the turbojet-powered airplane, and the Navy Bureau of Aeronautics (BuAer) began negotiations with Douglas Aircraft for the D-558 Skystreak in early 1945.[20]

These were the beginnings of the cooperative research airplane program. In reality, until the advent of the X-15 there were two distinct programs: one with the Army and one with the Navy. Just because the NACA did not agree with the path the Army had elected to pursue did not mean the Agency would not cooperate fully in the development of the XS-1. The Navy enjoyed the same level of cooperation for the D-558. John Stack noted in 1951 that "the research airplane program has been a cooperative venture from the start…. The extent of the cooperation is best illustrated by the fact that the X-1, sponsored by the Air Force, is powered with a Navy-sponsored rocket engine, and the D-558-1, sponsored by the Navy, is powered with an Air Force-sponsored turbojet engine." [21]

Although it gave the appearance of having a rather simple configuration, the X-15 was perhaps the most technologically complex single-seat aircraft yet built. The airplane would require the development of the largest and most sophisticated man-rated rocket engine yet, and a heated debate took place regarding the escape system for the pilot. Given the extreme environment in which it was to operate, engineers had to either invent or reinvent almost every system in the airplane. North American’s Harrison A. "Stormy" Storms, Jr., and Charles H. Feltz had a difficult job ahead of them. Both men were widely admired by their peers, who considered them among the best in the business (a fact confirmed much later when both men played key roles during the development of the Apollo spacecraft).

Harrison Storms had studied aeronautical engineering under Theodore von Krmn at the California Institute of Technology during the 1940s before joining North American Aviation. He was chief engineer for the entire Los Angeles division, and although he was greatly interested in the X-15 he had other responsibilities that precluded daily contact with the X-15 program. Nevertheless, he would be a powerful ally when bureaucratic hurdles had to be overcome or the customer needed to be put at ease.-11!

Feltz had joined the company in 1940, working on the P-51 Mustang and B-25 Mitchell during World War II, and later the B-45 Tornado and F-86 Sabre. As the X-15 project engineer, Feltz would lead the day-to-day activities of the design team. In those days at North American, the project engineer was in charge of the entire work force assigned to his airplane. Surprisingly, the 39-year-old Feltz had never heard of the X-15 until Storms pulled him off the F-86 program to be the project engineer, meaning that he had not been involved in the proposal effort and needed to catch up. Fortunately, Storms and Crossfield were there to help.[2]

Charles H. Feltz had joined North American Aviation just before the beginning of World War II and had worked on several high-profile projects prior to being assigned as the lead of the X-15 development effort. Feltz would go on to lead North American’s Apollo Command and Service Module and Space Shuttle efforts. (Boeing)

Directly assisting Storms and Feltz was the already legendary NACA test pilot A. Scott Crossfield, who had joined North American specifically to work on the X-15. Crossfield had been a Navy instructor pilot stationed at Corpus Christi, Texas, during World War II before receiving a bachelor of science degree in aeronautical engineering and a master’s in aeronautical science from the University of Washington. Crossfield describes Storms as "a man of wonderful imagination, technical depth, and courage…with a love affair with the X-15. He was a tremendous ally and kept the objectivity of the program intact.." According to Crossfield, Charlie Feltz was "a remarkable ‘can do and did’ engineer who was very much a source of the X-15 success story." In 2001, Crossfield called Feltz "the flywheel of common sense engineering who educated the world with the X-15, Apollo, and the Space Shuttle.’,[3]

The day Crossfield reported for work at North American, he defined his future role in the program. As he recounted in his autobiography, "I would be the X-15’s chief son-of-a-bitch. Anyone who wanted Charlie Feltz or North American to capriciously change anything or add anything…would first have to fight Crossfield and hence, I hoped, would at least think twice before proposing grand inventions." He played an essential role, for instance, in convincing the Air Force that an encapsulated ejection system was both impractical and unnecessary. His arguments in favor of an ejection seat capable of permitting safe emergency egress at speeds between 80 mph and Mach 4, and altitudes from sea level to 120,000 feet saved significant money, weight, and development time. Crossfield also championed the development of a full- pressure suit for the X-15 pilot. f4!

There has been considerable interest in whether Crossfield made the right decision in leaving the NACA, since it effectively locked him out of the high-speed, high-altitude portion of the X-15 flight program. Crossfield had no regrets: "I made the right decision to go to North American. I am an engineer, aerodynamicist, and designer by training…While I would very much have liked to participate in the flight research program, I am pretty well convinced that I was needed to supply a lot of the impetus that allowed the program to succeed in timeliness, in resources, and in technical return.. I was on the program for nine years from conception to closing the circle in flight test. Every step: concept, criteria, requirements, performance specifications, detailed design, manufacturing, quality control, and flight operations had all become an [obsession] to fight for, protect, and share—almost with a passion." Crossfield seldom lacked passion.[5!

A. Scott Crossfield resigned as a NACA test pilot and joined North American Aviation specifically to work on the X-15 project. Although an accomplished test pilot with many rocket-powered flights under his belt, Crossfield was primarily an engineer and wanted to apply what he had learned to the most advanced research airplane of the era. Crossfield led the charge on keeping the escape system simple and the airplane reliable, and later proved his mettle by flying the X – 15’s first flights. (NASA)

Essential members of the North American team included assistant project engineers Roland L. "Bud" Benner, George Owl, and Raun Robinson. Others included powerplant engineer Robert E. Field, regulators and relief-valve expert John W. Gibb, chief of aerodynamics Lawrence P. Greene, project aerodynamicist Edwin W. "Bill" Johnston, and test pilot Alvin S. White. Storms remembers

that "Al White went through all the required training to be the backup pilot to Crossfield and trained for several years—and was not even allowed one flight; that’s dedication!" In addition, L. Robert Carman, who (along with Hubert Drake) developed one of the earliest NACA ideas for a hypersonic airplane, had left the NACA and joined North American to work on the X-15.-6

Years later Storms remembered his first verbal instructions from Hartley Soule: "You have a little airplane and a big engine with a large thrust margin. We want to go to 250,000 feet altitude and Mach 6. We want to study aerodynamic heating. We do not want to worry about aerodynamic stability and control, or the airplane breaking up. So, if you make any errors, make them on the strong side. You should have enough thrust to do the job." Added Storms, "And so we did."-7

Soon after the contract was awarded, Storms and Soule began to know each other much better as North American and NACA began to interact in technical and management meetings. Storms insisted that the contractor team members stay in their own area of responsibility and not attempt to run each other’s areas. Soule agreed with the approach and directed the NACA members similarly. At least initially, Storms and Feltz were somewhat surprised that Soule insisted on frequent meetings between small groups—seldom more than 10 to 12 people. Nevertheless, Storms remembers, "[S]urprisingly, we managed to get much accomplished, and we all left the meetings with a good concept of what had to be accomplished and when." In later years, Storms was appreciative of the work done by Soule, and in 1989 commented that "I can’t say enough about how well, in my opinion, Hartley did his job. He was a very outstanding program manager and has been greatly neglected in recognition."-8

When North American signed the final contract, the X-15 was some three years away from its first flight. Although most of the basic research into the materials and structural science was complete, largely thanks to the researchers at Langley, a great deal of work remained. This included the development of fabrication and assembly techniques for Inconel X and the new hot-structure design. North American and its subcontractors met the challenge of each problem with a practical solution that eventually consumed some 2,000,000 engineering man-hours. These included 4,000 hours logged in 15 different wind tunnels that provided more than 2 million data points.-9

The Air Materiel Command had excluded the Langley study as a requirement in the invitation-to – bid letter circulated to the airframe contractors. Nevertheless, the influence of the Becker study was evident in North American’s winning proposal. The North American vertical stabilizers used the thick-wedge airfoil developed by Charles McClellan, and the dihedral in the horizontal stabilizer had been a feature of the Langley configuration. In addition, North American used Inconel X and a multi-spar wing with corrugated webs.

One major difference between the Becker study and that of North American was that the latter used all-movable horizontal stabilizers, resulting in the elimination of separate elevators and ailerons. The "rolling tail" allowed the horizontal stabilizers to deflect differentially to provide roll control, or together for pitch control. During the proposal evaluation the government considered this a "potential risk," and several evaluators believed that it represented an overly complicated approach. However, the rolling tail allowed North American to eliminate the protuberances covering the aileron actuators in the thin wing, and allowed a generally simpler structure for the entire wing. Although the additional drag of the protuberances was of little concern, they would have created another heating problem.-^

instead of the separate tanks inside a semi-monocoque fuselage envisioned by Langley. The monocoque tanks were lighter and stronger than separate tanks, but challenged the designers to find ways to route plumbing, wiring, and control cables—hence the tunnels.-1111

In mid-October 1955, both Ames and the HSFS sent comments to Hartley Soule expressing concerns about the North American design. Ames wanted to change the structure of the wing leading edge, the fuselage nose, and the ventral stabilizer, as well as to add an augmentation system to help control longitudinal damping. Ames also suggested additional study into the overall shape of the fuselage and the location of the horizontal stabilizer. Further, as they had during the proposal evaluation, researchers at Ames continued to believe that North American had overly simplified the heat transfer analysis. The HSFS recommended changing the design dynamic pressure, the load factors, the wing leading edge, the aerodynamic and ballistic control systems, the propellant system, the landing procedure, and various crew provisions. Engineers at the HSFS took this opportunity, again, to recommend using an interim LR8 engine during the early flight tests.1121

These and other concerns about the North American configuration prompted a meeting at Wright Field on 24-25 October 1955 that was attended by representatives from North American, Reaction Motors, the Air Force, and the NACA. The Navy did not attend. Subsequent meetings at the North American Inglewood plant took place on 27-28 October and 14-15 November; again, the Navy was not in attendance. Major discussion items included the fuselage tunnels and rolling tail. NACA researchers worried that vortices created by the side tunnels might interfere with the vertical stabilizer, and suggested making the tunnels as short as possible. North American agreed to investigate the tunnels’ effects during an early wind-tunnel model-testing program. The company also assured the government that the rolling tail had proven effective in wind-tunnel testing and appeared to offer significant benefits with few, if any, drawbacks.1131

In early November, Bill Johnston and members of the North American aerodynamic staff met with John Becker, Arthur Vogeley, and Hartley Soule to discuss NACA wind-tunnel support for the X – 15. North American proposed acquiring data at Mach numbers between 0.7 and 3.5 with a 1/10- scale model in the Ames Unitary Tunnel. High-speed information, obtained between Mach numbers 3.0 and 6.3, would come from a 1/50-scale model in the Ames 10 by 14-inch hypersonic tunnel. The use of Ames was logical because it was nearer to the North American facilities than Langley, and in the days of travel by car or piston-powered airliners, distance counted. John Becker and his staff believed that more tests were required, and proposed two different programs depending upon which facilities were available:1141

Not surprisingly, these tests were concentrated in Langley facilities. The meeting also covered dynamic stability tests, but researchers agreed that the desirability of such tests would be determined after information from Mach 5 flights at the PARD was evaluated. Two models would be tested—one based on the original Langley configuration, and the other based on the North American configuration. North American wanted to obtain the 1/50-scale results quickly to incorporate them into the 1/15-scale model used to test speed brake and control surface hinge moments.-151

The new rocket engine also came under scrutiny. Meetings held during early November among the HSFS, Lewis, and Reaction Motors included discussions about converting the XLR30 from anhydrous ammonia to a hydrocarbon fuel (JP-4 or kerosene). An earlier analysis had allowed Lewis to determine that the thrust and specific impulse would be almost identical between the two fuels. Lewis pointed out that pressure gages containing copper consistently failed within six months when used in a test cell with anhydrous ammonia, even though the gages were never in direct contact with the fuel. Researchers suggested converting the XLR30 to JP-4 to eliminate the perceived toxicity, corrosion, and handling problems entailed by the use of ammonia. Lewis also recommended that North American actively participate in the engine development program to ensure airframe compatibility. The researchers further suggested that a large number of engine parameters in the aircraft and on the ground should be recorded during each flight, and the engine should not be throttled below 50%.[16]

At the same time, John Sloop at Lewis wrote to Hartley Soule seconding the HSFS’s recommendation to use the LR8 as an interim engine for the initial flight tests. It was already evident that the airframe would be ready long before the engine. For its part, Reaction Motors believed that using the LR8 made a great deal of sense since the early flights would need little power, and it might be difficult to throttle the larger engine to such low levels.-1171

On an almost humorous note, it appears that when the issuing agency wrote the contracts for North American and Reaction Motors, it did not understand that North American had proposed to use integral propellant tanks for their X-15 design. The contracts stated that the engine manufacturer would supply the entire propulsion system, including the necessary propellant tanks. This resulted in some initial concerns over what parts of the propulsion system would be provided by which contractor. It obviously made no sense for Reaction Motors to provide major structural pieces of the airframe. A meeting on 7 November resulted in North American agreeing to furnish all of the tanks for the propulsion system, while Reaction Motors would supply all of the necessary valves and regulators. At the same meeting, everybody agreed that Reaction Motors would supply 12 engines for the program, subject to a contract modification from the Air Force to provide funds. Of these, two would be used for testing (one a spare), and one equivalent engine would be used as component spares, leaving nine engines for the flight program. As it turned out, the government later purchased a few more.-18

During late October 1955, the Air Force notified Reaction Motors that the winning North American entry in the airframe competition was the one that used the XLR30. On 1 December, the New Developments Office of the Fighter Aircraft Division directed the Power Plant Laboratory to prepare a $1,000,000 letter contract with Reaction Motors. However, at the same time the Power Plant Laboratory was further questioning the desirability of the Reaction Motors engine. During preliminary discussions with Reaction Motors, researchers from the NACA expressed concern that anhydrous ammonia would adversely affect the research instrumentation, and again brought up the possibility of converting to a hydrocarbon fuel. The Power Plant Laboratory did not support the change. Even during the initial evaluation the laboratory had not really believed the 2.5-year development estimate, and thought that was at least 6 months short. Changing the propellants would cost at least another year. The laboratory felt that if a 4-year development period was acceptable, the competition should be reopened, since anything over 2.5 years had been penalized during the original evaluation.111

Headquarters proposing to develop the X-15 engine as a continuation of the three years already spent on the XLR30. The admiral believed this arrangement would expedite development, especially since the Navy already had a satisfactory working relationship with Reaction Motors.

The Navy could also make the Reaction Motors test stands at Lake Denmark available to the X-15 program.[22]

On 9 December, Air Force Headquarters forwarded the letter to General Marvin C. Demler, commander of the ARDC. Demler forwarded the Navy request to the Power Plant Laboratory and X-15 Project Office for comment. On 29 December, ARDC Headquarters and the X-15 Project Office held a teletype conference (the predecessor of today’s conference call) to develop arguments against BuAer retaining the engine program. Demler summarized these and forwarded them to Air Force Headquarters on 3 January 1956. The ARDC rejected the Navy position because it felt a single agency should have management responsibility for the entire X-15 program. The Air Force argued that it was already familiar with the XLR30 and was well experienced in the development of man-rated rocket engines, such as the XLR11 (ignoring the fact that it was a derivative of the Navy XLR8). The Air Force also pointed out that it was already using the Reaction Motors at Lake Denmark. These arguments apparently put the matter to rest, since no additional correspondence on the subject seems to exist.[23]

Reaction Motors submitted this technical proposal on 24 January 1956, followed by the cost proposal on 8 February. The company expected to deliver the first engine "within thirty (30) months after we are authorized to proceed." Reaction Motors assigned the new engine the TR- 139 company designation. The Air Force also realized the engine needed a new designation, and on 21 February it formally requested assignment of the XLR99-RM-1 designation. This became official at Wright Field on 6 March and received Navy approval on 29 March. The Reaction Motors cost proposal showed that the entire program would cost $10,480,718 through the delivery of the first flight engine.[24]

During all of this, the NACA was becoming increasingly worried over the seemingly slow progress of the procurement negotiations. On 15 February, the deputy commander for development at the WADC, Brigadier General Victor R. Haugen, wrote to reassure Hugh Dryden that the process was progressing smoothly. Haugen reminded Dryden that one month of delay had been caused by the necessary studies associated with the NACA’s suggestion to change from anhydrous ammonia to a hydrocarbon fuel. Haugen assured Dryden that the procurement agency would issue a letter contract no later than 1 March. As it turned out, his letter was sent the day after the Reaction Motors letter contract had been signed.-125

Although most histories consider the development of the three flight vehicles the high mark of the X-15 program, in reality several ancillary areas were perhaps as important as the actual airplanes and left a more lasting legacy. Early in the program, engineers recognized the need for a carrier aircraft, although this was largely an extension of previous X-plane practice. Nevertheless, the two Boeing B-52s used by the X-15 program would go on to long careers carrying a variety of vehicles that researchers had not even dreamed of during the X-15 development. Most important, however, was the development of extensive engineering and mission simulation systems.

Although it was crude by today’s standards, the X-15 pioneered the use of simulators not just to train pilots, but also to engineer the aircraft, plan the missions, and understand the results. Not surprisingly, given the involvement of Charlie Feltz, Harrison Storms, and Walt Williams in both the X-15 and Apollo programs, the X-15 pointed the way to how America would conduct its space missions. Simulation is one of the enduring legacies of the small black airplanes.

SIMULATIONS

Immediately after World War II, the Air Force developed rudimentary simulators at Edwards AFB for the later phases of the X-1 and X-2 programs. In fact, an X-1 simulation powered by an analog computer led to an understanding of the roll-coupling phenomena, while another simulation accurately predicted the X-2 control problems at Mach 3. The importance of these discoveries led the NACA HSFS to acquire an analog computer capability in 1957, mostly because the engineering staff anticipated that simulation would play an important role in the upcoming X-15 program.-11