Category X-15 EXTENDING THE FRONTIERS OF FLIGHT

Although they had one of the most ideal test locations in the world, the Air Force and NACA could not simply go out and begin conducting X-15 operations. Several hurdles had to be overcome before the X-15 could ever do more than just conduct short flights over the Edwards reservation.

It had been recognized early during planning for the X-15 flights that suitable contingency landing locations would need to be found in the event of an abort after separation from the B-52 carrier aircraft, or if problems during the flight forced the pilot to terminate the mission before reaching Edwards. Since North American had designed the X-15 to land on dry lakebeds, the logical course of action was to identify suitable lakebeds along the flight path-in fact, these

lakebeds had been one of the factors used to determine the route followed by the High Range.

The Air Force and NACA had to identify lakebeds that would enable the X-15 to always be within gliding range of a landing site. In addition, the flight planners always selected a launch point that allowed the pilot a downwind landing pattern. Normally, the launch point was about 19 miles from the lakebed runway and the track passed the runway 14 miles abeam. To establish the proper launch point, flight planners used the fixed-base simulator to determine the gliding range of the airplane, including both forward glides and making a 180-degree turn and returning along its flight path. Another consideration was that the flight planners needed to selected lakes that would provide an overlap throughout the entire flight.[69]

The first hurdle for the Air Force was to secure permission from the individuals and several government agencies that owned or controlled the lakebeds. Next was seeking permission from the Federal Aviation Agency (FAA-it became an administration later) to conduct flight operations over public land.

Although responsibilities concerning the lakebeds continued throughout the life of the X-15 program, there were several spurts of activity (two major and one minor) concerning them. The first occurred, logically enough, just before the beginning of the flight program when efforts began to secure the rights to the lakebeds needed for the initial flight tests. The second involved securing the lakes needed for the higher-speed and higher-altitude flights made possible by the introduction of the XLR99 engine. One final push later in the program tailored the set of lakes for the improved-performance X-15A-2 and its external tanks.

Eventually, 10 different launch locations would be used, including eight dry lakes: Cuddeback supported a single launch; Delamar was the most used, with 62 launches; Hidden Hills saw 50 launches; Mud hosted 34; Railroad was used for only 2; Rosamond was used for 17, Silver hosted 14, and Smith Ranch was used for 10. In addition, the Palmdale VOR (OMNI) hosted eight launches, and a single flight originated over the outskirts of Lancaster. Hidden Hills was usually the intended site for the abortive 200th flight. The vast majority of these flights (188) would land on Rogers Dry Lake. Two would land at Cuddeback, one at Delamar, four at Mud, one at Rosamond, one at Silver, and one at Smith Ranch. The X-15-3 broke up in flight and did not land on its last flight.[70]

Rosamond Dry Lake, several miles southwest of Rogers, offered 21 square miles of smooth, flat surface that the Air Force used for routine flight test and research operations and emergency landings. This dry lakebed had served as the launch point for many of the early rocket-plane flights at Edwards. It is also the first lakebed that most visitors to Edwards see, since the road from Rosamond (and Highway 14) to Edwards crosses its northern tip on its way to the main base area. Scott Crossfield would make the X-15 glide flight over Rosamond Dry Lake, and no particular permission was necessary to use Rosamond since the lakebed was completely within the restricted area that made up the Edwards complex. Unfortunately, the lake was only 20 miles away from the base, so it did not allow much opportunity for high-speed work.

The Rogers and Rosamond lakebeds are among the lowest points in Antelope Valley, and they collect seasonal rain and snow runoff from surrounding hills and from the San Gabriel Mountains to the south and the Tehachapi Mountains to the west. At one time, the lakebeds contained water year-round, but changing geological and weather patterns now leave them wet only after infrequent rain or snow. A survey of the Rosamond lakebed surface showed its flatness, with a curvature of less than 18 inches over a distance of 30,000 feet.[71]

Beginning in early 1957, North American, AFFTC, and NACA personnel conducted numerous evaluations of various dry lakes along the High Range route to determine which were suitable for X-15 landings. The initial X-15 flights required 10 dry lakes (five as emergency landing sites near launch locations, and five as contingency landing sites downrange) spaced 30-50 miles apart.^72

The processes to obtain permission to use the various lakebeds outside the Edwards complex were as diverse as the locations themselves. For instance, permission to use approximately 2,560 acres of land at Cuddeback Lake as an emergency landing location was sought beginning in early 1957, with first use expected in January 1959. The lakebed was within the land area reserved for use by the Air Force at George AFB, California, but the Department of the Interior controlled the lakebed itself. Since the Air Force cannot acquire land directly, officials at the AFFTC contacted the Los Angeles District of the Army Corps of Engineers, only to find out that George AFB had already requested the Corps to withdraw the land from the public domain. The Bureau of Land Management controls all land in the public domain, although control may pass to other government agencies (such as the military) as stipulated in various laws (U. S. Code Title 43, for example). At the time, the Corps of Engineers acted as the land management agent for the U. S. Air Force, and John J. Shipley was the chief of the real estate division for the Los Angeles District.

This map shows the general location of the lakebeds as well as the radar coverage afforded by the three High Range stations. The two primary restricted airspace areas are shaded, although the entire flight path of the X-15 was restricted on flight day. (Dennis R. Jenkins)

Officials at George intended to use the lakebed as an emergency landing site. In turn, on 17 May 1957 the Corps wrote to the Bureau of Land Management on behalf of the Secretary of the Air Force, requesting a special land-use permit for Air Force operations at the lake. When the Los Angeles District received the request from the AFFTC, Shipley contacted Lieutenant Colonel C. E. Black, the

installations engineer at George AFB, requesting that a joint-use agreement be set up that would permit sharing the lake with the AFFTC for X-15 operations.-1731

By the end of July 1959, the Bureau of Land Management had approved the permit, and George AFB had agreed in principle to the sharing arrangement. The special-use permit gave George AFB landing rights for several years, and permitted the lakebed to be marked as needed to support flight operations. John Shipley, very intelligently, decided that the joint-use agreement between the AFFTC and George was an internal Air Force affair and bowed out of the process after the issuance of the Bureau of Land Management permit. Although there seemed to be no particular disagreement, the joint-use agreement had a long gestation period. The special-use permit was granted at the beginning of August, but at the end of September Colonel Carl A. Ousley, the chief of the Project Control Office at the AFFTC, questioned why a written joint-use agreement had not been signed. Major Resiner at George replied on 14 October that he had received verbal approval from all parties, but written approval was required from two separate Air Force commands (the ARDC and the Tactical Air Command (TAC)), the Corps of Engineers, and the Bureau of Land Management. He foresaw no difficulties in obtaining the signatures, and apparently the process worked itself out within a suitable period since there appears to have been no further correspondence on the matter. The joint-use agreement with George AFB essentially stated that the AFFTC was responsible for any unique preparations and marking of the lakebed required to support X-15 operations, although George did offer to supply emergency equipment and personnel as needed.-741

Simultaneously with the request to use Cuddeback, the AFFTC issued a similar request for Jakes Lake and Mud Lake, both in Nevada. Originally, the X-15 program had wanted to use Groom Lake, Nevada, as a launch site instead of Mud Lake. However, the security restrictions in place at Groom Lake (also known as "The Ranch") to protect the CIA-Lockheed reconnaissance programs led the AFFTC and NASA to abandon plans to use this facility. Officials at Nellis suggested Mud Lake as a compromise between the needs of the X-15 program and the highly classified CIA programs.751

The AFFTC asked for approximately 2,500 acres of land in the public domain at Jakes Lake; at Mud Lake, the request was for 3,088 acres. The indefinite-term special-use permits sought the right to install fencing to keep cattle from grazing in certain areas. Several ranchers had grazing rights on the public domain land, so this required modifying these agreements and compensating the ranchers with Air Force funds. In this case the Air Force did not want to remove the land from the public domain, but it did want to use approximately 9,262 acres of land at Mud Lake that had already been withdrawn from the public domain for use as part of the Las Vegas Bombing and Gunnery Range.761

October 1957 for approval and funding. By the end of January 1958, however, Lieutenant Colonel Donald J. Iddins at the AFFTC began to worry that the process was taking too long. The X-15 needed the lakes in July 1959, and there was no evidence of final action. Part of the problem was that land actions involving over 5,000 acres (which the two actions together did) required approval from the House Armed Services Committee. The AFFTC reminded the chief of engineers that they did not want to remove the land from the public domain, which seemingly eliminated the need for congressional approval, and brought the situation to the attention of the X-15 Project Office during a management review at Wright Field on 5 February 1958. The result was a renewed effort to ensure that all three lakes (Cuddeback, Jakes, and Mud) were available for X-15 use on schedule, including the right to build roads to the lakes, marking approach and landing areas, and fencing certain areas if necessary to ensure the safety of the X-15.-177

On 14 February 1958, the chief of engineers responded that he had initiated the process to grant special-use permits, but had terminated the effort when he noted that the AFFTC wanted to fence off the land. However, the law did not permit fencing to be erected on special-use permitted land. This meant that the land would have to be withdrawn from the public domain after all, or go unfenced. It appears that the answer to the problem was obtained by the AFFTC agreeing to a reduction in the Mud Lake acquisition to just under 2,500 acres (versus the original 3,088), bringing the total to under 5,000 and circumventing congressional approval. This allowed the land to be withdrawn from the public domain, and some of it was fenced as needed to keep stray cattle from wandering onto the marked runway.-178

Simply getting access to the lakebeds was not always sufficient. For instance, Mud Lake was in the extreme northwest corner of Restricted Area R-271, meaning that Sandia Corporation, which controlled R-271 for the Atomic Energy Commission (AEC), had to approve its use. A "Memorandum of Understanding between the Air Force Flight Test Center and Sandia Corporation" allowed AFFTC support aircraft to operate in the immediate vicinity of Mud Lake during X-15 flights. The AFFTC had to furnish flight schedules to Sandia one week before each anticipated mission, and Sandia made the point that it had no radar search capability and could not guarantee that the area was clear of traffic. Sandia also agreed not to schedule any tests within the restricted area that might conflict with X-15 flights. Once approved by Sandia, the AFFTC sought additional approval from Nellis AFB since Mud Lake was also within the Las Vegas Bombing and Gunnery Range. This approval was somewhat easier to negotiate because it was obtained from another Air Force organization.-1791

On 3 November 1958, a team from the AFFTC visited Mud Lake to conduct a preliminary study of lakebed conditions and to determine what action would be required to clear areas of the lakebed for use as a landing strip. When the group from the Flight Test Operations Division and Installations Engineer Division arrived over the lake, the pilot made several low passes to orient the group and obtain a general knowledge of the various obstructions that might conflict with landing on the lakebed. What the group saw was a general pattern of obstructions running east to west in a straight line across the center of the lakebed. The team landed at the Tonopah airport and proceeded by car to the lake, 16 miles away, for a closer inspection.-1801

They found that the obstructions observed down the center of the lake were a series of old gunnery-bombing targets dating from World War II. Practice bodies, wooden stakes, and good­sized rocks used to form bull’s-eyes for bombing practice littered the lakebed. The targets were in a narrow straight band down the center of the lake from west to east, but the debris covered a considerably wider area. As would become standard practice on all the lakes, the group dropped an 18-pound steel ball from a height of 6 feet and measured the diameter of the resulting impression. This gave a good indication of the relative hardness of the surface and its ability to support the weight of the X-15 and other aircraft and vehicles. At the edges of the lake, the ball left impressions of 3.25 inches or so, while toward the center of the lake the impressions were only 2.25-3.0 inches in diameter. At the time, the Air Force believed that impressions of 3.125 inches or less were acceptable. The general surface condition of the lakebed varied from relatively smooth and hard to cracked and soft. Although it was not ideal, the group thought the lakebed could be made useable with minor effort.-1811

More lakebed evaluations followed on 13-14 July 1959. X-15 pilot Bob White and the AFFTC chief of flight test operations, Colonel Clarence E. "Bud" Anderson, used a Helio L-28 Super Courier aircraft to visit 12 dry lakes along the High Range route. At each lake, Anderson and White dropped the "imperial ball" from six feet and measured the diameter of the resulting impression.

By this time, the Air Force had changed the criteria slightly: a diameter of 3.25 inches was acceptable, and anything above 3.5 inches was unacceptable. The survey included an evaluation of the surface hardness, surface smoothness, approximate elevation, length and direction of possible runways, and obstacles. Anderson remembers that there was "only one lake where we had to make a full power go-around as we watched the tires sink as we landed." Many future surveys would take personnel from AFFTC, NASA, and North American to most of the larger dry lakes along the High Range route.-1821

In addition, on 13 July 1959, four FAA representatives and two members of the AFFTC staff held a meeting at the FAA 4th Region Headquarters in Los Angeles to discuss using Silver Lake as a launch site for the X-15. Since some of the X-15 flight corridor would be outside existing restructured airspace, FAA approval was necessary. The FAA claimed jurisdiction under Civil Aeronautics Regulation 60.24, but was anxious to assist the Air Force within the limits of the law. The Air Force intended to use Silver Lake launches for early X-15 flights with the XLR11 engines. The proposed 100-mile flight path consisted of Silver Lake, Bicycle Lake, Cuddeback and/or Harpers Lake, and then on to landing at Edwards. The FAA had no particular problem with the concept, but since its charter was to protect the safety of all users of public airspace, it believed that certain restrictions needed to be in place before the flights could be approved. The participants spent most of the meeting discussing possible operational problems and concerns, and then developing limitations or restrictions that mitigated the concerns.1881

For Silver Lake launches, both the launch and the landing were performed in a restricted airspace called a "test area." Silver Lake was inside Flight Test Area Four, while Edwards was at the center of Flight Test Area One. However, none of the test areas surrounding Edwards were restricted 24 hours per day, or seven days per week. In fact, they were open to civilian traffic most of the time, and their closure had to be coordinated with the FAA (the airspace immediately around Edwards was always closed to civilian traffic). In addition, the flight path from Silver Lake to Edwards would take the X-15 out of restricted airspace and into civilian airspace for brief periods. Future flights using the northern portion of the High Range would also be outside normal test areas. The FAA, therefore, needed to approve the plans and procedures for using that airspace.1841

On 1 September 1959, L. N. Lightbody, the acting chief of the General Operations Branch of the Los Angeles office (4th Region) of the FAA wrote to Colonel Roger B. Phelan, deputy chief of staff for operations at the AFFTC. The letter contained a "certificate of waiver covering the release of the X-15 research vehicle over Silver Lake" subject to some special limitations. The FAA imposed the limitations to ensure "maximum safety not only to your AFFTC personnel and equipment, but also to other users of the immediate airspace. Further, the communications requirements will insure the blocked airspace may be returned to its normal use with minimum delay." The FAA approved the certificate of waiver (form ACA-400) on 1 September 1959 and listed the period of waiver as 1

October 1959 to 31 March 1961, although it was subsequently extended to 1 July 1963, and later still through the end of 1969.[85]

Given the effort that accompanied the acquisition of Cuddeback Lake in late 1957 and early 1958, it is surprising that the first serious survey of the lake does not appear to have taken place until 7 October 1959. Of course, conducting detailed surveys significantly ahead of the anticipated use was not a particularly useful exercise since the periodic rains that kept the lakebeds useable also changed their character each time, as did the effects of other vehicles (such as cars). By this time, the X-15 had already made its first two flights from over Rosamond Dry Lake, landing each time at Rogers. Since the Air Force expected the X-15 to begin rapidly to expand its flight envelope, North American sent George P. Lodge to Cuddeback in an Air Force Piasecki H-21 Shawnee helicopter.1861

Lodge conducted the standard hardness tests by dropping the same "imperial ball" used in the other surveys. He found that the ball left an impression of about 3 inches (which was considered acceptable) at the southern end of the proposed runway, but quickly degraded to 4-4.5 inches by the northern end. He noted that these measurements compared unfavorably to tests on Rogers (2 inches) and Rosamond (2 inches) conducted after the last rains. A note emphasized that there were a set of deep ruts running the length of the runway made by a vehicle when the lake was wet, and that although it was only a single set of ruts, they "wander around to some extent." The nature of the lakebeds was such that grading or other mechanical methods could not repair major damage-only nature could do that. Lodge recommended that "Cuddeback lake, in its present condition, not be considered as an alternate landing site for the X-15 airplane and should be used only as a last resort in an extreme emergency." He warned that "should a landing be attempted with the X-15 airplane on Cuddeback lake in its present condition, there would be more than a 50-50 chance of wiping out the nose gear." It was clear that the lakes had both good and bad qualities: they were largely self-repairing each time it rained, but they could also be self­destroying by the same process.-1871

Two weeks later, Lodge, who was a flight safety specialist for North American, performed a survey of Silver Lake and nine other lakes to determine their suitability as emergency landing sites. At Silver, Lodge found that the prevailing wind was out of the north, with the best landing heading estimated at 200-310 degrees magnetic. The southern portion of the lake was soft with numerous sinkholes, and not satisfactory for touchdown. Lodge also found an abandoned railroad bed, approximately 2 feet high and 10 feet wide, running north to south across the east side of the lakebed. There was also a dirt road with deep ruts running east to west across the northern part of the lake, a paved road going from Baker to Death Valley along the eastern perimeter, and another dirt road (this time with no ruts) running diagonally northwest to southeast.-1881

Despite these obstacles, there was approximately 16,000 feet of satisfactory lakebed between the soft southern portion and the northern road. There were a few sinkholes, most measuring about 7 inches across and 3-4 inches deep, but the Air Force would fill these before use. The usual imperial-ball tests resulted in impressions between 2.9 and 3.7 inches in diameter, although the main area was on the lower end of that range. In addition, Lodge pounded both 3/8-inch and 1/2-inch steel rods into the ground with 200 pounds of force to determine what the condition of the soil was under the upper crust. The 3/8-inch rod generally penetrated between 1 and 3 inches, while the 1/2-inch rod penetrated between 0.25 and 1.5 inches. The results of the tests led Lodge to recommend a location for a marked runway. Of the other nine lakebeds visited,

Lodge landed only on the east and west lakes in the Three Sisters group, and determined that both were satisfactory for emergency use despite having "a few rocks and ammo links strewn 1891

about.

As 1959 ended, George Lodge was a busy man, and at the end of November he conducted yet another lake survey, this time of approximately 50 lakes in California, Nevada, and Utah. Again, the intent was to find suitable emergency landing sites for the X-15 as it expanded its flight-test program. The test methods Lodge used on the lakes were the same as he had used the previous month at Silver Lake.-90

The Air Force and NASA continued to survey the established and previously used lakebeds periodically, particularly after it rained to determine that the lakebed was dry enough to support operations and that no sinkholes or gullies existed. Changing the direction of the available runways on a lakebed also required a revised survey. For instance, in early December 1959 Lodge conducted a new survey of Rosamond Dry Lake to determine whether the lake would support a marked runway running northeast to southwest. Marked runways already existed on headings of 10-190 degrees and 70-250 degrees. Starting from a location in the southwest corner of the lakebed, Lodge inspected a heading of approximately 30 degrees, roughly toward the telemetry station located on the edge of the lake. He found that the lakebed was hard and smooth for 2 miles, moderately smooth at 2.5 miles, smooth again at 3 miles, moderately rough at 3.5 miles, and rough from 4 miles to the edge of the lakebed. Imperial-ball drop tests yielded diameters of about 2.5 inches across the route. The conclusion was that the runway was practical, and, as viewed from above, would result in a runway approximately halfway between the two existing runways, with all three converging at the southwest edge of the lakebed.-1911

The second round of lake acquisitions began when the XLR99 engine came on line. First up was securing rights to use Hidden Hills dry lake, slightly west of the Hidden Hills Ranch airstrip. Simulator studies had confirmed that Hidden Hills would be ideal as an emergency landing site during the launches for the initial XLR99 flights that needed to be conducted further uprange than the XLR11 flights. The lakebed would continue to be used as a contingency site as the program continued to launch further uprange into Utah. At the beginning of 1960, it was expected that the program would need access to the lake by 1 October 1960.[92]

However, schedules change, and the XLR99 flight dates kept slipping. A revised plan showed that the XLR99 research buildup flights would use Silver Lake and Hidden Hills Lake in California, Mud Lake in Nevada, and Wah Wah Lake in Utah as launch sites. The program needed various intermediate lakes along the upper portion of the High Range to provide complete coverage for emergency landings along the route. The Air Force would staff the intermediate lakes with crash and emergency personnel during flights. Additional contingency lakes would have runways marked on them, but would not be staffed with support personnel. At first the AFFTC and NASA had wanted to mark "all lakes with a satisfactory 10,000 feet landing surface" to provide an additional factor of safety for the X-15 program. Although no plans existed to use these lakes, the planners believed that marking them would also allow continued X-15 operation when a primary intermediate lake was wet. However, legal personnel indicated that there was "NO possibility" (emphasis in original) of marking any lake unless a right-to-use permit was obtained. Since personnel and funds did not exist to negotiate all the required permits, this plan was abandoned and a list of essential contingency sites was drawn up.[93]

The 30 September 1960 plan included launching immediate flights from Silver Lake, with the west lake at Three Sisters and Cuddeback acting as intermediate emergency sites. By 1 February 1961, operations would move to Hidden Hills, with Cuddeback as the intermediate site. On 1 April, Mud Lake would become the primary launch lake, with Grapevine and Ballarat as the intermediate sites, and contingency sites located at Panamint Springs and Racetrack. Two months later the launches would move to Wah Wah Lake, with Groom Lake, Delamar, and Hidden Hills becoming the intermediate sites, and Dogbone and Indian Springs the contingency sites. The AFFTC sought permission from Nellis to use the last two sites because they were located on the Las Vegas range, as was Mud Lake.[94]

Planners had always considered Smith Ranch Lake as a backup site to Wah Wah Lake, using Mud Lake as the intermediate site and the same contingency sites used during Mud Lake launches. This was still true at the end of February 1961. The program expected to begin launches from Hidden Hills in March 1961, and the launch lake still needed to be surveyed and marked. NASA expected to begin using Mud Lake in April 1961 and two of the support lakes (Grapevine and Panamint) still required use permits, while Ballarat had replaced Racetrack as the second contingency site. The program still needed to survey and mark all three of the support lakes. Launches from Wah Wah would begin in June 1961, and all of the sites along that route (except for Hidden Hills) still had to be "acquired," surveyed, and marked. As the program continued, however, it abandoned plans to use Wah Wah Lake, in part because of difficulties in obtaining permission to use the Nellis contingency sites (particularly Groom Lake) and airspace rights over Nevada’s restricted areas. Instead, the government eventually acquired the alternate launch site at Smith Ranch Lake, although flights from this point did not begin until June 1963.[95]

Determining if a lakebed could support the weight of an X-15 and its support airplanes was a relatively non-technical endeavor. A large steel ball, nicknamed the "imperial ball" was dropped from a height of six feet and the resulting impression was measured. For most of the program, a diameter of 3.25 inches or less was considered acceptable to support operations. Neil Armstrong is kneeling beside the ball in this June 1958 photo at Hidden Hills. (NASA)

I owe a particular mention of Jay Miller, author of the popular The X-planes: X-1 to X-45, (Hinckley, England: Midland Publishing, 2001), among many other works. Anybody interested in reading about the other X-planes should pick up a copy of this excellent book. Jay was responsible for the first photograph I ever had published, and published my first book—a short monograph on the Space Shuttle. Somehow, I feel I have him to blame for the quagmire of aerospace history I find myself embroiled in. I truly appreciate the help and friendship from Jay and his lovely wife Susan over the past 25 years or so.

Thankfully, my mother, Mrs. Mary E. Jenkins, encouraged me to seize opportunities and taught me to write and type—such necessary attributes for this endeavor. As for so many things, I owe her a great deal of gratitude, along with my everlasting love and admiration. After listening to my trials and tribulations about this project for a decade, she passed away before publication. I hope she has found the peace and rest she so richly deserves.

A note regarding terminology: In the days before being politically correct became a prime influence on engineering and history, engineers called piloted vehicles "manned" aircraft, and the process of making them safe enough to fly was termed "man-rating." This work continues to use these terms since they are what were in use at the time.

[1] The Armstrong quote is in the foreword to Milton O. Thompson, At the Edge of Space: the X – 15 Flight Program (Washington, DC: Smithsonian Institution Press, 1992), p. xii.

[2] John V. Becker, "The X-15 Program in Retrospect," 3rd Eugen Sanger Memorial Lecture, Bonn, Germany, 5 December 1968, pp. 1-2

[3] Harrison A. Storms, "X-15 Hardware Design Challenges," a paper in the Proceedings of the X – 15 30th Anniversary Celebration, Dryden Flight Research Facility, Edwards, California, 8 June 1989, NASA CP-3105, p. 27.

[4] In the 3rd Eugen Sanger Memorial Lecture in 1968, John Becker stated that 109 flights exceeded Mach 5. A reevaluation of the flight data shows that only 108 actually did. See Becker, "The X-15 Program in Retrospect," p. 3 for Becker’s original numbers.

[5] Despite all that is written, the program held very few "official" records, mainly because it seldom invited the FAI out to witness the flights. In fact, it appears that the 314,750-foot altitude record set by Bob White is the only official record ever set by the program.

[6] Ronald G. Boston, "Outline of the X-15’s Contributions to Aerospace Technology," 21 November 1977. Unpublished preliminary version of the typescript available in the NASA Dryden History Office. For those interested in Boston’s original paper, the easiest place to find a copy is in the Hypersonic Revolution, republished by the Air Force History and Museums program. It constitutes the last section in the X-15 chapter; Letter, William H. Dana, Chief, Flight Crew Branch, DFRC, to Lee Saegesser NASA History Office, transmitting a copy of the SETP paper for the file. A slightly rewritten (more politically correct) version of the paper was later published as The X-15 Airplane-Lessons Learned (American Institute of Aeronautics and Astronautics, a paper prepared for the 31st Aerospace Sciences Meeting, Reno Nevada, AIAA-93-0309, 11-14 January 1993). Boston listed 1,300°F as the maximum temperature, but Bill Dana reported 1,350°F in his SETP and AIAA papers. Boston also listed the max-q as 2,000 psf, but in reality it was 2,202 psf on Flight 1-66-111.

[Z] Storms, "X-15 Hardware Design Challenges," pp. 32-33

[8] Becker, "The X-15 Program in Retrospect," pp. 1-2

[9] J. D. Hunley, "The Significance of the X-15," 1999, unpublished. Typescript available at the DFRC History Office.

[10] Officially, Johnny Armstrong (who is now the chief engineer in the Hypersonic Flight Test Team) maintains the AFFTC Hypersonic Flight Test Team Project Files and is, fortunately, something of a pack rat. However, to everybody at Edwards and Dryden, this wonderful collection is simply the Armstrong Memorial Library.

The airframe evaluation process lasted from mid May until late July, with the Air Force, NACA, and Navy conducting independent evaluations based on a number of preestablished criteria. The preliminary NACA evaluation of the proposals consumed the better part of three weeks before each of the laboratories forwarded preliminary results to Hartley Soule. On 3 June 1955, Ames tentatively ranked the submissions as 1) Douglas, 2) North American, 3) Bell, and 4) Republic. The Douglas ranking resulted from "the completeness and soundness of design study, awareness of factors in speed and altitude regime, and relative simplicity of approach." Ames, however, expressed skepticism over the Douglas magnesium hot-structure wing because it would preclude the study of problems associated with insulated-type structures that would potentially be used in future aircraft intended for greater flight duration. This seemed to be a major disconnect between Ames and Langley. It appears that Ames wanted to test a structure that would be representative of some future production aircraft; Langley just wanted to test a structure that would survive.

Another problem that worried the Ames evaluators was the flammability of magnesium. It seemed that "only a small area raised to the ignition temperature would be sufficient to destroy the aircraft." The researchers at Ames held that if Douglas should win the competition, the company should build two aircraft with the proposed HK31 structure, but a third aircraft "should have a wing based upon the alternative higher temperature insulated type of design approach." The Ames report continued to stress the need for a wing of greater leading-edge sweep angle (at least 53 degrees) "for the purpose of minimizing the rate of heat transfer to the leading edge."145

At Langley, on 6 June, researchers rated the North American proposal number one, followed by Douglas, Bell, and Republic. According to the Langley assessment, led by John Becker, the research utility of the North American hot-structure approach outweighed the advantages of the simplicity of the magnesium structure proposed by Douglas. Slightly rebuffing Ames, Langley noted that the 21% reduction in heat transfer gained by increasing the leading-edge sweep from the proposed 40 degrees to 53 degrees did not seem to justify the alteration of the planform. This was particularly true because the structure appeared capable of handling the heat load.-1146!

In a reminder to the evaluation teams, also on 6 June, Arthur Vogeley and Captain McCollough reiterated that the purpose of the evaluation was "to select a contractor rather than a particular design." Although certain features of the winning design could be unsatisfactory, it was the basic design approach as described in the proposal that might best be relied upon to produce an acceptable research airplane.147-

On 10 June 1955, the HSFS sent its airframe results to Soule, detailing the design approach and research utility aspects of the airframe, flight control system, propulsion unit, crew provisions, handling and launching, and miscellaneous systems. Researchers at the HSFS ranked the proposals as 1) Douglas, 2) North American, 3) Bell, and 4) Republic, although the proposals from Douglas and North American were essentially equal.148

The final evaluation by Ames, on 10 June, ranked the proposals as 1) North American, 2) Douglas, 3) Bell, and 4) Republic. This represented a change from the earlier Ames evaluation, based largely on researchers considering the North American structure superior in terms of research utility—an opinion voiced earlier by Langley. The Ames evaluators had apparently changed their minds about wanting to test a production-representative structure. The laboratory had also finally given up on advocating an insulated structure since no serious support for their earlier recommendation of equipping the third aircraft with a different wing structure had materialized (sufficient funds to construct an alternate wing were simply not available).-1149-

The final evaluation from Langley on 14 June ranked the proposals as 1) North American, 2) Douglas, 3) Republic, and 4) Bell. Although researchers at Langley thought the magnesium wing structure of Douglas was feasible, they feared that local hot spots caused by irregular aerodynamic heating could weaken or destroy the structure. The use of Inconel X by North American presented an advantage with regard to thermal limits—not only from the standpoint of margins for maneuverability within the design temperatures, but also from a safety viewpoint if the airplane ever exceeded its design temperature.

A few days after receiving all of the final evaluations, Soule sent copies of each to the WADC Project Office, along with a consolidated result. The final NACA ranking was (points based on a scale of 100) as follows:150-

Oddly, the final order representing the overall NACA evaluation was 1) North American, 2)

Douglas, 3) Bell, and 4) Republic, despite the fact that Douglas scored slightly more points in the evaluation (152 versus 150 for North American). Soule pointed out that although Ames, Langley, and the HSFS did not rank the four proposals in the same order, the final ranking did represent an overall NACA consensus. All of the laboratories involved in this portion of the evaluation considered both the Douglas and North American proposals to be much superior to those submitted by Bell and Republic. While researchers preferred the Inconel X structure of the North American proposal, the design was not without fault. For instance, the NACA thought that the landing-gear arrangement was undesirable, the differentially-operated horizontal stabilator design in lieu of ailerons was an overly complicated arrangement, and (at least at Langley) the replaceable fiberglass leading edges were unacceptable.

John Becker wrote to Hartley Soule on 16 June attempting to clarify why the North American design was superior to that of Douglas. The letter listed the thermal limits expected for the new aircraft, and showed that the Inconel X structure on the North American design was "impressively superior" to the magnesium alloy used by Douglas. The data were shown for three categories: 1) performance within the design temperature limits in terms of allowable velocity, altitude, and dependence on speed brakes; 2) reserve heat capacity (in case the design temperatures were exceeded by a moderate margin) such that the structure would still have a fair possibility of remaining intact; and 3) the possibility of melting or burning in case the design temperatures were greatly exceeded in local hot spots. There appears to be no further correspondence on this subject, so Becker’s explanation seems to have answered whatever unasked questions existed.-1151-

During the first two weeks in July, the WADC evaluation teams sent their final reports to the WADC Project Office. As with the NACA evaluations, the Air Force found little difference between the Douglas and North American designs, point-wise, with both proposals considered significantly superior to those of Bell and Republic.

George Spangenberg was in charge of the Navy evaluations, which got off to a late start and ended up being cursory. In the end, the Navy found much the same thing as the NACA and ranked the airframe proposals as 1) Douglas, 2) North American, 3) Republic, and 4) Bell. Given the Navy’s long—and successful-association with Douglas airplanes, the order was not surprising. Most Navy concerns centered on the selection of an engine. As Clotaire Wood explained, "the airframe-engine combination was to be evaluated and not the engine alone, since it had been agreed that the engine of the winning design would be the engine supported by the special development program." This was not how the Power Plant Laboratory saw the process, but it seemed to put the Navy at ease. In addition, Wood indicated that "it would be of real value to have the Bureau’s [BuAer] recommendations regarding an engine development program once the winner of the competition is determined."-152

In early July the Navy began to raise questions about the various airframe proposals. For instance, the BuAer electronics group did not believe the Bell design had a satisfactory electrical power system, and Navy researchers rated the North American design last from an equipment (e. g., life support) perspective. The Douglas and Republic designs had the best potential flying qualities, and BuAer researchers felt that North American had incorrectly assumed laminar flow over much of their design, and had therefore underestimated the heating values. It was a bit late to be raising concerns, but most of the issues were minor and did not materially affect the outcome of the competition. After conferring with his Air Force and NACA counterparts, on 15 July George Spangenberg finalized the Navy’s position as Douglas, North American, Republic, and Bell.-1153!

On 26-28 July, the Air Force, NACA, and Navy evaluation teams met at Wright Field to select an airframe contractor. George Spangenberg stated that it was unfortunate that the point system used in the evaluation "appeared to give no conclusive winner," since a contractor could score highly in one area and low in another yet still have a winning score, while another that was satisfactory in all areas would be rated lower. He also indicated that the goals of the project seem to have shifted somewhat, resulting in a "firm requirement" for 1,200°F skin temperature research instead of the previous "desire" for high temperatures.-1154!

Presaging events to come, discussions ensued concerning the amount of work recently awarded to North American and Republic, and whether additional awards would spread their engineering groups too thin. Other discussions included the possibility of selecting Douglas but directing it to redesign its aircraft using an Inconel hot structure instead of magnesium. In the end, the Air Force and the NACA concluded that the North American proposal best accommodated their requirements. The Navy did not want to cast the only dissenting vote and, after short deliberation, agreed to go along with the decision.-11551

During the week of 1-5 August 1955, the WADC Project Office prepared the final evaluation summary and oral presentation: "the evaluation of the proposals submitted in competition was made in five areas: performance, technical design, research suitability, development capability, and cost." It is interesting to note that this competition was not about the "lowest bidder," and none of the proposals were anywhere near the original $12.2 million estimate. The results of these evaluations were as follows:!156!

Performance: The performance evaluation consisted of a check of the probability of the different designs, considering present uncertainties, of meeting the specified speed and altitude requirements. The probabilities were calculated to be best for the North American proposal, equal for the Bell and Douglas proposals, and least for the Republic proposal; but because of the assumptions of the analysis, all designs were judged able to meet the requirements.

Technical Design: This factor was judged on the awareness shown by the contractor of the problems of high-speed, high-altitude flight and of the means, as indicated by the airplane designs, the contractor proposed for exploring and studying these problems. The general design competency of the contractor also was judged from the designs submitted: North American 81.5 points; Douglas 80.1 points; Bell 75.5 points; and Republic 72.2 points. No design, as submitted, was considered safe for the use intended. The Douglas design was considered best in this regard, but did not include adequate margins for ignorance factors and operational errors.

Research Suitability: In this area, the fundamental differences in the proposed structures were examined and rated because of their decisive importance in the research uses of this aircraft. North American was rated acceptable because of the Inconel X "hot-structure" heat­sink, which was most suitable for research and which was potentially the simplest to make safe for the mission. Republic and Bell were considered unsatisfactory because of the hazardous aspects associated with the insulated structures used, and Douglas was considered unsatisfactory because of the low safety margins available and because of the limited future usefulness of the "cool" magnesium heat-sink principle.

Development Capability: Ratings were based on the physical equipment and manpower the contractor had available for pursuing the project, and the resulting time proposed for development. Evaluation of this factor resulted in the following ratings: (1) Douglas was acceptable; (2) North American was acceptable; (3) Bell was less acceptable; (4) Republic was less acceptable. North American, Republic, and Douglas estimated that the first flight date would be within 30 months, but the Republic estimate was not believed to be credible, hence their lower score. Bell promised a first flight date within 40 months.

Costs: Costs for three aircraft plus static test article, engines, and spares as adjusted by AMC to a comparable basis are: Bell, $36.3 million; Douglas, $36.4 million; Republic, $47.0 million; and North American, $56.1 million.

On 9 August, Captain McCollough presented the results of the evaluation to Brigadier General Howell M. Estes, then chief of the Weapons Systems Division, under whose jurisdiction the WADC Project Office fell, and a select group of senior Air Force officers. McCollough made a second presentation in Baltimore on 11 August for Generals John W. Sessums and Marvin C. Demler, who were the commanders of the WADC and ARDC, respectively, and Hartley Soule from the NACA.-157

The final briefing to a combined meeting of Air Force, NACA, and Navy personnel was at NACA Headquarters on 12 August. The attendees included Hugh Dryden, Gus Crowley, Ira Abbott,

Richard Rhode, and Hartley Soule from the NACA; Brigadier General Kelsey, Colonel Donald H. Heaton, Lieutenant Colonels Gablecki and Maiersperger, and Major Heniesse from the Air Force; and Captain R. E. Dixon, Abraham Hyatt, and George Spangenberg from BuAer. Following this, the Research Airplane Committee met, accepted the findings of the evaluation groups, and agreed to present the recommendation to the Department of Defense.-1158!

Because the estimated costs submitted by North American were far above the amount tentatively allocated for the project, the Research Airplane Committee included a recommendation for a funding increase before signing the final contract. A further recommendation-one that would later take on greater importance-called for relaxing the proposed schedule by up to 18 months. The committee approved both recommendations and forwarded them to the Assistant Secretary of Defense for Research and Development.

Three companies-Aerojet, Bell, and Reaction Motors-submitted proposals for the X-15 engine on 9 May 1955, the same day as the airframe competitors. North American had already asked the Air Force and NACA to dismiss the NA-5400 as an alternative. A copy of the Aerojet XLR73 proposal could not be located.

Bell was conservative in its engine proposal and stated that "modifications have been limited to those necessary to permit the engine to be used in a piloted aircraft." The changes to the XLR81 were made primarily in the starting and control systems, mostly to provide additional safety margins. The modified engine would be capable of multiple starts with a safety system based on a similar device provided for use during ground testing. The modifications provided an engine that could operate at an 8,000-lbf thrust level in addition to the normal 14,500-lbf full thrust. The modifications included the addition of a propellant bypass valve just in front of the injector so that, at the reduced thrust level, approximately one-half of the propellants would return to the tanks instead of being injected into the thrust chamber. This eliminated the need to change the pump discharge pressures, and allowed the same amount of propellants to flow through the cooling system. Only one engine in each airplane would have the capability to provide the 8,000- lbf level, although this reflected the removal and capping of the bypass valve and not any major change in engine configuration. Bell also proposed changing the fuel as a safety measure. In an attempt to minimize the risk of mixed propellants accumulating and exploding, Bell wanted to exchange the jet fuel normally used in the XLR81 with a mixture of 40% unsymmetrical dimethylhydrazine (UDMH) and 60% jet fuel (Bell called this combination "JP-X"). This would make the two propellants hypergolic, eliminating the hazard. Bell also pointed out that these propellants would not need to be topped off from the carrier aircraft, since neither had an appreciable vaporization rate. Bell noted that "since tests of the major components of the XLR81-BA-1 engine have been successful, extensive development tests of these components will not be required for the X-15 engine program."10

Like the Bell proposal, the proposal from Reaction Motors was brief (Bell used 15 pages, and Reaction Motors used just 14). The XLR30 would be modified to "1) emphasize safety and minimum development time, 2) start, operate and shutdown at all altitudes and attitudes, and 3) be capable of at least five successive starts without servicing or manual attention other than cockpit controls." Instead of the thrust-stepping proposed by Bell, Reaction Motors offered an infinitely variable thrust ranging from 13,500 to 50,000 lbf at sea level. Reaction Motors believed that "the highly developed state of the major engine components, i. e., turbopump, thrust chamber and control valves allows RMI to meet the schedule…." Unlike Bell, which extensively discussed the modifications required to make its engine meet the X-15 requirements, Reaction Motors instead gave a technical overview of the XLR30, and it was not possible to determine what the modifications were. Nevertheless, the overall impression was that the state of XLR30 development was far along.-1111

As the X-15 program moved on to higher and faster flights, support became more difficult because it required more time to travel to the sites and more lakes for each flight. The minutes of the X-15 Operations Subcommittee on 9 March 1961 give some insight into the coordination required. The subcommittee membership included Richard J. Harer, Colonel Bud Anderson, Major Robert M. White, Major K. Lewis, Captain J. E. Varnadoe, Lieutenant R. L. Smith, Captain F. R. O’Clair, Joseph R. Vensel, Stanley P. Butchart, C. E. Sorensen, and Lieutenant Commander Forrest S. Petersen. White and Petersen were X-15 pilots, and several of the other members had long and distinguished flying careers (especially Anderson and Butchart), so the group was not without a certain amount of applicable expertise.-1961

The previous October Paul Bikle had written a letter to the X-15 Operations Subcommittee and the AFFTC outlining an increase in support that would be required as the X-15 program moved uprange to the more remote lakes. The letter provides insight into how complicated it really was to conduct X-15 flights. For instance, each of the uprange stations (Beatty and Ely) had an operating crew of eight people, and the Air Force had to arrange transportation for the crew "a few days prior to each X-15 flight and for their return to Edwards after the flight." Given that NASA frequently scheduled flights once per week, this required a constant movement of personnel. Beatty supported all launches, while the program only used Ely for the high-speed flights scheduled out of Wah Wah Lake beginning in June 1961.[97]

The subcommittee did not think that supporting Hidden Hills launches would place any additional burden on the AFFTC since the effort required was generally similar to that needed for Silver Lake. However, flights from Mud Lake and farther uprange would require a much greater level of support. In its letter, NASA increased the amount of support requested, largely based on the unknown factors of never having launched from uprange. The AFFTC agreed that the equipment and personnel requirements for the uprange lake sites (as listed in the NASA letter) were valid and, at least initially, appropriate. The Air Force hoped, however, that subsequent experience could reduce some of the requirements.[98]

One of the attachments to Bikle’s letter provided the details of the support he was requesting.

This example uses a launch from Wah Wah Lake because it was the most comprehensive. The X – 15 launch would take place 20 miles north of Wah Wah Lake and would require the X-15, NB-52, and two chase aircraft. An emergency team would be located at Wah Wah Lake in case the X-15 engine did not start or some other emergency required an immediate landing. This team would consist of two Air Force 500-gallon fire trucks, an H-21 helicopter, eight firemen, an Air Force pilot as lake controller, an Air Force crew chief, an Air Force doctor, an Air Force pressure-suit technician, and a NASA X-15 specialist. Delamar Lake, the next contingency landing site, was 120 miles away. One Air Force 500-gallon fire truck, four firemen, four Air Force flight crew, two Air Force paramedics, and a NASA X-15 specialist would staff it. A Jeep would carry a nitrogen purge system to safe the X-15 after landing. One hundred and fifteen miles closer to Edwards was Hidden Hills, the primary emergency site in case the pilot had to shut down the engine early. Orbiting this lake were two F-104 chase aircraft that were intended to pick up the X-15 as it slowed down at the nominal end-of-mission, but could also provide assistance in the event of emergency. An Air Force C-130 waited on the lake to evacuate the X-15 pilot in case of an emergency landing, along with an Air Force 500-gallon fire truck, four firemen, two pilots, four Air Force flight crew, two Air Force paramedics, and a NASA X-15 specialist.-1991

Back at Edwards, the NASA radio van, an H-21 helicopter, the NASA lake controller, two Air Force fire trucks, eight firemen, two Air Force flight crew, the Air Force flight surgeon, a pressure-suit technician, and a NASA X-15 specialist awaited. In addition, staged between Wah Wah Lake and Delamar were a NASA-provided Jeep and three NASA X-15 specialists in case the X-15 had to set down unexpectedly at a lake other than those manned for the flight. An F-104 also orbited between Delamar and Hidden Hills to provide chase if the X-15 had to slow down during mid­flight. It was a complex ballet.

As it turned out, however, the increase in support that NASA was requesting was not possible. For instance, NASA wanted three C-130 aircraft and four paramedics dedicated to each launch, but the AFFTC did not have these resources. The AFFTC only had four C-130s assigned, and two were normally at El Centro supporting activities at the National Parachute Range. The base flight surgeon indicated that he believed it would be acceptable to provide a capability for a flight surgeon to be on the scene of an accident "within one hour," and the AFFTC adopted this suggestion. In general, however, the level of support provided by the AFFTC was consistent with that requested by Bikle; it differed primarily in some convenience items, not in essential services. On the other hand, NASA had proposed sending crews to the uprange sites the morning of each flight (meaning in the dark, since the X-15 often flew near first light). The AFFTC believed it was easier to send the uprange crews up the day prior to each flight. In most cases the personnel stayed in hotels in the towns near the support sites and reported to the site by 0800 hours in order to be ready by 0830 to support a 0900 takeoff of the NB-52.[100]

By early 1961 the X-15 Operations Subcommittee reported that security restrictions concerning Groom Lake seemed to be easing, and everybody agreed that Groom Lake was a preferable landing site compared to Delamar Lake. The program hoped to gain permission to use Groom Lake in the future, and Captain Varnadoe agreed to contact the appropriate offices to determine the likelihood of that happening. As it ended up, although one black project (the U-2) was ending at Groom, another (the Blackbird) was getting set to begin, and the X-15 program never would obtain permission to use the lakebed.[101]

By this time the Edwards and Beatty sites of the High Range were operational and had supported 34 X-15 flights. The Ely station became operational in April 1961. One of the concerns of the X – 15 Operations Subcommittee involved directing rescue forces to a downed X-15 pilot. The H-21 rescue helicopters did not have onboard navigation equipment, and required direction to within five miles of the crash site. From that point they could use radio homing equipment to find the rescue beacon on the pilot. The beacon itself was relatively new and at that time NASA had only installed it on X-15-2; however, it would later install the beacon on the other two airplanes. North American had promised a 30-mile range for the beacon, but testing at Edwards revealed much less capability. The beacon was returned to North American and discovered to have only half­power in its battery (range is a square function, so this resulted in only one-quarter of the projected distance). The H-21 used an AN/ARA-25 direction (homing) finder to locate the beacon. The subcommittee believed it would be desirable to install an ARA-25 receiver on the NB-52s also to allow the carrier aircraft to locate the pilot and direct the H-21s to the site. In addition, the NASA budget included funds to install auto-trackers on the High Range telemetry antennas. Once installed, the antennas could be set to 2.443 MHz and automatically track the pilot rescue beacon.[102]

Jah *<вє

Each X-15 pilot was issued a typed summary of lakebed information, along with hand-drawn sketches of the lakes and the marked runways. These were the lakes available in January 1966. (North American Aviation)

handled by NASA, although an AFFTC crane would be provided to lift the airplane onto a flatbed trailer.-103-

The first 50 years of powered human flight were marked by a desire to always go faster and higher. At first, the daredevils-be they racers or barnstormers-drove this. By the end of the 1930s, however, increases in speed and altitude were largely the province of government-the cost of designing and building the ever-faster aircraft was becoming prohibitive for individuals.

As is usually the case, war increased the tempo of development, and two major conflicts within 30 years provided a tremendous impetus for advancements in aviation. By the end of World War II the next great challenge was in sight: the "sound barrier" that stood between the pilots and supersonic flight.

Contrary to general perception, the speed of sound was not a discovery of the 20th century. Over 250 years before Chuck Yeager made his now-famous flight in the X-1, it was known that sound propagated through air at some constant velocity. During the 17th century, artillerymen determined that the speed of sound was approximately 1,140 feet per second (fps) by standing a known distance away from a cannon and using simple timing devices to measure the delay between the muzzle flash and the sound of the discharge. Their conclusion was remarkably accurate. Two centuries later the National Advisory Committee for Aeronautics^1 (NACA) defined the speed of sound as 1,117 fps on an ISO standard day, although this number is for engineering convenience and does not represent a real value.-12!

The first person to recognize an aerodynamic anomaly near the speed of sound was probably Benjamin Robins, an 18th-century British scientist who invented a ballistic pendulum that measured the velocity of cannon projectiles. As described by Robins, a large wooden block was suspended in front of a cannon and the projectile was fired into it. The projectile transferred momentum to the block, and the force could be determined by measuring the amplitude of the pendulum. During these experiments, Robins observed that the drag on a projectile appeared to increase dramatically as it neared the speed of sound. It was an interesting piece of data, but there was no practical or theoretical basis for investigating it further.-13!

The concept of shock waves associated with the speed of sound also predated the 20th century. As an object moves through the atmosphere, the air molecules near the object are disturbed and move around the object. If the object passes at low speed (typically less than 200 mph), the density of the air will remain relatively constant, but at higher speeds some of the energy of the object will compress the air, locally changing its density. This compressibility effect alters the resulting force on the object and becomes more important as the speed increases. Near the speed of sound the compression waves merge into a strong shock wave that affects both the lift and drag of an object, resulting in significant challenges for aircraft designers.!41

Austrian physicist Ernst Mach took the first photographs of supersonic shock waves using a technique called shadowgraphy. In 1877 Mach presented a paper to the Academy of Sciences in Vienna, where he showed a shadowgraph of a bullet moving at supersonic speeds; the bow and trailing-edge shock waves were clearly visible. Mach was also the first to assign a numerical value to the ratio between the speed of a solid object passing through a gas and the speed of sound through the same gas. In his honor, the "Mach number" is used as the engineering unit for supersonic velocities. The concept of compressibility effects on objects moving at high speeds was established, but little actual knowledge of the phenomena existed.-131

None of these experiments had much impact on the airplanes of the early 20th century since their flight speeds were so low that compressibility effects were effectively nonexistent. However, within a few years things changed. Although the typical flight speeds during World War I were less than 125 mph, the propeller tips, because of their combined rotational and translational motion through the air, sometimes approached the compressibility phenomenon.-131

To better understand the nature of the problem, in 1918 G. H. Bryan began a theoretical analysis of subsonic and supersonic airflows for the British Advisory Committee for Aeronautics at the Royal Aeronautical Establishment. His analysis was cumbersome and provided little data of immediate value. At the same time, Frank W. Caldwell and Elisha N. Fales from the Army Air Service Engineering Division at McCook Field in Dayton, Ohio, took a purely experimental approach to the problem.171 To investigate the problems associated with propellers, in 1918 Caldwell and Fales designed the first high-speed wind tunnel built in the United States. This tunnel had a 14-inch-diameter test section that could generate velocities up to 465 mph, which was considered exceptional at the time. This was the beginning of a dichotomy between American and British research. Over the next two decades the United States—primarily the NACA—made most of the major experimental contributions to understanding compressibility effects, while the major theoretical contributions were made in Great Britain. This combination of American and British investigations of propellers constituted one of the first concerted efforts of the fledgling aeronautical community to investigate the sound barrier. 181

Within about five years, practical solutions, such as new thin-section propeller blades (made

practical by the use of metal instead of wood for their construction) that minimized the effects of compressibility, were in place. However, most of the solution was to avoid the problem. The development of reliable reduction-gearing systems and variable-pitch, constant-speed propellers eliminated the problem entirely for airplane speeds that were conceivable in 1925 because the propeller could be rotated at slower speeds. At the time, the best pursuit planes (the forerunners of what are now called fighters) could only achieve speeds of about 200 mph, and a scan of literature from the mid-1920s shows only rare suggestions of significantly higher speeds in the foreseeable future. Accordingly, most researchers moved on to other areas.-19

The public belief in the "sound barrier" apparently had its beginning in 1935 when the British aerodynamicist W. F. Hilton was explaining to a journalist about high-speed experiments he was conducting at the National Physical Laboratory. Pointing to a plot of airfoil drag, Hilton said, "See how the resistance of a wing shoots up like a barrier against higher speed as we approach the speed of sound." The next morning, the leading British newspapers were referring to the "sound barrier," and the notion that airplanes could never fly faster than the speed of sound became widespread among the public. Although most engineers refused to believe this, the considerable uncertainty about how significantly drag would increase in the transonic regime made them wonder whether engines of sufficient power to fly faster than sound would ever be available.-110!

John Stack, head of the Compressibility Research Division at NACA Langley, was one of the driving forces behind the original set of experimental airplanes, such as the Bell X-1 and Douglas D-558 series. Although he lent expertise and advice to the groups developing the X-15, he remained in the background and did not repeat the pivotal roles he had played on earlier projects. (NASA)

characteristics of the test sections. However, the beginning of the Second World War increased the urgency of the research. Therefore, on a spring morning in 1940, John V. Becker and John Stack, two researchers from the NACA Langley Memorial Aeronautical Laboratory in Hampton,

Virginia,11 drove to a remote beach to observe a Navy Brewster XF2A-2 attempting to obtain supercritical aerodynamic data in free flight over Chesapeake Bay. After it reached its terminal velocity in a steep dive—about 575 mph—the pilot made a pull-up that was near the design load factor of the airplane. This flight did not encounter any undue difficulties and provided some data, but the general feeling was that diving an operational-type airplane near its structural limits was probably not the best method of obtaining research information.-112!

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]