Category X-15 EXTENDING THE FRONTIERS OF FLIGHT

Bob Rushworth’s last flight (2-45-81), on 1 July 1966, was also the first flight with full external tanks. As Johnny Armstrong later observed, "with 20-20 hindsight, flight 45 was destined for failure." On X-15A-2, the propellants in the external tanks were pressure-fed to the internal tanks, and the engine received propellants from the internal tanks in the normal fashion. The fixed-base simulator had shown that the X-15 would quickly become uncontrollable if the propellant from one external tank transferred while that from the other tank did not, because the moment about the roll axis would be too large for the rolling tail to counter. If this situation developed, the pilot would jettison the tanks, shut down the engine, and make an emergency landing.-1272

The problem was that, for this first flight with full tanks, there was no direct method to determine whether the tanks were feeding correctly. Instrumentation was being developed to provide propellant transfer sensors (paddle switches), but it was not available for this flight. Instead, a pressure transducer across an orifice in the helium pressurization line provided the only information. Researchers had verified that the pressure transducer worked as expected during a planned captive-carry flight (2-C-80) with propellants in the external tanks.-282

During the flight to the launch lake, while still safely connected to the NB-52, Rushworth verified that the pressure transducer was working. Rushworth jettisoned a small amount of propellant from the internal tanks, and NASA-1 watched the helium pressure come up as the external propellants flowed into the airplane (NASA-1 had to do it since nobody had thought to provide the pilot with any indicators). However, 18 seconds after the X-15 dropped away from the NB-52, Jack McKay (NASA-1) called to Rushworth: "We see no flow on ammonia, Bob." Rushworth responded, "Roger, understand. What else to do?" McKay: "Shutdown. Tanks off, Bob." Rushworth got busy: "OK, tanks are away… I’m going into Mud." Any emergency landing is stressful, but this one ended well. Bruce Peterson in Chase-2 reported, "Airplane has landed, everything OK, real good shape."282

Jettisoning the tanks with the "full" button was supposed to initiate only the nose cartridges and not fire the separation rockets. However, in this case, apparently because of faulty circuitry, the separation rockets did fire. Fortunately, the separation occurred without the tanks recontacting the airplane. Engineers obtained a great deal of data on the tank separation because an FM telemetry system in the liquid-oxygen tank transmitted data on accelerations and rotational rates during separation. Post-flight inspection of the ejector bearing points on the aircraft indicated that the ammonia tank briefly hung on the aircraft, marring the ejector rack slightly. The drogue chutes deployed immediately after separation and the dump valve in the tank allowed the propellants to flow out. The main chute deployment was satisfactory; however, the mechanism designed to cut the main chute risers failed and high surface winds dragged the tanks across the desert. Nevertheless, the Air Force recovered both tanks in repairable condition.-1282-

Bob Rushworth left the program after this flight, going on to a distinguished career that included a tour as the AFFTC commander some years later. Rushworth had flown 34 flights, more than any other pilot and more than double the statistical average. He had flown the X-15 for almost 6 years and had made most of the heating flights. These flights were perhaps the hardest to get right, and Rushworth did so most of the time.[283]

Major Michael J. Adams, making his first flight (1-69-116) on 6 October 1966, replaced Rushworth in the flight lineup. He started his career with a bang, literally. X-15-1 launched over Hidden Hills on a scheduled low-altitude (70,000 feet) and low-speed (Mach 4) pilot – familiarization flight. The bang came when the XLR99 shut itself down 90 seconds into the planned 129-second burn after the forward bulkhead of the ammonia tank failed. Fortunately, the airplane did not explode and Adams successfully landed at Cuddeback without major incident. Perhaps Adams was just having a bad day. After he returned to Edwards, he jumped in a T-38 for a scheduled proficiency flight. Shortly after takeoff, one of the J85 engines in the T-38 quit; fortunately, the Talon has two engines. Adams made his second emergency landing of the day, this time on the concrete runway at Edwards.-1284

external tank transferred but the other one did not – the moment about the roll axis was too large for the rolling tail to counter. If this situation developed, the pilot would jettison the tanks, shut down the engine, and make an emergency landing. Unfortunately, this exact scenario played out on 1 July 1966 on the first flight with full tanks. Thankfully, Bob Rushworth managed to jettison the tanks and make an uneventful emergency landing at Mud Lake. (NASA)

Jack McKay seemed to have more than his share of problems, and holds the record for the most landings at uprange lakes (three). His last emergency landing was made during his last flight (1­68-113), on 8 September 1966. The flight plan showed this Smith Ranch launch going to 243,000 feet and Mach 5.42 before landing on Rogers Dry Lake. However, as McKay began his climb he noticed the fuel-line pressure was low. Mike Adams as NASA-1 recommended throttling back to 50% to see if the fuel pressure would catch up; it did not. McKay shut down the engine and began jettisoning propellants to land at Smith Lake. The landing was uneventful and NASA trucked the airplane back to Edwards.-285

The program had experienced a few flights where the pilot overshot the planned altitude for various reasons, but Bill Dana added one for the record books on 1 November 1966. On flight 3­56-83, Dana got the XLR99 lit on the first try and pulled into a 39-degree climb, or so he thought, heading for 267,000 feet. In reality, the climb angle was 42 degrees. Interestingly, Pete Knight in the NASA-1 control room did not notice the error either, and as the engine burned out he reported, "We got a burnout, Bill, 82 seconds, it looks good. Track and profile are looking very good." As Dana climbed through 230,000 feet, NASA-1 finally noticed and said, "[W]e got you going a little high on profile. Outside of that, it looks good." The flight eventually reached 306,900 feet-39,900 feet higher than planned.286

As Dana went ballistic over the top, he asked Knight if "Jack McKay [was] sending in congratulations." The reference was to flight 3-49-73 on 28 September 1965, when McKay had overshot his altitude by 35,600 feet. Dana had been NASA-1 on that flight and had needled McKay ever since. Dana’s fun, however, did not stop with the overshoot. As he reached to shut down the engine, Dana apparently bumped the checklists clipped to his kneepad with his arm. Dana later recalled, "At shutdown my checklist exploded. I don’t know how it came out of that alligator clamp, but anyway I had 27 pages of checklist floating around the cockpit with me, and it was a great deal like trying to read Shakespeare sitting under a maple tree in October during a high wind. I only saw one instrument at a time for the remainder of the ballistic portion… these will be in the camera film which I think we can probably sell to Walt Disney for a great deal." After an otherwise uneventful landing, Dana could not find the post-landing checklist, "Thank you, Pete," he joked. "Since my page 16 is somewhere down on the bottom of the floor, maybe you could go over the checklist with me?"287

1966 FLIGHT PERIOD

As was usual for the high desert during the winter, the rains had begun in late November 1966, and during early 1967 most of the lakebeds were wet, precluding flight operations. This gave North American and the FRC time to perform maintenance and modifications on the airplanes. For instance, X-15-1 was having its ammonia tank repaired and the third skid added, X-15A-2 was having instrumentation modified, and X-15-3 was having an advanced PCM telemetry system installed. By February the lakebeds at Three Sisters, Silver, Hidden Hills, and Grapevine were dry, and Rogers and Cuddeback were expected to be within two weeks. Unfortunately, snow and ice still covered Mud, Delamar, Smith Ranch, and Edwards Creek Valley. It would be late March before all the necessary lakes were dry enough to support flight operations.-1288!

The program was also making plans to add new pilots, allowing some of the existing pilots to rotate to other assignments. For instance, John A. Manke, a NASA test pilot, went through ground training and conducted a single engine run. Unfortunately, Mike Adams’s accident would eliminate any chance that Manke would ever fly the X-15.[289]

Pete Knight would eventually set the fastest flight of the program, but before that event he had at least one narrow escape while flying X-15-1. As he related in the pilot’s report after flight 1-73-

126:[290]

The launch and the flight was beautiful, up to a certain point. We had gotten on theta and I heard the 80,000-foot call. I checked that at about 3,100 fps. Things were looking real good and I was really enjoying the flight. All of a sudden, the engine went "blurp" and quit. There could not have been two seconds between the engine quit and everything else happening because it all went in order. The engine shut down. All three SAS lights came on. Both generator lights came on and then there was another light came on, and I think it was the fuel low line light. I am not sure. Then after all the lights got on, they all went out.

Everything quit. By this time, I was still heading up and the airplane was getting pretty sloppy. As far as I am concerned both APUs quit.

Once the X-15 began its reentry after an essentially uncontrolled exit, Knight managed to get one of the APUs started. Unfortunately, the generator would not engage, which meant Knight had hydraulics but no electrical power. He elected to land at Mud Lake.

Once I thought I was level enough I started a left turn back to Mud. Made a 6-g turn all the way around… Once I was sure I could make the east shore of Mud Lake with sufficient altitude I used some speed brakes to get it down to about 25,000 [feet altitude] and then varied the pattern to make the left turn into the runway landing to the west. On the final, all this time the trim was still at 5 degrees for the theta that we had. I was getting pretty tired of that side stick so I began to use both hands. One on the center stick and one on the side stick taking the pressure off the stick with the left hand and flying it with the right. Made the pattern and the airplane is a little squirrelly without the dampers but really not that bad. … I settled in and got it right down to the runway and it was a nice landing as far as the main skids were concerned, but the nose gear came down really hard.

After I got it on the ground I slid out to a stop. I started to open the canopy. I could not open the canopy. I tried twice and could not move that handle, so I sat there and rested for a while, I reached up and grabbed it again. Finally, it eased off and the canopy came open. Then I started to get out of the airplane and I could not get this connection off over here. I got the hat [helmet] off, to cool off a little bit, and tried it again. Then I was beginning to take the glove off to get a hand down in there also. I never did get that done. I tried it again and it would not come so I said the hell with it, and I’ll pull the emergency release. I pulled the emergency release and that headrest blew off and it went into the canopy and slammed back down and hit me in the head. I got out of the airplane and by that time, the C-130 was there. Got into the 130 and came home.

It was one of the few times an X-15 pilot extracted himself from the airplane without the assistance of ground crews. Normally a crew was present at each of the primary emergency lakes, but Mud was not primary for this flight and no equipment or personnel were stationed there.

Based on energy management, Knight probably should have landed at Grapevine. At the time, there was no energy-management display in the X-15, so NASA-1 made those decisions based on information in the control room. However, since the airplane had no power, and hence no

[2911

radio, decisions made by NASA-1 were not much help.

It is likely that the personnel on the ground were more worried than Knight was, because when the APUs failed they took all electrical power, including that to the radar transponder and radio. At the time, the radars were not skin tracking the X-15, so the ground lost track of the airplane. It was almost 8 minutes later when Bill Dana, flying Chase-2, caught sight of the X-15 just as it crossed the east edge of Mud Lake.[292]

The problem was most likely the result of electrical arcing in the Western Test Range launch monitoring experiment. Unlike most experiments, this one connected directly to the primary electrical bus. The arcing overloaded the associated APU, which subsequently stalled and performed an automatic safety shutdown. This transferred the entire load to the other APU, which also stalled because the load was still present. The APUs had been problematic since the beginning of the program, but toward the end they were generally reliable enough for the 30 minutes or so that they had to function. Each one was usually completely torn down and tested after each flight. In this case, something went wrong. After this flight, NASA moved the WTR and MIT experiments to the secondary electrical bus, which dropped out if a single generator shut down; this would preclude a complete power loss to the airplane.*293

Paul Bikle commented that Knight’s recovery of the airplane was one of the most impressive events of the program. The flight planners had spent many hours devising recovery methods after various malfunctions; all were highly dependent upon the accuracy of the simulator for reproducing the worst-case, bare-airframe aerodynamics. NASA constantly updated the simulator with the results from flights and wind-tunnel tests to keep it as accurate as possible. The flight by Knight was the only complete reentry flown without any dampers. As AFFTC flight planner Bob Hoey remembers, "[W]e would have given a month’s pay to be able to compare Pete’s entry with those predicted on the sim, but all instrumentation ceased when he lost both APUs, and so there was no data! Jack Kolf told Pete that we were planning to install a hand crank in the cockpit hooked to the oscillograph so he could get us some data next time this happened." Fortunately, it never happened again.*294

Despite the variety of artists’ concepts and popular press articles on an orbital X-15, in the end the new National Aeronautics and Space Administration (NASA) would decide to endorse a concept that had been initiated by the Air Force and use a small ballistic capsule for the first U. S. manned space program, renamed Mercury. Nevertheless, a small minority within NASA, mainly at Langley, continued to argue that lifting-reentry vehicles would be far superior to the non-lifting capsules. In fact, at the last NACA Conference on High-Speed Aerodynamics in March 1958, John Becker presented a concept for a manned 3,060-pound winged orbital satellite. According to Becker, this paper, which dissented from the consensus within the NACA favoring a ballistic capsule, created more industry reaction-"almost all of it favorable’-than any other he had ever written, including the initial X-15 study.-13"

What ruled out acceptance of his proposal, even more than the sheer momentum behind the capsules, was the fact that the 1,000 pounds of extra weight (compared to the capsule design presented by Max Faget) was beyond the capability of the Atlas ICBM. If the Titan had been further along, Becker’s concept would have worked, but the simple fact was that Atlas was the only game in town. If it had all happened a year or two later, when the Titan became available, Becker believes that "the first U. S. manned satellite might well have been a [one-man] landable winged vehicle." The decision to adopt the capsule concept made the X-15 a dead end, at least temporarily. It would be a decade later when the aerospace community again decided that a winged lifting-reentry vehicle was feasible; the result would be the space shuttle.

There was one other orbital X-15 proposal. At the end of 1959, Harrison Storms presented a version of the X-15B launched using a Saturn I first stage and an "ICBM-type" second stage. According to Storms, "We figure the X-15, carrying two pilots…could be put into orbit hundreds of miles above the earth. Or with a scientific or military payload of thousands of pounds…into a lower orbit." Storms estimated that it would take three to four years of development and presented the idea to both the Air Force and NASA, but neither organization was interested. NASA was too busy with Mercury, and the Air Force was occupied with Dyna-Soar and fighting off Robert McNamara.-1140-

By late 1961, most of the people involved in the flight program expected it to end in December 1964. This would allow an orderly investigation of the remaining aero-thermo environment, an evaluation of the MH-96 adaptive control system, and a few follow-on experiments. This was in general agreement with the original 1959 Air Force plan, although it consisted of only 100 flights instead of the anticipated 300 flights.11681

A quick look at the labor required to support the X-15 shows that it was not a small program. The following table counts only government employees, not contractors, in "equivalent" man years, meaning that there may have been more people actually supporting the program than shown, but they were doing so on a less than full-time basis. In general, the Air Force figures consisted of

about 55% civil servants and 45% military personnel. The Air Force paid the civilians an average of $8,370 per annum at the ASD and $7,850 at the AFFTC. The FY65 numbers reflect the period between June 1964 and December 1964 (the government fiscal years at the time ran from 1 July to 30 June).[169]

The next table shows the projected propellant and gas requirements at the same point in the program:[170]

required for the operation of the NB-52s, other support and chase aircraft, propellant analysis and servicing, instrumentation, data processing and acquisition, photo lab, biomedical support, engineering, and test operations.

X-15 FLIGHT RESEARCH PROGRAM

ЧЬЪЕДКОт ДІКНІ. ІЖЕ. ____ COMMIT TEL

JASA ІГШУ :U£AF

SFERFIY —1

The X-15 program was a joint venture between the Air Force, Navy, and NASA, although the Navy generally played the role of a silent partner. The Air Force developed and paid for the airplanes and operated much of the support infrastructure at Edwards AFB, while NASA flew the airplanes (often with military pilots) and performed the maintenance. This 1961 organizational chart delineates the various interrelationships. In all, it worked well. (NASA)

Additional funds were budgeted for travel. Again, these are only Air Force funds; the equivalent NASA funding could not be ascertained.

20 Dyna-Soar. At the time, Honeywell had tested the system on a McDonnell F-101 Voodoo, but many researchers wanted to get some high-performance experience with the system prior to committing it to space flight on the X-20. When an XLR99 ground test almost destroyed X-15-3, the Air Force seized the opportunity to include a prototype MH-96 when North American rebuilt the airplane.171

The MH-96 was the first command augmentation system with an adaptive gain feature that provided invariant aircraft response throughout the flight envelope. The MH-96 used a rate command control mode whereby a given control-stick deflection would produce a specific rate response for the airplane. For example, a 1-inch pitch stick deflection would result in a 5- degrees-per-second pitch rate, regardless of how far the control surfaces had to deflect to produce that rate. This meant that the response would be the same regardless of airplane speed or flight condition.1721

In a conventional aircraft of the period, the pitch rate response would vary with airspeed. In an airplane with a large speed envelope, such as the X-15, a 1-inch stick deflection with a conventional system could result in such disparate responses as almost none at low speed to an extremely violent one at high speed. The MH-96 was an attempt to cure this. However, nothing comes free. With an invariant response, the pilot lost the "feel" for the airplane; for example, the controls did not become sloppy as it approached a stall. The system automatically compensated for everything right up to the point that the airplane stopped flying. The same problem would confront the first fly-by-wire systems.-11731

The rate-command system eliminated the need to modify the trim settings because of configuration changes, such as deploying the landing gear or flaps. The system also masked any shifts in the center of gravity. In many respects, these were good things because they eliminated mundane tasks that otherwise needed to be accomplished by a pilot who already had his hands full of rocket plane. On the other hand, they eliminated many of the normal cues the pilots used to confirm that certain things had happened, such as the trim change after the landing gear deployed. It took an open mind-and some experience-to get comfortable flying the MH-96.-11741

The MH-96 was potentially superior to the basic flight-control system installed in the other two airplanes, for a couple of reasons. The first was that it was more redundant than the SAS (even after the ASAS was installed), which eliminated many of the concerns of flying to high altitudes. Also, the MH-96 blended the ballistic controls and the aerodynamic controls together beginning at 90,000 feet. The pilot moved the same stick regardless of altitude and the MH-96 decided which controls were appropriate to command the airplane. The MH-96 also offered a few autopilot modes (such as roll hold, pitch-attitude hold, and angle-of-attack hold) that significantly reduced the pilot’s workload during the exit phase.-1751

The system minimized any extraneous aircraft motions by providing much higher damper gains. The pilots appreciated this feature particularly during altitude flights, and X-15-3 was designated the primary airplane for altitude flights. Neil Armstrong had been heavily involved in the development and evaluation of the MH-96 and made the first four evaluation flights with the system.

North American moved the rebuilt X-15-3 from Inglewood to Edwards on 15 June 1961, and finally delivered the airplane, along with the XLR99 and MH-96, to the government on 30 September. After various ground tests were completed, Neil Armstrong attempted to take the airplane for its first flight on 19 December 1961, but a problem with the XLR99 resulted in an abort. The flight (3-1-2) successfully launched the next day, with additional flights on 17 January

and 5 April 1962. As it turned out, the MH-96 worked remarkably well, but Armstrong and others realized the system would require a considerable period of evaluation before researchers could thoroughly understand it. The MH-96 provided good service to the X-15 program until a fateful day in 1967.-176

Because the research program was the rationale for the X-15’s existence, flights to obtain basic aero-thermo data began as soon as North American and the government were sure the airplane was relatively safe for its intended purpose. Nevertheless, almost from the beginning, the airplanes carried a few minor experiments that had little to do with its basic aero-thermo research objectives; the B-70 emission coating and a radiation detector were early examples. Still, the first couple of years of the flight program were primarily dedicated to expanding the flight envelope and obtaining the basic data needed by aerodynamicists to validate the wind-tunnel predictions and theoretical models used to build the X-15.

As this goal was increasingly satisfied, more X-15 flights carried unrelated experiments, such as

tests of ablative materials and star trackers for the Apollo program. Usually these experiments required little support from the X-15 itself, other than some power and recording capacity. Later in the program, flights began to be conducted for the sole purpose of supporting the "follow-on" experiments, although even these usually gathered aero-thermo or stability and control data to support continued evaluation. In reality, the X-15 as an experiment ended sometime in 1963 (except for the advanced X-15A-2); after that, the airplane was mostly a carrier for other experiments.

With the appearance of high-performance aircraft and missiles during the mid-1950s, designers began to be concerned with the effects of a turbulent boundary layer on the performance of optical equipment. As early as 1956, wind-tunnel researchers determined that the effects of a narrow beam of light through a turbulent boundary layer were a function of the free-stream Mach number and the density of the stream. The effects of this "light spreading" on the accuracy of star trackers were studied by Autonetics in 1957 and again by North American in connection with the B-70 program. Researchers observed the first actual effects of aerodynamics on aerial photography in 1957 when pictures taken from a McDonnell RF-101 Voodoo at Mach 1.4, viewed stereoscopically, provided a false evaluation of the terrain. This led the Army Corps of Engineers to award a contract to Vidya (a division of Itek Corporation) during 1959-1960 to develop a theory that explained the phenomena. The Navy sponsored similar work at MIT during 1959 to determine the degrading effects of turbulent flow on the resolving power of cameras.1991

instrumented aerial cameras and multiple boundary-layer rakes.-1100!

Officially called the "induced turbulence experiment," this project sought "to determine the effects of aerodynamics associated with supersonic and hypersonic aircraft, typified by the X-15 research airplane, on the performance of (1) a high-acuity modern camera set, exemplified by the Fairchild KS-25, and (2) a cartographic camera, exemplified by the Fairchild KC-1." The cartographic aspects of the experiment were of interest to the U. S. Army Corps of Engineers, while the Air Force was interested in the possible effects on tactical and strategic aerial reconnaissance. This experiment also used data collected by the small two-camera package installed in X-15-2 as part of experiment #27.101

This program was very involved, and significantly funded under an Air Force contract to North American as part of Project 6220, Photographic Reconnaissance Technology. The Reconnaissance Division of the Air Force Avionics Laboratory under the direction of Donald I. Groening coordinated the experiments. Two principle subcontractors were also involved: Aeroflex Laboratories fabricated parts for the ART-15A stabilized mount, and Vidya provided theoretical and image analysis. Fairchild Camera and Instrument Corporation provided the KS-25 camera under a separate Air Force contract. The Hycon Manufacturing Company provided the camera lens and conducted resolution testing, and the Cornell Aeronautical Laboratory assisted in determining the final target design.-102!

Phase I

The Army Corps of Engineers and the ASD jointly sponsored Phase I. The initial requirement was for three separate flight profiles: high-speed, high-altitude, and one that mimicked the Mach 3 B-70 bomber. The exact profiles were important because the launch lakes had to be established well in advance of the flights so that the Air Force could erect 6 to 10 photo targets along the flight path. This involved removing yet more land from the public domain. The B-70 profile placed another constraint on the program because it required flying the XLR99 at 40% thrust, and the early engines were incapable of doing this reliably. There was also a desire to photograph the same targets during Phase II.103

The launch lakes were Delamar and Smith Ranch. The targets would be located along the flight path from Delamar to Edwards with single three-bar targets located near Pahrump and Indian Springs in Nevada, and two sets of three targets straddling the flight path at Pilot Knob and Cuddeback in California. The single target at Pahrump determined the performance of the camera primarily at the maximum altitude point on the high-altitude missions, while the single target at Indian Springs determined performance at the maximum speed point on the high-speed profile. Triple targets at Pilot Knob and Cuddeback allowed for accumulated navigation errors and measured performance at high-supersonic speeds. The Pilot Knob targets also measured the camera performance at the point of reentry from the high-altitude profile. Each target was a collection of white stripes of different widths on a black background (a standard Mil-Std-150A photo-calibration target pattern) with an additional large contract patch and two sharp edges normal to each other to determine the atmospheric attenuation and edge response. The Air Force called this the Delamar camera range.104

A photometric van from the Scripps Institute of Oceanography at the University of California was usually set up at the Pahrump site. This van had three photometers that measured the total sky radiance, solar radiance, and radiance of the surface of the target. Researchers located meteorological instrumentation near each target to provide compensation data for the analysis, and the Air Force launched standard radiosondes to support the experiment.105

The X-15 package for the cartographic program contained a KC-1 camera, an ART-15A stabilized mount, and photometric and environmental instrumentation to measure the conditions that prevailed during the time of the experiment. The KC-1 had been modified with a GEOCON I lens designed by Dr. J. Baker of Spica, Incorporated, to combine low distortion with relatively high acuity, and was adapted for operation at high altitude. The experiment package, minus the camera, weighed approximately 156 pounds. The KC-1 camera and lens added another 85-90 pounds depending on the film load, and occupied a space about 16 inches long by 18 inches wide by 21 inches high at the bottom of the instrument compartment. The GEOCON I low-distortion mapping lens had a focal length of 6 inches and a relative aperture of f/5.6, and could provide a resolution of 37 lines per millimeter on Super-XX film. North American modified X-15-1 to accept a KC-1 camera, including modification of the ART -15 mount and the addition of an 18- inch-diameter window that was 1.5 inches thick in the bottom of the instrument compartment. The film was nominally 9 by 9 inches, and 390 feet of it were stored in the magazine.-1106!

PHOTOGRAPHIC INSTALLATION

KC-1 CAMERA WITH GEOCON I LENS

PHOTOMETERS

(10° AND SCATTERED TIGHT)—i

PH CTO MEIER AN;’

SPECTROMETER

KS-25 CAMERA

PHOTO METERS

[10° AND SCATTERED LIGHT

PHOTOMETER AND

j^CTROMETER

The Photo Optical Degradation Experiment (#5) was used to determine the degradation of optical
imagery caused by supersonic and hypersonic shock waves, boundary layers, and rapid frictional heating of the photographic window. Several different experimental packages were employed using well-instrumented aerial cameras and multiple boundary-layer rakes. Two different camera systems were installed in the X-15 for the experiment. (NASA)

Bob Rushworth flew the first flight (1-33-54) with the KC-1 on 11 April 1963 and NASA shipped the exposed film to Westover AFB in Massachusetts for processing. The last of six flights (1-38­81) was made on 18 July 1963, again with Rushworth as the pilot. The majority of the detailed results are still classified, but a general overview is given in the Phase II discussion.-107

Paul F. Bikle was born on 5 June 1916 in Wilkensburg, Pennsylvania, and graduated from the University of Detroit with a bachelor of science degree in aeronautical engineering in 1939. His career with the Army Air Forces began in 1940 when he became an aeronautical engineer at Wright Field, and in 1944 he became chief of the aerodynamics branch of the Flight Test Division. While working closely with other government agencies in establishing the first flying qualities specifications for aircraft, he wrote AAF Technical Report 50693 ("Flight Test Methods"), which was used as a standard manual for conducting flight tests for more than five years. During World War II he was involved in more than 30 test projects and flew over 1,200 hours as an engineering observer.

In 1947, Bikle became chief of the performance engineering branch and directed tests of the XB – 43, XC-99, and F-86A. When the flight-test mission was transferred to the newly formed Air Force Flight Test Center (AFFTC) at Edwards, Bikle came to the desert and advanced to assistant chief of the flight-test engineering laboratory in 1951. From there, he advanced to the position of AFFTC technical director. He replaced Walt Williams as director of the NASA Flight Research Center (FRC) in September 1959. Like Williams, Bikle had little use for unnecessary paperwork, and often remarked that he would stay with NASA as long as the paperwork level remained below what he had experienced in the Air Force. He was also an avid soaring enthusiast and established two world soaring records during a flight near Lancaster on 25 February 1961 that still stands as of 2006. In July 1962, Bikle received the NASA Medal for Outstanding Leadership for directing the "successful X-15 flight operations and research activities," and he received the 1963 FAI Lilienthal Medal. Bikle retired from NASA in May 1971 and died on 20 January 1991.[6]

Al White was the second contractor pilot assigned to the X-15 project. He participated in the centrifuge program, attended the training sessions, flew the fixed-base simulator, practiced the landing-approach flights, and flew the photo chase airplane for many of the early X-15 flights. White never flew the X-15.

Alvin S. White was born in December 1918 in Berkeley, California. In 1936, he enrolled in the University of California at Davis to study electrical engineering, transferring to the Berkeley campus two years later. In 1941, he enlisted as an aviation cadet in the Army Air Corps, graduating from flight school at Williams Field, Arizona, in May 1942.[29]

After nearly two years as an advanced flight instructor at Williams Field, White joined the 355th Fighter Group in England on 4 June 1944. He flew two tours as a combat fighter pilot from D-Day until the end of the war in Europe. White returned to the University of California at the end of 1945, earning his degree in mechanical engineering with elective courses in aeronautical engineering in 1947.

In 1948, White reenlisted in the Air Force and spent nearly three years conducting parachute research at Wright-Patterson AFB and the National Parachute Range at El Centro. In 1952, White graduated from the Air Force Test Pilot School at Edwards and joined the fighter test section. In May 1954, he left the Air Force to join North American Aviation.

After four years of testing the F-86 series, the F-100 series, and the F-107, he became backup pilot to Scott Crossfield on the X-15. In 1957, White became project pilot for the XB-70, and concentrated his work on that program after the completion of the North American X-15 flights. After he retired from North American, White became a well-respected aviation consultant until his death on 29 April 2006.-130

During the development of the X-15, many wanted to expand the program beyond the three airplanes covered under the original agreements. This opinion obviously did not prevail, but the proposals are nonetheless of passing interest. Early on, North American suggested using X-15 as part of an extensive training program for astronauts and test pilots, believing that such a program could familiarize pilots with rocket-powered aircraft, the use of reaction controls, and the physiological sensations of space flight. The Air Force did not express any particular interest.-141

Early in 1958, researchers at the HSFS wanted to procure one additional X-15 for flight-control research, but NACA Headquarters did not concur. It was the first of several such proposals.142–

In mid-1958 the first serious proposal to expand the X-15 program came when Air Force Headquarters asked the ARDC if there was any merit to expanding the X-15 program. On 8 April 1958, headquarters requested recommendations for "configuration changes, estimated costs, aircraft availability, the increased performance expected, the test results to be obtained, and a brief substantiation of their value." Headquarters wanted the results of the study at an early date because it needed to make a decision before North American disbanded the engineering team.143–

The X-15 Project Office asked the AFFTC, North American, and WADC for recommendations. By 29 April, these organizations concluded that the best approach would be to improve performance using new structural materials and an improved rocket engine instead of the XLR99. The development difficulties with the XLR99 apparently influenced the call for a new engine, although the WADC suggested that any new engine should "be obtained as a result of across the board BMD [Ballistic Missile Division] and other efforts, and not as a sole X-15 effort."144-

The Navy verbally concurred with expanding the program on 19 May, and the NACA agreed a day later. On 13 June the X-15 Project Office recommended to the ARDC that three additional airplanes be constructed using higher-temperature structural materials than those used in the original design. The ARDC forwarded this recommendation to Air Force Headquarters on 16 June.145-

Apparently, the seeming urgency in the 8 April letter from headquarters had evaporated. On 18 November 1958, Major General Marvin C. Demler, director of research and development at Air Force Headquarters, finally informed the ARDC that the X-15 program would not be expanded. In the interim, the Research Airplane Committee had met on 31 October and Hugh Dryden concluded the three original airplanes were adequate for NASA’s purposes. Ultimately, the Research Airplane Committee recommended against procuring additional airplanes.146

There was, however, another fleeting prospect. After an explosion seriously damaged the X-15-3 during an XLR99 ground test, the X-15 Project Office had to solicit additional funds from the Pentagon to rebuild the aircraft. This prompted a renewed interest in the X-15 and the data it might deliver for future use in the Air Force space program. On 12 August 1960, Air Force Headquarters ordered a complete review of the X-15 program. The X-15 Project Office presented its results at the 17-18 October 1960 X-15 program review. The briefing identified original program objectives that were no longer valid, new objectives to consider, continuing objectives, and funding requirements. Surprisingly, the general officers who were briefed agreed that the X – 15 promised to be considerably more important to the Air Force space effort than had been foreseen when the program was initially conceived in 1954, or when the program expansion was rejected in late 1958. The Pentagon advised the ARDC that it would "entertain" proposals for additional X-15s to be operated exclusively by the Air Force.

As part of the ongoing discussion, the AFFTC put together its own recommendation for the program. On 26 October 1960 the AFFTC released a report that called for three additional X-15s and one more NB-52 "to carry out R&D objectives not presently covered by the present NASA-AF – Navy X-15 program." The AFFTC expected to "own and operate" these aircraft. Based on a 1 January 1961 start, the AFFTC expected the first aircraft to be delivered (along with a third NB-52) in September 1961, with the others following in March and June 1962. The flight program was to average 60 flights per year through December 1965. Some of the research objectives for the new aircraft included flight control and guidance, aero-thermo-elasticity, supersonic boundary-layer turbulence, sonic fatigue, landing-impact data, and electromagnetic propagation. The AFFTC expected that it would need an additional 330 people to support the X-15, plus 37 more to operate the High Range during AFFTC flights.147

Another proposal, originating from Brigadier General Donald R. Flickinger at ARDC Headquarters, was for a two-place biomedical research version of the airplane.-1148!

The Air Force called a meeting at Wright Field on 14 November that brought together representatives from the ARDC, the WADC,149 the command and control division of the Air Force Cambridge Research Laboratories, and the Army Corps of Engineers.-1501 It was immediately apparent to the X-15 Project Office that if all of the stated requirements for X-15-type aircraft were to be satisfied, "several additional X-15s will be required." Two weeks earlier the government had notified North American of the meeting, and Charlie Feltz prepared a briefing outlining several advanced X-15 configurations. Feltz presented his briefing on the afternoon of 14 November and provoked further interest in a comprehensive extension program.151

Although a two-seat X-15 engineering study had been required in the original proposals, the government had not taken any action on the idea. Nevertheless, it loomed in the background during much of the early X-15 program. The variant shown during the November 1960 meeting differed somewhat from the one originally proposed. North American optimized this version for "space training and biomedical research." Instead of simply deleting the research instrumentation and extending the canopy over the second cockpit, the new configuration extended the fuselage by approximately 14 inches and added a second cockpit with a separate canopy. The company deleted the aero-thermo research equipment, but the extension provided space for a variety biomedical equipment.-1152

North American environmentally separated the second cockpit from the primary cockpit so that it could study alternate atmospheres (i. e., not nitrogen-purged). A separate set of dummy controls could be installed that would allow the second pilot to react independently from the pilot flying the aircraft. His responses would be recorded and reconstructed on the ground to evaluate performance under acceleration and weightless conditions. It was expected that flight profiles could be developed that would allow five minutes under essentially weightless conditions during flights to altitudes in excess of 500,000 feet. The change added 354 pounds to the aircraft, but the use of an uprated XLR99 would have increased performance by 120 fps.[153]

The meetings resulted in NASA rearranging the existing X-15 program slightly to accommodate the Air Force research priorities, and relegating excess work to the new research extension program. The product was a revised System 605A plan released on 1 February 1961. Essentially, the X-15 Project Office requested approval for the construction of two additional aircraft, both of them slightly stretched two-seat versions similar to one proposed by Charlie Feltz in November. For the moment, the question of additional single-seat aircraft or advanced models was not considered pressing and was deferred. The two-seat aircraft would satisfy the need for biomedical research and training of future aerospace research pilots and Dyna-Soar astronauts.-1154

The idea was short-lived. On 20 March 1961, Major General Marcus F. Cooper, chief of research and engineering at ARDC Headquarters, disapproved the development plan. Cooper instructed the X-15 Project Office to revise the existing (October 1960) development plan to reflect funding changes proposed by the Pentagon. Nevertheless, in one paragraph Cooper instructed Wright Field to "give consideration to the election of the best type of vehicle to use in training future

Aerospace Research Pilots___ The possibility of using the existing X-15s for this purpose after

completion of the test program should be explored. In addition the need for additional X-15 aircraft or other vehicles, such as Dyna-Soar, for this purpose should be considered." The concept could potentially require additional X-15s.[155]

Although this kept hopes alive for an expanded X-15 program, it essentially buried the two-seat X-15. As Cooper explained, funding shortages for FY61 and FY62 would prevent "the additional heavy funding required in those years to support the proposed additional X-15 aircraft." It had also become apparent that the existing X-15s, with some additional equipment and telemetry installations, could acquire the majority of the desired biomedical data at far less cost. The X-15 Project Office had also begun to worry that stretching the X-15 fuselage might involve more engineering and development work than anticipated, although the subsequent development of X – 15A-2 proved this concern to be unfounded.-156

The ARDC Commanders Program Management Review in March 1961 tasked the X-15 Project Office to review "identified problem areas which might require investigation by X-15 type aircraft with particular attention given to the relationship between the problem areas and presently authorized advanced aerospace programs and studies." The response indicated that two additional single-place X-15s would be useful for investigating a variety of Air Force-specific areas of interest. The ARDC rejected this recommendation on 2 August 1961, and all thoughts of additional X-15s seemed to fade.-152

As near as can be determined, the three X-15s spent their entire career in and around Edwards, except for the occasional trip back to Inglewood to be repaired or modified. There was one exception, part of Project Eglin 1-62. On 2 May 1962, Jack Allavie and Bob White, along with a pressure-suit technician and a B-52 crew chief, took the NB-52A and X-15-3 to Eglin AFB in Florida for the 4-hour-long "Air Proving Ground Center Manned Weapons Fire Power Demonstration" attended by President John F. Kennedy. According to Allavie, "[W]e took off with an inert X-15 and flew all the way to Eglin AFB in Florida… that’s 1,625 miles and it was a simple flight. We landed there, put the X-15 on exhibit, and then flew it back to Edwards" on 5 May with a stop at Altus AFB, Oklahoma, for fuel. Photographic evidence shows a mission marking on the NB-52A depicting an X-15 oriented in the opposite direction of the regular launches (indicating, one guesses, a flight eastward) and the inscription "PRES. VISIT EGLIN FLA." Although it was by far the longest captive carry of the program, NASA did not assign the flight a program flight number.[185]

Back at Edwards, during the summer of 1962 Bob White made three flights in X-15-3 that demonstrated the potential problems of matching the preflight profile. On the first flight (3-5-9), White became disoriented during the exit and decided that he needed to push the nose down slightly so that he could visually acquire the horizon: "When we got up to 32 degrees, and at about 60 seconds in time, I guess it was just a small case of disorientation. I say a small case because I didn’t lose complete orientation but when I was up at this climb angle, and this is the first time that I’ve had this feeling, I looked at the ball, I had 32 degrees in pitch, but I had the darndest feeling that I was continuing to rotate. I couldn’t resist the urge just to push on back down until the light blue of the sky showed up. I never did get to the horizon, but I was satisfied that it wasn’t happening." By the time he was satisfied and began his climb again, his energy was such that he undershot his planned 206,000-foot peak altitude by 21,400 feet.[186]

White’s next flight (3-6-10) was only nine days later. This one was much better. White undershot by only 3,300 feet, about average for the program. White reported that the weather obscured most of his view of the ground: "I did look around quite a bit, and I was a little disappointed because of all the low clouds that obscured the coast line. I took a couple of definite looks because I wanted to try and scan up further north, and down along the Mexican coast, and pick out some places, but the cloud cover was so extensive that I couldn’t really do that. Then too, when you’re up there it feels like everything’s right under the nose. It was reassuring again to hear ground saying you’re right on profile and track. That eliminates any concern on the pilot’s part."^

If it seemed that White was getting better at hitting his planned altitude, the next flight would dispel any such thoughts. On 17 July 1962, White took X-15-3 on a flight that was supposed to go to 282,000 feet, which was sufficient to qualify him for an Air Force astronaut rating. The MH – 96 failed just before launch, which probably should have meant scrubbing for the day. Instead, White reached over and reset the circuit breakers. The MH-96 appeared to function correctly, so White called for a launch. White seemed to be trying to make up for the altitude he had not achieved on his last two flights. The climb angle was a bit steeper than called for, and the engine produced a bit more thrust than usual and burned a bit longer than expected. The result was a flight that was 32,750 feet higher than planned, setting a new Federation Aeronautique Internationale (FAI) record for piloted aircraft of 314,750 feet and becoming the first winged vehicle to exceed 300,000 feet, the first flight above 50 miles, and the first X-15 flight that qualified its pilot for an astronaut rating. This time, as the first astronaut from Edwards, White was suitably impressed with the view:11881

You could just see as far as you looked. I turned my head in both directions and you see nothing but the Earth. It’s just tremendous. You look off and the sky is real dark. I didn’t think the impression would be much different than it was up around 250,000 feet, but I was impressed remarkably more than I was at 250,000 feet. It amazed me. I looked up and was able to pick out San Francisco bay and it looked like it was down over there off the right wing and I could look out, way out. It was just tremendous, absolutely tremendous. You have seen pictures from high up in rockets, or these orbital pictures of what the guy sees out there. That’s exactly what it looked like. The same thing.

White reentered and arrived over the high key at Mach 3.5 and 80,000 feet. The potential for a repeat of Armstrong’s excursion to Pasadena was present, but White had learned from Armstrong’s mistake: "I was mainly concerned at this time with the possibility of overshooting the landing point. I think that was my overriding consideration at this point. I went by the lake and turned it around, and when I went around in the turn I just pushed in on the bottom rudder so I could get the nose down and stay in where I had some q. I didn’t want any bounce in altitude. If I had gotten bounce, I would never have gotten back."11891

A wide sweeping turn over Rosamond brought White back to a more normal high key at 28,000 feet and subsonic speeds. He continued around for a near-perfect landing at 191 knots. Milt Thompson in the chase plane commented, "Nice, you really hit that… Bob," and Joe Walker in the NASA-1 control room finished by saying, "This is your happy controller going off the air." Despite having overshot the altitude by more than 10%, White flew the flight nearly perfectly, and data from this flight would be used for several years to check out and calibrate the fixed-base simulator.11901

The altitude missions demanded precise piloting, and even then, several variables beyond the control of the pilot could result in significant altitude errors. On 17 July 1962, Bob White took X – 15-3 on a flight that was supposed to go to 282,000 feet. The climb angle was a bit steeper than called for, the XLR99 produced a bit more thrust than usual, and it burned a bit longer than expected. The result was a flight that was 32,750 feet higher than planned, setting a new FAI record for piloted aircraft of 314,750 and becoming the first winged vehicle to exceed 300,000 feet, the first flight above 50 miles, and the first X-15 flight that qualified its pilot for an astronaut rating. (NASA)

Interestingly, this flight will probably remain an altitude record for airplanes as long as the FAI has a category for rocket-powered aircraft. In theory, it is possible to break the record one time. According to the rules, new records must exceed the old mark by 3%, meaning that somebody will have to fly at least 324,193 feet altitude to beat White’s record. However, according the FAI, the atmosphere ends at 328,099 feet (100 kilometers). Therefore, it will be impossible to better the subsequent record without going into space, which would disqualify the attempt (as happened with Joe Walker’s 354,200-foot flight). The chances of somebody managing to get above 324,194 feet without exceeding 328,098 feet are extremely remote. It has been 40 years and nobody has tried yet.[191]

technological contributions to the advancement of flight and for great skill and courage as test pilots of the X-15." By this point Crossfield had been gone for two years, and Petersen had already left to become the commanding officer at VF-154. Nevertheless, all four pilots journeyed to Washington to accept the trophy on the South Lawn of the White House. The National Aeronautic Association annually awards the Collier Trophy, which is generally considered the most prestigious recognition for aerospace achievement in the United States. In the case of the X-15, the selection of the recipients was not arbitrary; it represented the first pilot from each organization (North American, Navy, NASA, and Air Force) to fly the airplane. The trophy itself was 7 feet tall and weighed 500 pounds, and when Kennedy presented it to Bob White (the spokesman for the group), he commented, "I don’t know what you are going to do with it."[192]

Later the same day the Air Force presented White with his astronaut wings during a small ceremony at the Pentagon, and that evening NASA feted all four pilots at a dinner where they received the NASA Distinguished Service Medal from Vice President Lyndon B. Johnson. NASA administrator James E. Webb commented at the dinner that the X-15 program was "a classic example of a most effective way to conduct research."

Since the beginning, the X-15 program had used four North American F-100 Super Sabres as Chase-1. However, the F-100 was getting old, and the AFFTC was happy to begin receiving new Northrop T-38 Talons during October 1961. Pilots reported that the T-38 "appears as good or better than the F-100F for X-15 support." The Air Force conducted several test flights, sans the X-15, to evaluate whether the T-38 could fly close chase at 45,000 feet when the NB-52 was in a right-hand turn-something the F-100 could not do. Such a capability would allow a right-hand NB-52 pattern prior to a launch, and would greatly improve ground telemetry reception during that period since the NB-52 fuselage would not block the X-15-to-ground line of sight. The previously used left-hand pattern resulted in a loss of telemetry during the turn until approximately 2 minutes prior to launch, but allowed the F-100F to remain in a suitable chase position during activation of the X-15 systems. The problem was that during a right turn the F – 100 was on the inside of the turn and had to fly at a slow indicated airspeed. In a left turn on the X-15 side, the F-100 was on the outside of the turn, flying at a higher and more acceptable indicated airspeed. The first flight (1-32-53) to use a T-38 was in July 1962 and the T-38 would be Chase-1 for almost every flight until the end of the program.-1193

On 18 July 1962, president John F. Kennedy presented the Robert J. Collier Trophy to the X-15 program. The award was accepted by Scott Cross field, Forrest Peterson, Joe Walker, and Bob White in a ceremony on the South Lawn of the White House.. The trophy is seven feet tall and weighs 500 pounds. (NASA)

Previous X-planes had recorded all of the research data onboard, mainly because telemetry systems were in a very early state of development and bandwidth was very limited. Nevertheless, several earlier programs did telemeter a small amount of data to the ground in real time. It was decided early on that all X-15 data would continue to be recorded onboard the aircraft, although much more extensive use of telemetry would also be made. The reason for recording everything onboard was "to eliminate the risk of data loss and degradation inherent in radio-frequency telemetry links." This took on more significance for the X-15 program since the airplane would frequently be out of range of the antennas at Edwards, and would have to rely on the new and untried High Range installations at Beatty and Ely.-11

Initially, the instrumentation centered on the aero-thermo environment that the researchers intended the X-15 to investigate. When the follow-on experiments began to arrive, more of the instrumentation and recording capacity shifted to support non-aero-thermo investigations. A group of researchers from the HSFS, Langley, and Lewis-with limited input from the WADC and AFFTC-came up with the initial requirement for between 1,000 and 1,100 data points. Per the original specification, instrumentation was limited to 800 pounds and 40 cubic feet, and could use up to 2.25 kilowatts of power. The approved design included 1,050 instrumented points (588 thermocouples, 64 strain gages, 28 control surface position indicators, 136 aerodynamic surface pressures, 22 basic flight parameters (angle of attack, etc.) and 212 airplane condition monitors). By contrast, the X-2 had used only 15 thermocouples and a few electrical pressure transducers, and carried only 550 pounds of research instrumentation.-12!

In mid-1957, the NACA asked the Air Force to modify the X-15 specification to double the amount of research instrumentation carried by the airplanes. Given that North American had already frozen the design by that time, this came as something of a shock. In order to keep the airplane’s weight (and hence performance) from being too seriously degraded, numerous structural and subsystem details were redesigned to save weight.-13

When the X-15 emerged from North American, it could carry 1,300 pounds of research instrumentation, the majority of which were installed in a removable elevator in the instrumentation compartment just aft of the cockpit. Engineers designed the cabling so that they could remove the entire elevator from the airplane, which allowed them to perform all pre – and postflight calibrations more easily. Originally, the engineers intended this feature to remove the instrumentation from possible ammonia contamination, but NASA seldom used it for that purpose. Within the airframe itself, all of the wiring and tubing were routed through the fuselage side tunnels.-4-

In addition to the instrumentation compartment, North American installed small amounts of equipment in the nose of the airplane, in a center-of-gravity compartment located between the oxidizer and fuel tanks, and in the rear fuselage. The main instrumentation compartment and the nose compartment were pressurized and temperature-controlled. The center-of-gravity

compartment was temperature-controlled but unpressurized, and the rear fuselage area was insulated against high temperatures but was otherwise uncontrolled. Individual instruments and equipment were shock-mounted or hard-mounted as necessary; hard mounting was preferred because it saved weight and space.[5]

In many respects, X-15 development occurred at an awkward time. Modern data-processing systems were in their infancy, but they promised to offer a substantial improvement over the largely mechanical systems that had preceded them. However, the simple fact was that they were not ready. This forced the instrumentation engineers to rely on oscillographs and precision photographic recorders for the aircraft instead of modern magnetic tape recorders. Most of the rationale was simple: these devices were available from commercial sources or from NACA stock, lessening the cost of an already over-budget program. The program could also procure and test them within the time available before the first flight.

However, they came with some handicaps. The time associated with processing data from an oscillograph system, especially when large quantities of data were involved, was long and tedious compared to that required for data from magnetic tape systems. The instrumentation community debated this problem at length, but finally decided that the 15,000 data points expected to be collected on each flight would not result in processing times that would be detrimental to the planned flight schedule. It was also a fact that during 1956-1957, a costly, time-consuming development program would have been required to obtain a fully automatic magnetic tape system that could withstand the X-15 environment.-^

Despite the "design" instrumentation list, as manufactured the first two airplanes each had 656 thermocouples, 112 strain gages, 140 pressure sensors, and 90 telemeter pickups. The thermocouples were 30-gage chromel-alumel leads that were spot-welded to the inside surface of the skin. The leads connected to 20-gage extensions that were routed to the signal­conditioning equipment and recorders. The use of 20-gage extensions was necessary to reduce circuit resistance in the thermocouple loops and to minimize measurement errors due to resistance changes caused by the large temperature variations along the wire. Since the thermocouples were inaccessible after the airplanes were constructed, North American designed the installation to function for the life of the airplane and require no maintenance. A silicone – impregnated fiberglass braid covered the leads and extensions, and those in close proximity to the skin used an outer sleeve of unimpregnated fiberglass. The silicone impregnation slowly sublimated during repeated exposure to elevated temperatures, but retained its electrical insulating properties. Its use, however, created a potential problem since tests showed that out – gassing could result in an explosion if the temperature quickly rose to 1,200°F for the first time. NASA eliminated this hazard on the X-15 by gradually building up to the maximum Mach number during the course of the envelope-expansion program.-71

The first two airplanes used Bakelite strain gages, but these lost their effectiveness as structural temperatures increased. Consequently, North American completed X-15-3 with Micro-Dot weldable-type strain gages designed for use at higher temperatures. The static pressure taps consisted of 0.3125-inch-outside-diameter tubing installed flush with the outside surface of the skin. A study was made of the lag effects of a tube-connected system, and it was determined that 0.25-inch tubing with lengths as great as 40 feet was acceptable for gradual maneuvers and steady-state data at altitudes up to 100,000 feet.-81

either side. Because of installation difficulties, no instrumentation was located near the integral propellant tanks. Similarly, North American did not initially install any pressure instrumentation in the horizontal stabilizers due to the difficulty of running tubing to this location. However, the company did install some strain gages in the horizontal, with the wiring running through the pivot point. As part of a loads study late in the program, North American manufactured a new set of horizontal stabilizers with electrical pressure transducers, loads sensors, and thermocouples. Toward the end of the flight program, researchers also installed instrumentation in the wing-tip pods and ventral stabilizer on some flights.-191

Precision NACA recorders that employed servo-repeater systems to position a light source on moving film recorded angle-of-attack and angle-of-sideslip data provided by the ball nose. Similar devices recorded the attitude-angle outputs from the stable platform. Electrical transducers sensed all other data. A central patch panel in the main instrumentation compartment collected the data, routed it to appropriate signal conditioners, and then sent it to recording oscillographs and the telemetry set. The NACA-developed photo-oscillographs were capable of recording 36 channels each. Recording speeds could be varied from 0.25 inch per second to 4.0 inches per second, resulting in recording times ranging from 56 minutes to only

3.5 minutes using 70-foot film magazines. The photo-oscillographs used a blue-sensitive polyester-based thin film with the trade name Cronar®. A variety of 16-mm motion picture cameras photographed portions of the pilot’s instrument panel, and the wings and empennage during flight.1101

This block diagram shows the basic interrelationship of the various pieces of research instrumentation carried on the X-15. The exact instrumentation varied considerably between airplanes, and flight to flight. Late in the program the X-15-3 received a much more modern PCM telemetry system. (NASA)

Recorder limitations restricted the number of installed sensors that could be recorded simultaneously. A 12-channel oscillograph recorded 40 thermocouples per channel at 1-second intervals, and four manometer-oscillographs recorded up to 96 pressure transducers. A NACA – designed aneroid-type 24-cell film-recording manometer similar to those used in previous flight programs recorded the surface pressures. Again, recorder limitations restricted the number of pressure measurements that could be recorded simultaneously. The exact data recorded often differed on each flight as researchers and engineers connected different sensors to the recorders and telemetry system. A single switch in the cockpit turned on all of the recorders, and an event switch allowed the pilot to mark the recording when something significant occurred.[11]

Two separate cockpit instrument panels were supplied with each of the first two airplanes: one for the initial low-speed flights using the XLR11 engines and the nose-mounted flight-test boom, the other for hypersonic flights using the XLR99 engine and the ball nose. NASA significantly revised the instrument panel in the first two airplanes early in the flight program based on pilots’ comments that the original panel was difficult to scan under all flight conditions, especially when they were wearing the MC-2 full-pressure suit. As initially completed, X-15-3 had an instrument panel identical to the XLR99 panels manufactured for the first two airplanes. However, when North American rebuilt the airplane following its XLR99 ground explosion, the Air Force decided to incorporate the Minneapolis-Honeywell MH-96 adaptive flight-control system, and this necessitated a unique instrument panel. NASA subsequently replaced this panel late in the flight program with a set of vertical-tape displays developed by Lear-Siegler. All of the instrument panels were in a constant state of flux as various switches and indicators were added to almost any available location in the cockpit to support the various experiments and data requirements for any given flight. Every attempt was made to keep the critical displays and switches in constant locations between the three airplanes (at least as much as possible given the radical difference in X-15-3), and twice the program created a "standard X-15" cockpit arrangement and brought the airplanes into compliance. This greatly eased the problems associated with keeping the simulator accurate, and made life much easier for the pilots and flight planners.-1121

Initially, the X-15s used a pulse-duration modulation (PDM) telemetry system that researchers considered state of the art when they selected it. However, the system was insufficient for many types of data that researchers wanted to view on the ground (particularly the biomedical parameters), and the AFFTC Human Factors Subcommittee requested the installation of a more sophisticated FM-FM telemetry system. Initially, the FRC objected to the proposed change because of the size and volume requirements of such a system. However, on 2 December 1960 Paul Bikle stated that he favored the installation of a FM-FM system if it fit into the space then used by the existing North American telemetry system. By then, the state of the art allowed the Air Force to purchase a 12-channel FM-FM system for use in the biomedical package. NASA subsequently installed this system in the X-15s as needed to support biomedical work, and the first flights took place in late 1961.-131

In May 1967, NASA installed a modern pulse-code modulation (PCM) system in X-15-3. The first flight (3-58-87) for the new system was on 26 April 1967 with Bill Dana at the controls. By all accounts, the new system worked well and provided a great deal more bandwidth than the old PDM and FM-FM telemetry systems. It appears that NASA never updated the other two aircraft to PCM.1141