Category X-15 THE WORLD’S FASTEST ROCKET PLANE AND. THE PILOTS WHO USHERED IN THE SPACE AGE

ROBERT A. RUSHWORTH

1924-1993

Bob Rushworth was the workhorse test pilot for the X-15, with thirty-four flights, more than the next most frequent flyer, Jack McKay, who flew the X-15 for twenty-nine flights. Rushworth set the high-speed record for the X-15-1 (the first X-15) on December 5, 1963, achieving Mach 6.06.

Bob Rushworth was born on October 9, 1924, in Madison, Maine. During World War II, he joined the Army Air Forces and flew C-46 and C-47 transports. He was called back into the Air Force to fly combat missions during the Korean War, after which he made the Air Force his career. He had graduated from Hebron Academy in 1943, and he continued his education at the University of Maine, where he received his bachelor of science degree in mechanical engineering in 1951. He followed this with a degree in aeronautical engineering from the Air Force Institute of Technology (AFIT) in Dayton in 1951. Much later, after completing his service as an X-15 test pilot, he graduated from the National War College at Fort McNair in Washington in 1967.

After receiving his AFIT degree in aeronautical engineering, Rushworth stayed at Wright Field in Dayton to start a flight-test career. In 1956, he was transferred to Edwards Air Force Base, where he graduated from the Experimental Test Pilot School just in time to join the X-15 program in 1958. His first flight in the X-15 was on November 4, 1960, an uneventful pilot-familiarization flight to obtain stability and control, and performance data, at Mach 1.95 at 48,900 feet. Rushworth was

Three X-15s were built and were unofficially labeled by people in the program as Ship 1,

Ship 2, and Ship 3. (This harks back to the early twentieth century when sometimes airplanes were referred to by the name of “ship.”) The official labels of the three X-15s were X-15-1, X-15-2 (later renamed the X-15A-2 after extensive modifications following an accident midway through the flight program), and X-15-3.

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Rushworth in the X-15-1. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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Rushworth in the X-15A-2. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

to fly thirty-three more times in the X-15, during which he achieved a maximum Mach number in the X-15-1 of 6.06, as noted earlier. Other accomplishments included the first ventral-off flight on October 3, 1961, and the highest dynamic pressure of 2,000 pounds per square foot (an aerodynamic high point that tested the structural integrity of the X-15) on May 8, 1962. When he attained an altitude of 285,000 feet on June 27, 1963, he qualified for Astronauts Wings.

Rushworth encountered numerous problems during his test flights. The right inner windshield
cracked during his Mach 6.06 flight, and it happened again six months later on May 12,

1964, after achieving Mach 5.72 and an altitude of 101,600 feet. On September 29, 1964, after achieving Mach 5.2, the nose gear scoop door came open at Mach 4.5 and 88,000 feet. Later, Rushworth calmly noted that the X-15 handled worse in that configuration than with the nose gear fully extended. On February 17, 1965, his right gear extended at Mach 4.3 at 85,000 feet, his inertial altitude indicator failed, and he momentarily lost engine power 23 seconds into the

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Rushworth after an X-15 flight. USAF, Air Force Flight Test Center Flistory Office, Edwards Air Force Base

flight. Despite all this, he continued with the flight, attaining Mach 5.27 at 95,000 feet and carrying out his test mission of stability and control evaluation, star tracker checkout, and advanced landing dynamics.

Rushworth’s last flight in the X-15 was on July 1, 1966, the 159th flight of the program, and again not without excitement. An indication of no propellant flow from one of the external tanks carried during that flight caused him to eject the external tanks and land prematurely, as he stripped off the top of a camper upon landing at Mud Lake.

Perhaps one of Rushworth’s most important contributions to the X-15 program was on the ground. Milton Thompson notes that because it was not a combat aircraft, the X-15 had low priority within the Department of Defense, and it was mainly due to Rushworth’s efforts that the X-15 schedule was reasonably maintained.

After leaving the X-15 program, Bob Rushworth moved to F-4 Phantom combat crew training at George AFB, and then assignment to Cam Ranh Bay Air Base in Vietnam as the assistant deputy commander for operations with the 12th Tactical Fighter Wing, where he flew 189 combat missions. He returned to the United States in 1969 as program director for the AGM-65 Maverick missile, and he became commander of the 4950th Test Wing at Wright-Patterson AFB in 1971. Two years later, he was inspector general for the Air Force Systems Command, and in 1974 he returned to Edwards as commander of the Air Force Flight Test Center. In 1975, he became commander of the Air Force Test and Evaluation Center at Kirtland Air Force Base in New Mexico. He was promoted to Major General on August 1, 1975. He retired from the Air Force in 1981 as a general and as vice commander of the Aeronautical Systems Division at Wright-Patterson Air Force Base.

On March 18, 1993, Bob Rushworth died of a heart attack in Camarillo, California. He left behind a stellar career as a test pilot and Air Force officer, and his expert handprints are all over the X-15 program.

NEIL A. ARMSTRONG

1930-2012

Neil Armstrong, by virtue of being the first man to step foot on the moon, is known and respected worldwide.

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Armstrong was in many ways an anomaly among the X-15 test pilots. Following in the steps of Bob Rushworth, who flew the X-15 a total of thirty-four times, seventh X-15 pilot Armstrong made only seven flights in the airplane. Like Scott Crossfield, Neil Armstrong was first and foremost an aeronautical engineer. Even when he was working with NASA as a test pilot, he was known as one of their best engineering minds. Much later,

Подпись:he said about himself, “I am, and ever will be, a white-socks, pocket-protector, nerdy engineer— born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow.”

Neil Armstrong was born on August 5, 1930, in Wapakoneta, Ohio. His interest in airplanes can
be traced back to the time when his father took him to the Cleveland Air Races when he was only two years old. When he was five, his father took him for his first airplane flight in Warren, Ohio, on a Ford Trimotor. Neil took flying lessons while attending high school, and he earned his flight certificate at the age of fifteen, before he had a driver’s license. He became an Eagle Scout, and for the remainder of his life he was a dedicated supporter of the Boy Scouts. (Among the few personal items that he carried with him to the moon was a World Scout Badge.)

In 1947, Armstrong began studies in aeronautical engineering at Purdue University, but he was interrupted by the Korean War. Armstrong became a Navy pilot, flying F9F Panthers for seventy-eight missions over Korea and achieving the Air Medal, the Gold Star, and the Korean Service Medal, all before the age of twenty-two. After leaving the Navy, he returned to Purdue and received his bachelor of aeronautical engineering degree in 1955. He joined NACA as an experimental research test pilot at the Lewis Flight Propulsion Laboratory in Cleveland, and he then moved to the NACA High Speed Flight Station (now the NASA Dryden Flight Research Center) as an aeronautical research scientist and test pilot. It was there that he attended the University of Southern California, earning a master’s degree in aeronautical engineering. And it was there that he became involved with the X-15 program as a test pilot.

Armstrong’s first flight in the X-15, the usual pilot-familiarization flight, took place on November 30, 1960, when he reached Mach 1.75 and an altitude of 48,840 feet. The upper No. 3 chamber of the rocket engine did not start, and the readout of inertial altitudes was incorrect.

His second flight came nine days later, when he evaluated a new ball nose for the airplane and measured stability and control data. His third flight was not until almost a year later, on

Подпись: ASIRUThe X-15 was equipped with an air data inertial reference unit (ASIRU), which provided measurements based on air pressure, airspeed, angle of attack and altitude, and measurements based on inertial reference (accelerometer plus computer) of position and altitude. Hence, the altitude of the X-15 was measured using two separate techniques.

Radar data from the ground provided a third measurement of altitude.

(See NASA TM X-51000, The X-15 Flight Test Instrumentation, by Kenneth C. Sanderson, presented at the Third International Flight Test Instrumentation Symposium, Buckinghamshire, England, April 13-16, 1964.)

December 20, 1961, when he carried out the checkout flight of the No. 3 airplane.

On April 20, 1962, Armstrong carried out the longest flight of the X-15 program, a duration of 12 minutes and 28 seconds. On this same flight, he achieved his highest altitude, 207,500 feet. On his return, Armstrong inadvertently pulled too high an angle of attack during pullout. The flight path took a bounce in the atmosphere, and he overshot the Edwards Air Force Base, heading south at Mach 3 and at 100,000 feet. He was able to turn back while over the Rose Bowl in Pasadena. Almost out of kinetic and potential energy, he was just barely able to reach the south end of Rogers Dry Lake at Edwards.

Armstrong’s fastest flight in the X-15 was on July 26, 1962, when he achieved Mach 5.74. This was also his last flight in the airplane, because on September 13 he was selected for the Astronaut Corp by NASA, making him at that time the only civilian pilot in the astronaut program. With that, Armstrong’s career took a dramatic turn, culminating in his steps on the moon. The date was July 21, 1969, less than a year after the X-15 program came to an end.

After his Apollo 11 flight, Armstrong chose not to fly in space again. In 1971, he resigned from NASA and took a position with the University of Cincinnati as the distinguished university professor of aerospace engineering. He taught for eight years and then resigned without explaining his reason for leaving. He withdrew from public life and refused most speaking invitations. On August 7, 2012, in Cincinnati, he underwent bypass surgery for blocked coronary arteries. He died on August 25 from complications. Based on his request, his ashes were scattered in the Atlantic Ocean during a burial-at-sea ceremony aboard the USS Philippine Sea.

ROCKET CONTROLS IN SPACE

The use of rocket controls in flight was demonstrated earlier on the Bell X-1B airplane. Therefore, it was natural that rocket controls would be used for the X-15 as the only effective controls in space, where the aerodynamic forces are inadequate or nonexistent. These low-thrust rocket engines, using a monopropellant (hydrogen peroxide), provided useful control in space and have been used by the Space Shuttle in outer space.

ACCOMPLISHMENTS

All the design goals of the X-15 were met during its flight-test program, and some were surpassed.

The design maximum altitude and Mach number were both reached. The hypersonic research data obtained provided a rich database that confirmed the viability of hypersonic wind tunnel data as well as the usefulness of the limited theoretical analyses available at that time. The airplane proved to be a successful hypersonic vehicle, and the X-15 pilots performed admirably over an almost ten-year period. The program ended when the funding ran out and research experiments no longer justified the associated costs of the flights.

The flight region explored and extended the known range to M=6.7 and an altitude of 354,200 feet. The X-15 pilots explored this hypersonic range and provided data for future manned flights and for manned space vehicles flying from space through the atmosphere to landing, such as the Space Shuttle.

The new large RMI rocket motor performed well, providing the acceleration needed and with an operating efficiency of about 97 percent in support of obtaining mission data. There were no blowups in flight, and although the partial thrust use and subsequent restart capability were not reliable, the engine was able to position the airplane in the flight regions to be studied.

The MH-96 adaptive control system proved adequate and useful for stability on all three axes of flight. Some form of adaptive controls (controls that adapt automatically to the changing flight environment that was encountered during the flight of the airplane) have been used by high- performance aircraft in the fifty-plus years since the X-15.

All three control systems worked. The pilots preferred the power assisted controls over pure manual controls for use in the atmosphere, and the reaction rocket controls performed well in space and where the aerodynamic forces were insufficient. They have since been incorporated into the design of the Space Shuttle. The transition
in use of the control system from space to the atmosphere where aerodynamic controls took over was easily effected.

The high-temperature material, Inconel X, maintained its strength as predicted at the high temperatures obtained in flight, and it supported the flight loads. This design approach, which allowed for thermal expansion of the hot structure while the cold understructure remained unstressed, was ultimately successful after the engineering team made a few corrections following initial hot flights.

The aero-thermodynamic analytical predictions were considerably higher than the actual measurements; analytics can now reliably use empirical data obtained from these flights. The research team also learned that the predicted high stagnation temperatures occurred where air could enter small gaps in wing construction, which then burned internal wires and structural features.

A ball nose instrument was attached at the extreme nose of the airplane and utilized Inconel X to withstand the high temperatures of hypersonic flight. This instrument, which provided angle of attack and angle of yaw data to the pilot, was necessary for flying and controlling the airplane at the high-speed and high-temperature conditions.

Replacement of ailerons was accomplished by using the horizontal stabilizer differentially deflected (i. e., right stabilizer angle increased while the left stabilizer angle decreased, and vice versa), providing satisfactory roll control and simplifying the knowledge of airflow conditions at the tail.

Подпись: The stable platform used to mate the X-15 to the B-52 malfunctioned at the start of the first X-15 government flight on March 25, 1960. Nevertheless, the flight took place. It was also test pilot Joe Walker’s first X-15 flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base Подпись:As a research airplane, the X-15 was also a useful platform for doing experiments at hypersonic speeds. Most important, the repeated and successful utility of this airplane over highly accelerated and decelerated flight from space to landing demonstrated that piloted aircraft are suitable for manned controlled return from space and for missions in the hypersonic regime.

AIRPLANE AND ITS ENGINES

THE AIRPLANE

The X-15 was born on October 5, 1954, when the NACA Committee on Aerodynamics finally decided on the need for a manned hypersonic research airplane. No airplane had even come close to flight at Mach 5 or higher. The Bell X-1 had achieved Mach 1, the Bell X-1A Mach 2.44, and the Bell X-2 Mach 3.2. But to greenlight the development of an airplane that could fly at Mach 7 was truly visionary. No such manned airplane had ever been designed, much less built. Normally, engineers study the previous incarnation of the plane they want to build, innovating from these earlier successful design ideas. But the X-15 was revolutionary—no “before” design even existed. The team would have to start from scratch.

image61image62And for good reason.

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X-15-3 on the lakebed. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

The X-15 airplane had to be able to accelerate to Mach 7 and climb to over 250,000 feet in order to fill in the unexplored range in speeds above Mach 3.2 and altitudes above 126,200 feet, the maximum achieved by the X-2. (The Bell X-1 had reached 71,902 feet, and the Bell X-1A had reached 90,440 feet.) Like its predecessors, the X-15 would be flown out of Edwards Air Force Base, which was the only installation that had the support equipment and personnel—it was the location of the Air Force Test Pilot School—to
handle the research test flights. Moreover, because of the high landing speed of the X-15, Edwards had the only “runway” long enough for landing the airplane—essentially the whole expanse of the Muroc Dry Lake bed.

The new airplane, like the X-1 and X-2 before it, would be rocket-powered with high thrust, and it would be carried aloft in a “mother ship” to save fuel by applying the thrust at an altitude where the air density was low (hence, low drag). The X-15 would also have to carry enough fuel

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▲ X-15 under the wing of the B-52 in flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

▼ X-15-1 mounted under the wing of the B-52 before its first flight, June 8, 1959, with Scott Crossfield in the cockpit. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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Подпись: MONOCOQUE

Monocoque is a French word meaning “single shell.” Here, the fuselage is a single, hollow shell that carries on its surface the aerodynamic loads exerted on the fuselage. A monocoque fuselage allows maximum space inside the fuselage for internal components, such as fuel and oxidizer tanks, and electronic equipment. A semi – monocoque structure has additional elements inside the shell, such as formers that conform to the cross-sectional shape of the fuselage and stringers that run longitudinally along the fuselage. These provide additional structural strength while still preserving volume inside the fuselage for other components. These structural elements can be seen in the cutaway view of the X-15A-2 shown on the opposite page.

to allow the high thrust to operate long enough to accelerate to the speeds and altitudes needed to perform the mission. So, the airplane had to be big enough for the fuel volume needed and be able to carry a rocket engine with far more thrust than employed previously, as well as structural materials that would maintain strength at the high temperatures to which the airplane would be subjected at its high speeds of flight.

The design also had to consider the requirements of the nonhypersonic flight regimes for the other portions of flight: It would drop from the mother ship at high subsonic speed, accelerate through Mach 1 and the transonic speed region,
then through supersonic and hypersonic flight in getting to and from the targeted data points, and finally it would have to decelerate from hypersonic flight to return to the landing site, followed by descent and landing that had to occur at relatively low subsonic conditions.

Because of these specific design requirements, the engineers started with a blank slate, using all of the latest technologies that might apply to the new airplane and the extreme conditions, known and unknown, that it would endure. They also built upon their previous experience and knowledge of the known flight regimes to design an aircraft that could unveil the mysteries of hypersonic flight.

The X-15’s fuselage, wings, tail, size, and weight generally look conventional. The fuselage structure is monocoque and semimonocoque. The pilot compartment was a little more ample than that of a fighter jet. The wing has a span of 22 feet, uses an NACA 66005 symmetric laminar flow airfoil, has an area of 200 square feet and an aspect ratio of 2.5, and features a sweepback angle at the quarter chord of 25 degrees. The horizontal tail is tilted down from the fuselage, and the upper vertical tail looks like most others except that the airfoil is wedge-shaped with a blunt trailing edge, unlike the usual airfoil shapes.

But there are two major changes that further distinguish the X-15:

First, there are no ailerons on the wing; roll – control is achieved by deflecting differentially the right and left sections of the horizontal tail. Also, the horizontal tail has no elevators; instead, the whole right and left sections deflect in the same direction together to provide pitch control.

Second, the vertical tail has an unusual airfoil section. It is essentially a vertical slab, small and rounded at the leading edge and flat-sided at a 5-degree half-angle out to the trailing edge, which is blunt.

X-15 cutaway schematic. The Hypersonic Revolution, Vol. 1, edited by Richard P. Hallion, p. 141, USAF History Office

 

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X-15 three-side view.

NASA Dryden Flight Research Center

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Mach waves (very weak shock waves) on a

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Oblique shock waves on a wedge-type body, demonstrating that the stronger shock wave is at a larger angle than the weak Mach wave.

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Demonstration of the constant pressure exerted on the face of the wedge, downstream of the shock wave.

The leading edge is rounded in order to reduce the aerodynamic heating in that region. Overall, the vertical tail is a geometrically simple 10-degree total angle wedge with a blunt, flat surface for the trailing edge. The wedge shape has two aerodynamic advantages at supersonic and hypersonic speeds. First, the pressure on the flat sides is a constant downstream on the nose, and this encourages attached flow over the whole surface all the way to the blunt trailing edge. Expansion waves occur at each corner of the trailing edge. These expansion waves are the direct opposite of shock waves. The pressure decreases through an expansion wave, whereas it increases through a shock wave. The flow leaves the trailing edge through an expansion wave, and hence the pressure on the flat base of the vertical tail is lower. This in turn increases the aerodynamic drag on the vertical tail, called base drag, but at hypersonic speeds the base drag is a very small fraction of the overall drag.

The second aerodynamic advantage, and the primary reason for the use of the wedge shape, is increased directional stability. In August 1954, Charles H. McLellan, head of the 11-inch hypersonic wind tunnel at the NACA Langley Aeronautical Research Laboratory, published some stunning and almost counterintuitive results in NACA Research Memorandum LF44F21 entitled “A Method for Increasing the Effectiveness of Stabilizing Surfaces at High Supersonic Mach Numbers.” His work showed that the wedge shape “should prove many times more effective than the conventional thin shapes optimum for lower speed.”

The wedge shape took advantage of the nonlinear physics of shock waves as follows: If a surface in a supersonic flow is already inclined at an angle to the flow, say 5 degrees like the surface of a 5-degree half-angle wedge, and then the wedge itself is further inclined by an additional 2 degrees due to a control input, the pressure and hence the aerodynamic force on that surface (which is now at 7 degrees to the flow) is much higher than what would occur on a thin airfoil shape simply deflected by 2 degrees. Aerodynamicists at North American were aware of McLellan’s work, and they put this NACA

Подпись: X-15 hanging in the National Air and Space Museum. NASM
research to good use in the design of the X-15. The wedge-shaped vertical tail is clearly seen in the three-view of the X-15 (page 51). Of course, the wave drag on the tail was higher for this wedge airfoil; but the necessity for effective control authority was more important than this slight increase in drag due to the vertical tail, especially at high altitudes where the number of pounds of aerodynamic drag was small compared to the rocket engine’s high thrust of 57,000 pounds.

In spite of the wedge shape, wind tunnel tests showed that the vertical tail needed to be enlarged to have the necessary control authority. To accomplish this, a ventral tail was added below the fuselage. It was so large, however, that it would hit the ground in landing, in advance of the landing skids, which the X-15 used instead of wheels. To solve this problem, the ventral tail was split into two parts, and the lower section was made ejectable to solve the landing problem, with

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X-15 rear view detail. X-15 nose detail.

NASM NASM

Подпись: X-15 ventral tail. NASM
Подпись: X-15 reaction control jets detail. NASM

the drop made during approach to landing. This ejectable section was designed to be recovered and reused. However, later in flight testing, the engineers found that the lower ejectable half was not needed, and it was thus no longer used.

The pilot controls are conventional at low speeds, including launch and landing; power assist is provided on a separate control stick on the right console for use when the dynamic pressure is too great for the pilot force alone to move the control surface. But when the dynamic pressure is very low
and the control surfaces are not effective because the aerodynamic forces are too low, or these forces are nonexistent as when in space, small rocket motors with nozzles at the wing tips for roll, and at the nose and tail, help control pitch and yaw. The fuel for these motors is the monopropellant hydrogen peroxide. These rockets give the pilot control in outer space, where the aerodynamic force is zero, with the pilot using a separate control stick on the left console.

The structure is conventional, but the material affected by the external heating is Inconel X, which maintains its strength to above 2,000 degrees Fahrenheit. The support structure underneath is mostly titanium.

Speed brakes, located on the lower part of the upper vertical tail, were used for energy management to dissipate much of the energy generated by the rocket thrust in accelerating to high speed. It reduced the energy to be dissipated during the return trip to landing by increasing the drag, thus allowing a safe landing approach and touchdown. The landing gear consisted of a normal nose gear and twin metal skids instead of a conventional twin-wheeled gear, to save both weight and volume. During flight, the nose wheel

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Method by which the X-15 is mated to the B-52. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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was stored internally, and the skids were external, flush against the fuselage.

The nose of the X-15 was round (a ball nose), which reduced the aerodynamic heating to that site. It also indicated to the pilot the angle of attack and the yaw angle at which the plane was flying, because an instrument supplied by Nortronics and installed in the nose faced into the direction of flight, supplying this information to the pilot. The nose had a spherical shape, 12 inches in diameter, and was made of Inconel X, which also helped the airplane survive the extreme heat at its nose.

Because the X-15 was designed to be air – launched, it was mounted under the right wing of a B-52 mother plane, where it was carried aloft from the ground at takeoff until dropped by the B-52 after hitching a free ride to 45,000 feet and a Mach number of 0.85. Unlike the earlier X-airplanes, with which the pilot rode to altitude in the bomber mother ship and then climbed aboard after the X-airplane checkout was complete and the liquid oxygen (LOX) was topped off (replacing what had boiled off during the climb to altitude), the test pilot was in the X-15 cabin right from the start, even before takeoff. If trouble occurred during this climb to altitude, he would have no way out unless the B-52 used its controls to drop the entire X-15 aircraft.

Engineers modified the third airplane, the X-15-A2, to have two external fuel tanks and an extension of 29 inches in the fuselage for equipment and instrumentation. These external fuel tanks are shown in the X-15 cutaway on page 51.

A stability augmentation system, made by Westinghouse, dampened the aerodynamic controls in all three axes. Later, the Minneapolis – Honeywell MH-96 adaptive control system replaced the SAS. These systems were necessary because analyses of the aerodynamic data indicated that the airplane would be dynamically

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X-15-3 with ablative coating mounted under the wing of the B-52 in flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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X-15A-2, showing the external fuel tanks on the ramp of the NASA Flight Research Center at Edwards. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

Подпись: A detail showing the X-15 being mounted under the wing of the B-52. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

unstable without the system. The airplane was designed with reasonable cockpit visibility; the pilot could see all around, but he could not see the wings or the nose of the airplane.

The fuel for the later X-15 flights using the XLR99 engine was anhydrous ammonia, and the oxidizer was liquid oxygen (LOX); the fuel for the earlier flights using the XLR11 engine was water-alcohol. Both fuel and oxidizer were carried in the fuselage and held by the outside structure of the fuselage. The fuselage also contained the hydrogen peroxide (H202), used for the small control rockets that operated at high altitudes. Nitrogen pressurized the cabin, and helium pressurized the fuel and oxidizer.

JOE HENRY ENGLE

1932-

Joe Engle is the only test pilot who has flown the two-winged vehicles to go into space, the X-15 and the Space Shuttle. He completed sixteen flights in the X-15 program before being chosen for the NASA astronaut program. His X-15 familiarization flight was on October 7,

1963. In a display of exuberance, at the end of this flight he slow-rolled the X-15 through 360 degrees, shocking the engineers in the control room who thought Engle had a control problem. He was thoroughly chastised by chief pilot Bob Rushworth. In the words of Milt Thompson, who was to be the next X-15 pilot, “Joe went on to

become a straight arrow after the flight.” Indeed, in the eyes of Milt Thompson, Engle was one of the better X-15 pilots.

Подпись: Engle suited up and ready for a flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base image137
Joe Engle was born in Abilene, Kansas, on August 26, 1932. He graduated from the University of Kansas at Lawrence in 1955 with a bachelor’s degree in aeronautical engineering. After a brief stint as a flight-test engineer for Cessna Aircraft, he was commissioned through the Air Force ROTC program, earning his pilot’s wings in 1958 and going on to fly F-100s. At that time, Engle had numerous opportunities to fly with then Lt. Col. Chuck Yeager, who in turn recommended Engle for admission to the Air Force Test Pilot School at Edwards. Graduating from the Test Pilot School in 1962, and getting a further recommendation from Yeager as “one of the sharpest pilots we had in the program,” Engle went on to the new Aerospace Research

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Engle in the X-15 cockpit with a view of the instrument panel. It’s his first flight in the X-15 (October 7, 1963). USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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Engle standing beside the X-15. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

Engle in the X-15 cockpit for his first flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

Pilot School, also at Edwards. The purpose of that school was to train military pilots to be astronauts.

Graduating in 1963, Engle was selected as a project pilot for the X-15 program. After his first X-15 flight in October, he went on to achieve Mach 5.71 on February 2, 1965. Typical of the maturing X-15 research program, on this flight Engle tested a Martin 255 ablative material on the ventral and nose panels, made skin friction measurements, checked out a nose gear modification, and took boundary layer noise data. On June 29, 1965, he reached 280,600 feet, qualifying him for an astronaut rating. His last flight in the X-15 was on October 14, 1965, which was also his third flight above an altitude of 50 miles.

In 1966, Engle was selected for the NASA astronaut program. He was thirty-two years of age, the youngest man to become an astronaut.

He was also the only person in the program to have flown in space, by virtue of his X-15 experience. First assigned to the Apollo program, he was on the support crew for the Apollo 10 before becoming the backup lunar module pilot for Apollo 14.

Since the Apollo program was coming to an end, he moved to the Space Shuttle program. In 1977, he was commander of one of the two crews that conducted atmospheric approach and landing tests with the Space Shuttle Enterprise. In November 1981, he commanded the second flight of the Space Shuttle Columbia (STS-2), during which he intentionally flew manually large portions of the reentry flight path, performing twenty-nine flight – test maneuvers from Mach 25 through landing.

This was the first and only time a winged spacecraft has been manually flown from orbit to landing.

His last flight into space was as commander of the Space Shuttle Discovery (STS-27) in August 1985.

Engle retired from the Air Force as a major general on November 30, 1986. He went on to participate in the Challenger disaster investigation in 1986 and consulted for the shuttle program into the 1990s. He is enjoying his retirement as an aerospace and sporting goods consultant.

One of the more important aspects of the X-15 program was the providing of technical data for the design of the Space Shuttle. Joe Engel was the human link between the two programs, and he represents the rather smooth transition from the X-15 to the success of the Space Shuttle.

AFTERWORD

T

he 199th flight by Bill Dana in 1969 was the last for the X-15. The two of these revolutionary airplanes that still remained were readied for installation in national aviation museums after the completion of the X-15 research program.

As early as 1962, the Smithsonian Institution had requested an X-15 airplane for eventual display in Washington, D. C. The first X-15 was installed by the Smithsonian on May 13, 1969, in what was then known as Silver Hill and is now called the Garber Facility. It was moved to the Smithsonian’s Arts and Industries Building in June 1969 and placed near the 1903 Wright Flyer. The Arts and Industries Building served as the National Air and Space Museum at that time. After being loaned out to the FAA and then to the NASA Flight Research Center for display, it returned to the Smithsonian to be installed in the new National Air and Space Museum in Washington, on the Mall, for its opening on July 1, 1976. It hangs there now in the Milestones of Flight Gallery.

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X-15-1 on display, October 15, 1958, after rollout at the North American factory, Inglewood, California. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

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B-52 in flight with the X-15 mounted under the right wing, with the T-38 chase plane alongside. USAF, Air Force Flight Test Center History Office,

Edwards Air Force Base

 

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X-15 test pilots Robert White and Joe Walker on parade. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

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The X-15 in transit on a truck bed. Not everything was serious about the X-15 program; the mule is in case extra power is needed. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

The X-15A-2 airplane went to the National Museum of the USAF at Wright-Patterson Air Force Base in Dayton, Ohio. A set of external tanks and a dummy supersonic combustion ramjet (scramjet) engine are part of that display.

The X-15-3 that crashed with Mike Adams was buried at an unknown location at Edwards Air Force Base.

The two B-52 carrier airplanes used by the X-15 program were reassigned by the Air Force after performing in the subsequent lifting body program at the NASA Flight Research Center. The X-15 pilots continued with their careers: Neil Armstrong became famous as one of the first three men to land on the moon. Selected to be in the second astronaut class, he left the X-15

Подпись: Neil Armstrong in the cockpit of the X-15-3 prior to its first flight, December 20, 1961. USAF, Air Force Flight Test Center Flistory Office, Edwards Air Force Base program, commanded Gemini 8, and on July 20, 1969, as commander of Apollo 11, became the first human to walk on the moon. His next position in NASA was deputy associate administrator for aeronautics at NASA headquarters. He left NASA to become professor of aeronautics at the University of Cincinnati, after which he served on the boards of several corporations. Neil Armstrong passed away on August 25, 2012.

Bill Dana became chief pilot at the Flight Research Center, then had progressively higher positions in Flight Operations, in F-18 research, and finally as chief engineer at the Flight Research Center, a position he held until his retirement in 1998.

Joe Engle was selected to become an astronaut in 1966 and performed as support crew on Apollo 10, then as backup lunar module pilot on Apollo 14. He commanded the Space Shuttle Columbia
and manually flew the reentry from Mach 25 through reentry and landing (the only time it was manually flown for an entire flight). His last flight in space was as pilot of Discovery in August 1985.

Pete Knight went to Southeast Asia and flew 253 combat missions in the F-100. He was test director of the F-15 System Program Office and piloted the airplane. He returned to Edwards Air Force Base as vice commander of the Flight Test Center and as an active F-16 pilot. He retired from the Air Force in 1982 and entered politics, rising to California state senator. He died on May 8, 2004.

Jack McKay retired from NASA in October 1971 and died on April 27, 1975, largely from complications from his X-15 crash.

Pete Peterson left NASA in 1962 and returned to the U. S. Navy, rising in rank after combat in Vietnam to be commander of the Naval Air Systems Command. He retired from active duty as vice admiral in May 1980. He died on December 8, 1990.

Bob Rushworth returned to the USAF after flying the X-15, and in the Vietnam conflict he flew 189 combat missions. He rose through the command ranks to become a general, and he retired as a major general from the position of vice commander of the Aeronautical Systems Division at Wright-Patterson Air Force Base. He died of a heart attack on March 17, 1993.

Milt Thompson remained with NASA after piloting the X-15, becoming chief of research projects. He then became chief engineer, a position he retained until his death on August 6, 1993. He wrote a wonderful book about his experiences flying the X-15, At the Edge of Space.

Joe Walker was helping obtain publicity shots of the XB70A while flying an F-104. Getting too close to the B-70 and caught in air currents between the two aircraft, he was killed in a midair collision on June 8, 1966.

Bob White continued in the United States Air Force. He became brigadier general and

Подпись:image191
commander of the Air Force Flight Test Center. He later became a major general and then chief of staff of the 4th Allied Tactical Air Force. He retired from the USAF in February 1981 and died on March 17, 2010.

Scott Crossfield, who left the NACA Flight
Research Center to join North American Aviation

to be a part of their X-15 design and flight-test team, ended his association with the X-15 program when the Air Force took it over. He then continued at NAA in many high-level and technical executive positions. He followed his NAA career with executive positions at Eastern Airlines and Hawker Siddeley Aviation. He then became a consultant to the House of Representatives Committee on Science and Technology. He lectured on aviation to many groups until his demise. It was after such a lecture at Maxwell AFB that he was killed in his Cessna 210 aircraft in a storm over Georgia while flying home on April 19, 2006.

At this writing, Joe Engle and Bill Dana are the only surviving X-15 pilots.

Collectively, the pilots who flew the X-15 airplane continued in their careers, flying for NASA in a research mode or for the military, where they progressed into positions of military leadership. Building upon their technical backgrounds and research piloting, they applied their work discipline to perform important responsibilities on behalf of the United States.

They were talented men, driven and successful in their endeavors.

The X-15 remains the fastest and highest – flying manned airplane in history. The fact that no

Test pilot Scott Crossfield in his pressure suit standing with colleagues in front of the B-52 mother ship. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

Joe Walker ready to enter the cockpit for his first flight on the X-15, March 25, 1960. This was the first government flight in the X-15 program. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base
other manned hypersonic airplane has followed in its wake is a testimonial to the difficulty and severity posed by the hypersonic flight regime. The authors remain convinced that the future will see manned hypersonic flight for sustained periods in the atmosphere, a development that will rely on the data produced during the X-15 program on hypersonic aerodynamics, flight dynamics, structures, flight control, and pilot behavior. These hypersonic airplanes will be powered by air­breathing jet engines, not rocket engines. Such air­breathing engines will be supersonic combustion ramjet engines (scramjets), which have been under development since the 1970s and which are still a subject of intense research.

Indeed, on May 1, 2013, the experimental X-51, an unmanned hypersonic vehicle, achieved the longest duration sustained flight powered by a scramjet of over 300 seconds at speeds above Mach 5. The future of practical, environmentally safe, and economically feasible hypersonic manned flight still lies before us, and when that happens, the X-15 will indeed be the “Wright Flyer” of its kind.

image194
▲ X-15 in flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

▼ The X-51 hypersonic research vehicle, powered by a supersonic combustion ramjet engine (scramj et). The X-51 is unmanned and is a waverider configuration for high lift-to-drag ratio. Its first flight was on May 26, 2010. Its fourth and final flight was on May 1, 2013, when it flew at Mach 5.1 for 240 seconds under scramjet

image195
propulsion, the longest air-breathing hypersonic flight to that time. USAF

THE ENGINES

Rocket engines carry their own fuel and oxidizer and have large thrust, and by launching at high altitude the airplane will encounter small drag. This will enable the aircraft to quickly reach hypersonic speeds and altitudes where it can obtain the desired data.

The design called for the XLR 99 engine, similar to the XLR11 engines that powered the X-1 airplane past Mach 1. The XLR99 had a thrust at sea level of 57,000 pounds, while the XLR11 had a thrust of 6,000 pounds in 1,500-pound increments. The scaling upward of
the engine was significant. This new engine was throttleable to about 30 percent of maximum thrust. Unfortunately, the engine shut down prematurely at partial thrust, so almost all flights were conducted at full thrust. It was later restricted to operate at a minimum of 43 percent max because of unwanted shutdown occurring followed by an inability to restart. The dry weight of the engine is 915 pounds.

The fuel for the XLR99 is anhydrous ammonia, with liquid oxygen as the oxidizer. The specific impulse of this fuel is 230 seconds at sea level and 276 seconds at 100,000 feet altitude. Specific impulse is defined as the thrust of the engine per

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Front view of the X-15A-2 with external fuel tanks. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

59

 

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image86Rear view of the loading process for mounting the X-15 under the wing of the B-52. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

weight of propellant used per second, and it is a measure of the efficiency of the fuel.

The engines were developed and supplied by Reaction Motors, Inc. (RMI), through NACA and the USAF as government-furnished equipment (GFE). The XLR99 was not ready in time for the X-15’s first flight, and a drop flight without an engine was performed to learn about the airplane’s flying and handling qualities. Since the XLR99 still wasn’t ready, the next series of flights were performed using two XLR11 engines. The XLR11 had been used singly at 6,000 pounds thrust in the X-1 and X-1A series of flights. The two XLR11s that were used in the early X-15 flights had only 12,000 pounds of thrust, much less than the 57,000 that would be available later in the XLR99. Even with the reduced acceleration, the two XLR11s enabled flights through the transonic speeds and to a supersonic speed of about a Mach number of 3. The two smaller engines were mounted in a cradle that was then mounted in the same attachments used for the XLR99. Both configurations used the same fuel tanks, even though the fuel used for the XLR11 was water alcohol instead of anhydrous ammonia. After the twenty-fifth flight, all X-15 flights used the XLR99 engine.

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X-15 rocket nozzle exit. NASM

61

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Rear view of the X-15 mounted under the wing of the B-52. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

The advantage of flying first with a proven engine was to ensure that both the airplane and the engine were not new and untested. It also prevented a delay in the program, which allowed continuity in flight testing.

RMI, which won a competition that included Bell Aircraft, and Aerojet encountered several problems in developing the new engine: leaks, pumps, fuel lines, vibration, liner failures, etc.

Costs increased, which delayed schedules. Scott Crossfield, the first X-15 test pilot, did not want to proceed with a temporary engine, preferring to wait for the XLR99. Fearing that the new engine would not be completed, both NAA Vice President Harrison Storms and Program Manager Charlie Feltz supported using the XLR11. Said Feltz, “I’ve been a little concerned about busting into space all at once with both a brand new

airplane and a brand new untried engine. . . . We’re trying to crack space, with a new pressure suit, reentry, landing, new metal, everything at once. I’ve got a real good buddy who’s going to be flying that airplane for the first time, and I’d just as soon have him around for a while.” [citation: Dennis Jenkins, X-15: Extending the Frontiers of Flight, NASA SP-2007-562, 1967, p. 203]

The engine was reliable, in part because it had thirty-seven dedicated people in the engine – maintenance shop at Edwards Air Force Base who obtained good results with the engine; 165 out of 169 successful engine operations indicated a
reliability of 97.6 percent. The total engine costs were initially estimated to be about $12.2 million, as originally bid. Because of many increases in scope during the design, the final costs were about $300 million.

Author Dennis Jenkins noted, “In retrospect the engine still casts a favorable impression.

The XLR99 pushed the state of the art further than any engine of its era, yet there were no catastrophic failures in flight or on the ground. There were, however, many minor design and manufacturing deficiencies. . . .”

X-15 Flight Summary

X-15 Pilots

Number of

Maximum Mach

Maximum Altitude

Flights

Number Achieved

Achieved (feet)

Scott Crossfield

14

2.97

86,116

Joseph A. Walker

25

5.92

354,200

Robert M. White

16

6.04

314,750

Forest S. Peterson

5

5.3

101,800

John B. McKay

29

5.65

295,600

Robert A. Rushworth

34

6.06

285,000

Neil A. Armstrong

7

5.74

207,500

Joe H. Engle

16

5.71

280,600

Milton O. Thompson

14

5.48

214,100

William J. Knight

16

6.7

280,500

William H. Dana

16

5.53

306,950

Michael J. Adams

7

5.59

266,000

Total Flights

199

Total Flight Time: 30 hours, 13 minutes, 49.4 seconds Total Distance Flown: 41, 763.8 statute miles

Times above Mach:

1

2

3

4

5

6

Hrs:Mins:Secs:

(cumulative)

18:16:28

12:10:44

8:51:33

5:58:52

1:25:33

0:1:18

image89

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image91Front view of the X-15. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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X-15 in flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

L

 

04

 

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For the X-15 program to be a success,

the airplane and the pilots had to have a home—a physical facility for servicing the aircraft and a takeoff and landing area. Each flight required teams of support people on the ground as well as other pilots and airplanes in the air. All of these constituted the test arena.

EDWARDS AIR FORCE BASE

The X-15 flight tests occurred at Edwards Air Force Base, located about 100 miles northeast of Los Angeles. It is located on Rogers Dry Lake, a 44-mile-long pluvial lake in the Mojave Desert, which is the world’s largest pluvial lake (sometimes called paleolakes because they are caused by heavy rain during periods of glaciation). This dry lake maintains a smooth surface because winds consistently sweep the winter rains back and forth across the lakebed. Most of the year, the lakebed is dry and flat with a variation of height of only about 18 inches from one end to the other.

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▲ X-15 in flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Basea

 

► X-15 run-up area at Edwards Air Force Base, 1958. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

There are a number of dry lakes in this high desert region, some of which made suitable alternate sites for the emergency landings that might occur, and occasionally did occur, during the flight-testing program. The lakebed had to be smooth enough and hard enough to support an airplane that landed on skids, without digging in and causing an accident, but also long enough for a normal landing. The maximum travel distance from launch to landing was set by the high – altitude flight, where the glide from altitude to landing required a 300-mile distance from launch to Edwards Air Force Base. The alternate fields selected were located within glide range at launch

along the path from the launch site to Rogers Dry Lake at Edwards.

The U. S. Army Air Force had used Rogers Dry Lake, then known as Muroc, since the 1930s. During World War II, the Army used the site for flight testing. The advantages of the site include the long, effective runway offered by the lakebed and the 15,000-foot concrete runway that had been built during the war. Other advantages that Rogers afforded were the good weather that enabled many flying days and the security of being essentially in the middle of nowhere, both of which ensured control over the flights. It also provided security for classified aircraft.

While Air Force personnel maintained tight security during the X-1 and X-2 flights, they were more relaxed with the X-15, primarily because it was a research airplane, not intended for combat. Edwards Air Force Base was where all the new military airplanes were tested, including airplanes of super-secret nature, earmarked for eventual combat. Thus, security was at a maximum. By the time of the X-15, however, research airplanes were viewed as just that, research tools. They were thus lower in the hierarchy of security. Most details of the X-15 airplane, the flight tests, and the data were not kept secret. Security for the X-15 was more in the nature of “watchman” and “housekeeping.” Those responsible made certain that no unauthorized people had access to the airplane, that tools were not left in the cockpit by accident, etc.

The first U. S. jet airplane, the Bell P-59, was tested on October 2, 1942, at Muroc by Bell’s chief
test pilot, Bob Stanley. When the X-1 outgrew the initial test site at Pinecastle, Florida, the Air Force selected Rogers Dry Lake for its subsequent flights. There, on October 14, 1947, Chuck Yeager flew the X-1 to the first supersonic flight, reaching a Mach number of 1.06 at 43,000 feet altitude. The NACA High Speed Flight Section under Walter Williams, who was responsible for the X-1 testing, continued in the testing of the Douglas D-558-2 and the Bell X-2 rocket-propelled aircraft, as well as other aircraft flown for test purposes before the creation of the X-15. The site also boasted the presence of the USAF Test Pilot School, whose pilots and aircraft supported the X-15 test flights in many ways, including flying chase aircraft deployed along the X-15 flight path.

The area was known as the high desert because Edwards Air Force Base was at 2,500 feet altitude and the alternate fields ranged up to 5,700 feet. Landing at an altitude higher than sea level requires

69

 

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DC-3 and C-130 support aircraft at Mud Lake. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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Flyover by the B-52. On the ground are the X-15, Piasecki X-21 helicopter, and ground support personnel and equipment. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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B-52 with the X-15 attached, taxiing before takeoff for its flight on November 3, 1965, with pilot Bob Rushworth in the X-15. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

a longer ground distance, since the air is less dense; thus, speed at landing has to be higher. Decelerating to stopping from a higher speed at landing by necessity requires a longer landing distance.

On November 9, 1962, X-15 pilot John McKay embarked on a routine flight to reach a Mach number of 5.5 and an altitude of 125,000 feet. Though McKay’s flight plan called for full power, the engine was putting out only 35 percent power, and ground control directed McKay to shut off the engine and land at Mud Lake, one of the emergency landing sites. McKay jettisoned some of the remaining fuel as required by protocol, but the routine emergency landing was complicated when the flaps didn’t deflect downward to increase lift, resulting in a dangerously high-speed landing at 257 knots. This caused a failure to the main landing skid, which in turn caused the left wing and stabilizer to dig into the lakebed, flipping the X-15 upside down.

McKay jettisoned his canopy during this flip – over, but his helmet was the first thing to hit the ground. The rescue crew and the fire truck sped to

the airplane. Fumes from the crash prevented them from approaching, but the H-21 helicopter pilot used his rotor blades to blow the fumes coming from the anhydrous ammonia fuel that leaked from the aircraft, so that rescue could proceed. The rescue crew was able to dig the ground out from under McKay and extract him.

A C-130 arrived with paramedics and more rescue personnel, and they flew McKay to Edwards Air Force Base before tending to the damaged X-15. The emergency preparation and actions saved McKay’s life and showed the crucial importance of alternate fields and the support teams who staffed them.

The X-15 pilots did not want to land at these alternate fields. They were for emergencies only. Landings there were the same as those as at Edwards—dead-stick landings with no power to make adjustments for height or location during landing, nor to abort the landing approach and go around to try again. In his book At the Edge of Space: The X-15 Flight Program, Milt Thompson summed up the pilots’ preferences:

Подпись: X-15 after engine failure forced pilot Jack McKay to crash-land upside down at Mud Lake, November 9, 1962. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base
Rogers (dry lake) was where God intended man to land rocket airplanes. It was big. It had many different runways. It was hard.

It had no obstructions in 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.

MILTON O. THOMPSON

1926-1993

Milt Thompson holds the distinction of being the only X-15 pilot to have written a book on the X-15 program. Entitled At the Edge of Space: The X-15 Flight Program, it was published by Smithsonian Institution Press in 1992, a year before Thompson’s death. It is a highly recommended read for anybody interested in the inside story of the X-15 flight program. As the ninth test pilot to join the X-15 program, Thompson flew the airplane fourteen times, beginning on October 29, 1963. On November 27, 1963, the inertials failed at launch. On January 16, 1964, he reached Mach 4.92, but the speed brakes were extremely hard to open during the high aerodynamic heating phase. On February 19, at Mach 5.29, he had a premature burnout due to a clogged liquid oxygen line. His highest Mach number was 5.48, reached on January 13, 1965, during which he lost the pitch-and-roll damping mechanism during the pull-up/roll maneuver after burnout and temporarily lost control. His last flight in the X-15 was on August 25, 1965, when he achieved his highest altitude of 214,100 feet. The technical difficulties encountered by Thompson were typical of those encountered by all of the X-15 test pilots; there were very few totally “good flights” during the 199 flights of the airplane.

Milt Thompson was born on May 4, 1926, in Crookston, Minnesota. He became a naval aviator

Подпись:

Подпись: LIFTING BODIES

at age nineteen and served in China and Japan during World War II. After six years of active duty, he left the Navy and entered the University of Washington, where he graduated with a bachelor’s degree in aeronautical engineering in 1953. Following graduation, like many Washington graduates, he joined the Boeing Aircraft Company as a structural-test and flight-test engineer. He is one of only two X-15 pilots (along with Scott Crossfield) to have worked in the aircraft industry. One of the projects to which Boeing assigned him was testing the new B-52. In March 1956, he seized the opportunity to go to work for the

A lifting body is a wingless aerodynamic configuration that generates its lift from the body at high angle of attack, somewhat like the Space Shuttle. In the period between the X-15 and the Space Shuttle, several “lifting bodies” were designed and flown to explore principally the subsonic characteristics of this hypersonic aerodynamic shape in order to provide data for the subsonic portion of the Space Shuttle flight.

NACA’s High Speed Flight Station at Edwards Air Force Base as a research pilot.

At the time, the NACA had only five pilots, including future X-15 pilots Joe Walker, Jack McKay, and Neil Armstrong. Thompson worked on the early X-airplanes. Of this experience, he admitted that he “watched apprehensively as these programs wound down and were terminated.” He felt that the glory days of the X-airplanes were over and that he had missed it all. “In the next few years,” he later wrote, “I realized that I was wrong. The golden years were still to come.”

For Thompson, those glory years began when he was selected by the Air Force to be the only civilian pilot on the X-20 Dyna-Soar winged hypersonic vehicle project. Although he again witnessed yet another cancelation when the Dyna-Soar project was prematurely stopped, his participation on lifting entry bodies continued.

He was the first person to fly such a lifting body, the lightweight M2-F1. He continued to fly this

aircraft a total of forty-seven times, after which he made the first five flights in the all-metal M2-F2. He took all this experience to the X-15 program.

Thompson finished his active flying career in 1967. Two years later, he became chief of Research Projects, and in 1975 he was appointed chief engineer, a position he held until his death on August 6, 1993.

THE B-52 CARRIER AIRCRAFT

The X-15 flights would not have been possible without the B-52A, which carried the airplane under its right wing. Edwards Air Force Base is huge, and it includes the whole of Muroc Dry Lake. Not only did the flights originate at Edwards, both the X-15 and its mother ship, the B-52, landed
there also, although on different plots of ground at the site. The B-52 started on the runway at zero velocity, accelerated to takeoff, and carried the X-15 to its launch position with a speed of approximately M=0.85 and an altitude of about 45,000 feet.

While the X-15 achieved a record speed of M=6.7, the first 0.85 was accomplished by the B-52 in the first phase of the flight. The B-52 also sometimes positioned the drop location as far away from Edwards as 300 miles, whereas the flight profile dictated for the X-15 to land at Edwards. The X-15 expended no fuel for such a running start, which was required to obtain the data sought by the test.

It took about an hour and a half from takeoff to get to the launch position; the rest of the X-15’s flight to its landing was an additional 10 minutes.

Both the X-1 and the X – 2 rocket-powered research aircraft were also carried aloft from

Подпись:Подпись: X-15 landing with an F-104 chase plane alongside. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base
Listed below are the number of landings that took place at alternate fields, to be compared with the 188 normal landings at Rogers Dry Lake.

2 Cuddeback

1 Delamar

4 Mud

1 Rosamond

1 Silver

1 Smith Ranch

Since these were emergency fields, they had to have equipment there and personnel on site to act in case they were needed. Prior to the flights, equipment such as a fire truck with 500 gallons of water, a helicopter, firemen, an Air Force pilot to act as the lake controller, an AF crew chief, an AF doctor, an AF pressure-suit technician, and a NASA X-15 specialist were deployed. A test flight was a big operation, and a cancelation was a waste of time for many.

Edwards Air Force Base by carrier or “mother” aircraft, the B-29 for the X-1 and the B-50 for the X-2. The mechanical alterations required to the carrier aircraft were principally in the bomb bay area in order to securely hold the research aircraft and to provide a reliable launch mechanism.

The research aircraft pilots rode to the launch altitude and speed in the carrier aircraft, did the checkout before launch within the carrier aircraft, and replaced the liquid oxygen that had boiled off during the climb, all before entering the research airplane. For the X-15, the mother ship was supposed to have been the B-36, and the X-15 would have been carried to its launch position in the bomb bay opening. Some of the reasons the B-52 made the cut instead were related to differences in the availability and cost of each aircraft and the parts required for its maintenance during the flight-test program.

The B-36, then in the process of being phased out as an active bomber in the Air Force inventory, was a maintenance nightmare, whereas the then – modern B-52 was (and still is today) the main bomber for the Strategic Air Command. Moreover, the weight of the X-15 increased during the design phase, and the extra capability of the B-52 could

image107еоооз

Подпись: Top: X-15 mating area. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

more easily achieve the speeds and altitudes required by the data regions. Changing from the B-36 to the B-52 meant that the X-15 pilot could not ride inside the carrier aircraft. Using the B-52 meant that the X-15 had to be mounted on a pylon under the B-52’s right wing.

There was no way for the pilot to transfer from the B-52 to the X-15 after takeoff, which meant that he had to remain inside the X-15 during takeoff and for the roughly hour-and-a-half climb to position. This increased the pilot’s risk significantly. In an emergency during the launch-to – climb phase, the B-52 would have to drop the X-15 and its pilot rather than risk the lives of the entire operation’s crew. If the X-15 could be dropped, its pilot could possibly glide to a dry lakebed, or eject if the altitude was high enough. There were a number of captive flights—i. e., while the X-15 was still attached to its mother ship—where problems arose of such a nature that the launch was aborted, such as the auxiliary power unit (APU) not functioning in checkout or electrical signals not transmitting properly. In these circumstances, the B-52 landed safely with the X-15 still tucked under its wing. On such occasions, it must have seemed like a long, fruitless mission for the captive X-15 pilot. Luckily, neither the B-52 nor the X-15 pilots ever had to face such an unplanned drop.

The B-52 required numerous modifications to allow both airplanes to replenish the liquid oxygen, to accommodate the mating of the two aircraft, to assure that the B-52 had adequate control for the mission, and to assure that structural sufficiency was proper for both aircraft. (The X-15’s fuel was anhydrous ammonia, which does not boil off and does not require topping off, meaning that only the liquid oxygen required replenishment.) Twenty-seven B-52 pilots supported the X-15 flights. Two of the first were Capt. Charles Bock and Capt. John Allavie.

Above: X-15 in the process of being mated to the B-52. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

X-15 being dropped from the B-52. USAF, Air Force Flight 75

Test Center History Office, Edwards Air Force Base

The activities of the B-52 airplanes and their USAF pilots over nine years were integral to the success of the X-15 program. It was not a minor expense.

WILLIAM J. KNIGHT

1929-2004

Подпись: Pete Knight kneeling beside the X-15. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base Подпись: Knight standing beside the X-15 after a flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base
During the course of his sixteen flights in the X-15, William “Pete” Knight experienced perhaps the most notable event of all the pilots who flew the airplane. On October 3, 1967, he achieved Mach 6.7, the fastest speed attained in the X-15.

Подпись: Knight in the cockpit of the X-15 after a flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

By virtue of this flight, Pete Knight still holds today the world’s speed record in a winged, powered aircraft.

On this same flight, the X-15 was coated with a white ablative heat shield. Attached underneath the X-15 was a dummy model of NASA’s high-speed research engine (HRE), part of a research program to develop a supersonic combustion ramjet engine (scramjet). During the course of the test, the shock wave from the engine cowling impinged on the bottom surface of the X-15. The intense aerodynamic heating in the impingement region burned through the attachment pylon, separating the dummy scramjet from the airplane. Had the dummy engine remained attached any longer to the airplane, the shock wave would have burned a hole into the primary structure of the fuselage
and most likely would have resulted in destruction of the X-15 in flight. Moreover, this was the last flight of the X-15A-2. The airplane is now on permanent display in the Air Force Museum at Wright-Patterson Air Force Base in Ohio.

Pete Knight was born on November 18, 1929, in Noblesville, Indiana. At the age of twenty – one, he enlisted in the Air Force, and he obtained his pilot’s wings in 1953. He was assigned to the 438th Fighter-Interceptor Squadron, flying Northrop F-89 Scorpions. While flying the F-89, he entered the National Air Show at Dayton,

Ohio, in 1954 and won the prestigious Allison Jet Trophy, becoming one of the youngest pilots to win the award. He then began his engineering study program, and he graduated from the Air Force Institute of Technology in 1958 with a

Подпись:bachelor’s degree in aeronautical engineering.

With his career on a fast track, he graduated from the Air Force Test Pilot School that same year. Assigned to Edwards Air Force Base, he was a project test pilot for the F-100, F-101 Voodoo, F-104 Starfighter, T-38, and F-5.

The Air Force recognized Knight’s expert piloting ability by selecting him in 1960 to be one of the six test pilots for the X-20 Dyna-Soar, a winged orbital space vehicle that was an early precursor to the Space Shuttle. The X-20 program was canceled in 1963, but Knight went ahead to complete the Air Force astronaut training program at Edwards Air Force Base. With this background, Pete Knight became the tenth X-15 test pilot, and he had his first flight in the airplane on September 30, 1965. He flew the X-15 sixteen times. On October 17, 1967, he achieved an altitude of 280,500 feet, qualifying him for official astronaut status.

On June 29, 1967, Knight experienced total power failure while going through 107,000 feet at Mach 4.17. All onboard systems shut down.

He coasted to a maximum altitude of 173,000 feet and calmly set up a visual landing approach. He resorted to the old “seat-of-the-pants” flying and glided safely to an emergency landing at Mud Lake, Nevada. For this expert example of flying, he earned a Distinguished Flying Cross.

On July 16, 1968, Knight had a hydraulic gauge malfunction during boost, which required him to push over to an alternate flight profile, which is the planned variation of speed, altitude, and location for the flight of the aircraft. On his glide back to Edwards, he experienced unexpected shaking and vibrations. His last flight in the X-15 was on September 13, 1968; this was the 198th flight of X-15, the next to last flight of the program.

Pete Knight went on to a stellar Air Force career. He went to Southeast Asia in 1969 and completed a total of 253 combat flights in the F-100. His testing career was then extended to the F-15 program at Wright-Patterson Air Force Base as test director; he became the tenth pilot to fly the F-15 Eagle. He then returned to Edwards in 1979 as vice commander of the Air Force Flight Test Center. After thirty-two years of service and more than 6,000 hours in the cockpits of more than a hundred different aircraft, he retired from the Air Force as a colonel in 1982.

Knight became the only X-15 pilot to go into politics. In 1984, he was elected to the city council of Palmdale, California, and he became the city’s first elected mayor four years later. After becoming the fastest airplane pilot in the world, he thus became mayor of the fastest growing city in the United States. He was elected to the California State Assembly in 1992 and to the California State Senate in 1996. Knight achieved widespread public notice as the author of Proposition 22, the purpose of which was to ban same-sex marriage. He continued to serve in the California State Senate, representing the 17th District, until his death on May 7, 2004.

CHASE AIRCRAFT

Chase aircraft are high-speed aircraft whose pilots observe the physical status of the X-15 during its mission, principally during its climb with the B-52 and then toward the end of the X-15’s test flight. They are positioned near alternate landing fields, at approach to landing through touchdown, and during the landing run-out.

During the climb, while the X-15 is attached to the B-52 mother ship, the chase pilot observes the X-15’s external features, makes control-
surface checks, and observes any irregularities during the climb. In making control-surface checks, the chase pilot observes the physical deflection of the control surfaces, which for the X-15 are the rudder and the horizontal tail, as deflected by the pilot in the cockpit and observed by the pilot in the chase plane. The pilot in the cockpit cannot see these control surfaces, and so it falls to the pilot of the chase plane to observe them. This check is done before the X-15 is dropped from the B-52. It is an essential safety check; if the control surfaces are not working, the flight is scrubbed.

At drop, the chase pilot watches the engine start up, observes the power levels, notes the clearance from the B-52 as the X-15 separates, and

B-52 in flight with the X-15 attached and the F-100 chase plane alongside. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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B-52 in flight with the X-15 attached and the T-38 chase plane alongside. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

 

is there to assist in descent to landing at Edwards AFB if, for example, the engine doesn’t start and the X-15 heads for an emergency landing at the dry lake designated for that particular launch.

He can note all the external features of the X-15, its sink rate, its progressive proximity to the ground, and anything unusual that would help the pilot during the landing, such as anomalies in configuration if the flaps did not deploy. The chase pilot can quickly land during an accident in order to physically assist or help rescue the pilot. In emergencies, he would perform the same functions when stationed near alternate landing sites.

With flights varying from launch close to Edwards Air Force Base to launch 300 miles distant, different numbers of chase planes were needed. Usually there were four, one for the climb of the X-15 and the B-52 mother ship, another
at drop, one at an intermediate station above an alternate landing field, and one to cover the descent and landing at Edwards. During the most distant launch, an additional chase plane was needed to cover additional emergency field locations. As a result, there were either four or five chase planes used per X-15 flight. These chase pilots were usually other X-15 pilots, NASA research pilots, or Air Force pilots from the Air Force Flight Test Center.

The chase airplanes that were chosen best matched the X-15’s flight characteristics required by the X-15 testing program. For the early flights launched at Edwards Air Force Base, an F-100 answered the call. Later, the team chose a Northrop T-38A because it better matched the B-52’s speed during its right turns. Both the F-100 and the T-38A could fly in the low supersonic

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▲ Another view of the X-15 landing with the F-104 chase plane alongside. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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▼ Another view of the F-104 chase plane. USAF, Air Force Flight Test
Center History Office, Edwards Air Force Base

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range, around Mach 1.5. If there was a problem in climb and cruise to launch, the chase pilot was thus in position to help in the landing.

For the launch at a distance from Edwards Air Force Base, an F-104 chase aircraft stayed with the X-15 until it accelerated out of sight. The F-104 was the first fighter airplane capable of sustained flight at Mach 2. The pilot of the F-104 observed the
separation from the B-52 at drop and watched the engine for proper light-up. If the engine did not fire properly, the F-104 would descend with the X-15 to landing and be on hand to help on the ground.

For the chase aircraft covering the intermediate emergency fields, F-104s assisted in the descent and landing of the X-15 and provided any assistance needed after touchdown. These aircraft

Подпись: B-52 in flight with the X-15 attached and the T-38 chase plane nearby. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base
delayed their takeoff for about 30 minutes after the B-52 took off so they would have enough fuel to loiter at their positions.

Other flight vehicles participated as well. A helicopter, the Piasecki H-21, ferried personnel to and from emergency fields as required. It also blew fumes away from damaged aircraft, as when Jack

McKay flipped over during his emergency landing. This allowed emergency personnel to extricate him from his airplane and perform other functions during his rescue.

Air Force C-130s transported equipment and personnel to emergency fields, including fire engines. Safety was taken seriously.

X-15 on the lakebed after the flight on October 17, 1961, with pilot Joe Walker still in the cockpit and the Pasecki H-21 helicopter in the background. USAF, Air Force Flight Test Center History Office,

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Edwards Air Force Base

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Rear view of the B-52 on the ground with the X-15 attached to its right wing. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

Support trucks and personnel at an X-15 landing site. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base