The Air Force entered the X-15 flight program when, on April 13, 1960, Maj. Bob White hoisted himself into the X-15 cockpit for a pilot- familiarization flight. It was the twelfth flight of the X-15, and on this flight White accelerated to Mach 1.9 and 48,000 feet, about the same as the previous flights. White, however, was to eventually set the formal FAI world altitude record of 314,750 feet on July 17, 1962; this record still stands. For this feat, he won the first Air Force rating of winged astronaut. He also set a series of speed records. On March 7, 1961, during

image127White entering the X-15 under the wing of the B-52. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

White in the cockpit of the X-15. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

the thirty-fourth flight, he achieved Mach 4.43, becoming the first pilot to exceed Mach 4. On June, 23, 1961, during the thirty-eighth flight of the X-15, he achieved Mach 5.27, becoming the first pilot to fly faster than Mach 5. Five months later on November 9, 1961, on the forty-fifth flight, he became the first to fly faster than Mach 6, reaching a speed of Mach 6.04.

Bob White was born on July 6, 1924, in the city of New York. He joined the Army Air Force in November 1942 at the age of eighteen and received his wings and commission as a second lieutenant in February 1944. White was the only X-15 pilot to be a prisoner of war. Flying a P-51 over Europe, he was shot down and captured in February 1945. He was not liberated until April. After the war, he studied at New York University, where he earned a bachelor’s degree in electrical engineering. The

Korean War brought him back to active duty, and he remained with the Air Force for the rest of his career. He became a pilot and engineering officer, serving at Mitchell Air Force Base, and then served as a flight commander with the 40th Fighter Squadron flying F-80s in Japan.

White’s road to the X-15 took him first to the Rome Air Development Center as a systems engineer and then to the Air Force’s Test Pilot School at Edwards Air Force Base. There, he became the deputy chief of the Flight Test Operations Division and assistant chief of the Manned Spacecraft Operations Branch. It was during this period that he became the third pilot to fly the X-15, serving as the primary Air Force pilot in the program and ultimately finishing sixteen flights in the airplane.

No X-15 test flight occurred without incident. On his flight exceeding Mach 5, the cockpit pressure dropped so much that White’s flight suit inflated. On his next flight, where he became the first pilot to exceed the altitude of 200,000 feet, his left windshield shattered during reentry. On his very next X-15 flight, where he exceeded Mach 6, his right outer windshield shattered at about Mach 2.7, during deceleration. White flew his last flight in the X-15 on December 14, 1962, achieving by that time the rather modest performance of Mach 5.65 and altitude of 141,400 feet.

After leaving the X-15 program, White continued his distinguished Air Force career. In 1963, he became the operations officer for the 36th Tactical Fighter Wing at Bitburg, Germany, and he then served as the commanding officer of the 53rd Tactical Fighter Squadron in Germany until August 1965. He returned to the United States, where he graduated from the Industrial College of the Armed Forces and obtained a master of science degree in business administration from George Washington University, both in 1966. From there, he was transferred to the Air Force


F-105 on display at the National Air and Space Museum’s Udvar Hazy Center. NASM

Systems Command at Wright-Patterson Air Force Base as chief of the F-111 systems program.

In May 1967, White went to Southeast Asia, where he flew seventy combat missions over Vietnam in F-105 aircraft. He returned to Wright – Patterson in June 1968 as director of the F-15 systems program. In August 1970, he returned to his familiar surroundings in California, becoming commander of the Flight Test Center at Edwards Air Force Base and brigadier general. He became commandant of the Air Force Reserve Officer Training Corps in October 1972. After receiving his second star, he became chief of staff of the 4th Allied Tactical Air Force in March 1975. He retired from active duty as a major general in February 1981.



The X-15 program was funded and run jointly by NASA, the Air Force, and the Navy. Forest “Pete” Peterson, USN, completed five flights in the X-15 from September 23, 1960, to January 10, 1962. The number of flights reflected the Navy’s smaller participation in the program compared to that of NASA and the Air Force. Peterson’s contributions were nonetheless important.

Forest Silas Peterson was born on May 16,

1922, in Holdrege, Nebraska. He attended the Naval Academy in Annapolis, graduated with a bachelor of science degree in electrical engineering, and was commissioned an ensign in June 1944.

As usual for Naval Academy graduates, his first assignment was sea duty. He saw action in the South Pacific, notably in the Philippines, Formosa, and Okinawa while serving on the destroyer USS Caperton. After the war, he switched from the Navy “black shoe” to the “brown shoe” of Naval Aviation. He graduated from flight training in 1947 and was assigned to the VF-20A squadron. Shortly thereafter, he attended Naval Postgraduate School, where he earned a bachelor’s degree in aeronautical engineering in July 1950. He then went to Princeton University, where he earned a master’s degree in engineering. From 1953 to 1956, he was back on flight duty, this time with Fighter Squadron 51. He was selected to attend the U. S. Naval Test Pilot School at Patuxent River, Maryland, in 1956, and he remained as an instructor following graduation. When the Navy became involved with the X-15 program, Peterson moved to the Dryden Flight Research Center in August 1958. He served at Dryden until January 1962.

Pete Peterson made five flights in the X-15, beginning with Flight 22 on September 23, 1960. The first flight for a new test pilot was always the pilot-familiarization flight; Peterson achieved Mach 1.68 and an altitude of 53,043 feet before the engines shut down prematurely and failed to restart. His next flight, on October 20, 1960, was good, and he achieved Mach 1.94 and 53,800 feet. He was the first pilot to check out the higher – thrust XLR99 engine for the X-15-1, achieving Mach 4.11 and an altitude of 78,000 feet. On September 28, 1961, he achieved his fastest and highest flight, Mach 5.30 and 101,800 feet.

His last flight in the X-15, on January 10,

1962, was a disappointment. Upon reaching Mach 0.97 and an altitude of 44,750 feet, he had a total engine malfunction and had to make an emergency landing at Mud Lake. Over his limited number of flights, Pete Peterson contributed to the X-15 data collection by carrying out high-angle-of-attack stability tests and collecting aerodynamic, heat transfer, thermostructural stability and control, and performance data.

Peterson went back to more traditional duty in the Navy. He served as commanding officer of VF-154 and then was assigned to the position of director, Division of Naval Reactors, Atomic Energy Commission for Nuclear Power Training. From 1964 to 1967, he was the executive officer on board the aircraft carrier USS Enterprise, and he participated in the Enterprise’s first combat tour in Vietnam. He was commanding officer of the Enterprise from July 1969 to December 1971. He then spent three years as an assistant director of Naval Program Planning in the Office of the Chief of Naval Operations. The following year, he commanded Combined Task Force 60 based in Athens, Greece. By 1975, he was back in the Pentagon heading the Naval Air Operations office and then the Naval Air Systems Command. He retired as a vice admiral in 1980.

On December 8, 1990, Admiral Peterson died in Georgetown, South Carolina, from a brain tumor. Although his naval career was varied, he stood apart as one of the select twelve who flew the X-15. He was the only active-duty Navy pilot to fly the X-15 (although four other pilots had been former Navy pilots).


The first hypersonic vehicles in flight were missiles, not airplanes. On February 24, 1949, a WAC Corporal rocket mounted on top of a captured German V-2 boost vehicle was fired from the White Sands Proving Ground in New Mexico, reaching an altitude of 244 miles and a velocity of 5,150 miles per hour. After nosing over, the WAC Corporal careened back into the atmosphere at over 5,000 miles per hour, becoming the first object of human origin to achieve hypersonic flight. In this same period, a hypersonic wind tunnel capable of Mach 7, with an 11- by 11-inch cross-section test section, went into operation on November 26, 1947, the brainchild of NACA Langley researcher John Becker. For three years following its first run, this wind tunnel was the only hypersonic wind tunnel in the United States. It later provided key data for the design of the X-15.

The real genesis of the X-15, however, was human thinking, not test facilities. On January 8, 1952, Robert Woods of Bell Aircraft sent a letter to the NACA Committee on Aerodynamics in which he proposed that the committee undertake the study of basic problems in hypersonic and space flight. At that time, several X-airplanes were already probing the mysteries of supersonic flight: the X-1, X-1A, and X-2. Accompanying Woods’s letter was a document from his colleague at Bell, Dr. Walter Dornberger, outlining the development of a hypersonic research airplane capable of Mach 6 and reaching an altitude of 75 miles. By June 1952, the NACA Committee on Aerodynamics recommended that the NACA expand its efforts to study the problems of hypersonic manned and unmanned flight, covering the Mach number range from 4 to 10.

After two more years of deliberation, the committee passed a resolution during its October 1954 meeting recommending the construction of a hypersonic research airplane. Among the members of this committee were Walter Williams and Scott Crossfield, who would later play strong roles in the X-15 program. Kelly Johnson, who not only was the Lockheed representative to the committee but was considered to be the country’s most famous airplane designer, opposed any extension of the manned research program, arguing that to date

Подпись: Wright Flyer on its first flight at Kitty Hawk (Kill Devil Hills), North Carolina, December 17, 1903. NASM

image19the research airplane program was “generally unsatisfactory” and had not contributed to the practical design of tactical aircraft. Johnson was the only dissenter; he later appended a minority opinion to the majority report. The spectacular success of the X-15 program and the volumes of hypersonic data it contributed to the design of the Space Shuttle later proved Johnson wrong. The X-15 program was launched.

The X-15 was designed to be, purely and simply, a research vehicle to provide aerodynamic, flight dynamic, and structural response data


Подпись: INCONEL X

for use in the development of future manned hypersonic vehicles, such as the Space Shuttle.

No hypersonic wind tunnels, past or present, can provide accurate data for the design of a full – scale hypersonic airplane. The frontiers of flight today are the same as they were in the 1950s: the exploration of hypersonic flight. The X-15 will ultimately be viewed as the Wright Flyer of hypersonic airplanes.

The X-15 was the third of a series of research aircraft that were designed specifically to obtain aerodynamic data, beginning with the Bell X-1, the first piloted airplane to fly faster than the speed of sound. The X-1 investigated aircraft behavior primarily in the transonic flight regime. The transonic regime is generally considered to be flight between Mach 0.8 and about 1.3. It begins when air is accelerated to Mach 1 at any local location on the airplane, usually when the airplane is flying at the subsonic airspeed of about Mach 0.8 The second research airplane, the Bell X-1A, investigated supersonic flight to a Mach number of 2.44. This was followed by the Bell X-2, a swept-wing aircraft of stainless steel construction designed to investigate the effects of sweepback and aerodynamic heating to a Mach number of 3.2.

Each of these aircraft, like the later X-15, was rocket-powered and carried aloft to be dropped at an altitude of about 30,000 feet. At these high altitudes, where the air is less dense and the drag is therefore low, the rocket provides maximum acceleration to the airplane following launch. This acceleration is sufficient to allow the airplane to reach the desired speeds and altitudes that allow scientists to study the flight regions between where aerodynamic forces are still useful, and outer space, where they are not, and to study speeds of almost Mach 7, which are solidly in the hypersonic regime.

The X-15 was designed with a very high thrust, 57,000 pounds, provided by an RMI rocket engine with enough fuel for about a minute and a half

Inconel X is a high-temperature alloy of 72.5 percent nickel, 15 percent chromium, and 1 percent columbium, the rest being iron. It has excellent strength at high temperatures, and it was a natural choice for the X-15 because it could withstand the high surface temperatures expected for the hypersonic flight regime up to Mach 7. Inconel X is a registered trademark of the Huntington Alloy Products Division, International Nickel Company, Huntington, West Virginia.

at full thrust. Researchers wanted to know if the analytical calculations and the wind tunnel data accurately predicted the performance, stability, and control of an airplane flying at Mach 7 at very high altitudes (over 250,000 feet); whether the aerodynamic heating at the high Mach numbers is as high as predicted theoretically; and if the Inconel X structure could maintain its strength at high temperatures.

They also wanted to learn whether the directional stability of the aircraft, which decreases at faster supersonic speeds, could be made sufficient by the X-15’s design and by the addition of a stabilization augmentation system (SAS) installed in the airplane. The 199 X-15 test flights evaluated all of these questions.

The risks of flying an airplane designed for testing in an unexplored flight regime are many, both for the known uncertainties and for the unknown. Any research airplane will have a new

Подпись: X-15 in captive flight; picture taken from the B-52. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base
design, new subsystems, and new materials, none of which have yet been tested in flight. Conversely, a new airliner that is intended to fly in a familiar speed range and with a conventional design usually has two years of test flights to prove that it is safe for passengers.

The X-15, designed to investigate hypersonic flight, needed to also fly in the supersonic, transonic, and subsonic regimes, and to land safely on the desert lakebed at about 220 miles per hour. Moreover, on its first flight it had to land after being dropped at altitude without any practice, so that the pilot and research team could learn the response of the airplane to the controls.

A risk example is the X-15’s first flight. Launched at 33,550 feet and without an engine, which otherwise would allow the pilot to go around again
if his approach was not right, the pilot had less than five minutes to learn how to handle the airplane in pitch, roll, and yaw, and to practice a simulated landing at altitude before doing the real thing. On this first flight, a longitudinal instability that caused the airplane to cycle up and down uncontrollably made it dangerously difficult to land. By good piloting, Scott Crossfield was able to touch down on the bottom part of this cycle, avoiding a serious, life-threatening crash. The problem was corrected later by merely resetting a valve.

Each flight was an adventure, with the pilot enduring up to 5 g of acceleration at full thrust for about 90 seconds until the fuel was used up. After burnout, the pilot had to fly, while coasting, to reach the speed and altitude required to conduct the necessary tests. Then the pilot would

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



return without fuel or power to the landing site at Edwards Air Force Base, which could be as far away as 300 miles from where the plane was originally dropped.

This history tells a single story, in two parts. The first details the goals and requirements of the X-15 program; the competition for the contract, eventually signed by North American Aviation (NAA) on December 5, 1955; NAA’s design and

Scott Crossfield, suited up prior to a flight. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base



The XLR-11 and XLR-99 are liquid-fueled rocket engines designed by Reaction Motors, Inc., specifically for use with high-speed airplanes. The fuel is anhydrous ammonia, and the oxidizer is liquid oxygen.


construction of the X-15; and NAA’s flight testing by Scott Crossfield, to show that the aircraft had met its contractual obligations. To demonstrate this achievement, Crossfield had to first fly the X-15 without an engine; then with two of the RMI-provided XLR11 rocket engines of the same type used in the X-1 flights (with 12,000 pounds thrust); and last, when it was ready, with the proposed RMI-provided XLR99 engine of 57,000 pounds thrust, all as specified in the contract.

The second part tells the thrilling story of the talented military pilots and NASA pilots who, under the direction of NASA’s Flight Research Center, were responsible for obtaining the data the X-15 was designed to provide. Eleven NASA and military pilots trained assiduously for each flight, flew each flight, managed the difficulties that arose with the aircraft or the engine in many of the flights, and dealt with crises that often placed them in mortal peril. They, along with the



Jack McKay flew the X-15 for twenty-nine flights, the second largest number of flights. He was the fifth pilot to fly the X-15. His pilot-familiarization flight took place on October 28, 1960, when he

Подпись:achieved Mach 2.02 and an altitude of 50,700 feet. As frequently occurred on the X-15 flights, there was a technical problem. In this case, the ventral chute did not open upon landing. McKay went on to achieve his highest Mach number of 5.65 on August 26, 1964, and his highest altitude of 295,600 feet on September 28, 1965.

On his seventh flight, which took place on November 9, 1962, he encountered a more serious problem. An electrical failure caused the rocket engine to peak out at only 30-percent power, forcing McKay to shut down the engine after achieving a Mach number of only 1.49 at an altitude of 53,950 feet. His airplane was still loaded with fuel, which he tried to jettison. He landed heavy at a much higher landing speed than normal because he could not extend the flaps. Upon touchdown on the lakebed, the rear skid collapsed, buckling the landing gear. The X-15 flipped on its back. Because McKay had jettisoned the canopy prior to rollover, his head hit the lakebed, crushing the upper vertebra in his neck.

In spite of chronic pain for the rest of his life, he flew the X-15 twenty-two more times. His last flight was on September 8, 1966, where ironically a fuel-line-low light caused a throttle-back, a shutdown, and an emergency landing at Smith Ranch. He achieved only Mach 2.44 (planned was Mach 5.42) and an altitude of 73,200 feet (planned was 243,000 feet).

John B. McKay was born on December 8,

1922, in Portsmouth, Virginia. During World War II, he served in the Pacific Theater as a pilot with the U. S. Navy. After the war, he attended Virginia Polytechnic Institute (now Virginia Tech), graduating in 1950 with a degree in aeronautical engineering. He joined the NACA, first as an engineer at the Langley Research Center and then as an engineer and research pilot at the NACA Dryden Flight Research Center. There he flew such experimental aircraft as the subsonic Douglas

D-558-1, the supersonic D-558-2, and the Bell X-1B and X-1E. He also tested some mainline Air Force aircraft such as the F-100, F-102,

F-104, and F-107. He was, however, first and foremost an aeronautical engineer. As a member of both the American Institute of Aeronautics and Astronautics and the Society of Experimental Test Pilots, McKay published several technical papers.

McKay died a relatively early death on April 27, 1975, in Lancaster, California, which may

Bob Rushworth suited up for a flight, standing in front of the X-15 (barely seen behind him). USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

Подпись: NUMBER OF X-15s BUILT

have been hastened by his neck injury in the X-15. In 2005, he was posthumously awarded Astronaut Wings. Of McKay, his fellow test pilot Milton Thompson simply wrote: “Jack was a true southern gentleman. I miss him.”


North American Aviation’s dedicated group of engineers, set up by Vice President Ray Rice and supported later by Vice President Harrison Storms under the direction and leadership of Charlie Feltz, was tasked with designing the X-15.

North American Aviation was founded in 1928 by Clement Keys, a financier noted for aviation companies. In 1934, James H. “Dutch” Kindelberger became president, and he guided the organization through some of its most iconic high­speed airplane designs, such as the P-51 Mustang of World War II and America’s first swept-wing jet fighter, the F-86 Sabre.

Подпись: F-86. USAF In addition to the X-15, North American designed the Apollo Command and Service Module and the Space Shuttle. Through a series of sales and mergers, NAA became part of the Boeing Airplane Company in 1996.

Подпись: X-15, rear; XRL-99 rocket. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base Подпись: X-15 and HL-10 lifting body. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

single civilian test pilot, Scott Crossfield of the NAA, achieved all the objectives of the program.

Indeed, the X-15 program was as much about the people involved as it was about the data the airplane was designed to collect, or even the airplane itself. The twelve distinguished test pilots who flew this extraordinary aircraft worked hard to learn its characteristics and idiosyncrasies as well as the unknown character of the new flight regime they were investigating. Truly accomplished aviators and apt students of each mission, they bravely addressed each flight with knowledge gained from long hours at flight simulators and with a detailed flight plan. As with any new airplane, difficulties arose. Equipment problems, design unknowns, and other circumstances caused

problems on many flights, although the X-15 flight-testing program claimed only one life in its nine-year history.

The NASA (NACA) flight research crew at Edwards AFB, now known as Dryden Flight Research Center, was a unique and motivated group that built upon their experience with the X-1 airplanes. The first director of the flight research crew for the X-15 was Walt Williams, who was director of the NACA High Speed Research Section, later to become the NASA Flight Research Center. He was also in charge of the early X-1 research flight tests at Pinecastle, Florida. He and his successor, Paul Bickle, ran a rigorous professional organization that continued research begun in the 1920s, when engineers at Langley Memorial Lab wanted to determine the most desirable characteristics for an airplane, as well as innovations in aircraft design that could make flying better, more effective, and safer.

These questions included what data to measure, how to fly to obtain it, how to measure and record it, and, finally, the commitment to publishing this data for the betterment of the industry.

As an example of this research trajectory, the X-15, with Pete Knight at the controls, reached a Mach number of 6.76 on October 3, 1967. On August 22, 1963, the X-15 had gained an altitude of 354,200 feet, more than 67 miles high, with Joe Walker piloting. These incredible achievements were made possible by the use of a supplementary automatic stabilization system, which the successful X-15 test flights proved was necessary in much of the new flight region. Moreover, the X-15 tests also showed that the thermal protection provided by special materials yielded desired favorable results.

The X-15 featured unique design features, including a rolling tail. Each side of the horizontal tail operated separately in opposite directions to roll the aircraft, eliminating the need for ailerons


Walter C. Williams. NASA

on the wings; ailerons would have induced shock waves at supersonic speeds that would have changed the airflow at the tail surfaces. These shock waves, produced at the deflection hinge lines, would have caused local regions of high aerodynamic heating at that location.

To provide longitudinal control, the two sides of the horizontal tail would operate together in the same direction. The airfoil of the vertical tail surfaces was slab-sided, with a blunt trailing edge; this configuration prevented separated flow on the surface and maintained control at supersonic speeds. The new materials included Inconel X, which maintains its strength at high Mach numbers. Also, the structure was designed

Подпись: X-15 in flight an instant after drop. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base
to minimize the effects of thermal gradients when the outside aircraft skin got hot and the inside stayed cool. The X-15 proved that each of these innovations was successful.

The X-15 was the third and last of a series of air-dropped rocket-powered aircraft designed to investigate high-speed flight regimes from transonic through supersonic to hypersonic velocities. At the time each airplane was conceived and built, there were inadequate wind tunnel or other test data available to assist in the design for flight at these speeds; or in the case of the X-15, the wind tunnel tests had yet to be validated by flight. The X-1, D-558-2, X-2, and X-15 were the first aircraft to fly at Mach 1, 2, 3.2, and 6.7, respectively.

The X-15 had to fly through all the flight regimes that had been pioneered by the earlier research aircraft before extending its speed and altitude range to include the hypersonic regime. These older research aircraft were essentially conventional configurations, with special design
variations required for their specific mission.

Like its predecessors, the X-15 had to be dropped successfully from a mother ship, which for the X-15 was the B-52. After drop, the X-15 had to accelerate from subsonic speed through Mach 1 with its attendant shock waves, flow changes, and trim changes. It then climbed and accelerated past the maximum speed of the X-2 to explore the hypersonic regime for which it was designed.

The X-15’s rocket engine was a new, much larger version of the RMI rocket engine that powered the X-1 and the X-1A. The new engine needed to increase its thrust from the 6,000 pounds used by the X-1 to the 57,000 pounds required by the X-15’s greater Mach number research goals. The new, larger engine was not ready for the early flights, which instead used two of the 6,000-pound engines, combined for 12,000 pounds of thrust. These placeholder engines allowed early flights to proceed, providing data and experience useful for the continuation of the

X-15; XLR-11 dual rockets. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

Подпись: КЕШ'Подпись: Space Shuttle Columbia, launching. NASAimage32

program. The full rocket thrust duration was limited by the quantity of fuel carried and lasted approximately 90 seconds. Since the total time of flight on most missions was about 10 minutes, measured from drop from the B-52 to touchdown on the lakebed at EAFB, this meant that the X-15 flew for about 8У2 minutes without any engine power. As in all the rocket research aircraft, the

fuel was exhausted in the accelerating portion of the flights so that deceleration, descent, approach, and landing were all performed without power. While the larger X-15 was modified to carry more fuel, this expanded capacity merely extended the plane’s speed further into the hypersonic range; it did not provide power for landing.

The X-15 program left an important legacy in the development of manned hypersonic flight. It was, and still is, the fastest, highest-flying piloted airplane in history, and there is no new airplane design being planned in the foreseeable future that could do better. The X-15 met all of its design goals, and the results from its research flights allowed the following, among many others:

1) A verification of existing hypersonic aerodynamic theory and hypersonic wind tunnel techniques

2) A study of aircraft structures under the influence of severe, sustained aerodynamic heating

3) An investigation of stability and control problems associated with acceleration to high altitude, and atmospheric entry at hypersonic speeds

4) A study of the biomedical effects of both weightless and high-acceleration flight

The X-15 was an important steppingstone in the development of the Space Shuttle, which was more space vehicle than airplane but which had to experience hypersonic flight through the atmosphere every time it came back to earth.

The spectacular success of the X-15 program is a testimonial to the vision and courage of the engineers and managers who initiated the idea in the first place, the designers who created the vehicle, and the pilots who flew the airplane in the face of many unknowns. It is one of the most important stories in the annals of aviation history in general and aeronautical engineering in particular.

X-15A-2, showing the extra fuel tanks. USAF, Air Force Flight Test Center Hlistory Office, Edwards Air Force Base








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.


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



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


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


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.



n 1933, a young aeronautical engineer at the NACA Langley Laboratory conceived the idea of a research airplane that would be designed, built, and flown strictly for the purpose of probing an unknown flight regime. John Stack, a research engineer working in Langley’s first high-speed wind tunnel, designed a hypothetical research airplane for the single purpose of collecting data in the subsonic flight regime near the speed of sound. In the early 1930s, little was known and understood about flight near the speed of sound. Because the governing flow equations were mathematically nonlinear in this region, no analytical solutions were available to predict the lift, drag, and stability characteristics for airplanes in this transonic regime. (Even today, the only reliable transonic flow solutions are numerical results obtained from computational fluid dynamics [CFD] using massive supercomputers.) In addition, no accurate transonic wind tunnel data could be obtained from existing high-speed tunnels due to adverse aerodynamic interactions between shock waves from the model, reflecting off the wind tunnel walls and impinging back on the model surfaces.


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



X-15A-2 in captive flight under the B-52. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base



In light of the complete lack of accurate theoretical results and wind tunnel data in the transonic regime, Stack turned to the airplane as the best way to study flight near Mach 1. One of his hand – drawn graphs from 1933, found in the John Stack archives at NASA Langley by one of the authors and replete with the original smudges and rusty paperclip marks, shows Stack’s calculations of the power required versus flight velocity for his propeller-driven design.

At the top of the graph, Stack drew a sketch of his research airplane. His ideas got as far as

Volume 1, Number 1 of the brand-new Journal of the Aeronautical Sciences, published by the newly formed Institute of the Aeronautical Sciences (IAS) in 1934 (now the American Institute of Aeronautics and Astronautics [AIAA]). The “Effects of Compressibility on High Speed Flight” both advances the concept and gives the results of his calculations for such an airplane. His idea, however, got no further than the journal at that time. He sent his results to the biannual meeting of the NACA in October 1933, but the committee chose not to help Stack find a developer for the airplane. His work, however, was the genesis of the idea that eventually resulted in the X-15 via three other research airplanes: the X-1, X-1A, and X-2.

John Stack’s hand-drawn graph showing the effects of compressibility on the power required for a high-speed airplane, 1933. NASA Langley Research Center Library, Stack archive file



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


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


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.


image38In 1939, Ezra Kotcher, an instructor at the U. S. Army Air Corps Engineering School (much later the Air Force Institute of Technology) at Wright Field near Dayton, Ohio, took up the banner for a high-speed research airplane. Like John Stack, Kotcher had come to the conclusion that viable technical data for the supersonic flight regime could be obtained only with a real airplane. In August 1939, after two years of analysis and study, Kotcher wrote a report describing his views on the problems that future aeronautical research and development would face. He concluded that a high-speed research airplane could be powered only by a gas turbine or a

X-15 just after being mounted to the wing of the B-52 mother ship. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base




Me 262. USAF


rocket engine; a propeller-driven airplane would encounter insurmountable compressibility problems—shock waves on the blades—that simply could not be overcome. (To this day, no propeller-driven airplane has ever attained sustained supersonic speeds.) His report was reviewed by other engineers at Wright Field, and it eventually landed on the desk of Gen. Hap Arnold, who forwarded it to the NACA Langley Aeronautical Research Laboratory. There it met the same fate as John Stack’s memorandum. War clouds in Europe threatened, and the U. S. Army and the NACA had other pressing business.

By early 1944, the situation had changed completely. Germany was flying the twin-jet Me 262 jet fighter, against which Allied fighters and bombers were virtually helpless. The United States entered the jet age with the Bell P-59, a large, rather cumbersome jet with disappointing performance. Front-line propeller-driven fighters such as the North American P-51 and Republic P-47 flew faster. The Air Force had to face the
reality of flying into the transonic region, where there was no theoretical, wind tunnel, or flight data. Kotcher’s earlier proposal for a high-speed research airplane suddenly received priority attention. In January 1944, the Air Force issued “Confidential Technical Instruction 1568,” initiating a study for the development of an experimental airplane to probe the transonic flight regime. Starting with Kotcher’s original calculations, a small team of aeronautical engineers at Wright Field prepared a concept design of a rocket-powered airplane, soon to be labeled Mach 0.999. This design was vetted at a meeting of Air Force, Navy, and NACA engineers held at the Langley Aeronautical Laboratory in Hampton in mid-May 1944, where Kotcher reported the results of the Wright Field “Mach 0.999” study.

The final link in the development of a transonic research airplane took place in Ezra Kotcher’s office on November 30, 1944, when Robert Woods, Bell Aircraft’s chief of engineering, dropped by for a casual visit and expressed a

Подпись: Republic P-47. USAF image43
general interest in transonic developments. Kotcher seized the moment and shared the results of the “Mach 0.999” project, adding that the Air Force was having some difficulty finding an airplane company with enough time and interest to build such an airplane. Woods said that Bell Aircraft could do the job. The Bell X-1 was born.

The usual method for designing a new airplane is to first look at the previous one and then improve on it. The Bell designers had to start from scratch. Operating in a completely new design
space, Bell went to the Army’s Aberdeen Proving Ground in Maryland to study the aerodynamics of.50-caliber machine gun bullets, which were known to be slightly supersonic. The shape was stable, and the scatter of the bullets was minimal. The shape of the Bell X-1 fuselage is that of a.50-caliber machine gun bullet.

The concept of swept wings for high-speed airplanes originated with German engineer Adolf Busemann in 1935, and extensive wind tunnel research on the aerodynamics of swept wings advanced under German engineers under the shroud of secrecy of World War II. These swept – wing data were uncovered by the surprised Allied scientists who went into the German laboratories in May 1945. The data and its significance, however, were too late to be of direct use to the Bell designers. The Bell X-1 had straight wings.

From pioneering studies of the aerodynamic flow over airfoils at high subsonic speeds by the NACA in the 1930s, it was well known that thin airfoils delayed the formation of shock waves over

Подпись: Bell X-1 at Smithsonian. Note the similarity between the shape of the M2 bullet and the nose. NASM
the airfoils to higher speeds, thus delaying the adverse compressibility effects of shock-induced flow separation, with the consequent large increase in drag, dramatic loss of lift, and almost instant change in stability characteristics. The wing of the Bell X-1, therefore, had a relatively thin airfoil. The precise airfoil thickness was, however, a compromise. Two wings for the X-1 were designed and utilized: an 8-percent thick wing using an NACA 65-108 laminar flow airfoil, and a 10-percent thick wing using an NACA 65-110 laminar flow airfoil.

The thinner wing was used for flights in which maximum speed was the object. The thicker wing, which would encounter compressibility effects at slower speeds, was used for detailed aerodynamic
research investigations of the physical nature of transonic flow over the wing. In this fashion, the Army could pursue the quest for supersonic speed using the thin wing, and the NACA could pursue its quest for obtaining detailed flight data using the thick wing. Because the Army was paying for the X-1, the early part of the X-1 flight program was focused on obtaining supersonic flight as a goal in itself.

The design of the X-1 set the mold for many of the research aircraft that followed. It was rocket – powered. The engine was especially designed for the X-1 by Reaction Motors and was labeled the XLR11, with a maximum of 6,000 pounds of thrust obtained from a total of four separate chambers. The thrust could be modulated by firing


Bell X-1 in flight. NASA Dryden Flight Research Center

Bell X-5 showing swept wings, composite photo. NASA

any one or more of the chambers. The X-1 was air- launched from a B-29 bomber; the alternative of taking off from the ground would have consumed too much fuel and not allowed the airplane to reach transonic speeds. Some researchers in the NACA, John Stack included, argued that the research airplane should be powered by a turbojet, thus allowing ground takeoff. Ezra Kotcher and the Army strongly argued against this scenario, and as mentioned earlier, the Army was putting up the money.

Three X-1 aircraft were manufactured by Bell. The first rolled out the Bell factory door on December 27, 1945, without its rocket engine.

The unpowered X-1 was transported to the Air Force’s Pinecastle Field near Orlando, Florida, for a series of glide tests to examine stability and control characteristics, and to examine low – speed behavior. Carried aloft by a B-29 bomber, the X-1 successfully completed ten glide flights.

In each, the airplane behaved beautifully at low speeds. This airplane was then transported back to Bell’s factory in Niagara Falls, New York, for installation of its rocket engine. The center of activity now shifted to the Muroc Army Air Field in California, where the powered flights were to take place. There, Bell test pilot Chalmers H. “Slick” Goodlin continued flying the X-1, as called for in the contract. The second X-1 was delivered to Muroc on October 7, 1946, followed shortly thereafter by the first X-1. By May 27, 1947, Bell had completed all the contractually required test flights (all subsonic), and the airplanes were turned over to the Army Air Force.

The Army selected Capt. Charles (Chuck) Yeager to be the next test pilot for the X-1. The Army’s first flight, with Yeager at the controls, took place on August 6, when the X-1 was carried aloft by the B-29 carrier aircraft above Muroc for a pilot-familiarization flight. It was the thirty – eighth time that any of the X-1s had taken to the
air. Over the next two months the flight-testing program called for a slow increase in speed, gradually approaching the speed of sound. On October 8, Yeager squeezed the airplane to a Mach number of 0.925; two days later, he flew at Mach 0.997. The fiftieth flight took place on October 14,

1947. Although the flight plan did not officially call for it, Yeager brazenly pushed the X-1 through Mach 1, to Mach 1.06. On that day, aviation history was made. It was the first supersonic flight of a piloted airplane, perhaps the most important event in aviation history since the Wright brothers’ first successful flight at Kitty Hawk on December 17, 1903. Moreover, the flight was smooth with no technical problems. The existing myth of a “sound barrier” had been broken.

The Bell X-1 lived up to its role as the first airplane designed purely for the acquisition of research data. In total, there were 151 flights,

35 of which were supersonic. The highest Mach number reached by the X-1 was 1.45 on March 26,

1948, with Yeager at the controls. The X-1 was the progenitor of the X-15 in several respects. Both airplanes were rocket-powered. The X-1 proved the viability of a rocket engine for achieving high­speed flight at a time when no other powerplant was available to accomplish the mission. Both were air-launched for the same reason, namely

to conserve fuel to enable enough power for a long enough duration to achieve the design Mach number. Ezra Kotcher had argued forcefully for an air launch as opposed to taking off from the ground; he was proven right. This approach carried through to the X-15. The last flight of the X-1 took place on July 31, 1951, piloted by Scott Crossfield, who was also the first pilot to fly the X-15.

Differences in the interests of the three parties involved in the X-1 program were contentious at times. The NACA wanted slow, continuous testing below Mach 1 to fully and safely analyze transonic flow; the Army Air Force wanted to


▲ X-1A in the belly of a B-29 bomber. USAF

▼ X-15 and X-1B. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base



image49reach supersonic capability quickly, to develop and build a fighter that would be faster than any enemy; Bell Aircraft wanted to meet its contract requirements and get paid, but also to reach the supersonic flight regime in a timely fashion and thus gain advantage in future procurements. The objectives of all parties were achieved. The NACA did its significant transonic testing and analysis, the Army Air Force had its supersonic airplane, and Bell Aircraft was rewarded for the design, building, and flight testing of the airplane.



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



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.