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

Scott Crossfield was more than just the first man to fly the X-15; he was the only one of the twelve test pilots who contributed directly to the
airplane’s design and to the design of its flight-test program. Crossfield successfully combined his master’s degree in aeronautical engineering with his exceptional piloting ability and experience to enhance the design and operation of an experimental vehicle that would go far beyond the known atmospheric flight spectrum, to speeds of almost Mach 7 and to altitudes higher than 350,000 feet.

Scott Crossfield was born on October 2, 1921, in Berkeley, California, and attended college at the University of Washington in Seattle, beginning in 1940. The outbreak of World War II interrupted

his studies in 1942, when he joined the Navy. After he received his pilot’s wings and ensign’s commission in 1943, the Navy assigned him to be a flight instructor and maintenance officer.

He served in the South Pacific for six months but did not see combat duty. His piloting skills put him at the helm of a Navy aerobatic team, and he flew Corsair fighters for a short period following the war. Crossfield was, however, an aeronautical engineer at heart, and he returned to the University of Washington in 1946 to finish his bachelor’s degree in aeronautical engineering, as well as his M. S., in 1949. During that time, he obtained valuable experience working in the Kirsten Wind Tunnel at Washington.

It was not a good time to graduate with an aeronautical engineering degree; the industry

was suffering from large government cutbacks in defense after World War II. However, the advent of the Korean War in 1950 reversed this situation, and suddenly the aircraft industry was back on its feet. Crossfield found a position as an aeronautical research pilot with the NACA High Speed Flight Station (now the NASA Dryden Flight Research Center) at Edwards Air Force Base in June 1950. The time and opportunity were ripe for Crossfield; over the next five years, he was to fly virtually all the experimental airplanes at Edwards, including the Bell X-1, the delta-wing XF-92, the X-4, the X-5, and the Douglas D-558- 1 Skystreak. On November 20, 1953, he became the first person to fly at Mach 2 while piloting the rocket-powered Douglas D-558-2 Skyrocket to a speed of 1,291 miles per hour in a shallow dive.

Powered by a rocket engine, and developed by Douglas for the U. S. Navy, the Douglas D-558-2 explored transonic and supersonic flight and the flight characteristics of swept-wing supersonic aircraft. Flight tested at the Muroc Flight Test Facility alongside other research aircraft such as the X-1, X-1A, and X-2, the D-558-2 was the Navy’s venture into the mysteries of supersonic flight. Controversy persists as to who deserves credit for the first Mach 2 flight. Crossfield reached Mach 2 in the D-558-2, but in a shallow dive. Just twenty-two days later, Chuck Yeager flew the Bell X-1A to Mach 2.44 in level flight.

This beautiful, swept-wing airplane now hangs in the Milestones of Flight Gallery at the National Air and Space Museum.

On June 24, 1952, the NACA Committee on Aerodynamics called for an airplane that could probe the unknown problems of flight at Mach numbers between 4 and 10 and at altitudes between 12 and 50 miles. On October 5, 1954, this same committee, in executive session, made the final decision to proceed with this manned hypersonic research airplane, which would eventually become the X-15; Crossfield was a
member of the committee. On May 9, 1955, four aircraft companies submitted proposals to the Air Force (which was paying for the airplane):

Bell, Douglas, North American, and Republic. After North American won the contract, Scott Crossfield left the NACA and joined North American as chief engineering test pilot and design consultant on the X-15.

After piloting the first test flight of the X-15 on June 8, 1959, Crossfield flew the airplane thirteen more times, his last X-15 flight taking place on December 6, 1960—the thirtieth test flight of the X-15 program. At this point, North American finished its contractor check flights and turned the aircraft over to the Air Force. Although Crossfield had expected to fly the X-15 during its entire program, because he was a NAA employee, not a NACA employee, his flight participation in the X-15 came to an end.

Crossfield continued with North American, first as the director responsible for systems tests, reliability engineering, and quality assurance for several aircraft and space vehicles, and then as its technical director, Research Engineering and Test. In 1967, he left the company to serve as a division vice president for Research and Development for Eastern Airlines until 1973, and he then served as senior vice president for Hawker Siddeley Aviation in 1974 and 1975. In 1977, nine years after the X-15 program ended, he became a technical consultant to the House Committee on Science and Technology. He served in this capacity for sixteen years, during which he was a steadfast proponent of manned hypersonic flight. He especially supported the massive U. S. X-30 supersonic combustion ramjet engine-(scramjet) powered single-stage to orbit aerospace plane project during the 1980s and early ’90s. He retired in 1993.

Scott Crossfield earned a number of prestigious awards during his life, including being a joint recipient of the 1961 Collier Trophy, the

International Clifford B. Harmon Trophy for 1960, the Lawrence Sperry Award for 1954, the Octave Chanute Award for 1954, and the Iven C. Kincheloe Award for 1960. He was inducted into the National Aviation Hall of Fame in 1983 and the International Space Hall of Fame in 1988. As a reflection on his aeronautical engineering accomplishments, the American Institute of Aeronautics and Astronautics elected him to the rank of Honorary Fellow in 1999, the highest recognition in that society.

In 2000, the National Air and Space Museum awarded him its most prestigious award, the Lifetime Achievement Award. An elementary school in Herndon, Virginia, and the terminal of the Chehalis-Centralia Airport in Washington State both bear his name.

On April 19, 2006, Crossfield got into his Cessna 210A to return home from Maxwell Air Force Base in Montgomery, Alabama, where he had just finished giving a speech to a class of young Air Force officers. Amid severe thunderstorms, his airplane broke up in midair; recovery teams found wreckage in three different locations within a quarter-mile region. Later, the National Transportation Board ruled the probable cause of his crash to be a combination of two failures: Crossfield had not obtained updated weather information en route, and the air traffic controller failed to provide adverse-weather avoidance assistance. Crossfield was survived by his wife of sixty-three years, Alice Crossfield, as well as six children and nine grandchildren. He is buried in Arlington National Cemetery.

Crossfield was unique among the X-15 pilots. He always considered himself an aeronautical engineer, although he was also an exceptional test pilot. Being an honorary fellow of the AIAA is indicative of his status within the aeronautical engineering profession. Although he flew the X-15 only fourteen times, never exceeded Mach 2.97 (Flight 26, November 15, 1960), and never flew any higher than 88,116 feet (Flight 6, February 11, 1960), he was arguably the most influential of all the pilots in the X-15 program.

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.

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.

1921-1966

Joe Walker flew the X-15 for his first time on March 25, 1960, during which he achieved Mach

2.0 and an altitude of 48,630 feet. He was the first NASA pilot in the test program.

Joe Walker was born on February 20, 1921, in Washington, Pennsylvania. He graduated with a bachelor of arts degree in physics from Washington & Jefferson College in 1942. He was caught up in the storm of World War II, joined the Army Air Force, and flew P-38 fighters in North Africa, for which he earned the Distinguished Flying Cross and the Air Medal with seven Oak Leaf clusters. In March 1945, he joined the NACA and became involved in the icing research program at the Aircraft Engine Research Laboratory
(now the NASA Glenn Research Laboratory) in Cleveland, Ohio. There, in the words of Milton Thompson, himself an X-15 pilot, Joe Walker “spent many hours droning around in the crappiest winter weather that they could find in the Great Lakes region.” [citation: Milton O. Thompson,

At the Edge of Space: The X-15 flight Program (Smithsonian Institution Press, 1992, p. 4)]

Walker transferred to the NACA High Speed Flight Station (later the Dryden Flight Research Center) in 1951, and his flying skills earned him the position of chief pilot in 1955. He flew as project pilot on some of the early, important
high-speed experimental airplanes, including the Douglas D-558-1 and 2 and the Bell X-1A and X-1E, X-3, X-4, and X-5. During his first year at the NACA High Speed Flight Station, Walker received an NACA medal for heroism. He was in the cockpit of the X-1A mounted in the bomb bay of a B-29 in flight. In preparation for his research flight, he pressurized the X-1A’s propellant tank. An explosion immediately occurred, and Walker passed out. Regaining consciousness as the B-29 crew opened the X-1A canopy and pulled him out, Walker realized that the X-1A had to be deactivated before a bigger explosion occurred. Risking his life, Walker crawled back into the cockpit and depressurized the remaining tanks. The smell of hot peroxide started to fill the B-29. The X-1A now resembled a bomb about ready to go off. Scrambling back into the B-29, Walker decided to jettison the X-1A. The experimental airplane spun down to the desert floor and was destroyed, but the B-29 and its crew returned safely.

In 1959, the NACA became part of the newly formed National Aeronautics and Space Administration. Hence, on March 25, 1960, Walker became the first NASA pilot to fly the X-15. Remarkably, on his first flight, Walker took the X-15 to Mach 2 and an altitude of 48,630 feet. During the course of his remaining twenty – four flights in the X-15, Walker achieved the highest altitude of all the X-15 flights, 354,200 feet on Flight 91, August 22, 1963. This is still the unofficial world record for winged vehicles.

During his twenty-five flights in the X-15, Walker collected data on stability and control, aerodynamic heating, flight performance, aerodynamics, thermostructural response, maximum speed, and maximum altitude characteristics. On Flight 91, in addition to setting the unofficial world altitude record, he obtained data on reentry flight with the ventral fin off, checked out an altitude predictor, and took physical atmospheric measurements with a Barnes spectrometer and a photometer. Collecting this scientific and engineering data was the core of the X-15’s research mission.

After his last X-15 flight on August 22, 1963, Walker continued in his position as chief pilot at the NASA High Speed Flight Station. Prior to his involvement with the X-15, he had logged a number of flights in the Lockheed F-104, the first airplane designed for sustained supersonic flight at Mach 2. It was in this airplane that he first carried out pioneering tests using reaction controls, taking the F-104 to altitudes of 90,000 feet. So it was natural that on June 8, 1966, he chose to pilot an F-104 on a routine photo shoot with the North American XB-70. General Electric had requested some promotional photographs of a family of airplanes powered by GE engines. Flying too close to the XB-70, his F-104 was caught in the trailing vortex of the large airplane and flipped onto the top of the bomber. Walker perished in the ensuing fireball. The XB-70 pilot, Al White, ejected, sustaining serious injury but surviving. Carl Cross, the copilot, was killed.

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.

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

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

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.

▲ 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

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

1924-2010

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

White 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

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.

1922-1990

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

the 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

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

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

1922-1975

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

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

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.

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.

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

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

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

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

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.

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

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.

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,

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

The 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.