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

THE BELL X-1

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

 

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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

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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

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▲ 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

 

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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.

ROBERT M. WHITE

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

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

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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.

NUMBER OF FLIGHTS CONDUCTED

In all, 199 flights were conducted over a nine-year period from June 1959 to October 1968. Three airplanes were built, repaired, and rebuilt during that period. The third airplane was a significant modification. This longer version included external fuel tanks to extend the flight time, the range of altitude, and the Mach number to be investigated. Most of the initial objectives for the airplane were reached in the early years. But because the X-15 could fly in the hypersonic regime, NASA wanted to conduct many experiments, some examining various materials using the airplane as a test bed.

One of the thermal protection techniques used to protect hypersonic vehicles from the intense aerodynamic heating environment is the covering of the vehicle surface with an ablative material. This material would directly absorb the heat and burn away (ablate), thus protecting the surface underneath. Some of the later X-15 test flights tested a specific ablative material, namely MA-25S developed by Martin Marietta. This silicon-based material was sprayed on the surface of the X-15. After several hours of curing, it was sprayed with a coating of Dow Corning DC90-090, a silicon – based sealer, which gave the X-15 a white color.

Подпись:Some of these caused problems in flight. For example, for some flights an ablative material was put on the airplane for testing purposes and for additional heat protection. As the material vaporized, it coalesced on the windshield, making it opaque, seriously affecting the visibility of the pilot. For further tests of the ablating material, the engineers had to install an external shield on half the windshield that could be moved away after ablation had obscured the other side in order to allow the pilot to have clear vision for the remainder of the flight.

THE BELL X-1A

Exactly one month after Chuck Yeager had made history by breaking the sound barrier in the X-1, the Army Air Force began a new study with Bell

for an airplane to fly at Mach 2. Labeled the X-1A, the new airplane had the same wing and horizontal stabilizer and the same rocket engine as the X-1, but it had a completely new fuselage with a more slender shape (higher fineness ratio and increased propellant storage).

On December 12, 1953, Yeager flew the X-1A to a Mach number of 2.44 at 70,000 feet. This set an unofficial world speed record. During the flight, while at this Mach number and altitude, the airplane suddenly encountered inertial roll-coupling and went out of control. Yeager was knocked semi-conscious in the cockpit as the airplane wildly descended. Fortunately, at 25,000 feet, Yeager was able to regain control. Although not intended to be part of the research flight plan, this was the

Douglas D-558-2 Skyrocket. NASA

 

US. NAVY

 

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ф’нф’фї

 

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X-1A on the lakebed. NASA Dryden Flight Research Center

first time that such roll-coupling at supersonic speeds had been encountered, although it had been predicted earlier by some aerodynamicists. The Air Force subsequently limited the top speed of the X-1A to Mach 2. Yeager, however, was not the first pilot to fly at Mach 2 or higher. This honor went to Scott Crossfield, who flew the swept – wing Douglas D-558-2 Skyrocket to Mach 2 on November 20, 1953.

The last flight of the X-1A was a captive flight in the carrier B-29. On August 8, 1955, as the B-29 was ascending to launch altitude, the X-1A suffered an internal explosion. The pilot, Joe Walker, in an act of heroism, saved himself and the crew of the B-29, but the X-1A was jettisoned and fell to the desert floor. Joe Walker was the second man to fly the X-15.

FOREST S. PETERSON

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).

LATERAL DIRECTIONAL STABILITY AND THE MH-96 FLIGHT CONTROL SYSTEM

As expected on the basis of experience with the earlier supersonic X-airplanes, the lateral – directional stability of the X-15 decreased as the Mach number rose to supersonic and hypersonic
speeds. Honeywell’s adaptive control system automatically compensated for the aircraft’s unstable lateral-directional behavior in various flight regimes, and it utilized the combined operation of the aerodynamic control surfaces and the rocket reaction controls in their respective regions of flight.

Originally, the vertical tail sections above and below the airplane were large. That section, located below the airplane, is called the ventral tail. Wind tunnel data showed a need for a large ventral tail, so large that it would hit the ground first before the landing skids. This necessitated designing the bottom part of the ventral to be ejected prior to landing. The flight data showed a lesser need for the large area of the ventral tail, and in subsequent flights the bottom half was left off.

A relationship between the wind tunnel data and the flight data was thus established. The Honeywell MH-96 adaptive control system allowed the airplane, unstable in certain regions of flight, to be operated in a conventional manner throughout. Moreover, it provided an automatic transition from the conventional aerodynamic control system (rudder, elevator, etc.) used within the sensible atmosphere to the reaction control system for high- altitude flight, where the aerodynamic forces were too weak. This relieved the pilot from manually making this change, both on ascent to high altitudes and back again for descent.

THE BELL X-2

As far back as 1935, German aerodynamicist Dr. Adolf Busemann gave a paper at the fifth Volta Conference in Rome in which he introduced the swept wing as an idea for reducing the drag of supersonic airplanes. The conference topic, “High Velocities in Aviation,” was forward­looking. At that time, the speeds of typical aircraft were in the range of 250 miles per hour, and supersonic aircraft were not yet on the radar. Busemann’s swept-wing idea was virtually ignored by the audience, an “invitation only” crowd that consisted of some of the most important aerodynamicists of the day. Ignored, that is, by everybody except the German Luftwaffe, which classified the concept in 1936—one year after the Volta Conference. During World War II,

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X-15 mounted under the wing of the B-52 for its first captive flight. USAF, Air Force Flight Test Center Flistory Office, Edwards Air Force Base

the Germans carried out secret, extensive aerodynamic research on swept wings, producing volumes of wind tunnel data, which was subsequently discovered by the Allied intelligence teams that went into German laboratories at the end of the war. Moreover, in 1944, R. T. Jones, one of the NACA’s best aerodynamicists, had independently proved the viability of the swept wing for reducing wave drag on high-speed wings.

This new information on swept wings, nevertheless, was too late for practical use by the designers of the X-1, who had already gone too far in the straight-wing design for the X-1.

But to compensate, the Air Force and Bell signed a new contract on December 14, 1945, for the design, development, and construction of an entirely new swept-wing X-aircraft, the X-2. This research aircraft was designed for speeds above Mach 3, which put it in the flight regime where aerodynamic heating becomes an important consideration. In fact, the investigation of aerodynamic heating at high Mach numbers was one of the principal drivers for the X-2. The skin temperature varies approximately as the square of the Mach number. Everything else being equal, the skin temperature of the X-2 (Mach 3) is nine times higher than that for the X-1 (Mach 1). This required that the X-2 be fabricated from K-monel and stainless steel alloys, rather than aluminum. Also, supersonic aerodynamics of the day dictated that an optimum supersonic airfoil shape be a thin bi-convex (circular arc) with an extremely sharp leading edge. The 40-degree swept wing of the X-2 had a thin, circular arc airfoil and an aspect ratio of 4.

Like its predecessors, the X-2 was rocket – powered. The X-2 contract included the engine, and Bell had designed for 15,000 pounds of thrust provided by two rockets, one with 5,000 pounds of thrust mounted above the other, which had 10,000 pounds of thrust. Each engine was oriented so that the thrust vector of each went through the center of gravity of the airplane. Each engine was throttleable to half, so there would be continuous thrust levels from 2,500 pounds to 15,000 pounds. The Air Force selected Curtiss-Wright, which— with Bell’s approval—took over the development of the rocket motors.

Bell Aircraft was responsible for the installation and testing of the rocket engine and for its operation during flight. Bill Smith, Bell’s chief of rocket engines, personally led these test efforts at Edwards Air Force Base, and he monitored the live static rocket testing on the ground from about 25 yards away from the airplane. (This was a far cry from modern rocket engine testing, which is conducted from concrete block houses to protect the test operators.)

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Подпись: CURTISS-WRIGHT

X-2 with its B-50 mother ship, support vehicles, support personnel, support helicopter, and chase planes. NASA Dryden Flight Research Center

The Air Force wanted to involve another company in the aircraft rocket engine business in addition to Reaction Motors, and with the agreement of

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Bell, they chose Curtiss-Wright. The Curtiss – Wright Corporation was formed in 1929 from the consolidation of the Wright Aeronautical and Glenn Curtiss companies, combining the two most important aeronautical pioneers in the history of early flight in the United States. Curtiss – Wright produced the famous P-40 during World War II, the airplane that was flown by the Flying Tigers in China. After the war, Curtiss-Wright fell behind in the design of jet airplanes and phased out of the aircraft design field, taking up the production of aircraft components and simulators.

Their excursion into aircraft rocket engines, prompted by the X-2, was transitory.

The decision to go with Curtiss-Wright for the engines ultimately resulted in delays. Although Bell produced two airframes by early 1953, only one engine was available, and that not until early 1953. Ironically, one X-2 was lost due to an engine explosion that took place in the bomb bay of the B-50 carrier aircraft. On May 12, 1953, company test pilot Jean Ziegler participated in a captive test flight that was intended to qualify the liquid oxygen top-off and jettisoning system. (A captive test flight is a flight in which the airplane is carried aloft by the mother plane but never released. The X-2 remained attached to the B-50 for the entire
flight—thus the name “captive” test flight.) When the B-50 was at 30,000 feet over the center of Lake Ontario, an explosion took place. The B-50 was tossed 650 feet upward, and the X-2 disintegrated. Both Ziegler and B-50 observer Frank Wolko were lost. The B-50 immediately returned to its home base. The weather was bad, with a heavy overcast ceiling of about 10 feet. It remained bad for a week, and searches to find the two men by Bell and government aircraft found nothing.

Test flying of the X-2 continued with the second aircraft. From August 8, 1954, to September 27, 1956, a total of seventeen flights were made in

the second X-2. On July 23, 1956, with Air Force Capt. Frank Everest at the controls, the X-2 set a new unofficial world speed record of Mach 2.87. Two months later, on September 27, 1956, the X-2 made aviation history, becoming the first airplane to fly faster than Mach 3. With Air Force Capt. Milburn Apt at the controls, the X-2 set an unofficial world speed record of Mach 3.196. This was Apt’s first flight in the X-2; he flew a near-perfect flight plan to a maximum altitude of 72,000 feet and nosed over, attaining the maximum Mach number at 66,000 feet. However, Apt then put the X-2 in a slight roll, not in the flight plan. The X-2, due to inertia coupling, was unstable in roll at that Mach number and went out of control. The airplane and pilot were both lost, underscoring the dangers of test flying in unknown flight regimes.

JOHN B. “JACK” McKAY

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

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.”

POWER ASSIST CONTROLS

In the early days of flight, the aerodynamic controls (ailerons, elevators, rudder) were directly connected to the cockpit via cables, and the pilot had to use physical force to operate these controls. As the speeds of airplanes increased, the aerodynamic forces became larger and required more physical force from the pilot to operate the controls. With the advent of high-speed jet flight, these forces
became too large for the pilot to overcome, and hydraulically boosted controls were introduced (much like power steering in your automobile). For the X-15, the power assist controls that gave force amplification to the pilot were effective; they were used by the pilots when the aerodynamic forces were high at the lower altitudes.

The power assist controls were used throughout by some of the pilots who did not use the conventional center stick and who only used the force amplification controls. The MH-96 also blended this control with the rocket controls, which were used when the air density was so low that the aerodynamic controls were ineffective because of the high altitude and resulting low dynamic pressure. It made the transition from aero control to rocket automatic. For use in future hypersonic aircraft, and in the Space Shuttle that actually followed, it simplified the piloting when flying in these varied regions of aerodynamic force. The X-15 demonstrated that airplanes in these regions, even while rapidly traversing from one region to another with high accelerations and decelerations, could be flown safely by trained pilots.

RELEVANCE TO THE X-15

The X-1, X-1A, and X-2 were precursors to the X-15 and were relevant to the future design of X-15, for the following reasons:

1) They were designed to be strictly research airplanes.

2) They were all powered by liquid-fuel rocket engines.

3) They were all air-launched. They were designed with no intention of ever evolving into viable military combat aircraft.

These research aircraft accomplished the first three steppingstones to high-speed flight: the X-1 to Mach 1, the X-1A to Mach 2.44, and the X-2 to Mach 3.2. The next phase was going to be huge, stepping into the regime of hypersonic flight. This was to be the role of the X-15.

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▲ B-52 mother ship taking off with the X-15 mated under its wing. USAF,

Air Force Flight Test Center History Office, Edwards Air Force Base

▼ X-15 landing with an F-104 chase plane following close by. USAF, Air Force Flight Test Center History Office, Edwards Air Force Base

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X-15A-2 under the wing of the B-52 mother ship in flight. USAF,

Air Force Flight Test Center History Office, Edwards Air Force Base

 

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