Page 13 - The Future of Aerospace is X - X-Planes 2021

X-15 Hypersonic Research Program

In the joint X-15 hypersonic research program searcher John Becker, who had been an early ad-
that NASA conducted with the Air Force, the vocate of the X-15 program, identified 25 specific
Navy, and North American Aviation, Inc., the accomplishments of the effort. These included:
aircraft flew over a period of nearly 10 years and • First application of hypersonic theory and
set the world’s unofficial speed and altitude re- wind tunnel work to an actual flight vehicle.
cords of 4,520 mph (Mach 6.7) and 354,200 feet, • First use of reaction controls for attitude con-
in a program to investigate all aspects of piloted trol in space.
hypersonic flight. • First reusable superalloy structure capable of
Information gained from the highly successful withstanding the temperatures and thermal gradi-
X-15 program contributed to the development of ents of hypersonic reentry.
the Mercury, Gemini, and Apollo piloted space- • Development of (a servo-actuated ball) nose
flight programs, as well as the Space Shuttle pro- flow direction sensor for operation over an ex-
gram. NASA photographs treme range of dynamic pressure and a stagnation
Manufactured by North American Aviation, Left: The X-15 #2 (56-6671) launches away from the B-52 mothership with its rocket engine air temperature of 1,900 degrees Fahrenheit F (for
Inc., three rocket-powered X-15s flew a total ignited. The white patches near the middle of the ship are frost from the liquid oxygen used in the accurate measurement of air speed and flow angle
of 199 times, with North American (and former propulsion system, although very cold liquid nitrogen was also used to cool the payload bay, cockpit, at supersonic and hypersonic speeds).
National Advisory Committee for Aeronautics or windshields, and nose. Right: After receiving a full scale ablative coating to protect the craft from • Development of the first practical full pres-
NACA) pilot Scott Crossfield making the first, the high temperatures associated with high-Mach-number supersonic flight, the X-15A-2 (56-6671) sure suit for pilot protection in space.
unpowered glide flight on June 8, 1959. NASA’s rocket powered research aircraft was then covered with a white sealant coat and mounted with • Development of inertial flight data systems
William H. Dana was the pilot for the final flight additional external fuel tanks. This ablative coating and sealant would help the #2 aircraft reach capable of functioning in a high dynamic pressure
the record speed of 4,520 mph (Mach 6.7). Under the lower fin is a dummy ramjet engine. It was
in the program on Oct. 24, 1968. All of these intended to use the X-15A-2 for tests of an actual engine but this never happened. and space environment.
flights took place within what was called the • Discovery that hypersonic boundary layer
“High Range” surrounding, but mostly to the east, flow is turbulent and not laminar.
of Edwards Air Force Base, Calif., and NASA’s regime from just below the speed of sound (Mach aircraft, the X-15 initially flew with two XLR- • Discovery that turbulent heating rates are
Flight Research Center (later called the NASA 1) to Mach 3.2. 11 engines, producing a thrust of 16,380 pounds. significantly lower than had been predicted by
Armstrong Flight Research Center). In 1952, NACA had begun preliminary re- Once the XLR-99 was installed, the thrust became theory.
There were 10 other pilots in the program for search into space flight and associated problems. 57,000 pounds. • First direct measurement of hypersonic air-
a total of 12: five from NASA, five from the Air Two years later, NACA’s Research Airplane The X-15 used conventional aerodynamic con- craft skin friction and discovery that skin friction
Force, one from the Navy, and one, Crossfield, Projects Panel discussed the need for a new re- trols for flight in the dense air of the usable atmo- is lower than had been predicted.
from North American. Generally, pilots used one search airplane to study hypersonic and space sphere. The controls consisted of rudder surfaces • Discovery of hot spots generated by surface
of two types of flight profiles: a speed profile that flight. NACA established the characteristics of on the vertical stabilizers to control yaw (move- irregularities. (These last four discoveries ben-
called for the pilot to maintain a level altitude what became the X-15 and presented them to ment of the nose left or right) and canted horizon- efited the Space Shuttle.)
until time for descent to a landing, and a high- the Air Force and Navy in July 1954. The two tal surfaces on the tail to control pitch (nose up • Discovery of methods to correlate base drag
altitude flight plan that required maintaining a services and NACA signed a memorandum of and down) when moving in synchronization, or measurements with tunnel test results so as to cor-
steep rate of climb until reaching altitude and understanding for the joint project in December roll when moved differentially. rect wind tunnel data (and thereby improve design
then descending. 1954, and the Air Force selected North American For flight in the thin air outside the Earth’s criteria for future air- and spacecraft).
Because of the large fuel consumption of its to develop three X-15 research aircraft in Sep- atmosphere, the X-15 used a reaction control • Demonstration of a pilot’s ability to control
rocket engine, the X-15 was air launched from tember 1955. system. Hydrogen peroxide thrust rockets on the a rocket boosted aerospace vehicle through at-
a B-52 aircraft at about 45,000 feet and speeds A North American team headed by Chief Proj- nose of the aircraft provided pitch and yaw con- mospheric exit.
upward of 500 mph. Depending on the mission, ect Engineer Charles Feltz designed the aircraft, trol. Those on the wings furnished roll control. • Successful transition from aerodynamic con-
the rocket engine provided thrust for the first 80 with technical guidance from the NACA’s Lang- The outer skin of the X-15 consisted of a nick- trols to reaction controls and back again.
to 120 seconds of flight. The remainder of the ley Aeronautical Laboratory, Hampton, Va., and el-chrome alloy called Inconel X, employed in • First application of energy-management tech-
normal 8- to 12-minute flight was without power the High-Speed Flight Station (as Armstrong was a heat sink structure to withstand the results of niques (for the positioning of the vehicle for all
and ended in a 200-mph glide landing. Because then called). aerodynamic heating when the aircraft was flying future reusable launch vehicles following their
the nose landing wheel lacked steering and the Although the number two aircraft was later within the atmosphere. The cabin was made of reentry from space.)
main landing gear employed skids, the X-15 had modified, the basic X-15 was a single-seat, mid- aluminum and was isolated from the outer struc- • Use of the three X-15 aircraft as testbeds to
to land on a dry lakebed. The Rogers Dry Lake wing monoplane designed to explore the areas of ture to keep it cool. carry a wide variety of experimental packages.
adjacent to Edwards and Armstrong was the in- high aerodynamic heating rates, stability and con- These experiments — 28 of them — ranged
tended landing location for all flights, but there trol, physiological phenomena, and other prob- The first X-15 arrived at the NASA High- from astronomy to micrometeorite collection.
were numerous emergency lakebeds selected in lems relating to hypersonic flight (above Mach 5). Speed Flight Station in the early months of 1959, They included tests of horizon definition and
advance for emergency landings. Because the Reaction Motors Division of Thio- and Scott Crossfield, who had helped with the proposed insulation that bore fruit in the naviga-
The X-15 was a follow-on research aircraft to kol Chemical Corp. did not have the throttleable design of the aircraft, soon began the contractor tion equipment and thermal protection used on
the early X-Planes, which had explored the flight XLR-99 engine ready for the early flights of the demonstration flights. the Saturn launch vehicles in the Apollo program,
During its research program, the aircraft set un- which dispatched 12 astronauts to the moon and
official world speed and altitude records of 4,520 back. Among the 12 was Neil Armstrong, the first
mph (Mach 6.7) on Oct. 3, 1967, with Air Force human to step on the moon’s surface and a former
pilot Pete Knight at the controls, and 354,200 X-15 pilot, who also flew many other research
feet on Aug. 22, 1963, with NASA pilot Joseph aircraft at the Flight Research Center.
Walker in the cockpit. In the area of physiology, researchers learned
More important than records, however, were that the heart rates of X-15 pilots ranged from 145
the X-15’s probing of hypersonic aerodynamic to 185 beats per minute during flight. This greatly
performance and heating rates, research into exceeded the normal 70 to 80 beats per minute
structural behavior during high heating and high experienced on test missions for other aircraft.
flight loads, study of hypersonic stability and The cause of the difference proved to be the stress
control during exit from and reentry of the at- X-15 pilots encountered during pre-launch in an-
mosphere, and examination of pilot performance ticipation of each mission. As it turned out, the
and physiology. higher rates proved typical for the future physi-
In the course of its flight research, the X-15’s ological behavior of pilot- astronauts.
pilots and instrumentation yielded data for more More intangibly but no less importantly, in the
than 765 research reports. As Dryden Chief Sci- words of John Becker, the X-15 project led to
entist Ken Iliff and his wife, aerospace research “the acquisition of new piloted aerospace flight
engineer Mary Shafer, wrote, “The aircraft re- ‘know how’ by many teams in government and
turned benchmark hypersonic data for aircraft industry. They had to learn to work together, face
performance, stability and control, materials, up to unprecedented problems, develop solutions,
shock interaction, hypersonic turbulent boundary and make this first manned [today, we would say
layer, skin friction, reaction control jets, aerody- piloted] aerospace project work. These teams
namic heating, and heat transfer.” The boundary were an important national asset in the ensuing
layer is the thin layer of air next to the body of space programs.”
the aircraft that has distinctive flow characteristics As the partial list of accomplishments suggests,
because of friction between the air and the surface the X-15 brilliantly achieved its basic purpose of
NASA photograph of the aircraft. Control of the flow in the boundary supporting piloted hypersonic flight within and
X-15 just after release. layer is critical to improving aircraft performance.
The distinguished Langley aeronautical re- See X-15, Page 14
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