"It was the ultimate flying machine, no
airplane can live up to what the x-15
did", that's what retired test pilot and
astronaut Joe angle said of the first
real space plane and 50 years after it's
record-breaking flight of October 3rd 1967
when US Air Force test pilot
William J Knight achieves a top speed of
mach 6.72, 4519 miles an hour or 7273 km/h
it is still the
fastest manned powered aircraft and if
you thought the SR-71 blackbird was the
fastest jet then you're absolutely
correct because the X-15 wasn't a jet, it
was a rocket-powered single seater
aircraft that looked a bit like an
oversized art and had to be launched from
the underside of a modified B-52 at
45,000 feet because the XLR 99 rocket
engine would burn through all of its
fuel in just two minutes. Not only did
the x-15 set speed records it also went
past the point of were space officially
starts at 100 kilometers 62.1 miles on
two occasions both times piloted by
Joseph A Walker at at 105.9km, 347,000 feet
and 107.8km 353,000 feet.
Although in the 1960s the US Air Force
considered space for start at 80
kilometers or 50 mile,s any crew that
flew over the 50 mile limit were awarded an
astronaut badge, 13 of the X-15 flights
went higher than this and two of the pilots
Neil Armstrong and Joe Engle went on to
become fully fledged astronauts in the
Apollo and space shuttle programs. But
apart from being a record-breaking
aircraft research from the X-15 program
led to things like the first full
pressure suit that would work in space, the
first use of reaction controls the
little gas jets at position spacecraft
in space, the first use of super alloys
in the plane structure that could
withstand the heat of a hypersonic
reentry and the development of the first
large restartable throttleable rocket engine,
the XLR 99. These are a small selection
of the developments and discoveries that
would go on to contribute to later space
programs including the Mercury, Gemini,
Apollo and the Space Shuttle. in the
early 1950s research that started with a
bell X-1 the first supersonic plane
began looking into the problems that
would be encountered by space flight. At
the time it was still unknown as to what
would happen to the stability as well as
other issues of a craft when traveling
at hypersonic speeds that's between Mach
5 and Mach 10 or between about or between about 3800
and 7,700 mph ( 6,200 to 12,400 km/h).
This will be the type
of speed that would be required to get
to the edge of space and the re-entry. In
1952 the National Advisory Committee for
Aeronautics or in NACA, NASA's
predecessor started looking into the
problems. By 1954 they had contacted both the
US Navy and the Air Force to propose
building a research aircraft that would
become the X-15. By 1956 the contract for
the airframe had gone to North American
Aviation and the rocket engine was to be
built by Reaction Motors. After the
contract had been awarded to North
American and before the launch of
Sputnik in october 1957, North American
had considered making an X-15B orbital
space plane that would carry a crew of two
by launching it into low-earth orbit on
top of a pair of SM-64 in Navajo missile
boosters. If this had been done it could
have predated the Space Shuttle by over
20 years. However after Sputnik the X-15B
orbital space plane idea was shelved
and revived several times until it was
finally over taken by the mercury
space program when NACA became NASA in
1958. In 1960 NASA considered using the
b-52 an X-15 as a launch system for the
Blue Scout rocket to carry small
satellites into orbit. The B-52 would be
the first stage with the x-15 being the
second stage carrying the Blue Scout
which will be the third stage to 180,000 feet
before it was launched, the payload into orbit. This idea of
using high-performance aircraft as
launch platforms is now gaining interest
once more as a method of launching for
new generation and nano satellites into
orbit. Three X-15's were built and performed 199
missions over a nine-year period from
1959 to 1968.
Due to delays in the engine
development the first 24 flights used to
smaller XLR 11 engines but in 1960 the
XLR-99 engines were fitted over
tripling the thrust to 57,000 pounds
and these will be used
throughout the remainder of the flight
programs. The X-15 generally performed
two types of research flight paths, level
high speed runs at around a 100,000
feet and altitude runs where it
would try to fly as high as possible.
because of the speeds that the x-15
could reach, the temperature on the
exposed areas like the leading edges of
the wings and the nose could reach 1,200
degrees Fahrenheit or 650 degrees
celsius at mach 6. The fuselage was made
from titanium and covered Inconel X, a
nickel chromium based super alloy used
to make the thrust chamber in the Saturn
F1 engines and could withstand the high
temperatures without weakening. Although
Inconel was capable of withstanding the
heat stress, the stresses that built up
between the hot and cooler areas was
causing concern as NASA was looking at
testing a hypersonic ramjet engine that
in theory could push the X-15 to around
Mach 8 that's around 6,000 miles an hour
or 9,900 km/h.
NASA were also looking for
an ablative coating, that's a layer of
material the burns and turns the gas to
protect the structure underneath and
could easily be applied to reusable
spacecraft to cut the refurbishment
costs and turnaround times, the X-15
would be an ideal test bed for this type
of heat shield. After a minor crash in
1967 the second X-15 was rebuilt and
renamed the X-15A-2 it was extended by
28" about 71 centimeters
for the extra hydrogen tanks of a
proposed ramjet engine and fitted with
detachable auxiliary fuel tanks that
increase the flight time by 60 seconds.
It was also coated in an experimental
ablative coating. It took six weeks to
apply of a spray-on coating and when it
was done the X-15A-2 was now white instead
black. It was also fitted with a
dummy ramjet to test the design but
during the record-breaking flight of
October 3rd 1967, it also revealed
major issues data from the flight
showed that in places like the nose cone
and the wing edges whilst the coating
had worked it also prevented the Inconel
structure underneath to cool as it was
designed and it nearly brought about the
structural failure of the X-15 due to
the uneven heat stresses that had built up,
also when the craft reached mach 6 the
gases released from the ablator
turned the cockpit glass opaque so the
pilot could no longer see out of it.
Luckily one of the two windows have been
fitted with a metal eyelid which was
raised before the landing so he could
use the other unaffected window. Due to
unexpected air flow problems the
temperature was so high that the dummy
ramjet was seriously heat damaged and
three of the four explosive bolts which
held it to the mounting pylon ignited,
it was then ripped from the aircraft as
the final bolt failed and this was
the end of the ramjet powered X-15. It was
said that the X-15A-2 came back looking
like a burnt-out firework and whilst it
was sent to be refurbished the idea of
the ablative coating was dropped due to
the problems of getting an adequate
depth of the ablator over the structure.
Due to the research nature of the X-15
there were accidents and incidents with
some of the test flights but there was
only one fatal crash on the 15th
November 1967, when Air Force test pilot
Major Michael J Adams lost control at
230,000 feet
with the X-15 entering a Mach 5 spin.
There were no recommended techniques to
recover from a supersonic spin as no one
knew what the X-15 would do
in such a situation. Although Adams tried
to recover it, at 65,000 feet whilst
traveling at Mach 3.93 and tumbling
through the air the X-15 broke up
scattering the wreckage over a 50 square
mile area. As the 1960s drew to a close
and after the fatal crash, support within
NASA of the X-15 project waned, many
of the major research goals have been
completed in the years before and now
spacecraft were the new priority. The last
flight took place on the 24th October
1968 piloted by Bill Dana and within a
year the remaining X-15's were retired and
one of the most influential aircraft
research programs was shut down for good.
The two remaining X-15's are now on
display in the National Air and Space
Museum Washington DC and in the National
Museum of United States Air Force at
Wright-Patterson Air Force Base. And as
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