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This article was first published in 2008.
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It’s approaching 60 years ago that a man attached himself to a
rocket-powered sled and started pushing the absolute limits of human endurance,
subjecting himself to forces that to this day remain almost unbelievable.
On June 1, 1951, US Air Force Colonel John Paul Stapp sat in a
sled that was poised on a 610-metre deceleration track. Moments later,
rocket thrust blasted him down the track and into a braking system.
For a brief instant, Stapp endured 48 times the force of
gravity, or g’s, with a rate of onset at roughly 500 g’s per second.
As his own volunteer subject, the colonel became known as the
world's fastest man when on December 10, 1954, he took a
bone-and-tissue-punishing 839-metre sled ride at Holloman Air Force Base in the
US. In less than a tenth of a second, rockets on back of the sled sent the
vehicle at 19 g’s with more than 18,000kg of thrust. Stapp's ride hit 1018 km/h
- nearly supersonic speeds - before coming to a dead stop in 1.4 seconds,
pushing him to 40 g’s. And, for an instant, his 76kg body weighed over 3 tonnes.
The colonel literally saw red for eight minutes as his eyeballs
pushed against upper eyelids, tugging at their attachments. He also suffered
double vision for 20 minutes.
So what sort of fruitcake would take part in tests like this?
And why on earth were they being performed, anyway?
John Paul Stapp
Dr John Paul Stapp was born July 11, 1910 in Bahia, Brazil. His
preliminary education was obtained at the Brownwood High School, Brownwood,
Texas, and San Marcos Academy, San Marcos, Texas. Dr Stapp received his
bachelor's degree in 1931 from Baylor University; his master of art degree from
Baylor in 1932; his doctorate from the University of Texas in 1940; and his
medical degree from the University of Minnesota in 1944. He interned for one
year at St. Mary's Hospital, before entering the US Air Force in 1944.
In 1946 Dr Stapp was transferred to the Aero Medical Laboratory
as project officer and medical consultant in the Bio-Physics Branch. His first
assignment as a project officer included a series of flights, testing various
oxygen systems in unpressurised aircraft at 40,000 feet. But the job assignment
that was the start of his fame came in March 1947 – he was sent to the
deceleration project.
The Deceleration Project
As far back as 1945, service personnel realized the need for a
comprehensive and controlled series of studies leading to fundamental concepts
that could be applied to better safeguard occupants of crashing airplanes. The
initial phase of the program, as set up by the Aero Medical Laboratory of the
Wright Air Development Center, was to develop equipment and instrumentation so
that:
-
airplane crashes could be simulated
-
the strength factors of seats and harnesses could be
assessed
-
human tolerance to the G forces encountered in simulated
airplane crashes could be measured
The crash survival research program was originally slated to be
conducted near the Aero Medical Laboratory, but Muroc (now Edwards Air Force
Base) was chosen because of the existence there of a 610 metretrack,
built originally for V-1 rocket research. That particular program had been
completed and was taken over for the deceleration research program to save
building a new track.
The "human decelerator" consisted basically of a 680kg carriage
mounted on a 610 metre standard gauge railway supported on a heavy concrete bed,
and a 13.7 metre mechanical braking system believed to be one of the most
powerful ever constructed. Four slippers secured the carriage to the rails while
permitting it to slide freely. At the rear of the carriage, 450kg-thrust
rockets provided the propelling force.
That phenomenal braking was accomplished by 45 sets of brakes,
each consisting of two clasping pairs of brake surfaces installed in the bed
between the rails. These brake pairs clasped the 3.3-metre-long braking plates
beneath the carriage chassis to apply the desired deceleration. By varying the
number and pattern of brake sets used and the number of carriage-propelling
rockets, it was possible to effect the controlled decelerations to almost any
g-force.
The first run on the decelerator took place on April 30, 1947,
using just ballast – no person rode the sled that run. That was just as well, as
the sled ran off the tracks... The first human run took place the following
December, and John Paul Stapp was a frequent sled occupant.
By May of the following year, he had rocketed down the track 16
times and withstood an incredible maximum of 35 g’s during deceleration.
What was this sudden stop at the end of the track like? Stapp
reported: "It felt as though my eyes were being pulled out of my head.... I
lifted my eyelids with my fingers, but I couldn't see a thing.... They put me on
a stretcher, and in a minute or two I saw some blue specks.... In about eight
minutes ... I saw one of the surgeons wiggle his fingers at me, and I was able
to count them. Then I knew my retinas had not been detached, and that I wasn't
going to be blind."
Most of these earlier tests were made to compare the standard
Air Force harnesses with a series of modified harnesses, to determine which type
gave the best protection to the pilot.
G’s?
All
objects are attracted towards the centre of the Earth at an acceleration of 9.8
metres per second per second. That is, each second, the 9.8 metres per second
(35.3 km/h) velocity of a falling object increases by 9.8 metres per
second. We feel this effect as gravity, and so give an acceleration of 9.8
metres per second per second the term of ‘one gravity’, or ‘1 g’.
Probably
the strongest accelerations that we generally feel are in cars – a typical car
under emergency braking develops a deceleration of about 1 g. Even a powerful
car, in first gear and with the accelerator flat to the floor, seldom develops
an acceleration of over about 0.7 g. In lateral (cornering) acceleration, again
even a sporting car is limited to about 1 g.
Some
amusement park rides peak at about 4.5 g, while high-g centrifuges used to train
fighter pilots have maximum ratings of 15 g, with a maximum onset of 15 g per
second.
So
as you can see, the accelerations that Dr Stapp endured were absolutely
incredible...
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Faster and Faster
In 1953 the research moved to the Holloman Air Force Base,
where it was specifically oriented toward the study of high-speed escape from
aircraft.
The problem of a high-speed escape from a fast travelling jet
aircraft was major. A pilot bailing out at transonic orsupersonic speed
had to face first the ejection force required to get him out of his plane, then
the sudden onslaught of windblast and wind-drag deceleration, likely to be
followed by dangerous tumbling and spinning. Any one of these forces taken
separately was a potential cause of injury or death. At the time of the
research, the escape systems available were either inadequate or of unproven
worth for aircraft having performance capabilities above mach one in speed and
45,000 feet in altitude.
In his previous experiments on the deceleration track at
Edwards Air Force Base, California, Colonel Stapp had already experienced forces
up to roughly 46 g's at 500 g's per second rate of increase. Both this
experiment and one in which a co-worker withstood over 38 g's at 1370 g's per
second produced definite signs of shock but no permanent ill effects. However,
the duration of decelerative forces was always very short. Durations ranged from
.15 to .42 second, which attained a top speed of ‘only’ 69 metres per second
(250 km/h); and there were no experiments on deceleration combined with the
windblast and tumbling that could be expected to batter an ejecting pilot.
The Holloman high-speed track - originally built in 1949 as a
rail launcher for the Snark missile - was especially well suited to the required
testing. It was then 1083 metreslong and was fully instrumented. It also
had a water braking system, as compared with the mechanical friction brakes used
on the 610 metre Edwards deceleration track. The water brakes permitted both
high deceleration forces and a wide range of duration and rate of increase in
g-forces.
On the 19thof March, 1954, Colonel Stapp was
strapped in for his first Holloman sled ride. Apart from testing the feasibility
of the equipment for human experiments, the objective of Colonel Stapp's first
ride was to "evaluate human reaction to exposure to about 15 g of linear
deceleration for about 0.6 seconds duration, approximately double the duration
possible for the same magnitude of force on the crash decelerator previously
used at Edwards...."
The run was essentially successful, reaching peak velocity of
188 metres per second (677 km/h) and up to twenty-two g's deceleration, with
only momentary ill-effects.
Other tests explored the affect of sudden windblast, with the
protective doors positioned in front of Stapp snapped opened at full speed.
During this testing, Colonel Stapp was exposed to an estimated maximum of 5.4
pounds per square inch of wind pressure, with maximum velocity of 224 metres per
second (just over 800 km/h). Sled rides where the occupant of the seat was
tumbled at the same time as being exposed to decelerations and high-speed
windblasts were also carried out, sometimes with chimpanzees replacing Stapp and
other workers.
The Fastest Man on Earth
But the most memorable of all Colonel Stapp's rocket sled rides
was the one of 10 December 1954. This test was designed to explore both
deceleration and windblast, but there was no attempt to simulate abrupt onset of
wind pressure. Instead of opening doors, in this test no windshield at all was
used. Colonel Stapp merely wore a helmet completely covering his head, and saw
to it that his arms and legs were well secured against flailing, which was one
effect of windblast already known to induce injuries in actual escape from
aircraft.
The run itself reached a maximum speed of 288 metres per
second, or over 1000 km/h. This was fast enough for the sled to overtake and
pass a T-33 aircraft that was flying overhead. Windblast was as high as 7.7
pounds per square inch, or better than 1,100 pounds per square foot, and water
brakes brought the sled to a stop in just 1.4 seconds from maximum velocity.
Rate of onset of deceleration was 600 g's per second, reaching a plateau of
twenty-five g's and over for more than a second, with peaks of thirty-five and
forty g's. The jolt Colonel Stapp received has been compared with that "an auto
driver would experience were he to crash into a solid brick wall at 120 miles
per hour (193 km/h)”.
As was to be expected, this time Colonel Stapp showed much more
obvious negative effects of his ride. There were some strap bruises and the
usual blood blisters from grains of sand, but in addition he suffered extremely
painful effects on the eyes. In Colonel Stapp's own words, on entry into the
water brakes his vision became a "shimmering salmon" followed by "a sensation in
the eyes ... somewhat like the extraction of a molar without an
anaesthetic."
Yet not even the eyes suffered any long-range or irreversible
damage - Colonel Stapp's experience left him with two black eyes but vision
returned in about eight and a half minutes.
To use his own words once again, “There was no fuzziness of
vision or sensations of retinal spasms as had been experienced in 1951 following
a run
[at Edwards]
in which a retinal haemorrhage occurred. Aside from
congestion of the nasal passages and blocking of paranasal sinuses, hoarseness
and occasional coughing from congestion of the larynx, and the usual burning
sensation from strap abrasions, there was only a feeling of relief and elation
in completing the run and in knowing that vision was unimpaired.”
That 10 December experiment was to give the Air Force doctor
the popular renown as "the fastest man on earth". His portrait appeared on the
cover of Time, and it was news throughout the nation when the "fastest
man" was cited by the Alamogordo, New Mexico, police for speeding at forty miles
an hour in a twenty-five-mile zone. However, the Justice of the Peace before
whom he appeared managed to divert part of the publicity to himself by
dismissing the charge against Stapp, issuing a new citation against a fictitious
"Capt Ray Darr," and paying the fine from his own pocket.
And He Survived...
Though black eyes, retinal haemorrhages, cracked ribs and
broken bones were frequently Stapp's reward for his labours, he came away from
these ordeals with the knowledge that countless lives would be saved by his
efforts. Those lives saved included more than just aircrews. His research for
the National Highway Traffic Safety Administration led to the standard use of
seatbelts and airbags in cars and trucks.
"Today, everyone who flies in an airplane or rides in an
automobile is safer because of his tremendous contributions," said Dr Jim Young,
Air Force Flight Test Center chief historian. "Although he never piloted an
airplane, Colonel Stapp was a true aerospace hero."
Some of Stapp's honors include: National Aviation Hall of Fame;
Jet Pioneers of America; International Space Hall of Fame; Safety Health Hall of
Fame; Air Force Cheney Award for Valor; and the Lovelace Award from NASA for
aerospace medical research.
Dr Stapp died peacefully at his home in Alamagordo, New Mexico
in 1999. He was 89.
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