John Stapp - Works On Effects of Deceleration

Works On Effects of Deceleration

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 aircraft occupants during a crash. 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 whereby aircraft crashes might be simulated, and to study the strength factors of seats and harnesses, and human tolerance to the deceleration encountered in simulated aircraft crashes.

When he began his research in 1947, the aerospace conventional wisdom was that a man would suffer fatally around 18 g. Stapp shattered this barrier in the process of his progressive work, experiencing more "peak" g-forces voluntarily than any other human. Stapp suffered repeated and various injuries including broken limbs, ribs, detached retina, and miscellaneous traumas which eventually resulted in lifelong lingering vision problems caused by permanently burst blood vessels in his eyes. In one of his final rocket-propelled rides, Stapp was subjected to 46.2 times the force of gravity. The aeronautical design changes this fundamental research wrought are widespread and hard to quantify, but fundamentally important.

The crash survival research program was originally slated to be conducted near the Aero Medical Laboratory, but Muroc Army Air Field (now Edwards AFB) was chosen because of the presence of a 2,000-foot (610-m) track, built originally for V-1 rocket research. That particular program had been completed and was taken over by the deceleration research program.

Designed to Aero Medical Laboratory specifications and fabricated by Northrop Aircraft of Hawthorne, California, equipment was maintained and operated on service contract by the Northrop Company.

The "human decelerator" (dubbed the "Gee Whiz" by the scientists) consisted of a 1,500-pound (680-kg) carriage mounted on a 2,000-foot (610-m) standard gauge railroad track supported on a heavy concrete bed, and a 45-foot (14-m) hydraulic 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, 1,000-lbf (4-kN) rockets provided the propelling force. Braking was accomplished by partitioned bins of water and scoops that picked up the water and threw it forward. By varying the number and pattern of brake buckets used and the number of carriage-propelling rockets, it was possible to control the deceleration.

The first run on the rocket sled took place on 30 April 1947 with ballast. The sled ran off the tracks. The first human run took place the following December. Instrumentation on all of the early runs was in the developmental stage, and it was not until August 1948 that it was adequate to begin recording. By August 1948, 16 human runs had been made, all in the backward- facing position. Forward-facing runs were started in August 1949. Most of the earlier tests were run to compare the standard Air Force harnesses with a series of modified harnesses, in order to determine which type gave the best protection to the pilot.

By June 8, 1951, a total of 74 human runs had been made on the decelerator, 19 with the subjects in the backward position, and 55 in the forward position. Stapp, one of the most frequent volunteers on the runs, sustained a fracture of his right wrist during the runs on two separate occasions.

Stapp's research on the decelerator had profound implications for both civilian and military aviation. For instance, the backward-facing seat concept, which was known previously, was given great impetus by the officer's crash research program, which proved beyond a doubt that this position was the safest for aircraft passengers and required little harness support, and that a human can withstand much greater deceleration than in the forward position. As a result, many Military Air Transport Service (MATS) aircraft in USAF were equipped or retrofitted with this type of seat. Commercial airlines were made aware of these findings, but still use mostly forward-facing seats. The British Royal Air Force also installed it on many of their military transport aircraft.

As a result of Stapp's findings, the acceleration requirement for fighter seats was increased considerably up to 32 g (310 m/s²) since his work showed that a pilot could walk away from crashes when properly protected by harnesses if the seat does not break loose.

The "side saddle" or sideways-facing harness was also developed by Stapp. The new triangular-shaped harness gave vastly increased protection to fully equipped paratroopers sitting side by side in Air Force aircraft. It was made of nylon mesh webbing, fit snugly over the shoulder facing the forward part of the aircraft, and protected the wearer from the force of crash impacts, takeoffs and landing bumps. It withstood a crash force of approximately 8,000 pounds of force (36 kN) at 32 g (310 m/s²) and was developed to replace the old-fashioned lap belts which gave inadequate protection to their wearers.

By riding the decelerator sled himself, Stapp demonstrated that a human can withstand at least 45 g (440 m/s²) in the forward position, with adequate harness. This is the highest known acceleration voluntarily encountered by a human. Stapp believed that the tolerance of humans to acceleration had not yet been reached in tests, and is much greater than ordinarily thought possible.

Also developed by Stapp as an added safety measure was an improved version of the currently used shoulder strap and lap belt. The new high-strength harness withstood 45.4 g (445 m/s²), compared to the 17 g (167 m/s²), which was the limit that could be tolerated with the old combination. Basically, the new pilot harness added an inverted "V" strap crossing the pilot's thighs added to the standard lap belt and shoulder straps. The leg and shoulder straps and the lap belt all fastened together at one point, and pressure was distributed evenly over the stronger body surfaces, hips, thighs and shoulders, rather than on the solar plexus, as was the case with the old harness.