Rocket sled

Extreme Motion Tests Brought Aerospace Safety Innovation

Colonel John Stapp risked life and limb to make the world safer.

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John’s 632-mph ride came to a stop in just 1.4 seconds. When it was over, he had suffered a few broken ribs, a pair of busted wrists, and windburn on his face. The blood vessels in his eyes burst, the retinas detached from the force of the stop, and he went blind for 45 minutes, wondering if his sight would ever return. Still, he was alive, and he walked away from the test with a smile, knowing that humans could survive an impact of 40 Gs or more without dying.  

No, that’s not an excerpt from a Tom Clancy novel, but rather the real-life escapades of Colonel John Stapp, who pioneered tests on the effects of sudden deceleration on the human body for military pilots at the beginning of the jet age in 1945. His tests were derived from a series of questions pertaining to whether or not pilots could survive ejecting out of a damaged aircraft traveling at near supersonic speeds or live through a forceful impact (aka, crash).

U.S. Air Force

In this photo, Colonel John Stapp is shown strapped to his Sonic Wind Rocket Sled 1, barreling down the Holloman High-Speed Test Track at 632 mph and decelerating to a stop in just 1.4 seconds. (Courtesy U.S. Air Force)

It’s safe to say Stapp’s entire career was filled with death-defying tests right from the get-go, but his results brought about innovation in both aircraft and vehicle safety. In 1944 he enlisted in the Army Air Corps as a physician, and shortly afterward was assigned to Aero Medical Laboratory, where he underwent a series of flights to test different oxygen systems to combat altitude and decompression sickness.

In pure Stapp fashion, he did this by flying up to 40,000 ft in a stripped-down, unpressurized B-17 with no protection and no cockpit windows─just a simple bottle of pure oxygen he used to keep from getting the bends. His results led to the creation of high-altitude reconnaissance aircraft oxygen platforms as well as HALO (High Altitude Low Opening) parachute insertion tactics.

After figuring out ways to keeps pilots alive at high altitudes, he then turned his attention toward developing ways to protect them in the event of fatal accidents. In scientific terms, Stapp was studying the effects of rapid deceleration on the human body, then applying that data to design systems that could keep pilots and aircrews alive in the event of a crash. In unscientific terms, he wanted to see how many Gs (g-force) a person could handle before their skeleton popped out of their skin.

Public Domain/Wikipedia

Shown is Stapp’s first-generation rocket sled at Edwards Air Force Base.

Stapp worked on the Deceleration Project in 1947 to develop equipment and instrumentation that could be applied to simulations for pilot training. They would also use the data to develop better harnesses and seats to help mitigate physical damage to the human body. At the time, scientists concluded that the human body could only withstand 18 Gs worth of force, but Stapp wasn’t sure their findings were correct. There was only one way to find out: use a rocket sled.

The first attempt at gathering data on g-force using a rocket sled ended in failure, in that the sled flew off the track and exploded. Instrumentation at the time was still being developed, and crash-test dummies were archaic at best, so John took it upon himself to become Lord of the Gs. He designed his own rocket sled and replaced the dummy with himself.

In 1953, Stapp partnered with the Northrop Corporation to develop the Sonic Wind Rocket Sled 1, which had a primitive modular system on the back that allowed the crew to add or remove a set number of rocket engines. The braking system on the Holloman test track consisted of using a scoop mounted underneath the sled to dig into a series of water dams at the end of the track. Six rockets were used on his first run, which propelled him at a speed of 421 mph using 27,000 lb. of thrust. When it stopped, his body underwent 22 Gs of force, significantly more than what scientists thought possible.

National Air and Space Museum

Stapp’s Sonic Wind Rocket Sled 1 was outfitted with nine solid-fuel rockets.

The culmination of the Deceleration Project saw Stapp’s sled outfitted with nine solid-fuel rockets, which powered the Sonic Wind to 632 mph in just five seconds and ended in much less time. The g-forces he underwent were astounding, causing him to weigh 6,800 lb at the moment of his deceleration. It was his last ride, and it netted him a world record of being the fastest person on land, which still stands today.

The data collected from Stapp’s tests allowed for the development of new pilot harnesses, sturdier aircraft seats, modern crash test dummies, development of the ejection seat, and high-altitude pilot suits. He even worked with the NTSB to conduct safety research and helped make it mandatory for auto manufacturers to equip their vehicles with seatbelts.

Stapp’s innovations have helped save millions of lives around the world, and the Holloman High-Speed Test Track is still being used today with experiments (aerodynamic and otherwise) that may go on to save lives in the future.

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