Pushing the G-Force Envelope: Seat Belts and Supersonic Sunday Drives
Among its many legacies, World War II also gave us unprecedented G-forces. With the advent of jet aircraft, humans were subject to more deliberate acceleration and deceleration than ever before. Although jets played a limited role in the war, the post-conflict period saw their rapid development as a fighting machine. This posed a particular problem for pilots who had to escape a damaged or malfunctioning airplane traveling at supersonic speeds. Punching out of a supersonic jet exposes pilots to 40 to 50 Gs, or the sudden increase of his body weight by 40 to 50 times.
At the time, G-force was considered fatal above 18 G. But no one was certain. Who would be crazy enough to willingly subject himself to that much force? A guy named John Paul Stapp, that’s who. The U.S. Air Force flight surgeon was the first to strap in for a series of self-inflicted experiments designed to test the limits of human G-force tolerance.
Beginning in 1946, he designed rocket-powered sleds that could reach speeds of 750 mph and slam to the kind of sudden stop similar to ejecting at speed. The first runs didn’t look good: A test dummy slipped out of its harness and was flung over 700 feet. So Stapp designed better restraints.
Then he went for a ride himself. First at 90 mph. Then at 150. Then 200, increasing speed for a total of 29 runs over seven years, during which time he suffered blackouts, headaches, concussions, broken and dislocated bones, and watched six fillings go flying out of his mouth. The sequence of photos (shown below) feature Stapp on a typical ride, with pictures 1 through 3 showing his appearance in the first five seconds of acceleration as his sled shot up to a speed of 421 mph. The last photo shows the start of deceleration, as Stapp’s body was subjected to 22 Gs.
His last ride, in 1954, was also his fastest. He blasted to 632 mph, withstood a windblast equivalent to an ejection at 1,000 mph at 35,000 feet of altitude, was subjected to over 46 Gs, and proved that humans could survive the extreme forces of their newest machines.
Stapp’s heroic work has saved many more lives than those of pilots. In a time of cars with no seat belts, his research showed that people could survive high-force impacts if properly restrained. Stapp himself became a vocal advocate for seat belts and auto safety and was at Lyndon Johnson’s side in 1966 when the then-president signed a law requiring carmakers to install seat belts.