On Sunday, Felix Baumgartner floated up over 128,000 and jumped. And lived! The RedBull Stratos jump was designed to push "human limits that have existed for 50 years." But there’s a problem with that tagline: the mention of human limits.
The human limits that prevent us from skydiving from the stratosphere without oxygen and pressure suits have existed far longer than 50 years, which mean Baumgartner's survival speaks more to the technology used on the jump (though I'll readily admit it would take some training to withstands the stresses he sustained during that high altitude spin). So I thought this would be a good opportunity to discuss a program designed to test human limits that has fascinated me for a while: the Navy's test of human tolerances to wind blasts.
In the late 1940s, leather-capped test pilots with oxygen masks were flying increasingly fast, often going supersonic to push their aircraft to their limits. The flip side of faster flight was that if pilots lost control at high speeds, they would have to eject at high speeds as well. No one really knew what kind of stresses the human body could sustain during a high speed ejection, particularly in exposed area like the hands and face. So, in 1948, the Navy decided to look into it. With the help of two volunteers and the National Advisory Committee for Aeronautics (NACA – often seen as the precursor to NASA), the Navy set out to see what the human limit was for a wind blast directly to the face.
German scientist had done some test years before to measure the effects of wind blasts on the human head, but their results weren't "pure." The Germans had exposed test subjects to strong winds with a protective headboard, greatly minimizing the effects. For its investigation, the NACA devised a simple method that would take any mitigating effects of the wind blast out of the equation: put a man in a wind tunnel without any facial protection and see what happens.
The NACA Langley's laboratory ran the test program in its eight foot, high speed wind tunnel. The wind speed range laid out at the start was from Mach 0.04 to Mach 0.65. The two test subjects were volunteers from the Navy, both enlisted men. For the test, they were outfitted in regular flight clothes: a summer flight jacket, a cloth helmet with a chin strap, and Navy-issued dungarees. Their faces were entirely exposed; pilots didn't wear full helmets in those days.
They sat in a Navy furnished seat, strapped in with regulation shoulder harnesses and seat belt. The seat rested on a carriage; a beam running through it allowed men outside the tunnel to lift and lower the seat.
The Langley eight-foot tunnel readying for action.
Behind the subject's head was a round, flat headrest measuring 5.5 inches in diameter, which was used up to a windspeed of Mach 0.25, at which point it was replaced by a curved, more aerodynamic version. In both cases, a strain gauge attached to the plate recorded the force of the air blast and the length of time the subject was exposed to the high winds.
Langley technicians decided they would get the wind tunnel up to speed, then raise the seat into the wind stream. This was an effort to protect the subjects from prolonged exposure to high winds, and it also mimicked the sudden blast associated with a high speed ejection.
The run of tests followed a standard procedure. Once technicians got the wind tunnel up to speed, the men outside the tunnel lifted the seat to put the subject right into the wind stream face first. On each test, subjects spent just two seconds in the full blast of the tunnel before the wind speeds started to drop.
The results published in November of 1948 showed the subjects' reactions clearly. Data from the force gauges indicated they tended to pull their heads away from the blast or else pushed forward against the stream. At wind speeds above Mach 0.4 – about 305 miles per hour – the wind overpowered their neck muscles and their heads were just blown straight back.
Tests never reached the planned windspeed of Mach 0.65. Technicians worried that anything above Mach 0.58 or 441 miles per hour, the upper limit of the tests, would cause the subjects serious injury. Data backed up this worry. The maximum force indicated on the strain gauges was about 95 pounds. That correlates to 35 pounds at 30,000 feet – a survivable ejection – but on the ground it was a lot of strain on the subjects.
Not long after the Navy ran these tests, pilots started flying with full face helmets and pressure suits as plane flew higher and faster. Escape capsules were used for safe ejection in some aircraft, while other used restraints to keep pilots firmly against their cockpit seats to minimize the forced on their necks and backs. Few pilots, after these two test subjects, were ever subjected to strong wind blasts to the face. As for Baumgartner, he can thank those two Navy test subjects for sparking the development of high-speed flight gear.