Gs & Men

Demons always threatening fast-moving humans are the G-forces (one G equals normal gravity) that strike during changes of direction or speed. They are felt when an airplane makes a turn or pulls out of a dive, when a rocket takes off, when any vehicle is braked or hits an obstacle. As man moves faster and faster, the Gs become more and more dangerous.

The effects of moderate Gs developed by a turning airplane have been studied in whirling "human centrifuges," but the brief, intense forces of sudden starting or stopping cannot be simulated in this way. The Air Force uses, instead, a rocket-propelled sled that slides along steel rails at Edwards Air Force Base. A human guinea pig rides on the sled. When it is shot down the rails, or stopped by powerful brakes, almost any number of Gs can be brought to bear on the man's body. Last week Colonel Donald D. Flickinger of the Air Research and Development Command told some of the results of playing with this toy. Main conclusion: In the battle of the Gs, the human body is pretty tough.

Into a Brick Wall. In a stunting airplane, where the G-forces last for several seconds, a sitting pilot can take about ten Gs, when he is dressed in a special suit to keep the blood from being drained from his brain. A man on the Air Force sled can take more for shorter periods. How much he can take depends on his position and how his body is supported.

When the passenger (not dressed in special clothing) is lying on the sled--head foremost--he can take only seven Gs for Moth of a second without being damaged. If he is lying feet foremost, he can stand as much as 32 Gs because the feet can take more impact than the head. When his body is at right angles to the motion of the sled, he can survive even more.

Champion G-survivor, so far, is Lieut. Colonel John P. Stapp, a husky flight surgeon whose sled rocketed at 175 m.p.h. before being braked. He was strapped facing backward in a specially built seat, which is what saved him. He took 46.8 Gs for .008 seconds (equivalent to running an automobile into a solid brick wall at 120 m.p.h.). His body at the moment of impact weighed close to four tons, and his blood was more than three times as heavy as mercury.

Practical Results. Colonel Flickinger believes that human tolerance might be increased to 90 or 100 Gs if the passenger took the impact lying transversely to the sled's motion on a properly contoured support. But he does not believe that this experiment will be tried soon. "It is not possible," he says, "to build that much tolerance into the hardware."

These unpleasant experiments have already brought practical results. Proof that a person facing backward is more likely to survive an airplane crash than one facing forward supported only by a body-cutting belt has convinced the Military Air Transport Service that it should turn its seats around. Some British Commonwealth airliners have already made the change. They have had several crashes, from which all the backward-facing passengers have walked away unhurt.

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