Watch Your Head!

What kills the passengers when an airplane crashes? to the nonscientific layman, that question might seem on a par with "What causes death to the fly when a flyswatter mashes it?'' But the Cornell Aeronautical Laboratory was interested in the scientific, not the commonsensible answer. If there is no fire, the Cornell investigators decided, the leading cause of death is cracked skulls. So the laboratory, backed by the Navy, set out to learn how a human skull cracks, and how to prevent it. Last week the experimenters described some of their findings.

Since they had to do without human skulls, the researchers, led by Edward R. Dye, started out with hens' eggs--which, Dye explained, are roughly equivalent, for experimental purposes. Both are about the same shape (ovoid), and both consist of a rigid, fragile shell containing gelatinous material. Eggs will break when dropped four inches on a hard surface, skulls about four feet. But skulls and eggs crack about the same way.

Dye and his associates made a gadget like a child's swing, put an egg in it, and swung it against a steel plate. When the egg was free to move (like a passenger with no safety belt) a very slight shock broke the shell. When held tightly, the egg survived harder shocks. When cushioned with rubber in front, it lasted even better. The hardiest eggs were snuggled against a cushioned block that slipped a little when the swing hit the steel, allowing the egg to come to a slow stop. It took a powerful shock to crack such a coddled egg.

Dye's group then developed a more realistic skull substitute. They made life-sized, head-shaped shells of brittle plastic and filled them with gelatin. They finally got an artificial human skull that reacted to shock almost exactly like a real one. Then they catapulted the models against solid objects resembling airplane parts that passengers' heads might hit in a crash.

Out of these skull-cracking labors came a theory to guide designers of aircraft. An airplane that is easiest on skulls, Cornell decided, should hold its passengers as tightly as possible. The things that skulls might strike against should not be small, hard objects, but should be made of thin metal formed around broad shapes of yielding plastic foam.

Seats should be made so that they slide a little when the plane crashes. Also, the plane's nose should be made of material that yields gradually. The Cornell men believe that if all these principles were followed, a pilot could fly a small plane into the ground at 150 m.p.h.--and walk away with a skull somewhat addled but still uncracked.

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