Fly's Instruments

Many important flight instruments are built around spinning gyroscopes, whose "rigidity in space" makes them try to keep pointing in a fixed direction. An instrument hitched to one or more of these gyros can tell how much the airplane is turning or canting, almost as if it were hitched to space itself. Similar gyros steer torpedoes and airborne guided missiles.

For most turn-sensing purposes, gyros work well enough, but they have serious faults. Neither the bearings on which they spin nor the gimbals on which they are suspended can be made entirely frictionless, and friction hurts their accuracy. So designers have longed for a turn-sensing instrument with no friction-plagued parts.

Last week the Navy permitted the Sperry Gyroscope Co. to tell about its "vibratory gyroscope." which uses vibrating parts that resist turning in somewhat the same way a gyroscope does.

The principle is not exactly new. It has been used by houseflies and other flying insects for perhaps 200 million years. Behind each wing a fly has small, ball-tipped rods that vibrate rapidly. If these "halteres" are cut off, the fly is like an airplane lost in a cloud with all its instruments out of order. It goes into a spin and crashes.

More than six years ago, Sperry engineers started to study fly flight (TIME, June 10, 1946). Then they set to copying flies' instrumentation. They fitted a tuning fork with electrical "drive coils" to keep it vibrating. When such a fork is turned on the axis running up through its stem, it alternately resists and helps the turning movement. This struggling of the fork can be transformed electronically into a current that shows how much the fork is being turned. Presumably flies have delicate nerves that make similar reports.

Sperry's artificial halteres are not yet perfected for use in the air, but they show exciting promise. Since they have no delicate bearings or gimbals, they can stand rough treatment, such as the violent acceleration forces of a guided missile darting into action. Even the rough prototyes can measure turning rates faster than 100 r.p.m. or as slow as the earth's rotation (half the speed of a clock's hour hand).

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