Science: Truer Compass

The compass—oldest known navigating instrument—has been revolutionized. Last week Bendix Aviation Corp. announced a new automatic compass that makes the old magnetic needle* look as obsolete as a warrior’s spear. The new “gyro flux gate” compass, designed especially for aircraft, is already at work guiding United Nations flyers unerringly to their targets.

For navigators, the traditional magnetic compass has the defect of being too crude. Despite modern refinements, it is still essentially a magnetized needle kept pointed north by the earth’s magnetic field. It must be corrected constantly by tricky calculations, because of 1) interfering magnetic fields from surrounding metallic objects, and 2) geographical variations in the earth’s magnetic field, some of which result from the fact that the magnetic poles are not the earth’s true poles.

The newer gyro compass (about thirty years old), which uses a gyroscope that tends to seek the North Pole, is an improvement for sea navigation. But its bulk and the quick, violent turns of airplane flight make the gyro compass impractical in the air. Plane movements also raise hob with a magnetic compass.

A Different Matter. The gyro flux gate compass, on which Bendix engineers worked seven years, is based on an entirely different principle. Exactly how it works is still a military secret (at least one of the instruments has fallen into Axis hands, but its inventors believe it will take Axis scientists years to figure it out). Its basic parts are a triangular set of coils and a gyroscope. The function of the gyroscope (which spins at 10,000 revolutions a minute) is simply to keep the instrument level during a plane’s turns and lunges. The coils, which replace the needle in the old compass, pick up currents from the earth’s magnetic field. This energy is converted into tiny electrical impulses, then amplified to turn a hand on a dial, showing the navigator the plane’s direction. Inside this dial are mechanisms that automatically correct errors resulting from magnetic interference and variations. There is less interference from ship metal or electrical apparatus than in the magnetic compass, because the pickup coils need not be in the navigator’s cabin, can be installed where they will not be affected by the ship’s bomb load or armor.

The result, according to a Bendix spokesman: “The new compass will not go off its reading when the plane dives or climbs rapidly ; it will not lag or overshoot during a turn, and it will not oscillate or hunt back and forth in rough weather.” It is also usable in regions where a magnetic compass breaks down completely—near the North & South Poles. Because of the weak magnetic currents there, a magnetic compass is useless within 1,200 miles of either Pole; the new compass, much more sensitive, works as close as 300 miles.

*According to Chinese claims the first use of a magnetic compass was by Chinese Emperor Hwang-ti in a battle in 2364 B.C. To guide his warriors through an enemy fog screen, he mounted on a cart a magnetized figure which steadily pointed south. But the real origin of the compass and its first use is uncertain.