I

MAGINE a world without a compass, a wold of uncertain

poles, depending entirely on the sun and the stars for

guidance in commerce or even in the everyday of human

relations. Imagine such a world, and you are thinking of

things as they were centuries before the birth of Christ ― by

any standards a world of primitive living, of laborious travel

with limitations which for generations now have been

nonexistent.

Vastly helping to bridge the gap between those tightly

circumscribed Old World centuries and the sprawling

civilization of today was the compass ― the common little

magnetized pole-seeking needle which has meant as much to

mankind as any other invention ever created.

The arrow that quivered, settled in man's early compasses,

was pointing to more than just the direction of north or

south.

It was pointing the way to progress and expansion and

men followed, until today an ocean is spanned, a continent is

crossed in a matter of hours, when weeks and months were

consumed before. The mosaic of progress would doubtless

have been there, but its framework might never have taken

the shape of things today had it not been for that little

swinging arrow.

Utilization of the compass in the past quarter century in

aerial navigation has contributed heavily to its earlier value

as exemplified in terrestrial navigation. Today, when men

and machines are locked in combat in uncharted skies, its

value finds an added, accentuated meaning. Warfare itself,

whether in the air or on the ground, is fundamentally a thing

of direction and of maps, which are based upon the north-

pointing compass needle.

This has always probably been true, for it was in

connection with warfare that the compass first made the pages

of history. Records show that the earliest mention of such a

device was in a battle communique issued in the sixty-fourth

year of the reign of a Chinese emperor named Ho-Ang-Ti,

about 2634 BCE.

When Ho-Ang-Ti found his troops frustrated in an attack on

Tchi-Yeou in the plains of Tchou-Lou by what may have been

the earliest smoke screen, he had built a tchi-nan, or compass

chariot, consisting of a figure on a magnetized base mounted

on a cart. Natural magnetic forces caused the hand of the

figure to point south. Having thus oriented himself, Ho-Ang-

Ti presumably went on to triumph. From primitive beginnings

of this sort, the compass changed little through the years until

American ingenuity created the first basically new device of

this kind for general use. The gyro compass, based on the

gyroscope invented by the French physicist, Foucault, was

developed in the middle of the Nineteenth Century.

That original gyro compass, though bulky, slow to assume

initial stability, did provide a meridian- seeking shipboard

compass, unaffected by rolling, turns or magnetic variations.

From it came the aircraft gyro compass, which offers stability

during rough air and turns for a brief period but which

requires initial setting from the magnetic compass and

frequent resetting in flight, especially when the going is rough

or erratic in direction.

It thus has been considered a compass aid, rather than a

primary navigation instrument.

Seven years ago necessity again proved the mother of

invention. W A Reichal, director of engineering at Eclipse-

Pioneer Division of the Bendix Aviation Corporation, started

working on a new compass.

Today that answer has materialized in the Gyro Flux Gate

Compass, a revolutionary type which enables Allied airmen to

fly straight to their target under virtually any conditions,

return just as unerringly to their bases after showering

destruction on enemy objectives.

Charles Marcus, vice president in charge of engineering,

calls the new device "as great an advance over the

conventional magnetic compass as that compass was over the

lodestone." It incorporates a new principle, for the sluggish

and frequently wavering needle is replaced by a fixed coil

system in which actuating currents combine with energy

generated by the earth's magnetic field to turn the compass

indicator.

Technically, the compass is called a remote indicating earth

inductor system, consisting of a gyro stabilized flux gate

transmitter, an amplifier, a master indicator and from one to

six Magnesyn remote indicating repeaters. It is designed

to provide an accurate indication of the magnetic

direction of an aircraft under all possible flight conditions

up to an angle of sixty-five degrees with the horizon.

The flux gate, or magnetic azimuth sensitive element

of the system (magnetic azimuth is direction with relation

to magnetic north) is fully electrical and is maintained at

the horizontal by an electrically driven horizon gyro.

Because of this arrangement, the compass system's

indications are not appreciably affected by the sudden

maneuvers in flight. A stable compass proves its worth to

airmen who dive, turn their planes at 300-400 mph.

The device will not go off its reading when the plane

dives or climbs suddenly, and as Reichel describes it,

"will not lag or overshoot during a turn and will not

oscillate or 'hunt' back and forth in rough weather."

One of the compass problems arising from use of

aircraft equipped with armament, armor plate and laden

with bombs has been solved with the remote indicating

phase of the system. The magnetic azimuth sensitive

element, or transmitter, is placed where interference will

be at a minimum ― that is, at a point remote from

current carrying conductors or causes of local magnetic

deviations such as armament, which would impair the

accuracy of the standard compass.

Through this arrangement, the indications of the

transmitter in its out-of-the-way place are registered on

the master indicator. Further, other indicators are linked

to the compass through the Magnesyn system, which makes

possible remote readings of measurements received from a

master source. Pilot, co-pilot navigator and bombardier have

their own dials, and compass readings are transmitted to

them or to as many as six different points about the aircraft.

In the ordinary compass, deflection must be considered,

and for this purpose a correction card is used. The pilot,

navigator have to refer to this card, correct the deviation. In

combat mistakes are inevitable. In the gyro flux gate system

provision has been made for compensating the compass,

with the result that fully corrected readings are immediately

available, and the possibility of human error in moments of

stress is eliminated.

This compensating mechanism takes care of both

variation, which is the work of natural forces, varying in

different parts of the world, and deviation, which is caused

by local magnetic influences like the armament mentioned

previously.

Variation correction is applied by rotating a knurled knob

on the face of the indicator. This knob offsets the dial either

East or West until the desired variation is indicated on the

lower part of the dial.

Compensation for deviation is applied by adjustment of

screws arranged around the periphery of the dial, which

control the contour of a cam plate. As all compensation

takes place at the main indicator, there is a mechanism for

duplicating the corrections at the other dials in the aircraft.

Position of the master indicator pointer is relayed to the

repeater indicators by a transmitting Magnesyn unit. This

unit is connected through a gear train to the main indicator

mechanism. When the automatic correction takes place on

the master dial, immediate transmission is recorded on the

repeater indicator indicators. To see uncorrected reading,

there is a cut-out at the top of the main dial which records

original indication.

Those seven years of research in the Bendix division's

laboratories have filled the need for fast, undisturbed and

accurate azimuth indication in flight, and through the

repeater arrangement has placed this information at the

fingertips of all key men in the aerial fighting team.

The Gyro Flux Gate Compass is now in production at the

Philadelphia Division of the Bendix Aviation, reputedly the

world's, largest aircraft instrument plant. This plant's

September production of scientific instruments which turn

the blazing guns of victory on the Axis, hit the staggering

total of 175,000 units ― enough to equip more than 100,000

planes with twenty-one instruments each in a year's time.

In order for the instrument to function perfectly, each one

of the 120 parts involved must be matched precisely. Even a

pin-point of perspiration would ruin the amazing accuracy

of the compass. All assembly on the gyro flux gate is done

in air conditioned, dust-free rooms. Once assembled, sealed

under exacting conditions, the compass can operate in any

climate, at any altitude.

One major problem was developing new test equipment

capable of measuring the accuracy, stability of the compass.

Test equipment had to represent flying speeds of 300-400

mph, extreme temperatures, and violent movement.

More aircraft instruments are shipped from this one plant

in six hours than were produced by the entire aviation

industry in one month before 1940, and it will ship more

instruments this year than were turned out in the world in all

the years before 1940.

That the flux. gate compass is, at this moment,

contributing to the rising crescendo of the all-out United

Nations effort to crush our enemies is indicated in the fact

that one or more of them have fallen into Axis hands ―

hence the revelation of its existence.

But possession of such a sample of American progress

will give the big and little Hitlers small comfort. Engineers

agree that there is no possibility that the enemy can catch up

with us, because it will be impossible for him to duplicate

the performance of this compass, much less put it into

volume production during the war.

This article was originally published in the March, 1944,

issue of Air News magazine, vol 6, no 2, pp 39-41.

The original printing was on 9½ by 12¾ paper. The pages

have been reduced here to print on letter-size paper.

Photos credited to Bendix.