Recently in Philadelphia, the War

A

NEW scientific marvel has come

out of the laboratories to back up

our fighting flyers. It's a device so small

that you could easily put it into your vest

pocket. If you had the blueprints and the

secret materials, you could probably

make one in a single evening in your

basement workshop. Yet this little gadget

has opened up a great new frontier to our

flyers. It guides them safely through

what was, until yesterday, a vast no-

man's-land of navigation.

More than that ― it helps our

bombers find distant objectives, brings

home thousands who might otherwise be

lost.

This tiny device of wire, plastic and

metal bears the curious name of the "flux

gate," and is so called because it may be

considered to allow the flux lines of the

earth's magnetism to flow through it. The

flux gate is the secret of the amazing

new gyro flux gate compass, one of the

most surprising and permanently useful

inventions to come out of this war.

Because the Germans and the Japs could

not duplicate the performance of this

compass, much less get it into mass

production during the war, its story can

be told without fear of aiding the enemy.

Three years ago the Government

asked the Bendix Aviation Corporation

to try to develop a compass that would

not go haywire when a plane flew closer

than 1,200 miles to either of the earth's

magnetic poles. Anywhere within that

distance the best magnetic compasses are

unreliable. If you look at a globe you can

easily see just what that means to flight

in North America. The North Magnetic

Pole (not to be confused with the

geographic North Pole) is located on

Boothia Peninsula, northwest of Hudson

Bay. With that as a center, draw a circle

to the scale of a 1,200 miles radius. Your

line encircles an area of nearly 5,000,000

square miles where many a plane and its

crew has disappeared, never to be found.

It takes in most of Canada, more than

half of Greenland, a corner of Alaska, all

of the Arctic Archipelago, and lots of

water.

The Government wanted that no-

man's-land opened up. To do so would

clip thousands of miles from the distance

between certain points on this continent

and points in North Asia, It would speed

up by millions of hour's in total our

shipment of men and material by air

around the globe.

The Government had asked only for a

compass that would open up the polar

regions to round-the-world navigation.

They got a great deal more than that. The

new compass will give the plane's true

heading even while the plane climbs,

dives or banks up to a dizzy angle.

A magnetic compass has a float card

that goes into a wild dance when the

plane maneuvers. A pilot cannot get his

direction until he levels off on a straight

course. Even then the card swings

uncertainly left and right, "hunting," as

the navigators call it. But the new

compass neither shoots ahead, lags

behind nor hunts. It points the plane's

direction through a needle on a dial as

easy to read as the face on an ordinary

alarm clock.

Yet that is not the whole story of the

new compass. It has not just one dial but

a number ― and in the great planes of

tomorrow it may have even more! The

master indicator is placed on the

navigator's plotting table. Repeater dials

face the pilot, co-pilot, and bombardier.

At all times these dials show exactly the

same reading. There is no longer a

chance that the pilot, after he gets his

course from the navigator, may go off

course because he is using a different

compass. And the bombardier, as he

plots his bombing run, can give the pilot

his course to a hair line!

The great advantage of these repeating

dials is that the flux gate itself may be

placed somewhere in the plane away

from the disturbing magnetic fields in

the pilot's cockpit. The ferrous metals

and the numerous electrical devices that

must be in the cockpit play hob with

magnetic compasses. The actual working

part of this first new magnetic compass

since Columbus' time is safely hidden

away from these magnetic fields.

With the gyro flux gate compass the

navigator no longer uses a correction

card. He corrects his compass

automatically by turning a couple of

knobs on the master dial.

While the flux gate is the heart of the

new compass it is really one of the

smallest parts of the whole. The compass

is actually a partnership of a number of

complex units, each of which has its own

special job. The flux gate itself is

mounted under a gyroscope. Turning at

10,500 revolutions a minute, this tiny

wheel holds the flux gate always level

with the earth. If the plane banks more

than a certain angle the compass must be

"stopped" or else it will tip, whereupon it

takes the small gyro about 10 minutes to

bring it upright again.

The flux gate is not only an intricate

magnet but a small transformer which

picks up the minute impulses of the

earth's magnetic field and changes them

into a weak alternating electric current.

This current is carried to a vacuum tube

amplifier which blows it up into a

current of sufficient strength to turn a

small motor. It is the shaft of this motor

that moves the needle on the navigator's

master dial. Actually, it is the relative

strength or weakness of the current

flowing from the flux gate that

determines the needle's position.

That is a simple explanation. To

understand exactly what happens in a

flux gate compass you would have to be

several kinds of an engineer. And there is

much about the workings of the flux gate

itself that is still secret.

The little plastic triangle that houses

the "gate" may not look like much but

engineers are sure that the enemy will

not be able to obtain the materials for the

core or reproduce the gyro flux gate for

many years to come.

Seven years of intensive work went

into the gyro flux gate compass. It was

finally perfected and installed on our

bombers shortly after we got into the

war.

The beginning was even earlier.

Scientists of Bendix Aviation

Corporation had been working on the

problem for some time, since the gyro

flux gate is a kind of great-great-great

grandchild to the "earth induction"

compass which Pioneer (a division of

Bendix) built for Lindberg's transatlantic

flight in 1927. Engineer Alfred Stuart

developed the principle of the flux gate.

Paul Noxson incorporated it into a

compass that would work reliably under

any conceivable condition. John

Emerson figured out a method of

manufacturing the compass in quantities

large enough to equip a giant air force.

All were working under the guidance of

W A Reichel, Eclipse-Pioneer's director

of engineering.

If the flux gate is the heart of the new

compass, then the master indicator on

the navigator's desk is its brain. The

compass even has its own nervous

system. for its various parts, at different

locations in the plane, must work

perfectly together. The transmitter unit

for example ― containing the gyro and

flux gate ― is mounted far out in the

plane's wing or tail to keep it away from

magnetic disturbances set up by

ammunition. armament or other metal.

Communication between the various

units of the compass is furnished by two

other Bendix inventions, the Autosyn

and the Magnesyn.

Recently in Philadelphia, the War

Department gave permission for half a

hundred aviation writers to view this

wonder of technical progress, What they

marveled at was not so much a

remarkable new compass but the

amazing engineering skill that had made

it possible to produce these complex

instruments― more intricately made

than the finest watches ― at the rate of

hundreds a month to match America's

huge production of fighting planes. They

saw a great military victory being won

right on the floor of an American factory.

For here American engineers had

accomplished what the Nazis ― with all

their vaunted science ― had utterly

failed to do. And they knew it was an

omen of a bigger victory to come.

This article was originally published in

the January, 1944, issue of Flying

magazine, vol 34, no 1, pp 69-70.

Photos credited to Bendix Aviation

Corporation.