Download the pioneer earth indicator compass

AUGUST 4, 1927
THE PIONEER EARTH INDICATOR COMPASS
Col. Lindbergh's successful flight from New compass. It is similar to any direct-current electric dyn
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an armature with
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Pioneer Earth Indicator Compass, to which Col. Lindbergh haying
but with no artificial field—the earth serving as field.
attributed the successful navigation of the " Spirit of St. The armature, which is suspended in gimbal rings, is driven
Louis " across the Atlantic.
by an anemometer or windmill, while the generator brushes
We have already briefly outlined the principles under- are mounted so that they may be rotated around the comlying this instrument, but we feel certain that further parti- mutator. The stability of the armature is maintained by
culars of its characteristics, construction and operation will the action of its own gyroscopic force and the use of a suitbe of interest to our readers. Mr. Maurice M. Titterington, able damping device.
Chief Engineer of the Pioneer Instrument Co., of Brooklyn,
The indicator is a sensitive zero centre galvanometer
N.Y., gives a detailed description of this instrument in our electrically
to the brushes of the generator. The
American contemporary Aviation, from which article we are controller isconnected
a
purely
mechanical
device for setting the angle
indebted for the following notes :—
of the generator brushes—as will be explained later—and is
In order to appreciate the advantages of the Power Earth
Indicator Compass, it is first necessary briefly to refer to The generator is usually mounted in the rear of the fuselage
certain characteristics of the ordinary magnetic compass— with the Windmill projecting above the fuselage into the
with which, no doubt, most of our readers are already familiar. slipstream. This position is usually good as regards magnetic
The force which causes the magnetic compass to point out conditions, but it may be mounted on almost any part of the
directions is the reaction between the compass magnets aircraft. The indicator and controller are usually mounted
and the earth's magnetic field. As long as the compass card, on the instrument board in front of the pilot.
Now, to explain the operation of this instrument. The
accompanying diagram shows a plan view of an armature
rotating on a vertical axis in the earth's magnetic field—
the latter being shown by dotted lines. A pair of brushes
are connected to an electric galvanometer of the zero centre
type and bear on diametrically opposite sides of the commutator. Such an armature rotating in a magneticfieldproduces electrical potential at the commutator. If the brushes
are rotated around the commutator, it will be found that the
indication of the meter will vary from zero to maximum in
one direction, back to zero, then to maximum in the other
direction, and to zero again when the brushes are returned
to the first position.
There are thus two diametrically opposite points on the
commutator when the meter shows zero potential and two
similar points 90° around from zero when the meter shows
maximum potential. The angular relation between a line
drawn between the points of zero potential on the commutator
and the direction of the earth's magnetism is always the
same.
If the armature is wound and connected to the commutator
so that the points of zero potential are in line with the
magnetism of the earth, the galvanometer will show zero
only when the brushes are in line with the direction of the
earth's magnetism. Therefore, when the galvanometer
The Pioneer Earth Indicator Compass : Diagram show- shows no indication, we know that the brushes are in a line
ing the generator-armature rotating in the earth's with magnetic north-routh.
magnetic field.
Let us follow its operation when fitted on an aeroplane.
First assume that the machine is swung round, on the ground,
with its magnets and pivot, is constrained to rotate in a until it points in some known direction, say north. Then,
horizontal plane the magnets tend to line up with the hori- with the armature running, the brushes are "rotated until the
zontal force of the earth's magnetism, thus indicating direc- galvanometer shows that no current is flowing, i.e., the brushes
tions in relation to magnetic north.
in line with earth's field, and pointers on both indicator and
Unfortunately, the direction of the earth's magnetism controller pointing to zero. If the aeroplane is now flown
is horizontal in only a few places ; in New York, for instance, directly north, the indicator will continue to show zero—
it is inclined downward at an angle of about 70° to the hori- the brushes being in contact with the points of zero potential
zontal. When the compass is mounted on a fixed support on the commutator.
where the magnetic element is held horizontal by the force
If, however, the machine be turned slightly, say, towards
of gravity, its magnets react with the horizontal component the east, then the brushes will move with the aeroplane
of the earth's magnetism.
relatively to the earth's field, or, in effect, around the comUnder these conditions the compass is very accurate, but mutator towards the points of maximum potential, and electric
on aircraft conditions are different and the well-known errors current will flow from the armature to the meter causing the
and troubles arise. For example, the fore and aft accelera- latter's pointer to move to one side of zero.
tion forces act on the pendulous magnetic element to tilt it
Now, the brushes are connected to the meter, so that its
out of the horizontal and cause it to act as if constrained to pointer will move in the direction in which the aeroplane
rotate about some axis inclined to the vertical. When so turns, and by steering so as to keep the pointer at zero, the
inclined the component of the earth's magnetism acts on the north course will be followed. Should it be desired to follow
compass so as to cause the compass element to rotate— another course, the angle of the brushes in relation to the
resulting in errors of as much as 180°.
aeroplane is changed by the angle and the desired heading
A second source of error arises from the angular movement differs from the zero or north heading.
of the aircraft in yawing, rolling, and pitching, which moveFor example, if it is desired toflyeast, or 90° from north,
ments are transmitted to the magnetic element through the the brushes would be rotated by hand through an angle of
liquid. Vibrations of the aircraft, which usually have rotary- 90°, so that the brush that was on the north side of the
components in the plane of the magnetic element, also cause commutator is now on the west side, and the brush that was
erratic readings, while another source of trouble is caused on the south side is now on the east side.
by magnetic materials in the vicinity of the compass.
Current will now flow through the meter in such a direction
In the Pioneer Earth Indicator Compass these defects are that the pointer would show " left," i.e., that the areoplanc
obviated or greatly reduced. Its outstanding feature lies was to the left of the desired heading. The pilot would,
in the separation of the magnetic element from the direction- therefore, turn towards the right, and when he had turned
indicating element. Briefly, it consists of three principal 90° the brushes would once more be returned to the northunits : a generator, a controller and an indicator. The south position (in line with field), and the pointer would
generator is the direction-determining element of the compass
again show zero ; the machine would then be flying east.
and corresponds to the magnetic needles of the ordinary' Similarly, any other course can be flown by adjusting the
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