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gyro tends to remain rigid in space, with its axis of
rotation pointed tin a constant direction.
Figure 4-22. Precession of a gyroscope results from
an applied deflective force.
Figure 4-23. Electric powered gyro system.
4-16
gyroscope, on a set of gimbal rings, the gyro is able to
rotate freely in any direction. Thus, if the gimbal rings
are tilted, twisted, or otherwise moved, the gyro
remains in the plane in which it was originally spinning.
[Figure 4-21]
PRECESSION
Precession is the tilting or turning of a gyro in
response to a deflective force. The reaction to this
force does not occur at the point where it was applied;
rather, it occurs at a point that is 90° later in the direction
of rotation. This principle allows the gyro to determine a
rate of turn by sensing the amount of pressure created by
a change in direction. The rate at which the gyro precesses
is inversely proportional to the speed of the rotor
and proportional to the deflective force. [Figure 4-22]
Gyroscopic instruments require a power source to keep
the gyro rotating at a constant rate. The most common
power source for gliders is an electric battery. [Figure
4-23]
The turn coordinator and turn-and-slip indicator both
provide an indication of turn direction, rate, and quality.
The main difference between the turn coordinator and
the turn-and-slip indicator is the manner in which turn
information is displayed. The turn coordinator uses a
miniature aircraft, while the turn-and-slip indicator utilizes
a pointer called a turn needle.
We will discuss the turn coordinator. During a turn, the
miniature aircraft in the turn coordinator banks in the
same direction the glider is banked. The turn coordinator
enables you to establish a standard-rate-turn. You
do this by aligning the wing of the miniature aircraft
with the turn index. At this rate, the aircraft will turn 3º
per second, completing a 360º turn in two minutes. The
turn coordinator is designed to indicate the rate of turn,
not the angle of bank. The turn coordinator is also
equipped with an inclinometer to help you coordinate
your turn. [Figure 4-24]
ATTITUDE INDICATOR
The attitude indicator, with its miniature aircraft and
horizon bar, displays a picture of the attitude of the
glider. The relationship of the miniature aircraft to the
horizon bar is the same as the relationship of the real
aircraft to the actual horizon. The instrument gives an
instantaneous indication of even the smallestchanges
in attitude. [Figure 4-25]
The gyro in the attitude indicator is mounted on a
horizontal plane and depends upon rigidity in space
for its operation. The horizon bar represents the true
horizon. This bar is fixed to the gyro and remains in a
horizontal plane as the glider is pitched or banked
about its lateral or longitudinal axis, indicating the attitude
of the glider relative to the true horizon.
An adjustment knob is provided to allow the pilot to
move the miniature aircraft up or down to align the
miniature aircraft with the horizon bar to suit the pilot’s
line of vision. Normally, the miniature aircraft is
adjusted so the wings overlap the horizon bar when the
glider is in straight-and-level cruising flight. The attitude
indicator is reliable and the most realistic flight
Figure 4-25. Attitude Indicator.
Figure 4-26. Setting the heading indicator.
4-17
instrument on the instrument panel. Its indications are
very close approximations of the actual attitude of the
glider.
HEADING INDICATOR
The operation of the heading indicator depends upon
the principle of rigidity in space. The rotor turns in a
vertical plane, and fixed to the rotor is a compass card.
Since the rotor remains rigid in space, the points on the
card hold the same position in space relative to the vertical
plane. As the instrument case and the glider
revolve around the vertical axis, the card provides clear
and accurate heading information.
Because of precession, caused chiefly by friction, the
heading indicator will creep or drift from a heading to
which it is set. Among other factors, the amount of drift
depends largely upon the condition of the instrument.
If the bearings are worn, dirty, or improperly lubricated,
the drift may be excessive.
Bear in mind that the heading indicator is not direction
seeking, as is the magnetic compass. It is important to
check the indications frequently and reset the heading
indicator to align it with the magnetic compass when
required. Adjusting the heading indicator to the magnetic
　
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