Figure 6-36.-Precession resulting from deflective force.
rigidity in the wheel, the wheel precesses and
The case of the gyro identically duplicates
topples over at the same time.
aircraft movement. The case is free to revolve
Any spinning mass exhibits the gyroscopic
around the stable gyro because of the mounting
of the gyro rotor in gimbals. It follows, there-
properties of rigidity in space and precession. The
rigidity of a spinning rotor is directly proportional
fore, that the aircraft itself actually revolves
to the weight and speed of the rotor speed and
around the rotor and is the complementing
inversely proportional to the deflective force.
factor in establishing the indications of the
instrument.
Attitude Indicator
Pilots determine aircraft attitude by referring
to the horizon when they can see it. Often,
however, the horizon is not visible. When it is
dark or when there are obstructions to visibility
such as overcast, smoke, or dust, the pilot cannot
use the earth's horizon as a reference. When this
condition exists, they refer to an instrument called
the attitude indicator. This instrument is also
known as a vertical gyro indicator (VGI), artificial
horizon, or gyro horizon. From these instruments,
pilots learn the relative position of the aircraft
with reference to the earth's horizon.
The attitude indicator gyro rotor revolves
with its spin axis in a vertical position to
the earth's surface. This vertical position is
rigidly maintained as the aircraft pitches and
Figure 6-37.-Aircraft reference and gyro stability.
