Piper Navajo PA-31 Service Manual page 636

PIPER NAVAJO SERVICE MANUAL
SECTION X
INSTRUMENTS
10-1. INTRODUCTION. The purpose of this section is to provide instructions
for
remedying difficulties which may arise in the operation of the various instruments and the
pneumatic system. The instructions are organized so that the mechanic can refer to
description,
for a basic understanding
of the instruments and pneumatic system;
troubleshooting,
for a methodical
approach
in locating the difficulty;
corrective
maintenance, for the removal, repair and installation of components; and adjustments and
tests, for the operation of the repaired system.
10-2. DESCRIPTION. The instrumentation of the PA-31 provides for all conditions of
flight. The instruments are designed to give a quick and actual indication of attitude,
performance and condition of the airplane. They are divided into four groups: Pressure
Gyro, Pitot-Static, Electrical and Miscellaneous. Some of the instruments are components of
indicating systems that indicate conditions at remote parts of the airplane. A few of the
instruments, however, are self-contained and merely have to be correctly installed to give an
indication. Warning lights are installed to indicate unsatisfactory or dangerous conditions in
some systems. Instruments requiring power from the electrical system are provided with
circuit breakers to isolate the individual systems in the event of trouble. For night
operation, each instrument is either individually lighted by shielded post lights or a light
incorporated as part of the instrument.
The panel has been arranged to accommodate flight instruments in the left side, in front
of the pilot, electronic equipment and some engine instruments in the center, and the
remaining engine and miscellaneous instruments to the right. A second set of flight
instruments may be installed in the right side of the panel for use by the copilot. Additional
instruments are mounted in a sub-panel located over the windshield. All instrument panels
have been shock mounted to minimize vibration and shock conditions transmitted to the
panel.
10-3. INSTRUMENTS.
10-4. PRESSURE-GYRO INSTRUMENTS. The directional gyro is a flight instrument
incorporating an air driven gyro stabilized in the vertical plane. The gyro is rotated at a high
rate of speed by allowing air pressure to enter the instrument against the gyro buckets. Air
from the instrument is vented through lines to the atmosphere. Due to gyroscopic inertia,
the spin axis continues to point in the same direction even though the airplane yaws to the
right or left. This relative motion between the gyro and the instrument case is shown on the
instrument dial which has a 360 degree direct reading. The dial, when set to agree with the
airplane magnetic compass, provides a positive indication free from swing and turning error.
Reissued: 10/12/79
INSTRUMENTS
3C22