Rockwell Commander 112 - POWER PLANT INSTRUMENTS

SECTION VIII
INSTRUMENTS
MAINTENANCE MANUAL
ROCKWELL
COMMANDER
112/B/TC/TCA
airspeed in both knots and miles-per-hour (see Figure
8-5). The indicator is operated by the pressure dif-
ferential between impact air pressure from the pitot
tube and barometric pressure sensed through the static
system. A white arc from 52 to 109 knots (60 to 125
mph) indicates the wing flap operating range. A green
arc from 57 to 143 knots (66 to 164 mph) indicates the
normal operating speed. A yellow arc from 143 to
180 knots (164 to 207 mph) indicates the caution range
in which all operations must be conducted with care
and then only in smooth air. A red radial line at 180
knots (207 mph) indicates the maximum speed at which
the aircraft may be safely flown.
RATE-Of-CLIMB INDICATOR (OPTIONAL)
The rate-of-climb indicator converts changes in bar-
ometric pressure to a rate of aircraft ascent or des-
cent in feet-per-minute. Barometric pressure is
sensed through the instrument static system. The
indicator has a single needle and two adjoining scales,
ranging from zero to 2,000 feet-per-minute to indi-
cate rate of climb or descent from a common zero
point. The 2,000 feet scales are divided into 100-
foot increments. A recessed slotted screw in the lower
left corner is used to zero the indicator when the air-
craft is on the ground.
MAGNETIC COMPASS
The magnetic compass is a semi-floating cylinder en-
cased in a liquid filled case with expansion provisions
to compensate for temperature changes. It is mount-
ed at eye level on the glare shield to afford better
visibility and lessen the effect of vibration and mag-
netic influences, which cause compass deviation.
It is equipped with compensating magnets that are
adjustable from the front of the case. The compass
should be air- swung and compensated at regular inter-
vals and at any time equipment installations are made
which may cause compass deviation. The compass
is individually lighted by a small bulb which may be
removed and replaced. Pivot covers on the compass
allow access to adjust the compensating magnets and
for the installation of the compass light.
MAGNETIC COMPASS COMPENSATION
Put airc raft in a simulated level flight attitude, see
Leveling in Section no Close doors and place flaps
in a retracted position. Set throttles at cruise posi-
tion with engines operating.. Place all electrical
switches, alternator, radio and other equipment in a
mode
normally used for navigational flight and pro-
ceed with the following:
a. Set adjustment screw s on compensating magnets
to zero. Zero position is when dot on screw is lined
up with dot on compass frame.
b. Position aircraft in a magnetically north direc-
tion. Adjust north-south adjustment screw until com-
pass reads exactly north.
8-8
c . Position airc raft in a magnetically east direc-
tion. Adjust east-west adjustment screw until com-
pass reads exactly east.
d. Position airc raft in a magnetically south direc-
tion. Notice resulting south error. Adjust north-
south adjustment screw so one-half of error is re-
moved.
e. Position aircraft in a magnetically west direc-
tion. Notice resulting west error. Adjust east-
west adjustment screw so one-half of the error is
removed.
f. Position aircraft in successive magnetically
30-degree directions and record all errors on devia-
tion card furnished with compass.
8-DAY CLOCK (OPTIONAL)
A conventional, spring-powered 8-day aircraft clock
with a sweep second hand is installed in the left in-
strument panel. A pair of red- tipped dummy hands
may be set to indicate takeoff time, estimated time of
arrival, or other uses. The adjustment and winding
knob
is in the left lower corner of the instrument.
ELECTRIC CLOCK {OPTIONAL}
An alternate 12 volt quartz crystal clock may be in-
stalled in the same location as the 8-day clock. The
clock has a second, minute and hour hand. An adjust-
ment knob, located in the lower left corner of the in-
strument, adjusts the clock to the proper time of day.
A pair of dummy hands may be set to indicate takeoff
time, estimated time of arrival, and other uses. The
knobs that set these hands are in the center of the
clock. The clock is operational only when the battery
switch is on. The clock must be reset to the proper
time prior to each flight.
POWER PLANT INSTRUMENTS
Power plant instruments provide the means for mon-
itoring the operation and condition of the engine and
include the tachometer indicator, manifold pressure
and fuel flow gage and the engine cluster units: cyl-
inder head temperature and oil temperature indicators
and oil pressure gage. These instruments are ope-
rated by fluid pressure; variations in electrical re-
sistance created by temperature sensing probes; or,
in the case of the tachometer, by a drive shaft con-
nected to the engine accessory housing.
ENGINE CLUSTER UNITS
The engine cluster units installed in the instrument
sub-panel indicate cylinder head temperature and oil
temperature in degrees Fahrenheit and oil pressure
in pounds per square inch (see Figure 8-5). The oil
pressure unit is a direct read instrument that is con-
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**unofficial copy**