Beechcraft C-12C, Operator And Technical Reference Manual

Page: 85 / 949

TM 1-1510-218-10
2-69
d. Rudder Trim Tab Control. The rudder trim
tab control knob, placarded RUDDER TAB / LEFT /
RIGHT , is on the control pedestal, and controls
adjustment of the rudder trim tab, Figures 2-7 and 2-9 .
The amount of rudder tab deflection, in degrees from a
neutral setting, is indicated by a position arrow.
2-49. WING FLAPS.
The all-metal slot-type wing flaps are electrically
operated and consist of two sections for each wing.
These sections extend from the inboard end of each
aileron to the junction of the wing and fuselage.
During extension, or retraction, the flaps are operated
as a single unit, each section being actuated by a
separate jackscrew actuator. The actuators are driven
through flexible shafts by a single, reversible electric
motor. Wing flap movement, either up or down, is
indicated in percent of travel by a flap position
indicator on the subpanel. Full flap extension and
retraction time is approximately 11 seconds. The flap
control switch is located on the control pedestal. No
emergency wing flap actuation system is provided.
With flaps extended beyond
APPROACH position
regardless of power setting, the landing gear warning
horn will sound, and the landing gear switch handle
lights will illuminate unless the landing gear is down
and locked. The circuit is protected by a 20-ampere
circuit breaker, placarded
FLAP MOTOR , located on
the overhead circuit breaker panel, Figure 2-16.
a. Wing Flap Control Switch. Flap operation is
controlled by a three-position switch with a flap-shaped
handle on the control pedestal, Figure 2-7 and 2-9 .
The handle of this switch is placarded FLAP and
switch positions are placarded FLAP UP /
APPROACH / DOWN . The amount of downward
extension of the flaps is established by position of the
flap switch, and is as follows:
UP – 0%, APPROACH –
40%, and DOWN – 100% . Limit switches, mounted on
the right inboard flap, control flap travel . The flap
control switch, limit switch, and relay circuits are
protected by a 5-ampere circuit breaker, placarded
FLAP CONTR , located on the overhead circuit breaker
panel, Figure 2-16 . Flap positions between UP and
APPROACH cannot be selected . For intermediate
flap positions between APPROACH and DOWN , the
APPROACH position acts as an off position . To return
the flaps to any position between full DOWN and
APPROACH place the flap switch to UP and when
desired flap position is obtained, return the switch to
APPROACH detent . In the event that any two
adjacent flap sections extend 3° to 5° out of phase
with the other, a safety mechanism is provided to
discontinue power to the flap motor.
b. Wing Flap Position Indicator. Flap position
in percent of travel from "0" ( UP ) to 100% ( DOWN ), is
shown on an indicator, placarded FLAPS , below the
instrument panel, Figure 2-17 . The APPROACH and
full DOWN or extended flap position is 14° and 34°,
respectively . The flap position indicator is protected by
a 5-ampere circuit breaker, placarded FLAP CONTR ,
located on the overhead circuit breaker panel.
Section VI. PROPELLERS
2-50. DESCRIPTION.
A three-bladed aluminum propeller is installed on
each engine. The propeller is of the full feathering,
constant speed, counter-weighted, reversing type,
controlled by engine oil pressure through single action,
engine driven propeller governors. The propeller is
flange mounted to the engine shaft. Centrifugal
counterweights, assisted by a feathering spring, move
the blades toward the low RPM (high pitch) position
and into the feathered position. Governor boosted
engine oil pressure moves the propeller to the high
RPM (low pitch) hydraulic stop and reverse position.
The propellers have no low RPM (high pitch) stops;
this allows the blades to feather after engine
shutdown. Low pitch propeller position is determined
by the low pitch stop which is a mechanically actuated,
hydraulic stop. Beta and reverse blade angles are
controlled by the power levers in the beta and reverse
range.
2-51. FEATHERING PROVISIONS.
The aircraft are equipped with both manual and
automatic propeller feathering. Manual feathering is
accomplished by pulling the corresponding propeller
lever aft past a friction detent. To unfeather, the
propeller lever is pushed forward into the governing
range. An automatic feathering system will sense loss
of torque oil pressure and will feather an unpowered
propeller. Feathering springs will feather the propeller
when it is not turning.
a. Automatic Feathering. The automatic
feathering system provides a means of immediately
dumping oil from the propeller servo to enable the
feathering spring and counterweights to start
feathering action of the blades in the event of an
engine failure
. Although the system is armed by a
switch on the overhead control panel, placarded
AUTOFEATHER ARM / OFF / TEST , the completion
of the arming phase occurs when both power levers
are advanced above 90% N
1
– at which time both
indicator lights on the caution/advisory annunciator