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flow rate at ground idle. The speed of the gas producer
with the lever at GND should be 60 to 63 percent N1.
When an ENG COND lever is moved to FLT, the engine
is operating within the N2 governing range, unless the
engine is “topped out” at which time it goes back to N1
governing. The N2 governor then takes control to maintain
selected rotor RPM (RRPM) in response to the engine
beep trim switches and collective pitch changes,
When an ENG COND lever is moved to STOP, the gas
producer lever closes the fuel control fuel shutoff valve
which stops fuel flow to the gas producer.
Each electrical system is completely separate and a failure
in one system will not affect the other. A built-in mechanical
brake holds the actuator at its last selected position
if loss of electrical power occurs. ENG COND lever
friction is provided to reduce the possibility of overtorquing
the engine transmissions by resisting movement of
the ENG COND levers. The ENG COND lever friction
brake cannot be adjusted by the pilot and a force of 4 to
5 pounds is needed to move them.
2-3-9. Normal Engine Beep Trim Switches.
712 On 712 engine installations engine beep trim
switches are active at all times during normal operation.
Two momentary switches are on the auxiliary switch
bracket of each THRUST CONT lever and are labeled
ENGINE BEEP TRIM (fig. 2-5-1). Both switches have an
RPM INCREASE, RPM DECREASE, and a neutral position.
712 One switch is labled NO. 1 & 2 which is normally
used to select desired RRPM. The second switch is
labeled NO. 1 which will only affect the No. 1 engine and
is used to match engine loads which are indicated by the
dual torquemeters.
TM 1-1520-240-10
2-3-3
712 Power to operate the beep trim system is supplied
by the DC and AC buses. DC power to operate a trim
motor in the power turbine control box, which unbalances
a control circuit, is supplied by the corresponding No. 1
or No. 2 DC buses through the ENGINE NO. 1 or NO. 2
TRIM circuit breakers on the No. 1 or No. 2 PDP. The
unbalanced control circuit causes the AC power from the
No. 1 or No. 2 AC buses through the ENGINE NO. 1 or
NO. 2 TRIM & TIMER circuit breakers on the No. 1 or No.
2 PDP to be transformed and rectified to DC voltage. This
DC power operates the power turbine actuator on the
engine fuel control.
NOTE
No two engines provide matched performance
with regard to torque, RPM, PTIT, or
fuel flow. With torque matched all other parameters
may not be matched.
712 Holding the No. 1 & 2 switch forward (RPM INCREASE)
will increase the RRPM. Holding the switch aft
(RPM DECREASE) will decrease the RRPM. When the
switch is released, it returns to the center or neutral position.
The switch electrically controls both power turbines
by movement of the N2 actuator through each engine
power turbine control box.
The procedure for matching engine load requires that
NO. 1 & 2 engine beep switch be used in conjunction with
NO. 1 engine beep switch. When NO. 1 engine beep
switch is moved forward (RPM INCREASE), the torque
of No. 1 engine increases. At the same time RRPM increases,
even though No. 2 engine torque decreases
slightly. Moving NO. 1 & 2 engine beep trim switch aft
(RPM DECREASE) causes both engine torques to decrease
and reduce RRPM. If torques are still not
matched, this procedure is continued until torques are
matched and desired RRPM is attained. The opposite
action occurs when NO. 1 engine beep switch is moved
aft.
The engine beep trim switches should not be used during
power changes initiated by thrust lever movement because
RRPM droop should only be momentary. The engine
beep trim system adjusts engine RPM only if the
respective ENG COND lever is at FLT. At STOP or GND,
it is possible to move the power turbine lever by moving
the engine beep trim switches to RPM DECREASE or
RPM INCREASE, but in either case, engine RPM will not
be affected because the engine is not operating in the N2
governing range.
2-3-10. EMERG ENG TRIM Panel 712
The EMERG ENG TRIM (emergency engine) panel is
located on the center console (fig, 2-3-2). The panel consists
of two guarded normal engine trim system disabled
switches and two momentary emergency engine trim
switches.
a. Normal Engine Trim System Disable
Switches. The guarded switches permit the pilot to disable
either or both normal beep trim systems. This prevents
unwanted signals from the normal beep trim system
to interfere with the operation of the emergency
engine trim system. Each switch is labeled AUTO and
　
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