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trims the aircraft and a synchronous standby mode is maintained if
the autopilot is engage. In flight, synchronization mayalso be accomplished
through the system test switch on the pilot's instrument
panel.
PITCH TRIM SELECTOR SWITCH - MACH TRIM FUNCTION
The Mach trim system utilizes the primary motor of the horizontal
stabilizer pitch trim actuator to increase longitudinal stability. If the
PITCH TRIM selector switch on the pedestal is in the PRI position,
Mach trim will automatically engage at approximately 0.70 MI if neither
autopilot is engaged. Mach trim will not engage or will disengage
when the PITCH TRIM selector switch is moved to the OFF or
Pilot's Manual
Learjet 31A
SEC position. If the PITCH TRIM selector switch is in OFFor SEC, the
Mach trim monitor will remain active and will illuminate the MACH
TRIM light and cause the overspeed warning horn to sound above
0.78 MI.
MACH TRIM LIGHT
The amberMACH TRIM annunciator light, located on the glareshield
annunciator panel, will illuminate whenever the Mach trim monitor
has disengaged the Mach trim system. Whenever the Mach trim system
is disengaged and Mach is above 0.78 Mb the overspeed warning
horn will sound if neither autopilot is engaged. The Mach trim monitor
continuously monitors input signals and power to the Mach trim
computer. In the event of loss of power to the Mach trim computer or
primary pitch trim system, loss of input signals to the Mach trim computer,
or a Mach/horizontal stabilizer position error, the Mach trim
monitor will disengage Mach trim and illuminate the MACH TRIM
light-
SYSTEM TEST SWITCH -MACH TRIM FUNCTON
The rotary-type system test switch, located on the pilot's instrument
panel, is used to test the Mach trim system and the Mach trim monitor
while the aircraft is on the ground . In flight, the switch may be
used to resynchronize the system if the Mach trim monitor has disengaged
the system. The test function is initiated by rotating the switch
to MACH TRIM and then depressing the switch PRESS TEST button.
When the aircraft is on the ground and the test sequence is initiated,
the test switch inserts a signal that causes the horizontal stabilizer to
trim in the nose-up direction. Since there is no corresponding airspeed
change, the Mach trim monitor senses aMach/horizontal stabilizer
position error, disengages Mach trim, and illuminates the
MACH TRIM light. In flight, depressing the PRESS TEST button will
resynchronize the Mach trim system to the horizontal stabilizer position
and Mach existing when the PRESS TESTbutton wasdepressed.
5- 10
PM-121
Original
Learjet 31A
Pilots Manual
PITCH TRIM SYSTEM
Pitch trim is accomplished by repositioning the horizontal stabilizer
to the desired trim setting through actuation of the horizontal stabilizer
pitch trim actuator. The actuator is a dual-motor, screwjack-type
actuator. The primary motor is operated by the aircraft primary pitch
trim system. The secondary motor is operated by the aircraft secondary
pitch trim system and the autopilot. A speed controller in the
primary pitch trim system changes primary pitch trim rate as a function
of flap position . The speed controller allows high trim rates when
the flaps are beyond 3° down and low trim rates when the flaps are
up. A trim speed monitor is incorporated into the speed controller to
alert the crew of a trim speed error. The primary and secondary pitch
trim systems are electrically independent and mode selection is made
through a selector switch . Primary pitch trim is pilot controlled
through trim switches on each control wheel. Secondary pitch trim is
pilot controlled through a switch on the pedestal. Emergency interrupt
is provided for both systems through the Control Wheel Master
switches (MSW). Horizontal stabilizer trim position is displayed on a
pedestal mounted indicator. Primary pitch trim control circuits operate
on 28 VDC supplied through the 3-amp PRI PITCH TRIM circuit
breaker on the pilot's circuit breaker panel. The primary motor operates
on 28 VDC supplied through a 20-amp current limiter. Secondary
pitch trim control circuits and actuator motor operate on 28 VDCsupplied
through the 75-amp SEC PrICH TRIM circuit breaker on the
copilot's circuit breaker panel. Primary and secondary pitch trim are
operative during EMER BUSmode.
PITCH TRIM SELECTOR SWITCH
ThePITCHTRIM selector switch, located on the pedestal trim control
panel, provides primary and secondary mode selection for the pitch
trim systems. The switch has three positions: PRI, OFF, and SEC.
When the switch is set to PRI, a ground path is provided for the primary
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