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TRIM
COLUMN
CONTROL
CUTOFF
COLUMN
CONTROL
STABILIZER
SWITCHES
TRIM
AUTOPILOT
A/P ENGAGE
R
CMD CMD CMD
L C
December 01, 1999
747 Operations Manual
Flight Controls -
System Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 9.20.7
Roll Control
Hydraulically powered inboard and outboard ailerons and spoilers provide roll
control.
Aileron and Spoiler Roll Control
Rotating either Control Wheel positions ailerons and spoilers to provide roll
control. An aileron lockout system locks the outboard ailerons in the neutral
position at high airspeeds and permits full travel of the outboard ailerons at low
airspeeds. This prevents overcontrolling at high airspeeds and provides the
required roll authority at low airspeeds.
All spoilers, except the inboard spoiler on each wing, function as flight spoilers
which operate with the ailerons to provide roll control. Spoiler mixers combine
Speedbrake Lever and Control Wheel inputs allowing roll inputs to deflect spoiler
panels up or down from their deployed positions when speedbrakes or ground
spoilers are in use.
Aileron positions display on the EICAS status display. Separate pointers indicate
the inboard and outboard aileron positions on each wing. A full scale deflection of
the position indicator corresponds to maximum aileron travel.
The control wheels connect through an override mechanism which allows either
wheel to move independently if the other wheel jams and significant manual force
is applied to the free wheel. Roll control is then available through the ailerons on
the wing corresponding to the free wheel. Approximately half of the flight spoilers
are also available for roll control under these conditions.
Each side of the mechanical system also incorporates shearouts which may allow
the jammed control wheel to be freed when a significant manual force is applied
to the jammed wheel.
Aileron Trim
Pushing both Aileron Trim switches in the desired direction causes the feel and
trim mechanism to reposition the aileron neutral point. Both control columns have
an aileron trim indicator.
If the Aileron Trim switches are activated with an autopilot engaged, the aileron
neutral point is repositioned. When the autopilot is disengaged, the wheel and
ailerons move to the repositioned aileron neutral point. The airplane responds with
roll proportional to the amount of aileron trim input.
October 1, 2000
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
9.20.8 D6-30151-425
Flight Controls -
System Description
Aileron Control Diagram
to hydraulic systems.
N__O_T_E: Numbers in boxes refer
OVERRIDE
TRIM
AND
FEEL
M
DOWN
WING
RIGHT
DOWN
WING
LEFT
AILERON
LOCKOUT
AILERON
OUTBOARD
SWITCHES
TRIM
CAPTAIN FIRST OFFICER
LOCKOUT
AILERON
OUTBOARD
December 01, 1999
747 Operations Manual
Flight Controls -
System Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 9.20.9
Yaw Control
The rudder control system provides yaw control.
Rudder Control and Trim
Either pilot’s rudder pedals control the hydraulically powered upper and lower
rudders. Rudder pedal inputs mechanically transfer to a single feel and trim
mechanism, then transfer through separate ratio changers to the upper and lower
rudder hydraulic actuators.
Rudder positions display on the EICAS status display. On the ground, pushing a
rudder pedal to the stop causes a full scale deflection of the upper and lower rudder
position indicators.
The rudder system shearouts allow rudder control to be regained if a jam occurs
and a significant manual force is applied to the rudder pedals.
When the Rudder Trim control is rotated in the desired direction, the rudder feel
and trim mechanism repositions the rudder pedal neutral point. The rudder trim
indicator displays units of rudder trim.
Pushing the Rudder Trim Centering switch causes rudder trim to move to the zero
units position. The zero position achieved by the centering function is not as
accurate as manually trimming to zero units.
Rudder Ratio Changers
Two rudder ratio changer systems gradually reduce each rudder surface’s response
to pedal inputs as airspeed increases. This protects the vertical tail structure from
stresses which could result from large rudder surface deflections at high airspeeds.
If a ratio changer system fails, the response of the related rudder surface to pedal
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