Flight Controls
GENERAL
The basic flight controls are the inboard and outboard ailerons, the elevators, and the rudders.
Additional flight controls consist of:
Inboard and outboard spoilers.
A moveable horizontal stabilizer.
Trailing and leading edge flaps and slats.
The flight controls are powered hydraulically except for the stabilizer, which is powered electrically.
Aerodynamic tabs are employed on the ailerons, elevators and rudders. Manual reversion is provided for the ailerons and elevators in the event of a dual hydraulic system failure. A standby hydraulic system is available to power the lower rudder if necessary.
Control feel-forces are generated artificially in all axes:
Elevator feel is generated by dual hydraulic feel computers and feel units.
Aileron and rudder feel is generatey by spring-loaded mechanical trim and centering systems.
Aerodynamic tabs provide elevator feel force in the manual reversion mode.
Balance panels, in a cavity just in front of the ailerons and eelevator, provide aerodynamic boost. There are no balance panels for the rudders.
The leading edge flaps and slats and trailing edge flaps are normally powered by hydraulic pressur. An alternate, electric system may be used to extend or retract the trailing edge flaps. The standby hydraulic system may be used to extend the leading edge devices.
Aerodynamic fences are attached tot he two inboard leading edge slats to improve airflow over the wing in those areas.
Vortex generators are installed on each side oft he vertical stabilizer.
Aileron and rudder trim is accomplished by means of mechanical trim, centering and feel systems which move the entire control surface and reposition the control system neutral position. Pitch trim is accomplished by changing the angle oft he horizontal sstabilizer.
The hydraulic control units acta s gust dampers when the hydraulic systems are depressurized, eliminating the need for surface locks.
(1) Aileron Switches Control aileron hydraulic shutoff valves. (2) Spoiler Switches Controls spoiler hydraulic shutoff valves. (3) Elevator Switches Controls elevator hydraulic shutoff valves. (4) System A and Standby Rudder Switches (ganged) Controls lower rudder hydraulic shutoff valve and standby hydraulic system. (5) System B Rudder Switch Controls upper rudder hydraulic shutoff valve.
ROLL CONTROL
AILERONS AND SPOILERS
Two ailerons on each wing, operating with spoilers, provide roll (lateral) control.
The roll control system is comprised of conventional control wheels which are bused together by cables. Aileron trim is accomplished by repositioning the roll control system’s neutral point.
The ailerons are augmented with flight spoilers when control wheel movement exceeds five degrees.
When the outboard flaps are retracted, the outboard ailerons are locked in a faired position. As the flaps extend, outboard aileron travel becomes progressively greater. At five degrees of flaps, omst oft he outboard aileron travel is available.
Control wheel movement operates the aileron power control unit (by cable) to provide hydraulic actuation oft he aileron cable bus drum and spoiler mixer. The cable bus drum actuates cables to mechanically position the ailerons in proportion to control wheel movement. The spoiler mixer allows proportional spoiler operation when control wheel movement exceeds five degrees. Autopilot inputs are supplied tot he aileron power control unit through the same cables used for control wheel input.
Aileron Trim
Aileron trim is provided by a trim wheel located on the aft pedestal. The wheel operates cables to reposition the trim, centering and feel system to change the aileron neutral point. The trim, centering and ffeel system operates the aileron power control unit to reposition the ailerons tot he new neutral point. The control wheels move with the trim input.
Aileron Feel
A feel and centering mechanism provides artificial control feel and centers the control wheels when control pressure is released.
SPOILERS AND SPEEDBRAKES
Seven spoilers are provided on each wing. Flight spoilers (spoilers 1 through 5 and 10 through 14) are used to assist the ailerons in lateral control.
Ground spoilers (spoilers 6, 7, 8, and 9) function only on the ground as speed brakes.
The flight spoilers also function as flight speedbrakes while all spoilers function as speedbrakes on the ground.
The hydraulic actuators that position the spoilers are designed to prevent spoiler float in the event of a hydraulic power loss, and permit spoiler blowdown at high speeds.
The spoilers may be operated as speedbrakes if manually selected in flight and after landing.
HYDRAULIC POWER
SYS A or SYS B hydraulic power may be turned off tot he aileron power control unit, and outboard spoilers (SYS A) or inboard spoilers (SYS B), by switches on the overhead panel.
PITCH CONTROL
An elevator on each side oft he airplane provides pitch control. Hydraulic power control units position the elevators in response to control column or autopilot inputs.
The power control units also limit elevator travel and provide snubbing action on the ground to protect the elevators against wind damage. Elevator feel is provided by an elevator feel unit.
Each elevator has a positionn transmitter to indicate elevator position relative tot he stabilizer.
ELEVATOR CONTROL
When the control column is moved, it mechanically controls the hydraulic power control units. The hydraulic actuators are mechanically interconnected by the input linkage from the aft control quadrant.
ELEVATOR FEEL
Because hydraulic actuators prevent aerodynamic forces from being transmitted back tot he control colun, feel forces are synthesited in the feel control unit by two feel computers.
The elevator feel control unit and dual feel computers are powered by the „A“ and „B“ hydraulic systems, respectively.
Inputs tot he elevator feel computers are dynamic air pressure as sensed by the elevator pitot system, and stabilizer position. In the event of a single feel computer failure, an amber ELEV FEEL DIFF PRESS light will illuminate on the flight engineer’s lower panel; however, no change in control forces will occur.
AUTOPILOT INPUTS
Electrical control signals from the autopilot are used to position the selected power control unit to drive the elevators. The other power control unit is controlled mechanically by input linkage from the aft control quadrant. When the autopilot signals the selected actuator (through ist power control unit) to move, the input linkage moves the aft control quadrant (and control columns) and the other power control unit to position the other elevator. This movement may be noted on the position indcator as a slight lag in response from the elevator not selected.
STABILIZER-ACTUATED ELEVATOR TRIM
Stabilizer actuated elevator trim positions the elevator feel control unit to a new elevator neutral point providing up elevator during airplane nose up stabilizer trim of 6 to 10 units.
When the stabilizer-actuated elevator trim system positions the feel control unit and the elevator, the control column moves aft, establishing a new neutral point.
HYDRAULIC POWER
Respective SYS A or SYS B hydraulic power tot he feel system and power control units may be turned off by use of switches on the overhead panel.
STABILIZER TRIM
The sstabilizer trim system trims the airplane longitudinally by varying the horizontal stabilizer angle. It pivots the stabilizer about ist rear attach point by driving an electrically-powered, trim drive mechanism. The mechanism consists oft wo stabilizer trim couplers and a ball-screw actuator driven by two electric motors; a main electric trim motor and an autopilot and cruise-trim ervomotor. The autopilot and cruise-trim servomotor trims the stabilizer at one-fifth the rate oft he main electric trim motor. This prevents excessive rim rates in cruise.
The trim system may be operated electrically by dual thumb-switches on each control wheel, the cruise-trim switch on the pedestal, or by inputs from the autopilot system. The trim system may also be operated manually by trim control wheels located on the control pedestal.
Travel-limiting devices control the range of stabilizer movement in all operating modes. In the electrical mode (including autopilot operation), limit switches prevent stabilizer travel beyond that required by the normal flight envelope for the prevailing operating condition. Mechanical stops on the actuator constrain absolute travel, but the trim system does not normally drive the stabilizer to these stops. Manual control permits travel beyond the electrical limits.
A mechanical brake is provided on the ball-screw actuator (jackscrew) to prevent the stabilizer from creeping when there are no trim inputs.
STABILIZER TRIM BRAKE
The stabilizere trim brake automatically stops stabilizer trimming when the control column is moved in an opposing direction. This ist he primary means of immediately stopping a runaway stabilizer trim condition. The stabilizer may be operated in the same direction as control column force with the brake engaged. The brake is released by releasing control column pressure or by pulling the stabilizer brake release knob on the pedestal.
MANUAL TRIM WHEELS
Manually operated trim wheels, one on each side oft he pedestal, are connected by cables tot he stabilizer actuating mechanism and provide direct manual trim capability. Retractable handles located in the wheels aid in manua operation. The trim wheels always rotate when the trim mechanism is actuated.
STABILIZER TRIM CUTOUT SWITCHES
Stabilizer trim cutout switches on the control pedestal are used to turn off electrical power to either the main electrical or the crusie trim motor.
STABILIZER TRIM LIGHT
The amber STAB TRIM light on the pedestal illuminates when either oft he following conditions exists:
When the main trim motor is powered.
When the autopilot cruise trim motor is powered by the cruise trim switch.
CRUISE TRIM SWITCH
A cruise trim switch on the control pedestal uses the autopilot trim motor to trim at a slow rate, which permits smooth trimming at high airplane speeds. If engaged, the autopilot ELEVATOR engage switch will disengage when the cruise trim switch is used.
AUTOPILOT STABILIZER TRIM
Dual trim couplers, A and B, are provided to remove elevator loading whenever the autopilot is in operation, by trimming the stabilizer to zero elevator load. Trim commands from the selected pitch channel trim coupler (initiated by a predetermined difference between the elevator and horizontal stabilizer) drive the stabilizer until the difference (standoff) is reduced below a predetermined amount.
YAW CONTROL
Two rudders provide yaw control. The upper rudder is powered by the „B“ hydraulic system. The lower rudder is normally powered by the „A“ hydraulic system; alternatively, it can be powered by the standby hydraulic system.
Each rudder has an anti-balance tab to increase rudder effectivity, and to fair the rudders when hydraulic power is lost or removed.
RUDDER CONTROL
The rudders are controlled manually by conventional ruddeer pedals. Pedal movement is transmitted by means of cables, to a feel, trim, and centerin unit in the tail. Motion is transmitted mechanically to each rudder’s power control unit.
Pedal feel forces are produced by the feel, trim, and centering unit.
The autopilot does not provide inputs tot he rudder system.
LOAD LIMITER
The load limiter, on the lower rudder actuator, reduces hydraulic pressure tot he lower rudder power control unit when the flaps are up. With flaps extended it allows increased pressure tot he lower ruddeer for improved directional control. The upper rudder operates at a reduced limit at all times.
RUDDER LOAD LIMITER LIGHT
The RUDDER LOAD LIMITER light, located on the flight engineer’s lower panel, will come on to indicate that hydraulic pressure tot he lower rudder power control unit is incorrect for the trailing edge flap position. With zero hydraulic pressure in system „A“, the RUDDER LOAD LIMITER light will be on with the trailing edge (inboard) flaps up.[MK3]
RUDDER TRIM
Rotation oft he rudder trim control wheel on the pedestal actuates a separate cable system to move the feel, trim, and centering unit. This movement changes the neutral point , thus oving the rudder pedals and actuating the power conrol units to reposition the rudder.
STANDBY HYDRAULIC POWER
Setting the SYS A RUDDER switch on the overhead panel to OFF, also moves the STANDBY switch to ON, energizing the standby hydraulic system. The standby system powerst he lower rudder standby power control unit. The lower yaw damper is inoperative when standby hydraulic power is selected.
POSITION INDICATOR
The rudder position indicator is located on the pilots‘ center panel. Two pointers on the center scale, marked UPPER RUDDER and LOWER RUDDER, indicate the positions oft he pper and lower rudders.
YAW DAMPER
Each hydraulic power control unit receives a separate yaw damper signal that is in series with pilots inputs, but is not felt at the rudder pedals. The yaw damper has approximately five degrees of authority.
CONTROL
Each yaw damper coupler, one for the upper rudder and one for the lower rudder, contains a rate gyro that senses yaw rate and moves the associated rudder to dampen the yaw acceleration. Once a steady yaw correction is established the damper inputs cease.
The yaw dampers move the rudders proportionally opposite to the yaw acceleration oft he airplane and do not move the rudder pedals. Two switches on the pilots‘ overhead panel control the yaw dampers.
ENGAGED INDICATION
A green ENG light, or a Y/D flat retracted, on the elevator and rudder position indicator, indicates that the associated yaw damper coupler is electrically powered. It does not, however, indicate that the yaw damper is operating. Movement oft he associated rudder position indicator during yaw acceleration indicates that the yaw damper is operating.
On the ground, the yaw damper rate gyros are not electrically powered, when on APU power or external power is plugged in.
TRAILING EDGE FLAPS
The trailing edge flaps are positioned by moving the flap lever. Flap lever movement operates cables which provide input tot wo control valves, one for the outboard flap drive; the other for the inboard flap drive. Both use pressure from the „A“ hydraulic system.
Hydraulic fluid passing through the control valve operates a hydraulic motor which is coupled through gears to a torque tube system. Each torque tube system extends laterally along both wings tot wo transmissions. Each transmission drives a ball-screw actuator to move the respective flap.
Flap position affects the operation of several systems as follows:
Inboard Flaps. The inboard flaps affect:
Lower rudder load limiting.
Stall warning.
Pack cooling fans.
Warning horn for speedbrakes/flaps
Auto pack trip.
Outboard Flaps. The outboard flaps affect:
Warning horn for takeoff and landing configuration.
Leading edge flaps.
Outboard aileron lockout.
Ground proximity warning.
Trailing edge flap position is displayed on two dual flap position indicators located on the center instrument panel.
FLAP LEVER
The flap lever is located on the pdestal. Gates are located at the 2 and 25 detents. The gate at the 2 detent is used for inflight verification of symmetrical extension or retraction oft he leading edge devices. The gate at the 25 detent is intended to prevent inadvertent flap over-retraction during a go-around.
FLAP POSITION INDICATORS
There is a position transmitter on each flap and two dual position indicators. One indicator indicates the position oft he two outboard trailing edge flaps, while the other indicates the position oft he two inboard flaps.
ASYMMETRY PROTECTION
Flap asymmetry is sensed inside the position indicators as pointer spread. When the spread reaches a predetermined difference between the left and the right pointers, a circuit is completed to close the inboard or outboard flap bypass valve. Energizing the bypass valve(s) stops inboard or outboard flap operation.
No split-flap protection is provided between inboard versus outboard flaps by either system.
ALTERNATE TRAILING EDGE FLAP SYSTEM
Alternate operation oft he trailing edge flaps is accomplished electrically, using the ALTERNATE FLAPS swiches on the overhead panel. The switches control two electric motors which drive the same torque tube system as the hydraulic motors.
Alternate Flap Switches
The ALTERNATE FLAPS switches consist of:
An alternate flap master switch, with an OFF and ON position.
Two directional switches labeled INBD and OUTBD.
The directional switches each have an OFF, UP and DN position.
Placing the alternate flaps master switch tot he ON position:
Actuates a bypass valve in each trailing edge flap hydraulic system.
Arms the two directional switches.
Turns on the standby hydraulic pump for leading edge device extension.
Closes the leading edge flap bypass valve.
LEADING EDGE DEVICES
There are seven leading edge devices on each wing, four of which are slats. The remaining three are krueger flaps.
The slats and flaps are divided into two sets. In sequence of operation during trailing edge flap extension, symmetrical set 1 (No. 2, No, 3, No. 6 and No. 7 slats) extends when the outboard trailing edge flaps move to 2 degrees. Symmetrical set 2 (No. 1, No. 4, No. 5 and No. 8 slats and No. 1, No. 2, No.3, No. 4, No. 5 and No.6 flaps) extends when the outboard trailing edge flaps move from 2 degrees to 5 degrees. In sequence of operation during trailing edge flap retraction, symmetrical set 2 retracts when the outboard trailing edge flaps move from 5 degrees and set 1 retracts when the outboard trailing edge flaps move from 2 degrees.
The leading edge devices are extended and retracted by hydraulic actuators using the „A“ hydraulic system.
Alternate extension oft he leading edge devices is achieved by use oft he standby hydraulic system.
A leading edge flap annunciator light system provides visual indication of flap operation.
ACTUATORS
Each leading edge device is extended and retracted by a hydraulic actuator.
Mechanical locks in each actuator:
Lock the leading edge flaps in the extended position only.
Look the leading edge slats in the retracted and extended positions.
Hydraulic power is required to unlock the actuators.
ALTERNATE EXTENSION SYSTEM
The standby hydraulic system can extend all leading edge devices using the normal actuators.
Alternate Flap Switches
Placing the ALTERNATE FLAPS master switch tot he ON position:
Arms the two trailing edge directional switches.
Turns on the standby hydraulic pump.
Closes the leading edge bypass valve.
Actuates a bypass valve in each trailing edge flap hydraulic system.
LEADING EDGE ANNUNCIATOR LIGHTS
Leading edge annunciator lights are located on the center instrument panel and at the flight engineer’s auxiliary panel.
Two lights on the center instrument panel, one amber and one green, display the status oft he leading edge flap system. When the amber LE FLAPS light is illuminated, the flaps are in transit.
When the green LE FLAPS light is illuminated, the leading edge flaps are extened as programmed. With both lights out, all leading and trailing edge flaps are retracted.
The lights will go through a normal amber-green sequence as set 1 extends and again when set 2 extends.
The LE FLAPS and SLATS annunciator panel on the flight engineer’s auxiliary panel contains amber and green lights for each leading edge flap and slat.
A check of this panel will indicate the position of any leading edge flap or slat.
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