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B. Flap Shutoff Valve:
A normally closed (spring-loaded) shutoff valve controls hydraulic fluid flow
to the flap selector valve. Electrically controlled by the flap control relay and
the follow-up switches, the valve is energized open to allow fluid flow to the
selector valve.
If an asymmetrical flap condition occurs, the flap asymmetry switches open
the flap control relay to de-energize the flap shutoff valve and stop
hydraulic pressure flow to the flap selector valve. Flap movement ceases at
this point.
C. Flap Selector Valve:
The solenoid-operated flap selector valve directs hydraulic pressure flow to
the hydraulic motor. When electrically actuated by the FLAP handle, one of
the valve’s two solenoids energizes to supply hydraulic pressure to the
hydraulic motor to drive it in the required direction to extend or retract the
flaps. When the flaps reach the commanded position, flap follow-up
switches de-energize the flap selector valve through the control relay.
Hydraulic pressure flow to motor is shut off and the motor stops.
Two flow regulators limit hydraulic fluid flow to the hydraulic motor to 2.6
Gallons Per Minute (GPM) and from the motor to return at 2.9 GPM.
D. Hydraulic Motor and Central Gearbox:
A fixed-displacement hydraulic motor powered by the Combined, Utility or
Auxiliary hydraulic systems provides power to the flap system central
gearbox. The gearbox employs 8.22:1 reduction gears to provide a 730
RPM output that drives the flap actuators.
The gearbox has three output shafts that drive the left and right flap
actuators and the horizontal stabilizer actuator. An additional output shaft
drives the flap follow-up switch assembly and flap position transmitter.
Multi-section torque shafts transmit rotational force from the gearbox to the
OPERATING MANUAL
2A-27-00 PRODUCTION AIRCRAFT SYSTEMS
Page 56
October 11/02
Revision 8
flap actuators and the horizontal stabilizer actuator. To compensate for
wing flexing and allow free running, universal joints connect the torque
shaft sections. Pillow blocks and bearings support the torque shafts to
prevent whiplash.
E. Flap Actuators:
Each flap actuator consists of a gearcase with a rotating jackshaft and a
ball nut connected to the flap structure. As the gearcase rotates the
screwjack, the ball nut is driven forward and aft to extend or retract the
flaps. Non-jamming mechanical stops are installed on each end of the
screwjack. Because the inboard and outboard actuator screwjacks are
different lengths, they rotate at different speeds to provide equal flap
movement.
An internal torque limiter in each screwjack prevents damage to the flap by
locking the input shaft if the flaps are extended at excessive airspeeds. By
locking the input shaft, the hydraulic motor is stalled and flap movement
stops. (This should not be confused with an asymmetrical flap condition, in
which flap movement is restrained.) Once airspeed is reduced to the
proper extension speed, flap movement can be resumed by moving the
FLAP handle to the next upward or downward position, then back to the
desired position.
If a torque shaft fails with the flaps extended, a “no-back” device in the
gearcase prevents the flaps from creeping up (retracting) under airloads.
The device consists of a clutch-type brake and a friction plate that senses
compression loads on the screwjack. During normal screwjack movement,
the brake remains released to allow flap retraction.
F. Flap Follow-Up Switches:
Twelve follow-up switches, actuated by a cam on the central gearbox, open
and close as the flaps extend and retract. Once the flaps reach a selected
position, the cam opens one of the switches to control the flaps and provide
signals to other systems that require flap position information.
Six of the twelve switches (S1 through S6) control flap position in
conjunction with the four flap handle switches. Once the flaps reach a
selected position, the cam opens the respective follow-up switch, breaking
the circuit to the flap control relay. The relay de-energizes to close the flap
shutoff valve. Hydraulic pressure stops and the flaps stop moving.
G. Flap Asymmetry Protection System:
A flap asymmetry protection system monitors left and right flap movement
to prevent an asymmetrical flap condition. Each outboard actuator has an
asymmetry switch assembly connected to the opposite flap asymmetry
switch to form an electrical circuit. The circuit serves to detect one flap
moving faster than the other or movement of only one flap. With the flaps
operating normally, the switches are in phase. If flap movement separates
　
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