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
¼ inch or more in any flap position, the circuit to the flap control relay is
broken. The relay de-energizes to close the flap shutoff valve. Hydraulic
pressure stops and the flaps stop moving. In order to maintain lateral
stability, once flap operation is stopped due to asymmetry, further flap
movement in either direction is not possible.
For SPZ-8400 equipped aircraft having ASC 69A (Flap Asymmetry
Indicator Installation) incorporated: When the flap control relay
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-27-00
Page 57
January 31/02
Revision 6
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