E.  
Flap Power Unit

 (1)  
The flap power unit houses gears which connect the hydraulic and electric motors to the torque tubes. The follow-up feedback mechanism is driven by the torque tube follow-up worm gear drive.

 6.  Torque Tubes and Angle Gearboxes (Fig. 2)
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 A.  The torque tubes and angle gearboxes transmit torque from the flap power units (gearboxes) to the flap transmissions. The inboard flap and outboard flap torque tube systems are independent.
 B.  The torque tubes are aluminum tubes connected with steel sleeve and spline couplings. Safety straps are installed to prevent damage to surrounding airplane systems if a torque tube fails.
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MAINTENANCE MANUAL

 C.  The angle gearboxes transmit power from torque tube to torque tube to allow for changes in direction. Each angle gearbox consists of a set of nonreducing, straight bevel gears contained in an aluminum housing. The housing is drained, vented, and has removable access coverplates to allow lubrication of the gears.
 7.  Transmissions and Ball Screw Assemblies (Fig. 3)
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 A.  Two transmission assemblies at each TE flap convert torque tube rotation to linear motion to extend and retract the flap. Each transmission assembly consists of a transmission gearbox, a universal joint, a ball screw and ball screw nut. The ball nut on each ball screw is trunnion mounted directly to midflap structure. Each transmission assembly is mounted on a flap track. The flap track fairings enclose the transmission assemblies.
 B.  The transmission gearbox contains mating bevel gears and a torque limiter. In the event of a jammed flap, the torque limiter locks against the transmission housing which in turn locks the drive system and stalls the flap drive motor. The inboard transmission assembly on each flap also contains a no-back friction brake consisting of a ratchet and a disk brake. The brake disk prevents airloads from retracting the flaps, but when power is applied to retract the flaps, the power unit overcomes the disk brake friction, allowing the flaps to be retracted. The brake disk does not oppose extension of the flaps but ratchets when the flaps are extended.
 C.  The ball screws are connected to the transmission gearboxes by a universal joint. There are two separate ball circuits between the ball screw and the grease-packed ball screw nut. Total ball screw travel is restricted by stops on the ball nut and at each end of the ball screw.
 8.  No-Coast Drag Brake (Fig. 2)
___________________
 A.  A no-coast drag brake is incorporated in the inboard flap drive system. The brake prevents the inboard flap from coasting down when the airplane is on the ground and the flap control module bypass valve is in bypass position. The brake consists of a ratchet, pawl gears and brake discs. When power is applied, the power package overcomes the disk brake friction, allowing the flaps to extend. During flap retraction, the brake ratchets to provide minimum resistance to the power unit.
 9.  Flap Tracks and Fairings (Fig. 3)
________________________
 A.  Each flap is mounted to two flap tracks. The flap tracks are curved, forged steel beams which attach to the lower surface of the wing. A flap transmission is mounted on each flap track. The flap tracks and transmissions are housed in aerodynamic fairings.
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A

747-400
MAINTENANCE MANUAL

BALL SCREW
TRANSMISSION
SEE
C
FLAP TRACK

AFTFLAP
BALL SCREW NUT
SEE
B

A
NOTE: LEFT INBOARD TRAILING EDGE FLAP SHOWN. OTHER TRAILING EDGE FLAPS SIMILAR.
Trailing Edge Flap
Figure 3 (Sheet 1)

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