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10.  Flap Power Unit
A.  The flap power unit transfers mechanical energy from the flap hydraulic motor and alternate drive unit to the flap drive system (Fig. 1). The power unit is an aluminum housing containing a reduction gear, two pinion gears, an output shaft with a worm gear, a worm wheel and a worm wheel shaft. The reduction gear is splined to the output shaft. Attached to the power unit is the flap hydraulic motor and the flap alternate drive unit. During normal flap system operation, power from the hydraulic motor is transmitted through a pinion gear to the reduction gear. During flap alternate drive operation, power from the alternate drive unit is transmitted through a second pinion gear to the reduction gear. Rotation of the reduction gear drives the flap system through the power unit output shaft.
11.  Flap Drive Gearboxes
A.  General
(1)  
There are four flap drive gearboxes, two are angle gearboxes and two are right angle gearboxes.

(2)  
The gearboxes are nonvented housings, with sealed ball bearings and butter lubricated bevel gears.

B.  Angle Gearboxes
(1)  The angle gearboxes are mounted on the aft side of the landing gear beam forward of the ground spoiler panels. The torque tubes attaching to the angle gearbox provide the flap drive between the inboard flap transmissions.
535  Figure 6 
May 01/75  (Deleted)  27-51-0 
Page 13/14 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

C.  Right Angle Gearboxes
(1)  The right angle gearboxes are mounted on the wheel well aft bulkhead aft of the inboard flap inboard transmissions. The gearboxes provide a 90-degree change in torque tube direction in the flap drive between the flap power unit and inboard flap inboard transmissions. The right angle gearbox in the right wheel well is a reversing gearbox which reverses torque tube rotation for the right wing.
12.  Flap Transmission Assembly
A.  The flap transmission assembly converts flap torque tube rotation into linear motion to extend or retract the trailing edge flaps. Each transmission assembly consists of a transmission gearbox, a universal joint and a ball nut and screw actuator. (See figure 7.)
B.  The transmission assemblies are mounted on the flap tracks just aft of the landing gear support beam and the wing rear spar. (See figure 1.) Each transmission assembly is enclosed in a flap track fairing. Flap drive system torque tubes attach to the input shafts on the transmission gearbox.
C.  The transmission gearbox contains mating bevel gears and a torque limiter. The inboard transmission assembly on each flap incorporates a no-back friction brake. The torque limiter consists basically of two springs wound together, an internal shaft with two bevel gears, an output shaft and a housing. If a flap jams, excessive torque on the screw actuator will cause the springs to expand and bind against the torque limiter housing. The torque limiter is designed to operate in either direction of flap travel. Excessive torque is absorbed by the torque limiter until the flap hydraulic motor stalls. At extended flap positions, the no-back friction brake prevents flap retraction due to airloads. The brake consists of a brake disk, ratchet wheel and two pawls. At extended flap positions, uploads transmitted to the jackscrew force the brake disk against the ratchet wheel resulting in a braking action. The brake action does not oppose flap extension since the pawls do not engage the ratchet wheel in this direction of rotation. As the flap is retracted, a tension load exerted on the actuator screw disengages the brake disk from the ratchet wheel. This action allows the jackscrew to rotate. The transmission gearbox is a sealed unit filled with MIL-H-5606 hydraulic oil.
500 
Feb 15/70  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  27-51-0 Page 15 

G11437
Flap Transmission Assembly  500 
27-51-0  Figure 7  Feb 15/67 
Page 16 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

D.  The ball nut and screw actuator consists of a jackscrew , a downstop nut and recirculating ball bearing nut. The universal joint attaches the jackscrew to the transmission gearbox. The universal joint allows angular deflection of the jackscrew during flap operation. The bal1 bearing nut is attached to the midflap through a gimbal assembly. During flap operation, the ball bearing nut is restrained from turning and travels fore and aft on the rotating screw to extend and retract the flaps. Total jackscrew travel is restricted by upstops and downstops on the ball nut and screw actuator. Upstop lugs on the ball bearing nut and on the universal joint limit flap travel when the flaps are retracted. Downstop lugs on the ball bearing nut and on the downstop nut limit flap travel when the flaps are extended. The ball bearing nut has drilled passages and externally mounted tubes that allow recirculation of the steel balls. Scrapers and wipers are incorporated at each end of the ball nut to remove foreign material from the jackscrew. An oil reservoir in the ball bearing nut provides lubrication of the nut and screw actuator.
　
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