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13.  Flap Alternate Drive Unit
A.  The flap alternate drive unit uses electrical power to drive the flap system if a failure prevents normal hydraulic operation of the flap system. The unit is mounted on the flap power unit which is located on the aft bulkhead in the right wheel well. The alternate drive unit is energized by actuating the alternate flaps arm switch and control switch located on overhead panel. A 115/200 volt ac motor and a gearbox are the primary alternate drive unit components. The gearbox incorporates a double planetary reduction gear train and a disconnect and overload clutch.
B.  The reduction gear train consists of a double planetary (epicyclic) gear. (See figure 8.) The ring gear of the first planet system is fixed to the motor housing. The input planet system carrier gears rotate around an input sun gear cut on the motor drive shaft. Attached to the input planet system carrier gears is the output sun gear. Rotation of the output sun gear drives the second planet system carrier gears to which the output shaft is attached. The output ring gear is a floating gear which is held fixed by a cable assembly during motor operation. The two terminals on the cable assembly are held by spring mechanisms which consist of a sensing spring, return spring and a spring collar. A threaded collar is provided to adjust spring tension. Since the normal spring load on the cable is not sufficient to prevent rotation of the output ring gear, a mechanism is provided to accomplish this function. The mechanism consists of a yoke, energizing pin, bellcrank and a solenoid. One arm of the bellcrank is attached to the solenoid and the energizing pin is inserted into a hole in the other arm of the bell crank. The opposite end of the energizing pin is attached to the yoke. The ends of the yoke are attached to the cable terminals. The electric motor and solenoid are energized simultaneously from 115 volt rectified ac power. Energizing the solenoid places the cable under tension by mechanically increasing the distance between the yoke and the output ring gear. The increased cable tension locks the output ring gear, allowing the motor to drive the output shaft. If binding occurs in the gear train, an overload clutch prevents damage to the unit. The output ring gear will slip when the load exceeds 1200 pound-inches. This is accomplished through the load sensing spring, which compresses to relieve tension in the cable. When the flap system is being driven hydraulically, a reduction gear in the power unit drives the output shaft. In this mode, neither the electric motor nor the solenoid is energized. With the solenoid de-energized, the cables are not under tension and the output ring gear is allowed to rotate with the carrier gears. This action prevents transmission of motion to the electric motor shaft.
500 
Aug 15/67  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  27-51-0 Page 17 

 

G11450
Alternate Flap Electric Drive Unit  500 
27-51-0  Figure 8  Nov 15/66 
Page 18 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

14. Limit Switches
A.  Limit switches are used to open the circuit to the flap alternate drive unit at either extreme of flap travel. The limit switches are located on the forward side of the flap control unit (Fig. 1). The switches are actuated by cams mounted on the control valve follow-up mechanism drum shaft.
15.  Flap Asymmetry Control System
A.  The flap asymmetry control system stops operation of the trailing edge flaps when a specified difference exists between the position of the left and right flaps. The system consists essentially of two-position transmitters mounted in the outboard flap drive system (Fig. 1), a dual synchro-type position indicator with comparator switch (Ref 27-58-01, D&O), and a flap asymmetry shutoff relay. (See Fig. 8B for system circuit.) An asymmetry test circuit, consisting of test switch and light mounted on the E-3 electronic equipment rack in the electronics bay, is an integral part of the position indicating system (Ref 27-58-01, D&O).
16.  Flap Takeoff Warning Switch
A.  A flap takeoff warning switch is mounted to the flap control unit (Fig. l). The switch is actuated by a cam mounted on the control valve follow-up drum shaft. The switch is adjusted to actuate with the flaps in a position other than the takeoff range. With the airplane on the ground and the throttle advanced, a warning horn will sound intermittently if the flaps are not in the takeoff range (Ref 31-26-0, Aural Warning Systems).
17.  Flap Load Limiter System
A.  The trailing edge flap system is protected from excessive airloads by a flap load limiter system. The load limiter system automatically retracts the flaps from 40 to 30 units at airspeeds in excess of 152 to 162 knots.
B.  With the flap control lever positioned to the 40-unit detent and the airplane off the ground, the load limiter system is armed. When the airspeed switches sense an airspeed in excess of 152 to 162 knots, the hydraulic solenoid valve attached to the trailing edge flap control valve is energized. Energizing the solenoid valve positions the trailing edge flap control valve to the 30-unit position, allowing pressurized fluid to flow to the hydraulic motor. As airspeed decreases to below 147 to 157 knots the solenoid valve is de-energized, the control valve is positioned to the 40-unit position and the flaps extend to 40 units.
　
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