18. Airspeed Switches
A. Two airspeed switches are installed in the lower compartment just below the flight compartment floor on the right-hand side forward of the station line common to the forward bulkhead of the nose wheel well. One airspeed switch is connected to the No. 1 auxiliary pitot static system and one to the No. 2 auxiliary pitot static system.
19. Flap-40-Unit Switches
A. Two flap-40-unit switches are installed on the flap control quadrant. The switches are actuated with the flap control lever positioned to 40 units, and complete a segment of the flap load limiter electrical circuit.
20. Operation
A. The trailing edge flaps are normally actuated by a hydraulically operated drive system (Fig. 9). The drive system is controlled by a manually operated flap control lever located on the upper right side of the control stand. When the control lever is rotated, flap control cables displace the flap control unit linkage. This positions the trailing edge flap control valve to port pressurized fluid from hydraulic system A to the flap hydraulic motor. The hydraulic motor drives a torque tube system through a reduction gear train. The torque tubes drive two transmission assemblies at each flap. Ball bearing nuts and gimbal assemblies transfer rotary motion from the flap transmission assemblies into linear motion to extend the flaps. As the flaps extend, cables from the flap power unit follow-up cable drum rotate a flap control valve follow-up mechanism. A cam in the follow-up mechanism then displaces the trailing edge flap control valve slide. When the desired flap position is reached, the control valve closes to prevent flow of pressurized fluid to the flap hydraulic motor.
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27-51-0 Page 20 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 20/82
G11581 G11941G12032
567 Trailing Edge Flap Electric Asymmetry System Circuit
Feb 20/85 Figure 8A 27-51-0
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
Trailing Edge Flap Electric Asymmetry System Circuit 532
27-51-0 Figure 8B Feb 20/84
Page 20B
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
535 Trailing Edge Flap System Hydraulic Schematic
May 01/75 Figure 9 27-51-0
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
Retraction of the flaps due to airloads is prevented by a no-back friction brake in the inboard transmission assembly at each flap. If a transmission assembly should fail, a torque limiter in the remaining transmission assembly on that flap will stall the flap drive system to prevent structural damage. Stopping the drive system also prevents operation of the remaining flaps, thus maintaining the airplane in a normal flight attitude.
B. The flap segments are mechanically separated during extension. As the flaps start to extend, an actuating mechanism moves the aftflap to form a slot between the aftflap and midflap. At about 8 units of midflap extension, the foreflap sequencing toggles contact stops on the main flap tracks. The stops prevent additional aft movement of the foreflap. Continued midflap extension creates a slot between the foreflap and midflap. As the midflap approaches full travel, the aftflap again moves relative to the midflap, increasing the width of the slot between the two segments.
C. A flap alternate drive unit is provided to operate the trailing edge flaps electrically if a failure prevents normal hydraulic operation. The flap alternate drive unit is controlled from two switches located on the overhead panel. (See figure 10.) The alternate flaps arm switch and control switch operate the system. Actuation of the alternate flaps arm switch to ARM supplies 28 volt dc power to the alternate flaps control switch. Simultaneously, 28 volt dc power is supplied to position the trailing edge flap bypass valve to BYPASS. This interconnects the flap hydraulic motor ports to allow circulation of hydraulic fluid and prevents fluid flow from the control valve to the hydraulic motor. Actuation of the alternate flaps control switch to DOWN energizes the alternate flap down relay to complete a circuit which extends the flaps. When the flaps are fully extended, a down limit switch opens to break circuit continuity. Positioning the alternate flaps control switch to UP closes the alternate flap up relay to complete a circuit to retract the flaps. When the flaps are fully retracted, an up limit switch opens to break circuit continuity. The trailing edge flaps may be stopped in any intermediate position by returning the alternate flaps control switch to OFF.
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