L-1011 Flight Controls: Flaps and Slats (27-46)

The L-1011 has four panels of double slotted Fowler flaps on the trailing edge of both wings. The flap system is hydraulically powered by a Power Drive Unit located in the hydraulic service center. This unit drives torque tubes which in turn power the flaps through recirculating ballscrew actuators.

The slat power drive unit is powered by hydraulic systems A and C same as the flap system and is located in the left wing root outside the fuselage pressurized area. Torque tubes run the length of the leading edge.

Flap and slat systems both are controlled through a single flap/slat handle located on the center console right side. Selection of 0º or 4º flaps causes flaps to extend to the selected 4º while slats extend completely. Flap handle movement is transmitted to both the slat Power Drive Unit (PDU) and the flap PDU through cable runs, rods and links. Cable break detectors monitor for broken cables. A broken cable shuts down the PDU by removing hydraulic power from the two hydraulic driven motors and the spring applied, hydraulically released, brake.

Both the flap and slat PDUs are powered by two hydraulic systems, A and C. Flaps/Slats operate normally with only one hydraulic system powering, but movement of the surfaces is slower. The PDU hydraulic motors, through gears, drive torque tubes along the length of the wing on both the front and rear spars. As the torque tubes rotate, they drive recirculating ballscrew actuators. The actuators, one for each slat panel , and two for each flap panel, drive the respective surface up and down on rigid tracks attached to the spars.

For assemblies, one on the end of each torque tube, contain a position transmitter that drives the respective slat indicator needs, and flap indicator tapes. The assemblies also contain spring applied mechanical brakes and asymmetry detectors. The detectors count torque shaft turns at both ends and thereby monitor for asymmetry.

Should an asymmetry be detected, the mechanical brakes at the ends of the Torque Tubes Lockup. Also the PDU hydraulics are shutoff applying the PDU brake and the system is lowed in position stopping any asymmetry well within the aileron control limits.