L-1011 Flight Controls: Rudder (27-28/29)

To get all the details, you might want to enlarge the picture above. The Rudder, on the L-1011, is a large single surface with servo and actuators near the lower end. There are no tabs on the L-1011 rudder. The rudder is fully hydraulically powered by the A, B and  C hydraulic systems.

The rudder is powered by two dual-tandem actuators (see image above) which operate as three in depended actuators and a controlling triple servo module. Hydraulic system A, B or C are capable of providing full rudder operation. Hydraulic power is manually controlled by the hydraulic limiting system.

The rudder servos are mechanically operated by the rudder peals through cables or electrically signaled by the Yaw Stability Augmentation System (YAW SAS).

Rudder Trim 

Pilot inputs can be made from either set of rudder pedals but control is provided by a cable run coming form the Co-Pilot's rudder pedals. Rudder trim is mechanical and simply establishes a new neutral position for the rudder feel mechanism. Rudder trim displease the ruder pedals.

Surface Position Indicator (SPI)

Top of the SPI, single indicator shows rudder position to 30º right and left.

Rudder Hydraulic Limiter 

The limit is controlled via a switch on the overhead that is normally latched in dark/no lights position. Amber "PUSH" with malfunction or loss of system pressure. White "OVRD" is switch pushed and unlatched. Powers back all available systems.

Rudder Power OFF Switch 

The Rudder Power OFF switch removes all power from the rudder. This also powers down the YAW SAS.


YAW SAS

The YAW SAS has two mods of operation. The first is called series and provides full time yaw damping and turn coordination. Series means that the YAW SAS is providing electric inputs to the rudder servo, but motion is not supplied to the rudder pedals - they remain in neutral. Manual inputs may be applied through the rudder pedals to override the servo with normal pedal forces. In this mode the YAW SAS has only 8º of authority over the rudder. The second mode is called parallel mode and provides runway alignment, rollout guidance and engine out go-around capability during autopilot operation. Parallel mode is different in that the rudder pedals are now connected through the servo and the pilot receives rudder movement feedback. The YAW SAS now also has the same authority as the Pilot ... or the full 30º.  Manual inputs may be applied through the rudder pedals to override the servo, but rudder pedal forces will be approximately one hundred pounds.