MD-11 Flight Crew Operations Manual
k
Flight Controls -
Description and Operation
Flt.10.9
Directional Trim System
Directional trim is accomplished with the rudder trim knob on the center pedestal.
The rudder trim knob repositions the neutral point of the rudders. Rudder trim
motion is limited to 13 degrees in both directions.
Rudder trim is indicated on the rudder trim indicator, on the surface position
indicator, and by physical displacement of the rudder pedals.
Longitudinal Trim System
Longitudinal trim is provided by a two-speed, hydraulically powered adjustable
stabilizer. The stabilizer is actuated by two hydraulic motors powered
independently by hydraulic systems 1 and 3. Hydraulic system 2 provides backup
hydraulic power to the stabilizer through the 2-1 NRMP.
The stabilizer operates automatically at two different trim rates as a function of
airspeed and/or altitude to provide optimum performance. To accomplish smooth
and appropriate longitudinal trim operation for all flight conditions, the two trim
rates are provided for each mode of operation. The rate change occurs at 250 knots
airspeed or at 33,000 feet, and is also dependent upon which stabilizer control
input is in use.
A compensator with a low fluid level switch automatically shuts off hydraulic
flow from hydraulic system 2 to the 2-1 NRMP if fluid level is low in the
compensator.
Four modes of operation are available as follows:
1. Autotrim [Longitudinal Stability Augmentation System (LSAS)]. When
LSAS is engaged in pitch attitude hold (force on column less than 2 pounds),
the automatic pitch trim moves the horizontal stabilizer to trim out steady
state elevator commands. The FCC operates one trim motor in this mode.
Rate (high or low) is based on altitude and airspeed.
2. Autotrim, using the autopilot. When the autopilot is engaged, the autotrim
function controls the stabilizer based on average elevator position offsets.
When the AFS OVRD switch on the FCP is pushed down, AP automatic
pitch trim turns off.
3. Manual trim, using switches. Full-time actuation of both trim motors is
available to the pilot through use of the manual trim switches on both control
wheels. These switches move the stabilizer in the commanded direction and
disengage the autopilot from any engaged mode (except DUAL or SINGLE
LAND).
October 02, 2006
To Next Page
Loading...