FUNCTIONAL DESCRIPTION
The elevator and tab subsystem consists of the following components:
FIN Component Panel Zone Access Door
LH (RH) control column 120, 210 211-GFZ, 211-FZF,
(212-EFZ, 212-FFZ)
LH (RH) cable tension regulator 120 211-LFZ, (212-KFZ)
control rods 120, 310, 320 various
control cables 120, 130, 140, 310 various
pulleys 120, 130, 140, 310 various
pressure bulkhead fairleads 230 231-EFZ
nose down spring 310 312-AL
quadrant assembly 310 312-AL
elevator disconnect unit 310 312-AL, 324-AL
25CX LH elevator position transmitter 310 312-AL, 324-AL
26CX RH elevator position transmitter 310 312-AL, 324-AL
8CW elevator disconnect micro switch 310 312-AL, 324-AL
LH and RH Control Column
from Tension Regulator
to Quadrant Assembly Tension Regulator
Control Columne
Cable Fairleads
Pressure Bulkhead fairleads
Fig. 30 Elevator - Control Column to Pressure Bulkhead
The control columns are pivot-mounted below the flight compartment floor between frames 7 and 8. The movement of each column is transmitted to the associated elevator control cable tension regulator by a short push-pull rod.
LH and RH Cable Tension Regulator
The elevator tension regulator is nearly identical to the aileron tension regulator (refer to ??) with the following differencies.
- It is connected to the control column with a push-pull rod
- The elevator gust lock engages with a notch in the RH (first officer's) tension regulator Control Cables
The elevator control cables transmit the flight crew elevator commands from the tension regulators to the quadrant assembly located between frames 46 and 47. The cables are 7 x 19 flexible steel wire ropes made from corrosion resistant steel and have a nominal diameter of 4 mm (0.157 in.). The LH and RH elevator control runs each consist of four separate cable sections. Cable sections are joined by turnbuckles and terminated by swaged end fittings.
Pulleys
The control cables are guided by pulleys equipped with cable guards. The pulleys are made of a phenolic material and run in sealed ball bearings. The cable run from each tension regulator to the associated cable quadrant is guided by a total of ten pulleys.
Control Rods
Each control column is connected to its associated cable tension regulator by a short aluminium push-pull control rod. Two further rods connect the quadrant assembly in the rear fuselage to the elevator disconnect unit and a series of rods complete the run to the elevators. The Flettner tab on each elevator is also controlled by rods.
Three types of rod are used:
- non-adjustable fixed length - one end adjustable, one end fixed - both ends adjustable.
Rod ends are either of the clevis or eye type. Eye type rod ends are equipped with self-aligning sealed ball bearings.
Levers and Bell cranks
The control rods in the vertical stabilizer are supported by idler levers and bell cranks running in sealed ball bearings. The connection points for the rod clevis ends are formed by self-aligning sealed ball bearings.
Pressure Bulkhead Fairleads
The elevator control cables exit the pressure compartment through special fairleads at the rear pressure bulkhead. Each fairlead consists of a ball headed cable sleeve sandwiched between two plates. The plates are fixed to a bracket installed on and sealed to the lower part of the pressure bulkhead. The cables pass through the sleeve which acts as a cable seal.
Quadrant Assembly
Pitch Servo
Stick Pusher Quadrant Assembly
Disconnect Unit
Nose Down Spring Position Transducers
Force Detection Rod
Fig. 31 Elevator - Pressure Bulkhead to Vertical Stabilizer
The quadrant assembly is installed in the upper part of the fuselage between frames 46 and 47. The assembly consists of two quadrants that are installed on a common shaft. The LH quadrant terminates the cable run from the captain's control column and is fixed to the shaft. The RH quadrant terminates the cable run from the first officer's control column and is free to rotate on the shaft. The autopilot pitch servo is connected by a cable to the elevator control run at the RH quadrant.
Two push-pull rods transmit the elevator commands from the LH and RH quadrants to the two halves of the elevator disconnect unit aft of frame 47. The LH quadrant has a connection to which a rod and tension spring arrangement is attached. The other end of the spring is attached to frame 47. The spring moves the elevators to the nose down position when the aircraft is parked.
The LH side of the quadrant shaft extends through the shaft mounting bracket. A lever is installed on but does not move with the extended portion of the shaft. The lever is connected to the stall prevention stick pusher and only moves when the pusher is activated.
Elevator Disconnect Unit
Push-Pull Rod to LH Elevator LH Elevator Position Transmitter
LH Half of Disconnect Unit
Input Rod from LH Quadrant Input Rod from RH Quadrant
RH Half of Disconnect Unit
RH Elevator Position Transmitter Push-Pull Rod to RH Elevator
to DAU1 to DAU2
Microswitch 8CW to DAU 2
Fig. 32 Elevator Disconnect Unit
The captain's and first officer's elevator control cable runs are routed completely separately along the left and right sides of the fuselage respectively. They are joined in the rear fuselage by an elevator disconnect unit located on the upper aft face of frame 47. Under normal circumstances the movement of one control column moves both elevators and the other control column. Should one elevator control become jammed the two control circuits can be separated by the application of a higher than normal force to a control column.
The unit has two halves which are held engaged by a spring and cam arrangement. Each half has connection points for two push-pull rods. The forward connection points are for the command input rods from the captain's and first officer's elevator control circuit. The aft connection points are for the output rods to the LH and RH elevator. Under normal operating conditions the two halves of the unit are firmly engaged and move together as a single unit. Should one of the elevator control circuits jam, the two halves can be disconnected from each other by the application of a higher than normal force at a control column. The disconnect force is approximately 50 daN (112 lbs). The applied force causes the cam to override the spring force and move out of its detent. The two halves of the unit are now disengaged, effectively isolating the jammed control circuit. In this situation the captain's control circuit is connected to the left elevator only and the first officer's to the right elevator only. The aircraft can be controlled about the pitch axis using the free control column. Once activated, the disconnect unit can only be reset on the ground (refer to AMM).
The unit has an integral micro switch 8CW which is operated if the disconnect unit is activated. The switch sends a signal to the electronic indicating, caution and advisory system EICAS.
Short rods connected to an auxiliary connection point on each half of the unit drive the LH and RH elevator position transmitters 25CX and 26CX.
Elevator Disconnect Micro switch 8CW
A micro switch in the elevator disconnect unit monitors the status of the unit. It sends a discrete signal to the EICAS for indicating purposes. The switch contacts are connected to ground under normal operating conditions and open under elevator disconnect conditions.
LH and RH Elevator Position Transmitters 25CX and 26CX
An elevator position transmitter is installed for each elevator. Each transmitter is driven by a short rod connected to the associated half of the elevator disconnect unit. The LH and RH transmitters are identical 0 to 10 kΩ three-wire potentiometers whose resistance changes as a function of the elevator position.
They send a variable resistance signal to the EICAS for processing.
OPERATION
Power Supplies
Electrical power is not required for the elevator control system. Power for the indicating part of the system is provided by the EICAS
Elevator Controls
Note:
The LH (captain's) and RH (first officer's) elevator controls from the flight compartment to the rear fuselage are similar. The operation of the LH subsystem is described. Differences for the RH side are covered in the text or given in parentheses.
Flight Compartment to Vertical Stabilizer Control Run
Control column movement is transmitted by a push-pull rod to the cable tension regulator located at frame 9. From the cable tension regulator, the movement is continued aft below the flight and passenger compartment floor by control cables and pulleys. The cables pass through guides in some frames under the floor. Cable fairleads equipped with small pulleys are used to guide the cables through the machined parts of frames 24 and 26. The cable run is virtually straight as far as a point between frames 31 and 32.
At this point the cables are routed inboard and then upwards to follow the contour of the fuselage. The cables exit the pressure compartment through sealed fairleads at the rear pressure bulkhead and terminate at a cable quadrant assembly located between frames 46 and 47. The autopilot pitch servo is connected by a cable to the elevator control run at the RH section of the quadrant assembly.
A rod and tension spring arrangement is connected between the LH section of the quadrant assembly. The spring moves the elevators to the nose down position when the aircraft is parked. This is the position for engaging the elevator gust lock.
Two push-pull rods transmit the elevator commands from the quadrant assembly to the two halves of the elevator disconnect unit. Two further push-pull rods transmit the commands to the control linkage in the vertical stabilizer.
The stall prevention stick pusher is connected to a lever installed on the quadrant assembly shaft. Under normal operating conditions the lever does not move with the shaft. If the pusher is activated the lever drives the elevators to a 10° down position and pushes the control columns forward.
The push-pull rods from the disconnect unit exit the fuselage forward of frame 48. These rods are the first of five LH and five RH push-pull rods which form the control run from the elevator disconnect unit to the LH and RH elevators. The ten rods are supported at intervals by idler levers and bell cranks in the vertical stabilizer. The last (top) rod on the LH and RH side connects to the associated elevator control horn. Each control horn is attached to the leading edge spar of the elevator at the control surface hinge line.
LH and RH Elevator Tab
A trim tab is installed on the inboard trailing edge of each elevator. The dual shaft trim actuators are installed in the trailing edge of the horizontal stabilizer. Each actuator drives its associated tab through a reduction lever installed in the leading edge of the elevator. Twin push-pull rods connect the lever to the tab.
SYSTEM INDICATIONS
Certain components of the elevator control system send signals to the electronic indicating, caution and advisory system (EICAS). The signals are sent to data acquisition units (DAU's) and are used:
- to display the position of the elevators by synoptics
- to indicate the status of the elevator disconnect unit by a synoptic - to display a caution message if the elevator disconnect unit is activated.
The position of the elevators and the status of the disconnect unit are displayed on the FLIGHT CONTROL page of the EICAS.
Elevator Position Indicating
An elevator position transmitter is installed for each elevator. Each transmitter is a three-wire potentiometer whose resistance changes as a function of the elevator position. The LH transmitter sends a variable resistance signal to data acquisition unit 1 (DAU 1) in the EICAS system for processing. The RH transmitter sends an identical signal to DAU 2. The resistance values correspond to the following elevator deflections:
- 0.5 kΩ corresponds to an elevator down deflection of +25°
- 5 kΩ corresponds to an elevator up deflection of -2.5°
- 9.5 kΩ corresponds to an elevator up deflection of -30°.
The position of each elevator is indicated by a blue synoptic on the FLIGHT CONTROL page of the EICAS. If the transmitter signal is invalid, the blue synoptic is replaced by an amber X. Under normal operating conditions the LH and RH elevator synoptics are joined by a white bar. The bar changes to amber if the elevator disconnect unit is activated below.
Elevator Disconnect Unit Monitoring
A micro switch 8CW in the elevator disconnect unit monitors the status of the unit. It sends a discrete ground or open signal to DAU 2 for processing. The signal line is connected to ground under normal operating conditions and open circuit if the disconnect unit is activated. If the captain's and first officer's elevator control runs are disconnected:
- an amber ELEV DISCONNECT caution message is displayed on the CAS field of the primary EICAS page and on the FLIGHT CONTROL page
- on the FLIGHT CONTROL page the white bar which connects the LH and RH elevator synoptics changes to amber.
CAS FIELD Indication MFD PAGE Indication Fault or Condition AMBER
ELEV DISCONNECT
AMBER
ELEV DISCONNECT
AMBER elevator connect bar
Elevator disconnect unit activated
- BLUE
LH elevator synoptic indicates position of LH elevator. If invalid the rudder synoptic is replaced by an amber X.
- BLUE
RH elevator synoptic indicates position of RH elevator. If invalid the rudder synoptic is replaced by an amber X.
328 DORNIER LUFTFAHR T
64- FOR TRAINING PURPOSES ONLY -Effectivity:328-100 Mod.10
TM-Flight Controls
Fig. 33 Elevator Controls - EICAS Indications