Logic N2 Power Turbine Control

Question 1

Purpose

Answer 1

Adjusts engine RPM by positioning N2 power lever on FCU. It is an electromechanical control system.

Consists of:

1. Engine beep switches on collective control head
2. Emergency engine trim switches and guarded MANUAL/AUTO switch
3. Dual droop eliminator Linear Variable Differential Transformer (LVDT)
4. Power turbine control actuators and linkages

Question 2

Droop Eliminator (LVDT)

Answer 2

Dual transformer with opposing sides for each engine which minimizes lag in engine response to power requirements created from collective control movements.

LVDT is mechanically linked to the collective control system in the lower portion of flight control closet

Question 3

Control Box

Answer 3

2 boxes, one per engine, located in upper radio compartment.

Analyze following conditions before making an output to N2 actuator:

1. Required fuel control position
2. Position of the fuel control arm as result of inputs from droop eliminator
3. Collective control head beep trim setting
4. MX adjustments
5. N2 actuator position

Question 4

Power Turbine Control Actuator

Answer 4

Contains motor, gear reduction train, sliding friction damper, and Rotary Variable Differential Transformer (RVDT)

RVDT provides feedback signal to control box relative to position of actuator, insuring correct position of actuator shaft

Question 5

Control Linkage

Answer 5

Transmits motion of actuator to N2 shaft on the FCU

Question 6

Engine Trim Switches (Beep Trim)

Answer 6

Located on collective and are electrically connected with the engine trim actuator when ECLs in FLIGHT

Allow pilot to adjust RRPM and synchronize engines as desired. Beep inputs are transmitted to control box and resulting output drives the fuel control actuator

Question 7

AUTO/MAN Switch

Answer 7

Located on overhead panel

In AUTO, N2 actuator angle is regulated by control box output. In MAN position, N2 speed is directly controlled by INC/DEC switches on Emergency Engine Trim panel

When switch is placed to MAN, the control box is disabled and last beep position is maintained in memory. LVDT is removed from system and any collective movement must be coordinated with Emergency Engine Trim Switches.

Question 8

Reset Logic N2

Answer 8

1. AUTO/MAN switch to MAN
2. Pull 5 amp EMER TRIM CB on overhead panel
3. Wait 15 sec minimum
4. Reset EMER TRIM CB
5. Reset AUTO/MAN switches to AUTO