Flight Control

Question 1

Three Sections

Answer 1

1. Mechanical system
2. Flight control servo system
3. Automatic flight control system

Question 2

Mechanical Control System

Answer 2

Cyclic, collective and tail rotor pedal flight controls routed aft and outboard, vertically up each side of the aircraft

Combined for each axis at the overhead torque shafts

Shafts transfer inputs from trim servos and flight controls through pilot assist servos and mixing unit

From mix unit, fore, aft and lateral inputs transferred to swashplate assembly via primary servos and bridge assembly

Yaw inputs to tail rotor servo transferred from mixing unit to tail rotor quadrant via cables

Question 3

Tail Rotor Control System

Answer 3

Provides directions control by varying pitch

Servo is mechanically actuated, requiring hydraulic pressure to operate pitch change shaft

Shaft moves tail rotor pitch beam, changing pitch angle through pitch-change links

Servo powered by #1 Hyd or Backup

Springs provide fly-home capability if both cables severed

Question 4

Flight Control Servo System

Answer 4

Primary servos, tail rotor servos and pilot-assist servos

Question 5

Primary Servos

Answer 5

Three servos, each having two stages that are independent and redundant (only linkage in common)

Question 6

Tail Rotor Servo

Answer 6

Two independent stages

If first stage loses pressure, backup pump automatically powers second stage

Question 7

Pilot-Assist Servos

Answer 7

Contain boost servos, SAS actuators and hydraulic (pitch and roll) trim actuators

Collective and yaw require lot more effort to move when not working

Servos (except pitch/roll trim) turned on/off by SAS/BOOST

Pitch and roll trim actuators turned on/off by TRIM

Question 8

Boost Servos

Answer 8

Collective, yaw and pitch

All boost servos and roll channel incorporate SAS actuator that provides rate damping

Question 9

Control Mixing (Mechanical/Electronic)

Answer 9

Name - Cause - Compensation Req - Compensation

Mechanical:

Collective to yaw - main rotor torque - nose yaws right when collective increased - tail rotor thrust increased

Collective to lateral - lateral lead (tail rotor propeller effect) - helo drifts right when collective increased - rotor disc tilted left

Collective to longitudinal - rotor downwash on stab - nose pitches up and helo drifts aft when collective increased - rotor disc tilted forward

Yaw to longitudinal - tail rotor lift vector - nose pitches down and helo drifts forward when left pedal applied - rotor disc tilted aft

Electronic:

Collective/airspeed to yaw - camber of tail pylon varies side load with airspeed - nose yaws left as airspeed increases - auto trim washes out as pylon side load increases with airspeed