Chapter 9: Flight Control System

Question 1

what are cables that are for flight control normally fabricated from?

Answer 1

carbon fibre / corrosion resistant steel wire

Question 2

what do pulleys do?

Answer 2

change direction of cable

Question 3

what are turnbuckles for?

Answer 3

adjusting tension of cables

Question 4

what is a bell crank used for?

Answer 4

transmit and change the direction of force

Question 5

what is push pull rod for?

Answer 5

transmit force and motion between bell crank and torque arm

Question 6

what is a quadrant for?

Answer 6

used at the base of control stick to impart force and motion to cable system

Question 7

what is a torque tube for?

Answer 7

changing linear motion to rotary motion

Question 8

what are cable guards/guard pins for?

Answer 8

installed in flanges of pulley to prevent cable from jumping out

Question 9

what are fairleads for?

Answer 9

guide control cables, dampen vibration, cable alignment, seal openings

Question 10

what is a cable tension regulator for?

Answer 10

ensure tension of cable is kept constant at different temperatures

Question 11

types of mechanical control system in aircraft

Answer 11

1) push-pull rod
2) cable and pulley
3) chain and sprocket

Question 12

how does a direct cable control system work?

Answer 12

cockpit controls are connected to control surfaces with high strength steel cables

Question 13

how does a push pull rod system work?

Answer 13

uses bell cranks, levers, torque tubes

controls are connected to the device with a hollow aluminium tube

Question 14

cable and pulley VS push pull rod

Answer 14

1) cable lighter than push pull rod
2) cable can only transmit pull, push pull rod can transmit both push & pull
3) cable system is more accurate transmission
4) cables shows warning signs before breaking, push pull rod breaks suddenly
5) cable tension reduces when fuselage contracts more than steel on cold weather, push pull rod remains the same

Question 15

2 circuits in hydraulic flight control system

Answer 15

mechanical - links cockpit controls with hydraulic circuit

hydraulic - actuators converts hydraulic pressure to control surface movements

Question 16

how does hydraulic power flight control system work?

Answer 16

pilot input to servo control unit > SCU moves control surface in direction and distance proportional to input signal

Question 17

what does the servo control unit do in hydraulic power flight control system?

Answer 17

amplify mechanical input by directing high pressure hydraulic fluid to move control surfaces

Question 18

what happens in the event of a hydraulic failure?

Answer 18

hydraulic actuator is bypassed and input force goes straight to control surface

Question 19

what is an artificial feel unit for?

Answer 19

simulate air load for pilot for hydraulic transmission system

Question 20

two types of feel in control systems

Answer 20

1) spring feel (low speed & high deflection demands)
2) “Q” feel (high speed & low deflection demands)

Question 21

advantages of fly-by-wire system

Answer 21

1) save weight (no rods, cables, pulley)
2) reduced maintenance downtime (no need to rig)

Question 22

what is the main concern for FBW?

Answer 22

reliability

loss of all flight computers will result in total loss of a/c control