Flight Control Systems (FCS) Introduction

Question 1

What are the primary flight control surfaces of fixed wing aircraft?

Answer 1

1. Ailerons
2. Rudder
3. Elevators

Question 2

What are secondary flight control surfaces?

Answer 2

1. Spoilers

2. Flaps

Question 3

What is usually used to reduce the force that a pilot must exert to make the aircraft pitch, roll or yaw?

Answer 3

Aerodynamically balanced or powered by the aircraft’s hydraulic &/or Electrical system

Question 4

What are some factors that make pilot’s inputs increasingly more difficult?

Answer 4

1. Larger flight control surfaces

2. Higher aircraft speeds

Question 5

What does lowering the flaps do?

Answer 5

Increase the camber/wing area to provide greater lift and control at lower speeds.

Question 6

What do the spoilers do?

Answer 6

Spoil the lift and increase drag

Question 7

What are some components of the mechanical flight control systems?

Answer 7

1. Cables
2. Turnbuckles
3. Pulleys
4. Push/Pull rods
5. Bellcranks
6. Gust Locks

Question 8

What does an increase in A/C speed do to control loads?

Answer 8

• Increases them.

- Pilot must use more effort to control surfaces at higher speeds.

Question 9

How can deflecting a large flight control surface against a fast airflow be made easier?

Answer 9

1. Aerodynamically balancing the surface

2. Using power to assist movement

Question 10

How do hydraulically powered flight controls work?

Answer 10

Use fluid pressure to increase control power.

Question 11

What does a Fly By Wire system refer to? How does it work?

Answer 11

• Describes a Flight Control System that uses a flight control computer to send and receive digital signals to control flight surfaces.
• Inputs by pilots controls/autopilot are converted to digital signals by a signal generator and transmitted to digital flight control computers.

Question 12

What does the flight control computer do?

Answer 12

• Receives digital information from NavAids and the air data computer
• Interprets the digital signals and transmit the commands to electro-hydraulic servos and the servos deflect flight control surfaces

Question 13

What are some examples of Flight Control Tabs?

Answer 13

1. Trim
2. Balance
3. Servo
4. Anti-balance/Anti-Servo
5. Spring

Question 14

What are trim tabs used for?

Answer 14

1) Trim or counteract the aerodynamic force on the control surface
2) Stabilize the aircraft is the axis of rotation associated with the primary control
3) Can either be fixed or flight adjustable.

Question 15

What are fixed trim tabs?

Answer 15

Changes on the ground and stay that way during flight.

Question 16

What are flight adjustable trim taps?

Answer 16

Adjustable trim tab that can be changed in flight to counter any variation in control loading that can occur through

1. Airspeed
2. Centre of gravity
3. Aircraft Configuration
4. Engine operation/failure

Question 17

What are balance tabs?

Answer 17

Hinged tabs at the trailing edge of the control surface to reduce control forces required.

Question 18

What are servo tabs?

Answer 18

Similar to balance tabs in location and effect but designed to operate the primary flight control surface and not just reduce the force needed to do so.

1. Back up means of primary control
2. Manual linkage to servo tab can be used to deflect it

Question 19

What are anti-balance/anti-servo tabs?

Answer 19

Used to increase control forces required in order to prevent inadvertent overstress.

Question 20

What are spring tabs?

Answer 20

Servo tabs that only activate after a certain point of deflection to increase control force available to deflect surface further.

Question 21

Where are flaps usually located?

Answer 21

Situated inboard on the wing TE adjacent to the fuselage and extend rearward and down from the inboard wing TE.

Question 22

What are the purpose of flaps?

Answer 22

1) Increase camber/wing area and provide greater lift and control at slow speeds
2) They enable landing at slower speeds and shorter the amount of runway required for take-off and landing.

Question 23

What are plain flaps?

Answer 23

• Form the TE of the wing when in retracted position
• Airflow over the wing continues over the upper/lower surfaces of the flap
• Flap is hinged so that the TE can be lowered which increases wing camber, providing greater lift.

Question 24

What are split flaps?

Answer 24

• Housed under the TE of the wing
• When operated, the split flap TE lowers away from the TE of the wing
• Airflow over the top of the wing remains the same
• Airflow under the wing follows the camber created by the lowered split flap, increasing lift.
• Creates significant drag requiring higher power setting and better engine response.

Question 25

What are slotted flaps?

Answer 25

- Increase wing camber and open up a slot between the wing and the flap - Allows high pressure air from the bottom of the wing to flow through the slot into the upper surface - Energy is added to the wing's boundary layer, delaying airflow separation (less drag) whilst increasing lift

Question 26

What are fowler flaps?

Answer 26

- Increase the wing area by extending out on rails/tracks - In first stage of extension, there is a large increase in lift but little increase in drag, making setting ideal for TO in a large jet - As the flaps continue to extend, the flaps move downward more and more, creating more lift but a lot more drag.

Question 27

What are leading edge (LE) slots?

Answer 27

- Ducts or passages in the LE of a wing that allow high-pressure air from the bottom of the wing to flow to the top of the wing - allowing boundary layer to remain on surface of the wing.

Question 28

What are leading edge (LE) slats?

Answer 28

Slats are movable and can be retracted when not needed - increasing camber of the wing.

Question 29

What is the point of spoilers and what are some of their uses?

Answer 29

- Increase drag, reduce lift. - Differentially provide roll control - Conjunction with/in lieu of ailerons, countering affect of adverse yaw - Deployed on landing to significantly reduce lift, increasing aerodynamic drag and increase braking effectiveness

Question 30

What are air brakes used for?

Answer 30

Used during landing - Increase drag - Increase angle of approach

Question 31

How are air brakes different from spoilers?

Answer 31

Air brakes increase drag without making much change to lift.

Question 32

What are the 3 primary flight controls?

Answer 32

- Elevator - Rudder - Aileron

Question 33

A Fly by wire system involves digital signals from an air data computer which operate what?

Answer 33

Servos/Flight Control Surfaces

Question 34

A mechanical flight control system uses what types of components to transfer inputs?

Answer 34

1. Pulleys 2. Cables 3. Turn buckles 4. Push/pull rods 5. Bellcranks

Question 35

What are flaps used for?

Answer 35

Increase lift and control at lower airspeeds

Question 36

Many large aircraft use fowler flaps. Why?

Answer 36

Allow for increased lift on TO without increasing drag substantially

Question 37

What are spoilers used for and what is a negative effect of spoilers?

Answer 37

Spoil lift/increase drag, reduction in lift.

Question 38

An airbrake will slow you down with little change to lift while increasing what?

Answer 38

Drag

Question 39

What is the function of wing slats?

Answer 39

Increase camber + lift of wing

Question 40

What are trim tabs used for?

Answer 40

Trim out control forces