Flight Controls

Question 1

Why do large jet transport aircraft have powered flight controls?

Answer 1

Do deal with the large loads and changes in CoG.

Question 2

What level of redundancy is required for powered flight controls?

Answer 2

Triple redundancy is required if manual reversion is NOT available.

Question 3

Would fly-by-wire require triple redundancy or could it use manual reversion?

Answer 3

triple redundancy would be required, because there are not direct cables (manual control), it is all electrically driven.

Question 4

What is Q feel and why does it exist?

Answer 4

Because hydraulic forces are used to move the control surfaces, Q feel is used to provide some sort of feedback to the pilot to stop them from overstressing the airframe.

Question 5

How does the Q feel system dictate what ‘feel’ is given to the pilots?

Answer 5

Based on airspeed.

Question 6

What is the purpose of ‘control balancing’?

Answer 6

To reduce control loads

Question 7

What is the purpose of the ‘flexible seal’?

Answer 7

To reduce the control pressure / hydraulic force

Question 8

What is jack stalling?

Answer 8

When air loads are so strong that they actually prevent the hydraulic system from moving the controls.

Question 9

What is the main benefit of a variable incidence tailplane?

Answer 9

Allows pitch to be trimmed over a large CoG range whilst still allowing full elevator control to be available. Compared to elevator trim tabs, it also produces less drag

Question 10

Do trailing edge devices increase or reduce the body angle on approach?

Answer 10

reduce (remember flaps typically give you better forward vision on final)

Question 11

What is the purpose of the fowler flaps?

Answer 11

Move back and down to increase surface area

Question 12

What is the purpose of slotted flaps?

Answer 12

Re-energise the boundary layer (gaps in between the flaps will accelerate air, like lots of little wings)

Question 13

What is a flap limiter?

Answer 13

A device which will automatically retract flaps (or prevent flap extension) if the speed is too high. NOTE that the flap position handle does NOT move.

Question 14

What is a hydraulic blow back valve?

Answer 14

Allows the flaps to get retracted when the air loads are excessive (a form of flap overspeed protection)

Question 15

Compared to a clean wing, what will trailing edge flaps do to the critical AoA?

Answer 15

Decrease (you will stall at a slower speed but lower nose attitude)

Question 16

Compared to a clean wing, what will leading edge devices do to the critical AoA?

Answer 16

Increase

Question 17

How do spoilers assist roll?

Answer 17

They are extended on the down-going wing to dump lift and increase drag.

Question 18

Why is height lost during a turn with spoilers?

Answer 18

Because they significantly reduce lift on the downgoing wing, resulting in height loss.

Question 19

What is aileron lockout?

Answer 19

A system which prevents OUTBOARD ailerons being used at high speeds. Inboard ailerons are active at all times.

Question 20

How are the spoilers stopped from being deployed at high speed?

Answer 20

Blow down: The air loads will simply prevent deployment of the spoilers.

Question 21

All powered flight controls have how many hydraulic units?

Answer 21

At least two (through 3 is required for certification)

Question 22

Why are there two switches for electric aileron trim?

Answer 22

To prevent inadvertent activation of trim.

Question 23

What is one of the risks associated with spoiler walk down?

Answer 23

Tendency for height to be lost when spoilers are used, therefore large roll inputs should be avoided at low aircraft speeds on approach.

Question 24

What is the benefit of speed brakes?

Answer 24

In addition to aerodynamic drag, it also places the weight on the wheels which assists with braking.

Question 25

To assist in yaw control redundancy, what systems are available?

Answer 25

Either have two components to the rudder (if one fails the other is still available), or have multiple actuators for the same rudder surface.

Question 26

When rudder trim is applied, to the pedals move?

Answer 26

Yes, they are displaced proportionally

Question 27

What is the purpose of a rudder ratio changer?

Answer 27

As speed increases, the hydraulic force available can overstress the rudder, so it will automatically reduce the amount of deflection available.

Question 28

What is a rudder comparator?

Answer 28

For systems which have an upper and lower rudder surface, it will detect if the rudder ratio changer has jammed, causing an uneven displacement of the rudder.

Question 29

What are the two types of yaw dampers?

Answer 29

Parallel type: rudder pedals are moved as the yaw damper moves (must be off for takeoff and landing)
Series type: rudder pedals are independent (therefore can be on at all times except gusty/crosswind conditions).

Question 30

What are the two main purposes of the moveable stabiliser?

Answer 30

Reduce drag compared to trim tab, and to deal with large changes in CoG.

Question 31

What is the natural tendency of the trim when trailing edge flaps are deployed?

Answer 31

Nose pitch down

Question 32

What is the natural tendency of the trim when leading edge flaps are deployed?

Answer 32

Nose pitch up

Question 33

When one of the two hydraulic systems controlling stab trim is inoperative, what happens to trim rate?

Answer 33

Halved

Question 34

What protection is in place to prevent stab trim runaway?

Answer 34

Hydraulic cutoff valves

Question 35

How are slats deployed?

Answer 35

they are deployed with the flaps (don’t have a seperate lever). Typically stage 1 of flaps will extend slats as well

Question 36

What happens if there is a failure of the hydraulic system which moves the flaps?

Answer 36

Electrical system as a backup

Question 37

What happens to the CoL if only the inboard flaps are extended on a swept wing aircraft?

Answer 37

Moves inwards and forward (pitch up)

Question 38

What happens to the CoL if only the outboard flaps are extended on a swept wing aircraft?

Answer 38

Moves outwards and rearwards (pitch down)

Question 39

How are flaps protected from operating asymmetrically?

Answer 39

There is a system which will identify if a specified value of flap asymmetry exists and will prevent further deployment of the flaps.

Question 40

What is the purpose of slats?

Answer 40

Re-energise the boundary layer by providing larger surface. Useful for low speeds as wings are designed for high speed.

Question 41

What systems can extend the leaing edge slats?

Answer 41

Hydraulics or pneumatics primarily, or electrically as a backup.

Question 42

Why do large transport category aircraft have flight control position monitoring?

Answer 42

Because the flight deck inhibits view of the control movement (in the same way you want 3 greens for gear down)

Question 43

What is a limitation of the flight control position monitoring system?

Answer 43

the system is used to indicate full control movement on the ground, however airborne full deflection is rarely used, and therefore doesn’t provide much information.

Question 44

What information does the Digital stall Warning Computer require to activate the stick pusher/shaker?

Answer 44

Angle of airflow vane, flap position indicator, N1 speed, N2 speed, air/ground relay, ADC, leading edge module. If these weren’t available, the system would engage the pusher at innapropriate times (e.g. on the ground)