Flight control systems

Question 1

What are the 4 fundamental forces acting on an aircraft during flight

Answer 1

Lift, drag, weight and thrust

Question 2

How does the aircraft move in different directions?

Answer 2

By changing the balance of these forces

Question 3

What are the 6 fundamental ways an aircraft can move in?

Answer 3

Move  linearly:-  
in a longitudinal direction
in a  lateral direction
in a vertical direction 
Rotate:-
in pitch about its lateral axis
in roll about its longitudinal axis 
in yaw about its vertical axis

Question 4

What controls does a pilot use to control the aircraft?

Answer 4

elevator, ailerons, rudder or throttle

Question 5

How Does an Aerofoil Produce an Aerodynamic Force?

Answer 5

Air sticks to surface due to its viscosity
Air must curve more to pass over upper surface of aerofoil than lower surface
Centripetal force needed to make air move in this curved path
Difference in static pressures between two aerofoil surfaces creates a force perpendicular to aerofoil - e.g. lift force produced by aircraft wing
Force produced is a function of pressure difference

Question 6

How is the centripetal force provided?

Answer 6

Provided by a pressure gradient perpendicular to direction of flow
Free stream stagnation pressure Po is constant
Static pressure P near surface reduces
Bernoulli:- as static pressure reduces , velocity increases

Question 7

What is pressure difference a function of?

Answer 7

Pressure difference is a function of:
Camber (curvature) of aerofoil
Angle of attack to approaching airflow
Speed & density of the airflow

Question 8

What is the purpose of the horizontal tail plane?

Answer 8

To produce an upward or downward force as required to enhance aircraft longitudinal stability in steady state or wind gust conditions

Question 9

Pushing/pulling of control column or Forward/backward movement of side-stick results in what?

Answer 9

Elevator moves up or down
Changes tail plane camber
Changes magnitude/direction of force
Rotates aircraft about its lateral axis
Changes aircraft pitch attitude

Question 10

What is the purpose of an All-Moving Horizontal Tail plane

Answer 10

Mainly used for high speed combat aircraft to enhance manoeuvrability
Pitch control achieved by rotating entire horizontal tailplane about a pivot
Varies its angle of attack to local airflow
Generates different amounts of upwards or downwards force

Question 11

How does a Canard Foreplane control pitch

Answer 11

By a moving foreplane ahead of main wing rather than by an elevator behind main wing

Question 12

What are the advantages and disadvantages of the canard foreplane?

Answer 12

Main advantage:
Elevator trims aircraft by downward lift
   Subtracts from lift sum
Canard trims aircraft by upward lift
   Adds to lift sum 
Main Disadvantage:
Canards have more stability/control & stall issues than conventional tail plane

Question 13

What does Rotation of control column or Sideways movement of sidestick result in?

Answer 13

Ailerons on each wing move differentially, one goes up & one goes down

Question 14

When the Ailerons on each wing move differentially, How does this affect the aircraft?

Answer 14

Change in local wing camber due to aileron position:
Difference in lift between two wings
Resultant rolling moment about aircraft longitudinal axis

Question 15

How does Pressing left or right rudder pedal affect the aircraft?

Answer 15

Rudder on tail fin moves sideways
Changes camber of tailfin vertical aerofoil
Provides sideways force
Rotates aircraft about its yaw axis

Question 16

What does the engine thrust do?

Answer 16

Provides runway acceleration to lift-off speed and counteracts aircraft aerodynamic drag

Question 17

What regulates the engine airflow in a carburetted engine

Answer 17

The throttle lever

Question 18

What regulates the engine fuel flow in an injection engine

Answer 18

The power lever

Question 19

What is the purpose of Full Authority Digital Engine Control (FADEC) Systems

Answer 19

Execute commands from cockpit thrust/power levers or auto-thrust systems
Control fuel flow into combustion chamber
Control other variable devices that moderate core airflow
Monitor numerous engine parameter

Question 20

Numerous engine parameters are monitored for what reason?

Answer 20

Temperature & shaft speed limits are not exceeded

Spool acceleration rates do not push compressor into damaging surge conditions

Question 21

How does an aircraft propulsion system generate thrust

Answer 21

By forcing a quantity of air rearwards (generally) so that it can fly forwards.

Question 22

What can Vectoring & varying propulsion system thrust also be used for?

Answer 22

To control aircraft in-flight manoeuvres

To take-off or land vertically