Flight Controls

Question 1

3 a/c axis

Answer 1

• Lateral (wingtip to wingtip)
• Longitudinal (nose to tail)
• Normal (top to bottom)

Question 2

Rotation about the normal axis

Answer 2

Yaw

Question 3

Rotation about the lateral axis

Answer 3

Pitch

Question 4

How is control in pitch achieved

Answer 4

Forward and back movements of the control column move the elevator (hinged to the trailing edge of the tailplane), this alters the aerodynamic force produced by the tailplane which rotates the the a/c about its CG to change pitch attitude

Question 5

Rotation about the longitudinal axis

Answer 5

Roll

Question 6

Control column back =

Answer 6

Elevator up = increased aerodynamic force on the tail =nose up

Question 7

Control column forward =

Answer 7

Elevator down = decreased aerodynamic force on the tail =nose down

Question 8

Secondary effect of the elevator

Answer 8

None

Question 9

How is control in roll achieved

Answer 9

By rotating the control column left / right, this moves the ailerons (which are hinged to the outer trailing edge of the wings) to roll the a/c

Question 10

Control column left =

Answer 10

Left aileron up + right aileron down = decreased lift in left wing and increased lift in right wing = roll to the left

Question 11

Control column right =

Answer 11

Right aileron up + Left aileron down = decreased lift in right wing and increased lift in left wing = roll to the right

Question 12

Secondary effect of roll

Answer 12

Yaw - when the a/c is banked the lift vector is tilted in the direction of the bank, this tilted lift vector combined with the weight of the a/c produce a resultant force that will cause the a/c to slip sideways toward the lower wingtip. Once this slip occurs the airflow impinging on the greater area of fin surface behind the CG will cause the a/c to weathercock in the direction of the bank

Question 13

Adverse yaw

Answer 13

It is another secondary effect of roll, when the aileron is applied to roll the a/c, the camber of the outer section of the up going wing is increased and so lift and drag of that wing is increased. conversely the camber of the down going wing is decreased and so the lift and drag of that wing is also decreased. This difference in aileron drag between each wing manifests itself as adverse yaw and the yaw is in the opposite direction to the application of aileron

Question 14

Counteracting adverse yaw

Answer 14

• Using rudder in the direction roll
• Frise - type aileron
• Differential ailerons
• Coupling of controls
• Differential spoilers

Question 15

Frise - type aileron - counteracting adverse yaw

Answer 15

Aileron nose protrudes below the wing when deflected upward thereby increasing drag at the same time lift is reduced resulting in the drag of each wing being more evenly balanced

Question 16

Differential ailerons - counteracting adverse yaw

Answer 16

For a given movement of the control column the down going aileron is deflected through a smaller angle then the up going aileron thereby reducing the difference in drag and adverse yaw

Question 17

Coupling of controls - counteracting adverse yaw

Answer 17

On some a/c the rudder is coupled to the ailerons so that when the aileron is moved by the control column the rudder moves automatically to counteract adverse yaw

Question 18

Differential spoilers - counteracting adverse yaw

Answer 18

Deployed on the down going wing decreasing lift and increasing drag which offsets the tendency for adverse yaw

Question 19

How is control in yaw achieved

Answer 19

Through the rudder which is operated by the pilot using the rudder pedals

Question 20

Secondary effect of the yaw

Answer 20

Is to cause roll, this is because of the following:
- The strong yawing of the nose to one side will speed up the outer wing which will then produce more lift
- Once the a/c begins to skid the wing which is to the rear is slightly shielded from the oncoming airflow resulting in less lift
- In a/c with dihedral the forward wing in the skid has a slightly higher effective AoA resulting in more lift

Question 21

What effects control effectiveness

Answer 21

Airspeed and slipstream

Question 22

Airspeed effect on control effectiveness

Answer 22

Increasing airspeed over the flight control surfaces makes them more effective

Question 23

Slipstream effect on control effectiveness

Answer 23

The slipstream is the body of faster moving air that is accelerated rearward by the propeller, as power increases the stronger slipstream increases the effectiveness of the elevator and rudder (particular at slow speed), it tends to make the nose rise and cause yaw to the left (vice versa as power is decreased)

Question 24

Trim controls purpose

Answer 24

Relieve the pilot from having to hold constant pressure on the control column / rudder

Question 25

Types on trim control

Answer 25

Handles, trim wheel, electrical buttons

Question 26

Operation of trim wheel / handle

Answer 26

It varies the angle at which the trim tab on the trailing edge of the control surface is set, it creates a small aerodynamic force that acts near the trailing edge of a control surface, the control surface will maintain its angle of deflection when the moment created by the trim tab is equal and opposite to the moment of the control surface itself

Question 27

Correct method of trimming

Answer 27

Hold the a/c in the required attitude with steady pressure on the controls and then trim this pressure off

Question 28

Trimming if steady elevator back pressure is needed

Answer 28

Rotate the top of the trim wheel / move the trim control backward

Question 29

Trimming if steady right rudder pressure is needed

Answer 29

Move / rotate the rudder trim to the right

Question 30

Trimming using an electrical button / switch trim control

Answer 30

It will be spring loaded in the central OFF position, if forward control pressure is required then the trim switch is held in the forward direction and once control pressure is relived the trim is released and it should return to the OFF position

Question 31

Types of control balancing

Answer 31

Aerodynamic and mass balancing

Question 32

Aerodynamic balancing - stick force

Answer 32

When a control surface is deflected the aerodynamic force produced by the control surface itself opposes its deflection, this causes a moment to act on the control surface about its hinge line which tries to return it to its original faired position, the pilot must overcome this moment to maintain the desired control position and feels this as stick force

Question 33

Main reason for aerodynamic balancing

Answer 33

Is to ease the difficulty with which the control can be moved. By altering the design of the control surface and the positioning of its hinge linei t is possible to adjust the control force moment so that the stick forces aren’t too heavy or too light

Question 34

Methods for achieving aerodynamic balance

Answer 34

• Hinges
• Horn Balance
• Balance tabs

Question 35

Inset hinges

Answer 35

If the hinge line of the control surface is inset the distance between the hinge line and the CP of the control in decreased therefore the control surface moment and stick force moment will also be decreased. In addition this means the nose of the control surface protrudes into the airflow when the control surface is defected and the acceleration of the airflow around the nose of the control surface causes a decrease in pressure in that area co CP of the control surface moves closer to the hinge line

Question 36

Horn balance

Answer 36

Is when a control surface is designed with a portion that protrudes ahead of the hinge line resulting the overall CP of the control surface moving closer to the hinge line