primary flight controls

Question 1

what are the properties of the balance point?

Answer 1

the point which all the weight of the aircraft acts and is the point which the three axes - lateral, longitudinal and normal intersect.

Question 2

what are the characteristics of the elevator? (3)

Answer 2

• located at the rear of the tail section
• controlled by forward and aft movement of control column in cockpit
• controls the aircraft in pitch around the lateral axis which run from the wingtip to wingtip.

Question 3

what are the characteristics of the aileron? (3)

Answer 3

• located on the outboard trialling edges of the wing.
• controlled by left and right movement of the control column
• control the aircraft in a roll around the longitudinal axis, running from the nose to the tail.

Question 4

what are the characteristics of the rudder? (3)

Answer 4

• located on the rear of the vertical stabiliser
• controlled by the left and right movement of the rudder pedals
• controls the aircraft in yaw around the normal (vertical) axis which runs vertically through aircraft CoG

Question 5

what is the reaction when the pilot has eased back on the control column deflecting the elevator up?

Answer 5

airflow travelling over the elevator is deflected upwards, and the reaction is a force pushing the tail of the aircraft downwards.

Question 6

what is the reaction when the pilot has moved the control column to the left deflecting the left aileron upwards?

what happens with the right-wing?

what is the result?

Answer 6

airflow travelling over the left aileron is deflected upwards, the reaction is a force pushing the left-wing downwards.

The right aileron moves downwards, which pushes the air downwards. the reaction is that the wing moves upwards.

results in aircraft rolling left

Question 7

what is the reaction when the pilot has depressed the left rudder pedal deflecting the rudder to the left?

Answer 7

airflow travelling around the rudder is deflected to the left and the reaction is to push the tail to the right causing nose of the aircraft to yaw.

Question 8

the reaction of all forces is caused by what?

Answer 8

newtons third law - for every action there’s an equal and opposite reaction.

Question 9

what are the primary effects of elevator, aileron and rudder movement?

Answer 9

Elevator - pitch up/down
Roll - left/right
yaw - left/right

Question 10

what are the secondary effects of the elevator?

Answer 10

none, except change of airspeed

Question 11

what are the secondary effects of the aileron? (4)

Answer 11

slip, yaw, spiral descent

• aircraft will slip into turn
• airflow will strike the tail at an angle
• aircraft will try to re-align with this airflow
• re-alignment causes aircraft to yaw

Question 12

what are the secondary effects of the rudder? (4)

Answer 12

skid, roll, spiral descent

• aircraft will skid out of the turn
• one wing will travel a greater distance in the same time, making it travel faster
• more lift is produced on this wing
• aircraft will roll

Question 13

how does airspeed affect control surfaces?

Answer 13

more airspeed = more air that will pass over the control surfaces = more air deflecting = greater resultant force.

Question 14

at low airspeeds what happens to control surfaces?

Answer 14

• controls are lighter, less effective

- more deflection is required for the desired result

Question 15

at high airspeeds what happens to control surfaces?

Answer 15

• control are heavier, more effective

- less deflection required for desired result

Question 16

what is slipstream, what is it caused by and increasing the amount of it does what?

Answer 16

the corkscrew motion of air travelling backwards and around the fuselage of an aircraft.

caused by the rotation of the propellor.

increases the flow of air over the elevator and rudder and so make those controls more effective.

Question 17

what does increasing power do to control surfaces? and what should you do when doing it? (3)

Answer 17

• nose pitches up due to increased thrust
• nose yaws left (if the propellor rotates clockwise) due to increased slipstream striking the tail
• ease forward on the control column slightly and apply the right rudder.

Question 18

what does decreasing power do to control surfaces? and what should you do when doing it? (3)

Answer 18

• nose pitches down due to a decrease in thrust
• nose yaws to the right due to reduced slipstream striking the tail
• ease back slightly on the control column and apply left rudder.

Question 19

what is the use of trim tabs and why are they important.

Answer 19

used to reduce manual energy and work required to stabilise an aircraft during flight.

without trim tabs, pilots are forced to hold the controls with greater force.

Question 20

where can trim tabs be located?

Answer 20

elevator, ailer, and rudder but the primary being on the elevator.

Question 21

what does the elevator trim do?

Answer 21

relives the pilot of control pressures and works in the natural sense of if you’re having to hold back on the controls to prevent nose drop, you trim wheel backwards.

Question 22

where are fixed trim tabs usually found and what are they used for?

Answer 22

trailing edge of the rudder

compensate for propellor slipstream which would otherwise cause an aircraft to yaw and roll instead of flying straight and level.

Question 23

what are the methods for obtaining aerodynamic balance?

Answer 23

• hydraulic for powered controls and by using some form of aerodynamic balance for smaller aircraft.

involves using tabs to alter the airflow over the control surface that reduces or increases the effort required to deflect the controls.

Question 24

what are the two types of tabs used?

Answer 24

balance and anti-balance tabs

Question 25

where are balance tabs attached and what are they used for?

Answer 25

to the control surface linkage so that when the control surface is deflected in a given direction, the balance tab moves in the other.

automatic movement so no control movement is needed and this results with a small resultant force holding or assisting in holding the control surface in that position.

Question 26

what do anti-balance tabs do?

Answer 26

similar to balance tabs but they move in the same direction as the control surface is moved.

Question 27

what happens if the plane does not have an anti-balance tab?

Answer 27

relatively easy to overcontrol the aircraft and possible overstress the airframe.

Also, the Centre of pressure of an all-flying tailplane could possibly move forward of the hinge line which would cause the tailplane to fully deflect with a very small movement from the pilot.

Question 28

what is the purpose of flaps?

Answer 28

to increase the amount of lift produced by an aerofoil. this reduces the stall speed, allowing the aircraft to be flown at slower speeds, thereby shortening take-off and landing distances.

Question 29

what are the characteristics of a plain flap? (2)

Answer 29

• trailing edge hinges down and into the airflow

- increases camber

Question 30

what are the characteristics of a split-flap? (4)

Answer 30

• the lower section of the trailing edge lowered into the airflow
• upper section of trailing edge remains undisturbed
• increases camber and therefore lift
• produces a significant amount of drag

Question 31

what are the characteristics of slotted flap? (3)

Answer 31

• trailing edge lowered into airflow whilst producing a slot between trailing edge of the wing and leading edge of the flap
• allows the re-energisation of the boundary layer over the flap which delays the separation of airflow
• allows for greater gain in lift resulting in greater drag

Question 32

what are the characteristics of fowler flap? (3)

Answer 32

• lower trailing edge section of the wings moves downwards and rearwards
• creates a slot with an increase in surface area producing more lift
• can have multiple stages
• most efficient

Question 33

what is the operation of flaps?

Answer 33

on approach to land, flap is lowered in stages. once on final and assuming the weather is suitable full flap is selected.

this allows for a slower approach speed without stalling and better forward visibility and reduces the amount of energy the aircraft has during the finals.

Question 34

when should flaps be retracted?

Answer 34

only at full power and at a safe height above the ground as you run the risk of the aircraft sinking.