Primary Flight Controls Flashcards
Identify the three aircraft axes, movement about those axes, and primary flight controls.
Lateral axis - pitch, controlled by elevator
Longitudinal axis - roll, controlled by ailerons
Normal axis - yaw, controlled by rudders
How is control in pitch achieved and what is the secondary effect
Movement of the nose up or down through the use of forward and backward movement of the of the control column.
This alters the aerodynamic force produced by the tailplane which rotates the aircraft about its CoG to change pitch attitude.
No secondary effect just changes in airspeed.
How is roll achieved?
Achieved with rotation of the control column left or right moving ailerons on the outer trialing edge of the wings.
E.g. Rolling to the left causes left aileron to go up causing an decrease in lift from the left wing and at the same time the right aileron goes down causing an increase in lift from the right wing.
Secondary effect is yaw and as the lift vector is tilted in the direction of the bank. The tilted lift vector combined with aircraft weight creates slip
How is yaw achieved?
Achieved through the rudder pedals operated by the pilot.
What is the secondary effect of aileron? And why
Yaw and then slip.
When aircraft is banked the lift vector is tilted in the direction of bank.
If ailerons alone are used to roll the aircraft and no other control is taken the tilted lift vector combined with the weight of the aircraft produce a slip sideways towards the lower wingtip.
Summary - roll slip then yaw
Explain adverse yaw and how to counteract it. (5 ways)
When aileron is applied to roll, camber of the outer wing is increased so lift and drag is increased for that wing. Opposite for the inner wing. This difference in aileron drag between each wing is adverse yaw.
Counteracted by the use of rudder in the direction of roll.
Frise ailerons - nose of the aileron protrudes below the wing when deflected upward, increasing drag at the same time as lift is reduced. Thus the drag of each wing is more evenly balanced out when aileron is applied.
Differential ailerons - down-going aileron is deflected through a smaller angle than the up-going aileron, reducing the difference in drag and adverse yaw.
Coupled controls - roll is used, automatic rudder is put in.
Spoilers - when deployed on down-going wing, lift is reduced and drag increased so adverse yaw is prevented.
Describe the secondary effect of rudder.
Roll.
Since strong yawing of the nose to one side will speed up the outer wing producing more lift.
Once aircraft begins to skid, the wing which is to the rear is shielded from oncoming flow resulting in left lift.
Describe the effects of airspeed on control effectiveness.
Increased airspeed over the flight control surfaces make them more effective.
Higher air speeds the force required to move the controls increases with speed, flight controls feel firmer and less movement reduced to achieve the same effect.
Low speed, stick forces are reduced and controls must be moved greater to achieve the same response.
Describe the effects of slipstream on control effectiveness. (6)
Increased and stronger slipstream:
- Increases effectiveness of elevator and rudder, particularly at slow speed.
- Tends to make nose rise
- Causes yaw to the left
Decreased and weakened slipstream
- decrease effectiveness of elevator and rudder
- make nose drop
- cause yaw to the right
What is slipstream?
The body of faster moving air thats accelerated rearward by the propellor. Typically prop aircraft usually envelop the slipstream over the fuselage and the empennage.
Explain the basic principles of trim tabs and describe the correct method of using trim controls.
The trim tab operates by creating a small force near trailing edge of a control surface which is used to hold the surface at the desired angle of deflection.
Correct method: hold aircraft at required altitude or rudder with steady pressure on the controls then trim the pressure.
Explain the reason for aerodynamic balancing of control surfaces.
Aerodynamic force produced by deflected control surfaces act through CoP for that control surface, and the greater the distance between the CoP and the hinge line, the greater the moment of the force that resists pilots input and higher stick force.
So aerodynamic balance is used to ease the difficulty with which a control can be moved.
Describe the main methods for achieving control balance
Inset hinges - if hinge line of control surfaces are inset, the distance between the hinge-line and the CoP is reduced. Therefore control force moment and stick force is reduced.
Horn balance - achieved when a control surface is designed with a portion that protrudes ahead of the hinge line. CoP is brought closer to hinge line and control moment is reduced.
Differentiate between a balance tab and an anti-balance tab.
Balance tab - incorporated part of the elevator where the tab unit generates a small upward aerodynamic force.
which helps to move the elevator up, thereby reducing the control load required of the pilot.
Anti balance tab - fitted onto all moving tail planes due to CoP of control surface and hinge lines being close and the possibility of overbalancing.
Works the opposite as balance as they move in the opposite direction e.g. if trailing edge of all moving tail is moved down, tab moves down as well to provide a small aerodynamic force to opposite control column movement.
Explain the purpose for mass balancing.
All structures twist and bend under load. This structural flexibility can lead to control flutter at high speeds on some aircraft which can impose severe loadings on the wings and empennage of an aircraft leading to structural failure
Mass balance must be applied to control system prone to flutter so that extra mass must be added to bring the CoG closer to the hinge line decreasing the tendency of the aircraft structure to bend or twist.
