Flight Controls Flashcards
22.14.2 Identify the three aircraft axes, movement about those axes, and primary flight controls.
The 3 axes are the lateral, longitudinal and normal (or vertical) axes.
Rotation about the lateral axis is known as pitch. (Wingtip to wingtip).
Rotation about the longitudinal axis is known as roll. (From nose to tail).
Rotation about the normal axis is known as yaw. (Vertical).
22.14.4 Explain how control in pitch, roll, and yaw is achieved.
Pull/push the yoke/stick for pitch. (Pull = Pitch up, Push = Pitch Down).
Roll yoke/tilt stick side to side for roll. (Left = Roll Left, Right = Roll Right).
Use foot pedals for rudder control. (Left = Yaw Left, Right = Yaw Right).
- 14.6 Identify and explain:
(a) the secondary effect of aileron;
The secondary effect of moving the ailerons is yaw. When the aircraft is banked, the lift vector is tilted in the direction of the bank. If the ailerons alone are used to roll the aircraft (no rudder), the tilted lift vector combined with the weight of the aircraft produce a resultant force causing the aircraft to slip sideways toward the lower wingtip. Once this slip occurs, the airflow forces the greater area of exposed tailplane behind the CoG to weathercock in the direction of the bank, i.e. to yaw.
- 14.6 Identify and explain:
(b) adverse yaw and methods used to counteract it;
Adverse yaw is the natural and undesirable tendency for an aircraft toof a roll. It is caused by the difference in profile drag between the upward and downward deflected ailerons, the difference in lift and thus induced drag between left and right wings, as well as an opposite rotation of each wing’s lift vector about the pitch axis due to the rolling trajectory of the aircraft.
For example roll left, left aileron goes up, right goes down. The right aileron causes more lift and drag, causing a roll to the left and a yaw to the right.
The effect can be greatly reduced with ailerons or spoilers deliberately designed to create more drag when deflected upward than downward or by coupling of controls which automatically applies some amount of coordinated rudder.
Frise-type aileron: consider a turn, raising one of the ailerons, the leading edge of that aileron (which has an offset hinge) projects down into the airflow and creates drag. This helps equalize the drag created by the lowered aileron on the opposite wing and thus reduces adverse yaw.
Differential type aileron: this aileron system raises one aileron a greater distance than the other aileron is lowered for a given movement of the control stick or wheel. In this case, since the raised aileron has as much or more surface area exposed to the airflow (thus increased drag) than the lowered aileron, the adverse yaw is greatly reduced.
Coupling ailerons with rudder: this is when the rudder is coupled with the ailerons so that when there is an aileron input, the rudder moves automatically to counteract adverse yaw.
Spoilers can also be used. Spoiling lift on the wing entering the turn and also creating drag helping to yaw in the direction of the turn.
- 14.6 Identify and explain:
(c) the secondary effect of rudder.
The secondary effect of rudder is to cause a roll since:
- Yawing of the nose to one side will mean the outside wing is going faster which will produce more lift.
- Once the aircraft begins to skid the wing which is now to the rear is slightly shielded from the RAF, resulting in less lift.
- Aicraft with dihedral will have a higher effective AoA on the forward wing resulting in more lift.
22.14.8 Describe the effects of airspeed and slipstream on control effectiveness.
Increased airspeed over the flight-control surfaces makes them more effective.
High airspeed = firm controls, less input required
Low airspeed = sloppy controls, controls must be moved through greater distance to achieve desired response.
The slipstream is the body if faster moving air that is accelerated rearward by the propeller. It affects mainly the elevator and rudder at high power settings and low airspeeds. Ailerons are not affected as they are outside the slipstream.
Further effects:
nose up effect with high thrust,
nose down effect with low thrust,
yaw left with increase of power (counteract with right rudder)
yaw right with decrease of power (counteract with left rudder)
22.14.10 Explain the basic principles of trim tabs, and describe the correct method of using trim controls.
Trim tabs are fitted to aircraft to alleviate control input when flying to make the aircraft more pleasant to fly. Trim tabs are adjusted in the cockpit by turning a trim wheel, handle or button which varies the angle of the trim tab on the control surface. The trim tab creates a small aerodynamic force acting on the trailing edge of the control surface to hold the desired angle of deflection.
The correct method of trimming an aircraft is as follows:
- Hold the aircraft at the desired attitude with steady pressure.
- Adjust trim control in cockpit until control pressure is relieved.
22.14.12 Explain the reason for aerodynamic balancing of control surfaces.
Aerodynamic balancing is to make ‘easy’ movement of controls by the pilot. This is achieved by designing the control surfaces so that its centre of pressure is at an appropriate distance from the hinge line.
22.14.18 Explain the purpose for mass balancing.
Mass balancing is done to eliminate the ‘flutter’ of controls. It is achieved by arranging the distribution of the mass of the control surface so that its centre of gravity is at an appropriate distance from the hinge line.
22.14.20 Describe and explain flexural flutter.
Flexural flutter is caused by the movement of the ailerons lagging behind the rise and fall of the outer portion of the wing as it flexes, thus tending to increase the oscillations. Mass balancing of the ailerons prevents this type of flutter. The positioning of the mass balance weight must be closer to the wing tip. Alternately, the weight can be distributed along the whole length of the aileron in the form of a leading-edge spar.
22.14.20 Describe and explain torsional flutter.
Torsional aileron flutter is a flutter caused by the wing twisting under loads imposed on it by the movement of the ailerons, about the lateral axis.
22.14.14 Describe the main methods for achieving control balance.
Aerodynamic balance, involves designing a control surface so that the center of pressure is close to the hinge line, make the control lighter for the pilot.
Mass balance, is designed to bring the center of gravity closer to the hinge line in a attempt to reduce flutter. You can use inset hinges, horn balances or weights.
22.14.16 Differentiate between a balance tab and an anti-balance tab.
A balance tab is attached to the back of the elevator and moves in the opposite direction. For example if the elevator moves up, the balance tab moves down which creates a small force to help lift the elevator.
A ANTI-balance tab moves in the same direction as the elevator, (normally an all moving tail plane). The centre of pressure is normally close to the hinge, so control feels light. Normal control input could result in accidental full deflection, so anti-balance tab is there to oppose this.
22.14.22 Describe the methods of providing mass balance.
Inset hinges, Horn balances, or extra mass concealed within the control surface itself, or even mass externally mounted on an arm ahead of the hinge line.
