Aerodynamics - 4

PRIMARY FLIGHT CONTROLS
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Aircraft primarily controls itself by using its primary flight controls. These are

• Ailerons-at the wing rear tip
• Elevator -at horizontal stabilizer
• Ruder -on the vertical stabilizer

All these controls airfoils, when it moves it alters the Angle of Attack (AoA) & there for the lift of the control surfaces moving aircraft in the desired directions

AILERON
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An aircraft controls itself in roll (movement around the aircraft's longitudinal axis (which extends from the nose to the tail of an airplane)) using its ailerons. Pairs of ailerons are typically interconnected so that when one is moved downward, the other is moved upward. Ailerons are usually situated near the wing tip, but may sometimes also be situated nearer the wing root. Modern airliners may also have a second pair of ailerons on their wings, and the terms 'outboard aileron' and 'inboard aileron' are used to describe these positions respectively.
 
 
 U can control this using the yoke (similar to steering in a car) in cockpit. To roll left u would move yoke left & this will cause the left aileron to move upwards & the right aileron move downwards. The aileron moving upwards decreases the AoA so the lift generated by the left wing is also decreased. On the right wing the ailerons moves down which increases the AoA increase in lift in the right wing. The imbalance of lift will cause the aircraft to roll to the left. This movement is called rolling or banking. For rolling towards right just reverse everything. i.e. steer yoke right then left aileron goes down which increase AoA & lift on the left wing, the right aileron goes up which decreases AoA & lift on the right wing. So the aircraft will roll to the right.
 
There are different kinds of Ailerons they are
 

• Single acting ailerons
• Wingtip ailerons
• Frise ailerons
• Differential ailerons

ELEVATOR

At the rear of the fuselage of most aircraft one finds a horizontal stabilizer and an elevator. The stabilizer is a fixed wing section whose job is to provide stability for the aircraft, to keep it flying straight. The horizontal stabilizer prevents up-and-down, or pitching, motion of the aircraft nose. The elevator is the small moving section at the rear of the stabilizer that is attached to the fixed sections by hinges. Because the elevator moves, it varies the amount of force generated by the tail surface and is used to generate and control the pitching motion of the aircraft. There is an elevator attached to each side of the fuselage. The elevators work in pairs; when the right elevator goes up, the left elevator also goes up

To climb u will pull the yoke backwards which will move the elevator upwards. So the AoA at the tail section decrease i.e.  It will cause a slight negative AoA at tail so it actually causes lift that acts downwards. This will push the tail down & move the nose up causing the aircraft to climb. To descent u will push the yoke forward the elevator move down & AoA of the tail will increase. The tail will be lifted which will push down the nose & the aircraft will descend.

 During takeoff the elevators are used to bring the nose of the aircraft up to begin the climb out. During a banked turn, elevator inputs can increase the lift and cause a tighter turn. That is why elevator performance is so important for fighter aircraft.
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 On many fighter planes, in order to meet their high maneuvering requirements, the stabilizer and elevator are combined into one large moving surface called a stabilator. The change in force is created by changing the inclination of the entire surface, not by changing its effective shape.

RUDDER

The combination of the vertical stabilizer & rudder works like a vertical wing. U can control the rudders using the rudder pedals or ruddels. Which you operates using your feet(Modern aircrafts uses joystick to control all flight control surfaces ). Push the right peddle & the rudder will move right this will cause lift act in the vertical stabilizer in the opposite direction which will pulls the tail left this yaws the aircraft to the right.

If you push the left rudder pedal the rudder will move left it moves the tail section in the opposite direction. The movement of tail section makes the aircraft yaw in the desired direction.
Although it appears that the rudder causes the airplane to turn, it must be pointed out that the ruder itself cannot cause the airplane to make a good turn. Newtons first law of motion states that a moving body tends to continue moving in a straight line unless some outside force changes its direction. When rudder is applied to an airplane in flight, the airplane will turn but it will continue the motion in the same direction until a correcting force is applied. Thus with rudder only, the airplane will turn sideways & skid. In order to prevent this skid in a turn, the ailerons are used to bank the airplane.

Too much of a bank without sufficient rudder in a turn will cause slipping; that is the airplane will slide down toward the inside of the turn. It is therefore necessary that the proper amount of rudder and aileron be applied when entering a turn in order to produce a co ordinate turn.
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U can also have different set ups with primary control surfaces. Where one surface can combine two of the other surfaces. For e.g. concord aircraft has no horizontal stabilizer so it doesn’t have elevators it controls itself in pitch & rolls using elevons which combine the functions of elevators & ailerons into one set off flight controls. They work by moving up & down together by like an elevator for pitch control & in opposite directions to control in roll.
Another e.g. is a kind of V-tail which combines elevator & the rudder called rudderrators to control yaw & pitch.

REFERENCE 

Wikipedia
grc.nasa.gov.in
different Reference text books