Aircraft controls

What for aileron is used? How its operation?

Aileron is used to make the rolling. To be more specific it creates a force at the fitted place due to aerodynamic effect, and that force causes a moment with respect to c.g.. of the aircraft.

Ailerons are fitted at the two ends of the main wing. So that distance is high from center of gravity. Even though if we deflect a small amount of angle of attack to the aileron aerofoil, we will have large amount of moment. See the fig. given inside the next question.

Ailerons operate on the differential mechanism. That means if the right aileron goes up, then left aileron goes down. Suppose if pilot wants to have a right turn, he must bring right aileron up.

What is adverse yaw?

If a pilot wants to have a right turn, then he will apply a control from the cockpit in such a way that the right aileron goes up. Say, for instance, right aileron goes 5 deg upward in AOA. Then you might think left aileron goes 5 deg downwards. If it is so, downward aileron with wing combination, has been increased by camber. Hence it can create large amount of lift and drag. The upward aileron with wing combination has less camber, hence produce less lift and less drag.

You just raise your two hands like bird wings. Imagine A guy with high power is pulling your left hand rearward, and a guy with less power is pulling you right hand rearwards. Now you say which side your body turns?  Yes. Body turns towards Left. The same thing is what happening in the airplane while making turn.

Because of the highest drag at the left side while making a right turn, the aircraft yaws towards left. This yaw is what called as adverse yaw.

To overcome this effect when rolling, the downward aileron has to undergo half deviation from that of upward aileron.

What for rudder is used?

Rudder is used for producing yawing moment while going along a flight path.

What for elevator is used? While takeoff how the elevator will be?

Elevator is used for creating pitching moment. Pitching is needed when aircraft climbs and descends. During takeoff the elevators located on the tail wing will be deflected upwards.