Ailerons
The angle of attack is the angle between the chord line and the relative wind. Therefore, if the trailing edge is moved, the chord line moves, changing the angle of attack.
If the airplane's yoke is turned to the right, the right aileron moves upward, and the left aileron moves downward. The right aileron's upward deflection moves the trailing edge for a portion of the wing. The result is a lower angle of attack and reduced lift over this portion of wing. The left aileron's downward deflection increases lift over a portion of the left wing. A right rolling force results.
If the airplane's yoke is turned to the left, the left aileron raises, and the right aileron moves downward. The produces more lift on the right side and less lift of the left side, resulting in a left rolling force.
Elevators and Rudder
When the elevators or rudder surfaces are deflected, an angle of attack is produced over the horizontal or vertical stabilizers. This results in forces over the horizontal or vertical stabilizers, respectively.
If the back pressure is applied to the yoke, the elevator is deflected upward, raising the trailing edge of the horizontal stabilizer. A downward force is applied to the tail, raising the nose of the airplane.
When the pilot applies forward pressure to the yoke, the elevator is deflected downward, lowering the trailing edge of the horizontal stabilizer. The resulting upward force placed on the tail acts to lower the airplane's nose.
The rudder is moved left or right by the rudder pedals. Stepping on the right or left rudder pedals deflects the rudder, resulting in left or right yaw.
Trim
It would be tedious and tiring for a pilot to maintain forces on the flight controls, in an effort to hold the airplane where it needs to be, over the course of the entire flight. Trim allows the pilot to neutralize control pressures. A properly trimmed airplane will need only minor corrections from the pilot, instead of constant control pressure.
The pilot sets the positions of trim tabs on the flight controls from inside the cockpit. The tabs place pressures on the flight control, holding it in the desired position. Airplanes may have aileron, rudder, and elevator trim. Many smaller airplanes only require elevator trim, however.
To properly use trim, the pilot uses the ailerons, elevators, and rudder to maintain the orientation desired. While maintaining the desired airplane orientation, the pilot then adjusts trim as necessary to alleviate flight control pressures.
For example, if the back pressure were required to keep the airplane from pitching down on its own, the pilot would apply nose up elevator trim to alleviate the pressure. The elevator trim tab would be deflected downward by this action, placing an upward force on the elevators. The elevators would then remain in the desired position without continuous pressure on the yoke by the pilot.
Servo Tabs
Sometimes servo tabs are placed on a control surface to assist the pilot in moving the controls during flight. Servo tabs act to make heavier flight controls feel lighter to the pilot.
As the pilot moves the flight control, the servo tab attached to that flight control is deflected in the opposite direction. The further the flight control is deflected, the further the servo tab is deflected. As a result, the tab places more and more pressure on the flight control the further the flight control is deflected.
Anti-Servo Tabs
Some aircraft designs use a moveable horizontal stabilizer, instead of elevators, to control pitch. When the pilot pulls back or pushes forward on the yoke of one of these airplanes, the entire horizontal stabilizer rotates to produce the desired pitching force. This design results in very light elevator controls. Such high sensitivity might not be as desirable from the pilot's perspective, and the possibility exists that the pilot might over control the airplane.
Anti-servo tabs solve these types of problems by making flight controls feel heavier to the pilot. Anti-servo tabs move in the same direction as the flight control and move a distance proportional to the deflection of the flight control. As a result, the more pressure the pilot places on a flight control, the more the flight control resists further movement.
Flaps
Wings are designed to produce little drag, allowing for more efficient flight at cruise speed. Without flaps, takeoff and landing would also have to be performed at these higher speeds, which poses several problems. The airplane would be limited to operating at airports having longer runways. And obstructions near the end of the runway would pose greater problems, since the pilot would need to approach the runway at a shallower angle.
If the wing were designed specifically for steep approaches and operation on shorter runways, it tends to produce a large amount of drag. This higher drag makes the airplane slow and inefficient in cruise flight.
Flaps solve these problems by allowing the pilot to effectively change the shape of the wing. Flaps on the left and right wings extend together, resulting in the production of higher lift and drag by the wings. When extended, the trailing edge of the wing and the wing's chord line, is moved downward. When not being used for takeoff or landing, the flaps may be retracted to a streamlined position for cruise flight.
Control effectiveness
The flight controls create forces on the airplane through interacting with moving air. As a result, they are more effective at higher speeds and less effective at lower speeds. For example, moving the flight controls will not do much when the airplane is stopped on the ground.
At high speeds, the controls are more sensitive, due to this higher effectiveness. At lower speeds, the controls feel mushy and much larger control inputs are necessary.
Engine power can affect control effectiveness, as well. Except in T-tail airplanes, a reduction of engine power results in the airplane pitching forward, unless counteracted by the pilot. This is due to the reduction of the propeller slipstream over the tail.