AIRCRAFT FLIGHT CONTROL

A conventional fixed-wing aircraft flight control system consists of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight. Aircraft engine controls are also considered as flight controls as they change speed. 

Basically, the Flight Controls are devided as Primary and Secondary Flight Control.

1. Primary Flight Control
 The primary flight control are consist of Aileron, Rudder, and Elevator.

The ailerons are attached to the outboard trailing edge of each wing and move in the opposite direction from each other. Ailerons control roll about the longitudinal axis. Moving the control wheel, or control stick, to the right causes the right aileron to deflect upward and the left aileron to deflect downward. The upward deflection of the right aileron decreases the camber resulting in decreased lift on the right wing. The corresponding downward deflection of the left aileron increases the camber resulting in increased lift on the left wing. Thus, the increased lift on the left wing and the decreased lift on the right wing causes the aircraft to roll to the right.

The Rudder controls the aircraft direction in vertical axis. The Rudder is attached in the trailing edge of vertical stabilizer. It moves to left and right depend of controlling the Pedal in cockpit. When the left pedal is pressed, the rudder moves to the left hand, then the aircraft will turn to left as impact of airflow in the rudder surface. The inversely occurred when the right pedal is pressed. The rudder moves to the right right, therefore the aircraft will turn to the right direction.

The third primary flight control is Elevator. The elevators are attached in left and right trailing edge of Horizontal stabilizer. They control the aircraft Pitching in Lateral axis. When the control column (Boeing) or side stick (Airbus) pulled to rear, the elevators move to upward. Therefore the aircraft pitched to up as impact of the airflow in the surface of elevators. When the control column (Boeing) or side stick (Airbus) pressed to forward, the elevators move to downward and the aircraft pitched to down.

The detail explanation about Primary flight control will update later.
 
2. Secondary Flight Control

n addition to primary flight controls, most airplanes have another group called secondary controls. These include trim devices of various types and wing flaps. The trim devices are adjusted so that the aircraft remains balanced in flight.

Flaps

Flaps are moveable surfaces on the trailing edge of the wing similar in shape to the ailerons. they are usually larger in surface area. They are located on inboard end if the wing next to the fuselage. Both sides are activated together so they do not produce a rolling action like the ailerons. 

Flaps are usually deployed in "degree" increments. In small aircraft deployment is usually in 10 degree increments from zero degrees (non-deployed) to 40 degrees maximum. Larger or more sophisticated aircraft may have a different range of settings. Normally, the flaps operate electrically through a 4 or 5 position switch located on the instrument panel. In earlier aircraft the flaps were operated using a manual flap handle.

Deployment of flaps increases both the lift and drag of the wing. Flap activation increases the angle of attack across the wing / flap section. At 10 degrees, more lift than drag is produced. As the flap angle is increased more drag and less lift is produced for each increment of deployment.  

Slats

Slats are auxiliary airfoils fitted to the leading edge of the wing. At high angles of attack, they automatically move out ahead of the wing. The angle of attack of the slat being less than that of the mainplane, there is a smooth airflow over the slat which tends to smooth out the eddies forming over the wing. Slats are usually fitted to the leading edge near the wing tips to improve lateral control. The Socata Rallye is an example of a light aircraft that utilizes leading edge slats.

Spoilers

Spoilers are devices fitted to the wing which increase drag and decrease lift. They usually consist of a long narrow strip of metal arranged spanwise along the top surface of the airfoil. In some airplanes, they are linked to the ailerons and work in unison with the ailerons for lateral control. As such, they open on the side of the upgoing aileron, spoil the lift on that wing and help drive the wing down and help the airplane to roll into a turn.

In some airplanes, spoilers have replaced ailerons as a means of roll control. The spoiler moves only upward in contrast to the aileron that moves upward to decrease lift and downward to increase lift. The spoiler moves only up, spoiling the wing lift. By using spoilers for roll control, full span flaps can be used to increase low speed lift.

Spoilers can also be connected to the brake controls and. when so fitted, work symmetrically across the airplane for producing drag and destroying lift after landing, thereby transferring all the weight of the airplane to the wheels and making braking action more effective.