Control surfaces

As aircraft move in three dimensions we need various control devices to control it. Fixed-wing aircrafts have control surfaces for each one of these dimensions. Usually these are placed in the extremes of the aircraft (tail and wings) to get the maximum strength and response using small moving parts thanks to the lever concept.

Note that an airplane is easier to maneuver as more unstable it is. Stability can be provided by stabilizers and fuselage and wing design.

Vertical stabilizer and rudder

The vertical stabilizer functions with the same principle a wing does, but being symmetrical. It is a main control surface of airplanes (fixed-wing aircrafts). Obviously, it has a vertical position, usually in the tail of the aircraft. There can be multiple vertical stabilizers (in large aircrafts usually).

The vertical stabilizer has a moving part which is called rudder. This acts as an aileron does in the wing. When it is moved to one or other side it produces a pressure difference over the stabilizer since its movement is equal to change the angle of attack of this 'wing'.

The rudder controls the Y-axis or yaw of the plane and it is controlled from the cockpit with the pedals. In a coordinated turn, rudder and ailerons must be coordinated, but you can use rudder only to 'slide' the aircraft.

Some rudders are mixed with elevators in the same control surface, creating V-tail aircrafts.

Horizontal stabilizer and elevator

The horizontal stabilizer is the main control surface of the aircraft, mainly of airplanes (fixed-wing aircraft). It functions as a wing does, creating a second point of lift along the fuselage which provides stability to the aircraft in the Z-axis. Its function is not to provide more lift but to control the pitch of the aircraft (by modifying the angle of attack of the wing). This is thanks to a moving part or parts called elevators, which act like an aileron, and are controlled by the longitudinal axis of the joystick or wheel.

Obviously, the horizontal stabilizer has a horizontal position, usually in the tail of the aircraft. It can be on top of the vertical stabilizer (T-tail aircraft), or divided in two parts crossing the vertical stabilizer. Some horizontal stabilizers have no elevators but are a whole elevator (mainly in gliders, since it has a better aerodynamic performance). In Canard-configuration planes, the horizontal stabilizer is positioned not in the tail but in the nose of the aircraft (note that its movement to reduce or increase pitch will be inverted from the one it does when it's placed in the tail).

Sometimes, elevators are mixed with rudders in the same control surface, creating V-tail aircrafts. It also can be combined with ailerons, mainly in delta-wing planes.

Aileron

Ailerons are moving surfaces usually placed near the tips of the wings. The function of an aileron is simple, by moving upwards or downwards it modifies the angle of attack of that section of the wing, sinking or lifting it. This change in the aerodynamic is due to the modification of relative curve of the airfoil. Note that ailerons are complementary, so if one moves the other will move on the other direction in the same proportion. This improves the effect as one wing is lifted and the other sunk. Ailerons control the X-axis or roll movement of the aircraft.

Ailerons are controlled by the pilot from the cockpit, with the lateral axis of the joystick. To make coordinated turns their movement must be combined with rudder in the same direction. In some planes ailerons are just divided elevators, being possible to use the same surface as aileron or elevator (delta-wing airplanes).

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