Airplane control surfaces

For an airplane to be controllable, control surfaces are necessary. The 4 main surfaces are ailerons, elevator, rudder and flaps as shown below:

 Focus on the 4 control surfaces ailerons, elevator, rudder and flaps

Before i discuss how every surface effect the plane motion you must know the center of gravity of the plane ( The point from which the weight of the plane effect downwards ) . From this point we can take three axis as shown below .(All 3 axis pass through the Center of Gravity)

As shown  the orange axis (z) When the plane rotates about it then the plane can be turned right or lift .
The  green axis (y) when the plane rotates about it then the plane can move upward or downward .
 The blue axis (x) rotating about it makes the plane roll .


Let's talk about the surfaces ( in the designing of the plane ) that controls these motions . 


1- Elevator:

The elevators control the movement of the airplane about its lateral axis. This motion is called pitch. The elevators form the rear part of the horizontal tail assembly and are free to swing up and down. They are hinged to a fixed surface—the horizontal stabilizer. Together the horizontal stabilizer and the elevators form a single airfoil. A change in the elevator's position modifies the camber of the airfoil, increasing or decreasing lift.
The elevators are connected to the control stick by control cables. Pushing the stick forward moves the elevators downward. This increases the lift produced by the horizontal tail surfaces and causes the nose to drop. Pulling back on the stick causes the elevators to move upward, decreasing the lift produced by the horizontal tail surfaces and forcing the nose upward.


 2 - FLAPS

Flaps are located on the trailing edge of each wing, between the fuselage and the ailerons, and extend outward and downward from the wing when put into use.
The purpose of the flaps is to generate more lift at slower airspeed, which enables the airplane to fly at a greatly reduced speed with a lower risk of stalling. When extended further flaps also generate more drag which slows the airplane down much faster than just reducing throttle power.
Although the risk of stalling is always present, an airplane has to be flying very slowly to stall when flaps are in use at, for example, 10 degrees deflection.

So all these factors are why and how airplanes fly. Radio control model airplanes can of course be more simple - for example, just have rudder and elevator control or perhaps just rudder and motor control. But the same fundamental principles always apply to all airplanes, regardless of size, shape and design.

  3- Ailerons :

Ailerons can be used to generate a rolling motion for an aircraft. Ailerons are small hinged sections on the outboard portion of a wing. Ailerons usually work in opposition: as the right aileron is deflected upward, the left is deflected downward, and vice versa. This slide shows what happens when the pilot deflects the right aileron upwards and the left aileron downwards.
The ailerons are used to bank the aircraft; to cause one wing tip to move up and the other wing tip to move down. The banking creates an unbalanced side force component of the large wing lift force which causes the aircraft's flight path to curve. (Airplanes turn because of banking created by the ailerons, not because of a rudder input). 

 4 - rudder

 for Airplane The rudder is located on the back edge of the vertical stabilizer, or fin, and is controlled by 2 pedals at the pilot's feet. When the pilot pushes the left pedal, the rudder moves to the left. The air flowing over the fin now pushes harder against the left side of the rudder, forcing

the nose of the airplane to yaw round to the left .And the same thing happen when the pilot pushes the right pedal but to right . 

HOW Airplane Fly ?

When we are talking about something fly in the air ,we must talk about four forces affect it's motion . These forces are called :(Aerodynamic Forces)
These are lift, drag, thrust and weight or (gravity) . The directions of these forces are shown in the figure below .
In simple terms, drag is the resistance of air (the backward force), thrust is the power of the airplane's engine (the forward force), lift is the upward force and gravity is the downward force. So for airplanes to fly, the thrust must be greater than the drag and the lift must be greater than the gravity (so as you can see, drag opposes thrust and lift opposes gravity).

We will talk about every force :

- The thrust is generated by the airplane's engine (propeller or jet) . After that we may talk about the airplane's engine types and how they work .

- gravity is a natural force acting upon the airplane ( actually it is the weight of the plane and every thing it contain ) and this force exerts vertically downwards .

- We know are going to talk about the ( Lift force ) :
It's a fact that the gases are compressible fluids this means that it's density can be changed because of the fact that says ( any amount of gas can full any volume )
but we still have some questions like ( how wings generate lift ? )
In fact not wings only who generate the lift but all the body of the plane is designed to generate lift but, the wing generates the most lift force and if you understood how do wings generate lift you will understand how the body generates lift .
A cross section of a typical airplane wing will show the top surface to be more curved than the bottom surface. This shaped profile is called an 'airfoil'
During flight air naturally flows over and beneath the wing. Any given 'parcel' of air gets split in two as it hits the leading edge of the wing, and both halves of that parcel actually meet up again at the same moment as they come off the trailing edge of the wing. So because the air moving over the top of the wing has more distance to cover (because of the curvature it is forced to follow) in the same amount of time as the air passing below the wing, it has to move faster.

Faster moving air is less dense than slower moving air, so this speed difference results in a lower air pressure on top of the wing, and a higher air pressure
this difference in pressure generates the lift force this is called below the wing. The result of this pressure gradient is that the wing, and hence the plane, is pushed upwards by the higher pressure.Bernoulli's principle expains the relation between acceleration and pressure .




The physics explanation, NEWTONIAN or ATTACK ANGLE: wings are forced upwards because they are tilted and they deflect air. A wing's trailing edge must be sharp, and it must be aimed diagonally downward if it's to create lift. Both the upper and lower surfaces of the wing act to deflect the air. The upper surface deflects air downwards because the airflow "sticks" to the wing surface and follows the tilted wing (this phenomena is called "Coanda effect" or "Flow Attachment.") After the wing has passed by, air remains flowing downwards. Airplanes fly because of Newton's 3rd law (action/reaction forces,) the law of Conservation of Momentum, and the Coanda effect.

Note well: Newton and Bernoulli do not contradict each other. Explanations which are based on Newton's and on Bernoulli's principles are completely compatible. Air-deflection and Newton's Laws explain 100% of the lifting force. Air velocity and Bernoulli's equation also explains 100% of the lift. For the most part they're just two different ways of simplifying a single complicated subject.
-Drag : it is the net aerodynamic force parallet to the relative wind and is generally a sum of two components :induced drag and parasite drag . ( the drag force is related to the angle of attack ) . I think that it's enough for you to know that the drag is the resistance force that tries to prevent the plane from moving in the fluid (air)
.
(these information are very complicated and there are many argues about this but i tried to simplify it as possible but if you want to study it all you can search in these fields
1- perfect gas theorem ,2- the layers of the atmosphere ,3- compressible fluids ,4-Bernoulli's principle 5-Newton's Laws 6-Aerodynamics .)
The next time we will talk about how the movements of the plane happens (it's very easy).