# Advice 1: How planes fly

Despite the fact that the plane weighs a ton, he is able to fly. The reason for this is a special wing design that allows you to change the density of air over and under the wing.
For a long time people saw birds fly. Some researchers appear crazy ideas – they wanted to fly, but why the result was so disastrous? Long ago there were attempts to attach to her wings and flapping them to fly in the sky like birds. It turned out that the man power is not enough to raise yourself on flapping wings.

The first craftsmen were naturalists from China. Information about them is recorded in the "Can-Han-Shu" in the first century of our era. Further history is replete with cases of this kind, which occurred in Europe and Asia, and Russia.

The first scientific justification of the process of the flight gave Leonardo da Vinci in 1505. He noticed that the birds do not have to flap their wings, they can stay on the still air. From this the scientist concluded that flight is possible, when the wings move through the air, i.e. when the flap their wings when there is no wind or when the wind blows when the fixed wings.

## Why did the plane fly?

To keep the plane in the air helps lift force, which acts only at high speeds. A special contraction allows the wing to create lift. The air that moves over and under the wing, is changing. Over the wing it is sparse, and under the wing is compressed. Creates two air flow directed vertically. Lower flow lifts the wings, i.e. the plane, and the top pushed up. Thus, it appears that at high speeds the air under the aircraft becomes hard.

Implemented as vertical movement, but what causes the aircraft to move horizontally? – Engines! Propellers as if the drill path in the air, overcoming wind resistance.

Thus, the lifting force overcomes the force of gravity, and the traction – braking force, and the plane flies.

## Physical phenomena underlying flight control

The aircraft rests on the balance of the lift force and the force of gravity. The plane flies straight. The increase in airspeed will increase the lift force, the plane will rise. To offset this effect, the pilot must lower the nose of the aircraft.

The rate decrease will have the opposite effect, and the pilot will need to raise the nose of the aircraft. If this is not done, the crash to happen. In connection with the above features there is a risk to break when the plane loses altitude. If this occurs close to the surface of the earth, the risk is almost 100%. If it occurs high above the ground, the pilot will have time to increase speed and to gain altitude.

# Advice 2 : Why airplanes fly

Actually, it's like a miracle. The winged machine, weighing tens or even hundreds of tons, overcoming the force of gravity, easily shoots up and hovers in the sky like a bird. What force holds it in the air?
Instruction
1
A bit of history

In 1738, Swiss scientist Daniel Bernoulli derived the law that bears his name. Under this law the higher the speed of flow of the fluid static pressure in them drops and Vice versa, decreasing the speed increases.

In 1904 the Russian scientist N. E. Zhukovsky developed the theory of the lifting force acting on the body, a streamlined plane-parallel flow of gas or liquid. According to this theorem, on the body (wing) in a moving liquid or gas medium, operates the lift, the value of which depends on the parameters of the environment and the body. The main result of the work of Zhukovsky became the formula for the lift coefficient.
2
The lifting force

Profile of an airplane wing are not symmetrical, the upper part is more convex than the lower. The motion of the aircraft the speed of air flow passing on top of the wing, the higher speed flow at the bottom. As a result, (according to the Bernoulli theorem) the air pressure under the wing becomes greater than the pressure above the wing. Because of the difference of these pressures occurs lifting force (Y) that pushes the wing up. Its value is:
Y = Cy*p*V2*S/2, where:
- Cy – lift coefficient;
- p – the density of the medium (air) in kg/m3;
- S – area in m2;
- V – flow velocity in m/s.
3
Under the action of different forces

The aircraft moving in the airspace, there are several forces:
the thrust of the engine (jet or screw) that pushes the plane forward;
- drag one sent back;
- force of gravity (the weight of the aircraft), is directed downwards;
- lift force pushing the plane up.

The value of lift and drag depends on wing shape, angle of attack (the angle at which the flow meets the wing) and the density of the air flow. The latter in turn depends on the speed of the aircraft and from the atmospheric air pressure.
4
During acceleration of the aircraft and increasing its speed, the lifting force increases. As soon as she exceeds the weight of the aircraft, he flies up. During horizontal movement of the aircraft with a constant speed, all forces are balanced, and their resultant (net force) is zero.
Wing shape is selected such that the drag as much as possible, and lift as much as possible. The lifting force can be increased by increasing speed and wing area. The higher the speed, the less may be the area of the wings and Vice versa.