Actually, it looks like a miracle. A winged machine weighing tens and even hundreds of tons, overcoming gravity, easily soars up and soars in the sky like a bird. What is the strength that keeps her in the air?
Instructions
Step 1
A bit of history
In 1738 the Swiss scientist Daniel Bernoulli developed a law named after him. According to this law, with an increase in the flow rate of a liquid or gas, the static pressure in them decreases and vice versa, with a decrease in the speed, it increases.
In 1904, the Russian scientist N. E. Zhukovsky developed a theorem on the lifting force acting on a body in a plane-parallel flow of gas or liquid. According to this theorem, a body (wing) located in a moving liquid or gaseous medium is subjected to a lifting force, the value of which depends on the parameters of the medium and the body. The main result of Zhukovsky's work was the formula for the lift coefficient.
Step 2
Lifting force
The airplane wing profile is asymmetrical, its upper part is more convex than the lower one. When the aircraft moves, the speed of the air flow passing from the top of the wing is higher than the speed of the flow passing from the bottom. As a result of this (according to Bernoulli's theorem) the air pressure under the wing of the aircraft becomes higher than the pressure above the wing. Due to the difference in these pressures, a lift (Y) arises, pushing the wing upward. Its value is:
Y = Cy * p * V² * S / 2, where:
- Cy - coefficient of lift;
- p is the density of the medium (air) in kg / m³;
- S - area in m²;
- V is the flow velocity in m / s.
Step 3
Under the influence of different forces
Several forces act on an aircraft moving in airspace:
- the thrust force of the engine (propeller or jet) pushing the aircraft forward;
- frontal resistance directed backward;
- the force of gravity of the Earth (weight of the aircraft), directed downward;
- lift pushing the plane up.
The value of lift and drag depends on the shape of the wing, the 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 on the atmospheric air pressure.
Step 4
As the aircraft accelerates and its speed increases, the lift increases. As soon as it exceeds the weight of the plane, it takes off upward. When the aircraft moves horizontally at a constant speed, all forces are balanced, their resultant (total force) is zero.
The shape of the wing is chosen such that the drag is as low as possible and the lift is as high as possible. Lift can be increased by increasing travel speed and wing area. The higher the speed of movement, the smaller the wing area can be and vice versa.
