Why do planes fly. How an airplane takes off and flies

Why do birds fly?

The wing of a bird is designed in such a way that it creates a force that counteracts the force of gravity. After all, the bird's wing is not flat, like a board, but arched . This means that the jet of air enveloping the wing must travel a longer distance along the upper side than along the concave lower side. For both air streams to reach the wing tip at the same time, the air stream above the wing must move faster than under the wing. Therefore, the speed of air flow over the wing increases, and the pressure decreases.

The difference in pressure under the wing and above it creates a lifting force directed upward and counteracting the force of gravity.

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Airplanes are very complex devices, sometimes frightening with their complexity to ordinary people, people who are not familiar with aerodynamics.

The mass of modern air liners can reach 400 tons, but they calmly stay in the air, move quickly and can cross great distances.

Why is the plane flying?

Because he, like a bird, has a wing!

If the engine fails - it's okay, the plane will fly on the second. If both engines failed, history knows cases that in such circumstances they landed. Chassis? Nothing prevents the plane from landing on its belly; subject to certain fire safety measures, it will not even catch fire. But an airplane can never fly without a wing. Because that's what creates lift.

Airplanes continuously "run into" the air with their wings set at a slight angle to the airflow velocity vector. This angle in aerodynamics is called the "angle of attack". The "angle of attack" is the angle of the wing to the invisible and abstract "flow velocity vector". (see fig 1)

Science says that an airplane flies because a zone of increased pressure is created on the lower surface of the wing, due to which an aerodynamic force arises on the wing, directed upwards perpendicular to the wing. For the convenience of understanding the flight process, this force is decomposed according to the rules of vector algebra into two components: the aerodynamic drag force X

(it is directed along the air flow) and lift Y (perpendicular to the air velocity vector). (see fig 2)

When creating an aircraft, great attention is paid to the wing, because the safety of flight performance will depend on it. Looking out the window, the passenger notices that it is bent and is about to break. Do not be afraid, it can withstand just enormous loads.

In flight and on the ground, the aircraft's wing is "clean", it has minimal air resistance and sufficient lift to keep the aircraft flying at high speeds.

But when it comes time to take off or land, the plane needs to fly as slowly as possible so that lift on one side does not disappear, and on the other, the wheels can withstand touching the ground. For this, the wing area is increased: flaps(planes at the back) and slats(in front of the wing).

If you need to further reduce the speed, then in the upper part of the wing are issued spoilers, which act as an air brake and reduce lift.

The plane becomes like a bristling beast slowly approaching the ground.

Together: flaps, slats and spoilers- called mechanization of the wing. Mechanization is released by pilots manually from the cockpit before takeoff or landing.

As a rule, a hydraulic system (rarely an electric one) is involved in this process. The mechanism looks very interesting, and at the same time is very reliable.

On the wing there are rudders (according to aviation ailerons), similar to those of a ship (no wonder the plane is called an aircraft), which deviate, tilting the plane in the right direction. Usually they deflect synchronously on the left and right side.

Also on the wing are navigation lights , which are designed to ensure that from the side (from the ground or another aircraft) it is always visible in which direction the aircraft is flying. The fact is that the left is always red, and the right is green. Sometimes white "flashing lights" are placed next to them, which are very clearly visible at night.

Most of the characteristics of an aircraft directly depend on the wing, its aerodynamic quality and other parameters. Fuel tanks are located inside the wing (the maximum amount of refueling fuel depends very much on the size of the wing), electric heaters are placed on the leading edge so that ice does not grow there in the rain, landing gear is attached to the root part ...

Aircraft speed reached using a power plant or turbine. Due to the power plant, which creates traction force, the aircraft is able to overcome air resistance.

Planes fly according to the laws of physics.

Aerodynamics as a science is based on t theorem of Nikolai Egorovich Zhukovsky, outstanding Russian scientist, founder of aerodynamics, which was formulated in 1904. A year later, in November 1905, Zhukovsky presented his theory of creating the lift force of an aircraft wing at a meeting of the Mathematical Society.

Why do planes fly so high?

The flight altitude of modern jet aircraft is within from 5000 to 10000 meters above sea level. This is explained very simply: at such a height, the air density is much less, and, consequently, the air resistance is also less. Airplanes fly at high altitudes because when flying at an altitude of 10 kilometers, the aircraft consumes 80% less fuel than when flying at an altitude of one kilometer.

However, why then do they not fly even higher, in the upper layers of the atmosphere, where the air density is even less?

The fact is that in order to create the necessary thrust by an aircraft engine a certain minimum air supply is required. Therefore, each aircraft has a maximum safe flight altitude limit, also called the "service ceiling". For example, the practical ceiling of the Tu-154 aircraft is about 12,100 meters.

Planes can fly, since at high speed the wing of the aircraft creates a force pushing the aircraft up. This force is called the lift force of the aircraft wing. According to the laws of physics, air pressure in places where the flow rate is higher will be lower, and vice versa. This pressure difference creates the lift force of the wing.

The scientific basis of aerodynamics is the theorem of the great Russian scientist Nikolai Yegorovich Zhukovsky, formulated by him in 1904. Zhukovsky presented the theory of the formation of aircraft lift at a meeting of the Mathematical Society in November 1905.

The wing of a modern aircraft has a sufficient area so that the lift force can lift the aircraft up, even if the aircraft weighs tens of tons. The lift force of a wing depends on many factors: profile, area, wing shape in plan, angle of attack, speed and air flow density. Each aircraft has a minimum speed at which the plane can take off, fly and don't fall. For modern passenger aircraft, it ranges from 180 to 250 km/h.

Why do planes fly so high?
Modern jet aircraft fly at altitudes between 5,000 and 11,000 meters above sea level for a very simple reason: at such altitudes, the air is much less dense, which allows the aircraft to achieve less air resistance. Fuel economy when flying at 10,000 meters can reach 80% of a flight at an altitude of 1000 meters. This is why airplanes fly at high altitudes. However, what prevents them from rising even higher, where the air is even more rarefied? - you ask. The fact is that aircraft engines need a certain minimum amount of air for combustion, otherwise the engine will not be able to create the necessary thrust. Therefore, each aircraft has a so-called "practical ceiling" - the highest altitude at which the aircraft can fly safely. For example, the Tu-154 has a practical ceiling of approximately 12,100 meters.

This short video demonstrates the principle of wing lift:

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Often, watching an airplane flying in the sky, we wonder how the plane rises into the air. How does he fly? After all, an airplane is much heavier than air.

Why does the airship rise

We know that balloons and airships are lifted into the air strength of Archimedes . Archimedes' law for gases states: " Hand a body immersed in a gas is subjected to a buoyant force equal to the force of gravity of the gas displaced by this body. . This force is opposite in direction to gravity. That is, the force of Archimedes is directed upwards.

If the force of gravity is equal to the force of Archimedes, then the body is in equilibrium. If the force of Archimedes is greater than the force of gravity, then the body rises in the air. Since the cylinders of balloons and airships are filled with a gas that is lighter than air, the Archimedes force pushes them up. Thus, the Archimedes force is the lifting force for aircraft lighter than air.

But the gravity of the aircraft is much greater than the force of Archimedes. Therefore, she cannot lift the plane into the air. So why is he still flying?

Aircraft wing lift

The emergence of lift is often explained by the difference in static pressure of air flows on the upper and lower surfaces of the wing of the aircraft.

Consider a simplified version of the appearance of the lifting force of the wing, which is located parallel to the air flow. The design of the wing is such that the upper part of its profile has a convex shape. The air flow around the wing is divided into two: upper and lower. The bottom flow rate remains virtually unchanged. But the speed of the upper one increases due to the fact that it must overcome a greater distance in the same time. According to Bernoulli's law, the higher the flow rate, the lower the pressure in it. Consequently, the pressure over the wing becomes lower. Due to the difference in these pressures, lifting force, which pushes the wing up, and with it the plane rises. And the greater this difference, the greater the lifting force.

But in this case it is impossible to explain why the lift force appears when the wing profile has a concave-convex or biconvex symmetrical shape. After all, here the air flows pass the same distance, and there is no pressure difference.

In practice, the wing profile of an aircraft is at an angle to the airflow. This corner is called angle of attack . And the air flow, colliding with the lower surface of such a wing, is beveled and acquires a downward movement. According to law of conservation of momentum the wing will be acted upon by a force directed in the opposite direction, that is, upward.

But this model, which describes the occurrence of lift, does not take into account the flow around the upper surface of the wing profile. Therefore, in this case, the magnitude of the lifting force is underestimated.

In fact, everything is much more complicated. The lift force of an aircraft wing does not exist as an independent quantity. This is one of the aerodynamic forces.

The oncoming air flow acts on the wing with a force called full aerodynamic force . And the lifting force is one of the components of this force. The second component is drag force. The total aerodynamic force vector is the sum of the lift and drag vectors. The lift force vector is directed perpendicular to the velocity vector of the incoming air flow. And the drag force vector is parallel.

The total aerodynamic force is defined as the integral of the pressure around the contour of the wing airfoil:

Y - lift force

R – traction

dΩ – profile boundary

R is the pressure value around the contour of the wing profile

n – profile normal

Zhukovsky's theorem

How the wing lift is formed was first explained by the Russian scientist Nikolai Yegorovich Zhukovsky, who is called the father of Russian aviation. In 1904, he formulated a theorem on the lifting force of a body in a plane-parallel flow of an ideal liquid or gas.

Zhukovsky introduced the concept of flow velocity circulation, which made it possible to take into account the flow slope and obtain a more accurate value of the lift force.

The lift force of an infinite span wing is equal to the product of the density of the gas (liquid), the velocity of the gas (liquid), the circulation velocity of the flow, and the length of the selected segment of the wing. The direction of the lift force is obtained by turning the velocity vector of the oncoming flow at a right angle against the circulation.

lifting force

Medium density

Flow rate at infinity

Flow velocity circulation (the vector is directed perpendicular to the plane of the profile, the direction of the vector depends on the direction of circulation),

The length of the wing segment (perpendicular to the profile plane).

The amount of lift depends on many factors: the angle of attack, the density and speed of the air flow, the geometry of the wing, etc.

Zhukovsky's theorem is the basis of modern wing theory.

An aircraft can only take off if the lift force is greater than its weight. It develops speed with the help of engines. As the speed increases, the lift also increases. And the plane takes off.

If the lift and weight of the aircraft are equal, then it flies horizontally. Aircraft engines create thrust - a force whose direction coincides with the direction of movement of the aircraft and is opposite to the direction of drag. The thrust pushes the aircraft through the air. In level flight at a constant speed, thrust and drag are balanced. If you increase the thrust, the plane will begin to accelerate. But the frontal resistance will also increase. And soon they will balance again. And the plane will fly at a constant, but higher speed.

If the speed decreases, then the lift force also decreases, and the aircraft begins to decline.

Mankind has long been interested in the question of how it happens that a multi-ton aircraft easily rises to heaven. How does takeoff take place and how do planes fly? When an airliner moves at high speed along the runway, the wings develop lift and work from the bottom up.

When the aircraft moves, a pressure difference is generated between the lower and upper sides of the wing, which results in a lift force that keeps the aircraft in the air. Those. high air pressure from below pushes the wing up, while low air pressure from above pulls the wing towards itself. As a result, the wing rises.

To take off an airliner, it needs a sufficient takeoff run. Wing lift increases as speed increases., which should exceed the takeoff limit. Then the pilot increases the angle of takeoff, pulling the steering wheel towards you. The bow of the liner rises up, and the car rises into the air.

Then retractable landing gear and exhaust lights. In order to reduce the wing lift, the pilot gradually retracts the mechanization. When the airliner reaches the required level, the pilot sets standard pressure, and engines - nominal mode. To see how the plane takes off, we suggest watching the video at the end of the article.

The ship takes off at an angle. From a practical point of view, this can be explained as follows. The elevator is a movable surface, by controlling which you can cause the aircraft to deviate in pitch.

The elevator can control the pitch angle, i.e. change the rate of climb or loss of altitude. This is due to a change in the angle of attack and lift force. By increasing the speed of the engine, the propeller starts spinning faster and lifts the airliner up. Conversely, by directing the elevators down, the nose of the aircraft goes down, while the engine speed should be reduced.

The tail section of an airliner equipped with a rudder and brakes on both sides of the wheels.

How do airliners fly

When answering the question why planes fly, one should remember the law of physics. The pressure difference affects the lift force of the wing.

The flow rate will be greater if the air pressure is low and vice versa.

Therefore, if the speed of an airliner is high, then its wings acquire lift, which pushes the aircraft.

Some circumstances also influence the lifting force of an airliner's wing: the angle of attack, the speed and density of the air flow, the area, profile and shape of the wing.

Modern liners have minimum speed from 180 to 250 km/h, at which takeoff is carried out, plans in the sky and does not fall.

Flight altitude

What is the maximum and safe altitude of the aircraft.

Not all ships have the same flight altitude, "air ceiling" can fluctuate at height from 5000 to 12100 meters. At high altitudes, the air density is minimal, while the liner achieves the lowest air resistance.

The engine of the liner needs a fixed amount of air for combustion, because the engine will not create the necessary thrust. Also, when flying at high altitude, the aircraft saves fuel up to 80%, in contrast to the altitude up to a kilometer.

What keeps the plane in the air

To answer why airplanes fly, it is necessary to analyze in turn the principles of its movement in the air. A jet airliner with passengers on board reaches several tons, but at the same time, it easily takes off and carries out a thousand-kilometer flight.

The movement in the air is also affected by the dynamic properties of the apparatus, the design of the units that form the flight configuration.

Forces affecting the movement of an aircraft in the air

The operation of an airliner begins with the engine starting. Small craft are powered by piston engines that turn propellers to create thrust to help the aircraft move through the air.

Large airliners are powered by jet engines, which emit a lot of air during operation, while the jet force propels the aircraft forward.

Why does an airplane take off and stay in the air for a long time? Because the shape of the wings has a different configuration: rounded on top and flat on the bottom, then the air flow on both sides is not the same. On top of the wings, the air glides and becomes rarefied, and its pressure is less than the air below the wing. Therefore, through uneven air pressure and the shape of the wings, a force arises that leads to the takeoff of the aircraft upwards.

But in order for an airliner to easily take off from the ground, it needs to take off at high speed along the runway.

From this follows the conclusion that in order for an airliner to be unhindered in flight, it needs moving air, which cuts through the wings and creates lift.

Airplane takeoff and speed

Many passengers are interested in the question, what speed does the plane develop during takeoff? There is a misconception that the takeoff speed for each aircraft is the same. To answer the question, what is the speed of the aircraft during takeoff, you should pay attention to important factors.

1. The airliner does not have a strictly fixed speed. The lifting force of an air liner depends on its mass and the length of the wings.. Takeoff is performed when a lift force is created in the oncoming flow, which is much greater than the mass of the aircraft. Therefore, the takeoff and speed of the aircraft depends on wind direction, atmospheric pressure, humidity, precipitation, runway length and condition.
2. To create lift and successfully lift off the ground, the aircraft needs to gain maximum takeoff speed and sufficient takeoff run. This requires long runways. The larger the aircraft, the longer the runway required.
3. Each aircraft has its own scale of takeoff speeds, because they all have their own purpose: passenger, sport, cargo. The lighter the aircraft, the lower the takeoff speed and vice versa.

Boeing 737 passenger jet takeoff

• The takeoff run of an airliner on the runway begins when the engine will reach 800 rpm per minute, the pilot slowly releases the brakes and holds the control stick at neutral. The aircraft then continues on three wheels;
• Before taking off from the ground the speed of the liner should reach 180 km per hour. Then the pilot pulls the lever, which leads to the deflection of the flaps - flaps and raising the nose of the aircraft. Further acceleration is carried out on two wheels;
• After, with a raised bow, the airliner accelerates on two wheels to 220 km per hour, and then take off from the ground.

Therefore, if you want to know in more detail how the plane takes off, to what height and at what speed, we offer you this information in our article. We hope you enjoy your air travel.



Most of us still sometimes ask ourselves how an aircraft weighing up to 600 tons or more can stay in the air.

From school textbooks it is clear that they rise, obeying the laws of physics, and all flying structures rise, starting with light sports airplanes and ending with heavy transport workers or shapeless helicopters. This happens due to the thrust force of the engine and the lifting force.

Almost everyone knows the phrase "lift force", but not everyone can explain how this happens. But in fact, this action can be explained without getting into mathematical formulas and axioms.

The wing of an aircraft is the main bearing surface of an aircraft. Almost always having a certain profile, in which the top is convex and the bottom is flat. When the air flow passes under the lower part of the aircraft profile, there is practically no change in its structure and shape. The air flow, passing over the upper part of the profile, narrows, since for the air flow the upper plane of the profile is like a concave wall in a pipe, it seems to flow in it.

In order to drive the same volume of air through a given “squeezed” pipe in a certain time, it must be moved faster. According to Bernoulli's law, which is passed in the school curriculum of physics, the higher the flow rate, the lower its pressure. It follows from this that the pressure above the entire wing, and hence above the airfoil, is lower than the pressure below it.

A force is formed that wants to squeeze out the wing, and, consequently, the entire aircraft. This is called lifting force. If it becomes more than the weight of the aircraft, it takes off. The greater the speed, the greater the lift. If the weight of the aircraft and the value of the lifting force are equal, then the aircraft will move to a horizontal position. Not a bad speed is given by its aircraft engine, i.e. the force it creates.

Using the above principles, it is possible, in theory, to make any object with any mass and shape take off. Not a standard form, i.e. different from airplanes, is a helicopter. It is strikingly different from an airplane, but it lifts it into the air for the same reason. A helicopter has a wing with an airfoil, which is the blade of its main rotor.

The blade creates lift by moving in the airstream as the propeller rotates, which lifts it and propels the helicopter forward. This happens when the inclination of the rotation of the propeller changes, as a result of which a horizontal component of the lifting force appears, which plays the role of the thrust force of an aircraft engine.