The principle of jet propulsion. Application of jet propulsion in technology

Today, most people, of course, primarily associate jet propulsion with the latest scientific and technical developments. From physics textbooks we know that by “reactive” we mean movement that occurs as a result of the separation of any part of it from an object (body). Man wanted to rise into the sky to the stars, he wanted to fly, but he was able to realize his dream only with the advent of jet aircraft and stepped spaceships, capable of traveling over vast distances, accelerating to supersonic speeds, thanks to the modern jet engines installed on them. Designers and engineers were developing the possibility of using jet propulsion in engines. Science fiction writers also did not stand aside, offering the most incredible ideas and ways to achieve this goal. Surprisingly, this principle of movement is widespread in wildlife. Just look around, you can notice the inhabitants of the seas and land, among which there are plants, the basis of whose movement is the reactive principle.

Story

Also in ancient times scientists studied and analyzed with interest the phenomena associated with jet motion in nature. One of the first to theoretically substantiate and describe its essence was Heron, a mechanic and theorist Ancient Greece, who invented the first steam engine, named after him. The Chinese were able to find practical applications for the reactive method. They were the first, taking as a basis the method of movement of cuttlefish and octopuses, to invent rockets back in the 13th century. They were used in fireworks, making a great impression, and also as signal flares, and possibly military missiles that were used as rocket artillery. Over time, this technology came to Europe.

The pioneer of modern times was N. Kibalchich, who came up with a design for a prototype aircraft with a jet engine. He was an outstanding inventor and a convinced revolutionary, for which he was imprisoned. It was while in prison that he made history by creating his project. After his execution for active revolutionary activity and speeches against the monarchy, his invention was forgotten on the archive shelves. After some time, K. Tsiolkovsky was able to improve Kibalchich’s ideas, proving the possibility of exploring outer space through the reactive propulsion of spaceships.

Later, during the Great Patriotic War, the famous Katyushas and field rocket artillery systems appeared. This is the affectionate name people informally used to refer to the powerful installations used by the USSR forces. It is not known for certain why the weapon received this name. The reason for this was either the popularity of Blanter’s song, or the letter “K” on the body of the mortar. Over time, front-line soldiers began to give nicknames to other weapons, thus creating new tradition. The Germans did this battle rocket launcher called "Stalin's organ" for appearance, which reminded musical instrument and the piercing sound that came from the launching rockets.

Vegetable world

Representatives of the fauna also use the laws of jet propulsion. Most plants with such properties are annuals and perennials: thorny carp, common spadefoot spadefoot, impatiens heartwood, two-cut pikulnik, three-veined meringia.

The prickly cucumber, also known as the crazy cucumber, belongs to the pumpkin family. This plant reaches large sizes, has a thick root with a rough stem and large leaves. Grows in the area Central Asia, Mediterranean, Caucasus, quite common in southern Russia and Ukraine. Inside the fruit, during the period of seed ripening, it is transformed into mucus, which, under the influence of temperatures, begins to ferment and release gas. Closer to ripening, the pressure inside the fruit can reach 8 atmospheres. Then, with a light touch, the fruit breaks away from the base and the seeds with liquid fly out of the fruit at a speed of 10 m/s. Due to its ability to shoot 12 m in length, the plant was called the “ladies pistol”.

Impatiens heartwood is a widespread annual species. It is found, as a rule, in shady forests, along the banks of rivers. Once in the northeastern part North America and to South Africa, successfully took root. Touch-me-not is propagated by seeds. The seeds of the impatiens are small, weighing no more than 5 mg, which are thrown at a distance of 90 cm. Thanks to this method of seed dispersal, the plant got its name.

Animal world

Jet propulsion — Interesting Facts relating to the animal world. In cephalopods, jet propulsion occurs through water exhaled through a siphon, which usually tapers to a small opening to obtain maximum expiratory flow. Water passes through the gills before exhalation, fulfilling the dual purpose of breathing and movement. Sea hares, also known as gastropods, use similar means of locomotion, but without the complex neurological apparatus of cephalopods, they move more clumsily.

Some knightfish have also developed jet propulsion, forcing water over their gills to complement fin movement.

In dragonfly larvae, reactive force is achieved by displacing water from a specialized cavity in the body. Scallops and cardids, siphonophores, tunics (such as salps) and some jellyfish also use jet propulsion.

Most of the time, scallops lie quietly on the bottom, but if danger arises, they quickly close the valves of their shells, so they push out the water. This behavior mechanism also speaks of the use of the principle of reactive movement. Thanks to it, scallops can float up and move over long distances using the opening-closing technique of the shell.

The squid also uses this method, absorbs water, and then enormous power pushing through the funnel moves at a speed of at least 70 km/h. By collecting the tentacles into one knot, the squid's body forms a streamlined shape. Using this squid engine as a basis, engineers designed a water cannon. The water in it is sucked into the chamber and then thrown out through the nozzle. Thus, the ship is sent to reverse side from the ejected jet.

Compared to squids, salps use the most efficient engines, spending an order of magnitude less energy than squids. Moving, the salpa releases water into the hole in the front, and then enters the wide cavity where the gills are stretched. After a sip, the hole closes, and with the help of contracting longitudinal and transverse muscles that compress the body, water is released through the hole at the back.

The most unusual of all locomotion mechanisms is the common cat. Marcel Despres suggested that the body is capable of moving and changing its position even with the help of only internal forces(without starting from anything or relying on anything), from which one could conclude that Newton’s laws may be erroneous. The proof of his assumption could be a cat that fell from a height. If she falls upside down, she will still land on all her paws; this has already become a kind of axiom. Having photographed the cat’s movement in detail, we were able to see from the frames everything that it did in the air. We saw her move her paw, which caused a response from her body, turning in the other direction relative to the movement of her paw. Acting according to Newton's laws, the cat landed successfully.

In animals, everything happens at the level of instinct; humans, in turn, do it consciously. Professional swimmers, having jumped from the tower, manage to turn around three times in the air, and having managed to stop the rotation, straighten up strictly vertically and dive into the water. The same principle applies to aerial circus gymnasts.

No matter how much people try to surpass nature by improving the inventions it has created, we still have not yet achieved that technological perfection when airplanes could repeat the actions of a dragonfly: hover in the air, instantly back up or move to the side. And all this happens at high speed. Perhaps a little more time will pass and airplanes, thanks to adjustments to the aerodynamics and jet capabilities of dragonflies, will be able to make sharp turns and become less susceptible to external conditions. Having looked at nature, man can still improve a lot for the benefit of technical progress.

Essay

Physics

On the topic of:

"Jet propulsion"

Completed by a student from Municipal Educational Institution Secondary School No. 5

G. Lobnya, 10 “B” class,

Stepanenko Inna Yurievna

Jet propulsion.

For many centuries, humanity has dreamed of space flight. Science fiction writers offered the most different means to achieve this goal. In the 17th century a story appeared French writer Cyrano de Bergerac about the flight to the moon. The hero of this story reached the Moon in an iron cart, over which he constantly threw a strong magnet. Attracted to him, the cart rose higher and higher above the Earth until it reached the Moon. And Baron Munchausen said that he climbed to the moon along a bean stalk.

But not a single scientist, not a single science fiction writer for many centuries could name the only means at a person’s disposal with which one can overcome the force of gravity and fly into space. This was accomplished by the Russian scientist Konstantin Eduardovich Tsiolkovsky (1857-1935). He showed that the only device capable of overcoming gravity is a rocket, i.e. a device with a jet engine that uses fuel and oxidizer located on the device itself.

A jet engine is an engine that converts the chemical energy of fuel into the kinetic energy of a gas jet, and the engine acquires speed in the opposite direction. On what principles and physical laws is its action based?

Everyone knows that a shot from a gun is accompanied by recoil. If the weight of the bullet were equal to the weight of the gun, they would fly apart at the same speed. Recoil occurs because the ejected mass of gases creates a reactive force, thanks to which movement can be ensured both in air and in airless space. And the greater the mass and speed of the flowing gases, the greater the recoil force our shoulder feels, the stronger the reaction of the gun, the greater the reactive force. This is easy to explain from the law of conservation of momentum, which states that the geometric (i.e. vector) sum of the momentum of the bodies that make up a closed system remains constant for any movements and interactions of the bodies of the system, i.e.

K. E. Tsiolkovsky derived a formula that allows one to calculate the maximum speed that a rocket can develop. Here is the formula:

Here v max is the maximum speed of the rocket, v 0 is the initial speed, v r is the speed of gas flow from the nozzle, m is the initial mass of the fuel, and M is the mass of the empty rocket. As can be seen from the formula, this maximum achievable speed depends primarily on the speed of gas flow from the nozzle, which in turn depends primarily on the type of fuel and the temperature of the gas jet. The higher the temperature, the greater the speed. This means that for a rocket you need to select the most high-calorie fuel that provides the greatest amount of heat. It also follows from the formula that this speed depends on both the initial and final mass of the rocket, i.e. depends on what part of its weight is fuel, and what part is useless (from the point of view of flight speed) structures: body, mechanisms, etc.

This Tsiolkovsky formula is the foundation on which the entire calculation of modern missiles is based. The ratio of the fuel mass to the mass of the rocket at the end of engine operation (i.e., essentially to the weight of the empty rocket) is called the Tsiolkovsky number.

The main conclusion from this formula is that in airless space a rocket will develop a higher speed, the higher the speed of gas outflow and the higher the Tsiolkovsky number.

Conclusion.

I would like to add that the description I gave of the operation of an intercontinental ballistic missile is outdated and corresponds to the level of development of science and technology of the 60s, but due to limited access to modern scientific materials, I am not able to give an accurate description of the operation of a modern ultra-long-range intercontinental ballistic missile . However, I highlighted the general properties inherent in all rockets, so I consider my task completed.

List of used literature:

Deryabin V. M. Conservation laws in physics. – M.: Education, 1982.

Gelfer Ya. M. Conservation laws. – M.: Nauka, 1967.

Body K. World without forms. – M.: Mir, 1976.

Children's encyclopedia. – M.: Publishing House of the USSR Academy of Sciences, 1959.

Jet propulsion in nature and technology

ABSTRACT ON PHYSICS

Jet propulsion- movement that occurs when any part of it is separated from the body at a certain speed.

Reactive force occurs without any interaction with external bodies.

Application of jet propulsion in nature

Many of us in our lives have encountered jellyfish while swimming in the sea. In any case, there are quite enough of them in the Black Sea. But few people thought that jellyfish also use jet propulsion to move. In addition, this is how dragonfly larvae and some types of marine plankton move. And often the efficiency of marine invertebrate animals when using jet propulsion is much higher than that of technological inventions.

Jet propulsion is used by many mollusks - octopuses, squids, cuttlefish. For example, a sea scallop mollusk moves forward due to the reactive force of a stream of water thrown out of the shell during a sharp compression of its valves.

Octopus

Cuttlefish

Jellyfish

Cuttlefish, like most cephalopods, moves in water in the following way. She takes water into the gill cavity through a side slit and a special funnel in front of the body, and then energetically throws out a stream of water through the funnel. The cuttlefish directs the funnel tube to the side or back and, quickly squeezing water out of it, can move in different directions.

The salpa is a marine animal with a transparent body; when moving, it receives water through the front opening, and the water enters a wide cavity, inside of which the gills are stretched diagonally. As soon as the animal takes a large sip of water, the hole closes. Then the longitudinal and transverse muscles of the salp contract, the whole body contracts, and water is pushed out through the posterior opening. The reaction of the escaping jet pushes the salpa forward.

The squid's jet engine is of greatest interest. The squid is the largest invertebrate inhabitant of the ocean depths. Squids have achieved the highest perfection in jet navigation. Even their body, with its external forms, copies the rocket (or better said, the rocket copies the squid, since it has indisputable priority in this matter). When moving slowly, the squid uses a large diamond-shaped fin that periodically bends. It uses a jet engine to throw quickly. Muscle tissue - the mantle surrounds the mollusk's body on all sides; the volume of its cavity is almost half the volume of the squid's body. The animal sucks water inside the mantle cavity, and then sharply throws out a stream of water through a narrow nozzle and moves backwards with high speed pushes. At the same time, all ten tentacles of the squid are gathered into a knot above its head, and it takes on a streamlined shape. The nozzle is equipped with a special valve, and the muscles can rotate it, changing the direction of movement. The squid engine is very economical, it is capable of reaching speeds of up to 60 - 70 km/h. (Some researchers believe that even up to 150 km/h!) No wonder the squid is called a “living torpedo.” By bending the bundled tentacles to the right, left, up or down, the squid turns in one direction or another. Since such a steering wheel, compared to the animal itself, has a very big sizes, then its slight movement is enough for the squid, even at full speed, to easily dodge a collision with an obstacle. A sharp turn of the steering wheel - and the swimmer rushes in the opposite direction. So he bent the end of the funnel back and now slides head first. He bent it to the right - and the jet push threw him to the left. But when you need to swim quickly, the funnel always sticks out right between the tentacles, and the squid rushes tail first, just as a crayfish would run - a fast walker endowed with the agility of a racer.

If there is no need to rush, squids and cuttlefish swim with undulating fins - miniature waves run over them from front to back, and the animal glides gracefully, occasionally pushing itself also with a stream of water thrown out from under the mantle. Then the individual shocks that the mollusk receives at the moment of eruption of water jets are clearly visible. Some cephalopods can reach speeds of up to fifty-five kilometers per hour. It seems that no one has made direct measurements, but this can be judged by the speed and flight range of flying squids. And it turns out that octopuses have such talents in their family! The best pilot among mollusks is the squid Stenoteuthis. English sailors call it flying squid (“flying squid”). This is a small animal about the size of a herring. It chases fish with such speed that it often jumps out of the water, skimming over its surface like an arrow. He resorts to this trick to save his life from predators - tuna and mackerel. Having developed maximum jet thrust in the water, the pilot squid takes off into the air and flies over the waves for more than fifty meters. The apogee of a living rocket's flight lies so high above the water that flying squids often end up on the decks of ocean-going ships. Four to five meters is not a record height to which squids rise into the sky. Sometimes they fly even higher.

The English mollusk researcher Dr. Rees described in a scientific article a squid (only 16 centimeters long), which, having flown a fair distance through the air, fell on the bridge of a yacht, which rose almost seven meters above the water.

It happens that a lot of flying squids fall on the ship in a sparkling cascade. The ancient writer Trebius Niger once told sad story about a ship that allegedly even sank under the weight of flying squids that fell on its deck. Squids can take off without acceleration.

Octopuses can also fly. French naturalist Jean Verani saw how an ordinary octopus accelerated in an aquarium and suddenly jumped out of the water backwards. Having described an arc about five meters long in the air, he plopped back into the aquarium. When picking up speed to jump, the octopus moved not only due to jet thrust, but also rowed with its tentacles.
Baggy octopuses swim, of course, worse than squids, but at critical moments they can show a record class for the best sprinters. California Aquarium staff tried to photograph an octopus attacking a crab. The octopus rushed at its prey with such speed that the film, even when filming at the highest speeds, always contained grease. This means that the throw lasted hundredths of a second! Typically, octopuses swim relatively slowly. Joseph Seinl, who studied the migrations of octopuses, calculated: an octopus half a meter in size swims through the sea at an average speed of about fifteen kilometers per hour. Each jet of water thrown out of the funnel pushes it forward (or rather, backward, since the octopus swims backwards) two to two and a half meters.

Knowing the law of conservation of momentum, you can change your own speed of movement in open space. If you are in a boat and you have several heavy stones, then throwing stones in a certain direction will move you in the opposite direction. The same will happen in outer space, but there they use jet engines for this.

Everyone knows that a shot from a gun is accompanied by recoil. If the weight of the bullet were equal to the weight of the gun, they would fly apart at the same speed. Recoil occurs because the ejected mass of gases creates a reactive force, thanks to which movement can be ensured both in air and in airless space. And the greater the mass and speed of the flowing gases, the greater the recoil force our shoulder feels, the stronger the reaction of the gun, the greater the reactive force.

Application of jet propulsion in technology

For many centuries, humanity has dreamed of space flight. Science fiction writers have proposed a variety of means to achieve this goal. In the 17th century, a story by the French writer Cyrano de Bergerac about a flight to the moon appeared. The hero of this story reached the Moon in an iron cart, over which he constantly threw a strong magnet. Attracted to him, the cart rose higher and higher above the Earth until it reached the Moon. And Baron Munchausen said that he climbed to the moon along a bean stalk.

At the end of the first millennium AD, China invented jet propulsion, which powered rockets - bamboo tubes filled with gunpowder, they were also used as fun. One of the first car projects was also with a jet engine and this project belonged to Newton

The author of the world's first project of a jet aircraft intended for human flight was the Russian revolutionary N.I. Kibalchich. He was executed on April 3, 1881 for his participation in the assassination attempt on Emperor Alexander II. He developed his project in prison after being sentenced to death. Kibalchich wrote: “While in prison, a few days before my death, I am writing this project. I believe in the feasibility of my idea, and this faith supports me in my terrible situation... I will calmly face death, knowing that my idea will not die with me.”

The idea of ​​using rockets for space flights was proposed at the beginning of this century by the Russian scientist Konstantin Eduardovich Tsiolkovsky. In 1903, an article by Kaluga gymnasium teacher K.E. appeared in print. Tsiolkovsky “Exploration of world spaces using reactive instruments.” This work contained the most important mathematical equation for astronautics, now known as the “Tsiolkovsky formula,” which described the motion of a body of variable mass. Later he developed a scheme rocket engine on liquid fuel, proposed a multi-stage rocket design, and expressed the idea of ​​​​the possibility of creating entire space cities in low-Earth orbit. He showed that the only device capable of overcoming gravity is a rocket, i.e. a device with a jet engine that uses fuel and oxidizer located on the device itself.

Jet engine is an engine that converts the chemical energy of fuel into kinetic energy gas jet, while the engine acquires speed in the opposite direction.

The idea of ​​K.E. Tsiolkovsky was implemented by Soviet scientists under the leadership of Academician Sergei Pavlovich Korolev. First ever artificial satellite Earth by rocket was launched into the Soviet Union on October 4, 1957.

The principle of jet propulsion finds wide practical application in aviation and astronautics. In outer space there is no medium with which a body could interact and thereby change the direction and magnitude of its speed, therefore only jet aircraft, i.e., rockets, can be used for space flights.

Rocket device

The motion of a rocket is based on the law of conservation of momentum. If at some point in time any body is thrown away from the rocket, it will acquire the same impulse, but directed in the opposite direction

Any rocket, regardless of its design, always has a shell and fuel with an oxidizer. The rocket shell includes the payload (in in this case this is a spaceship), the instrument compartment and the engine (combustion chamber, pumps, etc.).

The main mass of the rocket is fuel with an oxidizer (the oxidizer is needed to maintain fuel combustion, since there is no oxygen in space).

Fuel and oxidizer are supplied to the combustion chamber using pumps. Fuel, when burned, turns into a gas of high temperature and high pressure. Due to the large pressure difference in the combustion chamber and in outer space, gases from the combustion chamber rush out in a powerful jet through a specially shaped socket called a nozzle. The purpose of the nozzle is to increase the speed of the jet.

Before the rocket launches, its momentum equal to zero. As a result of the interaction of the gas in the combustion chamber and all other parts of the rocket, the gas escaping through the nozzle receives some impulse. Then the rocket is closed system, and its total momentum should be zero after launch. Therefore, the entire shell of the rocket that is in it receives an impulse equal in magnitude to the impulse of the gas, but opposite in direction.

The most massive part of the rocket, intended for launch and acceleration of the entire rocket, is called the first stage. When the first massive stage of a multi-stage rocket exhausts all its fuel reserves during acceleration, it separates. Further acceleration is continued by the second, less massive stage, and it adds some more speed to the speed previously achieved with the help of the first stage, and then separates. The third stage continues to increase speed to the required value and delivers the payload into orbit.

The first person to fly in outer space was a citizen Soviet Union Yuri Alekseyevich Gagarin. April 12, 1961 It flew around Earth on the satellite ship "Vostok"

Soviet rockets were the first to reach the Moon, circled the Moon and photographed its side invisible from Earth, and were the first to reach the planet Venus and deliver scientific instruments to its surface. In 1986, two Soviet spacecraft, Vega 1 and Vega 2, closely examined Halley's Comet, which approaches the Sun once every 76 years.

For many people, the very concept of “jet propulsion” is strongly associated with modern achievements of science and technology, especially physics, and images of jet aircraft or even spaceships flying at supersonic speeds using the notorious jet engines appear in their heads. In fact, the phenomenon of jet propulsion is much more ancient than even man himself, because it appeared long before us humans. Yes, jet propulsion is actively represented in nature: jellyfish and cuttlefish have been swimming in the depths of the sea for millions of years using the same principle by which modern supersonic jet aircraft fly today.

History of jet propulsion

Since ancient times, various scientists have observed the phenomena of reactive motion in nature; the ancient Greek mathematician and mechanic Heron was the first to write about it, although he never went further than theory.

If we talk about practical application jet propulsion, then the inventive Chinese were the first here. Around the 13th century, they figured out to borrow the principle of movement of octopuses and cuttlefish when inventing the first rockets, which they began to use both for fireworks and for military operations (as combat and signal weapons). A little later, this useful invention of the Chinese was adopted by the Arabs, and from them by the Europeans.

Of course, the first ones are conditional rockets had a relatively primitive design and for several centuries they practically did not develop at all; it seemed that the history of the development of jet propulsion froze. A breakthrough in this matter occurred only in the 19th century.

Who discovered jet propulsion?

Perhaps the laurels of the discoverer of jet propulsion in the “new era” can be awarded to Nikolai Kibalchich, not only a talented Russian inventor, but also a part-time revolutionary-People’s Volunteer. He created his project for a jet engine and an aircraft for people while sitting in a royal prison. Kibalchich was later executed for his revolutionary activities, and his project remained gathering dust on the shelves in the archives of the Tsarist secret police.

Later, Kibalchich’s work in this direction was discovered and supplemented by the works of another talented scientist K. E. Tsiolkovsky. From 1903 to 1914, he published a number of works in which he convincingly proved the possibility of using jet propulsion in creating spacecraft for research. outer space. He also formed the principle of using multi-stage rockets. To this day, many of Tsiolkovsky’s ideas are used in rocket science.

Examples of jet propulsion in nature

Surely, while swimming in the sea, you saw jellyfish, but you hardly thought that these amazing (and also slow) creatures move thanks to jet propulsion. Namely, by contracting their transparent dome, they squeeze out water, which serves as a kind of “jet engine” for the jellyfish.

The cuttlefish has a similar mechanism of movement - through a special funnel in front of the body and through a side slit, it draws water into its gill cavity, and then energetically throws it out through the funnel directed back or to the side (depending on the direction of movement needed by the cuttlefish).

But the most interesting jet engine created by nature is found in squids, which can quite rightly be called “living torpedoes.” After all, even the body of these animals resembles a rocket in its shape, although in truth everything is exactly the opposite - this rocket, with its design, copies the body of a squid.

If the squid needs to make a quick dash, it uses its natural jet engine. Its body is surrounded by a mantle, special muscle tissue, and half the volume of the entire squid is in the mantle cavity, into which it sucks water. Then he sharply throws out the collected stream of water through a narrow nozzle, while folding all his ten tentacles above his head in such a way as to acquire a streamlined shape. Thanks to such advanced reactive navigation, squids can reach an impressive speed of 60-70 km per hour.

Among the owners of a jet engine in nature there are also plants, namely the so-called “mad cucumber”. When its fruits ripen, in response to the slightest touch, it shoots gluten with seeds

Law of Jet Propulsion

Squids, “mad cucumbers”, jellyfish and other cuttlefish have been using jet motion since ancient times, without thinking about its physical essence, but we will try to figure out what the essence of jet motion is, what kind of motion is called jet motion, and give it a definition.

To begin with, you can resort to a simple experiment - if the usual balloon inflate it with air and, without stopping, let it fly, it will fly rapidly until its air supply is used up. This phenomenon is explained by Newton's third law, which says that two bodies interact with forces equal in magnitude and opposite in direction.

That is, the force of the ball’s influence on the air streams escaping from it is equal to the force with which the air pushes the ball away from itself. A rocket works on a similar principle to a ball, which ejects part of its mass at enormous speed, while receiving strong acceleration in the opposite direction.

Law of conservation of momentum and jet propulsion

Physics explains the process of jet propulsion. Momentum is the product of a body's mass and its speed (mv). When a rocket is at rest its momentum and speed are zero. When a jet stream begins to be ejected from it, then the rest, according to the law of conservation of momentum, must acquire such a speed at which the total momentum will still be equal to zero.

Jet propulsion formula

In general, jet motion can be described by the following formula:
m s v s +m р v р =0
m s v s =-m р v р

where m s v s is the impulse created by the gas jet, m p v p is the impulse received by the rocket.

The minus sign shows that the direction of motion of the rocket and the force of the jet's jet motion are opposite.

Jet propulsion in technology - the principle of operation of a jet engine

IN modern technology jet propulsion plays a very important role, as jet engines propel airplanes, spaceships. The design of the jet engine itself may vary depending on its size and purpose. But one way or another, each of them has

• fuel supply,
• chamber for fuel combustion,
• a nozzle whose task is to accelerate the jet stream.

This is what a jet engine looks like.

Jet propulsion, video

And finally, an entertaining video about physical experiments with jet propulsion.

Newton's laws help explain a very important mechanical phenomenon - jet propulsion. This is the name given to the movement of a body that occurs when some part of it is separated from it at any speed.

Let's take, for example, a children's rubber ball, inflate it and release it. We will see that when the air begins to leave it in one direction, the ball itself will fly in the other. This is reactive movement.

Some representatives of the animal world move according to the principle of jet propulsion, such as squids and octopuses. Periodically throwing out the water they absorb, they are able to reach speeds of up to 60-70 km/h. Jellyfish, cuttlefish and some other animals move in a similar way.

Examples of jet propulsion can also be found in the plant world. For example, the ripened fruits of a “mad” cucumber, with the slightest touch, bounce off the stalk and a bitter liquid with seeds is forcefully thrown out of the hole formed at the site of the separated stalk; the cucumbers themselves fly off in the opposite direction.

The reactive motion that occurs when water is released can be observed in the following experiment. Pour water into a glass funnel connected to a rubber tube with an L-shaped tip (Fig. 20). We will see that when the water begins to pour out of the tube, the tube itself will begin to move and tilt to the side, opposite direction water leakage.

Flights are based on the principle of jet propulsion missiles. Modern space rocket is very complex aircraft, consisting of hundreds of thousands and millions of parts. The mass of the rocket is enormous. It consists of the mass of the working fluid (i.e., hot gases formed as a result of fuel combustion and emitted in the form of a jet stream) and the final or, as they say, “dry” mass of the rocket remaining after the working fluid is ejected from the rocket.

The “dry” mass of the rocket, in turn, consists of the mass of the structure (i.e. the rocket shell, its engines and control system) and the mass of the payload (i.e. scientific equipment, the body of the spacecraft launched into orbit, the crew and the system ship life support).

As the working fluid expires, the released tanks, excess parts of the shell, etc. begin to burden the rocket with unnecessary cargo, making it difficult to accelerate. Therefore, to achieve cosmic speeds, composite (or multi-stage) rockets are used (Fig. 21). At first, only the first stage 1 blocks work in such rockets. When the fuel reserves in them run out, they are separated and the second stage 2 is turned on; after the fuel in it is exhausted, it is also separated and the third stage 3 is turned on. The satellite or any other spacecraft located in the head of the rocket is covered with a head fairing 4, the streamlined shape of which helps to reduce air resistance when the rocket flies in the Earth's atmosphere.

When a jet of gas is ejected from a rocket at high speed, the rocket itself rushes in the opposite direction. Why is this happening?

According to Newton's third law, the force F with which the rocket acts on the working fluid is equal in magnitude and opposite in direction to the force F" with which the working fluid acts on the rocket body:

Force F" (which is called reactive force) accelerates the rocket.

From equality (10.1) it follows that the impulse imparted to the body is equal to the product of the force and the time of its action. Therefore, the same forces acting for the same time impart to bodies equal impulses. In this case, the pulse m p v p acquired by the rocket must correspond to the pulse m gas v gas of the ejected gases:

m р v р = m gas v gas

It follows that the speed of the rocket

Let's analyze the resulting expression. We see that the speed of the rocket is greater, the greater the speed of the emitted gases and the more attitude the mass of the working fluid (i.e., the mass of the fuel) to the final (“dry”) mass of the rocket.

Formula (12.2) is approximate. It does not take into account that as the fuel burns, the mass of the flying rocket becomes less and less. The exact formula for rocket speed was first obtained in 1897 by K. E. Tsiolkovsky and therefore bears his name.

The Tsiolkovsky formula allows you to calculate the fuel reserves required to impart a given rocket speed. Table 3 shows the ratio of the initial mass of the rocket m0 to its final mass m, corresponding different speeds rockets at a gas jet speed (relative to the rocket) v = 4 km/s.

For example, to impart to a rocket a speed exceeding the speed of gas flow by 4 times (v p = 16 km/s), it is necessary that the initial mass of the rocket (including fuel) exceed the final (“dry”) mass of the rocket by 55 times (m 0 /m = 55). This means that the lion's share of the total mass of the rocket at launch should be the mass of fuel. The payload, in comparison, should have a very small mass.

An important contribution to the development of the theory of jet propulsion was made by a contemporary of K. E. Tsiolkovsky, the Russian scientist I. V. Meshchersky (1859-1935). The equation of motion of a body with variable mass is named after him.

1. What is jet propulsion? Give examples. 2. In the experiment shown in Figure 22, when water flows out through curved tubes, the bucket rotates in the direction indicated by the arrow. Explain the phenomenon. 3. What determines the speed acquired by a rocket after fuel combustion?