sound barrier

Sound barrier

a phenomenon that occurs during the flight of an aircraft or rocket at the moment of transition from subsonic to supersonic flight speed in the atmosphere. When the aircraft speed approaches the speed of sound (1200 km/h), a thin area appears in the air in front of it, in which there is a sharp increase in pressure and air density. This compaction of air in front of a flying aircraft is called a shock wave. On the ground, the passage of a shock wave is perceived as a pop, similar to the sound of a shot. Having exceeded , the aircraft passes through this area of ​​increased air density, as if piercing it - it overcomes the sound barrier. For a long time, breaking the sound barrier was considered a serious problem in the development of aviation. To solve it, it was necessary to change the profile and shape of the aircraft wing (it became thinner and swept), to make the front of the fuselage more pointed and to equip the aircraft with jet engines. For the first time, the speed of sound was exceeded in 1947 by C. Yeager on an X-1 aircraft (USA) with a liquid-propellant rocket engine launched from a B-29 aircraft. In Russia, the first to overcome the sound barrier in 1948 was O. V. Sokolovsky on an experimental La-176 aircraft with a turbojet engine.

Encyclopedia "Technology". - M.: Rosman. 2006 .

sound barrier

a sharp increase in aerodynamic drag aircraft at Mach flight numbers M(∞) slightly exceeding the critical number M*. The reason is that at numbers M(∞) > M* comes, accompanied by the appearance of wave resistance. The wave drag coefficient of aircraft increases very rapidly with increasing number M, starting from M(∞) = M*.
The presence of Z. b. makes it difficult to achieve a flight speed equal to the speed of sound, and the subsequent transition to supersonic flight. For this, it turned out to be necessary to create aircraft with thin swept wings, which made it possible to significantly reduce resistance, and jet engines, in which thrust increases with increasing speed.
In the USSR, a speed equal to the speed of sound was first achieved on the La-176 aircraft in 1948.

Aviation: Encyclopedia. - M.: Great Russian Encyclopedia. Chief Editor G.P. Svishchev. 1994 .

See what a "sound barrier" is in other dictionaries:

The sound barrier in aerodynamics is the name of a number of phenomena that accompany the movement of an aircraft (for example, a supersonic aircraft, rocket) at speeds close to or exceeding the speed of sound. Contents 1 Shock wave, ... ... Wikipedia

SOUND BARRIER, the cause of difficulties in aviation when increasing the speed of flight above the speed of sound (SUPERSONIC SPEED). Approaching the speed of sound, the aircraft experiences an unexpected increase in drag and a loss of aerodynamic LIFT ... ... Scientific and technical encyclopedic dictionary

sound barrier- garso barjeras statusas T sritis fizika atitikmenys: engl. sonic barrier; sound barrier vok. Schallbarriere, f; Schallmauer, f rus. sound barrier, m pranc. barrière sonique, f; frontiere sonique, f; mur de son, m … Fizikos terminų žodynas

sound barrier- garso barjeras statusas T sritis Energetika apibrėžtis Staigus aerodinaminio pasipriešinimo padidėjimas, kai orlaivio greitis tampa garso greičiu (viršijama kritinė Macho skaičiaus vertė). Aiškinamas bangų krize dėl staiga padidėjusio… … Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas

A sharp increase in aerodynamic drag when the aircraft flight speed approaches the speed of sound (the critical value of the Mach number of flight is exceeded). It is explained by a wave crisis, accompanied by an increase in wave resistance. Overcome 3.… … Big encyclopedic polytechnic dictionary

sound barrier- a sharp increase in the resistance of the air environment to the movement of the aircraft at. approach to speeds close to the speed of sound propagation. Overcoming 3. b. made possible by improving the aerodynamic forms of aircraft and the use of powerful ... ... Dictionary of military terms

sound barrier- sound barrier a sharp increase in the resistance of an aerodynamic aircraft at Mach flight numbers M∞, slightly exceeding the critical number M*. The reason is that for numbers M∞ > Encyclopedia "Aviation"

sound barrier- sound barrier a sharp increase in the resistance of an aerodynamic aircraft at Mach flight numbers M∞, slightly exceeding the critical number M*. The reason is that at numbers M∞ > M* a wave crisis sets in,… … Encyclopedia "Aviation"

- (French barriere outpost). 1) gates in fortresses. 2) in arenas and circuses, a fence, a log, a pole through which a horse jumps. 3) a sign that fighters reach in a duel. 4) railing, grating. Dictionary of foreign words included in ... ... Dictionary of foreign words of the Russian language

BARRIER, husband. 1. An obstacle (type of wall, crossbar) placed on the way (during jumps, running). Take b. (get over it). 2. Fence, fence. B. lodges, balconies. 3. trans. An obstacle, an obstacle to something. River natural b. For… … Explanatory dictionary of Ozhegov

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Officially, the first pilot from the USA, Chuck Yeager, overcame supersonic speed. The record was set on 10/14/1957 on the Bell X-1, which was specially designed for this purpose in early 1946 by Bell Aircraft. The aircraft was manufactured by order of the military, but had nothing to do with the conduct of hostilities. The car was literally crammed with research equipment. Outwardly, the Bell X-1 resembled a modern cruise missile.

Test pilot Chuck Yeager

Pilot in 1923 February 13. After graduating from school, the young man immediately entered the flight school, after which he had to fight in Europe. At the very beginning of his flying career, the pilot managed to shoot down the Messerschmitt-109, but later he himself was defeated in the French sky and was forced to parachute.

The pilot was picked up by partisans, but counterintelligence removed him from flying. Outraged, Chuck secured an appointment with Eisenhower, who commanded the Allied forces. He believed the young man and, as it turned out, not in vain: the brave pilot managed to shoot down another 13 aircraft before the end of the war.

Yeager returned home with an excellent track record, characteristics, awards, in the rank of captain. This contributed to the inclusion of the pilot in a special team of testers, who at that time were selected as carefully as astronauts. Chuck's plane became the Captivating Glenys, in honor of his wife. The aircraft was equipped with one jet engine and was launched from a B-52 bomber.

On a winged car, the pilot set speed records more than once: at the end of 1947, he first broke the previous altitude record (21372 m), and in 1953 he managed to disperse the device to almost 2800 km / h, or 2.5 M (the speed of sound is measured in “max” , named after the German philosopher, engineer; 1 M is approximately equal to 1200 km / h). Yeager retired as a brigadier general in 1975, having managed to take part in the Vietnam War and the fighting in Korea.

The USSR could not stay away from attempts to overcome the sound barrier; several design bureaus at once (Lavochkin, Yakovlev, Mikoyan) participated in the preparation of an aircraft that was supposed to fly faster than sound. Such an honor fell to the La-176 aircraft, from Lavochkin's "company". The car was fully prepared for flights in 1948, in December. And on the 26th, Colonel Fedorov overcame the notorious barrier, accelerating in a dive. Later, the pilot received the title of Hero of the Soviet Union.

What do we think of when we hear the expression "sound barrier"? A certain limit and which can seriously affect hearing and well-being. Usually the sound barrier is correlated with the conquest of airspace and

Overcoming this barrier can provoke the development of chronic diseases, pain syndromes and allergic reactions. Are these perceptions correct or are they stereotypes? Do they have a factual basis? What is a sound barrier? How and why does it occur? All this and some additional nuances, as well as historical facts related to this concept, we will try to find out in this article.

This mysterious science is aerodynamics

In the science of aerodynamics, designed to explain the phenomena that accompany the movement
aircraft, there is the concept of "sound barrier". This is a series of phenomena that occur during the movement of supersonic aircraft or rockets that move at speeds close to the speed of sound or greater.

What is a shock wave?

In the process of supersonic flow around the apparatus, a shock wave arises in the wind tunnel. Its traces can be seen even with the naked eye. On the ground they are marked with a yellow line. Outside the cone of the shock wave, in front of the yellow line, on the ground, the plane is not even audible. At a speed exceeding the sound, the bodies are subjected to a flow around the sound stream, which entails a shock wave. It may not be alone, depending on the shape of the body.

Shock wave transformation

The shock wave front, which is sometimes called a shock wave, has a rather small thickness, which, nevertheless, makes it possible to track abrupt changes in the properties of the flow, a decrease in its velocity relative to the body, and a corresponding increase in the pressure and temperature of the gas in the flow. In this case, the kinetic energy is partially converted into the internal energy of the gas. The number of these changes directly depends on the speed of the supersonic flow. As the shock wave moves away from the apparatus, the pressure drops decrease and the shock wave is converted into sound. She can reach an outside observer who will hear a characteristic sound resembling an explosion. There is an opinion that this indicates that the device has reached the speed of sound, when the sound barrier is left behind by the plane.

What is really going on?

The so-called moment of overcoming the sound barrier in practice is the passage of a shock wave with a growing rumble of aircraft engines. Now the unit is ahead of the accompanying sound, so the hum of the engine will be heard after it. The approach of speed to the speed of sound became possible during the Second World War, but at the same time, pilots noted alarm signals in the operation of aircraft.

After the end of the war, many aircraft designers and pilots sought to reach the speed of sound and break the sound barrier, but many of these attempts ended tragically. Pessimistic scientists argued that this limit could not be surpassed. By no means experimental, but scientific, it was possible to explain the nature of the concept of "sound barrier" and find ways to overcome it.

Safe flights at transonic and supersonic speeds are possible if a wave crisis is avoided, the occurrence of which depends on the aerodynamic parameters of the aircraft and the altitude of the flight. Transitions from one speed level to another should be carried out as quickly as possible using afterburner, which will help to avoid a long flight in the wave crisis zone. The wave crisis as a concept came from water transport. It arose at the moment of movement of ships at a speed close to the speed of waves on the surface of the water. Getting into a wave crisis entails a difficulty in increasing the speed, and if it is as simple as possible to overcome the wave crisis, then you can enter the mode of gliding or sliding on the water surface.

History in aircraft management

The first person to achieve supersonic flight speed in an experimental aircraft is American pilot Chuck Yeager. His achievement is noted in history on October 14, 1947. On the territory of the USSR, the sound barrier was overcome on December 26, 1948 by Sokolovsky and Fedorov, who flew an experienced fighter.

Of the civilians, the passenger liner Douglas DC-8 broke the sound barrier, which on August 21, 1961 reached a speed of 1.012 Mach, or 1262 km / h. The mission was to collect data for wing design. Among the aircraft, the world record was set by a hypersonic air-to-ground aeroballistic missile, which is in service with the Russian army. At an altitude of 31.2 kilometers, the rocket reached a speed of 6389 km / h.

50 years after breaking the sound barrier in the air, Englishman Andy Green made a similar achievement in a car. In free fall, the American Joe Kittinger tried to break the record, who conquered a height of 31.5 kilometers. Today, on October 14, 2012, Felix Baumgartner set a world record, without the help of a vehicle, in a free fall from a height of 39 kilometers, breaking the sound barrier. At the same time, its speed reached 1342.8 kilometers per hour.

The most unusual breaking of the sound barrier

It is strange to think, but the first invention in the world to overcome this limit was the ordinary whip, which was invented by the ancient Chinese almost 7 thousand years ago. Almost until the invention of instant photography in 1927, no one suspected that the snap of a whip was a miniature sonic boom. A sharp swing forms a loop, and the speed increases sharply, which confirms the click. The sound barrier is overcome at a speed of about 1200 km / h.

The mystery of the noisiest city

No wonder the inhabitants of small towns are shocked when they see the capital for the first time. The abundance of transport, hundreds of restaurants and entertainment centers confuse and unsettle. The beginning of spring in the capital is usually dated April, not the rebellious blizzard March. In April, the sky is clear, streams run and buds open. People, tired of the long winter, open their windows wide towards the sun, and street noise bursts into the houses. Birds are deafeningly chirping on the street, artists are singing, cheerful students are reciting poems, not to mention the noise in traffic jams and the subway. Employees of hygiene departments note that being in a noisy city for a long time is unhealthy. The sound background of the capital consists of transport,
aviation, industrial and domestic noise. The most harmful is just car noise, as planes fly high enough, and the noise from enterprises is dissolved in their buildings. The constant hum of cars on especially busy highways exceeds all permissible norms twice. How is the sound barrier overcome in the capital? Moscow is dangerous because of the abundance of sounds, so the residents of the capital install double-glazed windows to muffle the noise.

How is the sound barrier breached?

Until 1947, there was no actual data on the well-being of a person in the cockpit of an aircraft that flies faster than sound. As it turned out, breaking the sound barrier requires certain strength and courage. During the flight, it becomes clear that there are no guarantees to survive. Even a professional pilot cannot say for sure whether the design of the aircraft will withstand the attack of the elements. In a matter of minutes, the plane can simply fall apart. What explains this? It should be noted that movement at subsonic speed creates acoustic waves that scatter like circles from a fallen stone. Supersonic speed excites shock waves, and a person standing on the ground hears a sound similar to an explosion. Without powerful computers it was difficult to solve complex problems and had to rely on blowing models in wind tunnels. Sometimes, with insufficient acceleration of the aircraft, the shock wave reaches such strength that windows fly out of the houses over which the aircraft flies. Not everyone will be able to overcome the sound barrier, because at this moment the entire structure is shaking, the apparatus's fastenings can receive significant damage. Therefore, good health and emotional stability are so important for pilots. If the flight is smooth, and the sound barrier is overcome as quickly as possible, then neither the pilot nor possible passengers will feel particularly unpleasant sensations. Especially for the conquest of the sound barrier, a research aircraft was built in January 1946. The creation of the machine was initiated by an order from the Ministry of Defense, but instead of weapons, it was stuffed with scientific equipment that monitored the operation of mechanisms and instruments. This aircraft was like a modern cruise missile with a built-in rocket engine. The aircraft broke the sound barrier at a maximum speed of 2736 km/h.

Verbal and material monuments to the conquest of the speed of sound

Achievements in breaking the sound barrier are highly valued today. So, the plane on which Chuck Yeager first overcame it is now on display at the National Air and Space Museum, which is located in Washington. But the technical parameters of this human invention would be worth little without the merits of the pilot himself. Chuck Yeager went through flight school and fought in Europe, after which he returned to England. The unfair suspension from flying did not break the spirit of Yeager, and he obtained an appointment with the commander-in-chief of the troops of Europe. In the years remaining before the end of the war, Yeager participated in 64 sorties, during which he shot down 13 aircraft. Chuck Yeager returned to his homeland with the rank of captain. His characteristics indicate phenomenal intuition, incredible composure and endurance in critical situations. More than once, Yeager set records on his plane. His later career was in the Air Force, where he trained pilots. The last time Chuck Yeager broke the sound barrier was 74 years old, which was on the fiftieth anniversary of his flight history and in 1997.

Complex tasks of the creators of aircraft

The world-famous MiG-15 aircraft began to be created at a time when the developers realized that it was impossible to rely only on breaking the sound barrier, but complex problems should be solved. technical tasks. As a result, a machine was created so successful that its modifications were put into service. different countries. Several different design bureaus entered into a kind of competitive struggle, the prize of which was a patent for the most successful and functional aircraft. Developed aircraft with swept wings, which was a revolution in their design. The ideal apparatus would have to be powerful, fast, and incredibly resistant to any external damage. The swept wings of the aircraft became an element that helped them triple the speed of sound. Further, it continued to grow, which was explained by an increase in engine power, the use of innovative materials and the optimization of aerodynamic parameters. Breaking the sound barrier has become possible and real even for a non-professional, but it does not become less dangerous because of this, so any extreme seeker should sensibly assess his strengths before deciding on such an experiment.

Have you heard the loud explosion-like sound as a jet plane flies overhead? This sound is produced when an aircraft breaks the sound barrier. What is a sound barrier and why does an airplane make such a sound?

As you know, sound travels at a certain speed. The speed depends on the height. At sea level, the speed of sound is about 1220 kilometers per hour, and at an altitude of 11,000 meters it is 1060 kilometers per hour. When an aircraft flies at speeds close to the speed of sound, it is subjected to certain loads. When it flies at normal (subsonic) speeds, the front of the aircraft drives a pressure wave in front of it. This wave propagates at the speed of sound.

The pressure wave is due to the accumulation of air particles as the aircraft advances. The wave travels faster than the aircraft when the aircraft is flying at subsonic speeds. And as a result, it turns out that the air passes unhindered along the surfaces of the wings of the aircraft.

Now let's consider an airplane that flies at the speed of sound. The pressure wave in front of the aircraft does not appear. What happens instead is that a pressure wave forms in front of the wing (because the aircraft and the pressure wave are traveling at the same speed).

Now a shock wave is being formed, which causes large loads in the wing of the aircraft. The expression "sound barrier" was around before planes could fly at the speed of sound - and it was thought to describe the stresses an aircraft would experience at those speeds. This was considered a "barrier".

But the speed of sound is not a barrier at all! Engineers and aircraft designers have overcome the problem of new loads. And all we have left of the old views is that the impact is caused by a shock wave when the plane flies at supersonic speeds.

The term "sound barrier" does not correctly describe the conditions that occur when an aircraft is moving at a certain speed. It can be assumed that when the aircraft reaches the speed of sound, something like a “barrier” appears - but nothing of the kind happens!

To understand all this, consider an airplane flying at a slow, normal speed. As the aircraft moves forward, a compression wave forms in front of the aircraft. It is formed by an aircraft moving forward, which compresses air particles.

This wave travels ahead of the aircraft at the speed of sound. And its speed is higher than the speed of the aircraft, which, as we have already said, flies at a low speed. Moving ahead of the aircraft, this wave causes air currents to flow around the plane of the aircraft.

Now imagine that an airplane is flying at the speed of sound. There is no compression wave in front of the aircraft, since both the aircraft and the waves have the same speed. Therefore, the wave is formed in front of the wings.

As a result, a shock wave appears, which creates large loads on the wings of the aircraft. Before aircraft reached and exceeded the sound barrier, it was believed that such shock waves and g-forces would create something like a barrier for the aircraft - a "sonic barrier". However, there was no sound barrier, as aeronautical engineers developed a special aircraft design for this.

By the way, the strong “bang” that we hear when the plane passes the “sonic barrier” is the shock wave that we have already talked about - at the same speed of the plane and the compression wave.

Passed the sound barrier :-) ...

Before jumping into conversations on the topic, let's bring some clarity to the question of the accuracy of concepts (what I like :-)). There are two terms in common use today: sound barrier And supersonic barrier. They sound similar, but still not the same. However, there is no point in diluting it with particular rigor: in fact, this is one and the same thing. The definition of the sound barrier is used most often by people who are more knowledgeable and closer to aviation. And the second definition is usually all the rest.

I think that from the point of view of physics (and the Russian language :-)) it is more correct to say the sound barrier. There is simple logic here. After all, there is the concept of the speed of sound, but there is no fixed concept of the speed of supersonic, strictly speaking. Looking ahead a little, I’ll say that when an aircraft flies at supersonic, it has already passed this barrier, and when it passes (overcomes) it, then it passes a certain threshold value of speed equal to the speed of sound (and not supersonic).

Something like that:-). Moreover, the first concept is used much less frequently than the second. This is apparently because the word supersonic sounds more exotic and attractive. And in supersonic flight, the exotic is certainly present and, of course, attracts many. However, not all people who savor the words " supersonic barrier' really understand what it is. More than once I was convinced of this, looking at the forums, reading articles, even watching TV.

This question is actually rather complicated from the point of view of physics. But we, of course, will not climb into complexity. We will just try, as usual, to clarify the situation using the principle of "explaining aerodynamics on the fingers" :-).

So, to the barrier (sonic :-))!… Airplane in flight, acting on such an elastic medium as air, becomes a powerful source of sound waves. I think everyone knows what sound waves are in the air :-).

Sound waves (tuning fork).

This is an alternation of areas of compression and rarefaction, propagating in different directions from the sound source. Approximately like circles on the water, which are also just waves (but not sound :-)). It is these areas, acting on the eardrum, that allow us to hear all the sounds of this world, from human whispers to the roar of jet engines.

An example of sound waves.

The points of propagation of sound waves can be various nodes of the aircraft. For example, an engine (its sound is known to anyone :-)), or body parts (for example, bow), which, condensing the air in front of them when moving, create a certain type of pressure (compression) wave running forward.

All these sound waves propagate in the air at the speed of sound we already know. That is, if the plane is subsonic, and even flies at low speed, then they seem to run away from it. As a result, when such an aircraft approaches, we first hear its sound, and then it flies itself.

I will make a reservation, however, that this is true if the plane does not fly very high. After all, the speed of sound is not the speed of light :-). Its magnitude is not so great and sound waves need time to reach the listener. Therefore, the sequence of sound appearance for the listener and the aircraft, if it flies at high altitude, may change.

And since the sound is not so fast, then with an increase in its own speed, the plane begins to catch up with the waves emitted by it. That is, if he were motionless, then the waves would diverge from him in the form concentric circles like circles on the water from a thrown stone. And since the plane is moving, then in the sector of these circles, corresponding to the direction of flight, the boundaries of the waves (their fronts) begin to approach each other.

Subsonic motion of the body.

Accordingly, the gap between the aircraft (its nose) and the front of the very first (head) wave (that is, this is the area where gradual, to a certain extent, braking oncoming flow when meeting with the nose of the aircraft (wing, tail) and, as a result, increase in pressure and temperature) begins to decrease and the faster, the greater the flight speed.

There comes a moment when this gap practically disappears (or becomes minimal), turning into a special kind of area, which is called shock wave. This happens when the flight speed reaches the speed of sound, that is, the aircraft moves at the same speed as the waves emitted by it. The Mach number in this case is equal to one (M=1).

Sound movement of the body (M=1).

shock wave, is a very narrow area of ​​the medium (of the order of 10 -4 mm), when passing through which there is no longer a gradual, but a sharp (jump-like) change in the parameters of this medium - speed, pressure, temperature, density. In our case, the speed drops, pressure, temperature and density increase. Hence the name - the shock wave.

Somewhat simplistically, I would say this about all this. It is impossible to slow down a supersonic flow sharply, but it has to do this, because there is no longer the possibility of gradual deceleration to the speed of the flow in front of the very nose of the aircraft, as at moderate subsonic speeds. It seems to stumble upon a section of subsonic in front of the nose of the aircraft (or the toe of the wing) and collapses into a narrow jump, transferring to it the great energy of movement that it possesses.

By the way, it can also be said vice versa that the aircraft transfers part of its energy to the formation of shock waves in order to slow down the supersonic flow.

Supersonic motion of the body.

There is another name for the shock wave. Moving along with the aircraft in space, it is, in fact, the front of a sharp change in the above parameters of the environment (that is, the air flow). And this is the essence of the shock wave.

shock wave and a shock wave, in general, are equal definitions, but in aerodynamics the first is more commonly used.

The shock wave (or shock wave) can be almost perpendicular to the direction of flight, in which case they take an approximately circular shape in space and are called straight lines. This usually happens in modes close to M=1.

Modes of body movement. ! - subsonic, 2 - M=1, supersonic, 4 - shock wave (shock).

At numbers M > 1, they are already at an angle to the direction of flight. That is, the plane is already overtaking its own sound. In this case, they are called oblique and in space take the form of a cone, which, by the way, is called the Mach cone, after the scientist who studied supersonic flows (he mentioned him in one of).

Mach cone.

The shape of this cone (its “slimness”, so to speak) just depends on the number M and is related to it by the relation: M = 1 / sin α, where α is the angle between the axis of the cone and its generatrix. And the conical surface touches the fronts of all sound waves, the source of which was the aircraft, and which it “overtook”, reaching supersonic speed.

Besides shock waves may also be affiliated, when they are adjacent to the surface of a body moving at supersonic speed or retreated if they do not touch the body.

Types of shock waves in supersonic flow around bodies of various shapes.

Usually, shocks become attached if the supersonic flow flows around any pointed surfaces. For an aircraft, for example, this can be a pointed nose, a PVD, a sharp edge of an air intake. At the same time, they say “jump sits”, for example, on the nose.

And the receding shock can be obtained when flowing around rounded surfaces, for example, the front rounded edge of a thick aerodynamic wing profile.

Various components of the aircraft body create a rather complex shock wave system in flight. However, the most intense of them are two. One head on the bow and the second tail on the elements of the tail unit. At some distance from the aircraft, the intermediate jumps either overtake the head one and merge with it, or the tail one overtakes them.

The shock waves on the aircraft model when blowing in a wind tunnel (M=2).

As a result, two jumps remain, which, in general, are perceived by the earthly observer as one due to the small size of the aircraft compared to the flight altitude and, accordingly, a short time interval between them.

The intensity (in other words, energy) of the shock wave (compression shock) depends on various parameters (the speed of the aircraft, its design features, environmental conditions, etc.) and is determined by the pressure drop at its front.

As the distance from the top of the Mach cone, that is, from the aircraft, as a source of perturbations, the shock wave weakens, gradually turns into an ordinary sound wave and eventually completely disappears.

And on what degree of intensity it will have shock wave(or shockwave) that reaches the ground depends on the effect it can produce there. It's no secret that the well-known Concorde flew supersonic only over the Atlantic, and military supersonic aircraft go supersonic at high altitudes or in areas where there are no settlements (at least it seems like they should do it :-)).

These restrictions are very justified. For me, for example, the very definition of a shock wave is associated with an explosion. And the things that a sufficiently intense shock wave can do may well be up to it. At least the glass from the windows can fly out easily. There is enough evidence of this (especially in the history of Soviet aviation, when it was quite numerous and the flights were intense). But you can do worse things. You just have to fly lower :-) ...

However, for the most part, what remains of shock waves when they reach the ground is no longer dangerous. Just an outside observer on the ground can at the same time hear a sound similar to a roar or explosion. It is with this fact that one common and rather persistent misconception is associated.

People who are not too experienced in aviation science, hearing such a sound, say that this plane overcame sound barrier (supersonic barrier). Actually it is not. This statement has nothing to do with reality for at least two reasons.

Shock wave (compression shock).

Firstly, if a person on the ground hears a booming roar high in the sky, then this only means (I repeat :-)) that his ears have reached shock wave front(or shock wave) from an airplane flying somewhere. This plane is already flying at supersonic speed, and not just switched to it.

And if the same person could suddenly be a few kilometers ahead of the aircraft, then he would again hear the same sound from the same aircraft, because he would be affected by the same shock wave moving along with the aircraft.

It moves at supersonic speeds, and therefore approaches silently. And after it has had its not always pleasant effect on the eardrums (well, when only on them :-)) and safely passes on, the rumble of running engines becomes audible.

Approximate aircraft flight pattern for various values ​​of the M number on the example of the Saab 35 "Draken" fighter. The language, unfortunately, is German, but the scheme is generally understandable.

Moreover, the transition to supersonic itself is not accompanied by any one-time “booms”, pops, explosions, etc. On a modern supersonic aircraft, the pilot most often learns about such a transition only from the readings of the instruments. In this case, however, a certain process occurs, but it is practically not noticeable to him, subject to certain piloting rules.

But that's not all :-). I'll say more. in the form of just some kind of tangible, heavy, difficult-to-cross obstacle, against which the plane rests and which needs to be “pierced” (I have heard such judgments :-)) does not exist.

Strictly speaking, there is no barrier at all. Once upon a time, at the dawn of the development of high speeds in aviation, this concept was formed rather as a psychological belief about the difficulty of switching to supersonic speed and flying at it. There were even statements that it was impossible at all, especially since the prerequisites for such beliefs and statements were quite specific.

However, first things first…

In aerodynamics, there is another term that quite accurately describes the process of interaction with the air flow of a body moving in this flow and striving to switch to supersonic. This wave crisis. It is he who does some of the bad things that are traditionally associated with the concept sound barrier.

So something about the crisis :-). Any aircraft consists of parts, the air flow around which in flight may not be the same. Take, for example, a wing, or rather an ordinary classic subsonic profile.

From the basics of knowledge about how lifting force we are well aware that the flow velocity in the adjacent layer of the upper curved surface of the profile is different. Where the profile is more convex it is greater than the total flow velocity, then when the profile flattens it decreases.

When the wing moves in the flow at speeds close to the speed of sound, a moment may come when, for example, in such a convex region, the speed of the air layer, which is already greater than the total flow speed, becomes sonic and even supersonic.

Local shock that occurs on transonic during a wave crisis.

Further along the profile, this speed decreases and at some point again becomes subsonic. But, as we said above, the supersonic flow cannot quickly slow down, so the occurrence of shock wave.

Such shocks appear in different parts of the streamlined surfaces, and initially they are quite weak, but their number can be large, and with an increase in the total flow velocity, supersonic zones increase, the shocks “strengthen” and move towards the trailing edge of the airfoil. Later, the same shock waves appear on the bottom surface of the profile.

Full supersonic flow around the wing airfoil.

What is the risk of all this? But what. First- is significant increase in aerodynamic drag in the range of transonic speeds (about M=1, more or less). This resistance grows due to a sharp increase in one of its components - wave resistance. The same one that we did not take into account when considering flights at subsonic speeds.

For the formation of numerous shock waves (or shock waves) during the deceleration of a supersonic flow, as I said above, energy is spent, and it is taken from the kinetic energy of the aircraft. That is, the plane simply slows down (and very noticeably!). That's what it is wave resistance.

Moreover, shock waves, due to the sharp deceleration of the flow in them, contribute to the separation of the boundary layer after itself and its transformation from laminar to turbulent. This further increases the aerodynamic drag.

Airfoil flow at various M numbers. Shocks, local supersonic zones, turbulent zones.

Second. Due to the appearance of local supersonic zones on the wing profile and their further shift to the tail section of the profile with an increase in the flow velocity and, thereby, a change in the pressure distribution pattern on the profile, the point of application of aerodynamic forces (pressure center) also shifts to the trailing edge. As a result, there appears diving moment relative to the center of mass of the aircraft, causing it to lower its nose.

What does all this result in ... Due to the rather sharp increase in aerodynamic drag, the aircraft needs a significant engine power reserve to overcome the transonic zone and reach, so to speak, real supersonic.

A sharp increase in aerodynamic drag on transonic (wave crisis) due to an increase in wave drag. Cd is the drag coefficient.

Further. Due to the occurrence of a diving moment, difficulties arise in pitch control. In addition, due to the disorder and unevenness of the processes associated with the emergence of local supersonic zones with shock waves, too difficult to manage. For example, on a roll, due to different processes on the left and right planes.

Yes, plus the occurrence of vibrations, often quite strong due to local turbulence.

In general, a complete set of pleasures, which bears the name wave crisis. But, true, they all take place (there were, specific :-)) when using typical subsonic aircraft (with a thick profile of a straight wing) in order to achieve supersonic speeds.

Initially, when there was not enough knowledge yet, and the processes of reaching supersonics were not comprehensively studied, this very set was considered almost fatally insurmountable and was called sound barrier(or supersonic barrier, if you want to:-)).

When trying to overcome the speed of sound on conventional piston aircraft, there were many tragic cases. Strong vibration sometimes led to the destruction of the structure. The aircraft did not have enough power for the required acceleration. In level flight, it was impossible due to an effect of the same nature as wave crisis.

Therefore, a dive was used for acceleration. But it could very well be fatal. The dive moment that appeared during a wave crisis made the dive protracted, and sometimes there was no way out of it. Indeed, in order to restore control and eliminate the wave crisis, it was necessary to extinguish the speed. But to do this in a dive is extremely difficult (if not impossible).

Dragging into a dive from level flight is considered one of the main causes of the disaster in the USSR on May 27, 1943 of the famous experimental BI-1 fighter with a liquid rocket engine. Tests were carried out for the maximum flight speed, and according to the designers, the speed achieved was more than 800 km / h. Then there was a delay in the peak, from which the plane did not come out.

Experimental fighter BI-1.

In our time wave crisis already well enough studied and overcome sound barrier(if it is required :-)) is not difficult. On aircraft that are designed to fly at sufficiently high speeds, certain design solutions and restrictions are applied to facilitate their flight operation.

As is known, the wave crisis begins at numbers M close to unity. Therefore, almost all jet subsonic liners (passenger, in particular) have a flight limitation on the number M. Usually it is in the region of 0.8-0.9M. The pilot is instructed to follow this. In addition, on many aircraft, when the limit level is reached, after which the airspeed must be reduced.

Almost all aircraft flying at speeds of at least 800 km/h and above have swept wing(at least on the leading edge :-)). It allows you to push back the start of the offensive wave crisis up to speeds corresponding to M=0.85-0.95.

Arrow wing. Fundamental action.

The reason for this effect can be explained quite simply. For straight wing air flow with speed V runs almost at a right angle, and swept (sweep angle χ) at a certain slip angle β. The velocity V can be vectorially decomposed into two streams: Vτ and Vn .

The flow Vτ does not affect the pressure distribution on the wing, but it does the flow Vn, which determines the carrying properties of the wing. And it is obviously less in magnitude of the total flow V. Therefore, on the swept wing, the onset of a wave crisis and the growth wave resistance occurs noticeably later than on a straight wing at the same freestream velocity.

Experimental fighter E-2A (the predecessor of the MIG-21). Typical swept wing.

One of the modifications of the swept wing was the wing with supercritical profile(mentioned him). It also allows you to move the beginning of the wave crisis at high speeds, in addition, it allows you to increase efficiency, which is important for passenger liners.

SuperJet 100. Supercritical swept wing.

If the aircraft is intended to transit sound barrier(passing and wave crisis too :-)) and supersonic flight, then it usually always differs in certain design features. In particular, it usually has thin profile of the wing and plumage with sharp edges(including diamond-shaped or triangular) and a certain shape of the wing in plan (for example, triangular or trapezoidal with an influx, etc.).

Supersonic MIG-21. Follower E-2A. A typical triangular wing.

MIG-25. An example of a typical aircraft designed for supersonic flight. Thin profiles of the wing and plumage, sharp edges. Trapezoidal wing. profile

Passing the notorious sound barrier, that is, such aircraft carry out the transition to supersonic speed on afterburning engine operation due to the increase in aerodynamic resistance, and, of course, in order to quickly slip through the zone wave crisis. And the very moment of this transition is most often not felt in any way (I repeat :-)) neither by the pilot (he can only reduce the sound pressure level in the cockpit), nor by an outside observer, if, of course, he could observe this :-).

However, here it is worth mentioning one more misconception, connected with outside observers. Surely many have seen this kind of photographs, the captions under which say that this is the moment of overcoming the plane sound barrier so to speak, visually.

Prandtl-Gloert effect. Not related to passing the sound barrier.

Firstly, we already know that there is no sound barrier, as such, and the transition to supersonic itself is not accompanied by anything so extraordinary (including clap or explosion).

Secondly. What we saw in the photo is the so-called Prandtl-Gloert effect. I already wrote about him. It is in no way directly related to the transition to supersonic. It's just that at high speeds (subsonic, by the way :-)) the plane, moving a certain mass of air in front of it, creates some rarefaction area. Immediately after the passage, this area begins to fill with air from the nearby space with natural an increase in volume and a sharp drop in temperature.

If air humidity is sufficient and the temperature falls below the dew point of the ambient air, then moisture condensation from water vapor in the form of fog, which we see. As soon as conditions are restored to the original, this fog immediately disappears. This whole process is rather short.

Such a process at high transonic speeds can be facilitated by local surges I, sometimes helping to form something similar to a gentle cone around the aircraft.

High speeds favor this phenomenon, however, if the air humidity is sufficient, then it can occur (and occurs) at rather low speeds. For example, above the surface of water bodies. By the way, most beautiful photos of this nature were made on board an aircraft carrier, that is, in sufficiently humid air.

That's how it works. The shots, of course, are cool, the spectacle is spectacular :-), but this is not at all what it is most often called. nothing to do with it (and supersonic barrier Same:-)). And this is good, I think, otherwise the observers who take this kind of photo and video might not be good. shock wave, do you know:-)…

In conclusion, one video (I have already used it before), the authors of which show the effect of a shock wave from an aircraft flying at low altitude at supersonic speed. There is, of course, a certain exaggeration there :-), but general principle understandable. And again, it's amazing :-)

And that's all for today. Thank you for reading the article to the end :-). Until we meet again…

Photos are clickable.