The airplane is completely at the mercy of air waves. NASA showed a supersonic plane flying against the backdrop of the Sun. Should you panic?

Many people are afraid to fly by plane. Psychologists say that there is even such a thing as “aerophobia.” Patients with this diagnosis experience real horror at the mere thought of taking to the air. The strongest negative emotions are caused by getting into air pockets and turbulence. Such moments are unpleasant even for those who are not afraid of flying. However, pilots claim that this is actually quite common. natural phenomenon, which can be explained in scientific language, and it will not bring any harm to airline passengers. Today we decided to tell you what an air pocket really is, and whether you should be afraid of it.

Explanation of the term

It is quite difficult for an ordinary person to understand what an air pocket actually is. Everyone understands that there are no highways or road surfaces in the sky, and, therefore, there cannot be any potholes. For example, when it comes to driving a car, it is absolutely clear to anyone that there may be an obstacle or a hole on the road that an experienced driver will be able to steer around. But what if you find yourself in an air pocket? Is it possible to bypass it? And how dangerous is it? We will answer all these questions in the following sections of the article. But let's understand this difficult topic gradually.

Scientists have long found out that air flows are heterogeneous. They have different directions, temperatures and even densities. All this affects airliners flying on certain routes. In the case when the plane encounters flows of lower temperature on the way, a complete illusion of a short-term fall is created. Then we usually say that the ship fell into an air pocket. However, in reality this is just an illusion, which can be easily explained with the help of modern science.

Downward and upward flows

To understand how air pockets form, it is necessary to gain a complete understanding of the movement of air currents. According to the laws of physics, heated air always rises, and cooled air falls down. Warm currents are called ascending; they always tend upward. And cold air is considered to be descending, and like a funnel, it pulls down everything that gets in its way.

It is precisely because of the movement of these flows that air pockets, so unloved by passengers, are formed during flight. They make travelers experience very unpleasant sensations that many cannot forget for a long time.

The principle of formation of air pockets

Despite the fact that the modern aircraft industry has long equipped its new airliners with an abundance of technological innovations designed to make the flight comfortable and safe, so far no one has been able to relieve passengers from the unpleasant sensations caused by descending air masses. So, the plane fell into an air pocket. What is happening to him at this moment?

Even during a flight in good conditions weather conditions The airliner may encounter a stream of cold air. Since it is descending, it begins to significantly slow down the aircraft’s ascent speed. It is noteworthy that in a straight line it goes with the same performance, but loses a little altitude. This usually only lasts a few moments.

The airliner then encounters an updraft, which begins to push it upward. This allows aircraft gain the same altitude and continue the flight as normal.

Passengers' feelings

It is quite difficult for those who have never been trapped in air pockets to understand what airplane passengers feel. Typically, people complain that they experience stomach cramps, nausea rising in the throat, and even weightlessness that lasts a fraction of a second. All this is accompanied by the illusion of falling, which is perceived as realistically as possible. The combination of sensations leads to uncontrollable fear, which in the future does not allow most people to calmly endure flights and causes aerophobia.

Should we panic?

Unfortunately, not even the most highly professional pilot will be able to bypass the air pocket. It is impossible to fly around it, and even the make and class of the aircraft cannot protect passengers from unpleasant experiences.

Pilots claim that at the moment they hit downdraft the plane temporarily loses control. But there is no need to panic because of this; such a situation lasts no more than a few seconds and, apart from unpleasant sensations, does not threaten travelers with anything.

However, you need to know that the airliner is under serious pressure in the air pocket. At this moment, the plane encounters “churning” or turbulence, which, in turn, adds to the unpleasant sensations for frightened passengers.

Briefly about turbulence

This phenomenon causes a lot of inconvenience to travelers, but in fact it is not dangerous and cannot lead to an airliner crash. It is believed that the load on an airplane during turbulence is no higher than on a car moving on a rough road.

A zone of turbulence is formed when air flows at different speeds meet. At this moment, vortex waves are formed, which cause “chatter”. It is noteworthy that on some routes turbulence occurs regularly. For example, when flying over mountains, the plane always shakes. Such zones can be quite long, and the “chumpiness” can last from several minutes to half an hour.

Causes of turbulence

We have already talked about the most common cause of bumpiness, but in addition to this, other factors can cause it. For example, an airliner flying ahead often contributes to the formation of vortices, and they, in turn, form a turbulence zone.

Not far from the surface of the earth, the air warms up unevenly, which is why vortex flows are created, which cause turbulence.

It is noteworthy that pilots compare flying in the clouds to driving on a highway with potholes and potholes. Therefore, in cloudy weather, passengers most often experience all the “delights” of flying in a shaking plane.

Dangers of Turbulence

Most passengers seriously believe that turbulence can compromise the seal of the cabin and lead to a crash. But in fact, this is the safest phenomenon of all. The history of air transportation does not know a case when getting into a bumpy situation would lead to fatal consequences.

Aircraft designers always put a certain margin of safety into the aircraft body, which can easily withstand both turbulence and thunderstorms. Of course, such a phenomenon causes anxiety, unpleasant emotions and even panic among passengers. But in fact, you just need to calmly wait out this moment, without giving in to your own fear.

How to behave during a flight: a few simple rules

If you are very afraid of flying, and thoughts about air holes and turbulence causes you a feeling of horror, then try to follow a number of simple rules that will significantly ease your condition:

do not drink alcohol during the flight, it will only aggravate unpleasant emotions;
try to drink water with lemon, it will relieve attacks of nausea when you get into air pockets;
before traveling, set yourself up in a positive mood, otherwise you will always be tormented by forebodings and negative emotions;
be sure to fasten your seat belts; passengers may be injured while passing through the turbulence zone;
if you are very afraid of flying, then choose larger aircraft models that are less sensitive to various types of shaking.

We hope that after reading our article, your fear of flying will become less acute, and your next air travel It will be easy and pleasant.

An amazing sight is a cone of steam appearing around an airplane flying at transonic speed. This amazing effect, known as the Prandtl-Gloert effect, causes the eyes to open wide and the jaw to drop. But what is its essence?

(Total 12 photos)

1. Contrary to popular belief, this effect does not appear when the plane breaks the sound barrier. The Prandtl-Gloert effect is also often associated with supersonic bang, which is also not true. Ultra-high bypass aircraft engines can create this effect at takeoff speed because the engine inlet is low pressure and the fan blades themselves operate at transonic speed.

2. The reason for its occurrence is that an airplane flying at high speed creates an area of high air pressure in front of it and an area of low pressure behind it. After the plane passes, the area of low pressure begins to fill with ambient air. In this case, due to the sufficiently high inertia of air masses, first the entire low pressure area is filled with air from nearby areas adjacent to the low pressure area.

3. Imagine an object moving at transonic speed. Transonic speed is different from the speed of sound. The sound barrier is broken at a speed of 1235 km/h. Transonic speed is below, above or near the speed of sound and can vary from 965 to 1448 km/h. Therefore, this effect can occur when the aircraft is moving at a speed less than or equal to the speed of sound.

4. And yet it’s all about the sound - the “visibility” of this steam cone behind the plane depends on it. The cone shape is created by the force of sound (in the case of airplanes) moving faster than the sound waves it produces. The Prandtl-Gloert effect arises as a result of the wave nature of sounds.

5. Again, think of the plane as the source and the sound as the crest of the wave. These sound wave crests are a series or shell of overlapping circles. When the waves overlap each other, a cone shape is created, and the tip is the source of the sound. So far invisible.

6. For the effect to become visible to the human eye, one more thing is needed - humidity. When the humidity is high enough, the air around the cone condenses and forms the cloud we see. As soon as the air pressure returns to normal, the cloud disappears. The effect almost always occurs on planes flying over the ocean in the summer - the combination of water and heat gives the desired level of humidity.

7. Here you can destroy another one. Some believe that the Prandtl-Gloert effect occurs as a result of fuel combustion.

8. You can probably understand if you think that this effect is a contrail, that is, an unnatural cloud appearing from condensed water vapor produced by engine exhaust. However, this is not the same thing. The water vapor is already there - it's already in the air before the plane even passes through it.

9. Air pressure is also worth mentioning. When an airplane is moving at transonic speed, the air pressure around it is called an N-wave because when pressure varies with time, the result is similar to the letter N.

10. If we could slow down the blast wave passing through us, we would see the leading compression component. This is the beginning of the N. The horizontal stick occurs when the pressure drops, and when the normal atmospheric pressure returns to the final point, the letter N is created.

11. The effect is named after two outstanding scientists who discovered this phenomenon. Ludwig Prandtl (1875 – 1953) was a German scientist who studied the development of systematic mathematical analysis in aerodynamics. Hermann Glauert (1892 – 1934) was a British aerodynamicist.

12. Believe it or not, you can create this effect yourself. You only need two things: a whip and a day with high humidity. If you can whip a whip like Indiana Jones, you'll see a similar effect. Although, you shouldn't try this at home.

“Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines stopped. We're doing everything damned possible to get them up and running again. I’m sure you’re not completely in dire straits.”

There are a lot of real dangers to flying airplanes. All of them are quite well studied. Dozens of cases a year of airplane collisions with birds, as a rule, do not lead to disasters or accidents at all, and even more so do not serve as a reason for bans to limit flights to countries where there are birds. Cumulonimbus clouds represent mortal danger for airplanes, however, hundreds of airplanes daily simply circle these hotspots at a safe distance (about 50 kilometers midway between the clouds, or 15 kilometers away from a single cloud). Enumerating such phenomena is not the topic of the material; believe me, their presence in nature does not reduce overall flight safety.

To clarify the issue in detail, I talked by phone with Valery Georgievich Shelkovnikov, member of the board World Fund flight safety, and President of the Flight Safety Advisory and Analytical Agency. I present the results of our private conversation below in my own words and on my own behalf, because there is no way to separate the words of an expert from the words of a journalist:

The eruption of the Eyjafjallajokull volcano and the subsequent events associated with the cancellation of flights in Europe amused me a lot. I don't mind at all aviation security. Moreover, if a person can even joke about this topic, then he still does not know what a plane crash is. Nevertheless, I will continue the topic. Mythologized volcanic eruptions and press hysteria forced airlines to stop or postpone flights in those government territories where the “clouds” hit volcanic ash.

So was there a real danger to flights, or was there collective aviation hysteria, which was started by journalists, and then a domino effect took place? Let's try to figure it out.

Indeed, the entry of a large amount of abrasive dust into aircraft engines (and absolutely no matter what its origin) can cause an engine fire due to instant overheating and subsequent destruction of the turbine bearings. At a rotation speed of several thousand revolutions per minute, they will simply melt from friction. Therefore, if an aircraft hits a column of volcanic dust, such a situation is quite possible.

Another thing is the special structure of volcanic dust. Except particles rocks thrown out by the explosion, it still consists of amorphous particles (by the way, glass is also amorphous) of extremely irregular shape. If you look at volcanic dust under a microscope, you can clearly see that it consists of “ribbons”, “stars” and other particles that have a very large surface area despite their low weight. Those. Thanks to this feature, it can remain in the air many times longer without dissipating. Because due to electrification and other interactions of ash particles, such clouds dissipate extremely reluctantly.

Also its feature is its “stickiness”, i.e. the ability to stick to various objects or clog various holes. Moreover, the particles, being excellent condensation nuclei, after some time become absolutely outwardly indistinguishable from an ordinary cloud.

Another thing is that even at a distance of “hundreds” of kilometers from the volcano, the dust becomes so rare and finely dispersed that the likelihood of aircraft failure for this reason becomes only “theoretically” possible. And at a distance of a thousand kilometers or more, volcanic dust can only slightly cloud the air, which is nevertheless clearly visible to the naked eye, because sunrises and sunsets become most beautiful due to the special refraction of the sun's rays in the dusty air.

Those who have been to Egypt are well aware of the sandstorms over Hurghada airport. The suspension of sand in the air, and especially the concentration and size of particles in the air, is several orders of magnitude higher than the concentration of dust over Europe. And in Australia, flights in conditions of global dust storms are stopped only in cases of extreme deterioration in visibility. These examples can be continued endlessly. And now, attention!!! The only difference is that, unlike volcanic dust, other dangerous phenomena have been well studied, and there are clear recommendations for avoiding them, as well as clear regulations on prohibitions and permits “depending on.”

Let me now present my consistent version of what happened.

The influence of volcanic ash on the flight of aircraft has always been an insufficiently studied thing. Of course, volcanologists persistently studied each eruption, and meteorologists had a fairly clear idea of the direction and speed of the spread of ash, but future fate Nobody paid any attention to these particles, because already several hundred kilometers from the volcano in the direction of the wind, the ash was no more than an interesting optical illusion. Yes, and civil aviation had only known a couple of cases before when planes actually fell into very dense clouds of ash, and because of this, engines stopped and other unpleasant things happened. Of course, volcanic ash as a dangerous phenomenon is included in all textbooks and instructions.

In practice, both pilots and air traffic controllers treated these points of instruction rather mockingly and did not study them well enough. Due to its rarity and exoticism. And it was precisely these same aviation officials, who grew up from former pilots and air traffic controllers, who allocated practically no money for research into these phenomena in the interests of civil aviation, which, instead of “accurate” knowledge, immediately became overgrown with myths and legends. In general, some outright nonsense has happened in meteorology. Thanks to blind faith in “computers” and “satellites” around the world, the number of weather stations with “live” people has decreased by about 60%-70%. And existing “automated systems” can only build hypothetical mathematical models that have nothing to do with the real state of affairs.

So, journalists blew up the topic, and international aviation authorities, in particular Eurocontrol, immediately fell for it. Not only that, when aviation officials began to contact numerous experts in this field, they (the experts) rather vindictively reported something like the following: “This phenomenon is certainly dangerous, but has not been sufficiently studied. Our equipment practically does not allow us to distinguish clouds of dangerous concentrations of volcanic dust from ordinary ones. So we don’t know where these clouds are and whether they actually exist.”

And then it got even funnier. The danger zone was actually quite local (several hundred kilometers in diameter and duration), but in reality hundreds and hundreds of thousands of square kilometers of earth and water surface fell into the “closure” zone. At the same time, all levels from “0” to 35,000 feet (approximately 12 km) were also completely closed at altitudes, although even the most reinsurers predicted a dangerous closure of altitudes only from altitudes of 22,000 feet. In short, the flight ban became absolute, because even its initiators could no longer do anything. There was a domino effect.

Additionally, an absolutely unexpected thing was revealed. It was possible to fly in ash-free zones, and in some cases, deviations from the route or increasing its duration by several hundred kilometers did not play any role, but modern automated systems were simply not able to rearrange schedules en masse. And it has become impossible to do this on an individual basis. Automation, automation, and more automation. Specialists in “manual” scheduling simply died out like dinosaurs, and modern airlines simply do not have such specialists. Those who are in the know should imagine that drawing up even a regular class schedule at a university is already an action between science, art and mysticism. There was no talk of rearranging the schedule for Europe. There was a mess. I absolutely do not condemn any measures related to flight safety, but admit that in the 21st century it is quite funny to close half a continent for the sake of one mountain with smoke. Let them be strong.

“American” help only brought additional horror to Europe, and finally deprived European aviation officials of the remnants of their will.

As for Russia as a part of Europe, there was no panic at all. The fact is that many years of studying the Kuril Islands (as a zone of constant eruptions) brought a sufficient amount of knowledge and skills in identifying flight hazards. Therefore, Russia flew on its territory without problems.

Although in Russia the so-called “Storm Alert Ring” was previously destroyed, i.e. Hundreds and hundreds of weather stations were closed, where poorly paid girl weather forecasters sat, and the accuracy of predictions and warnings about dangerous phenomena was unprecedentedly high.

As for the “underfunded” scientists, we can immediately confidently say that they will be allocated a lot of money for research, as compensation for past torments. But the fact that this will disrupt world harmony, because this money will be taken away from other areas, is really bad. Business and charity are not very compatible, are they?

Nevertheless, I have no doubt that the leading scientists immediately contacted each other and called each other and developed a common position. Internet, mobile communications and email in terms of communications - work real miracles. Moreover, I also have such information. It’s not for nothing that I, at least for a short time, spent time as a geologist-geophysicist. So business will receive price lists from science in full.

And as an epilogue for those who took my words like “funny” and “ridiculous” literally, I present a short excerpt from Sergei Melnichenko’s article “The History of British Airways Flight 9”.

They could see the runway lights through a small scratch on the windshield, but the plane's landing lights were not illuminated. After landing, they were unable to taxi because the apron lights caused their windshields to become frosted. The city of Edinburgh was waiting for the tug to pull it off the runway...

It was subsequently determined that the plane entered an ash cloud. Because the ash cloud was dry, it did not show up on weather radar, which can only reflect moisture in clouds. The cloud acted as a sandblasting machine and made the surface of the windshields matte. Once in the engines, the ash melted in the combustion chambers and settled on the inside of the power plant.

Since the engines began to cool down due to their shutdown, after the aircraft exited the ash cloud, the molten ash began to solidify and began to fly out of the engines under air pressure, which allowed them to start again. The restart was made possible because one of the on-board batteries remained operational.

All 263 people on board survived.

Take care of yourself. Victor Galenko, air traffic controller, navigator, geologist-geophysicist

According to Eurocontrol, on April 18, 2010, approximately 5,000 flights were recorded in airspace Europe. For comparison: before the volcanic eruption in Iceland on Sunday, there were about 24,000 flights. Thus, air traffic fell by about 6 times. Since April 15, about 63,000 flights have been canceled. Below is a table with data on the reduction in the number of flights in European airspace:

Currently, air traffic services are not provided for civil aviation aircraft in most countries in Europe, including Austria, Belgium, Croatia, Czech Republic, Denmark, Estonia, Finland, almost all of France and Germany, as well as Hungary, Ireland, northern part Italy, the Netherlands, Norway, Poland, Romania, Serbia, Slovenia, Slovakia, northern Spain, Sweden, Switzerland and the UK.

In some countries on this list, the upper airspace is open due to the spread of the ash cloud, but given the complete closure of the airspace over the territory of other countries, it is not possible to use the permitted areas of the upper airspace.

The airspace of such territories and countries as southern Europe, including parts of Spain, Portugal, southern part The Balkans, southern Italy, Bulgaria, Greece and Turkey remain open with normal air traffic.

Approximately 30% of the total number of planned flights will operate today over 50% of the total European territory.

As of the morning of April 19, all air zones Ukraine is open. Airports of Ukraine for departure and arrival aircraft are operating normally, but a number of European airports remain closed. Flights are permitted under visual flight rules before nightfall. About further possible changes in the airspace of Ukraine due to the movement of a cloud of volcanic ash (volcanic eruption in Iceland) will be informed. Ukrainian airlines report that flights are not carried out only to closed airports in Europe; flights to all open airports in the world have been resumed.

Passed the sound barrier :-)...

Before we start talking about the topic, let's bring some clarity to the question of the accuracy of concepts (what I like :-)). Nowadays two terms are in fairly wide use: sound barrier And supersonic barrier. They sound similar, but still not the same. However, there is no point in being particularly strict: in essence, they are one and the same thing. The definition of sound barrier is most often used by people who are more knowledgeable and closer to aviation. And the second definition is usually everyone else.

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 a concept of the speed of sound, but, strictly speaking, there is no fixed concept of supersonic speed. Looking ahead a little, I will say that when an aircraft flies at supersonic speed, it has already passed this barrier, and when it passes (overcomes) it, it then passes a certain threshold speed value equal to the speed of sound (and not supersonic).

Something like this :-). 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, naturally, attracts many. However, not all people who savor the words “ supersonic barrier“They actually understand what it is. I have already been convinced of this more than once, looking at forums, reading articles, even watching TV.

This question is actually quite complex from a physics point of view. But, of course, we won’t bother with complexity. We’ll just try, as usual, to clarify the situation using the principle of “explaining aerodynamics on your fingers” :-).

So, to the barrier (sound :-))!... An 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 in air are :-).

Sound waves (tuning fork).

This is an alternation of areas of compression and rarefaction, spreading in different directions from the sound source. Something like circles on water, which are also waves (just not sound ones :-)). It is these areas, acting on the eardrum of the ear, 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 components of the aircraft. For example, an engine (its sound is known to anyone :-)), or body parts (for example, bow), which, compacting the air in front of them as they move, create a certain type of pressure (compression) wave running forward.

All these sound waves travel in air environment 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 itself flies by.

I will make a reservation, however, that this is true if the plane is not flying 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 order of sound appearance for the listener and the plane, if it flies 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 it emits. That is, if he were motionless, then the waves would diverge from him in the form concentric circles like ripples on the water caused by a thrown stone. And since the plane is moving, 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 body movement.

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 occurs free stream when meeting with the nose of the aircraft (wing, empennage) and, as a consequence, increase in pressure and temperature) begins to contract and the faster the higher the flight speed.

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

Sound movement of the body (M=1).

Shock shock, is a very narrow region of the medium (about 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 decreases, pressure, temperature and density increase. Hence the name - shock wave.

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

By the way, we can say the other way around: the plane transfers part of its energy to the formation of shock waves in order to slow down the supersonic flow.

Supersonic body movement.

There is another name for the shock wave. Moving with the aircraft in space, it essentially represents the front of a sharp change in the above-mentioned environmental parameters (that is, air flow). And this is the essence of a shock wave.

Shock shock and shock wave, in general, are equivalent definitions, but in aerodynamics the first one is more used.

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

Body movement modes. ! - subsonic, 2 - M=1, supersonic, 4 - shock wave (shock wave).

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

Mach cone.

The shape of this cone (its “slimness,” so to speak) depends precisely 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 plane, and which it “overtook”, reaching supersonic speed.

Besides shock waves may also be annexed, when they are adjacent to the surface of a body moving with supersonic speed or detached, if they do not come into contact with the body.

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

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

And a detached shock can occur when flowing around rounded surfaces, for example, the leading rounded edge of a thick airfoil of a wing.

Various housing components aircraft create a rather complex system of shock waves in flight. However, the most intense of them are two. One is the head one on the bow and the second is the tail one on the tail elements. At some distance from the aircraft, the intermediate shocks either catch up with the head one and merge with it, or the tail one catches up with them.

Shock shocks on a model aircraft during purging in a wind tunnel (M=2).

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

The intensity (in other words, energy) of a shock wave (shock wave) 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 it moves away from the top of the Mach cone, that is, from the aircraft, as a source of disturbance, the shock wave weakens, gradually turns into an ordinary sound wave and ultimately disappears completely.

And on what degree of intensity it will have shock wave(or shock wave) reaching 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 the 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 correspond to it. At least the glass from the windows can easily fly out. There is ample evidence of this (especially in history Soviet aviation, when it was quite numerous and flights were intense). But you can do worse things. You just have to fly lower :-)…

However, for the most part, what remains from shock waves when they reach the ground is no longer dangerous. Just an outside observer on the ground can 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 the plane overcame sound barrier (supersonic barrier). Actually this is not true. This statement has nothing to do with reality for at least two reasons.

Shock wave (shock wave).

Firstly, if a person on the ground hears a loud 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 has not just switched to it.

And if this same person could suddenly find himself several kilometers ahead of the plane, then he would again hear the same sound from the same plane, because he would be under the influence of the same shock wave moving with the plane.

It moves at supersonic speed, and therefore approaches silently. And after it has had its not always pleasant effect on the eardrums (it’s good, when only on them :-)) and has safely passed on, the roar of running engines becomes audible.

An approximate flight diagram of an aircraft at various values of the Mach number using the example of the Saab 35 "Draken" fighter. The language, unfortunately, is German, but the scheme is generally clear.

Moreover, the transition to supersonic speed 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 instrument readings. In this case, however, a certain process occurs, but if certain piloting rules are observed, it is practically invisible to him.

But that's not all :-). I'll say more. in the form of some tangible, heavy, difficult-to-cross obstacle that the plane rests on 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 transitioning to supersonic speed and flying at it. There were even statements that this was generally impossible, 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 tending to go supersonic. This wave crisis. It is he who does some 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 during flight may not be the same. Let's take, for example, a wing, or rather an ordinary classic subsonic profile.

From the basic knowledge of how lift is generated, we know well that the flow speed 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 overall flow velocity, then, when the profile is flattened, it decreases.

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

Local shock wave that occurs at transonics during a wave crisis.

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

Such shocks appear in different areas of the streamlined surfaces, and initially they are quite weak, but their number can be large, and with an increase in the overall flow speed, the supersonic zones increase, the shocks “get stronger” and shift to the trailing edge of the profile. Later, the same shock waves appear on the lower surface of the profile.

Full supersonic flow around the wing profile.

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

To form numerous shock waves (or shock waves) during deceleration of a supersonic flow, as I said above, energy is wasted, and it is taken from the kinetic energy of the aircraft’s motion. That is, the plane simply slows down (and very noticeably!). This is it wave resistance.

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

Profile swelling at different Mach numbers. Shock 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 part of the profile with an increase in flow speed and, thereby, a change in the pressure distribution pattern on the profile, the point of application of aerodynamic forces (the center of pressure) also shifts to the trailing edge. As a result, it appears diving moment relative to the aircraft's center of mass, causing it to lower its nose.

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

A sharp increase in aerodynamic drag at transonics (wave crisis) due to an increase in wave drag. Сd - resistance coefficient.

Next. 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, control becomes difficult. For example, in roll, due to different processes on the left and right planes.

Moreover, there is the occurrence of vibrations, often quite strong due to local turbulence.

In general, a complete set of pleasures, which is called wave crisis. But, the truth is, they all take place (had, concrete :-)) when using typical subsonic aircraft (with a thick straight wing profile) in order to achieve supersonic speeds.

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

There were many tragic incidents when trying to overcome the speed of sound on conventional piston aircraft. Strong vibration sometimes led to structural damage. The planes did not have enough power for the required acceleration. In horizontal flight it was impossible due to the effect, which has the same nature as wave crisis.

Therefore, a dive was used to accelerate. But it could well have been fatal. The diving moment that appeared during a wave crisis made the dive protracted, and sometimes there was no way out of it. After all, in order to restore control and eliminate the wave crisis, it was necessary to reduce the speed. But doing this in a dive is extremely difficult (if not impossible).

The pulling into a dive from horizontal flight is considered one of the main reasons for the disaster in the USSR on May 27, 1943, of the famous experimental fighter BI-1 with a liquid rocket engine. Tests were carried out for maximum flight speed, and according to the designers' estimates, the speed achieved was more than 800 km/h. After which there was a delay in the dive, from which the plane did not recover.

Experimental fighter BI-1.

Nowadays wave crisis is already quite well studied and overcoming sound barrier(if required :-)) is not difficult. On airplanes that are designed to fly at fairly high speeds, certain design solutions and restrictions are applied to facilitate their flight operation.

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

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

Swept wing. Basic action.

The reason for this effect can be explained quite simply. On a straight wing, the air flow with a speed V approaches almost at a right angle, and on a swept wing (sweep angle χ) at a certain gliding angle β. Velocity V can be vectorially decomposed into two flows: Vτ and Vn.

The flow Vτ does not affect the pressure distribution on the wing, but the flow Vn does, which precisely determines the load-bearing properties of the wing. And it is obviously smaller in magnitude of the total flow V. Therefore, on a swept wing, the onset of a wave crisis and an increase wave resistance occurs significantly later than on a straight wing at the same free-stream speed.

Experimental fighter E-2A (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 makes it possible to shift the onset of the wave crisis to higher speeds, and in addition, it makes it possible to increase efficiency, which is important for passenger airliners.

SuperJet 100. Swept wing with supercritical profile.

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

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

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

Passing the proverbial sound barrier, that is, such aircraft transition to supersonic speed at afterburner operation of the engine due to the increase in aerodynamic resistance, and, of course, in order to quickly pass through the zone wave crisis. And the very moment of this transition is most often not felt in any way (I repeat :-)) either by the pilot (he may only experience a decrease in the sound pressure level in the cockpit), or by an outside observer, if, of course, he could observe it :-).

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

Prandtl-Gloert effect. Does not involve breaking 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 extraordinary (including a bang or an explosion).

Secondly. What we saw in the photo is the so-called Prandtl-Gloert effect. I have already written 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 itself, creates a certain amount of air behind it rarefaction region. Immediately after the flight, this area begins to fill with air from the nearby natural space. an increase in volume and a sharp drop in temperature.

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

This process at high transonic speeds can be facilitated by local shock waves I, sometimes helping to form something like a gentle cone around the plane.

High speeds favor this phenomenon, however, if the air humidity is sufficient, it can (and does) occur at fairly low speeds. For example, above the surface of reservoirs. The majority, by the way, beautiful photos of this nature were made on board an aircraft carrier, that is, in fairly humid air.

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

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

That's all for today. Thank you for reading the article to the end :-). Until next time...

Photos are clickable.

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