On October 14, 1947, humanity crossed another milestone. The boundary is quite objective, expressed in a specific physical quantity - the speed of sound in air, which, under the conditions of the earth's atmosphere, depends on its temperature and pressure within 1100-1200 km/h. Supersonic speed was conquered by the American pilot Chuck Yeager (Charles Elwood "Chuck" Yeager) a young veteran of the Second World War, who had extraordinary courage and excellent photogenicity, thanks to which he immediately became popular in his homeland just like 14 years later Yuri Gagarin.
And the courage to go through the sound barrier was really required. Soviet pilot Ivan Fedorov, who repeated Yeager's achievement a year later, in 1948, recalled his feelings then: “Before flying to overcome the sound barrier, it became obvious that there was no guarantee to survive after it. No one practically knew what it was and whether the design of the aircraft would withstand the pressure of the elements. But we tried not to think about it.”
Indeed, there was no complete clarity on how the car would behave at supersonic speed. Aircraft designers were still fresh in their memory of the sudden misfortune of the 1930s, when, with the growth of aircraft speeds, it was necessary to urgently solve the problem of flutter self-oscillations that occur both in the rigid structures of the aircraft and in its skin, tearing the aircraft apart in a matter of minutes. The process developed like an avalanche, rapidly, the pilots did not have time to change the flight mode, and the cars fell apart in the air. For quite a long time, mathematicians and designers in various countries struggled to solve this problem. In the end, the theory of the phenomenon was created by the then young Russian mathematician Mstislav Vsevolodovich Keldysh (19111978), later president of the USSR Academy of Sciences. With the help of this theory, it was possible to find a way to permanently get rid of an unpleasant phenomenon.
It is quite understandable that equally unpleasant surprises were expected from the sound barrier. Numerical solution of complex differential equations of aerodynamics in the absence of powerful computers was impossible, and one had to rely on the "purge" of models in wind tunnels. But from qualitative considerations it was clear that when the speed of sound was reached, a shock wave appeared near the aircraft. The most crucial moment overcoming the sound barrier, when the speed of the aircraft is compared with the speed of sound. At this moment, the pressure difference on opposite sides of the wave front increases rapidly, and if the moment lasts longer than an instant, the plane can fall apart no worse than from a flutter. Sometimes, when breaking the sound barrier with insufficient acceleration, the shock wave created by the aircraft even knocks out the windows of the windows of houses on the ground below it.
The ratio of the speed of an aircraft to the speed of sound is called the Mach number (after the famous German mechanic and philosopher Ernst Mach). When passing the sound barrier, it seems to the pilot that the number M jumps over one in leaps and bounds: Chuck Yeager saw the tachometer needle jump from 0.98 to 1.02, after which there was a “divine” silence in the cockpit in fact, seeming: just a level sound pressure in the cockpit drops several times. This moment of "cleansing from the sound" is very insidious, it cost the lives of many testers. But the danger of falling apart for his X-1 aircraft was small.
The X-1, manufactured by Bell Aircraft in January 1946, was a purely research aircraft designed to break the sound barrier and nothing more. Despite the fact that the car was ordered by the Ministry of Defense, instead of weapons, it was stuffed with scientific equipment that monitors the operating modes of components, instruments and mechanisms. The X-1 was like a modern cruise missile. It had one Reaction Motors rocket engine with a thrust of 2722 kg. Maximum takeoff weight 6078 kg. Length 9.45 m, height 3.3 m, wingspan 8.53 m. Maximum speed at an altitude of 18290 m 2736 km / h. The car was started from strategic bomber B-29, but landed on steel "skis" on a dried-up salt lake.
No less impressive are the “tactical and technical parameters” of its pilot. Chuck Yeager was born on February 13, 1923. After school, he went to a flight school, and after graduation he went to fight in Europe. Shot down one Messerschmitt-109. He himself was shot down in the skies of France, but he was rescued by partisans. As if nothing had happened, he returned to the base in England. However, the vigilant counterintelligence service, not believing the miraculous deliverance from captivity, removed the pilot from flying and sent him to the rear. The ambitious Yeager obtained an appointment with the commander-in-chief of the allied forces in Europe, General Eisenhower, who believed Yeager. And he was not mistaken - in the six months remaining before the end of the war, the young pilot made 64 sorties, shot down 13 enemy aircraft, and 4 in one battle. And he returned to his homeland with the rank of captain with an excellent dossier, which indicated that he had a phenomenal flight intuition, incredible composure and amazing endurance in any critical situation. Thanks to this characteristic, he got into the team of supersonic testers, who were selected and trained as carefully as later astronauts.
Renaming the X-1 "Glamorous Glennis" in honor of his wife, Yeager set records on it more than once. At the end of October 1947, the previous altitude record fell 21,372 m. In December 1953, a new modification of the machine X-1A reached a speed of 2.35 M almost 2800 km / h, and six months later rose to a height of 27 430 m. In addition, there were tests of a number of fighters launched into a series and a run-in of our MiG-15, captured and transported to America during the Korean War. Subsequently, Yeager commanded various Air Force test units both in the United States and at American bases in Europe and Asia, took part in the fighting in Vietnam, and trained pilots. He retired in February 1975 with the rank of brigadier general, having flown 10 thousand hours during his valiant service, running 180 different supersonic models and collecting a unique collection of orders and medals. In the mid-80s, a film was made based on the biography of a brave guy who was the first in the world to break the sound barrier, and after that Chuck Yeager became not even a hero, but a national relic. He last flew an F-16 on October 14, 1997, and broke the sound barrier on the fiftieth anniversary of his historic flight. Yeager was then 74 years old. In general, as the poet said, nails should be made from these people.
There are many such people on the other side of the ocean Soviet designers began to try on conquering the sound barrier at the same time as the American ones. But for them it was not an end in itself, but a completely pragmatic act. If the X-1 was a purely research machine, then our sound barrier was stormed on prototype fighters, which were supposed to be put into series to equip Air Force units with them.
The competition included several design bureaus Lavochkin Design Bureau, Mikoyan Design Bureau and Yakovlev Design Bureau, in which swept-wing aircraft were developed in parallel, which was then a revolutionary design solution. They reached the supersonic finish in this order: La-176 (1948), MiG-15 (1949), Yak-50 (1950). However, there the problem was solved in a rather complex context: a military machine must have not only high speed, but also many other qualities maneuverability, survivability, minimum time pre-flight preparation, powerful weapons, impressive ammunition load, etc. etc. It should also be noted that in Soviet times the decision of the state acceptance commissions was often influenced not only by objective factors, but also by subjective moments associated with the political maneuvers of the developers. All this combination of circumstances led to the fact that the MiG-15 fighter was launched into the series, which showed itself perfectly in the local arenas of military operations in the 50s. It was this car, captured in Korea, as mentioned above, that Chuck Yeager “driving around”.
In La-176, a wing sweep equal to 45 degrees, a record for those times, was applied. The VK-1 turbojet engine provided thrust of 2700 kg. Length 10.97 m, wingspan 8.59 m, wing area 18.26 sq.m. Takeoff weight 4636 kg. Ceiling 15,000 m. Flight range 1,000 km. Armament one 37 mm gun and two 23 mm. The car was ready in the autumn of 1948, in December it began flight tests in the Crimea at a military airfield near the city of Saki. Among those who led the tests was the future academician Vladimir Vasilyevich Struminsky (19141998), the pilots of the experimental aircraft were Captain Oleg Sokolovsky and Colonel Ivan Fedorov, who later received the title of Hero Soviet Union. Sokolovsky, by an absurd accident, died during the fourth flight, forgetting to close the cockpit canopy.
Colonel Ivan Fedorov broke the sound barrier on December 26, 1948. Having risen to a height of 10 thousand meters, he rejected the control stick away from himself and began to accelerate in a dive. “I am accelerating my 176 from a great height,” the pilot recalled. A tedious low whistle is heard. Increasing speed, the plane rushes to the ground. On the scale of the machometer, the arrow changes from three-digit numbers to four-digit ones. The plane is shaking like it's in a fever. And suddenly silence! Taken the sound barrier. Subsequent interpretation of the oscillograms showed that the number M has exceeded one. It happened at an altitude of 7,000 meters, where a speed of 1.02M was recorded.
In the future, the speed of manned aircraft continued to steadily increase due to an increase in engine power, the use of new materials and the optimization of aerodynamic parameters. However, this process is not unlimited. On the one hand, it is hampered by considerations of rationality, when fuel consumption, development costs, flight safety and other not idle considerations are taken into account. And even in military aviation, where money and pilot safety are not so significant, the speeds of the most "nimble" cars are in the range from 1.5M to 3M. It doesn't seem like it needs more. (The speed record for manned vehicles with jet engines belongs to the American reconnaissance aircraft SR-71 and is Mach 3.2.)
On the other hand, there is an insurmountable thermal barrier: at a certain speed, the heating of the machine body by friction with air occurs so quickly that it is impossible to remove heat from its surface. Calculations show that at normal pressure this should occur at a speed of the order of 10M.
Nevertheless, the 10M limit was still reached at the same Edwards training ground. It happened in 2005. The record holder was the X-43A unmanned rocket aircraft, manufactured as part of the 7-year-old Hiper-X grandiose program to develop new types of technologies designed to radically change the face of rocket and space technology of the future. Its cost is $230 million. The record was set at an altitude of 33,000 meters. Used in drone new system overclocking. First, a traditional solid-propellant rocket is tested, with the help of which the X-43A reaches a speed of 7M, and then a new type of engine is turned on - a hypersonic ramjet engine (scramjet, or scramjet), in which ordinary atmospheric air is used as an oxidizer, and gaseous fuel is hydrogen (quite a classic scheme of an uncontrolled explosion).
In accordance with the program, three unmanned models were made, which, after completing the task, were drowned in the ocean. The next stage involves the creation of manned vehicles. After their testing, the results obtained will be taken into account when creating a wide variety of "useful" devices. Apart from aircraft for the needs of NASA will be created hypersonic military vehicles bombers, reconnaissance and transport vehicles. Boeing, which is participating in the Hiper-X program, plans to build a 250-passenger hypersonic airliner by 2030-2040. It is quite clear that there will be no windows that break aerodynamics at such speeds and cannot withstand thermal heating. Instead of portholes, screens with a video recording of passing clouds are supposed.
There is no doubt that this type of transport will be in demand, because the further, the more expensive time becomes, accommodating more and more emotions, dollars earned and other components of modern life per unit of time. In this regard, there is no doubt that someday people will turn into one-day butterflies: one day will be saturated like all the current (rather already yesterday) human life. And it can be assumed that someone or something is implementing the Hiper-X program in relation to humanity.
Sometimes, when a jet plane flies in the sky, you can hear a loud bang that sounds like an explosion. This "burst" is the result of the aircraft breaking the sound barrier.
What is a sound barrier and why do we hear an explosion? And who was the first to break the sound barrier ? We will consider these questions below.
What is a sound barrier and how is it formed?
Aerodynamic sound barrier - a series of phenomena that accompany the movement of any aircraft (aircraft, rocket, etc.), the speed of which is equal to or exceeds the speed of sound. In other words, the aerodynamic "sound barrier" is the sudden jump in air resistance that occurs when an aircraft reaches the speed of sound.
Sound waves move through space at a certain speed, which varies with altitude, temperature, and pressure. For example, at sea level, the speed of sound is approximately 1220 km/h, at an altitude of 15 thousand meters - up to 1000 km/h, etc. When the speed of an aircraft approaches the speed of sound, certain loads act on it. At normal speeds (subsonic), the nose of the aircraft “drives” a wave of compressed air in front of it, the speed of which corresponds to the speed of sound. The speed of the wave is greater than the normal speed of the aircraft. As a result, the air flows freely around the entire surface of the aircraft.
But, if the speed of the aircraft corresponds to the speed of sound, the compression wave is formed not on the nose, but in front of the wing. As a result, a shock wave is formed, which increases the load on the wings.
In order for an aircraft to overcome the sound barrier, in addition to a certain speed, it must have a special design. That is why aircraft designers have developed and applied in aircraft construction a special aerodynamic wing profile and other tricks. At the moment of breaking the sound barrier, the pilot of a modern supersonic aircraft feels vibrations, “jumps” and “aerodynamic impact”, which we perceive on the ground as a bang or an explosion.
Who was the first to break the sound barrier?
The question of the "pioneers" of the sound barrier is the same as the question of the first conquerors of space. To the question " Who was the first to break the supersonic barrier ? different answers can be given. This is the first person to break the sound barrier, and the first woman, and, oddly enough, the first device ...
The first to break the sound barrier was test pilot Charles Edwood Yeager (Chuck Yeager). On October 14, 1947, his experimental aircraft Bell X-1, equipped with rocket engine, going into a gentle dive from a height of 21379 m above Victorville (California, USA), reached the speed of sound. The speed of the aircraft at that moment was 1207 km / h.
Throughout his career, the military pilot made a great contribution to the development of not only American military aviation, but also astronautics. Charles Elwood Yeager ended his career as a General in the US Air Force, having traveled to many parts of the world. The experience of a military pilot came in handy even in Hollywood when staging spectacular aerial stunts in the feature film Pilot.
Chuck Yeager's story of breaking the sound barrier is told by the movie The Right Guys, which won four Oscars in 1984.
Other "conquerors" of the sound barrier
In addition to Charles Yeager, who was the first to break the sound barrier, there were other record holders.
- The first Soviet test pilot - Sokolovsky (December 26, 1948).
- The first woman was American Jacqueline Cochran (May 18, 1953). Flying over Edwards Air Force Base (California, USA), her F-86 aircraft broke the sound barrier at a speed of 1223 km / h.
- The first civilian aircraft was the American passenger airliner Douglas DC-8 (August 21, 1961). His flight, which took place at an altitude of about 12.5 thousand meters, was experimental and organized in order to collect data necessary for the future design of the leading edges of the wings.
- First car to break the sound barrier - Thrust SSC (October 15, 1997).
- First person to break the sound barrier in free fall- American Joe Kittinger (1960), who jumped with a parachute from a height of 31.5 km. However, after it, flying on October 14, 2012 over the American city of Roswell (New Mexico, USA), the Austrian Felix Baumgartner set a world record by leaving a balloon with a parachute at an altitude of 39 km. At the same time, its speed was about 1342.8 km / h, and the descent to the ground, most of which was in free fall, took only 10 minutes.
- The world record for breaking the sound barrier by an aircraft belongs to the X-15 air-to-ground hypersonic aeroballistic missile (1967), which is now in service with the Russian army. The rocket speed at an altitude of 31.2 km was 6389 km / h. I would like to note that the maximum possible speed of human movement in the history of manned aircraft is 39897 km / h, which was reached in 1969 by the American spaceship"Apollo 10".
First invention to break the sound barrier
Oddly enough, but the first invention that broke the sound barrier was ... a simple whip, invented by the ancient Chinese 7 thousand years ago.
Until the invention of instant photography in 1927, no one could have imagined that the snap of a whip was not just a strap hitting a handle, but a miniature supersonic snap. During a sharp swing, a loop is formed, the speed of which increases several tens of times and is accompanied by a click. The loop breaks the sound barrier at a speed of about 1200 km/h.
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 :-))!… Aircraft 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 parts of the body (for example, the nose), which, compacting the air in front of it 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 was 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 for 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. it 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 the lifting force is formed, 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 on top speed flight, and according to the estimates of 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.
Nowadays 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 Constructive decisions and restrictions 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. On a straight wing, an air flow with a speed V runs almost at a right angle, and on a swept wing (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 a 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 too:-)). 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.
Why is an airplane breaking the sound barrier accompanied by an explosive pop? And what is a "sound barrier"?
There is a misunderstanding with "cotton" caused by a misunderstanding of the term "sound barrier". This "clap" is properly called "sonic boom". An aircraft moving at supersonic speed creates shock waves, air pressure surges, in the surrounding air. Simplistically, these waves can be imagined as a cone accompanying the flight of an aircraft, with a vertex, as it were, tied to the forward part of the fuselage, and generators directed against the movement of the aircraft and propagating quite far, for example, to the surface of the earth.
When the boundary of this imaginary cone, denoting the front of the main sound wave, reaches the human ear, then a sharp pressure jump is perceived by ear as a pop. The sonic boom, like a tethered one, accompanies the entire flight of the aircraft, provided that the aircraft is moving fast enough, albeit at a constant speed. Cotton, on the other hand, seems to be the passage of the main sound shock wave over a fixed point on the earth's surface, where, for example, the listener is located.
In other words, if a supersonic aircraft with a constant but supersonic speed began to fly back and forth over the listener, then the clap would be heard every time, some time after the aircraft flew over the listener at a fairly close distance.
A “sound barrier” in aerodynamics is called a sharp jump in air resistance that occurs when an aircraft reaches a certain boundary speed close to the speed of sound. When this speed is reached, the nature of the air flow around the aircraft changes dramatically, which at one time made it very difficult to achieve supersonic speeds. A conventional, subsonic aircraft is not capable of sustainably flying faster than sound, no matter how it is accelerated - it will simply lose control and fall apart.
To overcome the sound barrier, scientists had to develop a wing with a special aerodynamic profile and come up with other tricks. It is interesting that the pilot of a modern supersonic aircraft is well aware of the “overcoming” of the sound barrier by his aircraft: when switching to a supersonic flow, an “aerodynamic impact” and characteristic “jumps” in controllability are felt. But these processes are not directly related to the “pops” on the ground.
Before the plane breaks the sound barrier, an unusual cloud may form, the origin of which is still not clear. According to the most popular hypothesis, there is a pressure drop near the aircraft and a so-called Prandtl-Glauert singularity followed by condensation of water droplets from humid air. Actually, you can see the condensate in the pictures below ...
Click on the picture to enlarge it.
An unusual picture can sometimes be observed during the flight of jet aircraft, which seem to emerge from a cloud of fog. This phenomenon is called the Prandtl-Gloert effect and consists in the appearance of a cloud behind an object moving at transonic speed in conditions of high humidity.
The reason for this unusual phenomenon is that flying on high speed the aircraft creates an area of high air pressure in front of it and an area of low pressure behind. After the flight of the aircraft, the area of low pressure begins to fill with ambient air. At the same time, due to the rather high inertia air masses first, the entire low pressure area is filled with air from nearby areas adjacent to the low pressure area.
This process is locally an adiabatic process, where the volume occupied by the air increases and its temperature decreases. If the air humidity is high enough, then the temperature can drop to such a value that it will be below the dew point. Then the water vapor contained in the air condenses into tiny droplets that form a small cloud.
Clickable 2600 px
As the air pressure normalizes, the temperature in it evens out and again becomes above the dew point, and the cloud quickly dissolves into the air. Usually, its lifetime does not exceed fractions of a second. Therefore, when an airplane flies, it seems that the cloud follows it - due to the fact that it constantly forms immediately behind the aircraft, and then disappears.
There is a common misconception that the appearance of a cloud due to the Prandtl-Gloert effect means that at this very moment the aircraft breaks the sound barrier. Under conditions of normal or slightly increased humidity, a cloud forms only at high speeds close to the speed of sound. At the same time, when flying at low altitude and under conditions of very high humidity (for example, over the ocean), this effect can also be observed at speeds much lower than the speed of sound.
Clickable 2100 px
There is a misunderstanding with "cotton" caused by a misunderstanding of the term "sound barrier". This "pop" is properly called "sonic boom". An aircraft moving at supersonic speed creates shock waves, air pressure surges, in the surrounding air. Simplistically, these waves can be imagined as a cone accompanying the flight of an aircraft, with a vertex, as it were, tied to the forward part of the fuselage, and generators directed against the movement of the aircraft and propagating quite far, for example, to the surface of the earth.
Clickable 2500 px
When the boundary of this imaginary cone, denoting the front of the main sound wave, reaches the human ear, then a sharp pressure jump is perceived by ear as a pop. The sonic boom, like a tethered one, accompanies the entire flight of the aircraft, provided that the aircraft is moving fast enough, albeit at a constant speed. Cotton, on the other hand, seems to be the passage of the main sound shock wave over a fixed point on the earth's surface, where, for example, the listener is located.
In other words, if a supersonic aircraft with a constant but supersonic speed began to fly back and forth over the listener, then the clap would be heard every time, some time after the aircraft flew over the listener at a fairly close distance.
And look what an interesting frame! First time I see this!
Clickable 1920 px
- who's on the table!
