Small unmanned aerial vehicles are becoming more widespread every year - they are used in the filming of television shows and music videos, for patrolling territories, or just for fun. Flying drones does not require special permission, and their cost is constantly decreasing. As a result, aviation authorities in some countries decided to study whether these devices pose a danger to passenger aircraft. The results of the first studies were contradictory, but in general regulators came to the conclusion that the flights of private drones should be brought under control.
In July 2015, the plane Lufthansa airlines, landing at Warsaw airport, almost collided with a multicopter, flying at a distance of less than a hundred meters from it. In April 2016, pilots passenger plane companies British Airways, which landed at London Airport, reported to air traffic controllers that it had collided with a drone during landing. Later, however, the investigation came to the conclusion that there was no drone, and what the pilots took for it was most likely an ordinary package lifted by the wind from the ground. However, already in July 2017, at the British Gatwick airport, a plane almost collided with a drone, after which air traffic controllers were forced to close one runway for landing and redirect five flights to reserve strips.
According to the British research organization UK Airprox Board, in 2016 in the UK there were 71 cases of dangerous encounters between passenger aircraft and drones. A dangerous proximity in aviation is considered to be the approach of an aircraft with another aircraft at a distance of less than 150 meters. Since the beginning of this year, 64 cases of drones approaching aircraft in the UK have already been recorded. In the US, last year aviation authorities recorded just under 200 cases of dangerous proximity. At the same time, aviation authorities still have a poor idea of exactly how dangerous small drones can be for passenger aircraft. Some experts previously assumed that a collision with a drone for a passenger airliner would be no more dangerous than a regular bird strike.
According to the specialized publication Aviation Week & Space Technology, since 1998, 219 people have died worldwide due to mid-air collisions between passenger flights and birds, with a significant proportion of them flying in small private aircraft. However, every year airlines around the world spend a total of $625–650 million to repair damage to passenger aircraft due to bird strikes. By the way, in general passenger liners are considered resistant to direct hits from birds. When developing and testing new aircraft, special checks are even carried out - the aircraft is fired at with the carcasses of various birds (ducks, geese, chickens) to determine its resistance to such damage. Checking engines for birds being thrown into them is generally mandatory.
In mid-March last year, researchers from the American George Mason University announced that the threat of drones to aviation has been greatly exaggerated. They studied bird strike statistics from 1990 to 2014, including incidents that resulted in fatalities. As a result, scientists came to the conclusion that the real probability of a dangerous collision between a drone and an airplane is not so high: just one case in 187 million years should end in a large-scale disaster.
To try to determine whether drones actually pose a threat to passenger aircraft, aviation authorities in the European Union and the United Kingdom commissioned two independent studies in 2016. The engineers who conduct these studies shoot various drone designs or drone parts at different parts of the aircraft to produce real-life damage that passenger aircraft might suffer in a collision. In parallel, mathematical modeling of such collisions is carried out. The research is carried out in several stages, the first of which have already been completed and the results are presented to customers. It is expected that after the work is fully completed, aviation authorities will develop new rules for the registration and operation of drones by private individuals.
A drone crashes into the windshield of a passenger plane during testing in the UK.
Today at different countries There are no uniform rules for drone flights. Thus, in the UK there is no requirement to register and license drones weighing less than 20 kilograms. Moreover, these devices must fly within the operator’s line of sight. Private drones with cameras are not allowed to fly within 50 meters of people, buildings or cars. In Italy, there are practically no special rules for drones, except for one thing - drones cannot be flown around large crowds of people. And in Ireland, for example, all drones weighing more than one kilogram must be registered with the Office civil aviation countries. By the way, in the European Union, Ireland is one of the ardent supporters of tightening the rules for the use of drones.
Meanwhile, while Europe plans to tighten the screws, in the United States, on the contrary, they intend to make drone flights more free. So, earlier this year, the US Federal Aviation Administration came to the conclusion that lightweight consumer quadcopters do not pose a big threat to aircraft, although their flights near airports are unacceptable. In February, American companies 3DR, Autodesk and Atkins already received permission to control drone flights at the world's busiest airport - International airport Hartsfield-Jackson Atlanta, which annually handles about one hundred million passengers. Here, quadcopters were used to create 3D maps of an airport in high resolution. They carried out flights in the direct line of sight of the operator and under the control of air traffic controllers.
The results of the study were first published in October last year by a working group of the European Agency for aviation security. These researchers concluded that amateur drones do not pose a serious threat to passenger aircraft. During their work, the working group participants focused on studying the consequences of air collisions between passenger aircraft and drones weighing up to 25 kilograms. For the study, drones were divided into four categories: large (weighing more than 3.5 kilograms), medium (up to 1.5 kilograms), small (up to 0.5 kilograms) and “harmless” (up to 250 grams). For each category, experts determined the degree of danger, which was assessed on a five-point scale: 1-2 - high, 3-5 - low. Devices that received four to five points were considered safe.
To determine the degree of danger, the researchers used data on aircraft flight altitudes by category, took into account the likelihood of their appearance in the same airspace as aircraft, as well as the results of computer and full-scale tests of collisions between drones and airliners. In addition, the individual degree of danger was assessed for each unmanned vehicle using four points: damage to the hull, threat to the lives of passengers, threat to the lives of the crew, threat of disruption to the flight schedule. To simplify the assessment, the researchers carried out calculations for aircraft flying at a speed of 340 knots (630 kilometers per hour) at an altitude of three thousand meters or more and at a speed of 250 knots at a lower altitude.
Based on the results of all the calculations, the participants of the European working group came to the conclusion that small drones at an altitude of up to three thousand meters pose virtually no threat to passenger aircraft. The fact is that such devices rise to high altitudes, where they can collide with an airplane, extremely rarely. In addition, they have very little mass. Medium drones, according to experts, do not pose a serious threat to airliners. Only if the device weighs 1.5 kilograms (this is the mass most of amateur drones) collides with an aircraft at an altitude of more than three thousand meters, it could threaten flight safety. Large aircraft are recognized as dangerous for passenger aircraft at all flight altitudes.
Based on the results of full-scale tests, it turned out that in the event of a collision with drones, the windshields of airliners, nose cones, leading edges of the wing, and engines can receive the greatest damage. In general, damage from drones weighing up to 1.5 kilograms can be comparable to damage from birds, which aircraft regularly collide with in the air. Now European experts are preparing for an expanded study. This time, the damage that drones can cause to passenger aircraft engines will be studied, and the likelihood of batteries getting into technological holes will be assessed.
By the way, earlier scientists from Virginia Tech University conducted computer simulations of situations in which various drones fall into a running aircraft engine. The researchers came to the conclusion that devices weighing more than 3.6 kilograms pose a serious danger to engines. Once in the engine, they will destroy the fan blades and collapse themselves. Then fragments of the fan blades and drone will fall into the external air circuit, from where they will be thrown out, as well as into the internal circuit - the compressor, combustion chamber and turbine area. The speed of debris inside the engine can reach 1,150 kilometers per hour. Thus, if a drone weighing 3.6 kilograms collides during takeoff, the engine will completely stop working in less than a second.
Meanwhile, the results of the British study were summed up in the middle of this year - in July, the company that carried out the work, QinetiQ, submitted a report to the UK National Air Traffic Control Service. The study, conducted by a British company, used a specially designed air gun that fired drones and drone parts at predetermined speeds into the fronts of decommissioned planes and helicopters. Quadcopters weighing 0.4, 1.2 and 4 kilograms, as well as aircraft-type drones weighing up to 3.5 kilograms, were used for shooting. Based on the results of the shooting, experts came to the conclusion that any drones are dangerous for light aircraft and helicopters that do not have a special certificate for protection against bird strikes.
Bird-resistant passenger aircraft can suffer serious damage from drones when flying at cruising speeds, which range from 700 to 890 kilometers per hour. The researchers considered serious damage to be the destruction of windshields in a collision with heavy parts of drones - metal parts of the body, camera and battery. These parts, breaking through the windshield, can fly into the cockpit, damage control panels and injure pilots. Devices weighing from two to four kilograms were considered dangerous for airliners. It should be noted that passenger aircraft develop cruising speed already at high altitude(usually about ten thousand meters), which amateur drones are simply unable to climb.
According to QinetiQ, drones weighing four kilograms can be dangerous for passenger aircraft at low flight speeds, such as during landing. At the same time, the severity of damage to the aircraft largely depends on the design of the drone. Thus, during tests it turned out that drones with a camera mounted on a gimbal under the body have little chance of breaking through the windshield of a passenger aircraft. The fact is that in a collision, the camera on the gimbal will hit the glass first, and then the drone body. In this case, the camera and its suspension will play the role of a kind of shock absorber, taking on part of the impact energy. British aviation authorities, who are pushing for a sharp tightening of drone flight regulations, are expected to commission additional research.
Some commercially produced drones today already have a geofencing function. This means that the device constantly updates a database of zones closed to drone flights. The drone simply will not take off in such an area. However, in addition to serial devices, there are also homemade drones that can fly into air space airports. And there are quite a lot of them. In general, so far not a single case of a collision between an aircraft and a drone has been recorded, but this is just a matter of time. And even if small drones do not pose a serious threat to passenger aircraft, they can still have a negative impact on aviation, increasing the already considerable costs for companies to repair airliners.
Vasily Sychev
The video was made using the Schlieren method to study shock waves.
NASA has published video footage of a T-38 Talon training aircraft flying at supersonic speed against the background of the Sun. It was made using the schlieren method to study shock waves generated at the edges of an aircraft airframe. Pictures and videos of shock waves are needed by NASA specialists for research carried out as part of the project to develop a “quiet” supersonic aircraft.
The Schlieren method is one of the main ways to study air flows when designing and testing new aircraft.
This method of photography allows one to detect optical inhomogeneities in transparent refractive media. Schlieren photography uses special lenses with a cut-off aperture.
In such cameras, direct rays pass through the lens and are concentrated on the cutting diaphragm, which is also called a Foucault knife. In this case, the reflected and scattered light by the lens is not focused on the knife and falls on the camera matrix. Thanks to this, the weakened light scattered and reflected by refractions in the air is not lost in direct rays.
Shock waves are clearly visible in the published video. They represent areas in which the pressure and temperature of the environment experience a sharp and strong jump. Shock waves are perceived by an observer on the ground as an explosion or as a very loud bang, depending on the distance from the supersonic object.
The sound of an explosion from shock waves is called a sonic boom, and it is this that is one of the main obstacles in the development of supersonic passenger aviation. Currently, aviation regulations prohibit supersonic flights of aircraft over populated land areas.
Aviation authorities may allow supersonic flights over populated land as long as the perceived noise level of passenger aircraft does not exceed 75 decibels. To make existence civil supersonic aviation possible, developers today are looking for different technical ways to make new aircraft “quiet.”
When flying at supersonic speeds, an airplane generates many shock waves. They typically occur at the tip of the nose cone, on the leading and trailing edges of the wing, on the leading edges of the tail, in the swirler areas and on the edges of the air intakes.
One way to reduce perceived noise levels is to change the aerodynamic design of the aircraft.
In particular, it is believed that redesigning some elements of the airframe will make it possible to avoid sharp pressure surges at the front of the shock wave and sharp drops in pressure in the rear part with subsequent normalization.
A shock wave with sharp jumps is called an N-wave, because on the graph it resembles this particular letter of the Latin alphabet. It is these shock waves that are perceived as an explosion. The new aerodynamic design of the aircraft will have to generate S-waves with a pressure drop that is smooth and not as significant as that of the N-wave. S-waves are expected to be perceived as a soft pulsation.
The American company Lockheed Martin is developing a technology demonstrator for a “quiet” supersonic aircraft as part of the QueSST project. The work is being carried out by order of NASA. In June of this year, the preliminary design of the aircraft was completed.
The first flight of the demonstrator is planned to take place in 2021. The “quiet” supersonic aircraft will be single-engine. Its length will be 28.7 meters. He will receive a glider, the fuselage and wing of which resemble an inverted airplane. The QueSST will have a conventional vertical fin and horizontal rudders for low-speed maneuvering.
A small T-shaped tail will be installed on the top of the fin, which will “break” shock waves from the nose and canopy. The nose of the aircraft will be significantly lengthened to reduce drag and reduce the number of changes in the airframe where shock waves can form during supersonic flight.
QueSST technology involves the development of such an aerodynamic aircraft structure, at the edges of which the smallest possible number of shock waves would form. At the same time, those waves that will still form should be much less intense.
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 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, 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 parts of the body (for example, the 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 propagate in the air at the speed of sound already known to us. 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 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 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, tail) and, as a result, 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 at moderate subsonic speeds. It seems to come across 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 at supersonic speed, or moving away, if they are not in 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, for example, this could be 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 components of the aircraft body 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 an earthly observer as one due to the small size of the 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 military supersonic aircraft reach supersonic speed 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 exposed to 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 sound 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!). 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 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 increasing flow speed and, thereby, changing 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 result in... Due to a 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.
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, 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 to:-)).
There have been 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.
In our time 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 make the 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 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. Most, 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, do 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 aircraft flying at low altitude at supersonic speed. There is, of course, a certain exaggeration there :-), but the general principle is clear. And again impressive :-)…
That's all for today. Thank you for reading the article to the end :-). Until next time...
Photos are clickable.
Illustration copyright Airbus Image caption An example of what the power package of an Airbus aircraft might look like in the future. Instead of the usual “skeleton” of frames, stringers and spars - a lightweight mesh of complex shape
Is it possible for the very concept of flight to change completely? It is possible that this will be the case in the future. Thanks to new materials and technologies, passenger drones may appear, and supersonic airliners will return to the skies. The BBC Russian service analyzed information about the latest projects of Airbus, Uber, Toyota and other companies to determine in which direction aviation will develop in the future.
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City sky
Nowadays, a fairly large layer of the atmosphere up to a kilometer high remains relatively free over cities. This space is used by special aviation, helicopters, as well as individual private or corporate aircraft.
But in this layer a new species is already beginning to develop air transport. It has many names - urban or personal aviation, the air transport system of the future, sky taxi, and so on. But its essence was formulated at the beginning of the 19th century by futurist artists: everyone will have the opportunity to use a small aircraft to fly short distances.
Illustration copyright Hulton Archive Image caption This is how the artist imagined the future in 1820. An individual aircraft was present in such pictures even then- What projects are aircraft designers working on around the world?
Engineers never gave up on this dream. But until now, the lack of durable and lightweight materials and imperfect electronics, without which many small devices cannot be launched, have been hampered. With the advent of high-strength, lightweight carbon fiber and the development of portable computers, everything changed.
The current stage of creating urban airmobile transport is somewhat reminiscent of the 1910s, the very beginning of the history of aircraft construction. Then the designers did not immediately find the optimal shape of the aircraft and boldly experimented, creating bizarre designs.
Now the common task - to make an aircraft for the urban environment - also allows us to build a wide variety of devices.
The Airbus corporation, for example, is developing three large projects at once - the manned single-seat Vahana, which, according to the corporation's plans, will be able to fly next year, and by 2021 will be ready for commercial flights. Two other projects: CityAirbus, an unmanned quadcopter taxi for several people, and Pop.Up, which the corporation is developing together with Italdesign. This is a single-seat unmanned module that can be used on a wheeled chassis for trips around the city, as well as suspended from a quadcopter for flights.
Airbus Pop.Up and CityAirbus use the quadcopter principle, and Vahana is a tiltrotor (that is, a device that takes off like a helicopter, and then turns its engines and then moves like an airplane).
Quadcopter and tiltrotor designs are now the main ones for passenger drones. Quadcopters are much more stable during flight. And tiltrotors allow you to reach higher speeds. But both schemes allow you to take off and land vertically. This is a key requirement for urban aviation, since conventional aircraft require a runway. This means that the construction of additional infrastructure for the city will be required.
Other notable projects include the Volocopter from the German company eVolo, which is a multicopter with 18 propellers. This is the most successful air taxi project so far; testing has already begun in Dubai in the fall of 2017. In June, Dubai's transport management company talks about this with eVolo.
Illustration copyright Lilium Image caption Lilium is propelled by 36 electric turbines installed in a row on planes and in two blocks at the front of the deviceAnother project from Germany - Lilium - is interesting due to its unusual layout. This is an electric tiltrotor with 36 small turbines installed in two blocks along the wing, and with two more blocks in the front of the device. The company has already begun test flights in unmanned mode.
Japanese automaker Toyota is investing in the Cartivator project.
And the online taxi service Uber is also developing its own unmanned system, in this project it is working closely with NASA to develop technologies and software service in cities with high population density.
Illustration copyright Ethan Miller/Getty Images Image caption The EHang 184 passenger drone, created by the Chinese company Beijing Yi-Hang Creation Science & Technology Co., Ltd. in 2016There are many aviation experts who are supporters of unmanned urban passenger transportation, and skeptics.
Among the latter is Avia.ru editor-in-chief Roman Gusarov. The main problem, in his opinion, is the low power of electric motors and batteries. And efficient passenger drones are unlikely to appear in the foreseeable future, despite the fact that a lot of money is being invested in their development.
“The technologies are still quite crude and the systems created using them are subject to technical failures,” Denis Fedutinov, editor-in-chief of the uav.ru portal, noted in an interview with the BBC.
According to him, such projects may simply be a nice publicity stunt and an opportunity to show that the company is engaged in cutting-edge research. He also does not rule out that, against the background of enthusiastic publications in the press, many startups may arise that, having found investor money, will not be able to create a flying passenger drone.
Executive Director of Infomost Consulting (a company engaged in consulting in the field of transport) Boris Rybak believes that so far the biggest problem in this area is fear. People will be afraid to trust their lives to an aircraft without a pilot for a long time.
“When the first self-propelled gasoline carts appeared, they rode next to the horses with smoke, smoke and roar, and people ran away. But this is normal, it was scary then, and it’s scary now,” Rybak said.
Between the houseamiand birdsami
Currently, NASA and the US Federal Aviation Administration are working on the Unmanned Aircraft System (UAS) Traffic Management (UTM) program. It is within the framework of this program that Uber is collaborating with NASA and the FAA.
The development of technologies in this area is far ahead of the development of rules for their regulation. The American program began to be developed in 2015, but in " road map“its development has not yet even marked the deadline for creating rules for flights in densely populated urban areas.
Illustration copyright Italdesign Image caption The Pop.Up passenger capsule can be used on a wheeled chassis or attached to a quadcopterThis refers to drone flights for mail delivery and news video recording. But the program says nothing at all about the transportation of passengers.
Judging by data from presentations studied by the BBC Russian Service, in the future, flights of passenger drones in cities will be regulated through the formation of routes in air corridors. The same principle applies in modern civil aviation. In this case, the drones will actively interact with each other and monitor the airspace around them to avoid collisions with other drones and other objects in the air (for example, birds).
However, as Boris Rybak believes, a system built on the principle of free flight, where routes would be built by computers taking into account the location of all aircraft in the air, would be much more effective.
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Will Russia remain on the sidelines?
In Russia, authorities are also trying to take cautious steps to regulate drone flights in urban environments. Thus, Rostelecom has been interested in drones for a long time. It is a contractor for the Russian Space Systems company, which in November 2015 won the Roscosmos competition for 723 million rubles ($12.3 million) to create the infrastructure of the Federal Network Operator.
Illustration copyright Tom Cooper/Getty Images Image caption Another supersonic business jet project - XB-1 from the American company Boom TechnologyThis infrastructure will have to provide surveillance of transport and unmanned vehicles (including aircraft), ground and water manned and unmanned transport, by rail, explained a representative of Rostelecom. The operator is creating a prototype of infrastructure that will control the movement of vehicles, primarily drones, and is ready to spend about 100 million rubles ($1.7 million) on subcontractors.
Deputy head of the Moscow Department of Science, Industrial Policy and Entrepreneurship Andrei Tikhonov told the BBC that the Russian capital does not yet have the conditions for the appearance of passenger drones.
“Firstly, the regulatory framework for unmanned aerial and ground vehicles has not been fully developed. Secondly, the Moscow infrastructure is not yet adapted for mass transportation of goods and passengers on unmanned vehicles. Thirdly, most of the vehicles intended for transporting people and large cargo, are still at the testing stage and must receive the appropriate documentation to work in urban conditions. Again, issues of compulsory passenger insurance and many others arise," he explained.
True, according to him, these problems do not so much stop the city authorities as force them to look for ways to solve them.
Faster than sound
Another area that many aircraft manufacturing corporations are working on is supersonic passenger transportation.
This idea is not new at all. November 22 marks the 40th anniversary of the start of regular commercial flights between New York, Paris and London on Concorde aircraft. In the 1970s, the idea of supersonic transport was embodied by British Airways together with Air France, as well as Aeroflot on the Tu-144. But in practice it turned out that the technologies of that time were not suitable for civil aviation.
As a result, the Soviet project was canceled after seven months of operation, and the British-French one after 27 years.
Illustration copyright Evening Standard Image caption Concorde, like the Tu-144, was ahead of its time, but showed how difficult it is to make a supersonic passenger planeFinance is usually cited as the main reason why the Concorde and Tu-144 projects were cancelled. These planes were expensive.
The engines of such devices consume much more fuel. For such aircraft it was necessary to create its own infrastructure. The Tu-144, for example, used its own type of aviation fuel, which was much more complex in composition; it required special maintenance, which was more thorough and expensive. For this aircraft it was even necessary to maintain separate ramps.
Another serious problem, in addition to the complexity and cost of maintenance, was noise. During flight at supersonic speed, a strong air seal occurs at all leading edges of the aircraft elements, which generates a shock wave. It reaches behind the plane in the form of a huge cone, and when it reaches the ground, the person through whom it passes hears a deafening sound, like an explosion. It is because of this that Concorde flights over US territory at supersonic speed were prohibited.
And it is noise that designers are now primarily trying to combat.
After the cessation of Concorde flights, attempts to build a new, more efficient supersonic passenger aircraft did not stop. And with the advent of new technologies in the field of materials, engine building and aerodynamics, people began to talk about them more and more often.
Several large projects in the field of supersonic civil aviation are being developed around the world. Basically, these are business jets. That is, designers initially try to target that market segment where the cost of tickets and service plays a lesser role than in route transportation.
Illustration copyright Aerion Image caption Aerion is developing the AS2 aircraft in partnership with AirbusNASA, together with Lockheed Martin Corporation, is developing a supersonic aircraft, trying, first of all, to solve the problem of the sound barrier. QueSST technology involves searching for a special aerodynamic shape of the aircraft, which would “smear” the hard sound barrier, making it blurry and less noisy. Currently, NASA has already developed the appearance of the aircraft, and its flight tests may begin in 2021.
Another notable project is AS2, which is being developed by Aerion in partnership with Airbus.
Airbus is also working on the Concord 2.0 project. This aircraft is planned to be equipped with three types of engines - a rocket in the tail section and two conventional jet engines, with the help of which the aircraft will be able to take off almost vertically, as well as one ramjet, which will already accelerate the aircraft to a speed of Mach 4.5.
True, Airbus deals with such projects quite carefully.
“Airbus continues to research in the field of supersonic/hypersonic technologies, we are also studying the market to understand whether these types of projects will be viable and feasible,” Airbus said in an official commentary to the BBC Russian Service. “We do not see a market for such aircraft now and in the foreseeable future due to the high costs of such systems. This may change with the advent of new technologies, or with changes in the economic or social environment. In general, for now this is more of an area of study, rather than a priority direction."
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Is it possible to revive Concorde?It is really difficult to predict whether there will be a demand for such aircraft. Boris Rybak notes that information technologies have also developed in parallel with aviation, and now a businessman who needs to quickly resolve an issue on the other side of the Atlantic can often do this not in person, but via the Internet.
“It’s six hours to fly business class or a business jet from London to New York. Otherwise, technically you’ll spend four, well, three and forty. Is this [game] worth the price?” - said Rybak regarding supersonic flights.
Based on the experience of the Tu-144
However, other Russian aviation experts think differently. Supersonic aircraft will be able to take their place in the market, says the rector of the Moscow Aviation Institute, Mikhail Pogosyan, the former head of the United Aircraft Corporation.
“A supersonic aircraft makes it possible to reach a qualitatively different level; it allows you to save global time - a day. Market forecasts indicate that the introduction of this kind of technology and this kind of project will be associated with the cost of such a flight. If such a cost is acceptable and will not times different from the cost of a flight on a subsonic aircraft, then I assure you that there is a market,” he told the BBC Russian Service.
Pogosyan spoke at the Aerospace Science Week forum at the Moscow Aviation Institute, where he, in particular, spoke about the prospects for creating a supersonic aircraft with the participation of Russian specialists. Russian enterprises (TsAGI, MAI, UAC) are participating in the large European research program Horizon 2020, one of the directions of which is the development of a supersonic passenger aircraft.
Poghosyan listed the main properties of such an aircraft - a low level of sonic boom (otherwise the aircraft will not be able to fly over populated areas), a variable cycle engine (it needs to work well at subsonic and supersonic speeds), new heat-resistant materials (at supersonic speeds the aircraft gets very hot), artificial intelligence, as well as the fact that such an aircraft can be controlled by one pilot.
At the same time, the rector of MAI is convinced that the supersonic aircraft project can only be created at the international level.
Illustration copyright Boris Korzin/TASS Image caption According to Sergei Chernyshev, Russia has preserved the school of creating supersonic passenger aircraftThe head of the Central Aerohydrodynamic Institute named after Professor N. E. Zhukovsky (TsAGI) Sergei Chernyshev said at the forum that Russian specialists are participating in three international projects in the field of supersonic passenger aviation - Hisac, Hexafly and Rumble. All three projects do not aim to create a final commercial product. Their main task is to study the properties of supersonic and hypersonic vehicles. According to him, now aircraft manufacturers are only creating the concept of such an aircraft.
In an interview with the BBC, Sergei Chernyshev said that strong point Russian aircraft manufacturers have experience in creating supersonic aircraft and operating them. According to him, this is a strong aerodynamic school, extensive experience in testing, including in extreme conditions. Russia also has a “traditionally strong school of materials scientists,” he added.
“My subjective forecast: on the horizon of 2030-35 a [business jet] will appear. Academician Pogosyan believes that between 2020 and 2030. He gave them ten years. This is true, but still closer to 2030,” - said Sergei Chernyshev.
"Ordinary" unusual liners
The main task of aircraft designers today is to achieve an increase in the fuel efficiency of the aircraft, while reducing harmful emissions and noise. The second task is to develop new control systems where the computer will perform more and more tasks.
Nowadays, no one will be surprised by the fly-by-wire control system of an aircraft, when signals from the control stick or steering wheel, pedals and other organs are transmitted to the rudders and other mechanization elements in the form of electrical signals. Such a system allows the on-board computer to control the pilot’s actions, making adjustments and correcting errors. However, this system is already yesterday.
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As Kirill Budaev, vice-president of the Irkut corporation for marketing and sales, told the BBC, the Russian company is working on a system where only one pilot will fly the plane, and the functions of the second during takeoff and landing will be performed by a specially trained senior flight attendant. During an airplane flight at flight level, one pilot is quite enough, Irkut believes.
According to the laws of nature
Another major innovation that has emerged in the last decade is composite materials. The development of lightweight, durable plastic can be compared to the use of aluminum in post-war aviation. This material, along with the advent of efficient turbojet engines, changed the face of aircraft. Now exactly the same revolution is happening with composites, which are gradually displacing metal from aircraft structures.
Aircraft design is increasingly using 3D printing, which allows it to create more complex shapes with high precision. And strive to reduce fuel consumption.
For example, Airbus and Boeing use the latest LEAP family engines manufactured by CFM International. The injectors in these engines are 3D printed. And this increased fuel efficiency by 15%.
In addition, the aviation industry has now begun to actively embrace bionic design.
Bionics is an applied science that studies the possibilities of practical application in various technical devices of principles and structures that appeared in nature thanks to evolution.
Illustration copyright Airbus Image caption Bracket designed using bionic technologyHere's a simple example - the picture above shows a bracket similar to the one used on an Airbus aircraft. Pay attention to its shape - usually such an element is a solid piece of triangular metal. However, by calculating on a computer the forces that would be applied to its various parts, the engineers figured out which parts could be removed and which could be modified in such a way as to not only lighten, but also strengthen such a component.
Much more complex work was carried out by a group of scientists led by Professor Niels Aage of the Technical University of Denmark. In October 2017, they published a report in the journal Nature in which they described how they calculated the force set of a Boeing 777 airliner wing on the French Curie supercomputer - a complex structure of rather thin jumpers and struts.
As a result, according to the researchers, the weight of the aircraft's two wings could be reduced by 2-5% without losing strength. Considering that both wings weigh a combined 20 tons, this would result in savings of up to 1 ton, which corresponds to an estimated reduction in fuel consumption of 40-200 tons per year. But this is already significant, isn’t it?
At the same time, bionic design in the future, as aircraft manufacturing corporations believe, will be used more and more. The plane in the first illustration to this text is just a sketch by Airbus engineers, but it already shows on what principle the powertrain of future aircraft will be created.
Electricity
The engine is the most important and most expensive part of the aircraft. And it is he who determines the configuration of any aircraft. Currently, most aircraft engines are either natural gas or internal combustion, gasoline or diesel. Only a very small part of them runs on electricity.
According to Boris Rybak, throughout the decades of the existence of jet aviation, the development of fundamentally new aircraft engines was not carried out. He sees this as a manifestation of the lobby of oil corporations. Whether this is true or not, during the entire post-war period an effective engine that did not burn hydrocarbon fuel never appeared. Although even atomic ones were tested.
The attitude towards electricity in the global aviation industry is currently changing dramatically. The concept of a “More Electric Aircraft” has emerged in global aviation. It implies greater electrification of the units and mechanisms of the device compared to modern ones.
In Russia, technology within the framework of this concept is carried out by the Technodinamika holding, part of Rostec. The company is developing electric reverse drives for the future Russian PD-14 engine, fuel system drives, and landing gear retraction and extension drives.
"In the long term, we are, of course, looking at large commercial aircraft projects. And in these big planes“We will most likely use a hybrid propulsion system before switching to full electric propulsion,” Airbus said in a commentary. - The fact is that the power-to-weight ratio in modern batteries is still very far from what we need. But we are preparing for a future where this is possible."
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.
