Why birds fly. Why the plane flies. Why airplanes can't take off in extreme heat

If you often fly or often watch airplanes on services like, then you probably asked yourself why the plane flies in this way and not otherwise. What's the logic? Let's try to figure it out.

Why is the plane flying not in a straight line, but in an arc?

If you look at the flight path on the display in the cabin or at home on a computer, then it does not look straight, but arched, curved towards the nearest pole (northern in the northern hemisphere, southern in the southern). In fact, the plane tries to fly in a straight line throughout almost the entire route (and the longer it is, the fairer it is). It's just that the displays are flat, and the Earth is round, and the projection of a volumetric map onto a flat one changes its proportions: the closer to the poles, the more curved the "arc" will be. It is very simple to check this: take a globe and pull a string between two cities over its surface. This will be the shortest route. If you now transfer the line of thread to the paper, you will get an arc.

That is, the plane always flies in a straight line?

The plane does not fly as it pleases, but along the airways, which are laid, of course, in such a way as to minimize the distance. Tracks consist of segments between control points: both radio beacons and simply coordinates on the map, which are assigned five-letter designations, are often easy to pronounce and therefore memorable, can be used as them. Rather, you need to pronounce them letter by letter, but, you see, remembering combinations like DOPIK or OKUDI is easier than GRDFT and UOIUA.

When laying a route for each specific flight, various parameters are used, including the type of the aircraft itself. So, for example, for twin-engine aircraft (and they are actively replacing three- and four-engine), the ETOPS (Extended range twin engine operational performance standards) are in force, which regulate route planning in such a way that the aircraft, crossing oceans, deserts or poles, is at the same time within a certain flight time to the nearest aerodrome capable of receiving this type of aircraft. Thanks to this, in the event of a failure of one of the engines, it can be guaranteed to reach the place of commission emergency landing... Various aircraft and airlines are certified for different time flight, it can be 60, 120 and even 180 and in rare cases 240 (!) minutes. Meanwhile, it is planned to certify the Airbus A350XWB for 350 minutes, and the Boeing-787 for 330; it will eliminate four-engine aircraft even on routes like Sydney-Santiago (the world's longest commercial route overseas).

How do planes move around the airport?

Firstly, it all depends on which lane in this moment takeoffs take place at the airport of departure and which board is taken at the airport of arrival. If there are several options, then for each of them there are several exit and approach schemes: if you explain it on your fingers, then each of the points of the scheme must be followed by the plane at a certain height at a certain (within the limits) speed. The choice of lane depends on the current airport load, as well as, in the first place, the wind. The fact is that both during takeoff and landing, the wind must be oncoming (or blow from the side, but still from the front): if the wind is blowing from behind, then the plane will have to have too high a speed relative to the ground to maintain the required speed relative to the air - maybe the length of the strip is not enough for a take-off run or braking. Therefore, depending on the direction of the wind, the aircraft moves either in one direction or the other during takeoff and landing, and the strip has two takeoff and landing courses, which, when rounded to tens of degrees, are used to designate the strip. For example, if the course is 90 in one direction, then 270 in the other direction, and the lane will be called "09/27". If, as is often the case in major airports, there are two parallel stripes, they are designated as left and right. For example, in Sheremetyevo 07L / 25R and 07R / 25L, respectively, and in Pulkovo - 10L / 28R and 10R / 28L.

At some airports, the lanes work only in one direction - for example, in Sochi on one side there are mountains, so you can take off only towards the sea and land only from the sea side: in any direction of the wind it will blow from behind or during takeoff, or landing, so that the pilots are guaranteed a little extreme.

Flight procedures in the airport area take into account numerous restrictions - for example, a ban on the presence of aircraft directly over cities or special zones: these can be both restricted objects and commonplace cottage villages Rublyovka, the residents of which do not really like the noise over their heads.

Why does the plane fly faster one way than the other?

This is a question from the category of "holivar" - perhaps more copies are broken only around the puzzle with an airplane standing on a moving belt - "will take off or not take off." Indeed, the plane flies to the east faster than to the west, and if you get from Moscow to Los Angeles in 13 hours, then you can get back in 12.

That is, it is faster to fly from west to east than from east to west.

The humanist thinks that the Earth is spinning, and when you fly to one of the sides, the destination point approaches, for the planet has time to turn under you.

If you hear such an explanation, urgently give the person a geography textbook for the sixth grade, where they will explain to him that, firstly, the Earth rotates from west to east (i.e., according to this theory, everything should be the other way around), and secondly, the atmosphere rotates with the Earth. Otherwise, one could take to the air for hot-air balloon and hang in place, waiting for a crank to where you need to land: free travel!

The technician tries to explain this phenomenon by the Coriolis force, which acts on the plane in the non-inertial frame of reference "Earth-plane": when moving in one direction, its weight becomes more, and in the other, accordingly, less. The only problem is that the difference in the weight of the aircraft created by the Coriolis force is very small even compared to the mass of the payload on board. But that's half the trouble: since when does mass affect speed? You can drive 100 km / h by car and one or five people. The only difference will be in fuel consumption.

The real reason that the plane flies to the east faster than to the west is that the winds at an altitude of several kilometers most often blow from west to east, and so that in one direction the wind turns out to be fair, increasing the speed relative to the Earth, and in the other - oncoming, slowing down. Why the winds blow like this - ask Coriolis, for example. By the way, the study of high-altitude jet currents (this strong winds in the form of relatively narrow air currents in certain zones of the atmosphere) allows you to lay routes in such a way that, once “in the stream”, maximize speed and save fuel.

The speed (V) of movement of liners is not constant - one is needed on the rise, and another in flight.

1. Takeoff actually begins from the moment the vessel moves along the strip. The device accelerates, picks up the pace required to break away from the canvas, and only then, due to the increase in lifting force, it soars up. The V required for separation is specified in the manual for each model and in the general instructions. The motors at this moment are working at full capacity, giving a huge load on the machine, which is why the process is considered one of the most difficult and dangerous.
2. To lock in space and occupy a dedicated flight level, it is necessary to achieve a different speed. Flight in the horizontal plane is possible only if the aircraft compensates for the Earth's gravity.

Indicators of the speed with which the aircraft is able to rise into the air and stay there for certain time, it is difficult to name. They depend on the characteristics of a particular machine and the environment. A small single-engine V will logically be lower than a giant passenger ship - the larger the craft, the faster it has to move.

For a Boeing 747-300, this is about 250 kilometers per hour, if the air density is 1.2 kilograms per cubic meter. The Cessna 172 has about 100. The Yak-40 gets off the road by 180 km / h, the Tu154M - by 210. For the Il 96, the average reaches 250, and for the Airbus A380 - 268.

Of the conditions independent of the model of the apparatus, when determining the number, they are based on:

• the direction and strength of the wind - the oncoming one helps by pushing the nose up
• the presence of precipitation and air humidity - can complicate or contribute to acceleration
• human factor - after evaluating all parameters, the decision is made by the pilot

The speed typical for the echelon, in technical characteristics ah is designated as "cruising" - this is 80% of the maximum capabilities of the car

The speed at the level itself also depends directly on the model of the ship. In the technical specifications, it is designated as "cruising" - this is 80% of the maximum capabilities of the machine. The first passenger "Ilya Muromets" accelerated to just 105 kilometers per hour. Now the number is on average 7 times higher.

If you fly an Airbus A220, the indicator is at 870 km / h. A310 usually travels at a speed of 860 kilometers per hour, A320 - 840, A330 - 871, A340-500 - 881, A350 - 903, and the giant A380 - 900. The Boeings have about the same. The Boeing 717 cruises at 810 kilometers per hour. Mass 737 - at 817-852, depending on the generation, long-haul 747 - 950, 757 - at 850 km / h, the first transatlantic 767 - 851, Triple Seven - 905, and the jet passenger 787 - 902. According to rumors, the company is developing a liner for civil aviation, which will deliver people from one point to another at V = 5000. But so far, the top fastest in the world are exclusively military:

• the American supersonic F-4 Phantom II, although it gave way to more modern ones, is still in the top ten with an indicator of 2370 kilometers per hour
• single-engine fighter Convair F-106 Delta Dart with 2450 km / h
• combat MiG-31 - 2993
• experimental E-152, whose design formed the basis for the MiG-25 - 3030
• prototype XB-70 Valkyrie - 3,308
• research Bell X-2 Starbuster - 3 370
• The MiG-25 is capable of reaching 3492, but it is impossible to stop at this mark and not damage the engine.
• SR-71 Blackbird - 3540
• world leader X-15 rocket-powered - 7,274

Perhaps, and civil ships someday be able to achieve these indicators. But definitely not in the near future, while the main factor in the issue is the safety of passengers.

4 parts of an airliner on which flight performance depends

Flying cars differ from ordinary ones in very complex designs, providing for every little thing. And besides the obvious details, other parts also affect the possibilities and characteristics of movement - in total, 4 main ones were assembled.

1. Wing. If, in the event of an engine failure, you can fly to the nearest airfield at the second, and in case of malfunctions in two at once, you can land with the experience of a pilot, you cannot move away from the point of departure without a wing. If it does not exist, there will be no necessary lifting force. It is not by chance that they speak of the wing in the singular. Contrary to popular belief, the plane has one. This concept denotes the entire plane diverging in both directions from the side.

Since this is the main part responsible for staying in the air, a lot of attention is paid to its design. The form is built according to precise calculations, verified and tested. In addition, the wing is capable of withstanding enormous loads so as not to jeopardize the main thing - the safety of people.

2. Flaps and slats. Large quantity Over time, the wing of the aircraft has a streamlined shape, but additional surfaces appear on it during takeoff and landing. Flaps and slats are available in order to increase the area and cope with the forces acting on the apparatus during severe loads at the beginning and end of the path. When landing, they slow down the liner, do not allow it to fall too quickly, and help to stay in the air on the rise.

3. Spoilers. Appear on the upper part of the wing at times when it is required to reduce the PS. They play the role of a kind of brake. This and the details from the previous paragraph are mechanization that pilots operate manually.

4. Engine. The propeller driven ones pull the car behind them, and the jet ones "push" it forward.

Even at the beginning of the last century, few believed in the idea of ​​creating a flying transport, today airplanes do not surprise anyone. Although only a few people understand the principles of their movement - the designs of the vehicles, the physics of flights seem too complicated and give rise to a lot of delusions. But an ordinary passenger does not need to know this. The main thing is to remember that the capabilities of each model of liners have been calculated, and it is possible to repeat the fate of Icarus only in rare cases.

Flight altitude is one of the most important aviation parameters. The speed and fuel consumption depend on it, in particular. Sometimes flight safety also depends on the choice of altitude. So, for example, pilots have to change altitude when the weather conditions change abruptly, due to dense fog, dense clouds, extensive thunderstorm front or turbulent zone.

What should be the flight altitude

The first flight altitude record was equal to ... three meters. It was to this height that the Wright Flyer of the brothers Wilbur and Orville Wright first flew on December 17, 1903. 74 years later, on August 31, 1977, Soviet test pilot Alexander Fedotov set a world altitude record of 37650 meters on a MiG-25 fighter. Until now, it remains the maximum flight altitude of the fighter.

At what height do passenger planes fly?

When determining the optimal flight altitude (level), the controller or the crew commander is guided by the following. As you know, the higher the altitude, the more discharged the air and the easier it is for the plane to fly - therefore it makes sense to climb higher. However, the wings of the plane need support, and on the extremely high altitude(for example, in the stratosphere) it is clearly not enough, and the car will start to "collapse", and the engines will stall.

The conclusion suggests itself: the commander (and today the on-board computer) chooses the "golden mean" - the ideal ratio of friction force and lift force. As a result, each type passenger liners(taking into account meteorological conditions, technical characteristics, duration and direction of flight) its optimal altitude.

Why do planes fly at 10,000 meters?

At what height do fighters fly

However, the prohibitive heights of fighters are now "not in vogue." And there is an explanation for this. Modern air defense systems and air-to-air fighter missiles are capable of destroying targets at any altitude. Therefore, the main problem for a fighter is to detect and destroy the enemy earlier, and go unnoticed himself. The optimal flight altitude of the 5th generation fighter (service ceiling) is 20,000 meters.

V modern world many people are interested in science and technology and try to at least general outline understand how the things that surround them work. Thanks to this drive for enlightenment, there is a scientific and educational literature and sites like Giktimes. And since it is difficult for most people to read and perceive the series of formulas, the theories presented in such editions inevitably undergo significant simplification in an attempt to convey to the reader the "essence" of the idea with the help of a simple and understandable explanation that is easy to perceive and remember. Unfortunately, some of these "simple explanations" are fundamentally wrong, but at the same time they turn out to be so “obvious” that, without being subject to special doubts, they begin to wander from one publication to another and often become the dominant point of view, despite their erroneousness.

As one example, try answering a simple question: "Where does the lift in an airplane wing come from?"

If your explanation includes "different lengths of the upper and lower wing surfaces", "different air flow rates at the upper and lower edges of the wing" and "Bernoulli's law", then I have to inform you that you are most likely a victim of the most popular myth that is taught sometimes even in the school curriculum.

Let's first remind what we are talking about

The mythical explanation for wing lift is as follows:

1. The wing has an asymmetrical profile at the bottom and top
2. The continuous flow of air is split by the wing into two parts, one of which passes over the wing and the other under it.
3. We are considering laminar flow, in which the air flow fits snugly against the wing surface
4. Since the profile is asymmetric, in order to converge again behind the wing at one point, the "upper" flow needs to travel a longer distance than the "lower" one, so the air above the wing has to move at a higher speed than under it
5. According to Bernoulli's law, the static pressure in the flow decreases with an increase in the flow rate, therefore, in the flow above the wing, the static pressure will be lower
6. The difference in pressure in the flow under the wing and above it is the lift

... or still not? ..

There is a story (I really don't know how true it is) that one of the first people to suggest such a theory was none other than Albert Einstein himself. According to this story, in 1916, he wrote a corresponding article and, based on it, proposed his own version of the "ideal wing", which, in his opinion, maximized the difference in speeds above and below the wing, and in profile it looked something like this:

A full-fledged wing model with this profile was blown through the wind tunnel, but alas - its aerodynamic qualities turned out to be extremely poor. In contrast, it is paradoxical! - from many wings with perfectly symmetrical profile, in which the air path above and below the wing had to be fundamentally the same. There was clearly something wrong with Einstein's reasoning. And perhaps the most obvious manifestation of this incorrectness was that some pilots, as an acrobatic stunt, began to fly their planes upside down. The first planes that tried to roll over in flight had problems with fuel and oil, which did not flow where it was needed, and flowed out where it was not needed, but after fuel and oil systems capable of operating for extended periods of time in an inverted position, flying upside down has become a common sight at air shows. In 1933, for example, an American flew upside down from San Diego to Los Angeles. Somehow magically, the inverted wing still generated upward lift.

Take a look at this picture - it shows an airplane similar to the one on which the upside-down flight record was set. Note the conventional wing profile (Boeing-106B airfoil), which, according to the above reasoning, should create lift from the bottom to the top.

So our simple wing lift model has some difficulties that can be summarized in two simple observations:

1. The lift of the wing depends on its orientation relative to the incoming air flow - angle of attack
2. Symmetrical profiles (including a banal flat sheet of plywood) also create lift.

Simply put, the air "does not know" that it needs to move at a certain speed around the wing in order to fulfill some condition that seems obvious to us. And although the flow rate above the wing is indeed higher than below it, this is not cause the formation of the lifting force a consequence the fact that there is an area of ​​reduced pressure above the wing, and an area of ​​increased pressure under the wing. Getting from the area of ​​normal pressure to the rarefied area, the air is accelerated by the pressure difference, and getting into the area with increased pressure, it is slowed down. An important particular example of such a "non-Bernoulle" behavior is clearly demonstrated by ekranoplanes: when the wing approaches the ground, its lift increases (the area of ​​increased pressure is compressed by the ground), while in the framework of Bernoulle reasoning, the wing paired with the ground forms something like a narrowing tunnel that within the framework of naive reasoning, it would have to accelerate the air and thereby attract the wing to the ground, just as it is done in the reasoning, similar in meaning, about the "mutual attraction of steamers passing on parallel courses." Moreover, in the case of an ekranoplan, the situation is in many respects even worse, since one of the "walls" of this tunnel moves at a high speed towards the wing, thereby additionally "accelerating" the air and contributing to an even greater decrease in lift. However, the real practice of the "screen effect" demonstrates the opposite tendency, clearly demonstrating the danger of the logic of reasoning about lift, built on naive attempts to guess the velocity field of the air flow around the wing.

Oddly enough, another incorrect theory of the lifting force, rejected back in the 19th century, gives a much closer explanation to the truth. Sir Isaac Newton suggested that the interaction of an object with an oncoming air stream could be modeled by assuming that the oncoming stream consists of tiny particles hitting and bouncing off the object. When the object is inclined relative to the incident flow, the particles will be predominantly reflected by the object downward and, by virtue of the law of conservation of momentum, for each downward deflection of a particle of the flow, the object will receive an upward momentum. An ideal wing in such a model would be a flat kite, inclined towards the incoming stream:

Lift in this model arises due to the fact that the wing directs part of the air flow downward, this redirection requires the application of a certain force to the air flow, and the lift is the corresponding counter force from the side of the air flow to the wing. And although the original "shock" model is, generally speaking, incorrect, in such a generalized formulation this explanation is really correct... Any wing works due to the fact that it deflects part of the incoming air flow downward and this, in particular, explains why the lift of the wing is proportional to the density of the air flow and the square of its speed. This gives us a first approximation to the correct answer: the wing creates lift because the air flow lines after passing the wing are on average directed downward. And the more we deflect the flow downward (for example, by increasing the angle of attack), the greater the lifting force is.

A bit of an unexpected result, isn't it? However, it still does not bring us closer to understanding that why the air after passing the wing turns out to be moving downward. That the Newtonian shock model is incorrect has been shown experimentally by experiments that have shown that the actual flow resistance is lower than predicted by the Newtonian model, and the generated lift is higher. The reason for these discrepancies is that in Newton's model, air particles do not interact with each other in any way, while real streamlines cannot intersect each other, as shown in the figure above. The conventional "air particles" "bouncing" under the wing downward collide with others and begin to "push" them away from the wing even before they collide with it, and the air current particles above the wing "push out" the air particles located below, into the empty space left behind the wing:

In other words, the interaction of the “bounced” and “oncoming” flows creates a high pressure area (red) under the wing, and the “shadow” pierced by the wing in the flow forms a low pressure area (blue). The first region deflects the flow under the wing downward even before this flow touches its surface, and the second causes the flow above the wing to bend downward, although it did not touch the wing at all. The cumulative pressure of these areas along the wing contour, in fact, ultimately forms the lift. At the same time, an interesting point is that the high pressure area in front of the wing in a properly designed wing comes into contact with its surface only over a small area in the leading edge of the wing, while the high pressure area under the wing and the area of ​​low pressure above it are in contact with the wing for much large area... As a result, the wing lift generated by the two regions around the upper and lower wing surfaces can be much greater than the air drag force generated by the high pressure region in front of the wing leading edge.

Since the presence of areas of different pressures bends the air flow lines, it is often convenient to define these areas precisely by this bend. For example, if the streamlines above the wing "bend down", then in this area there is a pressure gradient directed from top to bottom. And if at a sufficiently large distance above the wing the pressure is atmospheric, then as it approaches the wing from top to bottom, the pressure should drop and directly above the wing it will be below atmospheric. Having considered a similar "curvature downward", but already under the wing, we find that if we start from a sufficiently low point under the wing, then, approaching the wing from the bottom up, we will come to a pressure region that will be higher than atmospheric. Similarly, the “pushing back” of streamlines in front of the leading edge of the wing corresponds to the existence of a region of increased pressure in front of this edge. Within the framework of this logic, we can say that the wing creates lift by bending the air stream around the wing... Since the air streamlines seem to "stick" to the wing surface (Coanda effect) and to each other, changing the wing profile, we force the air to move around it along a curved trajectory and therefore form the pressure gradient we need. For example, to ensure upside-down flight, it is enough to create the desired angle of attack by directing the nose of the aircraft away from the ground:

A bit unexpected again, right? Nevertheless, this explanation is closer to the truth than the original version "the air is accelerating over the wing, because it needs to travel a greater distance above the wing than under it." In addition, in his terms, it is easiest to understand the phenomenon called "stalling" or "stalling the plane." In a normal situation, by increasing the angle of attack of the wing, we thereby increase the curvature of the air flow and, accordingly, the lift. The price for this is an increase in drag as the low pressure region gradually shifts from over-wing to slightly off-wing and thus begins to slow down the aircraft. However, after a certain limit, the situation suddenly changes sharply. The blue line on the graph is the lift coefficient, the red line is the drag coefficient, the horizontal axis corresponds to the angle of attack.

The fact is that the "stickiness" of the stream to the streamlined surface is limited, and if we try to bend the air stream too much, it will begin to "detach" from the wing surface. The low-pressure area formed behind the wing begins to "suck" not the air flow coming from the leading edge of the wing, but the air from the area left behind the wing, and the lift generated by the upper part of the wing completely or partially (depending on where the separation took place) will disappear, and the drag will increase.

For a conventional aircraft, a stall is an extremely unpleasant situation. The lift of the wing decreases with decreasing aircraft speed or decreasing air density, and in addition, turning the aircraft requires more lift than simply level flight. In normal flight, all these factors are compensated for by the choice of the angle of attack. The slower the plane flies, the less dense the air (the plane climbed great height or sits down in hot weather) and the steeper the turn, the more you have to make that corner. And if an unwary pilot crosses a certain line, then the lifting force rests against the "ceiling" and becomes insufficient to keep the aircraft in the air. Adding problems and increased air resistance, which leads to a loss of speed and a further decrease in lift. As a result, the plane begins to fall - "topple over". Along the way, control problems may arise due to the fact that the lift is redistributed over the wing and begins to try to "turn" the aircraft or the control surfaces find themselves in the area of ​​the stalled flow and cease to generate sufficient control force. And in a sharp turn, for example, the flow can be disrupted only from one wing, as a result of which the plane will not only begin to lose altitude, but also rotate - it will go into a tailspin. The combination of these factors remains one of the common causes of plane crashes. On the other hand, some modern combat aircraft are specially designed in such a special way to maintain controllability in such supercritical attack modes. This allows such fighters to brake sharply in the air if necessary. Sometimes this is used for braking in straight flight, but more often it is in demand in turns, since the lower the speed, the smaller, all other things being equal, the turning radius of the aircraft. And yes, you guessed it - this is the very "super-maneuverability" that specialists who have designed the aerodynamics of domestic fighters of the 4th and 5th generations are deservedly proud of.

However, we have not yet answered the main question: where, in fact, do areas of high and low pressure appear around the wing in the incoming air flow? After all, both phenomena ("adhesion of the flow to the wing" and "above the wing the air moves faster"), which can explain flight, are consequence a certain distribution of pressure around the wing, and not its cause. But why exactly such a picture of pressures is formed, and not some other?

Unfortunately, the answer to this question already inevitably requires the involvement of mathematics. Let's imagine that our wing is infinitely long and the same along its entire length, so that the movement of air around it can be modeled in a two-dimensional section. And let's suppose, for a start, that our wing is ... an infinitely long cylinder in the flow of an ideal fluid. Due to the infinity of the cylinder, such a problem can be reduced to considering an ideal fluid flow around a circle in a plane. For such a trivial and idealized case, there is an exact analytical solution that predicts that when the cylinder is stationary, the total effect of the fluid on the cylinder will be zero.

Now let's look at some tricky transformation of the plane onto itself, which mathematicians call conformal mapping. It turns out that you can choose a transformation that, on the one hand, preserves the equations of motion of the fluid flow, and on the other hand transforms the circle into a figure with a wing-like profile. Then the fluid flow lines for the cylinder transformed by the same transformation become the solution for the fluid flow around our improvised wing.

Our original circle in the flow of an ideal fluid has two points at which the streamlines are in contact with the surface of the circle, and therefore the same two points will exist on the surface of the profile after applying the transformation to the cylinder. And depending on the rotation of the flow relative to the original cylinder ("angle of attack"), they will be located in different places on the surface of the formed "wing". And almost always this will mean that some of the fluid streamlines around the airfoil will have to bend around the trailing, sharp edge of the wing, as shown in the picture above.

This is potentially possible for an ideal fluid. But not for the real one.

The presence of even a slight friction (viscosity) in a real liquid or gas leads to the fact that a flow similar to that shown in the picture is immediately disrupted - the upper flow will shift the point where the streamline touches the wing surface until it is strictly on the trailing edge of the wing (postulate of Zhukovsky-Chaplygin, aka Kutta's aerodynamic condition). And if we transform the "wing" back into a "cylinder", then the shifted streamlines will turn out to be something like this:

But if the viscosity of the liquid (or gas) is very low, then the solution obtained in a similar way should be suitable for the cylinder as well. And it turns out that such a solution can really be found if we assume that the cylinder revolves... That is, the physical limitations associated with the fluid flow around the trailing edge of the wing lead to the fact that the fluid movement from all possible solutions will tend to come to one specific solution, in which part of the fluid flow rotates around an equivalent cylinder, breaking away from it at a strictly defined point ... And since a rotating cylinder creates a lifting force in a fluid flow, the corresponding wing also creates it. The component of the flow motion corresponding to this "rotation rate of the cylinder" is called the flow circulation around the wing, and Zhukovsky's theorem says that a similar characteristic can be generalized for an arbitrary wing, and allows one to quantitatively calculate the wing lift based on it. Within the framework of this theory, the lift of the wing is provided by air circulation around the wing, which is generated and maintained at the moving wing by the above friction forces, which exclude air flow around its sharp trailing edge.

Amazing result, isn't it?

The theory described is, of course, highly idealized (infinitely long homogeneous wing, ideal homogeneous incompressible gas / liquid flow without friction around the wing), but gives a fairly accurate approximation for real wings and ordinary air. Just do not take circulation within it as evidence that the air is actually moving around the wing. Circulation is simply a number that shows how different in speed the flow at the upper and lower edges of the wing must be, so that the solution of the fluid flow motions ensures the separation of streamlines strictly at the trailing edge of the wing. You should also not take the "principle of a sharp trailing edge of the wing" as a necessary condition for the occurrence of lift: the sequence of reasoning instead sounds like "if the wing has a sharp trailing edge, then lift is formed this way."

Let's try to summarize. The interaction of the air with the wing creates areas of high and low pressure around the wing, which bend the air flow so that it bends around the wing. The sharp trailing edge of the wing leads to the fact that in the ideal flow, of all potential solutions of the equations of motion, only one specific one is realized, which excludes the overflow of air around the sharp trailing edge. This solution depends on the angle of attack and in a conventional wing has a region of reduced pressure above the wing and a region of increased pressure below it. The corresponding pressure difference forms the lift of the wing, makes the air move faster above the upper edge of the wing and slows the air below the lower edge. It is convenient to quantitatively describe the lift force numerically through this difference in speeds above and below the wing in the form of a characteristic called "circulation" of the flow. Moreover, in accordance with Newton's third law, the lifting force acting on the wing means that the wing deflects part of the incoming air flow downward - in order for the aircraft to fly, part of the air surrounding it must continuously move downward. Leaning on this downward flow of air, the plane “flies”.

The simple explanation of "air that needs to travel a longer distance above the wing than below it" is incorrect.

Jokes aside, but a certain touch of seriousness appears in such a situation not only in a person burdened with aviation knowledge. Moreover, the aforementioned forty-ton "fool" is, in general, a medium-sized aircraft of the Russian Air Force SU-24. Well, and if this "serious" person turns out to be a witness of a leisurely, but oh-oh-very confident take-off of the largest in the world transport aircraft AN-225 "Mriya" ("Dream" in Ukrainian, who does not know)? .. I will not comment on anything else. I will only add that the take-off weight of this "bird" is 600 tons.

Yes, impressions on this basis can be very deep. But, be that as it may, emotions have absolutely nothing to do with it. Physics. One naked physics. It is in obedience to the laws of physics that all aircraft are lifted into the air, starting with light sports aircraft and ending with heavy transport aircraft and seemingly completely shapeless helicopters that are incomprehensibly held in the air. And all this happens due to the lifting force and even the thrust force of the engine.

The phrase "lifting force" is familiar to almost any person, but the surprising thing is that not everyone can say where it comes from, this very force. Meanwhile, its origin can be explained simply, literally "on the fingers", without getting into the mathematical jungle.

As you know, the main bearing surface of an aircraft is the wing. It almost always has a certain profile, in which the lower part is flat, and the upper part is convex (according to a certain law). The air flow passing under the lower part of the profile hardly changes its structure and shape. But, passing over the upper part, it narrows, because for it the upper surface of the profile is like a concave wall in a pipe, through which this very stream seems to flow.

Now, in order to drive the same volume of air through this "squeezed" pipe for a certain time, it must be moved faster, which is actually happening. It remains to recall Bernoulli's law from a favorite school physics course, which says that the higher the flow rate, the lower its pressure. Thus, the pressure above the airfoil (and therefore over the entire wing) is lower than the pressure below it.

A force arises that tries to "squeeze" the wing, and hence the entire aircraft upward. This is the aforementioned lift. As soon as she gets more weight - hurray! We're in the air! We are flying! And by the way, the higher our speed, the greater the lift. If in the future the rise

The power and weight are equal in magnitude, then the plane will go into level flight. And a good speed will be given to us by a powerful aircraft engine, or, more precisely, by the thrust force that it creates.

Using this principle, it is possible, theoretically, to make an object of any mass and shape take off (and fly successfully). The main thing is to accurately calculate everything from the point of view of aerodynamics and other aviation sciences and correctly manufacture this very item. When I talk about the shape, I mean mainly the helicopter. The device, which does not at all look like an airplane, is kept in the air for the same reason. After all, each blade of its main, speaking in aviation language, carrying (a very characteristic word, already met above) propeller is the same wing with an aerodynamic profile.

Moving in the air flow with the rotation of the propeller, the blade creates a lifting force, which, by the way, not only lifts the helicopter, but also moves it forward. For this, the axis of rotation of the propeller is slightly tilted (a “skew” of the propeller is created), and a horizontal component of the lift appears, which plays the role of the thrust force of the aircraft engine. The screw pulls both up and forward at the same time. As a result, we get a confident and very reliable flight of such a “strange” apparatus like a helicopter. And, by the way, quite a beautiful flight. I have repeatedly watched the aerobatics of an MI-24 combat helicopter from the ground - the sight is simply mesmerizing.

By the way, I want to note that the propellers of aircraft with screw engines (turbo or piston) are akin to helicopter ones and use the same principle (guess which one?). Only the lifting force was completely "re-qualified" here due to the thrust force. Speaking in a helicopter way, the "skew" of the propeller is 90 degrees.

Yes, aviation is very beautiful. Words of admiration are applicable in the conversation about the flight of any sufficiently perfect aircraft. Be it the outwardly unhurried giant "Mriya", the hard worker-attack aircraft SU-25 or the nimble sports aerobatic pilot. All this beauty is the result of sometimes many years of painstaking work of scientists and aeronautical engineers, aerodynamics, engine engineers, strength specialists, etc.

And aviation science is actually just as difficult as it is interesting. But it is based on, in general, a simple physical principle of the formation of lift, the essence of which, if desired, can be very easily explained, and which, nevertheless, helps to realize the age-old desire of mankind to fly ...