Aircraft roll control. How does the aircraft control work in the horizontal and vertical planes? It all starts with the physics of flight
Man has always dreamed of flying in the sky. Remember the story of Icarus and his son? This, of course, is just a myth and we will never know how it really was, but this story fully reveals the thirst to soar in the sky. The first attempts to fly into the sky were made with the help of a huge one, which is now more of a means for romantic walks in the sky, then the airship appeared, and with this later airplanes and helicopters appeared. Nowadays, it is no longer news or something unusual for almost anyone that you can fly to another continent in 3 hours by plane. But how does this happen? Why do planes fly and not crash?
The explanation from a physical point of view is quite simple, but it is more difficult to implement in practice.
For many years, various experiments were carried out to create a flying car, and many prototypes were created. But to understand why planes fly, it is enough to know Newton’s second law and be able to reproduce it in practice. Now people, or rather engineers and scientists, are trying to create a machine that would fly at colossal speeds, several times the speed of sound. That is, the question is no longer how planes fly, but how to make them fly faster.
Two things for a plane to take off - powerful engines and proper wing design
The engines create enormous thrust that pushes forward. But this is not enough, because we also need to go up, and in this situation it turns out that for now we can only accelerate along the surface to enormous speed. The next important point is the shape of the wings and the aircraft body itself. They are the ones who create the lifting force. The wings are made in such a way that the air under them becomes slower than above them, and as a result it turns out that the air from below pushes the body upward, and the air above the wing is unable to resist this influence when the plane reaches a certain speed. This phenomenon is called lift in physics, and to understand this in more detail, you need to have a little knowledge of aerodynamics and other related laws. But to understand why planes fly, this knowledge is enough.
Landing and takeoff - what does the car need for this?
An airplane requires a huge runway, or rather, a long runway. This is due to the fact that it first needs to gain a certain speed to take off. In order for the lifting force to begin to act, it is necessary to accelerate the aircraft to such a speed that the air from below the wings begins to lift the structure upward. The question of why planes fly low concerns precisely this part, when the car is taking off or landing. A low start makes it possible for the plane to rise very high into the sky, and we often see this in clear weather - scheduled planes, leaving a white trail behind them, move people from one point to another much faster than can be done using ground transport or sea.
Airplane fuel
Also interested in why planes fly on kerosene. Yes, this is basically true, but the fact is that some types of equipment use regular gasoline and even diesel fuel as fuel.
But what is the advantage of kerosene? There are several of them.
The first one can probably be called its cost. It is significantly cheaper than gasoline. The second reason can be called its lightness, in comparison with the same gasoline. Kerosene also tends to burn, so to speak, smoothly. In cars - cars or trucks - we need the ability to abruptly turn on and off the engine when the aircraft is designed to start it and constantly keep the turbines moving at a given speed for a long time, if we talk about passenger planes. Light-engine aircraft, which are not intended for transporting huge cargo, but are mostly associated with the military industry, agriculture, etc. (such a car can only accommodate up to two people), is small and maneuverable, and therefore gasoline is suitable for this area. Its explosive combustion is suitable for the type of turbines found in light aircraft.
Is a helicopter a competitor or a friend to an airplane?
An interesting invention of mankind related to moving to airspace- helicopter. It has the main advantage over an airplane - vertical takeoff and landing. It does not require a huge space for acceleration, and why do planes fly only from places equipped for this purpose? That's right, you need a fairly long and smooth surface. Otherwise, the outcome of landing somewhere in a field could be fraught with the destruction of the machine, and even worse - human casualties. And a helicopter can land on the roof of a building, which is adapted, in a stadium, etc. This function is not available for an airplane, although designers are already working on combining power with vertical take-off.
When creating the aircraft, engineers had to solve the difficult problem of controlling a winged machine. After all, the plane moves not only in the horizontal plane. A car and a ship have only one steering wheel, which allows you to turn left or right. The plane needs an additional rudder for maneuvers in the vertical plane - down and up.
As a result, the plane was equipped with two rudders - a rudder and an elevator (depth).
To control an airplane in a horizontal plane, a rudder is used. Its structure resembles the rudder of an ordinary ship. The rudder is connected by two cables to the aileron of the rear fuselage. When the aileron turns to the right, the plane turns to the right due to the air flow. Everything is extremely simple.
The elevator allows you to tilt the aircraft down and up relative to the transverse axis of the fuselage. By lowering the ailerons on the planes of the aircraft, the air flow pushes the car down or up. The elevator handle is located opposite the pilot's seat. When the pilot “takes over” the helm, the ailerons move up, air masses rush upward and put pressure on the back of the wing. The tail of the plane drops and the plane flies up.
When the pilot lowers the control wheel, “gives away,” the altitude ailerons move down and the plane rushes down. The action of air on the plane occurs from below the wing according to the same principle as when the ailerons rise. The plane loses altitude due to the raising of the tail of the fuselage.
When the elevator is tilted to the side, the plane rolls accordingly. This happens thanks to the elevator's articulated system. The roll of an aircraft occurs as a result of the alternating lowering or raising of the ailerons. This principle is used to balance the aircraft in the horizontal axis of planes.
Through the simultaneous use of elevator and rudder, the aircraft can simultaneously change altitude and direction of flight. The pilot controls the elevator with his right hand. Very rarely, when it is necessary to exert force on a turn, the pilot takes the helm with both hands. In modern aircraft, due to hydraulics, very little force is needed on the elevator.
The pilot's left hand controls the levers that control the engine. All other instruments and devices that ensure flight stability are controlled by the pilot’s left hand.
The principle of operation of the rudders and ailerons is quite simple. This principle has not changed with the development of aircraft manufacturing. The difference lies only in the engineering solutions for the layout of the control system, which would correspond to the tasks of the designed model. In modern aircraft, lightweight metal frames covered with duralumin sheets are used for the manufacture of ailerons. Also, hydraulic and electric drives are widely used to ensure optimal operating conditions of the aircraft.
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Every flight begins when the engine is started and ends when the aircraft's engine is turned off on the ground. Thus, taxiing (Exercise 4 according to the Canadian Code of Practice) is the same element of flight as climbing or landing. And, I must say, the element is not at all simple, as it seems at first glance. What's so complicated about it? In principle, there is nothing complicated. Provided that you get rid of the stereotype of a car enthusiast. This is the most difficult thing! :)
So, let's look at how small aircraft are controlled on the ground. By and large, there are only two options here. The first of these is a controlled "leg" of the landing gear, driven by rudder pedals. The rudder plane itself has only a slight aerodynamic effect on the direction of movement, because the oncoming flow is still too weak or absent altogether. However, the tail of the aircraft continues to wag while taxiing when the pilot operates the pedals. In addition, blowing the rudder with a propeller still provides some assistance in the direction of rotation.
The main turning moment is created by the nose (or controlled tail) strut. This is how the controls are made on all popular Cessnas (150, 152, 172, 182) and on many other aircraft.
It should be noted that when the nose gear of these aircraft is completely unloaded (which usually happens during takeoff), foot control stops automatically, and from that moment on the pedals only affect the rudder, which by this time is already quite aerodynamically efficient.
The second scheme for controlling an aircraft on the ground is simpler and probably cheaper, but requires greater pilot qualifications. This is the so-called “self-orienting nose strut”, which, like the free wheels of a shopping cart, turns after the turning aircraft. But what makes a plane turn? Basically, the use of separate braking. By holding the brake on just one wheel and adding thrust to the engine, you can make the plane rotate around the stationary wheel. Sounds very simple, right? You'll remember this simplicity when you're taxiing in tight spaces between parked planes, trying to keep the plane on the yellow centerline.
On the Russian Yak-18T and Yak-52 the situation is further complicated by the fact that the brakes are located not at the ends of the rudder pedals, but on the steering column. When the pedals are in neutral, the brake applies to both wheels. However, if you press only one of the pedals, a special bypass valve will send more pressure to the wheel brake on that pedal's side, and the plane will begin to turn in the desired direction. The only problem is that, due to the self-aligning strut, this rotation will not stop on its own, even when you release the brake on the helm. You will have to stop the turn by vigorously counteracting the pedals while pressing the brake lever again. Believe me, this is a very difficult skill. Instructors joke that taxiing these planes is more difficult than flying them. This is not entirely true, but “every joke has a grain of humor in it.” If the opposite pedal movement is done too late, the plane will not stop turning in time and you will definitely go off axis. Accordingly, it is necessary to develop the skill of some foresight in order to apply timely corrections. You should always taxi at a low speed, so that in case of an error or slippery surface you can completely stop the plane, and then slowly, almost rotating in place and holding the plane with the opposite “foot,” use significant engine thrust and return the plane to the taxiway axis.
It's time to remember the above-mentioned "car enthusiast stereotype" that you have to fight. Basically, it consists in the fact that the plane on the ground is steered with its FEET, and turning the steering wheel left and right is useless. You may even be shocked by the “lost control” when you turn the yoke all the way to try to stop the turn, but this will have no effect on the airplane at all. Which is not surprising. Drive with your feet! Oh, by the way, if you have ever kayaked, then you already have the appropriate skill: a kayak is very close to an airplane in fact. Duralumin frame construction and pedal control.
In addition, when taxiing on an airplane with a self-orienting strut, you will be unpleasantly surprised by the absence of a rigid connection between the “rudder” and the “road.” The plane seems to be dangling as it wants, now to the left, now to the right, and you catch it, wildly and awkwardly kicking your legs. Nothing, over time your movements will become economical and sufficient to keep it “within reasonable limits of deviation” from the axial one. Typically, mastering this skill takes at least 10 flights (when you taxi to the start and taxi back). Be prepared for the fact that this skill will degrade in the event of long breaks in flights, just like other flying skills.
There are several important points that need to be especially taken into account when taxiing.
About the first One of them I have already mentioned is speed. The well-known rule states that “you should steer at a speed no greater than the speed of a fast-walking person.” This provides the ability to quickly stop in case of any unexpected events: a derailment, an obstacle, an unexpected slip on bare ice during a turn or under the influence of a gust of wind, etc. Also think about the possible damage that a taxiing aircraft could cause to another aircraft if you make a mistake. The lower the collision speed, the less damage.
To control speed we have traction and brakes. Both need to be used to a sufficient extent, in a timely manner, but carefully. To get the plane moving (especially uphill, especially on dirt or snow) you need significantly more thrust. But thoughtlessly thrusting takeoff mode on a “stationary” aircraft is not the best solution. If it doesn't move, it may be tied up, the parking brake has not been released, or you have not removed the chocks from under the tires.
As soon as the plane rolls, the thrust must be immediately removed. Often, low throttle is sufficient for straight-line motion. At the same time, when turning, you sometimes have to increase the mode a little, especially if you use the brakes for steering. Here are the stops and sharp turns you need to anticipate in advance and set the gas to low in advance. Otherwise, you will have to actively and often use the brakes. Hot brakes become ineffective, and you won't like it at all if you have an aborted takeoff. In addition, in winter, snow sometimes falls on heated brake mechanisms and quickly melts. As the water cools, it turns into ice again and permanently blocks the brakes. standing plane. Moreover, often only one of the brakes, therefore, when you start taxiing for the next departure, you can perform a very dangerous “compass” right at the parking lot.
While taxiing, you should never “fight the engine with the brakes” - this is a serious mistake. Before driving, place your heels on the floor and fully release the brakes. If you want to slow down or stop, set the throttle to low and apply the brakes.
Using a brake (one of the wheels!) in conjunction with engine thrust is only permissible when making small radius turns. If the turn is very sharp, then pressing the pedal/lever must be periodically loosened, which allows the braked wheel to turn a little. This significantly reduces rubber wear and reduces dangerous torque loads on the landing gear. Round-the-wheel turns, such as at the end of a runway, should be generally avoided. In this case, you need to use the entire width of the strip to increase the turning radius: start turning from the very edge and end on the other side of the center line. Then, of course, you will have to “stretch” a few meters to align the plane with the takeoff course.
Second, What needs to be taken as a rule is to taxi strictly along the yellow center line. A yellow line is drawn on the asphalt to ensure maximum distance between your wings and obstacles. Resist the urge to cut corners like in a supermarket parking lot.
Third point again touches on the stereotype of a motorist, which can serve you very badly. You need to realize that you are not riding in the cockpit of an airplane like a frog in a box. You are a big bird! Remember the wings. These are YOUR wings, they are large, fragile, and you don’t want to catch anything with them. Get used to the fact that your dimensions are not limited to the cabin at all. You are much more! At least wider. Turn your head, be glad that you are not in the cabin of an airliner, from where the wings are visible only if you lean out the window and look back.
When performing turns in a confined space, in addition to the wings, you must also remember about the tail. It describes a wide arc behind you, and there is every chance of “reaching” it to the wing of an airplane parked next to it. If you are not sure about the safety of the turn, then it is better to turn off the engine and roll the plane into the parking lot manually. It will be cheaper that way.
Well fourth moment, which at first will be very difficult for you to pay attention to, but nevertheless you will have to, since it is an integral part of the flight exam. This important point (rather traditional for aviation) is taking into account the wind. But his technique is specific, since in this case it is performed on the ground.
Before you start taxiing, you must get the wind direction from the dispatcher or ATIS (at least, look at the airfield “sorcerer”). Further, during taxiing, you should always set the ailerons and elevator (read “twist and move the steering wheel”) in such a position as to reduce the influence of the wind on the aircraft. The wind, as you know, even on the ground tends to turn and even overturn an airplane. This is especially dangerous when it blows from the side, simultaneously acting on both the rudder and fuselage (which have a fairly large area and create a weather vane effect), and on the wings, creating more lift on one of them than on the other. It is impossible to completely eliminate these effects, but we must try to reduce their influence. To do this, depending on which direction the wind is blowing from, you need to set the steering wheel in the following positions:
- If the wind is blowing from the front, then you need to take the helm and turn it all the way in the direction of the wind. This will make it easier to taxi on an airplane with a self-orienting strut and will reduce the lift on the windward wing.
- If the wind is blowing from behind, then the steering wheel must be set to the “away from the wind” position, that is, completely away from you and turned all the way in the direction opposite to where the wind is blowing. Let's say, if the wind is from the right or behind, then the steering wheel needs to be turned to the left and given forward.
This illustration, specific to a Cessna 150/172 POH, demonstrates the correct rudder position for wind correction when taxiing. note that The ailerons are always set to their extreme position(to obtain maximum effect), but the elevator is not, because if the wind is in front, then it is advisable to take the helm only to unload the self-orienting strut. It is enough to just lightly unload the controllable rack, that is, select the steering wheel only a little, or even leave it in a neutral position. But if the wind is from behind, then the elevator is also placed in the extreme position (the helm is completely away from you).
A person will fly relying not on the strength of his muscles, but on the strength of his mind.
N. E. Zhukovsky
Photo by I. Dmitriev.
Rice. 1. When a flat plate interacts with an air flow, a lifting force and a drag force arise.
Rice. 2. When air flows around a curved wing, the pressure on its lower surface will be higher than on the upper. The difference in pressure gives lift.
Rice. 3. By deflecting the control stick, the pilot changes the shape of the elevator (1-3) and wings (4-6).
Rice. 4. The rudder is deflected by pedals.
Have you ever flown? Not on a plane, not on a helicopter, not on hot-air balloon, and you yourself are like a bird? Didn't you have to? And I didn't have the chance. However, as far as I know, no one succeeded.
Why couldn’t a person do this, because it seems that all you need to do is copy the wings of a bird, attach them to your hands and, imitating the birds, soar into the sky. But it was not there. It turned out that the man did not have enough strength to lift himself into the air on flapping wings. The annals of all peoples are replete with stories about such attempts, from ancient Chinese and Arab (the first mention is in the Chinese chronicle “Canhanshu”, written back in the 1st century AD) to European and Russian. Masters in different countries They used mica, thin rods, leather, and feathers to make wings, but no one managed to fly.
In 1505, the great Leonardo da Vinci wrote: “... when a bird is in the wind, it can stay in it without flapping its wings, for the same role that the wing plays in relation to the air when the air is still, the moving air plays in relation to the wings when the wings are stationary " This sounds complicated, but in essence it is not just true, but brilliant. From this idea it follows: in order to fly, you don’t need to flap your wings, you need to make them move relative to the air. And to do this, the wing just needs to be given horizontal speed. From the interaction of the wing with the air, a lifting force will arise, and as soon as its value is greater than the weight of the wing itself and everything connected with it, flight will begin. All that was left to do was to make a suitable wing and be able to accelerate it to the required speed.
But again the question arose: what shape should the wing be? The first experiments were carried out with flat-shaped wings. Look at the diagram (Fig. 1). If an incoming air flow acts on a flat plate at a small angle, then a lifting force and a drag force arise. The drag force tries to “blow” the plate back, and the lift force tries to lift it up. The angle at which air blows onto the wing is called the angle of attack. The greater the angle of attack, that is, the steeper the plate is inclined to the flow, the greater the lifting force, but the drag force also increases.
Back in the 80s of the 19th century, scientists found that the optimal angle of attack for a flat wing ranged from 2 to 9 degrees. If the angle is made smaller, the drag will be small, but the lift will also be small. If you turn more steeply towards the flow, the resistance will be so great that the wing will turn into a sail. The ratio of the magnitude of the lift force to the magnitude of the drag force is called aerodynamic quality. This is one of the most important criteria related to an aircraft. This is understandable, because the higher the aerodynamic quality, the less energy the aircraft spends on overcoming air resistance.
Let's return to the wing. Observant people noticed a long time ago that birds’ wings are not flat. All in the same 1880s, the English physicist Horatio Phillips conducted experiments in a wind tunnel of his own design and proved that the aerodynamic quality of a convex plate is much greater than that of a flat one. There was also a fairly simple explanation for this fact.
Imagine that you managed to make a wing whose lower surface is flat and the upper surface is convex. (It’s very easy to glue a model of such a wing from a regular sheet of paper.) Now let’s look at the second diagram (Fig. 2). The air flow flowing onto the leading edge of the wing is divided into two parts: one flows around the wing from below, the other from above. Please note that the air from above has to travel a slightly longer path than from below, therefore, the air speed from above will also be slightly greater than from below, right? But physicists know that as the speed increases, the pressure in the gas flow drops. Look what happens: the air pressure under the wing turns out to be higher than above it! The pressure difference is directed upward, and that’s the lifting force. And if you add an angle of attack, the lift will increase even more.
One of the first to make concave wings was the talented German engineer Otto Lilienthal. He built 12 glider models and made about a thousand flights on them. On August 10, 1896, while flying in Berlin, his glider was overturned by a sudden gust of wind and the brave explorer pilot died. The theoretical substantiation of bird soaring, continued by our great compatriot Nikolai Egorovich Zhukovsky, determined the entire further development of aviation.
Now let’s try to figure out how lift can be changed and used to control an airplane. All modern aircraft have wings made of several elements. The main part of the wing is stationary relative to the fuselage, and small additional wing flaps are installed on the trailing edge. In flight, they continue the profile of the wing, and during takeoff, landing or during maneuvers in the air they can deviate downwards. At the same time, the lifting force of the wing increases. The same small additional rotating wings are on the vertical tail (this is the rudder) and on horizontal tail(this is the elevator). If such an additional part is rejected, then the shape of the wing or tail changes, and its lifting force changes. Let's look at the third diagram (Fig. 3 on p. 83). In general, lift increases in the direction opposite to the deflection of the control surface.
I’ll tell you in very general terms how the plane is controlled. To go up, you need to lower the tail slightly, then the angle of attack of the wing will increase, and the plane will begin to gain altitude. To do this, the pilot must pull the steering wheel (control stick) towards himself. The elevator on the stabilizer deflects upward, its lifting force decreases and the tail lowers. At the same time, the angle of attack of the wing increases and its lifting force increases. To dive, the pilot tilts the control wheel forward. The elevator deflects down, the plane lifts its tail and begins to descend.
You can tilt the car to the right or left using the ailerons. They are located at the ends of the wings. Tilt of the control stick (or rotation of the wheel) to starboard causes the right aileron to go up and the left aileron to go down. Accordingly, the lift on the left wing increases, and on the right it decreases, and the plane tilts to the right. Well, figure out for yourself how to tilt the plane to the left.
The rudder is controlled using pedals (Fig. 4). Push the left pedal forward - the plane turns left, push the right pedal - right. But the machine does this “lazy”. But in order for the plane to quickly turn around, you need to make several movements. Let's say you're about to turn left. To do this, you need to tilt the car to the left (turn the steering wheel or tilt the control stick) and at the same time press the left pedal and take the steering wheel.
That's all, actually. You may ask why pilots are taught to fly for several years? Yes, because everything is just on paper. So you gave the plane a roll, took the stick, and the plane suddenly began to slide sideways, as if on a slippery hill. Why? What to do? Or, in a horizontal flight, you decided to fly higher, took the helm, and the plane suddenly, instead of climbing to a height, nosed down and flew down in a spiral, as they say, went into a “tailspin.”
During the flight, the pilot needs to monitor the operation of the engines, the direction and altitude, the weather and passengers, his own course and the courses of other aircraft, and many other important parameters. The pilot must know the theory of flight, the location and operation of the controls, must be attentive and courageous, healthy, and most importantly, love to fly.
Often, watching a plane flying in the sky, we wonder how the plane gets into the air. How does it fly? After all, an airplane is much heavier than air.
Why does the airship rise
We know that balloons and airships are lifted into the air Archimedes' force . Archimedes' law for gases states: " Nand a body immersed in gas experiences a buoyancy force equal to the force of gravity of the gas displaced by this body.” . This force is opposite in direction to gravity. That is, Archimedes' force is directed upward.
If the force of gravity is equal to the force of Archimedes, then the body is in equilibrium. If the force of Archimedes is greater than the force of gravity, then the body rises in the air. Since the cylinders of balloons and airships are filled with gas, which is lighter than air, the Archimedes force pushes them upward. Thus, the Archimedes force is a lifting force for aircraft lighter than air.
But the gravity of the aircraft significantly exceeds the force of Archimedes. Therefore, she cannot lift the plane into the air. So why does it still take off?
Airplane wing lift
The occurrence of lift is often explained by the difference in static pressures of air flows on the upper and lower surfaces of the aircraft wing.
Let's consider a simplified version of the appearance of the lifting force of a wing, which is located parallel to the air flow. The design of the wing is such that the upper part of its profile has a convex shape. The air flow flowing around the wing is divided into two: upper and lower. The speed of the bottom flow remains almost unchanged. But the speed of the top one increases due to the fact that it must cover a greater distance in the same time. According to Bernoulli's law, the higher the flow speed, the lower the pressure in it. Consequently, the pressure above the wing becomes lower. Due to the difference in these pressures, lift, which pushes the wing up, and with it the plane rises. And the greater this difference, the greater the lifting force.
But in this case, it is impossible to explain why lift appears when the wing profile has a concave-convex or biconvex symmetrical shape. After all, here the air flows travel the same distance, and there is no pressure difference.
In practice, the profile of an airplane wing is located at an angle to the air flow. This angle is called angle of attack . And the air flow, colliding with the lower surface of such a wing, is beveled and begins to move downwards. According to law of conservation of momentum the wing will be acted upon by a force directed in the opposite direction, that is, upward.
But this model, which describes the occurrence of lift, does not take into account the flow around the upper surface of the wing profile. Therefore, in this case, the magnitude of the lifting force is underestimated.
In reality, everything is much more complicated. The lift of an airplane wing does not exist as an independent quantity. This is one of the aerodynamic forces.
The oncoming air flow acts on the wing with a force called total aerodynamic force . And lifting force is one of the components of this force. The second component is drag force. The total aerodynamic force vector is the sum of the lift and drag force vectors. The lift vector is directed perpendicular to the velocity vector of the incoming air flow. And the drag force vector is parallel.
The total aerodynamic force is defined as the integral of the pressure around the contour of the wing profile:
Y – lifting force
R – traction
dΩ – profile boundary
R – the amount of pressure around the contour of the wing profile
n – normal to profile
Zhukovsky's theorem
How the lifting force of a wing is formed was first explained by the Russian scientist Nikolai Egorovich Zhukovsky, who is called the father of Russian aviation. In 1904, he formulated a theorem on the lifting force of a body flowing around a plane-parallel flow of an ideal liquid or gas.
Zhukovsky introduced the concept of flow velocity circulation, which made it possible to take into account the flow slope and obtain a more accurate value of the lift force.
The lift of a wing of infinite span is equal to the product of gas (liquid) density, gas (liquid) velocity, circulation flow velocity and the length of a selected section of the wing. The direction of action of the lifting force is obtained by rotating the oncoming flow velocity vector at a right angle against the circulation.
Lifting force
Medium density
Flow velocity at infinity
Flow velocity circulation (the vector is directed perpendicular to the profile plane, the direction of the vector depends on the direction of circulation),
Length of the wing segment (perpendicular to the profile plane).
The amount of lift depends on many factors: angle of attack, air flow density and speed, wing geometry, etc.
Zhukovsky's theorem forms the basis of modern wing theory.
An airplane can only take off if the lift force is greater than its weight. It develops speed with the help of engines. As speed increases, lift also increases. And the plane rises up.
If the lift and weight of an airplane are equal, then it flies horizontally. Airplane engines create thrust - a force whose direction coincides with the direction of movement of the aircraft and is opposite to the direction of drag. Thrust pushes the plane through the air. In horizontal flight at a constant speed, thrust and drag are balanced. If you increase thrust, the plane will begin to accelerate. But drag will also increase. And soon they will balance again. And the plane will fly at a constant, but higher speed.
If the speed decreases, then the lift force becomes less, and the plane begins to descend.
