Why do birds fly. Why does an airplane fly. Why planes can't take off in extreme heat
An airplane is an aircraft that has a mass greater than the mass of air, and a lifting force created according to the aerodynamic principle (throwing down part of the air due to the flow around the wing). Lift is the answer to the question of why airplanes fly. It is created by bearing surfaces (mainly wings) when moving towards the air flow of an aircraft that develops speed with the help of power plant or turbines. Due to the power plant, which creates traction force, the aircraft is able to overcome air resistance.
Planes fly according to the laws of physics.
Aerodynamics as a science is based on the theorem of Nikolai Egorovich Zhukovsky, an outstanding Russian scientist, the founder of aerodynamics, which was formulated back in 1904. A year later, in November 1905, Zhukovsky outlined his theory of creating wing lift. aircraft at a meeting of the Mathematical Society.
In order for the lifting force to be able to lift a modern aircraft into the air, even weighing tens of tons, its wing must have sufficient area. The lift force of a wing is affected by many parameters, such as profile, area, wing planform, angle of attack, speed and airflow density. Each aircraft has its own minimum speed at which it can take off and fly without falling. So, minimum speed contemporary passenger aircraft is in the range from 180 to 250 km / h.
Why do planes fly at different speeds?
The size of the aircraft depends on the required speed of the aircraft. Wing area slow transport aircraft must be large enough, since the lift force of the wing and the speed developed by the aircraft are directly proportional. Big square wings of slow aircraft is due to the fact that at sufficiently low speeds the lift force is small.
High-speed aircraft tend to have much smaller wings, while still providing sufficient lift. How less density air, the lower the lift force of the wing becomes, therefore, on high altitude the speed of the aircraft must be higher than when flying at low altitude.
Why do planes fly so high?
Flight altitude of modern jet aircraft located between 5,000 and 10,000 meters above sea level. This is explained very simply: at such a height, the air density is much less, and, consequently, the air resistance is also less. Planes fly to high altitudes, because when flying at an altitude of 10 kilometers, the aircraft consumes 80% less fuel than when flying at an altitude of one kilometer. However, why then do they not fly even higher, in the upper layers of the atmosphere, where the air density is even less? The fact is that in order to create the necessary thrust by an aircraft engine, a certain minimum supply of air is required. Therefore, each aircraft has a maximum safe flight altitude limit, also called the "service ceiling". For example, the practical ceiling of the Tu-154 aircraft is about 12,100 meters.
Some researchers had crazy ideas - they wanted to fly, but why was the result so deplorable? For a long time there have been attempts to attach wings to oneself, and, waving them, fly up into the sky like birds. It turned out that human strength is not enough to lift oneself on flapping wings.
First craftsmen were naturalists from China. Information about them is recorded in the "Tsan-han-shu" in the first century AD. Further, history is replete with cases of this kind, which occurred in Europe, and in Asia, and in Russia.
The first scientific justification for the process of flight was given by Leonardo da Vinci in 1505. He noticed that birds do not have to wave, they can stay in still air. From this, the scientist concluded that flight is possible when the wings move relative to the air, i.e. when they flap their wings in the absence of wind or when with fixed wings.
Why is the plane flying?
The lifting force, which acts only on high speeds. The special contraction of the wing allows you to create lift. The air that moves above and below the wing undergoes changes. Above the wing it is sparse, and under the wing -. Two air streams directed vertically are created. The lower one raises the wings, i.e. plane while the top pushes up. Thus, it turns out that at high speeds the air under the aircraft becomes solid.
This is how vertical motion is realized, but what makes the plane move horizontally? - Engines! The propellers seem to drill their way into airspace overcoming air resistance.
Thus, the lifting force overcomes the force of attraction, and the traction force overcomes the braking force, and the plane flies.
Physical phenomena underlying flight control
Everything is based on the balance of the lifting force and the force of gravity. The plane is flying straight ahead. Increasing the flight speed will increase the lift force, the aircraft will rise. To neutralize this effect, the pilot must lower the nose of the aircraft.
Reducing the speed will have the exact opposite effect, and the pilot will need to raise the nose of the aircraft. If this is not done, a crash will occur. Due to the above features, there is a risk of crashing when the aircraft loses altitude. If it happens close to the ground, the risk is almost 100%. If this happens high above the ground, the pilot will have time to increase speed and gain altitude.
How do planes fly?
An aircraft is a heavier-than-air aircraft. This means that certain conditions are needed for its flight, a combination of precisely calculated factors. The flight of an aircraft is the result of the lift force that occurs when air flows towards the wing. It is turned at a precisely calculated angle and has an aerodynamic shape, due to which, at a certain speed, it begins to rise upwards, as the pilots say, “gets up in the air”.
The engines accelerate the aircraft and maintain its speed. Jets push the plane forward due to the combustion of kerosene and the flow of gases escaping from the nozzle with great force. Screw engines "pull" the plane behind them.
The wing of modern aircraft is a static structure and cannot generate lift on its own. The ability to lift a multi-ton machine into the air occurs only after the forward movement (acceleration) of the aircraft with the help of a power plant. In this case, the wing, set at an acute angle to the direction of the air flow, creates a different pressure: it will be less above the iron plate, and more below the product. It is the pressure difference that leads to the emergence of an aerodynamic force that contributes to the climb.
Related materials:
Why does a plane leave a trail, and sometimes not?
Aircraft lift consists of the following factors:
- Angle of attack
- Asymmetric wing profile
The inclination of a metal plate (wing) to the air flow is commonly called the angle of attack. Usually, when the aircraft is lifting, the mentioned value does not exceed 3-5 °, which is sufficient for the take-off of most aircraft models. The fact is that the design of the wings has undergone major changes since the creation of the first aircraft and today it is an asymmetric profile with a more convex top sheet of metal. The bottom sheet of the product is characterized by a flat surface for an almost unhindered passage of air flows.
Schematically, the process of generating lift looks like this: the upper air streams need to travel a longer distance (due to the convex shape of the wing) than the lower ones, while the amount of air behind the plate should remain the same. As a result, the upper jets will move faster, creating a region of low pressure according to the Bernoulli equation. Directly, the difference in pressure above and below the wing, coupled with the operation of the engines, helps the aircraft gain the required height. It should be remembered that the value of the angle of attack should not exceed the critical mark, otherwise the lifting force will drop.
Wings and engines are not enough for a controlled, safe and comfortable flight. The plane needs to be controlled, and control accuracy is most needed during landing. Pilots call landing a controlled fall - the speed of the aircraft is reduced so that it begins to lose altitude. At a certain speed, this fall can be very smooth, resulting in a soft touch of the landing gear wheels on the strip.
Related materials:
Why are rivets used in aviation?
Flying an airplane is completely different from driving a car. The pilot's yoke is designed to tilt up and down and create a roll. “To yourself” is a climb. “From oneself” is a decrease, a dive. In order to turn, change course, you need to press one of the pedals and use the steering wheel to tilt the plane in the direction of the turn ... By the way, in the language of pilots, this is called a “turn” or “turn”.
For turning and stabilizing the flight, a vertical keel is located in the tail of the aircraft. And the small “wings” below and above it are horizontal stabilizers that do not allow the huge machine to rise and fall uncontrollably. On the stabilizers for control there are movable planes - elevators.
To control the engines, there are levers between the pilots' seats - during takeoff they are transferred completely forward, to maximum thrust, this is the takeoff mode necessary to gain takeoff speed. When landing, the levers are retracted completely back - in the minimum thrust mode.
Many passengers watch with interest as the back of the huge wing suddenly drops down before landing. These are flaps, the “mechanization” of the wing, which performs several tasks. When descending, fully extended mechanization slows down the aircraft in order to prevent it from accelerating too much. When landing, when the speed is very low, the flaps create additional lift for a smooth loss of height. During takeoff, they help the main wing keep the car in the air.
Since ancient times, watching the flight of birds, man himself wanted to learn how to fly. The desire to fly like a bird is reflected in ancient myths and legends. One such legend is that of Icarus, who made wings to fly high into the sky, closer to the radiant sun. And although the flight of Icarus ended tragically, birds fly perfectly, despite the fact that they are significantly heavier than air. Three thousand years after the origin of this legend, at the very beginning of the 20th century, the first human flight in an airplane was carried out. This flight lasted only 59 seconds, and the plane flew only 260 meters. Thus, a man's long-standing dream of flying came true. Modern aircraft fly farther and longer. Let's try to figure out why a plane with a huge mass flies, why it can fly faster, higher and farther than any bird, why a glider without a motor can soar in the air for a long time. Despite the fact that during the flight, unlike birds, the wings of an aircraft are rigidly fixed to the body, the aircraft flies precisely thanks to them, as well as the engines that create thrust and accelerate the aircraft to the required speed. The cross section of an airplane wing is very similar to that of a bird's wing. And this is not accidental, since when designing an airplane, people, first of all, were guided by the flight of birds. During the flight, four forces act on the wing of an aircraft: the thrust force created by the engines, the force of gravity directed towards the Earth, the force of air resistance that impedes the movement of the aircraft, and, finally, the lift force, which provides climb. The ratio of these forces determines the ability of the aircraft to fly. When flying at a constant speed, the sum of these forces must be equal to 0: the thrust force compensates for the drag force, and the lift force compensates for the force of gravity. It is important for anyone who is interested in aeromodelling to know this in order to make a reliable flying model of an aircraft. A very important parameter is the angle of attack - the angle between the chord of the wing (the line connecting the leading and trailing edges of the wing) and the direction of the air flow around the wing. The smaller the angle of attack, the lower the drag force, but at the same time, the lower the lift force, which ensures takeoff and stable flight. Therefore, an increase in the angle of attack provides sufficient lift for takeoff and flight. Due to the asymmetry of the shape of the wing, the air above the wing moves faster than under it, and, according to the Bernoulli equation, the air pressure under the wing is greater than above it. However, the resulting lift force is not sufficient for takeoff, and the main effect is achieved due to air compaction under the wing by the oncoming flow, which essentially depends on the angle of attack of the aircraft wing. By changing the angle of attack, you can control the flight of the aircraft, this function is performed by flaps - deflected surfaces symmetrically located on the trailing edge of the wing. They are used to improve the carrying capacity of the wing during takeoff, climb, descent and landing, as well as when flying at low speeds. The great Russian mechanic, founder of the science of aerodynamics, Nikolai Egorovich Zhukovsky, having comprehensively studied the dynamics of bird flight, discovered the law that determines the lift force of the wing. This force is determined by the pressure difference above and below the wing and is calculated using the following formula: where is the air density, is the speed of the incoming air flow, is the area of the aircraft wings, is the speed of air circulation near the wing. The dependence of lift on the angle of attack can be obtained using the law of conservation of momentum: A similar formula for calculating the lift force of the first aircraft in the history of mankind was used by the Wright brothers: Where where - acceleration free fall, m is the mass of the aircraft. Let's calculate the takeoff speed of the Boeing 747-300. Its mass is approximately 3 10 5 kg, and the wing area is 511 m 2. Considering that the air density is 1.2 kg/m 3 , we get a speed value of about 70 m/s or about 250 km/h. It is at this speed that modern passenger planes take off. Using the proposed method, we suggest that you calculate the speed that a model aircraft with a mass of 5 kg and a wing area of 0.04 m 2 must have in order to take off. Airplanes, especially up close, impress with their g dimensions and ma ssoy. At the same time, it remains unclear how such a bulky and heavy object rises to the heavenly heights. Moreover, not even all adults can answer this, and children's questions can often bewilder. The emergence of lift is often explained by the difference in static pressure of air flows on the upper and lower surfaces of the wing of the aircraft. The design of the wing is such that the upper part of its profile has a convex shape. The air flow around the wing is divided into two: upper and lower. The bottom flow rate remains virtually unchanged. But the speed of the upper one increases due to the fact that it must overcome a greater distance in the same time. Consequently, the pressure over the wing becomes lower. Due to the difference in these pressures, a lifting force arises that pushes the wing up, and with it the aircraft rises. And the greater this difference, the greater the lifting force lei. As the speed increases, the lift also increases. And the plane takes off. Each of you has probably done paper airplanes and launched them with force. WITH A modern aircraft, even weighing tens of tons, must have a sufficient wing area. The lift force of a wing is affected by many parameters, such as profile, area, wing planform, angle of attack, speed and airflow density. Each aircraft has its own minimum speed at which it can take off and fly without falling. Thus, the minimum speed of modern passenger aircraft is in the range of 180 to 250 km/h.In order for the lifting force to be able to lift into the air It is precisely if such an airplane is thrown up with force that it can fly far, and if it is let out lightly, it will immediately fall to the ground. This means that in order for a paper airplane to stay in the air, it must constantly move forward. big planes move forward due to powerful engines that rotate the propeller. A rapidly rotating propeller throws out huge masses of air behind itself, providing the forward movement of the aircraft. If the lift and weight of the aircraft are equal, then it flies horizontally. When creating an aircraft, great attention is paid to the wing, because the safety of flight performance will depend on it. Looking out the window, the passenger notices that it is bent and is about to break. Do not be afraid, it can withstand just enormous loads. History knows cases that in such circumstances they landed. Chassis? Nothing prevents the plane from landing on its belly; subject to certain fire safety measures, it will not even catch fire. But an airplane can never fly without a wing. Why do planes fly so high?
Because that's what creates lift. The flight altitude of modern jet aircraft is in the range from 5000 to 10000 meters above sea level. This is explained very simply: at such a height, the air density is much less, and, consequently, the air resistance is also less. Airplanes fly at high altitudes because when flying at an altitude of 10 kilometers, the aircraft consumes 80% less fuel than when flying at an altitude of one kilometer. However, why then do they not fly even higher, in the upper layers of the atmosphere, where the air density is even less? The fact is that in order to create the necessary thrust by an aircraft engine, a certain minimum supply of air is required. Therefore, each aircraft has a maximum safe flight altitude limit, also called the "service ceiling". For example, the practical ceiling of the Tu-154 aircraft is about 12,100 meters. Why does an airplane need to burn all its fuel before landing? Summarizing, we can say that the aircraft burns fuel so that the load on the landing gear does not exceed the maximum load, otherwise the landing gear simply will not withstand. Many are afraid to fall down from a height of 10 km. This is not possible due to the strong pressure under the aircraft's wings. It stays in the air as well as a car on the highway. It can be put on the tail, rotated around its axis by 100 degrees, directed down - and if you release the steering wheel, the plane will simply sway in the air, like a boat on the waves.
- Smeaton's coefficient, obtained back in the 18th century. This formula is obtained from the previous one at an angle of attack equal to 45 0 . Using this formula, you can calculate the minimum speed an aircraft needs to take off:
An aircraft can only take off if the lift force is greater than its weight. It develops speed with the help of an engine
If the aircraft engine fails, it's okay, the plane will fly on the second one. If both engines fail
When designing an aircraft (both civil and military, by the way) and in particular its landing gear, there is always such a parameter as the maximum landing weight. It is quite obvious that this maximum weight which the landing gear will withstand during landing. When the aircraft is being prepared for a mission, it is filled with enough fuel to fly to the planned landing site + navigational fuel supply. When everything is normal, the fuel is not drained. If the crew decided to land the car, and its mass exceeds the maximum landing weight, then they get rid of the fuel. Especially often such situations occur in the event of a serious failure immediately after takeoff. It should also be noted that not all aircraft simply “burn out” fuel in order to “lose weight”, some are equipped with an emergency fuel drain system.
