The principle of aircraft take off wing airflow

The side profile of the wing is a shape in which the upper edge is arched upwards and the lower edge is basically straight. Therefore, the air flow blowing through the upper and lower surfaces of the wing and from the front end of the wing to the rear end at the same time will pass through the upper edge faster than the lower edge (because the upper edge has a large arc and a longer arc length, which means that the distance is longer).

According to the Bernoulli equation of physics, the same fluid flowing through a certain surface has less pressure on the surface at a faster speed. Therefore, it is concluded that the atmospheric pressure on the upper surface of the wing is smaller than that on the lower surface, so that the lift force is generated, and the lift force reaches a certain level, and the aircraft can lift off the ground.

There's a formula that I don't know if you've ever seen: l cl*1 2* *v*v*s.

Its significance is that the lift of an aircraft is the product of the following five quantities:

1.The lift coefficient cl (that c represents the coefficient, l is the corner code, I don't have a character tool can not type), its value is related to many fine variables such as the windward angle of the aircraft, generally in a few tenths, the details are not very affectionate: (

2.One in two is.

3.Atmospheric density (the environment in which the aircraft is located, which can be high or low altitude).

4.The square v*v of the airplane relative to the velocity of the surrounding atmosphere (it can only be expressed as this without a corner code).

5.Wing area s

s=vt, t should be the same, v should be faster, child, listen to me, let's not delve into why the time is the same, there is no need, if you do this every time you will suffer. You just have to think: if the time is different, there will be a vacuum on the earth, of course, we physics beginners think that there is no vacuum on the earth, I am only in the third grade, physics is not bad, I learned this way.

The distance above is long, so the flow rate will increase and the pressure will decrease.

The bottom is a straight plate, and there is a certain angle of attack, which can be understood as accepting the impact of the air flow, and the pressure increases.

The pressure difference supports the aircraft, and the lift can be increased by increasing the speed or increasing the nose attitude of the aircraft to increase the angle of attack.

After a long journey, there is no air, and if there is no air and no air pressure, it will be actively sucked over, and at the same time lead to an overall decrease in pressure, an explanation of Bernoulli's principle.

Nonsense, why is the time different for the same forward flight?

In the same time, the distance is long, and the speed is fast.

The principle of wing lift is the difference in air pressure caused by the difference in velocity between the airflow on the upper and lower surfaces of the wing.

Lift is the upward force. The force that makes you rise. There are many kinds of them. Generally said in the air. That is, the upward force is greater than the downward force, and its resultant force can make the object rise.

The difference in air pressure caused by the difference in lift ** in the velocity of the airflow on the upper and lower surfaces of the wing. However, the explanation of the cause of the velocity difference between the upper and lower surfaces of the wing is complicated, and the isochronous theory and fluid continuity theory used in popular science cannot fully explain the cause of the velocity difference. Two-dimensional wing theory is commonly used in the aviation community, which mainly relies on the Kuta condition, the circumference around the wing, the Kuta-Zhukovsky theorem and the Bernoulli theorem.

Lift applications. The vast majority of the lift of the aircraft is generated by the wings, the tail usually produces negative lift, and the lift generated by other parts of the aircraft is very small and generally not considered. The principle of lift is that the presence of the ring around the wing (attachment vortex) causes the flow velocity of the upper and lower surfaces of the wing to be different, the pressure is different, and the direction is perpendicular to the relative air flow.

The generation of wing lift mainly depends on the action of the upper surface suction, rather than the effect of the positive pressure on the lower surface, the suction formed on the upper surface of the wing accounts for about 60-80% of the total lift, and the lift formed by the positive pressure on the lower surface only accounts for about 20-40% of the total lift. So it cannot be assumed that the aircraft is supported in the air, mainly as a result of the impact of air from under the wing.

There will be various drags in the air when an airplane flies, and the drag force is the aerodynamic force that is opposite to the direction of the airplane's movement, which hinders the progress of the aircraft, and here we also need to understand it. According to the causes of resistance, it can be divided into friction resistance, differential pressure resistance, induced resistance and interference resistance.

The four types of resistance are for low-speed aircraft, and for high-speed aircraft, in addition to these resistances, other drags such as wave resistance are also generated.

Introduction: The upper half of the wing is flat, the air is not blocked, and it flows directly, and the lower part is an arc, and the air has a certain resistance, and the flow speed is relatively slow. The reason for this design is that the pressure is low where the flow rate is fast, the pressure is high where the flow rate is slow, and the flow speed under the wing is slow, and the pressure is stronger than that of the square team, so the air pressure will lift the plane and the plane will take off.

The top of the wing is curved and the bottom is planar, so the length of the sides of the wing is different, but the projection length is the same. The time it takes for air to flow through the same projection length is the same, but the wing length of the upper arc will be longer, the air on the wing will flow faster, the pressure of the gas will be less where the flow velocity is high, and the pressure will be stronger where the flow velocity is small, so the wing will have a rising lift to attract the aircraft.

For scientific reasons, we had to revise the description of the "propensity" of the fluid above and below the flying wing to arrive at the same time. If the flow is hindered by the alien factor of wings, the flow will evolve towards the situation that requires "simultaneity". This explanation is fine, and it is also the starting point for asymmetrical airfoil design.

As for whether the actual fluids arrived at the same time, it is uncertain. You can also say that "if there is an X tendency, it will happen". Because, at the end of the day, everyone gravitates towards a perfect score on the physics exam.

Assuming that the fluid separates from the leading edge of the airfoil and the trailing edge converges (does not need to be reached at the same time), the separation point is the same as the upper and lower surface velocities of the confluence point, and the top path is more curved. Let's start by assuming that the fluid velocity on the upper and lower surfaces is the same and see what happens. Since the flow on the top surface bends more and at the same velocity, the top surface needs to provide a higher centripetal force for the distant airflow to "press" the gas to the surface.

At the same time, we consider the gas pressure at a distance to be constant. That is, no matter which direction you look from above or below the wing, as long as the distance is large enough to reach a certain level, the pressure will converge. As a result, the fluid pressure on the upper surface close to the wing is lower to provide centripetal force.

In addition, due to Bernoulli's principle, the pressure is low and the speed is fast. Therefore, the phase velocity needs to be a little faster than we assume in order to maintain this centripetal force.

Because the arc on the wing can determine the length of the wing, the longer the length of the wing, the faster the flow velocity, the less affected by the pressure.

It can be explained by hypotheses, or by understanding the situation of air pressure, and by using relevant physical theories to explain such a situation.

You can use the relevant knowledge of air pressure, or the problem of distance, to explain the relevant content, and you can also explain this aspect through the theory of physics.

3 All one: This airflow speed is the same as the speed of the aircraft, which is the speed of the aircraft dominant.

Second: If the speed is too fast, there will be no negative pressure, but the wing structure.

Three: I personally believe that the lift gained by the wing is the skateboard effect, and the negative pressure is just a component of the force generated in order to balance the attitude of the wing.

I don't want to dwell on it here. 】

Upstairs, you misunderstood, the air flow on the upper surface of the wing is already faster than the lower surface.

First of all, the upper surface is convex and the lower surface is flat, which means that the upper surface is longer when air flows through the surface of the wing. So according to the fluid continuity theorem of fluid mechanics, when the fluid flows continuously and steadily through a pipe of unequal thickness, because any part of the fluid in the pipeline cannot be interrupted or squeezed up, so at the same time, the mass of the fluid flowing into any surface and the mass of the fluid flowing out from the other section is equal.

Also, if the air flow on the upper surface is slow, how can the lift be generated? I don't know how you learned fluid mechanics, Bernoulli's theorem says that the pressure is small where the flow rate is fast, and the pressure is high where the flow rate is slow, if the flow rate below is large according to what you said, then the pressure is smaller than the top, the pressure above is large and the pressure below is small, so what direction is this resultant force going? Downward, right?

Can downward force be called lift? Can such a plane fly?

As for the landlord asked, why the air flow rate on the upper surface is fast, the image can be so an example, I think we have all used rubber water pipes, one end is connected to the faucet, one end is in the hand, in the case of the size of the faucet does not move, pinch the nozzle, then the water will be sprayed far away, pinch the middle of the nozzle, the water will be divided into two forks, if the opening on both sides is not the same thickness at this time, then it must be the thin side of the water spray farther, that is, the speed of the water flow is faster. Similarly, when the air blows head-on to the leading edge of the wing, it is bifurcated by the wing, and the upper surface is convex, so it can be considered that the air flow channel on the upper surface is less protruding than the lower surface, that is, it is narrowed, so the flow rate will be faster.

According to the model, the speed of the large aircraft is generally about 180 knots, the cruising speed is 300 knots, and the take-off of the medium-sized aircraft is about 150 knots, and the cruise speed is about 280.

The question of air currents does not make sense for the speed of the aircraft. It's like when you ride a bike in a windless environment, you create an airflow. The upper surface of the wing is curved upwards and the airflow velocity is greater than below, creating lift.

p+(1 2)* v2 constantLet's take a look at Bernoulli's equation.

The wings and engines of the aircraft, the upper wing of the aircraft is curved, and the lower part is straight, when the aircraft is moving, the air flow above the wing is fast, and the air flow under the wing is slow, so that an upward lift is generated, and the aircraft will fly smoothly into the sky. In addition, the engine in the aircraft is connected to the propeller, and the propeller rotates to drive the airflow, and the aircraft can fly in the sky for a long time.

The main thing is that the aircraft has a pair of wings with a special profile shape, and the wing profile is also called an airfoil. A typical airfoil is convex at the top and flat at the bottom, and is often referred to as streamlined. According to the continuity of the fluid and Bernoulli's theorem, the air flow through the upper surface is squeezed compared to the air far ahead, and the flow velocity accelerates and the pressure decreases, and even suction (negative pressure) is formed, and the flow velocity of the air flowing through the lower surface slows down.

As a result, a pressure difference is formed between the upper and lower wing surfaces. This pressure difference is aerodynamic. According to the law of force decomposition, it is broken down along the direction of flight into upward lift and backward resistance.

The drag is overcome by the thrust provided by the engine. The lift is just enough to overcome its own gravity and lift the aircraft into the air.

The airplane is a heavier than air, so it needs to consume its own power to gain lift And the ** of lift is the effect of the air on the wing in flight In the following diagram, there is a schematic profile of the wing The upper surface of the wing is curved and the lower surface is flat, so when the wing is in relative motion to the air, the air flowing through the upper surface travels the distance (s1) in the same time (t) than the air flowing through the lower surface (s2), so the relative velocity of the air on the upper surface is faster than the air on the lower surface(v1=s1 t >v2=s2 t1) According to Panulli's theorem – "The pressure exerted by the fluid on the surrounding matter is inversely proportional to the relative velocity of the fluid", so the pressure exerted by the air on the upper surface of the wing f1 is less than the f2 on the lower surface The resultant force of f1, f2 must be upward, which produces lift

From the principle of the wing, we can also understand the working principle of the propeller The propeller is like a vertical wing, the bulge faces forward, and the smooth face is backward The resultant force of the pressure when rotating is forward, pushing the propeller forward, thereby driving the aircraft forward Of course, the propeller is not simply convex and smooth, but has a complex curved surface structure The old propeller is a fixed shape, and the later design adopts the design of the relative angle that can be changed to improve the performance of the propeller

Power principle: turbojet engine, turbofan engine, ramjet engine, turboshaft engine.

Flight needs power to make the aircraft move forward, and more importantly, to make the aircraft gain lift Early airplanes usually use piston engines as power, and four-stroke piston engines are the main The principle of this type of engine is shown in the figure, mainly for inhaling air, mixing with fuel and igniting and expanding, driving the piston to reciprocate, and then converting into the rotary output of the drive shaft:

The power emitted by a single piston engine is very limited, so people connect multiple piston engines in parallel to form a star or V-piston engine The picture below shows a typical star piston engine

Most modern high-speed aircraft use jet engines, the principle is to suck the air in, mix with fuel, ignition, ** the expanded air is sprayed backwards, and its reaction force pushes the aircraft forward In the engine profile diagram below, compressed air fans draw air from the air intake, and the compressed air is one by one, so that the air can better participate in the combustion The orange-red cavity behind the fan is the combustion chamber, where the mixed gas of air and oil is ignited, and the combustion expansion is sprayed backwards, pushing the last two fans to rotate, Finally, the engine gas is discharged, thus completing an outer The last two fans and the compressor fan in front are installed on the same central shaft, so the compressor fan is driven to continue to suck in the empty work cycle