Why do airplanes fly? The secret lies in their wings

"It's so fast that it's about to fly." We often use similar language to describe an object that is moving very fast, but in fact it is an object that cannot fly. No matter how fast it moves, it will not fly.

The speed of an airplane when it takes off is related to many factors such as the wind speed at the time and the load of the airplane. It is not a fixed value, but roughly speaking, the take-off speed of a general civil airliner is about 250 kilometers to 290 kilometers per hour, while the take-off speed of a fighter jet is about 350 kilometers per hour. There is no doubt that acceleration is an important part of the aircraft take-off process, but it is not the most critical factor, otherwise the high-speed rail would have taken off long ago. Take the "Fuxing" EMU designed and manufactured by China as an example. Its maximum speed can reach 400 kilometers per hour, which is faster than the speed of an airplane when it takes off, but it still stays firmly on the track.

If an object wants to fly, it must obtain lift, and lift is not directly provided by speed. Only when a special structure and speed work together can the force that makes an object fly be generated.

What are the structural differences between airplanes, high-speed trains and cars? The biggest difference is that airplanes have two wings. Since the Wright brothers invented the airplane in 1903, the appearance of airplanes has undergone various changes. Now, airplanes with various appearances and structures are emerging in an endless stream. However, as long as it is an airplane, there is one thing that cannot be missing, that is, "wings". The full load weight of a civil airliner can reach hundreds of tons. Can such a huge aircraft of hundreds of tons fly just by installing two wings? It is true.

How do wings enable an aircraft to gain lift? This has to start with a principle, the Bernoulli principle.

Bernoulli's principle was proposed by Daniel Bernoulli in 1726. Simply put, in an ideal water flow or air flow with negligible viscosity, the lower the flow rate of the fluid, the greater the pressure, and vice versa. The most common example of Bernoulli's principle in our daily life is waiting for the subway. When many people stand together at the platform waiting for the subway to arrive, a human wall is formed, isolating the air in front and behind. At this time, the subway arrives at the station, and the air in front flows at a high speed, so the pressure becomes smaller, while the air flow speed in the back is still very slow, so the pressure is very high, so we will feel a force pushing us forward. This force is caused by the pressure difference between the front and the back. Many times we will mistakenly think that the people behind are deliberately squeezing forward, which causes conflicts.

In history, there was a safety accident in a certain country where many people fell onto the subway tracks due to Bernoulli's principle.

The wings of an airplane also utilize the Bernoulli principle. If we observe carefully, we will find that no matter how unusual the appearance of an airplane is, its wings have similar characteristics, that is, the front end of the wing cross-section is rounded and blunt, while the rear end is sharp. When viewed from top to bottom, the top of the wing appears to be raised, while the bottom of the wing is basically flat. The reason for this design is to allow the airflow above and below the wing to differ in flow rate.

When the plane starts running on the runway, the airflow speed above the wing will differ from the airflow speed below the wing, with the airflow speed above being faster and the airflow speed below being slower.

As the speed of the aircraft increases, the difference in the flow speed of the airflow above and below the wing will become larger and larger, that is, the pressure above the aircraft becomes smaller and smaller, while the pressure below is relatively large, so lift is generated. As the speed increases, the lift gradually increases until the lift is greater than the aircraft's own gravity, at which point the aircraft can fly. The amount of lift an aircraft obtains is closely related to two factors: one is the speed of the aircraft, and the other is the size of the aircraft's wings. The larger the wing, the greater the lift it obtains, so the transport aircraft we see usually have very spectacular "wings".

After taking off, the aircraft will pass through the troposphere as quickly as possible and reach a cruising altitude of 6,000 to 12,000 meters. Because the air flow movement here is mainly horizontal, it is called the "stratosphere."

When the plane flies in the stratosphere, it is basically not affected by the air currents and is relatively stable, so the flight attendants will start to provide services for us at this time. When the plane takes off and lands, it is easy to get bumpy because it wants to pass through the troposphere. If you walk around in the plane at this time, it is easy to cause a safety accident, so we are usually required to sit in our seats and fasten our seat belts. Since the lift of the plane is based on the difference in gas flow speed, it is impossible for the plane to leave the earth and fly into space. As for the space plane developed by a British company, it actually only has the appearance and name of an airplane. In fact, it is not an airplane, just like a turtle is not a fish.

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