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Qinghai-Tibet Plateau is the "third pole" of the earth. The Qinghai-Tibet Plateau shares the same place with the north and south poles on the earth. This is the cold climate. But it also has its own high extreme characteristics: that is, the air is thin and the air pressure is low. Most people who travel to Tibet for the first time will be impressed. They will have a lot of exercise on the plateau, such as running, fast up and downhill, etc., will pant for breath, sometimes feel dizzy, nausea, etc. This is the plateau. Reaction Typical reaction. Humans have typical altitude sickness on the plateau. In fact, aircraft, such as airplanes, will also experience altitude sickness such as insufficient power on the plateau. What is going on?
aircraft can take off. The principle is simply the thrust provided by the engine and the lift provided by the air pressure difference between the upper and lower edges of the wings. We can see from the cross section of the airplane wing that the arc of the upper edge is obviously larger than that of the lower side. When the airplane is moving forward, the wing will divide the front airflow into two upper and lower air streams, because the upper arc is large. Therefore, the air flow travels farther than the bottom, and the air flow speed is faster. According to the Berger’s theorem, the air above the airflow produces less pressure on the wing. This creates an upward direction for the fuselage. The "lifting force", this upward lifting force ensures that the aircraft can take off smoothly.
When the area of the wing increases, the same amount of lift is generated on the fuselage. The smaller the angle of attack required, the easier the aircraft will climb. At the same time, the air resistance of the aircraft will increase accordingly. Large, hindering the climb of the aircraft to a certain extent. Therefore, in the design phase of the aircraft, a certain balance must be achieved in the aircraft’s engine thrust, wing area, and angle to obtain the most ideal and economical flight angle of attack and lift-to-drag ratio, that is, to ensure that there is The higher travel speed ensures that the increase in lift is effectively greater than the increase in resistance, that is, an efficient lift-to-drag ratio.
Whether an aircraft rises to tens of thousands of meters or several kilometers, take-off and landing require high output power, which is the key to whether the aircraft can sail normally.For airplanes to take off normally, the lift obtained from the air is particularly important, and this lift is not only related to the output power of the flying engine, but also depends on the size of the air density, just like the ping pong ball is placed in salt water or ordinary water. The depth of immersion is different.
For areas with an altitude of 4000 meters on the Qinghai-Tibet Plateau, the air density is about 60~70% of sea level, which is 30~40% lower than that of a plain airport. Thin air will also lead to insufficient lift of the aircraft, which is like no air support. As water cannot hold an iron ball, it is difficult for an airplane to take off. Secondly, the high altitude of the plateau has low oxygen content, insufficient combustion, and the engine power drops by about 40%. The engine cannot obtain better power and it is difficult to take off.
Why the plane can fly at an altitude of 10,000 meters,
but it has insufficient power on the plateau?
This is because the planes take off at different altitudes. Take off on the plains at an altitude of about 200 meters and rise to 10000 meters, while plateau airport is 4000 meters above sea level and flies to 10000 meters. These are two different altitudes. Low altitude takeoff air density and oxygen content are normal, engine output power is normal, but high altitude atmospheric environment is different, for this reason, take off on plateau, the aircraft power appears to be insufficient.
If the planes are all at 4000 meters high and rise to 10000 meters, one is the inertial aircraft obtained after take-off on the plain, and the other is the aircraft that is 4000 meters above sea level and is waiting to take off. The power output of the engine is very different. . The initial inertia of the aircraft on the plateau is zero, and the output power is insufficient. From this point of view, the altitude of the aircraft during the initial take-off is very important and often determines the success or failure of the voyage.
In addition, although the air has become thinner at an altitude of 10,000 meters, the aircraft is already at a high speed. In this case, on the one hand, the engine uses very little power consumption to overcome the smaller air resistance. On the other hand, at high speeds, a little angle of attack can produce a larger lift, which is balanced with gravity. Therefore, at an altitude of 10,000 meters, all aspects of the aircraft's resistance have become smaller, even if the engine's thrust is attenuated due to the sharp reduction in air density,But it is also sufficient to maintain the balance of forces in the horizontal and vertical directions of the aircraft.
Then, since the plane will be underpowered when taking off and landing on the plateau, is it safe to go to the plateau by plane? In fact, as one of the vehicles with the highest safety factor at present, after a hundred years of technological updates and the continuous emergence of new models, airplanes have ranked first in terms of safety and reliability. It is an essential airframe inspection before each flight Work such as maintenance and maintenance are not available in other vehicles. In addition, in order to adapt to the plateau terrain, it is suitable for aircraft engines to have more time for combustion efficiency during the take-off phase. The airports on the plateau are generally much longer than those on the plain. Therefore, it is safe to fly on the plateau as long as the flight take-off and landing under extreme weather conditions are excluded.
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