Why do some planes emit white smoke in the sky, while others don't? Is it artificial?

On the blue sky background with no clouds or only a few thin clouds in Wan Li, people often see some planes pulling out beautiful white smoke.

There are several reasons for the formation of aircraft wake, which cannot be generalized. Most of the time, all we see are air force fighters. They fly very high, sometimes in a straight line, sometimes in a curve, flying freely, with a white belt behind them, picturesque. Are they performing? Is that white smoke? No. In fact, this is only the training of fighters at high altitudes. The white smoke behind them was not intentionally ejected, but the trail passively left by engine exhaust gas in the air. It is also called tail cloud and tail cloud, which is also commonly known as aircraft smoke.

In addition to artificial smoke pulling in air show, this kind of passive smoke pulling is exhaust wake, aerodynamic wake and convection wake.

Exhaust wake is the most common phenomenon of aircraft white smoke. There are two reasons for this wake, one is the tail of exhaust gas condensation, and the other is the tail of exhaust gas evaporation.

The reason of exhaust gas condensation wake is that the waste heat and water vapor after fuel consumption are discharged to the outside of the aircraft with exhaust gas when the aircraft is flying. When it meets cold air at high altitude, it will condense into water droplets or ice crystals and drag a long white smoke-like tail behind the plane. The condition for the formation of exhaust condensate tail flow is high altitude and low temperature. Generally, when the plane is above 8000m, the temperature will only appear between -4 1℃ and -60℃, but not above -40℃ or below -60℃.

So when the plane is at high altitude, sometimes there is white smoke, and sometimes there is no white smoke; Sometimes when the plane flies at low altitude, it will intermittently produce white smoke. The higher it flies, the more obvious it is. When it flew higher, it was intermittent, and finally it disappeared. This is a fact.

There are also some differences in different seasons at the tail of exhaust gas condensation. Generally, there are more winters and less summers. This is because the temperature is lower in winter, the height of exhaust gas will be lower, and the height of exhaust gas will be higher in summer. The tail of exhaust gas condensation exists for a long time, with a thickness of 2 kilometers, and generally exists for more than 1 hour or even longer. The road to death with more traces will even expand into clouds.

The evaporation trail of exhaust gas generally appears in the low-level air, where the temperature does not meet the condition of condensation of exhaust gas trail. The thermal effect of aircraft exhaust gas leads to the decrease of humidity in the nearby air and the evaporation of water vapor, leaving a transparent gap in white clouds, which usually appears in thin clouds.

The generation process of aerodynamic wake. This wake is caused by the plane flying in nearly saturated air. Due to the different pressure difference between the upper and lower wings or the spiral air vortex formed by the agitation at the top of the propeller, the air pressure in the center of this vortex is reduced and condensed into small water droplets, forming an aircraft stay wire. Different from engine exhaust, this kind of pull wire is generally formed in the low-level air. It does not appear at the nozzle of the aircraft engine, but at the two tips of the wing, pulling out two sharp white lines, just like two shock waves, which is very spectacular. This awakening is short-lived and will soon disappear.

The cause of convective wake. This wake is also related to the exhaust gas emitted by aircraft. The difference between the condensation and evaporation trajectory of the above exhaust gas is that it usually occurs at low altitude. After the exhaust gas from the plane is mixed with air, the air is heated, which leads to the formation of exhaust gas similar to white smoke. This wake will be thousands of meters behind the plane, much wider and longer than the condensed exhaust gas.

There are two natural phenomena in the flight of aircraft and two unnatural phenomena in the wake. One is to put oil in the air, and the other is for flight performers to smoke cigarettes artificially.

The reason for releasing oil in the air is that the oil load exceeds the allowable landing weight of the aircraft, so how much more oil must be released in the air. When an airplane is designed, it has a maximum takeoff weight and a maximum landing weight. The takeoff weight is usually greater than the landing weight. For example, the A380 has a maximum takeoff weight of 560 tons, while its maximum landing weight is only 386 tons.

The maximum landing weight of the aircraft should not only ensure that the aircraft structure can land safely, but also ensure that the passenger plane can climb smoothly when it stops landing and goes around or encounters engine failure. Therefore, when the plane takes off, it should refuel according to the destination it needs to reach. However, if this oil is not used in a certain amount, it will be overloaded when landing, thus causing damage to the landing gear and other structures of the aircraft and even causing major accidents.

However, there will always be some accidents in flight, which will prevent the plane from reaching its destination or returning, so there will be more fuel, some of which must be released in the air. There is a special release hole for aircraft oil discharge, which will crush the fuel under pressure to release a small droplet, which will minimize the pollution to the environment and the ground. So the plane will smoke when it releases oil. There is still a fighting chance to ignite and burn when discharging oil.

All kinds of smoking activities in the air show are man-made effects. In some airshows, we often see one or several planes making all kinds of graceful movements in the sky, sometimes merging into a sword and soaring into the sky, sometimes spreading their wings and letting a hundred flowers blossom. These planes are dragging colorful ribbons of smoke, just like fairy ribbons, which are gorgeous and spectacular. This is the colorful smoke in the performance. This kind of colored smoke is to put some chemical reagents into a high-pressure container. When the pilot opens the valves of these containers, these chemicals will be sprayed out and combined with water vapor in the air to form smoke.

Different recipes will show different colors. Just like the colorful fireworks we see in the night sky, they are made according to different chemical formulas. It is the most commonly used smoke-pulling technology in various countries to spray diesel oil at the jet port of the aircraft and burn the exhaust gas from the aircraft into white smoke. Every country has its own special color smoking method and formula, so it is generally confidential. But it is not difficult to pull out beautiful cigarettes. It is difficult to pull out beautiful smoke and environmentally friendly formula that is safe, non-toxic and harmless to aircraft.

Someone on the Internet has exposed various recipes, and I don't know if they are true or false. Our popular science is not scientific research, so we won't be bad in this matter. In a word, there are many reasons why airplanes smoke in the sky, and the most important one is the above reasons.

Aircraft smoking has a great influence on military research and the environment. For example, in the military, plane smoking is not only conducive to finding the traces of local planes, but also easy to expose itself, so it is a double-edged sword. In this way, in the war, all parties will study ways to reduce exhaust smoke, avoid smoke by mastering the weather conditions and high-altitude temperature conditions of the mission, and minimize the impact of exhaust gas from the aspects of aircraft engine and shape design to hide themselves.

Some scientific studies believe that ice crystals formed by aircraft smoke will scatter sunlight and reduce its exposure to the ground. More and more aircraft smoke effect on the atmosphere has a certain impact on climate and temperature. Some scientists are interested in America? 9 1 1? It was found that when the plane stayed on the ground, the temperature increased by 3℃ during the day and at night.

At present, some studies generally believe that aircraft exhaust clouds have unconsciously affected the weather, and call for not abusing this influence, including air shows.

That's it. Welcome to discuss. Thank you for reading.

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