In life, we often see a white smoke left after the plane flies in the sky, but many people usually don't understand what causes it. Do you know how the white smoke behind the plane is produced? Let's have a look
Natural phenomenon, called aircraft cloud, the formation of white smoke and white line behind the aircraft:
Only when the jet aircraft flies in the air layer below - 20 ℃, the air humidity is close to or reaches saturation, and the atmosphere is relatively stable can tail smoke be produced, that is, wake cloud.
The formation principle of wake cloud is: when the jet aircraft flies at a rather cold altitude with high water vapor content, the hot gas ejected from the tail of the aircraft condenses in cold and high humidity air to form a cloud belt.
Another process of generating wake cloud is that the aircraft flies in nearly saturated air, and the air near the top of the propeller and wing condenses due to adiabatic cooling due to dynamic pressure reduction, but this is rare.
Generally speaking, at an altitude of 10000 meters to 7000 meters, the aircraft is easy to form wake clouds. Beyond this range, the aircraft will not produce 'smoke' phenomenon.
Introduce the white smoke line behind the aircraft in detail
People often see jet aircraft flying at high altitude in a clear sky, and one or several long 'white smoke and white lines' will appear behind the fuselage.
In fact, the white smoke line behind the aircraft is not the smoke emitted by the jet aircraft, but a special cloud system formed by the condensation of water vapor after the exhaust gas emitted by the aircraft is mixed with the surrounding air. It is called the aircraft wake in the aviation industry and aviation meteorology, which is commonly known as' aircraft smoke '. So how did it form?
According to the causes, aircraft wake can be divided into exhaust wake, aerodynamic wake and convective wake. Exhaust gas wake can be divided into exhaust gas condensation wake and exhaust gas evaporation wake. Among them, the most common is the exhaust gas condensation wake, which is the aircraft condensation wake discussed in this paper.
The aircraft consumes a lot of fuel during flight. The water vapor and some heat generated are discharged out of the aircraft with the exhaust gas, enter the atmosphere, and quickly mix with the surrounding air to form a condensation wake. Its formation process is different from the common dew, frost on the ground and clouds in the air. The exhaust gas emitted by the aircraft flying at high altitude is mixed with the ambient air. The saturation degree of the mixed gas depends on the net effect of heat and water vapor increment. When the humidification effect is dominant and exceeds a given critical value, condensation wake will be formed; When the heating effect is dominant, there will be no condensation phenomenon and condensation wake. Since the heating and humidification effects of waste gas are certain, whether condensation will occur in this mixed gas will depend on the temperature, humidity and atmospheric pressure of the ambient air itself. In short, high ambient air temperature is not conducive to the formation of condensation wake. Aircraft condensation wake may occur only when the ambient temperature is quite low (usually below - 40 ℃). According to relevant data, when aircraft wake occurs, the air temperature is mostly - 41 ℃ ~ - 60 ℃, accounting for about 86% of the aircraft wake. If the air temperature is higher than - 40 ℃ or lower than - 60 ℃, aircraft wake generally rarely occurs.
The seasonal variation of the height of the white line behind the aircraft is not very obvious. Generally speaking, the number of occurrences in the winter half year is more than that in the summer half year. The average thickness of the wake layer is 1 ~ 2km, and the lower limit height is the lowest in winter and the highest in summer. In the thicker aircraft condensation wake, the length and concentration of the wake formed at different heights are also different. Usually, the wake with short length and light concentration appears at the bottom, which gradually lengthens and thickens upward. When it reaches a certain height, it turns into an intermittent wake with light tone.
The white smoke and white line behind the aircraft has important military value. Since modern times, it has always been valued by military experts all over the world. Jet combat aircraft are most prone to aircraft wake when flying at a suitable altitude. In aviation operations, the emergence of aircraft wake is easy to expose the aircraft track and position. In order to avoid exposing the target, we must understand the altitude of the aircraft wake and choose the flight altitude away from the aircraft wake in order to achieve the purpose of concealing ourselves.
There are two situations for the white smoke line behind the fighter
1: In the flight performance, there is a special smoke extractor or that the pilot can control to spray diesel oil onto the tail nozzle (there is usually a separate tank containing diesel oil. For example, some Su-30 participating in the performance have a spindle shaped diesel tank at the tail). White smoke is generated due to the gasification of high-temperature diesel oil.
2: Condensation marks caused by high speed when an aircraft flies at supersonic speed.
If shot, it should emit black smoke, and once the aircraft emits black smoke, the pilot will parachute. (black smoke proves that the aircraft oil circuit is on fire and will generally explode in a short time.)