Why Do Airplanes Leave White Traces In the Sky?


We have all seen airplanes flying across a blue sky, right? We can even remember how fascinated we were by them when we were young and how we used to trace an airplane’s path by following that white line that airplanes leave behind them. But here comes the question: what are those white lines?contrails

Well, the answer is rather surprising: those white traces are actually artificial clouds. Yes, this is not a mistake! They are artificial clouds but their official name is contrails which is the short version of the phrase “condensation trail.”

Airplanes have an engine and, just like cars, they produce exhaust which contains water vapours. But here comes the cool part: when hot exhaust gases escape from a plane, they “meet” an extremely cold environment (sometimes more than -40° F). The cold air condenses the water vapour which means that it transforms into tiny water droplets or even freeze into ice crystals before they evaporate. This condensed water vapour, combined with ice crystals are the elements that make up the trails that we see in the sky.

But things are slightly different if we go to an air show. You might have seen airplanes creating messages in the sky with something that looks like clouds. But this should not be confused with contrails! Those messages are created with smoke machines and the pilots fly the airplane following a special pattern. Those smoke machines are pressurized containers full of oil. The pilot can control them and, at his signal, the machines spray oil onto the plane’s hot exhaust system, creating dense clouds of white smoke. This means that they are simply mimicking what happens when contrails appear.airshow

So, next time you’ll see an airplane flying you’ll know why it leaves white traces on the sky! Because it creates its own tiny cloud!



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