You may have observed that an airplane leaves behind a white cloud-like trail, during fly across a clear sky on a cold day. So, what exactly are these trails? Are they made of smoke? Here is the reason behind this secret.
First of all, smoke is not the main constituent of these white trails. In fact, these trails are ‘condensation trails,’ named shortly as Contrails. An airplane engine produces exhaust when it burns.
The exhaust contains some gases like carbon dioxide, nitrogen oxides, hydrocarbons, soot and lots of water vapors. The airplanes fly at heights above 30,000 feet where the temperature can get extremely low.
When the water vapors in the exhaust hit the cold air, they condense. The tiny condensed droplets can freeze into ice crystals. This mixture of droplets and ice crystals form cloud-like trails mid-air where ever the plane has passed.
It is hard to imagine how water is readily available in such a large amount to create these visible trails at great distances. In reality, the airplane exhaust gas contains lots of water. The Boeing 747 ejects up to 2.75 kg of water per second, enough to leave quite thick trails.
The white trails are just the condensation trails but what about the colored ones that you see in aerobatics exhibitions? They are certainly not contrails. The sky typing and sky writing trails are made by injecting hot oil into the exhaust.