The contrails or defractory trails left by airplanes in the sky are caused by a complex polynomial involving several factors. Firstly, clouds form when air condenses, which occurs when its humidity reaches 100% and the temperature is extremely low. Commercial airplanes fly in the highest layer of the troposphere, where temperatures can drop to -56°C.
The engines used by airplanes generate thrust by burning fuel and oxygen, producing a series of combustion gases and water vapor. The water vapor is much hotter than the ambient air, so it condenses and creates the snowy groove that airplanes are known for. Additionally, as the gas expands when it leaves the plane, this also contributes to the formation of contrails.
The Anglo-Saxons refer to the wake of airplanes as “contrail,” which is short for “condensation trail.” The next question arises: why don’t all airplanes leave a trail? The efficiency of a turbojet engine is determined by its coefficient between the work done by the engine and the chemical energy it produces. Interestingly, weather conditions can be predicted based on the nature and persistence of contrails.
During air shows, contrails may appear colored due to dyes being mixed and released at specific times. These ‘polychrome grooves’ are not true condensation trails. Finally, there is a fascinating type of contrail called Prandtl-Glauert condensation clouds that form when an aircraft exceeds the speed of sound. These clouds take on a disk or cone shape due to a sudden drop in air pressure as they travel through supersonic speed zones.