Airplanes leave behind white grooves in the sky known as contrails or defractory trails. These grooves are the result of a complex polynomial that involves 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 reach -56°C.
The second factor to consider is the engines of airplanes. They generate thrust force by burning fuel and oxygen, producing combustion gases and water vapor. The water vapor is much hotter than ambient air, so it condenses and creates the snowy trail that airplanes are known for. Additionally, as the gas expands when leaving the plane, this also contributes to the formation of contrails.
Contrails are called “contrail” by the Anglo-Saxons, which is a contraction of “condensation” and “trail”. The next question raised by this phenomenon is why not all airplanes leave a wake behind them. The efficiency of a turbojet engine is measured by its coefficient between the work done by it and the chemical energy it produces. An interesting aspect about contrails is that their nature and persistence can be used to predict weather conditions.
During air shows, we may see colored contrails known as “polychrome grooves”. These are achieved by mixing dyes and releasing them at just the right time, so they are not true condensation trails. Finally, there are certain types of contrails that form when an airplane exceeds its speed of sound: these are called Prandtl-Glauert condensation clouds and occur due to a sudden drop in air pressure