Air forces and intelligence agencies are indeed interested in predicting whether condensation trails (contrails) will be visible or not during aircraft operations.
Photo: C-CYOW at Photobucket
Among existing prediction algorithms, Appleman's method, devised in 1953, is frequently cited, even if more accurate or refined algorithms exist, like JETRAX.
From Predicting Contrails Using an Appleman Chart (Nasa), the principle is based on air saturation characteristics:
At first, scientists were not sure how contrails formed. We now know that they are a type of mixing cloud, similar to the cloud that sometimes forms from your breath during a cold winter day.
Appleman showed that when the air outside of the airplane is cold enough and moist enough, the mixture of the jet exhaust and the air would form a cloud.
Since 1953, civil turbofans have replaced turbojets, with various air bypass ratios. What is the effect of this replacement on the occurrence of contrails?
- Does turbofan reduce or increase contrail occurrence?
- Does bypass ratio play a role?