Question: At school we are learning about engineering stuff. how does the white lines come out of an aeroplane in the sky and how does the red arrows steam come out in different colours

Andres Rivero answered on 11 Mar 2017:

Hi 442amph28,

This is a very interesting question!

The red arrows and other planes that you see at airshows have some smoke machines near their engines. The machines usually sprays oil on the engine, and since the engine is so hot, it turns the oil into oil vapour. The pilot controls when the oil gets sprayed and the colour is added to the oil (they dye it).

When you see commercial planes flying at cruise altitude during a sunny day, and you see the white lines that they leave behind, it is due to a different thing. It is super cold at those altitudes (way below zero degrees) and the engine is so hot, that any water vapour that it is in the air that goes through the engine becomes water vapour inside the engine, and then condenses again due to the low temperature when it leaves the engine. So, in other words, these are sort of artificial clouds that the airplane forms.

Andres