Jet-streams

[allen ives]

Why do some aircraft produce jet-streams while others don't? And they're not really 'jet'-oriented, as WW2 bombers made them, too.

[sabrinah]

Yes, atmospheric conditions determine the formation of these lines of cloud, known as condensation trails, or contrails, rather than the type of plane. (Jet streams are actually something totally different, a natural weather feature). Airplane exhaust contains, amongst other things, water, normally this is invisible. But if the air it mixes with is cold enough then the moisture has to condense, forming a cloud, becasue cold air can't hold very much moisture.