What is the white smoke that comes out of a plane?

Question:
Things that make you go Hummmm
why is it sometimes you see a plane in the sky and it has white smoke striking the sky, and some times not?

Answers:

?since the A380 has been delayed, how possible is a BWB (blended wing body) airliner?

Usually it's the vapour trail that is caused by water condensing in the heat of the aircrafts engines. You often see that with aircraft flying at a high altitude, but the effect can be produced at any altitude if the atmospheric conditions are right.

Tell me about working of an Aeroplane.?

Other times it can be a smoke trail that is created by deliberately injecting oil on the aircrafts exhaust manifold. This done by either skywriters or stunt pilots for extra effect at airshows.

Which airline to take over?

water vapor,,, depends on temp and moisture in the air

Why do Pilots say "Roger" ?

That is from people smoking in the bathroom.

Any engineers turned pilot here?

Coach

What is the maximum speed of a a B777-300ER during take-off?

it's actually not smoke it's called a Contrail
short for condensation trail
it's water condensation from the wings.

Help with this aircraft pneumatics question? how to make aircraft serviceable main storage bottle, engineer?

............. the exhaust gases freezing with the surrounding moisture ....... if present .......... at those low temperatures ...........

can any one help me out with how ac electrisity is generated and distributed on an aircraft?

its a condensation trail... basically a relavtivly short living cloud.