Originally Posted by
beardy
Ah, now I see your confusion. The contrails are formed from the water produced from burning hydrocarbons in the fuel. The carbon produces CO2 and the hydrogen produces H2O. Look out the window and you will see that they form in the exhaust from the engines, not at the wing tips. Four from a four engined aircraft, two from a twin which then merge.
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I see ... ... ...
So I suppose those very short contrails are when the aeroplane is not using much fuel and the long contrails are when they
are using a
lot?
(Does a contrail 'come out of the engine', or does it forms in the disturbed air behind that high speed exhaust air? But I really do like the idea that the length of the contrails could be an indicator of the engine power settings!!)
However contrails do form at night
Yes, and they look very pretty in the moonlight, especially when you see them close up.