R2OK!

SantaFefan

So there I was driving along this afternoon, beautiful day, blue skies and lots and lots of jet streams from airliners....

"Why do they do that?" asked the wife,

"errrm, er, rurm.. water vapour!" I said in my best Radcliffe voice. Rolling Eyes

" but that one is - and that one is only doing it now and then, why's that?"

"maybe it's to do with altitude,.... or heat, or something. I don't really know" I said weakly but I know someone who will! Wink

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Barkingbiker · Joined: 11 Dec 2006 Posts: 2313 Location: Lincolnshire

Vapour trails are caused by one of the by products of combustion within the gas turbine engine, namely water. When this is ejected into very cold and moist air it forms ice crystals which can take hours to evaporate back into the atmosphere, these ice crystals are the vapour trails that are visable. If the atmosphere is not cold enough, the water content of the jet exhaust does not form these ice cryatals and hence no vapour trail; well thats what I am lead to believe Santa, could be wrong. No doubt someone will tell me, and you, if I am wrong. Wink

BB

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Barkingbiker · Joined: 11 Dec 2006 Posts: 2313 Location: Lincolnshire

Just looked at Wikipedia Santa and there is a fairly good explanation, so go have a look:- http://en.wikipedia.org/wiki/contrail

BB Twisted Evil

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Lord Evan Elpuss · Joined: 10 Dec 2006 Posts: 3417 Location: Cloud Cuckoo Land

I think that how long they persist after the aircraft has gone depends on how moist the atmosphere is at the aircraft's altitude. If contrails persist & spread out many hours after the aircraft has flown by, this can forewarn of deteriorating weather.
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Cherskiy · Posted: Fri Oct 05, 2007 11:42 am Post subject:

Couldn't add anything more to what BB has posted, except that there are also members of the 'tin-foil helmet' brigade who would have you believe that civilian airliners 'routinely' spread so-called 'chem-trails' across the skies in some contrived cunning military-industrial society plot.

Do a search for 'chem-trails' and I'm sure you'll find them.
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nod · Joined: 24 Dec 2006 Posts: 3558

I'll just add that they can ruin a perfect good blue sky Evil or Very Mad

SantaFefan · Posted: Fri Oct 05, 2007 9:40 pm Post subject:

Thanks BB/Cherskiy/Lee Very Happy

I was kind of right after all.
I read the Wikipedia section but long haul airliners don't issue these trails for the whole trans Atlantic flight do they?
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Johnnie Walker read out my message on Pirate Radio! Very Happy

13/8/07
I have heard how radio should be.

SantaFefan · Posted: Fri Oct 05, 2007 9:46 pm Post subject:

Nod, you're right of course but sometimes, as I look out over the North Sea here in the early morning sunrise, some of the many trails look absolutely stunning, almost gold against the red, yellow and blue skies at that time of the day.
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Johnnie Walker read out my message on Pirate Radio! Very Happy

13/8/07
I have heard how radio should be.