sky trails, how are they formed?

[purple haze]

hi

i just wnated to know, how are sky trails formed from a/c. today was an absolutely clear day and i still saw them.

i know what wing tip vortices are, are they different from this.

i just couldnt stop staring out of the window, there were some beautiful sights today.


cheers

[Checkboard]

You might want to look at the Contrailb altitudes (http://www.pprune.org/cgibin/ultimatebb.cgi?ubb=get_topic&f=3&t=002447) thread for some informaiton and some links to other sites.

Basically, when you burn fuel you get a bunch of gasses, mostly carbon dioxide and monoxide, some sulfides and others, but one of these gases is water vapour.

If the air is cold enough, and not too dry, then when the exhaust hits that cold air, the water vapour condenses into water, which then freezes into ice crystals, forming a contrail.

[Mycroft]

Often at altitude you have a situation where ther is sufficient water vapour in the air to condense. Although this does occur naturally (forming clouds) it can be induced by adding condensation nuclei, cloud seeding uses Silver Iodide or (usually) dry ice, but if there is sufficient vapour engine exhaust is quite effective (sometimes the fuselage is enough to do it, but generally many small particles are more effective)

[EGGD]

Here just north of Bristol, we quite often get aircraft from LHR or LGW that aren't quite up to altitude, and so go in and out of cold air, so the vapour trails form for a while, and then dissapear again as it goes into a warmer pocket :cool:

Great huh?

[Agaricus bisporus]

PH, beware the establishment cover-up propaganda pedaled by the above government dupes.

It is a well known "fact" that these are the visible sign of a worldwide governmental conspiracy to subjugate the worlds proletarian population by means of noxious mind-altering chemicals sprayed from every commercial airliner, all of which have been secretly modified for the purpose.

If for any bizarre reason you chose to disbelieve me type "chemtrails" into your search engine, lock your front door and turn up the stereo real loud or your neighbours will call the men in white coats after the first hour of your hysterical uncontrollable laughter...

Great entertainment (if it wasn't so tragically sad)

[Young Paul]

At risk of establishing a reputation as a real saddo....

I spent an hour or so on a long charter working out what the density of a contrail is. I think it worked out at a weight of grams per metre. Obvious that it can't be much more than that, of course, because it stays up.

[loggerhead]

Im a Buyer for a uk airline, and you sould see how much that stuff costs... :D