con trails.....why..........

[webbo3]

Ive just got back from my parents place in central western france and the skies were crystal clear and blue most of the time, sitting in the garden we could see 30+ planes an hour flying from west to east, most of the planes looked to be at approx the same height but some had con trails and some didnt my question is why?
is it the height
is it the type of aircraft

ty all in advance .

hopefully ill be abale to ring my dad and tell him the answer.

[Buenchico]

It's most likely to be the height of the aircraft that makes the difference. Humidity levels will vary at different heights, so the probability of water condensing into contraisl will vary.

The type of aircraft (or, more specifically, the type of engines) might affect the probability of seeing smoke (rather than water). You might find this of interest:
http://www.theanswerbank.co.uk/Travel/Question 398118.html

Chris

[webbo3]

thanks very much, we guessed it may be the height but they did all look roughly the same height but at 30k ft + they all look pretty similar.


Dave.