Usnseallt82 From United States of America, joined Jan 2004, 4891 posts, RR: 52
Reply 4, posted (10 years 9 months 1 week 4 days 10 hours ago) and read 2460 times:
Actually, one user had it down pretty well. The contrails are formed by the extreme heat in the aircraft engines reacting with extremely cold air found at high altitudes. The thickness of the contrail itself, usually whether or not it stays place in the air for long or dissipates, depends on the moisture located in the air at the time. However, they are usually formed regardless, unless it is unusually dry air, because of the speed to which the temperature of the air is changed...most undoubtedly in microseconds. Any change in temp that has that vast of a range will produce thick moisture. Then, if the air is cold enough, the newly created moisture becomes tiny ice crystals, suspended in the upper layers of the atmosphere. These are the ones that never seem to go away and are usually very thick.
Klaus From Germany, joined Jul 2001, 21495 posts, RR: 53
Reply 5, posted (10 years 9 months 6 days 18 hours ago) and read 2364 times:
The combustion of hydrocarbons (like Jet-A or even ordinary car gasoline) produces significant amounts of water vapour which adds to the preexisting air humidity; If the conditions are right, this can make the air cross the condensation point.
InnocuousFox From United States of America, joined Dec 2003, 2805 posts, RR: 14
Reply 6, posted (10 years 9 months 6 days 18 hours ago) and read 2350 times:
Condensation forms when air cools to the dew point. The water vapor has to come from the fuel itself. Otherwise the amount of moisture in the air would have already formed clouds at that altitude and the heating of the air by the engines would make the clouds go away temporarily. However, if the aircraft creates the water vapor and disperses it behind, that is water that is over and above what the colder air at that altitude can handle... so it condenses into contrails (i.e. clouds).
(side note... do y'all think it's time to bump my "Cloud Dreaming" poem up to the top?)
Dave Mark - Intrinsic Algorithm - Reducing the world to mathematical equations!