Message posted by Andy P on July 04, 2004 at 13:05:10 PST:
Hi folks What this means is that the appearence on condensation (contrails) is very dependent on both the temperature and the moisture content of the air and the style or design of the contrail will also change dependent on the wind speed and direction at the altitude the contrails appear at. Not all weather conditions are conducive to their formation and the altitude that they do form at varies depending on a varierty of atmospheric conditions. It is a key piece of knowledge for pilots of military aircraft becasue they will want to transit these altitudes well away from enemy territory so as not to betray their presence ( a particular worry in pre-radar warefare conditions) Short contrails may be formed by aircraft ascending (or descending) through the contrail "zone" ie the contrails start as they enter the right temperature/moisture zone and cease once they leave the zone. High winds perpendicular to the line of flight will broaden the contrail whilst turbulent conditions will tend to break the contrail up quickly. Ok, sorry if I've repeated any previous posts but it's important (I think) to clarify this issue about contrails and whether they releate to a particular aircraft or engine type. Regards Andy P
I'm not an expert in these matters but....contrails are the result of condensation that occurs when the hot, humid air from a jet exhaust mixes with the prevailing atmosphere and where the atmosphere has a low vapour pressure and low temperature. This is very similar to the clouds one sees when one exhales on a cold, dry day. In a very simplistic model it could be said that the air can no longer disolve any more water or the temperature is too low for the water to be fully "absorbed" and the consequent vapour remains visible as "steam". As an example, examine a boiling kettle - true steam is an small portion of boiling water vapour right above the kettle spout and it's invisible. As the air becomes fully saturated and can take no more water and the temperature of the vapour drops slightly it becomes visibel to the human eye and is what we commonly refer to as steam.
In Reply to: short contrails by Nellis jets posted by Herb on July 03, 2004 at 15:17:01 PST:
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