Condensation trails

[Bill G Kerr]

Maybe a pilots' site isn't the best to ask this question, since you, of all folks, never see your own! But here goes anyway.

Speaking from a land-lubber's perspective.... Although I do fly (a paramotor).
Some days there are no contrails to be seen, some days they last for a short time then disappear, and some days there are multitudes of them in the sky.
What makes the difference? Isn't always pretty cold up there?

Next, a couple of weeks ago I watched 2 planes making very well defined twin trails. As I watched a fuzzy much wider one could be seen, apparently above the two sharp ones. It looked like an old trail, but it wasn't there in front of either plane. Could it be the apu?

[BOAC]

Contrails - how do I predict them? [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-178738.html)

[Richard Le page]

I think the temperature,altiude and how much moisture is in the air determines how defined the contrail is,the colder it is and the more moisture will make a heavy and long contrail,sometimes up to 50 miles long,large contrails are usually seen in winter and in the summer usually very short wispy ones or none at all.
I think contrails start to form around 25000ft if the conditions are right.

I think the fuzzy one that you are talking about is some sort of optical illusion.maybe someone can give a more detailed explanation.
hope that helps

Regards

Rick

[Mr Optimistic]

Seem to remember that calculating at what altitude contrails would form (and avoiding it/them) was a planning issue for the bombing raids in WW2. Fuzziness ? Isn't this just the effect of wind (burp)?

[Chris Scott]

The APU could have been running, but it's not normally done.

Contrails can also form (as I guess you know) from wing tips, corners of flaps, etc.. If it was above the other two, it might be from the top of the fin. But these usually occur at low altitude in saturated air, and quickly disperse.

Used to see our own contrails regularly after completing a 70-deg turn over Nice en-route Tripoli many years ago...

[TedUnderwood]

The easiest way to predict contrails is to look in the local news, when the masses are wising up to corrupt government policies, the government starts the spraying program again in order to control the people!!! Duh! :ok:

[Morrisman1]

.... or are they chemtrails. Better grab your tin-foil hats fullas

[Scotty Beamup]

I once observed a contrail of a 747 using an astronomical telescope. The four lines from the engines were quite distinct. It appeared that they were moving backwards as fast as the 74 was moving forwards and eventually curled over each other, presumably in the vortex. They were still moving aft minutes later.

Speaking of vortexes, on a very rare day in Wellington NZ,s harbour I was completely becalmed off the end of runway 16 in my small yacht. I lay back in the sun waiting for a breeze when a QF SP flew over and landed. A few seconds later, hearing an odd noise, I looked up in time to see two dark pointed marks of turbulence racing across the water straight at me. I just had time to hang on before we were blasted over on our ear with me gazing at the keel. A few seconds of lashing thrashing drama before we rolled upright and everything returned to normal.
A perfect demonstration of vortex.