NW7E7
Topic Author
Posts: 479
Joined: Sun Jun 20, 2004 11:43 am

Contrails

Sat Jun 26, 2004 11:28 am

This has probably been asked before but the search turned up negative.

1. What weather conditions must take place in order for contrails to appear?
2. Is there a certain altitude that you have to be above to have contrails?

Thanx
NW7E7

 
InnocuousFox
Posts: 2556
Joined: Sat Dec 06, 2003 1:30 am

RE: Contrails

Sat Jun 26, 2004 12:03 pm

The same ones that make your breath appear in front of your face.
Dave Mark - Intrinsic Algorithm - Reducing the world to mathematical equations!
 
NWADC9
Posts: 3942
Joined: Tue Jun 01, 2004 12:33 am

RE: Contrails

Sat Jun 26, 2004 12:07 pm

Yes, altitude-wise, I start seeing them on FS around 18,000 Ft. with fair conditions, but in real life it may be different.
I convert Jet A and 100LL into noise.
 
jadedmonkeys
Posts: 58
Joined: Thu May 27, 2004 8:51 am

RE: Contrails

Sat Jun 26, 2004 12:33 pm

A small difference between temperature and dew point. If temparature is say 4 celsius and dew point is 2 then that could be ideal because when a fast moving aircraft moves through the air, it compresses air and as air compresses, it cools down and if temperature and dewpoint is the same, you will have visible moisture as in clouds and contrails. the dewpoint is the temperature at which moist air saturates and condenses which in turn becomes clouds and contrails. This also explains why you get that cloud ring when an aircraft goes Mach 1.
 
NW7E7
Topic Author
Posts: 479
Joined: Sun Jun 20, 2004 11:43 am

RE: Contrails

Sat Jun 26, 2004 12:42 pm

INNOCUOUSFOX:
If it is the same ones that make your breath appear in front of your face then how come I never see any contrails at sea level or when an aircraft is taking off??

NW7E7
 
AJet
Posts: 50
Joined: Mon Jan 05, 2004 12:29 pm

RE: Contrails

Sat Jun 26, 2004 9:25 pm

NWADC9,

contrails may or may not appear depending on the current weather conditions; contrails' altitude range changes every day.
When you're planning a visual interception and dogfight mission, the military weather service will tell you where to expect contrails, so that you don't fly at those altitude ranges and keep visually discreet.
 
InnocuousFox
Posts: 2556
Joined: Sat Dec 06, 2003 1:30 am

RE: Contrails

Sun Jun 27, 2004 1:32 am

"If it is the same ones that make your breath appear in front of your face then how come I never see any contrails at sea level or when an aircraft is taking off??"

Because the difference in relative humidity and/or dew points between the two airmasses isn't enough.
Dave Mark - Intrinsic Algorithm - Reducing the world to mathematical equations!
 
geoffm
Posts: 2082
Joined: Fri Feb 27, 2004 5:58 am

RE: Contrails

Sun Jun 27, 2004 5:13 am

I was just thinking about this the other day. I was near Weston-super-Mare in the UK and was watching a few planes fly over at high altitude. Both had contrails right up to the point where they crossed over to land (instead of the sea) where they abruptly stopped. It was most interesting to see!

Geoff M.
 
crjdispatchkid
Posts: 97
Joined: Tue Feb 17, 2004 3:15 pm

RE: Contrails

Sun Jun 27, 2004 6:26 am

Let's see if I can use some of my meteorology background to explain.

First a definition:
Contrails - Long, narrow, ice-crystal clouds that form behind jet planes flying at high altitudes in below-freezing temperatures


Contrails are generally found at high levels (where the temperature is roughly -25c/-32F about FL250) in nearly saturated conditions. Aircraft inflight emit water droplets into the atmosphere (from the exhaust) which then freeze in this cold / moist atmosphere. That's how you get 'em.

I remember a study being done during the period when no a/c were flying after 9/11 and the results stated that average daily variations in temperature (between high and low temps) increase by 2F.

Kinda intersting
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