Guys
I was wondering about this:
I was looking at the sky today and I was thinking about the white lines caused by jet exhaust (is this correct?).
Now my question about this is: What are they exactly, by what are they caused and at which height do they appear?
I'm sorry if this is a stupid question
Thx feedback
Regards
Capt
Vortices?
Moderator: Plane spotting team
Those white lines are called "contrails" or condensation trails.
If I'm correct it's caused by the hot exhaust gasses ( something about 600-800°C ). I think it's nothing else than ice chrystals. Imagine the air is -50°C, the exhaust gasses warm the air and it becomes vapour, when that vapour freezes you get ice chrystals and they form those white lines as you call it.
How long they become and stay up there has everything to do with the air temperature and humidity, I think.
At least that's what I think to know of it.
Anyone else another try...
If I'm correct it's caused by the hot exhaust gasses ( something about 600-800°C ). I think it's nothing else than ice chrystals. Imagine the air is -50°C, the exhaust gasses warm the air and it becomes vapour, when that vapour freezes you get ice chrystals and they form those white lines as you call it.
How long they become and stay up there has everything to do with the air temperature and humidity, I think.
At least that's what I think to know of it.
Anyone else another try...
When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
CanonFreak 
Capt,
What you are talking about is called a contrail and not a vortex.
One of the products of burning kerosene is water vapour. When this very hot vapour comes out of the engine it reaches very cold air. As you may know, hot air can contain more water vapour than cold air. When the hot air (with a lot of water vapour in it) comes out of the engine, it'll saturate the cold air and you'll get clouds who will be forming. The clouds are formed because of the condensation. When flying in higher altitudes the water dropplets will transform into ice crystals because of the very cold air.
The shape and length of those contrails only depends on the different layers of air you have. You can also have some pockets of air which are cooler etc....
The contrails usually appear when the plane is very high, because the higher you rae the colder the air, but there are exceptions
Here are 2 pics that show some nice contrails that come out of an engine :
http://www.airliners.net/open.file/498094/M/
http://www.airliners.net/open.file/425100/M/
On the second picture you can clearly see that the contrail doesn't form itself directly behind the engine that's simply because the process is taking some time.
Contrails are not always produced by engines, but also sometimes by wings. This is due to the air cooling when flowing over the wing. This phenoma mainly happens when the humidity in the air is very high, which means that the air will nearly be saturated. In a result you'll get some condensation by cooling the air when flying through.
Here's a picture that illustrades the phenomena: http://www.airliners.net/open.file/270240/M/
As a side note, I heard a couple of weeks ago in a tv show, that on 11.09.2001, when all flights where grounded in the USA, the avergae temperature over the continent rose a litlle bit more than 1°C. By seeing this you can clearly see the impact that all those contrails have 8O
I hope I was able to answer your questions
Greetz
Chris
8)
What you are talking about is called a contrail and not a vortex.
One of the products of burning kerosene is water vapour. When this very hot vapour comes out of the engine it reaches very cold air. As you may know, hot air can contain more water vapour than cold air. When the hot air (with a lot of water vapour in it) comes out of the engine, it'll saturate the cold air and you'll get clouds who will be forming. The clouds are formed because of the condensation. When flying in higher altitudes the water dropplets will transform into ice crystals because of the very cold air.
The shape and length of those contrails only depends on the different layers of air you have. You can also have some pockets of air which are cooler etc....
The contrails usually appear when the plane is very high, because the higher you rae the colder the air, but there are exceptions
Here are 2 pics that show some nice contrails that come out of an engine :
http://www.airliners.net/open.file/498094/M/
http://www.airliners.net/open.file/425100/M/
On the second picture you can clearly see that the contrail doesn't form itself directly behind the engine that's simply because the process is taking some time.
Contrails are not always produced by engines, but also sometimes by wings. This is due to the air cooling when flowing over the wing. This phenoma mainly happens when the humidity in the air is very high, which means that the air will nearly be saturated. In a result you'll get some condensation by cooling the air when flying through.
Here's a picture that illustrades the phenomena: http://www.airliners.net/open.file/270240/M/
As a side note, I heard a couple of weeks ago in a tv show, that on 11.09.2001, when all flights where grounded in the USA, the avergae temperature over the continent rose a litlle bit more than 1°C. By seeing this you can clearly see the impact that all those contrails have 8O
I hope I was able to answer your questions
Greetz
Chris
8)
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EBAW_flyer
- Posts: 557
- Joined: 29 Sep 2003, 00:00
You are correct about the high altitude contrails, there the difference in temperature causes the relative humidity to rise (and form condensation).
But this is not correct. Here the temperature does not change. The change in pressure makes the air saturated, not the change of temperature. As you know, above the wing there is a large area of low pressure (wich produces most of the lift). The pressure of the air drops and the relative humidity rises. So you get the same result: condensation (only here it are watter droplets and high in the sky ice crystals).Contrails are not always produced by engines, but also sometimes by wings. This is due to the air cooling when flowing over the wing. This phenoma mainly happens when the humidity in the air is very high, which means that the air will nearly be saturated. In a result you'll get some condensation by cooling the air when flying through.
Very good explanations from all of you.
One more thing: the air in the engines is compressed to a high pressure, not only by the blades, but also because combustion increases the volume (and the pressure) of the gases.
When reverting to the low atmospheric pressure existing at high altitude, thegases undergo a strong cooling (in the same way as compression causes heating: check with your bicycle pump!) with transformation of the water vapour resulting from combustion into ice crystals. One more reason for the formation of contrails.
One more thing: the air in the engines is compressed to a high pressure, not only by the blades, but also because combustion increases the volume (and the pressure) of the gases.
When reverting to the low atmospheric pressure existing at high altitude, thegases undergo a strong cooling (in the same way as compression causes heating: check with your bicycle pump!) with transformation of the water vapour resulting from combustion into ice crystals. One more reason for the formation of contrails.
André
ex Sabena #26567
ex Sabena #26567
Indeed Chris that is correct, a contrail is made by the addition of water in the surrounding air, but don't forget that this air must be humid enough to produce contrails. Sometimes its to dry to form the "clouds".Avro wrote:Capt,
What you are talking about is called a contrail and not a vortex.
One of the products of burning kerosene is water vapour. When this very hot vapour comes out of the engine it reaches very cold air. As you may know, hot air can contain more water vapour than cold air. When the hot air (with a lot of water vapour in it) comes out of the engine, it'll saturate the cold air and you'll get clouds who will be forming. The clouds are formed because of the condensation. When flying in higher altitudes the water dropplets will transform into ice crystals because of the very cold air.
The shape and length of those contrails only depends on the different layers of air you have. You can also have some pockets of air which are cooler etc....
Calculations can easely be made from the upper weather humidy charts to see if conditions are favorable for (persisting) contrails or not, and especially the military aviation is very interested and still make those forecasts. U probable know why
SS
Thanks for putting it straight EBAW_FlyerEBAW_flyer wrote:
But this is not correct. Here the temperature does not change. The change in pressure makes the air saturated, not the change of temperature. As you know, above the wing there is a large area of low pressure (wich produces most of the lift). The pressure of the air drops and the relative humidity rises. So you get the same result: condensation (only here it are watter droplets and high in the sky ice crystals).
Because they don't like to be seen, from far awayU probable know why
Ciao
Chris
8)
When on vacation in Germany ( Kell am See, not far from Trier, to be exact ) I saw these nice contrails.
The latest pic is special with 3 contrails very close to each other 8O
The latest pic is special with 3 contrails very close to each other 8O
When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
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OCR_ole_ole
- Posts: 50
- Joined: 26 Oct 2003, 00:00