SEA nw DC10
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That Vapor Trail Jets Make..why Don't

Thu Nov 04, 1999 5:42 am

Ok folks this may be a dumb question.

When I see planes at cruising altitude making that white vapor trail in the sky, I use my binoculars somtimes, and can see that the trail is coming generally from the engines in that area. Now, I just flew on a DC-10, and during cruising, I looked out my window, and I was sitting behind the wing, I could see the back of the engine, but didn't see that trail the entire flight. I looked also on a 757 and 777, and didn't see it either during flight. Where's that dang trail, I wanna see it in flight. haha Thanks
 
Ben2
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RE: That Vapor Trail Jets Make..why Don't

Thu Nov 04, 1999 5:48 am

When you look at those trails with your binoculars do you ever notice that they are "delayed"? It takes a few seconds for that hot air to condense when it makes contact with the cold air. On the flights where you could see the back of the engine, the plane was most likely making a vapor trail, but when the jet is at Mach.78 that vapor trail gets left behind and you cant' see it. Hope this helps...
 
mikeyyz
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RE: That Vapor Trail Jets Make..why Don't

Thu Nov 04, 1999 6:53 am


You can see the vapour trail if you fly a 4 engined plane and look out the last door (easier to see the trail on quads than twins because of the outbord engine). Of course it depends on the conditions altitude, temp....
I once sat in the last row of a 777 flight and saw the trail when i look back towards the horiz stab.

MIKEYYZ
 
Hagi
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RE: That Vapor Trail Jets Make..why Don't

Thu Nov 04, 1999 7:07 am

I did once see the vapour trail. The plane was a 757, and I was sitting maybe halfway back from the trailing edge. I looked back and the trail seemed to start at about the tail of the plane.
 
AC_A340
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RE: That Vapor Trail Jets Make..why Don't

Thu Nov 04, 1999 7:40 am

The best conditions for seeing them is mid winter, at a high altitude and sitting in the back of a plane. That the way the air condenses faster. Also I've noticed high bypass engines have the trail appear sooner. I think this happened because the bypass air doesn't get as hot as the air going through the combustion and therefore condenses quicker. Has anyone else noticed that?  
 
dustweek
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Puzzling Sight

Thu Nov 04, 1999 7:42 am

Slightly unrelated, but...

On a flight from Fairbanks, Alaska to Barrow on the Arctic Ocean, I saw a fat dark line--parallel to our route--ahead of us on the flat snowy tundra.

As there are NO manmade objects in that area it was quite puzzling, until I realized it must be the shadow of our own vapor trail.

 
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Bruce
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RE: Puzzling Sight

Thu Nov 04, 1999 9:39 am

Can you see the trail from a smaller jet like 727 or DC9? Everyone seems to have seen it from a big one like a DC10 orr 777. I have been on a couple flights this year and didn't see it....but I do frequently see them from the ground.....white streak cutting across the clear crystal blue sky. I think they're easier to see when the sun is low in the sky, not high overhead. When I see one I often wonder where they're going to...
Bruce Leibowitz - Jackson, MS (KJAN) - Canon 50D/100-400L IS lens
 
LH423
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RE: That Vapor Trail Jets Make..why Don't

Thu Nov 04, 1999 11:49 am

I know that it takes a while for the vapour to appear, but last winter 1 Jan to be exact, I flew on Lufthansa, and as we were around 10,000 metres I could see the vapour trail forming right outside my window (51A, in the centre of the wing and the lest exit. I was surprised by this, because I live in Boston which it the motorway of the sky for all New York bound flights, so I often will try to identify planes way up, and will notice the vapour not starting until well aft the horizontal stabiliser. This has puzzled me, so maybe someone could answer this one: Why did the vapour trail form almost directly out of the engine, instead of nehind the aeroplane.

LH423
« On ne voit bien qu'avec le cœur. L'essentiel est invisible pour les yeux » Antoine de Saint-Exupéry
 
william
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Look For The Shadow On The Ground

Thu Nov 04, 1999 11:51 am

Depending on what side you sit on,if you look on the ground or on the clouds you can see the shadow of the contrail. I wonder if the people on the ground even notice when the shadow passes over them.
 
AC_A340
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LH423

Thu Nov 04, 1999 12:04 pm

Ita ppeared sooner because it was winter so it was colder. Because it was colder, it condenses faster, thats why you noticed it quickly.
 
jim
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Here's A Strange One!

Thu Nov 04, 1999 1:16 pm

Not entirely related, but, once I was sitting in the middle of the wing on a 737-200, heading Southeast-ish into the early morning sun. I noticed a thin shadow running from the fuselage all the way out to the wing tip. It moved maybe one inch back and forth for the whole time I watched it, maybe 20 minutes. It looked like the shadow of a rope, snaking back and forth.

My question to all you junior physicists out there: Was this the shadow of the center of pressure along the wing MAC? I feel it was the shadow of a disurbance in the airflow, and that theory is the only thing I can think of.

Let me know what you think, Okay?

jim
 
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Bruce
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About Jet Trails...

Fri Nov 05, 1999 12:01 pm

I have seen some real bright ones (from the ground) and I don't live in a cold climate. Keep in mind that even if it is warm on the ground it is very cold at 35,000 feet. Remember Payne Stewart's plane? Flying from MCO to South Dakota it was definitely not winter and experts said that the cabin temperature could have been as low as -70f. !!!! The Air Force jet saw ice on the windows!

When I lived in Tallahassee, Florida, I would sometimes see half a dozen trails or more streaking across the sky on a clear day! It was amazing. That area is right in the path of jets going to MCO, TPA, MIA, even JAX from places in the midwest so there was lots of traffic. Over here at GPT, I see trails coming from MSY and ones going from southeast to northwest, which I can figure would be a TPA - DFW, or MIA-DEN. Boy, do I have too much time on my hands!!  
Bruce Leibowitz - Jackson, MS (KJAN) - Canon 50D/100-400L IS lens
 
Guest

RE: That Vapor Trail Jets Make..why Don't

Fri Nov 05, 1999 12:31 pm

The trail is behind the plane not right behind the engine...It forms wants the exhaust stream has slowed and cooled and that doesn't happen right outside of the engine. I've seen it twice on flights i've been on. I was in the very back of a United DC-8 and saw it when i looked back and I saw it when i looked back on a Virgin A340....check it out next time


 
Guest

RE: That Vapor Trail Jets Make..why Don't

Fri Nov 05, 1999 3:25 pm

i always notice the trail at the edge of the wings behind the tiny winglets of A300s i fly on. not behind the engines.
 
montenegro
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But Why The Military Jets Do Not Have It?

Fri Nov 05, 1999 6:24 pm

Another dumb question related to the topic, why the military jet's do not have the condensed line behind??


Thanks
 
TriStar
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Highly Visible Vapor Trail

Fri Nov 05, 1999 6:38 pm

Adding my two cents, I can say I saw a vapor trail coming from a small business jet at BRU yesterday, shortly after take-off. It was there all along, and *right* behind the aircraft.

By the way, it was a very clear and sunny day, yesterday. I never thought I'd see anything coming from the aircraft taking off - other than exhaust gases, in the worst case. ;-)

This small jet *was* in fact the *only* aircraft that had a vapor trail that I saw, during those couple of hours that I was there.

Since I don't have any explanation, I may just have added to the confusion... Sorry about that. ;-)

TriStar
 
Night Hawk
Posts: 264
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Jaemz

Sat Nov 06, 1999 1:12 am

Hi There

I believe what you are seeing there is the wingtip vortices produced by the winglets. Can someone correct me if Im wrong please :-)

Regards

Greg
 
Buff
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RE: That Vapor Trail Jets Make..why Don't

Sat Nov 06, 1999 4:20 am

I'm surprised nobody has figured this one out yet!

Has anyone seen a high flying jet from the ground leaving no vapour trail? What is another name for vapour trail? With reference to the rainbow sightings, what is essential for a rainbow to be seen?

The answer is: water vapour. A "vapour" trail is formed by condensate on particulate matter from the engines. Clouds form when the moisture in the air has something upon which to condense, OR if the moisture in the air is cooled enough (dewpoint) to produce condensation (clouds). Exhaust from an engine is similar to the idea of "cloud seeding" - when aircraft dispense that iodide mixture to precipitate the moisture in the air, usually to accelerate rainfall and preclude the occurence of violent thunderstorms (if memory serves me correctly).

Normally the higher altitudes are quite dry, but in the advance of a warm front, moisture occurs in varying degrees at those altitudes. When I asked earlier about planes leaving no condensation trails, there are times when they leaves a short trail that sublimates almost immediately - a sign that there is some moisture in the air; sometimes the trail lasts for an hour - a sign that there is a lot of moisture in the air.

So like the appearance of high cirrus cloud advents the approach of bad weather, so might the appearance of long standing condensation trails.

Waddya'all think about that?!

Note of interest: While in the arctic, it was a common occurence to see the turboprops landing with a stream of "smoke" coming from their exhausts. Our company got calls on more than one occasion suggesting an airplane was on fire! It was just so cold and damp that a condensation trail occured.

Note of interest #2: about 6 months ago, I was returning from Hamburg to Toronto at FL390, when out of the corner of my eye, I saw a condensation trail above us, but quite high, and moving a lot faster than our M0.80! Sure enough, BA1 checked in with Gander OCA as we watched this "speck" (we could not see the actual plane at the head of the trail) continue its trek at FL585/M2.0. A week later, in virtually the same spot, the same occurence, but just the radio call - no contrail. After talking with other pilots who have done the route many more times than I, this was a rare sighting.

Great question, by the way.
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: That Vapor Trail Jets Make..why Don't

Sat Nov 06, 1999 4:21 am

I'm surprised nobody has figured this one out yet!

Has anyone seen a high flying jet from the ground leaving no vapour trail? What is another name for vapour trail? With reference to the rainbow sightings, what is essential for a rainbow to be seen?

The answer is: water vapour. A "vapour" trail is formed by condensate on particulate matter from the engines. Clouds form when the moisture in the air has something upon which to condense, OR if the moisture in the air is cooled enough (dewpoint) to produce condensation (clouds). Exhaust from an engine is similar to the idea of "cloud seeding" - when aircraft dispense that iodide mixture to precipitate the moisture in the air, usually to accelerate rainfall and preclude the occurence of violent thunderstorms (if memory serves me correctly).

Normally the higher altitudes are quite dry, but in the advance of a warm front, moisture occurs in varying degrees at those altitudes. When I asked earlier about planes leaving no condensation trails, there are times when they leaves a short trail that sublimates almost immediately - a sign that there is some moisture in the air; sometimes the trail lasts for an hour - a sign that there is a lot of moisture in the air.

So like the appearance of high cirrus cloud advents the approach of bad weather, so might the appearance of long standing condensation trails.

Waddya'all think about that?!

Note of interest: While in the arctic, it was a common occurence to see the turboprops landing with a stream of "smoke" coming from their exhausts. Our company got calls on more than one occasion suggesting an airplane was on fire! It was just so cold and damp that a condensation trail occured.

Note of interest #2: about 6 months ago, I was returning from Hamburg to Toronto at FL390, when out of the corner of my eye, I saw a condensation trail above us, but quite high, and moving a lot faster than our M0.80! Sure enough, BA1 checked in with Gander OCA as we watched this "speck" (we could not see the actual plane at the head of the trail) continue its trek at FL585/M2.0. A week later, in virtually the same spot, the same occurence, but just the radio call - no contrail. After talking with other pilots who have done the route many more times than I, this was a rare sighting.

Great question, by the way.

Best Regards,

Buff
 
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Bruce
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Joined: Tue May 18, 1999 2:46 am

Wingtip Trails...

Sat Nov 06, 1999 4:21 am

I have also seen wingtip vortices while flying - coming off the wing of a 737 and a 757. Its a combination of hot humid weather, low altitude (landing), slower than cruise speed. Its condensation that is being blown off the wing. On the other hand the vapor trails from behind the jet in cruise is from the engine exhaust condensing. 2 different things.
Bruce Leibowitz - Jackson, MS (KJAN) - Canon 50D/100-400L IS lens
 
ATA757
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RE: That Vapor Trail Jets Make..why Don't

Sat Nov 06, 1999 4:53 am

I have never seen a vapor trail aboard an aircraft, but I always grab my binoculars and go outside to see if I can see what kind of plane it is. One day I was outside and I saw a 747 fly over with 4 well-identified streams, shortly after that I saw a Southwest 737(with the red belly) without vapot trails.

ATA757
 
Spence
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RE: That Vapor Trail Jets Make..why Don't

Sat Nov 06, 1999 10:18 am

I've seen BAe ATP's leave contrails at 6000 feet on a cold winter day.

Also, if you have seen WW2 footage, B-17's at 20,000 feet leave contrails.
 
Guest

Contrail & Vortex

Sat Nov 06, 1999 11:22 am

The correct name for the vapour trail when you see a jet at cruise altitude is called a CONTRAIL. They are the white lines you see being left behind an aircraft when the warm air from the engines condenses with the cold air at the high altitude or something along those lines.

When an aircraft is landing or taking off you often see vortex or vortices forming on the wings, winglets, etc. Have a look next time you are on final approach or if you are watching and aircraft land and you will see the vortex.

The concorde also makes great vortex off the wings as it takes off.

Please correct me if I am wrong because I am just a aviation enthusiest and don't know all the technical/scientific terms regarding contrail or vortex.

I just think they look great. Here in Sydney, Australia we get SQ285/286 over flying the Sydney VOR enroute from Auckland to Singapore/ Singapore to Auckland. Also if you live west of Sydney you would see alot of aircraft over flying the KAT NDB (Katoomba NDB), etc.

Regards,
Steven
 
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Bruce
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RE: Contrail & Vortex

Sun Nov 07, 1999 3:15 am

I think you're right, Kaplano1.

In addition to the vortices coming off wingtips & winglets they can also come off of the edges of the flaps when they are fully extended in landing configuration. Thats what i saw on a CO757. And the vortex was visible all the way until the plane was "over the numbers" right before touchdown!
Bruce Leibowitz - Jackson, MS (KJAN) - Canon 50D/100-400L IS lens
 
TriStar
Posts: 834
Joined: Sun Oct 24, 1999 9:03 pm

Highly Visible... Vortex?

Sun Nov 07, 1999 3:36 am

Since you guys obviously know more about this, I'd like to elaborate on the "vapor trail" I mentioned earlier. This one was very clearly coming from the *center* of the aircraft, and it was there right after take-off. No wingtips involved, no flaps involved.
This was a small businessjet with two engines mounted to the fuselage - comparable to the Canadair RJ, let's say.

So what did I see if it wasn't vortex, and it sure wasn't contrail?

TriStar

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