Vapour....trails that is

[JaXanim]

For several weeks now, our regional newspaper has published letters to the editor on the subject of aircraft vapour trails and how they are formed.

Many readers have submitted their observations about these fascinating phenomena and have put forward their hypotheses as to the physics involved. Many people have said that the trails are created by the jet engines. However, several writers have dismissed that idea. Instead, they assert with apparent authority, that the trails are caused by the precipitation of water vapour in low pressure vortices at the wingtips of planes.

Anyone care to comment on the physics of vapour trails?

Cheers,

JaX

[KennyR]

It's easy, not a matter of physics, but rather, chemistry.

Hydrocarbon + oxygen --> carbon dioxide + water

The water vapour comes from the combustion itself.

[blobrana]

i`ve a feeling that soot , or impurities in the exhaust, actually form the `seed` around which ice crystals can grow...
Due to the combination of vortexes and water produced by the engines (+ that in the air already)...

[bloodline]

JaXanim wrote:
For several weeks now, our regional newspaper has published letters to the editor on the subject of aircraft vapour trails and how they are formed.

Many readers have submitted their observations about these fascinating phenomena and have put forward their hypotheses as to the physics involved. Many people have said that the trails are created by the jet engines. However, several writers have dismissed that idea. Instead, they assert with apparent authority, that the trails are caused by the precipitation of water vapour in low pressure vortices at the wingtips of planes.

Anyone care to comment on the physics of vapour trails?

Cheers,

JaX

Actually it's both. The Vapour trails you see from large Jet airliners are from the exhaust water, heat, soot and NOX etc from the engines.

But at the wing tip you have a point where high pressure under the wing "leaks" up around the wing tip to the low pressure above the wing, commercial aeroplanes have Winglets (those little vertical fins on the wing tips) to top this, and as it leaks up it forms a vortex. These vortices heat and compress the air and it mixes with the cool air around it, water condenses out.. etc...

You will only really see a wintip vortex on a small military jet, usually when it in a high G turn and there is a lot of energy in the vortex.

[JaXanim]

Let's have some physics. Water from combustion, high-g flight, etc don't tell us much about the mechanism of vapour trail formation. What conditions prevail when trails are formed? Some days they do, some days they don't. Why?

JaX

[sumner7]

JaXanim wrote:
Let's have some physics. Water from combustion, high-g flight, etc don't tell us much about the mechanism of vapour trail formation. What conditions prevail when trails are formed? Some days they do, some days they don't. Why?

JaX

I don't know. :-(

[bloodline]

JaXanim wrote:
Let's have some physics. Water from combustion, high-g flight, etc don't tell us much about the mechanism of vapour trail formation. What conditions prevail when trails are formed? Some days they do, some days they don't. Why?

JaX

When conditions are right they will form :-)

[sumner7]

THANKS FOR THAT, BLOODLINE. :-)

[wytevett]

Vapor trails are a concerted effort by the government to spread a mind controlling substance over the population.

Resistance is futile...

:pissed:














 :-o

[JaXanim]

OK, now we're gettin' somewhere. But what's the physics? Surely, someone knows a bit about water vapour?

JaX

[KennyR]

I think the simple fact is that in cooler air the water vapour becomes supercooled upon leaving the engine. As it hits the jetstream formed by the plane, it drops out of vapour and forms liquid droplets - giving the misty white haze that you see from jets, and occassionally, scraped from the air by wingtips.

[QuikSanz]

Hi,
Well, it takes a certain amount of humidity. A wing flies by creating a VERY low pressure above the wing. expanding air cools, water vapor condenses in this low pressure area and becomes visable. if cold enough this vapor will freaze and stay suspended for a while.

Chris

[QuikSanz]

Hi,
Well, it takes a certain amount of humidity. A wing flies by creating a VERY low pressure above the wing. expanding air cools, water vapor condenses in this low pressure area and becomes visable. if cold enough this vapor will freaze and stay suspended for a while.

Chris
Darn double post

[JaXanim]

Watching films of high speed/high-g flight, it's clear that vapour precipitation from the upper side of the wing is quite transient. You can see a standing wave of fog at the lowest pressure zones. However, this re-evaporates towards the trailing edge, where the upper and lower wing pressures equilibrate. I can't see this being the mechanism for vapour trails. In any case, commercial flights do not create those conditions. It's usually seen in military aircraft. Concorde showed it when landing, but most civil flights do not.

Why do trails form on some days and not others? What's the physics?

JaX

[QuikSanz]

Hi,

Altitude and humidity are the big factors here.If cold enough in the low presure area, the vapor can freaze, the conditions must be just right. combination air temp, wet and dry bulb, which factors in humidity. also altitude and velocity have a role and also wing loading.

Chris