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theshack440

Wing Contrails

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Whenever I am on a 737 (of any kind), or for that matter, most planes that I have been on, when on approach (usually short final) the airplane produces contrails but not coming from the ends of the wings, rather from the middle of the wing, near the the flaps.Here is a video to describe what I mean

(goto about 2:20 for the best view of this). Looking at the pictures on facebook and others that have been posted, I just started to wonder when/why those different spots produce the same effect? The only fs addon that does this for me is my Quality Wings 757 and I don't know if any of the others should.ThanksRegards

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Those are called trailing vortices or wingtip vortices and they are caused by the wing generating lift. They can occur on any point of the wing where there is a sudden change in the wing's shape and also the amount of lift being created like such as flaps.

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I've experienced this today arriving with a 737 from SunExpress flight XQ872 in Stuttgart, slightly raining with overcast weather. Came from my vacation :D

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Strictly speaking, what you are referring to are 'vortex trails' and not 'contrails', which are something different. Vortices which you see trailing from the wingtips and flaps of aeroplanes are caused by moisture condensation occurring at the low pressure core of a vortex. Typically, this will be where the low pressure air from the upper surface of the wing meets the higher pressure air from the wing's underside, which is usually why such vortices form at the wingtip, where the low pressure air from underneath the wing spills over to the top surface.This is why the vortex trails appear to spiral. That spiral disturbed airflow is also why modern aeroplanes have winglets, because the winglet's function is to mix the two different air pressure masses above and below the wing more gradually so that the air is smoothed out and creates less aerodynamic drag, which improves the wing's efficiency. Since the flaps on an aeroplane create a lot of lift, and you need a pressure differential to have lift, you see the same thing happen around the flap canoes where there is often a small localised pressure differential as the air flows around the flap track mechanisms. The reason you don't always see it is because it is dependent on the atmospheric temperature and the amount of water present in the air mass, most typically when passing through low cloud cover.Engine contrails on the other hand are formed when moisture in the surrounding air latches onto microscopic particles of crap in the exhaust of a jet or prop aircraft flying at altitude, forming a trailing cloud as the air cools and the water vapour condenses into ice crystals. This is essentially the same as how natural clouds form, since in addition to requiring the moisture in the air to cool and condense into a cloud, the moisture that makes up a cloud will only form around a tiny particle of grit in the air because it needs that present as the additional catalyst for the process to commence (i.e. every ice crystal in a cloud has a tiny bit of grit in the middle of it). So it is the bits of crap in the exhaust of an aircraft, as well as the cooling gasses, which provide the catalyst for the contrail to form.Al

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Just to add, these particular vortices are being created from the higher angle of attack of the flaps. I like to think of flaps as airfoils on a bigger airfoil. In the 737/727/747/etc's case there are many airfoils in the flap system.Not mentioned above is why it happens. Very simply, the aerodynamic cooling caused by the low pressure on the top of the wing (the air's temperature drops when passed over the wing and accelerated [Thanks Bernoulli, google him]) brings the temperature of the air to dew point. This causes the air to saturate with what was before invisible water vapor.It's the same principle when temperature meets dew point and you get fog, but in this case it's caused aerodynamically on a small scale. With this in mind, it should only happen with certain weather conditions as Al mentioned.

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Thank you for your answers I understand the difference now. I wonder ifthe NGX will have this effect. :( Regards

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Chock,Your explanation of contrails didn't sound correct. I would think there is hardly any atmospheric vapour at these altitudes but tons of water vapour being pumped out by the engines burning the fuel and being quickly condensed by the very cold atmospheric temperature. Of course, I could be wrong.Dugald Walker.

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The vortex always exists, but the visible water vapor in the vortex is essentially a cloud. Clouds occur when the air is saturated with water vapor (i.e. relative humidity = 100%). You can reach saturation a few ways, including lowering the air pressure. Vortices form a low pressure core. Also watch the low pressure side of the wing (NB: the top, not the bottom as was suggested previously) when in any high angle of attack situations (fighter jets pulling g's, or even airliners establishing an initial climb).

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Chock,Your explanation of contrails didn't sound correct. I would think there is hardly any atmospheric vapour at these altitudes but tons of water vapour being pumped out by the engines burning the fuel and being quickly condensed by the very cold atmospheric temperature. Of course, I could be wrong.Dugald Walker.
You are both wrong!!! They're biological agents being spread by the new world order overlords! Wikipedia even says so...http://en.wikipedia.org/wiki/Chemtrail_conspiracy_theory

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Well, I'm glad we cleared that one up.Dugald Walker

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You are both wrong!!! They're biological agents being spread by the new world order overlords! Wikipedia even says so...http://en.wikipedia.org/wiki/Chemtrail_conspiracy_theory
That's the answer I was looking for. Thanks lol

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Dug, you are correct, a lot of what makes up a contrail is indeed moisture from the aircraft exhaust itself, but I decided to keep the explanation simple since that was really a bit of aside information in addition to talking about the vortices, which was the real topic. I really only mentioned contrails as the terminology sometimes gets confused with that of vortices.Personally, I think the 'chemtrails' fruitcakes have a much more fun explanation anyway, even if it is lunacy. Interestingly, one person who actually believes that rubbish is a stupid cousin of mine, who refuses to believe my explanations and gets annoyed at my laughter at the notion of a network of secret airbases and special airliners with all the logistics that would involve. I should point out that he is one sandwich short of a picnic, apparently from smoking too much exotic tobacco, to put it politely. He even showed me a picture of what was supposedly one such secretly equipped airliner - it was a picture of the refuelling drogue housing under the wing of a military tanker.Al

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I was wondering if this could be vapor from the fuel vent located under the wing. Looks like its coming from a point close to the vents position.

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Al,I realised afterwards that I might have misinterpreted your reference to "moisture in the surrounding air" so I was hoping you'd respond as you have. Thanks.Dugald Walker.

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Just to add, these particular vortices are being created from the higher angle of attack of the flaps. I like to think of flaps as airfoils on a bigger airfoil. In the 737/727/747/etc's case there are many airfoils in the flap system.Not mentioned above is why it happens. Very simply, the aerodynamic cooling caused by the low pressure on the top of the wing (the air's temperature drops when passed over the wing and accelerated [Thanks Bernoulli, google him]) brings the temperature of the air to dew point. This causes the air to saturate with what was before invisible water vapor.It's the same principle when temperature meets dew point and you get fog, but in this case it's caused aerodynamically on a small scale. With this in mind, it should only happen with certain weather conditions as Al mentioned.
The vortices are due to the greater lift generated over the flap sections, not necessarily any greater angle of attack (the angle of attack of the wing is not affected by flap angle). It's analagous to the wing tip vortex, as you say yourself the flap is a separate aerofoil, so the flap edge is another wing tip with a vortex attached.While it's true the upper wing surface has slightly lower air pressure that isn't where the condensation starts. There is much lower pressure at the centre of the vortex itself, and that is why they become visible if there is moisture in the air. If you watch the water swirling out of a washbasin plug-hole you will see the centre of the vortex created is much lower than the surrounding water surface, indicating a water lower pressure in the centre.Kevin

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The vortices are due to the greater lift generated over the flap sections, not necessarily any greater angle of attack (the angle of attack of the wing is not affected by flap angle). It's analagous to the wing tip vortex, as you say yourself the flap is a separate aerofoil, so the flap edge is another wing tip with a vortex attached.While it's true the upper wing surface has slightly lower air pressure that isn't where the condensation starts. There is much lower pressure at the centre of the vortex itself, and that is why they become visible if there is moisture in the air. If you watch the water swirling out of a washbasin plug-hole you will see the centre of the vortex created is much lower than the surrounding water surface, indicating a water lower pressure in the centre.Kevin
Well this seems a bit pedantic. The flap is at a higher angle of attack in this case(or any case) and therefore ultimately does produce more lift than the wing/airfoil. I was speaking in terms of the pictured 737 the OP mentioned.The second part I can't argue with, but again I think my post summed it up reasonably well. :(

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Well this seems a bit pedantic. The flap is at a higher angle of attack in this case(or any case) and therefore ultimately does produce more lift than the wing/airfoil. I was speaking in terms of the pictured 737 the OP mentioned.The second part I can't argue with, but again I think my post summed it up reasonably well. :(
It may be pedantic but if you use terms like angle of attack they should be used properly. Deflecting a TE flap increases wing camber (and so lift), it doesn't change AOA.The second part of your post mentioned Bernoulli (whose famous equation does not explain the acceleration of air over an aerofoil). You also talked about air reaching the dew point on the wing upper surface (it doesn't, except under extreme conditions behind a shock wave), and didn't explain why there's condensation in the vortex. Apart from that you did OK. :( Kevin

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It may be pedantic but if you use terms like angle of attack they should be used properly. Deflecting a TE flap increases wing camber (and so lift), it doesn't change AOA.
Yes, the wings camber is increased. BUT when thinking of the flap as a separate airfoil (I mentioned that, didn't I?) it is at a higher angle of attack relative to the wing it is attached to. You're arguing nomenclature to a point where it confuses less knowledgeable people (the folks I was addressing).I'm not arguing your accuracy but rather that there's more than one way to explain the phenomenon.

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Huh?The condensation is the result of reduced pressure over the top of the wing - nothing else! Same reason you get condensation in the fuselage when it undergoes rapid decompression - the air pressure drops, the air temperature drops (this is the actual mechanism) and the water can no longer be supported, so it condensates out and we see it as a white cloud. It soon dissipates back into the air, or falls as rain.It is related to AoA because as you increase the AoA, you are asking the wing to produce more lift, so there is a lower pressure over the top of the wing, and the effect is more likely (which is why it is most pronounced during takeoff and landing, but particularly landing).It has nothing to do with being only "extreme conditions behind a shock wave" or anything like it. The reason you get the white cloud behind the shockwave is the exact same reason - pressure drop that results in cooler air and the water condensates out.The flap is not a separate airfoil - it is part of the same airfoil - the wing! Extending flaps increases the wing area (not always), and the camber. It is camber that gives lift. When you extend the flaps the aircraft pitches down. I'll let you research why. Hint: center of pressure.Best regards,Robin.

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The flap is not a separate airfoil - it is part of the same airfoil - the wing! Extending flaps increases the wing area (not always), and the camber. It is camber that gives lift. When you extend the flaps the aircraft pitches down. I'll let you research why. Hint: center of pressure.
"Huh?" :( We don't have to get rude here. But since you went there, I've taken 3 courses of aerodynamics. What you're saying is true. But you're too near sighted...Have you looked at a flap on modern airliners lately? It's technically an airfoil in itself in some cases. In particular this 737. I can assure you I know how flaps work. I digress.EDIT: No I don't. The cross sections speak for themselves. How do you think the flaps increase camber without severely separating air from the top of the airfoil? Think SLOTTED flaps: http://www.rcuniverse.com/forum/m_786417/anchors_786417/mpage_1/key_/anchor/tm.htm#786417 HINT: Note how the flaps and the slots between them form what looks like an airfoil(s)... :( "Coanda effect" (Just poking fun at the attitude of your post :( )*Condescending mode off*

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I see George (Falcon999) has his official Beta Banner... I wonder :( :(

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I see George (Falcon999) has his official Beta Banner... I wonder :( :(
I noticed that too! Lucky guy if it's true!

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I see George (Falcon999) has his official Beta Banner... I wonder :( :(
I am hoping that's where production is at!!

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I see George (Falcon999) has his official Beta Banner... I wonder :( :(
Look again... :(

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Look again... :(
Are you teasing me George :( :(

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