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Strange contrail south of London today

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Strange contrail south of London today

Old 20th Nov 2005, 17:08
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Could this be the result of wave lift as used by glider pilots? I'm told that wave lift is very smooth and can sometimes be found in the east of england. I didn't see the trails mentioned.
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Old 20th Nov 2005, 17:12
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<<Plus there is separation provided of a few miles in front, behind and to the side of the aircraft. Where this seperation cannot be maintained, different altitudes are flown by the aircraft.>>

I think most of us are aware of that but my point is that no controller at London Control is going to watch an aircraft weave about in that manner without doing something. Aeroplanes simply do not weave about the sky in a random fashion in busy airspace. They will either fly recognised tracks on standard routes or they will be on radar headings. In either case they will fly virtually straight lines. Even the slightest deviation would be observed on radar and queried. An aircraft flying the sort of pattern described here in the current security climate would raise considerable concern.
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Old 20th Nov 2005, 19:46
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There's a possible but perhaps far-fetched answer to my original question here:

http://vehicle.me.berkeley.edu/Publi...s_ains2003.pdf

Very thin trail, course roughly aligned with the M3....

Time to wait for the men in black to arrive!
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Old 20th Nov 2005, 20:19
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HD-with reference to your comment I am begining to think it is the contrail and not the aircraftproducing this phenomenum(?). Although from where I saw it the aircraft had passed me I dont recall the actual head of the trail diverging, and the apparent angles to either side of track were I am sure large enought o have been noticed on radar.As yousay that was a busy time and the controller wouldnt let one aircraft in a crowded sky zig zag along like it appeared to.

One idea that comes to mind that might fit the picture is say a two or three engine biz jet -tail engines and thus from the ground only one contrail.

A previous poster poster described how the engines could perhaps 'hunt' a bit trying to maintain Mach number -perhaps it was very high and it was unsually cold I am sure -and that produced the blobby -uneven trail effect .

Would it be possible for the occasional extra jet efflux from say one engine to deflect the contrails away to the side slightly where after a while the tip vortices spin them back inwards so that the actual trail is a sort of spiral-the sircraft of course runs pretty much straight and the spirals from the ground looks like a low amplitude sine wave.
Anyway thats my little hypothesis based upon whats been posted by others- any takers?
PB
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Old 20th Nov 2005, 21:25
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How about instead of poor navigational performance it could be the opposite? Given the accuracy of modern equipment, were it that calm and still aloft, it's not impossible a 2nd aircraft may have made good the same track and height I imagine - would it in that case be possible that it's the result of couple of contrails interacting in this interesting manner?
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Old 20th Nov 2005, 23:21
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Cool Unusual Contrails....

Hello people,
Was out walking on the marshes of the Ribble estuary in Lancashire on saturday afternoon and noticed the most number of contrails I've ever seen in a single day. They were almost all SE-NW in orientation with the bulk of traffic consisting of the usual 'Trannies' heading for the NAT Track system but 2 were distinctive and I'm not talking 'Donuts on a rope'.
They were both 'U' shaped, about 20 miles apart and untouched by any other trails. One looked as though it was originally southbound along UA25 before executing a '180', the other was exactly the opposite on airway UA1.
I've often seen unusually shaped 'trails off the nearby coast due to the Irish Sea Air Refuelling Area and stuff on test from BAe Warton but never anything like this. It resembled a holding pattern cut in half.
Any info. gratefully received.

Yours faithfully

Confused of Preston.


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Old 20th Nov 2005, 23:29
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I'm told that aircraft sometimes 'tack' like this to lose a little time when approaching a busy hold. Could it be as simple as that?

Last edited by derekl; 20th Nov 2005 at 23:54.
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Old 20th Nov 2005, 23:57
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Meteor ? Leonid not Gloster.
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Old 21st Nov 2005, 06:51
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I don't think so, Paper Tiger, although there have certainly been reports of meteors following erratic courses. What I saw was too regular, both in sinuosity, speed and height to have been caused by the Leonid variety careering into the atmosphere.

Oh, and I'm afraid the very precise single trail ruled out the Gloster version, although I suppose with one engine out.......
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Old 21st Nov 2005, 07:36
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derekl.. I don't think so - once they get close to holding areas they're under pretty tight radar control. In any event, this aircraft was very high and if it needed to lose time a reduction in speed would have been the technique. In extreme cases it would simply enter a holding pattern.

If we're not going to get a definite answer here's another one for the pot - couple of years ago I saw a satellite image of the North Sea which clearly showed a long, spiral vapour trail - just as if a fast jet had flown some distance doing barrel rolls. Never had that fully explained but, of course, "Aurora" featured in suggestions!
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Old 21st Nov 2005, 13:01
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Have just seen a shape like that originally discussed; I've seen them before and it was just a matter of time, but so nice and promptly ...... !

Must have been directly overhead Heathrow, at crusing altitude, headed southwest, about 1230 local today. And as before when I have noticed this, as it was laid out from the aircraft it was perfectly normal and straight, but then got distorted into the discussed sinusoidal shape. It then vapourised quite quickly after doing that, breaking up into separate sections like bananas in line astern first.

So it seems it is not a feature of the aircraft, but of the air currents afterwards.
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Old 21st Nov 2005, 13:43
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Here's another theory to add to the pot: perhaps it was an AWACS (except I would have expected more obvious multiple contrails and what I saw looked like a single trail).
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Old 21st Nov 2005, 14:03
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Sounds very much like Contrail seperation as a result of the vortex wake of the aircraft meeting the trail. Vortex wake in my basic understanding will drop behind an aircraft. So perhaps the current conditions will allow this interaction to occur...

any use?
81
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Old 21st Nov 2005, 14:47
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It sounds very much like vortex interaction. I think this navigational and hunting stuff are red herrings.

I have seen contrails break up into sinusoidal patterns before - usually not very long lived. If you fly up close to a contrail you see two distinct sections. The first is a tight spiral and the second a diffuse apparently structureless haze. They often separate, with the distinct spiral dropping away below the haze. Two engines produce two spirals and if these interact you can get some very interesting shapes formed (like the pic above).

I doubt if it is to do with the cold either - more likely the airflow up high being smooth and slow.

Look carefully into the water behind an oar, or a vertical structure stood in water. At certain flow rates, vortices are shed from the tip of the blade and interact downstream in a vortex street. These often form sinusoidal patterns which then break up further downstream. Higher velocities give more random shapes and beyond that it all blends into turbulence. Very slow velocities will provide a more stable downstream flow.

Contrails are a bit like the oar above, but in three dimensions (water in the above example is 2 dimensional because of the surface). The difference in viscosity of the fluid (air) makes the velocities very different for the same effects in water.
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Old 21st Nov 2005, 15:50
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I've had the chance to study a few more trails above SW London today and, whilst several of them exhibited distortion that might be considered wave-like, it was relatively random, short-lived and accompanied by a general diffucion of the trail itself. As such it is easy to see how these could have been caused by wake vortex or air current effects.

However none of these observations, or indeed those proposed by others above, coincide with the essential characteristics of what I and others observed on Saturday, namely:

* a single trail that remained extremely thin and well defined prior to evaporation
* a regular sine pattern that remained stable and consistent behind the aircraft for perhaps 20-30 miles
* a consistent wavelength and amplitude of the sinusoidal curve
* a pattern that was not replicated by any of the many other trails in the same area and at the same time that day, which generally decayed through slow and stable diffusion prior to evaporation.

I don't think we yet have the answer!
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