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Old Nov 06, 2010, 12:27 AM
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Aerogance's Avatar
United States, CA, Ventura County
Joined Sep 2008
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Contrails, vortex and pressure "clouds"

There has been a bit of discussion recently behind the scenes about contrails and other condensation effects. We are trying to figure out why we do not see such effects with our large and fast DS planes. Why do we not see such effects? Is it theoretically possible to generate such effects with a high-speed model glider?

(To clarify, a contrail is the result of jet engine gasses at altitude. I couldn't find a better term so I am using it loosely to indicate any type of condensation effect)

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Old Nov 06, 2010, 02:07 AM
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Joined Jan 2007
4,957 Posts
That B-2 is going very fast, that 's caled vaping what happening is the surrounding air is compressing so much and it's compressing any h2o as well. It's not a contrail as it's only around the A/C.Now on the airliner photo the O/B flap's are creating a vortex. Contrail's are caused by a couple thing's like any moisture in the fuel tank's and various temperature's at different. Ever notice how they stop sometime's.
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Old Nov 06, 2010, 06:38 PM
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Wirral, (UK)
Joined Dec 2003
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Interesting, this thread has some good links and contributions on the subject:
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Old Nov 14, 2010, 11:47 AM
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Even more cool with propellers

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Old Nov 15, 2010, 03:34 AM
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New Zealand
Joined Aug 2007
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You don't have to be going that fast, as long as it's humid and the pressure differential is high enough

QANTAS A380 Amazing Wet LANDING 27L | LHR (0 min 57 sec)
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Old Nov 17, 2010, 11:16 PM
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NE Denver, CO
Joined Sep 2007
751 Posts
An engineer could tell you but I believe there is something about a large aircraft close to max L/D and the pressure differentials that leads to these kinds of vapor events. Watch airplanes around SEATAC and you will see it a lot. From what I remember seeing your more likely to view it during approach and landing when the wing is in a slow and steady configuration with maximum flap deployment and therefore close to L/D max. You do see it on takeoff right at rotation where occasionally the entire wing will break out into mist. After that I think that because the aircraft is generally continuously accelerating, moving to a smaller AOA, the phenomena is generally not seen as much. I've also seen this quite frequently during air shows when fighters do their high g demonstrations. I also think that the vortices created at the wingtips and sometimes around areas like the edge of the flaps further reduce pressures so that frequently you only get the vapor in these areas.
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