1. Clouds Givemethewillies

    Clouds Givemethewillies Active Member

    DLH440 36,000 ft. Airbus A380-841, wales uk.
    Anybody know why the inner trails spread so much more than the outer?

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    Last edited by a moderator: Jan 6, 2017
  2. Trailspotter

    Trailspotter Senior Member

    I think this is due to the wake vortices, which deform the inner trail differently than the outer ones. I have an unpublished video of a symmetrical evolution of A380 contrails, showing the above. I'll dig up and post at the weekend.
     
  3. Trailblazer

    Trailblazer Moderator Staff Member

    I think it's to do with the wing vortices.


    Source: https://www.youtube.com/watch?v=xl6iR7w7a_Q


    The outer trails get "folded back on themselves" by the vortex while the inner ones sink below and spread out a bit.

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    • Agree Agree x 1
  4. Clouds Givemethewillies

    Clouds Givemethewillies Active Member

    Nice video, but I am not entirely convinced that spinning holds things together..
     
  5. Trailblazer

    Trailblazer Moderator Staff Member

    Looking at the video the outer trails appear denser because they are folded into more of a tubular shape. You can also see that the more persistent trails are behind the outer engines, while the inner ones seem to dissipate more quickly.
     
  6. Clouds Givemethewillies

    Clouds Givemethewillies Active Member

    It might just be a greater mismatch between the exhaust velocity (relative to ground) and the surrounding air causing more turbulence/mixing.
     
  7. Mick West

    Mick West Administrator Staff Member

    The outer trails get twisted around by the wing vortices. The inner trails get spread by the vortex sheet.

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    The area of low pressure coming off the wing of a plane is not just two vortices, it's a sheet of low pressure that begins immediately to fold up at the ends. You can see this in that aerodynamic contrail:
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    The exhaust contrails are injected into this sheet, and the spreading and curling of the sheet is what creates the initial shape:
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  8. Clouds Givemethewillies

    Clouds Givemethewillies Active Member

    Why does the 'vortex sheet' spread the trails?
     
    Last edited: Jan 6, 2017
  9. Mick West

    Mick West Administrator Staff Member

    Initially the trails are just expand with mixing, but they continue to spread essentially because the sheet is spreading out.
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    It's kind of like the rolling up of the vortices is pulling the sheet from either side. Watch the development of the vortices at 3:15 here:

    Source: https://youtu.be/dfY5ZQDzC5s?t=3m15s
     
  10. Clouds Givemethewillies

    Clouds Givemethewillies Active Member

    I think you have explained how two trails can roll-up one, but I am not sure it explains why it is thicker within one plane's length. If it spreads horizontally it should thin vertically, and I have not seen this... yet.