# Why do inner contrails spread more than outer contrails?

Discussion in 'Contrails and Chemtrails' started by Clouds Givemethewillies, Jan 6, 2017.

1. ### Clouds GivemethewilliesActive 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. ### TrailspotterSenior 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 I have an unpublished video of a symmetrical evolution of A380 contrails, showing the above.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. ### TrailblazerModeratorStaff Member

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

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

• Agree x 1
4. ### Clouds GivemethewilliesActive Member

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

5. ### TrailblazerModeratorStaff 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 GivemethewilliesActive Member

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

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

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:

The exhaust contrails are injected into this sheet, and the spreading and curling of the sheet is what creates the initial shape:

8. ### Clouds GivemethewilliesActive Member

Why does the 'vortex sheet' spread the trails?

Last edited: Jan 6, 2017