747 touch down smoke vortices

[applecrumble]

Hello PPrunes,

https://youtu.be/6btf7jRBL2A

Here is a video of a 747 touchdown.
I am just curious about the touch down rubber smoke vortices formed.
If you watch the point of touchdown, the smoke gets funnelled up to the tailplane and then makes a vortice.
The one on the right moves clockwise and the one on the left moves anti-clockwise. This is the opposite of the wing tip vortice directions.
My thought is that it's due to the tailplane somehow, as in the flare the low pressure would typically be on the underside as the elevator is deflected up?
Any ideas, just out of curiosity?

[mustafagander]

The tailplane is an inverted wing section.

[Slatye]

As mustafagander has said, the tailplane is an inverted wing.

For stability the centre of mass of the plane is ahead of the centre of lift of the main wing. Therefore the tailplane actually has to be pushing down to keep the plane level - in regular flight it would be providing a small downward force. Pushing down = higher pressure on the top than underneath = inverted vortices compared to a normal wing.

In the flare, it's pushing down more than usual - because of the low airspeed (more deflection needed for the same effect), because the main wing centre of lift has moved back (due to flaps being extended), and obviously because the pilot is trying to maintain a relatively high pitch attitude.

[applecrumble]

Cheers guys. As suspected :)

[Tinstaafl]

Those vortices aren't being caused by the tailplane. If they were from the tailplane they'd be at the outboard end of the L & R tailplane ie similarly to a wingtip vortex, but opposite rotation

These ones can be seen to occur inboard near the fuselage, just as the smoke passes the flap. At that point higher pressure air from below the flap flows around the the inboard tip to the lower pressure air above. Same as a wingtip vortex, but the wing 'tip' is the inboard end of the flap.

[applecrumble]

Interesting, I see your logic.