The setup: two fans facing each other, distance around 1m. Both are turned on. In between them, place a simple paper plane and according to this video, it will fly.
https://www.youtube.com/watch?v=0ca9rxQkEiA
Is this really true? If yes, what is the physics behind it?
The fan that is blowing from behind seems to run at less RPM.
Intuitively, it seems entirely possible.
The "shape" of the air current blown out by both fans looks like a hollow cylinder, since the air is blown at high velocity near the ends of the blades, and lower velocity towards the center.
If you put two of these fans facing each other, the two "cylinders" of air current will collide with each other and create a "toroid" of positive pressure, in which you can suspend a light object, which is exactly what's observed in the video.
The "pressure toroid" is probably not stable (the slightest random motion of the object will lead to faster and faster motion out of the toroid), and this is also observed in the video.
I would assume that both fans should be spinning at equal RPM, if we want the point of equilibrium to be in the midpoint between the fans.
I disagree with @Dmitry's answer. Although in the border the air has more speed it still has velocity in the middle and when the two "cylinders" of air collide the would create turbulence that would make it impossible to create a toroid. And if you managed to get a toroid with positive pressure it should be the same above and below the plane (as it would be a cylinder it should be symmetric) and then there wouldn't be a net force to counter gravity.
Apart from that, the video has a low resolution, the plane always pivots around the same point (like hanging from a wire), it goes near one of the fans with a no perfect aligned axis which should make it shake a lot and "fly" away. So, in my opinion, the video is fake.
