It’s been years since I worked in Fluid Dynamics, but I still love a good fluids paper; especially a good unsteady flow solution. Check out this one which was just highlighted on ScienceNow. You can find the original paper at Jun Zhang’s website. The basic idea is that you place a little pyramid with an open bottom in an air field which is oscillating up and down. When the air goes up, it pushes hard against the wide open bottom of the pyramid. When the air goes down, it flows smoothly around the pointy top. The result is that the pyramid will float. I especially love this Schlieren video of the vortices forming off the edges of the pyramid.
But that’s not the coolest part. You can adjust things so that the pyramid is stable. If you tip it to one side, it’ll right itself. The interesting bit is that to get this behavior, you need to make the whole thing top heavy. That seems counter intuitive doesn’t it? The geometry of the thing sort of seems like the exact opposite of the dihedral effect.
OK, here’s a DIY project for you. Can you figure out how to cobble together a flying machine using a paper (or carbon fiber) pyramid and something like the motor from a cell phone vibrator? It seems unlikely because the effect probably isn’t going to scale up far enough to carry that much weight. In the experiment, they’re moving the air using a big subwoofer below the pyramid.