Downwind car uses clever physics to produce movement against the wind by leveraging a lot of it against the ground.
So, he invented sailing?
The easiest part to understand is to just skip to the end where he breaks out the plastic wheels and the board.
Producing movement against the wind by leveraging a lot of it against the ground would be inventing sailing, yes; but that's not what he's doing -- he's producing movement with the wind, but faster than the wind. Turns out that takes a lot more cleverness. This contraption is not a land sailboat, pushed by the wind. It appears to actually be a perpetual motion machine, pushed by itself, but exploiting the wind to make up for its energy losses.
Sure, but straight downwind? Heeled over means the wind is from the side. Most of that "faster than the wind" is in the crosswind component of your velocity vector. You can't get the downwind component of the velocity vector to reach the wind speed that way -- if you did then your boat wouldn't heel over. Getting a Hobie Cat to sail with its downwind component faster than the wind would be a very neat trick.
Its more just the fact that using leverage and a force differential, something can be made to transfer the energy of the differential into a moving object.
The windmill powers a traction drive axle. The challenge is to produce a vehicle speed faster than the wind ground speed. Considering the drive train has to make two 90 degree turns, that's a tall order.
