The point of the demonstration was to show that a vehicle can "sail" faster than the wind dead down wind (DDW)...and this one does. What stumped me was that the vehicle outruns the treadmill and that there was no visible sign of energy being added to the car to keep the propeller turning. Some of you undoubtedly saw the right things right away.

The propeller is pushing the vehicle forward against air that is not otherwise moving. The treadmill is pushing rearward on the cart, but the propeller is pushing harder against the static air and this imbalance is what allows the cart to move forward but still draw energy from the treadmill.

In a real world scenario with the cart moving on an open road in still air it would have an apparent wind and would have much less traction with the air ... so it would never be able to self sustain speed. However, put some wind at the back of it...and enough to get it to a certain speed, it's capable of pushing itself off the air and move faster downwind than the wind is blowing. This is exactly what the treadmill is demonstrating...that it can move faster than the still air.