Counter-intuitive they say, that a wind-powered craft going straight downwind can go faster (no angled tacking/gybing) than the wind itself.
They built a three-wheeled land craft with a twin-bladed propeller/turbine, the Blackbird to test and prove their wind challenge. The bluff-body Blackbird first gets started by the wind from behind then the forward rolling wheels turn a geared sprocket that turns the propeller to push air rearward and provides added forward thrust! In their video you see the windsock showing the wind direction but the Blackbird's telltale streamer is waving backwards from an apparent headwind - it is moving faster the the wind.
Aerodynamicist Rick Cavallaro tweaked the Blackbird and achieved a top speed 2.86 times faster the the wind speed in 2010.
In 2012, they achieved a top speed 2.01 times faster the wind speed - headed UPWIND with a turbine rotating the opposite direction to transmit power to the wheels!
Blew my mind but it all made sense with the 'cylindrical Earth demonstration'