No explanation within the article. That was annoying.
Any ordinary sailboat sails faster than the wind when going roughly perpendicular to the wind direction. But this is apparently something different.
Any ordinary sailboat sails faster than the wind when going roughly perpendicular to the wind direction. But this is apparently something different.
An iceboat is a better example than a sailboat. They go substantially faster than the wind. They can do this because their sails are very efficient in terms of being able to sail a very low angles of attack and because they have very low friction WRT their motion.
According to this article, http://www.idniyra.org/articles/IceboatSailingPerformance.ht... the iceboat in question could sail 8 degrees off the wind and achieve a speed 7 times the wind speed.
Picture the propeller of the vehicle being a sail at a very small degree angle of attack (e.g. 8 degrees) while it is "sailing" in circles. Rather than pushing the vehicle body directly like with an iceboat, the energy is coupled to the wheels to drive the body at an arbitrary (but fixed for the vehicle in question) angle relative to the "sail" angle of attack.
While it is true that with only ratio changes the vehicle can be made to drive directly upwind, it would not be all that efficient as the airfoils currently on the vehicle are propeller blades and not turbine blades. A set of properly cambered blades will need to be fabricated and installed and then the test could be done.
One thing to remember is that when traveling upwind, the apparent wind over the chassis will be higher for any given multiple of wind speed. Upwind at 1x WS gives the same apparent wind as going 3x downwind.
The current 'record' for directly upwind is ~64% of wind speed.
http://www.gizmag.com/the-first-race-for-wind-powered-vehicl...
But any type of "sailing" that isn't directly downwind depends on the speed difference between the air and the surface (land or water). If you have this type of speed differential your vehicle speed is limited only by friction and sail size.
What they've done is applied this principle to direct-downwind sailing. While you can't get any energy from apparent wind in this situation, you can use the speed of the wind (and the vehicle) relative to the ground to extract some energy, which can then be used to increase the speed of the vehicle.
From an energy perspective, it's not unlike a having lever fixed to the ground at one end, with a sail in the middle, and the vehicle at the other end. In this situation the vehicle can clearly travel faster than the sail without assuming any kind of perpetual motion.
Contrary to popular believe, the spinning rotor is not a turbine (as you describe), but rather a garden variety prop which is driven by the wheels.