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No explanation within the article. That was annoying. Any ordinary sailboat sails faster than the wind when going roughly perpendicular to the wind direction.

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.

lotharbot 16y ago
It's easy to get the thing moving at the same speed as the wind. The key is transforming some of the energy that went into bringing it up to that speed into the propeller. The propeller is driven by the wheels, so once they get moving, the propeller starts producing thrust, and the craft begins moving faster than the wind.
- naz 16y ago
  The propeller isn't producing thrust, it is acting as a sail in the wind and transferring that power to the drive shaft
  - ThinAirDesigns 16y ago
    Actually naz, that is one of the key and common misconceptions of this vehicle -- the propeller IS producing thrust. 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.
    - deleted 16y ago
      [deleted]
frankus 16y ago
When you're traveling downwind at the wind speed, like the article says, there's no more apparent wind that you can harness to go any faster. That much is uncontroversial. 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.
gvb 16y ago
No, it is the same thing. What is counter-intuitive is that the body of the car is going directly downwind. The thing is, the sails of the car (the propeller) are not going directly downwind, they have an angle of attack relative to the wind because they are angled relative to the car body. Ignore the car body and draw a propeller blade, the actual wind, and the apparent wind WRT the blade. 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.html 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.
- herdrick 16y ago
  Oh.... Wow. That's awesome. Thank you!
- electromagnetic 16y ago
  Could you shed light on how well this vehicle would perform 'sailing into the wind' as it were? (Obviously with modifications to its transmission)
  - ThinAirDesigns 16y ago
    It is likely that the team from San Jose State University will use this vehicle to answer that very question during the next academic year, but it will involve a bit more work than just transmission changes. 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-vehicles/9953/ http://www.gizmag.com/the-first-race-for-wind-powered-vehicl...

lotharbot 16y ago

It's easy to get the thing moving at the same speed as the wind. The key is transforming some of the energy that went into bringing it up to that speed into the propeller. The propeller is driven by the wheels, so once they get moving, the propeller starts producing thrust, and the craft begins moving faster than the wind.

naz 16y ago
The propeller isn't producing thrust, it is acting as a sail in the wind and transferring that power to the drive shaft
- ThinAirDesigns 16y ago
  Actually naz, that is one of the key and common misconceptions of this vehicle -- the propeller IS producing thrust. 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.
  - deleted 16y ago
    [deleted]

frankus 16y ago

When you're traveling downwind at the wind speed, like the article says, there's no more apparent wind that you can harness to go any faster. That much is uncontroversial. 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.

gvb 16y ago

No, it is the same thing. What is counter-intuitive is that the body of the car is going directly downwind. The thing is, the sails of the car (the propeller) are not going directly downwind, they have an angle of attack relative to the wind because they are angled relative to the car body. Ignore the car body and draw a propeller blade, the actual wind, and the apparent wind WRT the blade. 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.html 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.

herdrick 16y ago
Oh.... Wow. That's awesome. Thank you!
electromagnetic 16y ago
Could you shed light on how well this vehicle would perform 'sailing into the wind' as it were? (Obviously with modifications to its transmission)
- ThinAirDesigns 16y ago
  It is likely that the team from San Jose State University will use this vehicle to answer that very question during the next academic year, but it will involve a bit more work than just transmission changes. 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-vehicles/9953/ http://www.gizmag.com/the-first-race-for-wind-powered-vehicl...