- Tue Feb 12, 2008 11:16 am
#50459
Is it possible to build a vehicle that's powered only by the wind, and goes DIRECTLY downwind, FASTER than the wind, steady state?
xerxes wrote:Where does the extra energy come from?Who said there's "extra energy"?
boarini2003 wrote:I know you can sail faster than the wind speed, but not directly downwind.But can you make a downwind tack in which your downwind component is faster than the wind? If so, that would be a good start.
Rick M wrote:When I am on downwind in my hang glider I'm going faster than the wind. Of course gravity is adding the extra energy. So yes, you can do this. It just requires the use of altitude and gravity.Sorry Rick, you're not going "directly" downwind. You're losing altitude. Or if you're flying in lift there's a vertical wind component you're not matching.
sg wrote: The problem is, its an airfoil that stops generating lift when you approach downwind. So change the type of airfoil you are using Hint hint...Perhaps I'll make it harder for you sg, and require that it be done with typical sails moving in a typical manner.
sg wrote: Now think about the sail. Its a lift generating airfoil right? The problem is, its an airfoil that stops generating lift when you approach downwind. So change the type of airfoil you are using Hint hint...
Rick M wrote:When I am on downwind in my hang glider I'm going faster than the wind. Of course gravity is adding the extra energy. So yes, you can do this. It just requires the use of altitude and gravity.Of course that brings up another interesting HG question:
JDyer wrote:Check this out. I believe it is impossible and that this is a hoax but believe what ever you want....D'OH!!! You jumped the gun. That's not a hoax. That is one of several methods that can be done (the most practical one in fact). There are several more approaches as well.
Not sure if this is what you're thinking about, and you've got to be totally nuts to try it but:Hmmm.... Dynamic soarding requires a wind gradient. Good catch. I suspect you can beat the average wind vector directly downwind this way. You wouldn't be going directly downwind, but tacking in a sense. But with the right amount of trickery, that can probably be taken care of.
JDyer wrote:if you can go dwfttw with no other energy you just invented perpetual motionI wish it were so. Then I'd be filthy rich. It can in fact be done, and doesn't require perpetual motion. The secret is that we're extracting the real energy that arises from the difference in speed between the wind and water (or wind and ground, or wind and wind). That's why we need a "special" vehicle. A typical sailing vessel primarily extracts the energy arising out of the difference in speed between the wind and the vehicle (this is only strictly true when running directly downwind).
sg wrote:Exactly.. Not possible in steady wind... At least not sustainably.gerg wrote:So, yes, you could do it, but not sustainably.Nope, he said "steady state" in the original post.
E.g. you could store extra energy until you hit wind-speed, and then use it to accelerate past wind speed for a period of time. You could store this energy via fly-wheel (e.g. spinning propeller), or just momentum of going back/forth downwind. On the cross-wind sections you're storing energy (building up cross-wind momentum) and then releasing it as you turn back downwind. Average speed downwind (of downwind and crosswind legs) would never be greater than that of the wind.
gerg wrote:So, yes, you could do it, but not sustainably.Indeed you could. That's what steady state means.
E.g. you could store extra energy until you hit wind-speed, and then use it to accelerate past wind speed for a period of time. You could store this energy via fly-wheel (e.g. spinning propeller), or just momentum of going back/forth downwind. On the cross-wind sections you're storing energy (building up cross-wind momentum) and then releasing it as you turn back downwind.No storing of energy is needed, nor is it used in the video posted above.
Average speed downwind (of downwind and crosswind legs) would never be greater than that of the wind.Not only can the average downwind speed beat the windspeed directly downwind, the constant downwind speed can. The above video demonstrates one way to do that.