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Wind-Powered Car Travels Downwind Faster Than The Wind
- te_platt 16y agoFrom the article: “I thought people would say, ‘That’s cool,’ but they didn’t. They said, ‘Wow, you’re an idiot.'" If I had a dollar for every time I heard that ...
- CapitalistCartr 16y agoI have learned to quickly sort people out by telling them about whatever is the most improbable project I'm fiddling with at the moment. The project is unimportant; what is telling is their response. I get one of three responses, no interest, that's cool, or you're an idiot. Quickly tells me whether they're worth further time or not.
- DrSprout 16y agoWhich ones do you keep around? The yes men, the indifferent, or the naysayers?
- stcredzero 16y agoYes, but in such a system, one would also probably lose a dollar every time they said that mistakenly. In a way, we are in such a system. This is what makes startups so dandy!
- mtinkerhess 16y agoIt seems like they're using the propeller as a combination flywheel / accelerator. If you're allowed to store energy as rotational momentum, why not in a battery?
- ThinAirDesigns 16y agoThere is no stored energy involved in the acceleration -- it is all powered by slowing the air down relative to the surface(as all wind powered craft do).
- cma 16y agoGeneral explanation of how this is possible: http://terrytao.wordpress.com/2009/03/23/sailing-into-the-wind-or-faster-than-the-wind/ http://terrytao.wordpress.com/2009/03/23/sailing-into-the-wi...
- Groxx 16y agoI remember that one. And this comment: The author does a good job of taking a complicated subject and explaining in such a way that it becomes extra extra complicated. [ http://news.ycombinator.com/item?id=1323665 http://news.ycombinator.com/item?id=1323665 ] which still seems accurate to me.
- herdrick 16y agoNo 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 agoIt'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 agoThe propeller isn't producing thrust, it is acting as a sail in the wind and transferring that power to the drive shaft
- ThinAirDesigns 16y agoActually 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 agoWhen 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.
- stcredzero 16y agoA good visual analogy: http://www.youtube.com/watch?v=E7vcQcIaWSQ&feature=related http://www.youtube.com/watch?v=E7vcQcIaWSQ&feature=relat...
- mey 16y agohttp://www.youtube.com/watch#!v=JJVsoLcdGMY&feature=related http://www.youtube.com/watch#!v=JJVsoLcdGMY&feature=rela...
- Groxx 16y agoI can see why it's a hard thing to come up with, but I'm puzzled as to people's problem accepting it. The blades create backward-thrust, pushing against the wind, accelerating the car, creating more thrust, pushing harder against the wind, etc. It stops a seemingly-endless increase when you hit the break-even point. The reason it goes faster is because, when it finally catches up to the speed of the wind (which is obviously possible), the blades are already spinning, thrusting the car forward beyond just the wind speed. If they weren't spinning at all, 1x wind speed would be the max, fairly easily approached (though not achieved). This video is particularly telling of this effect: http://www.youtube.com/watch?v=dgHBDESd38M&feature=related http://www.youtube.com/watch?v=dgHBDESd38M&feature=relat...
- torial 16y agoThere is another video from the same series that is more impressive, with the treadmill going fast: http://www.youtube.com/watch?v=7xL8gRJ5F6k&feature=related http://www.youtube.com/watch?v=7xL8gRJ5F6k&feature=relat...
- barmstrong 16y agoIn this case you could surpass it momentarily but the average speed of the vehicle would still never go faster than the wind speed, like one of the posters mentioned above.
- Groxx 16y agoBoth the article and the linked video would imply the exact opposite. And I see no such post. The propeller generates thrust, and both result in faster-than-wind movement. It's not a momentary burst of acceleration - the propeller spins relative to your wheels. If it's going fast enough to burst you, it will stay at that burst speed because its speed is tied to the craft's.
- orblivion 16y agoWhat's hard to intuitively understand is that it's a positive feedback loop after reaching wind speed, rather than negative. EDIT: Also that video is hilarious.
- deleted 16y ago[deleted]
- Semiapies 16y ago" Yes, it’s possible that SJSU, Google, and Joby Energy are all being hoaxed here. What do you think?" Could be, especially considering the video linked on this page to the treadmill demonstration. I'd like to see this "blackbird" actually "spread its wings" on more than a short sprint, after a thorough inspection. I suspect its average speed would end up below that of the wind.
- ThinAirDesigns 16y ago@Semiapies: A: if the vehicle can accelerate under the power of the wind to several multiples of the windspeed, what would suddenly make it slow down? Are you suspecting stored energy is being used somehow? B: How long of a run would convince you?
- Semiapies 16y agoA) It is admittedly using stored energy - the propellers are spun by the wheels, which are spinning due to the vehicle's forward motion. I suspect that they may have come up with a clever trick to manage a burst of speed before slowing down back below the speed of the wind. The treadmill demo video shows the model speeding up, then slowing down. B) I'm not sure how long the temporary burst of speed would last on a larger model; I'd prefer an engineer coming up with that. My WAG would have that period be rather less than an hour. I'm reminded of perpetual motion scams, especially by someone creating a login to start defending them and demanding what would convince someone. Trying to put skeptics on the defensive and trying to force them to disprove the remarkable claim put forth is a classic shtick. And I think the perpetual motion bit is fair - if we take the treadmill video on its face, this is a vehicle that, in still air, would go uphill under its own lack of power - and even accelerate for a while after an initial push. This has nothing to do with apparent wind velocity.
- ThinAirDesigns 16y ago@Semiapies: >It is admittedly using stored energy - the propellers are spun by the wheels, which are spinning due to the vehicle's forward motion. I'm sorry, but by that logic your car is also "admittedly using stored energy" to accelerate (as the wheels and other parts are turning due to the vehicles forward motion) and we know this isn't the case. Just because there exists stored energy in a system, doesn't mean that this stored energy is being used and in fact, as the vehicle accelerates, more energy is stored rather than energy being used. In the case of this vehicle, it can't be using the stored energy in the propeller without it turning progressively slower and the videos show the propeller simply continuing to spin faster as the vehicle accelerates. The gearing between the prop and the wheels is fixed ... there's no way to slow the prop down and speed the wheels up -- that would require a variable ratio between the two. Semiapies: <<Trying to put skeptics on the defensive and trying to force them to disprove the remarkable claim put forth is a classic shtick. I don't recall attempting to force you to disprove anything. I simply asked period of time would convince you. You can call it "shtick" if you like -- I call it attempting to learn your position.
- pontifier 16y agoSo, the propeller creates a virtual surface for the wind to act on. The speed of this surface is slower than the vehicle. It sounds like perhaps the blades would spin at a rate such that they would slice cleanly through the air without moving it forward or backward when the vehicle is moving in the absence of wind.
- wdewind 16y agoThis seems to be the same issue as horsepower: If the engine has horsepower doesn't that mean it can only go as fast as horses do? Of course not, that's the intuitive "apples and oranges" type mistake, the two numbers aren't really correlated like that. It's like leaving your foot on the gas at the same level will keep it accelerating until it hits the most it can do with that much gas.
- alex_h 16y agoA helpful way to understand sailing into the wind (for me at least) is to think of a stationary wind turbine producing eg. 2MW of power. Now if you were to mount that turbine on the roof of your electric car, that 2MW is more than enough to power the car at great speed in a windward direction. This seems to be the same concept except with a pure mechanical linkage.
- eru 16y agoNot really. Here the propeller isn't generating the power, but doing the acceleration.
- tocomment 16y agoWhen I follow this link in my iPhone I get redirected to wireds mobile site. Is anyone else experiencing this? It really grinds my gears when websites do this! Grrr