Google-Backed Wind-Powered Car Goes Faster Than the Wind 393
sterlingda writes "A wind-powered car has been clocked in the US traveling downwind 2.85 times faster than the 13.5 mph wind. The definitive research by Rick Cavallaro of FasterThanTheWind.org is being funded by Google and Joby Energy. The run should now settle the DWFTTW (downwind faster than the wind) debate that has been raging for some time on the Internet about whether or not such a feat was possible."
Debate? (Score:5, Interesting)
Sailing vessels can go faster than the wind, why shouldn't a car be able to?
Re:Debate? (Score:5, Insightful)
Sailing vessels only go faster than the wind when they travel with the wind coming from the side. No matter how fast the vessel goes, the wind keeps blowing from the side and delivering energy to the vehicle. When you try to go faster than the wind in the direction of the wind, the relative motion to the air goes down to zero and then you start going against a head wind. Obviously the wind can not be the propelling force beyond the point where you go as fast as the wind in the conventional sailing sense, because at that speed there is no wind (motion is relative). The described device uses the sailing force to accelerate and then produces its own faster wind, so to speak, by driving a propeller via a transmission from the wheels.
Re:Debate? (Score:4, Insightful)
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All the energy there comes from the wind. The wheels act as keel, providing resistance against the surface. The propeller (rotating sail, really) is what tacks to the side (by rotating...but it doesn't make any difference from "to the side" as far as wind is concerned), so the whole vehicle doesn't have to and can move "forward", with the wind.
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You understand 180 degrees wrongly.
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Sailing vessels can go faster than the wind ACROSS the wind. They use a keel to do this. But the keel does nothing (except drag) when they travel directly downwind. They can't go faster than the wind in the direction of the wind. If you think it through what these guys are doing is pretty clever, making the car travel faster than the wind providing it's power in the direction the wind is blowing is cool.
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But sailing vessels can't go faster than the wind directly downwind, this car does.
FTFA:
Re:Debate? (Score:5, Interesting)
Look at the experiment I would say sure its possible because there is no resistance. As they say they can't do this on a gym floor, but a tread mill.
As a mechanical engineer who studied dynamics I would say the reason is because the resistance that is normally hit due to acceleration or keeping the thing moving is not present. Thus this thing could accelerate faster than the wind.
What I would find interesting is what are they exploiting in specific? As they say, is there some neato resistance, aero-dynamic trick that nobody has yet thought of?
It reminds me of the ram jet that below a certain speed is useless. YET at higher speeds it becomes more effective than a regular jet.
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Sure they can [wikipedia.org]. The key is to couple the wind power to an mechanism providing thrust, like the wheels in this scenario, or a propeller for a boat.
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The wheels don't provide thrust in this example. The wheels turn the propellor, not the other way around.
DWFTTW--Except where the car couples to the wind! (Score:4, Interesting)
Read carefully the excerpt in the parent's post.
This is a demonstration of some basic physics and geometry, but it is not "DWFTTW" at the point where the car actually couples to the wind.
A science project where the participants and the public learn some interesting physics and engineering principles--or are entertained by watching--this is a very good thing. It gets the public (if you can call /. the public) talking about science.
We need more demonstrations like this--no, what we really need is another Sputnik!
Be careful.
People have been known to use the counterintuitive nature of the physical world to argue they have discovered a new way to get rich quick--and you can get in on it if you want! We like to think were too hip for perpetual motion, but a lot of folks will still hand over real green (dollars) for bogus green (environmental scams). Don't you care about the environment?
So, what is the "magic" here, and what's the physics?
The fundamental error in the statement "DWFTTW" is the fallacy of dual definitions.
This is kind of cheating--a really good science demonstrator doesn't actually lie to you; they just show you something that exposes your misconceptions. Either way, the point is to get you to say "I see it, but it's impossible!". Then you are more ready to learn some science. (or maybe to invest in a free-energy scam).
DWFTTW is simply the koan. It actually means nothing--just gets us ready to study and learn something new.
When the experimenters say "faster than the wind", they are referring to motion of the bulk (center of mass) of the car.
BUT--the wind couples to a very specific portion of the car, which has a completely different (and somewhat more complex) velocity than the center of mass of the car.
The propeller--or more specifically, the surface of the propeller that pushes against the wind.
And the part of the car that connects to the wind NOT traveling "DWFTTW".
Read the article and look at the pictures--this is why they took such care to "streamline" the car. The rest of the car (except the propeller) is built so that it presents the very minimum cross-section (drag coefficient), and is effectively transparent to the wind. So, it is the part of the propeller that pushes against the wind that matters when we try to analyze the downwind motion.
So--what is the the portion of the propeller's motion that is "downwind"?
You could say "parallel to the direction of the wind" if you like, but for this case, "downwind" works fine.
A little math (just two equations, I promise--and only to describe the geometry!):
The propeller surface has a pitch angle, theta, from zero (parallel to the plane in which the propeller rotates) to 90 degrees (parallel to the propeller shaft), and it spins at some angular velocity w (omega).
At any instant, the linear velocity, v, of a point a distance r from the shaft of the propeller is simply v=Rw
And the perpendicular (downwind) component is just v(p)=v*sin(theta).
By controlling the diameter of the propeller, the pitch angle, and the rotational speed, the experimenters cause the relevant part of the car--that is, that portion of the car that connects to the wind!--to travel downwind much slower than the wind.
But, I hear you say "We keep talking about "slower" than the wind, and cars move fast.".
This seems strange because we started with the reference frame of the road, and we compare the velocity of the car and the air. The comparative term "Faster" describes the downwind velocity of the car, which, for consistency, we continue to reference.
In Newtonian physics, there are no preferred reference frames. This is true in other cases as well, but they are not significant at the speeds this car is traveling. This means we are permitted to say "the car is traveling slower than the wind" or "the wind is traveling faster than the car" and they mean EXACTLY the same thing.
Recall again that the pertinent part of the car is that part
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they can't go downwind faster than the wind.
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sailing vessels cannot go faster than the wind when sailing directly downwind.
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Sailing vessels can go faster than the wind, why shouldn't a car be able to?
Sail boats can sail faster than the wind... while sailing into the wind, it's their fastest tack. Let's see a car do that.
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IANAP (physicist) - The wind hits the sail. Since it's hitting the sail on one side and not the other, the pressure is higher on the side where the wind is hitting. This means that the sail is sucked towards the low pressure side. The speed of the craft is dependent upon the pressure difference that you are able to make and the amount of inertia and friction of the vehicle. It's not really related to the speed of the wind (other than higher speeds can create higher pressure differentials).
Re:Debate? (Score:5, Funny)
I started to think about this more. And the more I thought about it, the more confused I became.
Finally, I came to the conclusion: Thank god I'm not a physicist!
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I just read the article and here is how I understood this.
This propeller is like an active sail, it becomes more and more 'solid' the faster the wheels are turning.
To understand it, imagine this car without any wind, it's still. So the car is standing, propeller and wheels are stopped. Start moving the car forward by hand, and the propeller attached to the wheels will turn. It will turn pushing the air from front to back.
Now if there is wind from the back of the car, it pushes the propeller, which cannot
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Oh, so that was my description of the reason for the car to move and for the propeller to turn in the opposite direction to the wind. But the reason why the car is moving faster than the wind is because the propeller is pushing the air from the front of the car to the back, thus it is pushed by the wind forward by the sail properties of the propeller, but it goes faster than the wind by the actual propeller properties, which push the air from front of the car to the back.
Re:Debate? (Score:5, Informative)
I hate spelling nazis, but since you are suggesting a search, the correct spelling is Ascher H. Shapiro [wikipedia.org]. I only found this out as I was trying to take your advice and search for him.
Re:Debate? (Score:5, Informative)
http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind [wikipedia.org]
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Same way an aircraft can move forward faster than it is descending while gliding. But I don't see how a sail boat can move faster than the wind when moving with the wind, unless you invoke storage.
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Iceboats hare typically clocked in the 50mph+ range, with wind as low as 5 mph, though more typically 10 mph wind. The wing shape of the sail and the angle of apparent wind make the vessel move faster downwind by tacking than going in a straight line.
http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind [wikipedia.org]
http://torontoist.com/2010/01/historicist_sailing_faster_than_the_wind.php [torontoist.com]
http://www.straightdope.com/columns/read/2908/how-can-racing-yachts-sail-faster-than-the-wind [straightdope.com]
video of the mentioned BUFC
http://sk [skepticblog.org]
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The important concept is that the wind force is not what moves the boat, but what accelerates the boat. If the boat is moving dead downwind, then the sail is moving downwind at the same speed as the boat is moving, and there is no acceleration beyond the wind speed because wind and sail are relatively motionless.
But if the boat is sailing at an angle phi > 0 to the wind at speed v, the sail is only moving downwind at a rate of cos(phi)*v (and laterally at sin(phi)*v). Disregarding all friction, the sail
Re:Debate? (Score:4, Informative)
Read TFA, parent is correct concerning the wheels :
Cavallaro explained the car is able to move faster than the wind because the propeller is not turned by the wind. The wind pushes the vehicle forward, and once moving the wheels turn the propeller. The propeller spins in the opposite direction to that expected, pushing the wind backwards, which in turn pushes the car forwards, turning the wheels, and thus turning the propeller faster still.
Re:Debate? (Score:5, Insightful)
The more I look at that description and think about it, the more skeptical I become. It reminds me of someone trying to sell a perpetual motion machine. You have this battery to start it, and it shines this light. And all around it are solar panels, that absorb the light and keep the battery charged. Of course this doesn't work, there's never any net gain, and since there's losses in the system, it fails.
Here, the wind speeds the vehicle up to say 15mph, same as the wind. The wheels rob the vehicle of some speed in exchange to spin the propeller backwards. (which I must admit is a very interesting, novel approach!) which provides a force on the wind blowing the vehicle, which by itself would appear to accelerate the vehicle faster than 15mph.
But I see no reason why the drag from the wheels isn't exactly canceling out the benefit of rotating the propeller. And then the losses of friction etc step in, and you end up with a vehicle traveling slightly slower than the speed of the wind.
Basically, you can't turn the propeller without investing energy, because you're turning it against a resistance, namely the wind blowing on it. The more you want to resist the wind, (the faster you want to go than the wind) the more energy is required on the prop. And so as this theoretical vehicle accelerates and more energy is available from the wheels, (and is being robbed from the vehicle speed) the more energy you have to invest in the propeller. It's the same as a perpetual motion machine. You can't get more out without putting more in, and you can't put more in until you've gotten more out.
But then of course everyone asks "but he proved it with his prototype. I would ask if this was a sustained speed. Here's a scenario where it could work for a short time only:
First it looks like the blades on the prop can be pitched. That makes sense for control anyway. Lets say the car is blown up to speed while the blades are pitched at 0 degrees. Power is drawn from the wheels to spin up the prop. This slows the vehicle initially but the wind is constant and eventually the prop is up to full speed (perhaps very fast!) and the wind continues to blow and brings the vehicle back up to about it's speed. (probably only close, due to various friction elements)
Then suddenly the blades on the prop are pitched heavily, and now there's a good wind blowing out the back.
The vehicle would surely lurch forward. This is spending the energy of the inertia of the prop to accelerate the vehicle. This will only last a short time. Yes, the vehicle is traveling faster now and the wheels are turning faster, but you can't rob power off the wheels to keep the prop up to speed because that would slow the vehicle down. Remember the perpetual motion machine above. Any energy you take from the wheels to spin the prop to keep it up to speed must provide equal or less energy in the end to the prop than you are taking from the wheels. And the vehicle's acceleration crests.
At this point the prop will be spinning slower but still backward, enough to reach equilibrium, such that the energy of pushing on the prop to accelerate the vehicle is equal to the energy being taken from the wheels.
And then it starts to slow down, slowly, due to drag. And during which the prop slows down, STOPS, and reverses direction.
How can it stop and even reverse direction while the wheels still turn? Good question! The prop is currently working against the wind. Energy must be invested in the motor, not merely to spin it in the direction you want, but to even resist being spup the other way. It's easier to understand if you look at a prop being spun freely by the wind. If you put a dead battery on the terminals, the battery will start to charge, but the blades will slow down. You are providing a load on the prop, and are withdrawing energy from the prop's speed and transferring it to the battery. Energy is always moved around, never created or destroyed. In the
Energy != Velocity. (Score:5, Insightful)
But I see no reason why the drag from the wheels isn't exactly canceling out the benefit of rotating the propeller.
The Energy generated from the wheels has to match the Energy lost by the propeller. Thanks to gearing, the force is not the same.
Energy isn't the problem, a decent sized windmill can generate a megawatt of power. And it can generate the energy perpetually (assuming perpetual wind).
Consider if the vehicle was stationary, then we could easily generate the power from the wind: the force against the wheels wouldn't lose us any energy because E=mv^2 and so dE/dv=0 when v=0. Now imagine we are travelling at exactly the speed of the wind. Then our velocity relative to the wind is 0 so dE/dv=0. Thus we can push against wind without losing any energy, the same way a stationary windmill can push against the ground without losing energy. And so we can generate energy from the ground speed without losing kinetic energy (ignoring for the moment that the propeller doesn't have perfect grip on the air)
So we are currently travelling at wind speed, and generating energy from the ground. We now use that energy to push against the the wind to make us go even faster. Note that even a 50KW engine feels powerful when we are going slow and in first gear, and even a 200KWH engine can't burn rubber when we are going at 100KM/h. This comes back to E=mv^2, because Energy is proportional to the square of the Velocity, it takes more energy to speed up the faster we are going.
Note that we are still travelling faster relative to the ground than the air. Thus we can use the same trick as gears in an engine, we use a high gear relative the ground so have only a small force. We use a low gear relative to the air so we generate more force (for the same energy). We continue to speed up until the energy we gain from the different gearing ceases to make up for friction and other inefficiencies in the system (such as the propeller not having perfect grip on the air).
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Thanks for rehashing basically the entire debate.
However, there's one hitch. They've already done this out on the salt flats with an actual person in the vehicle, and done it dozens of times in front of hundreds of people. No tricks, a very simple mechanism. It isn't perpetual motion any more than a DN Iceboat that can go insane speeds of 70+ mph in a breeze of 20 - downwind.
In addition, you'll find hundreds of pages of discussion on sailing websites. Specifically here:
http://forums.sailinganarchy.com/i [sailinganarchy.com]
Re:Debate? (Score:5, Interesting)
Ah, no. I can do no better than to quote ThinAirDesigns [physorg.com]:
________
[1] As he is about to mention, this is best considered at the moment when the car is moving at the speed of the wind. In this case, there is no wind over the propeller, since the car and the wind are traveling at the same rate in the same direction; however, the wheels are moving relative to the ground at the speed of the wind, and therefore turn the propeller and supply additional thrust to the car, accelerating it.
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however, the wheels are moving relative to the ground at the speed of the wind, and therefore turn the propeller and supply additional thrust to the car, accelerating it.
Am I stupid, or is there another reality where the laws of thermodynamics don't apply?
What you described can't increase the vehicle's momentum, because it's adding resistance to the car wheels (there's no actual gain in energy being described in your statement, just gibberish about potentials).
The only way to go faster than the wind is to resist gaining speed (store energy), and when wind speed is eventually reached, expend the stored energy to go a bit faster than the wind. After that stored energy is used
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The rotating sails (i.e., propeller blades) are inclined to the wind; it's how all propellers work -- when rotated, they provide the force to the car that accelerates it to speeds higher than the wind. However, the power flow is from the wheels to rotate the propeller, not the other way around.
He states quite clearly, several times, that they don't use the "sail" word, because it confuses people into thinking that the power flow is in the opposite direction. Like all propeller-driven craft, the power flow
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Like all propeller-driven craft, the power flow is from the craft to the propeller.
I do not see that as being true here, as there is no mechanical gain from the body to the air, and the claim is that the craft is moving faster than the prevailing wind, therefore there is a headwind on the chassis.
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The energy comes, ultimately, from the wind. One might as well ask, "Where would the energy to move a sailboat faster than the prevailing wind come from?"
It also comes from the wind, but I know that you know that. A boat (an iceboat, a sandboat, a windsurf) might be much faster than the real wind but it's never faster than the apparent wind. By the way, that's an unfortunate name because it's very real. Did everybody try to wave a hand out of a car on an highway and feel the strength of the apparent wind, right? :-)
This is a good read for everybody http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind#Speed_made_good [wikipedia.org] (link to the part about getting from
Very old news. (Score:2, Informative)
It shouldn't really be a debate -- sailors have done this for decades. Essentially you turn your vessel/vehicle at an angle to the wind such that you utilize both the positive pressure from the wind and the negative pressure created by the curved sails which create an air foil. Positive pressure pushes you forward while negative pressure pulls you forward == faster than the wind. The same effect is at play with the "propeller" on the car. It's also the same principle that keeps planes in the air -- high
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Could you explain it a bit more? When you start going faster than the wind, don't you lose the "positive pressure" of the wind, since it is now against you? What am I missing?
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apparent wind angles and speed.
The faster you go the direction of wind, and it's speed changes. What is hard for most people to under stand there are really no lines on a boat that are solid. even the lines that hold the mast up can be tweaked. while any given boat has a top hull speed, you can design boats with hull speed numbers many times that of the wind. The fastest sailboat to date was clocked doing 60mph, (55knots) in a 30mph(25 knot) breeze. That's doing twice wind speed.
Sailing is areodynamics
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Except that car travels at 2.85 times the speed of the wind, when directly downwind, ie. when the boat and wind velocity vectors are on the same axis.
Of course, since the "sails" (the propeller blades) are moving on a different trajectory, their apparent wind is not directly downwind.
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Some genius!
Re:Very old news. (Score:5, Informative)
You are correct, but only for boats sailing across the wind or to windward. Modern yachts cannot sail faster than the wind *downwind*. Indeed, downwind is their slowest point of sailing, which is why many yachts tack downwind rather than sail dead downwind. Sailing boats cannot do what is claimed here. What is claimed here is substantially cool.
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It is cool, but there's wiggle-room in the debate :-)
The device extracts energy from the wind, and using only that, the vehicle *as a whole* progresses downwind faster than the windspeed.
The cunning part is the prop; because it's rotating, the blades themselves aren't moving directly downwind (well, considered instantaneously, they're moving across it), and that's the "trick" of it. It's a very clever idea indeed.
Re:Very old news. (Score:5, Informative)
For sailors: By using a propeller rather than a sail, the "sail" this boat is using is simulating a continuous optimal downwind tack (the propeller blades are at a tack angle to the wind)
For cyclists: The wind is being turned into rotational force like the cranks on a bicycle. Since they now have rotational force, they can use gearing to take maximum advantage of that force.
Does that make it clearer?
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That would make sense- if they hadn't gone out of their way to state that the propeller is driven by the wheels and spinning against the wind.
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Except that is not what the DDWFTTW people are claiming. They claim that the propeller is propelling the vehicle not acting as a turbine that sends energy to the wheels.
If you think about it, at the point when the vehicle catches up to the speed of the wind the propeller can't act as a turbine as relative air speed is zero.
(Note, I'm not sure I believe their claims, but I'm pretty sure that is what they are claiming.)
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Sorry to self reply, but they also claim it can self start so to get it started the propeller can't be getting energy from the wheels either (as they are stopped). It is all very strange.
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Sorry to self reply, but they also claim it can self start so to get it started the propeller can't be getting energy from the wheels either (as they are stopped). It is all very strange.
Below wind speed, use the prop to run the wheels. Over wind speed, use the wheels to run the prop.
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No this is not old news. I thought it was this trick as well. Its not. It the direct downwind problem, not side to wind problem.
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Sailors can't go faster than the wind directly down-wind. From TFA which you didn't read:
Cavallaro explained the car is able to move faster than the wind because the propeller is not turned by the wind. The wind pushes the vehicle forward, and once moving the wheels turn the propeller. The propeller spins in the opposite direction to that expected, pushing the wind backwards, which in turn pushes the car forwards, turning the wheels, and thus turning the propeller faster still.
This isn't at all like sailing boats, or aerofoil-based boats.
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This work has proven that it is in fact possible to go downwind, with the wind behind you, faster than the wind could push you alone. I personally can't quite understand how this is possible
It seems to be like you have this big propeller which is pushing the air backwards at 10 m/s. The wind pushes your vehicle forwards at 5 m/s but it also pushes the air from the propeller forwards at 5 m/s. Because this air is already being pushed back at 10 m/s the wind pushes it forwards at 15 m/s. In doing so it pushes the propeller and the car forwards at 15 m/s.
A million monkeys at a million keyboards... (Score:5, Informative)
"The run should now settle the DWFTTW (downwind faster than the wind) debate that has been raging for some time on the Internet about whether or not such a feat was possible."
You're new to the internet, aren't you, son? No amount of reality can end an internet debate.
Gearbox analogy (Score:2)
From my understanding of the wheel-powered propeller system, this works basically like a gearbox that converts a lower RPM to higher. There is nothing unphysical about converting a lower velocity to a higher one this way.
Of course, in the gearbox analogy, the torque is lower in proportion, meaning less acceleration. Also, since the vehicle is now moving relatively against the wind, it needs power even to maintain that velocity.
Another way to look at this. (Score:5, Insightful)
Firstly, ignore that it's moving.
You have 0m/s ground, and a 10m/s wind.
You put up a wind turbine - it can extract power from this 10m/s difference.
The funky part of this idea is that this still works when you're moving faster than 10m/s.
For the moment - imagine that the turbine is a pure 'airscrew'.
It describes a helix in space - like the DNA molecule.
For every meter the air moves "forward" relative to it, it turns 1m clockwise.
Considering the air as completely rigid for the moment, the airscrew goes forward in a rigid helix, unchanged by load.
So - 10m/s wind - airscrew turns at 10m/s. Simple.
You can extract - say - 100N * 10m/s = 1kW of power.
Funky part coming up.
Now. You're moving at 20m/s. Twice as fast as the wind.
Of course this will slow you down - you can't use this to make power!
Well - not quite.
If you are moving at 20m/s in the direction of the wind - for a total speed with regards to the wind of
30m/s then the blades need to be spinning at 30m/s in order to keep up.
But, you can use gearing from the wheels so that the 'base' speed of this spin is 20m/s.
That is - when you push the car along on a windless day - the airscrew creates no drag - because it is spun at exactly the right speed by gearing from the wheels. It has effectively - by rotating at the right speed - cancelled out the movement of the car.
This cancellation then allows you to ignore the speed of the car, and instead work off the speed difference between the wind and ground!
In reality - it's very far from an airscrew, and turbines have a lot of drag. It's the same basic concept though.
Another beautiful and 'obvious' when you think of it bit of physics.
Not impressed (Score:5, Funny)
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The Oracle Trimaran..250% faster than the wind... (Score:4, Informative)
The Oracle trimaran [bmworacleracing.com] that recently won the America's Cup had no problem exceeding wind speed due to aerodynamics, and the insanely cool carbon fiber wing that added to sail volume and power, and allowed them to use a fixed-shape sail - a huge advantage. They had no problem sailing between 16 and 24 knots upwind in 5 to 10 knots of wind—that’s 2.5 times wind speed.
They went even quicker periodically, and had a five knot downwind advantage. The first race report [boats.com] shows that the Oracle trimaran was able to almost constantly fly both outer and center hulls (amazing on a boat this big.,.I sail Hobies [hobiecat.com] and this shit is HARD) and execute some slick pre-race maneuvers (which is how you really win sailing races).
So yes, sailboats have been exceeding wind speed for a while, but not by 250%..until now. When a car does that, I'll be impressed.
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Sailing boats don't go faster than the wind when moving directly downwind. They tack at an angle which allows them to go faster than the wind speed in the downwind direction while never actually travelling directly downwind.
Apparent Wind (Score:2)
Consider the apparent wind, not the actual wind.
When a sailboat or iceboat is sailing across the wind (beam reach), the apparent wind (the velocity of wind relative to the sail) diminishes more slowly than the velocity of the vessel increases. This is why it is possible for a vessel on a reach to exceed the surface-relative wind velocity.
When a sailboat, iceboat, or hoax travels directly downwind, the apparent wind is equal to the velocity of the wind minus the velocity of the vessel. The force imparted on
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In short, this did not happen. The vehicle did not reach steady state direct downwind travel above the ground-relative velocity of the wind.
You are incorrect. It did just this.
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...Which is exactly why it is so damn bothersome and confusing that this appears to have happened.
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It works because you are using a fraction of the applied power to create a counter force to your source of power.
Remember your old toy, the yoyo? Put it on the floor with the string extended to it's entirety, now pull the string until it's in your hand.
How far did your hand travel? how far did the yoyo travel?
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So what you're saying is, if you change the design substantially and it wouldn't work, this is proof of the original design not working?
Just because you can't understand how this actually works and don't understand the aerodynamics doesn't mean that it's impossible. This situation is not analogous to either of your examples, you really don't even understand how this car works.
It's a wind powered car. The wind has a lot of energy, it has been harnessed to go faster than it's own speed long ago by tacking sai
Explanation (Score:2)
I think I can give a pretty good explanation how this works.
Let's start at the point where the vehicle is going at exact the same speed as the wind. The propeller is seeing exactly zero wind speed. Now look to the wheels and their link to the ground. Lets put a 100 pound load on the wheels, a force acting to slow the vehicle down. This supplies us power to drive the propeller. So now we have a 100 pound rotary force to spin the propeller. The propeller has a lift-to-drag-ratio greater than 1. 100 pounds of
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I think I explained part of that badly.
We'll assume vehicle speed is twice the wind speed. We'll imagine a 1 second period where the wind moves forwards 100 feet and the vehicle moves forwards 200 feet. Work is a force through a distance. The wheels are seeing 100 pounds of force through 200 feet of ground travel. The propeller is experiencing 100 pounds of force, but the propeller only moves 100 feet relative to the air. The wheels are doing twice as much work (and producing double the power) than the prop
Conservation (Score:2)
lets look at a specific state.
If the wind is directly behind the vehicle and the vehicle is travelling at exactly the speed of the wind the wind speed relative to the vehicle would be 0.
Since it takes power from the forward momentum of the vehicle to turn the propeller that would cause the vehicle to slow down.
The propeller would push against the air with a most the same force as supplied by the wheels causing the energy to be put back into the momentum of the vehicle at most bringing the speed back up to t
the propeller is going backwards? (Score:2)
If the cart is going directly downwind faster than the wind, then the apparent wind (the velocity of the air relative to the cart) is backwards. So, as the cart accelerates from slower than the wind to faster than the wind, why doesn't the propeller change direction? Shouldn't it be going "backwards"?
In any case, if this does turn out to not be a hoax, I think that the inventor in the video should thank his lucky stars that the wind happened to be blowing in exactly the same direction as the street in fr
It's Easy (Score:2)
Sail boats have been going much faster than the wind for quite a few years. Measurements have been made and established. This should be quite a proof of concept as it is surely easier to do with wheels on land than with hydrofoils on water.
Ice boats have beein doing this for a long time (Score:2)
Using a sail (airfoil/wing) to go faster than the wind is nothing new. All you need is low drag and a quartering wind (~4 or 8 o'clock). Dead aft does _not_ work. Iceboats reach ~4x windspeed, I believe some catamarins and windsurfers can exceed windspeed even in water.
It is all about apparent wind: as you start up on a tack known to sailors as a broad reach, and you accelerate, the apparent wind shift foreward and you trim your sails to go onto a beam reach. That accelerates further and you trim your
Here's another one (Score:2)
There are many physical principles that seem to run counter to intuition.
This is why we called freshman physics lectures "Magic Shows". Here's one you can try at home:
Put a string on a spool and pull the string.
The spool will come toward you faster than you are pulling the string; it will even roll up the string as it moves forward!
Lay the spool on its side so that it can roll along a table, and wrap one end of the string around the shaft of the spool.
The string comes off of the spool at the bottom.
Make su
Re:What debate ? (Score:5, Informative)
If you'd read some of the provided links, you'd have seen that the requirement was for the vehicle to be powered solely by wind, so no gravity involved except in its usual role of keeping the wheels on the ground ;-)
In other news, scientists actually getting their hands dirty turn out to know more about their chosen field than a bunch of people on the interwebz.
Oh come on man think! (Score:2)
What is claimed is impossible: sustained faster than wind speed. You could have transient bursts of faster than wind speed using energy that was stored when you were going slower than the wind. What I'm not perfectly sure of is if you could sustain an average (not continuous) speed greater than the wind. But I don't think so.
first why it can't be sustained: consider that you are traveling at wind speed. At this point there is no energy input to the car as a closed system. It can have stored energy bu
Re: (Score:2)
Re:Oh come on man think! (Score:4, Funny)
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the energy imparted to an object by wind is basically area x density of air x speed.
given a constant wind speed and density you find you need a specific area 'A' to propel a mass forward.
You then double the area 'A' - what happens to all the extra energy you are inputting into the system? All you need to do is find a way to use this extra energy for forward propulsion and you will find a way to go faster than the wind, which apparently these guys have done, contrary to the supposed impossibility of it.
Proof this is possible. (Score:2)
After pondering my own argument for a while I realized that the fourth case I described could be escaped. (as I noted, I was not sure of that fourth argument)
That is you can create a vehicle which can sustain an average speed above windspeed even though you cannot sustain a continuous speed above wind speed.
here's how. You have an arbitrarily large sail or kite such that when you are below windspeed by any infinitesimal amount you can gather an arbitrarily large amount of energy in a fixed time us
Re: (Score:3, Informative)
What you are ignoring is that once the prop gets rotating, it has a velocity component perpendicular to the wind. Therefore, the prop blade is not going downwind, and can generate a forward force even when the vehicle is going the same velocity as the wind, or faster.
Re:How it could possibly work (Score:5, Informative)
Physicsforum explained it well at http://www.physicsforums.com/showthread.php?t=274996 [physicsforums.com]
Re: (Score:3, Funny)
Re: (Score:3, Funny)
True. I bought some water skis and spent ages looking for a lake with a slope.
Re: (Score:3, Informative)
In related news, kitebuggies will generally travel at three times the wind speed, depending on the aspect ration of the kite.
Re: (Score:3, Insightful)
In related news, kitebuggies will generally travel at three times the wind speed, depending on the aspect ration of the kite.
Many sail-based vehicles travel much faster than wind-speed. What they don't do, though, is travel directly downwind faster than wind-speed. This vehicle does.
Re: (Score:2)
I'm no engineer but my reading of TFA suggests -1 Troll is a little harsh.
OK I'm speculating in my ignorance here,
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No, that is not what it is saying. Given an open plain and constant wind, it will move faster than the wind indefinitely.
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The part that's hard to wrap your head around is that you need to be very careful about friction losses and efficiency of the drivetrain, and that the car needs to have the lowest cross section possible to r
Re: (Score:3, Interesting)
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Because I'm pretty sure that the vehicle has stopped moving.
Re: (Score:3, Insightful)
Because there is an energy input into the system (wind). The car's momentum will tend to keep it moving at its current speed, so the wind power only has to be enough to overcome friction/drag for the car to accelerate. The wheels and prop are directly linked (they can't rotate independently--if you held the prop still and turned the wheels or vice-versa, you'd break the car).
Basically, the blades of the prop act like tacking sails; once you get your head around that it becomes easy to see that it works.
Re: (Score:3, Insightful)
Huh? That's news to all the sailors out there who do routinely sail faster than the wind.
Physics explained here in the "How can boats sail faster than the wind?" section:
http://www.animations.physics.unsw.edu.au/jw/sailing.html [unsw.edu.au]
You don't need input energy to maintain your momentum--you only need enough input energy to overcome friction/drag, anything beyond that can acc
Re: (Score:2)
As other people have noted, this is a complete non-issue, sailors already do it, and there's no reason cars can't too.
"Land Yachts" are actually faster and more deadly than the version which travels on water because wheels have less rolling resistance (than moving through water) and they move across the wind with greater efficiency.
Re: (Score:2)
This is however substantially different to sailing.
Sailing uses an aerofoil with a high lift/drag ratio.
This works when the wind is not directly ahead of you.
When a sailboat - nomatter how advanced - tries to sail directly into the wind - it goes backwards.
This contraption however can go forward directly into a headwind.
(Indeed it wouldn't be as efficient on the water, as you would need a somewhat lossy water-screw too, instead of nice low-loss wheels - to act as the 'reference' for the 'differential'.
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As other people have noted, this is a complete non-issue, sailors already do it, and there's no reason cars can't too.
Those other people were just as wrong as you. This is about going directly downwind, not at an angle.
Why did you feel the need to say what they already said, and miss the point just as much as they already did?
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It's possible to design a car that will travel into the wind, although the net power flows in the reverse from the present example -- going upwind, the power would flow from the propeller (which would probably look more like a turbine than a propeller) to the wheels.
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Why are they wasting this money in this gimmick where there are real energy-related science and engineering problems that can be pursued?
Generally speaking, scientists who requested funding feel better when they get some results, any results.
Re:Stupid exercise (Score:5, Insightful)
Boats can not go downwind faster than the wind. Rather than jump out and try to announce to the world how much smarter you are than the people who actually did stuff, maybe you should first go read and comprehend what they actually did.
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Boats can not go downwind faster than the wind. Rather than jump out and try to announce to the world how much smarter you are than the people who actually did stuff, maybe you should first go read and comprehend what they actually did.
A "boat" skating on ice can do it no problem: Say 10 mph wind. Go at a very sharp angle; the wind will accelerate you to say 8 mph in wind direction but say 30 mph real speed. Now go into a sharp curve and turn into the direction of the wind, changing the sails to minimal wind resistance. You don't lose your speed instantly, so you can go 30 mph in wind direction for a bit and gradually slow down. Set sails again at a sharp angle to get your 30 mph speed again and repeat. It should be no problem to have an
Re: (Score:3, Insightful)
YOur intuition tells you it was not possible for a car, and now they prove you wrong.
I am not sure who you are talking to. I know how the car works and that it works. I am saying that regular sailboats can not do the same that the car does, and that all the people yelling about how this is "nothing new" do not understand what is being done.
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That is exactly what they did.