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Google-Backed Wind-Powered Car Goes Faster Than the Wind
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."
I misread this initially, and thought the car travelled into the wind.
It's still pretty weird thinking through it.
Sailing vessels can go faster than the wind, why shouldn't a car be able to?
Great minds think alike; fools seldom differ.
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.
People replying to my sig annoy me. That's why I change it all the time.
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 -- higher pressure on the bottom of the wing relative to the top.
https://www.eff.org/https-everywhere
True. I bought some water skis and spent ages looking for a lake with a slope.
As other people have noted, this is a complete non-issue, sailors already do it, and there's no reason cars can't too.
I never really understood this for a long time, but the way I understand it is as follows:
Say you have a boat sailing straight downwind, it's going to go at a max of the speed of the wind.
Now consider a boat sailing at 45 degrees to the wind. Say travelling along the line y = x, and the wind's going along the x axis. The boat can potentially move at up to the speed of the wind in the x direction. But if it's moving diagonally, and at the speed of the wind along the x direction, it's going to be moving significantly faster (sqrt(2)) along the direction it's travelling.
This is all due to the friction of the water and that the boat travels more easily the way it's facing, which is similar for a vehicle. If there were no friction, the wind would just push the boat so it's side would be going first, but this obviously doesn't happen.
Why don't we just put Keith Olbermann and Sean Hannity on opposite sides of this device? The pressure differential could power North and South America forever.
...powered record.
"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.
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.
Escher was the first MC and Giger invented the HR department.
Heck, I can fart and people move faster than the fart cloud. Thus, I have prior art and will file a claim of patent theft against Google, et al.
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.
The things you're looking for are called "waves" ;) http://www.youtube.com/watch?v=y7mmO0CsyZA
In related news, kitebuggies will generally travel at three times the wind speed, depending on the aspect ration of the kite.
Please consider this account deleted, I just can't be bothered with the spam anymore.
I couldn't help but laugh.
Not sure about anywhere else, but Joby (or Jobby) in the UK is a slang term for the crap that comes out your behind.
That plus a car going faster than wind is pretty damn hilarious.
I hate illiterate dummies who revel in their own, or more often, other's ignorance, preferring for everyone to be ignorant rather than have to make the effort to communicate more efficiently.
Mind you, the other poster put it better. Crab in a bucket.
> I bought some water skis and spent ages looking for a lake with a slope.
The term is "Asian", you politically incorrect clod!
Yawn. Listen, call me back when you get it to go twice as fast - in the same direction as the wind. Using the rather vague, "down wind" isn't fooling anyone.
Let me know when you have a solar powered car traveling faster than light.
The Oracle trimaran 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 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 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.
"The pie shall be cut in half and each man shall receive.....death. I'll eat the pie."
I'm no engineer but my reading of TFA suggests -1 Troll is a little harsh.
OK I'm speculating in my ignorance here, but isn't this basically saying the wind pushes the car forward initially slower than the wind, but building up momentum that it later utilises to power the propeller (activating stored energy)? The initial bit is fundamentally the same as pushing a (non-propeller) vehicle up a slope to store the energy. Or simply compressing a spring or whatever.
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 the vessel by the wind is related to the sail area times that apparent velocity. When the vessel is traveling at the same surface-relative velocity as the wind, the apparent wind drops to zero and the force imparted on the vessel drops to zero. No amount of gearing can multiply a force of zero to make it greater than zero.
http://en.wikipedia.org/wiki/Apparent_wind
To come at this from a slightly different direction, consider that propellers are not terribly efficient thrust producing devices. Ground cars do not use propellers (except for novelty purposes) because it is more efficient to use tires, which have higher efficiency (or metal wheels in the case of trains, which are better still on a very smooth surface). Suppose that instead of confusing things by adding a propeller, they claimed that they had one set of wheels being turned by the wind-powered forward motion of the vehicle. They then had a gear train running from those "power" wheels and connected to a set of "drive" wheels. They claimed that the wind power pushing the vehicle forward caused the "power" wheels to spin, to turn the gear train, and hence to spin the "drive" wheels faster than the power wheels -- propelling the vehicle forward.
If you would not believe the two-sets-of-wheels design, you should not believe this one.
In short, this did not happen. The vehicle did not reach steady state direct downwind travel above the ground-relative velocity of the wind.
Stop-Prism.org: Opt Out of Surveillance
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.
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 rotary force spins the propeller up until the drag equals 100 pounds. The propeller spinning at this rate generates more than 100 pounds of thrust. The first 100 pounds of thrust balances out against the 100 pound load on the wheels, and the remaining thrust accelerates the vehicle.
There is no energy violation going on because we are extracting energy from the difference between wind speed and ground speed. When the vehicle is moving faster than the wind the wind is still pushing forwards on the backwash air from the propeller, that backwash air from the propeller is pushing forwards on the propeller, and the propeller is pushing the vehicle forwards against the ground. We have a chain of forces where the wind is in effect pushing forwards against the ground, and we extract that wind-to-ground force to accelerate the vehicle. That wind-vs-ground energy source exists no matter what speed the vehicle is traveling. We can use that energy to accelerate the vehicle up to ANY speed, either upwind or downwind, and we are limited only by energy losses to friction and drag.
When the wind stops the energy supply stops. The vehicle will then slow due to friction and drag.
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- - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
watching those who know how simple the principle is and know it *can* work try and convince those who know it *can't* work.
Dave
There was really a debate?
Attach a big propeller, and gear up (mechanically or electrically).
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 the original speed.
To accelerate the vehicle would require additional energy from somewhere. At 0 relative wind speed where does that additional energy come from?
Land vehicles have been exceeding the speed of wind for quite some time also. The difference here is that this vehicle will exceed the speed of wind while moving directly downwind.
No, that is not what it is saying. Given an open plain and constant wind, it will move faster than the wind indefinitely.
Although the average wind speed is 13.5mph, this is obviously an average. It is clear that individual wind molecules can travel faster than this, whilst others travel slower, for an average of 13.5mph. If the vehicle is light enough, it is not impossible that this sprinkling of ultrafast wind molecules can push it. However, the upper speed limit is the volume of solid-form wind molecules at any given speed (or faster) that exist to transfer their momentum to the vehicle.
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.
The revolutionary claim is that a vehicle powered only by the wind can travel downwind faster than the wind. When they put the model on the treadmill and it fights it's way uphill it is NOT going faster than the wind. There still is a tailwind from the vehicle's perspective. So, I know not if the feat is possible, I just know that it is not demonstrated by the model on the treadmill. Interesting claim, bad experiment.
Paul Beardsell
negative, as soon as the vehicle moves forward at all, a direct link to the propeller moves the prop in a direction against the wind (backwards for the vehicle) instantly providing some extra force against the wind. This is actually pretty ingenious. I like where this is going.
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 front of his house, because the experiment is void if the wind is at a slightly different angle (tacking downwind faster than the wind is no big deal), and what are odds of that?
Am I part of the core demographic for Swedish Fish?
That's BS. It's not like it's using gravity to move the vehicle forward like on a decline slope. The wind pushes the vehicle forward, which then turns the wheels, which moves the propellers. So all energy that is involved is wind, so this does qualify.
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.
We want to demonstrate that a device can sail or propel itself dead downwind faster than the wind. We decide to use a treadmill. We assume a tailwind of 10mph and so we set the treadmill at 10mph and we leave it flat - no incline required. We leave the electric fan turned off because, at 10mph, there is no apparent wind. We put out miraculous model on the treadmill and hold it there with our finger so it neither moves forward or backward. It's wheels are turning and they're geared to the model's propeller. We remove our restraining finger. Does the device accelerate forward on the treadmill? That's the experiment I want to see. I know the result and I am offering long odds to all comers!
Another way to demonstrate the perpetual motion nature of this is to ask what the theoretically maximum multiplier of the downwind speed is. Downwind 10mph, what 's the limit of the vehicle's speed? No limit according to the reasoning presented!
Also, those who say that one can sail a boat directly downwind faster than the wind by not proceeding directly but at an angle are WRONG. A floating baloon still get's to the directly downwind point before you no matter how you tack. You tack a modern sailboat because it is quicker to do that and gybe to get to a point directly downwind than trying to do it directly but that's still not quicker than the balloon.
Paul Beardsell
Basically, imagine that instead of a propeller, the car's wheels turned an internal flywheel. The wind pushes the car, and the car accelerates up to (very near to) the wind speed. No switch the internal load for the propeller, which adds an additional acceleration. The car is now moving above wind speed.
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 reduce drag. While theoretically a physical car would eventually reach wind speed on an impossibly long straight road with an impossibly constant unidirectional wind, for the sake of practicality it needs to be brought up to wind speed by a regular car.
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
"Reality is that which, when you stop believing in it, it doesn't go away." - Philip K. Dick
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 sails further (closer to centerline) onto a close reach. Then maybe further to close hauled.
These ain't square riggers, boys! Look at it another way -- when beating (going upwind), you are going faster than the wind because you are going in a net negative direction wrt the wind.
The same concepts can apply with vertical turbines, windmills and power extraction devices. The device merely need to extract energy to cover the drag losses. Again, some lateral wind direction is needed.
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 sure the spool is well coupled to the table (weight, friction), and the string is tightly tied to the spool and comes off at the bottom.
Pull on the string in a direction parallel to the table.
Ooh---magic (waving Jazz hands...)
The math is here.
Try different angles.
Notice how the force required on the string varies with the speed that the spool eventually moves towards you.
(That last one should help you debunk some of the free energy charlatans)
"Reality is that which, when you stop believing in it, it doesn't go away." - Philip K. Dick
I'm not trolling, honestly. How is this not perpetual motion?
Because I'm pretty sure that the vehicle has stopped moving.
signature is pants
They have a long way to go then. Peolpe have been doing this since 1500's and the world record is 126.1 mph on 26 March 2009 by Richard Jenkins. http://en.wikipedia.org/wiki/Land_sailing
It looks like the car is going against the wind... correct? If so, any increase in vehicle speed (relative to the wind) from the "wind turbine" through the gearing will make the vehicle go faster (accelerate), which will make the wind speed against the turbine faster, which makes it accelerate... until the air resistance from the drag of the whole setup matches the force delivered from by the turbine to the wheels, which here must be 2.85 times the wind speed (at least at 13.5 mph wind speed). It doesn't have anything to do with sails! If the wind speed is 10 m/s, and the vehicle is moving at 20 m/s, the relative speed seen by the turbine is 30 m/s. That energy is used to make the car go faster, say 15 m/s, which then of course makes the relative speed seen by the turbine 35 m/s, etc. It would seem that this could go on until the car is moving at c, but of course there is finite air resistance on the car and this resistance limits the speed the car can go. At that point, more energy would be needed to make it go that little bit faster... which the turbine can't extract from the wind. Interesting concept.
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 but it can't be getting new energy. If you were to start going faster than wind speed then there is a head wind and it will now be draining energy from the car's stored energy.
You could oscillate about wind speed however. wehn you go slower the wind is inputting energy. Let's ignore the friction losses. If the net force * time of the wind on the car is greater than change in momentum of the car then there energy input to the car can be greater than the kinetic energy of the car. THat is the car could store energy.
You already know this intuitively. A windmill always has a force*time greater than it's momentum since is does not move and it generates energy.
Third above wind speed is possible transiently using this stored energy. Here's a trivial device to prove it. tie a rubber band between a kite and an anchor on the ground. the kite stretched the band. Now release the anchor and it is flung forward. By adjusting the masses you can find a place where the arbitrariily light but forceful kite will fling the anchor such that their center of mass is higher than the wind. QED
Fourth is it possible to sustain an average not instantaneous speed above the wind? I don't think so
imagine the following car. it has an enourmous kite pulling it. the wheels are hooked to dynamos that soak up energy and store it in a battery. you can make the kite as large as you like so you can inject an arbitratily large amount of energy in a given time into the battery. You then use this to drive the car faster than the wind. during this time you are using stored energy. Also during this time the kite is falling behind at a rate equal to the car-windspeed.
In order for the kit to catch up the car needs to go slower than wind speed such delta speed times time equals that distance lost by the kite.
I think those two cancel to give an average speed equal to the wind. I could be wrong.
Some drink at the fountain of knowledge. Others just gargle.
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 average speed of > 10 mph in direction of the wind.
Now with this particular arrangement you don't get 10 mph in wind direction _all the time_, but much higher _on the average_.
Just because current sail boats do not do it, that does not mean it is impossible. If it is economical is a different issue. YOur intuition tells you it was not possible for a car, and now they prove you wrong. You can apply the same kind of aerodynamics to a ship Just that is is much less practical:Propelling the ship through water creates its own inefficiencies (hull drag, propeller efficiency) you will have to overcome.
And oil getting more expensive it becomes more important to understand all of the aerodynamics of a big ship.
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 using the dynamo wheels.
you then collapse the sail or kite and use the dynamo to propel you faster than the wind. This can last a long time and only depends on the drag.
When you finally fall back to below wind speed the sail is re-deployed.
thus the sail is up only for a tiny fraction of the time compared to the above wind speed time. the amount below wind speed you need to tap the energy can be aribtratily small and the time to gather it can be arbitrarily small for a big enough sail.
thus you can travel on average above wind speed in theory. But I assert you still cannot sustain an continuous instantaeous speed above windspeed for the reasons I noted above.
Some drink at the fountain of knowledge. Others just gargle.
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.
rage, rage against the dying of the light
Initially, it seems like you couldn't get a wind-powered vehicle to go faster than the wind. For example, let us imagine a wind going 20mph North. If our vehicle is going to travel North with the wind at its back, the max speed would be 20 mph because any greater speed would result in an opposing force. However, if your vehicle is traveling West, and your sail is near perpedicular to the North-going wind, the translational velocity of the vehicle has no effect on the sail and the vehicles top speed would be set by the force applied to the sail and vehicle friction & weight, and if you got a good run at it, I don't see any reason you couldn't break wind speed that way.
Suppose the wind blows relative to the ground at ten m/s. That remains true regardless of how fast the model's moving. By careful gearing, arrange that the wheels of the model turn the propeller so it generates a wind of exactly the same backward velocity as the forward velocity of the model, regardless of its ground speed. Thus the propeller has subtracted out the ground speed. But the wind is still blowing relative to the ground (and thus our propeller) at 10m/s, and that difference between wind speed and ground speed can be used to turn the propeller faster and accelerate the model further.
Eventually the wind-relative-to-ground power into the propeller will balance the friction and air resistance losses and the model will accelerate no further.
Incidentally a test on a treadmill is not equivalent, because there's no air resistance losses.
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.
It says in the summary that this car went 2.85 times the speed of the wind, while travelling directly downwind. Isn't that 285%? Seems like now would be a fine time to start being impressed. :)
That was an interesting article about the America's Cup yachts, though. Incredible sophistication in those things - and damn impressive to see a trimaran scooting along balanced on one "outrigger". Thanks for the linkage - you deserve a mod up.
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.
Now that I think about it, I'm pretty sure everything I just said is completely wrong.
Anyone who's sailed before knows you can sail into a headwind.
Because you're drawing the box around the system wrong- you're modeling a closed system and seeing perpetual motion where there is not. Without the wind, it couldn't move at all for starters. I'm not sure where the anomaly with what we "know" and what we're seeing with this is coming from, mind, but if there's no measurement error with things here you've got one that needs to be looked into.
I am not merely a "consumer" or a "taxpayer". I am a Citizen of the State of Texas
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.
Took me a while to understand how this can work, but it does. Assume the wind is blowing North to South at 10 m/s.
Change to a frame of reference moving with the air. Now what we have is a volume of stationary air with one surface, the ground, moving South to North at 10 m/s. So our vehicle has to extract as much energy and as little momentum as possible from this moving surface and use it to propel itself North to South. It is the moving surface that defeats most of the arguments that this can't happen.
Yeah, but the big problem is that it doesn't correlate to that analogy- you can't go faster than the wind you're tacking against with a sail. You can get close to that speed, but not to it or faster. It doesn't correlate with anything they've taught us in high-school or college physics classes and it's where the "perpetual motion" and "impossible" remarks are coming from.
It's not perpetual motion and it's apparently not "impossible" if they've not had a measurement error (don't presume that yet either)- which means that our understanding of things is in error and it's time to analyze just precisely WHY this does what it does to adjust our understanding of the model we have or the very model itself as needed.
I am not merely a "consumer" or a "taxpayer". I am a Citizen of the State of Texas
Driving downhill?
If you think I'm wrong, just consider the example from the article (and I've got plenty more to back up my case, not just this): if 38 is 2.85 times greater than 13.5, what number is two times greater? 27, you say? OK, what number is one time greater? Oh, only 13.5? I thought we said it was greater? OK, what number is ZERO times greater? Surely it can't be zero, since we're just saying it's no greater, not that it's lesser. Basically, "X is N times greater than Y" means "X = N*Y + Y" (the plus is what greatER means). The article thinks it means "X = N*Y". What really does mean that is "X is N times Y".
What do you do when you run out of wind?
"Who is the Journal of Quantum Physics going to believe?" --Stephen Hawking
None of the explanations I've seen here make any sense. I've spent too many hours on a bike running ahead of a tail wind and trimming my speed so that the relative wind is zero to believe someone can somehow extract energy from a net-zero, much less a net-negative, tailwind.
You'll notice in the pictures that there aren't any wind indicators other than the wind strip on the craft itself so it's not clear what the wind is actually doing. It appears as if they start off with a tailwind, the wind turns 180 degrees and they're heading upwind. To me, it looks like they've just figured out a way to tack straight upwind which is different than sailing downwind faster than the wind.
I won't believe these guys until they publish blueprints that someone else can use to build another craft and replicate what these guys are claiming. If they're legit, that's what they'll do. If they scamming folks, they'll claim that their design is a trade secret and for some strange reason never get around to manufacturing these things so that other people can do the same thing.
http://www.thefutureisawesome.com/category/energy/
http://www.youtube.com/watch?v=VxoA8rnJj0U&feature=player_embedded
The vehicle in the article will never see widespread use, on crowsed highways. Replace those propellors with a verticle turbine, and you might have something that sell.
"Windows is like the faint smell of piss in a subway: it's there, and there's nothing you can do about it." - Charlie Br
Easiest way to think about this problem is from an energy perspective. Don't think about forces, it'll just mess you up.
Initially, the car has a certain amount of kinetic energy; the wind also has kinetic energy.
Question: using its propeller, can the car slow down the wind?
Answer: yes...
Question: where does the wind's kinetic energy go when it slows down?
Answer: it's either A) wasted, or B) TRANSFERRED TO THE CAR.
What do you do when you run out of wind?
Same as when you run out of gasoline--walk.
This ain't rocket surgery.
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).
in the sense everyone assumes. it is really a prop driven vehicle.
the wind is not driving the turbine. the wind pushes on the car frame slightly, and the wheels drive the prop, the prop then acting like most vehicular props.
rather than being the energy collector (standard assumption in "wind power"), the prop is instead the energy consumer as it is providing thrust.
The explanations I've seen thus far are annoying and hard to turn into concepts I can grasp.
Here's how it appears to me. . .
1. Think of a cube of air inside which is contained the car.
2. That cube of air is moving at 10 mph. It takes a certain amount of energy to do this.
3. The car absorbs and uses some of that energy.
4. Does the cube of air stop moving once the car has absorbed its energy? (A: No.)
5. So there's MORE energy than is contained in that one cube of air. Where is it coming from?
6. The rest of the surrounding air. The wind is very big. A HUGE amount of energy is required to move the atmosphere along like that.
7. The car is a kind of energy capacitor which, by the time it is spending the energy at the same speed it absorbs it, happens to be moving faster than the wind. (The propeller becomes a type of energy-storing gyro.)
8. The speed of the wind and the speed of the car aren't directly related.
That's what occurs to me, anyway.
-FL
For me (IAAP), I immediately think about energy conservation. Where can the energy come from to propel the vehicle? IMO, the simplest frame of reference is the one where the ground is standing still (you can quote me on this point). In this frame, the total energy is the kinetic energy of the vehicle (1/2 m v^2) and the kinetic energy of the air (same formula).
The vehicle can go faster than the wind if it can remove enough kinetic energy from the wind and transfer it to kinetic energy of the vehicle. The tricky part (of course) is to do this when the vehicle is already going faster than the wind. Think of it as a device to slow the wind down as efficiently as possible. In some ways it is analogous to a heat pump which can heat up your house more efficiently than a normal resistive heater because it uses electricity to further cool the outside even when the outside is already colder than the house. The vehicle uses the big propeller and the gearing connected to the wheels to further slow down the wind, even when the wind is moving slower than the vehicle.
As long as the energy it gains by slowing down the wind is greater than the energy of all the losses, the vehicle can accelerate. It's confusing because they use the spinning of the wheels to power the propeller. Common sense tells us that it is impossible to gain enough energy from the wheels to accelerate the vehicle faster than the wind. But if common sense was always correct, there would be no need for science.
We don't see the world as it is, we see it as we are.
-- Anais Nin
Energy is conserved. It is transferred from the wind to the vehicle. Consider a 1MW wind power station connected to tiny electric car. It is clear that that car would take off like a rocket.
The only question is how to generate energy from the wind when travelling as fast or faster than the wind. This has been discussed to death in the Slashdot comments as well as the comments on TFA.
Next time read the article first, saves you from writing a lot of wrong and misleading text. The propeller does not act as a sail and the motion vectors of all points on the propeller have a positive component (in the direction of travel) relative to the wind, i.e. go faster than the wind in the direction of the wind. The propeller is attached to the vehicle and no amount of pitch tweaking can change the motion vector component in the direction of travel. The propeller works the same as an airplane propeller, moving the vehicle forward relative to the surrounding air.
As seen in the video, it travels slowly as the propeller picks up speeds. When it reaches the equilibrium speed, the propeller is spinning rapidly and is able to push the vehicle faster. But at that point there is no more energy being added to the vehicle and it starts to slow down, until the rotational energy from the propeller has been expended.
The can go up wind.
They can also sail faster than the wind (very much faster).
"Modern designs of iceboats are very efficient, utilizing aerodynamic designs and low friction, and can achieve speeds as high as ten times the wind speed in good conditions."
http://en.wikipedia.org/wiki/Ice_boat
When the wind stops, so does the car?
Coding with assembly is like playing with Legos. Coding an application in assembly is like building a car with Legos.
heres a video of it in action - http://www.youtube.com/watch?v=DPvGTjmn9y0
If we replace the wind with a linear gear, I think I know how this works.
Setup:
Question: What happens to the vehicle gears?
Answer: If vehicle moves some distance "x" relative to the wind (where positive represents moving faster than the wind), then it must move three times that distance (i.e. "3x") relative to the road. Suppose the wind has moved distance "y" relative to then road. The speed of the vehicle relative to the wind ("x") plus the speed of the wind relative to the road ("y") also gives the speed of the vehicle relative to the road ("x+y"). Equating the two values for the speed relative to the road we have the equation "x+y=3x". Solving this for "x" we get "x=y/2". This positive value represents movement faster than the wind. Thus the vehicle will travel over the road at 1.5 times the speed of the wind! (Note, that as the ratios get closer to 1:1, the speed increases until a singularity at 1:1).
At least I think that's how it could work. I don't have the gears to construct and test this, and the result doesn't sit well with my physics intuition. I'd love to see someone build this gear variant and see if it works. (Though I might suggest they start with a fairly high gear ratio to keep the relative speeds low and reduce strain on the mechanism.) If it does work, I suspect this sort of gear mechanism is already known and has a name. Too bad I know have any mechanical engineers that might know what it would be called.
Actually, you don't know what happened internally.
It was Larry @google that initially approached the experimenters. The experimenters in this case didn't want, nor need google financial help. But in the end, accepted the financial investment mainly to procure instrumentation and diagnostic equipment to help precisely document the vehicle.
Disclaimer: Yes, I personally know some of the people involved in this endeavor.
AND, if you are interested, the original builder is the guy who helped develop, owns, and runs Sportvision...the company that put the first down line digitally on the football field; known as 1st and Ten
Posting anonymously so that I don't violate anybody's NDA (I am personally not under an NDA).
-quack a doodle do to me. ;) (inside joke)
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
You don't need input energy to maintain your momentum--you only need enough input energy to overcome friction/drag, anything beyond that can accelerate you.
rage, rage against the dying of the light
A more thorough look from the Straight Dope, which also notes that America's Cup yachts travel at 2 to 3 times the speed of the winds propelling them:
http://www.straightdope.com/columns/read/2908/how-can-racing-yachts-sail-faster-than-the-wind
rage, rage against the dying of the light
After writing all that it turns out someone has already posted two very good explanations using the same analogy: Along the paper faster than the paper and Under the ruler faster than the ruler.
Ah. Now I get it. Thanks for the explanation.
Yeah I was just speculating. I read that Google is investing in a multi-million dollar wind farm. So this might provide some useful technology for that.
Boats have been doing this for about 100 centuries. They can travel against headwinds.
However, for anyone (Google) to invest good money in this technology marketing gimmick seems to be a bit nutty. Why are they wasting this money in this gimmick where there are real energy-related science and engineering problems that can be pursued?
An old aphorism comes to mind here: Better to be silent and thought a fool, than to speak and remove all doubt.
Note to ACs: I usually delete AC replies without reading them. If you want to talk to me, log in.
Discovery Channel video! Very cool!
Get out of Mom's basement. Check out this real stuff: http://www.nalsa.org/
It only takes undergraduate fluid mechanics to fully analyze this problem. It's a sad commentary on US science literacy that a debate on something simple can go on so long.
Heck, folks in this thread can't even get the difference between energy and power right. Some of the posters that claim to be engineers in this thread are spewing nonsense. I hope I never ride in an airplane they helped design.
It is remarkable how self-proclaimed experts are skeptical of this yet it is so immediately obvious once you look at the videos.
So if you guys haven't figured out how this really works, here is a much simplified way of looking at it.
The important thing here is that a a turbine is not a sail - to me this radically changes any assertions about DWFTTW I've read. We straight away need to throw away many assumptions and look at some differences between the two.
Directly downwind, a sail can only generate net thrust along a vector with a pressure differential in that same direction.
Lets look at the turbine in isolation. Air blowing along the axis of rotation, causes torque and therefore available power around that axis, that can be used to drive a vehicle forward.
So what happens if you reverse the airflow in the opposite direction? Well, a turbine can still generate rotational torque IF THE AIRFLOW IS REVERSED.
Opps. It seems every armchair skeptic I've read so far has not picked up on this simple point.
When the vehicle is traveling faster than the wind the airflow reverses over the turbine, relative to it. So any skeptic has to explain to me exactly how is it suddenly impossible for a turbine to not be able to generate work with a net airflow along it's axis?
This alone means that a vehicle can generate power from the wind,in any direction, even as it travels faster than the wind, downwind, provided there is some kind of differential in airflow that work can be extracted from.
Relative to the turbine the air has stopped and then begun to flow in the opposite direction. All that is required is a net airflow relative to the turbine itself. The slightly counter-intuitive effect of APPARENT WIND applies and throws off people who perhaps have been too quick to dismiss. Turbines love apparent wind, it's all they need.
A prerequisite is that there is a speed differential between airflow, the ground and the vehicle, therefore useful work can be extracted somehow. This is not energy from nothing, nor perpetual motion, nor some energy storage scheme.
It is remarkably simple. I am not a mechanical engineer nor a aerodynamics and have no other qualification other than I've stared at the videos for a while until the 'Ah Ha!' momment.
Oh but there is more to it than that I know, like how the thing transitions past equilibrium which I don't quite get, but now I see the main rule of thumb that allows this to work. I've moved on with my day.
But the outcome of all this is a quite remarkable discovery, this means that a wind turbine powered car can feasibly travel faster than the wind IN ANY DIRECTION. Cool!
After logging in slashdot still does not take you back to the page you were on. It's been that way for 20 years.
This could not work without the propeller airfoil, creating lift forces. Momentum forces generated by the propeller are canceled out by the force required to drive the propeller, which is the intuitive part. The lift forces are the aspect that are not typically part of our intuition. The lift-to-drag force ratio can be quite high. For an indisputable example, think about how massive airplanes stay afloat using forces at only a fraction of their weight. A 747 can generate about 2-300,000lb of force, but weighs 350,000-1,000,000lb, and has to overcome very large drag forces.
http://en.wikipedia.org/wiki/Lift-to-drag_ratio
http://en.wikipedia.org/wiki/Propeller
http://en.wikipedia.org/wiki/Boeing_747
It's not perpetual motion because it stops when the wind stops, and it doesn't accelerate indefinitely.
Let us remember that Joby Energy also sponsors this excellent project!
I would also like to add my insight to the previous excellent comments, as this is what allowed me to understand how the car goes faster than the wind:
What is the wind hitting to drive the vehicle forward? Where is the flat spot on the back of the vehicle the wind is pushing against? It is the rear surface of the propeller. The wheels are not driving the propeller to make the car go, they are keeping the relative speed of the air hitting the rear surface of the propeller at the proper speed so the car acts like a sailboat sailing at an angle to the wind.
The fact that this seems counter-intuitive at first makes it a cool problem. With the above, I now feel this makes sense and I have no problem believing it.
I hope this helps other people.
-Todd
p.s. I am a systems architect/software developer available for employment.
Omne ignotum pro magnifico.
tldr
The "sail" is a red herring. I'm not talking about a sail (though it does seem to be a popular topic around here!).
With regard to the propeller, you almost got it, but you dropped a sign.
But don't take my word for it: The wonderful thing about this sort of physics is that you have all the equipment you need to perform the experiment yourself.
Make yourself a propeller out of a folded sheet of paper. 3/4" wide or so, and give it half a twist. Stick a pencil through it, hold it up in front of your face so that the propeller is between your hands and your face. Spin the propeller so that you feel the wind in your face. If you spin it the other way, you should feel the wind on your hand and NOT your face. Yes, I did the experiment a moment ago, and it does work. It's readily apparent which way the wind blows when you spin the little homemade prop.
OK, so do you have the propeller spinning in the correct direction, and it pushes the air backward into into your face? Good. You are now standing behind the car, looking in the same direction as the driver, and the propeller is pushing the car forward.
Look at the leading edge of the propeller. It is more distant from your face than the trailing edge. Remember that you are looking forward in the direction that the driver looks as we analyze the motion of the surface of the blade.
This means as the the surface of the blade passes in front of your eye, first it is more distant, then it is closer to your face. That is to say first the blade surface (at the leading edge) is more forward, then later the blade surface (at the trailing edge) is less forward.
So, again the parallel-to-the-shaft component of the blade surface moves from a more forward to a less forward position. It's moving backwards.
They all do--that's how propellers work! They push BACK and the airplane, boat, or car moves FORWARD.
As far as changing the motion vector by pitch tweaking--sure you can reverse the motion vector. Just change the pitch in the other direction.
Try it with your paper propeller--mark an arrow on the blade once you've got it spinning the right way, and then give it an opposite twist. Spin it in the same direction, and it blows the other way.
You just reversed thrust, and all you changed was the blade pitch.
I think a DDW watercraft could be made to do this as well. Have two propellers: one in the air and the other in the water. Mechanically link the water propeller to the wind propeller. Assuming friction with the water isn't too great (flat bottom boat?) and the ratio between the water prop and the air prop is tuned, you should be able to make a DDW watercraft move faster than the wind.
Here is the math.
http://projects.m-qp-m.us/donkeypuss/wp-content/uploads/2009/05/drela_energy.pdf
http://projects.m-qp-m.us/donkeypuss/wp-content/uploads/2009/05/drela_efficiency.pdf
Just do the math. All of the hand waving has to stop.
Mass, Momentum, and Energy are conserved. Do the math. Get the correct answer. End of discussion.
Let's adopt the earth's inertial frame. If the wind velocity relative to the ground is higher before, than after the vehicle passes through it, then there is missing energy. Where did that energy go, "skeptics"?
Seastead this.
To me - and probably anybody else who isn't a pedantic asshat - the car is "traveling faster than the wind" if the main body of the car is moving faster than the wind speed. The "car" is the box with wheels, not some imaginary surface spinning along with the propeller.
What are you talking about? The /. headline calls this a "car" and TFA calls it a "vehicle". Being generous, that's misleading. It's neither: it's a frame with a propeller at best; it isn't designed for turning or transit. In fact, you'd probably get arrested for even trying to bring something like this onto a public road.
Best case, this is an engineering example. It's not even a prototype. Necessary scale (particularly for passengers and/or a load) and land (as opposed to sea) friction make such a "vehicle" as close to impossible as impractical can.
Don't get me wrong - it's an awesome demonstration but arguably nothing that's going to go anywhere anytime soon.
Now, derringers... that's something else. If we could figure out how to haul cargo over long distances with minimal wind resistance (slipstreamed airframes with internal cargo space) using sealed helium compartments (so it's a one-time investment), that'd be something. Even if they only do a very slight mileage, they'd be a huge win in many regards. But I doubt we'll be going back to derringers for some time.
~/ssh slashdot.org ssh: connect to host slashdot.org port 22: too many beers
Huh? That's news to all the sailors out there who do routinely sail faster than the wind.
Yes, but in this thread you'll find plenty of proof that what they've been doing is impossible. Therefore they can't.
Well, I doubt you'd be interested spending a hundred grand building a device that you don't think works, so I guess you'll be glad to know that there is a simplified version of the device demonstrated on Youtube: http://tech.slashdot.org/comments.pl?sid=1676544&cid=32477460
(Thanks to http://tech.slashdot.org/comments.pl?sid=1676544&cid=32477460)
There are almost 300 comments but only really two arguments against this device: "The third law of thermodynamics says this can't happen!" and "How can you extract energy from the wind when you are travelling at the same speed as the wind?". As it is dozens of people are making these arguments and dozens of people of people are rebutting them. I think it would read a lot better if we could merge threads and see all rebuttals against the same argument in the same place.
The interesting thing is that Google is also sponsoring them to do some crazy advanced stuff with aviation. You heard it here first. Just FYI....
Look up 'tacking'. They do it both upwind and downwind. Downwind they go faster than the wind & they've known they can go faster for just as long. No debate about it.
Deleted
Tacking (or more precisely jibing, as we're trying to go downwind) is the very definition of not going dead down wind but at an angle to the wind (zig-zagging to end up at a location straight down wind). This story is about traveling exactly in the same direction as the wind, not just about reaching a point straight down wind faster than the wind.
Sorry if this is redundant but I see a LOT of posts saying it's impossible and a LOT of explanations of why it is but that have nothing to do with the setup described in the article. Here is a relatively simple explanation:
Imagine an efficient, aerodynamic vehicle with a very big propeller on it. Imagine the vehicle is moving at some arbitrary speed down a very smooth level road. If the propeller isn't moving fast enough, it will cause a lot of drag against its front side. If it is moving fast enough, it will push air backward and propel the vehicle forward.
Now imagine the propeller is mechanically linked to the wheels so that at any arbitrary speed, it is neither moving slow enough to cause drag against its front side, nor fast enough to create a forward force. Instead, all it is doing is cutting through the air as efficiently as possible. In this case, it takes very little energy to keep it going. It is cutting through the air like the spokes of a bicycle, not pushing the air around like a ceiling fan.
Imagine our vehicle moving at 10 kph forward on a windless day. The air is moving like a 10 kph headwind relative to the vehicle. However, because the propeller is cutting through the air, rather than being dragged by it or pushing it, it is as if the wind is moving at 0 kph relative to the propeller.
Now imagine that the vehicle is moving 10 kph with a 10 kph tail wind. The air is no longer moving at all relative to the vehicle. The propeller which was slicing effortlessly through the air with a 10 kph headwind, now has an extra 10 kph relative wind at its back, pushing both forward on the propeller and pushing it around faster (returning some energy to the wheels as forward drive).
Likewise, if the vehicle is moving at 50 kph with a 10 kph tail wind, the propeller which would slice effortlessly through a 50 kph relative headwind, would feel an extra 10 kph relative tailwind as it cuts into the 40 kph relative headwind.
If the prop is tuned to cut perfectly through the relative headwind that is opposite the vehicle's velocity relative to the ground, then regardless of the speed the vehicle is moving, the propeller will always "feel" the windspeed as it is relative to the ground.
If the vehicle is built efficiently enough, the energy gained from the constant 10 kph tail wind against the propeller could be greater than energy lost through vehicle drag, friction, mechanical inefficiencies, and propeller drag, and the vehicle could accelerate faster than the speed of the tailwind, until it reaches a speed where the energy gained and lost balance each other out.
The car people are claiming to have a steady state where they take power from the road, deliver it out the back through the fan and maintain a faster than wind speed. However at a faster than wind speed there's a constant drag force requiring an amount of power to overcome it and maintain that faster than wind speed. When the car travels faster than the wind, it can get no power from the wind, so I don't believe that the car can maintain it's speed because there isn't enough power - at a speed faster than the wind, the car, as a whole body, only feels a drain on its energy and will have to slow down. I think that the faster than wind speed can only ever be temporary and a steady state will be less than or equal to the wind speed. Although some of the comments above have offered some very confusing yet convincing reasons to the contrary, I believe that they all ignore certain elements to arrive at their conclusions. Power is the key to the discussion.
Ice boats, multi-hulls and fast planing hulls have been sailing faster than the wind for well over a century, provided the hull is not limited by the length of the wave it makes (due to hull design and weight). The wind which the vessel "sees" is the "apparent wind", the vector resultant of the true wind and the speed of the vessel, so the faster the vessel travels, the faster the "apparent wind". Unfortunately, this effect pulls the wind forward so the sails have to be pulled in until either lateral forces stop the hull planing or, in the case of ice boats, the sails are pointing as high into the wind as possible. For multi-hulls and planing hulls, this is about 90 deg. off the wind but an ice boat can sail to within 40 - 45 deg. off the wind. To achieve maximum aerodynamic lift, ice boats use rotating deep masts and fully battened sails with very heavy sail cloth to maintain shape.
If you built a cart with something like this http://en.wikipedia.org/wiki/Wind_turbine#Vertical_axis_design could you then move into any direction relative to the wind as long as there is SOME wind?
You make a good point, but do you mean "dirigible" rather than "derringer"?
This explanation is completely wrong! Even if the propeller is spinning you can de-construct it's speed into the two components of downwind and perpendicular to the wind. The downwind speed is identical to the speed of the car since they are rigidly attached to each other. So if the car is travelling downwind faster that the speed of the wind then the propeller is also travelling down wind faster than the speed of the wind. It is simple!
-- ssoorrrryy,, dduupplleexx sswwiittcchh oonn.. -Quote found on actual fortune cookie.
The downwind speed is identical to the speed of the car since they are rigidly attached to each other.
Rigidly attached? Did you notice that the propeller turns around in circles?
(If you're trolling, OK ya got me!)
There is probably no one involved in that project and very few people on this site that do not know that. Given that people don't normally spend years trying to prove something that is already known, it's not a stretch to think that maybe there's more to this than your immediate understanding.
Rotational rates are not measured in m/s.
Radians/s
Your analysis is wrong.
The prop first acts as a static sail. Just a big blob catching the wind. That gets the car to moving.
Now there is a dynamic effect that comes into play. The moving car makes the propeller turn. The propeller turns into a much larger pseudo sail. The pseudo sail is drawing energy from the 13mph wind, which pushes the car forward, and draws off some of the energy. The rest of the wind derived energy is pushed back into the prop which drives the car forward even faster. You can think of the propeller backwash as pushing against the wind.
The system only works because there is excess energy beyond what is necessary to drive the car forward.
Aah, change is good. -- Rafiki
Yeah, but it ain't easy. -- Simba
No. The velocity of the propellor in the direction the driver is facing is exactly the same as the velocity of the vehicle in the direction the driver is facing, since the propellor's motion is the same as the vehicles plus some orthogonal component from rotation. Furthermore, since the car is going directly downwind faster than the wind, the velocity of the propellor in the direction the driver is facing is actually greater than the wind velocity, at the surface of the propellor.
In other words, the propellor, while extracting energy from the wind, is actually moving downwind faster than the wind. This is just like a sailboat sailing downwind faster than the wind (which is possible). Of course the sailboat isn't sailing directly downwind faster than the wind (which is impossible in an ordinary sailboat), but neither is the propellor. However, because of the relative motion of the propellor and the vehicle, the vehicle is moving directly downwind faster than the wind—all without violating any laws of physics.
The car is NOT traveling UP wind its traveling DOWN wind.
AND it IS traveling FASTER then the wind ... ... that is the wind RELATIVE to the car.
So relative to the car the wind speed IS ... ... -20 MPH, or NEGATIVE 20 MPH !?!?!?!
So if the car is SITTING on the track going NOWARE, 0 MPH ... ... it IS traveling FASTER then the WIND which is going the WRONG WAY it is going backwards !!!
Would this work in a liquid ?
How about a boat in a channel that has flow with the boat using a propeller on the keel beneath the water to crank a water wheel on the surface of the water ???
If it's so damn "immediately obvious", how the hell did you screw it up so badly -- your description is NOTHING like how it works at all. I should know, I'm the co-designer/builder of the silly thing. JB
So, once the vehicle reaches the wind speed, it uses its wheels to power itself? That doesn't seem to add up. Presumably if the wind is 5 mph it can go faster than 5mph, if the wind is 1 mph it can go faster than that, etc, until the wind speed is zero. When the wind speed is zero, the car uses its wheels to power itself?!?
If you give it a little push, it will speed itself up and keep going forever? It doesn't make sense. Thats perpetual motion to my ears. It seems something else is going on here, probably a misunderstanding of the effects of short wind bursts accelerating the vehicle faster than the average wind speed.
Okay, think about iceboats. Iceboats can go downwind -- but not directly downwind -- very fast. With me so far?
Okay, imagine a featureless plane of ice, with a wind blowing over it constantly. Iceboats could go downwind, at an angle, such that the downwind component of their velocity is faster than the wind's speed. This is not hard to do -- they can easily get to twice the speed of the wind. But they're not moving directly downwind, they're moving at an angle.
Now, take this featureless plane, and wrap it around until it's a featureless cylinder, with iceboats on its surface. They can still go downwind, faster than the wind, on their path that's not directly-down-wind at all, but rather going at an angle to the wind. Their paths describe a sort of helix.
Okay, now. Get several of these boats, all doing this helix, and all starting at the same point. And tie them together. And look... While each individual boat is clearly moving sideways with respect to the wind, the collection of boats, as a whole, is moving directly downwind, while rotating.
Now imagine that you make the cylinder thinner and thinner, and eventually you'll recognize that what you have here is nothing but a fancy way of describing a propeller. Essentially, a propeller that is in some way forced to turn by its motion... And that's what the wheels-geared-to-prop do. They force the prop to turn, and so the prop is doing exactly what all those ice boats were doing on the featureless cylinder.
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Right. Just like the blades on a propeller, which are effectively "tacking" on a helical path. (Actually, I think they're "moving downwind on a broad reach", because tacking is supposed to be upwind, maybe? Memory's not great.)
My blog: http://www.seebs.net/log/ --- My iPhone/iPad app: http://www.seebs.net/seebsfrac/
http://en.wikipedia.org/wiki/Talk:Sailing_faster_than_the_wind
Now with pages and pages of rants that this is obviously impossible, from someone who has a couple of times edited the page to remove the claims that it's possible on the grounds that he's quite sure it isn't. Funny!
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> And the perpendicular (downwind) component is just v(p)=v*sin(theta).
No it's not, the perpendicular (downwind) component of the velocity of _any_ point on the craft, _including_ every single point on the propellor blade's surface, is the same, and equal to the downwind velocity of the centre of mass of the craft. The propellor is rotating in an axis parallel to the wind, so the propellor's rotation has no effect on the downwind component of the velocities.
I'm not saying DWFTTW is impossible, but your long explanation doesn't shine much light on it.
Hi again. Took some time to think about this. I'm actually going to reverse my conclusion that it's fundamentally impossible. Indeed I can now prove it is possible.
Before I do that I'm going to note that 1) I don't buy your explanation 2) and I don't yet buy that this propeller car actually implements what I will describe. Indeed I suspect it may not.
First what's my issue with your explanation. You use a shifting reference frame that confuses forces with simple Lorentz frame shifts. That is, take your explanation and remove the propeller: if I have a wheeled cart on a conveyor belt it can stay in a single place in the frictionless limit. It can even move forward or backward relative to an observer off the conveyor depending with a small push. All the effect you describe apply to this wheeled cart. Now you can glue a propeller on it if you want. But that's not creating a force that causes this effect.
Now here's an actual constructive proof you can do this. The proof takes the form of a gendanken experiment which, if you don't know the term, means a thought experiment that describes something that is idealized and probably not the way you would actually do something practically but simply shows that you can do something or the converse.
So build a hypothetical art like this: you put a huge spinnaker/parachute on the front to act as a wind ratchet (it pulls one way, but collapses and has no drag the other). You also put a dynamo on the wheel that can charge a battery. When the cart is below wind speed the parachute pulls the cart with a strong force, and the dyanmo charges the battery. I can then discharge the battery to drive the cart forward faster than the wind. eventually this battery runs down and the cart slows to below wind speed. I can repeat this cycle to maintain an average speed faster than the wind downwind since I can make the sail as large as I want to get as much energy I want in a fixed interval of time. that is total distance divided by total time can be faster than the wind, including the time it take to charge the battery.
SO far this does not achieve continuous faster than wind speed just an average that is faster than wind speed.
Now I place over this a black box I cannot see though but allows wind to pass with no effect. The black box is very very long and hooked to the cart by some rails that can slide forward and backward on command.
What I do is I carefully slide these rails so that no matter what speed the cart is currently moving, the black box is moving forward at the average speed of the cart. THat is when the cart is moving slower than wind speed it is sliding the rails forward so that the black box covering is moving forawrd relative to the cart. When the cart is moving faster than average, it pulls the rails back to the carts position in the black box moves forward.
Since the black box itself has no mass or wind resistance, we assume it takes no energy to move it.
From the outside all I see is a black box moving at a continus speed that is always faster than the wind. The center of mass of the contraption is not moving on average faster than the wind since the cart is invisibly changing it's position under the black box. But to all observers the exterior is moving faster than the wind perpetually.
SO to recap: yes this us rube goldberg. That's the nature of a gedanken experiment. But the point is it proves that it could be done without violating any laws of physics.
Now is the tested propeller craft actually achieving this? By this I mean both
1) maintaining an average speed faster than the wind
2) Capable of implementing continuous faster than windspeed.
I'd say neither. If you look at the plots of their speed (see the original website). you will see that if you take total distance and divide it by total time the average is less than wind speed. They did get a peak value greater than wind speed not an average value. That is not very impressive since this can be trivially achieved by tappping potential energy stored in the turning wheels and propeller for a brief but unsustainable boost.
thus since (1) is not proven yet (2) is definitely not proven yet.
However my argument shows the idea is not impossible.
Some drink at the fountain of knowledge. Others just gargle.