58 thoughts on “Don’t Know Much About Thermodynamics”
Vehicles go faster than the wind that’s pushing them all the time. It’s not the speed, but the energy that matters. This isn’t the same argument as perpetual motion.
“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.”
That’s perpetual motion. In fact, it’s creating energy from nothing.
It wouldn’t surprise me if he was able to go faster than the wind that was supplying the drive force, sail boats and especially ice boats do it all the time. Whether he understands what he’s doing is another question. If he disconnected that wheel drive system he might find out that he will go even faster.
Thank God the wind always blows in the direction you need to go.
You are so seldom wrong that I am in shock. Perpetual motion involves no outside the system energy being added (and even the claim that energy can be drawn out.)
Here we have wind energy being added to the system. While 3 times windspeed is surprising, the only question is how that wind energy is used.
Sailboats often travel faster than the wind. The explanations I’ve read is that relative wind is a factor.
I don’t like the idea of riding in a car made of foam, but if it works, you can’t argue with success.
Thank God the wind always blows in the direction you need to go.
You forgot the /sarc tag but did you forget about tacking?
The thought experiment that shows that it is possible:
Build a 10 mile long vehicle, in a 1 mph wind. Set up a stationary windmill at the front, using the converted energy to power the forward motion of the vehicle. After half an hour, take down the windmill and move it to the front of the vehicle. Rinse and repeat.
The key to understanding this class of vehicle (and backward flowing props) is that what they have found is a way to build a windmill that uses the flow differential between the ground and the air, not the vehicle and the air.
Perpetual motion involves no outside the system energy being added (and even the claim that energy can be drawn out.)
No, perpetual motion involves a claim that the system is internally generating more energy than what is being externally added. As briand noted, it is possible for a wind-driven vehicle to go faster than the wind, but his explanation for how this is occurring is physical nonsense.
A sailboat or iceboat travels faster than the wind because the wind is putting in energy faster than friction takes out, so the kinetic energy of the boat increases until the two forces are in balance. Again, that’s not what he claims is happening here. He’s using the wind to drive wheels to drive a propeller to create wind to drive wheels to…
The only way this vehicle could travel faster that the wind in the downwind direction is if the prop to vehicle connection were geared and it would only go faster that the wind for a short period of time it would take the prop to lose the inertia it had built up while traveling slower than the wind. The direction of the wind vain is determined by apparent wind and this would also quickly change direction as the vehicle speed increased to near the speed of the actual wind. Yes sailboats and ice boats are capable of traveling faster that the actual wind speed, depending on the boat or ice boat much faster, however not in the downwind direction.
OK, jjs, try this:
You have a tracked vehicle. The bottom of the track stays motionless relative to the vehicle. You arrange things so that the windmill is attached to the track, and freewheels unless it is in contact with the ground.
Can you see that with that setup you can get energy from the wind regardless of speed and direction of the vehicle? This is just using a more clever implementation of that.
He’s using the wind to drive wheels to drive a propeller to create wind to drive wheels to…
Which leaves the possibility that it works, but his explanation for why is wrong.
He claims the wheels turn the prop, but the reality is that they are simply chained together. The prop is extracting energy from the wind. Each airfoil is moving against a relative wind extracting energy. This is the energy driving the wheels.
The true explanation for how it works may be yet to come. We all know perpetual motion doesn’t work, so either this doesn’t work or there is a different explanation.
Sorry, that should have been: “You have a tracked vehicle. The bottom of the track stays motionless relative to the ground.”
The bottom of a tire stays motionless relative to the ground as well… unless you do a burn out.
perpetual motion involves a claim that the system is internally generating more energy than what is being externally added.
So nuclear power plants are perpetual motion?
Which leaves the possibility that it works, but his explanation for why is wrong.
And crop circles could be evidence of alien visitations.
Based on numerous past examples of energy through exotic science in someone’s garage, the most likely principle in effect here is chicanery. The only question is where does he store the batteries?
No, a nuclear power plant is a power plant, not a perpetual motion machine.
1) It appears to physically work. Airflow streamers pointing upwind iand counter to the direction of travel n the picture.
2) His actual explanation is either incomprehensible or flat wrong. Or both. Squared.
So screw his explanation, and let’s postulate on WTF.
The piece that seems to be missing in both explanations is either a “clutch” or blade-pitch adjustment. Or perhaps both.
With the prop disengaged, sail action on the hull alone gets you to a decent fraction of windspeed. With the prop at a ‘neutral’ pitch, engaging the links between the wheels and the prop can get the prop spinning at a high speed while maintaining a similar almost-windspeed velocity. (Every timeslice the slight-but-positive push from wind boosts hull velocity a smidge. That same smidge is then transferred into the angular momentum of the blades – slowing the hull slightly. Repeat.)
So now we have a hull moving at, say 90% of windspeed and a whole pack of stored rotational energy. Stored energy is stored energy, I don’t much care how much they hype the “No battery!” line. Adjust the pitch of the blades and they go from ‘neutral’ to ‘providing thrust’. Voila.
To know whether or not something along the above lines was happening, you’d need to know how long the vehicle took from rest-to-windspeed and how long the vehicle maintained a velocity higher than windspeed.
My point is that one of the ways to debunk a perpetual motion device is to show it has an external energy source.
We know wind can drive a vehicle. We also know that a wind driven vehicle like a sailboat may go faster than the wind.
What we don’t know until proven is if this vehicle is an example of one that can go faster than the wind… afterwhich we will then have to understand why (even if the inventor himself doesn’t know.)
You forgot the /sarc tag but did you forget about tacking?
True. But we outgrew sail-powered passenger and cargo transportation at least a hundred years ago.
One can still employ 18th-century methods of transit today, and you can even utilize 21st century materials in doing so. But unless they can develop a means to utilize our existing transportation infrastructure instead of a dry lake bed or hundreds of square miles of open water then this kind of stuff will stay in the “gee whiz” bin
It looks like a fixed pitch device.
this kind of stuff will stay in the “gee whiz” bin
Yup.
So nuclear power plants are perpetual motion?
Technically, the energy from a nuclear power plant is already in the atoms, and is “generated” by taking the atoms apart to let the energy out (“This episode of Sesame Street is brought to you by the letter Omigawd.”), so it doesn’t violate any physical laws — ergo, not “perpetual motion.”
Unless this wind-powered car is somehow tapping the entropy inherent in the structure of the vehicle to generate the energy that moves it, I don’t see how it can work either.
Note that after the chain broke the prop reverses direction. This would indicate a large relative wind when operating before the break.
Talking about wind may be a misdirection however; It’s the airfoil cutting through the air (regardless of wind) that adds energy to the system. The faster the vehicle moves the more energy added until total friction of the system equalizes with the additional energy until terminal velocity is reached… or the chain breaks.
tapping the entropy inherent in the structure of the vehicle
No, airfoils are adding energy to the chain, which suggests why it broke.
it seems to me the airfoil (Propeller) needs a variable pitch.
start with a zero Angle of Attack, and as you begin moving,
keep adjusting pitch to force induced lift.
This particular vehicle looks full of fail. However I am in favor of electric vehicles as a way to divorce the energy source from transportation. Or synthetic fuels for that matter.
Using wheels to drive a propeller works, but the “inventor’s” description is inarticulate, to be generous. I have a book about the difference between crank and genius, title not handy at the moment, but in the book (and illustrated on the cover) is a bicycle with a propeller mounted on it, that the builder used to demonstrate traveling downwind at greater than the wind speed.
The idea isn’t new, only the implementation, thus the scare quotes.
Ken said: We know wind can drive a vehicle. We also know that a wind driven vehicle like a sailboat may go faster than the wind.
A minor point, but a sailboat cannot go downwind faster than the wind, whereas the whole point of the blackbird was to go downwind.
A sailboat can sometimes go faster than the wind when it’s close hauled or on a close reach (i.e. into the wind at an angle). The apparent wind speed becomes higher than true wind speed, and that makes a big difference.
Obviously a wind-powered machine can theoretically reach speeds higher than the wind, going straight downwind. Suppose a very light sail with a very large collection area — say 10 square miles that weigh 4 ounces. How much momentum and energy could such a sail collect? Huge amounts. We collect and store as much energy and momentum as we like, and then transfer it to the engine to accelerate our craft. The only limitations on our final speed are determined by mass density of the sail, and for a small enough density, we can reach any speed you like.
But the key here is storing the energy, because once we’re actually going faster than the wind, in the direct downwind direction, it’s no longer possible to collect more momentum and energy from the friction forces that the wind exerts on the sail than are needed to compensate for the loss of speed produced by those forces. (We can still do it if we’re traveling obliquely, so long as the component of our velocity in the downwind direction hasn’t yet exceeded the velocity of the wind.)
As I understand it, that’s all that’s going on here. He’s just finding a way to store the wind momentum and energy in the momentum of the craft and prop, so that he can use it during lulls in the wind to exceed the instantaneous wind velocity. And if I read the story right, that’s all they’re doing: exceeding the instantaneous wind velocity at various points during the trip. I do not think the average speed of the craft is exceeding the average wind speed.
I don’t think it’s possible for the average velocity in the downwind direction of a wind-powered craft to indefinitely exceed the average wind velocity. But that’s a different question.
Carl, the wheels are driving the prop- exactly the inverse of a wind powered vehicle. Consider a wind speed of 10 m/s, with the vehicle traveling at 11 m/s downwind. If you put a 100 Watt load on the wheels, the drag force is power/velocity, or 10 newtons. Put that 100 W of power into the propeller, accelerating some air from -1 to -2 m/s relative velocity. By E=mv2/2, the kinetic energy change of the air passing through the prop _as_seen_by_the_prop_ goes from 0.5 J/kg to 2.0 J/kg, and the delta is 1.5 J/kg. If the prop is 66% efficient, it can add about 66 J of energy to 44 kg/s of mass flow. Those 44 kg/s, times 1 m/s velocity change, give 44 Newtons of thrust, and the vehicle accelerates downwind, leaving a wake of air that has been slowed from 10 m/s down to 9 m/s. Add vortices at the edges, of course.
With higher speeds, the power demand of the prop goes up faster than the power output of the wheels, and the speed is limited by the lift to drag ratio of the system.
I wonder if he realizes it will go directly upwind too?
The explanation is quite accurate though perhaps written in such a way as to catch people who do not entirely understand basic physics. That is likely its intent, this problem is used as a basic test of people’s understanding of physics. I remember being exposed to it when I was a school kid.
This particular demonstration is just a physics toy, anyone who has sailed a decent yacht, land yacht, ice yacht, etc., has likely exceeded wind speed down wind – it is standard operating procedure.
Thank you Doug for your good explanation.
A simple way to understand it is from an energy perspective, and from that perspective it matters little which direction one sails in. One is simply exploiting the energy difference between two fluid streams traveling at different speeds. Inefficiencies in the vehicle eventually limit the number of times one can multiply the wind speed.
The classic version of this physics problem is that there is a yacht sailing down a river. The first day it has a 10 knot tail wind and the water current is zero, the second day it has a 10 knot tail wind and the water current speed is also 10 knots in the same direction as the wind. Which day does it travel the furtherest? The first day of course because that is when there is an exploitable speed difference between the wind and water streams.
I’m a bit confused by this discussion.
I see at least four things we could be discussing here:
1) whether or not is it possible at all to do downwind faster than the wind (or directly against the wind for that matter)
2) whether this particular device is a fraud or not
3) assuming the device in question isn’t a fraud, whether the explaination of how it works makes sense
4) how the device in question works, assuming it isn’t a fraud and is working
My thinking on each is as follows
1–possible, because it may be possible to cleverly use the eternal power input of the wind
2–probably not a fraud, since I think it’s possible and I don’t get any sense of hoaxsterism going on (but I could certainly be wrong)
3–the explaination cited makes no sense to me, and I think it doesn’t explain what is going on in the device (assuming the device isn’t a fraud)
4–this is probably the most interesting discussion. Is it the one we’re having?
OK, I think I get what Jones and Borgelt are saying.
The prop is geared to the wheels, and you have some kind of pitch control on the prop so the prop is “feathered” when the apparent wind speed across the prop is equal to vehicle speed — this is the calm wind condition. If you have the wind behind you, the prop is no longer “feathered” and you get a force on the prop that supplies power to the wheels. If you have the wind in your face, the prop is no applying a retarding or braking force to wheels. But if you change the blade angle, you can change that braking force to a thrust.
So to control whether the car goes or slows requires a control to adjust blade pitch, and the car can go any speed in relation to either a head or tail wind provided the prop operates at a high enough lift/drag values and the driver has supplied the correct blade angle.
It is a standard basic question to catch out poor physics students, and from what I can tell it caught quite a few. It is meant to be an exercise for the student, explaining it spoils the fun. The student is meant to first solve it on their own before being given the answer.
Not knowing much about thermodynamics is probably not a problem either – it is not at heart a thermodynamics question.
OMG. Rand, we don’t agree on a lot of things, but doesn’t this discussion cause you to question many of your readers grasp of simple science? Someone once told me that most of the “new space” supporters are computer hacker/programmers with little understanding of fluid, thermo, or solid body dynamics, etc. I’m starting to believe that’s true.
brian d:
I am a computer programmer and had college level thermodynamics. I know the three laws, what a Carnot engine is, and some of the other engine cycles. Many computer programmers know thermodynamics. I started learning basic thermodynamics, kinematics and fluids before college. I may not know it in depth like a mechanical engineer but I know enough of the basics to have an informed opinion.
This is clearly bullshit, like Rand said: 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.
It violates the first law of thermodynamics. There will be energy losses on the wheels pushing against the pavement, the propeller, etc. The system cannot power itself in perpetuity without an external power source. As for considering the existing wind resource as an external power source, the wind does not blow 100% of the time, nor at the same speed. The efficiency of how you can harvest the wind resource depend on several factors including wind speed, turbine diameter, etc.
a sailboat cannot go downwind faster than the wind
A sail on a sailboat is an airfoil with two forces acting on it. You have the wind pushing, that’s the weaker force. Then you have lift perpendicular to the wind, that’s the stronger force. This vehicle is not using a simple sail. It’s using a propeller. A propeller generates that perpendicular lift by slicing through the air rather than passively letting the air flow over it like a simple sail.
What does this all mean? First, it screws up any intuition you may have about how things with airfoils work.
When a sailboat is going downwind you open the sail to get the push without the lift (which would push you over sideways.) Any angle but straight into or away from the wind you can use the sail as an airfoil to gain speed.
I’m not sure how this device with the propellers works, but it would certainly get a lot of force applied if it had any relative wind at all, meaning even if there is no wind, but it is moving, force would be generated. If you’ve ever sailed or windsurfed you know the wind is like a living thing with a lot of power.
I don’t know if that power can drive the vehicle because it seems too complicated to analyze but the video seems to support that. Those are not variable pitch propellers so I don’t think it’s a case of stored energy. I’d like to know more.
pushing the wind backwards
This is wrong, like saying a rocket pushes against the atmosphere to give you lift. IT’S AN AIRFOIL. You know, bernouli. Wind at leading edge joins back together at trailing edge. Pressure differential means perpendicular lift.
As for considering the existing wind resource as an external power source, the wind does not blow 100% of the time, nor at the same speed.
Right, and for a turning prop it doesn’t matter. With no wind it probably would wind down, but with more wind, adding energy, it may compensate for the loss and give it a terminal velocity greater than zero.
Anyone who proposes perpetual motion is either a fool or a charlatan.
Either way don’t invest.
Even if it is a mere “Land sailboat”…. so? That’s not exactly a useful tech.
Wind is very low energy density. Given the destiny of air and the windage velocities seen in normal operation.
The physics of the system DO work, but yes, wind power is generally low power density and unreliable. It’s just a stunt, but the entire purpose was just to win the equivalent of a bar bet anyway 🙂
This is clearly bullshit, like Rand said:
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 is very amusing – that statement is quite correct, but it is left as an exercise for the student to figure out why. 🙂
The problem is not that you do not know anything about thermo, the problem is that you do not know anything about basic Newtonian physics – F=ma. 🙂
Forget the propeller, wings or anything like that and just use basic momentum theory. Of course the second law is not violated, but that comes later (I studied thermo, though my chemistry is weak). The second law prevents the wind speed being multiplied an infinite number of times – one gets into diminishing returns. The power component that gets added to forward thrust becomes a smaller and smaller proportion of the total power and in practice is soon overwhelmed by inefficiencies – especially for inefficient craft.
Just consider this as a closed system with two input/output.
Relative wind is adding energy, friction is subtracting.
The only real question is how much wind does it take? A tornado would do it. One knot probably wouldn’t. Did any of you look at the video of it starting from almost a standing start and accelerate (just less than 1.5 minutes into the video.) I posted it on my site.
It can be a difficult problem to visualize, but that doesn’t make it bogus, just a non-intuitive result.
Rand, actually its not perpetual motion. What its doing is getting its initial speed from the wind pushing the vehicle downwind, and this velocity causes the wheels to turn the propeller, the propeller generates thrust IN OPPOSITION TO THE WIND, which allows it to thrust against the wind vector, which is what allows it to travel faster than the wind. It is essentially creating a “sail” out of air that it is propelling backward against the tailwind.
This is actually pretty ingenious. I dont know if the mechanism is efficient enough to actually accomplish this, but its no more a perpetual motion machine than a sailboat is.
Okay if you still dont think so, imagine a blimp, with propellers that is cabled to a railroad car. Wind blows the blimp down the rail, dragging the car with it. The car’s wheels have a generator that generates power thats fed up to the blimps propellers motors, so the blimp can thrust AGAINST THE WIND to go faster downwind than the wind is moving…. its perfectly functional.
Okay if you still dont think so, imagine a blimp, with propellers that is cabled to a railroad car.
Here’s another thought experiment that might help:
Imagine a car with a propeller mounted sideways with the propeller driving the wheels. It’s easy to see that with good design the car could go faster than the blowing wind in a direction perpendicular to the wind, because the the power supplied to the propeller by the wind could certainly be greater than the power necessary to move the vehicle just at windspeed. The power from the wind is converted to (sideways) motion via the wheels interacting with the ground. This is fine, as long as the vehicle doesn’t tip over.
The confusing issue is that in moving in exactly the same direction that the wind is blowing, the relative windspeed goes to zero when you are moving at the same speed as the wind. Thus how can the wind turn the propeller to drive the wheels? It cannot in that simple configuration.
We run into a similar issue with a sailboat, but much more quickly–if I have the simplest imaginiable sailboat, how do I go any direction except directly downwind? The answer in a sailboat is that I stick a keel in the water, and, as others have mentioned, I use the sideways lifting force acting on the sail to act with the water and the keep, and I get a force vector which is not directly downwind. In fact, I can head into the wind, at least at some angle.
Here’s maybe the key. The simplest propeller car wouldn’t go downwind faster than the wind. But as we can stick a keel in the water with a sailboat, we can do something clever with the vehicle wheels and the propeller. The relative windspeed might go to zero for the vehicle, but the props of our clever propeller are moving through the air much faster than the relative windspeed. With clever design, we are using the propeller to extract energy from wind, using the wheels in a way (somewhat) analogous to the boat keel (and hull), even though we happen to be travelling in the same direction as the wind.
I haven’t tried to work the math yet but it ought to be interesting. If you start in the state where the vehicle is going at exactly wind speed, there is no direct force from the wind on the vehicle in either direction. So the only force slowing the vehicle down is the friction between the tires and the road. And, if freewheeling, the propeller would not be spinning. If you make assumptions about how the propeller is set up, you can make calculations from this point and see if there is a net positive force pushing in the same direction as the wind is blowing. If there is, then the vehicle must move faster than the wind.
(I think other explainations earlier might be better than this last paragraph, but noting that it is not difficult to go faster than the wind in another direction as a sailboat does with a keel, and the observation that a propeller blade is moving much faster than the wind might provide the intuition to help see how this is possible).
The trick is that it’s not a sail powered vehicle at all.
Here’s an analogy that may help. Imagine a boat on a narrow canal headed down stream. Slowly the current of the water starts to move the boat until it’s travelling at some speed slower than the current but definitely not stationary relative to the shore. Now imagine that the captain extends a contraption over the side of the boat to the shore. On this contraption is a wheel which touches the shore and turns in the direction of motion.
It should be obvious that this wheel generates power, as it is rotating due to the differential speed of the boat and the shore. Now imagine this wheel is connected via direct gear linkage to a prop in the stern of the boat which provides thrust. It ought to be intuitive that with this set up it should be possible for the boat to achieve at least some small increment of speed beyond the speed of the current of the water, because you can achieve nearly the speed of the current with 0 power, but you have a power source available. In actuality though the speed in such a scenario can be much higher than the speed of the water current. As long as you can extract energy from the differential between the ground and fluid speeds you can go as fast as drag and friction allow.
The trick is that the fluid and the ground are not stationary to each other. So the power gained from the faster moving wheels can be greater than the power lost through the prop being turned in the relatively slower wind. It’s quite counter intuitive at 2x or 3x the wind speed, but it works nonetheless.
Vehicles go faster than the wind that’s pushing them all the time. It’s not the speed, but the energy that matters. This isn’t the same argument as perpetual motion.
“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.”
That’s perpetual motion. In fact, it’s creating energy from nothing.
It wouldn’t surprise me if he was able to go faster than the wind that was supplying the drive force, sail boats and especially ice boats do it all the time. Whether he understands what he’s doing is another question. If he disconnected that wheel drive system he might find out that he will go even faster.
Thank God the wind always blows in the direction you need to go.
You are so seldom wrong that I am in shock. Perpetual motion involves no outside the system energy being added (and even the claim that energy can be drawn out.)
Here we have wind energy being added to the system. While 3 times windspeed is surprising, the only question is how that wind energy is used.
Sailboats often travel faster than the wind. The explanations I’ve read is that relative wind is a factor.
I don’t like the idea of riding in a car made of foam, but if it works, you can’t argue with success.
Thank God the wind always blows in the direction you need to go.
You forgot the /sarc tag but did you forget about tacking?
The thought experiment that shows that it is possible:
Build a 10 mile long vehicle, in a 1 mph wind. Set up a stationary windmill at the front, using the converted energy to power the forward motion of the vehicle. After half an hour, take down the windmill and move it to the front of the vehicle. Rinse and repeat.
The key to understanding this class of vehicle (and backward flowing props) is that what they have found is a way to build a windmill that uses the flow differential between the ground and the air, not the vehicle and the air.
Perpetual motion involves no outside the system energy being added (and even the claim that energy can be drawn out.)
No, perpetual motion involves a claim that the system is internally generating more energy than what is being externally added. As briand noted, it is possible for a wind-driven vehicle to go faster than the wind, but his explanation for how this is occurring is physical nonsense.
A sailboat or iceboat travels faster than the wind because the wind is putting in energy faster than friction takes out, so the kinetic energy of the boat increases until the two forces are in balance. Again, that’s not what he claims is happening here. He’s using the wind to drive wheels to drive a propeller to create wind to drive wheels to…
The only way this vehicle could travel faster that the wind in the downwind direction is if the prop to vehicle connection were geared and it would only go faster that the wind for a short period of time it would take the prop to lose the inertia it had built up while traveling slower than the wind. The direction of the wind vain is determined by apparent wind and this would also quickly change direction as the vehicle speed increased to near the speed of the actual wind. Yes sailboats and ice boats are capable of traveling faster that the actual wind speed, depending on the boat or ice boat much faster, however not in the downwind direction.
OK, jjs, try this:
You have a tracked vehicle. The bottom of the track stays motionless relative to the vehicle. You arrange things so that the windmill is attached to the track, and freewheels unless it is in contact with the ground.
Can you see that with that setup you can get energy from the wind regardless of speed and direction of the vehicle? This is just using a more clever implementation of that.
He’s using the wind to drive wheels to drive a propeller to create wind to drive wheels to…
Which leaves the possibility that it works, but his explanation for why is wrong.
He claims the wheels turn the prop, but the reality is that they are simply chained together. The prop is extracting energy from the wind. Each airfoil is moving against a relative wind extracting energy. This is the energy driving the wheels.
The true explanation for how it works may be yet to come. We all know perpetual motion doesn’t work, so either this doesn’t work or there is a different explanation.
Sorry, that should have been: “You have a tracked vehicle. The bottom of the track stays motionless relative to the ground.”
The bottom of a tire stays motionless relative to the ground as well… unless you do a burn out.
perpetual motion involves a claim that the system is internally generating more energy than what is being externally added.
So nuclear power plants are perpetual motion?
Which leaves the possibility that it works, but his explanation for why is wrong.
And crop circles could be evidence of alien visitations.
Based on numerous past examples of energy through exotic science in someone’s garage, the most likely principle in effect here is chicanery. The only question is where does he store the batteries?
No, a nuclear power plant is a power plant, not a perpetual motion machine.
1) It appears to physically work. Airflow streamers pointing upwind iand counter to the direction of travel n the picture.
2) His actual explanation is either incomprehensible or flat wrong. Or both. Squared.
So screw his explanation, and let’s postulate on WTF.
The piece that seems to be missing in both explanations is either a “clutch” or blade-pitch adjustment. Or perhaps both.
With the prop disengaged, sail action on the hull alone gets you to a decent fraction of windspeed. With the prop at a ‘neutral’ pitch, engaging the links between the wheels and the prop can get the prop spinning at a high speed while maintaining a similar almost-windspeed velocity. (Every timeslice the slight-but-positive push from wind boosts hull velocity a smidge. That same smidge is then transferred into the angular momentum of the blades – slowing the hull slightly. Repeat.)
So now we have a hull moving at, say 90% of windspeed and a whole pack of stored rotational energy. Stored energy is stored energy, I don’t much care how much they hype the “No battery!” line. Adjust the pitch of the blades and they go from ‘neutral’ to ‘providing thrust’. Voila.
To know whether or not something along the above lines was happening, you’d need to know how long the vehicle took from rest-to-windspeed and how long the vehicle maintained a velocity higher than windspeed.
My point is that one of the ways to debunk a perpetual motion device is to show it has an external energy source.
We know wind can drive a vehicle. We also know that a wind driven vehicle like a sailboat may go faster than the wind.
What we don’t know until proven is if this vehicle is an example of one that can go faster than the wind… afterwhich we will then have to understand why (even if the inventor himself doesn’t know.)
You forgot the /sarc tag but did you forget about tacking?
True. But we outgrew sail-powered passenger and cargo transportation at least a hundred years ago.
One can still employ 18th-century methods of transit today, and you can even utilize 21st century materials in doing so. But unless they can develop a means to utilize our existing transportation infrastructure instead of a dry lake bed or hundreds of square miles of open water then this kind of stuff will stay in the “gee whiz” bin
It looks like a fixed pitch device.
this kind of stuff will stay in the “gee whiz” bin
Yup.
Technically, the energy from a nuclear power plant is already in the atoms, and is “generated” by taking the atoms apart to let the energy out (“This episode of Sesame Street is brought to you by the letter Omigawd.”), so it doesn’t violate any physical laws — ergo, not “perpetual motion.”
Unless this wind-powered car is somehow tapping the entropy inherent in the structure of the vehicle to generate the energy that moves it, I don’t see how it can work either.
Note that after the chain broke the prop reverses direction. This would indicate a large relative wind when operating before the break.
Talking about wind may be a misdirection however; It’s the airfoil cutting through the air (regardless of wind) that adds energy to the system. The faster the vehicle moves the more energy added until total friction of the system equalizes with the additional energy until terminal velocity is reached… or the chain breaks.
tapping the entropy inherent in the structure of the vehicle
No, airfoils are adding energy to the chain, which suggests why it broke.
it seems to me the airfoil (Propeller) needs a variable pitch.
start with a zero Angle of Attack, and as you begin moving,
keep adjusting pitch to force induced lift.
This particular vehicle looks full of fail. However I am in favor of electric vehicles as a way to divorce the energy source from transportation. Or synthetic fuels for that matter.
Using wheels to drive a propeller works, but the “inventor’s” description is inarticulate, to be generous. I have a book about the difference between crank and genius, title not handy at the moment, but in the book (and illustrated on the cover) is a bicycle with a propeller mounted on it, that the builder used to demonstrate traveling downwind at greater than the wind speed.
The idea isn’t new, only the implementation, thus the scare quotes.
Ken said:
We know wind can drive a vehicle. We also know that a wind driven vehicle like a sailboat may go faster than the wind.
A minor point, but a sailboat cannot go downwind faster than the wind, whereas the whole point of the blackbird was to go downwind.
A sailboat can sometimes go faster than the wind when it’s close hauled or on a close reach (i.e. into the wind at an angle). The apparent wind speed becomes higher than true wind speed, and that makes a big difference.
Obviously a wind-powered machine can theoretically reach speeds higher than the wind, going straight downwind. Suppose a very light sail with a very large collection area — say 10 square miles that weigh 4 ounces. How much momentum and energy could such a sail collect? Huge amounts. We collect and store as much energy and momentum as we like, and then transfer it to the engine to accelerate our craft. The only limitations on our final speed are determined by mass density of the sail, and for a small enough density, we can reach any speed you like.
But the key here is storing the energy, because once we’re actually going faster than the wind, in the direct downwind direction, it’s no longer possible to collect more momentum and energy from the friction forces that the wind exerts on the sail than are needed to compensate for the loss of speed produced by those forces. (We can still do it if we’re traveling obliquely, so long as the component of our velocity in the downwind direction hasn’t yet exceeded the velocity of the wind.)
As I understand it, that’s all that’s going on here. He’s just finding a way to store the wind momentum and energy in the momentum of the craft and prop, so that he can use it during lulls in the wind to exceed the instantaneous wind velocity. And if I read the story right, that’s all they’re doing: exceeding the instantaneous wind velocity at various points during the trip. I do not think the average speed of the craft is exceeding the average wind speed.
I don’t think it’s possible for the average velocity in the downwind direction of a wind-powered craft to indefinitely exceed the average wind velocity. But that’s a different question.
Carl, the wheels are driving the prop- exactly the inverse of a wind powered vehicle. Consider a wind speed of 10 m/s, with the vehicle traveling at 11 m/s downwind. If you put a 100 Watt load on the wheels, the drag force is power/velocity, or 10 newtons. Put that 100 W of power into the propeller, accelerating some air from -1 to -2 m/s relative velocity. By E=mv2/2, the kinetic energy change of the air passing through the prop _as_seen_by_the_prop_ goes from 0.5 J/kg to 2.0 J/kg, and the delta is 1.5 J/kg. If the prop is 66% efficient, it can add about 66 J of energy to 44 kg/s of mass flow. Those 44 kg/s, times 1 m/s velocity change, give 44 Newtons of thrust, and the vehicle accelerates downwind, leaving a wake of air that has been slowed from 10 m/s down to 9 m/s. Add vortices at the edges, of course.
With higher speeds, the power demand of the prop goes up faster than the power output of the wheels, and the speed is limited by the lift to drag ratio of the system.
I wonder if he realizes it will go directly upwind too?
The explanation is quite accurate though perhaps written in such a way as to catch people who do not entirely understand basic physics. That is likely its intent, this problem is used as a basic test of people’s understanding of physics. I remember being exposed to it when I was a school kid.
This particular demonstration is just a physics toy, anyone who has sailed a decent yacht, land yacht, ice yacht, etc., has likely exceeded wind speed down wind – it is standard operating procedure.
Thank you Doug for your good explanation.
A simple way to understand it is from an energy perspective, and from that perspective it matters little which direction one sails in. One is simply exploiting the energy difference between two fluid streams traveling at different speeds. Inefficiencies in the vehicle eventually limit the number of times one can multiply the wind speed.
The classic version of this physics problem is that there is a yacht sailing down a river. The first day it has a 10 knot tail wind and the water current is zero, the second day it has a 10 knot tail wind and the water current speed is also 10 knots in the same direction as the wind. Which day does it travel the furtherest? The first day of course because that is when there is an exploitable speed difference between the wind and water streams.
I’m a bit confused by this discussion.
I see at least four things we could be discussing here:
1) whether or not is it possible at all to do downwind faster than the wind (or directly against the wind for that matter)
2) whether this particular device is a fraud or not
3) assuming the device in question isn’t a fraud, whether the explaination of how it works makes sense
4) how the device in question works, assuming it isn’t a fraud and is working
My thinking on each is as follows
1–possible, because it may be possible to cleverly use the eternal power input of the wind
2–probably not a fraud, since I think it’s possible and I don’t get any sense of hoaxsterism going on (but I could certainly be wrong)
3–the explaination cited makes no sense to me, and I think it doesn’t explain what is going on in the device (assuming the device isn’t a fraud)
4–this is probably the most interesting discussion. Is it the one we’re having?
OK, I think I get what Jones and Borgelt are saying.
The prop is geared to the wheels, and you have some kind of pitch control on the prop so the prop is “feathered” when the apparent wind speed across the prop is equal to vehicle speed — this is the calm wind condition. If you have the wind behind you, the prop is no longer “feathered” and you get a force on the prop that supplies power to the wheels. If you have the wind in your face, the prop is no applying a retarding or braking force to wheels. But if you change the blade angle, you can change that braking force to a thrust.
So to control whether the car goes or slows requires a control to adjust blade pitch, and the car can go any speed in relation to either a head or tail wind provided the prop operates at a high enough lift/drag values and the driver has supplied the correct blade angle.
It is a standard basic question to catch out poor physics students, and from what I can tell it caught quite a few. It is meant to be an exercise for the student, explaining it spoils the fun. The student is meant to first solve it on their own before being given the answer.
Not knowing much about thermodynamics is probably not a problem either – it is not at heart a thermodynamics question.
A few good youtube links-
http://www.youtube.com/watch?v=PhD_3vdIvu4
Turok has several videos-
http://www.youtube.com/profile?user=TraderTurok#g/u
OMG. Rand, we don’t agree on a lot of things, but doesn’t this discussion cause you to question many of your readers grasp of simple science? Someone once told me that most of the “new space” supporters are computer hacker/programmers with little understanding of fluid, thermo, or solid body dynamics, etc. I’m starting to believe that’s true.
brian d:
I am a computer programmer and had college level thermodynamics. I know the three laws, what a Carnot engine is, and some of the other engine cycles. Many computer programmers know thermodynamics. I started learning basic thermodynamics, kinematics and fluids before college. I may not know it in depth like a mechanical engineer but I know enough of the basics to have an informed opinion.
This is clearly bullshit, like Rand said:
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.
It violates the first law of thermodynamics. There will be energy losses on the wheels pushing against the pavement, the propeller, etc. The system cannot power itself in perpetuity without an external power source. As for considering the existing wind resource as an external power source, the wind does not blow 100% of the time, nor at the same speed. The efficiency of how you can harvest the wind resource depend on several factors including wind speed, turbine diameter, etc.
a sailboat cannot go downwind faster than the wind
A sail on a sailboat is an airfoil with two forces acting on it. You have the wind pushing, that’s the weaker force. Then you have lift perpendicular to the wind, that’s the stronger force. This vehicle is not using a simple sail. It’s using a propeller. A propeller generates that perpendicular lift by slicing through the air rather than passively letting the air flow over it like a simple sail.
What does this all mean? First, it screws up any intuition you may have about how things with airfoils work.
When a sailboat is going downwind you open the sail to get the push without the lift (which would push you over sideways.) Any angle but straight into or away from the wind you can use the sail as an airfoil to gain speed.
I’m not sure how this device with the propellers works, but it would certainly get a lot of force applied if it had any relative wind at all, meaning even if there is no wind, but it is moving, force would be generated. If you’ve ever sailed or windsurfed you know the wind is like a living thing with a lot of power.
I don’t know if that power can drive the vehicle because it seems too complicated to analyze but the video seems to support that. Those are not variable pitch propellers so I don’t think it’s a case of stored energy. I’d like to know more.
pushing the wind backwards
This is wrong, like saying a rocket pushes against the atmosphere to give you lift. IT’S AN AIRFOIL. You know, bernouli. Wind at leading edge joins back together at trailing edge. Pressure differential means perpendicular lift.
As for considering the existing wind resource as an external power source, the wind does not blow 100% of the time, nor at the same speed.
Right, and for a turning prop it doesn’t matter. With no wind it probably would wind down, but with more wind, adding energy, it may compensate for the loss and give it a terminal velocity greater than zero.
Anyone who proposes perpetual motion is either a fool or a charlatan.
Either way don’t invest.
Even if it is a mere “Land sailboat”…. so? That’s not exactly a useful tech.
Wind is very low energy density. Given the destiny of air and the windage velocities seen in normal operation.
The physics of the system DO work, but yes, wind power is generally low power density and unreliable. It’s just a stunt, but the entire purpose was just to win the equivalent of a bar bet anyway 🙂
This is clearly bullshit, like Rand said:
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 is very amusing – that statement is quite correct, but it is left as an exercise for the student to figure out why. 🙂
The problem is not that you do not know anything about thermo, the problem is that you do not know anything about basic Newtonian physics – F=ma. 🙂
Forget the propeller, wings or anything like that and just use basic momentum theory. Of course the second law is not violated, but that comes later (I studied thermo, though my chemistry is weak). The second law prevents the wind speed being multiplied an infinite number of times – one gets into diminishing returns. The power component that gets added to forward thrust becomes a smaller and smaller proportion of the total power and in practice is soon overwhelmed by inefficiencies – especially for inefficient craft.
Just consider this as a closed system with two input/output.
Relative wind is adding energy, friction is subtracting.
The only real question is how much wind does it take? A tornado would do it. One knot probably wouldn’t. Did any of you look at the video of it starting from almost a standing start and accelerate (just less than 1.5 minutes into the video.) I posted it on my site.
This breaks no laws of thermodynamics, see:
http://www.youtube.com/watch?v=E7vcQcIaWSQ
and,
http://www.youtube.com/watch?v=JJVsoLcdGMY
It can be a difficult problem to visualize, but that doesn’t make it bogus, just a non-intuitive result.
Rand, actually its not perpetual motion. What its doing is getting its initial speed from the wind pushing the vehicle downwind, and this velocity causes the wheels to turn the propeller, the propeller generates thrust IN OPPOSITION TO THE WIND, which allows it to thrust against the wind vector, which is what allows it to travel faster than the wind. It is essentially creating a “sail” out of air that it is propelling backward against the tailwind.
This is actually pretty ingenious. I dont know if the mechanism is efficient enough to actually accomplish this, but its no more a perpetual motion machine than a sailboat is.
Okay if you still dont think so, imagine a blimp, with propellers that is cabled to a railroad car. Wind blows the blimp down the rail, dragging the car with it. The car’s wheels have a generator that generates power thats fed up to the blimps propellers motors, so the blimp can thrust AGAINST THE WIND to go faster downwind than the wind is moving…. its perfectly functional.
After all these mechanical analogies, all I can imagine now is a large wooden rabbit with wheels…</a<
Here’s another thought experiment that might help:
Imagine a car with a propeller mounted sideways with the propeller driving the wheels. It’s easy to see that with good design the car could go faster than the blowing wind in a direction perpendicular to the wind, because the the power supplied to the propeller by the wind could certainly be greater than the power necessary to move the vehicle just at windspeed. The power from the wind is converted to (sideways) motion via the wheels interacting with the ground. This is fine, as long as the vehicle doesn’t tip over.
The confusing issue is that in moving in exactly the same direction that the wind is blowing, the relative windspeed goes to zero when you are moving at the same speed as the wind. Thus how can the wind turn the propeller to drive the wheels? It cannot in that simple configuration.
We run into a similar issue with a sailboat, but much more quickly–if I have the simplest imaginiable sailboat, how do I go any direction except directly downwind? The answer in a sailboat is that I stick a keel in the water, and, as others have mentioned, I use the sideways lifting force acting on the sail to act with the water and the keep, and I get a force vector which is not directly downwind. In fact, I can head into the wind, at least at some angle.
Here’s maybe the key. The simplest propeller car wouldn’t go downwind faster than the wind. But as we can stick a keel in the water with a sailboat, we can do something clever with the vehicle wheels and the propeller. The relative windspeed might go to zero for the vehicle, but the props of our clever propeller are moving through the air much faster than the relative windspeed. With clever design, we are using the propeller to extract energy from wind, using the wheels in a way (somewhat) analogous to the boat keel (and hull), even though we happen to be travelling in the same direction as the wind.
I haven’t tried to work the math yet but it ought to be interesting. If you start in the state where the vehicle is going at exactly wind speed, there is no direct force from the wind on the vehicle in either direction. So the only force slowing the vehicle down is the friction between the tires and the road. And, if freewheeling, the propeller would not be spinning. If you make assumptions about how the propeller is set up, you can make calculations from this point and see if there is a net positive force pushing in the same direction as the wind is blowing. If there is, then the vehicle must move faster than the wind.
(I think other explainations earlier might be better than this last paragraph, but noting that it is not difficult to go faster than the wind in another direction as a sailboat does with a keel, and the observation that a propeller blade is moving much faster than the wind might provide the intuition to help see how this is possible).
The trick is that it’s not a sail powered vehicle at all.
Here’s an analogy that may help. Imagine a boat on a narrow canal headed down stream. Slowly the current of the water starts to move the boat until it’s travelling at some speed slower than the current but definitely not stationary relative to the shore. Now imagine that the captain extends a contraption over the side of the boat to the shore. On this contraption is a wheel which touches the shore and turns in the direction of motion.
It should be obvious that this wheel generates power, as it is rotating due to the differential speed of the boat and the shore. Now imagine this wheel is connected via direct gear linkage to a prop in the stern of the boat which provides thrust. It ought to be intuitive that with this set up it should be possible for the boat to achieve at least some small increment of speed beyond the speed of the current of the water, because you can achieve nearly the speed of the current with 0 power, but you have a power source available. In actuality though the speed in such a scenario can be much higher than the speed of the water current. As long as you can extract energy from the differential between the ground and fluid speeds you can go as fast as drag and friction allow.
The trick is that the fluid and the ground are not stationary to each other. So the power gained from the faster moving wheels can be greater than the power lost through the prop being turned in the relatively slower wind. It’s quite counter intuitive at 2x or 3x the wind speed, but it works nonetheless.