Can a Wind-Powered Vehicle Travel Downwind Faster Than the Wind?

[spork]

Ok, now I see why the treadmill is related to the wind. But in the case of the wind, there's no need for you to hold the vehicle in place at start up, and the wind will push it along.

That's correct. If our treadmill were long enough we could start the vehicle moving backward at the speed of the belt (equivalent to setting it down on a road with a tailwind). Eventually the relative wind would get the vehicle up to speed and it would finally outpace the wind and advance on the treadmill

Can the vehicle move up the treadmill, or at least remain stationary relative to the treadmill, all the time?

The vehicle will advance on the treadmill. It can even go up a small incline.

This video shows the vehicle advancing on the treadmill:

http://www.youtube.com/watch?v=1BRvYZd81AQ&fmt=18

1BRvYZd81AQ&fmt=18[/youtube]

 

[my_wan]

Of course it's drawing energy from somewhere. It's drawing energy from the interface between the air and road surface. And in either scenario, that interface is identical.

Agreed, but in what direction is this energy being propagated through the craft? Either the prop is powering the wheel or the wheel is powering the prop. The two cases are not equivalent. Trying to describe it like that is like saying it is physically equivalent to say the road is tuning the motor in an automobile. Energy consumption/dissipation always has an absolute direction. Even in General Relativity the curvature of space is an absolute.

That's all fine and dandy, but not relevant.

It's more relevant than what you may think.

You're confusing the question of an irreversible process with the question of equivalency of inertial frames. If what you're telling me were true, you would have discovered an experiment (namely the efficiency of this vehicle) that distinguishes between different inertial frames. And we know no such experiment exists.

It is not a distinction between inertial frames. Your craft is accelerating which is an absolute in both Galilean and Special Relativity. The absolute is determined by what system lost energy and what system that energy was dissipated into. In the treadmill case the treadmill lost energy for every possible observer in any frame of reference and the air gained energy for all observers. If it weren't true you would be getting the electricity for your craft from the treadmill for free. The reverse is true for the air craft case. It is not a difference in inertial frames but what system the energy was dissipated from which then determines the direction the energy propagates through your craft.

 

[my_wan]

There is a simple way to determine unambiguously whether the prop is powering the wheel or the wheel is powering the prop. Run the shaft from the prop to a ring with a peg. The shaft can rotate freely in the ring until a flange on the shaft meets the peg. If the wheel is doing the powering the flange will be on one side of the peg and if the prop is doing the powering it will be on the other side. Surely it can't be on both sides at the same time.

 

[OmCheeto]

Yes it was. We were attacked as charlatans when we presented perfectly valid analyses and analogies. In the end it comes down to this - we were told no such vehicle could be built. We have now built and demonstrated it.

Despite your theory - no transient conditions are involved - nor is any "greater than unity effect". We take the laws of physics pretty seriously where I come from. I wouldn't break even one.

You may not be convinced by the performance in that video. But I assure you there will be no room for doubt with the video we will post within the next day or two.

I think the reason they don't lock these threads immediately is because they want to see how much time and money you can waste trying to convince us that these things work in a way that is not obvious from watching them. This new one seems to operate on a different principle from the outdoor device, that of the wind up toy.

 

[spork]

Either the prop is powering the wheel or the wheel is powering the prop.

That is not true. Just as a sailboat is like a watermelon seed being squeezed between thumb and forefinger, this cart is being "squeezed" between road and wind. The prop pushes on the wheels in the longitudinal sense, and the wheels push on the prop in the rotational sense. The wheels and trasmission provide the equivalent kinematic constraint as the skates on the ice boat.

Trying to describe it like that is like saying it is physically equivalent to say the road is tuning the motor in an automobile.

Your badly mistaken.

Energy consumption/dissipation always has an absolute direction.

Of course. Just as it does on this cart. And that direction is the same whether the road moves or the wind moves. You continue to fail to answer the question of how you can have been the first to discover an experiment that distinquishes between equivalent inertial frames.

It's more relevant than what you may think.

I assure you it's not relevant to this problem.

It is not a distinction between inertial frames. Your craft is accelerating which is an absolute in both Galilean and Special Relativity.

It will accelerate in either case. Just as it will reach equilibrium - faster than the wind - in either case. The two cases are identical.

If it weren't true you would be getting the electricity for your craft from the treadmill for free. The reverse is true for the air craft case.

You're not understanding how this craft works.

There is a simple way to determine unambiguously whether the prop is powering the wheel or the wheel is powering the prop. Run the shaft from the prop to a ring with a peg. The shaft can rotate freely in the ring until a flange on the shaft meets the peg. If the wheel is doing the powering the flange will be on one side of the peg and if the prop is doing the powering it will be on the other side. Surely it can't be on both sides at the same time.

No - it can't. The prop pushes the wheels. The wheels rotate the prop.

I think the reason they don't lock these threads immediately is because they want to see how much time and money you can waste trying to convince us that these things work in a way that is not obvious from watching them. This new one seems to operate on a different principle from the outdoor device, that of the wind up toy.

Before the insults were aimed at me claiming perpetual motion. I should never have been able to make this thing. I'm glad to see you have a new line of insults - equally invalid - at the ready.

 

[OmCheeto]

Before the insults were aimed at me claiming perpetual motion. I should never have been able to make this thing. I'm glad to see you have a new line of insults - equally invalid - at the ready.

hmmm... I thought I'd deleted my statement that the reason they called you charlatans was because you are charlatans.

 

[my_wan]

To this:

There is a simple way to determine unambiguously whether the prop is powering the wheel or the wheel is powering the prop. Run the shaft from the prop to a ring with a peg. The shaft can rotate freely in the ring until a flange on the shaft meets the peg. If the wheel is doing the powering the flange will be on one side of the peg and if the prop is doing the powering it will be on the other side. Surely it can't be on both sides at the same time.

You responded with this:

No - it can't. The prop pushes the wheels. The wheels rotate the prop.

So does that mean that by adding the limiting ring the craft will no longer work? Does the shaft jump back and forth in the ring? Does it go to one side of the ring yet still get powered from both wheel and prop? If such a slip ring can't distinguish between them give me a clue what effects the slip ring should be expected to have.

I had no doubt the principle was sound when you first posted the OP on this thread. I commend you for sticking with your guns and actually building a demonstration. Something many people would do well to emulate. You deserve a lot of credit. That said with the manner in which you are describing the physics there wasn't much choice but to lock the previous thread. It wasn't then nor is it now an insult of any sort. The fundamental problems with the description remain the same. Sorry, that's how science works. Some people unfortunately don't have the stomach for it. Claiming you were attacked for your ideas goes against the very methods we depend on in science. You even got a direct apology from Russ even though he didn't technically owe it. So hold your head up and avoid these claims of personal attacks lest you force what you claim. The science will speak for itself.

 

[spork]

I had no doubt the principle was sound when you first posted the OP on this thread.

Perhaps so, but you didn't speak up. I was being called out as a charlatan and told I was proposing a perpetual motion machine when that was clearly never the case. I was being told I knew nothing of physics or aerodynamics by a group of people that didn't even understand the equivalency of inertial frames.

That said with the manner in which you are describing the physics there wasn't much choice but to lock the previous thread.

It had nothing to do with how I described the physics. People claimed I was a charlatan and a fool. They claimed this thing could never work. I defended myself against these spurious claims, as I now have to defend against people that are telling me it doesn't work for the reasons I know it does - quite possibly the same people who thought it could not work in the first place. I hope you can understand how that gets old. The thread was closed either because the administrators, like the other participants of the thread, thought this was tantamount to perpetual motion OR becuase I defended myself against personal attacks. It was NOT closed because of how I described the physics.

It wasn't then nor is it now an insult of any sort.

If the original thread is still there I recommend you go back and read it.

The fundamental problems with the description remain the same.

The problem being that you're not able to follow them?

Sorry, that's how science works.

It kills me when someone like yourself tells me "how science works". Let's not pull our johnsons out - you won't like how it ends up.

Some people unfortunately don't have the stomach for it.

Grow up.

Claiming you were attacked for your ideas goes against the very methods we depend on in science.

Oh, now we depend on calling people idiots and charlatans? When they're RIGHT!?

You even got a direct apology from Russ even though he didn't technically owe it.

You didn't see what Russ posted. He deleted some of his posts before you could. You don't know what my responses would have been - the thread was locked so that only the moderators could get their licks in - and they did.

So hold your head up and avoid these claims of personal attacks lest you force what you claim. The science will speak for itself.

The science DOES speak for itself - unfortunately too many people can't seem to follow it.

You don't really even see the slightest bit of irony in this, do you? The members of this forum called me a charlatan and a fool, and locked my threads, because I claimed I could do EXACTLY what I did go and do. What I did works for EXACTLY the reasons I said it would. And NOW you want to tell me that it doesn't work like I think it does. But I've got news for you - it does. I conceived of this thing (although others had also done so independently), I built it, and I demonstrated it does what I said it would. How about you actually *do* something rather than tell me "how science works" and how I don't understand the thing I concieved of, built, and demonstrated.

hmmm... I thought I'd deleted my statement that the reason they called you charlatans was because you are charlatans.

And this is AFTER I proved him wrong. So tell me my_wan - this is how science works?

 

[spork]

I had no doubt the principle was sound when you first posted the OP on this thread.

When you think about it, that's not such a leap since the post included a video of a vehicle doing exactly what I claimed. What was your opinion when people were piling on me BEFORE I built one - and was simply explaining that it was quite doable?

 

[spork]

In response to... "How can a vehicle move faster than the wind that is powering it?"

OmCheeto wrote:
"It cannot go faster than the wind when going directly downwind."

Then I built a cart that does exactly that, made a video, and posted it.

Now OmCheeto incredulously writes:

hmmm... I thought I'd deleted my statement that the reason they called you charlatans was because you are charlatans.

and my_wan tells me I haven't been insulted, I may not have the stomach for this, and this is "how science works".

There's a kind of twilight-zone sort of entertainment to this I suppose.

 

[atyy]

That's correct. If our treadmill were long enough we could start the vehicle moving backward at the speed of the belt (equivalent to setting it down on a road with a tailwind). Eventually the relative wind would get the vehicle up to speed and it would finally outpace the wind and advance on the treadmill

It' not obvious to me this is like the wind. A vehicle in the wind doesn't need wheels, and the wind will just blow it along. The less friction between the ground and the vehicle, the easier it is for the wind to get the vehicle moving.

This seems more devious (I mean that as a compliment!) to me. Here friction between the vehicle and the treadmill is essential. With wheels there is the ability to make friction useful. The treadmill exerts a torque on the wheels and this is converted into the propellor movement which pushes the vehicle up. The question is how do you get friction to point in the right direction? Is holding the vehicle in place at the start necessary to do this? Does the propeller sort of "replace the hand" once it has sufficient speed?

 

[rcgldr]

Either the prop is powering the wheel or the wheel is powering the prop.

The wheels are turning the prop. The prop is generating a small amount of thrust, enough to allow the cart to move slightly faster than the wind.

 

[spork]

It' not obvious to me this is like the wind.

But it is. Imagine you were on your sailboat in the middle of the ocean. You wake up, go up on deck, and feel a 10 knot breeze on your face. How do you know if that's "real" wind? You don't. Maybe there is no current and the wind is blowing 10 knots, or maybe there is actually no wind, and there's a 10 knot current. To the boat (and to your face) it's all the same thing. And that's all we're doing here, we move the road and let the air sit still. This makes it much easier to prove the concept indoors with very controlled conditions.

A vehicle in the wind doesn't need wheels, and the wind will just blow it along. The less friction between the ground and the vehicle, the easier it is for the wind to get the vehicle moving.

Yes, but that vehicle can never go directly downwind faster than the wind. Because this vehicle extracts the needed energy from the air/ground interface, it must have a way of working against the ground. You could use skate blades, wheels, or other things.

The treadmill exerts a torque on the wheels and this is converted into the propellor movement which pushes the vehicle up.

You could look at it that way, but it's probably better to see it as the treadmill (or ground) holding the bottom of the wheel still so the cart can produce a torque on the wheels by pushing them forward at the hub.

Is holding the vehicle in place at the start necessary to do this?

No, but our treadmill would probably have to be over 100' long if we just set it on the belt. It would be going backward until it reached wind speed. It then starts advancing on the treadmill when it exceeds wind speed.

The wheels are turning the prop. The prop is generating a small amount of thrust, enough to allow the cart to move slightly faster than the wind.

To say the wheels are turning the prop oversimplifies it slightly (in my opinion). Not only does the prop have to create the thrust to overcome rolling friction and other transmission losses - it also has to create enough additional thrust to cause the wheels to turn.

The whole thing is simply caught between the ground and the wind. The prop pushes the wheels forward so they have to turn, and the wheels are geared to the prop so it has to turn when the cart moves forward. I know, it sounds like perpetual motion, but it's extracting that energy from the ground/air interface. Wouldn't do a thing without it.

 

[rcgldr]

The wheels are turning the prop. The prop is generating a small amount of thrust, enough to allow the cart to move slightly faster than the wind.

To say the wheels are turning the prop oversimplifies it slightly (in my opinion). Not only does the prop have to create the thrust to overcome rolling friction and other transmission losses - it also has to create enough additional thrust to cause the wheels to turn.

The wheels interact with the ground and turn the prop. The prop interacts with the air to generate thrust that affects the entire cart. The drive train torque from the wheels is opposed by an equal an opposite drag torque from the prop. This should answer my_wan's question.

simple explanation of the DDWFTTW cart

Ignore the land sail comparason for these carts, here's a much simpler explantion. Power input = equals the force at the driving wheels times the speed of the cart relative to the ground, because the wheels interact with the ground. Power output equals the thrust at the prop times the speed of the cart relative to the air, because the prop interacts with the air. The ratio of (power output) / (power input) = (thrust times air speed) / (force times ground speed) and with a ratio well less than unity, the cart can still go DDWFTTW.

To compensate for rolling resistance and other drag factors, the thrust from the prop is greater than the force at the driving wheels, but as long as the speed between prop and air is relatively smaller than the speed between wheels and ground, the power output is less than the power input, and the cart works.

Given this perspective, a rotating prop isn't required. Any thrust producing device would work as long as it was similarly efficient to a prop. Regarding the prop, a range of pitches will probably work, changing the pitch changes both the thrust and drag torque from the prop, and these are offsetting, depending on the lift to drag ratio of the prop.

 

[spork]

The wheels interact with the ground and turn the prop. The prop interacts with the air to generate thrust that affects the entire cart. The drive train torque from the wheels is opposed by an equal an opposite drag torque from the prop.

That's a perfectly fair characterization.

This should answer my_wan's question.

I will be surprised and impressed if it does.

Ignore the land sail comparason for these carts, here's a much simpler explantion.

Everyone's got a "simpler" explanation, because everyone had a different point where it clicked for them. For me the land sail explanation is the most accurate and intuitive given. If another explanation works better for you - that's great - as long as it's accurate.

Power input = equals the force at the driving wheels times the speed of the cart relative to the ground, because the wheels interact with the ground. Power output equals the thrust at the prop times the speed of the cart relative to the air...

This suggests there is no power output when it's going downwind at exactly wind speed. Depending on how you define your system this can be true. Is this how you're looking at it? I would be more inclined to say the power output is equal to the work the prop actually does on the air (which will be greater than thrust * speed of cart relative to air).

...but as long as the speed between prop and air is relatively smaller than the speed between wheels and ground, the power output is less than the power input, and the cart works.

True - as long as that difference is enough to allow for the inefficiencies of the prop, rolling resistance, and drivetrain losses.

Given this perspective, a rotating prop isn't required. Any thrust producing device would work as long as it was similarly efficient to a prop...

...and indexed to the ground in a way similar to the prop. This is required to extract the energy from the ground/air interface so that we can go faster than the wind.

Regarding the prop, a range of pitches will probably work, changing the pitch changes both the thrust and drag torque from the prop, and these are offsetting, depending on the lift to drag ratio of the prop.

Agreed - as long as the efficiency is still sufficient and the advance ratio of the prop vs. wheels is less than 1.

 

[ThinAirDesign]

Ignore the land sail comparason for these carts, here's a much simpler explantion.

Ok, let's hear your simpler explanation:

Power input = equals the force at the driving wheels times the speed of the cart relative to the ground, because the wheels interact with the ground. Power output equals the thrust at the prop times the speed of the cart relative to the air, because the prop interacts with the air. The ratio of (power output) / (power input) = (thrust times air speed) / (force times ground speed) and with a ratio well less than unity, the cart can still go DDWFTTW.

You didn't pass the "simpler" test ... my girlfriend says the above is all gibberish. :-)

JB

PS Meant in good fun Jeff.

 

[schroder]

It has taken me a while, but for what it’s worth, I finally understand the principle of this thing. It is not a pmm at all. I won’t apologize for being dense, but if I directly insulted anyone I sincerely apologize for that. As I understand it now, the cart is employing positive feedback, not unlike a turbo charger, from output device (propeller) to input device (wheels). In that sense, the cart is being driven by both the wheels and the prop at the same time. My mental block concerned advancing against the treadmill, while drawing all its power from the treadmill. If the device were using two wheels to extract power from the tread and an additional set of wheels working against the tread, clearly that would not work. What finally convinced me was to imagine a threaded rod run parallel to the treadmill, and instead of a propeller a worm gear was used to drive the cart along the threaded rod. That would certainly work, and the cart would accelerate until it either burned itself up from friction and heat, or it reached some terminal velocity dictated by the available energy, mass and friction forces. I then extrapolated that idea to the propeller drive and found it is not much different. Of course, saying all this after seeing the very convincing video does not establish me as a good intuitionalist but at least my brand of formalism does allow some flexibility. But all of these concessions are to the machine on the treadmill. As a formalist, I still have reservations about the ability to outrun the wind, going directly downwind. As Atyy pointed out, any contact with the ground must introduce friction forces which would not be present with the wind alone, but those same friction forces can be used to advantage as well. In that case, from both an intuitionalist and a formalist point of view, it does seem rather questionable as to which of the forces would be greater. However, having been proven wrong about the treadmill I concede that I may well be wrong about the wind as well.

 

[spork]

I won’t apologize for being dense

An apology is never required or expected for simply not quickly understanding unintuitive things.

..but if I directly insulted anyone I sincerely apologize for that.

Thank you. I accept.

If the device were using two wheels to extract power from the tread and an additional set of wheels working against the tread, clearly that would not work.

Agreed. The cart extracts its energy from the road/air interface. As such it has to have something working against the air.

What finally convinced me was to imagine a threaded rod run parallel to the treadmill, and instead of a propeller a worm gear was used to drive the cart along the threaded rod. That would certainly work, and the cart would accelerate until it either burned itself up from friction and heat, or it reached some terminal velocity dictated by the available energy, mass and friction forces.

Perfectly accurate.

I then extrapolated that idea to the propeller drive and found it is not much different.

Also true.

Of course, saying all this after seeing the very convincing video does not establish me as a good intuitionalist but at least my brand of formalism does allow some flexibility. But all of these concessions are to the machine on the treadmill. As a formalist, I still have reservations about the ability to outrun the wind, going directly downwind.

But the two cases are identical. The same experiment is being performed in two different inertial frames. As such the results must be identical.

However, having been proven wrong about the treadmill I concede that I may well be wrong about the wind as well.

It *has* to work in the wind - because wind across a stationary road is identical to a road moving beneath a stationary mass of air.

 

[ThinAirDesign]

Schroder, I commend not only your ability to learn and in return model and describe your observations, but even more so your ability to stand up and apologize -- that demonstrates a quality that really matters.

Kudos.

JB

 

[ThinAirDesign]

my_wan, I respect knowledge and you clearly hold more physics knowledge than I. I must say however that if you are correct, the Physics world will be rocked by your discovery and you will likely get a Nobel.

You are holding that there is now a test which can be performed which will yield varying results based on differing 'amounts' of purely linear motion.

I'm quite surprised frankly that there are not more folks on a physics forum piping up and taking a position on a debate so fundamental to one of the most basic and long-standing physics principles.

JB

 

[spork]

I'm quite surprised frankly that there are not more folks on a physics forum piping up and taking a position on a debate so fundamental to one of the most basic and long-standing physics principles.

No need frankly. They can wait for you and I to go and provide physical proof once again by taking the cart out on the road in a smooth tailwind, to show it behaves the same way.

 

[OmCheeto]

In response to... "How can a vehicle move faster than the wind that is powering it?"

OmCheeto wrote:
"It cannot go faster than the wind when going directly downwind."

Then I built a cart that does exactly that, made a video, and posted it.

Yes you did, but as I pointed out, the parameters of the experiment changed.
For you next experiment, I think you should remove the RC steering control from the first vehicle, add it to your new mini-me "faster than wind" vehicle, and put it back on the treadmill. I bet it would go even faster.

Now OmCheeto incredulously writes:

hmmm... I thought I'd deleted my statement that the reason they called you charlatans was because you are charlatans.

For the record, you used the term before I did.

and my_wan tells me I haven't been insulted, I may not have the stomach for this, and this is "how science works".

There's a kind of twilight-zone sort of entertainment to this I suppose.

I agree. I keep unsubscribing to this thread, yet somehow I keep getting sucked back into this vortex.

I guess it's like forcing ones self to read some poorly written mystery novel, because no matter how bad it gets, you just have to know how it ends.

 

[spork]

...but as I pointed out, the parameters of the experiment changed.

And as I pointed out - you're wrong. I defined the parameters of the experiment. I concieved of the solution. JB and I built the cart, and we demonstrated it doing EXACTLY what we claimed.

For the record, you used the term before I did.

In point of fact I NEVER used to word "charlatan" except to complain about people calling me that.

I agree. I keep unsubscribing to this thread, yet somehow I keep getting sucked back into this vortex.

Next time you feel you're about to get sucked back in you really should call a friend and have them talk you down.

I guess it's like forcing ones self to read some poorly written mystery novel, because no matter how bad it gets, you just have to know how it ends.

I'll save you the trouble - I'm right. Sorry for the spoiler, but now you have no need to get "sucked back in" just to hurl insults at the ones who HAVE proved their point.

 

[cristo]

Some members have a very bizarre definition of an "insult." Let me remind you that comments against someone's ideas, or someone's experiments are completely different to comments which are meant to solely put a member down, or insult them. The latter set are not permitted, as per the global guidelines.

The OP has given out way more than he has received, and in fact threw insults in his very first post here at PF. Thus, any remarks along the line of "self defence" are not going to wash.

Since there is clearly no hope of a civil discussion of this topic, this thread is done.