Mark Chu-Carroll is wrong, wrong, wrong

Wow, I don’t get to say that very often! But it’s true. In this post, Mark claims that it’s impossible to make a wind-powered vehicle that goes faster than the wind, while traveling in the exact same direction as the wind. He is wrong, and in his post, he gives us the empirical evidence why he is wrong.

Rather than fisk his entire argument, I think instead I’ll just show why he is wrong. Here’s the video that shows how faster-than-wind travel is possible:

The problem is, this video doesn’t do a very good job explaining the principle behind the engineering.

It’s hard to understand at first why it’s possible for a vehicle driven by the wind to move faster than the wind. Imagine a helium balloon being driven by the wind. There’s simply no way for it to move faster in a horizontal direction than the wind itself is blowing.

But think about this. There’s a tremendous amount of force in the wind. Drive a sturdy 10-foot stake into the ground. Now imagine a steady 20-MPH wind blowing across the stake. The stake’s not going to budge. Now attach a 10-foot-square sail to the stake, holding it with ropes so it stays perpendicular to the path of the wind. All the sudden a tremendous force is imparted. It may be difficult for you to hold the sail in place. Eventually the wind would rip the sail from your hands. Yet you could easily throw the same piece of cloth (bundled up in a wad) faster than 20 MPH. So that 20-MPH wind has enough energy to propel something faster than the speed of the wind. It’s stronger than you, and you can throw the object faster than the wind is moving.

Sailors know this, and there is no dispute that it’s possible to sail a boat across the wind at a speed faster than the wind speed. You can even sail into the wind. There’s plenty of energy in the wind to move a vehicle faster than the wind is blowing.

So how does the vehicle in the video work?

It’s mind-numbingly simple.

It’s just a little cart with a propeller driven by the wheels. The propeller is oriented so that when the wheels roll forward, it propels the air backwards, giving a little extra forward propulsion.

The wind pushes on the propeller, which starts by acting like a sail. This causes the car to roll forward, which makes the propeller spin. The spin of the propeller adds a little extra thrust. As long as the propeller is big enough, there’s plenty of energy to not just propel the car forward at wind speed, but a little faster as well.

In the video you can see that the treadmill is not only moving at a high rate of speed backwards, it’s also angled up. This craft can actually “sail” uphill, faster than the wind is blowing.

Mark argues that this isn’t a true perpetual motion machine, because the treadmill is constantly adding energy to the equation. That’s correct, but it’s only simulating a steady wind. Since the air in the room is still, the motion of the treadmill is equivalent to wind moving across the ground at the same speed. The vehicle is moving FASTER than the treadmill is spinning — faster than the “wind.” It’s not a perpetual motion machine, it’s converting the energy in the wind into forward motion. If there is no wind, the cart goes nowhere.

Mark also says that because the treadmill isn’t level, it’s not a fair experiment. But the treadmill is angled uphill. If it was angled downhill, he’d have a point. But it’s angled uphill. This simply adds to the force that the cart must overcome to move faster than the wind. The experiment would also work on a flat treadmill.

So now I get to truthfully say something I’ve never said before — and probably won’t ever say again. Mark Chu-Carroll is wrong, wrong, wrong. He’s a very smart guy, but he’s wrong on this one.

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30 Responses to Mark Chu-Carroll is wrong, wrong, wrong

  1. Mark Chu-Carroll says:

    Sorry Dave, but you’re still wrong.

    The wind pushes on the propeller – but only up to the point where it’s moving at the same speed as the wind. Once you’ve accelerated the vehicle up to the speed where it’s moving at the same rate as the wind, *the wind can’t push the propellor anymore*.

    It’s driving me crazy: What is so hard to understand about that?

    On the treadmill, the slope does contribute. What’s going on is:
    – The slope of the treadmill creates a small backwards force on the vehicle.
    – That force is enough to stop the vehicle from just moving with the moving belt; it’s enough to engage the wheels into spinning against the moving treadmill.
    – The treadmill spins the vehicles wheels.
    – The vehicle gearing spins the propeller.
    – The propeller pushes the vehicle.

    The treadmill is acting as a motor providing energy to the vehicle by way of the wheels.

    The question that should make it obvious is: where’s the wind? What’s suppposedly pushing on the propellor here, when it’s stationary relative to the air around it? If it’s not direct motive force from the treadmill, then where’s the force coming from? From the still air?

  2. Scott says:

    Mark,

    I think you have got are misunderstanding what’s going on in the video. Grainy youtube and all…

    You seem to think that the slope and the movement of the treadmill are acting against each other and the vehicle is in the middle, using the slope to capture energy from the treadmill.

    In actuality, the slope would push the vehicle to the left. Also, the movement of the belt would also push the vehicle to the left. The only thing pushing the vehicle to the right appears to be the propeller. How does the vehicle both climb the slope while also working against the treadmill? It is clearly doing just that.

    The “wind”, is of course the still air in the room, which relative to the treadmill is moving. Think of the same experiment performed on a breezeless day performed on the deck of an aircraft carrier making a steady 10 miles per hour.

  3. Mark Chu-Carroll says:

    But the wind in the room *is not moving* relative to the vehicle.

    If you put the vehicle on the deck of the aircraft carrier, there would be a “wind” of 10 miles per hour relative to the vehicle – *when the vehicle was stationary relative to the deck underneath it*. But if the vehicle was accelerated up to 10mph, so that it was on the deck stationary relative to the ocean surface beneath it, there would be no “wind” to push on it.

    In the treadmill, they carefully hold the vehicle steady until the wheels are spun up so that it’s “stationary” relative to the air. There’s no “wind”; it’s *not moving* relative to the air, and the air isn’t moving relative to it.

    How is the air pushing on the vehicle, when the vehicle has *no motion* relative to the air? There’s no force coming from the air. But there’s *lots* of force coming from friction on the treadmill.

  4. Dave says:

    *the wind can’t push the propellor anymore*.

    The wind *isn’t* pushing the propeller. The propeller is pushing the air backwards, as it would if the car was driven by a motor. The excess wind force (beyond what is needed to drive the car forward at the same speed as the wind) is converted into rotational motion on the propeller. This propels the car forward, faster than the wind.

  5. Scott says:

    Mark,

    The treadmill isn’t long enough for the device to get up to speed, so they have to skip the 0 – 100% part of the test. But that’s not the interesting part anyway, right? We know that a vehicle can go at the wind speed — can it go 110% or more?

    The blades you see, are geared to the ground. So when there is no “wind”, the moving ground is turning the blades, the blades are creating a vacuum in front of the vehicle, and energy of the treadmill is being converted to usefull work, in this case by pulling the cart up a slope.

    The treadmill is trying to push the cart down the hill, but the cart is actually leveraging the still air to resist the treadmill.

    So, if the vehicle is moving at airspeed across the ground, how can it find more energy? Remember, when we started, we were at rest relative to one of our two surfaces. Now we are at rest relative to the other. The situation is reversed, but as long as we can apply a “wheel” to both surfaces we can extract energy.

  6. Freiddie says:

    Wow, now here’s a confusing problem. One side says yes, the other says no.

    Here’s what I think is happening: Mark is rejecting the idea that a *simple* sail-based device could be faster than wind. On the other hand, there is nothing prevent the fact that the object could harvest energy from the wind and convert it into kinetic energy via method X, where X is some mechanism, because it doesn’t violate the conservation of energy. But the problem here is that whenever an object moves faster than the wind, the relative velocity between the object and the air is such that it now *resists* the object, so the object can no longer harvest energy. Therefore, a device cannot harvest wind energy to move faster than constant wind (simply because the relative velocity of the object with the air). So I don’t think Mark is wrong here (at least for constant wind).

    Correct me if you see a flaw in my reasoning, please.

  7. Freiddie says:

    Oh wait, I forgot, there is also the relative motion with the ground… Never mind what I said. I am totally lost.

  8. Don says:

    I assume you are talking about the small vehicle on the treadmill. The treadmill slopes downward from right to left but the treadmill is moving from left to right(watch the wheels at the point when they are just being placed on the treadmill). The slope and the propeller are working together to move the vehicle left and the treadmill works to move the vehicle right. The vehicle moves right, so gravity plus the energy extrcted by the wheels to power the propeller is not quite enough to overcome the treadmill. Increase the slope and it will move left, Decrease it and it will move left. I suspect there was a bit of experimentation to get it just right for near zero motion.

  9. Don says:

    I assume you are talking about the small vehicle on the treadmill. The treadmill slopes downward from right to left but the treadmill is moving from left to right(watch the wheels at the point when they are just being placed on the treadmill). The slope and the propeller are working together to move the vehicle left and the treadmill works to move the vehicle right. The vehicle moves right, so gravity plus the energy extracted by the wheels to power the propeller is not quite enough to overcome the treadmill. Increase the slope and it will move left, Decrease it and it will move left. I suspect there was a bit of experimentation to get it just right for near zero motion.

  10. Scott says:

    Don,

    The treadmill is moving from right to left. Specifically around 4:10, there is both an angle in the treadmill which pushes the cart to the left, and the treadmill is pushing the cart to the left.

    It’s not easy to see this from the video, but you’ll see that the controls are on the right, and treadmills always push the user away from the control panel.

  11. Don says:

    Lookat the wheels.

  12. Scott says:

    Don,

    I’m going to guess that you are seeing some sort or “wagon-wheel” effect which is making the wheels appear to go backwards.

    http://en.wikipedia.org/wiki/Wagon-wheel_effect

    But believe me, treadmills move their belts away from the control panel (on the right). Otherwise, you’d have to run backwards.

  13. Don says:

    Look at the wheels. Particularly when he picks it up at about 4:54 and they are slowing down to a stop.

  14. dave says:

    Don,

    The treadmill is moving from right to left. It’s obvious; there are large stripes on the the treadmill. As expected, the wheels rotate in a clockwise direction when placed on the treadmill, meaning the vehicle is moving from left to right relative to the surface of the treadmill.

  15. Don says:

    Whoops, you are right. My bad.

  16. dave says:

    At 4:54 what you’re seeing is the wagon-wheel effect. Watch them as they slow to a complete stop. They are clearly rotating clockwise. Unless you believe that the cart can spontaneously change the direction of the wheels, that’s the only explanation for what you see.

  17. Scott says:

    Wow Don, you may have just committed an internet first. We have all seen history.

    Seriously, I think that a lot of the back and forth is caused by the fact that the treadmill demonstration is extremely confusing. I know I was expecting a fan or something.

    But that’s it for now; I’m going to bed.

  18. Don says:

    You are right that the treadmill experiment is confusing. It is actually meaningless as far as the wind propulsion is concerned. All we are seeing is a treadmill powered fan. There is nothing there that represents wind.

    As for the wind powered situation, consider this situation.
    Dead flat and a steady wind so the only source of energy is the wind. Have the cart traveling at the same speed as the wind. Under these conditions there is no energy input to the cart.
    But you have a propeller providing thrust. Where does that energy come from? Why, from the wheels of the moving cart. Where do they get their energy? Why, from the forward motion of the cart. But with no wind inputting energy, any energy for thrust must come from slowing down the cart. And absent perfect conversion of that energy to thrust, the cart will slow down until the energy input from the wind equals the losses in the system.

  19. Stephen Wells says:

    The demo is hilarious. It’s clear that the treaadmill is running in normal treadmill direction (right to left in this video), that the treadmill spins up the wheels _while the cart is held stationary_ and that sets the propellor going, and that the rotating propellor drives the cart. If you set the cart down without holding it it’d be flung off the treadmill immediately. No energy is being extracted from the wind.

    I’m pretty sure on energy conservation grounds that if you set the thing on a long enough treadmill and spun it up then let it go, it would only move a finite distance up-slope before reaching steady-state or heading downhill again. With this short treadmill the guy can keep catching it on the up-slope part of the journey, which is being powered by the energy stored when the prop was first spun up.

    Always be very suspicious of demos that interrupt a process and then assert it would have continued indefinitely.

  20. dave says:

    with no wind inputting energy, any energy for thrust must come from slowing down the cart

    That is where you are wrong. Imagine a cart with six-inch propeller that cannot rotate. Suppose this prop has just enough surface area to capture enough wind to propel the cart at a speed equal to the wind speed. Now make the propeller a little bigger. It’s capturing additional energy from the wind. All we need is a way to harness that extra energy and devote it to the forward motion of the cart. The energy is captured by the rotation of the wheels, and redirected into spinning the propeller. Since the blades of the propeller are angled, the effect of the rotation is that the wind hits the propeller at a higher relative speed than it would if the propeller was not moving. Now this extra energy made available due to using a larger propeller can be devoted to moving the cart faster.

  21. Stephen Wells says:

    Dave, in the situation comment 18 described, the cart is moving at exactly the wind speed. You could give it a propellor the size of Godzilla’s tail and it wouldn’t extract any energy from the wind whatsoever. If the propellor is still accelerating the cart it’s because the propellor has momentum and energy that it gained when it was spun-up.

  22. Dave says:

    Stephen,

    It’s moving across the ground. Energy can be extracted from the motion of the cart across the ground, via the wheels, and used to rotate the propeller. This generates additional propulsion beyond the speed of the wind. The larger the propeller, the more energy is available in this fashion. Imagine the propeller was a sail. The larger the sail, the more energy would be required to stop the car. In our case, instead of stopping the car, it’s used to rotate the propeller. This generates additional propulsion beyond the speed of the wind.

  23. MartinM says:

    Energy can be extracted from the motion of the cart across the ground…

    …to drive the motion of the cart across the ground.

  24. dave says:

    Martin: Your retort would be funny if the implication were true, but it’s not.

    Maybe another example will help. Imagine a small, lightweight vehicle with a sail on it sitting in a windless room. If you put a small motor with a propeller on the top of the mast, would it move?

    Of course it would, although the sail would be resisting that motion a bit.

    Now imagine that the wind starts to blow, and instead of powering the propeller with a battery, you use the motion of the wheels to power the propeller. Would this craft go faster than the wind? Maybe not, but only because it’s not very efficiently designed.

    By making the vehicle very light weight, and using the propeller itself as a sail, it can travel faster than the wind.

  25. dave says:

    Here’s a completely different way of explaining why this is theoretically possible using a different solution (from the creator of the craft itself) (emphasis mine):

    My buddy JB and I made the cart in the video in question. We have posted the complete parts list and the key build notes so that anyone can build one for themselves and test it under whatever conditions they like. I have agreed to build about 12 of these for people both skeptics and believers that want to test them.

    The cart is real and there is no trickery in the videos.

    The cart does not represent perpetual motion. It is a simple novelty, but something of a mind-bender. It is wind powered, but through a somewhat clever mechanism is able to outpace (but not outrun) the wind. This mechanism, like a mechanical gear, allows the cart to trade force for speed.

    The energy is exploited from the ground/air interface. The cart leaves in its wake a “tube” of air that is now moving downwind more slowly than the free-stream wind, it’s energy having been used to propel the cart.

    If the wind stops, the cart stops.

    I’ve explained this MANY times on many forums, and I regret that my patience runs out when I’m called a fool or a scam artist. I’m neither – and I have nothing to gain by scamming anyone. So, I will do my best to explain this here and now, and will try my best to answer any questions – I just ask that I not be attacked for my effort.

    First question: can ANY wind powered vehicle go directly downwind faster than the wind (never mind our little cart)? Ans: YES.

    Let me explain… We know that ice boats can follow a downwind course – say 45 degrees off the direct downwind vector – at several times the wind’s speed. This means they can actually take two such tacks and arrive at a point well downwind of their starting point before a leaf floating in the wind that started at the same point.

    This is true. I do NOT mean that they can simply go cross-wind faster than the wind. They can and do maintain a steady-state course whose downwind velocity vector is 3X to 4X the wind speed. We know this from measurements (GPS and anemometers), as well as from simple vector analysis. I won’t clutter this post with that, but I will be happy to provide such evidence upon request. You can also look at the response when the question was posed on a landsailing forum.

    Now, let’s imagine I have two of these ice-boats that can tack their way downwind faster than the wind. I can start them side by side and keep them on alternate tacks as they do their thing. I could in theory connect the two with a telescoping pole with a seat right in the middle. I could then sit in that seat and I would travel downwind, faster than the wind. And my vehicle (which admittedtly has some significant moving parts) would have it’s center of gravity also traveling downwind faster than the wind.

    Does this in and of itself prove our cart can or does do as we claim? No. But it does, and I’m confident I can convince most anyone with an open mind (as I have with many already).

    And I ENCOURAGE people to try this for themselves. I have nothing to hide. I’ve posted the complete parts list in many places, and I’ll be happy to post it here. I will answer any serious question to the best of my ability, and do my best to insure anyone who attempts to duplicate our results succeeds. With the right parts it’s really not very difficult.

    I am aware this is only a little teeny part of the story, but it would be very easy to write a chapter on this silly thing. As I said, I have nothing to hide, but let’s start with this, and I’ll add to it as we go. Fair enough?

  26. Tim Eisele says:

    “But the wind in the room *is not moving* relative to the vehicle.”

    Maybe I missed somebody else mentioning this, but isn’t there a wind from the treadmill? The moving belt should be dragging some air along with it, making a breeze. I’m pretty sure I’ve felt such a breeze off of a treadmill before.

  27. Don says:

    Sorry Dave, Martin is correct. You are describing a perpetual motion machine. If you were correct then giving the cart a slight push on a windless day would allow it to continue at that slightly greater than wind speed forever.

  28. dave says:

    Tim:

    If there’s a wind from the treadmill it’s going in the direction of the treadmill’s motion, making the task even more difficult.

  29. spork says:

    “Sorry Dave, Martin is correct. You are describing a perpetual motion machine. If you were correct then giving the cart a slight push on a windless day would allow it to continue at that slightly greater than wind speed forever.”

    Well, I built the machine, and I can tell you it doesn’t represent perpetual motion. It’s wind powered, it will go directly downwind faster than the wind, and it won’t move at all if there is no wind. If you push it when there’s no wind, it will just coast to a stop.

    If you don’t believe it I encourage you to come see ours – or even build your own. I’ve posted the parts list and build notes, and would be happy to provide a link.

  30. John Davis says:

    All,

    The vehicle is an impossibility. Imagine that YOU are sitting in the vehicle. With the vehicle moving at a speed EQUAL to that of the wind, you will feel NO WIND on your face or body. You are moving along within a body of air traveling from a high-pressure region to a low-pressure region (wind) so there is no net windspeed at the vehicle. At a speed FASTER than that of the wind, the body of air will act upon the vehicle from the FRONT.

    The propeller, attached to the vehicle, experiences the same windspeed as the rest of the vehicle. Therefore, although it is able to propel the vehicle at a sub-wind speed because the wind is back-to-front across the vehicle, the propeller will produce progressively less torque as the vehicle approaches windspeed until zero torque is produced at windspeed since airspeed through the propeller has reached zero. Can a wind turbine turn or produce power at zero windspeed? No. With the vehicle theoretically moving faster than windspeed, the propellor will experience a negative windspeed, i.e. in the REVERSE direction. Geared to the wheels, the propellor’s reversed rotation would theoretically rotate the wheels in reverse.

    Another point- some might say “why don’t we just gear the propeller in reverse, so that when the vehicle is moving faster than the wind, the reverse air motion over the propellor will spin the wheels forward? We’ll just start the thing moving faster than the wind, so the wheels will spin forward to start with. As long as the vehicle maintains its speed, the propellor will continue to spin the wheels in the forward direction.”

    Not so fast. Just think: how could the vehicle possibly accelerate at this point? In order to accelerate the vehicle, the propeller, coupled to the wheels, would have to increase its speed of rotation. The vehicle must simply accelerate to accomplish this, so that the front-to back wind velocity increases. Simply? BUT HOW CAN IT ACCELERATE WITHOUT AN INCREASE IN THE SPEED OF THE WHEELS? It’s a paradox.

    Still, nobody said the vehicle had to accelerate. All it has to do is maintain the faster-than-wind speed that it was started out at. But there’s another factor, isn’t there? DRAG ON THE VEHICLE. Impacting the front of the vehicle, the wind will produce a force in the reverse direction, trying to slow the vehicle down. The vehicle can’t accelerate; it can only move at its original speed. The wind acting upon the vehicle from the front will thus slow it down until it reaches windspeed, at which point the propellor will cease to function due to zero airspeed across it.

    In conclusion, it is physically impossible for this vehicle to travel at a speed greater than that of the wind.

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