Down wind faster than the wind

[ThinAirDesigns]

Spork, JB,

if you're reading this: can you please tell me whether I was right in what I was trying to explain to my_wan?

If I'm mistaken in some way, I'd rather find out.

Thabiguy and my_wan, spork and I would love to contribute anyway we can, but the discussion between you very very long (and that's not a criticism).

If you would summerize the point of conflict I'm sure we'd be happy to comment.

JB

 

[sol invictus]

JB, when I said "I've done the experiment", I was referring to the craft spork posted the plans for. Basically your craft is a prop coupled to a wheel, no weird gearing, no flywheel, just very simple. Had one of those as a kid, couldn't understand why it wouldn't run forever. After all, the wind turns the prop, providing energy to the wheel; the wheel turning provides energy to the prop. That's how I learned about entropy.
But if that's not what is supposedly happening, what is?

What, precisely, did you learn about entropy? Do you think a dust mote caught in the Gulf Stream that circles indefinitely is a violation of the laws of thermodynamics?

All entropy tells you is that the wind will eventually die (think billions of years, after the sun has gone out). Assuming it doesn't go nova and swallow the earth first, that is. It says precisely nothing about this device.

There's no problem with using stored energy to travel downwind faster than the wind.

OK. But one way to store energy is to hold a propeller into the wind and wind up a spring. Or hold a wheel against the ground you're moving with respect to and do the same.

The problem is that the craft in question is not using stored energy, but generating the energy to maintain it's faster than-the-wind velocity from it's own headwind.

No - it's using the fact that the wind moves with respect to the ground. That motion is there regardless of the motion of the craft.

MHaze,
Well, what I was saying is that is not an inertial frame of reference. This platform is not notional in any way. It's rolling-road model. It's not the wheels that are the ground it's the treadmill belt. Everything is literal. The wheels are wheels, the air is the air, the propeller is the propeller.

I have no idea what you're trying to say. I suggest you learn some basic facts about Lorentz transformations - or Galilean, which are simpler and suffice in this case.

I am not saying that a windblown model cannot be, of course not, but that this model is not an indicator of the potential for greater then wind-speed vehicles, other than flywheel driven, of course.

Flywheel, or by jibing, or with a spring - you seem to agree that all of those methods allow travel downwind faster than the wind. Why do you think this is so different?

I haven't seen one single rational objection to this device. Not one of the "skeptics" has identified a single physical principle it violates. The best you seem to be able to do is yell and/or ramble incoherently. As I said before, it's not obvious that this device works from the design. But it does NOT violate any law of physics, it's easy to see how it COULD work, the videos are pretty convincing, and not one real argument has been produced in this thread against it.

 

[spork]

So when you say that you have calculations that prove you right, you actually don't have them? or you don't want to show them? or?

It's just that with the tone you are taking when you mention your analysis and how your analysis predicted the performance of the device you built...I dunno, I was expecting something a little more like, umm analysis.

You have me at a complete loss. You clearly seem to be one of the VERY few people that understand this thing completely. I point to my vector analysis and say that along with the necessary description it will prove this is viable. I offer to give that description as soon as anyone wants to discuss it. What tone are you refering to?

 

[spork]

I hadn't thought of thinking of the propeller as being used as a sail while below wind-speed, but that doesn't affect what happens when it goes faster than wind-speed.

I've mentioned more than once that this is the exact analog of an ice-boat on a downwind tack. We simply send the sail in a spiraling continuous tack. This is true below the wind speed and above. The blades of the prop act exactly as the sail of the ice-boat with the wheels and transmission providing the same kinematic constraint as the blades of the ice boat.

From later posts, it looks like he means the spinning of the propeller would push the air backwards, providing the craft with a forward thrust which turns the wheels faster, which would then turn the propeller faster, which would provide more forward thrust... and so on.

I don't think I'd word it that way, but that's the gist of it.

If so, he's forgetting that the energy imparted to the propeller to produce this forward thrust is taken from forwards momentum of the craft itself, so he's subtracting forward momentum in order to spin a propeller to provide forward momentum. Somehow he thinks he can get more power out of the propeller than the propeller takes from the craft via the wheels.

I'm not forgetting anything. It's just that I understand exactly how this thing can exploit the energy of the wind relative to the ground - and you can't. This has you claiming that the very object I built must be an example of perpetual motion.

 

[Thabiguy]

If you would summerize the point of conflict I'm sure we'd be happy to comment.

I say that even under ideal conditions (no unwanted friction, no unwanted drag) the device would not accelerate indefinitely, but only up to a certain, well-defined multiple of wind speed (depending on the transmission between the wheels and the propeller), at which the wind will no longer exert forward force on the propeller, making it impossible to accelerate further (unless the device is adjusted to change the transmission).

my_wan says that the maximum speed of the device is only limited by practical considerations (such as drag on the device as it moves at higher than wind speed), and that no matter how fast the device is going, it would always be (in theory) able to utilize the power of the wind for further acceleration, if it weren't for the drag etc. (I hope I have not misrepresented what he says. If I have, I apologize, and invite him to offer his own summary.)

 

[spork]

Brian-M, Mhaze. At least 3 of us understand.

Perhaps, but it clearly isn't you three. In fact I can tell you more or less definitively, JB, Sol, TheBigGuy, and I clearly understand the mechanics of this. Some others have parts of it right.

 

[technoextreme]

The important force is the force of the air pushing the propeller forward.

And the force of air pushing the propeller backwards.

Other than that, it's ground friction, internal friction, lateral drag on the propeller as it rotates...

And the force of air pushing the propeller backwards.

The force that is key to accelerating above wind speed is the force of the air pushing the propeller forward.

But the force of air also pushes the propeller backwards.

Flywheel, or by jibing, or with a spring - you seem to agree that all of those methods allow travel downwind faster than the wind. Why do you think this is so different?

Because it's a screw. If you start running straight into the wind you develop a force that is opposite to the cart. Half the people here have no idea how a screw works. Half the people here have no idea about frames of references. Pick your butchering of science. I was in the frame of reference group but then I just realized that you will see the same problems no matter what frame of reference you jump to.

 

[spork]

Spork, JB,

if you're reading this: can you please tell me whether I was right in what I was trying to explain to my_wan?

If I'm mistaken in some way, I'd rather find out.

Sorry for the delay. Yes you are completely right. You are one of the VERY few people that seem to understand even the subtle aspects of this thing.

I honestly consider it a fairly simple (if unintuitive) thing, based on the simpler analogies. While it's hard to imagine there could ever be this much debate about it is astonishing. But I have to remind myself that people argued about the plane on a treadmill (which was infinitely simpler still).

I am beginning to find more people on the forums that do understand the physics and aero behind it, and some that are getting closer. But that number is still quite small.

Probably the most amazing thing is that there are still so many people that claim it can't be done. Hell, we've described how to build the thing and offered to send them to critics. I can only assume these are the same folks that don't believe we've put men on the moon.

 

[humber]

No, think Mythbusters. Any time that their plane is NOT touching the belt, is its real-world speed, agree? When it is in the air, you can turn off the treadmill, agree? If the plane does a hop, when it lands, it will land at some speed relative to the belt. This might be only a little slower. I say this to demonstrate, that when the plane is on the belt, it IS its real world speed, when it takes off, that's its real-world speed too. You must agree.

The real world speed, of the cart is not its speed relative to the belt, but relative to the ground. That is how fast it is going. It's exactly as Briam_M described. Your using the wind to stay (almost) stopped.

You are on the same ground as the belt, but at different velocities, same inertial reference, save for that small difference we attribute to Einstein, which is infinitesimally small at that speed. You are not standing on the belt, but on the static ground. That is your observer's view.

Do you think that the plane jumps from -takeoff speed, to +takeoff speed instantaneously?

What you see, IS the cart's speed. What you are seeing, is the cart's inability to remain at zero velocity. Also, the frictional components cannot be scaled to a bigger real-world value in any useful way. The cart is like a nearly floating gyroscope. See how it twists?

Tell me I'm wrong.

 

[ThinAirDesigns]

Perfect Thabiguy. Perfect.

JB

I say that even under ideal conditions (no unwanted friction, no unwanted drag) the device would not accelerate indefinitely, but only up to a certain, well-defined multiple of wind speed (depending on the transmission between the wheels and the propeller), at which the wind will no longer exert forward force on the propeller, making it impossible to accelerate further (unless the device is adjusted to change the transmission).

my_wan says that the maximum speed of the device is only limited by practical considerations (such as drag on the device as it moves at higher than wind speed), and that no matter how fast the device is going, it would always be (in theory) able to utilize the power of the wind for further acceleration, if it weren't for the drag etc. (I hope I have not misrepresented what he says. If I have, I apologize, and invite him to offer his own summary.)

 

[ThinAirDesigns]

humber:

What you see, IS the cart's speed. What you are seeing, is the cart's inability to remain at zero velocity. Also, the frictional components cannot be scaled to a bigger real-world value in any useful way. The cart is like a nearly floating gyroscope. See how it twists?

Tell me I'm wrong.

-

When a door is left open that wide is must be taken.

You're wrong.

JB

 

[JWideman]

What, precisely, did you learn about entropy? Do you think a dust mote caught in the Gulf Stream that circles indefinitely is a violation of the laws of thermodynamics?

All entropy tells you is that the wind will eventually die (think billions of years, after the sun has gone out). Assuming it doesn't go nova and swallow the earth first, that is. It says precisely nothing about this device.

Sorry, I sometimes say things that suggest a more direct connection than I mean to imply. My childish experiment led me to learn why perpetual motion doesn't work, which included the lesson on entropy.

From later posts, it looks like he means the spinning of the propeller would push the air backwards, providing the craft with a forward thrust which turns the wheels faster, which would then turn the propeller faster, which would provide more forward thrust... and so on.

I don't think I'd word it that way, but that's the gist of it.

This has you claiming that the very object I built must be an example of perpetual motion.

Brian-M was describing perpetual motion.

 

[Brian-M]

No - it's using the fact that the wind moves with respect to the ground. That motion is there regardless of the motion of the craft.

No... if this was simply a wind-powered device that travels upwind (or downwind), I'd agree with you.

From what he's claiming (or from what I think he's claiming) is this:

<------< Wind (Slow)
<------------< Speed (Fast)

      X|
       |
  O------O
Ground (Still)

Traveling faster than, but in the same direction as the wind on a fixed surface, which is logically equivalent to putting it on a treadmill on a windless day like this:

Wind (none)
<------< Speed (slow)

      X|
       |
  O------O
>------> Ground (slow)

Traveling against a treadmill on a windless day.
Apparently, he thinks it should accelerate to the left.

(Correct me if I have misunderstood the claim.)

 

[humber]

Really. Put the cart on the belt as usual and get it moving forward.
Kick the underside of the treadmill, so as to make the cart jump.
At what speed is it traveling, at the moment it leaves the belt?

Answer: Very slowly.
What's the 'windspeed'? Answer: Belt speed, -belt speed.

ETA:
Imagine a small aircraft on the belt. Launch it against the belt, so that it takes off. Hide behind the bench so that you can't see the belt. How fast is it going? The speed at which it just left the belt.
Same with cart, hide so that you cannot see. How fast is it going, slowly to the right.
Put an object on the belt, how fast is it going. Belt speed to the left.

Let's say the belt speed is 10 knots. Imagine the cart in a 10 knot wind. It would be blown along at whatever speed. This is not a simulation of a cart in wind. It's the speed above zero. It would be, windspeed if attached to the belt, then the propeller would be driven at windspeed.

 

[spork]

Traveling against a treadmill on a windless day.
Apparently, he thinks it should accelerate to the left.

(Correct me if I have misunderstood the claim.)

I'm not going to parse the ascii art, but I can tell you what mine DOES do. It will advance on a treadmill in a room with no wind.

Come to think of it - maybe I can get some video showing this. Maybe post it on youtube.

 

[Brian-M]

I'm not going to parse the ascii art, but I can tell you what mine DOES do. It will advance on a treadmill in a room with no wind.

Come to think of it - maybe I can get some video showing this. Maybe post it on youtube.

That's what I thought. I'd be interested in seeing the video.

 

[spork]

That's what I thought. I'd be interested in seeing the video.

Normally I'd assume you're joking, but after 3 days on this forum I'm not going to make such assumptions.

Search on spork33 on youtube. I've got a pile of videos on this.

 

[humber]

The wind on the cart, is not a tail wind, but a simulated headwind. Just like Mythbusters.
It simulates the wind blowing from propeller to tail. So it is for the cart. Its progress is not against belt zero, but it is the (-windspeed + forward speed)
It's going backwards. That is, how a real cart would behave in a real 10 knot headwind, but blown backwards. Or can it make it's own wind-powered effort against a headwind as that would suggest.

 

[technoextreme]

I'm not going to parse the ascii art, but I can tell you what mine DOES do. It will advance on a treadmill in a room with no wind.

Come to think of it - maybe I can get some video showing this. Maybe post it on youtube.

Yes but it will also stop accelerating at one point. That is whats important. That's the proof in the pudding. And that's what missing.

 

[spork]

Yes but it will also stop accelerating at one point. That is whats important. That's the proof in the pudding. And that's what missing.

Yes, it will stop accelerating at some point. But that point is at a speed faster than the wind - downwind. This is clearly true and clearly demonstrated, and the only point we set out to make.