DDWFTTW Turntable Test: 5 Min Video - Is It Conclusive?

[Subductionzon]

OmCheeto, I am sure that Thin Air Design was talking about his and spork's cart. These are the various videos you can find on Youtube under the submitter spork33. swerdna made his cart because of his own doubts that it would work from discussions with spork on another thread. Spork and JB (aka TAD) made a cart that they ran on an everyday treadmill. They did this because of their own interest and doubters like me who said "If you believe it works why don't you make one and run it on a treadmill, that would be a good test and their would be no doubt about it running faster than the wind". Well they did and I was wrong in two ways. First off I thought it would not run as claimed. When it did and I immediately admitted I was wrong and congratulated them I was still wrong since I thought the treadmill demonstration would clearly demonstrate to doubters that it works. It did not, people who may not have had the aeronautical ability to see how this works but still have enough physics knowledge that they HAVE to see the frame of reference equivalence still have problems with this device. I personally know an actual NASA type rocket scientist who's mind boggled at this. He blew it off by saying to me "Well when they have a technical paper that explains this then I will look at it". Though not any where near as important that is like blowing off the Wright brothers flight until he say a paper that described the technical aspects that made their flight possible. Now that I know it can be done I am much more interested in learning how it works, I don't need any more convincing.

 

[uart]

I am rather curious as to why this issue has not been settled.

This phenomena expression, including all variants, is readily testable and arguably affordable; thus well within the confines of even basic scientific inspection.

There should be a definitive, "this is how it works/doesn't work" answer.

But I'm not seeing that.

This really isn't a controversial issue. I think that everyone with a decent understanding of physics accepts it, but that doesn't stop those who can't grasp the basic physics behind it from arguing indefinitely.

I guess it's a little bit like the Physics equivalent the "controversial" Maths issue of :

0.\bar{9} = 1

(that is, zero point 9 repeated equals one)
It's true and not in the least bit controversial to any real mathematician, but search the Maths forum and you'll find no end of "lay" people wanting to argue the point.

 

[OmCheeto]

OmCheeto, I am sure that Thin Air Design was talking about his and spork's cart. These are the various videos you can find on Youtube under the submitter spork33. swerdna made his cart because of his own doubts that it would work from discussions with spork on another thread. Spork and JB (aka TAD) made a cart that they ran on an everyday treadmill. They did this because of their own interest and doubters like me who said "If you believe it works why don't you make one and run it on a treadmill, that would be a good test and their would be no doubt about it running faster than the wind". Well they did and I was wrong in two ways. First off I thought it would not run as claimed. When it did and I immediately admitted I was wrong and congratulated them I was still wrong since I thought the treadmill demonstration would clearly demonstrate to doubters that it works. It did not, people who may not have had the aeronautical ability to see how this works but still have enough physics knowledge that they HAVE to see the frame of reference equivalence still have problems with this device. I personally know an actual NASA type rocket scientist who's mind boggled at this. He blew it off by saying to me "Well when they have a technical paper that explains this then I will look at it". Though not any where near as important that is like blowing off the Wright brothers flight until he say a paper that described the technical aspects that made their flight possible. Now that I know it can be done I am much more interested in learning how it works, I don't need any more convincing.

I agree with your NASA type rocket scientist.
Viewing the 3 different carts, I can come up with 3 different sets of equations that explain why none of them satisfy the DDWFTTW scenario. For as far as I can tell, each of them has a slightly different modus operandi, contrary to vanesch's apparent assertion that they are all somehow equivalent.
So why don't I publish these findings you might ask.
Because I like looking at these devices and figuring out how they work.
I'm now waiting for someone to build a cart that goes 3 times faster than the wind.
I would like to build one myself, but it's no longer the weekend, I've a full time job, and weekends are better suited for consumption of time devoted to preparation for the fishing season.
Perhaps I'll send the plans to Zooby for him to build.
Or perhaps later in the spring, while waiting for a bite, I'll put a fourth version together, utilizing water of course. And the backdrop scenery in my video will be much more spectacular than someone's messy old garage. Perhaps I'll add music. http://www.youtube.com/watch?v=Gz3Cc7wlfkI&feature=related" might be appropriate. Oh what an idea. A whole squadron of DDWFFTW devices attacking the beach head, with people running and screaming for their lives! I wonder if Coppola is available?

 

[zoobyshoe]

This really isn't a controversial issue. I think that everyone with a decent understanding of physics accepts it, but that doesn't stop those who can't grasp the basic physics behind it from arguing indefinitely.

I guess it's a little bit like the Physics equivalent the "controversial" Maths issue of :

0.\bar{9} = 1

(that is, zero point 9 repeated equals one)
It's true and not in the least bit controversial to any real mathematician, but search the Maths forum and you'll find no end of "lay" people wanting to argue the point.

It's not the principles I object to: it should be possible. It's the practical side. Archimedes boasted that with a long enough lever and a place to stand he could move the earth. In principle he was absolutely right. There are so many practical impossibilities to his ever being able to do it that the principle become moot.

As I mentioned before there is no principle prohibiting a human powered helicopter, yet (to the best of my knowledge) no one has yet been able to engineer one that fulfills the criteria to get the $30,000.00 prize for the first one.

The other problem is the vaguery of the claim DDWFTTW. The actual, specific, real problem that must be tackled is whether a device can accelerate into an apparent head wind, a wind that only exists by virtue of its own motion relative to the ground, powered only by the difference in speed of that apparent head wind and the apparent ground speed. Doubts become more justifies when you realize that both speeds are only apparent ones, relative to the cart and both are applying force to the cart in a direction that will act to slow the cart down. Everything rides on the propeller. Can the propeller divert the force in such a way to create the thrust needed for acceleration? Jeff is hard at work on this.

 

[ThinAirDesign]

I know, and for only $50.00 I can find out how wrong I am!

Yes you can, but since I can't know for sure what you are implying here let me be clear: I don't sell carts, cart parts, nor parts kits. Other than online hobby stores, I don't even *recommend* where to buy cart parts.

Here's the parts list (not my link) and build videos (not my videos).

http://www.rtfa.net/2008/12/23/ddwfttw-the-perfect-holiday-project

You've just stated that you believe it can be done in principle, but you are arguing against it in practice ... yes, for only $50.00 you can end the argument you are having against reality.

JB

 

[rcgldr]

Can the propeller divert the force in such a way to create the thrust needed for acceleration? Jeff is hard at work on this.

I thought I was done with the explanations.

...

Prop power input = force at wheels times ground speed at wheels
Prop power output = force at prop times air speed at prop

The power input is used to create the torque and angular velocity used to drive the prop. The prop generates a higher force but at a lower speed than the wheel + ground interface. A tailwind allows the prop to interact with air that is moving slower than the ground (using the cart as a frame of reference), so that the slower speed at the prop still results in a net upwind thrust.

The net upwind thrust opposes the tailwind, slowing the wind down significantly below cart speed, allowing the cart to operate DDWFTTW.

 

[ThinAirDesign]

Viewing the 3 different carts, I can come up with 3 different sets of equations that explain why none of them satisfy the DDWFTTW scenario.

(the following assumes you are talking about three different prop-carts seen on youtube videos)

And since all three of the carts in the videos can demonstrate DDWFTTW upon demand, there's an obvious flaw in all three of your equation sets.

For as far as I can tell, each of them has a slightly different modus operandi, ...

Well, then you can't tell far enough, as each of those carts uses a combination of gearing and prop pitch to place them all three within the same operating range and thus identical operating principles and "modus operandi".

... contrary to vanesch's apparent assertion that they are all somehow equivalent.

I'm just not sure how they could *not* be equivalent, as they are all of essentially identical design and operation.

So why don't I publish these findings you might ask.
Because I like looking at these devices and figuring out how they work.

Perhaps you will like it, perhaps you won't -- but to know you must first accomplish it. It's obvious from the above you have not reached that point yet.

I'm now waiting for someone to build a cart that goes 3 times faster than the wind.

You may be waiting a while ... I just don't seem to remember anyone making any DDW3XFTTW claims. Right now the 1.5x range is the best I've seen.


JB

 

[tsig]

I thought I was done with the explanations.



Prop power input = force at wheels times ground speed at wheels
Prop power output = force at prop times air speed at prop

The power input is used to create the torque and angular velocity used to drive the prop. The prop generates a higher force but at a lower speed than the wheel + ground interface. A tailwind allows the prop to interact with air that is moving slower than the ground (using the cart as a frame of reference), so that the slower speed at the prop still results in a net upwind thrust.

The net upwind thrust opposes the tailwind, slowing the wind down significantly below cart speed, allowing the cart to operate DDWFTTW.

According to your second equation when air speed at prop = zero there is no power out.This conditions happens when cart speed = wind speed.

If you have one pound of thrust from the propeller then there will also be one pound drag on the wheels since that is where the energy to drive the prop comes from.

 

[vanesch]

According to your second equation when air speed at prop = zero there is no power out.This conditions happens when cart speed = wind speed.
.

What equation ?

The MOMENTUM change is:

(mass of air per second) x (v_out - v_in)

The ENERGY change is:

1/2 (mass of air per second) x (v_out^2 - v_in^2)


The momentum change is nothing but the force. The energy change is what is needed to drive the propeller.

Now, here's something interesting to see. If you change reference frames, you have:

v_out' = v_out - v_frame
v_in' = v_in - v_frame


and notice that this DOESN'T change the expression for the momentum change (so the force is independent of the choice of frame), but notice that this DOES change the energy balance!

So whether you GIVE energy to the air, or whether you RECEIVE energy from the air, is dependent on what frame one looks at it.

 

[rcgldr]

According to your second equation when air speed at prop = zero there is no power out.This conditions happens when cart speed = wind speed.

Air speed at the prop includes induced wash. When cart speed == wind speed, there is significant induced wash at the prop. There is some sub wind speed where the average speed of air near the prop is zero as it accelerates an apparent tailwind into an apparent headwind, and at this speed, the prop could be considered to be doing no work since the kinetic energy of the air doesn't change, just the direction.

If you have one pound of thrust from the propeller then there will also be one pound drag on the wheels since that is where the energy to drive the prop comes from.

The one pound of thrust corresponds to some amount of torque applied to the prop by the wheels. The DDWFTTW carts are configured (effectively geared) so that the force at the prop is greater than the opposing force at the wheels, but the speed at the prop is much less than the speed of the wheels, so that the power output (prop thrust x prop air speed) is less than power input (wheel force x wheel ground speed).

 

[zoobyshoe]

I thought I was done with the explanations.

I thought you were still calculating the best propeller for the job.

 

[OmCheeto]

I'm just not sure how they could *not* be equivalent, as they are all of essentially identical design and operation.

JB

Cart #1 goes in a semi-straight line and is powered by the wind.
Cart #2 goes in a semi-straight line and is powered by a treadmill.
Cart #3 goes in a circle and is powered by a spinning piece of plywood.

I guess, as a "systems thinker", the similarities in cart design are overwhelmed by the differences in how the carts are propelled.

 

[Subductionzon]

Cart #1 goes in a semi-straight line and is powered by the wind.
Cart #2 goes in a semi-straight line and is powered by a treadmill.
Cart #3 goes in a circle and is powered by a spinning piece of plywood.

I guess, as a "systems thinker", the similarities in cart design are overwhelmed by the differences in how the carts are propelled.

Actually all three run off of the same thing, the difference between the speed of the air and the speed of the medium it is running on. If you watch enough of spork33's videos you will also see an outdoor test where the cart starts from zero. Though they were not testing for faster than the wind in that video, they just wanted to show that it could take off on its own, it looked like it may have been going faster than the wind by the time JB (aka Thin Air Design) caught up to it. Wait a second that would imply that JB could run like the wind so we will have to say nah.

 

[vanesch]

Cart #1 goes in a semi-straight line and is powered by the wind.
Cart #2 goes in a semi-straight line and is powered by a treadmill.
Cart #3 goes in a circle and is powered by a spinning piece of plywood.

I guess, as a "systems thinker", the similarities in cart design are overwhelmed by the differences in how the carts are propelled.

The similarities come about when you make a free-body force diagram for each of them.

 

[rcgldr]

I thought I was done with the explanations.

I thought you were still calculating the best propeller for the job.

I haven't looked into optimizing for maximum speed. It's not a speed contest (yet), and except for swerdna's turn table there's no easy way to let the models reach their maximum speed. We're stuck with the selection of slow flyer model props that are available that work well with the relatively slow apparent headwinds (compared to the speed of model airplanes).

 

[ThinAirDesign]

Cart #1 goes in a semi-straight line and is powered by the wind.
Cart #2 goes in a semi-straight line and is powered by a treadmill.
Cart #3 goes in a circle and is powered by a spinning piece of plywood.

I guess, as a "systems thinker", the similarities in cart design are overwhelmed by the differences in how the carts are propelled.

And once again we bang up against your inability to understand basic inertial frames of reference.

Until you come to understand and accept this FACT: An object powered by the relative motion between mediums/objects, cares not nor can differentiate which medium/object is moving and which is still.

• A wind turbine generates just as much electricity bolted to the deck of an aircraft carrier steaming at 15 knots on a still air day as does one mounted on the ridge in a 15 knot wind. Wind turbine can't know. Wind turbine doesn't care.
• Neither sailor nor sailboat can differentiate between still water and moving air versus a river on a still air day. Sailboat can't know. Sailboat doesn't care.
• While standing still on a long treadmill moving at 6mph, a child can fly a kite on a still day just the same as standing on the lawn with a 6mph wind -- or they can run across the lawn at 6mph on a still day. Kite can't know. Kite doesn't care.
• DDWFTTW cart runs the same way no matter if the air is moving and the plywood is still, or the plywood is moving and the air is still. Cart can't know. Cart doesn't care.

This is a physics forum for cryin' out loud, and the above facts can withstand and have withstood the scrutiny of the entire physics community for four centuries now. If you manage to refute any of the above, you will be beyond Nobel territory.

JB

 

[tsig]

And once again we bang up against your inability to understand basic inertial frames of reference.

Until you come to understand and accept this FACT: An object powered by the relative motion between mediums/objects, cares not nor can differentiate which medium/object is moving and which is still.

• A wind turbine generates just as much electricity bolted to the deck of an aircraft carrier steaming at 15 knots on a still air day as does one mounted on the ridge in a 15 knot wind. Wind turbine can't know. Wind turbine doesn't care.
• Neither sailor nor sailboat can differentiate between still water and moving air versus a river on a still air day. Sailboat can't know. Sailboat doesn't care.
• While standing still on a long treadmill moving at 6mph, a child can fly a kite on a still day just the same as standing on the lawn with a 6mph wind -- or they can run across the lawn at 6mph on a still day. Kite can't know. Kite doesn't care.
• DDWFTTW cart runs the same way no matter if the air is moving and the plywood is still, or the plywood is moving and the air is still. Cart can't know. Cart doesn't care.

This is a physics forum for cryin' out loud, and the above facts can withstand and have withstood the scrutiny of the entire physics community for four centuries now. If you manage to refute any of the above, you will be beyond Nobel territory.

JB

When you look at the whole system you see that the windmill on the carrier is being powered by the carrier's steam turbines.

 

[A.T.]

When you look at the whole system you see that the windmill on the carrier is being powered by the carrier's steam turbines.

Wow, schroder registered under a new name.

Is this the longest thread ever already?

 

[ThinAirDesign]

When you look at the whole system you see that the windmill on the carrier is being powered by the carrier's steam turbines.

Of course it is -- no one questions that, but we don't argue about whether it's the same wind turbine as the one up on the hill do we? We don't argue about whether it works exactly the same way do we?

What *creates* the wind is irrelevant to a wind powered device -- it's doesn't know nor does it care. Solar wind (outdoors), nuke wind (aircraft carrier), elecric wind (wind tunnel, treadmill), gravity (river), all the same to a turbine, sailboat, DDWFTTW cart.

One more time, a wind turbine, sail and DDWFTTW cart are all examples of wind powered devices -- arguments about what powers the wind that powers the devices are not relevant to the details of how a wind powered device works.

JB

 

[cesiumfrog]

Is this the longest thread ever already?

In this forum at least, by a factor of >2. Still less viewed than the FAQ however (unless you include the previous attempts at this thread).

 

[rcgldr]

When you look at the whole system you see that the windmill on the carrier is being powered by the carrier's steam turbines.

Well just imagine than an outdoor wind is being generated by steam powered wind turbines. Does it matter what the power source is that creates the relative wind?

 

[OmCheeto]

The similarities come about when you make a free-body force diagram for each of them.

The first time I tried to do a free body diagram of swerdna's device, I spent 20 minutes cursing and swearing before I threw down my notebook.

I really think his devise was the mindchild of some sadistic professor's idea of a joke problem that he gave to a bunch of his 2nd year physics students for their final exam.

I think that is why I like it so much.

 

[schroder]

Wow, schroder registered under a new name.

Is this the longest thread ever already?

No. Schroder has not registered under a new name. There is no need for me to do that, I can speak for myself.

 

[schroder]

And once again we bang up against your inability to understand basic inertial frames of reference.

Until you come to understand and accept this FACT: An object powered by the relative motion between mediums/objects, cares not nor can differentiate which medium/object is moving and which is still.


DDWFTTW cart runs the same way no matter if the air is moving and the plywood is still, or the plywood is moving and the air is still. Cart can't know. Cart doesn't care.

This is a physics forum for cryin' out loud, and the above facts can withstand and have withstood the scrutiny of the entire physics community for four centuries now. If you manage to refute any of the above, you will be beyond Nobel territory.

JB

I agree with this statement. So, if I can prove to you that the cart is actually running slower than the tread, while being powered by the tread, even as it is advancing on the tread, then will you accept that it will also be running slower than the wind, while being powered by the wind?

 

[vanesch]

I think that is why I like it so much.

Me too

 

[vanesch]

I agree with this statement. So, if I can prove to you that the cart is actually running slower than the tread, while being powered by the tread, even as it is advancing on the tread, then will you accept that it will also be running slower than the wind, while being powered by the wind?

No, of course not. Because what you say is equivalent to:
"if I can prove that the cart is actually running slower THAN THE GROUND".

The equivalences are:
cart < - > cart
air < - > air
ground < - > tread

 

[schroder]

No, of course not. Because what you say is equivalent to:
"if I can prove that the cart is actually running slower THAN THE GROUND".

The equivalences are:
cart < - > cart
air < - > air
ground < - > tread

You are changing the rules of the game, again Vanesch.
The claim of Galilean relativity is that when on the treadmill, the tread is moving with respect to the stationary air while when in the wind the air is moving with respect to the stationary ground and the frames are equivocal.
And the observation made on the treadmill is that the cart, by virtue of advancing in the opposite direction to the motion of the tread, is going faster than the tread.
Then, by the equivalence of reference frames, the claim is being made that the cart, when in the wind, will go faster than the wind.
What I am saying is: I can show that the cart on the treadmill is actually not going faster than the tread, with respect to the tread but is going slower. This is the case even as the cart is seen to be moving in the opposite direction as the tread.


And, once I show this, I want to know if everyone will then accept that when in the wind, the cart will move slower than the wind.

 

[vanesch]

You are changing the rules of the game, again Vanesch.
The claim of Galilean relativity is that when on the treadmill, the tread is moving with respect to the stationary air while when in the wind the air is moving with respect to the stationary ground and the frames are equivocal.

Yes, so the treadmill in one setup is the equivalent of the ground in the other.

And the observation made on the treadmill is that the cart, by virtue of advancing in the opposite direction to the motion of the tread, is going faster than the tread.

No, of course not. It is not "going faster than the thread". It is going faster WITH RESPECT TO THE TREAD, than the air is WITH RESPECT TO THE TREAD.

Then, by the equivalence of reference frames, the claim is being made that the cart, when in the wind, will go faster than the wind.

Yes, because here also, the cart, WITH RESPECT TO THE GROUND is going faster than the air, WITH RESPECT TO THE GROUND.

It would be a a bit silly to say that the cart is going faster than the ground, wouldn't it ?

What I am saying is: I can show that the cart on the treadmill is actually not going faster than the tread,

Sure, but nobody is claiming that.

with respect to the tread but is going slower.

You cannot have a thing X which goes slower WRT to a thing Y, than the thing Y ITSELF is going WRT to itself, can you ?

Because a thing doesn't move wrt itself. So it is hard to go slower than a thing that doesn't move, right ?

And, once I show this, I want to know if everyone will then accept that when in the wind, the cart will move slower than the wind.

Nope. You compare the wrong things.
What you show is that the cart is going slower WRT the air than the ground is WRT the air.
What people claim is that the cart is going FASTER wrt the ground than the air is WRT the ground.

For that, you have to understand negative numbers of course.

What you show is: | C - A | < | G - A|

What is claimed is that |C - G| > |A - G| = | G - A |

What you show doesn't invalidate the second claim.

Take as an example: C = -2, A = 0, G = 10.

You show: | -2 - 0 | < | 10 - 0| OK

Nevertheless, we have: | C - G | = | -2 - 10| = 12 > |G - A| = |10 - 0| = 10
(yes, 12 > 10)

Note: as in the above inequalities, we only have differences, it doesn't matter if we add or subtract a common number to all of them, right ?
That's the mathematical expression of saying that relative velocities can be calculated in any frame, BTW.

 

[rcgldr]

So, if I can prove to you that the cart is actually running slower than the tread

No one has made any claim about cart speed versus tread speed. The claim can be mathematically stated as:

|cart_speed - tread_speed| > |wind_speed - tread_speed|.

powered by the tread ... powered by the wind

The DDWFTTW carts are powered by utilizing the difference between wind speed and ground speed to slow the wind affected by the prop relative to the ground speed. Since the mass of tread and/or ground is much greater than the air interacted with by the prop, most of the transfer of energy is from the air (reduction in kinetic energy with respect to the ground) to the cart (increase in kinetic energy with respect to the ground) (plus a tiny amount of kinetic energy change transferred to the tread and/or ground).

 

[vanesch]

But, to add to your confusion, let us consider the following.

Let us consider that we put the treadmill on an open truck. Let us first assume a windless day, the truck is standing still, and we do the treadmill experience. The tread moves 10 mph in the direction of the back of the truck, and the we see the cart moving forward by 2 mph. I guess that it doesn't matter whether we do that experience on a steady truck on a windless day, or whether we do it in a gymclub, right ?

Now, let us assume that we put a cover over the truck, so that the treadmill is protected from the outside wind. Let us assume that the truck is driving at 10 mph. I suppose you can accept that the experience still gives the same result, no ? Whether this happens in a cabin on a truck, or in a gymclub, we can take it that if we have the treadmill run 10 mph, that the cart is still moving forward 2 mph on it, right ? It is not because the truck is slowly driving that it changes anything, right ?

Now, next step: assume that there is a wind, blowing in the sense of the truck, at 10 mph. We don't change anything. There's no reason that the experiment INSIDE the cabin is affected the slightest bit by any wind condition outside, right ?

However, as the truck is now driving at exactly the same speed as the wind (10 mph), as seen from the truck, it is windstill right ? So we can remove the cover of the cabin, it won't give any wind on our treadmill, right ? So we can assume that our experiment still runs in the same way, with the treadmill running 10 mph, and the cart advancing 2 mph forward on it, right ?
So we are now on an open truck moving at 10 mph, in a wind of 10 mph in the same direction, and the experiment still works out, right ?

Now, we have a mechanical arm on the truck, and we take the treadmill on the arm. It is not because we lift it a bit that anything changes, right ? If the treadmill is running, the cart is still moving 2 mph on it.

Now, move the treadmill with the arm next to the truck, closer to the road. That won't change anything, right ? The truck is driving forward at 10 mph, the wind is blowing also 10 mph, on the truck we think there is no wind, the treadmill is running 10 mph backward and the cart advances 2 mph on it, right ?

But look: the surface of the treadmill is now at rest with the road ! If we let the cart actually run off the treadmill, it will smoothly go on the road, and it won't notice the difference. It will still go 2 mph forward wrt the truck. In other words, it will be on the road and advance at 2 mph as seen from the truck.

Now, the truck has an accident. The cart isn't affected by that: it continues its way. Wrt the road it continues at 2 mph faster than the truck was driving, so at 12 mph. The wind was blowing at 10 mph in the same direction.

Where don't you believe me anymore ?