Understanding DDWFTTW: Exploring Its Principles and Addressing Common Questions

[spork]

From this, we can see that "DDWFTTW" phenomenon isn't limited to sails or propellers

The very fact that these are "anomalous" tells us that they're not all that similar to DDWFTTW. DDWFTTW may be counter-intuitive, but it's very easily explained with very traditional physics.

 

[kmarinas86]

The very fact that these are "anomalous" tells us that they're not all that similar to DDWFTTW.

I'm not sure that follows.

Bill Stronge of Cambridge University in England describes the indentation as a kind of ski jump, which redirects the sphere’s velocity skyward.

The rotation and pitch of a propeller could create an interface between incoming wind that, due to changes in the propeller's position and the change of wind's angle of attack with the propeller's surface over time, the propeller may appear to the wind as if it were a "ski jump". That might be going beyond the minimum to explain DDWFTTW, but it also would explain why a different propeller design might be better at DDWFTTW than another.

 

[jduffy77]

From this, we can see that "DDWFTTW" phenomenon isn't limited to sails or propellers:

Anomalous behavior of normal kinematic restitution in the oblique impacts of a hard sphere on an elastoplastic plate

This article has absolutely nothing to do with ddwfttw whatsoever. Your apparent desire to over complicate the simple lever which is the ddwfttw cart is fascinating to me. I believe your confusion stems from the fact that you still wish to see the cart as being pushed along by the wind. You need to think about the cart's prop exactly as you would the prop in a powered airplane. In this case the cart is powered by the wheels but it is generating thrust in exactly the same manner as the airplane.

 

[kmarinas86]

From this, we can see that "DDWFTTW" phenomenon isn't limited to sails or propellers:

Anomalous behavior of normal kinematic restitution in the oblique impacts of a hard sphere on an elastoplastic plate
http://masters.donntu.edu.ua/2010/fimm/kutnyashenko/library/nem_1/nem_1.pdf

This article has absolutely nothing to do with ddwfttw whatsoever. Your apparent desire to over complicate the simple lever which is the ddwfttw cart is fascinating to me. I believe your confusion stems from the fact that you still wish to see the cart as being pushed along by the wind. You need to think about the cart's prop exactly as you would the prop in a powered airplane. In this case the cart is powered by the wheels but it is generating thrust in exactly the same manner as the airplane.

"Powered by the wheels" makes no sense. They're not the source of energy.
The relative motion of the wind with respect to the ground is also not necessary, otherwise, dynamic soaring would not work. Dynamic soaring could also work in the upper atmosphere bordering the vacuum of space, by dipping in and out of it, but you can't give a vacuum a "velocity" with respect to the ground. So you don't even need to reduce the relative velocity of two masses to accelerate a third with respect to the first and the second.

Replace the "hard sphere" with the propeller and the "elastoplastic plate" with the wind (the wind deforms faster than the propeller). That seems analogous to me.

And do you think that DD"W"FTT"W" can only happen with sails and propellers? I think just about any two interfaces will do. One of them doesn't have to be "wind". That's my point. I'm saying that DD"W"FTT"W" could done with anything, even with two "solids" if the angles are just right. DD"W"FTT"W" could also happen inside a fluid, where particles in the fluid can be likened to "ships" or "wind".

 

[jduffy77]

"Powered by the wheels" makes no sense. They're not the source of energy.

No, in fact the only thing that does make sense to say about the props power source is that it is the wheels. The ground is in fact the source of energy if you choose to analyze the cart in a frame other than that of the ground.

The relative motion of the wind with respect to the ground is also not necessary, otherwise, dynamic soaring would not work.

This is completely wrong. The relative motion of the wind with respect to the ground is central to the carts functioning and the cart has nothing to do with dynamic soaring.

And do you think that DD"W"FTT"W" can only happen with sails and propellers? I think just about any two interfaces will do. One of them doesn't have to be "wind". That's my point. I'm saying that DD"W"FTT"W" could done with anything, even with two "solids" if the angles are just right. DD"W"FTT"W" could also happen inside a fluid, where particles in the fluid can be likened to "ships" or "wind".

This is correct but completely contradicting what you said earlier about relative motion.
As long as you have two surfaces which are in motion with respect to each other, you could design a vehicle which used leverage to travel faster than its power source.

 

[jduffy77]

Kmarinas Have you checked out coolaun's excellent videos?

http://www.youtube.com/user/coolaun/videos

He shows various d"w"ftt"w" examples.

 

[kmarinas86]

"Powered by the wheels" makes no sense. They're not the source of energy.

No, in fact the only thing that does make sense to say about the props power source is that it is the wheels. The ground is in fact the source of energy if you choose to analyze the cart in a frame other than that of the ground.

I said:

Dynamic soaring could also work in the upper atmosphere bordering the vacuum of space, by dipping in and out of it, but you can't give a vacuum a "velocity" with respect to the ground. So you don't even need to reduce the relative velocity of two masses to accelerate a third with respect to the first and the second.

Here, one air layer is "replaced with a vacuum", and I am saying that dynamic soaring will work, even with that.
So, the ground is not necessary. It "helps" but it is not necessary. So you would just need the blade and the wind.

The relative motion of the wind with respect to the ground is also not necessary, otherwise, dynamic soaring would not work.

This is completely wrong. The relative motion of the wind with respect to the ground is central to the carts functioning and the cart has nothing to do with dynamic soaring.

Tacking applies to all of them. So I canNOT see how they are NOT related.
Also, I'm not talking about the DD"W"FTT"W" cart specifically, but DD"W"FTT"W" in general, which includes dynamic soaring (possible with a helical path so as to emulate one of the blades on the propeller of the DD"W"FTT"W" cart).

And do you think that DD"W"FTT"W" can only happen with sails and propellers? I think just about any two interfaces will do. One of them doesn't have to be "wind". That's my point. I'm saying that DD"W"FTT"W" could done with anything, even with two "solids" if the angles are just right. DD"W"FTT"W" could also happen inside a fluid, where particles in the fluid can be likened to "ships" or "wind".

This is correct but completely contradicting what you said earlier about relative motion. As long as you have two surfaces which are in motion with respect to each other, you could design a vehicle which used leverage to travel faster than its power source.

What I said about relative motion is, "The relative motion of the wind with respect to the ground is also not necessary, otherwise, dynamic soaring would not work."

This is not necessary because what you have instead is relative motion between the wind and the wings of a glider. You only need two things like you said. I did not contradict myself here.

 

[jduffy77]

I said:

Here, one air layer is "replaced with a vacuum", and I am saying that dynamic soaring will work, even with that.
So, the ground is not necessary. It "helps" but it is not necessary. So you would just need the blade and the wind.

I know what you said, its just that you are completely wrong. Your confusion seems to be fairly well entrenched at this point and I do not really know how to help you. At this point I will answer questions if you have any or hopefully others more expert than I am might chime in and help you understand.

 

[kmarinas86]

I said:

Dynamic soaring could also work in the upper atmosphere bordering the vacuum of space, by dipping in and out of it, but you can't give a vacuum a "velocity" with respect to the ground. So you don't even need to reduce the relative velocity of two masses to accelerate a third with respect to the first and the second.

Here, one air layer is "replaced with a vacuum", and I am saying that dynamic soaring will work, even with that.
So, the ground is not necessary. It "helps" but it is not necessary. So you would just need the blade and the wind.

I know what you said, its just that you are completely wrong. Your confusion seems to be fairly well entrenched at this point and I do not really know how to help you. At this point I will answer questions if you have any or hopefully others more expert than I am might chime in and help you understand.

So in other words, you think dynamic soaring cannot work between a vacuum (which lacks a velocity) and the upper atmosphere. Well, I'd like to see proof of that.

 

[spork]

...the cart has nothing to do with dynamic soaring.

I think there's a connection between the two only in that both exploit the energy available at the interface of two media moving relative to one another. In the case of the cart, it's the ground and air. In the case of dynamic soaring, it's two different layers of air separated by a gradient.

The cart uses mechanical means to act as a lever between the two media, while dynamic soaring relies on the inertia of the body to make the connection between the two media.

But you definitely cannot go DDWFTTW using dynamic soaring. And dynamic soaring is definitely not possible between the atmosphere and the vacuum of space.

 

[jduffy77]

So in other words, you think dynamic soaring cannot work between a vacuum (which lacks a velocity) and the upper atmosphere. Well, I'd like to see proof of that.

No, I only said that dynamic soaring has nothing to do with the ddwfttw cart. It is true that both extract energy from the difference in velocity between two masses but that is as far as it goes.

You state that the ddwfttw cart does not need the ground. That is nonsense. There is no shear layer in the air mass the cart is traveling through which can be exploited even if a mechanism existed to do so. The ddwfttw cart is a lever. There most be a fulcrum for the force. The cart uses the ground as a fulcrum.

 

[spork]

So in other words, you think dynamic soaring cannot work between a vacuum (which lacks a velocity) and the upper atmosphere. Well, I'd like to see proof of that.

It cannot. And that's not how proof works. If you think it can be done, it's up to you to tell us how.

 

[kmarinas86]

So in other words, you think dynamic soaring cannot work between a vacuum (which lacks a velocity) and the upper atmosphere. Well, I'd like to see proof of that.

It cannot. And that's not how proof works. If you think it can be done, it's up to you to tell us how.

Well, to me it is no more mysterious to propose this than it is to propose the slingshot effect.

http://www.schoolphysics.co.uk/age14-16/Astronomy/text/Slingshot_/images/1.gif

In the case for the atmosphere interacting with a blade, instead of being pulled, it is being kicked.

http://www.schoolphysics.co.uk/age14-16/Astronomy/text/Slingshot_/images/2.gif

Replace the "train" with the wind, and replace the "ball" with the plane, DDWFTTW cart, or whatever you like. Like what was explained to me a few months ago, the -5 m/s can be created due the effective velocity due to the rotation of the blade and its angle of pitch, making the blade surfaces "appear to move backwards" thus enabling the wind to hit it from the back.

This would also work even if the train were to fly off a cliff. The "ground" does not matter at all.

The proper leverage only serves to make this effect more efficient (I.O.W. to make it easily engineerable). It does not, like you claim, constitute a necessary condition for DDTWFTTW.

 

[jduffy77]

Well, to me it is no more mysterious to propose this than it is to propose the slingshot effect.

http://www.schoolphysics.co.uk/age14-16/Astronomy/text/Slingshot_/images/1.gif

In the case for the atmosphere interacting with a blade, instead of being pulled, it is being kicked.

http://www.schoolphysics.co.uk/age14-16/Astronomy/text/Slingshot_/images/2.gif

Replace the "train" with the wind, and replace the "ball" with the plane, DDWFTTW cart, or whatever you like. Like what was explained to me a few months ago, the -5 m/s can be created due the effective velocity due to the rotation of the blade and its angle of pitch, making the blade surfaces "appear to move backwards" thus enabling the wind to hit it from the back.

This would also work even if the train were to fly off a cliff. The "ground" does not matter at all.

The proper leverage only serves to make this effect more efficient. It does not, like you claim, constitute a necessary condition for DTTWFTTW.

You are wrong, the leverage is central to the carts functioning. A cart could not ddwfttw without the ground any more than a balloon could. Your diagrams above introduced two more scenarios which have absolutely nothing to do with the cart. The cart can travel ddwfttw indefinitely. It is not being assisted by gravity or a diesel engine.

 

[kmarinas86]

You are wrong, the leverage is central to the carts functioning.

That's because the cart is not efficient enough without this leverage, and you wouldn't see DDWFTTW in that case.

A cart could not ddwfttw without the ground any more than a balloon could.

But a balloon still can go DDWFTTW, if it acted like a sailboat and spun like a football.

Your diagrams above introduced two more scenarios which have absolutely nothing to do with the cart. The cart can travel ddwfttw indefinitely. It is not being assisted by gravity or a diesel engine.

Nor is a sailboat.
A balloon can act like sail, albeit, very ineffectively for the purpose of going DDWFTTW.

1) The only reason why DDWFTTW is DDW (in the sense of a straight line) is that the sail flips end over end, forming a helix, and the axis travels parallel to the wind.
2) But all of these examples demonstrate "D"DWFTTW (in the sense of its overall trajectory being parallel to the wind (depending on the frame of reference, path chosen, number of interactions, and so forth)), though not in a straight line.

Has it is been assumed by you all that "DDWFTTW" refers only to the former? I see it as meaning both the former and the latter. This might explain our "disagreement".

 

[jduffy77]

That's because the cart is not efficient enough without this leverage, and you wouldn't see DDWFTTW in that case.

It is not because it is not efficient enough. it is because it is impossible. There could be no mechanism to extract energy.

But a balloon still can go DDWFTTW, if it acted like a sailboat.

But it can't. Maybe now we are getting somewhere. The sailboat needs the water or more importantly the keel.

Nor is a sailboat.
A balloon can act like sail, albeit, very ineffectively for the purpose of going DDWFTTW.

It cannot.

 

[kmarinas86]

It cannot.

What if the "balloon" is shaped like a sailboat?
What if the sailboat is inflatable?
It's still a "balloon".

 

[jduffy77]

What if the "balloon" is shaped like a sailboat?
What if the sailboat is inflatable?
It's still a "balloon".

The craft needs a fulcrum.

 

[kmarinas86]

It is not because it is not efficient enough. it is because it is impossible. There could be no mechanism to extract energy.

http://www.wired.co.uk/magazine/archive/2011/04/features/faster?page=all

And the balloon-versus-sailing boat hypothesis he came up with took him to another planet altogether: a cylindrical planet entirely covered by water, with a constant wind blowing down its length. Call it "Planet Water-Barrel" and visualise a balloon racing a sailing boat from one end to the other.

The advantage of holding a race on this planet is that because the boat can sail completely around the cylinder, it never has to zigzag to end up at the same end point as the balloon. Instead, the craft can stay on one continuous crosswind heading and spiral all the way around the barrel, ending up at the finish line. On Planet Water-Barrel, the maths simplifies. But forget the maths for a moment and concentrate on the visual picture.

What if the balloon-versus-sailing-boat race ran a down cylindrical planet of much a smaller diameter: Planet Steel-Rod? In that case, the boat would essentially be spinning around its own axis and its sail would suddenly look a lot like a turning propeller blade.

There's no mention of gearing here whatsoever.

The craft needs a fulcrum.

The only "leverage" you would need is at the axis of angular momentum of the spinning prop, corkscrewing plane, or what have you. What "ground" is required here?

 

[jduffy77]

http://www.wired.co.uk/magazine/archive/2011/04/features/faster?page=all
There's no mention of gearing here whatsoever.

No but the steel rod is required.

The only "leverage" you would need is at the axis of angular momentum of the spinning prop, corkscrewing plane, or what have you. What "ground" is required here?

We were talking about the ability of a balloon which you said could "act like a sail" to travel ddwfttw.

 

[spork]

This is going in some pretty bizarre directions. Until kmarinas understands the basics of the DDWFTTW cart, it's kind of pointless to go off in the direction of slingshot effect, dynamic soaring, etc.

 

[kmarinas86]

No but the steel rod is required.

We were talking about the ability of a balloon which you said could "act like a sail" to travel ddwfttw.

I never said you couldn't attach the balloon to the rod.

In that case, such a rod isn't a equivalent to the "ground", because it is moving with the balloon.

In the DDWFTTW cart, the rod is not moving at the same speed as the ground and the wind.

The friction with ground (or sea) (or rod) is only there to prevent it from veering off course (it increases the effective moment of inertia around that axis). Without such friction, you could use counter-rotating propellers, just like what is done with some toy helicopters and various jet engines. I.e. to cancel the leverage that you don't want or need.

And why does it have to be steel? That makes no sense.
The "rod" itself can be a balloon.

 

[spork]

I never said you couldn't attach the balloon to the rod.

In that case, such a rod isn't a equivalent to the "ground", because it is moving with the balloon.

That won't work either.

In the DDWFTTW cart, the rod is not moving at the same speed as the ground and the wind.

You're getting the analogy badly mixed up.

The ground (or sea) (or rod) is only there to prevent it from veering off course

Definitely wrong.

Without such support, you could use counter-rotating propellers...

You could use counter-rotating props if you like, but they'd still have to work against the ground or some other medium moving relative to the air they're in.

 

[kmarinas86]

You could use counter-rotating props if you like, but they'd still have to work against the ground or some other medium moving relative to the air they're in.

Sure. Each prop has another medium to work with that moves relative to the air it's in. It's called the other prop.
If you don't have the other prop, there is a hub. You can even have a gearing mechanism if you like. But no connection to the ground is necessary.

 

[spork]

Sure. Each prop has another medium to work with that moves relative to the air it's in. It's called the other prop.
If you don't have the other prop, there is a hub. You can even have a gearing mechanism if you like. But no connection to the ground is necessary.

You're just all over the place. How about if we take a single one of your ideas and discuss it until we reach some understanding.

You talked about counter-rotating props. That alone will do you no good in the attempt to go DDWFTTW. Yes, putting one prop in one air-mass and the other in a separate air-mass that moves relative to the first could potentially be used to make a vehicle go DDWFTTW relative to one of those air-masses.

But in reality, you wouldn't use two props, but rather a prop and a turbine.

Of course you could answer this by bringing up railroad cars, balloons, and the slingshot effect. Or we could try and discuss this point until we reach some understanding.

 

[kmarinas86]

You're just all over the place. How about if we take a single one of your ideas and discuss it until we reach some understanding.

You talked about counter-rotating props. That alone will do you no good in the attempt to go DDWFTTW. Yes, putting one prop in one air-mass and the other in a separate air-mass that moves relative to the first could potentially be used to make a vehicle go DDWFTTW relative to one of those air-masses.

But in reality, you wouldn't use two props, but rather a prop and a turbine.

Of course you could answer this by bringing up railroad cars, balloons, and the slingshot effect. Or we could try and discuss this point until we reach some understanding.

What about a submarine with counter-rotating props? (i.e. DDSFTTS or Directly DownStream Faster Than The Stream)

 

[spork]

What about a submarine with counter-rotating props? (i.e. DDSFTTS or Directly DownStream Faster Than The Stream)

What about a helium powered baby buggy that's catapulted into space and uses the moon as a slingshot? Or a nuclear fusion reactor that harnesses wind power and rectifies that using crystals?

 

[jduffy77]

What about a submarine with counter-rotating props? (i.e. DDSFTTS or Directly DownStream Faster Than The Stream)

Are these props powered only by the stream?

 

[kmarinas86]

Are these props powered only by the stream?

If the stream is uniform, you would first have to drop the submarine in and then activate the propellers. This is nothing more than the submarine equivalent of Spork's treadmill. This acts as a break slowing the water behind it, so it is slower as it passes over (water flow, unlike the treadmill conveyor, is not uniform). You then already have a velocity difference. The crane which lowered the submarine can be divorced, and is no longer necessary.

So I can make one correction here. Some object is needed to hold it in place at first, but after that, it should not matter.
So either:
The amount of work required is similar to that required to apply brake discs - it's not very much at all - but that's only if the external actor holding the submarine is fixed (by superior inertia)... or
The external actor is not fixed (due to inferior inertia), in which case, significant work must be done to put the submarine there in the first place.

Otherwise, if you make the submarine lead the front of the water flow (i.e. if the water ahead is stagnant), then you shouldn't need either kind of actor.

So, yes, you would have to have some kind of velocity difference.
Perhaps in the case of an external conservative force such as gravity, we might have an exception to that though. I don't know yet. But if gravity itself is due to velocity differences (GR seems to imply this), then maybe that is not an exception either.

 

[jduffy77]

If the stream is uniform, you would first have to drop the submarine in and then activate the propellers. This is nothing more than the submarine equivalent of Spork's treadmill. This acts as a break slowing the water behind it, so it is slower as it passes over (water flow, unlike the treadmill conveyor, is not uniform). You then already have a velocity difference. The crane which lowered the submarine can be divorced, and is no longer necessary.

So I can make one correction here. Some object is needed to hold it in place at first, but after that, it should not matter.

Congratulations, you have designed a PM machine.

 

[A.T.]

What about a submarine with counter-rotating props?

What is this obsession with counter rotation about? You can use two rotors (prop & tubine) in two different media (that move relative to each other) to move relative to one of the media faster than the other medium. But the rotation direction of the rotors is irrelevant.

 

[spork]

We're not even going to talk about my nuclear powered baby buggy with crystal rectification that catapults around the moon?

 

[A.T.]

If the stream is uniform, you would first have to drop the submarine in and then activate the propellers. This is nothing more than the submarine equivalent of Spork's treadmill. This acts as a break slowing the water behind it, so it is slower as it passes over (water flow, unlike the treadmill conveyor, is not uniform). You then already have a velocity difference.

It cannot be powered by the velocity difference, that it creates itself. This would be perpetual motion.

The DDWFTTW cart is powered by the velocity difference that already exists (free stream air vs. surface) and not by the one it creates (free stream air vs. prop wash air).

 

[kmarinas86]

Congratulations, you have designed a PM machine.

Or we simply have energy transferring from the water to the submarine.
Sails work above water. There's no reason why an adapted sail couldn't do the same thing for a submarine. Sails can even work in space. Nothing about air is special or magical.

 

[kmarinas86]

It cannot be powered by the velocity difference, that it creates itself. This would be perpetual motion.

The DDWFTTW cart is powered by the velocity difference that already exists (free stream air vs. surface) and not by the one it creates (free stream air vs. prop wash air).

The velocity difference is already there. Propellers can be used to trade one difference (crane and treadmill) for another difference (air in front and air in back) at an entropy loss. During that transition, yes, you would need at least 3 (or at least 4 in the treadmill case) mediums and not two. I guess you can call that "leverage" in a sense. Increases of entropy occur due to frictional losses. These frictional losses are not recovered by the DDWFTTW. Other machines can only recover some of it, but they never get all of it.