Down wind faster than the wind

[humber]

I thought the same thing too. I only came to understand how it works when I realized that it wasn't extracting energy from the wind. It's actually extracting energy from the ground through the wheels. The only function the air serves is as something for the device to push against to move forwards.

As long as the gearing is below 1, the device will be able to accelerate against the relative direction of the ground, buy pushing the air behind it.

The faster the air moves over the device, the higher the gearing needs to be in order to push the air back faster than it is already moving. If air speed
and ground speed were the same, the gearing would have to greater than 1, and the device would be trying to use more energy than it's extracting from the ground, and wouldn't work.

That's why it needs a tail-wind. Not as a source of power, but for something to push against.

Brian-M, thanks for the considered reply.
But there is no other source than the wind. This idea of energy between the ground and air, or remote relative sources is quite unfounded, and unsupported. All the gearing can ever do is change the load seen by the propeller. ALL the energy comes from the wind. When an object is blown downwind, it accelerates. However, drag increases as the velocity increases, until these two forces are in balance. This is the maximum downwind speed and is less than the windspeed. It is this very fact that stops any windblown object from achieving windspeed. It is the same for this design. The difference is the "evidence" of the treadmill, but that is not valid, as I will later show.

Actually Spork's videos show that his device does accelerate in still wind, if the ground is moving (ie. on a treadmill). That's because the device isn't extracting energy from the propeller, but from the wheels. Watch this video again.

The device remains (almost) static on a moving belt is more accurate, but the explanation is quite simple. All the energy comes from the belt, some of which is dissipated, that is wasted, as drag produced by the propeller.
I have stated this a few times, and have not been understood, so I will post a diagram a little later, when I have time to scan the drawing.

The car's velocity in it's inertial frame is measured by it's speedometer. In order for your example to be valid, the speedometer would have to be the same in both situations. For example...

Using the car's speedometer to determine velocity:
Drive a car 10mph down a street and hit the brakes.
Drive a car 10mph on a giant treadmill (with a belt moving 10mph the other way, so the car is stationary relative to the ground) and hit the brakes.
There is no difference.

When you hit the breaks on the street, you are decelerating 10mph relative to the street. In this case the street is your frame of reference.

When you hit the breaks on the treadmill, you are decelerating relative to the 10mph relative to the belt. In this case the treadmill belt is the frame of reference.

As the device in question is pushing against the air to accelerate, I think it's logical to use the air as the frame of reference. If it's sitting in place on a treadmill in an enclosed room, it is traveling at 0mph relative to the air. If it is rolling down the street at wind-speed, it is traveling at 0mph relative to the air. The two scenarios are exactly equivalent.

This is not quite the interpretation I meant, but if I take your example of breaking on a treadmill. What are wheels? If you drag something, there will be friction between it and the surface. If the same object has wheels, but they are locked so as not to rotate, then there will also be much friction.
Wheels are moving pads of friction. This is called "rolling resistance" and is lower than the static resistance of the other two cases. There is nothing "special" about wheels.
When braking, the rolling resistance, moves towards the value of the static friction, and so resists the vehicles motion. There will be greater friction between the car and the belt, so it will move backwards with it. So, if the car is said to be static, it will be accelerated backwards, and if it is thought of as moving forward, then it will be slowed. In each case, the difference will be felt.
It is also worth reminding yourself of how a speedometer works. It does not measure speed directly, but infers it from how fast the wheel that drives it (or the drive shaft) is turning.

If it's moving 1mph up a treadmill, it has a 1mph headwind pushing it back.
If it's moving 1mph faster than the wind, down the road, it has a 1mph headwind pushing it back.
If the treadmill is moving it backwards at 1mph, it has a 1mph tailwind pushing it forward.
If it's moving 1mph slower than the wind, down the road, it has a 1mph tailwind pushing it forward.

The two situations are exactly equivalent.

Imagine a treadmill of infinite length. As the belt pushes the cart backwards, the wind resistance (ie. tailwind) slows the cart's backwards momentum (ie. adds forwards momentum), and the belt passing under the cart turns the wheels, which spins the propeller, which increases the cart's forwards momentum even more, so the belt turns the wheels even faster, which turns the propeller faster... and so on.

The faster it goes, the greater the forwards force provided by the propeller. This force is more than enough to overcome drag and propel it to wind speed and beyond.

Actually, your are close, but the forces are opposite to what you appear to think. Instead of driving the vehicle forward, they drive it to a standstill.
OK, I think that a diagram will help. Words would take forever.

 

[CyCrow]

A dyno stores energy in the air ?

No, the air is what keeps the vehicle from accelerating backwards on the treadmill. Besides, you have STILL not gotten it into your head that kinetic energy is relative and depends on the reference frame.

No misconception. That is a definite denial of your claim. Your device, must be over unity to achieve windspeed, let alone exceed it.

So do you believe that iceboats are magic? Or just this device? Sailboats routinely sail faster than the true wind. Why not this device?

We are now coming up with some alternatives:
1 - The treadmill video was faked.
2 - The treadmill isn't equivalent to travelling downwind at windspeed
3 - The device is over-unity
4 - Your analysis is wrong.

I'm guessing you will keep arguing (2), perhaps detour to (1). The question is if you will ever follow the others to (4). (3) is a red herring.

It should be noted, that claims for aerodynamic effects for the cart, may be a two-edged sword. Lift that causes loss of contact with the road, may serve to invalidate your hypothesis re the gearing.

Do you realise that the lift that has been discussed is on the propeller blades? It has no net vertical component. In fact, the treadmill vehicle has a downward tilted propeller, so the propeller thrust pushes the wheels down.

It is not that I expect all motive forces and drag to be equal, but that in stasis, is it so. "Opposite and equal reaction" refers to acceleration.
The treadmill is such a case, and indeed, the forces are equal, by its very design.

Again: the vehicle accelerates against the treadmill. The wheels drive the prop, and the prop creates more thrust than it takes to spin the prop. This requires a tailwind relative to the treadmill surface.

No need. Drop an autogyro in a vacuum. Observe. Add some gas. Observe.
The energy lost to the gas is drag, because it retards motion, but you may call it lift. It is the difference in the kinetic energy at impact. The "lift" that you appear to mean, requires additional energy.

This is getting repetitive. You do not understand aerodynamic lift. We are not birds, so we don't have an intuitive understanding. That's OK. Boneheadedly clinging to false notions is not OK.

// CyCrow

 

[Brian-M]

Errr.... Is that in relation to the prop vesrus the wheel or the wheel versus the prop. I think you might want that backwards because you want the prop rotating twice as fast as the tailwind right?

There are several factors which affect the "gearing", such as prop pitch, wheel diameter and the actual gears connecting the wheel to the prop. Overall, it really comes down to the speed the prop is pushing the air to the speed of the ground (in both cases relative to the cart).

So, with a gear ratio of 2/3, when the cart is rolling along the ground at 3 mph, its pushing the air backwards at 2 mph.

As its always pushing the air backwards at less than the speed it is moving, it can't work without a tailwind.

If the gearing was the other way around, it wouldn't work as a DDWFTTW craft, but it should be able to accelerate against the wind instead. (I'm not sure how efficiently the prop would work as a windmill.)

 

[humber]

No, the air is what keeps the vehicle from accelerating backwards on the treadmill. Besides, you have STILL not gotten it into your head that kinetic energy is relative and depends on the reference frame.

So do you believe that iceboats are magic? Or just this device? Sailboats routinely sail faster than the true wind. Why not this device?

This is to conflate two arguments. I have never said that vehicles cannot tack the wind. This is a direct down-wind device, which does not, and cannot exploit this method.

We are now coming up with some alternatives:
1 - The treadmill video was faked.
2 - The treadmill isn't equivalent to travelling downwind at windspeed
3 - The device is over-unity
4 - Your analysis is wrong.

I'm guessing you will keep arguing (2), perhaps detour to (1). The question is if you will ever follow the others to (4). (3) is a red herring.

No need to guess.
1. If the treadmill concept is irrelevant, so are videos. The treadmill is quite explicable by other means.
2. That is what I contend, and that what it displays is meaningless, and so are the "thought experiments" that use it.
3. Not the treadmill. A real cart, in real wind, would need to be over-unity to obtain windspeed.
4. That follows, and applies to the frame concept

Do you realise that the lift that has been discussed is on the propeller blades? It has no net vertical component. In fact, the treadmill vehicle has a downward tilted propeller, so the propeller thrust pushes the wheels down.

I was reminding you that you have not demonstrated that the device is aerodynamically stable enough to ensure that the wheels are always in contact with the ground. The videos indicate otherwise, disclaimers or other wise. Precession could be a real problem for the wheel contact, and for straight-line stability.

Again: the vehicle accelerates against the treadmill. The wheels drive the prop, and the prop creates more thrust than it takes to spin the prop. This requires a tailwind relative to the treadmill surface.

This is getting repetitive. You do not understand aerodynamic lift. We are not birds, so we don't have an intuitive understanding. That's OK. Boneheadedly clinging to false notions is not OK.

// CyCrow

The belt drives the wheels which drive the prop, which creates drag to over come the opposite force generated by the belt.

You may opine that I have false notions of aerodynamic lift.
Which part of the gyro-in-gas remark do you say is incorrect?
How is lift generated without the expenditure of energy?

 

[Brian-M]

But there is no other source than the wind. This idea of energy between the ground and air, or remote relative sources is quite unfounded, and unsupported. All the gearing can ever do is change the load seen by the propeller. ALL the energy comes from the wind.

Humber, I understand what you're getting at here. This is exactly what had me confused at the start of this thread. The problem is, it's just plain wrong.

If you were talking about a windmill fixed to the ground, you'd be exactly right.

Remember, all velocity is relative. It's meaningless to talk about how fast something is moving without a reference point to measure it from. Normally, we use the surface of the earth as this reference point, but that is not always a valid reference.

For example, if you're in an enclosed vehicle which isn't undergoing any acceleration, the vehicle itself would be the point of reference for everything inside it. It doesn't matter how fast the vehicle is moving relative to the earth, that has no effect on anything inside the vehicle. You could be traveling at 99.9999999% the speed of light, and still nobody inside would be able to tell whether or not they're actually moving (without looking outside).

If you're on a surface moving at a constant rate then that surface is usually the most valid point of reference, regardless of whether the surface is the floor of a vehicle traveling at 99.9999999% light speed, the surface of the earth which is moving at 330.27 mph along the equator, or the belt of a treadmill moving at 3 mph. The physics is identical in all cases.

Wind is the velocity of the air. Normally we measure this as velocity against the velocity of the ground (which, as you know, is itself moving), as that is our usual reference point.

Now here's the confusing part... this device is not fixed to the ground. It's not attached to the ground like a windmill, nor is it pushing against the ground to accelerate in the opposite direction like a car. It is pushing against the air to accelerate, the same way a car pushes against the ground. This makes it the air, not the ground that's the most valid reference point.

When it's traveling at wind speed, it's effectively stationary relative to the air. In this frame of reference, it isn't actually moving. Instead, the ground is rushing along underneath it, while it remains motionless. (Exactly like on a treadmill.)

It's using the ground as a source of power to push itself through the air. I've mentioned before that you can have a wind powered device that pushes on the ground to move against the direction of the wind. This device is doing exactly the same thing, except it's a ground powered device that pushes on the air to move against the direction of the ground. The principle is exactly the same.

At least, that's the viewpoint I find most useful when thinking about it.

When an object is blown downwind, it accelerates. However, drag increases as the velocity increases, until these two forces are in balance. This is the maximum downwind speed and is less than the windspeed. It is this very fact that stops any windblown object from achieving windspeed.

Actually, windspeed is the speed at which these forces are in balance. In fact, thrust from the blowing of the wind, and drag from moving against the wind are exactly the same force. A stationary object in a 10 mph wind is effectively moving through the air at 10 mph. The thrust of a 10 mph wind is the drag on the object passing through the air, regardless of whether or not it is stationary relative to the ground.

The device remains (almost) static on a moving belt is more accurate, but the explanation is quite simple. All the energy comes from the belt, some of which is dissipated, that is wasted, as drag produced by the propeller.
I have stated this a few times, and have not been understood, so I will post a diagram a little later, when I have time to scan the drawing.

In the video I posted a link to, he holds it stationary at one end of the belt, lets go, and it accelerates, moving along the belt against the direction of the belt. That's a big difference from remaining "(almost) static".

It is also worth reminding yourself of how a speedometer works. It does not measure speed directly, but infers it from how fast the wheel that drives it (or the drive shaft) is turning.

That's exactly why I brought up the speedometer. The forces for accelerating/decelerating are applied through the wheels, which makes whatever medium they are pushing against the frame of reference.

If the car is on a giant treadmill with a 10 mph belt, and the speedometer is reading 10 mph as you drive directly against the belt, you are stationary relative to the ground, and to the people standing next to the treadmill, you aren't moving at all.

If the surface of the earth is your frame of reference, you aren't actually moving.

As soon as you hit the breaks (or run over someone on the belt), it should be obvious why the belt and not the surface of the ground is the correct frame of reference in this situation. (Although, if you're interacting with people beside the treadmill, then it's the ground and not the belt that's the correct frame of reference.)

And when you hit the breaks, the breaks will absorb the same amount of kinetic energy as they would have if you were traveling at 10 mph down the road, proving that kinetic energy is relative to your frame of reference.

 

[Michael C]

Your device, must be over unity to achieve windspeed, let alone exceed it.

Do you consider any machine where output is faster than input to be an over-unity device?

 

[CyCrow]

This is to conflate two arguments. I have never said that vehicles cannot tack the wind. This is a direct down-wind device, which does not, and cannot exploit this method.

It does and it can. The propeller blades are not moving directly downwind.

I was reminding you that you have not demonstrated that the device is aerodynamically stable enough to ensure that the wheels are always in contact with the ground. The videos indicate otherwise, disclaimers or other wise. Precession could be a real problem for the wheel contact, and for straight-line stability.

Irrelevant. You are reaching.

The belt drives the wheels which drive the prop, which creates drag to over come the opposite force generated by the belt.

You may opine that I have false notions of aerodynamic lift.
Which part of the gyro-in-gas remark do you say is incorrect?
How is lift generated without the expenditure of energy?

Not drag. Thrust. You seem unable to distinguish between lift and drag. Reread the previous posts where it is explained. You seem to think of the prop as nothing more than a parachute or drag device.

The prop expends energy from the wheels to generate thrust, and if there is a difference between ground speed and airspeed, it can generate more thrust than the braking force on the wheels that is used to drive it.

If we have a fan that pushes 1 kg of air every second, at 10 m/s, the kinetic energy of that air is 1/2 * m * v *v = 50 J/s or 50W. Using f=ma, we get 10N. Now consider another fan that is pushing 0.1 kg of air at 100m/s. The kinetic energy of the air per second is 500J, or 500W. Thrust is the same 10N. So thrust is not linear with power. It is an error to assume that the same amount of energy is required to generate a given amount of lift.

// CyCrow

 

[ThinAirDesigns]

George:

Your device, must be over unity to achieve windspeed, let alone exceed it.

And yet it does it without breaking a single law of physics.

"Over unity", must not mean what you think it means.

JB

 

[sol invictus]

Actually, he is right. Your ignoring the fact that the air always blows back. In one frame of reference the windspeeds add. In the other frame of reference the windspeeds subtract.

What do you mean, "windspeeds"? There is only one wind speed in any frame. Moving with the wind (at rest with respect to the air) means the wind speed is zero. Moving with the ground means it's not. That's all there is to it.

Ooohh, sharp. But I would like to see the book that supports your assertion.

Every book does. I already directed you to a wiki page - which you declared was all wrong. Here's a high-school physics text book: http://www.motionmountain.net/motionmountain-part1.pdf . Page 97:

Galileo explained that only relative velocities between bodies produce ešects, not the absolute values of the
velocities. For the senses, there is no dišerence between constant, undisturbed motion,
however rapid it may be, and rest. is is now called Galileo’s principle of relativity. In
everyday life we feel motion only if the means of transportation trembles (thus if it ac-
celerates), or if we move against the air.erefore Galileo concludes that two observers
in straight and undisturbed motion against each other cannot say who is ‘really’ moving.
Whatever their relative speed, neither of them ‘feels’ in motion.

 

[technoextreme]

Moving with the wind (at rest with respect to the air) means the wind speed is zero.

No. If the cart is standing still that is wrong. If the cart isn't moving at wind speed that is wrong.

 

[technoextreme]

Beauty! So I'm flying along in my C172 at 80% power. I climb into the jetstream (yeah my C172 is badass) - just how fast do the winds have to be for my prop to start windmilling?

You know you could just give me the math. For an engineer you sure are really adverse to math.

 

[sol invictus]

No. If the cart is standing still that is wrong. If the cart isn't moving at wind speed that is wrong.

Standing still with respect to what???

Earlier you claimed you were an engineer. You must have studied at least a little physics at some point. Did you learn anything at all?

There. is. no. such. thing. as. absolute. velocity.

If the cart is at rest with respect to the air but moving with respect to the ground/belt, that is all that matters. It doesn't make any difference if the air is still and the ground is moving, or the ground is still and the air is moving, or both are moving but at different speeds. Those situations are utterly and completely identical - in fact there is no way to distinguish between them - it means nothing to try. The earth is hurtling through space with respect to every other body in the universe - so NOTHING is "at rest". You can conduct this experiment by moving the cart at wind speed outside, or in still air by moving the ground at that same speed in the other direction. IT DOESN'T MAKE ANY DIFFERENCE.

It's incredible that you are still arguing about this. It is stated in every physics text. It has been understood since Galileo and perhaps before. It is the basis of Newtonian dynamics AND Einstein's relativity. It is taught to every high school and college student that studies physics. It is supported by an uncountable number of experimental results. And every other poster in this thread understands it.

For ****'s sake, learn something.

 

[Modified]

Please define "steady state".

At constant speed long enough for engine behavior to stabilize. Otherwise, to reproduce the conditions of acceleration on the road, the wind would have to increase to match vehicle speed as it increases, and the loading system would have to vary in the same way that the dyno drum loads do.

Are you definitely claiming that if I drive or tow a vehicle at windspeed, that is the same as being on a dyno at that same speed? (In general I mean, noise and perhaps some turbulence excepted)

Assuming you have a vehicle to carry the non-driving wheels at the same exact speed and load, and excepting any difference in surface characteristics (including round drum vs flat road), yes. In both cases there are no wind effects, only a pull between the surface of the driving wheels and the restraints and/or non-driving wheels. It doesn't matter to the car which end the load is on.

Imagine pushing against the supports of a treadmill that provides a load, thus turning the belt. At constant speed, that will feel equivalent to pushing a similar load down the road at the speed of the wind. Either way you feel no wind, and a load between what you are pushing against and the surface. It doesn't matter which of those is "fixed", if the loads behave equivalently.

 

[technoextreme]

Standing still with respect to what???

I meant to say the ground with nothing moving at all.

It's incredible that you are still arguing about this. It is stated in every physics text. It has been understood since Galileo and perhaps before. It is the basis of Newtonian dynamics AND Einstein's relativity. It is taught to every high school and college student that studies physics. It is supported by an uncountable number of experimental results. And every other poster in this thread understands it.

No because every other poster has done half a physics problem except Brain-M. The cart will travel faster than wind if the cart can accelerate to wind velocity with respect to the ground. That if part is what I've been questioning and the treadmill doesn't prove that part of the problem. And the annoying part is that you can't run the experiment backwards to prove the other half. You've got the people who thinks that one half of a physics problem is all they need. Two people who can look at the whole entire part of the physics problem and one that has no clue what he is talking about. I would like to apologize for annoying you over a concept I thoroughly understand. It's the other aspect of the problem that doesn't make any sense what so ever and even the explanation that Brain-M gives is as cryptic as hell.

 

[sol invictus]

I meant to say the ground with nothing moving at all.

"With nothing moving at all" - who in the world ever suggested that? For the 40th time, what matters is that there be a relative velocity between the air and the ground (or treadmill belt). That's either because you're outside and there's wind, or because you're inside and the belt is moving. If neither is moving, obviously the cart cannot accelerate from rest - where would it get the energy from?

I would like to apologize for annoying you over a concept I thoroughly understand. It's the other aspect of the problem that doesn't make any sense what so ever and even the explanation that Brain-M gives is as cryptic as hell.

You obviously don't understand. But let me get this straight - the part you are questioning is not whether once the cart is traveling at wind speed it will accelerate to faster than the wind - you agree the treadmill proves that - but rather whether it would get to wind speed in the first place? Is that right?

If so I suggest you watch the videos of the cart outside in the wind (where it plainly does that). And regardless, that wasn't really the claim at issue here - the issue is whether a wind powered vehicle can travel steadily faster than the wind, and the treadmill answers that.

 

[portlandatheist]

I don't know if this analogy will help anybody at all but consider this:
Does any aircraft "care" what the ground is doing? The only thing that matters to your aircraft is the wind that is hitting it, it doesn't matter if that means you are flying forwards, backwards, or sideways relative to the ground, it doesn't change aerodynamics.
Likewise, it makes no difference if its the air that is moving or the road that is moving in this experiment, the math is the same.

 

[GreyICE]

Techno, if it wasn't for the fact I majored in it, I'd question whether you were an engineer.

As it is, I simply note it's a miracle of quality control that more people don't die because of an inability to reconcile theory and fact.

FYI Sol, I've had engineers argue with me over whether a computer consuming 250W of power produces 250W of heat, and other amazingly painful things, so yes, we're entirely capable of being v. v. stupid.

 

[ThinAirDesigns]

But let me get this straight - the part you are questioning is not whether once the cart is traveling at wind speed it will accelerate to faster than the wind - you agree the treadmill proves that - but rather whether it would get to wind speed in the first place? Is that right?

If so I suggest you watch the videos of the cart outside in the wind (where it plainly does that). And regardless, that wasn't really the claim at issue here - the issue is whether a wind powered vehicle can travel steadily faster than the wind, and the treadmill answers that.

Sol is right on here on two counts:

A: the car *does* self start as shown in the videos

B: Who gives a cr** if it doesn't -- that's not part of our claim.

If the silly thing *did* needed more drag to get self started it would be trivial to give it more drag -- a simple flap that sticks up and catches the tailwind and then falls backward when encountering the reverse flow accross the chassis. Get over the self starting issue already.

JB

 

[humber]

Do you consider any machine where output is faster than input to be an over-unity device?

Not faster, per se, but requires more energy than is available to get there.
More output than input.

 

[humber]

It does and it can. The propeller blades are not moving directly downwind.

That is the contended "tip" idea, the very argument that is being denied

Irrelevant. You are reaching.

No, I have used this before to demonstrate that if the wheels do not remain in contact with the ground, the prop/cart may gain momentum. In this way, a greater velocity could be achieved by exploiting gusts or other bursts.

Not drag. Thrust. You seem unable to distinguish between lift and drag. Reread the previous posts where it is explained. You seem to think of the prop as nothing more than a parachute or drag device.

A prop. is neither a lift nor drag generator, but a device for exchanging momentum. It is some times a parachute, in the way it is sometimes a flywheel or static mass. It also has an energy budget, like everything else.
You did not say in what way you disagreed with the auto-gyro-in gas argument, or how lift can be generated without energy.

The prop expends energy from the wheels to generate thrust, and if there is a difference between ground speed and airspeed, it can generate more thrust than the braking force on the wheels that is used to drive it.

Are you equating equal energy with equal thrust? There is no other source of energy than the kinetic energy of the wind. That it moves over, or faster than something else, may have implications for the potential of extraction, but there no more than is available.

If we have a fan that pushes 1 kg of air every second, at 10 m/s, the kinetic energy of that air is 1/2 * m * v *v = 50 J/s or 50W. Using f=ma, we get 10N. Now consider another fan that is pushing 0.1 kg of air at 100m/s. The kinetic energy of the air per second is 500J, or 500W. Thrust is the same 10N. So thrust is not linear with power. It is an error to assume that the same amount of energy is required to generate a given amount of lift.

// CyCrow

We are not talking about powered devices. As I have said, all energy comes from the wind.
A prop has a non-linear load line ? OK