Mess with your minds: A wind powered craft going faster than a tail wind speed.

[electrodacus]

Jesus Christ! STILL can't spell BRAKING correctly? 

Not quite sure what that fictional character has to do with me not spelling braking correctly but I get your point and I try to improve. I did not made the English grammar rules where two words with completely different meaning have the same pronunciation but different spelling. And the limited spell checker is not able to help me here.

Look, the spinning propeller creates a virtual sail behind the vehicle. It pushes against the wind, if you sum the velocities you end up with 0, but since it's blowing backwards, it adds to the ground velocity of the vehicle.

You can view this virtual sail as storing the initial energy of the vehicle being blown from rest to its cruising velocity.
(Attachment Link)

If you sum up the wind speed with the artificial one created by the propeller you do not end up with zero but with the sum of the two. Both the natural wind and the one created by the propeller push against vehicle in the same direction so they will add up and since air is compressible energy is being stored in there.
You can see this energy storage like a spring with wind pushing from one end and the propeller created wind from the other end compressing this spring. This is a very simplified view as there is another spring on the other side of the propeller that is extended.

A sail also has stored energy behind when wind speed is higher than sail speed but that stored energy is only large enough to push the vehicle up to wind speed in ideal case.

So a stationary sail will have the max stored energy behind is like a compressed spring due to high pressure (higher than ambient) at the back of the sail and similarly there is a low pressure on the front of the sail and this pressure differential represent stored energy.
Equivalent will be a propeller that is at wind speed (ideal case) and here the stored energy is equivalent with the pressure differential created by the artificial wind that is dependent on propeller pitch and rotational speed.
A propeller that is not connected to wheel will still accelerate the vehicle but for a very short time and this is what you are thinking when you say there is insignificant amount of energy stored in pressure differential (it is not it just gets wasted in this way). But if you connect the propeller to the wheel then the pressure differential stored energy can be maintained for longer as part of energy is used to maintain that artificial wind so much more of the pressure differential stored energy can be used by the vehicle.

[Kleinstein]

The flyheel effect of the propeller can not be used to accelerate the vehicle, unless they have a variable gear box that they would switch. The speed is linkt to the wheels and thus the speed to ground. So like heavy wheels the flywheel part acts similar to additional mass of the vehicle, making it harder to accelerate.   From that argument there is also no real way to osciallate energy between the pressure field around the vehicle and the propeller RPM.

Keep in mind that the time scale for the pressure field is the speed of sound divided by the dimensions - so this is less than 1/10 s. Without a container, compressed air is not really effective storrage. So if at all you may get a very short time effect, hard to see on a normal video.  So the air pressure around the vehicle can not be the magical energy storrage to drive the vehicle.

It is the stationary pressure field that builds up that drives the vehicle. The wind and the power from the wheels transferred to the prop keep this pressure field around the vehicle alife. Usually one uses a simpler pricture of the working the prop and calls it the prop driving the vehilcle.

[electrodacus]

is completely invalid.  You presume your presentation models the Blackbird mechanism - which it clearly does not.

Obviously it is an analogy and not exactly the same thing but the idea is the same.
The vehicle in my video shows the belt as an energy storage device allowing vehicle to accelerate from left to right and even exceed moving paper speed for short periods.
Blackbird stores energy in pressure differential  (equivalent of the rubber band) and can exceed wind speed both direct down wind and against wind direction.
Is just that pressure differential energy storage is much larger and vehicle friction much lower so that time scales are different.
If you will record blackbird for say maybe half an hour and speed up the video you will see the same sort movement as in my wheel only model.
So blackbird average speed over that longer duration will be way lower than wind speed but there will be peak periods where blackbird exceeded wind speed even significantly.
So the experiment done by blackbird team was just to short to show the entire story and based on that experimental result and lack of physics knowledge wrong conclusions where extracted from that.

[ejeffrey]

You also need to consider what the example represents.
Moving paper is the energy source for the vehicle and is the analog of win in a wind powered vehicle. So in my video you see the equivalent of a vehicle moving in the opposite direction to wind direction at around half the wind speed.

Sure, it was your demo proposal, not mine.  You claimed this was a demo that would satisfy you and that it was impossible for the cart to go the opposite direction from the applied force. It clearly is possible as I have demonstrated and as I have explained both in terms of forces and torques as well as power transfer.

You can alter it to go the other way if you want, or faster than the paper in either direction with a suitable choice of gear ratio.  The traction requirement becomes larger so you will probable need to add some weight to the cart and pull carefully.  I can sort of get that to work with the same cart just putting the paper under the other wheel but it's hard to do without slip.

If you want to see things in modified reference frame

I would caution you against trying to think in multiple reference frames at once,.  It's true that you can solve the problem in any reference frame you want and get the right answer but in practice it is an easy way to get led astray.  This is because it is easy to come up with "invariants" that are not actually true in other frames.

One example is that the change of frame itself does not conserve energy.  In fact in any reference frame other than the lab frame the kinetic energy of the ground is "infinite" so you basically can't use global conservation of energy. Also if you solve part of the problem in one frame and switch you will get inconsistent results.  Another problem people have is that they accidentally use an accelerating reference frame such as a vehicle that isn't moving at constant speed.

All this is why I stick to the lab frame in all of these discussions.

[electrodacus]

The flyheel effect of the propeller can not be used to accelerate the vehicle, unless they have a variable gear box that they would switch. The speed is linkt to the wheels and thus the speed to ground. So like heavy wheels the flywheel part acts similar to additional mass of the vehicle, making it harder to accelerate.   From that argument there is also no real way to osciallate energy between the pressure field around the vehicle and the propeller RPM.

Yes correct the flywheel can not accelerate the vehicle above wind speed can only slow down the rate of deceleration. And yes having a gear box will have allowed vehicle to exceed wind speed using that stored energy alone.  They actually have a gear box on blackbird is just less obvious and that is the fact that they can control the propeller pitch. By increasing the pitch angle they can use the flywheel stored energy to accelerate.
Obviously flywheel is not what accelerates this type of vehicle above wind speed since it was shown with the small treadmill model that wind speed can be exceeded without propeller pitch control.

Keep in mind that the time scale for the pressure field is the speed of sound divided by the dimensions - so this is less than 1/10 s. Without a container, compressed air is not really effective storrage. So if at all you may get a very short time effect, hard to see on a normal video.  So the air pressure around the vehicle can not be the magical energy storrage to drive the vehicle.

It is the stationary pressure field that builds up that drives the vehicle. The wind and the power from the wheels transferred to the prop keep this pressure field around the vehicle alife. Usually one uses a simpler pricture of the working the prop and calls it the prop driving the vehilcle.

No container is needed you just need to have a feedback loop in this case the wheel of the vehicle connected to propeller.
That pressure field you are referring to is increased as vehicle accelerates initially (either pushed by wind or by humans) and from the moment vehicle is no longer pushed by humans or wind that pressure differential starts to drop as it is being used up to power the vehicle that is linked to propeller so propeller is also powered from that.
This link between wheel and propeller is what makes utilizing the pressure differential stored energy much more effective and why it lasts minutes instead of just seconds without that connection.
Same energy is stored in pressure differential with or without the connection to wheel but without the connection to wheel much more of the energy will end up as heat plus you can not just start the vehicle directly with wind or even just pushed you will need something to spin the propeller to proper speed.

[electrodacus]

Sure, it was your demo proposal, not mine.  You claimed this was a demo that would satisfy you and that it was impossible for the cart to go the opposite direction from the applied force. It clearly is possible as I have demonstrated and as I have explained both in terms of forces and torques as well as power transfer.

You can alter it to go the other way if you want, or faster than the paper in either direction with a suitable choice of gear ratio.  The traction requirement becomes larger so you will probable need to add some weight to the cart and pull carefully.  I can sort of get that to work with the same cart just putting the paper under the other wheel but it's hard to do without slip.

Yes it is impossible without energy storage to move the vehicle from left to right.  The force at wheel difference is a bad explanation as is about power at the wheel not force.
Vehicle can not travel faster than paper unless it uses energy storage. It may be that even in my video for some fraction of seconds vehicle was moving faster than paper but average speed was well below paper speed.  No amount of weight added to the cart will allow you to drive in average faster than the paper.
You can not put the paper under the other wheels as then vehicle will not move opposite to paper direction but it will move in the same direction as the paper (and I did just confirmed by testing on my model same one in the slow motion video).

If you want to see things in modified reference frame

I would caution you against trying to think in multiple reference frames at once,.  It's true that you can solve the problem in any reference frame you want and get the right answer but in practice it is an easy way to get led astray.  This is because it is easy to come up with "invariants" that are not actually true in other frames.

One example is that the change of frame itself does not conserve energy.  In fact in any reference frame other than the lab frame the kinetic energy of the ground is "infinite" so you basically can't use global conservation of energy. Also if you solve part of the problem in one frame and switch you will get inconsistent results.  Another problem people have is that they accidentally use an accelerating reference frame such as a vehicle that isn't moving at constant speed.

All this is why I stick to the lab frame in all of these discussions.

You only get inconsistent results if you do not know how to calculate in a modified frame of reference.  Results in any reference frame will be exactly the same if you do things correctly.
You do not do the calculations correctly that is why I insist you do not modify the reference frame as it is the easier way to not mess things up.

[Kleinstein]

Yes it is impossible without energy storage to move the vehicle from left to right.  The force at wheel difference is a bad explanation as is about power at the wheel not force.
Vehicle can not travel faster than paper unless it uses energy storage.

Using force is the easier way and the normal way one does the calculation if one understand what force is.
Using power works, but has to take the different velocities into account and than gets the same result as using power.

[PlainName]

Yes it is impossible without energy storage to move the vehicle from left to right.

I see two situations here:

1. There is no energy storage and you are wrong.

2. There is energy storage but it doesn't matter because the vehicle moves from left to right as long as the paper is moving.

That's the crucial thing, is it? That the movement is not a temporary 'until the energy is gone' thing. Even if the alleged energy store was storing and releasing, storing and releasing, the thing is moving left to right without at any point moving right to left. And it will keep doing that for as long as the paper holds out. So how it does that in movement terms, in what way the energy is tranferred, is just a sideshow and irrelevant.

You entire supposition of the energy store is that it cannot last indefinitely, so the Blackbird can only slow down to below wind speed once it has used the store to get above wind speed. But here your store (that is, your energy store, wherever you happen to think it is) is able to keep supplying the left-to-right motion forever.

[electrodacus]

Using force is the easier way and the normal way one does the calculation if one understand what force is.
Using power works, but has to take the different velocities into account and than gets the same result as using power.

I understand forces what most people do not understand is how forces act against the vehicle.
Power include the force and speed so is the other way around. You need to think about speed when looking at forces.
There are to many things you do not understand thus the reason it is hard for me to explain how things work.
You are just looking at real world examples and you do not understand how they work or why.

Imagine you have two electric motors on that vehicle both same exact model.
One motor is connected to front wheel trying to move the vehicle from right to left and one connected to the back wheel trying to move the vehicle from left to right (so opposite direction).
Front motor is directly connected 1:1 gear ratio and the other is connected trough a 2:1 gear ratio with 90% efficiency.
Both motors are getting 100W and say they are 100% efficient so 100W is also available at the shaft.
Now the front wheel will see 100W since is direct drive (hub motor if you prefer) and the back wheel spins at half the motor RPM so just 1.8x the force as it needs to go trough that 90% efficient gear.

Say wheels are not able to slip what direction will that vehicle travel ?
I say since there is 100W available at the front wheels they will move the vehicle backwards for right to left.
You say since force is higher at the back wheel 1.8x higher to be exact vehicle will move from left to right and you will be wrong.

In real world there are many more factors than the theoretical problem I explained above including possibly wheel slip (there is a threshold force for a wheel to start slipping and when that happens force possible at that wheel is lower as there is a hysteresis). That effect is seen in my slow motion video since as soon as the front wheel starts to slip the back wheels can just start pushing the vehicle forward using the stored energy.

[electrodacus]

Yes it is impossible without energy storage to move the vehicle from left to right.

I see two situations here:

1. There is no energy storage and you are wrong.

2. There is energy storage but it doesn't matter because the vehicle moves from left to right as long as the paper is moving.

That's the crucial thing, is it? That the movement is not a temporary 'until the energy is gone' thing. Even if the alleged energy store was storing and releasing, storing and releasing, the thing is moving left to right without at any point moving right to left. And it will keep doing that for as long as the paper holds out. So how it does that in movement terms, in what way the energy is tranferred, is just a sideshow and irrelevant.

You entire supposition of the energy store is that it cannot last indefinitely, so the Blackbird can only slow down to below wind speed once it has used the store to get above wind speed. But here your store (that is, your energy store, wherever you happen to think it is) is able to keep supplying the left-to-right motion forever.

1. Sorry but how can you say there is no energy storage when is so clear seen in video and is clear to see the stretching of the rubber belt.
2. Look more closely at the video and read about stick-slip hysteresis if you did not heard about that before. The combination of those two the energy storage and stick slip hysteresis is what makes the vehicle move forward you just need to understand what you see in the video.

Vehicle is powered by the paper (hope you agree with that) so it can move forever but speed of the paper will always be higher than average speed of the vehicle. Vehicle speed can exceed temporarily the speed of the paper due to energy storage but the average speed is much lower.
What you see represented there is a the equivalent of the blackbird version that uses the propeller as a wind turbine and drives against the wind direction.

Please explain how vehicle is able to move from left to right.
Here is my explanation
Front wheel starts to spin while back wheel is locked and this is only possible if there is energy storage.
The belt acts with exactly the same force against the large pulley on the back wheel as it is against the small pulley on the front wheel.
Since the front wheel pulley is smaller the front wheel is the one that rotates but not slipping up to this point.
When enough energy is stored in to the belt the force that belt acts against the wheels will make the front wheel slip.
There is a minimum force threshold needed for the wheel to start slipping but once that happens the force needed to keep the wheel slipping (you may have experienced this if you ever drove a car on ice or snow).
Because of this since the back wheel is not slipping it can push the vehicle forward using the energy stored in the rubber belt and when the rubber belt energy drops low enough that it can no longer push the vehicle the front wheel stops slipping and things as seen in the video repeat.

If you do not agree with my explanation of what happen to the vehicle in my slow motion video please provide your explanation in a similar way.

[Kleinstein]

The problem with the motor example is that a motor with a given fixed efficency is kind of including an automatic gear box to adjust the torq to the speed. So it does not make sense to consider such an ideallized motor with a gear reduction. So the example just does not make sense. With only one vehichel on one groud the wheels see the same speed and thus in this special case with ideallized motors power is directly proportional to force. So in this special case there is no consequence in confusing power and force - except that you can't transfer this to other cases.
So the example is a bad example.

Things get different if the 2 wheels are on different grounds moving relative to each other.

[electrodacus]

The problem with the motor example is that a motor with a given fixed efficency is kind of including an automatic gear box to adjust the torq to the speed. So it does not make sense to consider such an ideallized motor with a gear reduction. So the example just does not make sense. With only one vehichel on one groud the wheels see the same speed and thus in this special case with ideallized motors power is directly proportional to force. So in this special case there is no consequence in confusing power and force - except that you can't transfer this to other cases.
So the example is a bad example.

Things get different if the 2 wheels are on different grounds moving relative to each other.

Not sure what you try to do here.
Let me modify the example to see if that makes things better for you.
Motor is the same and has 100W available at the motor axle.
For back wheel the motors is connected trough a 0.5:1 gear ratio with 90% efficiency so you have 90W available at the wheel
On the front wheel motor is connected trough a 1:1 gear ratio with say 95% efficiency so you have 95W available at the wheel.

Do you even care what gear ratio was used to know what direction will the vehicle move ? 

[PlainName]

Vehicle is powered by the paper (hope you agree with that)

Yes!

so it can move forever

YES!!!

but speed of the paper will always be higher than average speed of the vehicle

Irrelevant and meaningless. Does the vehicle move left to right? Yes! Does it move right to left? No! That's it - how, when, with what, at what speed, anything else is not relevant and just adding to the noise.

[electrodacus]

Irrelevant and meaningless. Does the vehicle move left to right? Yes! Does it move right to left? No! That's it - how, when, with what, at what speed, anything else is not relevant and just adding to the noise.

It moves from left to right because there is energy storage and that was not considered in the theoretical problem.
Remove the energy storage and vehicle will not be able to move from left to right. Or maybe simpler to do remove the ability of front wheel to slip and again vehicle will not be able to move from left to right.
This represents a vehicle with a wind turbine driving against the wind direction at about 0.5x the wind speed so no traveling indefinitely above wind speed as the original claim is for blackbird.

So this video proves my point that using energy storage allows the vehicle to exceed wind speed (paper speed) for a limited amount of time proportional with the amount of energy storage capacity available but average speed is way below wind speed.

Your claim is that vehicle can maintain above wind speed indefinitely and that is not shown at all in my video or any other experiment I'm aware of since that will not be possible.

[PlainName]

It moves from left to right because there is energy storage

Whatever, it's irrelevant. It wouldn't be if...

for a limited amount of time proportional with the amount of energy storage capacity available

but that's not what's happening. It works indefinitely.

This represents a vehicle with a wind turbine driving against the wind direction at about 0.5x

Irrelevant. It was impossible in this experiment for the vehicle to move left to right. You said that yourself, based on your thinking (and knowledge that none of the rest of us have). Forget the wind, this experiment shows that your thinking was not appropriate and the model does something you said was impossible. So, now this is possible what else that you've decided isn't might be after all? Clearly, somewhere along the way your thinking has jumped the rails. Doesn't matter if it's this energy storage thing you bang on about or something else - you didn't have a grip on this aspect. Maybe you should review your preconceptions and figure out what you missed.

[fourfathom]

Here's a demonstration I like (most have probably already seen it), and it's pretty similar to the moving paper test.  In this one the upper board represents the wind, and the floor represents the ground, so there's no reference frame issue.  And there's no energy storage, and it can continue, faster than the "wind", forever.



(It's in Veritasium's "A Physics Prof Bet Me $10,000 I'm Wrong" video where he has his "roller" demonstration)

I can't get the embedded video to start at the right time, so skip ahead to 13:34

[electrodacus]

Here's a demonstration I like (most have probably already seen it), and it's pretty similar to the moving paper test.  In this one the upper board represents the wind, and the floor represents the ground, so there's no reference frame issue.  And there's no energy storage, and it can continue, faster than the "wind", forever.

That demonstration is wrongly interpreted.
The floor is the wind and the vehicle travels on the moving lumber.
Small wheels are the generator wheels and the large wheel is the motor wheel. Please look closer to understand how that works.
So what is shown there is a vehicle traveling at about 2.8x lower speed on the lumber (road) powered by the floor (wind) in the opposite direction.
 

[Psi]

I don't think it really matters if the wood is the wind or the floor is the wind.
The important factor is that two forces together can move the object faster than either of them are moving.

It's the best demonstration of how this can be possible that i have seen so far.

[Brumby]

1. Sorry but how can you say there is no energy storage when is so clear seen in video and is clear to see the stretching of the rubber belt.

Here is a classic example of YOU not understanding physics.

The jerkiness of motion as seen in your video is the direct cause of friction in your system.  You are taking a practical experiment - with all its flaws - and creating a theoretical model based on a completely wrong interpretation.

Remove the friction and it will run smoothly.  Use an inelastic chain and it will run smoothly, too.  In the ideal scenario, there is NO energy storage, just energy transfer.  Your demonstration is nowhere near ideal.

You are only compounding the lack of understanding you have in physics.  You are making it very clear that you are either a troll or the epitome of Dunning-Kruger.

[electrodacus]

I don't think it really matters if the wood is the wind or the floor is the wind.
The important factor is that two forces together can move the object faster than either of them are moving.

It's the best demonstration of how this can be possible that i have seen so far.

It maters what is the input and what is the output.
Is like looking at the gear box input and output power and saying if you look from this side efficiency is 90% but if you look from this other side is over 100%
Do you understand what I'm trying to say ?
It is very important to know that the input and outputs are so in that case input is the floor (wind equivalent) and the output is the vehicle moves using the large wheel on the lumber.
This is the only correct interpretation and you can not invert them and ignore that reference frame change as you get to wrong conclusions.

[electrodacus]

1. Sorry but how can you say there is no energy storage when is so clear seen in video and is clear to see the stretching of the rubber belt.

Here is a classic example of YOU not understanding physics.

The jerkiness of motion as seen in your video is the direct cause of friction in your system.  You are taking a practical experiment - with all its flaws - and creating a theoretical model based on a completely wrong interpretation.

Remove the friction and it will run smoothly.  Use an inelastic chain and it will run smoothly, too.  In the ideal scenario, there is NO energy storage, just energy transfer.  Your demonstration is nowhere near ideal.

You are only compounding the lack of understanding you have in physics.  You are making it very clear that you are either a troll or the epitome of Dunning-Kruger.

What are you claiming exactly ?
a) belt is not an energy storage device ?
b) energy storage is not needed for the vehicle to move ?
c) something else ?

[Psi]

It maters what is the input and what is the output.
Is like looking at the gear box input and output power and saying if you look from this side efficiency is 90% but if you look from this other side is over 100%
Do you understand what I'm trying to say ?

yes, I understand what you mean now.  It does matter which is wind and which is ground.

But I still think the demonstration shows how blackbird can move downwind faster than the wind.

[electrodacus]

It maters what is the input and what is the output.
Is like looking at the gear box input and output power and saying if you look from this side efficiency is 90% but if you look from this other side is over 100%
Do you understand what I'm trying to say ?

yes, I understand what you mean now.  It does matter which is wind and which is ground.

But I still think the demonstration shows how blackbird can move downwind faster than the wind.

That demonstration is just a linear gear box and if it is to show something is blackbird version that travels against the wind direction (not the same as the one driving down wind as is a different vehicle). It shows vehicle traveling 2.8x slower than the wind in the opposite to wind direction.


And to be clear I never claimed that blackbird can not travel faster than the wind I just mentioned that it needs energy storage to do that and that means it can only travel above wind speed for a limited amount of time then it will slow down below wind speed.

[electrodacus]

I mentioned a few times the stick slip but I do not think that is needed just the energy storage is enough as I do not think any wheel is losing traction at any point in my video.
The thing is that power is provided to the vehicle by the moving paper and if there was no energy storage then either back or front wheel will slip before having any rotation.  Rotation of the front wheel is only possible tanks to energy storage and when enough energy is stored vehicle can move forward (left to right).
 
I looked a bit at the numbers and yes there is stick slip on the back wheels.

[Psi]

A good demo might be

- Toroidal pipe, maybe 4inch diameter and 1m toroid radius.
- Angled air in/out tubes to get known air flow moving around the tube.
- Small cart with propeller and ball bearing wheels touching 3 or 4 sides of the tube. (so it can move freely around the toroid)
- Could test with water or air flowing around the tube, water might make coupling/gearing easier to show the effect.
- The relationship of air flow into tube and speed of cart around toroid should be very different if the effect happens vs does not happen.

It seems that most peoples arguments against the results of blackbird are that the wind was going faster than stated.
So this would allow windspeed to be known/measurable