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

[electrodacus]

The rug is pulled at constant speed and I'm siting on it and I can just relax. On a treadmill at constant speed I still need to burn plenty of calories.

Here is someone standing on a treadmill, feeling very relaxed, and not burning any calories:

https://youtu.be/GvfF4TeXz7U

There are no weird scenarios is just you (most of you) (all of us) not able to understand there is a big difference between a treadmill and that rug.

There, fixed that for you.

Yes that is a very long treadmill so he has some time but not as much as me on a rug.
The thing is that he is not driving the opposite way on the long treadmill as the vehicle in my diagram will need to in order to not move from right to left.
Is all of you here there are sure other people capable of understanding what I'm saying.
But feel free to run the experiment as in my diagram and if you can prove me wrong (vehicle driving from left to right) then I will pay for your expenses in making that experiment.

I have no better way to explain the difference between a treadmill and a rug or piece of paper that moves relative to the ground other than the ones I mentioned before.  If I think of something better I will make sure to let you know but for you the most convincing will be to do your own experiment and see that you can not get the result you expect or want meaning you can not make the vehicle moving from left to right. 

[Kleinstein]

The difference between the belt of the treadmill and the piece of paper pulled is that the belt is going around and reused from time to time.
However for the sake of the experiments there is no relevant difference: both present a moving (driven by an external) surface.

Would it make a different if the paper is pulled by a motor (e.g. wind up a roll of toillet paper) and not a human ?

[cbutlera]

Much earlier in the thread you talked about aphantasia and you gave a detailed description of your mental image of air.

The way peoples brain work is very different likely way more different than you imagine.  You should search about Aphantaisia that affects maybe 1 to 3% of the population the others have a spectrum of capabilities in creating a mental image. And you should also look-up "Internal monologue" where an estimated 30% of the population has no internal monologue.  You will be blown away.
I can create a mental image (sort of average) and I sure have an internal monologue so I think more abstract using language.
I can simulate fairly accurately in my head how a simple cart like those in my diagram will work including what wheel is the generator and witch is the motor and I can know the outcome.
I can also imagine air as a multitude of small particles moving at a relatively constant speed above the ground and that have elastic forces keeping them apart like repelling magnets and then imagine a vehicle driving in the same direction at higher speed than this air molecules and can see that air molecules can no longer help accelerate the vehicle (impossible) but I can also imagine this now higher pressure behind the vehicle meaning higher density (more air particle in the same volume now with higher forces keeping them apart same as force increases when you try to bring two opposing magnets closer).
This is the so called stored energy and as vehicle continues to accelerate this pressure will reduce meaning the density of air molecules drops up to the point that there is not enough pressure to cover the vehicle losses and so vehicle will start to decelerate until it will get below wind speed.
If this description created for you a mental image (visualizing this moving animation) then you will also know vehicle can not be powered by wind when vehicle speed is higher than wind speed in the same direction.

With this mental model of air, what you have been saying about energy storage, and other characteristics of gases, would make some sense.

Unfortunately this is a very poor model for air, or any other gas.  For example, the particles in your model appear to only be moving at the speed of the wind, so it is very easy for a vehicle to outrun them.  In reality, the molecules of nitrogen, oxygen and other gases that make up the air, are moving randomly and at speeds comparable to and often higher than the speed of sound.  There are also no significant forces between the molecules keeping them apart, except briefly when they collide with one another or with other objects.

A far better model is that used in the kinetic theory of gases.  The Wikipedia page on this subject includes an animation that may help you to form a much more useful mental image. https://en.wikipedia.org/wiki/Kinetic_theory_of_gases  Once you have moved over to using that model, a lot of the things that others on this thread have said should begin to make sense.

I think that your other sources of disagreement with the rest of us may be due to poorly defined frames of reference.  In particular, the wrong choice of reference frame can obscure the simple relationships between force, distance and energy or work done.  I tried to explore this earlier with my thought experiment with a passenger walking down the aisle of an aircraft.

I have aphantasia myself, so I do have some sympathy with you.  I can't form any kind of internal visual images, but I can form what I can best describe as invisible wire-frame images, that I can freely manipulate and rotate.  I can't see them in any visual sense, but I can sense them.

[armandine2]

mechanical systems are familiar and knowledge of them is often taken for granted - I think you'd be less likely to do so for their electrical or chemical equivalents.

... mechanical paradoxes seem though accessible challenges to us:

[electrodacus]

With this mental model of air, what you have been saying about energy storage, and other characteristics of gases, would make some sense.

Unfortunately this is a very poor model for air, or any other gas.  For example, the particles in your model appear to only be moving at the speed of the wind, so it is very easy for a vehicle to outrun them.  In reality, the molecules of nitrogen, oxygen and other gases that make up the air, are moving randomly and at speeds comparable to and often higher than the speed of sound.  There are also no significant forces between the molecules keeping them apart, except briefly when they collide with one another or with other objects.

A far better model is that used in the kinetic theory of gases.  The Wikipedia page on this subject includes an animation that may help you to form a much more useful mental image. https://en.wikipedia.org/wiki/Kinetic_theory_of_gases  Once you have moved over to using that model, a lot of the things that others on this thread have said should begin to make sense.

I think that your other sources of disagreement with the rest of us may be due to poorly defined frames of reference.  In particular, the wrong choice of reference frame can obscure the simple relationships between force, distance and energy or work done.  I tried to explore this earlier with my thought experiment with a passenger walking down the aisle of an aircraft.

I have aphantasia myself, so I do have some sympathy with you.  I can't form any kind of internal visual images, but I can form what I can best describe as invisible wire-frame images, that I can freely manipulate and rotate.  I can't see them in any visual sense, but I can sense them.

Thanks for the comment. It is possible that others same as you have the wrong model of gases.  What you see in that Wikipedia animation is true for a gas that is at a temperature higher than zero kelvin so applies to air in the atmosphere also.
But all that shown in the animation is random motion so not useful in any way. If you have a sail in there no wind particle of air will collide with the sail from all directions but there will be no net force as all collisions will average to zero.
No when there is wind the particles move in the same chaotic way but on top of that there is a net movement in a particular direction and that will be called wind.

The thing is that you can not just randomly change frames of reference without considering the consequences of doing so. No matter from how many frame of reference you look at the same problem the results need to be the same else you did something wrong (not considered what the change in reference frame changed in how you need to interpret the results).
When I thing about all forces (prefer to think in therms of power for this particular problem as is more useful and less likely to make mistakes) I think in an unmodified reference frame and by that I mean that I do not change the frame of reference for vehicle with the road.
Most people for some reason prefer to have the vehicle not moving when thinking about it and instead the road moves underneath the vehicle thus the reason people started to use a treadmill and that was a good choice as that is isolated from the ground and the air.
When I think in my head I imagine the vehicle still moving and the road is what is stationary so I do not modify the frame of reference.  When for example people stop the vehicle and make the road the one that moves they also need to consider that they also flipped the kinetic energy so now the vehicle kinetic energy is the road kinetic energy and vice versa.
Since treadmill is powered by a motor connected to the grid it has no finite kinetic energy like the vehicle did so if you where to break a bit the treadmill the kinetic energy will not be reduced as it will be the case if you break the vehicle. The treadmill has an external energy source and a speed controller so it will try to maintain the speed.

In any case the propeller cart tested on treadmill works perfectly fine as an analogy and experiment is correct. The only problem with that experiment is that treadmill is to short so there is no time to observe how the cart/vehicle gets to top speed and then starts to slow down. So experiment is just not long enough to show what happens.
Since people can not accept that there is energy storage even if it is a well known fact that air is compressible I changed the air for a solid and so the propeller for a wheel thus my diagram that you likely seen.

When I presented that diagram to my surprise people claimed that the wheel only vehicle in my diagram can move from left to right powered only by the treadmill.
So based on this new info I do not think people misunderstand this problem because of not understanding air or propeller (tho that may still be a factor) but they just do not understand the conservation of energy.
I think I expressed fairly clearly that power available to motor wheel comes only from generator wheel and so in real world Motor wheel will have lower power to move vehicle from left to right than the generator wheel opposing that movement trough generating that power for the motor.

If you will be able to understand this problem before other people that likely do not have aphantasia (not very common) then that will mean that phantasia may be more detrimental than helpful for solving this sort of problems.
In any case even those that can form mental images have different levels. I think I'm somewhere average and on the other end there are people that have such vivid mental images that can not even distinguish from real images and that is way more of a problem than not having any mental image.       

[cbutlera]

No when there is wind the particles move in the same chaotic way but on top of that there is a net movement in a particular direction and that will be called wind.

That is right, but the wind speed in all the circumstances that we have been discussing is a tiny fraction of the average individual speeds of the air molecules.

When I think in my head I imagine the vehicle still moving and the road is what is stationary so I do not modify the frame of reference.

That is fine when considering the interaction between the wheels and the stationary platform, but when considering the interaction between the other wheels and the treadmill, the stationary frame of reference is not the best choice.

However you can still do it, as long as you remember to include the work done by the treadmill on the vehicle, as well as the work done by the vehicle on the treadmill.  What you seem to keep doing is forgetting the work done by the treadmill, and then concluding that conservation of energy prevents the vehicle from moving to the right.

Going back to my aircraft thought experiment.  The aircraft is travelling at 200 m/s, I get out my seat and walk forwards at 1 m/s, I weigh 70 kg.  How much energy did I have to expend to accelerate from 200 m/s to 201 m/s in the frame of reference of the ground?  From the ground frame of reference my kinetic energy has increased from 1,400,000 joules to 1,414,035 joules. A difference of 14,035 joules.

[electrodacus]

That is right, but the wind speed in all the circumstances that we have been discussing is a tiny fraction of the average individual speeds of the air molecules.

That thermal jiggling of the air molecules is not useful to extract energy from. When vehicle is at same speed as wind speed it can no longer extract any wind energy is the same as a non moving vehicle in a day with no wind or indoors.
The treadmill experiment was done indoors so no wind energy available and and still it showed the vehicle moving forward against the treadmill direction clearly meaning that stored energy was involved. But people instead of getting to this proper conclusion decided to think that energy from the treadmill can be used to push against air and be able to move forward and if that was to be true it will violate the conservation of energy (obviously that is not true).

That is fine when considering the interaction between the wheels and the stationary platform, but when considering the interaction between the other wheels and the treadmill, the stationary frame of reference is not the best choice.

However you can still do it, as long as you remember to include the work done by the treadmill on the vehicle, as well as the work done by the vehicle on the treadmill.  What you seem to keep doing is forgetting the work done by the treadmill, and then concluding that conservation of energy prevents the vehicle from moving to the right.

Any experiment where my diagram is respected will show that vehicle can not move from left to right. There is not even one experiment showing that.

Going back to my aircraft thought experiment.  The aircraft is travelling at 200 m/s, I get out my seat and walk forwards at 1 m/s, I weigh 70 kg.  How much energy did I have to expend to accelerate from 200 m/s to 201 m/s in the frame of reference of the ground?  From the ground frame of reference my kinetic energy has increased from 1,400,000 joules to 1,414,035 joules. A difference of 14,035 joules.

What do you mean by aircraft ? For me an aircraft will be something that travels in air not on ground so something like an airplane.
I can not imagine you getting out of an aircraft and then walking.
But say you are referring to an airplane driving very close to ground and then you get out of that (it will be very painful) as that 200m/s speed of aircraft is relative to stationary ground so if you get out of the airplane as soon as you touch the ground all you kinetic energy will be reduced close to zero in seconds so you will likely not survive let alone be able to walk.
Have you ever got down from a moving vehicle like maybe a train ? It will need to move very slowly so that you are able to absorb all that change in kinetic energy else you will get hurt.

I have mentioned a more appropriate analogy of what you are trying to describe.
That will be a road with two lanes where one lane is fixed so no speed and one lane moves forward (like the surface of a treadmill) at a certain speed say 10m/s and you can call this moving lane wind speed.
Now you have an non powered vehicle that can have access to both lanes and you want to drive faster than 10m/s but it will be impossible.
Best you can do have the entire vehicle moved on the 10m/s lane and so vehicle travels on that lane at same speed (like a hydrogen balloon carried by the wind).
Trying to have part of the vehicle (some wheels) on the stationary lane and part of the vehicle on the moving lane will just result in vehicle driving slower than 10m/s relative to the stationary lane.
   

[PlainName]

Any experiment where my diagram is respected will show that vehicle can not move from left to right. There is not even one experiment showing that.

There are at least two, and you've posted one yourself. I doubt if there will be another because it's obvious you will find some issue that allegedly negates the experiment.

How about you show the experiment that proves your hypothesis?

[cbutlera]

What do you mean by aircraft ? For me an aircraft will be something that travels in air not on ground so something like an airplane.
I can not imagine you getting out of an aircraft and then walking.
But say you are referring to an airplane driving very close to ground and then you get out of that (it will be very painful) as that 200m/s speed of aircraft is relative to stationary ground so if you get out of the airplane as soon as you touch the ground all you kinetic energy will be reduced close to zero in seconds so you will likely not survive let alone be able to walk.
Have you ever got down from a moving vehicle like maybe a train ? It will need to move very slowly so that you are able to absorb all that change in kinetic energy else you will get hurt.

My apologies, but I thought it was obvious. I am a passenger in a normal aeroplane flying at normal cruising altitude at 200 m/s.  I stand up from my seat and walk down the aisle of the aeroplane towards the front of the aeroplane at 1 m/s, relative to the aeroplane.  I weigh 70 kg.

To an observer on the ground (using the ground frame of reference), by getting up and walking along the aisle, I have accelerated from 200 m/s to 201 m/s. To this observer on the ground, I have increased my kinetic energy by 14,035 joules.  Where did this energy come from?

[electrodacus]

There are at least two, and you've posted one yourself. I doubt if there will be another because it's obvious you will find some issue that allegedly negates the experiment.

How about you show the experiment that proves your hypothesis?

That is because you do not understand the difference between my diagram and a flipped vehicle.  The person that posted the video needed to flip the vehicle else if is as shown in my diagram it will not work so it will be unable to show what it thinks it represent.
I guess you are referring to that treadmill experiment where motor wheel where on the other side of the generator wheels compared to my diagram.
While you think flipping the vehicle has no consequence the real consequences are huge as one can move in any direction and the other (the one in my diagram can move just from right to left).
That guy can easily flip the vehicle and show that is not working the same way but he has not done that.
I do not have any wheel based toys as I will have made a short video. Also me doing a video even if I show it is now working you will think I did something to trick you thus best thing is one of you to do the experiment.
One of you showed the vehicle and paper video and is not much to glue a piece of paper in a loop and put that on two cylinders then move that treadmill my hand. The cylinders of course will need to be fixed to the table or whatever surface the motor wheel stand on. 

[electrodacus]

My apologies, but I thought it was obvious. I am a passenger in a normal aeroplane flying at normal cruising altitude at 200 m/s.  I stand up from my seat and walk down the aisle of the aeroplane towards the front of the aeroplane at 1 m/s, relative to the aeroplane.  I weigh 70 kg.

To an observer on the ground (using the ground frame of reference), by getting up and walking along the aisle, I have accelerated from 200 m/s to 201 m/s. To this observer on the ground, I have increased my kinetic energy by 14,035 joules.  Where did this energy come from?

I did not understand because your proposal demonstrates nothing.
You are not between two mediums you are just on one medium that moves relative to the ground. So you walking inside the plane requires energy that you will provide by burning some extra calories while in motion at 1m/s and as soon as you stop walking you will be back at 200m/s.
This vehicle discussed here has no other energy source other than the wind (there is the energy storage that is why it works for a bit) but the claims made by people is that it can run forever since they do not consider the existence of the energy storage.
Also your kinetic energy only increased by 35J (35Ws) relative to the airplane and that increase you mentioned relative to ground was provided to you by the plane. So while you where accelerating forward at 1m/s you increase the airplane fuel consumption by a bit. But when you returned to your seat you compensated by slightly reducing the fuel consumption.
I know for a large panel this increase and decrease in fuel consumption as you where acceleration inside the plane are so insignificant that can not even be measured they are provided by the plane and not by you. Else you will be fairly hungry after this small few second walk.

[PlainName]

That is because you do not understand the difference between my diagram and a flipped vehicle.

Undoubtedly! Nor your explanations, such as they are. So, just demonstrate it with an actual experiment. Imagine: no more misunderstandings, talking at cross-purposes, undecipherable diagrams - it will just be obvious once you show us it happening.

Why don't you?

[PlainName]

even if I show it is now working you will think I did something to trick you

But, obviously, we would never suspect you of doing that when we show you an actual experiment demonstrating the opposite!

[cbutlera]

My apologies, but I thought it was obvious. I am a passenger in a normal aeroplane flying at normal cruising altitude at 200 m/s.  I stand up from my seat and walk down the aisle of the aeroplane towards the front of the aeroplane at 1 m/s, relative to the aeroplane.  I weigh 70 kg.

To an observer on the ground (using the ground frame of reference), by getting up and walking along the aisle, I have accelerated from 200 m/s to 201 m/s. To this observer on the ground, I have increased my kinetic energy by 14,035 joules.  Where did this energy come from?

I did not understand because your proposal demonstrates nothing.
You are not between two mediums you are just on one medium that moves relative to the ground. So you walking inside the plane requires energy that you will provide by burning some extra calories while in motion at 1m/s and as soon as you stop walking you will be back at 200m/s.

I am not talking about operating between two mediums.  I'm taking a step back and considering a simpler case, which will turn out to be very relevant to the original more complex case.

I ask you again, to the observer on the ground (in my thought experiment above), I have increased my kinetic energy by 14,035 joules.  Where did this energy come from?

[electrodacus]

I am not talking about operating between two mediums.  I'm taking a step back and considering a simpler case, which will turn out to be very relevant to the original more complex case.

I ask you again, to the observer on the ground (in my thought experiment above), I have increased my kinetic energy by 14,035 joules.  Where did this energy come from?

I may not have been very clear.  In your tough experiment there are two sources of energy both contributing to your increase in kinetic energy.
Out of that 14035J you contributed 35J and the plane contributed with 14000J.  You used some of your stored energy from food while plane used kerosene or whatever that plane was using for fuel.
This will not apply to vehicle having a single energy source (wind energy).
Of course a vehicle traveling in same direction as the wind can exceed that wind speed if it has access to another energy source like say a human pedaling or a battery or as it is the case a pressure differential energy source.
If experiment is done for just a limited amount of time so that energy source is not all used up you will get to the wrong conclusion that wind alone powers the vehicle but if you run the experiment a bit more you will see the entire picture with vehicle decelerating below wind speed once the stored energy is used up.

[cbutlera]

I may not have been very clear.  In your tough experiment there are two sources of energy both contributing to your increase in kinetic energy.
Out of that 14035J you contributed 35J and the plane contributed with 14000J.  You used some of your stored energy from food while plane used kerosene or whatever that plane was using for fuel.

That is correct.  So relative to the ground, I have accelerated to a speed slightly in excess of that of of the aeroplane, and I was able to do that by taking the majority of the required energy from the aeroplane.  You have repeatedly claimed that it is impossible to take energy from a moving medium when moving faster than that medium, whether that medium is a treadmill, a sliding piece of paper, the air, or the floor of the aisle of an aeroplane.  In your calculation above you have just demonstrated that this is indeed possible.

This will not apply to vehicle having a single energy source (wind energy).

Yes it does apply.  It shows that the generator and motor of the vehicle only have to provide a portion of the kinetic energy required to increase the speed of the vehicle in excess of the speed of the moving medium. The remainder of the kinetic energy is provided directly by the moving medium.  So while the motor will itself return a little less kinetic energy to the vehicle than was taken by the generator, the additional direct contribution of the medium will more than compensate for this. So the vehicle can accelerate beyond the speed of the moving medium.

In my example above my internal motor (my muscles) only had to supply 35 joules to gain 14,035 joules (relative to the ground).  So if my muscles were powered by some small hypothetical wind turbine, held in my hand and in contact with the air outside of the aeroplane, that generator would only have had to extract 35 joules out of my 1,400,000 joules of kinetic energy (travelling at 200 m/s).  So I would lose 35 joules of kinetic energy through the drag of the hypothetical generator, but gain about 14,035 joules of kinetic energy through the propulsion of my internal motor.

[Kleinstein]

Excluding energy storage in the experiments is not easy - at least I sone see a very simple way. It is clear that there is no battery or spring storage - they are just not there and a bayttery would also need a motor. Kinetic energy (like flywheel) goes up when the vehicle gets faster, so it can not provide energy. It is only theoretical air pressure in the free space before / behind the fan. Without a container the energy/ pressure field would not stay there very long - more like lenghtscale divided by speed of sound - so in the low ms range. Compared to this the experiment with the free running vehicle on the tradmill was allready very long. A few seconds may not look long, but it is sufficiently long. Even the vehicle size divided by wind speed would be short compared.
Similar for the larger backbrid vehicle, with a pressure field that may last a few 1/100 of a second and time traveled at speed higher than the wind of more like a minute or more.

There is another point that shows that the vehicle did harmess the power of the wind, even if at the wind speed: When held at position at the treadmill there was a forward force, as when left free the vehicle accelerated forward. This forward force means the the wheels could use even more force and generate extra power. So the vehicle would be able to generate some power even if at the speed of the wind. The time the vehicle was hold in position pretty long and the time is definitely sufficient to esteblisch a steady state air pressure around the prop. There is also absolutely no reason to assume one could not hold the vehicle longer before letting it run forward.  So this is steady state and thus has nothing to do with energy storage.  It may be against some peoples intuition, but the experiment still shows it.

The though experiment with the man walking in the plane is good, as it shows that the use of just power / energy to avoid looking at forces can get pretty complicated when looking at different refrence frames. Similar complications also apply to the system on the treadmill: you get different energies / power when you use different refrence systems.  So looking at the power is tricky and prone to error. It is much easier to look at force and speed seprate. The forces don't change when one changes the reference system, and the speeds simply add.

[electrodacus]

That is correct.  So relative to the ground, I have accelerated to a speed slightly in excess of that of of the aeroplane, and I was able to do that by taking the majority of the required energy from the aeroplane.  You have repeatedly claimed that it is impossible to take energy from a moving medium when moving faster than that medium, whether that medium is a treadmill, a sliding piece of paper, the air, or the floor of the aisle of an aeroplane.  In your calculation above you have just demonstrated that this is indeed possible.

You did not took energy from the aeroplane. If the aeroplane did not had a constant speed controller say maybe even engines turned off then you will have slowed down the aeroplane while you where traveling at 1m/s.
And what you did was run walk relative to aeroplane at 1m/s using your own internal stored energy.  There was no way for you to accelerate to 1m/s using just the aeroplane energy.
You somehow forget that while you are for example in blackbird you are not allowed to use your own energy to exceed wind speed
So if you want to push the analogy you will be in blackbird siting not doing anything and the wind is the aeroplane driving at constant speed.
Now the best Blackbird can do is get pushed by the aeroplane up to same speed but using just that energy alone and nothing else it can not accelerate past that speed as that will be already 100% efficient way of using the available energy.
Now if you start to pedal you can exceed aeroplane(wind) speed but that is no longer a wind (aeroplane) only powered vehicle.

 

Yes it does apply.  It shows that the generator and motor of the vehicle only have to provide a portion of the kinetic energy required to increase the speed of the vehicle in excess of the speed of the moving medium. The remainder of the kinetic energy is provided directly by the moving medium.  So while the motor will itself return a little less kinetic energy to the vehicle than was taken by the generator, the additional direct contribution of the medium will more than compensate for this. So the vehicle can accelerate beyond the speed of the moving medium.

In my example above my internal motor (my muscles) only had to supply 35 joules to gain 14,035 joules (relative to the ground).  So if my muscles were powered by some small hypothetical wind turbine, held in my hand and in contact with the air outside of the aeroplane, that generator would only have had to extract 35 joules out of my 1,400,000 joules of kinetic energy (travelling at 200 m/s).  So I would lose 35 joules of kinetic energy through the drag of the hypothetical generator, but gain about 14,035 joules of kinetic energy through the propulsion of my internal motor.

You maybe are not considering that treadmill surface moves in the opposite direction that you want to travel so you start with zero kinetic energy and if you do nothing Generator and motor disconnected and this is ideal vehicle the vehicle will stay in the same place and generator wheel will just turn at the same speed as the treadmill as there will be no friction.
As soon as you try to take any energy from the generator then treadmill will push the vehicle back by the exact same amount so you can call that negative kinetic energy as you are moving and have kinetic energy but it is in the opposite direction than what you will like.
And ideal case the best you can do is put all that energy in to motor wheel and that can bring you back to the place you started but it can not advance you further than that. In real world due to friction you will move from right to left no matter how you set the gear ratio between the generator and the motor.


Let me try and give you another example that includes you in the equation.
So say you are the wind so the only energy source in the system and say you have a top speed of 12m/s so no matter what you can not run faster.
Now you can push a fairly light vehicle with little friction and say you can still push that to 12m/s.  As soon as you get to 12m/s the vehicle can not use you to exceed that speed no matter what. So even if say I will help you to double the power if my speed is also limited to 12m/s then we together still can not push the vehicle faster in the same direction that we are running.
What relay happens in air is that say we had some very long springs attached to our arms maybe 10m or 20m long compressible springs and now we start pushing the vehicle it will take longer to get the vehicle to speed as we will need to compress the springs initially then vehicle will see higher and higher force and we will get then to our top speed of 12m/s but since at that point the springs are full compressed the springs will continue to push the vehicle and so vehicle can exceed our speed for as long as there is enough compression force in the spring to be able to accelerate the vehicle and cover vehicle losses.
As any analogy it has limitations but basically that is what happens for blackbird in air because air is compressible. If instead of air it was water (not compressible) then you can still use a propeller designed for water but you will not be able to exceed water speed not even for a few seconds or minutes as it is the case in air. And same is true for solids that are also in general not compressible.

So the vehicle in my diagram done exactly as shown there with treadmill and generator wheel in front of the motor wheel will not be able to move at all from left to right. It is proven both mathematically with the power in and out equation and you can observe it in practice if you build it.
And that spiral spring is meant to simulate the air comprehensibility so if you add that to the motor wheel then you will observe exactly the same behavior as the treadmill propeller based cart.

[electrodacus]

Excluding energy storage in the experiments is not easy - at least I sone see a very simple way. It is clear that there is no battery or spring storage - they are just not there and a bayttery would also need a motor. Kinetic energy (like flywheel) goes up when the vehicle gets faster, so it can not provide energy. It is only theoretical air pressure in the free space before / behind the fan. Without a container the energy/ pressure field would not stay there very long - more like lenghtscale divided by speed of sound - so in the low ms range. Compared to this the experiment with the free running vehicle on the tradmill was allready very long. A few seconds may not look long, but it is sufficiently long. Even the vehicle size divided by wind speed would be short compared.
Similar for the larger backbrid vehicle, with a pressure field that may last a few 1/100 of a second and time traveled at speed higher than the wind of more like a minute or more.

There is another point that shows that the vehicle did harmess the power of the wind, even if at the wind speed: When held at position at the treadmill there was a forward force, as when left free the vehicle accelerated forward. This forward force means the the wheels could use even more force and generate extra power. So the vehicle would be able to generate some power even if at the speed of the wind. The time the vehicle was hold in position pretty long and the time is definitely sufficient to esteblisch a steady state air pressure around the prop. There is also absolutely no reason to assume one could not hold the vehicle longer before letting it run forward.  So this is steady state and thus has nothing to do with energy storage.  It may be against some peoples intuition, but the experiment still shows it.

The though experiment with the man walking in the plane is good, as it shows that the use of just power / energy to avoid looking at forces can get pretty complicated when looking at different refrence frames. Similar complications also apply to the system on the treadmill: you get different energies / power when you use different refrence systems.  So looking at the power is tricky and prone to error. It is much easier to look at force and speed seprate. The forces don't change when one changes the reference system, and the speeds simply add.

So your claim is that pressure differential has no enough energy to power the vehicle from 10mph to 30mph ?
The thing is that you do not understand how much energy is needed to do that (just about 6Wh) and you also do not get the scale of the stored energy and the fact that is self feed due to the connection between the wheel and propeller.
So pressure differential drops slowly only to cover the losses and small bit to accelerate the vehicle.
Do you know how much energy will an ideal wind turbine of the same diameter as the propeller in Blackbird will generate in only one second at 10mph (4.5m/s) ?
It will be 4800Ws. But there are quite a few seconds during the acceleration phase when the propeller at maybe 70% can compress the air behind in a huge volume of tens of thousand of liters (20m^2 propeller area times the length behind the propeller where pressure drops in a gradient to ambient pressure).
There will be more than sufficient to power a vehicle like blackbird to get to that record they set and a little bit extra but not much.
So yes a real wind turbine of that size will have about a 2kW output in that wind speed of just 4.5m/s but during the period they made that record wind speed fluctuated from 4m/s to 6.5m/s and at that peak 6.5m/s a real wind turbine with just 40% efficiency will output 5.8kW or 14kW at 100% ideal case.
Keep in mid that is basically the same drag and rolling resistance as a bicycle or tricycle.     

[bdunham7]

Assuming without checking or agreeing that your math is correct...

6Wh = 21600Ws

4800Ws = 1.5Wh.

and so on.  Not keeping your units tidy can make things look different--and wrong.

and then you have to ask by what mechanism is the propeller compressing this air if the wind is pushing the vehicle and not the other way around?

[Alex Eisenhut]

This is Wind Cube territory, with apologies to real companies called Wind Cube.

[electrodacus]

Assuming without checking or agreeing that your math is correct...

6Wh = 21600Ws

4800Ws = 1.5Wh.

and so on.  Not keeping your units tidy can make things look different--and wrong.

and then you have to ask by what mechanism is the propeller compressing this air if the wind is pushing the vehicle and not the other way around?

The wind is pushing the vehicle and the blackbird takes a big part of that energy and put it back in the propeller generating an "artificial wind" in the opposite direction. When vehicle is way below half the wind speed the so called artificial wind will be stronger than the actual wind and this is where energy is stored as pressure differential.
But even before getting to wind speed this pressure differential will start to drop as the stored energy is already being used and at some point the pressure differential is so small that it can no longer cover the vehicle friction and that is the point of max speed from witch point the vehicle will start to decelerate.


Yes I should have used maybe just one unit like Ws but for most people Ws has no much meaning compared to Wh where most people may know that 6Wh is about half of what you have available in a smartphone battery.
Many people may also own an eBike and may know what 6Wh compared to their eBike battery of of maybe 500 to 600Wh so they can do 100x of those records with the energy in their eBikes.
But Ws are easier to use when making calculations as is the same with Joules.
In any case you do have a point.

[bdunham7]

The wind is pushing the vehicle and the blackbird takes a big part of that energy and put it back in the propeller generating an "artificial wind" in the opposite direction. When vehicle is way below half the wind speed the so called artificial wind will be stronger than the actual wind and this is where energy is stored as pressure differential.

How can there be an 'artificial wind' coexisting with and opposite to the actual wind?  Can you demonstrate that somehow with a fan or something?

And setting that aside, if the resultant artificial wind is stronger than the real wind, where would the energy for that come from?  Wouldn't that violate your conservation of energy principles?

[electrodacus]

This is Wind Cube territory, with apologies to real companies called Wind Cube.

Not quite sure what you want to say by wind cube territory. It seems Wind Cube (never heard of them) make some wind speed measuring devices.
I designed my own wind turbine and wind turbine calculated about 10 years ago. I just never build it as solar PV was just way more cost effective and it did not made any economic sense to build or even buy a wind generator to power my house.
My English is quite bad so it may be hard to watch this old video

 

[electrodacus]

The wind is pushing the vehicle and the blackbird takes a big part of that energy and put it back in the propeller generating an "artificial wind" in the opposite direction. When vehicle is way below half the wind speed the so called artificial wind will be stronger than the actual wind and this is where energy is stored as pressure differential.

How can there be an 'artificial wind' coexisting with and opposite to the actual wind?  Can you demonstrate that somehow with a fan or something?

And setting that aside, if the resultant artificial wind is stronger than the real wind, where would the energy for that come from?  Wouldn't that violate your conservation of energy principles?

No it will not violate the conservation of energy as all this is done when you have access to wind energy since you are well below wind speed.
Think about this way. You have a large wind turbine generator in low wind speed supplying a much smaller fan that creates even hurricane level winds but since the diameter of the fan is much smaller much less wind is actually moved so is like a gear box.
So say you will want to use the fan to supply the wind turbine then that will not work as power output is much smaller from the fan than what the wind turbine will need to supply the fan.
The propeller is like a diode it can leave air molecules travel from upwind to down wind but not the other way around so it acts as a one way sail while spinning.
In any case no conservation of energy is broken as energy is stored. You could as well drive a EV with empty battery just use regenerative brakes while pushed by the wind then after you stored enough just accelerate to whatever speed you want but only for a limited time depending on how much you spent storing energy.
That is why the Blackbird will work even in a day with no wind just push the vehicle to sufficient speed to charge the energy storage and vehicle will drive faster that the speed you pushed it at for some limited amount of time.