Author Topic: Mess with your minds: A wind powered craft going faster than a tail wind speed.  (Read 147635 times)

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Offline PlainName

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Serious question:  How do you store energy in air which is not contained in any way?

Air compresses, so although the storage is leaky (and then some) isn't there some brief storage?

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If you are not convinced by my correct calculations

Can you tell me which post your calculations were shown in? So far as I can recall, your 'calculations' are basically descriptions and where actual figures are concerned you don't show the workings that got to those.
 

Offline electrodacus

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The pole you are getting up on is getting very high, remember the distance to fall is also getting longer all the time.....

I'm not guessing that it will not work I know that vehicle in my diagram can only move from right to left no matter what you do to the vehicle unless you add energy storage or some energy source other than the treadmill.

All experiments you seen before has the vehicle flipped and that changes everything. The experiment needs to be setup as in my diagram.



What was demonstrated is if you lift the M wheel and rotate 180 degree so that motor wheel and red box are not on the other side of the treadmill but you do not change anything else and that if you can not see is a very different system.


Serious question:  How do you store energy in air which is not contained in any way?

Your previous hand-waving and "intuition" has not been informative, let alone convincing.

If I can not convince you that the above vehicle in my diagram can only move from right to left not sure what chance I have explaining how pressure differential energy storage works.
The simple answer is that air is a compressible material so when you try to push yourself against air like with a propeller/fan you are creating higher pressure on one side and lower pressure on the other side (higher and lower density of air molecules) so is like compressing a spring on one side and stretching a spring on the other side.  This will want to get back to equilibrium but as long as propeller rotates this pressure differential is maintained.
And if somehow you understand how an inductor stores energy then this will be as good as analogy as anyone can get. With inductor storing energy in the magnetic field around the coil and if you stop the current flow or better reduce the current flow trough inductor this magnetic field will collapse to try and maintain the current flow.

I posted before the diagram from Wikipedia that shows the pressure differential for an axial fan. You an see P1 and P2 is much higher than PA (ambient pressure) and keep in mind Blackbird has a huge propeller with a sweep area of about 20m^2 and all that vehicle needs to accelerate from 10mph to 28mph in that record is about 6Wh so half the energy contained in a modern smartphone.



Offline PlainName

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Can you cite any examples

Musical wind instrument?
 

Offline PlainName

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All experiments you seen before has the vehicle flipped and that changes everything

You keep saying that. Why does it change everything? And in what way?
 

Offline bdunham7

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Air compresses, so although the storage is leaky (and then some) isn't there some brief storage?

Very brief.  Differences in pressure in uncontained air will dissipate at the speed of sound....

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Musical wind instrument?

Well, like I said... :)
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline electrodacus

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You keep saying that. Why does it change everything? And in what way?

You keep thinking about that, since me making all the thinking seems not to be helpful.

Offline IanB

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I posted before the diagram from Wikipedia that shows the pressure differential for an axial fan. You an see P1 and P2 is much higher than PA (ambient pressure)

And I linked you to a video of a real experiment which shows the pressure in front of a fan is lower than the ambient pressure. Which means that diagram does not show what you think it shows.

Why do you keep asking us to do experiments, but when I show you an example of an experiment you refuse to believe it?
 

Offline electrodacus

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And I linked you to a video of a real experiment which shows the pressure in front of a fan is lower than the ambient pressure. Which means that diagram does not show what you think it shows.

Why do you keep asking us to do experiments, but when I show you an example of an experiment you refuse to believe it?

You have no idea how to interpret that experiment and neither the person that made the video.
While Wikipedia is not always a reliable source of information it is at least a step above average people posting a video on youtube not understanding what they are testing.

Offline IanB

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You have no idea how to interpret that experiment and neither the person that made the video.

It does not need to be interpreted to observe the simple fact that it demonstrates, which is that the pressure in front of the fan is lower than the ambient pressure.

The fact is that fans and propellers do not compress air. What they do is accelerate the air passing through them. This acceleration generates a reaction force that drives the propeller forwards.

Unfortunately, if we show you the experiment where the cart in your diagram moves from left to right, you will dispute that too, and will claim that experiment also is being misinterpreted. So it's not worth our time showing you results that you will refuse to believe.
 

Offline electrodacus

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It does not need to be interpreted to observe the simple fact that it demonstrates, which is that the pressure in front of the fan is lower than the ambient pressure.

The fact is that fans and propellers do not compress air. What they do is accelerate the air passing through them. This acceleration generates a reaction force that drives the propeller forwards.

Unfortunately, if we show you the experiment where the cart in your diagram moves from left to right, you will dispute that too, and will claim that experiment also is being misinterpreted. So it's not worth our time showing you results that you will refuse to believe.

I almost feel like I'm talking with flat earthers and so nothing I can say will convince you. The best I can suggest is you do the experiment and see that what happens is exactly what I predict.
So have a vehicle as shown in my diagram (not flipped) and observe that whatever you do in therms of gear ratio the vehicle will move from right to left.
The flipped vehicle is completely different due to the way the forces act on the vehicle are different and that vehicle can travel in both directions based on gear ratio. That flipped vehicle represents the analog of the propeller vehicle where propeller is the generator (not a fan) and so it drives against the wind direction.
What you can observe on that one if you want is that it can not exceed the wind speed meaning vehicle relative to stationary ground can not travel faster than the speed of the treadmill.
So the vehicle in my diagram is very different from the vehicle that was demonstrated where vehicle was flipped.
I will like to show the below diagram but hopefully that will not create even more confusion for you. That shows what happens when you flip a vehicle and top of the wheel will touch the surface instead of the bottom of the wheel.
This diagram was to explain Derek what his wheel vehicle with the floor and lumber represents.

 


In any case just build the vehicle in my original diagram and experience the fact that vehicle will always move from right to left. This will be analog to getting a flat earther in to space to see for himself that earth is an approximately spherical object.

Offline PlainName

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It does not need to be interpreted to observe the simple fact that it demonstrates, which is that the pressure in front of the fan is lower than the ambient pressure.

Once again, I don't think it is showing what you (and the chap in the video) think it is. Blow across a pipe and it will suck the air out.

Last time I raised this issue you didn't catch on for whatever reason, so here's a video I just ran off to demonstrate:



That's an ally pipe with a plastic bag cellotaped on the end. The vacuum cleaner nozzle is actually the output of my vacuum, so blowing instead of sucking. (FYI it's a DeWalt DC500 so not particularly strong, but I think we can agree that it is higher pressure than ambient and absolutely not a vacuum.) As you can see, blowing air across the pipe sucks air out of the bag, giving the exact same effect as the chap in your video.

How does he, and you, know that he is not recreating this situation?
 

Offline PlainName

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I will like to show the below diagram but hopefully that will not create even more confusion for you.

Well it has! What's the blue wheel, the green thing, etc? Is the green thing touching the blue wheel? What do the arrows mean? It would be less confusing if you told us what the things represent instead of leaving us to guess (and then tell us we're wrong about our conclusions based on those quesses)  :-//
 

Offline IanB

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It does not need to be interpreted to observe the simple fact that it demonstrates, which is that the pressure in front of the fan is lower than the ambient pressure.

Once again, I don't think it is showing what you (and the chap in the video) think it is. Blow across a pipe and it will suck the air out.
Oh, absolutely it is showing what I think it is.

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Last time I raised this issue you didn't catch on for whatever reason, so here's a video I just ran off to demonstrate:
I did catch on, and I gave the explanation.

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That's an ally pipe with a plastic bag cellotaped on the end. The vacuum cleaner nozzle is actually the output of my vacuum, so blowing instead of sucking.
That's excellent that you did the experiment. Far better than drawing pictures and just imagining what will happen.

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(FYI it's a DeWalt DC500 so not particularly strong, but I think we can agree that it is higher pressure than ambient and absolutely not a vacuum.)
No, I can't agree there, as you will see. It is actually a vacuum.

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As you can see, blowing air across the pipe sucks air out of the bag, giving the exact same effect as the chap in your video.

How does he, and you, know that he is not recreating this situation?
Yes, I can see what you see, and here is the explanation.

Firstly, there is no such thing as "suction". Therefore, the pipe cannot suck air out of the bag. When we talk about suction this is just loose and imprecise terminology.

Gases (like air) consist of particles that are all pushing each other apart and trying to spread out. In the absence of overriding gravitational or accelerating fields, gases will spread out to evenly fill any container. The gas pushing against the walls of the container manifests as pressure, which can be measured. There is no such thing as "suction" because gases are pushing apart and trying to spread out, not pulling together. To have "suction" requires a "pull", which gases do not have.

Next, in the absence of gravity or acceleration, gases will flow from regions of higher pressure to regions of lower pressure. So we see, and can deduce, that the air flows out of the bag and through the pipe because the pressure inside the bag is higher than the pressure at the end of the pipe. The pressure in the bag is ambient pressure, and the pressure at the end of the pipe in the vacuum exhaust stream is less than ambient.

A follow on question is to ask, how, exactly, does a vacuum cleaner work? What basically happens here is that the motor creates low pressure inside the canister by "throwing" air out through the exhaust nozzle at high speed (it is a centrifugal blower). It works by catching air in the rotating blades, spinning it round really fast and throwing it out, much like you might get thrown off a roundabout if it is spinning fast and you let go.

By creating low pressure inside the canister, the high pressure atmosphere now pushes in through the vacuum nozzle to fill the void, and that is why the nozzle "sucks". But also, the low pressure air inside the canister is the same air the the blower is ejecting. This is partly why the stream of air coming out is at lower pressure than the surrounding air.

There are more technical details of course, but this is the gist of it.
 
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Offline bdunham7

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But also, the low pressure air inside the canister is the same air the the blower is ejecting. This is partly why the stream of air coming out is at lower pressure than the surrounding air.

Are you saying the air within the nozzle, before it gets out, is below ambient atmospheric pressure?  And does it follow that a vacuum cleaner is incapable of generating a pressure from it's nozzle when you connect to the out port?
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline IanB

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But also, the low pressure air inside the canister is the same air the the blower is ejecting. This is partly why the stream of air coming out is at lower pressure than the surrounding air.

Are you saying the air within the nozzle, before it gets out, is below ambient atmospheric pressure?
Yes, most likely. The air stream can only increase in pressure as it slows down and mixes with the surrounding air, so the pressure inside the nozzle will be at its lowest point. In fluid mechanics, the place where the flow is fastest and the stream is narrowest is called the vena contracta. This is also the point where the pressure is lowest.

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And does it follow that a vacuum cleaner is incapable of generating a pressure from it's nozzle when you connect to the out port?
No, it does not follow. A flowing fluid obeys the energy conservation law, and each element of fluid has two components to its energy: its pressure energy and its kinetic energy. The fast flowing fluid has higher kinetic energy, which is why the pressure decreases as it goes faster (the total energy must remain the same). However, if you capture that fast flowing fluid inside a container, some of the kinetic energy can be converted back to pressure energy, and this will cause the pressure to rise. Since the vacuum blower has given a lot of kinetic energy to the fast flowing air, if you slow down that air you can get back a higher pressure than it started with. This is the principle of operation of centrifugal compressors.

You don't get back all the kinetic energy though. Some of it is dissipated as waste heat through turbulence, but in a well designed system you can get 80% or more of the kinetic energy back as a pressure increase.
 

Offline bdunham7

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(the total energy must remain the same).

This is the principle of operation of centrifugal compressors.

I'm not doubting your assertion, as I haven't tested it but I guess it's plausible for some nozzles anyway.  But I'm not sure why you assert that the energy must remain the same--and I'm familiar with Bernoulli's experiments and equations.  The vacuum cleaner is a centrifugal compressor and it imparts a great deal of energy to the air.  I would have thought it would have positive (above atmospheric) pressure from the outlet of the motor to the nozzle.  Obviously I see why a narrowed nozzle will have a lower pressure than in the hose--that's straight out of a high school physics class--but I don't see why it has to be lower than atmospheric.  I can (and have) easily reproduce the vacuum experiment using an air compressor and a nozzle, but I'm completely sure that the pressure is higher than atmospheric right up to the nozzle.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline IanB

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Obviously the compressor or blower itself increases the energy of the air, so when the air goes through the compressor the conservation of energy principle includes (some of) the power output from the motor. But after the air leaves the compressor, you can then apply the conservation of energy principle downstream from there.

So the air inside the machine, before it gets to the outlet nozzle, might have a higher pressure than atmospheric, depending on how fast it is moving at that point. But inside the nozzle, when the air is flowing very fast, that is when the pressure is going to be lower.

However, vacuum cleaners do not tend to have compressors inside them, they have something more like a blower. The difference is that a compressor is designed mainly to raise a smaller flow of air to a high pressure, whereas a blower is designed mostly to move a large volume of air without increasing the pressure all that much.

In short, your question about the pressure of the air inside the nozzle depends on where you measure it. I interpreted your question to be about the pressure inside the nozzle itself, rather than before the nozzle. On the other hand, vacuum cleaners are all about achieving a clean, unobstructed flow path for the air without too many obstacles in the way (there are enough dust filters there already without adding any more resistance). So it is a reasonable assumption that the pressure is not very high on the outlet side of a vacuum cleaner, unless you block up the outlet nozzle.
 

Offline electrodacus

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Well it has! What's the blue wheel, the green thing, etc? Is the green thing touching the blue wheel? What do the arrows mean? It would be less confusing if you told us what the things represent instead of leaving us to guess (and then tell us we're wrong about our conclusions based on those quesses)  :-//

The diagram was made for Derek to explain to him that a a wheel touching a plain on that top or bottom is not the same thing.
I think the analogy I made for him was a car put in drive (froward) but the car had only the top of the wheels touching a surface that they can drive on and in that case vehicle will move in reverse.

The diagram represents a simplified version of the device he shows in his video that device has 4 small wheels and a large wheel driven by the small wheels.
I only used a small wheel and a large wheel for simplicity.
In figure a) it is about the same thing as he tried to demonstrate a proof for higher than wind speed travel powered only by the wind but in fact what he demonstrated was vehicle powered by wind traveling at lower speed than wind speed.
His claim was green bar (lumber in his experiment) was the wind so input source for vehicle and floor was the road that vehicle traveled on.
My interpretation of a) (there can only be one correct interpretation) is that floor is the input source (wind equivalent) the small wheel is the generator wheel driving the large wheel than then travels on the lumber in opposite direction to floor (wind) direction.
The arrows represent relative speed so two arrows on the red bar (vehicle body) shows a speed 2x larger than that of the green bar (lumber) but since wind is the floor that moves much faster comparing to vehicle that travels on the lumber and actual lumber also moves in that same direction as vehicle.

Then b) is taking that lumber and touching the bottom of the wheel so you can imagine the large wheel as wider than small wheel and so there is space to run a lumber under the wheel to power the vehicle. In this scenario the green bar lumber will represent the input (so wind) and it will move 2x faster than vehicle in the same direction and so this will represent the vehicle traveling in same direction as the wind.

The idea was that for you should show why flipping the vehicle 180 degree so that Motor wheel touches the ground with what was before the top of the wheel makes a huge difference in what the vehicle represents and it will no longer be the same vehicle shown in my diagram.

If you look at forces acting on the vehicle in my diagram you will see a breaking force on the generator pointing from right to left and then a opposing force from the Motor wheel pointing from left to right and since power for the motor is only provided by the Generator wheel one of the wheels will slip or if not possible then treadmill will be locked and unable to move.  What is impossible is for this vehicle to travel from left to right.
   
On the flipped vehicle where motor wheel is to the right of the generator wheel the forces are also opposing but instead of pointing to each other they point away from each other that means that generator is powered both by propeller but also by motor wheel when vehicle travels from left to right witch is very possible in this configuration since this is a completely different vehicle just because it was flipped.

You maybe see why I did not wanted to make an explanation as it is long and people usually do not have the patience to read what I write.

Offline ejeffrey

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It does not need to be interpreted to observe the simple fact that it demonstrates, which is that the pressure in front of the fan is lower than the ambient pressure.

The fact is that fans and propellers do not compress air. What they do is accelerate the air passing through them. This acceleration generates a reaction force that drives the propeller forwards.

Unfortunately, if we show you the experiment where the cart in your diagram moves from left to right, you will dispute that too, and will claim that experiment also is being misinterpreted. So it's not worth our time showing you results that you will refuse to believe.

I almost feel like I'm talking with flat earthers and so nothing I can say will convince you. The best I can suggest is you do the experiment and see that what happens is exactly what I predict.
So have a vehicle as shown in my diagram (not flipped) and observe that whatever you do in therms of gear ratio the vehicle will move from right to left.
The flipped vehicle is completely different due to the way the forces act on the vehicle are different and that vehicle can travel in both directions based on gear ratio. That flipped vehicle represents the analog of the propeller vehicle where propeller is the generator (not a fan) and so it drives against the wind direction.
What you can observe on that one if you want is that it can not exceed the wind speed meaning vehicle relative to stationary ground can not travel faster than the speed of the treadmill.
So the vehicle in my diagram is very different from the vehicle that was demonstrated where vehicle was flipped.
I will like to show the below diagram but hopefully that will not create even more confusion for you. That shows what happens when you flip a vehicle and top of the wheel will touch the surface instead of the bottom of the wheel.
This diagram was to explain Derek what his wheel vehicle with the floor and lumber represents.

 


In any case just build the vehicle in my original diagram and experience the fact that vehicle will always move from right to left. This will be analog to getting a flat earther in to space to see for himself that earth is an approximately spherical object.

Here you go.  The setup is a little janky, but clearly demonstrates the effect.  The right wheel rotates ~2.5 times for every rotation of the left wheel.  I don't have a treadmill so I used a piece of paper which I slide back and forth under the right wheel to push on it.  I can push with the paper "treadmill" in either direction and the cart moves in the opposite direction: towards the application of force.  This is due to the gear ratio, and the formula which I posted above that you ignored and claimed had to be wrong without describing why.  No slippage is occurring on the wheels or the belt.  It works at very low speeds or moderately fast speeds, if I go faster it obviously starts to slip.

Apparently the eevblog forum won't allow video embeds regardless of size, so sorry about the imgur link:

https://imgur.com/a/lTqAFg6
 
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Offline Brumby

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We are still talking about "motor wheels" and "generator wheels"....??

:palm:
« Last Edit: August 31, 2021, 04:23:04 am by Brumby »
 

Offline electrodacus

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Here you go.  The setup is a little janky, but clearly demonstrates the effect.  The right wheel rotates ~2.5 times for every rotation of the left wheel.  I don't have a treadmill so I used a piece of paper which I slide back and forth under the right wheel to push on it.  I can push with the paper "treadmill" in either direction and the cart moves in the opposite direction: towards the application of force.  This is due to the gear ratio, and the formula which I posted above that you ignored and claimed had to be wrong without describing why.  No slippage is occurring on the wheels or the belt.  It works at very low speeds or moderately fast speeds, if I go faster it obviously starts to slip.

Apparently the eevblog forum won't allow video embeds regardless of size, so sorry about the imgur link:

https://imgur.com/a/lTqAFg6

Sorry a piece of paper is not a treadmill but you can build a simple treadmill made of paper. The paper will need to be glued in a loop and then use two cylinders with axis fixed to the table.
The reason the piece of paper is not a treadmill is because the paper moves relative to the ground/table where a treadmill will not do that. It is like powering OFF a treadmill and push it under the vehicle.
The paper will not push against the generator wheels it will just slide under while on a treadmill the treadmill will push against the vehicle as it is anchored to the ground is no moving relative to the ground.
You will just need to build as basic of a treadmill as you want to see the big difference between your paper and a treadmill (can also be made out of paper).

Offline electrodacus

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We are still talking about "motor wheels" and "generator wheels"....??

Yes one of the wheel will drive the other there is no other way. If you prefer different names than generator and motor I'm OK with that.

Offline Brumby

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Nomenclature is not the problem.  It's the use of two 'sets' of wheels - it is completely invalid for the mechanism being debated.
 

Offline electrodacus

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Nomenclature is not the problem.  It's the use of two 'sets' of wheels - it is completely invalid for the mechanism being debated.

Are you saying a propeller is something other than equivalent of a wheel but for a gas or liquid ?
A wheel is more efficient than a propeller so if anything my setup with wheels only gives you an advantage.
The point of using just wheels is to have a better intuition of what happens as air is invisible to human eyes and propeller is a bit magical for some.

Offline Brumby

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But two 'sets' of wheels is not an appropriate analogue.

Excluding the propeller and it's interaction with the air is as relevant to this discussion as me saying I want to test a space suit by jumping into a pool with it.  Whatever else it might simulate, such an exercise does not reflect the real world environment.

Your wheels argument does not reflect the real world environment governing the blackbird AT ALL.

Continuing to do so simple underlines your ignorance, stubbornness and, dare I say (what is increasingly difficult to dismiss) your delusion.
 


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