Author Topic: Mess with your minds: A wind powered craft going faster than a tail wind speed.  (Read 147286 times)

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Offline electrodacus

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So, if you are moving at 60 km/h in still air, the speed is 60 km/h, and the drag force corresponds to a wind velocity of 60 km/h.

On the other hand, if you are moving at 10 km/h against a 50 km/h headwind, the speed is 10 km/h, and the drag force corresponds to an apparent wind velocity of 10 + 50 = 60 km/h (same).

The drag force is the same in both cases, but in the second case the speed is 1/6 of the first case, so the power required is also 1/6.

You are almost there.  The power a vehicle needs to overcome drag is the same for 60km/h vehicle and 10km/h vehicle with 50km/h wind.
Thus you need to calculate using power then if you want to convert to force needed. You can not calculate using force directly unless you want to get super complicated.

Do you agree that a vehicle consumption (can be an electric bicycle) if we ignore the small friction and roiling resistance is mostly about drag and drag power will be the exact same for 60km/h bicycle with no wind or 10km/h bicycle with 50km/h headwind.
If you agree that power will need to be the same in both cases the force will be fairly different but not in the direction you are thinking about.

Once this is settled and understood I think it will be very important in understanding why Blackbird can not work without energy storage.

Offline electrodacus

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Full disclosure, I skipped quite a few pages of this discussion, for obvious reasons.
In any case, how I interpret the downwind faster than wind is just as a simple lever. The wind has arbitrarily large amount of energy (size of the propeller is not specified), it's just a matter of devising a mechanism to push against the huge energy source that is the wind.
A simple demonstration is a yo-yo (yes, the spiny toy on a string).
  (Attachment Link)

Put the yo-yo on the table with the string coming from the underside of the bobbin part and pull. The yo-yo will catch up with you.
If you don't have a yo-yo at hand, substitute with a spool of solder wire.

Can you not see that direction of travel is the same as pulling direction ?  This has nothing to do with either direct down wind when above wind speed or direct upwind version of Blackbird.
Also all those yo-yo games are based on energy storage.

Online Kleinstein

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Full disclosure, I skipped quite a few pages of this discussion, for obvious reasons.
In any case, how I interpret the downwind faster than wind is just as a simple lever. The wind has arbitrarily large amount of energy (size of the propeller is not specified), it's just a matter of devising a mechanism to push against the huge energy source that is the wind.
A simple demonstration is a yo-yo (yes, the spiny toy on a string).
  (Attachment Link)

Put the yo-yo on the table with the string coming from the underside of the bobbin part and pull. The yo-yo will catch up with you.
If you don't have a yo-yo at hand, substitute with a spool of solder wire.

Can you not see that direction of travel is the same as pulling direction ?  This has nothing to do with either direct down wind when above wind speed or direct upwind version of Blackbird.
Also all those yo-yo games are based on energy storage.

The yo-yo toy is based on stored energy, but here it is only about the same toy, used in a  different way.

The yo-yo is moving in the same direction as the string is pulled, but faster than the string is pulled.
This is just like blackbird going the direchtion of the wind, and faster than the wind.


 

Offline electrodacus

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The yo-yo toy is based on stored energy, but here it is only about the same toy, used in a  different way.

The yo-yo is moving in the same direction as the string is pulled, but faster than the string is pulled.
This is just like blackbird going the direchtion of the wind, and faster than the wind.

The thing you seems to ignore is that vehicle being faster than wind in same direction can not be pushed by the wind.
There is no such problem in the yo-yo example.

Offline IanB

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The thing you seems to ignore is that vehicle being faster than wind in same direction can not be pushed by the wind.
There is no such problem in the yo-yo example.

The yo-yo going faster than the string in the same direction as the string cannot be pulled by the string?
« Last Edit: December 23, 2021, 11:14:13 pm by IanB »
 

Offline fourfathom

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The thing you seems to ignore is that vehicle being faster than wind in same direction can not be pushed by the wind.
There is no such problem in the yo-yo example.

The yo-yo going faster than the string in the same direction as the string cannot be pulled by the string.

Yesterday I tried that yo-yo experiment, using a spool of rope (I have spools of rope I use on my boat).  I wanted to check that the difference in circumference between the spool and the level of the rope gave the same result as the "geared wheels on two conveyor belt".  It was as close as I could measure.  I would have been astounded if the result were otherwise, but since this whole subject can be non-intuitive I figured it was a test worth doing.  I could shoot a video, but that's already been done.
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Offline IanB

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Yesterday I tried that yo-yo experiment, using a spool of rope (I have spools of rope I use on my boat).  I wanted to check that the difference in circumference between the spool and the level of the rope gave the same result as the "geared wheels on two conveyor belt".  It was as close as I could measure.  I would have been astounded if the result were otherwise, but since this whole subject can be non-intuitive I figured it was a test worth doing.  I could shoot a video, but that's already been done.

No, no, no, you don't understand. If the string is being pulled along at, say, 1 cm/s, then the yo-yo cannot go faster than 1 cm/s in the same direction, because then it would be going faster than the string that is pulling it, and it could no longer receive any energy from the string   ;)

Don't you see how obvious this is?
 

Online bdunham7

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If the string is being pulled along at, say, 1 cm/s, then the yo-yo cannot go faster than 1 cm/s in the same direction, because then it would be going faster than the string that is pulling it, and it could no longer receive any energy from the string   ;)

Don't you see how obvious this is?

You obviously don't understand quantum stick-slip hysteresis in tensioned fiber traction systems.  But of course, the yo-yo can't go faster than the string indefinitely, only for short period of time.  Or string.
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Offline Brumby

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I draw attention to my earlier question:

Quote
Blackbird propeller swept area is a massive 20m^2 and all the energy Blackbird needs to get to that record 28mph speed is just around 6Wh easily stored with not much pressure on such a massive swept area.
Are you saying that energy is stored across the entire swept area of the propeller?
 

Offline electrodacus

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No, no, no, you don't understand. If the string is being pulled along at, say, 1 cm/s, then the yo-yo cannot go faster than 1 cm/s in the same direction, because then it would be going faster than the string that is pulling it, and it could no longer receive any energy from the string   ;)

Don't you see how obvious this is?

Funny you get this but do not get that wind can not push a vehicle when vehicle travels faster than the wind in same direction.

Offline electrodacus

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I draw attention to my earlier question:
Quote
Are you saying that energy is stored across the entire swept area of the propeller?

Yes the entire swept area of the propeller acts as a barrier keeping the low and high pressure volumes separate.

Offline Alex Eisenhut

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The yo-yo toy is based on stored energy, but here it is only about the same toy, used in a  different way.

The yo-yo is moving in the same direction as the string is pulled, but faster than the string is pulled.
This is just like blackbird going the direchtion of the wind, and faster than the wind.

The thing you seems to ignore is that vehicle being faster than wind in same direction can not be pushed by the wind.


Good thing the propeller is creating its own wind going the other way, therefore adding to the total speed.

The Earth's wind is pushing against the propeller wind, which are both pushing against the propeller.
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Offline electrodacus

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Good thing the propeller is creating its own wind going the other way, therefore adding to the total speed.

The Earth's wind is pushing against the propeller wind, which are both pushing against the propeller.

Propeller is powered by what ?
This is a wind powered only vehicle. No wind power then no power. Unless you can accept that there is energy stored in pressure differential that pushes the vehicle even when above wind speed. Of course as any stored energy it will be finite thus vehicle will slow down below wind speed after that is used up.

Offline Alex Eisenhut

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Good thing the propeller is creating its own wind going the other way, therefore adding to the total speed.

The Earth's wind is pushing against the propeller wind, which are both pushing against the propeller.

Propeller is powered by what ?
This is a wind powered only vehicle. No wind power then no power. Unless you can accept that there is energy stored in pressure differential that pushes the vehicle even when above wind speed. Of course as any stored energy it will be finite thus vehicle will slow down below wind speed after that is used up.

By stored energy, ie the kinetic energy of the moving vehicle as it moves up to wind speed. It never experiences a relative zero wind speed as it approaches wind speed, as the propeller is always blowing backwards. It will reach some sort of equilibrium state but wind is not that steady.

The kinetic energy of the vehicle is being drained by the propeller contraption, luckily, the wind keeps blowing, much like this thread.

Here's the main question; you surely consider yourself deeply scientific: so, for a theory to be scientific it must be falsifiable. What evidence would you accept to show your theory is false?

https://en.wikipedia.org/wiki/Falsifiability
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Online thm_w

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Yes that bicycle calculator is incorrect (you are not the only one to get this wrong so that includes those people that did the calculator)
That calculator will say you can drive at 1km/h in 230km/h headwind with just 300W (easy for a cyclist)
This is maybe 80km/h no where near 230km/h and here is what happens
youtube.com/watch?v=IoX-JUPvrwo

That is not "maybe 80km/h", it says in the article "over 100km/h". How would you possibly stay upright?
and how would you stay upright traveling at 1km/h?
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Offline electrodacus

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By stored energy, ie the kinetic energy of the moving vehicle as it moves up to wind speed. It never experiences a relative zero wind speed as it approaches wind speed, as the propeller is always blowing backwards. It will reach some sort of equilibrium state but wind is not that steady.

The kinetic energy of the vehicle is being drained by the propeller contraption, luckily, the wind keeps blowing, much like this thread.

Here's the main question; you surely consider yourself deeply scientific: so, for a theory to be scientific it must be falsifiable. What evidence would you accept to show your theory is false?

https://en.wikipedia.org/wiki/Falsifiability

Blackbird continues to accelerate after it exceeds wind speed meaning kinetic energy of the vehicle continues to increase thus it can not be the one powering the vehicle at that stage.

It is quite easy. Show that vehicle acceleration rate continues to increase instead of decreasing or show that vehicle can maintain speed after there no longer is any acceleration.
It is super clear that acceleration rate drops it can be easily measured and is observed on both the large blackbird and the treadmill model.
Since that drops it will get to zero acceleration that will be the point where I say the vehicle will start to slow down while you claim it will continue to stay at that speed.

But all the theoretical analysis like Derek's (vehicle speed - wind speed) will predict increased rate of acceleration and that is just never observed or measured in any real test.
So there is not even the need for any other test than the ones already performed to show that the equations Derek and others claim to express how this vehicle works are not matching reality.

Offline electrodacus

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Yes that bicycle calculator is incorrect (you are not the only one to get this wrong so that includes those people that did the calculator)
That calculator will say you can drive at 1km/h in 230km/h headwind with just 300W (easy for a cyclist)
This is maybe 80km/h no where near 230km/h and here is what happens
youtube.com/watch?v=IoX-JUPvrwo

That is not "maybe 80km/h", it says in the article "over 100km/h". How would you possibly stay upright?
and how would you stay upright traveling at 1km/h?

What you see in the video is about 80km/h at most. The article probably mentioned peak gust speed as they like to exaggerate as much as possible. I live in a windy area and we get fairly frequent 60km/h with 80km/h gusts and the max I ever seen here was 110km/h gusts.

But irrelevant of the speed 80 or 100km/h the bicycle calculator claims 300W is just enough power to drive at 1km/h in 230km/h winds and that is order of magnitude higher power than needed for even 100km/h.
Each 2x increase in wind speed increases the wind power by 8x

Offline fourfathom

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But all the theoretical analysis like Derek's (vehicle speed - wind speed) will predict increased rate of acceleration and that is just never observed or measured in any real test.
So there is not even the need for any other test than the ones already performed to show that the equations Derek and others claim to express how this vehicle works are not matching reality.

The geared-wheel and the pulled-yo-yo models don't predict continuous acceleration.  They show downwind travel at some fixed multiple of windspeed.  Once they accelerate to that speed they will remain at that speed.
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Offline electrodacus

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The geared-wheel and the pulled-yo-yo models don't predict continuous acceleration.  They show downwind travel at some fixed multiple of windspeed.  Once they accelerate to that speed they will remain at that speed.

Again (I repeated this many times) but none of the wheels only vehicles can demonstrate direct down wind only direct upwind equivalent. You are just confusing the input of the vehicle with the output.
On Blackbird direct downwind the input is the wind + pressure differential pushing the vehicle up to wind speed then above that is just the pressure differential that pushes the vehicle.
On direct upwind the wind is always powering the vehicle but vehicle works in short charge discharge cycles not continues and that is exactly how all wheels only toys work (all of them) as there is no pressure differential since air (compressible fluid) is not involved there.

Offline fourfathom

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Again (I repeated this many times) [...]

There are none so blind as those who will not see.
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Offline electrodacus

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There are none so blind as those who will not see.

I showed you where to look and you do not want to look.
Check any video or speed graph on Blackbird and see how acceleration rate drops consistent with reduced available power both when below and when above wind speed consistent with a finite stored energy source.
If you calculate for a few points using Derek's equation the one containing vehicle speed - wind speed you get an ever increase in acceleration rate not observed in any real test.

Offline PlainName

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I think the big problem for electrodacus is that at wind speed (and faster) there seems to be no relative wind to power anything. The only way to go faster than what's pushing is via some stored energy, ergo there must be some stored energy somewhere. Where? The only possible place, given that the prop is quite important, is the prop wash.

Which seems reasonable if you haven't seen this thing work, and all the explanations so far seem to run up against the problem that at wind speed there is no push (or even pull), so there is no obvious way this could be working.

So... how about an alternative explanation without the maths that no-one can agree on...

ISTM the most important thing to bear in mind is the prop is rotating and pushing air back. For a given rotational speed, the air will flow backwards at some derived speed - the faster the prop goes the faster the air flows back. You could use this to push the vehicle at a given speed by altering the speed of the prop, so we could say that the prop turning at xrpm is equivalent to airflow of ym/s. It works in reverse, of course - push the vehicle and the airflow will cause the prop to turn proportionally to the vehicle speed through the air.

So, back to wind speed and no push. But there is a push - the prop wash is effectively a wall (albeit quite flimsy!) moving at a negative speed relative to the vehicle and tied to the vehicle. If the vehicle is moving at wind speed, the prop wash is moving backwards at some speed relative to the vehicle and thus the wind. The wind can push against the prop wash to continue pushing the vehicle a little faster. In effect, the prop wash is an infinite length of the string we see with that yo-yo.

By what powers the  prop? It is still the wind because it is able to be pushing the vehicle still. With the prop wash moving backwards and effectively part of the vehicle, the vehicle is not at maximum speed relative to the wind, so the wind can keep pushing it.
 

Online Kleinstein

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There where several expalinations given how the Backbrid vehicle can work. It is just that electrodacus repeatedly ignored them or claimed they must be wrong because they contradict his preconception.  The contradiction to his claim however is not a valid agument against the calculation. It more shows that his preconception is wrong, as there is no error in the calculation.

There should be no problem with math, as the only math part is simple multiply and additions. The problem is getting electrodacus to accept (or understand) the basics of mechanic, like the formula  for mechanic power and the balance of forces.  The whole energy storrage and aero dynamics part is more like confusiion tactics only - they are not part of the proof. There were attemps to show up the flaws in his formula / conception of wind power - but somehow the perception of walking against the wind seems to be different. At least to most reader is should be clear the the (w-v) ³ formula is nonsense.
 

Offline Brumby

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I draw attention to my earlier question:
Quote
Are you saying that energy is stored across the entire swept area of the propeller?

Yes the entire swept area of the propeller acts as a barrier keeping the low and high pressure volumes separate.

How does that work?  (I think this needs a diagram.)
 

Online BrianHGTopic starter

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I draw attention to my earlier question:
Quote
Are you saying that energy is stored across the entire swept area of the propeller?

Yes the entire swept area of the propeller acts as a barrier keeping the low and high pressure volumes separate.

How does that work?  (I think this needs a diagram.)
What if the propeller is spinning slower than the moving air it is cutting into?
What if it is stationary?
 


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