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

[fourfathom]

It seems that most peoples arguments against the results of blackbird are that the wind was going faster than stated.

All I needed to see was the wind indicator telltale (like we have on sailboats).  Blackbird and other craft have ribbons or something similar and they have shown the ribbons streaming backwards for extended periods of time.  This shows, without question, that the craft is moving downwind faster than the wind. 

Yes, there is windspeed differential (slower closer to the ground) and the relatively low placement of the telltale on Blackbird isn't ideal.  But I've seen videos of similar craft with multiple wind indicators above and below the propeller radius.  These also stream backwards.

[fourfathom]

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

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

And I say you are the one misinterpreting the demonstration.  The floor is the ground and the board is the wind.

[electrodacus]

A good demo might be

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

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

I have no doubt that blackbird exceeded wind speed and it did so with sufficient margins not be be a measurement error.
If you replace air with water then it will no longer work as air is a compressible medium and that is how energy is stored and without energy storage vehicle can not exceed water speed as water is not compressible.

[electrodacus]

And I say you are the one misinterpreting the demonstration.  The floor is the ground and the board is the wind.

You say I misinterpret the demo based on what ?
The small wheels in contact with the floor are the generator wheels and they power the motor wheel witch is the large wheel that drives on the lumber at about 2.8x lower speed than floor and opposite to floor moving direction.

Only one interpretation can be correct and it the the one I mentioned.

[Labrat101]

The ribbon at the front faced backward during the test so even if the wind speed did increase wouldn't make any difference.
When the ribbon indicator move from facing forward to backward. Its going faster than tail wind speed.

[electrodacus]

I made a video about this and created a new post https://www.eevblog.com/forum/chat/veritasium-wrong-about-faster-than-wind-direct-down-wind/
I will release the video in a few days for now is just unlisted but you can watch using the link https://youtu.be/4Hol57vTIkE

[Psi]

Whenever I look at attempts to disprove that blackbird can travel continuously downwind faster than the wind. I always come back to the fact that, if a sailboat can do it then how can it suddenly become impossible on land.

Regardless of the design or implementation of blackbird, if it's possible on water, it should be possible on land. And if it is possible on land, how would it be done?

I think the core of the issue is going back to first principles. What the difference between a vehicle going from point A to point B faster than the wind on water vs on land.
Because it's accepted fact that you can do it on water without breaking any physics

[PlainName]

What the difference between a vehicle going from point A to point B faster than the wind on water vs on land.

I think the difference is that your sail boat is traveling across the wind, whereas the land vehicle is traveling with the wind. The business of the prop and everything is simply 'cheating' to get the effect of going across the wind (the prop turning) while actually traveling with a following wind. That kind of muddies things and perhaps is a distraction once you start getting into detail.

[Kleinstein]

The sailboat explaination is a bit more tricky. There is no doubt a sailboat can go faster than the wind to the side, but an not a 100% sure this is also true for the component with the wind. It may work, but is way more tricky with the aerodynamics than the vehincle on land.
I can absolutely understand that one would have trouble with the explaination base on the sail going around the shaft. I think this is even wrong.

However the case with driving the prop from the wheels is relatively easy - just get the difference between forces and power. This way one can avoid al the complication from aerodynamics and wing profiles.

[Psi]

The sail boat travels alternating between an + and - angle to the wind.
Is it farfetched to think of this change in direction happening faster and faster until it appears to travel in a straight line? Assuming you had a sailboat that could change direction instantly with no speed penalty in doing so.

[PlainName]

Edit: Sorry - removed a post after considering I might be being sucked into something I know little about.

[electrodacus]

Whenever I look at attempts to disprove that blackbird can travel continuously downwind faster than the wind. I always come back to the fact that, if a sailboat can do it then how can it suddenly become impossible on land.

Regardless of the design or implementation of blackbird, if it's possible on water, it should be possible on land. And if it is possible on land, how would it be done?

I think the core of the issue is going back to first principles. What the difference between a vehicle going from point A to point B faster than the wind on water vs on land.
Because it's accepted fact that you can do it on water without breaking any physics

If a boat can do this it is done the same way with using energy storage. sailing at an angle and not directly down wind allows you to increase the speed above wind speed and if friction losses are small enough like zero in case of ideal vehicle then you can maintain that speed even after you stop zigzagging.
Blackbird drives directly down wind and that means it can not increase speed above wind speed same way as no sail vehicle land or water can exceed wind speed directly downwind.
When vehicle speed equal wind speed there is zero wind power available and the only way to exceed that speed while only moving directly down wind is by storing energy before that point and using that stored energy to do so.  Same is valid for directly upwind tho there it works fairly different still impossible without energy storage.

You can not do this on water or on land (directly down wind no direction change) without energy storage.
I do not claim that blackbird can not exceed wind speed significantly because it can but is only for a limited amount of time (as long as the stored energy will last).
This is an electronics forum so if you know how an inductor works then propeller is a very good analogy since inductor is also an energy storage device storing the energy in the magnetic field around same as propeller stores energy in pressure differential that it creates.


To be clear my claim is not that blackbird is not exceeding wind speed (that was demonstrated clearly in many forms) the claim I make is that energy storage is used to do so meaning that it can maintain above wind speed only for a limited amount of time maybe a few minutes depending on design and how low are the friction losses.   

[electrodacus]

I can absolutely understand that one would have trouble with the explaination base on the sail going around the shaft. I think this is even wrong.

Yes that explanation is very wrong as the propeller is connected to vehicle and moves at the same speed so once at wind speed or above the propeller can not see any force from the wind.

However the case with driving the prop from the wheels is relatively easy - just get the difference between forces and power. This way one can avoid al the complication from aerodynamics and wing profiles.

The thing is that power out (propeller) can not be higher than power in (wheels).
Above wind speed that power in (wheels) is provided by the vehicle kinetic energy so is like braking the speed will be reduced if propeller is not able to put all that power back. So ideal case where propeller is 100% ideal and there is no friction this vehicle will not be able to accelerate when above wind speed at best (ideal case) just maintain the speed.  The stored energy in pressure differential is what actually accelerates the blackbird when above wind speed and so that means when that is used up it will slow down below wind speed.
Propeller is nothing more than the wheel equivalent for traveling trough a medium as opposed to traveling on the surface of a medium for regular wheel.
What helps in this case store energy is the fact that air is a compressible fluid.
That is why you can not demonstrate this faster than wind direct down wind with wheels only on solid non elastic surfaces.

All the wheels only demonstrations including the one in Derek's video are the equivalent of directly upwind and presented wrongly as directly downwind since people confuse the input with the output.
I demonstrated fairly well (I think) in my video that a direct upwind vehicle still uses energy storage but is very different not needing air but energy storage device is part of the vehicle mechanism as in my example the belt was the energy storage device and that is charged and discharged multiple times per second. So any of those devices will show the same jerky movement due to multiple charge discharge cycles and with a high speed camera this is super obvious.  Without energy storage and stick slip hysteresis none of those vehicles will be able to move upwind as they are locked gearboxes.   

[Kleinstein]

When vehicle speed equal wind speed there is zero wind power available and the only way to exceed that speed while only moving directly down wind is by storing energy before that point and using that stored energy to do so.

We are running in circles here. The video showed that it works (2 experiments) and give an explaination how, it just is not so easy to understand, and thus the title.
The point is, that there is power from the wind available, even when moving with the wind at exactly the speed of the wind or somewhat faster. This does not work with a passive sail, but it does work with the fan.

The energy storage idea to explain the experiment is just not working: both the large vehicle driving outside and the small one on the treadmill have quite some friction. There is nowhere enough stored energy to drive the vehicle for the time they where going faster that the wind or against the treadmill. The kinetic energy does not count here as it is not available to accelerate or keep the speed.

[electrodacus]

Edit: Sorry - removed a post after considering I might be being sucked into something I know little about.

This is just made up to look complicated because people have little experience with propellers and air (compressible fluids).
To make this work with math they just modified a formula. They used vehicle speed minus wind speed instead of the other way around and only looked at the case when vehicle is above wind speed. If they have tried to use that wrong modified formula below wind speed they will have realized they have a problem.
By considering the energy storage problem is super simple but air is invisible and propeller is a bit magic (it is not).


An ideal sail vehicle is 100% efficient meaning all available wind power can be converted immediately to kinetic energy and everybody agrees it can not exceed wind speed directly down wind and can also not travel at any speed directly upwind.
To claim that without energy storage you can travel directly upwind or directly down wind at faster then wind speed is silly.

Analogy in electronics will be a linear converter than can either get a higher voltage or current than the input source. You need an energy storage device either an inductor or capacitor to do that or both but can not be done with just resistor dividers.   

[electrodacus]

When vehicle speed equal wind speed there is zero wind power available and the only way to exceed that speed while only moving directly down wind is by storing energy before that point and using that stored energy to do so.

We are running in circles here. The video showed that it works (2 experiments) and give an explaination how, it just is not so easy to understand, and thus the title.
The point is, that there is power from the wind available, even when moving with the wind at exactly the speed of the wind or somewhat faster. This does not work with a passive sail, but it does work with the fan.

The energy storage idea to explain the experiment is just not working: both the large vehicle driving outside and the small one on the treadmill have quite some friction. There is nowhere enough stored energy to drive the vehicle for the time they where going faster that the wind or against the treadmill. The kinetic energy does not count here as it is not available to accelerate or keep the speed.

The power that is available and accelerates the vehicles both blackbird and the treadmill model is the stored one in pressure differential.
If you where to replace air (compressible fluid) with say water (non compressible fluid) the it will no longer work (Imagine a blackbird type vehicle at the bottom of a river trying to drive faster than the river flow speed directly downstream).

You underestimate the amount of energy that can be stored in the pressure differential and also how much energy is needed for those tests.
For example blackbird is basically a tricycle super low friction and it has a 5.3m diameter propeller that has a swept area of around 20m^2
Total energy needed to do that record of 2.8x wind speed they did require less than 6Wh of energy so less than half the energy in a modern smartphone.

[PlainName]

... and everybody agrees it can not exceed wind speed directly down wind and can also not travel at any speed directly upwind.

Yes, but we can't agree why. There is plenty of energy available from the wind, it's just that we can't reap it because there is no relative movement between the vehicle and the wind. It's not like the faster the vehicle goes the more energy it needs to overcome air friction, because there is less of that when we travel with the wind.

The problem can thus be reduced to merely finding some means of making the wind move relative to us, and that's what the prop does.

[electrodacus]

... and everybody agrees it can not exceed wind speed directly down wind and can also not travel at any speed directly upwind.

Yes, but we can't agree why. There is plenty of energy available from the wind, it's just that we can't reap it because there is no relative movement between the vehicle and the wind. It's not like the faster the vehicle goes the more energy it needs to overcome air friction, because there is less of that when we travel with the wind.

The problem can thus be reduced to merely finding some means of making the wind move relative to us, and that's what the prop does.

That is simple. Is not about the available energy is about available power to vehicle.

Here is the formula for wind power

0.5 * air density * area * (w-v)^3

air density is usually around 1.2kg/m^3
area is the sail area or equivalent (the area facing the wind direction) so direct down wind this is also a constant for a sail
and then is that w (wind speed) minus v (vehicle speed) so there there is max power when vehicle just starts moving super low vehicle speed and decreases significantly as vehicle approaches wind speed and equal with zero when at wind speed.

You can stay as long as you want below wind speed and have as much energy as you want but unless you have a way to store that energy you can not exceed wind speed as wind power is zero when vehicle speed is equal with wind speed (ideal case).

Derek to justify blackbird just subtracted the wind speed from vehicle speed instead of the other way around. So he just modified the formula to fit with his theory on how the vehicle works.

[PlainName]

You can stay as long as you want below wind speed and have as much energy as you want

Well, this is it, isn't it? It's not the vehicle that is extracting the energy from the wind, and is therefore dependent on relative wind speed, but the prop. Apply your formula to the prop instead of the vehicle and things are a bit different, no?

Of course, the vehicle is being pushed by the wind, but when it is at wind speed everything is balanced - there is enough push to keep it moving but nothing extra to let it go faster. But the prop is not moving at wind speed and can therefore extract power from the wind. Add that to the balance and not the vehicle can go faster.

[fourfathom]

And the idea that energy storage is necessary (the underpinning of the electrodacus theory) is just plain wrong.  Yes, air is compressible, but there is no storage in the system that is adequate to accelerate the craft beyond windspeed for more than a very brief period.  The various craft have demonstrated an ability to move well beyond windspeed, effectively continuously, no energy storage required.

And I still claim that that demonstration with the wheeled fixture, rolling on the floor, with the board above it being pushed, is a good analogy.  The floor represents the ground, the board represents the wind, and the large coupled wheel represent the propeller.  The fixture moves "downwind" faster than the "wind".  electrodacus disagrees.  But regardless, the "energy storage" notion is wrong, and this nullifies the electrodacus theory.

[electrodacus]

You can stay as long as you want below wind speed and have as much energy as you want

Well, this is it, isn't it? It's not the vehicle that is extracting the energy from the wind, and is therefore dependent on relative wind speed, but the prop. Apply your formula to the prop instead of the vehicle and things are a bit different, no?

Of course, the vehicle is being pushed by the wind, but when it is at wind speed everything is balanced - there is enough push to keep it moving but nothing extra to let it go faster. But the prop is not moving at wind speed and can therefore extract power from the wind. Add that to the balance and not the vehicle can go faster.

You are getting very close.
The energy from wind used by vehicle is split in multiple ways.
For a real vehicle you have
-the losses trough friction those end up as heat so not useful.
-the energy put in accelerating the mass of the vehicle so kinetic energy proportional with vehicle speed relative to ground.
-the energy that is taken form wheels (less available for acceleration) and put in to propeller (wheel for traveling trough air). This energy results in increase pressure differential as the air is a compressible fluid.
Then when you are at wind speed you have all this pressure differential that you stored when you had wind power available and now you can use that stored pressure differential (potential energy) to accelerate the vehicle (increase kinetic energy).  But since this is a finite resource vehicle will at some point reach the top speed maybe 2x wind speed then it will start to slow down.

At minute 10:30 in the video I show the calculator I made based on this description I just made ans showed how vehicle can exceed wind speed https://youtu.be/4Hol57vTIkE?t=631
     

[electrodacus]

And the idea that energy storage is necessary (the underpinning of the electrodacus theory) is just plain wrong.  Yes, air is compressible, but there is no storage in the system that is adequate to accelerate the craft beyond windspeed for more than a very brief period.  The various craft have demonstrated an ability to move well beyond windspeed, effectively continuously, no energy storage required.

And I still claim that that demonstration with the wheeled fixture, rolling on the floor, with the board above it being pushed, is a good analogy.  The floor represents the ground, the board represents the wind, and the large coupled wheel represent the propeller.  The fixture moves "downwind" faster than the "wind".  electrodacus disagrees.  But regardless, the "energy storage" notion is wrong, and this nullifies the electrodacus theory.

What craft has demonstrated direct down wind faster than wind continuously ?
The wheel analogy represents a direct upwind and it also uses energy storage but in a very different way and it is not pressure differential.
Mathematical proof was done wrong as Derek modified the formula to fit his theory.

Try use his equation in my example and see what you get especially in case A.

[Labrat101]

Wind is powering the propeller not the wheels .
The wind tread mill is not correct .
Sorry you can't emerlate wind with a tread mill

[fourfathom]

What craft has demonstrated direct down wind faster than wind continuously ?
The wheel analogy represents a direct upwind and it also uses energy storage but in a very different way and it is not pressure differential.

You and I have seen videos of craft accelerating or traveling steadily FTTWDW for many seconds, or even minutes, with the telltales streaming backwards.  I claim that there is no energy storage mechanism in play.  Unenclosed air-pressure differences will not store energy for more than a moment.

I also claim that the wheeled demonstration is a direct downwind analogy.  And what is the "different way" of using energy storage in that demonstration?  Please explain it in words.

I also claim that the video tests of propeller/wheel vehicles running on treadmills demonstrate the principle, harnessing the difference between groundspeed and airspeed.  The treadmill is level, or even uphill, and the vehicle does not roll up-treadmill when the treadmill is stopped.  Again, no energy storage at work.

You have latched onto this "energy storage" idea, even though there is no appreciable energy storage, and none is required, in the examples I mention.

[IanB]

Here is the formula for wind power

0.5 * air density * area * (w-v)^3

air density is usually around 1.2kg/m^3
area is the sail area or equivalent (the area facing the wind direction) so direct down wind this is also a constant for a sail
and then is that w (wind speed) minus v (vehicle speed) so there there is max power when vehicle just starts moving super low vehicle speed and decreases significantly as vehicle approaches wind speed and equal with zero when at wind speed.

This formula is quite wrong. It is not w (wind speed) minus v (vehicle speed), it is w (wind speed) - g (ground speed), where g is usually zero (unless on a treadmill).

This means the available power from the wind does not depend on the speed of the vehicle, and so it does not matter if the vehicle is travelling at the speed of the wind or faster than it. As long as the vehicle has contact with the ground (wheels with friction), and contact with the air (some kind of sail, fan or propeller), then the vehicle can extract power from the wind/ground system and can go faster then either.

Wheel friction is important here. If the vehicle was skating on ice, then it couldn't go faster than the wind speed, since it would have no grip on the surface between it.

Similarly, it is easy to make a wheeled vehicle run directly into a headwind, and any number of experiments can be built to demonstrate this.