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

[electrodacus]

The vehicle won't accelerate faster than pushed speed when there is no wind, because there is no wind! It won't accelerate at all, it will slow down and stop.

So we can do this experiment of pushing the vehicle when there is no wind, and the vehicle will coast to a standstill. And we will not be surprised, because this is the expected outcome. There is nothing for us to be convinced about, because we are already convinced about this.

It will accelerate faster because you create a pressure differential when pushing the vehicle. The wheel drives the propeller so while there is no wind there will be a high pressure (high air density) behind the propeller and low air density in front and this pressure differential is a form of energy storage so when you let go after pushing it to sufficient speed  (sufficient speed means this pressure differential power on vehicle needs to be higher than vehicle friction) the vehicle will continue to accelerate.
This stored energy is also the reason why the vehicle can exceed wind speed when pushed by the wind.

[electrodacus]

This is the whole point we've been trying to hammer into your head for the past umpteen posts.  You are completely ignoring the basic principle of force multiplication.  Your so-called knowledge of physics doesn't even encompass the basic principles of Archimedes, let alone Newton.  A less-powerful motor can easily overcome a more powerful one with force multiplication via a gearset or some other mechanism.  This is how the propeller-powered vehicle can move upwind, which you your self seem to have acknowledged as a workable concept.  Similarly whatever force is applied to get your G wheel to generate power, that can be overcome with an arbitrarily lesser-powered motor given sufficient gear reduction.  The initial case I'm trying to get you to consider just starts with zero speed and thus zero power.  But you deflect this point with the objection that if we keep it from turning it then is not a wheel.  Really?  And so what?  And even if you persist with that, then instead let motor M be a very small, low-powered motor with a very high gear reduction ratio.  Each force will push the car in opposite directions, but the one with greater force will win, period.

What you are thinking about is a tractor with low power motor pulling a vehicle with higher power motor but the reason that happen's is very different.
The tractor will have better traction either because of weight or amount of surface contact with the ground or a combination of both so the lower traction vehicle will be dragged no mater how powerful the motor is or what gear ratio he is using since he just has lower traction so it can not use the available power.
Now in my example things are very different because one wheel power the other one so no matter witch one has better traction power at the motor will be lower so vehicle will be dragged down by the treadmill meaning moved from right to left.     

[bdunham7]

What you are thinking about is a tractor with low power motor pulling a vehicle with higher power motor but the reason that happen's is very different.
The tractor will have better traction either because of weight or amount of surface contact with the ground or a combination of both so the lower traction vehicle will be dragged no mater how powerful the motor is or what gear ratio he is using since he just has lower traction so it can not use the available power.   

No, I'm not thinking of a situation where one vehicle loses traction.  Suppose you have two very heavy vehicles that are otherwise identical except one of them has a small motor with great deal of gear reduction and the second a more powerful motor without gear reduction.  In fact, just to make calculations easy, lets make the second one have a motor that consists of 4 of the small motors in the first vehicle all connected axially so that they function identically except that in combination they have 4 times the power and torque.  OTOH, the first vehicle will have 8:1 mechanical gearing, the second will be 1:1.  Further assume that neither vehicle's motor is powerful enough to make the wheels slip.  Which one wins?

[Kleinstein]

Without wind, pushing the vehicle to design speed is easy, as the design speed is something like 1.2 times the wind speed and without wind this is zero  .   Startuing a zero speed and no wind is pretty boring. But maybe this experiment is enough convince electrodacus.

For the model system with constant velocities one is free to choose a suitable identification of the refrence frames. The gear ratios work in all cases and it does not depend which system you choose as ground and which system is moving. This is the whole idea behind using the treadmill and similar analog model.

@electrodacus:  If you have problems with math / equations, please do a simple hand on experiment:
Have an axle with 2 wheels at the ends and a string wound up around the axle. This could be something like a relatively empty spool of thread, or just use 2 round pieces of cardboard (for the wheels) and a pencil.  The string kind of represents the wind  - this time pullung, because we are not good at pushing the string.
Than pull horizontal on the string and watch it move. The interresting case is with the string at the underside of the axle.   
 It is not as mind-blowing as the experiment with the prop driven car, but enough to surprize.

[IanB]

It will accelerate faster because you create a pressure differential when pushing the vehicle. The wheel drives the propeller so while there is no wind there will be a high pressure (high air density) behind the propeller and low air density in front and this pressure differential is a form of energy storage so when you let go after pushing it to sufficient speed  (sufficient speed means this pressure differential power on vehicle needs to be higher than vehicle friction) the vehicle will continue to accelerate.

No, this will not happen the way you think. Storing energy in compressed gas (air) only works in enclosed vessels like gas cylinders. The space behind the propeller is not a closed space, it is open to the surroundings, so it is not possible to store any compression energy there.

[electrodacus]

No, I'm not thinking of a situation where one vehicle loses traction.  Suppose you have two very heavy vehicles that are otherwise identical except one of them has a small motor with great deal of gear reduction and the second a more powerful motor without gear reduction.  In fact, just to make calculations easy, lets make the second one have a motor that consists of 4 of the small motors in the first vehicle all connected axially so that they function identically except that in combination they have 4 times the power and torque.  OTOH, the first vehicle will have 8:1 mechanical gearing, the second will be 1:1.  Further assume that neither vehicle's motor is powerful enough to make the wheels slip.  Which one wins?

If none of the vehicle can lose traction the one with 4 small motors will win fairly easy and just damage the single small motor on the other vehicle.
It is probably hard for you to think about power. You are probably thinking that since the 4 motors can not spin up fast enough they will have lower available power but you need to be careful when you say 4x higher power since that is at any moment.
You probably think that torque of the motor is constant and since one motor can spin 8x faster will provide more power and that will be true but you mentioned the 4 motors can deliver 4x the power of the single motor.
So a better way to think at this is to consider they are electric motors powered by a constant power power supply and they at any speed can use that power.
You are just thinking like the 4 motors connected together have 4x the torque but torque is limited instead of thinking that power is limited and not the torque since else if torque at motor is limited you can not provide the power you want at very low RPM

Think in this way. Say motors are 100kW each and say they are supplied with a constant power supply that limits power to each motor to 1kW only then motors that will spin say 8x slower will have 8x higher torque in order to be at same power level as the motor spinning 8x faster and will have 8x lower torque.
Else what you are thinking of is not 4x higher power.

[electrodacus]

Without wind, pushing the vehicle to design speed is easy, as the design speed is something like 1.2 times the wind speed and without wind this is zero  .   Startuing a zero speed and no wind is pretty boring. But maybe this experiment is enough convince electrodacus.

For the model system with constant velocities one is free to choose a suitable identification of the refrence frames. The gear ratios work in all cases and it does not depend which system you choose as ground and which system is moving. This is the whole idea behind using the treadmill and similar analog model.

@electrodacus:  If you have problems with math / equations, please do a simple hand on experiment:
Have an axle with 2 wheels at the ends and a string wound up around the axle. This could be something like a relatively empty spool of thread, or just use 2 round pieces of cardboard (for the wheels) and a pencil.  The string kind of represents the wind  - this time pullung, because we are not good at pushing the string.
Than pull horizontal on the string and watch it move. The interresting case is with the string at the underside of the axle.   
 It is not as mind-blowing as the experiment with the prop driven car, but enough to surprize.

Yes you think that if funny as you do not understand what I mean by design speed.
If you watched Derek's (Veritasium) video where they tested the treadmill propeller vehicle. They needed a treadmill that can work at 10mph as vehicle was not working below that speed.
The thing is that power available from stored energy was to small to cover the vehicle friction losses and that is what I mean by designed speed.
Those vehicle need a minimum wind speed to be able to accelerate above wind speed so when pushing you need to push to at least that minimum speed in order to see the effect of accelerating past that speed.

You can select your reference frame as you want but you also need to consider the consequences of that change when you interpret the results else you will come to different conclusions for each reference frame and that will be incorrect. You need to get the exact same result no matter the reference frame and if you get a different result then you applied the reference change incorrectly.

You need to understand that wind can power the vehicle as you mention as long as wind speed is below vehicle speed and as soon as that is not the case zero power will be available from the wind (and yes we are just talking about the special case where wind direction is the exact same as vehicle direction).  For any other wind direction wind can still power the vehicle no matter how fast the vehicle is moving. This was a well known fact but unfortunately someone decided to build a useless vehicle and confuse a lot of people even smart well educated people that only know physics and do not understand it (my definition of what understanding means). 

[electrodacus]

No, this will not happen the way you think. Storing energy in compressed gas (air) only works in enclosed vessels like gas cylinders. The space behind the propeller is not a closed space, it is open to the surroundings, so it is not possible to store any compression energy there.

You can think about this as a very large gas cylinder orders of magnitude larger than what you are thinking of with also orders of magnitude lower pressure and a very large opening in the tank.
So large in fact that it only has one wall and that is the sweep area of the propeller (a disk with a 20m^2 area so as much as the floor of a large room). Air with higher pressure can not  go on the other side of the propeller and on the other side there is lower pressure tan atmospheric pressure so another small difference to a typical compressed air cylinder.
Maybe this is hard to imagine but energy can be stored there. Thus the reason I first just want to disprove that vehicle can not accelerate above wind speed without another energy source like an energy storage device then you will see that this pressure differential is what stores the energy.
There is not much energy stored there as not much is needed around half of what a modern cellphone battery contains for the large Blackbird.

[IanB]

You can think about this as a very large gas cylinder orders of magnitude larger than what you are thinking of with also orders of magnitude lower pressure and a very large opening in the tank.

You know that the pressure downstream of a propeller is actually lower than atmospheric pressure, right? The propeller does not compress the air, it creates a vacuum. You can see that demonstrated here:

https://youtu.be/f2QfVJe7yEg?t=198

[electrodacus]

You know that the pressure downstream of a propeller is actually lower than atmospheric pressure, right? The propeller does not compress the air, it creates a vacuum. You can see that demonstrated here:

https://youtu.be/f2QfVJe7yEg?t=198

another flawed conclusion drawn from a test.
So you risk being sucked in the propeller if you stand down stream of it

[bdunham7]

If none of the vehicle can lose traction the one with 4 small motors will win fairly easy and just damage the single small motor on the other vehicle.

So the gear reduction on the single motor vehicle doesn't matter?  I think this shows that we've verified at least one of your misconceptions, although I'm sure there are others.

It is probably hard for you to think about power.....what you are thinking of is not 4x higher power.

Um, no, it's not hard for me to think about power.  I think you are having enough trouble understanding what you are thinking yourself let alone imagining what I'm thinking.  I'm only using the concept of the motor having 'power' because you insist on using the term even though you clearly demonstrate that you don't actually know what it means.  In a static situation, for example where two stationary vehicles are pulling against each other from a stopped position, the relevant parameter would be torque.  I simply used the example of 4 identical motors vs 1 just so that all characteristics would be the same--power, torque, etc.  In my example 1 motor with 8:1 gearing has twice the output torque of 4 parallel motors with 1:1 gearing, thus it would be able to pull twice as hard, winning out over the 4-motor version. 

You need to start with Archimedes and the concept of the lever.  Then move on to gears. 

[Kleinstein]

You need to understand that wind can power the vehicle as you mention as long as wind speed is below vehicle speed and as soon as that is not the case zero power will be available from the wind (and yes we are just talking about the special case where wind direction is the exact same as vehicle direction).  For any other wind direction wind can still power the vehicle no matter how fast the vehicle is moving. This was a well known fact but unfortunately someone decided to build a useless vehicle and confuse a lot of people even smart well educated people that only know physics and do not understand it (my definition of what understanding means).

For a simple sail it is impossible to extract power from the wind when the vehicle is moving at the speed of the wind or faster with the wind from behind. Surprisingly this is no longer true for the vehicle with the propeller and wheels to interact with the ground. This is the slightly confusing effect the whole discussion is about.  For the discussion you can not start with the assumption that this is not possible - it is not a well known fact, but a more or less widespread misconception.

It is known that one can extract wind energy it the wind comes from a different direction. The wings of the prop move and the apparent wind is no longer coming from the front. So in principle they can extract wind power. So you see that with moving winds it is no longer clear one can not extract power. I would not explain the effect this way (the vehicle used a different principle), but it shows that a clever construction can do things a fixed sail can not do.

An ideal propeller is kind of working like a srew in a solid, though real world the efficiency is lower.
With such an ideallized prop the problem get transformes to something like 2 platforms / referenc surfaces moving relativ to each other. With a simple mechanical systen, like with wheels and pullies, it is relatively easy to understand that the difference in speed can be used to power a vehicle at any sensible speed and direction. This part may confuse a child, but is not really surprising.
It only take basic mechanics to understand. For understanding it may be easier to just calculate speeds and use the wheels, links and gears as conditions to link different movements. So all without, without looking at power or forces, just at position and coordinates.  This usually leads to linear equations that are not so hard so solve. If such a mechanical system allows a movement (solution for the equations) it would do so with only friction forces when forced to by the boundary conditions (e.g. moving plantforms).

The arguments with motor power to decide which side is stronger tricky as motor power sometimes means maximum power and real motors are more limited in torque and not actual physical power (in W). This is especially true at low speed or starting from 0.

The point how good a prop can rally work is hard to calculate - I fully understant if one does not follow the math behind the limits there - that is hard core aero dynamics and may not have closed solutions. It is sensible that a suitable size prob can have enough efficiency to get at least a speed slightly higher than the wind speed. Working with a relatively low relative speed it should be even easier for a prop to work in water.

[electrodacus]

For a simple sail it is impossible to extract power from the wind when the vehicle is moving at the speed of the wind or faster with the wind from behind. Surprisingly this is no longer true for the vehicle with the propeller and wheels to interact with the ground. This is the slightly confusing effect the whole discussion is about.  For the discussion you can not start with the assumption that this is not possible - it is not a well known fact, but a more or less widespread misconception.

It is known that one can extract wind energy it the wind comes from a different direction. The wings of the prop move and the apparent wind is no longer coming from the front. So in principle they can extract wind power. So you see that with moving winds it is no longer clear one can not extract power. I would not explain the effect this way (the vehicle used a different principle), but it shows that a clever construction can do things a fixed sail can not do.

An ideal propeller is kind of working like a srew in a solid, though real world the efficiency is lower.
With such an ideallized prop the problem get transformes to something like 2 platforms / referenc surfaces moving relativ to each other. With a simple mechanical systen, like with wheels and pullies, it is relatively easy to understand that the difference in speed can be used to power a vehicle at any sensible speed and direction. This part may confuse a child, but is not really surprising.
It only take basic mechanics to understand. For understanding it may be easier to just calculate speeds and use the wheels, links and gears as conditions to link different movements. So all without, without looking at power or forces, just at position and coordinates.  This usually leads to linear equations that are not so hard so solve. If such a mechanical system allows a movement (solution for the equations) it would do so with only friction forces when forced to by the boundary conditions (e.g. moving plantforms).

The arguments with motor power to decide which side is stronger tricky as motor power sometimes means maximum power and real motors are more limited in torque and not actual physical power (in W). This is especially true at low speed or starting from 0.

The point how good a prop can rally work is hard to calculate - I fully understant if one does not follow the math behind the limits there - that is hard core aero dynamics and may not have closed solutions. It is sensible that a suitable size prob can have enough efficiency to get at least a speed slightly higher than the wind speed. Working with a relatively low relative speed it should be even easier for a prop to work in water.

I looked at all explanations available in details but the current explanation is wrong.
Propeller can not magically have access to wind energy when wind speed is below vehicle speed and both are in the exact same direction.
A sail is the most efficient way to use wind energy and ideal case a sail that is at the same speed as the wind speed has nothing more to extract from the wind and you will call that a 100% efficient sail powered vehicle (not in real world just ideal case).
No matter what other device you use to replace the sail you will not be able to extract energy from the wind when vehicle and that device (propeller or anything else) drives above wind speed.

Think about it this way. Say you have a wind turbine on wheels and when stationary you extract the most you can from the wind (real wind turbine is just at most around 40% efficient but that is irrelevant). Now you start to move the wind turbine in the same direction as wind direction so when you get at half wind speed the wind turbine will experience just half of the wind speed so just 12.5% of the power level compared to stationery wind turbine.
When your turbine move at the same speed as wind it will experience zero wind speed so it will not be able to produce anything and above that things will not change as apparent wind will now be from the other side and if you try to access that by rotating the wind turbine 180 degree you will slow the vehicle down way more than you produce from the wind turbine.
The same applies here with a propeller used as a fan and the only difference is that pressure differential energy storage witch allows vehicle as you see in tests to exceed momentarily the wind speed may be a few minutes depending on design and amount of stored energy.


Yes a propeller works as a screw in a solid now imagine a piece of wood or butter for lower friction where a screw stile propeller will advance and below this wood the vehicle moves on the ground. As long as wood moves above ground (floating) the vehicle can be powered by this wood but as soon as vehicle speed same as wood speed there is no longer any way to power the vehicle as taking power from vehicle wheel and transferring that to the screw will result in vehicle slowing down as not all power from the wheel can be transferred to the screw.
What you are confusing is the apparent wind speed direction relative to vehicle. Below wind speed vehicle will see a positive power available above wind speed the power will be negative meaning counter productive so vehicle will be slowed down rather than accelerated.

I know the limitations of a real motor but we are talking about power here so it is assumed the motor at whatever speed is capable of that power. The same is true about a generator so you need to remember that a generator powers the motor and while this is an electrical analogy using sprockets and a chain to transfer power from one wheel to the other will be constrained by the same rules.
Yes fluid dynamics is not easy (I had done both mechanics and fluid dynamic curses at university) but you do not need to know fluid dynamics (you will usually have a computer to simulate something like this) all you need to know is that if your only power source is the generator wheel that will not be able to provide the motor with more power than the breaking power.
Breaking (generating power) will be from the vehicle kinetic energy and if that kinetic energy is not put all back the vehicle will slow down.

[CatalinaWOW]

For a simple sail it is impossible to extract power from the wind when the vehicle is moving at the speed of the wind or faster with the wind from behind. Surprisingly this is no longer true for the vehicle with the propeller and wheels to interact with the ground. This is the slightly confusing effect the whole discussion is about.  For the discussion you can not start with the assumption that this is not possible - it is not a well known fact, but a more or less widespread misconception.

It is known that one can extract wind energy it the wind comes from a different direction. The wings of the prop move and the apparent wind is no longer coming from the front. So in principle they can extract wind power. So you see that with moving winds it is no longer clear one can not extract power. I would not explain the effect this way (the vehicle used a different principle), but it shows that a clever construction can do things a fixed sail can not do.

An ideal propeller is kind of working like a srew in a solid, though real world the efficiency is lower.
With such an ideallized prop the problem get transformes to something like 2 platforms / referenc surfaces moving relativ to each other. With a simple mechanical systen, like with wheels and pullies, it is relatively easy to understand that the difference in speed can be used to power a vehicle at any sensible speed and direction. This part may confuse a child, but is not really surprising.
It only take basic mechanics to understand. For understanding it may be easier to just calculate speeds and use the wheels, links and gears as conditions to link different movements. So all without, without looking at power or forces, just at position and coordinates.  This usually leads to linear equations that are not so hard so solve. If such a mechanical system allows a movement (solution for the equations) it would do so with only friction forces when forced to by the boundary conditions (e.g. moving plantforms).

The arguments with motor power to decide which side is stronger tricky as motor power sometimes means maximum power and real motors are more limited in torque and not actual physical power (in W). This is especially true at low speed or starting from 0.

The point how good a prop can rally work is hard to calculate - I fully understant if one does not follow the math behind the limits there - that is hard core aero dynamics and may not have closed solutions. It is sensible that a suitable size prob can have enough efficiency to get at least a speed slightly higher than the wind speed. Working with a relatively low relative speed it should be even easier for a prop to work in water.

I looked at all explanations available in details but the current explanation is wrong.
Propeller can not magically have access to wind energy when wind speed is below vehicle speed and both are in the exact same direction.
A sail is the most efficient way to use wind energy and ideal case a sail that is at the same speed as the wind speed has nothing more to extract from the wind and you will call that a 100% efficient sail powered vehicle (not in real world just ideal case).
No matter what other device you use to replace the sail you will not be able to extract energy from the wind when vehicle and that device (propeller or anything else) drives above wind speed.

Think about it this way. Say you have a wind turbine on wheels and when stationary you extract the most you can from the wind (real wind turbine is just at most around 40% efficient but that is irrelevant). Now you start to move the wind turbine in the same direction as wind direction so when you get at half wind speed the wind turbine will experience just half of the wind speed so just 12.5% of the power level compared to stationery wind turbine.
When your turbine move at the same speed as wind it will experience zero wind speed so it will not be able to produce anything and above that things will not change as apparent wind will now be from the other side and if you try to access that by rotating the wind turbine 180 degree you will slow the vehicle down way more than you produce from the wind turbine.
The same applies here with a propeller used as a fan and the only difference is that pressure differential energy storage witch allows vehicle as you see in tests to exceed momentarily the wind speed may be a few minutes depending on design and amount of stored energy.


Yes a propeller works as a screw in a solid now imagine a piece of wood or butter for lower friction where a screw stile propeller will advance and below this wood the vehicle moves on the ground. As long as wood moves above ground (floating) the vehicle can be powered by this wood but as soon as vehicle speed same as wood speed there is no longer any way to power the vehicle as taking power from vehicle wheel and transferring that to the screw will result in vehicle slowing down as not all power from the wheel can be transferred to the screw.
What you are confusing is the apparent wind speed direction relative to vehicle. Below wind speed vehicle will see a positive power available above wind speed the power will be negative meaning counter productive so vehicle will be slowed down rather than accelerated.

I know the limitations of a real motor but we are talking about power here so it is assumed the motor at whatever speed is capable of that power. The same is true about a generator so you need to remember that a generator powers the motor and while this is an electrical analogy using sprockets and a chain to transfer power from one wheel to the other will be constrained by the same rules.
Yes fluid dynamics is not easy (I had done both mechanics and fluid dynamic curses at university) but you do not need to know fluid dynamics (you will usually have a computer to simulate something like this) all you need to know is that if your only power source is the generator wheel that will not be able to provide the motor with more power than the breaking power.
Breaking (generating power) will be from the vehicle kinetic energy and if that kinetic energy is not put all back the vehicle will slow down.

I won't claim to understand this well enough to make a definitive statement.  But if you look at the original video's explanation all of the reference is to the similarity to tacking.  Your argument that a sail cannot go faster than the wind is only true when the sail is going directly downwind.  Light speedy sailboats can easily have a water speed much greater than the wind speed when tacking cross wind.

I believe that the key here is that the windspeed relative to the vehicle is not the pertinent answer.  It is the wind direction in the coordinate frame of the propeller blade.  I still haven't wrapped my head around all of this to be able to explain it more simply than others, but that line of thinking gives me a way to believe it is possible, and I choose to believe that the vehicle is not a scam, with hidden batteries and electric motors.  With that assumption facts speak louder than any theory.   Just like conventional aerodynamics had no explanation for how bees could fly for decades.  Nevertheless they did and do.  And finally in the 1980s as I recall it was finally figured out how it worked.

I have recommended and will recommend again a book written by Arthur C. Clarke, "Profiles of the Future".  The book attempts to identify traps in predicting the future, methods for predicting it, and attempts to define the real limits on what is possible.  In chapter one of the book he describes what he calls failure of nerve and gives numerous examples of highly trained people proving something was impractical or even impossible.  Using well established facts and theorems and impeccable math.  But applied in ways that turned out to be incorrect.  Some of the examples:  proof that heavier than air flight was impossible, then once that had happened, proof that airplanes could never carry multiple passengers or travel hundreds of miles per hour, proof that no man-made object could be sent to the moon and proof that electric lighting would never work for private houses.  He calls it failure of nerve because in several cases the individuals providing these proofs had access to descriptions of how the problems they were analyzing could be avoided, but just couldn't bring themselves to believe that they really worked because they contradicted their sense of how the world worked.  While the book was written in 1961-1962 it has stood the test of time well.  It is well worth finding and reading.  It is both cautionary and humbling for those who are assessing new ideas, and particularly worth paying attention if such assessments are part of your profession.

A more recent example of such failures of nerve are the many proofs that it is impossible to intercept a ballistic missile (hit a bullet with a bullet was the popular way of describing it).  During the 1980s many prominent scientists outlined why it was "impossible".  While it is still debatable whether such systems can be effective enough, cost effective, or politically wise, impossible is an adjective that definitely does not apply.

[electrodacus]

I won't claim to understand this well enough to make a definitive statement.  But if you look at the original video's explanation all of the reference is to the similarity to tacking.  Your argument that a sail cannot go faster than the wind is only true when the sail is going directly downwind.  Light speedy sailboats can easily have a water speed much greater than the wind speed when tacking cross wind.

I believe that the key here is that the windspeed relative to the vehicle is not the pertinent answer.  It is the wind direction in the coordinate frame of the propeller blade.  I still haven't wrapped my head around all of this to be able to explain it more simply than others, but that line of thinking gives me a way to believe it is possible, and I choose to believe that the vehicle is not a scam, with hidden batteries and electric motors.  With that assumption facts speak louder than any theory.   Just like conventional aerodynamics had no explanation for how bees could fly for decades.  Nevertheless they did and do.  And finally in the 1980s as I recall it was finally figured out how it worked.

I have recommended and will recommend again a book written by Arthur C. Clarke, "Profiles of the Future".  The book attempts to identify traps in predicting the future, methods for predicting it, and attempts to define the real limits on what is possible.  In chapter one of the book he describes what he calls failure of nerve and gives numerous examples of highly trained people proving something was impractical or even impossible.  Using well established facts and theorems and impeccable math.  But applied in ways that turned out to be incorrect.  Some of the examples:  proof that heavier than air flight was impossible, then once that had happened, proof that airplanes could never carry multiple passengers or travel hundreds of miles per hour, proof that no man-made object could be sent to the moon and proof that electric lighting would never work for private houses.  He calls it failure of nerve because in several cases the individuals providing these proofs had access to descriptions of how the problems they were analyzing could be avoided, but just couldn't bring themselves to believe that they really worked because they contradicted their sense of how the world worked.  While the book was written in 1961-1962 it has stood the test of time well.  It is well worth finding and reading.  It is both cautionary and humbling for those who are assessing new ideas, and particularly worth paying attention if such assessments are part of your profession.

A more recent example of such failures of nerve are the many proofs that it is impossible to intercept a ballistic missile (hit a bullet with a bullet was the popular way of describing it).  During the 1980s many prominent scientists outlined why it was "impossible".  While it is still debatable whether such systems can be effective enough, cost effective, or politically wise, impossible is an adjective that definitely does not apply.

Yes we are only discussing the specific case when vehicle drives in the exact same direction as wind. Any other direction and vehicle can get to almost any higher speed limited only by the vehicle friction.
Vehicle itself (blackbird) is not a scam and it works as shown in tests. The only problem is that the description of how it works is wrong. Claim is vehicle can travel indefinitely above wind speed in the same direction as the wind. The reality is that vehicle can travel for a limited time above wind speed likely 2 to 3 minutes until peak speed then about the same amount until it gets bellow wind speed and this is all thanks to energy storage.
My explanation using energy storage will not contradict the experimental results but they will have needed to continue the test for about another minute to start observing decrease in speed.

The explanation presented by the creator of Blackbird makes no sense so I'm sure he even after discussion with me has no understanding of how the vehicle works and he just applied the formula wrong to fit the data and what he thinks happens as he is unable to see the pressure differential energy storage that is key to accelerating past wind speed.

To me it is very obvious and simple to understand how the vehicle works but it may be related with my area of expertise.
In any case I have no doubt the vehicle works the way I say it does and I even made the full calculations for the Blackbird based on sort of limited amount of data I was able to find (but enough data to be very close).

I do observe that most people do a similar sort of mistake when thinking on how the vehicle works and many are influenced by the explanation Derek (Veritasium) made.
I had a fairly long email exchange with Derek but I was unable to convince him tho he is likely not sure of his explanation as he can not have a full understanding since his current theory is wrong.

In any case I think I mentioned earlier but human brain works way different for each person. Look up Aphantasia and then internal monologue (It is only maybe a year since I first heard about this two and I was extremely surprised of how different people can think).
Like Aphantasia only affects maybe 1 to 3% of the population (no proper studies where conducted) and this is the inability to form a mental image like visualizing an object in your head those 1 to 3% can not even visualize a simple line. The others are on a spectrum from some simple visualization up to visualization so vivid that they can confuse what they see with reality (that is the other extreme and not such a good thing).
Then there is the internal monologue thing that affects around 30% of the population and that is the ability to speak inside your head (have a conversation with yourself). It seems those 30% did not knew that others can speak words in their head and where thinking this is just a sort of figure of speech and they do not think in words (using language) is more sensations and feelings plus some visualization for those that do not also have Aphantasia.
There are probably other large differences even less studied but I was super surprised to hear about this two as you will not be able to see a difference in those people and they function the same way even if the miss both the internal monologue and the mental image.

[PlainName]

The propeller does not compress the air, it creates a vacuum. You can see that demonstrated here:

What you see there is a stream passing over a tube sucking the contents of the tube out. That stream might be very compressed indeed but it will still cause a vacuum in that tube so long as it's whizzing past the end.

[IanB]

What you see there is a stream passing over a tube sucking the contents of the tube out. That stream might be very compressed indeed but it will still cause a vacuum in that tube so long as it's whizzing past the end.

You may think it could be compressed, but it's not. When you insert a tube at right angles to a flowing stream, the end of the tube measures the actual pressure of the fluid inside the stream. The tube sucks air in because the air pressure in the flowing stream from the fan is lower than the surrounding air pressure. Inserting a tube at right angles to the flow stream is exactly how pressure measurements are made. For example, this is how aircraft measure the atmospheric pressure around them to determine their altitude.

The pressure of the air is directly related to its density (its amount of compression) by the ideal gas law. This basically says:
$$\frac{P}{\rho}=RT$$
where \$P\$ is pressure, \$\rho\$ is density, \$T\$ is temperature, and \$R\$ is a constant (in appropriate units).

Effectively, if \$P\$ goes down, \$\rho\$ goes down, and vice versa. If the pressure is lower, the density is lower, and the air is less compressed.

[IanB]

When students arrive to study engineering, one of the first things that happens in the "Fluid Mechanics 101" class is to dispel all sorts of wrong intuition about the way flowing fluids behave. It takes various experiments to show what really happens, vs. what students think is going to happen.

[electrodacus]

When students arrive to study engineering, one of the first things that happens in the "Fluid Mechanics 101" class is to dispel all sorts of wrong intuition about the way flowing fluids behave. It takes various experiments to show what really happens, vs. what students think is going to happen.

Unfortunately professors are not immune to making mistakes.
What happens on both sides of the propeller is described in this diagram that I posted earlier


Notice the pressure gradient from high pressure P2 to ambient pressure PA downstream from propeller and the reverse of that upstream and this is what I call pressure differential energy storage.
Of course this is valid for zero wind and vehicle speed or when wind speed equals vehicle speed after that as vehicle speed increases above wind speed the pressure differential will drop as it is used up but also because there is now apparent wind from the front of the vehicle so pressure upwind will increase (from negative/ below ambient) so at some point the pressure differential will be so small that will no longer be able to cover the vehicle losses and then vehicle will start to slow down. 

[bdunham7]

What happens on both sides of the propeller is described in this diagram that I posted earlier

Where does that diagram come from?

[IanB]

When students arrive to study engineering, one of the first things that happens in the "Fluid Mechanics 101" class is to dispel all sorts of wrong intuition about the way flowing fluids behave. It takes various experiments to show what really happens, vs. what students think is going to happen.

Unfortunately professors are not immune to making mistakes.

That is why I specifically mentioned "experiments" there. Humans may make mistakes, but the physical world does not. What the universe does is what the universe does, whether we like it or not.

If you want to compare a diagram presented without context or attribution on the one hand, with the real world on the other, I am going to believe the real world every time.

[IanB]

Unfortunately professors are not immune to making mistakes.

But electrodacus is immune, right? 

[electrodacus]

Where does that diagram come from?

Comes from a quick google search and I selected the one that looked to contains the info I wanted to show.
Seems photo is from a Wikipedia article on axial fans  https://en.wikipedia.org/wiki/Axial_fan_design

But electrodacus is immune, right? 

I'm sure not immune. I'm just not wrong in this particular case.
As for experiments they can be interpreted wrong like it is the case here.
You see blackbird and treadmill model exceed wind speed and you immediately think is wind that powers the vehicle (in a way it is but is stored wind energy so you will not stay above wind speed indefinitely).

The thing is that there are relatively easy ways to test if I'm wrong but nobody has bothered to test.
I was sure everyone will see the problem when I mention that vehicle traveling at wind speed in exact same direction as wind is 100% efficient as all available energy is used.
But I got different replays including that more than 100% efficiency is possible (absolutely ridiculous in my book but I have nothing to convince someone like that other that he making a test to see that is not possible).
Also me doing the test is not only pointless when I know (not believe) what the result will be and on top of that sharing an experiment I have done will not help as people will claim my test was improperly done.     

[Alex Eisenhut]

No one tell this guy about heat pumps.

[BrianHG]

No one tell this guy about heat pumps.

I'm just sitting back and enjoying...