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

[Brumby]

.... not everyone agrees that a treadmill is a valid analog.

Those people do not understand "frames of reference".

This fundamental lack of understanding of a very simple principle within physics and perfectly applicable to Newtonian mechanics means they are handicapped in comprehending what is going on.  I would go so far as to say some would be incapable of allowing the possibility and could actively engage in presenting arguments attempting to disprove (something that has already been demonstrated).

When such arguments come from those who cannot understand fundamental principles, their process is bound to be flawed and their conclusions will be of no value to anyone but their delusion.  (Now why does that seem familiar?      Oh... yeah.)

[Kleinstein]

Compare the film of the experiment on the treadmill with the film made from the car driving at the speed of the wind.
In both films the air is essentially stationary and the ground is moving relatively fast.  So the Treadmil is kind of wind tunnel to test the vehicle at a speed very close to wind speed.  The only thing really missing to make this a wind tunnel is the fan to produce zero wind speed.

The belt drags some air with it, but so does the wall in a wind tunnel and in real world the wind is also different at different hights. So the concept of 1 wind speed is an approximation only.

The points that could have been done better in the treadmill experiments could be using a string and force meter to hold the vehicle and to show the direction of the air flow produced by the prop. It was already quite instructive that they showed the failed attempt with the prop with too much pitch / too small wheels.

[Alex Eisenhut]

For someone just starting to read all these posts, I think this would be the right song to play in the background

[Labrat101]

. There seems to be a fixation on treadmills etc.

That's because a treadmill is a convenient mechanism to demonstrate the principle.  This is because of the validity of the concept of "Frames of reference".

I will give a just a few reasons why they are not used other than exercising the Dog .

This will be entertaining.... 
 Answer  You have No idea of what the difference between a treadmill that you have in your house and a wind tunnel

First they have a very high friction as the belt runs over the rollers the surface gets warm to hot .

So?  How does that affect things?
Answer The Added Friction will give bad results ..

the bottom of the belt that hangs down at the bottom has to be loose . So it flaps .

So?  How does that affect things?
 Answer  You are really Funny that you don't know why, Must have slept thought entire physics lesson

Having to moving surfaces running in parallel in opposite directions causes side air distortion  and turbulence.   .

So?  As a factor that is somewhat minimal, how does that affect things?
 Answer : OMG   somewhat minimal  If this was your oscilloscope giving these error would you except it

Even at airports they did away with this due to belts getting hot . Now they use just rolling beds .. Belt-less.
In other places the belts were replaced with slated belts that were self cooling ..

So?  The temperature of belts is not going to affect the experiment unless they've burst into flames or gone so tacky as to be unable to allow rolling.  This is a non-argument.
Answer it proves that the industry has excepted they are a waste of energy and useless

The aerospace industry , Lockheed , NASA , and all the others .
Don't use this in a wind tunnels or for replacing the use of a wind tunnel due to there significance and disturbance in testing.

Don't see this being significant for the scale of test we are talking about.
 Answer the smaller the item being tested the greater the accuracy has to be

The test item in a wind tunnel is usably suspended . in the car test rollers are used and the wheels are placed between 2  controlled
rollers . 2 at the front and 2 at the back . and are computer controlled . The rollers are covered by a plate so no other side effects
mess with the final tests .

OK.  Fine.  The rollers are a perfect analogy for travelling over the ground (Just as a treadmill belt is, BTW) - but the only thing is that they constrain the movement of the wheels.  In such an experiment, the rollers would need to be programmed to increase speed to match the performance of the vehicle, while the wind speed remains constant.

Do that and you'll find the Blackbird does work.  Oh now you agree with me ..
 what's this .. I said " computer controlled " your remark  "would need to be programmed "  has to be spiting hairs 

Treadmills etc work great on paper and for demonstrating  science projects . And not to for get the GYM .
or moving lots of odd shaped stuff from containers etc .
So Please get over the treadmill . .. hamsters likes them .

OK - a dismissive wave of the hand and it all goes away...?  That is classic denial.  answer  By whom

I am sorry and not being rude but you have not got any idea in real world industrial physics 
  If this had been your own personal project Then you would look at it differently  and in that case I would not have cared .

This a wind tunnel from a car manufacture ..   If they could do this on a Treadmill, That are relatively cheap .
  .   
 NO..  They go too all that trouble in building a wind tunnel that costs $ Millions .

     They could have just got a Treadmill from BangUgood  for $200 .
 
        Enjoy the video .

   

[Kleinstein]

The interesting part for the prop powered vehicle is at a speed very close to the speed of wind and especially the case with the vehicle at the speed of wind. This means the case where the vehicle does not see any external wind and only the ground is moving.  So in a wind tunnel with the vehicle fixed this would be zero wind speed. 

The treadmill is perfectly fine to produce zero wind speed, especially for a more hobby / fun project and basic demonstration. This is not about a precision measurement but demonstration of the principle workings.

[CatalinaWOW]

The automakers have not much interest in the zero wind speed case.  For their purposes a treadmill does not work.  But the zero relative windspeed case is absolutely the point of most interest for this particular problem.

[bdunham7]

But the zero relative windspeed case is absolutely the point of most interest for this particular problem.

I'm not sure I agree that the case where the vehicle speed matches the wind speed is particularly special in terms of operating the vehicle or laying out the equations that govern its operation.  It may be the point where ones initial intuition is challenged, but that's about it.  The operational mode where the wheels power the propeller has to be started well before this point.

[bdunham7]

When such arguments come from those who cannot understand fundamental principles, their process is bound to be flawed and their conclusions will be of no value to anyone but their delusion.

I was trying for the longest time to figure out where the problem in understanding was, but at one earlier point, and then again in reply #445 it became apparent that the contentious one had been exposed to and was aware of the basic principles that I was trying to explain, but has chosen to deny that they are true.  Education can't fix that.  I think people have a tendency to try to rationalize other people's irrationality instead of just seeing it for what it is, which is why it took me so long to recognize what was going on.

[jeffjmr]

Tally me on the skeptic side.

The sail analogy doesn’t hold water, pardon the pun.  The sailboat sail is not traveling along the same vector as the wind. The propellor on this contraption is.  At ground speed equivalent to wind velocity, there is no longer any wind force being applied to the propellor airfoil, unlike a tacking boat sail. Envision a ball traveling down an incline. Its speed relative to the surface of the incline is faster than its velocity vector towards the ground, and in the absence of friction, its acceleration across the surface of the incline would exceed the acceleration of gravity. Simple vector analysis. Doesn’t apply to this vehicle if it is aligned with the wind.

Carefully edited video showing the wind string indicating forward airspeed could result under a number of different, TEMPORARY scenarios. I never saw a view from directly in front of the vehicle to confirm perfect alignment with the wind.

Not only do I not believe this vehicle’s speed can exceed the wind speed when aligned downwind, I don’t believe it can equal the wind speed due to frictional losses. Believers will have to explain to me what source of energy can accelerate this vehicle above the wind speed once the speed is equivalent, at which point every molecule of air surrounding and in contact with it has 0 relative velocity, and overcoming frictional losses at the same time!

Set this up with anemometers along the path to confirm the constant wind velocity, evidence of perfect alignment with the wind, a long enough course to eliminate the possible effects of wind gusts, and an unedited, continuous video, and you’ll have my attention. Until then, to me this myth is busted.

Jeff

[bdunham7]

Tally me on the skeptic side.

Oh dear!  How much of the thread have you read?  Have you read reply#20 earlier?

You can be skeptical, that's fine.  But before anyone tries to convince you, are you familiar with Newton's laws of motion and are you willing to analyze and consider basic equations of motion?  If not, there's not much point...

[IanB]

Not only do I not believe this vehicle’s speed can exceed the wind speed when aligned downwind, I don’t believe it can equal the wind speed due to frictional losses. Believers will have to explain to me what source of energy can accelerate this vehicle above the wind speed once the speed is equivalent, at which point every molecule of air surrounding and in contact with it has 0 relative velocity, and overcoming frictional losses at the same time!

Set this up with anemometers along the path to confirm the constant wind velocity, evidence of perfect alignment with the wind, a long enough course to eliminate the possible effects of wind gusts, and an unedited, continuous video, and you’ll have my attention. Until then, to me this myth is busted.

The key point is that the air surrounding the vehicle may have zero relative velocity, but in the vehicle's frame of reference, the ground beneath the wheels is moving very fast. By coupling the wheels to the propeller, the propeller can produce additional thrust to exceed the wind's velocity.

On a calm day this wouldn't work because frictional drag from the surrounding air would exceed the power generated from the wheels and the vehicle would slow down to a standstill. But when the air has no relative velocity to the vehicle there is no aerodynamic drag to overcome, and the entire thrust from the propeller can accelerate the vehicle.

The wind is still the source of energy, but it is indirectly coupled to the vehicle by various mechanical linkages through the wheels and propeller, rather than by direct action on a sail.

The "zero wind velocity, fast moving ground" is the rationale for the treadmill experiment, as it exactly duplicates this scenario. With the treadmill, it is only necessary for the propeller to generate a forward force large enough to overcome the backward push of the moving belt under the wheels. If it can do that, the vehicle can move forwards. With the right gearing and pitch on the propeller it is possible.

[Psi]

I wonder if this might be easier to demonstrate if you replace the air for water.

Water flowing through a pipe is somewhat easier to DIY than a wind tunnel.

And you can also show the flow of water visually using a flow indicator.

The coupling of a propeller to water is also much stronger than to air, so the effect maybe more dramatic and easier to see?

Do you get laminar flow issues in a water pipe? I would imagine it's much easer to do than air?

Obviously need to set it up so the scale model can be stationary like in treadmill demo, so you don't need a huge setup with an impractically long pipe.
However if the people against the idea have issues with frames of reference then they would probably have issues with that too.

I dunno.

[IanB]

I think there is not much point demonstrating things with experiments, because if people don't like what the experiment shows they will find reasons to dismiss what they see.

[Psi]

I think there is not much point demonstrating things with experiments, because if people don't like what the experiment shows they will find reasons to dismiss what they see.

Sure, some have definitely made up their mind and wont accept any evidence. but i don't think that describes everyone.

[Brumby]

I am sorry and not being rude but you have not got any idea in real world industrial physics

Passive-aggressive much?   

  If this had been your own personal project Then you would look at it differently  and in that case I would not have cared .

This a wind tunnel from a car manufacture ..   If they could do this on a Treadmill, That are relatively cheap .
  .   
 NO..  They go too all that trouble in building a wind tunnel that costs $ Millions .

     They could have just got a Treadmill from BangUgood  for $200 .
 
        Enjoy the video .

    << Link to totally irrelevant video >>

This perfectly illustrates the fact that you have no clue about the actual processes involved.  You should be embarrassed - but I doubt you will.

The principle of the Blackbird can be demonstrated in a wind tunnel, as long as it is properly set up - which is no mean feat.  But it can also be demonstrated on a treadmill with far less effort.  If you have trouble with that, then you have no idea about frames of reference and you should give up now.  All the subtle eddies and other artifacts you throw around like confetti have no significant role in such a demonstration.

Certainly, if you wanted to do a full aerodynamic analysis with the purpose of maximising efficiency, say, then by all means the treadmill will be inappropriate and the wind tunnel is the way to go.  Motor vehicle and aerospace designers are way beyond demonstrating principles which is why they go for the high tech wind tunnel.


But that seems to be a subtlety beyond your comprehension.

[Brumby]

I think there is not much point demonstrating things with experiments, because if people don't like what the experiment shows they will find reasons to dismiss what they see.

Sure, some have definitely made up their mind and wont accept any evidence. but i don't think that describes everyone.

I'm with these guys ^^^^^^^

[Alex Eisenhut]

But that seems to be a subtlety beyond your comprehension.

He sounds like the kind of guy who will argue that no one should use a dead carbon-zinc battery when learning Ohm's Law ... and will describe fifteen different kinds of batteries.

Then after six weeks of exhaustive and exhausting explanation, will reluctantly agree that the battery is just an illustration...

Then just as everyone is ready for lunch, he'll say "yeah but no one uses incandescent lights anymore!"

[iMo]

.. The sailboat sail is not traveling along the same vector as the wind. The propellor on this contraption is.  At ground speed equivalent to wind velocity, there is no longer any wind force being applied to the propellor airfoil, unlike a tacking boat sail. ..

A blade of the propeller has got an angle of attack (like 10-20 degrees), where the blade then works as the sailboat's sail when tacking. The propeller is then self-tacking while rotating. The "by tacking created" energy is fed into the storage (the Blackbird's body) and the wheels (via the proper gear) may speed up the craft (minus losses in the friction which are rather high)..
For example, with an IceBoat (where its 3 runners do not slip on the ice but keep the direction) while tacking the IceBoat's sail you may travel up to 5x speed of the wind (people say)..

[Brumby]

He sounds like the kind of guy who will argue that no one should use a dead carbon-zinc battery when learning Ohm's Law ... and will describe fifteen different kinds of batteries.

Then after six weeks of exhaustive and exhausting explanation, will reluctantly agree that the battery is just an illustration...

Then just as everyone is ready for lunch, he'll say "yeah but no one uses incandescent lights anymore!"

   Well said!

[Labrat101]

This perfectly illustrates the fact that you have no clue about the actual processes involved.  You should be embarrassed - but I doubt you will.

For sure not . I'm jealous. That I could No way match your supreme gift in Scepticism.
But I am sure with just a little more help we will succeed  in advancing you  To the higher level  .
 Not just a mere,  Supporter of Scepticism .. Upgrade To ::    Major Sceptic   looks far better .
But be warned with Great Scepticism comes apparently No responsibility .
 So there maybe a time when you can't believe yourself  .

 

[Alex Eisenhut]

[Brumby]

Why call  me a skeptic?

I believe the Blackbird does what Veritasium demonstrated.   

[Alex Eisenhut]

https://youtu.be/ZqUvbYb-x2Y?t=70

but...

[Labrat101]

https://youtu.be/ZqUvbYb-x2Y?t=70

but...

This defiantly messed with the mind . 

[Labrat101]

Ulrika
“Downhill from everywhere/Downhill from all you see/The ocean is downhill from gravity,” Browne sings along a smooth guitar riff. “Downhill from here/Downhill from everywhere/Downhill from all of humanity.”

This guy may have solved our argument . The Blackbird is always travelling down Hill


https://www.rollingstone.com/music/music-news/jackson-browne-earth-day-2020-986611/