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

[Domagoj T]

Yoyo has always access to energy trough the string as long as the string is under tension and it can only do so as long as there is enough string so it has a limited range of motion.

The design I proposed in Reply #1102 on page 45 of this thread has string in a loop, so it has infinite range.

[electrodacus]

For my own interest, I made a geometrical model to show how a cart with appropriate gearing can travel in the opposite direction to the moving belts it is sitting on.

When the belts are moving to the right the cart moves to the left, and vice versa.

The works because one belt is moving twice as fast as the other, and the two wheels are the cart are connected by a geared pulley, so that both wheels turn together. The difference in belt speeds is used to make the wheels of the cart turn in the opposite direction of the belts.

Your model is missing a physics engine.
Nothing has any mass so there are no forces involved at all.

Your model describes the steady state for an ideal vehicle and an ideal vehicle since there is no friction will continue to keep whatever steady state is in without requiring any energy. If in real world anyone will be able to demonstrate something like this it will be called a perpetuum mobile.

[IanB]

Your model is missing a physics engine.
Nothing has any mass so there are no forces involved at all.

Your model describes the steady state for an ideal vehicle and an ideal vehicle since there is no friction will continue to keep whatever steady state is in without requiring any energy. If in real world anyone will be able to demonstrate something like this it will be called a perpetuum mobile.

Forces and mass play no part in the analysis, it is pure geometry. If you were to build this model using exactly the same geometry, it would behave in exactly the same way.

If you say the real world model needs power to work, that is true, but the power comes from the belts it sits on. You move the belts under the wheels and the cart follows as shown. It is just the same as a gear chain. If you turn one gear, all the others follow according to the gear ratios.

[electrodacus]

Your model is missing a physics engine.
Nothing has any mass so there are no forces involved at all.

Your model describes the steady state for an ideal vehicle and an ideal vehicle since there is no friction will continue to keep whatever steady state is in without requiring any energy. If in real world anyone will be able to demonstrate something like this it will be called a perpetuum mobile.

Forces and mass play no part in the analysis, it is pure geometry. If you were to build this model using exactly the same geometry, it would behave in exactly the same way.

If you say the real world model needs power to work, that is true, but the power comes from the belts it sits on. You move the belts under the wheels and the cart follows as shown. It is just the same as a gear chain. If you turn one gear, all the others follow according to the gear ratios.

It will behave the same way if you push the cart with your hand.  If cart needs to be powered by the two treadmill then it will not behave anywhere close to this it will just move backwards.
There is a lot of confusion as you seen those toy cars that move against the paper moving direction but that will also not work that way without energy storage and stick slip tho it has nothing to do with direct down wind and it is a good representation for direct upwind witch is a very different problem.
And while I explained the direct upwind problem and even showed real test proof it seems not be helpful.
Demonstrating direct down wind will require a propeller based model and that is more expensive for me to demonstrate but I'm afraid even demonstrating that will result in same reaction as you have about the direct upwind.
If I could not convince you that stick slip hysteresis and energy storage are true for those vehicle with wheels where everything is visible what will be my chance to convince you about the pressure differential where that is not even visible.

The advantage I have is that I understand power and energy and you always work with forces and speed only not understanding what forces and speeds need to be combined in the equation to get the correct result.
If done correctly both using force and speed and using power and energy will provide the same result but chances to make mistakes are much, much smaller when using power to make the calculation.

[IanB]

Air is a fluid trough with your vehicle moves and while driving directly down wind with vehicle speed lower than fluid speed the fluid can push your vehicle but as soon as fluid speed and vehicle speed are the same the fluid can no longer provide any power to the vehicle and if by some chance your vehicle is above fluid speed the fluid will oppose your vehicle motion thus not only there is no way for your vehicle to accelerate but your vehicle will be slowed down.

This is true for a simple sail-driven vehicle, but is not necessarily true for a vehicle with a more complex mechanism like a propeller.

And mathematically tat will be seen as the direction of the fluid motion will change relative to vehicle.

Relative to the vehicle, but not necessarily relative to the pitch angle of the propeller.

All that moves is the fluid relative to ground and vehicle also relative to ground and as soon as fluid and vehicle have the same speed there is no way for the vehicle to be powered by the fluid.

This is an assertion without proof. Nor is it something you can prove, since once you use words like "there is no way", you are required to prove that no possibility exists out of all the infinite ways it might be done. You cannot feasibly analyze an infinity of designs and eliminate all of them.

[IanB]

It will behave the same way if you push the cart with your hand.  If cart needs to be powered by the two treadmill then it will not behave anywhere close to this it will just move backwards.

If you say the cart will behave differently than the diagram when powered by the treadmill, then you need to explain what part of the geometric model will behave differently in the physical model. What will be different in the real world?

There is a lot of confusion as you seen those toy cars that move against the paper moving direction but that will also not work that way without energy storage and stick slip

It's a geometric diagram. Where is the energy storage and stick slip in a drawing on the screen? It cannot have any of those things.

[electrodacus]

This is true for a simple sail-driven vehicle, but is not necessarily true for a vehicle with a more complex mechanism like a propeller.

The reason propeller makes any diffrence has to do with air being compressible and the ability of the propeller to create a pressure differential when used in air.

Relative to the vehicle, but not necessarily relative to the pitch angle of the propeller.

The propeller pitch angle is the same as the gear ratio on a gearbox. That means output power will be lower than input power same as with any gear box thus it offers no advantage.

This is an assertion without proof. Nor is it something you can prove, since once you use words like "there is no way", you are required to prove that no possibility exists out of all the infinite ways it might be done. You cannot feasibly analyze an infinity of designs and eliminate all of them.

It is already proven look at the data. Use my exhumations and get the exact results as seen in all tests done use yours and get some crazy results that where never observed in practice.
And yes I can say "there is no way" because I can understand conservation of energy.

[gnuarm]

The energy which is extracted from slowing down the wind.

Yes that is a perfectly fine explanation for when vehicle is below wind speed. But how you do that when you are above wind speed and apparent wind speed changes direction?

In the blackbird type craft the propeller blows the car forward in the same direction as the wind.  In that case the propeller blows against the wind slowing it.  Even when the car is traveling down wind faster than the wind, the exhaust from the prop leaves the prop faster than the wind recedes and so is slower (relative to the ground) than the wind. 

The gearing between the prop and the wheels provides the power to turn the prop.  The wind is pushing against the prop wash and the combination of forces between the prop and the wheels provides the energy, i.e. the power to make this work.  The fact that the wheels move with the full velocity of the vehicle while the wind speed is a part and the prop wash is the other part means the wheels get power from the force of the wind and the prop, but only have to power the prop.  Net power input is from the wind. 

[electrodacus]

The energy which is extracted from slowing down the wind.

Yes that is a perfectly fine explanation for when vehicle is below wind speed. But how you do that when you are above wind speed and apparent wind speed changes direction?

In the blackbird type craft the propeller blows the car forward in the same direction as the wind.  In that case the propeller blows against the wind slowing it.  Even when the car is traveling down wind faster than the wind, the exhaust from the prop leaves the prop faster than the wind recedes and so is slower (relative to the ground) than the wind. 

The gearing between the prop and the wheels provides the power to turn the prop.  The wind is pushing against the prop wash and the combination of forces between the prop and the wheels provides the energy, i.e. the power to make this work.  The fact that the wheels move with the full velocity of the vehicle while the wind speed is a part and the prop wash is the other part means the wheels get power from the force of the wind and the prop, but only have to power the prop.  Net power input is from the wind.

Just noticed your signature so I will assume you may be owning an EV.
Imagine your EV has an empty battery (completely empty) and you have a strong wind from the back of the vehicle and you are on a perfectly flat road.
Now the wind will push your vehicle and your vehicle max speed while pushed by the wind can not exceed wind speed. (I hope you will agree with that).
But now you can use your regenerative brake to start charging battery while your vehicle wind speed will be way lower than wind speed since now there is a lot of resistance as you take wind energy and store it in to the battery and at some point you decide you got enough maybe 1% SOC and even with that you can exceed wind speed for a few minutes.
That is exactly how blackbird works other than propulsion is delivered by a propeller fan (instead of the more efficient wheel) and the energy is not stored in a lithium battery but in the air as pressure differential so as you charge you also start using some of the energy.

And to make it even more clear say your Tesla has a flat rear end with a total surface area of 2m^2 (not aerodynamic at all so CoD of 1).
We will also make the assumption that vehicle drive train is perfectly efficient no friction or even rolling resistance.
Also let say wind speed is a constant 25m/s = 90km/h = 55.9mph

Then direct down wind Tesla will have this amount of wind power available  0.5 * 1.2kg/m^3 * 2m^2 * (25m/s-vehicle speed)^3
If vehicle speed is zero (friction brakes ON then there is of course no wind power available to charge the battery).
Then as soon as you remove the friction brakes wind power will be available.

Say vehicle barely moves at 2m/s then if you want to maintain this low speed all you need to do is charge the battery at this rate
0.5 * 1.2 * 2 * (25-2)^3 = 14.6kW  (it may be just half of this in a real vehicle as there is a wind gradient due to interaction with road and vehicle has quite a bit of friction loss).

If you where to drive at 10m/s while you where charging then less wind power will be available  0.5* 1.2 * 2 * (25-10)^3 = 4.05kW

And at 20m/s vehicle speed it is only 0.5* 1.2 *2 * (25-20)^3 = 150W

You can see where this is going.
There is no wind power available to a direct down wind vehicle even if it is ideal case no friction loss and if there is no energy storage device then it is not possible to exceed wind speed.

[gnuarm]

The energy which is extracted from slowing down the wind.

Yes that is a perfectly fine explanation for when vehicle is below wind speed. But how you do that when you are above wind speed and apparent wind speed changes direction?

In the blackbird type craft the propeller blows the car forward in the same direction as the wind.  In that case the propeller blows against the wind slowing it.  Even when the car is traveling down wind faster than the wind, the exhaust from the prop leaves the prop faster than the wind recedes and so is slower (relative to the ground) than the wind. 

The gearing between the prop and the wheels provides the power to turn the prop.  The wind is pushing against the prop wash and the combination of forces between the prop and the wheels provides the energy, i.e. the power to make this work.  The fact that the wheels move with the full velocity of the vehicle while the wind speed is a part and the prop wash is the other part means the wheels get power from the force of the wind and the prop, but only have to power the prop.  Net power input is from the wind.

Just noticed your signature so I will assume you may be owning an EV.
Imagine your EV has an empty battery (completely empty) and you have a strong wind from the back of the vehicle and you are on a perfectly flat road.
Now the wind will push your vehicle and your vehicle max speed while pushed by the wind can not exceed wind speed. (I hope you will agree with that).
But now you can use your regenerative brake to start charging battery while your vehicle wind speed will be way lower than wind speed since now there is a lot of resistance as you take wind energy and store it in to the battery and at some point you decide you got enough maybe 1% SOC and even with that you can exceed wind speed for a few minutes.
That is exactly how blackbird works other than propulsion is delivered by a propeller fan (instead of the more efficient wheel) and the energy is not stored in a lithium battery but in the air as pressure differential so as you charge you also start using some of the energy.

Except my car has no battery and neither does the blackbird.  Also, the blackbird has both a wheel and a propeller while my car ONLY has a wheel. 

And to make it even more clear say your Tesla has a flat rear end with a total surface area of 2m^2 (not aerodynamic at all so CoD of 1).

Ok, now you are going into pointless details because this is not how the blackbird works.

We will also make the assumption that vehicle drive train is perfectly efficient no friction or even rolling resistance.
Also let say wind speed is a constant 25m/s = 90km/h = 55.9mph

More pointless details...

Then direct down wind Tesla will have this amount of wind power available  0.5 * 1.2kg/m^3 * 2m^2 * (25m/s-vehicle speed)^3
If vehicle speed is zero (friction brakes ON then there is of course no wind power available to charge the battery).
Then as soon as you remove the friction brakes wind power will be available.

Say vehicle barely moves at 2m/s then if you want to maintain this low speed all you need to do is charge the battery at this rate
0.5 * 1.2 * 2 * (25-2)^3 = 14.6kW  (it may be just half of this in a real vehicle as there is a wind gradient due to interaction with road and vehicle has quite a bit of friction loss).

If you where to drive at 10m/s while you where charging then less wind power will be available  0.5* 1.2 * 2 * (25-10)^3 = 4.05kW

And at 20m/s vehicle speed it is only 0.5* 1.2 *2 * (25-20)^3 = 150W

You can see where this is going.
There is no wind power available to a direct down wind vehicle even if it is ideal case no friction loss and if there is no energy storage device then it is not possible to exceed wind speed.

Nothing, literally NOTHING you have talked about here has to do with the blackbird, so just stop the insanity! 

It is clear that you will never understand anything anyone tells you that doesn't agree with your idea because you reject it out of hand without understanding it. 

I keep coming to the conclusion that you can't be taught anything, but I get suckered in when I see a point that is so crystal clear to anyone else that it must be possible to show it to you.  However, as others have pointed out, instead of understanding what they tell you, you simply duck the issue and start talking about something different. 

So no more replying to your nonsense. 

[bdunham7]

because I can understand conservation of energy.

No, you really don't and that's where you are failing hard.  You do not understand or correctly apply the basic tenets of junior high-school level physics, namely:

1.  The principles of Archimedes
2.  Newton's laws of motion
3.  The principle of conservation of energy--the one you keep bringing up but clearly have no clue as to how to apply it.

[electrodacus]

Except my car has no battery and neither does the blackbird.  Also, the blackbird has both a wheel and a propeller while my car ONLY has a wheel. 

It was my assumption that you own a Tesla due to referral program mentioned in your signature.
Why do you think a propeller that is less efficient than a wheel can help ? The propeller itself has no advantages over wheels other than it is to travel trough air and it can store energy as pressure differential.

Ok, now you are going into pointless details because this is not how the blackbird works.

That is exactly how blackbird or any wind powered vehicle works.

Nothing, literally NOTHING you have talked about here has to do with the blackbird, so just stop the insanity! 

It is clear that you will never understand anything anyone tells you that doesn't agree with your idea because you reject it out of hand without understanding it. 

I keep coming to the conclusion that you can't be taught anything, but I get suckered in when I see a point that is so crystal clear to anyone else that it must be possible to show it to you.  However, as others have pointed out, instead of understanding what they tell you, you simply duck the issue and start talking about something different. 

So no more replying to your nonsense.

The fact that you do not understand how blackbird works will not make all that I mentioned very relevant.
That is about what I think about you but I'm still hopeful.

[electrodacus]

No, you really don't and that's where you are failing hard.  You do not understand or correctly apply the basic tenets of junior high-school level physics, namely:

1.  The principles of Archimedes
2.  Newton's laws of motion
3.  The principle of conservation of energy--the one you keep bringing up but clearly have no clue as to how to apply it.

OK answer this.

Max wind power available to a direct down wind powered vehicle is when vehicle just starts moving so low speed (Fact 1).
equation for ideal 100% power available to any direct down wind powered vehicle is 0.5 * air density * area * (wind speed - vehicle speed)^3 (Fact 2)

What powers the vehicle when vehicle speed is above wind speed ?

Clearly not wind power (at least not directly but stored wind power).
I'm starting to get very tiered by this level of stupidity.
I asked for the equation showing the available wind power for Blackbird and nobody presented one that will match the observed results in both blackbird and treadmill model.

[IanB]

equation for ideal 100% power available to any direct down wind powered vehicle is 0.5 * air density * area * (wind speed - vehicle speed)^3 (Fact 2)

Except:
a) You cannot derive this equation from first principles when asked to do so,
b) You have not pointed to any authoritative source that gives this equation (online or textbook).

Therefore you cannot take this as fact, and if you rely on it all your arguments are flawed.

[electrodacus]

equation for ideal 100% power available to any direct down wind powered vehicle is 0.5 * air density * area * (wind speed - vehicle speed)^3 (Fact 2)

Except:
a) You cannot derive this equation from first principles when asked to do so,
b) You have not pointed to any authoritative source that gives this equation (online or textbook).

Therefore you cannot take this as fact, and if you rely on it all your arguments are flawed.

It is a fact.  Please provide an equation that you think is correct.
This equation is used everywhere from wind turbine design to vehicle drag so it is one of the most used equations and you can find it literally everywhere.
Your problem seems to be not understanding power and working with forces only not understanding what speed will correspond to get the correct result. 

[electrodacus]

See this link and scroll down to air drag https://en.wikipedia.org/wiki/Bicycle_performance
You will find two equations

This is the same that I use for max wind power available.
And this

That is incorrect (you can not always expect much from wikipedia).

To prove that equation is wrong we can just do an example.
Everything else is basically a constant so will just look at v_r³ and v_a²*v_r

Drag power at 20m/s with no wind should be the same as drag for vehicle/bicycle at 10m/s vehicle + 10m/s head wind all other things being equal.

20³= 8000
20² * 10 = 4000 so half of the correct result.
Thus this sort of wrong understanding is fairly common as it ended up in Wikipedia.

[Brumby]

OK ... Trying to get a feel as to where this energy storage is taking place.

Is this what you mean?



If not, then where?

[electrodacus]

OK ... Trying to get a feel as to where this energy storage is taking place.

Is this what you mean?



If not, then where?

It is symmetrical that is why I say pressure differential. The one you marked is half, it is the side with the higher than atmospheric pressure and the other half is on the other side of the propeller the part with lower than atmospheric pressure.
So propeller is both pushed by the high pressure zone and pulled by the low pressure zone.  So energy is stored in that volume on both sides of the propeller.   

[bdunham7]

Thus this sort of wrong understanding is fairly common as it ended up in Wikipedia.

No, they got it exactly right here and we've all been telling you the exact same thing....

By 'this sort of wrong understanding' you mean anything that doesn't align with your misconceptions.  And yeah, that so-called 'wrong understanding' is indeed very common and will be the consensus of every sane physicist as well as almost anyone with a grasp of introductory physics (mechanics).  Are they all wrong?

[electrodacus]

No, they got it exactly right here and we've all been telling you the exact same thing....

OK then why that second formula that should represent the same thing provide a different value ?

[bdunham7]

OK then why that second formula that should represent the same thing provide a different value ?

Because it doesn't represent the same thing.  You are 'intuiting' (assuming wrongly) what the result should be and then assuming the formula is wrong when it doesn't match  your preconceived notion.  The result of the formula, which is correct,  is that it takes more power to go 20km/h in still air than it does to go 10km/h against a 10km/h headwind. 

[electrodacus]

Because it doesn't represent the same thing.  You are 'intuiting' (assuming wrongly) what the result should be and then assuming the formula is wrong when it doesn't match  your preconceived notion.  The result of the formula, which is correct,  is that it takes more power to go 20km/h in still air than it does to go 10km/h against a 10km/h headwind.

We are only talking about power needed to counter drag not the other things like rolling resistance and friction in the internal mechanism.
And whatever you have in front of the vehicle as an area or a sail or a wind turbine it will not be able to see a difference between you traveling at 20m/s or traveling at just 10m/s with 10m/s head wind it will still see the same equivalent 20m/s air relative to vehicle.
It is irrelevant if air moves or vehicle moves.
This is true for a vehicle, for a sail or for a wind turbine.
This is not a question of general knowledge is a question of logic alone. So you did not need to learn this in school to understand the two cases are the same as far as drag is concerned.

[bdunham7]

This is not a question of general knowledge is a question of logic alone. So you did not need to learn this in school to understand the two cases are the same as far as drag is concerned.

I don't know what you should and shouldn't learn in school, but I do agree that the question is extremely simple.  And you have simply gotten it wrong.  The drag is the same, the power is not.  Drag is a force and is the same in each case.  Thus when I pedal the bicycle, I will have to apply a certain amount of force to the pedals to counter that drag.  If I'm going 20km/h in still air however, I have to pedal twice as fast with the same force as I do pedaling an identical bicycle at 10km/h into a 10km/h wind.  Same force, twice as fast.  Twice the power.  Extremely simple.  No calculus.  Everybody understands it except you.

[electrodacus]

This is not a question of general knowledge is a question of logic alone. So you did not need to learn this in school to understand the two cases are the same as far as drag is concerned.

I don't know what you should and shouldn't learn in school, but I do agree that the question is extremely simple.  And you have simply gotten it wrong.  The drag is the same, the power is not.  Drag is a force and is the same in each case.  Thus when I pedal the bicycle, I will have to apply a certain amount of force to the pedals to counter that drag.  If I'm going 20km/h in still air however, I have to pedal twice as fast with the same force as I do pedaling an identical bicycle at 10km/h into a 10km/h wind.  Same force, twice as fast.  Twice the power.  Extremely simple.  No calculus.  Everybody understands it except you.

The power needed to overcome that drag is the same.
When you drive at 20km/h with no wind you experience an apparent headwind of 20km/h
When you drive at 10km/h with no wind you experience an apparent headwind of 10km/h but if to that you add a 10km/h headwind then you have an apparent head wind of 20km/h.
Also if you double the speed drag power increases 8x not 2x or even 4x

[IanB]

Thus this sort of wrong understanding is fairly common as it ended up in Wikipedia.

But every physicist in the world, every engineer in the world, every textbook in the world, agrees with that formula in Wikipedia. So are you going to tell the whole world they have been getting it wrong for the past 200 years and re-write all the physics textbooks?

This is not a question of general knowledge is a question of logic alone. So you did not need to learn this in school to understand the two cases are the same as far as drag is concerned.

This is interesting. That formula that appears in Wikipedia is not derived from logic. It is derived from experiment. Many experiments. Over the years, scientists and experimenters measured the amount of power required in different situations, and they found that all of their experiments match the formula given by Wikipedia. What is more, you can repeat those experiments yourself, and if you do so, you will also obtain results matching that formula.