Author Topic: Mess with your minds: A wind powered craft going faster than a tail wind speed.  (Read 147231 times)

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Offline gnuarm

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I didn't say anything about a brake.  I said zero motion.  Work is force over a distance.  You can push as hard as you want against an object and if it does not move you have done no work on it.  You may have sweated up a storm, but that's internal inefficiencies.  Actually, I can lean into a wall without any real effort on my part.  I'm just using my weight and gravity to provide the force.

I would construct some examples to show you there is no work being done, but it really gets tiresome that you just can't understand the basic concepts. 

So you think that holding an object in a fixed position against a force requires performing work on the object?  Do you understand what is meant by "performing work" in the physics sense?  If the wind is blowing, and something is pushing against the object, but not moving it against the wind, is the something doing work?

I remove the brakes from a bicycle you can sit on that and then in a 230km/h head wind and see if you can have a low speed close to zero relative to ground. In fact you can keep the brakes and you will still have no change against 230km/h wind.
A wall is anchored to ground.

I see what bdunham7 meant...

Ok, how about a 20 km/h wind?  I don't even need to work.  I just have to keep pressure on one pedal which I can do easily without doing work on the bicycle.  No motion, no work.  Do you agree with that?

I debated with myself over the stationary vs. infinitesimal speed issue realizing that either way you would find some inane point to argue about.  230 km/h head wind is pretty much reductio ad absurdum. 
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Offline electrodacus

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I see what bdunham7 meant...

Ok, how about a 20 km/h wind?  I don't even need to work.  I just have to keep pressure on one pedal which I can do easily without doing work on the bicycle.  No motion, no work.  Do you agree with that?

I debated with myself over the stationary vs. infinitesimal speed issue realizing that either way you would find some inane point to argue about.  230 km/h head wind is pretty much reductio ad absurdum.

Yes 230km/h is absurd that is why I selected that speed. I set 1km/h for the bike so it is low speed but possible while keeping your balance then increased the head wind in the calculator until power required was equal with 300W as 300W can be done by a fit person.
Obviously power needed is not 300W else you will see electric bikes with 300W motor and 230km/h top speed.

20km/h (5.55m/s) head wind is no challenge as power need to slyly move forward will be
0.5 * 1.225 * 0.408 * (5.55)^3 = 42W so basically a breeze.
And yes you can just stay still by leaving your body weight on the pedal at just 20km/h head wind.     

Online IanB

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No vehicle can move directly upwind powered only by wind without energy storage (Fact).

What would you say if someone showed you a wind powered vehicle that moves directly upwind without energy storage?
 

Offline gnuarm

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I see what bdunham7 meant...

Ok, how about a 20 km/h wind?  I don't even need to work.  I just have to keep pressure on one pedal which I can do easily without doing work on the bicycle.  No motion, no work.  Do you agree with that?

I debated with myself over the stationary vs. infinitesimal speed issue realizing that either way you would find some inane point to argue about.  230 km/h head wind is pretty much reductio ad absurdum.

Yes 230km/h is absurd that is why I selected that speed. I set 1km/h for the bike so it is low speed but possible while keeping your balance then increased the head wind in the calculator until power required was equal with 300W as 300W can be done by a fit person.
Obviously power needed is not 300W else you will see electric bikes with 300W motor and 230km/h top speed.

20km/h (5.55m/s) head wind is no challenge as power need to slyly move forward will be
0.5 * 1.225 * 0.408 * (5.55)^3 = 42W so basically a breeze.
And yes you can just stay still by leaving your body weight on the pedal at just 20km/h head wind.   

Ok, so if the user is stationary in a 20 km/h head wind, how much power is required to maintain this position?  If you come up with any answer other than zero, you can't explain how a brake works.  The brake can maintain this position into the 20 km/h wind while dissipating no power.  A rider can do the same thing by simply standing on the pedal preventing it from rising up.  One foot on the ground for balance, one foot on the pedal to maintain position.  No power transfer.  ZERO

You seem to have already agreed that this is correct.  In that case you must agree there is no power transfer at the wheels for a stationary bike/car/blackbird and that the equation that predicts power at the wheels based solely on the wind relative speed must be wrong. 
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Offline electrodacus

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What would you say if someone showed you a wind powered vehicle that moves directly upwind without energy storage?

That is not possible so I will show him where energy storage is. Maybe for this particular case I will ask him to take a video with a high speed camera to notice how the movement is not constant but it fluctuates as energy storage is charged and discharged.

Online Kleinstein

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I see what bdunham7 meant...

Ok, how about a 20 km/h wind?  I don't even need to work.  I just have to keep pressure on one pedal which I can do easily without doing work on the bicycle.  No motion, no work.  Do you agree with that?

I debated with myself over the stationary vs. infinitesimal speed issue realizing that either way you would find some inane point to argue about.  230 km/h head wind is pretty much reductio ad absurdum.

Yes 230km/h is absurd that is why I selected that speed. I set 1km/h for the bike so it is low speed but possible while keeping your balance then increased the head wind in the calculator until power required was equal with 300W as 300W can be done by a fit person.
Obviously power needed is not 300W else you will see electric bikes with 300W motor and 230km/h top speed.

20km/h (5.55m/s) head wind is no challenge as power need to slyly move forward will be
0.5 * 1.225 * 0.408 * (5.55)^3 = 42W so basically a breeze.
And yes you can just stay still by leaving your body weight on the pedal at just 20km/h head wind.     

A very high wind speed will give very high forces - there is nothing ridiculous about that. The problem is with the wrong equation it gets ridiculous as it predicts too high a power at low speeds, like 20 km/h wind and 0.001 m/s movement relative to ground. 42 W of power don't looks so bad, but at the snails pace that would be still 42 kN if you calculate the power as force times speed.

I know the snails speed may not be so common, but things always start slow.
 
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Offline electrodacus

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Ok, so if the user is stationary in a 20 km/h head wind, how much power is required to maintain this position?  If you come up with any answer other than zero, you can't explain how a brake works.  The brake can maintain this position into the 20 km/h wind while dissipating no power.  A rider can do the same thing by simply standing on the pedal preventing it from rising up.  One foot on the ground for balance, one foot on the pedal to maintain position.  No power transfer.  ZERO

You seem to have already agreed that this is correct.  In that case you must agree there is no power transfer at the wheels for a stationary bike/car/blackbird and that the equation that predicts power at the wheels based solely on the wind relative speed must be wrong.

If there are no sort of brakes it will require around 42W. A brake will anchor the vehicle to the ground thus no work is done on the vehicle.
A rider with sufficient weight standing on the pedal will still be a form of brake. It is a gravitational based one but still a brake.
There is potential wind power that can not be used because of the brake but there are 42W available at 20km/h wind speed and that 0.408m^2 equivalent area.
The equilibrium state will be the bike being pushed at 20km/h relative to ground so that there is no more force on the bike and no potential energy relative to air but there is now a potential energy relative to ground based on vehicle weight and speed relative to ground.
Without any energy storage the bike can be between zero speed relative to ground if anchored to ground and wind speed if there is no friction loss so not anchored to ground.
The vehicle can be anywhere between this two speed directly down wind at wind speed relative to ground and zero speed relative to ground and at this ends it will have potential energy storage relative to ground or to air.
This kinetic energy while it is a form of energy storage can not help the vehicle get outside this speed limits if it travels directly down wind at all times.
This kinetic energy can be used if vehicle travels at an angle to the wind direction that is how a sail vehicle can exceed wind speed.

In case of blackbird direct downwind version pressure differential is used to exceed wind speed for a limited amount of time.
In case of blackbird direct upwind version elastic and or gravitational energy storage in combination with stick slip hysteresis is what is used to drive at any speed (limited by frictional losses) for any amount of time.

Offline electrodacus

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A very high wind speed will give very high forces - there is nothing ridiculous about that. The problem is with the wrong equation it gets ridiculous as it predicts too high a power at low speeds, like 20 km/h wind and 0.001 m/s movement relative to ground. 42 W of power don't looks so bad, but at the snails pace that would be still 42 kN if you calculate the power as force times speed.

I know the snails speed may not be so common, but things always start slow.

The 42W are not for that 0.001m/s but for the effect of drag due to a fluid traveling in the opposite direction at 20km/h.
The 42kN are valid just in theoretical world in reality you will not be able to drive at 0.001m/s as the wheels will slip due to this huge force so speed will become higher very fast so fast that your brain (or mine) will not be able to see the transition.
That is like saying no vehicle can ever leave from standing still as the force needed to move that vehicle will be to high.
Wheel will have a force at with it will start to slip and that will be the max force you will be able to provide at the wheel.
You can see the effect when you try to accelerate a vehicle to fast and wheel will spin.

Online Kleinstein

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The 42W are not for that 0.001m/s but for the effect of drag due to a fluid traveling in the opposite direction at 20km/h.
The 42kN are valid just in theoretical world in reality you will not be able to drive at 0.001m/s as the wheels will slip due to this huge force so speed will become higher very fast so fast that your brain (or mine) will not be able to see the transition.
That is like saying no vehicle can ever leave from standing still as the force needed to move that vehicle will be to high.
Wheel will have a force at with it will start to slip and that will be the max force you will be able to provide at the wheel.
You can see the effect when you try to accelerate a vehicle to fast and wheel will spin.
You claimed the power would be the power needed to drive against the wind - I (and most others here) were in doubt of that. That is your theory that gives the wrong result !   I just enteres a very small speed and used the very basic force = power / speed  formula for a mechanical movement.
 

Online IanB

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What would you say if someone showed you a wind powered vehicle that moves directly upwind without energy storage?

That is not possible so I will show him where energy storage is. Maybe for this particular case I will ask him to take a video with a high speed camera to notice how the movement is not constant but it fluctuates as energy storage is charged and discharged.

That is the wrong answer. Maybe you would like to try again?
 

Online IanB

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Due to the power of The Algorithm, I came across this very appropriate video just now. It is rather apposite to this thread.


 
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Offline electrodacus

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You claimed the power would be the power needed to drive against the wind - I (and most others here) were in doubt of that. That is your theory that gives the wrong result !   I just enteres a very small speed and used the very basic force = power / speed  formula for a mechanical movement.

It is not my claim as in I did not discovered anything new.

Just imagine this.
You are stationary anchored to the ground.  You can chose to "lift the anchor" and your vehicle will be accelerated direct down wind or down stream (boat on a river). This power to accelerate is provided to you by the wind or stream of water but if you decide to drive swim upstream then you need way more power as you are going against the stream.
So while your vehicle in the wind is stationary or boat on a river is stationary relative to ground you are likely anchored.

Have you ever had the chance to swim in a river ?  What amount of power do you need to swim upstream compared to down stream ?   

Online IanB

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Just imagine this.
You are stationary anchored to the ground.  You can chose to "lift the anchor" and your vehicle will be accelerated direct down wind or down stream (boat on a river). This power to accelerate is provided to you by the wind or stream of water but if you decide to drive swim upstream then you need way more power as you are going against the stream.

Here is the graph of power vs. speed:



If you want to drive upstream at a slow speed, then you need very little power, as you can see from the graph.

If the boat wants to go upstream at a tiny fraction of the speed of the current, it only needs a tiny amount of power.

(If you care about "anchor", imagine the boat is anchored by a rope, and it can go upstream by pulling on the rope. If the gearing on the pulley is low enough, it can go upstream with the power from a tiny little battery and a little tiny motor.)
« Last Edit: December 28, 2021, 12:15:47 am by IanB »
 

Offline electrodacus

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That is the wrong answer. Maybe you would like to try again?

I will ask you the same thing as it is a decently good analogy.
Have you ever had the chance to swim in a river ?

Offline gnuarm

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What would you say if someone showed you a wind powered vehicle that moves directly upwind without energy storage?

That is not possible so I will show him where energy storage is. Maybe for this particular case I will ask him to take a video with a high speed camera to notice how the movement is not constant but it fluctuates as energy storage is charged and discharged.

How is the energy storage relevant?  If the vehicle continues against the wind indefinitely, it is moving against the wind.  Who cares if there are tiny variations in the speed?  This sort of storage of energy is not relevant to the issue.  At no time does the velocity fall below the wind speed.
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Online IanB

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That is the wrong answer. Maybe you would like to try again?

I will ask you the same thing as it is a decently good analogy.
Have you ever had the chance to swim in a river ?

https://youtu.be/Qf03U04rqGQ?t=134
« Last Edit: December 28, 2021, 12:18:07 am by IanB »
 

Offline electrodacus

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How is the energy storage relevant?  If the vehicle continues against the wind indefinitely, it is moving against the wind.  Who cares if there are tiny variations in the speed?  This sort of storage of energy is not relevant to the issue.  At no time does the velocity fall below the wind speed.

Wind will charge the energy storage device (small capacity) then slip will allow the stored energy to be discharged and thus vehicle will move forward against wind direction that small amount that is possible with that stored energy. Then wheel will lock and energy storage will be again charge then everything repeats  multiple times per second. All energy used to advance the vehicle against wind direction was stored energy.
The above is valid for a direct upwind vehicle but based on your "At no time does the velocity fall below the wind speed" comment you may be talking about direct downwind and that is a completely different thing.

Offline electrodacus

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That is the wrong answer. Maybe you would like to try again?

I will ask you the same thing as it is a decently good analogy.
Have you ever had the chance to swim in a river ?

https://youtu.be/Qf03U04rqGQ?t=134

How is that video that you already posted relevant to my question about swimming in a river ?
Do you think air is not a fluid ?

Online IanB

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That is the wrong answer. Maybe you would like to try again?

I will ask you the same thing as it is a decently good analogy.
Have you ever had the chance to swim in a river ?

https://youtu.be/Qf03U04rqGQ?t=134

How is that video that you already posted relevant to my question about swimming in a river ?
Do you think air is not a fluid ?

Your reply is a red herring. Swimming in a river has nothing to do with my question.

Let me ask you again: what would you say if someone showed you a demonstration of a vehicle moving directly against the wind, powered by the wind, with no energy storage?

It's a very simple question. It doesn't involve rivers, or swimming, or any bullshit like that.
 

Offline gnuarm

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Ok, so if the user is stationary in a 20 km/h head wind, how much power is required to maintain this position?  If you come up with any answer other than zero, you can't explain how a brake works.  The brake can maintain this position into the 20 km/h wind while dissipating no power.  A rider can do the same thing by simply standing on the pedal preventing it from rising up.  One foot on the ground for balance, one foot on the pedal to maintain position.  No power transfer.  ZERO

You seem to have already agreed that this is correct.  In that case you must agree there is no power transfer at the wheels for a stationary bike/car/blackbird and that the equation that predicts power at the wheels based solely on the wind relative speed must be wrong.

If there are no sort of brakes it will require around 42W. A brake will anchor the vehicle to the ground thus no work is done on the vehicle.
A rider with sufficient weight standing on the pedal will still be a form of brake. It is a gravitational based one but still a brake.

Ok, so no movement, no power, right?


Quote
There is potential wind power that can not be used because of the brake but there are 42W available at 20km/h wind speed and that 0.408m^2 equivalent area.

Not talking about wind power or using it.  I'm talking about the power involved in moving or not moving the vehicle.  So once you acknowledge the equation for the power to move the vehicle has to return a zero value at zero speed, it is clear which equation is correct. 


Quote
The equilibrium state will be the bike being pushed at 20km/h relative to ground so that there is no more force on the bike and no potential energy relative to air but there is now a potential energy relative to ground based on vehicle weight and speed relative to ground.

I thought the speed was zero?  So no power, no energy relative to the ground.


Quote
Without any energy storage the bike can be between zero speed relative to ground if anchored to ground and wind speed if there is no friction loss so not anchored to ground.
The vehicle can be anywhere between this two speed directly down wind at wind speed relative to ground and zero speed relative to ground and at this ends it will have potential energy storage relative to ground or to air.
This kinetic energy while it is a form of energy storage can not help the vehicle get outside this speed limits if it travels directly down wind at all times.
This kinetic energy can be used if vehicle travels at an angle to the wind direction that is how a sail vehicle can exceed wind speed.

In case of blackbird direct downwind version pressure differential is used to exceed wind speed for a limited amount of time.
In case of blackbird direct upwind version elastic and or gravitational energy storage in combination with stick slip hysteresis is what is used to drive at any speed (limited by frictional losses) for any amount of time.

Ok, you are off task again.  Let's just deal with one detail at a time.  So do you acknowledge that the correct equation for the power at the wheels to move the vehicle into the wind must contain a factor which is just the velocity of the vehicle relative to the ground the wheel is pushing against? 

The force from the wind is 

Fd = 1/2 · Cd · A · p · (vw + vo)^2

The power required at the vehicle wheels to maintain a speed into the wind is 

Pv = 1/2 · Cd · A · p · (vw + vo)^2 · vo

Correct?
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Online Kleinstein

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....
My earlier example is perfectly correct and for a bicycle to move at 1km/h against a 230km/h head wind it will require a minimum of 66kW and gears can not help with anything as a cyclist may be able to provide 300W for minutes and maybe peak around 1kW it will never be able to provide 66kW and so never be able to move against a 230km/h head wind let a lone the possibility that 300W is enough to do that as the wrong formula and that calculator will imply.

You claimed the power would be the power needed to drive against the wind - I (and most others here) were in doubt of that. That is your theory that gives the wrong result !   I just enteres a very small speed and used the very basic force = power / speed  formula for a mechanical movement.

It is not my claim as in I did not discovered anything new.

Just imagine this.
You are stationary anchored to the ground.  You can chose to "lift the anchor" and your vehicle will be accelerated direct down wind or down stream (boat on a river). This power to accelerate is provided to you by the wind or stream of water but if you decide to drive swim upstream then you need way more power as you are going against the stream.
So while your vehicle in the wind is stationary or boat on a river is stationary relative to ground you are likely anchored.

Have you ever had the chance to swim in a river ?  What amount of power do you need to swim upstream compared to down stream ?   
Swiming in the rive is something for a red herring: it removes the 2nd moving plane and thus the whole point.
 

Offline electrodacus

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Your reply is a red herring. Swimming in a river has nothing to do with my question.

Let me ask you again: what would you say if someone showed you a demonstration of a vehicle moving directly against the wind, powered by the wind, with no energy storage?

It's a very simple question. It doesn't involve rivers, or swimming, or any bullshit like that.

My question is super relevant but you likely do not understand what air is.
And as already answer no vehicle powered only by wind can go directly upwind without energy storage.

Offline electrodacus

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Swiming in the rive is something for a red herring: it removes the 2nd moving plane and thus the whole point.

Ground is still stationary the swimmer is the vehicle and water is air.  I do not see anything removed.
 

Online IanB

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Your reply is a red herring. Swimming in a river has nothing to do with my question.

Let me ask you again: what would you say if someone showed you a demonstration of a vehicle moving directly against the wind, powered by the wind, with no energy storage?

It's a very simple question. It doesn't involve rivers, or swimming, or any bullshit like that.

My question is super relevant but you likely do not understand what air is.
And as already answer no vehicle powered only by wind can go directly upwind without energy storage.

That's still the wrong answer.

If you cannot answer a simple question like this one, which almost anyone else on the planet would know how to answer, then continuing the debate in this thread is rather pointless, wouldn't you agree?
 

Offline PlainName

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Your reply is a red herring. Swimming in a river has nothing to do with my question.

Let me ask you again: what would you say if someone showed you a demonstration of a vehicle moving directly against the wind, powered by the wind, with no energy storage?

It's a very simple question. It doesn't involve rivers, or swimming, or any bullshit like that.

My question is super relevant but you likely do not understand what air is.
And as already answer no vehicle powered only by wind can go directly upwind without energy storage.

Can't believe this. Are you afraid that he'll actually produce the goods and show you? Why else wouldn't you jump at this and say "Alright, show me then"?

Gosh, he hasn't even asked you to renounce your stated opinion on stuff, just asking what you'd say. Of course, after 1000 posts we know jolly well that if he did manage to demonstrate this you would still deny it in some way, probably by some distraction technique like changing the subject or introducing a strawman or similar :(
 


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