Author Topic: Mess with your minds: A wind powered craft going faster than a tail wind speed.  (Read 147204 times)

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Offline gnuarm

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I hope you keep your microphone on the floor and I'm getting tired to explain the same thing multiple times to someone that will not understand power, energy and conservation of energy.

I'm sure you are getting tired, but you haven't explained anything.  You obfuscate and bicker, but never actually make sense.  When someone shows you proof, you ignore it and change the topic.  But you never, ever explain anything.  You also don't respond to anything that is a clear, simple explanation of how you are wrong.  You just repeat the same old tired assertions that you perceive as fact.

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Offline gnuarm

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Also to store that energy the vehicle will accelerate much slower when below wind speed compared to a sail vehicle that will not store anything other than kinetic energy.

I've asked you this before, but why does a sail not store energy when below windspeed, but a propeller does?

A sail "stores" energy in exactly the same way as the propeller.  ED doesn't actually understand either the sail or the propeller.  The propeller blades work best when they have an airfoil which creates a high pressure on the flatter side and a low pressure on the more curved side.  There is also an adjustable pitch to the blades which works more like a kite.  The blades move through the air pushing air behind creating a higher pressure behind and a low pressure in front.  This pressure gradient is what ED claims is storing energy.  It does, but not very much.  It dissipates very quickly, almost instantaneously, when the blades are stopped. 

The sail works very similarly.  The wind blows across the sail creating the same high pressure and low pressure for the exact same reasons.  This pulls on the sail dragging the boat along.  The resulting forces actually propel the boat faster than the wind and can even move the boat upwind.  If such a vessel were examined closely while moving, it would be found there is no periodic release of energy to make the boat move the way it does.  The ideal situation is for the sail to be trimmed so the boat is in an optimal state to get the maximum movement from the wind.  At that point unless the wind direction changes, everything is stable.

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Offline Brumby

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The blades move through the air pushing air behind creating a higher pressure behind and a low pressure in front.  This pressure gradient is what ED claims is storing energy.  It does, but not very much.  It dissipates very quickly, almost instantaneously, when the blades are stopped.

But the blades of the Blackbird never stop.  True?
 

Offline electrodacus

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The blades move through the air pushing air behind creating a higher pressure behind and a low pressure in front.  This pressure gradient is what ED claims is storing energy.  It does, but not very much.  It dissipates very quickly, almost instantaneously, when the blades are stopped.

But the blades of the Blackbird never stop.  True?

They rotate as long as the vehicle moves as they are connected to wheels. But the vehicle will get to a peak speed / kinetic energy when all stored energy (pressure differential) is used up then it will start to slow down well below wind speed.

Online IanB

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They rotate as long as the vehicle moves as they are connected to wheels. But the vehicle will get to a peak speed / kinetic energy when all stored energy (pressure differential) is used up then it will start to slow down well below wind speed.

This kind of response, overshooting and then coming back down again, can only be observed in a system with second order dynamics, and a second order system requires some kind of inertia or momentum term. A compressed gas is a first order system, so it cannot explain this kind of system behavior. Where is the second order inertial term found in Blackbird?
 

Offline electrodacus

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They rotate as long as the vehicle moves as they are connected to wheels. But the vehicle will get to a peak speed / kinetic energy when all stored energy (pressure differential) is used up then it will start to slow down well below wind speed.

This kind of response, overshooting and then coming back down again, can only be observed in a system with second order dynamics, and a second order system requires some kind of inertia or momentum term. A compressed gas is a first order system, so it cannot explain this kind of system behavior. Where is the second order inertial term found in Blackbird?

What are you even talking about.
Of course energy stored in pressure differential will exactly result in this sort behavior where as the pressure differential drops the rate of acceleration drops until there is no longer any acceleration and deceleration phase will start.   

Offline Brumby

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They rotate as long as the vehicle moves as they are connected to wheels. But the vehicle will get to a peak speed / kinetic energy when all stored energy (pressure differential) is used up then it will start to slow down well below wind speed.
But won't the propeller still be pushing back and causing another pressure differential?
 

Online IanB

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What are you even talking about.
Of course energy stored in pressure differential will exactly result in this sort behavior where as the pressure differential drops the rate of acceleration drops until there is no longer any acceleration and deceleration phase will start.   

But where does the stored energy in the pressure differential come from? There is no external power source to charge it up. The vehicle starts from a standstill and gets blown along by the wind like a sail, until it speeds up and goes faster than the wind. Until this point, all the wind energy is being used to make Blackbird go faster. Where does the extra energy come from to charge up a pressure bubble?
 

Offline electrodacus

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But won't the propeller still be pushing back and causing another pressure differential?

The entire vehicle is pushed by this pressure differential not by the propeller. Propeller is powered by this pressure differential so part of the power from the pressure differential is used to accelerate the vehicle and another part is used by propeller to put something back in to increasing the pressure differential but net pressure differential drops as much more is used (for acceleration and friction losses) than it is put back.
Propeller itself is just a device allowing to store energy in surrounding air.

In the beginning is the wind pushing the vehicle part of the wind power will go to (accelerating the vehicle and friction losses) and the other part will be used by propeller to increase the pressure differential and even before vehicle gets to half the wind speed the stored pressure differential will take most of the part of powering the vehicle but still some small percentage will also be covered by wind and when vehicle above wind speed there is no more wind power available so all acceleration is done by the remaining pressure differential.
The higher the percentage of push power will go to propeller the more energy will be stored (resulting in a slower acceleration rate to allow more time to charge) and then also after exceeding wind speed the power from pressure differential will just be "recycled" meaning push the vehicle then take big part of that trough the wheel maybe 60 or 70% of that ending back as pressure differential. Process is not efficient but good enough that it can keep this pressure differential pushing the vehicle for a few minutes.

In a very simplistic way you can think of natural wind speed providing the initial energy and part of that will be used to increase the artificial wind speed (made by propeller) and so max speed the vehicle can reach is no longer the natural wind speed but the artificial wind speed (a bit less of course as there are multiple losses) still way above "natural wind speed"

Offline electrodacus

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But where does the stored energy in the pressure differential come from? There is no external power source to charge it up. The vehicle starts from a standstill and gets blown along by the wind like a sail, until it speeds up and goes faster than the wind. Until this point, all the wind energy is being used to make Blackbird go faster. Where does the extra energy come from to charge up a pressure bubble?

It comes from the wind while vehicle is well below wind speed. As soon as the vehicle starts to move pushed by the wind the propeller will start to rotate and not only push air back but increase the equivalent sail area. So in the initial phase the sail size increases from the vehicle back are plus the propeller blades area up to full propeller swept area.
Only small part of the wind energy is used to accelerate the Blackbird that ratio is given by the gear ratio between wheel and propeller and the propeller pitch.
So wind pushes against vehicle body and later propeller swept area and that power is split say 60% to propeller and 40% to acceleration so even more time spend charging as the acceleration is slowed then from those 60% say about 70% (assuming 70% efficient propeller) is stored but that stored energy will increase a bit the pressure differential so part of what you just stored a moment ago also starts to power the vehicle and at some point (below half wind speed according to my calculations) the pressure differential becomes more significant than the wind power.
So most of the charged energy happens well before vehicle gets to half the wind speed.

Offline gnuarm

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But where does the stored energy in the pressure differential come from? There is no external power source to charge it up. The vehicle starts from a standstill and gets blown along by the wind like a sail, until it speeds up and goes faster than the wind. Until this point, all the wind energy is being used to make Blackbird go faster. Where does the extra energy come from to charge up a pressure bubble?

It comes from the wind while vehicle is well below wind speed. As soon as the vehicle starts to move pushed by the wind the propeller will start to rotate and not only push air back but increase the equivalent sail area. So in the initial phase the sail size increases from the vehicle back are plus the propeller blades area up to full propeller swept area.
Only small part of the wind energy is used to accelerate the Blackbird that ratio is given by the gear ratio between wheel and propeller and the propeller pitch.
So wind pushes against vehicle body and later propeller swept area and that power is split say 60% to propeller and 40% to acceleration so even more time spend charging as the acceleration is slowed then from those 60% say about 70% (assuming 70% efficient propeller) is stored but that stored energy will increase a bit the pressure differential so part of what you just stored a moment ago also starts to power the vehicle and at some point (below half wind speed according to my calculations) the pressure differential becomes more significant than the wind power.
So most of the charged energy happens well before vehicle gets to half the wind speed.

Ok, you are right.
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Online Kleinstein

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But where does the stored energy in the pressure differential come from? There is no external power source to charge it up. The vehicle starts from a standstill and gets blown along by the wind like a sail, until it speeds up and goes faster than the wind. Until this point, all the wind energy is being used to make Blackbird go faster. Where does the extra energy come from to charge up a pressure bubble?

It comes from the wind while vehicle is well below wind speed. As soon as the vehicle starts to move pushed by the wind the propeller will start to rotate and not only push air back but increase the equivalent sail area. So in the initial phase the sail size increases from the vehicle back are plus the propeller blades area up to full propeller swept area.
Only small part of the wind energy is used to accelerate the Blackbird that ratio is given by the gear ratio between wheel and propeller and the propeller pitch.
So wind pushes against vehicle body and later propeller swept area and that power is split say 60% to propeller and 40% to acceleration so even more time spend charging as the acceleration is slowed then from those 60% say about 70% (assuming 70% efficient propeller) is stored but that stored energy will increase a bit the pressure differential so part of what you just stored a moment ago also starts to power the vehicle and at some point (below half wind speed according to my calculations) the pressure differential becomes more significant than the wind power.
So most of the charged energy happens well before vehicle gets to half the wind speed.
I still don't get why the pressure differential is more efficient in pushing the vehicle forward when the vehicle is above wind speed than opposed to below the wind speed.  So what slows down the conversion of energy so much that is needs quite some time from reaching the speed of the wind to reaching the maximum speed ?
 

Offline Domagoj T

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Well it is very relevant as the direct downwind vehicle will not travel indefinitely at 2x or 3x the wind speed but only for a limited amount of time proportional with the amount of stored energy.
Also to store that energy the vehicle will accelerate much slower when below wind speed compared to a sail vehicle that will not store anything other than kinetic energy. So Blackbird direct down wind version spends more time below wind speed to charge the energy storage (pressure differential) then uses that stored energy to accelerate above wind speed and stay a bit above that speed before returning to below wind speed.

I'm still waiting for you to respond to my wind powered toy design from page 45.
It has no storage, operates in steady state continuously and has infinite range. At no point do extended sails travel faster than the wind, but the vehicle as a whole does.
I'm waiting.
 

Offline electrodacus

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I still don't get why the pressure differential is more efficient in pushing the vehicle forward when the vehicle is above wind speed than opposed to below the wind speed.  So what slows down the conversion of energy so much that is needs quite some time from reaching the speed of the wind to reaching the maximum speed ?

Pressure differential drops as it is being used up thus less power is available to accelerate and so acceleration rate drops.
Is like having a light bulb connected to a capacitor at first the pressure (voltage) is high so you get a lot of light (high acceleration rate) then as voltage (pressure) drops it will take longer and longer to use the remaining energy in the capacitor. 

Offline electrodacus

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I'm still waiting for you to respond to my wind powered toy design from page 45.
It has no storage, operates in steady state continuously and has infinite range. At no point do extended sails travel faster than the wind, but the vehicle as a whole does.
I'm waiting.

There are two very different versions of blackbird. There is the direct downwind that works based on pressure differential energy storage and there is the direct upwind version that uses small capacity internal storage and stick slip hysteresis and that version since it always have access to wind power it can work continuously as long as there is wind.
All the wheels only toys where air is not involved are the equivalent of that direct upwind version of blackbird using small capacity energy storage device maybe charging in a few ms and then discharging triggered by stick slip hysteresis either internally in the mechanism or externally at the wheels.

The wrong equation for power either drag or generation is what made the math possible without energy storage. If the correct equation for power is used then is clear from the math that neither direct downwind faster than wind nor direct up wind at any speed is not possible without energy storage.

Offline gnuarm

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The never ending diversion from the real issues.  Just like Andrea Rossi.  This guy should try the cold fusion business, he seems a natural. 
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Offline electrodacus

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The never ending diversion from the real issues.  Just like Andrea Rossi.  This guy should try the cold fusion business, he seems a natural.

Is hard to know what the real issue is but currently my best guess is the wrong equation for wind power.
That wrong equation seems to be present everywhere.

correct one is below and can be tested but also demonstrated.

0.5 * air density * area * (wind speed - vehicle speed)3
For direct upwind vehicle direction is negative so it will be (wind speed - (-vehicle speed))3  thus (wind speed + vehicle speed)

People sees to like to use force for witch in most case they use the correct equation that includes (wind speed - vehicle speed)2 but then when it gets the time to calculate power they only multiply with vehicle speed instead of multiplying with (wind speed - vehicle speed).
Basically the wind speed is considered for force but ignored for power.

Not sure witch person did this mistake first but it seems it got everywhere.

Offline PlainName

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Quote
Is hard to know what the real issue is but currently my best guess is the wrong equation for wind power.

The real issue is your habit of diverting when it looks like something is going places. As I pointed out earlier, you're afraid that you might be shown to be wrong, so you do or say whatever is necessary to ensure we never get there.

I might remind you of the outstanding questions I asked which were designed to be small steps along such a route, but you appear to have figured there might be something in it and dropped it pretty quickly.
 

Offline electrodacus

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The real issue is your habit of diverting when it looks like something is going places. As I pointed out earlier, you're afraid that you might be shown to be wrong, so you do or say whatever is necessary to ensure we never get there.

I might remind you of the outstanding questions I asked which were designed to be small steps along such a route, but you appear to have figured there might be something in it and dropped it pretty quickly.

If there was some question you asked and I did not answered was likely because it was useless for me to do so and probably answered before.
Most important equation for any wind powered vehicle is the one showing the available wind power to the vehicle and of course if that is wrong you will get to wrong conclusions.

Online Kleinstein

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All the wheels only toys where air is not involved are the equivalent of that direct upwind version of blackbird using small capacity energy storage device maybe charging in a few ms and then discharging triggered by stick slip hysteresis either internally in the mechanism or externally at the wheels.

The wrong equation for power either drag or generation is what made the math possible without energy storage. If the correct equation for power is used then is clear from the math that neither direct downwind faster than wind nor direct up wind at any speed is not possible without energy storage.

The wheel based versions can be interpreted both ways. It is just a question on which plane is identified as the ground or "wind". It is somewimes a bit trikcky to look at the same thing with different referene frames, but this a major point of doing though experiments.

Quite some wheeled models may show some slip stick like action, but this does not say that this is essentially for them to work, there are some with little visible slip stick.

The equation for the power from a sail vehicle is not used in the calculatoins for the backbird at all, as there is no sail involved, only an active driven prop. So there is no need and no sense in using the equation for a sail dirven vehicle.

Trying to use the equation to show that the blackbird vehickle would not work also makes little sense, as at best this would only show that with passive sails it would not work downwind. This is accepted and one would even get the some conclusion with the wrong (w-v)³ type form and the correct (w-v)²*v type form. However this does not proof that a different type of vehicle could no work - it just does not apply.

To proof that the backbrid vehicle would not work the way would be to calculate the power available from the wheels and the power needed to drive the prop. If the prop needs more power than the wheels can provide, it does not work (at least not without energy storage or other methods not inlcuded in the model). So this already quite close to the calculation in the video. Just need to calculate (e.g. get an upper / lower limit) the power needed to drive to prop, so kind of the other way around from a wind turbine, maybe include the Betz limit or a similar factor for the prop.


People sees to like to use force for witch in most case they use the correct equation that includes (wind speed - vehicle speed)2 but then when it gets the time to calculate power they only multiply with vehicle speed instead of multiplying with (wind speed - vehicle speed).
Basically the wind speed is considered for force but ignored for power.

Not sure witch person did this mistake first but it seems it got everywhere.
There may have been other before, but the first to bring up the mistake here was electrodacus.

The form with (wind speed - vehicle speed)2  only applies to vehicle speed < wind speed or would need to include the sign of (wind speed - vehicle speed), but at least it gets the low velocity range right.
 

Offline PlainName

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The real issue is your habit of diverting when it looks like something is going places. As I pointed out earlier, you're afraid that you might be shown to be wrong, so you do or say whatever is necessary to ensure we never get there.

I might remind you of the outstanding questions I asked which were designed to be small steps along such a route, but you appear to have figured there might be something in it and dropped it pretty quickly.

If there was some question you asked and I did not answered was likely because it was useless for me to do so and probably answered before.
Most important equation for any wind powered vehicle is the one showing the available wind power to the vehicle and of course if that is wrong you will get to wrong conclusions.

Wrong again. The aim was to end up with full agreement on both sides at the position where a single small thing, easily resolved, diverges. But due to your propensity to continually disappear off-piste it was necessary to get you to agree to each tiny step along the way. Which, of course, you now won't because you know you will stumble at the final hurdle.
 

Offline electrodacus

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The wheel based versions can be interpreted both ways. It is just a question on which plane is identified as the ground or "wind". It is somewimes a bit trikcky to look at the same thing with different referene frames, but this a major point of doing though experiments.

Quite some wheeled models may show some slip stick like action, but this does not say that this is essentially for them to work, there are some with little visible slip stick.

The equation for the power from a sail vehicle is not used in the calculatoins for the backbird at all, as there is no sail involved, only an active driven prop. So there is no need and no sense in using the equation for a sail dirven vehicle.

Trying to use the equation to show that the blackbird vehickle would not work also makes little sense, as at best this would only show that with passive sails it would not work downwind. This is accepted and one would even get the some conclusion with the wrong (w-v)³ type form and the correct (w-v)²*v type form. However this does not proof that a different type of vehicle could no work - it just does not apply.

To proof that the backbrid vehicle would not work the way would be to calculate the power available from the wheels and the power needed to drive the prop. If the prop needs more power than the wheels can provide, it does not work (at least not without energy storage or other methods not inlcuded in the model). So this already quite close to the calculation in the video. Just need to calculate (e.g. get an upper / lower limit) the power needed to drive to prop, so kind of the other way around from a wind turbine, maybe include the Betz limit or a similar factor for the prop.


There may have been other before, but the first to bring up the mistake here was electrodacus.

The form with (wind speed - vehicle speed)2  only applies to vehicle speed < wind speed or would need to include the sign of (wind speed - vehicle speed), but at least it gets the low velocity range right.

No you can not interpret something in both ways as only one can be correct and since the other one is impossible is clear witch one is correct even trough elimination.
And yes both energy storage and stick slip hysteresis is essential for them to work else they are just a locked gearbox as I showed by eliminating the slip of the generator wheel.

Wind can interact with a vehicle any vehicle only by pushing against an area thus all vehicle work the same as the sail vehicle.
That wind power equation is universal and applies to any wind powered vehicle including blackbird.

The correct form of that equation contains (w-v)3 or if you prefer (w-v)2 * (w-v)

I can prove this equation is true you will not be able to prove that wrong equation is true unless wind speed is zero.

Offline gnuarm

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The equation 0.5 * air density * area * (wind speed - vehicle speed)3 may be the right equation, but for the wrong purpose.

In determining the power required to move the vehicle into (or away from) the wind, the above equation is wrong.  It uses (wind speed - vehicle speed) as the speed of the applied force which would be talking about the power of the wind.  No one is asking about the power from the wind.  The question is the power applied to the VEHICLE to maintain a speed relative to the ground, "vehicle speed".

So the full equation for the power applied to the vehicle through the wheels is

0.5 * air density * area * (wind speed - vehicle speed)² * vehicle speed

It's very simple.  You need to apply the right equation to the right purpose.  This equation tells you how much power is needed to move the vehicle.  I don't know for sure what the other equation is telling you.  It probably includes the power lost in turbulence and all the hard to calculate effects when trying to calculate turbulent air flow.  Many PhDs have been earned in that field.

Listen and learn son... listen and learn. 
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Offline PlainName

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... may be the right equation, but for the wrong purpose

Reminds me of (jump to 1:21):

 

Offline electrodacus

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The equation 0.5 * air density * area * (wind speed - vehicle speed)3 may be the right equation, but for the wrong purpose.

In determining the power required to move the vehicle into (or away from) the wind, the above equation is wrong.  It uses (wind speed - vehicle speed) as the speed of the applied force which would be talking about the power of the wind.  No one is asking about the power from the wind.  The question is the power applied to the VEHICLE to maintain a speed relative to the ground, "vehicle speed".

So the full equation for the power applied to the vehicle through the wheels is

0.5 * air density * area * (wind speed - vehicle speed)² * vehicle speed

It's very simple.  You need to apply the right equation to the right purpose.  This equation tells you how much power is needed to move the vehicle.  I don't know for sure what the other equation is telling you.  It probably includes the power lost in turbulence and all the hard to calculate effects when trying to calculate turbulent air flow.  Many PhDs have been earned in that field.

Listen and learn son... listen and learn.

For a wind only powered vehicle the most important equation is the one that provides you with the answer to how much wind power is available to the vehicle.

The correct one is (if you prefer to be written like this)

0.5 * air density * area * (wind speed - vehicle speed)² * (wind speed - vehicle speed)

This is provable both in theory and in practice.

I think swimming in a river was a good example but you can think on a boat on a river or a submarine in a river.
Think about the power you need to just stay still relative to ground.
Air is not different it is a fluid same as water.
Or you can imagine balls hitting the vehicle.


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