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

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CatalinaWOW:

--- Quote from: electrodacus on December 30, 2021, 06:43:45 pm ---
--- Quote from: Domagoj T on December 30, 2021, 10:49:16 am ---Don't worry about my feelings, I'm a big boy, I can handle it. Will I'll have no clue what you would have said because you think I have reduced mental capability or because you just can't provide an argument?
You keep saying that at wind speed a sail has no power, yet when I give you an example of sail traveling below wind speed, you deflect and avoid.


So let's focus not on generic, but on this specific example.
And yes, this vehicle does have an external energy source - the wind.

--- End quote ---

I do think people mental capabilities are very different.
There is no wind power available to a sail vehicle traveling at wind speed. There is of course plenty of power available to a sail traveling below wind speed. The slower it travels relative to wind speed the higher the available wind power.
It is clearly seen form the equation that I constantly post here.

Pw = 0.5 * air density * area * (wind speed - vehicle speed)3

I even provided examples. Maybe you got here more recently and did not see them but here is one example just for you

area 1m2
air density 1.2kg/m3
Wind speed 20m/s
Vehicle speed:
a)0m/s
b)5m/s
c)10m/s
d)15m/s
e)20m/s
Wind power available to vehicle
a)4800W
b)2025W
c)600W
d)75W
e)0W

--- End quote ---

A.  Have you read the paper provided by IanB?

B.  You claim you have the correct equation.  Which is clearly preposterous because it doesn't show the effect of the fan (propeller).  Take the really simple case of a fan with blades parallel to the direction of motion.  These blades subtract power, stirring the air and creating heat.  Conceptually with a large enough gear ratio the vehicle would not attain perceptible motion regardless of wind speed.  So your equation is at best part of the story.  It is a perhaps correct equation for a flat plate on a frictionless vehicle, but isn't a representation of the vehicle in question.  Adding angle of attack for the blades and an efficient airfoil shape further adds to the complexity of a correct description.  At this point I refer you to A. again, which is a clear and understandable description of the entire system.

Kleinstein:

--- Quote from: electrodacus on December 30, 2021, 06:59:42 pm ---...
The main point I want to make since this is ester to understand (at least is what I was thinking) is that there is no wind power available to a direct down wind traveling at or above wind speed.
I provided the correct equation and anyone that is not agreeing with that equation is welcome to provide the correct one.
Nobody can claim to understand a wind powered only vehicle without being able to provide an equation describing the amount of wind power available to vehicle.

--- End quote ---

Using the wind power available is not at all an easy way to look at the problem. Calculating the available wind power depends on the method used to harness the power and it is not really clear which way is the best. At least I don't know an expression for the available wind power. I consider the way with calculating the maximum awailable wind power a very difficult way. The point here is that it is not enough to show a result, but one would also need to derive that result from known parts. This may need rather envolved aero-dynaimics  - a field I am not good at and would best avoid. One some-times should also know the areas one is not good at or areas that are just difficult and maybe just lack simple solutions.

However I know that the avaiable wind power is not the same as the power needed to drive into the head wind. The available wind power is power that is available - so there is already plenty of power around, why should one need the same power once again. For opposing forces it is about a balance of forces, not a balance of power. In some cases (1 D and 100% efficient adapted gears and only 1 ref frame) it may look that it works with power, but that does not mean this is the right way. Wind power generally not 100% efficient and is pure power based calculation likely does not work.

The problem is a bit one sided: it is often quite difficult to show that something is not possible, while if a claimed construction is possible it is often relatively easy to proof that it is working in deed. Compare it a bit to Phytagoras law, that is easy to proof and Fermat's last Theorem which is really hard to proof.
Calculating the maximum wind power would in theory be a way to to show what is impossible, but it is a really hard way and would need lots of explainations on how the power is derived. I would expect this more like a 100 page work, and maybe still open to debate. The proof that the blackbird vehichle indeed works is in comparison simple, more like 10-20 lines.
Things get a bit easier by limiting the calculation to the give working principle (prop to push and wheels for the power) and see if there is enough power around from the wheels to drive the prop. It is about just doing the math: more power from the wheel side and this principle is possible, more power needed for the prop and this idea does no work ( it would still not exclude a different working principle).

For the proof that the blackbird vehicle does indeed work, there is no need to calculate the maximum available power. One does not even need to calculation the available power to such a vehicle. It is enough to show that there is actually some power available. Everything else, like the maximum possible velocity as a function of friction and prop efficiency is a bonus: see the linked old paper from this post https://www.eevblog.com/forum/chat/mess-with-your-minds-a-wind-powered-craft-going-faster-than-a-tail-wind-speed/msg3905936/#msg3905936.

PlainName:

--- Quote ---The energy storage is a separate equation and it is not relevant since I claim energy storage is involved
--- End quote ---

How would you demonstrate this energy storage? Just saying it's involved does mean a thing - you could just as easily say starlight pushes it all. But if we wanted to demonstrate that air is compressible, we could do that easily enough. So, how would you demonstrate that an unconstrained volume of air can store energy for a significant period (where 'significant' is more than 1 second)?

gnuarm:

--- Quote from: electrodacus on December 29, 2021, 04:50:01 am ---
--- Quote from: gnuarm on December 29, 2021, 04:41:39 am ---You ignored the rest of my post just as I expected you would.  if you looked at the calculations you would see that the force is only multiplied by the vehicle speed to get the power required to maintain speed.  But you don't want to admit that, so you ignored it.  That was my first prediction, that you would duck the question.

You are hopeless.  You know you are wrong, but refuse to discuss it in any meaningful way.  Silly rabbit.  Trix are for kids. 

Yeah, I do pity anyone depending on you for sound engineering.  I don't believe you even have a technical job.  How may quarters???

--- End quote ---

:) So I correct your mistake and you are saying that I ignored your post ?
You should do a test and see that your assumption is wrong.
You just believe the same absurd thing that those people that designed those online bicycle calculators.
Like 300W is plenty to bike at 1km/h against a 230km/h head wind.  People that say that is a possibility are just clueless.

--- End quote ---

Yes, you ignored this...


--- Quote ---Now, forget wind.  Lets say there is a drag on the vehicle defined by

Fdrag = Kdrag * (vehicle speed)2

What is the power required to maintain the speed of this vehicle?
--- End quote ---

Yes, you absolutely ignored this.  There is no wind, no air in fact.  Some drag against a vehicle that is powered internally through the wheels.

gnuarm:

--- Quote from: electrodacus on December 29, 2021, 06:36:54 am ---You can be offended if you want but you do not even deserve an answer as it will be a long and involved one from me and you will have no clue of what I just said.

--- End quote ---

That is correct, no one has any idea of what you have been saying and you don't either.  That is our point, but because you don't understand even what you say, you can't possibly understand what others say.

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