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Newton's third law problem.

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fourfathom:

--- Quote from: electrodacus on November 29, 2022, 06:57:26 pm ---For example the direct downwind faster than wind vehicles both the large blackbird and the small treadmill model will accelerate to a max speed (can be 2x or even 3x the wind speed) and then they will slow down as there is no longer any stored energy to cover the friction losses.
--- End quote ---

Would you mind providing more information on this energy stored in the pressure differential behind the propeller?  The amount, and duration of this storage would be helpful.  There are equations for the dissipation of a pressurized area -- the one I've seen apply to bomb blast overpressure, and the rate of dissipation seems quite high, the pressure dissipates much too quickly to provide power beyond a few milliseconds.  Of course there is also kinetic energy stored in the spinning propeller blades, and in the momentum of the vehicle.  Do you have numbers for those as well?

You have obviously studied this in some detail, and I'm sure we would all be interested in what you have learned.

electrodacus:

--- Quote from: Kleinstein on November 29, 2022, 07:01:34 pm ---Doing much of the math with numbers can be confusing, but it can sometimes also help. Getting obviously wrong resucts (e.g. reduculous numbers that contradict experiance) is one way to show that a claimed equation is obviously wrong. However this still does not work with electrodacus: he refuses to see how rediculous his claims are (e.g. walking against a 30 km/h head wind would need some 400 W of power and thus be a kind of heavy sports).

--- End quote ---

You may not get strong winds at your location so your intuition may be wrong. Also keep in mind that wind speed close to ground is lower and this is a theoretical calculation that asume same wind speed on the entire surface.



--- Quote from: Kleinstein on November 29, 2022, 07:01:34 pm ---The problem is that AFAIK there is no such simple, easy to accept equation for the maximum available power.  At least I don't see such an equation that I would take for granted. So it would still need a proof or at least good plausibile explaination. 
Aerodynamics can be be quite tricky and I would consider getting such an euqation and proving it rather hard. So the way via the available power is a hard one.
The equation claimed by electrodacus is known to be wrong. AFAIR his reasoning kind of works for a simple sail, but it does not apply for the fan/ porp case. There are cases when a prop can be more efficient than a sail.  The calculations for the prop drivne vehicle show that one can get more power and one can go faster than the wind. So the equation claimed by electrodacus is proven wrong - it is just that he refuses to accept (and maybe understand - though it is relatively easy) the proof.

Beside the calculation there are also videos to show that it is possible to go faster than the wind / or the equivalent case of moving against the moving treadmil, driven by a prop. With the plausible forms of ernergy storage the times shown are well long enough to consider them to show a stationary case - so the energy storrage argument / read herring is dead. :horse:

--- End quote ---

It will be your job to prove the equation is wrong as that equation is used by almost all engineers to build things that work in real world as predicted by it.

Equation is universal and the fan/prop is powered by the wind power provided by that equation.

I can build a vehicle with sail that exceeds wind speed and will not involve any propeller.
All you do is take wind energy at the wheel and store it in a battery. The same thing is done by the propeller version but instead of a battery it uses pressure differential to store energy.

If you could prove that vehicle (direct downwind blackbird or the analog treadmill model) can maintain above wind speed indefinitely then you will be right but nobody has proved that because they can not.
All those examples are incomplete and people rushed to get the wrong conclusion about how they work. Going as far as to modify correct equations and posible one of the reasons all those wrong equations are everywhere.

The large heavy blackbird needed about 6Wh less than half the energy in a cell phone battery to achieve that speed record that with pressure differential on each side of a 20m2 swept area propeller.
The small lightweight treadmill model will need orders of magnitude less energy storage.

I showed that calculating using that equation and alternative kinetic energy equation will provide the same result.

You will need to prove the same that calculating in this two different ways you get the same result.
The only alternative I seen to my equation is that incorrect one where for drag force you have (w-v) correctly but for power you want to use just vehicle speed.


All anyone needs to prove me wrong is show a vehicle powered by an electric motor upwind at very low speed and show that power needed for vehicle is lower than the equation I claim to be correct predicts.

And why do you not contact this guys https://www.electromotive.eu/?page_id=12&lang=en  to let them know they have a defective calculator and explanation on their website ?

electrodacus:

--- Quote from: fourfathom on November 29, 2022, 07:09:53 pm ---
--- Quote from: electrodacus on November 29, 2022, 06:57:26 pm ---For example the direct downwind faster than wind vehicles both the large blackbird and the small treadmill model will accelerate to a max speed (can be 2x or even 3x the wind speed) and then they will slow down as there is no longer any stored energy to cover the friction losses.
--- End quote ---

Would you mind providing more information on this energy stored in the pressure differential behind the propeller?  The amount, and duration of this storage would be helpful.  There are equations for the dissipation of a pressurized area -- the one I've seen apply to bomb blast overpressure, and the rate of dissipation seems quite high, the pressure dissipates much too quickly to provide power beyond a few milliseconds.  Of course there is also kinetic energy stored in the spinning propeller blades, and in the momentum of the vehicle.  Do you have numbers for those as well?

You have obviously studied this in some detail, and I'm sure we would all be interested in what you have learned.

--- End quote ---

Yes you can watch my video starting at  10:30     calculations there do not include friction and that is important if you want to know how long it will take until vehicle will slow down below wind speed.
And starting at 15:35 you can see the details about pressure differential

PlainName:

--- Quote ---All anyone needs to prove me wrong is show a vehicle powered by an electric motor upwind at very low speed
--- End quote ---

The previously posted video shows the electric motor version. It DOES NOT WORK AT LOW SPEED as we keep pointing out - it  has to get up to speed somehow and then it works fine.

I also stressed that in the explanation of why your love child of an equation is inappropriate.

electrodacus:

--- Quote from: PlainName on November 29, 2022, 07:51:29 pm ---
--- Quote ---All anyone needs to prove me wrong is show a vehicle powered by an electric motor upwind at very low speed
--- End quote ---

The previously posted video shows the electric motor version. It DOES NOT WORK AT LOW SPEED as we keep pointing out - it  has to get up to speed somehow and then it works fine.

I also stressed that in the explanation of why your love child of an equation is inappropriate.

--- End quote ---

I remember some video with an electric wind turbine probably battery and motor. Is that what you refer to or something else ?
The minimum wind speed is related to wind turbine. Wind speed needs to be above a minimum threshold 3 to 4m/s in order to be enough wind power to cover the turbine friction losses. That is valid for any wind turbine no matter if it is connected to an electric generator or directly to wheels.

The equation is both correct and appropriate as it predicts exactly what it is observed.  You did not provide an alternative equation that works (can do correct predictions).
 

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