General > General Technical Chat
Mess with your minds: A wind powered craft going faster than a tail wind speed.
electrodacus:
--- Quote from: Kleinstein on December 29, 2021, 07:21:48 pm ---
The calculation this way is absolutely not easy, as there is no accepted formula for the maximum power available to a vehicle. So the difficulty is in deriving (not just propose a solution and claim it must but ture as an act of god). As there are multiple possible ways to harness the wind power this is a really difficult task. To make it a proof it needs a really good explaination that most people would agree with.
--- End quote ---
There is an accepted formula is the one that I posted and that is the ideal case (best case if you want) of available wind power to any vehicle you can imagine.
You can see in the formula what influences the available wind power and that is wind speed relative to vehicle and area that wind/air has to interact with.
That is all it can not be any simpler than that.
--- Quote from: Kleinstein on December 29, 2021, 07:21:48 pm ---Just presenting an expression that most people think is wrong is far from supporting the claim. It is more like showing poor understanding of logic and science in general.
The V_w * F_w form was never claimed to be the available wind power, but the power needed by the vehicle. Just like for another force to push against the power is force times speed (by definition and not by mistake). Thinking the power would stay constant, essentially independent of the speed is just a rediculous idea, that causes obvious contradictions. One such contraticion would be that the power when going in the same direction as the wind would be the same as the maximum avialable power and thus all wind genrator would be 100% efficient. I don't think that sounds plausible.
--- End quote ---
What are you even talking about ? When have I ever said that wind power available to vehicle is not dependent on speed (it is clearly show in the equation).
I even provided an example yesterday showing highest wind power available is when vehicle is just starting to move super low by the time it gets to half the wind speed and zero when vehicle speed equals wind speed.
Kleinstein:
--- Quote from: electrodacus on December 29, 2021, 07:30:48 pm ---
--- Quote from: Kleinstein on December 29, 2021, 07:21:48 pm ---
The calculation this way is absolutely not easy, as there is no accepted formula for the maximum power available to a vehicle. So the difficulty is in deriving (not just propose a solution and claim it must but ture as an act of god). As there are multiple possible ways to harness the wind power this is a really difficult task. To make it a proof it needs a really good explaination that most people would agree with.
--- End quote ---
There is an accepted formula is the one that I posted and that is the ideal case (best case if you want) of available wind power to any vehicle you can imagine.
You can see in the formula what influences the available wind power and that is wind speed relative to vehicle and area that wind/air has to interact with.
That is all it can not be any simpler than that.
--- Quote from: Kleinstein on December 29, 2021, 07:21:48 pm ---Just presenting an expression that most people think is wrong is far from supporting the claim. It is more like showing poor understanding of logic and science in general.
The V_w * F_w form was never claimed to be the available wind power, but the power needed by the vehicle. Just like for another force to push against the power is force times speed (by definition and not by mistake). Thinking the power would stay constant, essentially independent of the speed is just a rediculous idea, that causes obvious contradictions. One such contraticion would be that the power when going in the same direction as the wind would be the same as the maximum avialable power and thus all wind genrator would be 100% efficient. I don't think that sounds plausible.
--- End quote ---
What are you even talking about ? When have I ever said that wind power available to vehicle is not dependent on speed (it is clearly show in the equation).
I even provided an example yesterday showing highest wind power available is when vehicle is just starting to move super low by the time it gets to half the wind speed and zero when vehicle speed equals wind speed.
--- End quote ---
The formula presented is not an accepted formula for the available wind power for the moving vehicle - it is not even correct. If it would be show us a reliable source ! If you can't , just give up on repeating that formula.
The point of essentially independet of velocity was for the low velocity case (e.g. vehicle much slower than the wind). Sorry forgot about hat detail.
The slower one goes the more rediculous your claim gets.
IanB:
--- Quote from: electrodacus on December 29, 2021, 06:31:48 pm ---The easiest part will be to show that directly down wind faster than wind is not possible without some sort of energy storage device or an external energy source.
That can be proved with the correct equation for wind power available to any wind powered vehicle
Pw = 0.5 * air density * area * (wind speed - vehicle speed)3
It is irrelevant how vehicle is build as long as wind power is the only source then the above is the correct formula for an ideal system (so absolutely best case scenario).
--- End quote ---
It's a very circular argument:
"Why can no vehicle go downwind faster than the wind speed? Because this correct formula says so."
"Why is this formula correct? Because no vehicle can go downwind faster than the wind speed."
Each conclusion depends on the other.
electrodacus:
--- Quote from: Kleinstein on December 29, 2021, 07:38:00 pm ---The formula presented is not an accepted formula for the available wind power for the moving vehicle - it is not even correct. If it would be show us a reliable source ! If you can't , just give up on repeating that formula.
The point of essentially independet of velocity was for the low velocity case (e.g. vehicle much slower than the wind). Sorry forgot about hat detail.
The slower one goes the more rediculous your claim gets.
--- End quote ---
I do not need to provide you with any source. That formula works in all real world applications.
If you disagree with the one I provided just provide the one you think is the correct and we can test that.
electrodacus:
--- Quote from: IanB on December 29, 2021, 07:42:33 pm ---It's a very circular argument:
"Why can no vehicle go downwind faster than the wind speed? Because this correct formula says so."
"Why is this formula correct? Because no vehicle can go downwind faster than the wind speed."
Each conclusion depends on the other.
--- End quote ---
Provide an equation that you think is the correct one for a wind powered vehicle.
The one I provided is valid for any case and it perfectly predicts what happens in reality.
Even the incorrect formula used by many predicts no wind power available above wind speed so that is not an argument either.
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