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Mess with your minds: A wind powered craft going faster than a tail wind speed.
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electrodacus:
Not sure how you all managed to change the subject.

The question is what is the available wind power to a vehicle driving directly downwind.
This question is to prove that no wind power vehicle can exceed wind speed without either external energy source or an energy storage device.

Correct answer is this below but if you disagree please feel free to offer the correct equation.

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

bdunham7:

--- Quote from: electrodacus on December 13, 2021, 01:42:25 am ---Correct answer is this below but if you disagree please feel free to offer the correct equation.

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

--- End quote ---

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

The equation for total power available does not have vehicle speed in it.  :)
electrodacus:

--- Quote from: bdunham7 on December 13, 2021, 01:49:13 am ---
--- Quote from: electrodacus on December 13, 2021, 01:42:25 am ---Correct answer is this below but if you disagree please feel free to offer the correct equation.

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

--- End quote ---

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

The equation for total power available does not have vehicle speed in it.  :)

--- End quote ---

The equation is correct as I stated for a direct down wind vehicle.
Wind speed relative to a directly downwind vehicle is wind speed - vehicle speed.
bdunham7:

--- Quote from: electrodacus on December 13, 2021, 02:08:24 am ---The equation is correct as I stated for a direct down wind vehicle.

--- End quote ---

Nope.


--- Quote ---Wind speed relative to a directly downwind vehicle is wind speed - vehicle speed.

--- End quote ---

True but irrelevant.  The power theoretically available to the vehicle, if you want to try and use that as the basis for some calculations, depends on the wind speed relative to the ground.
electrodacus:

--- Quote from: bdunham7 on December 13, 2021, 02:17:19 am ---True but irrelevant.  The power theoretically available to the vehicle, if you want to try and use that as the basis for some calculations, depends on the wind speed relative to the ground.

--- End quote ---


Think about this way.

You have a 100% efficient wind turbine so output will be 0.5 * air density * swept area * w^3
Now you put that wind turbine on top of a vehicle and drive directly downwind at say at a quarter wind speed
Then your wind turbine will output this 0.5 * air density * swept area * (w -(w/4))^3
Anyone that has ever calculate the wind power available to a sail vehicle going directly downwind will know the equation
0.5 * air density * area * (wind speed - vehicle speed)^3
That is the reason a sail vehicle can never exceed wind speed directly downwind.
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