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Mess with your minds: A wind powered craft going faster than a tail wind speed.
electrodacus:
--- Quote from: Kleinstein on December 14, 2021, 10:00:55 am ---With some 500W at only 0.001 m/s would require a force of 500 kN from the sail.
This value is obviously wrong (way to high) and shows that the formular used above must be wrong, not just at zero speed.
--- End quote ---
The formula used above is correct you used the wrong speed to calculate the force on the sail. You need to use 10-0.001 = 9.999m/s
An ideal 1m^2 sail in 10m/s speed will see a 60N force. I considered the generator 90% efficient in that formula that is why is less than 600W
bdunham7:
--- Quote from: electrodacus on December 14, 2021, 07:25:09 pm ---
--- Quote from: Kleinstein on December 14, 2021, 10:00:55 am ---With some 500W at only 0.001 m/s would require a force of 500 kN from the sail.
This value is obviously wrong (way to high) and shows that the formular used above must be wrong, not just at zero speed.
--- End quote ---
The formula used above is correct you used the wrong speed to calculate the force on the sail. You need to use 10-0.001 = 9.999m/s
An ideal 1m^2 sail in 10m/s speed will see a 60N force. I considered the generator 90% efficient in that formula that is why is less than 600W
--- End quote ---
OK, so 60N of force x 0.001m/s is how much power?
electrodacus:
--- Quote from: bdunham7 on December 14, 2021, 09:52:06 pm ---
OK, so 60N of force x 0.001m/s is how much power?
--- End quote ---
That is not how you will make the calculation. It will be 60N * (10m/s-0.001m/s).
This sort of things is what also make people think Blackbird can exceed wind speed powered only the the wind with no energy storage.
That 0.001m/s is unreasonable and as a theoretical exercise.
Just made some quick calculation and for a 10kg vehicle with a 1m^2 sail it takes just around 2ms (0.002 seconds) to get from zero to 0.5m/s
bdunham7:
--- Quote from: electrodacus on December 14, 2021, 10:15:49 pm ---That is not how you will make the calculation. It will be 60N * (10m/s-0.001m/s).
This sort of things is what also make people think Blackbird can exceed wind speed powered only the the wind with no energy storage.
--- End quote ---
OK, if that is the case, then what is the power at 0 m/s?
electrodacus:
--- Quote from: bdunham7 on December 14, 2021, 10:20:50 pm ---
--- Quote from: electrodacus on December 14, 2021, 10:15:49 pm ---That is not how you will make the calculation. It will be 60N * (10m/s-0.001m/s).
This sort of things is what also make people think Blackbird can exceed wind speed powered only the the wind with no energy storage.
--- End quote ---
OK, if that is the case, then what is the power at 0 m/s?
--- End quote ---
No motion of the vehicle means zero power can be generated at the wheel.
but see my edited comment above where I mentioned it takes just around 0.002 seconds 2ms for a 10kg vehicle with a 1m^2 sail to get from 0m/s to 0.5m/s and so maybe around 10ns that is nanoseconds to get to 0.001m/s (that is the step increment I used in my graph calculator the one in the video).
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