General > General Technical Chat
Mess with your minds: A wind powered craft going faster than a tail wind speed.
bdunham7:
--- Quote from: electrodacus on December 12, 2021, 08:34:21 pm ---The lack of understanding is coming from you.
--- End quote ---
Really? Do you not see the inherent fallacy in the term "25W of thrust"?
electrodacus:
--- Quote from: bdunham7 on December 12, 2021, 08:37:03 pm ---
--- Quote from: electrodacus on December 12, 2021, 08:34:21 pm ---The lack of understanding is coming from you.
--- End quote ---
Really? Do you not see the inherent fallacy in the term "25W of thrust"?
--- End quote ---
There is absolutely nothing wrong in the way I presented thrust and you will understand that if you knew what power is.
IanB:
--- Quote from: electrodacus on December 12, 2021, 08:27:59 pm ---The main point of the propeller in this design is to store energy so that it can be used to accelerate the vehicle above wind speed.
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No, the main point of the propeller in this design is the change the effective wind velocity at the vehicle. If the vehicle was travelling at wind speed with a sail, the difference in speed between the wind and the sail would be zero. No force available. But if the vehicle is travelling at wind speed with a rotating propeller, the difference in speed between the wind and the moving surfaces of the propeller can be greater than zero. Hence, with a propeller, the wind can still provide force.
IanB:
--- Quote from: electrodacus on December 12, 2021, 08:46:46 pm ---There is absolutely nothing wrong in the way I presented thrust and you will understand that if you knew what power is.
--- End quote ---
Thrust has dimensions of force and is measured in Newtons.
Power has dimensions of rate of doing work, and is measured in Newton-meters per second, or Watts.
electrodacus:
--- Quote from: IanB on December 12, 2021, 08:50:32 pm ---
--- Quote from: electrodacus on December 12, 2021, 08:27:59 pm ---The main point of the propeller in this design is to store energy so that it can be used to accelerate the vehicle above wind speed.
--- End quote ---
No, the main point of the propeller in this design is the change the effective wind velocity at the vehicle. If the vehicle was travelling at wind speed with a sail, the difference in speed between the wind and the sail would be zero. No force available. But if the vehicle is travelling at wind speed with a rotating propeller, the difference in speed between the wind and the moving surfaces of the propeller can be greater than zero. Hence, with a propeller, the wind can still provide force.
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That speed at the propeller is needed in order to increase pressure differential so basically storing energy. If air was not a compressible fluid then having the propeller will have been very useless and vehicle will not have been able to exceed wind speed.
The same wind power equation applies to a direct down wind sail vehicle as it applies to this propeller based one. The difference is that while wind power is available so below wind speed some amount of energy will be stored in an energy storage device then that stored energy is used to accelerate above wind speed.
Same thing can be had with a sail type vehicle just add an electric generator/motor and a battery and you can charge the battery while below wind speed then use that stored energy to accelerate above wind speed.
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