| General > General Technical Chat |
| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
| << < (134/285) > >> |
| electrodacus:
--- Quote from: IanB on December 12, 2021, 08:53:10 pm --- --- 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. --- End quote --- You can have Force without having power means vehicle speed and kinetic energy will not change. Power is a more than Force especially in this context. |
| PlainName:
--- Quote ---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. --- End quote --- Contrary to your presumed intuition, having the propeller feathered until reaching wind speed would be better since it would present less drag. So no storage of anything before then to release after. In fact, I think that's demonstrated with the treadmill models, which go from nothing to tread speed almost instantly. |
| electrodacus:
--- Quote from: dunkemhigh on December 12, 2021, 09:14:21 pm --- --- Quote ---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. --- End quote --- Contrary to your presumed intuition, having the propeller feathered until reaching wind speed would be better since it would present less drag. So no storage of anything before then to release after. In fact, I think that's demonstrated with the treadmill models, which go from nothing to tread speed almost instantly. --- End quote --- It is not about intuition but the reality of how this universe works. The treadmill model is being held not dropped on the treadmill. During those few seconds the treadmill charges all energy storage devices available on the vehicle the multiple flywheel devices and the pressure differential. That is a light weight vehicle so it will not require much energy to accelerate. That treadmill is running at about 5.4m/s Vehicle seems super lightweight maybe 0.5kg (just a guess) Energy needed to get that vehicle from 0m/s to 1m/s (way higher speed that was ever seen in video) will be 0.5 * 0.5kg * 1^2 = 0.25Ws (0.25J if you prefer). Do you have a sense of how much energy is 0.25Ws ? That is about 0.07mWh Typical smartphone battery is about 15Wh You can take out your smartphone battery and accelerate that vehicle over 100000 times from 0 to 1m/s assuming 50% efficient propeller/motor combination. |
| IanB:
--- Quote from: electrodacus on December 12, 2021, 09:04:04 pm ---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. --- End quote --- Air being a compressible fluid is not a means of energy storage, as the moving air in the propeller stream is less dense (lower pressure) than the still air in the surroundings. This can be learned in every physics or aerodynamics textbook as Bernoulli's principle. There is no way that the lower pressure air can "push" from behind. |
| PlainName:
--- Quote ---Do you have a sense of how much energy is 0.25Ws ? --- End quote --- Where is this energy being stored. It ain't in a flywheel and it's not inertia of the model. It can't be the airstream because, as pointed out many times, there is nothing to retain it. |
| Navigation |
| Message Index |
| Next page |
| Previous page |