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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| Brumby:
--- Quote from: electrodacus on December 22, 2021, 07:25:00 am ---There is nothing you need to do to that equation. The correct one is the one I presented. --- End quote --- Wrong. --- Quote ---The extra bit that is missing the the stored energy. The propeller was powered by wind power when well below wind speed then as the wind power decreased the stored energy started to provide most of the power to vehicle. --- End quote --- Wow. Just, wow. That is just so wrong. There is no energy storage as you maintain. There can't be. --- Quote ---The way that stored energy is calculated is a bit complicated but it can be done as I already did in the spreadsheet calculator. Say 60% of wind power is sent to propeller (from the wheel) then the other 40% gets to accelerate the vehicle increasing the vehicle kinetic energy and obviously speed. The 60% that gets to propeller will be contributing to increased pressure differential (of course propeller may be 50% efficient so half of that 60% ends up as stored energy) You can see this increase in pressure differential about the same way as if natural wind speed has increased. --- End quote --- Again, you are aware of the phenomenon, but you continually misrepresent it! The "pressure differential" is thrust. This thrust is not stored energy - it is continuously created moment by moment. Disconnect the drive shaft and it will cease as soon as the rotational momentum of the propeller is spent. --- Quote ---In the calculator all that energy put in the propeller increases the potential wind energy and with such a mechanism 2x even 3x wind speed is not a problem but since this is stored energy as soon as it is all used up vehicle will slow down below wind speed. --- End quote --- You need to get over this "stored energy" thing. It's stopping you from seeing the correct picture. --- Quote ---All that it will need to be done is to run the experiment fully not stop the experiment just before vehicle will start to slow down. --- End quote --- Now this is a problem I have with you. This is an assertion on your part. Aside from your own, self-serving claims, there is (as far as I know) NO evidence that this will happen. You can't say "I've proven it" because you are biased. Your opinion does not count. What is needed is an INDEPENDENT, authoritative source. --- Quote ---It is a shame that this problem is wrongly presented in some schools and I wish I could do something about it. I was much more optimistic about being able to explain this but it seems so far I'm failing to do so. --- End quote --- Oh - you are doing an EXCELLENT job in helping people understand what is going on. By presenting an absolutely flawed explanation - one that has been disproven experimentally - you have engaged curious minds in a process of examination of the problem. As a result, they are much more aware of how the mechanism actually works. And for that, I thank you. |
| Kleinstein:
--- Quote from: Brumby on December 22, 2021, 06:41:54 am ---Besides, I use the word "thrust" here simply as a descriptive term. If you want something less controversial, then I could have said: 0.5 * air density * area * (wind speed - vehicle speed + speed of the air being blown backwards by the propeller)^3 --- End quote --- The trust is a force and not power ( please don't make the same error as electrodacus). So the is only a square. If you want the power, than one has to multiply by a speed, that may depend on the reference system used and this often is not the same as the one used for the thrust. The is still the point when the force changes direction - this is not included in the expression. The calculation done to show that the blackbird can work are usually steady state, so they don't need to care about possibly energy storrage. The idea of energy storrage is only introduced to cast some doubt on the experiments. A closer look however does not support it: there can be some energy in the compressible air, but this would be only very short time (and thus to little) and there is no control for it and thus the energy in the air going up when the vehicle goes faster. So the energy in the air behaves more like the kinetic energy in the vehicle, working against the vehicle going faster. |
| Brumby:
--- Quote from: Kleinstein on December 22, 2021, 09:44:48 am --- --- Quote from: Brumby on December 22, 2021, 06:41:54 am ---Besides, I use the word "thrust" here simply as a descriptive term. If you want something less controversial, then I could have said: 0.5 * air density * area * (wind speed - vehicle speed + speed of the air being blown backwards by the propeller)^3 --- End quote --- The trust is a force and not power ( please don't make the same error as electrodacus). So the is only a square. --- End quote --- Again - I used the term "thrust" in a conversational sense, not an engineering one, which is why I offered the verbose form. |
| Kleinstein:
--- Quote from: Brumby on December 22, 2021, 11:05:02 am --- --- Quote from: Kleinstein on December 22, 2021, 09:44:48 am --- --- Quote from: Brumby on December 22, 2021, 06:41:54 am ---Besides, I use the word "thrust" here simply as a descriptive term. If you want something less controversial, then I could have said: 0.5 * air density * area * (wind speed - vehicle speed + speed of the air being blown backwards by the propeller)^3 --- End quote --- The trust is a force and not power ( please don't make the same error as electrodacus). So the is only a square. --- End quote --- Again - I used the term "thrust" in a conversational sense, not an engineering one, which is why I offered the verbose form. --- End quote --- Even in the verbose form it is still not allways right to use a simple speed difference to the 3rd power. There is a 2nd power for the force and than an often different speed for the speed to make is a power. |
| Brumby:
Then you are saying there is a fundamental problem with our friend's original formula? I would have characterised the bit I added as completing the net air speed component. It's not a separate entity, but one part in the determination of effective air speed. |
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