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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| bdunham7:
--- Quote from: electrodacus on September 02, 2021, 01:12:32 am ---But instead of using all wind energy to accelerate fast you divert large part of the energy to power the propeller that creates a sort of artificial wind eventually at multiple times the wind speed. --- End quote --- So lets focus on just that for now. How can there be two winds in opposite directions in the same space? After all, the original wind has to continue to reach the prop to power it, right? |
| electrodacus:
--- Quote from: IanB on September 02, 2021, 02:23:38 am ---You have a problem here in that experiments show what happens in real life. The observations from an experiment are a hard, solid, fact, independent of the knowledge of the person performing the experiment. You could have a two year old perform an experiment, and without them knowing anything, the experiment would still display the factual behavior of the universe. On the other hand, a written document is simply what someone wrote. It may or may not be accurate, and conveys no factual weight in and of itself. In this case, there is an obvious flaw. The diagram shows an abrupt change in pressure between P1 and P2, but it shows no simultaneous change in velocity. Since the mass flow between 1 and 2 must be equal by continuity, and since a change in pressure requires a change in density, it follows that the velocity must change abruptly if the pressure changes abruptly. Therefore, the diagram cannot be accepted at face value and must be rejected as an accurate description. --- End quote --- Is clear you do not know how a fan works or/and what air is. There is a fairly sudden change in pressure, density and speed of air molecules from one side to the other of the blades. What happens is that any air molecule that will want to escape from the high density high pressure side will be hit by the propeller blade and sent back in the same direction with quite some speed and the molecules of air that will get to the propeller from the low pressure low density side will also be pushed in to the high density side to maintain the pressure differential. Have you ever seen a fan in real life ? Was that working like a black hole attracting air molecules from both side and make them disappear ? Or is your vacuum cleaner sucking air from both sides. Are you even a real human or a decently clever AI ? :) |
| electrodacus:
--- Quote from: bdunham7 on September 02, 2021, 02:34:50 am ---So lets focus on just that for now. How can there be two winds in opposite directions in the same space? After all, the original wind has to continue to reach the prop to power it, right? --- End quote --- No the "original wind" does not need to get to propeller to push the vehicle. Some of the molecules moved by original wind if lucky may get to propeller but most of them will hit another air molecule from the high density side that moves in opposite direction and so same things happens as if you have two marbles hitting each-other. It is a very fast game of baseball where air particles are the balls almost floating and pushing against each-other as small opposite magnets but doing so from all sides. The propeller blades are like the bat (maybe more like a cricket bat) and they hit the air molecules downwind against the wind keeping much higher density of balls on the downwind side due to the angle of the blades. I will like to find an animation but with a simple google search I can not find anything to properly show this. This seems a good explanation of air but nothing about a propeller |
| bdunham7:
I do understand air and molecules, thanks. But this misses the point. In air, the molecules are always moving about and something like wind represents a net movement of all of them as an average. What you seem to be proposing is that a wind that hits a propeller or fan will somehow generate a counterwind as or more powerful than the original wind, yet still get power from the original wind. If so, what wind would an observer standing behind the vehicle see? |
| electrodacus:
--- Quote from: bdunham7 on September 02, 2021, 02:59:45 am ---I do understand air and molecules, thanks. But this misses the point. In air, the molecules are always moving about and something like wind represents a net movement of all of them as an average. What you seem to be proposing is that a wind that hits a propeller or fan will somehow generate a counterwind as or more powerful than the original wind, yet still get power from the original wind. If so, what wind would an observer standing behind the vehicle see? --- End quote --- Air molecules are hit by the propeller blades and sent at high speed in the opposite direction from the air molecules moved by natural wind. Over time the propeller rotates faster and faster so it will push the air molecules that it will hit at quite a bit higher speed. So this adds up over time it is not violate the conservation of energy. Both the kinetic energy of the rotating blade but also that of the vehicle will maintain the propeller ever increasing speed. So at the start propeller hits air molecules but it will not push them faster in average than those coming from opposite direction from natural wind. All this time energy from wind increases the kinetic energy of both vehicle and propeller and that allows the propeller to increase the speed of that artificial wind. That is also why I can say that pushing the vehicle without any natural wind will make the vehicle work the same way meaning at some point that pressure differential will be large enough that vehicle will accelerate past the speed you pushed the vehicle at. So that is a good test that should convince anyone about pressure differential energy storage. |
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