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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| Labrat101:
It's from the variable pitch propeller that gives it the extra push . No magic involved. How this works in real life . It does many early aviation used it on small low power crafts. The new silent running drones use this method as well. |
| IanB:
--- Quote from: Kleinstein on December 21, 2021, 09:22:58 am ---The naming is a bit confusing, but it is OK to calculate this way, if the stick to the vehicle drawing frame as the reference and also use it for the rest of the calulation. In this case however we must have a closer look at the center part, especially the question, what is the meaning of P_net ? edit: Looking at it again, I realized that the formular is calculating the power in a difference reference frame. So I don't see a good way for calulating this way. It kind of lead nowhere. You get a number but no good way use to it, at least I don't see one. The logical way is to calculate the power that is needed to power the motor, as that is what we would have to compare to the power from the generator. --- End quote --- Actually, if you look at the car/wheel/belt system carefully, and make the following assumptions: 1. The system is in steady state (no acceleration) 2. The system is ideal (no friction losses from bearings or air resistance) Then from these assumptions the power everywhere is zero, as power is only required to overcome losses or produce acceleration. Since the power is everywhere zero, it is not possible to analyze this system in terms of power flows, and no conclusions can be drawn using that approach. To analyze the system correctly, a different approach is required. |
| bdunham7:
--- Quote from: IanB on December 21, 2021, 05:03:27 pm ---To analyze the system correctly, a different approach is required. --- End quote --- As I pointed out much earlier, starting with reply #20 to this thread, you can pretty much explain it without much more than the principles of Archimedes. |
| bdunham7:
--- Quote from: gnuarm on December 21, 2021, 02:41:13 pm ---I didn't read the whole thread. --- End quote --- Don't, unless you want brain damage. --- Quote --- How long has electrodacus been insisting the car that goes down wind faster than the wind doesn't? How long has he insisted energy involves time and power doesn't? --- End quote --- a) forever and b) that's a relatively recent claim He has previously rejected Newton's laws of motion, the principles of Archimedes (simple machines, levers) and insisted that 'conservation of energy' somehow means 'conservation of kinetic energy' without even defining a closed system. Now this, and the novel concept that work and energy are entirely distinct in a way that would matter in this particular case. His main contentions seem to be that you can store a significant amount of energy in a localized pressure field in the uncontained atmosphere, and that the small-model experiments that clearly disprove his ideas are the result of energy storage due to 'stick-slip hysteresis'. |
| electrodacus:
--- Quote from: Brumby on December 21, 2021, 02:51:13 pm ---A question, if I may.... Let's say the Blackbird has gone through all this "energy storage" exercise and has been running along the ground for long enough that the "stored energy" is all gone. We are looking for the steady state where the speed is constant - no acceleration nor deceleration. (I don't care how long this will take as we can imagine a test track as long as we want and a nice, consistent wind.) electrodacus - what do you say it's speed will be? 1. Greater than wind speed 2. Equal to wind speed 3. Less than wind speed --- End quote --- In the ideal case no friction direct down wind blackbird will get to designed wind speed higher than wind speed in an infinite amount of time same way a sail vehicle will take forever to get to wind speed (it will never quite get there). In real world where there is friction at the point that remaining stored energy can no longer fully cover the friction losses the vehicle will start to slow down and the slow down part will take some time as now the kinetic energy will be the one supplying the losses. The vehicle will continue to decelerate until it gets below wind speed and my best guess here is that it will get to some steady state below wind speed if it is in a perfectly constant wind but in real life outside wind variation is just super high so vehicle will accelerate again when it will get a wind gust so it will sort of oscillate between above wind speed and below wind seeped. During that so called 2.8x wind speed record wind speed was between 8mph and 15mph so a fairly high variation and since a 2x increase in wind speed means 8x increase in available wind power the variation is just huge. |
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