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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| gnuarm:
Ok, if you are going to invoke relativity to discuss distance, then I think we will never find a common ground to discuss. Enjoy |
| electrodacus:
--- Quote from: gnuarm on December 21, 2021, 07:00:09 am ---I don't think I'm willing to watch a 25 minute video that is hard to understand when I find an error in the first four minutes. You define the power from the wind as some stuff * (w-v). You claim this is the reason why a propeller vehicle can't exceed the wind speed. This ignores the rotation of the propeller which is the whole point! I also skipped ahead to 19 minutes where you claim the geared wheels and stick are not being analyzed correctly. I don't see how you can say anything of the sort. The analogy is not perfect between the propeller car and the gear car because the gear ratio of the gear car makes it move instantly while the propeller car has to accelerate to beat the wind speed. Maybe I'll watch the rest of this video someday, but for now it's just too much work. So how far would they need to drive the propeller car for you to say it's not running on stored power? --- End quote --- w-v wind speed - vehicle speed is the wind relative to a vehicle driving directly down wind so absolutely the correct equation. Propeller is nothing more than a wheel to travel trough a medium instead of the top surface of a medium like a regular wheel. The wheel only vehicles will always be an analogy to direct up wind version only. Because for direct down wind the air is required (air is a compressible fluid so energy can be stored) and that is how direct down wind blackbird actually works. Propeller is used to create a pressure differential and that is a way to store energy. It depends on design. If you design it to accelerate slower thus spend more time below wind speed and store more energy then it can run for longer above wind speed. Is easy to see that acceleration rate drops so you can calculate from that how long until it gets to peak speed and starts to slow down. The v-w equation Derek used is wrong and will imply that vehicle acceleration rate increases while in all experiments done that was not the case. Based on data Blackbird was super close to use all stored energy when it got around 30mph in that 2.8x wind speed record (that was more like 2x in reality). |
| electrodacus:
--- Quote from: gnuarm on December 21, 2021, 07:02:21 am ---Ok, if you are going to invoke relativity to discuss distance, then I think we will never find a common ground to discuss. Enjoy --- End quote --- That was maybe over the top but looking at speed or power as anything to do with time is also the wrong way to look at a rate of change. This is of course a personal opinion but people do confuse Power with Energy and in many cases Force with Power. Thus having a hard time understanding the problem I explained in the video and seen in the image below This problem proves that w-v is the correct equation and also that without energy storage higher than wind speed is not possible. If you disagree try and use v-w for all 3 cases and see what you get and if it make any sense. Clearly not what will happen in reality. |
| Kleinstein:
--- Quote from: electrodacus on December 20, 2021, 11:55:15 pm --- --- Quote from: Kleinstein on December 20, 2021, 09:59:18 pm ---What does output of the motor wheel mean ? This is not really clear to me. It that the same as the power needed to supply the motor = the ouput power of the motor ? For now it is just about the equation, so we don' t need to dicuss the 3 cases. We need to understand the equation first. --- End quote --- Output at the motor wheel is the input power in the motor from generator wheel plus the power that wind treadmill provide to that same wheel or subtract from the wheel as it is the case at C. There are just two sources of energy available to vehicle one is the road treadmill and one is the wind treadmill. This is because we are looking in the frame of reference of the vehicle so vehicle is the reference thus is not moving. You can salve the same problem in multiple way this is just the one I selected mostly based on the fact that people seems to prefer looking at this problem form the vehicle frame of reference and that is how Derek also solved this same problem. You can look from the ground reference frame where ground / Road treadmill is not moving at 2m/s but vehicle moves forward at 2m/s left to right and in that case the wind treadmill will have moved at 6m/s the wind speed relative to ground/road but it will still be just 4m/s relative to vehicle. --- End quote --- 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. |
| PlainName:
--- Quote ---We can agree to disagree. --- End quote --- What!??!!! After 958 comments? NOOOOOooooooo |
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