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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| Kleinstein:
Going with 1 km/h against a heat wind of 35 km/h would need the force of going 36 km/h with no wind (irgnoring wheel friction and similar other power needs) with only 1/km/h instead of 36 km/h this would be 1/36 of the power needed for 36 km/h with zero wind. So taking the graph below to get a number, this for be bit below 300 W for 36 km/h and some 0.8 W for 1 km/h. Other than for a rough number the chart is not really helping. |
| CatalinaWOW:
--- Quote from: fourfathom on December 15, 2021, 06:31:59 pm --- --- Quote from: CatalinaWOW on December 15, 2021, 06:00:28 pm ---Having said all of that, it has been regularly asserted that a sailboat can tack downwind faster than a balloon blown down wind. If this is indeed true the advantage must be small and dependent on perfect execution and perhaps on boat configurations which perform poorly in other conditions. I say this because racing yachts consistently set spinnakers and run nearly directly downwind rather than tacking to get there faster. These people spend millions of dollars to win, they wouldn't ignore any consistent advantage. --- End quote --- It wasn't until recently that sailboats have been able to reduce drag sufficiently to be able to beat a balloon DDW. Iceboats can easily do this, but traditional "displacement" sailboats (such as mine) just can't overcome the drag to be able to do it. When I fly a spinnaker in heavy wind my best angle is DDW, not jibing, because I am limited by my "hull speed". In lighter wind I will jibe back and forth, using the spinnaker, and make better progress than I would by sailing DDW. The more modern "ultralight" boats have reduced drag to where they can beat the balloon by jibing. Foiling boats (such as the Americas Cup catamarans that I posted the polars for) have even less drag and can very comfortably beat that balloon, and not by a small margin. These boats don't even carry spinnakers as, even downwind jibing, the AWA is so far forward that the spinnaker would not be an efficient sail shape. (AWA = Apparent Wind Angle, DDW = Dead Down Wind) --- End quote --- Thanks for the input. I haven't watched the cup races for a couple of decades now and wasn't aware of the new reality. I lost interest when the rules committee seemed more interested in controlling the winner than in providing a competition. |
| fourfathom:
You can push against a brick wall with lots of force, but no work will be done, so there's no power. If the wind pushes against a vehicle with a the wheels locked and not rolling, no work will be done, so there's no power. But if the wind pushes against a vehicle and a motor used to keep the wheels from rolling, there's definitely force, but the motor will also burn Watts to keep the wheels from rolling. Watts is power. I suppose the motor is operating at 0% efficiency. And this actually has nothing to do with the reality of the demonstrated sustained DDWFTTW vehicles. |
| bdunham7:
--- Quote from: fourfathom on December 15, 2021, 09:24:26 pm ---But if the wind pushes against a vehicle and a motor used to keep the wheels from rolling, there's definitely force, but the motor will also burn Watts to keep the wheels from rolling. Watts is power. --- End quote --- Yes, but arbitrarily small power depending on the design of the system. --- Quote ---And this actually has nothing to do with the reality of the demonstrated sustained DDWFTTW vehicles. --- End quote --- No, it has to do with the specific misunderstandings regarding 'conservation of energy' that are not allowing Electrodacus to understand how and why they work. |
| electrodacus:
--- Quote from: bdunham7 on December 15, 2021, 09:17:10 pm --- A (nearly) stationary bicycle with a wind is a different problem with different results. --- End quote --- That is where you are wrong. The problem is basically the same. Why do you think 300W are needed constantly to maintain that speed ? Is the air drag and you have that if you are cycling at 36km/h with no wind or at 1km/h with a 35km/h head wind. Same drag so same amount of power required. |
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