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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| IanB:
--- Quote from: electrodacus on December 21, 2021, 08:29:51 pm ---He just looked at what gear ratio he will need if he wanted to push the vehicle with 1m/s (by push I mean apply external power to the system as that is the only way that vehicle can move from left to right). --- End quote --- The system does, of course, have external power. The two belts are not moving by themselves, so we must assume there is some kind of motor driving them, and if we make any attempt to slow down the belts then the motors must supply more power to maintain the belt speed. So the cart can pick up any power it needs from the difference in speed of the belts. But leaving that aside, power is only required to overcome friction or to accelerate the cart. In an ideal system, in steady conditions, with no friction, then the power requirement is zero. So no external power is actually needed for the cart to be moving at any steady velocity. |
| Kleinstein:
--- Quote from: electrodacus on December 21, 2021, 08:26:43 pm --- --- Quote from: bdunham7 on December 21, 2021, 08:10:52 pm --- --- Quote from: electrodacus on December 21, 2021, 08:08:34 pm ---If you remove the brakes those 600W will be available to vehicle instead of earth. --- End quote --- And if you release the brakes, but not all the way, so that the vehicle creeps, isn't most of your 600W still 'available to the earth'? The vehicle is still pushing on the earth... --- End quote --- As soon as you start moving those now less than 600W will be split between vehicle acceleration and brake friction (lost as heat). Say you want to maintain a 1m/s then brakes will need to deal with 0.5 * 1.2 * 1 * (10-1)^3 = 437.4W If your brakes where not designed to be able to get rid of those 437.4W then they will overheat and get damaged. We can setup a scale down model of this if you do not believe that will be the case. --- End quote --- No need to build a model, just have think: The mechanical power from a sail is transferered as force times vehicle speed. So the force would be power divided by speed. Does it really make sense to get an even increasing force from the sail, the slower you make the vehicle. Thas is obviously not going to happen. The wind power of some 600 W is theoretically (that is with an ideallized wind turbine, ignoring the Beetz limit and similar details) available at zero speed, but a simple sail can not harvest it. A sail is not 100% efficient. So doing the math with a sail you can not exclude anything for a vehichle used other means than a simple sail. Using the wrong equations comes one top of this. |
| electrodacus:
--- Quote from: Kleinstein on December 21, 2021, 08:54:27 pm --- No need to build a model, just have think: The mechanical power from a sail is transferered as force times vehicle speed. So the force would be power divided by speed. Does it really make sense to get an even increasing force from the sail, the slower you make the vehicle. Thas is obviously not going to happen. The wind power of some 600 W is theoretically (that is with an ideallized wind turbine, ignoring the Beetz limit and similar details) available at zero speed, but a simple sail can not harvest it. A sail is not 100% efficient. So doing the math with a sail you can not exclude anything for a vehichle used other means than a simple sail. Using the wrong equations comes one top of this. --- End quote --- Yes it makes sense and that is exactly what you will get when a compressible fluid like air is involved. Yes 600W is the ideal case no friction losses so a theoretical 100% efficient wind turbine will get 600W Benz limit is somewhere around 59% if I remember correctly and a real wind turbine can extract about 40% so about 240W A sail even a real one will be very close to having access to 100% of that an ideal sail as discussed here will be exactly 100% and if that 100% ideal sail can no help vehicle exceed wind speed then is clear no vehicle no matter the design can do that unless energy storage is used. That equation will apply to all cases where wind power is involved that means wind turbines and any type of wind powered direct down wind vehicle. Also same equation will be used to calculate the power needed to overcome drag on any vehicle. |
| bdunham7:
--- Quote from: electrodacus on December 21, 2021, 08:26:43 pm ---As soon as you start moving those now less than 600W will be split between vehicle acceleration and brake friction (lost as heat). --- End quote --- Is the car (and the wind through the car) not still pushing on the earth? |
| electrodacus:
--- Quote from: IanB on December 21, 2021, 08:45:40 pm --- --- Quote from: electrodacus on December 21, 2021, 08:29:51 pm ---He just looked at what gear ratio he will need if he wanted to push the vehicle with 1m/s (by push I mean apply external power to the system as that is the only way that vehicle can move from left to right). --- End quote --- The system does, of course, have external power. The two belts are not moving by themselves, so we must assume there is some kind of motor driving them, and if we make any attempt to slow down the belts then the motors must supply more power to maintain the belt speed. So the cart can pick up any power it needs from the difference in speed of the belts. But leaving that aside, power is only required to overcome friction or to accelerate the cart. In an ideal system, in steady conditions, with no friction, then the power requirement is zero. So no external power is actually needed for the cart to be moving at any steady velocity. --- End quote --- When I mentioned external power I was excluding the two belts / treadmills. You need to be able to demonstrate that using the energy from road treadmill (generator wheel) and applying that to Motor wheel you are able to advance forward (meaning accelerate from left to right). You will not be able to do that without adding energy storage. But your equations involved just speeds like thus are completely unable to demonstrate anything. I do not think I can continue to argue here as your level of understanding is way below what is required. Not sure if this is a failing of the education system or a limitation of most humans brain (or maybe a combination of both). Even if I setup an experiment and show conclusively that my theory is correct all you will do is defend the new theory without understanding what you are defending. |
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