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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| cbutlera:
--- Quote from: electrodacus on September 01, 2021, 08:17:36 pm ---I may not have been very clear. In your tough experiment there are two sources of energy both contributing to your increase in kinetic energy. Out of that 14035J you contributed 35J and the plane contributed with 14000J. You used some of your stored energy from food while plane used kerosene or whatever that plane was using for fuel. --- End quote --- That is correct. So relative to the ground, I have accelerated to a speed slightly in excess of that of of the aeroplane, and I was able to do that by taking the majority of the required energy from the aeroplane. You have repeatedly claimed that it is impossible to take energy from a moving medium when moving faster than that medium, whether that medium is a treadmill, a sliding piece of paper, the air, or the floor of the aisle of an aeroplane. In your calculation above you have just demonstrated that this is indeed possible. --- Quote from: electrodacus on September 01, 2021, 08:17:36 pm ---This will not apply to vehicle having a single energy source (wind energy). --- End quote --- Yes it does apply. It shows that the generator and motor of the vehicle only have to provide a portion of the kinetic energy required to increase the speed of the vehicle in excess of the speed of the moving medium. The remainder of the kinetic energy is provided directly by the moving medium. So while the motor will itself return a little less kinetic energy to the vehicle than was taken by the generator, the additional direct contribution of the medium will more than compensate for this. So the vehicle can accelerate beyond the speed of the moving medium. In my example above my internal motor (my muscles) only had to supply 35 joules to gain 14,035 joules (relative to the ground). So if my muscles were powered by some small hypothetical wind turbine, held in my hand and in contact with the air outside of the aeroplane, that generator would only have had to extract 35 joules out of my 1,400,000 joules of kinetic energy (travelling at 200 m/s). So I would lose 35 joules of kinetic energy through the drag of the hypothetical generator, but gain about 14,035 joules of kinetic energy through the propulsion of my internal motor. |
| Kleinstein:
Excluding energy storage in the experiments is not easy - at least I sone see a very simple way. It is clear that there is no battery or spring storage - they are just not there and a bayttery would also need a motor. Kinetic energy (like flywheel) goes up when the vehicle gets faster, so it can not provide energy. It is only theoretical air pressure in the free space before / behind the fan. Without a container the energy/ pressure field would not stay there very long - more like lenghtscale divided by speed of sound - so in the low ms range. Compared to this the experiment with the free running vehicle on the tradmill was allready very long. A few seconds may not look long, but it is sufficiently long. Even the vehicle size divided by wind speed would be short compared. Similar for the larger backbrid vehicle, with a pressure field that may last a few 1/100 of a second and time traveled at speed higher than the wind of more like a minute or more. There is another point that shows that the vehicle did harmess the power of the wind, even if at the wind speed: When held at position at the treadmill there was a forward force, as when left free the vehicle accelerated forward. This forward force means the the wheels could use even more force and generate extra power. So the vehicle would be able to generate some power even if at the speed of the wind. The time the vehicle was hold in position pretty long and the time is definitely sufficient to esteblisch a steady state air pressure around the prop. There is also absolutely no reason to assume one could not hold the vehicle longer before letting it run forward. So this is steady state and thus has nothing to do with energy storage. It may be against some peoples intuition, but the experiment still shows it. The though experiment with the man walking in the plane is good, as it shows that the use of just power / energy to avoid looking at forces can get pretty complicated when looking at different refrence frames. Similar complications also apply to the system on the treadmill: you get different energies / power when you use different refrence systems. So looking at the power is tricky and prone to error. It is much easier to look at force and speed seprate. The forces don't change when one changes the reference system, and the speeds simply add. |
| electrodacus:
--- Quote from: cbutlera on September 01, 2021, 09:09:22 pm ---That is correct. So relative to the ground, I have accelerated to a speed slightly in excess of that of of the aeroplane, and I was able to do that by taking the majority of the required energy from the aeroplane. You have repeatedly claimed that it is impossible to take energy from a moving medium when moving faster than that medium, whether that medium is a treadmill, a sliding piece of paper, the air, or the floor of the aisle of an aeroplane. In your calculation above you have just demonstrated that this is indeed possible. --- End quote --- You did not took energy from the aeroplane. If the aeroplane did not had a constant speed controller say maybe even engines turned off then you will have slowed down the aeroplane while you where traveling at 1m/s. And what you did was run walk relative to aeroplane at 1m/s using your own internal stored energy. There was no way for you to accelerate to 1m/s using just the aeroplane energy. You somehow forget that while you are for example in blackbird you are not allowed to use your own energy to exceed wind speed So if you want to push the analogy you will be in blackbird siting not doing anything and the wind is the aeroplane driving at constant speed. Now the best Blackbird can do is get pushed by the aeroplane up to same speed but using just that energy alone and nothing else it can not accelerate past that speed as that will be already 100% efficient way of using the available energy. Now if you start to pedal you can exceed aeroplane(wind) speed but that is no longer a wind (aeroplane) only powered vehicle. --- Quote from: cbutlera on September 01, 2021, 09:09:22 pm ---Yes it does apply. It shows that the generator and motor of the vehicle only have to provide a portion of the kinetic energy required to increase the speed of the vehicle in excess of the speed of the moving medium. The remainder of the kinetic energy is provided directly by the moving medium. So while the motor will itself return a little less kinetic energy to the vehicle than was taken by the generator, the additional direct contribution of the medium will more than compensate for this. So the vehicle can accelerate beyond the speed of the moving medium. In my example above my internal motor (my muscles) only had to supply 35 joules to gain 14,035 joules (relative to the ground). So if my muscles were powered by some small hypothetical wind turbine, held in my hand and in contact with the air outside of the aeroplane, that generator would only have had to extract 35 joules out of my 1,400,000 joules of kinetic energy (travelling at 200 m/s). So I would lose 35 joules of kinetic energy through the drag of the hypothetical generator, but gain about 14,035 joules of kinetic energy through the propulsion of my internal motor. --- End quote --- You maybe are not considering that treadmill surface moves in the opposite direction that you want to travel so you start with zero kinetic energy and if you do nothing Generator and motor disconnected and this is ideal vehicle the vehicle will stay in the same place and generator wheel will just turn at the same speed as the treadmill as there will be no friction. As soon as you try to take any energy from the generator then treadmill will push the vehicle back by the exact same amount so you can call that negative kinetic energy as you are moving and have kinetic energy but it is in the opposite direction than what you will like. And ideal case the best you can do is put all that energy in to motor wheel and that can bring you back to the place you started but it can not advance you further than that. In real world due to friction you will move from right to left no matter how you set the gear ratio between the generator and the motor. Let me try and give you another example that includes you in the equation. So say you are the wind so the only energy source in the system and say you have a top speed of 12m/s so no matter what you can not run faster. Now you can push a fairly light vehicle with little friction and say you can still push that to 12m/s. As soon as you get to 12m/s the vehicle can not use you to exceed that speed no matter what. So even if say I will help you to double the power if my speed is also limited to 12m/s then we together still can not push the vehicle faster in the same direction that we are running. What relay happens in air is that say we had some very long springs attached to our arms maybe 10m or 20m long compressible springs and now we start pushing the vehicle it will take longer to get the vehicle to speed as we will need to compress the springs initially then vehicle will see higher and higher force and we will get then to our top speed of 12m/s but since at that point the springs are full compressed the springs will continue to push the vehicle and so vehicle can exceed our speed for as long as there is enough compression force in the spring to be able to accelerate the vehicle and cover vehicle losses. As any analogy it has limitations but basically that is what happens for blackbird in air because air is compressible. If instead of air it was water (not compressible) then you can still use a propeller designed for water but you will not be able to exceed water speed not even for a few seconds or minutes as it is the case in air. And same is true for solids that are also in general not compressible. So the vehicle in my diagram done exactly as shown there with treadmill and generator wheel in front of the motor wheel will not be able to move at all from left to right. It is proven both mathematically with the power in and out equation and you can observe it in practice if you build it. And that spiral spring is meant to simulate the air comprehensibility so if you add that to the motor wheel then you will observe exactly the same behavior as the treadmill propeller based cart. |
| electrodacus:
--- Quote from: Kleinstein on September 01, 2021, 09:28:05 pm ---Excluding energy storage in the experiments is not easy - at least I sone see a very simple way. It is clear that there is no battery or spring storage - they are just not there and a bayttery would also need a motor. Kinetic energy (like flywheel) goes up when the vehicle gets faster, so it can not provide energy. It is only theoretical air pressure in the free space before / behind the fan. Without a container the energy/ pressure field would not stay there very long - more like lenghtscale divided by speed of sound - so in the low ms range. Compared to this the experiment with the free running vehicle on the tradmill was allready very long. A few seconds may not look long, but it is sufficiently long. Even the vehicle size divided by wind speed would be short compared. Similar for the larger backbrid vehicle, with a pressure field that may last a few 1/100 of a second and time traveled at speed higher than the wind of more like a minute or more. There is another point that shows that the vehicle did harmess the power of the wind, even if at the wind speed: When held at position at the treadmill there was a forward force, as when left free the vehicle accelerated forward. This forward force means the the wheels could use even more force and generate extra power. So the vehicle would be able to generate some power even if at the speed of the wind. The time the vehicle was hold in position pretty long and the time is definitely sufficient to esteblisch a steady state air pressure around the prop. There is also absolutely no reason to assume one could not hold the vehicle longer before letting it run forward. So this is steady state and thus has nothing to do with energy storage. It may be against some peoples intuition, but the experiment still shows it. The though experiment with the man walking in the plane is good, as it shows that the use of just power / energy to avoid looking at forces can get pretty complicated when looking at different refrence frames. Similar complications also apply to the system on the treadmill: you get different energies / power when you use different refrence systems. So looking at the power is tricky and prone to error. It is much easier to look at force and speed seprate. The forces don't change when one changes the reference system, and the speeds simply add. --- End quote --- So your claim is that pressure differential has no enough energy to power the vehicle from 10mph to 30mph ? The thing is that you do not understand how much energy is needed to do that (just about 6Wh) and you also do not get the scale of the stored energy and the fact that is self feed due to the connection between the wheel and propeller. So pressure differential drops slowly only to cover the losses and small bit to accelerate the vehicle. Do you know how much energy will an ideal wind turbine of the same diameter as the propeller in Blackbird will generate in only one second at 10mph (4.5m/s) ? It will be 4800Ws. But there are quite a few seconds during the acceleration phase when the propeller at maybe 70% can compress the air behind in a huge volume of tens of thousand of liters (20m^2 propeller area times the length behind the propeller where pressure drops in a gradient to ambient pressure). There will be more than sufficient to power a vehicle like blackbird to get to that record they set and a little bit extra but not much. So yes a real wind turbine of that size will have about a 2kW output in that wind speed of just 4.5m/s but during the period they made that record wind speed fluctuated from 4m/s to 6.5m/s and at that peak 6.5m/s a real wind turbine with just 40% efficiency will output 5.8kW or 14kW at 100% ideal case. Keep in mid that is basically the same drag and rolling resistance as a bicycle or tricycle. |
| bdunham7:
Assuming without checking or agreeing that your math is correct... 6Wh = 21600Ws 4800Ws = 1.5Wh. and so on. Not keeping your units tidy can make things look different--and wrong. and then you have to ask by what mechanism is the propeller compressing this air if the wind is pushing the vehicle and not the other way around? |
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