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Mess with your minds: A wind powered craft going faster than a tail wind speed.
bdunham7:
--- Quote from: electrodacus on December 15, 2021, 08:32:45 pm ---So what do you think is needed if not 600W to prevent the vehicle from being pushed by the wind ?
We can do this test relatively easily.
The equation showing that is simple and it is this one you can find everywhere for ideal case 0.5 * air density * area * (wind speed)^3
So 0.5 * 1.2 * 1 * 10^3 = 600W
--- End quote ---
An arbitrarily small amount of power is needed to hold it in place because power is force x speed. Because the speed is zero, you can use as much gear reduction as you like.
If you can do the test easily, go ahead.
Your equation (the second one--I'm not commenting on the first) doesn't make any sense. The motor output power is the force produced by the motor multiplied by the speed of the motor. It doesn't know or care how fast the wind is blowing to produce the force that it is working against.
electrodacus:
--- Quote from: bdunham7 on December 15, 2021, 08:42:29 pm ---
An arbitrarily small amount of power is needed to hold it in place because power is force x speed. Because the speed is zero, you can use as much gear reduction as you like.
--- End quote ---
See my edited comment above.
You try pedaling at 1km/h direct upwind with 35km/h wind and let me know how much power you need to do that.
bdunham7:
--- Quote from: electrodacus on December 15, 2021, 08:50:28 pm ---You try pedaling at 1km/s direct upwind with 35km/h wind and let me know how much power you need to do that.
--- End quote ---
1 km/s is going to be spectacular, with or without the headwind.
Seriously, what sort of argument is that? If your motor setup is stupidly inefficient, it could take any amount of input power--even much more than 600W if you like--but at zero speed the output power is zero, so if you improve the design you can make it as efficient as you like, thus my 'arbitrarily small' statement. For the .001m/s upwind example, you can make it arbitrarily close to 60mW because that is the output power.
electrodacus:
--- Quote from: bdunham7 on December 15, 2021, 09:07:35 pm ---
1 km/s is going to be spectacular, with or without the headwind.
Seriously, what sort of argument is that? If your motor setup is stupidly inefficient, it could take any amount of input power--even much more than 600W if you like--but at zero speed the output power is zero, so if you improve the design you can make it as efficient as you like, thus my 'arbitrarily small' statement. For the .001m/s upwind example, you can make it arbitrarily close to 60mW because that is the output power.
--- End quote ---
It was a typo is obviously 1km/h (0.28m/s)
Just take a bicycle if you have one and try to drive direct upwind at as slow of a speed as you need to maintain balance (maybe 1km/h is a bit slow) and you will see you do not need mW but hundreds of watts with 10m/s (36km/h) as clearly seen in that graph I posted.
bdunham7:
--- Quote from: electrodacus on December 15, 2021, 09:11:57 pm ---Just take a bicycle if you have one and try to drive direct upwind at as slow of a speed as you need to maintain balance (maybe 1km/h is a bit slow) and you will see you do not need mW but hundreds of watts with 10m/s (36km/h) as clearly seen in that graph I posted.
--- End quote ---
A human on a bicycle is not efficient in this configuration so the input power is high even with a low output. And the 60mW was for 1mm/s. Your chart is not relevant, it shows the energy input? for for a moving bicycle against air resistance. A (nearly) stationary bicycle with a wind is a different problem with different results.
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