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Veritasium wrong about faster than wind direct down wind.
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electrodacus:

--- Quote from: Alex Eisenhut on December 11, 2021, 07:23:35 pm ---Then what does the relative movement have to do with anything? The power source, as you state yourself, is the stored energy of the moving vehicle using some energy to spin the prop.

How fast would the vehicle move if the prop blew forward?

--- End quote ---

You mean the vehicle kinetic energy ?
If you take out energy from there to generate some at the wheel and then put back in propeller the net result will be same end kinetic energy in ideal case and lower kinetic energy in real case.
Say kinetic energy is 100Ws and you take 1W for 1s at the wheel then result will be 99Ws vehicle kinetic energy then put that 1W for 1 second in the ideal propeller and get back to 100Ws so ideal case no acceleration real world deceleration.

Kleinstein:

--- Quote from: electrodacus on December 11, 2021, 08:44:36 pm ---Say kinetic energy is 100Ws and you take 1W for 1s at the wheel then result will be 99Ws vehicle kinetic energy then put that 1W for 1 second in the ideal propeller and get back to 100Ws so ideal case no acceleration real world deceleration.

--- End quote ---
No, this simple calculation is wrong. It would work this way with zero wind speed.

However with wind speed you have to take the energy of the wind into account too. With the wind in the same direction as the movement an ideal propeller can add more to the kinetic energy of the vehicle than the power it needs, as it also takes some energy from the wind. The important point is that there are different relative volocities that the wheels (to the ground) and the propeller (to the air) see. The propeller only has to work against the relative wind speed (low), but the energy added to the vehicle is from force times speed to ground (assumes the ground as the reference to calculate kinetic energy). So more energy can be added to the vehicle than the work the propeller does. That extra energy comes from the wind, that is slowed down by the prop.
electrodacus:

--- Quote from: Kleinstein on December 11, 2021, 09:18:44 pm ---
--- Quote from: electrodacus on December 11, 2021, 08:44:36 pm ---Say kinetic energy is 100Ws and you take 1W for 1s at the wheel then result will be 99Ws vehicle kinetic energy then put that 1W for 1 second in the ideal propeller and get back to 100Ws so ideal case no acceleration real world deceleration.

--- End quote ---
No, this simple calculation is wrong. It would work this way with zero wind speed.

However with wind speed you have to take the energy of the wind into account too. With the wind in the same direction as the movement an ideal propeller can add more to the kinetic energy of the vehicle than the power it needs, as it also takes some energy from the wind. The important point is that there are different relative volocities that the wheels (to the ground) and the propeller (to the air) see. The propeller only has to work against the relative wind speed (low), but the energy added to the vehicle is from force times speed to ground (assumes the ground as the reference to calculate kinetic energy). So more energy can be added to the vehicle than the work the propeller does. That extra energy comes from the wind, that is slowed down by the prop.

--- End quote ---

Yes there is no available wind power when vehicle speed is the same as wind speed or above (above is actually worse as it is negative).

formula for wind power for a vehicle traveling directly down wind is this
0.5 * air density * area * (w-v)^3
This can not be changed just so that it fits some experimental data that is not fully understood.
There is energy storage and that can be calculated separately and added to the balance of power but wind power formula is the one I mentioned not as Derek showed where he subtracted wind speed from vehicle speed.
And you can not use one formula for below wind speed and above it needs to be the same one as it is the same vehicle (no changes are done to vehicle when wind speed is exceeded).
fourfathom:
Do we agree that when the wind is blowing that there is energy available to a stationary device?
Does this change if the device is moving?  There is still a speed difference between the wind and the ground, regardless of the speed and direction of the device.
In the case where the device is moving directly downwind at windspeed, there is zero apparent wind (a sailing term, wind relative to the boat), but there is groundspeed, and the available energy still exists.

Accept this, and there is no need for energy storage, "slip-stick hysteresis", or any of that stuff.  All that remains is to devise a method of extracting energy from the air/ground speed difference.  This has been demonstrated.
electrodacus:

--- Quote from: fourfathom on December 11, 2021, 10:54:11 pm ---Do we agree that when the wind is blowing that there is energy available to a stationary device?

--- End quote ---
There is a potential energy available yes that will be 0.5 * vehicle mass * (wind speed)^2
That potential energy can be converted in to kinetic energy
This is true for a vehicle with no energy storage device like a sail type vehicle.
This type of vehicle can drive directly down wind up to wind speed (depends on friction losses) and can not drive directly upwind at any speed.


--- Quote from: fourfathom on December 11, 2021, 10:54:11 pm ---Does this change if the device is moving?  There is still a speed difference between the wind and the ground, regardless of the speed and direction of the device.
In the case where the device is moving directly downwind at windspeed, there is zero apparent wind (a sailing term, wind relative to the boat), but there is groundspeed, and the available energy still exists.

--- End quote ---

If vehicle is not moving there is no power available just a static force.
Power available to a vehicle moving directly down wind is this:   0.5 * air density * area * (w-v)^3  where w - wind speed and v- vehicle speed
From this you see that vehicle speed can be any as long as it is between zero and wind speed since when vehicle is at wind speed no wind power is available.




--- Quote from: fourfathom on December 11, 2021, 10:54:11 pm ---Accept this, and there is no need for energy storage, "slip-stick hysteresis", or any of that stuff.  All that remains is to devise a method of extracting energy from the air/ground speed difference.  This has been demonstrated.

--- End quote ---

If you want to exceed wind speed directly down wind then you need an energy storage device so that you can store energy while below wind speed and then use the stored energy to exceed wind speed.
Yes what was demonstrated was a vehicle with an energy storage device (pressure differential) and that can exceed wind speed. The test was incomplete else it will have showed how vehicle will start to slow down below wind speed as stored energy was used up.

It is fairly frustrating to see this disregard for energy conservation on an electronics forum.

If you have electrical knowledge think about this:

You have a 10V 3A CC-CV lab power supply and you can not output higher voltage or current using a device that has no energy storage device same for a negative voltage relative to ground/GND
You will need to use either inductors or capacitors or both in order to build a DC-DC boost converter.   Using just resistor dividers you can get any voltage as long as it is between 0V and 10V to get more or less (negative) you need an energy storage device.
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