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Mess with your minds: A wind powered craft going faster than a tail wind speed.
electrodacus:
--- Quote from: dunkemhigh on December 10, 2021, 06:39:09 pm ---
--- Quote ---You can stay as long as you want below wind speed and have as much energy as you want
--- End quote ---
Well, this is it, isn't it? It's not the vehicle that is extracting the energy from the wind, and is therefore dependent on relative wind speed, but the prop. Apply your formula to the prop instead of the vehicle and things are a bit different, no?
Of course, the vehicle is being pushed by the wind, but when it is at wind speed everything is balanced - there is enough push to keep it moving but nothing extra to let it go faster. But the prop is not moving at wind speed and can therefore extract power from the wind. Add that to the balance and not the vehicle can go faster.
--- End quote ---
You are getting very close.
The energy from wind used by vehicle is split in multiple ways.
For a real vehicle you have
-the losses trough friction those end up as heat so not useful.
-the energy put in accelerating the mass of the vehicle so kinetic energy proportional with vehicle speed relative to ground.
-the energy that is taken form wheels (less available for acceleration) and put in to propeller (wheel for traveling trough air). This energy results in increase pressure differential as the air is a compressible fluid.
Then when you are at wind speed you have all this pressure differential that you stored when you had wind power available and now you can use that stored pressure differential (potential energy) to accelerate the vehicle (increase kinetic energy). But since this is a finite resource vehicle will at some point reach the top speed maybe 2x wind speed then it will start to slow down.
At minute 10:30 in the video I show the calculator I made based on this description I just made ans showed how vehicle can exceed wind speed https://youtu.be/4Hol57vTIkE?t=631
electrodacus:
--- Quote from: fourfathom on December 10, 2021, 07:20:22 pm ---And the idea that energy storage is necessary (the underpinning of the electrodacus theory) is just plain wrong. Yes, air is compressible, but there is no storage in the system that is adequate to accelerate the craft beyond windspeed for more than a very brief period. The various craft have demonstrated an ability to move well beyond windspeed, effectively continuously, no energy storage required.
And I still claim that that demonstration with the wheeled fixture, rolling on the floor, with the board above it being pushed, is a good analogy. The floor represents the ground, the board represents the wind, and the large coupled wheel represent the propeller. The fixture moves "downwind" faster than the "wind". electrodacus disagrees. But regardless, the "energy storage" notion is wrong, and this nullifies the electrodacus theory.
--- End quote ---
What craft has demonstrated direct down wind faster than wind continuously ?
The wheel analogy represents a direct upwind and it also uses energy storage but in a very different way and it is not pressure differential.
Mathematical proof was done wrong as Derek modified the formula to fit his theory.
Try use his equation in my example and see what you get especially in case A.
Labrat101:
Wind is powering the propeller not the wheels .
The wind tread mill is not correct .
Sorry you can't emerlate wind with a tread mill
fourfathom:
--- Quote from: electrodacus on December 10, 2021, 07:55:59 pm ---What craft has demonstrated direct down wind faster than wind continuously ?
The wheel analogy represents a direct upwind and it also uses energy storage but in a very different way and it is not pressure differential.
--- End quote ---
You and I have seen videos of craft accelerating or traveling steadily FTTWDW for many seconds, or even minutes, with the telltales streaming backwards. I claim that there is no energy storage mechanism in play. Unenclosed air-pressure differences will not store energy for more than a moment.
I also claim that the wheeled demonstration is a direct downwind analogy. And what is the "different way" of using energy storage in that demonstration? Please explain it in words.
I also claim that the video tests of propeller/wheel vehicles running on treadmills demonstrate the principle, harnessing the difference between groundspeed and airspeed. The treadmill is level, or even uphill, and the vehicle does not roll up-treadmill when the treadmill is stopped. Again, no energy storage at work.
You have latched onto this "energy storage" idea, even though there is no appreciable energy storage, and none is required, in the examples I mention.
IanB:
--- Quote from: electrodacus on December 10, 2021, 06:21:43 pm ---Here is the formula for wind power
0.5 * air density * area * (w-v)^3
air density is usually around 1.2kg/m^3
area is the sail area or equivalent (the area facing the wind direction) so direct down wind this is also a constant for a sail
and then is that w (wind speed) minus v (vehicle speed) so there there is max power when vehicle just starts moving super low vehicle speed and decreases significantly as vehicle approaches wind speed and equal with zero when at wind speed.
--- End quote ---
This formula is quite wrong. It is not w (wind speed) minus v (vehicle speed), it is w (wind speed) - g (ground speed), where g is usually zero (unless on a treadmill).
This means the available power from the wind does not depend on the speed of the vehicle, and so it does not matter if the vehicle is travelling at the speed of the wind or faster than it. As long as the vehicle has contact with the ground (wheels with friction), and contact with the air (some kind of sail, fan or propeller), then the vehicle can extract power from the wind/ground system and can go faster then either.
Wheel friction is important here. If the vehicle was skating on ice, then it couldn't go faster than the wind speed, since it would have no grip on the surface between it.
Similarly, it is easy to make a wheeled vehicle run directly into a headwind, and any number of experiments can be built to demonstrate this.
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