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Mess with your minds: A wind powered craft going faster than a tail wind speed.
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electrodacus:

--- Quote from: Kleinstein on December 10, 2021, 05:15:49 pm ---
--- Quote from: electrodacus on December 10, 2021, 04:59:07 pm ---When vehicle speed equal wind speed there is zero wind power available and the only way to exceed that speed while only moving directly down wind is by storing energy before that point and using that stored energy to do so.

--- End quote ---
We are running in circles here. The video showed that it works (2 experiments) and give an explaination how, it just is not so easy to understand, and thus the title.
The point is, that there is power from the wind available, even when moving with the wind at exactly the speed of the wind or somewhat faster. This does not work with a passive sail, but it does work with the fan.

The energy storage idea to explain the experiment is just not working: both the large vehicle driving outside and the small one on the treadmill have quite some friction. There is nowhere enough stored energy to drive the vehicle for the time they where going faster that the wind or against the treadmill. The kinetic energy does not count here as it is not available to accelerate or keep the speed.

--- End quote ---

The power that is available and accelerates the vehicles both blackbird and the treadmill model is the stored one in pressure differential.
If you where to replace air (compressible fluid) with say water (non compressible fluid) the it will no longer work (Imagine a blackbird type vehicle at the bottom of a river trying to drive faster than the river flow speed directly downstream).

You underestimate the amount of energy that can be stored in the pressure differential and also how much energy is needed for those tests.
For example blackbird is basically a tricycle super low friction and it has a 5.3m diameter propeller that has a swept area of around 20m^2
Total energy needed to do that record of 2.8x wind speed they did require less than 6Wh of energy so less than half the energy in a modern smartphone.
PlainName:

--- Quote ---... and everybody agrees it can not exceed wind speed directly down wind and can also not travel at any speed directly upwind.
--- End quote ---

Yes, but we can't agree why. There is plenty of energy available from the wind, it's just that we can't reap it because there is no relative movement between the vehicle and the wind. It's not like the faster the vehicle goes the more energy it needs to overcome air friction, because there is less of that when we travel with the wind.

The problem can thus be reduced to merely finding some means of making the wind move relative to us, and that's what the prop does.
electrodacus:

--- Quote from: dunkemhigh on December 10, 2021, 06:03:30 pm ---
--- Quote ---... and everybody agrees it can not exceed wind speed directly down wind and can also not travel at any speed directly upwind.
--- End quote ---

Yes, but we can't agree why. There is plenty of energy available from the wind, it's just that we can't reap it because there is no relative movement between the vehicle and the wind. It's not like the faster the vehicle goes the more energy it needs to overcome air friction, because there is less of that when we travel with the wind.

The problem can thus be reduced to merely finding some means of making the wind move relative to us, and that's what the prop does.

--- End quote ---

That is simple. Is not about the available energy is about available power to vehicle.

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.

You can stay as long as you want below wind speed and have as much energy as you want but unless you have a way to store that energy you can not exceed wind speed as wind power is zero when vehicle speed is equal with wind speed (ideal case).

Derek to justify blackbird just subtracted the wind speed from vehicle speed instead of the other way around. So he just modified the formula to fit with his theory on how the vehicle works.
PlainName:

--- 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.
fourfathom:
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.
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