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Mess with your minds: A wind powered craft going faster than a tail wind speed.
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bdunham7:

--- Quote from: electrodacus on September 02, 2021, 12:20:01 am ---Think about this way. You have a large wind turbine generator in low wind speed supplying a much smaller fan that creates even hurricane level winds but since the diameter of the fan is much smaller much less wind is actually moved so is like a gear box.
So say you will want to use the fan to supply the wind turbine then that will not work as power output is much smaller from the fan than what the wind turbine will need to supply the fan.
The propeller is like a diode it can leave air molecules travel from upwind to down wind but not the other way around so it acts as a one way sail while spinning.

--- End quote ---

But here you only have one fan, the propeller, and it obviously the same size as itself and is pushing directly back at the same wind that is powering it.  So first, I don't see how your 'gearbox' analogy works and second, you didn't respond to the question of how the wind and the 'artificial wind', which you claim can be stronger, can coexist in the same space.
electrodacus:

--- Quote from: bdunham7 on September 02, 2021, 12:45:17 am ---
But here you only have one fan, the propeller, and it obviously the same size as itself and is pushing directly back at the same wind that is powering it.  So first, I don't see how your 'gearbox' analogy works and second, you didn't respond to the question of how the wind and the 'artificial wind', which you claim can be stronger, can coexist in the same space.

--- End quote ---

On blackbird the vehicle is like a sail at initial start so wind pushes against the vehicle body and the propeller blades (much smaller area then when the propeller rotates).  This power is split between accelerating the vehicle and powering the propeller by taking energy from the wheel.
So if you disconnect the propeller from the wheel then vehicle in same wind condition can accelerate much faster and get much faster to some speed below wind speed.
But instead of using all wind energy to accelerate fast you divert large part of the energy to power the propeller that creates a sort of artificial wind eventually at multiple times the wind speed.
So wind energy will be stored in vehicle kinetic energy then in propeller kinetic energy (spinning mass flywheel) and finally in pressure differential energy storage.
As you start to put more and more energy in the pressure differential energy storage that starts to also get used by the vehicle but even this is put back in all this 3 forms of energy storage the vehicle kinetic energy the propeller kinetic energy and also very important propeller pressure differential.
But when this pressure differential is the main or even only energy source it is put back in to kinetic energy of the vehicle and propeller kinetic energy so propeller spins faster but because vehicle also move faster the pressure differential drops.
When pressure differential gets so low that it can no longer power the vehicle and max speed is reached the vehicle starts to decelerate and now it is powered both by the vehicle kinetic energy and propeller kinetic energy that at this max speed point are at max charge and as they get used up the vehicle gets to the point where is again below wind speed.     
IanB:

--- Quote from: electrodacus on September 01, 2021, 11:35:17 pm ---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).
--- End quote ---

Except for the huge problem that propellers do not compress air. As has been shown by more than one experiment in this thread, the air behind a propeller is actually a vacuum.

The facts are simple: no walls, no containment, no compression, no pressure differential.
electrodacus:

--- Quote from: IanB on September 02, 2021, 01:30:32 am ---
Except for the huge problem that propellers do not compress air. As has been shown by more than one experiment in this thread, the air behind a propeller is actually a vacuum.

The facts are simple: no walls, no containment, no compression, no pressure differential.

--- End quote ---

There is a low level vacuum on one side so lower than ambient pressure and on the other side there is a higher than ambient pressure.
As I mentioned before Wikipedia is not always a source of reliable information but it is sure way better for this than the youtube video performed by someone with no knowledge about the subject.
Link to articlehttps://en.wikipedia.org/wiki/Axial_fan_design
And diagram I posted before showing clearly the pressure differential

IanB:

--- Quote from: electrodacus on September 02, 2021, 01:37:35 am ---As I mentioned before Wikipedia is not always a source of reliable information but it is sure way better for this than the youtube video performed by someone with no knowledge about the subject.
--- End quote ---

You have a problem here in that experiments show what happens in real life. The observations from an experiment are a hard, solid, fact, independent of the knowledge of the person performing the experiment. You could have a two year old perform an experiment, and without them knowing anything, the experiment would still display the factual behavior of the universe.

On the other hand, a written document is simply what someone wrote. It may or may not be accurate, and conveys no factual weight in and of itself.

In this case, there is an obvious flaw. The diagram shows an abrupt change in pressure between P1 and P2, but it shows no simultaneous change in velocity. Since the mass flow between 1 and 2 must be equal by continuity, and since a change in pressure requires a change in density, it follows that the velocity must change abruptly if the pressure changes abruptly. Therefore, the diagram cannot be accepted at face value and must be rejected as an accurate description.
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