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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 September 02, 2021, 06:45:57 pm --- Ok you introduce the case with the powerd of an pushed treadmil as a 3rd scenario. If it help you to make clear were the diffence is Ok.
However I still don't see, if the powered off and manually pushed treadmill is more like the running treadmill, or more like the piece of paper pulled across the floor.

The next question is, how does the vehicle know which of the 2 (or 3) cases is present and which way to go ? So there should be a difference to the vehicle, not just to your mind.

--- End quote ---

Powered off and pushed treadmill is exactly like the piece of paper.
The difference is in changing the reference frames without considering you did that.
That is why case b is a perfect intermediary example.
As you can see case b) as a treadmill rotating at 2m/s and the ground moving in opposite direction at 2m/s
Ground was considered the wind speed in my diagram and was not moving so vehicle and wind had the same speed.
While pushing the treadmill from right to left at 2m/s or pushing the ground from left to right means the same thing
But then if you do that push the ground from left to right it clearly shows a 2m/s wind speed.

So a) where a rotating treadmill is used the analog is a vehicle traveling at 4m/s with wind speed of 4m/s in the same direction
and c) will be the analog of vehicle traveling in the opposite to wind direction at lower speed than the wind. So as different as it can be.
electrodacus:

--- Quote from: Labrat101 on September 02, 2021, 06:52:40 pm ---
The Fan is not just a Propeller as it has several functions in this type of setup . I was sorry that they did not use a smoker to show how the air was moving.
the wind is turning the fan . that is connected to the drive wheels . that energy move it forward . the fan/Propeller starts to spin faster . The tips of the propeller
are now creating a rotating vortex . Screw effect . so the air to the side of the vortex will move outwards >  So the when equilibrium is reached the front
should have a lower air pressure . less resistance (vacuum)  the propeller is now blowing the craft .  Yes there is ground resistance but it gets faster the
propeller will try to tilt back and will stay . More like a gyroscope would Ballance.
I see how this works but find it hard to explain exactly why .

--- End quote ---

You describe what happens before vehicle exceeds wind speed.
What do you think will power the vehicle after the wind speed is exceeded ? As wind can no longer power the vehicle that travels in the exact same direction?
IanB:

--- Quote from: electrodacus on September 02, 2021, 06:18:03 pm ---Please the the case b) intermediary state to understand that there is a big difference between a treadmill that is not moving relative to the ground and a powered off treadmill moved relative to the ground (powered off treadmill is your piece of paper or moving flat surface).
I think case b) is a good way to explain/visualize the difference between a) treadmill  and c) piece of paper

--- End quote ---

a treadmill that is not moving relative to the ground
- is a flat surface moving from right to left under the front wheels of the cart, relative to a stationary surface on which the back wheels rest.
a powered off treadmill moved relative to the ground     
- is a flat surface moving from right to left under the front wheels of the cart, relative to a stationary surface on which the back wheels rest.

There is no difference between these two cases.
Kleinstein:

--- Quote from: Labrat101 on September 02, 2021, 06:52:40 pm ---
--- Quote from: electrodacus on September 02, 2021, 06:30:29 pm ---
--- Quote from: Labrat101 on September 02, 2021, 06:25:59 pm ---Hi , Really interesting and cool,
Yes this is totally possible ,and should work .
as the subject says Mess with your mind . there are 4 forces all working together here  . Plus the fan is not just a propeller .
This experiment just would not work on a tread mill as in real life they ran it on a very large flat open surface without opticals .
The bit were the fan started wobbling but as the wind increased it stop .. this is caused by fan tip speeds and centrifugal force which in turn stabilizes
the craft and the tip air flow will be faster than wind speed . So when all the forces balance it will travel faster .
These guys really went to the next level .
 :popcorn:

--- End quote ---

Yes it seems it messes with many peoples mind.
What do you mean by the fan is not just a propeller ?
The experiment worked perfectly fine on a treadmill see the propeller based cart showing as moving forward on a treadmill.

--- End quote ---
The Fan is not just a Propeller as it has several functions in this type of setup . I was sorry that they did not use a smoker to show how the air was moving.
the wind is turning the fan . that is connected to the drive wheels . that energy move it forward . the fan/Propeller starts to spin faster . The tips of the propeller
are now creating a rotating vortex . Screw effect . so the air to the side of the vortex will move outwards >  So the when equilibrium is reached the front
should have a lower air pressure . less resistance (vacuum)  the propeller is now blowing the craft .  Yes there is ground resistance but it gets faster the
propeller will try to tilt back and will stay . More like a gyroscope would Ballance.
I see how this works but find it hard to explain exactly why .


--- Quote ---The experiment worked perfectly fine on a treadmill see the propeller based cart showing as moving forward on a treadmill.
--- End quote ---
Yes I saw that experiment with a small model and a good wind source  but it needs the distance to get all forces balanced very hard .


Update whats with the treadmill . this is thinking back 100years when people thought if a Car went faster than 7mph you would get sucked out

--- End quote ---

I totally agree that they should use something like smoke or a small thread on a pole to indicate air movement for the experiment on the treadmill.
This would show that when at the speed of the wind (e.g. whicle stand still on the picture) the prop is pushing the air against the direction of the belt of the treadmill.  So the wheels are powering the prop, and not the other way around. This is the main point for the understanding.

There is no need to include complications like a vortex around the prop, just consider the prop as a way to drive the vehicle relative to the air and generate thrust. To make the vehicle go forward the porp has to generate a little more forward force than the wheels generate backward force when they generate the power for the fan.  The technical difficulty is getting the fan to produce enough thrust with the given power. So while the principle is simple, getting the prop at the right speed and pitch is not so much.


--- Quote from: electrodacus on September 02, 2021, 07:17:42 pm ---....
What do you think will power the vehicle after the wind speed is exceeded ? As wind can no longer power the vehicle that travels in the exact same direction?

--- End quote ---

The wind can not longer power the prop, when the vehicle goes faster than the wind. However the wind can still power the vehicle. This is the special effect shown here.

When looking  in the reference frame of the vehicle (or wind when at the same speed), the prop takes energy from the wheels and blows air forward against the wind.
When looking  in the reference frame of the ground, the prop takes energy from the wheels and as it produces thrust (asignst the wind) it also absorbes power from the wind. If designed well the power absorbed from the wind can be larger than the power needed to drive the fan.
Labrat101:

--- Quote from: electrodacus on September 02, 2021, 07:17:42 pm ---
--- Quote from: Labrat101 on September 02, 2021, 06:52:40 pm ---
The Fan is not just a Propeller as it has several functions in this type of setup . I was sorry that they did not use a smoker to show how the air was moving.
the wind is turning the fan . that is connected to the drive wheels . that energy move it forward . the fan/Propeller starts to spin faster . The tips of the propeller
are now creating a rotating vortex . Screw effect . so the air to the side of the vortex will move outwards >  So the when equilibrium is reached the front
should have a lower air pressure . less resistance (vacuum)  the propeller is now blowing the craft .  Yes there is ground resistance but it gets faster the
propeller will try to tilt back and will stay . More like a gyroscope would Ballance.
I see how this works but find it hard to explain exactly why .

--- End quote ---

You describe what happens before vehicle exceeds wind speed.
What do you think will power the vehicle after the wind speed is exceeded ? As wind can no longer power the vehicle that travels in the exact same direction?

--- End quote ---
As said I find it hard to explain exactly how this happens.
Can I give you another example .  A torpedo travelling though water (sea) with currents in any direction .
As travels it is spinning and creates a tubercular vortex around it so the out casing is no longer in contact with the water .
The new Torpedo's  can have almost zero surface resistance losses
Just like when you pull the plug out the bath you get that lovely vortex whirlpool that if your are careful one put ones finger in the middle without getting wet .
The propeller also blows
The same thing happens with air it just harder to see
Did that help !!

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