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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: IanB on September 02, 2021, 07:36:06 pm ---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.

--- End quote ---

I think your confusion comes from the shape of the treadmill. If that treadmill was just a rotating wheel with central axis not moving relative to the ground you will have seen things differently. Maybe think about the treadmill like a track (like you see on tanks or some construction equipment).
Look at the center of the treadmill or axis of one of the two cylinders and see if they move relative to the ground.
Then power off the treadmill and push it relative to the ground now the center of the treadmill or center of the cylinders move relative to the ground.

There is a very big difference between the two cases and key in understanding what will happen in my diagram and why vehicle will not be able to move from left to right if you use a treadmill. 

electrodacus:

--- Quote from: Labrat101 on September 02, 2021, 07:39:47 pm ---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 !!

--- End quote ---

Sorry not sure how your torpedo example has anything to do with the wind powered vehicle.
First the torpedo travels only in a single medium (water).

If you want a proper example then think about a vehicle driving on wheels at the bottom of a river so the water flow will represent the wind in air and the bottom of the river the road.
Now in this case since air is replaced with water the vehicle will be unable to exceed the water flow speed. The reason that is not possible is because water is a non compressible fluid and so energy can not be stored thus vehicle can not exceed water flow speed.
In air vehicle can exceed wind speed but only for a limited amount of time dictated by the amount of stored energy and vehicle losses.

Labrat101:

--- Quote from: electrodacus on September 02, 2021, 01:37:35 am ---

--- 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

[/quote]
Totally correct   It would help others if maybe some could do a 3D model   :-+ :popcorn:

iMo:
Imaging a small zeppelin (an airship) with the same propeller as it is in the Blackbird configuration. The zeppelin will fly, say, 5m high above the ground.
Will the zeppelin fly faster then the tail wind speed?
 

IanB:
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.

This is really simple. If you think there is something wrong with one of these two statements, change some of the green words to make it correct.

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