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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: Labrat101 on September 02, 2021, 07:53:29 pm ---
Totally correct   It would help others if maybe some could do a 3D model   :-+ :popcorn:

--- End quote ---

The 3D component is irrelevant in this discussion as all I wanted to show was that energy can be stored in pressure differential created by the propeller and this pressure differential energy storage is what allows vehicle to exceed wind speed for a limited amount of time.
As vehicle exceeds wind speed this pressure differential will decrease as energy is used to accelerate the vehicle and when this pressure differential is smaller than what vehicle needs to cover the losses the vehicle will start to slow down.
electrodacus:

--- Quote from: imo on September 02, 2021, 07:59:01 pm ---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?

--- End quote ---

What powers the propeller on your zeppelin ?
For this zeppelin to be equivalent you will need to have a wheel ruining on the ground connected trough a cord that may be also the electric cable and then energy generated from that will power the propeller. In this case that is the same as blackbird the zeppelin can not exceed wind speed other than for a few moments based on pressure differential energy storage. The drag from the generator wheel will be higher than the trust you can get from the propeller powered only the the power coming from the wheel on the ground. 
electrodacus:

--- Quote from: IanB on September 02, 2021, 08:00:40 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.

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.

--- End quote ---

Yes it is fairly simple but you are the one that is not seeing the difference.
Imagine two wheels and on top of them there is a piece of heavy lumber.
Both wheels are anchored to ground and you rotate one of the wheels. What will happen is that lumber will move relative to the ground.
Now disconnect one of the wheels from the ground (the wheel is free to move) and you put the effort in pushing (sliding that wheel) relative to the ground.
The lumber will stay where it is relative to the ground and only your wheel moved.
This is the reason you think the vehicle in my diagram can move from left to right powered only by the treadmill. You need to do the experiment to see that will never be the case. That vehicle when you use a treadmill will move from right to left only no matter how you setup the gear ratio.
iMo:

--- Quote from: electrodacus on September 02, 2021, 08:05:59 pm ---..What powers the propeller on your zeppelin ?

--- End quote ---
With the zeppelin case I've been trying to disconnect the "propeller" and "wheels" concepts here.
I can also ask you the same: "What powers the propeller on you Blackbird?"


electrodacus:

--- Quote from: imo on September 02, 2021, 08:15:04 pm ---
--- Quote from: electrodacus on September 02, 2021, 08:05:59 pm ---..What powers the propeller on your zeppelin ?

--- End quote ---
With the zeppelin case I've been trying to disconnect the "propeller" and "wheels" concepts here.
I can also ask you the same: "What powers the propeller on you Blackbird?"

--- End quote ---

Above wind speed the propeller is powered by energy stored in pressure differential. Once that energy is used up vehicle will slow down below wind speed.
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