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

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Domagoj T:

--- Quote from: electrodacus on December 28, 2021, 06:20:41 pm ---
--- Quote from: Domagoj T on December 28, 2021, 10:26:17 am ---I'm still waiting for you to respond to my wind powered toy design from page 45.
It has no storage, operates in steady state continuously and has infinite range. At no point do extended sails travel faster than the wind, but the vehicle as a whole does.
I'm waiting.

--- End quote ---

There are two very different versions of blackbird. There is the direct downwind that works based on pressure differential energy storage and there is the direct upwind version that uses small capacity internal storage and stick slip hysteresis and that version since it always have access to wind power it can work continuously as long as there is wind.
All the wheels only toys where air is not involved are the equivalent of that direct upwind version of blackbird using small capacity energy storage device maybe charging in a few ms and then discharging triggered by stick slip hysteresis either internally in the mechanism or externally at the wheels.

The wrong equation for power either drag or generation is what made the math possible without energy storage. If the correct equation for power is used then is clear from the math that neither direct downwind faster than wind nor direct up wind at any speed is not possible without energy storage.

--- End quote ---
And again you manage to deflect and avoid answering.
My design is different than Blackbird, so let's stick to mine, please.
I'm not talking about upwind, only downwind.
There is no stick slip hysteresis in my design (substitute string with chain, and wheels and ground with rack and pinion, if you so choose).
There is no energy storage in my design, unless you consider sails themselves to be storage, in which case sure, whatever, doesn't matter, let's not mention it ever again since it's irrelevant.
The steady state of this design is that the vehicle as a whole will continuously travel above wind speed, directly downwind.

electrodacus:

--- Quote from: Domagoj T on December 29, 2021, 06:27:39 am ---And again you manage to deflect and avoid answering.
My design is different than Blackbird, so let's stick to mine, please.
I'm not talking about upwind, only downwind.
There is no stick slip hysteresis in my design (substitute string with chain, and wheels and ground with rack and pinion, if you so choose).
There is no energy storage in my design, unless you consider sails themselves to be storage, in which case sure, whatever, doesn't matter, let's not mention it ever again since it's irrelevant.
The steady state of this design is that the vehicle as a whole will continuously travel above wind speed, directly downwind.

--- End quote ---

You can be offended if you want but you do not even deserve an answer as it will be a long and involved one from me and you will have no clue of what I just said.
My answer was generic and included all possible vehicle types powered only by wind directly down wind and no vehicle can exceed wind speed unless it uses an energy storage device or an external energy source.
Not only the correct equation for wind power will show that but even the wrong equation will predict the same as I just shown in an example earlier today.

lordium:
@electrodacus,

Is it possible to get an summary from start to finish about why it is impossible?
Examples and illustrations along to way would be helpful so that I can follow all the steps.
I'm really struggling to follow the thought process here. Guess I'm not smart enough. So please put it as plainly as possible.

PlainName:

--- Quote ---and no vehicle can exceed wind speed unless it uses an energy storage device or an external energy source.
--- End quote ---

The authoratitive source for that statement of fact?

Well, seems to be just you. Surprised you aren't the nobel laureate yet.

Kleinstein:

--- Quote from: electrodacus on December 29, 2021, 04:27:37 am ---...

It is quite simple. Power needed to counter drag will be

Fw * (wind speed + vehicle speed).

--- End quote ---
This only applies if you use the power to drive the vehicle with a prop.

The drag force is not different from other forces and the mechanical power is force times speed between the 2 part that the force is acting between (ground and the vehicle).



--- Quote from: electrodacus on December 28, 2021, 10:29:21 pm ---OK lets compare the output of the two equations

air density 1.2kg/m3
area 1m2
Wind speed 20m/s
Vehicle speed a) 0m/s, b)  10m/s, c) 20m/s

0.5 * air density * area * (wind speed - vehicle speed)2 * (wind speed - vehicle speed)
a)  4800W
b)  600W
c)  0W

0.5 * air density * area * (wind speed - vehicle speed)2 * (vehicle speed)
a) 0W  (how will your wind powered vehicle ever start)
b) 600W
c) 0W

Any comments ?
Seems even with your wrong equation there is no wind power available to any wind powered vehicle when at and above wind speed.

--- End quote ---
The 2nd expression (it is not even an equation, as there is no "=" sign ) never claimed to calculate the available wind power, but the power available from a sail (which is not the most power efficient way) or the power needed to drive against the wind, like a sail in reverse.
The 1 st expression is the power available to a wind turbine on a muving vehicle, not including the power needed or available from moving the vehicle. The problem is using that same expression for different things. So why not use Ohms law instead ? This give a wrong result too, and arguably maybe sometimes even a correct if the result is 0.

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