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

--- Quote from: electrodacus on December 28, 2021, 12:09:30 am ---
--- Quote from: IanB on December 27, 2021, 11:59:20 pm ---
That is the wrong answer. Maybe you would like to try again?

--- End quote ---

I will ask you the same thing as it is a decently good analogy.
Have you ever had the chance to swim in a river ?

--- End quote ---

https://youtu.be/Qf03U04rqGQ?t=134
electrodacus:

--- Quote from: gnuarm on December 28, 2021, 12:12:53 am ---
How is the energy storage relevant?  If the vehicle continues against the wind indefinitely, it is moving against the wind.  Who cares if there are tiny variations in the speed?  This sort of storage of energy is not relevant to the issue.  At no time does the velocity fall below the wind speed.

--- End quote ---

Wind will charge the energy storage device (small capacity) then slip will allow the stored energy to be discharged and thus vehicle will move forward against wind direction that small amount that is possible with that stored energy. Then wheel will lock and energy storage will be again charge then everything repeats  multiple times per second. All energy used to advance the vehicle against wind direction was stored energy.
The above is valid for a direct upwind vehicle but based on your "At no time does the velocity fall below the wind speed" comment you may be talking about direct downwind and that is a completely different thing.
electrodacus:

--- Quote from: IanB on December 28, 2021, 12:14:59 am ---
--- Quote from: electrodacus on December 28, 2021, 12:09:30 am ---
--- Quote from: IanB on December 27, 2021, 11:59:20 pm ---
That is the wrong answer. Maybe you would like to try again?

--- End quote ---

I will ask you the same thing as it is a decently good analogy.
Have you ever had the chance to swim in a river ?

--- End quote ---

https://youtu.be/Qf03U04rqGQ?t=134

--- End quote ---

How is that video that you already posted relevant to my question about swimming in a river ?
Do you think air is not a fluid ?
IanB:

--- Quote from: electrodacus on December 28, 2021, 12:20:12 am ---
--- Quote from: IanB on December 28, 2021, 12:14:59 am ---
--- Quote from: electrodacus on December 28, 2021, 12:09:30 am ---
--- Quote from: IanB on December 27, 2021, 11:59:20 pm ---
That is the wrong answer. Maybe you would like to try again?

--- End quote ---

I will ask you the same thing as it is a decently good analogy.
Have you ever had the chance to swim in a river ?

--- End quote ---

https://youtu.be/Qf03U04rqGQ?t=134

--- End quote ---

How is that video that you already posted relevant to my question about swimming in a river ?
Do you think air is not a fluid ?

--- End quote ---

Your reply is a red herring. Swimming in a river has nothing to do with my question.

Let me ask you again: what would you say if someone showed you a demonstration of a vehicle moving directly against the wind, powered by the wind, with no energy storage?

It's a very simple question. It doesn't involve rivers, or swimming, or any bullshit like that.
gnuarm:

--- Quote from: electrodacus on December 27, 2021, 11:33:23 pm ---
--- Quote from: gnuarm on December 27, 2021, 11:16:30 pm ---
Ok, so if the user is stationary in a 20 km/h head wind, how much power is required to maintain this position?  If you come up with any answer other than zero, you can't explain how a brake works.  The brake can maintain this position into the 20 km/h wind while dissipating no power.  A rider can do the same thing by simply standing on the pedal preventing it from rising up.  One foot on the ground for balance, one foot on the pedal to maintain position.  No power transfer.  ZERO

You seem to have already agreed that this is correct.  In that case you must agree there is no power transfer at the wheels for a stationary bike/car/blackbird and that the equation that predicts power at the wheels based solely on the wind relative speed must be wrong.

--- End quote ---

If there are no sort of brakes it will require around 42W. A brake will anchor the vehicle to the ground thus no work is done on the vehicle.
A rider with sufficient weight standing on the pedal will still be a form of brake. It is a gravitational based one but still a brake.
--- End quote ---

Ok, so no movement, no power, right?



--- Quote ---There is potential wind power that can not be used because of the brake but there are 42W available at 20km/h wind speed and that 0.408m^2 equivalent area.
--- End quote ---

Not talking about wind power or using it.  I'm talking about the power involved in moving or not moving the vehicle.  So once you acknowledge the equation for the power to move the vehicle has to return a zero value at zero speed, it is clear which equation is correct. 



--- Quote ---The equilibrium state will be the bike being pushed at 20km/h relative to ground so that there is no more force on the bike and no potential energy relative to air but there is now a potential energy relative to ground based on vehicle weight and speed relative to ground.
--- End quote ---

I thought the speed was zero?  So no power, no energy relative to the ground.



--- Quote ---Without any energy storage the bike can be between zero speed relative to ground if anchored to ground and wind speed if there is no friction loss so not anchored to ground.
The vehicle can be anywhere between this two speed directly down wind at wind speed relative to ground and zero speed relative to ground and at this ends it will have potential energy storage relative to ground or to air.
This kinetic energy while it is a form of energy storage can not help the vehicle get outside this speed limits if it travels directly down wind at all times.
This kinetic energy can be used if vehicle travels at an angle to the wind direction that is how a sail vehicle can exceed wind speed.

In case of blackbird direct downwind version pressure differential is used to exceed wind speed for a limited amount of time.
In case of blackbird direct upwind version elastic and or gravitational energy storage in combination with stick slip hysteresis is what is used to drive at any speed (limited by frictional losses) for any amount of time.

--- End quote ---

Ok, you are off task again.  Let's just deal with one detail at a time.  So do you acknowledge that the correct equation for the power at the wheels to move the vehicle into the wind must contain a factor which is just the velocity of the vehicle relative to the ground the wheel is pushing against? 

The force from the wind is 

Fd = 1/2 · Cd · A · p · (vw + vo)^2

The power required at the vehicle wheels to maintain a speed into the wind is 

Pv = 1/2 · Cd · A · p · (vw + vo)^2 · vo

Correct?
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