I Power available to a wind powered vehicle traveling directly downwind

[A.T.]

It seems to many people struggle with understanding energy conservation.

There is nothing in Energy Conservation that prevents reducing the air-ground velocity difference (extracting wind energy) when moving downwind at wind speed, if you have contact to the ground too.

 

[russ_watters]

Where is your equation for available wind power?

[from post 5]
0.5 * air density * area * (wind speed - vehicle speed)3

Your answer doesn't match your question. The amount of power available in the wind is not a function of the vehicle speed it is a function of the wind speed relative to the ground only. Adding the term for vehicle speed inserts additional unstated constraints/assumptions about the nature of the vehicle and how/how effectively it extracts that power. It's a very different question.

To be specific, subtracting the wind vehicle speed assumes you are using a sail or turbine on the vehicle to extract power.

[typo strike through]

 

[electrodacus]

Your answer doesn't match your question. The amount of power available in the wind is not a function of the vehicle speed it is a function of the wind speed relative to the ground only. Adding the term for vehicle speed inserts additional unstated constraints/assumptions about the nature of the vehicle. It's a very different question.

To be specific, subtracting the wind vehicle speed assumes you are using a sail or turbine on the vehicle.

If vehicle is stationary then wind speed relative to vehicle will be the same as wind speed relative to ground.
Once the vehicle starts moving in the exact same direction as wind (downwind) the wind speed relative to vehicle drops and thus so is the wind power available to vehicle.
The vehicle design is irrelevant as the only important aspect is the vehicle area facing the wind and coefficient of drag.
So equation will be the same no matter the vehicle design.

 

[russ_watters]

Once the vehicle starts moving in the exact same direction as wind (downwind) the wind speed relative to vehicle drops and thus so is the wind power available to vehicle.

That isn't correct in general. It is true for some types of designs/vehicles but not true for others.

 

[electrodacus]

There is nothing in Energy Conservation that prevents reducing the air-ground velocity difference (extracting wind energy) when moving downwind at wind speed, if you have contact to the ground too.

Again provide the equation showing that there is any wind power available to a vehicle that travels direct downwind at the same speed as wind speed.
The equation I provided shows there is zero wind power available to vehicle in those conditions.

Vehicle has stored kinetic energy relative to the ground while it moves at same speed as wind speed so when you want to take energy at the wheel that energy will come from stored vehicle kinetic energy thus will result in vehicle slowing down if there is no other energy storage available as it is the case with Blackbird that stores energy in the pressure differential created by the large propeller.

 

[russ_watters]

Again provide the equation showing that there is any wind power available to a vehicle that travels direct downwind at the same speed as wind speed.
The equation I provided shows there is zero wind power available to vehicle in those conditions.

It just takes correcting your equation: 0.5 * air density * area * (wind speed)3

Since the wheels are coupled to the propeller/turbine the vehicle is harnessing the differential between ground speed and wind speed. That differential never changes regardless of cart speed.

Vehicle has stored kinetic energy relative to the ground while it moves at same speed as wind speed so when you want to take energy at the wheel that energy will come from stored vehicle kinetic energy thus will result in vehicle slowing down if there is no other energy storage available as it is the case with Blackbird that stores energy in the pressure differential created by the large propeller.

That's a run-on sentence that makes no sense. Obviously if you couple the turbine/propeller to the wheels, then one is propelling the cart and the other is powering it.

 

[electrodacus]

That isn't correct in general. It is true for some types of designs/vehicles but not true for others.

It is true for any vehicle design.
The equation is not dependent on vehicle design.

Imagine a simple sail vehicle (maybe just a cube on wheels).
The equation will perfectly describe what will happen to that vehicle.
Then imagine the exact same vehicle but you add an electrical generator at the wheel and a battery.
Now to know what happens to that vehicle you will also need to know how much power you extract at the wheel. And if you then use that stored energy in the battery you are able to exceed wind speed direct down wind but vehicle will eventually slow down below wind speed as that stored energy is being used up.
So you can not say the vehicle is powered by wind while it is accelerating using the energy stored in the battery.
That is exactly how blackbird vehicle works is just that instead of an electrochemical battery it uses pressure differential for energy storage.

 

[russ_watters]

It is true for any vehicle design.
The equation is not dependent on vehicle design.

Imagine a simple sail vehicle (maybe just a cube on wheels).
The equation will perfectly describe what will happen to that vehicle.

Um...yes, the equation applies to that design. But not to DWFTW designs.

That's the point. It's up to you where this goes from here - we can end the thread or you can try learning how the DWFTW vehicles work, but continuing to make the false claim is not one of your options.

You're trying to prove that they can't work based on an inaccurate understanding of how they work instead of learning how they actually work.

That is exactly how blackbird vehicle works is just that instead of an electrochemical battery it uses pressure differential for energy storage.

That is nonsense. "uses pressure differential for energy storage" isn't a thing.

 

[electrodacus]

It just takes correcting your equation: 0.5 * air density * area * (wind speed)3

Since the wheels are coupled to the propeller/turbine the vehicle is harnessing the differential between ground speed and wind speed. That differential never changes regardless of cart speed.

That's a run-on sentence that makes no sense. Obviously if you couple the turbine/propeller to the wheels, then one is propelling the cart and the other is powering it.

That equation will be true for a stationary vehicle or for a vehicle traveling perpendicular to wind direction.
The discussion is about a vehicle traveling direct downwind.

What you describe is an overunity device like those electric generators powered by an electric motor and electric motor is supplied by the electric generator and on top of that you can also power a light bulb.
As I already mentioned not understanding energy conservation.

 

[erobz]

So you say (sorry I can still not see your equations maybe a problem with my browser).
P = 0.5 * air density * Area * coefficient of drag * (w-v)² * v
Where I say
P = 0.5 * air density * Area * coefficient of drag * (w-v)² * (w-v)

Seems we are super close we just need a few examples to see which one matches reality.

Mine follows logically from fundamental physics, yours does not. You shouldn't need any examples to understand that.

There is a force $F_D = \propto ( w-v)^2$ ( from drag ) on the vehicle that is traveling along with the vehicle at velocity $v$. $P = F_D \, v$ is the power of that force. This is a basic application of Newtons Laws. The vehicle (which the force of drag is doing work on) is NOT traveling at speed $( w- v)$ w.r.t. a stationary frame (ground).

 

[russ_watters]

What you describe is an overunity device like those electric generators powered by an electric motor and electric motor is supplied by the electric generator and on top of that you can also power a light bulb.
As I already mentioned not understanding energy conservation.

Incorrect. The power extracted never exceeds the power available per the equation. At this point I'm going to lock the thread since you seem to be uninterested in learning how these devices actually work and we're stuck in a loop where you just keep referring back to the wrong equation.