General > General Technical Chat

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

<< < (181/285) > >>

electrodacus:

--- Quote from: Brumby on December 19, 2021, 05:27:10 am ---It's not outputting any more.  It's extracting power from a wheel system that is travelling at one speed (frame of reference is the ground) and then applying that power to a propeller system travelling at a different speed (frame of reference is the wind).

This is the concept you continually dismiss, bypass or ignore.  It is THE heart of the Blackbird doing what it can - and has - done.  By refusing to even consider this concept as a possibility you are condemned to remain ignorant.

--- End quote ---

Do you understand that power you take from the wheel will brake the vehicle ? Then putting that power even all (ideal case) in propeller will not do more than just compensate (ideal case).
That is the part that you all get wrong power is not force so you can not play in the same way.  You are talking about different speed at the wheel and at the propeller but when you use power that is already included there is nothing to talk about.



--- Quote from: Brumby on December 19, 2021, 05:27:10 am ---
--- Quote --- That university professor that lost the bet (his fault for gambling) said nothing wrong in Derek's video but since it was unable to explain how the treadmill prototype worked it was forced to pay the money not to be seen as not honoring his obligations.  He should have asked for help and try to understand why it works then make that information public.
--- End quote ---
Poor, dumb professor.

--- End quote ---

He is not dumb just did not think about the obvious energy storage and without that he will not be able to explain how this vehicle works as there is no other alternative solution.

I do suggest you spend more time thinking about this (valid for all people here).
I spent enough time trying to help and I feel I repeated my self more than I needed to so it will not be helpful for me to help if you do not want to put the brain to work.
Try to learn what power and energy is as that should help.

IanB:
You did not comment on the vector diagram of the wind and the boat, so I assume you agree that a boat can indeed sail faster than the wind in the direction of the wind?

Brumby:

--- Quote from: electrodacus on December 19, 2021, 05:45:16 am ---I do suggest you spend more time thinking about this (valid for all people here).
I spent enough time trying to help and I feel I repeated my self more than I needed to so it will not be helpful for me to help if you do not want to put the brain to work.
Try to learn what power and energy is as that should help.

--- End quote ---
"There Are None So Blind As Those Who Will Not See."

*sigh*

Let's try once more....


--- Quote ---Do you understand that power you take from the wheel will brake the vehicle ?
--- End quote ---
I certainly do - and the fact you want to make a point of this seems to be a desperate move to discredit me.

Do you realise that while that extraction of power will slow the vehicle, that the loss of velocity will result in the wind directly applying more force to the vehicle as it will be travelling below wind speed?  This results in an increase in total power applied to the vehicle.  Pull 5.5W from the wheels and, as the vehicle slows, the wind adds more power.  Even if that additional power is just 2W or 1W or even 1mW, the overall power delivered to the vehicle by the wind has increased.

You have never mentioned this increased power, which indicates your understanding is less than comprehensive and your analysis certainly incomplete.

And we haven't even looked at the harvested power component.  Apply that harvested power into driving the propeller and now the backward thrust will be trying to slow the wind, but the wind (having a practically infinite energy store) will just push against this - applying even more power into the system.

The extra power required for the Blackbird to do its thing, comes precisely from the wind as the wind pushes against those forces which come from the elements that are trying to slow the vehicle down down.

At this point, even your intuition must be curious as to where this total system will settle - and what parameters will affect that point.

I would really encourage you to do a proper job of investigating this - rather than do your typical handwaving dismissal.  The total power has increased, so you cannot just say the additional power is of no significance without providing real numbers.

Kleinstein:

--- Quote from: electrodacus on December 19, 2021, 01:02:47 am ---
Please read again my formula as you forgot a very important part and that is the area that wind pushes against.
0.5 * air density * area * windspeed3
This is the formula anyone designing a wind turbine will use except that is is ideal 100% of available wind power and to this they need to add the turbine efficiency usually around 40% and the generator efficiency that can be over 90%
For a vehicle driving directly down wind ideal case all you need is to subtract vehicle speed from wind speed since wind speed relative to vehicle is what can power the vehicle.
This formula
0.5 * air density * area * (wind speed - vehicle speed)3 is what will apply to any wind only powered vehicle driving directly downwind.
This is also the ideal case so absolutely max that is available to the vehicle meaning that if you do not add an energy storage device to this vehicle or some external energy source like gasoline and an engine then your vehicle can not exceed wind speed.
For direct downwind blackbird is clear to me that energy is stored in pressure differential generated by the propeller and that is what allows it to exceed wind speed even if it may be for just a few minutes depending on the design, how fast it will use that stored energy.

--- End quote ---

The point is not in reading the euqations, the point is understand what they are actually calculating. The first one is the power theortically available from the wind as the kinetic energy in the moving air.

The second equation is giving the energy available at the reduces wind speed, e.g. for a wind-turbine on the moving vehicle. This is not the maximum energy available to the vehicle.

The wind turbine also creates some drag force, comparable to a sail and this drag force also creates power to a moving vehicle. This power contribution is force times vehicle speed. For a sail this is the only way it creates power.

The wind turbine (=porp) on the vehicle could create some extra power directly. For the sail the drag force is proportional to (wind_speed-vehicle_speed)². For the prop the drag force (called thrust when caused by the driven prop) also depends on the speed the prop rotates.  depending on the direction and speed this can be less, but also more than just a sail.  With the driven prop there can be drag/thrust even with zero wind speed. 

electrodacus:

--- Quote from: Brumby on December 19, 2021, 08:44:42 am ---I certainly do - and the fact you want to make a point of this seems to be a desperate move to discredit me.

Do you realise that while that extraction of power will slow the vehicle, that the loss of velocity will result in the wind directly applying more force to the vehicle as it will be travelling below wind speed?  This results in an increase in total power applied to the vehicle.  Pull 5.5W from the wheels and, as the vehicle slows, the wind adds more power.  Even if that additional power is just 2W or 1W or even 1mW, the overall power delivered to the vehicle by the wind has increased.

You have never mentioned this increased power, which indicates your understanding is less than comprehensive and your analysis certainly incomplete.

And we haven't even looked at the harvested power component.  Apply that harvested power into driving the propeller and now the backward thrust will be trying to slow the wind, but the wind (having a practically infinite energy store) will just push against this - applying even more power into the system.

The extra power required for the Blackbird to do its thing, comes precisely from the wind as the wind pushes against those forces which come from the elements that are trying to slow the vehicle down down.

At this point, even your intuition must be curious as to where this total system will settle - and what parameters will affect that point.

I would really encourage you to do a proper job of investigating this - rather than do your typical handwaving dismissal.  The total power has increased, so you cannot just say the additional power is of no significance without providing real numbers.

--- End quote ---

Again do we discus about power or energy.  You seems to confuse the two way to much.
If you talk about power and taking a power from the wheel then there is no speed change as power is instantaneous contains no time dimension.
So if your conditions are vehicle exactly at same speed as wind speed and you are talking in therms of power you take 5.5W from wheel speed will be the same and then apply those 5.5W to propeller (ideal case) and since there is no imbalance of power between input and output nothing will change thus no deceleration but also no acceleration.
 

Not sure if I can help you. Try to understand the difference between power and energy then you will not even need my help in understanding this problem. 

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod