General > General Technical Chat

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

<< < (210/285) > >>

fourfathom:

--- Quote from: electrodacus on December 22, 2021, 08:30:28 pm ---And also this formula is used if you want to know how what is the minimum power your vehicle engine or motor requires in order to overcome the drag due to wind.

Most small passenger vehicles have around 2.5m^2 of frontal area and if they are aerodynamic the Coefficient of Drag may be around 0.3 thus effective frontal area 2.5m^2 * 0.3 = 0.75m^2
So say this vehicle needs to drive on highway at 120km/h about 33m/s and there is no wind.
Then vehicle will need 0.5 * 1.2 * 0.75 * (33)^3 = 16.2kW just to deal with the drag. A bit more will of course be needed to deal with other friction losses internal and rolling resistance but this air drag will be the most significant.
So no vehicle with those characteristics 0.75m^2 effective frontal area can ever claim it needs less than 16.2kW/120km/h = 135Wh/km
--- End quote ---

To be fair, while I initially was thinking "but DDW at windspeed there's no drag at all", in further reflection I read this as an interesting digression from the DDWFTTW arguments, and an illustration of how drag affects automobiles at speed.  I don't think that electrodacus is claiming that a vehicle driving 120 km/h downwind in a 120 km/h wind will see 16.2 kW of drag.

IanB:

--- Quote from: fourfathom on December 23, 2021, 12:50:07 am ---To be fair, while I initially was thinking "but DDW at windspeed there's no drag at all", in further reflection I read this as an interesting digression from the DDWFTTW arguments, and an illustration of how drag affects automobiles at speed.  I don't think that electrodacus is claiming that a vehicle driving 120 km/h downwind in a 120 km/h wind will see 16.2 kW of drag.

--- End quote ---

However, drag is a force, with SI units of Newtons. So "16.2 kW of drag" is not a statement that can be made. What you can say is that the vehicle will require 16.2 kW to overcome the drag resistance. This may seem picky, but it matters when the wind speed and the vehicle speed are different.

Power comes into the equation involving force and speed, hence:

   (power) = (force) x (velocity)

Wherein it must be understood that force is the magnitude of a vector pointing in the opposite direction of velocity.

The drag force comes from the apparent wind velocity impeding the vehicle, and the velocity itself is the velocity of the vehicle over the ground. Since these can be different, it is important to keep the separate in the equation.

Brumby:

--- Quote from: fourfathom on December 22, 2021, 02:38:02 pm ---In the electrodacus theory, this pressure differential is stored and accumulated while the vehicle is below wind speed (sort of like inflating a balloon behind the vehicle).  As the vehicle reaches wind speed, the balloon begins to deflate, blowing the vehicle above windspeed for a while.  Once the balloon is deflated the vehicle slows down until it is again under windspeed.
--- End quote ---

My apologies for being so dense as to not see this.  Such a concept is so absurd that I never pictured it this way.


--- Quote ---I don't buy it.  There is no stored pressure differential.

--- End quote ---

Absolutely.




--- Quote from: electrodacus on December 22, 2021, 06:14:14 pm ---
--- Quote from: Brumby on December 22, 2021, 08:10:01 am ---Wow.  Just, wow.  That is just so wrong.  There is no energy storage as you maintain.  There can't be.

--- End quote ---

Is air a compressible fluid ? If so using a propeller/fan will create a pressure differential.
--- End quote ---

Which causes air movement, since there is no containment.  Air will flow in any available direction, dissipating any energy contained into the surrounding environment.


--- Quote ---...
Having a pressure delta is similar to having a compressed spring so energy can be stored that way.
--- End quote ---

A compressed spring contains energy within that spring - but only while the compression is held.  That is, the energy is contained.  There is no containment in an unbounded air mass, therefore energy cannot be stored.  A balloon can store energy, as the air under compression is bounded by the balloon, but once ruptured, that energy is dissipated within milliseconds.

If you disagree, please illustrate in a diagram how energy can be stored as you claim.

IanB:

--- Quote from: Brumby on December 23, 2021, 01:25:22 am ---
--- Quote ---...
Having a pressure delta is similar to having a compressed spring so energy can be stored that way.
--- End quote ---

A compressed spring contains energy within that spring - but only while the compression is held.  That is, the energy is contained.  There is no containment in an unbounded air mass, therefore energy cannot be stored.  A balloon can store energy, as the air under compression is bounded by the balloon, but once ruptured, that energy is dissipated within milliseconds.

--- End quote ---

Well, obviously you can compress a spring by pressing on only one end of it, while leaving the other end free...  :-//

Brumby:

--- Quote from: electrodacus on December 22, 2021, 06:14:14 pm ---Not only the formula is correct it also shows that without energy storage no direct down wind vehicle can exceed wind speed.
--- End quote ---

Since this "energy storage" mechanism is so critical to your theory, I would ask that we take a moment to examine it.

You seem keen to find ways to help us understand, so I would invite you to put together a diagram (or series of diagrams) showing how this energy is captured, stored and released.  Include any necessary description and formulae that would be required for it to stand up to examination.

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