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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 26, 2021, 05:51:20 pm ---Yoyo has always access to energy trough the string as long as the string is under tension and it can only do so as long as there is enough string so it has a limited range of motion.

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The design I proposed in Reply #1102 on page 45 of this thread has string in a loop, so it has infinite range.
electrodacus:

--- Quote from: IanB on December 26, 2021, 11:34:03 am ---For my own interest, I made a geometrical model to show how a cart with appropriate gearing can travel in the opposite direction to the moving belts it is sitting on.

When the belts are moving to the right the cart moves to the left, and vice versa.

The works because one belt is moving twice as fast as the other, and the two wheels are the cart are connected by a geared pulley, so that both wheels turn together. The difference in belt speeds is used to make the wheels of the cart turn in the opposite direction of the belts.



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Your model is missing a physics engine.
Nothing has any mass so there are no forces involved at all.

Your model describes the steady state for an ideal vehicle and an ideal vehicle since there is no friction will continue to keep whatever steady state is in without requiring any energy. If in real world anyone will be able to demonstrate something like this it will be called a perpetuum mobile.
IanB:

--- Quote from: electrodacus on December 26, 2021, 06:07:09 pm ---Your model is missing a physics engine.
Nothing has any mass so there are no forces involved at all.

Your model describes the steady state for an ideal vehicle and an ideal vehicle since there is no friction will continue to keep whatever steady state is in without requiring any energy. If in real world anyone will be able to demonstrate something like this it will be called a perpetuum mobile.

--- End quote ---

Forces and mass play no part in the analysis, it is pure geometry. If you were to build this model using exactly the same geometry, it would behave in exactly the same way.

If you say the real world model needs power to work, that is true, but the power comes from the belts it sits on. You move the belts under the wheels and the cart follows as shown. It is just the same as a gear chain. If you turn one gear, all the others follow according to the gear ratios.
electrodacus:

--- Quote from: IanB on December 26, 2021, 06:43:24 pm ---
--- Quote from: electrodacus on December 26, 2021, 06:07:09 pm ---Your model is missing a physics engine.
Nothing has any mass so there are no forces involved at all.

Your model describes the steady state for an ideal vehicle and an ideal vehicle since there is no friction will continue to keep whatever steady state is in without requiring any energy. If in real world anyone will be able to demonstrate something like this it will be called a perpetuum mobile.

--- End quote ---

Forces and mass play no part in the analysis, it is pure geometry. If you were to build this model using exactly the same geometry, it would behave in exactly the same way.

If you say the real world model needs power to work, that is true, but the power comes from the belts it sits on. You move the belts under the wheels and the cart follows as shown. It is just the same as a gear chain. If you turn one gear, all the others follow according to the gear ratios.

--- End quote ---

It will behave the same way if you push the cart with your hand.  If cart needs to be powered by the two treadmill then it will not behave anywhere close to this it will just move backwards.
There is a lot of confusion as you seen those toy cars that move against the paper moving direction but that will also not work that way without energy storage and stick slip tho it has nothing to do with direct down wind and it is a good representation for direct upwind witch is a very different problem.
And while I explained the direct upwind problem and even showed real test proof it seems not be helpful.
Demonstrating direct down wind will require a propeller based model and that is more expensive for me to demonstrate but I'm afraid even demonstrating that will result in same reaction as you have about the direct upwind.
If I could not convince you that stick slip hysteresis and energy storage are true for those vehicle with wheels where everything is visible what will be my chance to convince you about the pressure differential where that is not even visible.

The advantage I have is that I understand power and energy and you always work with forces and speed only not understanding what forces and speeds need to be combined in the equation to get the correct result.
If done correctly both using force and speed and using power and energy will provide the same result but chances to make mistakes are much, much smaller when using power to make the calculation.
IanB:

--- Quote from: electrodacus on December 26, 2021, 05:51:20 pm ---Air is a fluid trough with your vehicle moves and while driving directly down wind with vehicle speed lower than fluid speed the fluid can push your vehicle but as soon as fluid speed and vehicle speed are the same the fluid can no longer provide any power to the vehicle and if by some chance your vehicle is above fluid speed the fluid will oppose your vehicle motion thus not only there is no way for your vehicle to accelerate but your vehicle will be slowed down.
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This is true for a simple sail-driven vehicle, but is not necessarily true for a vehicle with a more complex mechanism like a propeller.


--- Quote ---And mathematically tat will be seen as the direction of the fluid motion will change relative to vehicle.
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Relative to the vehicle, but not necessarily relative to the pitch angle of the propeller.


--- Quote ---All that moves is the fluid relative to ground and vehicle also relative to ground and as soon as fluid and vehicle have the same speed there is no way for the vehicle to be powered by the fluid.
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This is an assertion without proof. Nor is it something you can prove, since once you use words like "there is no way", you are required to prove that no possibility exists out of all the infinite ways it might be done. You cannot feasibly analyze an infinity of designs and eliminate all of them.
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