General > General Technical Chat
Mess with your minds: A wind powered craft going faster than a tail wind speed.
IanB:
--- Quote from: MikeP on December 30, 2021, 09:13:34 am ---Finally, regarding the background for the invention. Under certain conditions, the movement of a sailboat at an angle to the wind can have a higher speed than the wind. But not in the direction the wind is blowing!
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In fact, certain racing yachts can beat the wind: they can get from A to B faster than a balloon carried by the wind could achieve. This is done by sailing at an angle to the wind and using the action of the keel pushing against the water to make the boat move incredibly fast (for a visual analogy, consider pushing down hard on a marble on the table until it pops out sideways).
IanB:
--- Quote from: MikeP on December 30, 2021, 09:13:34 am ---Friends, I found this thread by accident. There appears to be no consensus. 54 pages is beyond my strength, but I saw the film. This is incredible! New horizons are before us!
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Certainly there is consensus. A set of equations describing how to design such a vehicle has been put together using established principles of physics, and accepted as correct by qualified professors of engineering. Both full size and scale models have been constructed and shown to work.
This was first done as long ago as 1969. Reference here: https://projects.m-qp-m.us/donkeypuss/wp-content/uploads/2009/06/Bauer-Faster-Than-The-Wind-The-Ancient-Interface.pdf
Kleinstein:
--- Quote from: electrodacus on December 30, 2021, 03:08:32 am ---
--- Quote from: thm_w on December 30, 2021, 02:13:29 am ---
It is 100% not possible on a racing bike with wind blowing in gusts.
The highest gear ratio (53/39 + 25 cassette + 60rpm) puts you at 12km/hr. Try to pedal at 6rpm (10s per rotation) with any power.
If you were crazy enough to build a high enough gear ratio, and have guides preventing the bike from falling over, it should work.
Keep in mind, as pointed out to you already, moving 0 km/h takes ZERO power. So its a matter of interpolating after that point. 0.001km/h might take 1W say. It sounds "wrong" but its not.
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Not quite sure you understand.
I provide you with a bike that has no brakes and put you in a head wind of 36km/h. If you input no power your bike will accelerate in theory up to wind speed 36km/h in practice it will be less than that due to friction.
So in order for you to keep some speed around 0km/h relative to ground (exactly 0 will not be practical same as balancing something on the edge of a knife) but some arbitrary low speed 1km/h or 2km/h against the head wind will require 300W.
In the other direction direct down wind with friction brakes enabled to maintain 1 or 2km/h the friction brakes will need to be capable to dissipate around 300W as heat.
A bike that is not moving because is anchored to the ground has nothing to do with this problem as you basically become one with the earth and so that power accelerates the earth rotation witch considering the earth mass is just ridiculously low and nobody will ever care about that and so earth is just considered stationary.
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When going at a very low speed, that is low RPM on the pedeal on will not be able to get 300 W. The driver has the same problem as the vehicle: it is hard to get the same power, as the forces have to go up.
The problem why going 1 km/h again a 40 km/h head wind with a normal bicyle is not possible is not because the 300 W are needed, but because it is hard to produce even 30 W at such a low speed, as this needs very high force.
The is just not enough force to produce 100 W at a very low speed. So if the magic (..)³ expression would be true one would never be able to start from a stand still aginst any headwind. One allways starts with infinitesimal low speed and thus infintesimal small (essentially zero) mechanical power.
There is no need to repeat the supposed formula for the maximum available wind power for the moving vehicle. Without a good source or maybe an acceptable explaination this is worthless like repeating "The earth is flat.".
The (w-v)³ type equation is not only withput a good source, but in addition also proven wrong (see above).
Domagoj T:
--- Quote from: electrodacus on December 29, 2021, 06:36:54 am ---You can be offended if you want but you do not even deserve an answer as it will be a long and involved one from me and you will have no clue of what I just said.
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Don't worry about my feelings, I'm a big boy, I can handle it. Will I'll have no clue what you would have said because you think I have reduced mental capability or because you just can't provide an argument?
You keep saying that at wind speed a sail has no power, yet when I give you an example of sail traveling below wind speed, you deflect and avoid.
--- Quote from: electrodacus on December 29, 2021, 06:36:54 am ---My answer was generic and included all possible vehicle types powered only by wind directly down wind and no vehicle can exceed wind speed unless it uses an energy storage device or an external energy source.
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So let's focus not on generic, but on this specific example.
And yes, this vehicle does have an external energy source - the wind.
Brumby:
--- Quote from: electrodacus on December 30, 2021, 09:11:21 am ---
--- Quote from: Brumby on December 30, 2021, 09:06:02 am ---You skipped over the question.
I asked about the interaction between this thrust and the surrounding air.
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There is nothing skipped.
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Yes, there was.... but let me pick up from your next statement:
--- Quote ---Propeller will create a pressure differential thus energy is being stored.
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Other people call it thrust - and you call it a pressure differential - but the question is on the energy storage.
Rather than running around with words - where we all seem to get nowhere - it would make life so much easier if you could provide the formula which tells us how much energy is stored.
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