Ubergeekian
Well-Known Member
It's not. There are significant disturbances to both air and water, so energy transfer is possible.
Sailing downwind - faster than the wind?
- Thread starter Pierrome
- Start date
It's not. There are significant disturbances to both air and water, so energy transfer is possible.
Ubergeekian
Well-Known Member
Although the people who build these things will tell you that there is no attempt to collect energy from the wind. Propellors work quite happily in still air ...
Malo37
Well-Known Member
I wonder if we should be doing something useful ??
bbg
Well-Known Member
Good idea. I'm going to undo my shoelaces and see if I can, by pulling hard enough, lift myself off the ground.
DJE
Well-Known Member
Just a minute. From earlier comments, and as recently demonstrated in the Americas Cup, I assume that we are all happy that there is no problem going a lot faster than the wind on a broad reach. It's the dead downwind bit that seems to be causing all the fuss. OK so far?
Well I respectfully suggest that the tips of the propellor blades are not travelling dead downwind; they are describing a helical path at an angle to the wind direction. They are generating a lot of "apparent wind" due to their rotation. This needs more careful consideration than it's getting here.
Well I respectfully suggest that the tips of the propellor blades are not travelling dead downwind; they are describing a helical path at an angle to the wind direction. They are generating a lot of "apparent wind" due to their rotation. This needs more careful consideration than it's getting here.
Malo37
Well-Known Member
Well, according to the new laws of physics as proposed in this conversation not only should you lift off the ground but if you keep pulling hard enough you should accelerate to an infininte speed and eventually become a spec of pure energy. Safer to stick to slip-ons.
pmagowan
Well-Known Member
Inventing a perpetual motion machine (which this is) is almost as impossible as explaining why it can't be done to someone who believes in it.
There is only one energy source in this system and you can't create more energy. It is impossible and has no relationship between the curvature, or not, of the earth.
And the reason why I said 'relative' is not the issue is because the relative movement of anything in this system is unimportant and not related to the fundamental question. The balloon analogy has already been debunked above and far from revealing a point just reveals a lack of understanding of basic physics.
I am sorry but this doesn't and never will work. You would have a lot better luck blowing at your own sails.
There is only one energy source in this system and you can't create more energy. It is impossible and has no relationship between the curvature, or not, of the earth.
And the reason why I said 'relative' is not the issue is because the relative movement of anything in this system is unimportant and not related to the fundamental question. The balloon analogy has already been debunked above and far from revealing a point just reveals a lack of understanding of basic physics.
I am sorry but this doesn't and never will work. You would have a lot better luck blowing at your own sails.
xxyyzz
Well-Known Member
It's syntactically impossible, once you exceed the windspeed downwind you start sailing upwind and downwind is then the opposite direction.
Pierrome
Well-Known Member
Do you think that if this was "perpetual motion" there would be different people demonstrating it on youtube? - and so many different videos, why would they bother. Some sort of conspiracy?
If it's not possible, why are this American Team spending all their time building a man-carrying version to demonstrate at a land-sailing event?
It's hard to think how it can be proved to you when you won't believe the body of evidence.
flaming
Well-Known Member
Come on guys, we've got a massive amount of catching up to do!
the thread on anarchy with this title currently stands at more than 3600 posts.
All of them riveting....
the thread on anarchy with this title currently stands at more than 3600 posts.
All of them riveting....
Ubergeekian
Well-Known Member
Here's a little thought experiment for you. You accept, I presume, that BMW Oracle can sail downwind - in the sense of have a VMG - higher than the windspeed? OK, now get two of them and join them together with a light beam, exactly perpendicular to the wind direction, along which they can both slide. Now have them tack downwind on exactly mirror image courses, pushing the beam directly downwind, faster than the windspeed, between them.
Voila. You've created a sailing vessel, albeit a rather complicated one, which can sail directly downwind faster than the wind. The principle has been demonstrated - now all you need is a neater implementation.
RichV
Member
The idea that the treadmill is the same as outdoors in the wind is not correct. Whilst it's true that an aircraft can be modelled in a wind tunnel, you would still need the engine in the aircraft (or a stick that holds the model in place) to provide the forwards thrust. What the treadmill people are trying to do is say that a multi-engine propeller aircraft is the same as a windfarm if you make the ground move rather than the plane. The flow of energy is completely reversed and therefore the systems are not comparable.
The craft on the treadmill is a treadmill-powered propeller-driven craft. The treadmill drives the wheels on the craft which have a direct connection to the propeller. The turning propeller provides thrust to keep the craft in place on the treadmill, or advance along it. It all depends on the efficiency of the craft, and it works a treat.
What you can't do is state that this is the same as being outdoors. You cannot take any energy from the road and use that to power the craft through a relative headwind. The road provides as much energy as if I put a piece of asphalt in my fuel tank.
Suppose that the craft outdoors has been towed along to go faster than the wind downwind. What the supporters are saying is that if we remove the tow, then the craft will continue. However, if the true wind were to speed up then there would be a lower apparent headwind on the craft. There would be no source of energy to make the thing go faster, so it would slow down. If the true wind were to slow down, then there would be a stronger apparent headwind, the propeller will be turning at the same speed as the instant before the wind dropped and therefore will produce less thrust, and so the craft slows down. So whatever the true wind does, the craft has to slow down.
The craft on the treadmill is a treadmill-powered propeller-driven craft. The treadmill drives the wheels on the craft which have a direct connection to the propeller. The turning propeller provides thrust to keep the craft in place on the treadmill, or advance along it. It all depends on the efficiency of the craft, and it works a treat.
What you can't do is state that this is the same as being outdoors. You cannot take any energy from the road and use that to power the craft through a relative headwind. The road provides as much energy as if I put a piece of asphalt in my fuel tank.
Suppose that the craft outdoors has been towed along to go faster than the wind downwind. What the supporters are saying is that if we remove the tow, then the craft will continue. However, if the true wind were to speed up then there would be a lower apparent headwind on the craft. There would be no source of energy to make the thing go faster, so it would slow down. If the true wind were to slow down, then there would be a stronger apparent headwind, the propeller will be turning at the same speed as the instant before the wind dropped and therefore will produce less thrust, and so the craft slows down. So whatever the true wind does, the craft has to slow down.
bbg
Well-Known Member
At a guess, because they didn't pass high-school physics?
DJE
Well-Known Member
Brilliant! The team includes a professor of Aeronautical Engineering and several graduate students but as usual the forum knows best. Priceless!
bbg
Well-Known Member
If the explanation were along those lines, it would merit further thought. But it isn't. The explanation is that the moving vehicle extracts some energy from its own motion, and converts that energy into thrust (via a propellor). Straight line motion energy in one direction is extracted and converted - wait for it - back into straight line motion energy in the same direction. It is impossible for the energy to have increased. On the contrary, due to losses in the system it will have decreased.
Smoke. Mirrors. Snake oil.
bbg
Well-Known Member
Edit - At a guess, because they don't understand high school physics?
pmagowan
Well-Known Member
Type in perpetual motion into youtube, or try zero point energy etc etc. You will find a lot of Americans spending a lot of time with magnets and other 'magic' stuff making 'magic' machines that can go on for ever. The body of evidence is not being refuted. The evidence for the laws of thermodynamics is so strong they called it a law.
Also someone talked about the windmills blades moving on a broad reach. This is fine and a windmill attached to the ground could spin faster then the wind speed, the problem is on a vehicle the relative windspeed would approach zero and then the blades would stop turning. There are many other very complicated ways of trying to get round it, with cogs, magnets, lasers etc but it is all smoke and mirrors.
What we are talking about here is the same as an electric car being powered by an electric dynamo on its own wheels. It doesn't work, if you cant understand it then I'm afraid you need to rerad a few more physics books
xxyyzz
Well-Known Member
Ok, another take on it, although I still insist that once it's moving faster than the wind it is travelling upwind.
Couldn't it simply be remaining inertia in the rotors, like a big flywheel?
It'd get you a sprint past wind speed and is entirely powered by the wind.
Or is that cheating?
Couldn't it simply be remaining inertia in the rotors, like a big flywheel?
It'd get you a sprint past wind speed and is entirely powered by the wind.
Or is that cheating?
bbg
Well-Known Member
The more I read about this, the more convinced I am that this is an April Fool's windup, and all will be revealed in just over two weeks. That's my last post on this subject. I'm outta here.
HoratioHB
Well-Known Member
Er well I have a degree in aircraft engineering and aeronautics, I used to be a member of the Royal Aeronautical Society and the AYRS. And I still say that if the wind from behind rotates the propellor to start the vehicle moving it must turn in one direction and if it then extracts energy from the air with the wind coming from the opposite direction then it has to reverse its rotation and as the propellor is geared to the wheels that would mean the vehilce would reverse direction!!!