It has been known for a long time that sailboats can travel faster than the wind, but could never do so traveling directly downwind. This feat was achieved recently by a wind-powered land yacht, the Blackbird, which is capable of traveling directly downwind at over twice the speed of the wind. The team who built the Blackbird defined their project as follows:
What is the theoretical limit to how many times the speed of the wind such a craft could go? The Blackbird has recorded steady state speed of 2.8 times the speed of the wind.
They’re now working on a version of the Blackbird that goes upwind faster than the speed of the wind. Both are quite interesting thought problems.
I imagine the mathematics of thermodynamics would determine the maximum (but I’m not interested enough to go find out). Steadily outrunning the wind on flat ground seems kind of interesting. I have managed that in conversations, but haven’t tried it physically.
It may have to do with the properties of the fluid through which the craft is traveling; though lift would increase with drag, it’s certainly possible to go much faster through air than through water, even with an entirely propeller driven craft.
Do you think the ratio of speed to wind speed is affected by windspeed? My understanding of wind resistance is that it does not increase linearly with speed, but exponentially. That would suggest that a well built craft with low friction could get a higher ratio at low speeds, though at very low speeds friction is much higher.
I’ll be interested to see how their upwind craft works. It seems absolutely counter-intuitive that a craft could be made to move in one direction by a push in the opposite direction.
That part seems easy and obvious to me. The concept of a propeller is that of a wing spinning. The wing causes more “lift” (into a circle) than the wind pushing against it (else airplanes couldn’t fly). Then using leverage, the prop is forced even harder into that same wind. If not for that friction that you mentioned, the craft would go exponentially faster without end.
I’m more curious of the opposite, how to steadily outrun the source of your push. Once you match the wind speed, it seems that you would have no difference in pressure from which to obtain energy. How could you turn a prop?? There is probably a simple trick. I just haven’t seen it yet.
It seems that it would be identical to a craft not merely standing still on a conveyor belt, but actually traveling against the direction of the belt without any added energy with which to do so.
If you use the initial wind to drive an angled prop, giving side ways thrust, you effectively create your own wind. And then you can use that wind in the same way as you were pushing against the wind in the other craft and push harder against the side wind that you created until friction catches up with you. The vacuum energy in the air provides the energy for lift and thrust.
It would take some serious engineering to make everything as perfect as it would need to be and also keep the craft as a whole moving in a straight line even though you are using side winds.
…but now after watching the videos, I can see that they cheated a bit. They use a truck to push them faster than the backwind and then use the prop to push faster still. I was trying to figure out how they could get past the natural windspeed from a standstill without losing momentum. And still, a side wind or angled wind mechanism might allow them to forgo using the truck to get it going.
…and now after watching even more videos, it seems that merely the kinetic energy within the prop is sufficient to get it past that null zone where it is traveling exactly with the wind… as long as you can get the prop turning fast enough to begin with… kewl.
The vacuum energy (the vacuum between the molecules) within any atmosphere is what provides the energy for all flight and proper propellers. What they are displaying is a means to convert that vacuum energy into a usable mechanism. The energy goes from a gaseous storage mechanism, the atmosphere, and the wind, to a turning propeller that absorbs the gaseous form of kinetic energy and converts it into mechanical motion which in turn returns the energy back to the atmosphere through friction. The end result is that the craft is merely further down the road, which doesn’t violate any laws concerning conservation of energy.
I remember having to make that kind of argument back in the early '70s. Of course any argument against the current religion is met with harsh consequences. I had designed a microscopic device that absorbed that same vacuum energy and gave the impression of perpetual motion but converted the energy into electric power which merely transferred the energy to another location where it returned to the atmosphere. No conservation laws need be broken to merely relocate energy (or objects) from one point to another. Hell, it is hard enough to prevent energy from locating itself.
I later calculated that you could design a 400 horsepower automobile that actually used no fuel at all and never broke any laws of physics.
Politics is the energy that runs your world, not Science.
Mostly I am just fumbling around trying to express a concept.
But thinking this through a little more, the answer is waves.
If a given perturbation causes wind and wave, then the wave will travel faster than wind because waves are in a denser medium.
Perhaps you are familiar with the fact that light travels faster in a glass than in a vacuum.
It is also why waves crest, because as they travel in shallow water, a less dense medium, they slow down which in turn leaves the kinetic energy of the lighter tops to speed by their bases.
Sailing craft have moved against the wind since they were first invented. “Tacking” against the wind is the most common technique in sailing known. At it’s most simple explanation, a barrier (the sail) re-directs the direction of the on-coming wind, and the boat “slips” past the sail on a continous basis. Movement is accomplished by vector changes. Sailing down wind uses the sail as a force multiplier although a good sailor will still “cheat” and sail at a slight angle to the wind direction to maximize speed.
Without getting into this too deep, I’d guess that these people have figured out ways of maximizing vector changes to multiply boat speed compared to wind speed. Sailing downwind may involve slight changes of the sail angle to the wind while maintaining direct downwind direction of the boat itself.
I’d bet these people have sensitive sensors on both sides of the sail measuring differences in air pressure and adjusting boat course to maximize pressure differential. Even though sailors may not have understood the science, they understood the effects and used those effects to the full advantage of the equipment they had. We just have better equipment.
Yeah, I think they only use the truck in the building stage because they had less space to work with. This video shows them accelerating from stopped with only the wind at their back to move them:
[youtube]http://www.youtube.com/watch?v=5CcgmpBGSCI[/youtube]
I don’t think this relies on anything that violates the standard “religious” physics. My understanding is that each unit of wind is used to both add kinetic energy to the vehicle directly down wind, and to the propeller orthogonal to the wind. I don’t think the calculations that led to the belief that this is possible relied on anything like vacuum energy, and I don’t think this vehicle is taken to demonstrate the viability of vacuum energy.
Ed, I don’t think the rules that apply to wave motion can be applied to boat motion. A wave is compose of the medium, so it functions differently from something traveling through the medium that isn’t composed of it. In fact, I think things travel more slowly through water than through air for the same reason that waves travel more quickly through water than through air: the molecules in the water are mound more tightly to each other, meaning both that they offer more resistance to something trying to push them apart (making thing travel more slowly), and that the neighboring molecules respond more quickly to changes in pressure (making waves travel more quickly)
Tentative, that’s a great point, I don’t know why I didn’t think of boats traveling upwind when I said “It seems absolutely counter-intuitive that a craft could be made to move in one direction by a push in the opposite direction.” I don’t know why, it still seems different when we’re talking directly upwind, but I see how the principle is the same and I’m certain that my intuition is wrong.
One interesting thought I had about this, I don’t think the design employed by the Blackbird could be used to power something that floated off the ground. I get the impression that the backward force exerted by the ground is crucial, and I don’t see how the effect could be created without it. Perhaps this is a just another failure of my intuition or my imagination, but I’d be curious if I’m alone in thinking this.
I’m pretty sure they didn’t call it “vacuum energy” and that term is really just referring to the commonly understood thermal energy in any gas. I call it “vacuum energy” merely because of how a propeller or wing functions, by creating a vacuum above the wing. The pressure of the air beneath the wing then pushes the wing upward (or the vacuum pulls it upward) or the propeller around. The point is that the energy isn’t coming from merely the wind speed, but is being extracted from the air pressure. A different air pressure would produce difference results. A more dense atmosphere would allow a faster propeller speed (which is probably what Ed3 was referring to). It allows for that because there is more energy in that atmosphere. I call it the “vacuum energy”, most call it the “thermal energy”, either way.
What is sad is that they have done nothing that wasn’t proposed at least 50 years ago. They are merely still fighting the politics or religion. What I call “real Science” would never have argued against them in the first place (nor with my device from the 70’s… pretty much the same thing, just microscopic called “KD”).
Actually the water sailing is a little different. The water is used in leverage to create what I had mentioned as “side wind”, but in that case would be a side draft. Water sailing upwind requires that the boat slightly zigzag. And that was my first thought before I saw the videos.
No, I’m pretty certain that the ground doesn’t really have anything to do with it. As long as you get the prop turning (which could be merely your initial inertia, not ground resistance). Once that prop is turning, the game is over.
My KD device didn’t use a prop, but it could fly through the air with no visible means of support nor energy (somewhat like the common UFO picture), yet still broke no common laws of physics. It just wasn’t the allowed belief at the time. And I suffered big time for not being aware that it is only politics (aka “religion”) that governs your society.
But this contradicts what we see in water. Water doesn’t allow for a faster propeller speed.
In terms of craft speed, I imagine there’s an equilibrium point between a denser medium building up more pressure behind the craft and creating more lift on the propeller blades, and offering more resistance to the spinning of the propeller and to the craft once it passes the point of zero effective wind.
The prop and the wheels are part of the same system. They’re coupled by a belt. The prop only spins as it does because it is driven by the wheels as they are moved over the ground by the force of the wind. So if you agree that the prop turning is necessary for the craft to work, you must also agree that the ground is necessary; without the ground, the prop doesn’t spin.
To put it differently, a similar craft that had a propeller that wasn’t connected to the wheels would not pass the speed of the wind.
I don’t think water propellers use lift (or not intentionally). They are almost entirely just angular push. Water is not compressible in the normal sense like a gas. To turn fast enough to pull a vacuum in water and not create a hell of a friction in the process would be pretty tough, although not impossible. I haven’t really studied that. They have “supersonic” underwater missiles now, outrunning the sonar trying to track them.
But that is merely the convenience at the time. A sail or windmill would accomplish the same thing without the wheels at all. And if ratcheted or flapped, would only be affected by a back wind. The point is that the prop can be spun by the wind without any ground present.
But since a back wind on the prop itself would turn it backwards and I see no other device, I guess your right that they are using the wheels as reverse leverage to get the prop turning properly.
In fact, if they want to get serious with a low wind, they could just use a low wind generator to store energy until it had enough to use an electric starter, then let the prop take over. They could do that on skids.
