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Own the Controversy! Blackbird DDWFTTW Up For Auction!
Alsee writes "Center of flaming controversy across the Internet and here on Slashdot for claiming to travel 'Directly Downwind Faster Than The Wind, Powered Only By The Wind, Steady State' (DDWFTTW), the Blackbird is now up for auction on Ebay. It has been certified by the North American Land Sailing Association and Guinness World Records to have reached 2.8 times wind speed directly downwind and was subsequently modded to also achieve more than double windspeed directly upwind. It has been the subject of an MIT physics paper and was included as a model problem in the International Physics Olympiad, yet many still argue it would violate the laws of physics. Let the bidding (and debate) commence!"
Seems like a simple conservation of energy problem to me. Why compare wind speed to a vessel's speed? Wind would be better measured in terms of flux. If it can impart enough energy on the vessel, of course the vessel could go faster than the wind.
DDWFTTW? WTF? UUDDLRLRBA?
A squid eating dough in a polyethylene bag is fast and bulbous, got me?
...please check out the jet plane on a treadmill that I'm auctioning off - free shipping if it gets airborne!
"I've got half a mind to close my eyes and let this string go..."
-- Loggins & Messina, "Sailing the Wind"
Do not mock my vision of impractical footwear
Arguing that this violates the laws of physics would be like arguing that electric cars can't move faster than an electron travelling through a wire (and don't get cute with instantaneous velocity, you know what I meant).
I want to see older news and I am asking for a login, this site is now for paid users? :(
What the hell? It was just here a second ago!
Dude! When's my car?!
So,
What would happen if you put this thing on a giant treadmill, and pointed it either upwind or downwind?
enefesdi bhootparamdi
if a thing is worth doing at all, it's worth doing right. -- H.S. Thompson
wow I didn't know one had been built full size. I seen this concept used in RC sailboats, and they do very well upwind. http://youtu.be/OlqLHRE8ReQ
I love the DDWFTTW controversy because I initially was convinced it had to be rubbish then revised my opinion as I convinced myself it was possible. As you note from an energy conservation argument it isn't that bothersome. TO see this just imagine the following. Stop the vehicle. Let it suck up some energy. Then let it power itself downwind. It's easily possible that the net downwind speed averaged over the stops could be faster than the wind. Now you just have to extend that to the infinitesimal limit. Thus energetically no problem.
The problem is that it's mind bending to figure out the forces involved. How can wind push anything faster than the wind? Even if you rationalize that with the angle of attack on the proellor or something, you then have to ask, well then doesn't the apparent wind (the wind as seen by the moving cart) lead to a positive feedback loop (faster than the wind --> more power to go faster than the wind --> increased speed faster then wind --> .... ). Like wise how come a cart that is not moving at all, could not be pushed to create some apparent wind, then propel itself using that? Clearly, the gain on that feedback loop has not only to be less than unity, but it has to have a very special curve that leads to net integral such that a cart that is shoved on a windless day cannot go faster (on average) than the shove would provide. Otherwise I think you have a paradox.
It's this latter subtely that I can't connect all thr way through all the complicated force arguments.
Now when the wind is blowing, we know the force arguments have to be valid for a very simple reason. We already know that sailboats not heading directly downwind can go faster than the wind in the net downwind direction. They do this by jibing (i.e tacking down wind) in a zig zag path. If you were to drop a large black box over such a sailboat then you would not be able to see the actual motion of the boat, but you would see a black box going directly downwind faster than the wind. thus we know this happens empirically. It's not some werid stored energy issue. the forces directly allow this. but it's hard to figure. Even the apparent wind effect of increasing the effective windspeed on a sailboat is real.
So it's only truly mindbending at the second order level of how somehow the force argument still has to conserve energy.
Some drink at the fountain of knowledge. Others just gargle.
Anybody that claims this violates the laws of physics is a sufferer from the Dunning-Kruger effect, i.e. they are stupid but do not realize it. This is not even high-school physics.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
Finally, a "slashvertiement" that doesn't reek of spam!
Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
A treadmill is motion is no different to a still surface being affected by a wind. The ground is moving relative to the air, and vice versa. The movement of the treadmill would drive the wheels, the wheels would drive the propeller, and it would move forward relative to the air.
Prediction for end of Universe #42: Fencepost error in Quantum_bogosort.cpp
All the best acronyms which are way too long have BBQ at the end.
Is it just my observation, or are there way too many stupid people in the world?
So let me throw out the question I just posed in a simple case.
when the vehicle is going downwind faster than the wind, the apparent wind is actually in the reverse direction. to apparently you can extract power from a headwind that will push you into a head wind, and you can do this in a continuous way and maintain a constant speed.
1) how is that possible as a force argument not an energy one?
but the more important question is this:
2) if there is no wind at all, and I give the cart a shove, there is now a headwind. If I can extract power from the head wind, I can increase the total impetus to the cart. Why doesn't more impetus lead to faster speed? It can't lead to faster speed, otherwise we'd have a positive feedback loop. thus it must somehow always be less than the net drag that is slowing it down. thus the cart must slow down due to drag, and the effect of the device is to make it slow down less rapidly than when the propeller is not hooked to the wheels.
So the real question is this:
given your answer to question 1, what attribute of your answer bounds the headwind derived impetus on a windless day to be less than the drag at any vehicle speed?
I'm baffled.
Some drink at the fountain of knowledge. Others just gargle.
Back in November, 2007, I wrote a fantasy novel (unpublished) for NaNoWriMo that contained a fair sized boat that was powered this way. And, at the time, I had a few links that showed the idea in action, but not only have I lost them, I'd bet that they'd be 404 compliant anyway.
Good, inexpensive web hosting
Sails work like airplane wings. There's no magic there. Tacking and getting a net speed greater than the wind takes skills; but it doesn't violate any physical laws.
...violate the laws of physics, too. Because that's really all that this is: a form of leverage that multiplies speed while decreasing force.
"How to Do Nothing," kids activities, back in print!
Arggghhh. the slashdot formatter ate my less than sigh. I meant to write "consider the case V_land LESSTHAN V_wind.
Some drink at the fountain of knowledge. Others just gargle.
Stick it in my front yard. Besides the HOA disapproved my architectural modification to put a WWII howitzer with flag pole in the front yard, so this may be approvable.
Harrison's Postulate - "For every action there is an equal and opposite criticism"
Anybody else notice that Hitler is in the photo posted to ebay?
At risk of great embarrassment, I can see that this is possible. I can't fully explain this particular device, but my windsurfing experience tells me that if my drag didn't increase so massively with speed, and my sail didn't stall as the apparent wind closed in, I could keep accelerating off the wind. Faster than wind sailing is well understood (balance of lift and drag at a particular velocity, that is greater than windspeed) I suspect there's some sort of polar function of wind speed and boat speed that obeys the conservation of energy stuff, that can't be achieved with a fixed wing.
It's been shown that ice-boats can travel at more than 5x wind speed, and be heading within 20deg of downwind at this time. The VMG (average velocity), accounting for tacking, can be directly downwind, and way in excess of wind speed (the analogy is that if you raced a balloon, you can beat it). They can't just take off in the downwind direction and achieve that, they need to reach speed first, then head downwind, and the faster they go, the further downwind they can point. By towing another vehicle that travels directly downwind, we have a wind powered vessel travelling directly downwind at more than wind speed.
Replace the sail with a pivoting turbine driving some very efficient drive mechanism, I can see how we could make a turbine powered iceboat, or land yacht. Because the turbine blade angle of attack is largely dependant on airspeed (not the direction we are travelling, but how fast the air is passing through the turbine), even when travelling downwind (at faster than airspeed), the turbine is going to be able to generate rotational force, that can drive the vehicle.
Where does the energy come from to overcome those losses? I had to think about that, and it's about where we draw the bounding box for working out if energy is conserved. The energy source is the same as ordinary sailing. The wind is travelling across the ground, so has kinetic energy when compared to the ground. Provided we are able to attach to the ground and the air, we can extract some of that difference in energy.
And that's what it boils down to: the speed of a wind powered vessel is determined by the energy available, and the energy required to travel at a particular speed. It's not about the direction you are travelling in. The direction of travel just requires diffent means to extract the energy.
Whew - Even I believe me know...
between the ground speed and the wind speed. No matter how fast you are going and no matter what direction if you stay in this shear then you can extract some energy from it. As long as that energy is sufficient to overcome the energy losses of friction and drag, you can accelerate. However in "still" (wrt the ground) air there is never shear - even if you push the vehicle so that there is "wind" (wrt the cart).
It's a simple question of weight ratios!
Sounds like something spoken by a Dallas-based DJ with a stutter.
Not only can I Travel DDWFTTW.
But I can get 2% back and have 6 months to pay with BillMeLater!
It's unbelievable the number of people posting in this article that don't realize that what makes this interesting is that, once the vehicle reaches wind speed, air movement relative to its propeller is zero, and so one would assume that there's no longer any energy there to propel the vehicle faster. Never the less, they're perfectly willing to post about how people are so stupid because they think this isn't possible when it's obviously just a matter of gearing the propeller and wheels so that the wheels spin faster than the propeller.
There's an interesting lesson here: Everyone with an IQ over 100 thinks they're smarter than everyone else.
At least dumb people know they're dumb and don't say anything. These semi-intelligent people are annoying as fuck. Any attempt at intelligent conversation is killed by their non-stop attempts to tell everyone what everyone already knows. Semi-intelligent people are by far the worst thing about the internet.
It's a thing that has to do with where the wind interacts to provide power to this particular vehicle. Although the wind is hitting the vehicle flat on (dead downwind), it's not doing that relative to the actual blades of the wind turbine powering the vehicle. When you look at where the wind is hitting the blade surface, it's still deflecting off at an angle. And considering that the blades are rotating, the effect is the same as having a regular sail which is moving at some angle to the wind. (It's all relative to how you look at it. And most people think the principles of relativity is just a nuclear physics kind of thing.)
Also the power here comes from the airspeed difference relative to the ground, and the same concept also works on water. (Because like the ground, the water isn't going to be moving at the same speed as air.) Interestingly enough, if you can exploit the airspeed difference over a wind-shear boundary the same concept may even work for aircraft. Something that may work is using tractor kite or turbine on a tether at a different altitude where winds are much higher, or perhaps flying at the very boundary of a strong wind shear and using the mechanics of that to gain momentum.
Does the propeller drive the wheels or do the wheels drive the propeller? None of the technical documentation from the team, such as it is, indicates what the mechanics actually are. (I found their writing to be exceptionally poor and that contributes a lot to the difficulty they have proving their claims.)
Most of the people trying to explain it without a working model say that the wheels drive the propeller, but never explain what keeps the wheels going. The only external energy source is the wind so their must be some way for the wind to keep the wheels moving.
If I were to try to build a theory from first principles I would have said that the propeller drives the wheels: lift of the airfoils perpendicular to the propeller shaft create a torque on the propeller that drives the linkage that turns the wheels to overcome the drag on the propeller and keep the cart in motion. However, there are so many more claims that the wheels drive the propeller that the must be some steps that seems so obvious that no one bothers to mention it.
Who cares about DDWFTTW Blackbird? :)
Call me when an SR-71 is for sale
I would like to thank the original poster, this is one of the best story I've read for weeks. I should have known this earlier but I didn't... Thanks again for pointing out this enlightening discovery.
First I really doubt it was real, then I wondered how it could be possible, now I understand how it works !
My short explaination: the propeller harvests the wind energy (relative to ground) that was in front of the vehicle. The more it moves forward, the more it stops different masses of air, accumulating wind's forward momentum.
A stream of particles traveling above a surface in uniform motion. A vehicle hovering above the surface could only be pushed as fast as the stream is moving.
A wheel on the surface moving at the same speed as the surface isn't all moving at that speed, even if it's center of mass is. The part that touches the surface is stationary w.r.t. the surface, and the top is moving faster than the center speed. If the stream of particles is directed at the center of mass, the most it could be pushed is up to the speed of the particles.
If the stream is directed more to the bottom of the wheel, the center of the wheel could be pushed faster than the stream of particles is moving.
I'm not saying that this is what is happening, just that it could be.
All ideas^H^H^H^H^Hprocesses in this post are Patent Pending. (as well as the process of patenting all postings)
Any non conservative field can have energy extracted from it, so this is clearly possible -as long as there is something-in this case the water-that is moving at a different velocity than the wind
Imagine a VERY light wind generator module in the vehicle that:
- collapses it's fan to avoid air drag
- moves all the way forward in the vehicle
- attaches itself to the ground
- unfurles it's fan
- generates power till the rear of the vehicle arrives
You have extracted energy from the wind in a downwind traveling vehicle.
It does not matter what speed the vehicle travels.
Apply the energy to motors that drive the vehicle wheels.
There are many other ways of doing this, but this one is conceptually easy to understand.
So you physicists and engineers out there.... Can you make propellers that do this very thing to assist ( regular ) cars?
Of course I understand you can't do it unpowered, but can it given you any assistance? Would seem like a good cheap way to get some increased mileage.
One of the more amusing aspects of this thread is that there are two contradictory explanations earnestly being presented. One side thinks the windmill is a turbine that drives the wheels, while the other thinks the windmill is a propeller being driven by the wheels.
For the latter group, I would like to propose a modification: replace the propeller with a generator, and use the power generated to run a linear induction motor which propels the device downwind along a track, which is level, straight and aligned with the wind. You can give the device a push to start it moving, if you like. What happens?