"One Man’s Quest to Outrace Wind"

Sailing directly downwind faster than the wind

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Re: "One Man’s Quest to Outrace Wind"

#21  Postby reksio » Mar 05, 2011 2:52 pm

Xaihe wrote:This whole technology is easier to understand when you understand that a cart with a propellor (connected to the wheels) can start moving directly upwind.

For moving directly upwind, the rotor acts as a turbine, that turns the wheels.
For moving directly downwind faster than wind, the rotor acts as a propeller, that is turned by the wheels.

So it is not exactly the same, but a similar, symmetrically opposite situation. Both cases are shown here:

[youtube]http://www.youtube.com/watch?v=FqJOVHHf6mQ[/youtube]
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Re: "One Man’s Quest to Outrace Wind"

#22  Postby The_Metatron » Mar 05, 2011 3:46 pm

reksio wrote:
The_Metatron wrote:Maybe you can explain to us how to extract kinetic energy from moving air molecules that haven't yet reached your craft, then.

You don't. You extract kinetic energy (in the ground frame) from molecules currently passing at the airfoil.

And, what makes them go past the airfoil?
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Re: "One Man’s Quest to Outrace Wind"

#23  Postby reksio » Mar 05, 2011 3:58 pm

The_Metatron wrote:
reksio wrote:
The_Metatron wrote:Maybe you can explain to us how to extract kinetic energy from moving air molecules that haven't yet reached your craft, then.

You don't. You extract kinetic energy (in the ground frame) from molecules currently passing at the airfoil.

And, what makes them go past the airfoil?

The velocity difference between them and the airfoil.
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Re: "One Man’s Quest to Outrace Wind"

#24  Postby Macdoc » Mar 05, 2011 4:52 pm

Meta - it's constant tacking by the airfoil and the drive wheels sum the vectors - it is nothing particularly new.
New materials can make for an efficient mechanism.
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Re: "One Man’s Quest to Outrace Wind"

#25  Postby recursive prophet » Mar 05, 2011 8:08 pm

Made of Stars wrote:Cue post from Recursive Prophet in 3... 2...

Sorry I'm late MOS. :mrgreen: And yes, I brought this circus to RDF 2 years ago after the thread was put on moderated status at Randi.net. It broke all records for daily traffic at both sites, and is now on part 23 at TalkRational. (And they don't close threads until after roughly 2500 replies, usually over 100 pages.) A prolific poster there-humber-is still contesting the NALSA results, using their own data to show that the many shifts in wind direction during the record run indicate the Blackbird was simply tacking.

It is interesting to note that as natural wind never moves in one direction or velocity steady state, this brain teaser may be similar to one of Gödel’s undecidables in that even if true it can never be proven. Unless, of course, you accept that the 16g model cart they built that goes up a treadmill is an instance of DDWFTTW. I suspect macdoc's perspective is pretty accurate, and have seen a prop vector analysis that shows the effect of tacking will be achieved even when the cart is moving in the exact same direction as the wind.

@The Metatron: You should click on the TR link above and join the discussion. You can converse directly with the designer of BB, Rick Cavallaro (spork) and the guy who built it, John Borton. (ThinAirDesigns) I'm still a bit skeptical, largely owing to the way all this was presented-smacks of net-woo-and the fact that Rick is George P. Burdell on Skype and a Georgia Tech alum. If you Google/Wiki that name you will understand why.

For those interested in this epic cyber-strand, below is an index I prepared for TR. There are many threads out there on this worldwide-I post on one in Russia-debate-but the 3 from the Randi, Dawkins, and TR strand were by far the most extensive. Look for the rabbit with an anemometer in his vest pocket. Image Solid physics, or a Harrypothesis based on 3 reference frame Monte??

BTW-I would really appreciate some opinions on the Solaculture thread I started here. I have some responses by the designer on critiques posted at Randi.net.


Welcome to thread 23. The previous talkrational.org threads can be found at:

Wind powered vehicle that goes downwind faster than the wind Part 1
Wind powered vehicle that goes downwind faster than the wind Part 2
Wind powered vehicle that goes downwind faster than the wind Part 3
Wind powered vehicle that goes downwind faster than the wind Part 4
Wind powered vehicle that goes downwind faster than the wind Part 5
Wind powered vehicle that goes downwind faster than the wind Part 6.
Wind powered vehicle that goes downwind faster than the wind Part 7
Wind powered vehicle that goes downwind faster than the wind Part 8
Wind powered vehicle that goes downwind faster than the wind Part 9
Wind powered vehicle that goes downwind faster than the wind Part 10
Wind powered vehicle that goes downwind faster than the wind Part 11
Wind powered vehicle that goes downwind faster than the wind Part 12
Wind powered vehicle that goes downwind faster than the wind Part 13
Wind powered vehicle that goes downwind faster than the wind Part 14
Wind Powered Vehicle that goes downwind faster than the wind Part 15
Wind Powered Vehicle that goes downwind faster than the wind Part 16
Wind Powered Vehicle that goes downwind faster than the wind Part 17
Wind Powered Vehicle that goes downwind faster than the wind Part 18
Wind Powered Vehicle that goes downwind faster than the wind Part 19
Wind Powered Vehicle that goes downwind faster than the wind Part 20
Wind powered vehicle that goes downwind faster than the wind Part 21
Wind powered vehicle that goes downwind faster than the wind Part 22

Prior to its arrival at TR, this discussion took place at JREF and RDnet. Some related threads at JREF include:

http://forums.randi.org/showthread.php?t=128483
http://forums.randi.org/showthread.php?t=131646
http://forums.randi.org/showthread.php?t=130705

Related threads at RDnet include:

http://forum.richarddawkins.net/view...=73123&start=0
http://forum.richarddawkins.net/viewtopic.php?t=74154
http://forum.richarddawkins.net/viewtopic.php?t=74988
http://forum.richarddawkins.net/viewtopic.php?t=75643
http://forum.richarddawkins.net/viewtopic.php?t=76400
http://forum.richarddawkins.net/viewtopic.php?t=77451
http://forum.richarddawkins.net/viewtopic.php?t=80402
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Re: "One Man’s Quest to Outrace Wind"

#26  Postby The_Metatron » Mar 05, 2011 8:21 pm

reksio wrote:
The_Metatron wrote:
reksio wrote:
You don't. You extract kinetic energy (in the ground frame) from molecules currently passing at the airfoil.

And, what makes them go past the airfoil?

The velocity difference between them and the airfoil.

And, what causes that relative motion?
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Re: "One Man’s Quest to Outrace Wind"

#27  Postby spork » Mar 06, 2011 3:01 am

The_Metatron wrote:Bullshit.


A compelling argument indeed - but you're wrong.
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Re: "One Man’s Quest to Outrace Wind"

#28  Postby spork » Mar 06, 2011 3:56 am

The_Metatron wrote:It peeves me to no end to be told what I have or haven't read.


Perhaps they should have said that you failed to understand it, rather than saying you failed to read it. Frankly, it peeves me to no end when someone claims I'm pulling a hoax because they simply don't understand how it works.

While sailing at an angle to the wind direction can, and does, achieve vehicle speeds in its direction of travel that are greater than the wind speed in its direction, in no case does the vector component of the vehicle's velocity in the same direction as the wind equal the wind velocity, let alone exceed it.


That is just entirely wrong. I can only assume you reached that conclusion by digging deep into your powers of intuition. A quick vector analysis or about 30 seconds on Google would tell you differently.

There's no such thing as a free lunch.


But you seem to be the only one claiming that a wind powered vehicle is tantamount to a free lunch.
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Re: "One Man’s Quest to Outrace Wind"

#29  Postby spork » Mar 06, 2011 4:01 am

The_Metatron wrote: True wind is a force...


No - wind is moving air particles. You're not even trying - are you?

Wind is a force, just like gravity is a force.


That's kind of true in a bizarre sense. Yes, wind is a force in the same sense that gravity is a force (in that neither one is a force).

I bring this up as an example to illustrate that you cannot break up vector components of a force in such a way that their vector totals exceed the original force. Ever.


Of course you can - it's just rarely a useful thing to do. There's no law that says the components of a vector have to be orthogonal. In any event, that's not relevant to the question at hand. If you want to understand how the cart works - just say the word. Otherwise, just keep yelling "bullshit".
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Re: "One Man’s Quest to Outrace Wind"

#30  Postby Onyx8 » Mar 06, 2011 6:46 am

reksio wrote:
Onyx8 wrote:
In the video quite a deal is made when the ribbons fluttering from the mast start being blown to the rear of the craft,

You mean this at about 3:00 ?
[youtube]http://www.youtube.com/watch?v=EEuAqq8FINw[/youtube]

Onyx8 wrote:it also would seem that it would mean that the wind is now acting to slow the craft down.

The apparent wind at the chassis is creating drag that acts to slow the craft. The apparent wind at the rotating airfoils is creating lift that acts to accelerate the craft.

Onyx8 wrote:
Or has the pitch on the propellor changed to now provide forward force to the cart even though the wind is now from the front?

No, on this early prototype the blade pitch was fixed. You don't need to change the pitch, to accelerate past windspeed. Just like you don't need to change the sail setting on an ice boat, to accelerate past downwind VMG = windspeed on a downwind tack.

Onyx8 wrote:
Variable pitch propellors are non-trivial things, you notice if you happen to build one.

They later implemented variable pitch to optimize acceleration. But it works without it, just very slowly at the start as you see in the video.



Well, I am still struggling. When the ribbons are hanging straight down, the craft is traveling at the same speed as the air at the propellor. That means that there is no air moving past the propellor, ergo no force on the propellor. How then with no force being applied to the propellor by the wind can the propellor provide force to the wheels to drive the craft faster? The only thing keeping the propellor turning at that point is inertia. :scratch:
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Re: "One Man’s Quest to Outrace Wind"

#31  Postby Macdoc » Mar 06, 2011 6:55 am

Recursive ....I STILL want to know what happens with say the Blackbird when it is on very low friction ice.

That would separate the airfoil influence from the vector summing at the drive wheels.

I suspect in a theoretical zero friction situation the machine would simply wag around it's vertical axis.

Meta I had a minor battle over at JREF as I agree with TANSTAAFL - and I have issues with using a turntable as a test bed of any sort.

But if you narrow it down to a simple concept of a rapidly tacking ice boat (using an ice boat due it's efficient conversion of vectors into forward motion ) then it should make sense for you.

Trouble is there is a lot of woo surrounding it.
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Re: "One Man’s Quest to Outrace Wind"

#32  Postby Macdoc » Mar 06, 2011 7:10 am

The only thing keeping the propellor turning at that point is inertia.


Freeze the prop in angle to the wind as an ice boat or sail boat does when tacking into the wind - there is still relative wind.

http://www.aip.org/dbis/stories/2007/17133.html

The prop just acts as a constant set of tacking angles and the summed vectors are transmitted to the wheels which drives the vehicle forward.

Adjusting the airfoils of the prop for optimum is just like a sailor adjusting the sails for optimum performance sailing into the wind.

A boat or even an ice boat cannot tack continually as there is a lot of loss against an ideal sail shape and angle on a continous tacking angle.

This is just a different set of trade offs as the prop describing a circle passes through the optimum points of tacking angle frequently so you have this sine curve of vector summing being transmitted by the chain to the drive wheels.

The sailor makes the decision how often to tack to get to a goal fastest in a given wind.
The prop designer does that here.

I'm quite certain a well handled ice boat would get to an upwind goal far faster than one of these - and faster than the wind speed as the ice boat stays at a high gain tack longer while the prop rise and falls in performance.
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Re: "One Man’s Quest to Outrace Wind"

#33  Postby Macdoc » Mar 06, 2011 7:37 am

OUTRACING THE WIND: Lots of boats can sail faster than the wind ---especially 18-foot skiffs. Ask a sailor how, and he'll say that these boats are so fast that they make their own wind. This is true. But ask a physicist, and she'll say that it's just a question of vectors and relative velocities. Downwind is easy. If the wind is 10 knots, and the boat makes 6 knots in the same direction, then the crew feels a wind of 4 knots coming over the stern of the boat. The true wind equals the speed of the boat plus the relative wind. As the boat speed approaches the wind speed, the relative wind drops towards zero and so there is no force on the sail. So you can't go faster than the wind. When the wind is at an angle, we have to add vectors representing these velocities. The faster that the boat goes, the greater the relative wind, the more force there is on the sails, so the greater the force dragging the boat forwards. So the boat accelerates until the drag from the water balances the forward component of the force from the sails. In a fast boat, there's no point going straight downwind: y



When the wind is at an angle, we have to add vectors representing these velocities.

there is the key

from the above link - the prop allows continous angles to the wind despite the travelling body being aligned directly down wind.
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Re: "One Man’s Quest to Outrace Wind"

#34  Postby Onyx8 » Mar 06, 2011 7:51 am

Macdoc wrote:
OUTRACING THE WIND: Lots of boats can sail faster than the wind ---especially 18-foot skiffs. Ask a sailor how, and he'll say that these boats are so fast that they make their own wind. This is true. But ask a physicist, and she'll say that it's just a question of vectors and relative velocities. Downwind is easy. If the wind is 10 knots, and the boat makes 6 knots in the same direction, then the crew feels a wind of 4 knots coming over the stern of the boat. The true wind equals the speed of the boat plus the relative wind. As the boat speed approaches the wind speed, the relative wind drops towards zero and so there is no force on the sail. So you can't go faster than the wind. When the wind is at an angle, we have to add vectors representing these velocities. The faster that the boat goes, the greater the relative wind, the more force there is on the sails, so the greater the force dragging the boat forwards. So the boat accelerates until the drag from the water balances the forward component of the force from the sails. In a fast boat, there's no point going straight downwind: y



When the wind is at an angle, we have to add vectors representing these velocities.

there is the key

from the above link - the prop allows continous angles to the wind despite the travelling body being aligned directly down wind.



But there is no wind at the propellor, if there were then the ribbons would not be hanging down. It seems to me that it is advisable to keep the problem simple at first, so lets leave tacking out of the issue for now. If there is no air movement at the propellor, from where does it find the energy to drive the wheels? You can't tack if there is no wind.
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Re: "One Man’s Quest to Outrace Wind"

#35  Postby reksio » Mar 06, 2011 8:11 am

The_Metatron wrote:
reksio wrote:
The_Metatron wrote:
And, what makes them go past the airfoil?

The velocity difference between them and the airfoil.

And, what causes that relative motion?

It's implied by the scenario. With true wind and coupling between wheels and rotor, it is kinematically impossible to have zero relative airflow at the rotor blades.
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Re: "One Man’s Quest to Outrace Wind"

#36  Postby reksio » Mar 06, 2011 8:25 am

Onyx8 wrote:
That means that there is no air moving past the propellor, ergo no force on the propellor.

There is always air flow relative to the blade (see previous post), ergo there is always a force on the propeller.
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Re: "One Man’s Quest to Outrace Wind"

#37  Postby Onyx8 » Mar 06, 2011 8:37 am

But only because the blade is turning due to inertia. If there is no net airflow across the blade, where does the energy come from to power the wheels? Remember, the ribbons are hanging down, there is no air movement other than that generated by the spinning of the blades.

Are you saying that if I give a propellor a push with my hands, then that will create airflow relative to the blade which will provide a force to spin the propellor? Where does the energy come from once I stop pushing? Why doesn't it work if I whack the blades of a fan?
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Re: "One Man’s Quest to Outrace Wind"

#38  Postby reksio » Mar 06, 2011 8:46 am

Macdoc wrote:I STILL want to know what happens with say the Blackbird when it is on very low friction ice.

With spikes it might work just as well as on sand. But I guess you mean no wheel traction?

How would a sail boat behave without a keel (a raft with sail)? It would drift downwind, slower than wind. The same applies to the sliding Blackbird.
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Re: "One Man’s Quest to Outrace Wind"

#39  Postby spork » Mar 06, 2011 8:52 am

Four things to keep in mind:
1) The prop never turns the wheels. The wheels turn the prop
2) Inertia doesn't factor into it. Even exactly at wind speed we can tow a trailer all day long.
3) When the vehicle is going directly downwind at wind speed, it feels no wind over it. The "prop" is also going downwind at wind speed. The blades of the prop however are not going directly downwind. The blades are following a spiraling path so they will always feel relative wind even when the cart is going downwind at wind speed - remember their tangential velocity.
4) When the cart is going the speed of the wind - it feels no wind. But that doesn't mean there is no wind. It simply means there is no relative wind. There's still wind moving over the ground, and that's precisely the energy this vehicle exploits. It leaves a path of slower moving air in its wake - having taken some of its energy.
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Re: "One Man’s Quest to Outrace Wind"

#40  Postby reksio » Mar 06, 2011 9:02 am

Onyx8 wrote:If there is no net airflow across the blade

But there is always a relative airflow at the blade in this scenario.

Onyx8 wrote:where does the energy come from to power the wheels

Kinetic energy is frame dependent, so it depends which frame of reference you look at.

Onyx8 wrote:there is no air movement other than that generated by the spinning of the blades.

For the force generated by the blade it is irrelevant why there is a relative airflow at the blade. The force depends only on the relative air velocity and blade orientation.

Onyx8 wrote:Are you saying that if I give a propellor a push with my hands, then that will create airflow relative to the blade which will provide a force to spin the propellor?

No, propellers need a torque applied at the shaft to turn against the torque generated by the air. Here this torque is transmitted from the wheels.
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