Going downwind faster than the wind

[RogueSpidor]

"I Love Me" wall? Do I detect military background?

Calling it cartoon physics isn't intended to make you look silly; it's just the only place I've seen it done.

It reminds me of a Steven Wright joke. "I like to pick up hitch-hikers and then not say anything for thirty minutes. Then I say 'So, how far did you think you were going? Buckle up... I want to try something. I saw it on a cartoon, but I'm pretty sure I can do it.'"

[ThinAirDesigns]

RogueSpidor, I'm speaking for myself here, but having been around or seen quite a number of posts from Spork and Roofingguy I think the following from me would also apply to them to a great degree:

Like you I am an automatic "skeptic" and I applaud that position.  Until there is extraordinary evidence to back up the extraordinary claims, I don't believe water is "witched", magnets don't endlessly spin "motors" without an extension cord hooked up, there is no 200mpg carb and no one has died trying to protect it.  HHO isn't real, Stan's buggie was a fraud, I don't trust a video just because it's exists and hypnosis attempts has never had a shred of effect on me.

In short, I'm with you. 

JB

[Cybermortis]

Spork; You don't have to be as aggressive in your replies here as you have been. As you noted this is a 'civil' board, while members may disagree on their views I have yet to notice any of the regulars here deliberately attempting to insult or attack each other - and if they have accidentally given offence they have always apologised quickly and/or made it clear what they were trying to say. This is exactly what RogueSpidor has done in regards to calling this 'cartoon physics'.

RogueSpidor's comments about seeing a video without your name on it was not an accusation that you (or the makers of a video) are or were 'faking' anything. Rather I understand the point that was trying to be made - that it can't strictly speaking be considered as an independent source of information, or at least that could be questioned. Again, this is not intended to accuse anyone of lying in any shape or form - it is simply the attitude that anyone seriously investigating anything has to take. (Question the evidence, and question the person/people giving such evidence)

I'll be honest, if you had replied to one of my posts in the sameway you did to RogueSpidor's I would have found it insulting.


My thoughts on the fan on a sail-boat would lead me to conclude that it would not work on a real ship/boat. My reasons for thinking this are;

The 'sail' on the model is wrapped around the fan in a way that would be next to impossible with a real sail.

I'd estimate the fan's diameter as roughly 20 inches, while the 'sail' if standard A4 paper would be 28 inches long. This means that the fans diameter is 71% of the total sail width.
The smallest type of sailing ship to use a square rig is a brig, and their mainyard/mainsail would be around 22 feet wide (Going off the Lady Washington Brig). Therefore if you scaled it up you'd need a fan of a diameter of 15.6 feet, plus motor, plus power supply.
All this weight would drastically add to the weight of the ship, pushing it deeper into the water and increasing the drag from the hull. Worse is that the fan itself would have to be located on the quarterdeck and raised several feet above the deck. This weight so high above the waterline would roll the ship over unless you added extra ballast...which in turn would make the ship even lower in the water - and this is ignoring the any effects a rotating fan might have on the ships rolling.

In all I'd consider this an unworkable system on any sailing ship - the only direction you are likely to move is straight down.

[ThinAirDesigns]

Cyber, I don't think anyone is or would argue that it's practical to use a fan to motivate a ship in *any* configuration.  The only point being made from the demonstration is that there are no laws of physics preventing such and thus it's not "cartoon physics".

JB

[JMenning]

While I do agree that it is possible for that configuration to work, it is far from practical.  If someone is willing to use up that much space, and add that much weight to the ship, you might as well put a gas engine and a propeller on, instead on a fan.  This would at least give more power and better control.

Even in a last minute survival situation, oar (or even planks of wood used as oars) would be faster and more efficient.  I just can’t seem to find a good use for this, other than to prove that it could be done.  Even then, that is a very difficult task.

OK, there is my 

[spork]

Spork; You don't have to be as aggressive in your replies here as you have been.

I give up.  There is absolutely no way I can reply to anything without being accused of being overly agressive. 

As you noted this is a 'civil' board, while members may disagree on their views I have yet to notice any of the regulars here deliberately attempting to insult or attack each other

It would be a *stretch* to say I've attacked anyone on this board in any way.  It would be *accurate* to say I've been attacked - more than once - by an administrator of this board.  I sent that administrator a PM saying that I apologize if anything I've said *appeared* to be an attack because it wasn't intended that way.  He has apologized to me for his words as well.  It seems you want to fuel this thing however.

RogueSpidor's comments about seeing a video without your name on it was not an accusation that you (or the makers of a video) are or were 'faking' anything.

I strongly recommend you re-read the post.

...it is simply the attitude that anyone seriously investigating anything has to take. (Question the evidence, and question the person/people giving such evidence)

Thanks for that advice.  I don't know how I managed to become chief scientist of a silicon valley high-tech company without knowing this.

I'll be honest, if you had replied to one of my posts in the sameway you did to RogueSpidor's I would have found it insulting.

Well, I said I could take the insults - and until now I could.  But this is over the top.  I can't imagine worse bias than you're displaying.  What do I have to do to be on the other side of your bias?  Do I need to be a long-time poster - an administrator?   Just for the sake of argument, please point out to me where I've posted anything even slightly agressive.

My thoughts on the fan on a sail-boat would lead me to conclude that it would not work on a real ship/boat.

Swell.

If you detect any sense of frustration or anger, that's because it's real.  Yes - I'm mad as hell at your response in attacking ME for .... well, who knows?

[thetroll]

Ok folks, take a deep breath.

I will be unlocking this thread tomorrow and keeping a very close eye on this thread.

There will be no more personal attacks, no more discussion of anything other then the topic.  Yes this is a hotly contested idea but we can discus it without all the "extra" stuff. 

So all the "other" stuff will be dropped and will not be discussed.  You will stay on topic and only on topic.  I think that this is a pretty good idea, mainly because it is so hotly contested. 

If someone says something you find objectionable then send me a quick PM and I will read it and deal with it if needed.  There is no topic that we shouldn't be able to discus without it getting into a war.  Yes, people might disagree but keep it civil and keep it about the subject and not about each other.  If you can't do that, then I will.

theTroll, Forum Diplomat.

[thetroll]

It seems like everyone has calmed down and things are back to the way they should be.

Have fun and treat each other right.

theTroll,  Forum Diplomat

[RoofingGuy]

Ok, back to basics, to start with.  We'll ignore the cart for the moment and just stick to principles, and I'll stick to sailboats on water.

As is overviewed here http://www.physclips.unsw.edu.au/jw/sailing.html there are some basic facts about wind power.

• Trying to sail directly downwind faster than the wind is impossible.  No matter what rig you use, you can only sail slower than the wind in a direct path, or else you do outrun your power source.
• However, contrary to that, if you tack, with a suitable rig your downwind component can exceed the wind by making use of the relative wind "created" by the boat.  With numerous tacks you can have a path that roughly approximates a direct downwind path in the long run, and your speed in the downwind direction will exceed the wind speed.
• All the sail really cares about is the relative wind it sees... it doesn't know (or care) what the air is "really" doing.  Whether it's using the relative wind created while tacking, or using the relative wind created by drifting in the current in still air, all the sail needs is a difference between the sail and the keel (drifting with the current, with the wind matching the current, the relative air is zero and the sails will hang limp).

The second and third points do kind of reek of over-unity or magic.  "You create your own wind and then use it to propel yourself?"  But sailboats do, in fact, do it all the time, no matter how "wrong" it feels.  The math says it works fine, and practice bears the math out.

Accepting that relative wind usage does not make it over-unity, nor is it impossible, is the first step in moving forward (or at least it was for me).

So I'll stop myself here, for now, and let people give those 3 points some thought, before moving on to the actual cart from the OP.

[ThinAirDesigns]

Many folks have quite a hard time imagining the relationship between the parts on Jack's cart so I will attempt to describe a simply as possible how each major part interacts.

I reference sailing terms quite a bit since the prop is being utilized in exactly that manner ... a spinning sail on one continuous angled tack. 


Following is the force path (probably not a real term, so excuse it please).

1: The relative wind powers the tacking sails (spins the prop).

2: The sails (prop) pull the cart forward. If you know the purpose of a "thrust bearing", it would be this bearing on the prop shaft transfering the load from the sails to the cart.

3: The cart's movement relative to the ground spins the wheels, axle and lower pulley.

4: The lower pulley *pulls down* on the belt. (this is key to remember, it's the side of the belt going DOWN that's under tension. If one used two spools of hi-strength line rather than a belt, the line would move from the upper to the lower spool)

5: The upper pulley rotates in response to the belt/line tension, constraining the prop to a fixed tacking angle. The gearing ratio between the wheels, these pulleys and the prop pitch determine the angle of the sail tack.

(Notice in the above, I didn't say "powering the prop", I said "constraining the prop" -- the line merely provides a 'keel constraint', and there's a BIG difference between "constrain" and "power" -- it only takes a small force (less than the thrust bearing is absorbing) to provide the constraint. If the belt/line were *powering* the prop, we'd have a perpetual motion device on our hands, and we all know how those work out)

JB

PS: I actually think that if the cart DID use spooled line rather than a belt is would eliminate much confusion and argument -- everyone always get's stuck on what is powering what.

[Killick]

Just to toss in my own 2¢, as someone woefully lacking in physics who understood almost nothing of the in-depth explainations offered by Spork and Roofingguy.....

When this first came up on Disco, I was sure it didn't work and that the video was faked somehow (or simply misleading).  As Spork said, it is entirely counterintuative, especially to anyone who has done any sailing.  After reading Roofingguys analogy of a boat in a current, however, I think it would work.  I still don't pretend to understand the physics of it, and my gut says "no!", but after thinking about a boat in a current, the apparant wind it would generate, and the ability of the boat to use that wind, I've got to say that my initial reaction is probably wrong.

And, for the record, I was one of those on Disco who responded to the "fan on a sailboat" with the standard answer (although I don't recall ever mentioning cartoons).  Until Spork brought up the idea of thrust reversers, that is.  I concede then that I was wrong, however I still maintain that the correct answer is still (usually) "no", because the question is almost always phrased such that the idea is to simply stick a big fan on a standard sailboat - no custom sails.

[ThinAirDesigns]

Roofingguy gave a good link to the traditional sailing side.  Here is a link to the ice yachting world.

http://www.nalsa.org/Articles/Cetus/Iceboat%20Sailing%20Performance-Cetus.pdf

They are talking craft performance and gps plots.  There is somewhere on that site that the actual data file from the GPS can be downloaded (I did it to confirm their numbers a long time ago).  To believe that the published data and discussion is false, one has to believe that the primary association for land sailing in the US (who incidently don't give a darn about our little debate btw) are forging gps data and publishing it on their home website.

The data is there for anyone to double check, but I don't have the time at this moment to demonstrate all the math showing that these craft are achieving (as I recall) something over 3x velocity made good as compared to the ground based wind velocity.

What this means is that if you set up a start point and then a finish one mile straight downwind and release a neutral bouyancy balloon into the wind as the yacht whizzed by on an angled tack, the yacht could reverse the tack at the half way mark, stop at the finish mark and twiddle thumbs while waiting for the balloon to show up.

I've never met anyone who continues to believe that direct DWFTTW is impossible once they accept the realities of the above.  There are of course however endless multitudes of people who will immediately call you a whacko and inform you that you are breaking every single law of physics just in even suggesting that the above is possible.

Of course all the gut instinct reactions and sure positions (on both sides) is what makes a good myth.

JB

[RoofingGuy]

I've never met anyone who continues to believe that direct DWFTTW is impossible once they accept the realities of the above.

I wouldn't quite go that far... it seems that many can accept that the wind can be beaten on an angled heading, but can't see how that would apply to the cart from the OP.

Which is why I stopped my post before getting into the subject of the cart itself.

Once you get your head around the fact that the sail is getting its energy from the relative wind that it sees, regardless of what the wind is actually doing, the leap to the cart isn't that hard, and is rather painless.  One point to keep in mind that it isn't just the sail.  The sailboat needs the keel to "push against", as it were, in order to effectively beat the wind.  (Or, the iceboats need the skates to "push against".)  There is a constraint working in tandem with the sail itself to effect the propulsion.

So... on to the mysterious cart.

Let's imagine something silly.  Let's imagine the cart is moving faster than the wind, no matter how wrong that feels instinctively.  Not the same speed, but faster.  What can we surmise about it?

Well if it were at the same speed as the wind, it would feel the air as being still, but if it is exceeding the wind speed then there will be a relative wind from the front.

If it were a boat, it could tack into this relative wind and maintain its overwind speed, but it would need to do so at an angle, and not directly downwind.

But, by using a rotary sail, propeller, doohickey, thingamabob, whatever you'd like to call it, you can have the sail continually tacking into the relative wind, without the cart itself having to follow an angled path.

As ThinAir pointed out, the relative wind spins the prop/sails and pulls the cart forward through tacking.

The gearing back to the wheels provides the constraint that the prop/sails need to "push against".

The cart "makes its own wind", just like a sailboat, and uses the available energy to maintain propulsion and keep "pulling" itself in a steady state.

The important note, again as ThinAir points out, is that the wheels aren't physically driving the prop... they are keeping the prop from being three sheets to the wind

It feels and looks utterly wrong, and yet no laws of physics are being broken, and no energy is coming out of nowhere.

Now, if the cart is placed on a treadmill in still air, then initially the wheels would drive the prop... but as soon as they begin their tack, they will pull the cart forwards and the cart will advance.  The difference between what the wheels "see" and what the sail "sees" is where the energy is being extracted from to effect the propulsion, exactly analogous to tacking into the relative wind once drifting with the current, and the intimate connection is needed between the prop and the wheels in order to make use of this difference.

[ThinAirDesigns]

I wouldn't quite go that far... it seems that many can accept that the wind can be beaten on an angled heading, but can't see how that would apply to the cart from the OP.

We may be speaking of different "Eureka" moments.   Many people can and have come to understand that sailing craft can exceed the speed of the wind on an angle.  Not many of them realize that it can be done in the "velocity made good" sense -- meaning that not only is the speed they are directly traveling exceeding the speed of the wind, but the downwind component of their angled travel is also exceeding the speed of the wind.

It is that VMG "Eureka" moment to which I referred and in my experience has held true.  DDWFTTW believers rarely argue the details of how it can be done because they can't get past the "to outrun your power source defies the laws of physics and requires more power out than in." positions.   Once someone gets past their physics issues, the rest can usually be overcome.

JB

[ThinAirDesigns]

Now, if the cart is placed on a treadmill in still air, then initially the wheels would drive the prop... but as soon as they begin their tack, they will pull the cart forwards and the cart will advance.  The difference between what the wheels "see" and what the sail "sees" is where the energy is being extracted from to effect the propulsion, exactly analogous to tacking into the relative wind once drifting with the current, and the intimate connection is needed between the prop and the wheels in order to make use of this difference.

For those that believe that the cart advancing against the treadmill in still air must constitute getting "something for nothing", the power to advance the cart is coming from the treadmill -- place an amprobe on the treadmill cord and you will see the current draw exceed the no load amps of the empty treadmill.  The device is actually 'electrically powered' when used in that context.

JB