Merged DDWFTTW in a “Real” Wind

[ThinAirDesigns]

You will definitely need to be good to tell me that I didn't make things correctly, ...

Yeah ... because you haven't done *anything*.

That's where I Ratant has you beat to hell -- he may be insulting, arrogant and regularly wrong, but he's not afraid to actually DO somthing.

Good on him in comparison.

JB

 

[humber]

Yeah ... because you haven't done *anything*.

That's where I Ratant has you beat to hell -- he may be insulting, arrogant and regularly wrong, but he's not afraid to actually DO somthing.

Good on him in comparison.

JB

Your trivial pursuit? A team that took a year?

That posted TM cart is the crap one, the other has no wheels. I may be the only one who has one. The prop one works too, but that's only for laughs.

 

[windgrins]

Humber,

I can't really answer for them but I would venture a guess that it would be helpful for anyone in his position to adopt the attitude:

If I know someone has done something that I don't know how to do and I want to learn it for free, I should adopt the attitude that being nice could have a positive impact and not being nice could have a negative impact on their willingness to waste their valuable time to teach me.

Your response was nice and I appreciate it. Thanks,

 

[humber]

Humber,

I can't really answer for them but I would venture a guess that it would be helpful for anyone in his position to adopt the attitude:

If I know someone has done something that I don't know how to do and I want to learn it for free, I should adopt the attitude that being nice could have a positive impact and not being nice could have a negative impact on their willingness to waste their valuable time to teach me.

Your response was nice and I appreciate it. Thanks,

I Ratant has already mentioned that Mender and I provided helpful hints, though Mender and I are definitely on opposite sides of the fence.
There is a distinct difference between promotion and education, Windgrins.
Charles Platt also spent his time and effort, with no potential for reward.
I Ratant too, yet they mock his entirely innocent aero-friend, because he disagrees with them. Like so many who claim to have an open mind, they seem to close early.

 

[windgrins]

Humber,

I disagree with I Ratant's aero-friend also but I don't mock him. His lack of understanding is reasonable but wrong. It's a subtle point that the prop is not acting in the relative wind that the cart is. This is a reasonable confusion. If one could ride along with one of the blades of the prop, I believe it would always be like watching a sail on a broad reach once it starts spinning. It's counterintuitive (but that's what makes this fun) to realize that 0 WS for the cart is not 0 WS for the prop blade and that it merrily accelerates past this point with no change in dynamics. This was the epiphany that made me realize this would work. I originally thought it wouldn't also. But, after thinking about it for a couple of hours and looking at the explanations and vectors, it became clear it would work and does! Very cool!

 

[spork]

Spork and team built not just one, but many carts that can go DDWFTTW.

Windgrins - I really appreciate your posts. The only slight clarification I'd like to make is that it's not really accurate to talk about "spork's team". It was a joint effort by me and JB. The concept was mine, but it turns out I wasn't the first to think of it. The motivation and more than half of the energy was JB's. I consider it very unfortunate that the media considers this "one man's quest to beat the wind".

this was a bit convoluted but a very clever demonstration of a principle.

Indeed. But being convoluted was sort of the point of the exercise. I originally posed this as a brain-teaser.

 

[spork]

I still have a text book from when I flew gliders that incorrectly describes how lift is generated (the same way that humber is wrong about how lift is generated).. not saying your friend has an incorrect model in his mind, but there are a TON of pilots out there that have the wrong idea concerning how lift is generated.

As both a pilot and an aero engineer, I can tell you this much... if you want convoluted and inaccurate explanations relating to aerodynamics, ask a pilot. If you want some seriously messed up info, without a hint of uncertainty, ask a military pilot. Obviously that rule isn't 100% - but I find it to be FAR too common that this is the case.

I disagree with I Ratant's aero-friend also but I don't mock him.

I'm pretty sure no one did. He's simply wrong. There's no reason to mock that - not until he becomes wrong, certain, and insulting (like I Ratant).

 

[CORed]

OK by me, Windgrins, but if they are so helpful and knowledgeable, why do they present their remarks to I Ratant in mocking riddles? It does sound like they want him to fail.

I have one for them. This cart goes up the TM belt, no prop, motors or tricks.

[qimg]http://www.internationalskeptics.com/forums/attachment.php?attachmentid=21828&stc=1&d=1302838596[/qimg]

Back to plain old lying again, I see.

 

[3point14]

1) Where are the text book references that suggest a prop is like a tacking sail.
2) Where do text books, or even general sailing references, liken a tacking sail to a prop?

Every post from now on.

This:

Take a cart.

Put two long tracks along the same axis as the axles, one fore, one aft.

Put a sail at an end of each of those, one on each track, one on the left one on the right.

As the wind blows DDW with respect to the cart create enough friction between the sails and the cart such that the sails both push the cart and push themselves along the track.

When each sail reaches the end of the rail, turn it around.

Hey presto. There may be engineering problems that would make this approach impossible, but as this is a thought experiment I don't have to worry about them.

(I have a better one about a planet sized, Rama shaped world covered in water, but I haven't quite worked out the details yet.)


If it's possible to go downwind faster than the wind then it's possible to go directly downwind faster than the wind.



ETA: It's just occurred to me that the final part of this thought experiment is to loop the rails all the way around so the sail doesn't have to stop and change direction...

Go on, tell me which mit doesn't work? You can't, and you won't even try because you know that, even knowing all the fancy equations (and, it seems, misapplying them) you know that there is no hole in the logic at all.



Better still, this:

http://www.youtube.com/watch?v=IMEerIkOVZ0

Shows exactly how you get from a tacking sail into a DDWFTTW cart. It's not difficult. It is, in fact, really, really easy to understand that one.

Bottom line, if it's possible to go DWFTTW then it's possible to go DDWFTTW even if you have to build a convoluted little device like the one in the video.

I predict that you won't attack either of these models because you can't. You might claim that the maths doesn't work, but as your (as I understand it, flawed) mathematics doesn't encompass that then you just sit there not believeing reality and retreating further into absurdity.

You're like a man watching Mercury appear at the wrong time and declaring that, as Newton declared it not possible, that you just couldn't see it.

 

[Jack by the hedge]

This cart goes up the TM belt, no prop, motors or tricks.

[qimg]http://www.internationalskeptics.com/forums/attachment.php?attachmentid=21828&stc=1&d=1302838596[/qimg]

And you have actually tested it? No tricks?

My first guess is it has a flywheel and must initially be pushed to greater than belt speed. But such stored energy is not allowed, so that would certainly count as a "trick".

It would be really cool if this turned out to be a genuinely novel and interesting design, which worked as advertised, but on track record alone I'm braced for disappointment.

 

[A.T.]

So? You want a text book to do your thinking for you?

Well, if thinking is not exactly one of your strengths, then you require an authority to tell you what is correct. He is completely unable to understand a general concept, and apply it to a new situation. His "Gimme a text book on that" is also a white flag. It translates to: "I cannot refute your simple and correct argument, therefore I just keep asking about a book, so I don't have to admit being wrong"

 

[A.T.]

.

Are you sure you have the chamber of the airfoil on the right side? It is correct in your diagram on the lower picture, but seems wrong on your cart.

 

[ThinAirDesigns]

Some are better at "one of these things is not like the other" than others. Even a non-regular contributor rang in nearly instantly with the answer long ago.

From earlier exchanges regarding A.T.s excellent drawings (I Ratant's claim they didn't apply to the BB) it's clear that I Ratant is very weak in 3D visualization and manipulation. Of course we know that humber is a disaster. Turns out (and it's likely related) that neither of them are good at the "not like the other' game either.

JB

 

[ArmillarySphere]

The two carts are operating in different "modes" here.

I Ratant's cart is "freewheeling" - the wheels are free to rotate any way they choose. Since the wind is hitting it from the front, the wheels are rotating in the "forward" direction. In the same mode, with the wind from behind, they would spin in the "backward" direction - as long as the cart is held in the air. To put it bluntly, the prop is driving the wheels, since there's no ground contact to resist this.

The blackbird is in contact with the ground. The wind, hitting from behind, is trying to turn the prop so that the wheels would rotate "backwards" (if not for the sprocket). However, this force is overcome by the cart's forward motion, which turns the prop in the other direction. The wheels are driving the prop.

As far as I can tell, there's no difference in how the gearing is hooked up, but the carts are not performing in the same circumstances. The prop may have to be turned around though - I can't tell from the picture.

 

[ThinAirDesigns]

I think you'll find that I Ratant has one cart that like the Blackbird, is equipped with a geared prop rather than a freewheeling prop.

JB

 

[H'ethetheth]

Well, if thinking is not exactly one of your strengths, then you require an authority to tell you what is correct. He is completely unable to understand a general concept, and apply it to a new situation. His "Gimme a text book on that" is also a white flag. It translates to: "I cannot refute your simple and correct argument, therefore I just keep asking about a book, so I don't have to admit being wrong"

And, of course, when you do support an argument with a ubiquitous, well established fact, to be found in any textbook, it's "rote learning", or "your inability to correctly apply textbook knowledge".

 

[ArmillarySphere]

Yes, the gearing connects the wheels with the prop. However, the wheels are spinning freely since he's holding it up into the air. The ground contact makes all the difference. It's freewheeling, not freepropping

 

[windgrins]

Reply to Spork

Spork, JB,

I stand corrected-Your team= JB and Spork! An even more impressive achievement.

I won't take your remarks about "bad info from pilots" personally. I've seen lots of that myself even though I am one.

I also was very impressed by Jack Goodman's cart. You guys scaled the concept well on a shoestring budget and get full credit for the record in my book. Great engineering! A fine long term addition to the lineage of "Ramblin' Wrecks"

What I thought was most clever was how the cart transforms an iceboat concept into the cart. It was a reasonably straightforward idea to turn a sail into a prop but it took me a while to wrap my slow witted brain around the idea of a keel force being translated into the prop drive wheels resistance while generating the power to turn the prop. I think the credit goes to Jack Goodman or the guy in the 50s that preceded him for this. Truly a clever concept and one that I wouldn't have thought up in a million years! (I guess that's why I think its so clever!) It also took me a bit of head scratching to realize that the keel of the ice boat is what keeps it from ever having zero wind in its sail when it is on the reach. If not for the keel, the ice boat would just skitter along a little slower than wind speed downwind as opposed to easily being able to sail at a VMG>1X downwind speed.

When I was originally thinking about this, my hangup was very similar to I Ratant's aero friend's. When I realized that the prop never experiences a zero-wind condition (unlike the cart body), the beauty of the concept dawned upon me. For those still skeptical, Once one gets through this mental block, the rest should follow pretty straightforwardly. In fact, from the videos, when the cart hits 0 WS, the BB prop seems to be just reaching its stride and really starting to push!

Originally, I was concerned about writing this and giving away the "secret" to the brainteaser. But looking back at the posts, there seems to be no danger of running out of skeptics even if one explains every piece in excruciating detail (which makes it a first class brainteaser!)

Thanks for your nice replys!

 

[jduffy77]

I have one for them. This cart goes up the TM belt, no prop, motors or tricks.

Humber is out right lying again. He has no such cart.

 

[humber]

Back to plain old lying again, I see.

Keep going Cored. All the sweeter when you see it. Even though I have given part of the game away by showing you what is not there, you still can't conceive of how it may be possible.
ETA:
And you too, Duffy.
And I am not trying to "convince" newcomer Windgrins. Anyone if free to make up their mind, without "assistance" from biased points of view.