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Dora mia:
>It appears that no one has been able
>to replicate this experiment and post
>their results here? That's proof enough
>for me.

Dora, several people have built the carts and posted videos. Search "DDWFTTW" on Youtube.

Here's another one:

http://www.youtube.com/user/pelesl

Dora mia, no need to take my word for it. He did fail initially and then just after we demonstrated our large cart, he built another one and surprised himself with success.

Here is his video:

http://www.youtube.com/watch?v=MfZt19F-OA4

Contact him directly and he'll confirm.

JB

Send me a PM on the hang gliding forum

http://www.hanggliding.org/index.php

I'll be happy to meet you. You can see it with your own eyes and touch it with your own hands.

You're in the SF bay area, right? I'd like to see this for my own eyes.

The fact that the physics police failed doesn't make it impossible - it makes them incompetent. I built one that works as advertised.

Build my own? No thanks. I can find better ways to waste $80. ThePhysicsPolice built one, and it failed to work. Well, Bubbleboy insists that thats not the case, so I suppose we should all take his word.

"It appears that no one has been able to replicate this experiment and post their results here? That's proof enough for me."

Or at least no one has tried. Jack has done it and we have done it. I've posted parts list and build plans so you can do it to. Or you can simply be satisfied that it's impossible.

It appears that no one has been able to replicate this experiment and post their results here? That's proof enough for me.

We've been going down wind faster than the speed of the wind for years now. We do it with kites, and we do it in a kite buggy.

It is easiest to do on a hard flat surface(dry lake bed) but it's just using apparent wind, which allows us to travel almost 3 times the wind speed.

nabx.net

If the vehicle always went twice the speed of the wind, it could still be said to go faster than the wind at any speed (I think). This would not represent perpetual motion.

Such a vehicle can't exist in the real world however, since real world losses will always require some minimum wind speed before the vehicle will move.

Forgive me if this point has been pointed out somewhere else in this exchange; I've only had the stomach to read about half the messages.

Assume that this machine moves DFTTW without external energy input.
Assume that this ability to move DFTTW is not specific to a particular windspeed.
Set windspeed to zero.
If the machine moves DFTTW, then when windspeed is zero, the vehicle should maintain a positive and non-zero speed.
Or to put it another way (and make my conclusion pretty clear), in the absence of wind and external energy input, the machine should have motion perpetually.

John,

Good analogy. Please read the previous posts before posting.

Sincerely,
Zafner

I thought of an analogy to help explain this phenomenon. Instead of wind, imagine a string moving at a constant velocity along a flat track. Is it possible to design a vehicle that can use the string to move faster than the string? The answer is yes, and can be easily demonstrated by "walking the dog" with a yo-yo. This is not perpetual motion; it does not violate any laws of physics; still, it is pretty cool. I'm wondering if it might have any real-world applications...

JC

I wrote, when the gear ratios are reversed, not the propeller rotation.

Edited by author 11-29-2008 09:48 AM
It should be noted that the poster on this thread called "ThePhysicsPolice" (see post 272) has since his last post been able to duplicate Goodmans tests and is now an absolutely convinced (with his own eyes) believer.

JB

No relation to Guy. I live in Oklahoma, but know Spork. He is right and everyone else is wrong. I have seen the device work - it is real.

Edited by author 10-26-2008 02:47 AM
Wow. Lots of words. Some of it right. None of it uncertain. Sounds like you're wanting to take my bet. Unless you're just trolling like our other friend, you can take my $100K - since you're so certain this cart can't work.

Of course if you wanted to understand how it *does* work, I'm more than happy to explain it - in any number of ways. But if you're certain it can't (as it seems), you should really just take the bet - and take my money.

A sailboat is not powered by the wind it’s ultimately powered by relative airflow. The wind certainly makes up a large part of this relative airflow. The wind causes the initial motion of the sailboat but as soon as the sailboat starts to move its relative airflow is cause by a combination of the wind and its own motion. This is why sailboats and iceboats can sail faster than the wind but they cannot sail faster than the relative airflow that is influencing them.

Sailboats, iceboats and the “vehicle such as THIS “ that you mention cannot go directly downwind faster than the wind. Drag is in the direction of the relative airflow that caused it so the more a vehicle moves as a result of drag the less drag it generates. With no outside force
opposing its motion a vehicle will accelerate to the speed of the wind (as a result of drag) where its drag will be zero. There is an aircraft that shares this dynamic. The faster it goes the less drag it generates until it reaches top speed where drag is zero. A balloon does not move readily with the wind if it did there would be no difference in velocity between the balloon and the air and thus no relative airflow and thus no aerodynamic force to accelerate down wind. The balloon is held in the flow by its own inertia.

When a vehicle moves as a result of lift it does not lose any of the relative airflow that caused it to move and now has more relative airflow as a result of its motion due to lift. A sail boat cannot sail directly downwind faster than the wind using only drag but it can sail faster to a point downwind using lift by jibing. This fact has nothing to do with the prop cart despite the fact that it has a lift-generating propeller. The propeller on the cart is powered by the carts downwind motion and that motion is due to drag. The faster this cart goes the more it gives out of power and if it had no rolling drag at all it would totally give out of power when it reached the speed of the wind. The only way to increase its power is to slow it down. The cart is propelled by drag and drag will only be at its maximum when the cart is being held still in the wind. If the propeller helps it go downwind faster it only helps it to give out of power faster.

Ahhh - still trolling I see.

Demonstrate what exactly? You didn't like my descriptions and terms, and you refused to propose your own.

My money is here Spork, I can write the cheque today.

Demonstrate and you will get it or name a secure independent escrow that holds your 100,000 and he will get mine but you will still need to demonstrate or come up with the cash yourself.


Guy



Guy

What's wrong - no stupid "give me money for nothing" comments?

>> Demostrate or pay.

You seem to be forgetting a critical factor. There is no agreement in place. You refused to accept mine or produce your own. There is no "demonstrate or pay" to it. I haven't "agreed" to pay. I "offered" to pay simply to prove that you wouldn't conduct this transaction over this public forum as you insisted we do.

Post your address or STFU

Ive refused nothing.

Demostrate or pay.

Thank you for agreeing to pay, I have given you the address to post the check so I assume its on the way.

My home address it is publicly available in a myriad of places but I would like the check sent to the address I have given you please.

Thanks


Guy

< replied-to message removed by QT >

Edited by author 09-18-2008 03:52 AM
Post your address and the check is on it's way.

This is swell. How many times do you want to go around this loop?

Demonstrate or pay as you said you would.

Guy

< replied-to message removed by QT >

Edited by author 09-17-2008 11:41 PM
>> I offer a simple thought.

I'll offer a simple thought as well. You were so sure it couldn't be done, that you *appeared* to be willing to put $100K on it. But when the rubber meets the road, you just want to flap your gums about it again.

>>
Of course, none of this proves or disproves the possibility of making vehicle that goes downwind faster than the wind. However it does demonstrate that THIS vehicle cannot.
<<

In fact the only thing it actually proves is that you can't understand aerodynamics. So here is where it stands now...

1) For anyone that actually wants to know how and why Jack's vehicle can and does work (rather than just explaining confidently that it can't), I'll be happy to explain it in ways that are easily understandable.

2) I realize "Guy" doesn't have the money to take my bet (or even a home it seems), but I'm going to improve on the bet. I'll prove it can be done with the actual cart seen in the video. Not another type of cart, and not one *like* it, but with the actual cart used in the YouTube video.

Of course it would be smarter to ask to see my cards rather than take my bet, but that's the deal.

If there is anyone but Spork and his alter ego left spectating this sad exposition, I offer a simple thought.

On the presented video of the cart accelerating from zero to being faster than the wind, consider the moment when the cart is moving at the same speed as the wind. At this point there is no relative movement between the air and the cart and thus the only relevant forces on the cart are the thrust of the propeller, tending to accelerate the cart, and the drag on the wheels tending to decelerate it.

The drag on the wheels is the sum of the load they deliver to turn the propeller and the total friction in the system.

We know that the thrust output from any propeller is less than the input to the propeller. Thus the drag on the wheels is more than the thrust from the propeller by the sum of the friction losses and the propeller efficiency losses.

The deceleration forces are greater than the accelerating forces, the cart must inevitably be slowing. It can never go faster than the wind.



Jack makes a startling comment in his description. He states that, if the gearing is reversed so the propeller turns in the opposite direction, then the cart will go up wind.

But in both cases (the cart travelling faster than the wind and the cart going up wind) the relative airflow passes the cart (and thus the propeller) in the same direction. The direction of rotation of the propeller would be the same in both cases! The gearing therefore needs to be in the SAME direction.

The reference to a change of direction is a profound logical gaffe.
The truth is that, if the gearing is sufficient to overcome the starting forces then the cart, as configured in the video, will go up wind (whichever way round it is pointing).

There have been many vehicles made, both land and water based, that demonstrate this.

Of course, none of this proves or disproves the possibility of making vehicle that goes downwind faster than the wind. However it does demonstrate that THIS vehicle cannot.

Guy

>> You have really lost the plot haven't you?

Let's see... I'm toying with an internet troll that claimed he knew for sure that it was physically and theoretically impossible to build a wind powered vehicle that goes directly downwind faster than the wind. Then that troll claimed he would accept a bet to that effect, but refused all possible scenarios in which that bet could be carried out. When given the option of suggesting his own rules and such, that same troll simply refused. Finally, to call his bluff, I tell this troll I'll simply send him the money - all he has to do is provide his address. And the troll refuses even that!

So no - I think I'm following the plot just fine. Short version: you're still a useless internet troll that wants to make bold innaccurate claims, but you're not willing to put your money where your mouth is.

You have really lost the plot haven't you?

< replied-to message removed by QT >

>> You have it.

I have the address of the skateboard park where you go to gawk at young boys. Are you telling me that's also your residence?

You have it.

< replied-to message removed by QT >

Please post your mailing address.

Please send the check.


Guy

< replied-to message removed by QT >

>> now when will I get my 100,000?

When you send me your address.

>> I've never been at all secretive.

Right, you just refused to even tell me what country you live in. You still refuse to give me your address to send the check to.

Fine with me, now when will I get my 100,000?

Guy

< replied-to message removed by QT >

I've never been at all secretive. You have always been able to look me up.
It is you who has no name.

Now when can I expect my 100,000?

Guy

< replied-to message removed by QT >

I've gone ahead and sent a link to this discussion to your employer. I just think they might enjoy this forum as much as you.

Finally we're getting somewhere. It seems you're a managing director for the Corus Group (in the steel tubes division). You live in the U.K.

You sure are an awfully secretive troll for someone who claims this entire thing has to be conducted directly on this forum without any direct contact even via email.

Will you post your true address for me to send the check to, or should I?

OK please send it to

Guy Glover
Adrenaline Alley
Arnsley Road,
Corby,
Northants
United Kingdom
NN17 5QW

Thanks

< replied-to message removed by QT >

Sorry, that's not the deal. We're going to do this on-line in the public forum as you specified. Once I send you the money you can do whatever you want with it. Hell, you even have an excuse about taking payment.

Friggen uber-troll

OK, that would be good.

I have a charity I would like to donate it to.

Adrenaline Alley
Arnsley Road,
Corby,
Northants
United Kingdom
NN17 5QW

I will let them know it is coming.

Thanks

Guy




< replied-to message removed by QT >

Edited by author 09-16-2008 04:12 AM
>> I just wish to get on with it in whatever is the easiest way for you.

You're right. Perhaps I should just send the money. How should I make out the check, and where should I send it?

>> What do you want me to do to help you?

All of the things you said you were going to do, when you complained that my approach was insufficient. But we're past that all now. Just tell me where to send the money.

What do you want me to do to help you?

Guy

< replied-to message removed by QT >

I believe we have sufficient in the exchange of emails for an enforceable agreement. Of course if you want to help by suggesting something more formal please go ahead. I am open to anything however I appreciate that the more I say the more you will try to cloud the matter with insults.

I just wish to get on with it in whatever is the easiest way for you.

Guy

< replied-to message removed by QT >

>> Amazing trollmanship.

I think it just shows that if you do what you love, and play to your strengths, you really can achieve amazing things.

Hmmmm ...

You would like Sport to demonstrate what?

Spork defined the task and you didn't like the definition. You said *you* would come up with one in ~7day ... that was TWO MONTHS AGO.

You're just making yourself look silly by now saying "I'm happy to pay once you have demonstrated".

Amazing trollmanship.

JB

No excuses here, you offered a demonstration for 100,000. I have the money, happy to deposit it with an escrow, please name one who holds your 100,000 (but I don't see the need).

You said some time ago it would take you a month. So demonstrate within a month from now please, I'm happy to pay once you have demonstrated.


Guy



< replied-to message removed by QT >

"Guy":
>No more excuses, just your demonstration.

ROFLAO! "demonstration"? Demonstration of what? Demonstration for what?

Suddenly, "the money is here" and "all you have to do is your demonstration" is good enough.

A non-troll makes the contacts, negotiates the agreements, opens escrow with mutually agreed upon agent, etc.

A troll won't make contact, never completes his counter offers, and avoids escrow altogether with the words "the money is here".

One of these two parties appears willing to move forward, but is sure as hell isn't you "guy". Big words until it's time to actually do something and then fffffttttttt.

JB

Oh I see, your new excuse is that we don't have to have an agreement of any sort (the agreement you've be drafting for many weeks). I don't have to know what country you live in. We don't have to use an escrow account. I should just post a video on YouTube or something and you'll send my $100K in SecondLife?

F'in troll!

Cut the crap Spork.

The money is here, all you have to do is your demonstration.

No more excuses, just your demonstration.

Guy

< replied-to message removed by QT >

Ahhh - very clever is this troll. His new excuse is NO excuse. I had no idea it would be as simple as telling him my name.

Yo' BubbleBoy. I've got an idea. We could have a little side bet. What do you think his next excuse will be?

Edited by author 09-11-2008 10:53 AM
O.K. Troll Glover. My name is Dave Atkins. What country are you from? Please post all the info (acct number, bank name, address, phone, etc.) for the escrow acct. Also please post the exact details of the proposed contract.

It's unclear to me how we're going to sign contracts if you're completely unwilling to contact me directly through the email address I provided.

Oh - wait - no it's not. You've never had $100K, and have clearly had no idea what you're talking about on this thread. You're a troll that can't or won't put your money where your mouth is.


Incidentally, it seems clear there IS no public here. We can know this because:

A) Only you, me, and BubbleBoy have responded to any of this
B) They would have laughed you out of here long ago.

The money is here waiting for you but you have to conduct this in public where you started it Your refusal to do so makes it clear to me that you do not intend to stand behind your words.


Guy

< replied-to message removed by QT >

>> So, "Guy" won't use the email address Spork provided to exchange personal contact information.
 
Nope. Because then he'd be cornered into putting his money where his mouth is.

So, "Guy" won't use the email address Spork provided to exchange personal contact information.

If two people are serious about consumating a 100k bet, they will give each other their private info, cell phone numbers, etc. to make it happen (after all, these individuals aren't going to publish an escrow account number, etc. here on a crawler harvestable site).

It appears that Spork is willing to do that. It appears that the "Guy (AKA "troll)" won't even tell Spork what country he lives in let alone drop a note to the provided email to get the Sporks information.

It's pretty simple -- "Guy" doesn't want this thing to happen or that email address would have been pinged just after it was posted.

That's the only one real answer I can come up with to the "why won't "Guy" ping the email address" question -- If you have another one "Guy", I'd sure love to hear it.

JB

Still trolling I see.

I thought you had gone away!

The draft agreement was nearly complete but I began to suspect that you were not going to stand behind your words and so finishing it off would be throwing away good time after bad.

If we don't know who you are how is any agreement enforceable?

Guy


< replied-to message removed by QT >

How you comin' with that escrow acct there Guy? You got your $100K in there yet?

In the absence of any comment concerning my proposed treadmill methodology and suggestion to contact the Chief Executive of RORC I assume they are acceptable to you.

We cannot rely on only one potential source of independent observers, do you have any suggestions of others?

Best regards,

Guy

< replied-to message removed by QT >

Edited by author 08-20-2008 08:19 AM
Classic troll.

>> It was his decision to do this in public...

It's hard to make a public offer of a bet in private

>> I have responded openly.

On the contrary. You refuse to even tell me what continent you're on.

>> He did not make anonymity a condition of his public offer - if he had everyone would have laughed.

I told you I wouldn't put my personal info on this forum, and I provided a means of contacting me directly to share all info. And yes, everyone is laughing - at the troll.

>>It is implicit in his proposal that he identify himself at some point

And yet you refuse to contact me to proceed.

>>I intend to see the agreement I have with him through to completion.

You have no agreement. You've said you don't like my words, but have failed to produce your own. You've said you don't like my arbiters, but have failed to provide your own.

You have no agreement, you have no money, and you have no intention of being anything more than a troll.

>> I am using my own name...

And are unwilling to tell me what continent you are on, or this demonstration would have to take place on.


Classic troll!

"Most private contact information" = his name?

It was his decision to do this in public, I have responded openly. He did not make anonymity a condition of his public offer - if he had everyone would have laughed.

It is implicit in his proposal that he identify himself at some point (without that nothing can happen) - until he does there has to be significant doubt that he is willing to stand behind his own words.
I intend to see the agreement I have with him through to completion. I am using my own name and fully willing to conduct the entire exercise in the particular public arena he has chosen.

I have taken the step of responding in my name, he has not reciprocated. I find it strange that you attempt to portray my wish to know his name as a reason for doubting my seriousness.


Guy



< replied-to message removed by QT >

Edited by author 08-20-2008 03:24 AM
>> It intrigues me that, while I am the one to do you the favour of accepting your challenge...

Classic troll. You *pretented* to accept my challenge because that's what trolls do. If you really had the ability and intent to accept my challenge, it would be because you think you could win. But if you really wanted to do me a favor you'd just send me the money. Classic troll.

>> but you wont tell us your name.

I posted an email address to exchange all necessary personal data. You won't even tell me what country you're in. Nor will you contact me via the email I posted. Classic troll.

>> I am the one who is deadly serious here.

You're a serious troll - and I'm embarrassed to admit I got sucked in by your silliness.

Guy:
>I am the one who is deadly serious here.

Guy to Spork:
> ... you wont tell us your name. Please do so.

Why would you be expect to be taken seriously when you continue to ask a question that has already been addressed. That's not the sign of "serious", but rather the sign of "troll". Seems to me that Mr. "Serious" would have been using the email that Spork provided to get your questions answered.

I can't imagine why you would expect someone to post private contact information on a public forum -- after all, you wouldn't even take the first step of providing an email address as he requested ... Spork took that first step when you would not, so how does that make you serious again?

Action says "serious" like nothing else -- so far, by giving you a private email to use Spork has demonstrated such. Why not just cut the crap and make the contact?

JB

I did explain why I had not.

I am the one who is deadly serious here.


Guy

< replied-to message removed by QT >

Guy ... just an observation. Just because party "A" says they don't have a deadline, doesn't mean that this releases party "B" from being judged by their actions.

When you say you will do something by a certain time and without update repeatedly do not do it, it's fair to assume a lack of seriousness.

JB

It intrigues me that, while I am the one to do you the favour of accepting your challenge, you continually throw childish insults at me. This one is particularly bizarre as only a few days before you stated that you had no deadline. Don't worry, the agreement will come in good time.

Having chosen this place to offer your challenge, to strut your confidence and to throw insults about but you wont tell us your name. Please do so.

On to more substantive matters.

Following your lead on sailors as a source of independence, I was introduced to the Chief Exec of RORC on the Squadron lawn last week. We don't know each other and I suggest I se the introduction to contact him and ask him if he would nominate an independent observer. RORC are a highly respected world wide in the highly sensitive role of adjudication racing yacht ratings and are ideally suited t the task. I suggest that we finds several more similar sources both to aid the logistics an to allow there to be a small panel.

On the matter of the test itself, I would be happy to accept your preference for the treadmill methodology and have an approach that accommodates my inertial concerns (not a frame of reference matters). My proposal is that the cart has a flexible tether attached to the rear. The cart is placed on a stationary, level treadmill and the treadmill is then accelerated up to steady speed. To pass the test the cart should move forward (against the direction of the movement of the treadmill) until the tether becomes tight preventing it moving further and off the end of the treadmill, from which point it continuously exerts a tension upon the tether. Assuming that this is acceptable to you I will have it drafted into the proposed agreement.
Best Regards,

Guy

< replied-to message removed by QT >

Edited by author 08-18-2008 11:01 AM
Wow. That Guy can sure talk a mean physics game.

JB

>> I aim to have a first draft as you requested within 7 days.

Well, 7 days has now become 4 weeks. Clearly Guy is a troll. He was plenty confident of his position to call people scammers and to call others' intelligence into question; but in the end Guy is clearly not as sure of his position as he claimed to be.

I'm officially done being waltzed around by this troll. If anyone ELSE actually has the conviction they claim to about this thing being completely impossible, the offer still stands. Or if $100K sounds like too little or too much, I'll be happy to consider any other proposal.

Guy,

Here's an email address. Send me your contact info.

Th3in22Air8De8sig9ns@aol.com (remove the numbers; use only the letters)

>>It appears that the two you propose have, by your own admission, a preconceived opinion of the outcome.

I never admitted any such thing. I know that one of them does have an opinion on the matter because we've discussed it in the distant past. The other one I imagine will agree it's possible only because he's intelligent and an aerodynamicist. He's a friend of a friend. I don't think I've ever met him.

>>That would appear to exclude them as independent.

Once again, we're back to you. You didn't like my statement of the bet and arrangement, so I invited you to make your own. You don't want people with any intlligence to decide on this, so again I invite you to name them yourself. I imagine it will go about the same way as the first plan did.

>> opinions of mathematics and physics will just get in the way.

Yeah - facts can be inconvenient.

>>Are you going to tell us your real name?

Yes, as I said I'll be happy to share my name, address, credentials, etc. with you. Just give me an email address. I won't post all this on a public forum (do you even read my posts?).

Are you even going to tell me what country you live in? This is the third time I've asked. As I said before, I'm in the S.F. bay area of CA.

Listen, if you really want out of this thing, just say so. The sandbagging is getting tiresome.

It appears that the two you propose have, by your own admission, a preconceived opinion of the outcome. That would appear to exclude them as independent.

The issue is not what may or may not be possible but whether or not you provide a machine that moves the way you say it will. This needs people who have judgement and integrity opinions of mathematics and physics will just get in the way. It is said that the USA has some of the best judges that money can buy, which probably rules them out as well.

Are you going to tell us your real name?

Guy

< replied-to message removed by QT >

>>While I am working on this could you consider how we should select an individual (or panel?) to be the independent assessors.

I have two people in mind that I think will agree to it. One was the navigator on the winning boat from the most recent sailing race around the world (the Volvo cup). He was also the founder and CEO of one high-tech company in Silicon Valley, and the CTO of another. The other is an aero professor at Stanford.

I suggest you do the same. Find one or more people that you're confident can understand the math and aerodynamics involved. But I warn you, if you choose someone with these qualifications they will almost certainly tell you it can be done.

>> Do you have a particular deadline for some reason?

Nope. It's just that when you missed your own suggested deadline by more than a factor of 3 I assumed you had "lost interest".

>>While I am working on this could you consider how we should select an individual (or panel?) to be the independent assessors.

Sure.

>>Please can you let me know your real name.

Happy to. But so far you've been unwilling to even tell me what country or state you live in. Do you have a contact method by which we can trade personal info?

Hi all,

Sorry for vanishing for some days, when I got back from my business trip I discovered that a long standing obstacle to my participating in an offshore sailing passage had been removed and I had to drop everything and rush. I have just arrived back at my home port and have downloaded my email for the first time for 2 weeks.

I have an outline structure of the agreement in place and I will work to flesh it out. Do you have a particular deadline for some reason?

While I am working on this could you consider how we should select an individual (or panel?) to be the independent assessors.

Please can you let me know your real name.


Thanks


Guy


< replied-to message removed by QT >

So what's up? Of ALL those people on here that are so sure the video is a hoax, no one wants to take my money? I don't think people were quite as sure as they thought they were.

Edited by author 08-07-2008 12:00 AM
>> " ... this is an obvious hoax"

I guess we can say that about Guy's agreement to take up this bet. In the time I've debated this thing I've found a number of people that are absolutely convinced it's not possible. I've also found a bunch that have been convinced, even when some of them thought they could never be convinced. I've only ever had one person actually take me up on the bet (that doesn't include every idiot that says "yeah - I'll take the bet - send me the money"). In that one case, this person was unquestionably the most ubnoxious and condescending of anyone I've debated the topic with. Once he agreed to the bet he went to raise the money. As part of his due diligence he of course did the necessary research for the first time (because simply insulting me wouldn't satisfy his backers). And the most astonishing thing happened. He found it was possible and asked if I'd let him out of the bet. Neither of us had yet put the money in escrow, and I obviously let him out (not that I could force his hand even if I wanted to).

But the interesting thing of course is that even in that extreme case, this guy didn't hide. He admitted he'd learned something.

I overestimated Guy.


EDIT:

Look at this - I just went back to look at Guy's first claim that he'd accept the bet. Here it is:

"Yeah, OK.

Ill take your money.

Whats the easiest way for you to send it to me?"

So it looks like he's in the category of people I mentioned above - people that don't even understand how a bet works.

>> I aim to have a first draft as you requested within 7 days.

Well, it's been 21 days. It looks like this one got away. I suspect he did go off and do a little research with the added incentive of $100K on the line.

Edited by author 08-04-2008 02:26 AM
The truth of the matter is this - I hope you're right that this has caused Guy to do the research necessary to see that this is quite real. It's not perpetual motion, and it breaks no laws of physics.

There's no shame in getting something like this wrong and later admitting you've learned something. It's not exactly intuitive. It's a little shameful to be stubborn, wrong, and insulting all at once, but I've been guilty of that plenty of times (incidentally, this isn't one of those times - and I'm ready to put my money where my mouth is).

If Guy wants to put the bet aside and learn how this is possible I'm confident I can explain it to his satisfaction. I offered the bet because guy and others aren't asking how it can be done. They've told us it definitely can't be.

Though I'm rather late to this thread party, I have read the entire thread and Guy Glover has been one of, if not *the* most adamant regarding this thread topic. Here's a few quotes from Guy -- we'll call them "Guy's greatest hits":

** " ... this is an obvious hoax"
** "You are right to be confused, you see a video of something impossible."
** "Youre lucky Jack hadn't worked out a way of getting money out of you with his scam!"
** "Oh come on Jack, you repeatedly misrepresent a very simple bit of physics."
** " Jack knows there is another energy source, maybe its being towed, maybe it is rolling down hill, the possibilities are endless."
** " It is blindingly simple and obviously cant work"
** "It is just a mechanism that clearly cant work"
** "... the law of physics that is being broken is the conservation of energy."
** "However low the friction, it will never go faster than the wind."
** "If we dump the propeller and connected its drive to another wheel the cart should go even faster!"
** "The real job of the propellor is to confuse thinking"
** " ... the addition of the propeller slows the vehicle down."
** "It is just a propeller being driven in air. It is not a turbine being driven by the wind."
** "If you can explain to me how you get more energy out of a propeller in thrust than you put into it as drive, maybe I will get my glider to stay up permanently."
** " I am afraid this is an extremely simple issue, there is nothing complicated about the cart."
** "Frankly I don’t understand all the debate about down wind because it is such a simple situation and very easy to model and understand."

Apparently, once the rubber hits the pavement it Guy is not quite as sure of his position. He has been given a chance to quite profitably support his assertions but I see nothing but stalling. Perhaps he's done a bit more research -- the opportunity to put money on the line will do that to a Guy.

In the end, it's the following quote from one of Guy's posts that I find most relevent:

** "If you seek the truth you will learn, if you seek to prove you have nothing to learn you will make a fool of yourself."


I can say I'd love for a fool and his money to be soon be parted, but sadly it looks like it's not going to happen. I sure hope I'm wrong.

JB

>> I aim to have a first draft as you requested within 7 days.

14 days and counting...

For some reason your post of the 15th never arrived here as an email but I have now seen it on the web.

I am now back in the country and will start work on the agreement.
Regards,

Guy

< replied-to message removed by QT >

>> it will be a week before I can do it.

I'm so excited. It's been one week now, so I imagine I'll be seeing the proposed agreement in short order.

>>In the mean time I asked what time frame you need

Yes - and you may have noticed I answered your question in the very next post.

One of my emails must have gone astray. I will prepare an agreement as you requested but, as I am travelling at the moment, it will be a week before I can do it. In the mean time I asked what time frame you need.

Guy

< replied-to message removed by QT >

Let's just get the first one going. I'm looking for any taker. It just seemed that you were complaining about my definition buy not offering one of your own - so I put the net out again.

Are you offering a second 100k? We already have an agreement on the first.
I aim to have a first draft as you requested within 7 days.

Guy

< replied-to message removed by QT >

Just so we don't lose sight of it in all the "details", I'm looking for anyone that wants to take my bet that I can demonstrate a vehicle that is powered solely by the wind, and goes direclty downwind, faster than the wind, steady state. I've got $100K that says it'll work.

Yet another great reason to do it on the treadmill.

I agree, my only concern is to rule out any inertial effects and to have sufficient distance to demonstrate performance in steady state.

Guy


< replied-to message removed by QT >

Edited by author 07-15-2008 11:00 PM
>> The definition needs to be somewhat tighter than that, a bicycle would fulfil that description.

I don't see how a bike could fit the description of a vehicle that goes directly downwind, faster than the wind, and powered only by the wind. But that's fine. You've said more than once you don't like my definition, and I've said I'd accept any reasonable definition from you. I'm still waiting.

>> please confirm that you have the cash available.

Of course I have. I'm the one that offered the bet.

>>(I warrant that I have)

Oh well, if you "warrant it" then I guess we're all set. I "warrant" that this vehicle will go downwind, faster than the wind, powered only by the wind, and steady state. Is it settled then?

>>
The problem is that your definition is satisfies by any "vehicle" capable of travelling faster than the wind.
<<

Quit talking about my definition and supply one that satisfies you.

>>I am pleased to hear it, you will find that I am very reasonable.

You're pleased to hear that I'm open to your definition, but we're not making much progress getting a definition out of you. So far all I've heard is that a car, bus, or bicycle is a wind powered vehicle that can go downwind faster than the wind (though I don't know or care how).

>> How much time will you need to demonstrate your vehicle?

If you're satisfied to do it on a treadmill I'll want one month. If you need to see it outdoors we're slaves to the weather. We'd need to find a day with very steady wind going over a perfectly flat slope along a long straight path.

Jack, thanks for the advice on the treadmill. I know you're absolutely right, but I'm not so sure Guy will understand the whole inertial reference frame thing and be satisfied that the scenarios are identical.

I suggest you do the test indoors on a treadmill with no wind. Outdoors, the speed, wind direction and windsheer can be very difficult. You may have to wait weeks to get the right conditions, even then it could be contested. The treadmell test is simple and impossible to fake. If the cart moves forward, it is going faster than the wind.
Jack

>>I guess it would be more usual for the person who lays down
>>the challenge to also define what the challenge is.

>I think "the challenge" is to make a vehicle that goes directly
>downwind, faster than the wind, and to demonstrate it.

The definition needs to be somewhat tighter than that, a bicycle would fulfil that description.

>I guess you think the challenge is to come up with $100K.

I hadn't until I read that, please confirm that you have the cash available. (I warrant that I have)

>In any event, no matter. I have proposed a scenario for the challenge, how
to
>decide the winner,

The problem is that your definition is satisfies by any "vehicle" capable of travelling faster than the wind. I appreciate that it was not your intent but our agreement needs to be clear and enforceable.

>You weren't fully satisfied, so I invited you to offer any reasonable terms
>at all. I will accept them.

I am pleased to hear it, you will find that I am very reasonable.
How much time will you need to demonstrate your vehicle?

Guy

>>I guess it would be more usual for the person who lays down the challenge to also define what the challenge is.

I think "the challenge" is to make a vehicle that goes directly downwind, faster than the wind, and to demonstrate it. I guess you think the challenge is to come up with $100K. In any event, no matter. I have proposed a scenario for the challenge, how to decide the winner, and how to handle the funds. You weren't fully satisfied, so I invited you to offer any reasonable terms at all. I will accept them.

I guess it would be more usual for the person who lays down the challenge to also define what the challenge is. However I recognise it is in my interest to make it as easy a process as possible. I will come up with a proposal. Unfortunately I am travelling all this week and so it may take a few days.

Guy


< replied-to message removed by QT >

Yo BubbleBoy - how about you ixnay with the actsfay. I've got one on the line that wants to give my $100K. But it ain't gonna happen if he learns some physics.

Actually, it's beginning to look like maybe he took the bait but swam away.

Anyone else want to put some money on the outcome you're so sure of?

ThePhysicsPolice

First, before posting a quote from you I want to commend you on your model build with the RC parts. I thought it was quite clever and I so appreciate people who not only calculate, but also *do*. Kudos.

Now to your comments from waaay earlier in the thread.

ThePhysicsPolice:
>Ask any good yachtsman, land or water and he will tell you
>that is what a spinnaker is used for - sailing downwind -
>don't bother tacking it is a waste of time and energy.

Well, I consider Stan Honey (just google that name) as "good a yachtsman" as they come. Just a tiny sample of his accomplishment:
-----------
Stan Honey has navigated in fourteen transpacific races, finishing first six times. As navigator, Stan has set the single-handed, double-handed, and fully-crewed passage records for monohulls to Hawaii. In 1996, Stan and Sally (Lindsay Honey) won the Pacific Cup overall, sailing their Cal 40 Illusion doublehanded. This year Stan will be navigating the Turbosled Pyewacket.
-----------

Stan, as my boss of many years, holds the above statement to be nonsense. In fact, in many high performance sailing endeavours they tack downwind because it's more productive than a spinnaker -- it all depends on the design class your in.

More from ThePhysicsPolice:
>At oblique angles upwind iceboats can certainly achieve
>incredible speeds and as they tack and their inertia can
>continue to carry them at higher VMG downwind briefly but
>then as they continue to tack back to best forward velocity
>their VMG downwind falls well below wind speed and the
>overall end result is a lower than VMG downwind.

This above statement is easily disproven. One can go to the NALSA.org web site (the North American Land Sailing Association) and download gps plots from vehicles during actual sanctioned races. These plots, along with the wind data from the race, show that their VMG exceeds the wind by large margins.

>Argue it as you may these boasts of iceboats exceeding VMG
>downwind almost always EXCLUSIVELY appear in the DWFTTW debate.

There's a good reason for that ... in the iceboat and landsailing communities, it's been done for so many decades it isn't even a topic of debate. They would laugh at you if you told them it couldn't be done.

Is it true they get their fastest speeds upwind? ... yes. Is it true their VMG doesn't exceed the wind ... absolutely not.

>Nevertheless, the challenge still stands for anyone: sailboat,
>land yacht, iceboat, or wind boarder to release a balloon into
>the wind and recapture it or pass beneath it. This challenge has
>yet to be accepted, accomplished and documented in any fashion.
>If it were indeed possible, this debate would be over.

You might want to check out those gps plots before you hold that statement too strongly.

I would happily listen to your arguments as to why the posted data is a fraud -- remember, this is a National sanctioning organization, and the articles aren't even about "downwind faster than the wind" so I find no reason to believe they are grinding an axe.

JB

Oh my, this is gonna get good.

We either get a well defined and executed test, or someone P*s*ies out.

(my money's on the latter)

I sure hope we get to see the definition process done here in public.

JB

All right, I'll tell you what... you should post any reasonable criteria you want. I'll be happy to go with any reasonable scheme you have.

I think we need something that is sufficiently robust to be legally enforceable and clear as to what is being decided.

For example the term "vehicle" has to be well defined (I have several vehicles capable of travelling faster than wind). The conditions for the test need to be defined (for example, can it be given a push to start?). The pass/fail definition needs to be precise - for example does the vehicle have to travel exactly downwind? If not what speed is to be measures (speed of vehicle or VMG downwind?). Are you permitted to try more than once? Who pays the professional and other costs?

Importantly there need to be a time limit upon you to pass the test, I don't want to have to wait to the end of time to get my money.


Guy

< replied-to message removed by QT >

I'll build a vehicle like Jack Goodman's or borrow his. We will operate it on a day with a steady wind - or use a treadmill if that's suitable to you. The advantage to the treadmill of course is that it produces the equivalent of a steady wind, and we can insure the vehicle is tracking directly downwind. If the treadmill is not acceptable to you, we'll do it outdoors in a "real" wind. A mutually acceptable third party will judge whether it manages to go faster than the wind, directly downwind, powered only by the wind. If he claims it does, the funds in escrow will be deposited to my account. If he claims it fails to do so, they'll be deposited in your account.

OK that's what I had in mind, with one exception.

I suggest we agree on the agreement first and select escrow and judges second. Please send me your proposed draft.


Guy

< replied-to message removed by QT >

Edited by author 07-13-2008 11:11 AM
Excellent, I have one on the line. Not a bright one obviously since you don't understand what a "bet" is, but still it's a start.

Here's how I plan to "send you my money":

- We open an escrow and we each put $100K in it.
- We draw up escrow instructions to deposit the sum to the account of the winner of the bet as defined by a clearly written agreement and demonstration.
- There will have to be one or more mutually agreed upon judges, because they will be the ones to issue the final instructions to the escrow company.

Where are you located? I'm in CA. The first order of business is to select a mutually acceptable escrow company and to draw up the terms of the test.

And for what it's worth, everyone that's ever claimed they'd take my bet has started out with "yeah - I'll take your bet - send me the money".

It's kind of embarrassing for them really.

Yeah, OK.

Ill take your money.

Whats the easiest way for you to send it to me?

Guy

Jack's a good man, and he's not looking to scam anyone. I on the other hand am looking for someone to bet me as to whether this works. I've got $100K that says it does. Seems like easy money for those of you that are sure it doesn't.

Just what we need, some video cameras from all angles to check for hidden fishlines. Is that what they meant?

Memberships to the site only cost $4.99 and you get 100% access to all of the live webcams for this price. There are no gimmicks at all. You can see full video with sound for one flat rate of only $4.99. Other sites charge that much per minute for the same exact thing!There are several categories to choose from.

Live Webcams

The wheels are 3.2" in diameter. the wheels turn 2.8 rotations for each fan rotation. The fan pitch is app. 16.3 inches per turn. at 10 mph. the force to turn the fan and misc friction is 402 grams. This was arrived at by reversing the fan, and subtracting out the difference.

I have been working on one of these for weeks. It's almost identical to Jack's.

Unfortunately, I have also been working on a bunch of other things for weeks. Also, my workshop doubles as my living room/bike shop/surfboard repair bay/ebay studio.

I have a lot going on.

Thanks for trying, by the way. All I can say is, if you don't like the result of a recipe, but you changed a bunch of ingredients, it's still possible the problem isn't the recipe.

What kind of RPM were you getting on the helicopter blades at 10 mph? What's their design RPM?

Edited by author 05-21-2007 10:14 PM
[Jack - You need to pitch the propeller so that it blows the air backwards at about .6 of the track speed.]
With the adjustable pitch range I'm able to do that easily. It doesn't make a difference. The more pitch I apply, the greater the force against the scale.

[Jack - Those foam wheels are pretty high loss. I prefer roller blade wheels.]
I actually have 4 sets of wheels (one set are skateboard composition - the same as Rollerblades) but I selected these for their best traction on the treadmill. Don't be fooled because they are foam - they are actually 17 years old and as hard as wood except for the very surface which bites the textured treadmill perfectly. Without the blades on the cart it has so little friction it hardly registers a couple of grams against the scale at 8mph.

[Jack - Also the propeller your are using does not appear to have any twist in it.]
Neither does Mr. Bauer's. His blades taper at the inner roots but don't appear twisted. Again, I do have a set that are made from stacked balsa strips that look like yours but the results using them were not as good as the airfoils in the photos.

[Jack - I don't know what your are doing wrong,...]

Neither do I but I had a hell of a lot of fun doing it.


Again, I do look forward to seeing videos from others here.

http://s167.photobucket.com/albums/u123/Da...w¤t=MyBauerCart.flv

Were any of them able to explain how the thrust from the propeller is greater than the drag the propeller puts on the wheel?

I can't tell much about your car from the photos. You need to pitch the propeller so that it blows the air backwards at about .6 of the track speed. Those foam wheels are pretty high loss. I prefer roller blade wheels. Also the propeller your are using does not appear to have any twist in it. I don't know what your are doing wrong, the car I made is not marginal at all. The only thing I can think of is that if you don't want to be wrong, it is easier to fail. Don't feel bad, this is a common fault in the science world. I have shown the car to many people, they all thought it was impossible at first. They all changed their theory after they saw it in action. Once they under stood how it works, it seemed logical.

It looks like your experiment may have proved my hypothesis that the cart was designed to go up wind.

But to really reperform the experiment you need to be in Chessapeake.

Neat machine.


Guy

Edited by author 05-21-2007 06:42 PM
One of the things that I find really interesting about this discussion is that not a single poster here yet has attempted to validate/duplicate Mr. Goodman's results. We are talking about an incredibly simple machine, equipment, and testing.

Since I love science projects I took advantage of one of my bouts with insomnia and ventured out to my workshop and in just a couple short hours I built myself this:

http://i167.photobucket.com/albums/u123/DarwinAward/CartView4.jpg
http://i167.photobucket.com/albums/u123/DarwinAward/CartView3.jpg

It is a cart much like Mr. Goodman's. (Actually it is more like Mr. Bauer's - I will explain later). I scaled it down and specifically designed it for use on the treadmill. It is strictly the treadmill test that I am interested in duplicating the results. I did my very best to approach this objectively and build the best cart I could. If there is hole in my logic I want to learn it, know it and repair it. I did not set out to fail. If it is all possible that such a device will make forward progress on the treadmill then I intend to witness it for myself.

This system was built largely from off the shelf components that make up the working airframe of a remote controlled model helicopter. Every rotating component is supported by sealed bearings. From my experience, I already knew I could decrease some of the drag of the drive components by trading the belt design out for a design that uses a drive shaft. This design is clean and simple, there is no steering system needed since I only intend to run it on the treadmill. Furthermore, this design has a great advantage over Mr. Goodman's because it has completely variable pitch on the blades. This holds it more true to the original Bauer design and allows for a complete range of testing. This design also supports quick mounting and testing of several different blade styles and lengths I had on hand. I installed an RC receiver and only used one channel so the blade pitch could be adjusted in real time. With the adjustable pitch on the blades, it is possible to obtain a cart to propeller speed all the way from -9.5:1 down to 0 and all the way up to 11.4:1.

Initial construction was likely less than 4 hours since so many components were readily available. After some initial playing around with it on the treadmill, I took about an hour more to pull the cart apart and take all possible measures to minimize the friction in the system. The excess grease was spun out of the bearings, axles were trued up, and all blades were balanced. Once retested, the cart was for all practical purposes friction free and vibration free.

I also realized that in order to take good data points the complete test fixture would need to be fitted with guides to keep the cart centered on the treadmill and a method of measuring the force exerted by the cart. Simple guide rails were built to fit over the sides of the treadmill and a second guide rod mounted on the back of the cart that would push against the scale in order to take measurements. A piece of soft foam was placed on the scale platform to absorb any minor vibrations.

Here is a photo of the test setup with the guides and scale:
http://i167.photobucket.com/albums/u123/Da...CompleteTestBed.jpg

After some more testing, it was found that the pitch range was so extreme that the wheels could not maintain traction on the belt with the force required to spin the highly angled blades at the greater pitch ranges while on a 10mph treadmill. I turned off the treadmill and placed a large fan behind the cart. With a wind source behind the cart I could play with the blade pitch and find the exact point where the blades would start to spin backwards and the cart move backwards toward the fan. Since a design where the blades would spin the wrong way was impractical for the downwind application, I decided that this would be the upper limit of the pitch range testing. For the bottom of the pitch range, I simply selected 0 degrees. The RC transmitter was adjusted so the final cart to propeller speed range was limited to a more practical adjustable range from 0 through 5.0:1 in real-time by only changing the blade pitch.

After exhaustive testing on the treadmill, I did not see the results that Mr. Goodman has documented. The car would not make forward progress on the treadmill regardless of the blade pitch setting. Speeds all the way up to the upper 10mph limit of the treadmill were tested to no avail along with the full pitch range at every speed setting. Three different sets of blades and three different wheel sizes (to regear the system) in almost every combination with speed and pitch were tested as well. I also had a set of blades constructed in a similar fashion to Mr. Goodman's using balsa strips fanned out. I abandoned these as I found that they gave the least efficient results. Since all the airfoils I used likely have origins in some of the more popular airfoil design databases and Mr. Bauer appeared to have used standard airfoils I decided to stick with the mainstream.

BTW, here is a photo of the original Bauer Cart with Mr. Bauer:
http://i167.photobucket.com/albums/u123/Da...ward/bauer_cart.jpg

After quite a few hours of toying with the system (which is my kind of fun!) and trying all possibilities I pretty much have come to the conclusion that any increase in pitch or any increase in treadmill speed resulted in more force against the scale. Never at any time did the cart exhibit behavior indicating that it was getting lighter on the scale. There is some interesting behavior from -2 to +2 degrees of blade pitch where the blades exhibit nearly the same cross sectional drag yet their lift is varying. You can detect the point in the pitch curve where the blades are most efficient - but nowhere near efficient enough to "create" the energy required to move the cart forward. My final conclusion is that the best results were to simply remove the blades.

Here is a quick video of some testing highlights:
http://s167.photobucket.com/albums/u123/Da...w¤t=MyBauerCart.flv

Feel free to look over any photos of the device in my album:
http://s167.photobucket.com/albums/u123/DarwinAward/


--------------------------------------------------------- ----

So here is the challenge I present to anyone who wishes to continue the debate:

Simply prove it.

This situation demands verification of the results. No more debating. The trial phase of this case is over. All the arguments for/against this case have been heard.

If you believe it is possible then go build it and put it on the treadmill. Take good movies and post up the results. If you get it working then please help me get mine working (I'm not kidding or being sarcastic). This machine is dead easy to build. No rocket science here. It's 50 bucks worth of parts and million dollars worth of education. You or someone you know has a treadmill. If not, your local health club has one and for some small bribe your buddy at the desk will let you use it.

Even if you don't believe it is possible give it a go anyway. You will have fun at it I promise. Almost any bearing, gear, belt, pulley, and shaft imaginable can be obtained online from http://www.sdp-si.com/. RC radio gear is easy to find at any online hobby shop. Dust of your video cameras and go for it.


I anxiously await the videos.

Over and out.

If you see something that is clearly a scam that is fooling people I suggest the honest thing is to say so. Jack knows there is another energy source, maybe its being towed, maybe it is rolling down hill, the possibilities are endless.

You will have to explain more about 1 & 2. How can there be some potential energy stored? What form is it in? How can energy be put into a propeller from the wind when the propeller is accelerating the air?

Academia is rolling on the floor laughing. There has been no rush of engineers to examine the possibility of lowering a fifth wheel from automobiles in order to utilise the energy available from the road rushing past and to feed it into the drive train in order to get better vehicle performance.


Guy

Don't be so condescending. I am sure that everyone in this conversation has the most honest of intentions to understand and learn. In this regard, you shouldn't call Jack's machine "a scam". Why would any person go to these lengths to fool a small number of people for no money or fame? If Jack's machine does not work as he claims, it must be for a reason that deludes even a convinced, skilled engineer.

Yet the burden is to prove the theory, not to disprove it.

Guy says "propellers give out less energy in thrust than they take to drive". There is no reason to reiterate it, we all agree on that. I see two possibilities:

1) there is potential energy built up when vehicle approaches wind speed. Release of such energy could temporarily overcome wind speed, but could not be sustained.

2) There is energy input at v _vehicle >= v _wind. An earlier poster (Caspian, way back) suggested that there is weak energy input on the propeller from the wind even at this condition (i.e. the rotor works mostly as a propeller but in small part as a wind mill). I can't see any other
possibility of energy input here.

Where does academia stand in all this?

Edited by author 05-19-2007 07:07 AM
Your hypothesis appears to be that because some things that you don't understand do work then anything you don’t understand will work.

There is only one simple thing that needs considering, the rest is obfuscation. The propeller drag on the wheel tends to slow the cart, the thrust of the propeller tends to accelerate it. Whichever is bigger will decide whether the propeller makes the cart go faster or slower.

There is nothing counter intuitive about it at all. It is just a mechanism that clearly cant work because we all know that propellers give out less energy in thrust than they take to drive.

If you seek the truth you will learn, if you seek to prove you have nothing to learn you will make a fool of yourself.

Guy

It's not what's happening in the device. I realize you think it is. It isn't.

Lots of things are blindingly simple and obvious. The earth is flat. There is no such number as zero. If someone is in a position of authority, they're always right. The moon and the sun are about the same size. A substance can be subdivided indefinitely and will always remain the same substance. Republicans are fiscally responsible.

Man will never fly. I mean, duh. We're heavier than the air. You want me to do the math? It's blindingly simple and obviously can't work. I can prove, mathematically, that humans are heavier than air. Q.E.D. Plane tickets are, therefore, a scam.

The energy is available. There is no logical, physical reason why it would of necessity take more energy to move a vehicle like this than is available in the wind. It doesn't break any laws of physics; it's just counterintuitive. The force drawn from the wind is dependent mostly on speed and surface area and shape. The force holding the machine back is dependent mostly on mass and friction. A clever person could find a way to balance these quantities to get the result they want. At least two clever people have.

You're right about this: once the machine is moving at the wind speed, there is no available wind energy. There is, however, "ground energy", in the form of cement moving by. Also, and you seem to have missed this entirely, the blades of the propeller are never, ever moving at wind speed, in the system, as described. They are always moving faster.

I understand the relativity of velocity vectors, thank you very much. And if Jack was asking for money, I would have been just as skeptical as I was when all this came to my attention: very. And I almost certainly would not have sent him any money regardless, because I always assume that someone on the internet who wants money is running a scam, although I may have spent some on stuff at the hardware store to try this out for myself. Because that's what researchers do: they find things out, and sometimes they have to spend to do it. If you think you've spent nothing working on this problem, you're misestimating the value of your time -- grossly.

There are some problems which are just hard to grasp. Some are so hard they may actually be impossible to understand. Quantum mechanics. Extremely distant history. Human behavior. Some are just counterintuitive, and if you work with them long enough you get them. Try working with this one some more. I suggest you build one of these for yourself.

Zafner,

It is exactly what is happening in the device. If it goes faster because of the propeller then the trust from the propeller must be greater than the load the propeller puts on the wheel.

It is blindingly simple and obviously cant work.

In any event, if you ignore that issue, once the machine is moving at the wind speed there is no wind energy! Speed is relativistic. When you see a windless day it doesn’t mean the air isn’t moving, its just moving at the same speed as you.

Youre lucky Jack hadn't worked out a way of getting money out of you with his scam!

Guy

In fact, looked at that way, the machine itself implies the exact opposite, that the amount of energy available in wind moving at a certain speed is more than that required to move some device at a greater speed.

"If you can explain to me how you get more energy out of a propeller in thrust than you put into it as drive, maybe I will get my glider to stay up permanently."

No one has suggested that this is possible or what is happening in this device.

I appreciate living on a boat, last year was exceptional, I had 4 weeks continuous on mine and I was beginning to chill but unfortunately having an employer to satisfy as well means I’ve only squeezed one weekend so far this year.

But this weekend is gliding for me. If you can explain to me how you get more energy out of a propeller in thrust than you put into it as drive, maybe I will get my glider to stay up permanently.

The car goes into the wind just fine with the proper gearing(no suprise). It goes down wind even better. Instead of trying to prove why it can't go down wind try thinking out of the box. It goes faster than the wind down wind whether it fits your current theory or not. I havent been able to explain it to you, I will be glad to prove it. Since I live on a boat it is a little harder to demonstrate it. Just let me know when you will be in the chessapeake area.

However low the friction, it will never go faster than the wind. You will never get the thrust out of the propellor to be greater than the load the propellor puts on the wheel.

But get the gearing really high (many turns of the propellor for few turns of the wheel) and it will go direct into wind, which I think would be cool.


Guy

The propeller is made of butternut wood, but only because it was laying around. You take strips of wood and fan them out like a deck of cards. If the spacing between the strips is right, the twist and profile will automatically be correct. There is an article in AYRS on how to do this.

Hey, how did you build the prop? Is it made of balsa? What?

When I built the car, I had no idea of how marginal it would be. So it was designed with all ball or roller bearings, and a very efficient propeller. The car will roll down a 1 inch in a 12 foot incline, my garage floor. As it turns out, there is energy to burn. I believe it will go twice windspeed in perfect conditions. The biggest problem is wind sheer. There is almost no wind six inches off the ground, and I could not find a longer timing belt. This limits the hight of the propeller, and means the lower half is in less wind than the top half. Even though I was reasonably certain it wouldwork, it was still a shock to see it roll the wrong way up the treadmill.

No, I built it to go straight down wind, because that is the direction most people have trouble with.

Its looks like a well built cart Jack.

Tell me, did you really build it to go straight up wind?

Guy

Guy
   You did a great job of describing how the wind car works. That is the first good explanation I have seen.

Fredrik

I don’t understand the question.

The wind direction or speed has no significant impact on the propeller (other than a small and irrelevant change in the angle of attack). It is just a propeller being driven in air. It is not a turbine being driven by the wind.


Guy

That last one was a reply to Zafner, suddenly there are more messages in here!

You appear to be mesmerized by the idea that the lift from a wing can be greater than the force driving it forwards. But this principle occurs everywhere in our daily lives; it is not some mysterious capability of wings. The same is true of levers, pulleys, hydraulics, gearboxes, inclined planes and so on. It is very simple stuff and is called mechanical advantage.

I am afraid this is an extremely simple issue, there is nothing complicated about the cart.

Transforming a force to a greater force is easy, you can get whatever force you want from any other force but in all cases an increase in force has to be matched by an identical proportional decrease in the distance moved because the total energy has to remain the same (ignoring frictional and efficiency losses). In Jack’s cart the energy in and the energy out operate over the same distance, the distance the cart travels.

Forget aircraft and wings for a moment, think of pushing a vehicle up an inclined plane. In order to push a car up an infinitesimally small slope does not requires you to push at the total weight of the car even though you are accelerating it upwards. I cannot lift my car but I can push it up a slight slope. There is no wing involved.

An aircraft with the engine turned off can be considered to be sliding down an inclined plane. The Cessna example will, without the engine going, glide at a 13% glide slope. It is just like a car rolling down a 13% slope, the maximum speed will be achieved when the total drag = weight x 13%. The slope gives a mechanical advantage of 13%.

If you want to make the Cessna fly level rather than descend the 13% slope you need to add enough power to counteract gravity at a mechanical advantage of 13% i.e. the force needs to be 13% of the weight.

Look at it from the point of view of energy. With the engine off, for every 100 metres the Cessna moves forwards it will descend 13 metres. Therefore the energy the engine must generate vertically in order to counteract this is the weight x 13 metres (because the work done = force x distanced moved = energy). But the thrust is delivered in the horizontal component over 100 metres so the energy is the thrust x 100 metres.

Therefore the thrust needed x 100 = weight of aircraft x 13

The thrust = weight x 13/100


But remember, this energy is needed to be input to the Cessna in order to keep it going at constant speed and constant height. It is all lost energy due to the aerodynamic inefficiencies.

Turn it through 90 degrees and Jacks cart will also have aerodynamic inefficiencies and will need (say) 13% energy to be added in order for energy conservation to be maintained. That energy comes from the difference between the force at the road needed to drive the propeller and the thrust from the propeller multiplied by the distance the cart moves. Its effect is to slow the cart down.

Guy

Concerning ThePhysicsPolice example,

imagine two treadmills, one with a rough belt
(high friction drag) and a fine belt (low friction drag).
In both examples, the vehicle is at steady state
at wind speed. In both examples, the force produced to
overcome friction drag is different, but the force needed
to lift the cart is the same. This way, the friction
of the belt is building up potential energy, which
is released when the gear shifts to propeller. How much
depends on the roughness of the belt. If the belt is
frictionless, a net force gain is certainly impossible.
Am I wrong?

But I am more concerned what happens next. Energy
dissipates, new must come in.

Oops, a mishap,

dE/dv should be dE/dt, where E=E(v).

Guy,

Do you mean that regardless of propeller shape,
this inequality always holds?

dE/dv < 0 for v < 0

where E is kinetic energy (the rotational component*)
of the propeller and v is
relative wind speed? Or, in plain English, will
the rotation of a propeller (idealized with
no friction on the rotor) always be retarded by
upwind, in any circumstance? If you can convince
me of that, I would agree with you.

* I am not concerned about the moving cart here,
and not the drag, only how propeller rotation is
affected by wind.

Edited by author 04-24-2007 02:58 AM
Ok, one more time Zafner. If you are pushing the plane forward with 130lb of thrust at a cruising speed of 80mph (117.33 ft/s) you are expending 15,840 ft-lb/s of energy in order to maintain your altitude and forward speed - enough energy to lift 6.5 Cessnas given the proper efficiency.

If the cart is on the treadmill at a steady state speed of 4mph and it is not moving forward or backwards then the forces are balanced. This means that 100% of the energy consumed at the wheels of the machine is being converted to thrust in order to balance the forces.

Mankind has yet to invent a machine simple or complex that outputs 100% of the energy it consumes. The propeller is the most blatant example of waste in this system.

If the treadmill is running at 4mph which is 1.78816 meters per second and it requires 92 grams to drive the wheels at that speed then the wheels are appllying 164.5 gram meters per second (expressed as g•m/s) of drag on the belt. In order for the forces to be balanced, the propeller MUST be outputting 164.5 g•m/s of thrust. Therefore you are claiming that the machine outputs 100% of the energy it consumes. Given that the propeller efficiency is much less than 100% then this cannot work.

I challenge you to show me the exact math where I am wrong.

Tell me, Is it:

A. The wheels are not applying 164.5 g•m/s of drag on the belt
B. The propeller is not producing 164.5 g•m/s of thrust
C. The propeller is more than 100% efficient.

For the machine to stationary on the belt at 4mph both A & B have to be true. If you believe it is C then I can steer you to the proper research on propeller efficiency studies.

So I have reduced it to the simplest possible question. Is it A, B, or C?

I await your answer.

Guy, I don't understand how _you_ can continually misrepresent this as some sort of overunity-energy idea. The Cessna prop's 130 lbs of thrust is a lot less than the weight of the aircraft. There's no over-unity hocus pocus because we're not transforming some energy into a greater amount of energy; we're transforming some force into a greater force. There is simply no efficiency problem there. Once again, you're confusing force with energy. When the machine reaches a steady speed, the forces are balanced.

Leaving gravity out of the Cessna's straight-and-level flight, there's a tremendous extra lift force component directed upwards. The propeller on Jack's machine is not working against gravity because it's sitting on the ground, so really all that's happening is that we're rotating the output force ninety degrees. If the Cessna were released from gravity it would accelerate upwards at one g immediately.

Oh come on Jack, you repeatedly misrepresent a very simple bit of physics.

The 130 lbs thrust of the Cessna is all lost energy, it is a measure of the inefficiency of the system and it is the reverse of your representation of it as some form of energy multiplier.

If the aerodynamic efficiency of your propeller were to be the same as that of the Cessna then the thrust out of it would only utilise 87% of the energy put in to it. Therefore it would be LESS than the drag the propeller causes on the wheels and therefore the net effect would be to slow the vehicle and not to accelerate it.

Fundamentally there is no energy needed to keep anything at a constant height and speed. My laptop will not sink through the table when I turn it off.

Unfortunately we have not yet found a means of aerodynamic flight that is 100% efficient (lighter than air machines are) and so energy is lost. Of course we are getting better at it and thus aircraft need less power and gliders go longer distances in zero air movement but the best that we could ever achieve is 100% efficient. When we find how to do that, and you build it into your cart, then the thrust from the propeller will represent 100% of the power put into the propeller. Unfortunately, even when that happens, it will still slow the cart down because of the frictional losses in the drive mechanism between the wheels and the propeller.

Have a good sail, Ive done none yet this season, but the gliding has been good.

Guy

  I am in transit to Maryland on my catamaran sailboat. The wind car will be in Solomans Maryland in early June. I would be glad to show it to you if you will will report it on this site. Let me know when you can be there.
  You answered your own question. Your cesna engine only provides about 135 lbs of thrust at 50 HP. App 13& of the planes weight. This is all that is required to keep it in level flight.
  This applies to anyone.

Fredrik

[“I find the recent posts by ThePhysicsPolice and Guy more confusing than elucidating. Nothing new has come about. Zafner refutes them well.”]

You are right to be confused, you see a video of something impossible.

Maybe a helpful way of thinking of it is like this:-

If the propeller were to be disconnected from the wheels and be free to turn, then, from stationary, the wind would cause the prop to windmill in the opposite direction to that which it does in the video; the drag from this and the windage on the rest of the structure would cause the cart to accelerate.

As it accelerates so the relative wind speed decreases as so the force driving the cart decrease as it gets faster. Also as the speed increases so does the friction. These two effects eventually result in equilibrium at some point and the cart achieves a constant speed at something less than full wind speed.

We are being asked to believe is that if, instead, the propeller is connected to the wheels such that it turns against the wind then it will go faster and that the equilibrium point is faster than the wind speed.

But we know that the energy output as thrust by the propeller must be lsss than the energy input to the wheels to drive the propellor because of frictional loses in the system and the propeller being less than 100% efficient.

Therefore the addition force at the wheels (slowing) has to be more than the thrust of the propeller (accelerating) and so the equilibrium point is inevitably at a slower speed, not faster.

Personall, given the low windage on the rest of the structure, I think it would be dufficult to get it moving at all.

[“I still don't find an answer to my question, though: for the system to remain at a steady state (v _max > v _wind), some energy input has to counterbalance dissipation. And the only source of energy is the wind. How does the wind sustain propeller speed? Is it explainable, or an experimental finding?”]

It can’t.


Guy

"In order to have balanced forces in such a system the system cannot have ANY losses due to inefficiencies or friction".

Sure we agree on that. But at v = v _wind, the gear shift in Jack's machine may release potential energy, which could accelerate it at least temporarily. For it to be sustained, there must be some kind of energy input. How is the propeller speed affected by upwind?

Edited by author 04-19-2007 01:33 AM
[“The propeller is in stationary air and not moving at 4 mph, therefore you can not use gram meters per second.”]

Aw come on!! Output thrust from a propeller over time can be measured it foot pounds per second, inch ounces per second, newtons per second, SI units, and yes, even gram meters per second. I converted it to gram meters/second since you had units of MPH and crossed up with grams of force and any good engineer knows you don’t cross up your units.

[“Also , lift to drag is as I have explained it. If not they would call it distance to drop. It is not important, because the results are the same anyway.”]

No. Lift to drag is well defined and not as you have explained it. It is in inversely related to the steady state glide angle. You feel free to go argue with NASA: http://wright.nasa.gov/airplane/ldrat.html

[“I am sure the cessna company will be glad to hear that their aeroplanes are capable or straight up flight.”]

Only the way you describe it. You would claim that you could pick a propeller with an L/D ratio of 10:1 and put 150hp into it and get 1500 hp out. I know better than that. You are the one making that claim.

[“Actually if you take the lift to drag numbers you gave and calculate the horsepower using the force times the speed in feet per second, you will arrive at about 35 hp . Which is about what is required to keep it flat and level.”]

Hey.. Close enough. You say 35 I say 50. And my numbers are from actual charts – real data. The likely difference between yours and my numbers are because your calculation did not take the inefficiency of the propeller into the equation which happens to be about 70% at crusing speed. And that would put our numbers just about in agreement.

[“I have been in research for about 30 years. I have learned to look for a solution before I arguing something can't be done.”]

Same here. 30 years in research. And I would bet at least a dollar that you would be surprised on how deeply I have worked on this problem.

[“I find the recent posts by ThePhysicsPolice and Guy more confusing than elucidating.”]

Then let me lay it out even simpler: When the cart is on the treadmill running at 4mph and it is not moving either forward or backwards then the forces are BALANCED. Now if you have a problem understanding balanced forces please go Google it. In order to have balanced forces in such a system the system cannot have ANY losses due to inefficiencies or friction. Since no human is yet to invent a propeller that is 100% efficient then this is flat out impossible. Take the added friction of belts and wheels and pulleys into effect and this ship is sunk. I cannot lay it out any simpler than that.


Jack, I’ll leave this thread be. I will check back on this thread now and again to see if someone may be able to answer the rather simple questions I have posed. It is likely that I will be in Florida soon. I would really like to see that cart run on the treadmill.

I find the recent posts by ThePhysicsPolice and Guy more confusing than elucidating. Nothing new has come about. Zafner refutes them well.

I still don't find an answer to my question, though: for the system to remain at a steady state (v _max > v _wind), some energy input has to counterbalance dissipation. And the only source of energy is the wind. How does the wind sustain propeller speed? Is it explainable, or an experimental finding?

(unfortunately for me, Florida is literally half a world away. I really would love to see this for real, Jack)

  The propeller is in stationary air and not moving at 4 mph, therefore you can not use gram meters per second. Also , lift to drag is as I have explained it. If not they would call it distance to drop. It is not important, because the results are the same anyway.
  I am sure the cessna company will be glad to hear that their aeroplanes are capable or straight up flight. Actually if you take the lift to drag numbers you gave and calculate the horsepower using the force times the speed in feet per second, you will arrive at about 35 hp. Which is about what is required to keep it flat and level. I have been in research for about 30 years. I have learned to look for a solution before I arguing something can't be done.

Edited by author 04-18-2007 05:53 PM
Ok Jack. Let us use your exact numbers.

If the treadmill is running at 4mph and it requires 92 grams to drive the wheels at that speed (you really like crossing up your units there!) and the cart is perfectly stationary therefore the forces are balanced then you are expending 164.5 gram meters per second (expressed as g•m/s). Therefore the propeller is outputting 164.5 g•m/s so the forces are balanced. I knew we would end up in the metric system dammit! :)

So let me now restate the question using your exact numbers:

Considering that at BEST your propeller is only 85% efficient (one of my numbers), in order for the propeller to expend 164.5 g•m/s we have to be expending 193.54 g•m/s into shaft of the propeller. But we know that the treadmill is applying only 164.5 g•m/s to the wheels, the wheels are applying 164.5 g•m/s to the axle, the axle is applying 164.5 g•m/s to the belt and the belt is in turn applying only 164.5 g•m/s to the propeller shaft.

So where is that extra 29.03 g•m/s of energy coming from?

   The wheels are moving at 4 mph, and require 92 grams of force. The propeller is in still air, not moving air, and is not generating motion, only enough lift to stay in one place. That is why it does not have to be 100% efficient. To go back to the airplane example. A 1300 lb plane does not require 1300 lbs of thrust to push it forward.
   I would gladly take anyone up on the ballon test. Just make it worth my setting it up.
   I did this experiment to settle an argument. If I had known it would interest so many people I would have made better movies. I do have a video of the car on a tread mill, I just don't know how to get it to anyone. And yes, iceboats really do go faster than the wind tacking down wind.

Hi Zafner

“I can't disprove it off the top of my head except to say that if the force isn't enough to move a load it doesn't move at all, so both ends of the lever don't move at all, so they move the same distance, and yet what we have is still the same set of four forces (lever vs. you, you vs. lever, lever vs. load, load vs. lever), with the ones on the other end of the lever from you being greater. So for the special case of zero movement it's certainly not true. I think it's just a ratio, which would still work at zero.”

Your hypothesis appears to be that Jack’s machine multiplies the energy put into it but only in the special case when that energy is zero?

If I hadn’t got to know you better I might think you were taking the piss! ;-)

The formula for a lever is very simple

Force x distance moved at the long end = force x distance moved at the short end

The formula holds true with zeros in it.

(Force x distance moved = work done = energy)


“But wait: maybe the force on the wheels is greater, so the prop actually has less force, and so moves a longer distance!”

Entirely plausible (as long as you can continue to deliver the drive to the propeller) but Jack sensibly prevents this happening by designing a structure that keeps the distance between the propeller and the wheels constant.


“I was really just trying to say in a roundabout way that people keep comparing energy and forces, when this is not valid.”

I hadn’t noticed that, but, of course, if the distance traveled is the same the force will be the same for constant energy.

“I think the problem with your analysis of the sixteenth is that you failed to take into account the wind.”

I did not consider the wind to be part of the mechanism of transferring energy from the wheels to the propeller. Please suggest modifications to my analysis to adequately include the wind effects.


A question – If you saw Jack’s machine stationary on the ground, which direction would you expect it to travel if a wind were to blow on the propeller from the direction is does in the video? Why?

Guy

Hi Zaphner. Thanks for the responses! I will try harder not to insult anyone :).

I had a full list of responses to your responses and finally decided that was just too much clutter (and maybe to blunt again). So I threw them out. I would like to lay this out from a different angle and show you where I see it from. At the end I have only one simple question.

Earlier you had said:
[No. Power, like energy, is not equivalent to force. What he's claiming here is that he has a machine that takes a force, the force required to turn the wheels, and magnifies it through the machine, so that the resultant opposing force is greater, and the machine, therefore, moves. This is not impossible. It's what all sailboats do, and levers as well.]

When Mr. Goodman stated “'At 4 mph the measured lift of the propeller is 92 grams and the force required to turn the wheels at that speed is 92 grams, for a L/D of 1 to 1.” This automatically leveled the velocity quantities – The belt was moving 4mph to the right and the cart was moving 4mph to the left. You can compare the force quantities all day given that the velocity vectors are equal.

So to remove confusion, let’s talk in terms of ft•lb/s from now on - unless you are really into the metric system. That is nice and clean since 10 pounds moved one foot in one second is the same as 1 foot moved 10 feet in one second. It represents all the vectors wee need and applies to torque loads as well. Case in point: the lever you guys were talking about. If I have a lever that is 2:1 and apply 5 pounds of energy to the handle and move it 2 feet in one second and the output side will move 1 foot with 10 pounds of force in one second – 10 ft•lb/s of energy in and 10 ft•lb/s of energy out.
 
Now... earlier you stated:

[“A force in one location does not imply the exact opposite force in another _given_ location, or even that all forces in a system equal one another. If they don't, the system moves.”]

This is dead on the money. Let’s lock on to that. Unbalanced forces result either in stress or motion which can be measured.

OK, as I promised, here it is from a slightly different angle:

We have a really long treadmill in a really long windless hallway. It is traveling 4mph to the east.

For the initial condition, we are standing on the belt holding our trusty Bauer cart beside us – all of us traveling 4mph to the east.
We release our cart. It is pointed west. It begins to move. As time passes, it achieves a steady state. From a third party observer standpoint (not on the treadmill), the cart now appears to be standing dead still.

So now, the forces are balanced. The forces driving the cart to the east are balanced with the forces driving the cart to the west. Let’s throw out a number. Let’s say that the treadmill is expending 10 ft•lb/s of energy driving the cart east. Since the forces are balanced, the propeller on the cart is expending 10 ft•lb/s of energy driving the cart west.

Now, from our earlier discussions, we agreed that it is impossible to have a propeller that is 100% efficient. Even in the best of cases, an 85% efficient propeller is a dream come true. We won’t even worry about any other inefficiencies or friction components.

So, for the 85% efficient propeller to expend 10 ft•lb/s we have to be expending 11.76 ft•lb/s into shaft of the propeller. But we know that the treadmill is applying 10 ft•lb/s to the wheels, the wheels are applying 10 ft•lb/s to the axle, the axle is applying 10 ft•lb/s to the belt the belt is in turn applying 10 ft•lb/s to the propeller shaft.

So now for that magic question: Where is that extra 1.76 ft•lb/s of energy coming from?

"But, in order for a lever (or anything other form of mechanical advantage) to increase a force the increased force must act over a shorter distance. As the vehicle only moves one distance (it doesn’t fall apart) it can not be happening here."

First off, technically I don't think this is always true. I can't disprove it off the top of my head except to say that if the force isn't enough to move a load it doesn't move at all, so both ends of the lever don't move at all, so they move the same distance, and yet what we have is still the same set of four forces (lever vs. you, you vs. lever, lever vs. load, load vs. lever), with the ones on the other end of the lever from you being greater. So for the special case of zero movement it's certainly not true. I think it's just a ratio, which would still work at zero.

Secondly, the load force corresponding to the force coming from the wheels isn't the force on the prop -- it's the force on the air. The _opposing_ force to that force is the force on the prop, pushing the machine. So maybe if what you said above is broadly true but not for the special case of zero then the answer to your question is that the distance moved by the air is less, but the force is greater. Although I'm not sure about that.

But wait: maybe the force on the wheels is greater, so the prop actually has less force, and so moves a longer distance! I just thought of that. It works with the lever analogy though, and certainly with the energy densities of the two mediums. Have to think about it. I'm sorry, but the lever analogy just occured to me and I haven't really had time to consider it.

"No energy has entered the system, energy has left the system. The glider is now 1m lower and at same speed therefore less total energy. L/D is a measure of the inefficiency of the system."

Yes, I'm sorry, I should have said "How much energy has been _expended_?" I actually realized that after the post.

The glider has stored energy in the form of altitude. It expends enough altitude to move it down one meter. The energy from moving the glider down one meter is enough to overcome drag for thirty meters. I was really just trying to say in a roundabout way that people keep comparing energy and forces, when this is not valid.

I think the problem with your analysis of the sixteenth is that you failed to take into account the wind.

“What he's claiming here is that he has a machine that takes a force, the force required to turn the wheels, and magnifies it through the machine, so that the resultant opposing force is greater, and the machine, therefore, moves. This is not impossible. It's what all sailboats do, and levers as well.”

But, in order for a lever (or anything other form of mechanical advantage) to increase a force the increased force must act over a shorter distance. As the vehicle only moves one distance (it doesn’t fall apart) it can not be happening here.

Guy

Re Glider question:

No energy has entered the system, energy has left the system. The glider is now 1m lower and at same speed therefore less total energy. L/D is a measure of the inefficiency of the system.

Force to hold glider in air (at constant speed) = glider weight

On the second post, we are talking energy not forces. Forces can be whatever you want (that’s how a lever works) but energy has to be conserved.

Can you explain how my analysis (16th April) can be improved?

Guy

Crap. I sent that before it was finished.

Anyway:

"Nevertheless, the challenge still stands for anyone: sailboat, land yacht, iceboat, or wind boarder to release a balloon into the wind and recapture it or pass beneath it. This challenge has yet to be accepted, accomplished and documented in any fashion. If it were indeed possible, this debate would be over."
I have never heard of this challenge of which you speak. I've never even asked Google about it. So, assuming you're not just using this as an illustration and it is indeed a real challenge someone is offering prize money for, perhaps it's not as well known as you think. I'm just a kiteboarding stack tester, not a yachtsman.

"'At 4 mph the measured lift of the propeller is 92 grams and the force required to turn the wheels at that speed is 92 grams, for a L/D of 1 to 1. By ten mph the lift of the propeller is 552 grams and the force required to turn the wheels at that speed is 402 grams, for a L/D of 1.37 to 1.'
And so by making this statement you have claimed to have developed a machine that produces power in excess of the power required to run it."
No. Power, like energy, is not equivalent to force. What he's claiming here is that he has a machine that takes a force, the force required to turn the wheels, and magnifies it through the machine, so that the resultant opposing force is greater, and the machine, therefore, moves. This is not impossible. It's what all sailboats do, and levers as well.

ThePhysicsPolice:

Also I'd like to point out a couple of things in your post.

"#1 'The lift from a helicopter rotor is more than the energy required to turn it.' This is absolutely incorrect."
Actually, it's not just incorrect; out of context it's nonsensical. A force is neither greater nor less than a quantity of energy. Energy and force are not equivalent quantities. The energy from the propeller which does work on the aircraft is less than the energy which goes into the propeller, yes; but see below.

"You get less energy out of a propeller than you put in."
The same could be said for all mechanical devices. However, in this instance, it's irrelevant, because we're not talking about energy. We're talking about forces. A force in one location does not imply the exact opposite force in another _given_ location, or even that all forces in a system equal one another. If they don't, the system moves. While forces do come in pairs, as they propagate through a system, they can change wildly in magnitude. This causes no problems with energy losses through the system, violations of thermodynamics, etc. Case in point: a lever.

Furthermore, we all know that you can't get more energy out of a system than you put into it. We don't need you to tell us that. If you did read all the posts, you caught quite a few snide remarks about perpetual motion. We get it: perpetual motion is impossible. Thanks. We actually had that already. All the world's problems solved if that were the case, chuckle chuckle, let's move on. I appreciate that you're trying not to insult us. Try harder.

"If you applied the full 180 horsepower required to take off a 1300lb (Max Gross) Robinson R-22 helicopter 1 foot in the air to an overhead crane instead, you could easily lift 76 of those same helicopters 1 foot high."
Don't lift the helicopter: just suspend it at one foot and leave it there. Now the energy required by the engine is some number, but the energy required by the crane is zero: you just lock it in place with a brake of some kind. So the ratio you're talking about here becomes, instead, some finite number to infinity. In other words, it's a nonsensical quantity.

Now, rotate the system on its side, and put wheels on it. The crane isn't moving the machine at all, but without gravity the prop is accelerating the machine. The whole analogy breaks down.

We're not talking about energy. We're talking about forces.

"Again, Incorrect. At wind speed the cart is sitting as if in a room with no wind."
Incorrect. At wind speed the cart is sitting as if in a room _on a moving treadmill_ with no wind. This is a vital point.

"#3 'L/D of 50 to 1 means that a glider that weighs 500 pounds only requires 10 pounds of forward force to keep it from loosing altitude.'
Much like #1, this is a misuse/misunderstanding of the true meaning of the L/D ratio."
Actually this is a perfectly valid interpretation of the lift to drag ratio. Like many physical laws, the meaning of the L/D ratio can be expressed in several ways, all of which are equivalent and imply each other.

As to your discussion of iceboats, I invite you to look at these two sites:

http://www.nalsa.org/Articles/Cetus/Iceboa...rformance-Cetus.pdf
http://www.time.com/time/magazine/article/0,9171,870822,00.html

... and also talk to an iceboater. Iceboats do go downwind faster than the actual windspeed at angles close to windspeed. There's a vector diagram on the first site that makes it pretty clear. Sorry it's a pdf.

"That is completely possible and easy to understand - but that analogy is too dissimilar to what is discussed here. The cart, which now travels through the air is powered by a third external force - the ceiling. For the analogy to be more accurate, the ceiling and the floor would have to touch (no atmosphere) and the cart would have to bore it's way through the ceiling like a mole while it was traveling faster than the ceiling. Good luck."
So put the room under a vacuum. With no air in the room, you're back to the same issue, with no boring of the ceiling necessary. Not that it matters. What you're talking about here is of negligible effect; with no structure to specifically garner force from it the air is hardly an important part of the analogy.

Say a glider with a 30:1 glide ratio moves forward thirty meters and down one.

How much energy has entered the system in that time?

How much force was necessary to support the glider in the air?

Edited by author 04-17-2007 03:54 PM
OK spamcan driver, you think you can come in here and spoil our fun?

I detect a weak spot in your appreciation.

Do you think (in a zero friction environment) that a sailing vessel (let’s call it an iceboat) can, in a straight line, have a VMG greater than the wind speed?

Please provide your workings.

Guy

You are hereby ordered to cease and desist! Just kidding....
Bear in mind that I have now caught up and have indeed read every post on this topic. There are certainly some very intelligent people commenting here - some quite passionately, most everyone very gentlemanly. So let me say beforehand that it is not my intention to insult anyone here. I do enjoy a good debate.

I seem to stumble across this argument (DWFTTW) quite often. Each time I do the supporters of DWFTTW all make very similar statements from which they build their theories upon - some of which I believe to be very misleading or incorrect. I would like to discuss them:

#1 "The lift from a helicopter rotor is more than the energy required to turn it."
This is absolutely incorrect. If you applied the full 180 horsepower required to take off a 1300lb (Max Gross) Robinson R-22 helicopter 1 foot in the air to an overhead crane instead, you could easily lift 76 of those same helicopters 1 foot high.

1 horsepower = 550 ft·lbf/s. Anyone can do the math.

I will put it to you this way: The finest athlete when placed in a human powered helicopter weighing 77 pounds can barely bring it up 30cm off the floor for 20 seconds in an all out sprint. That same athlete could easily put 77 pounds on his/her back and climb several flights of stairs in 20 seconds. If you believe me to be wrong then the Sikorsky prize is certainly yours for the taking.

Remember: Propeller efficiency is ALWAYS LESS THAN 100%. You get less energy out of a propeller than you put in. Google "Propeller Efficiency Charts" and you won't make that mistake again.


#2 "Once at wind speed, from the cart's point of view, there is no wind! The wheels are spinning, and thus turning the prop, which is now making almost no thrust or drag because it's almost completely slicing through the air."

Again, Incorrect. At wind speed the cart is sitting as if in a room with no wind. Just like a fan placed in a room with no wind, it takes horsepower to spin the fan blades. When I turn on a fan in my house, the wattmeter outside certainly reflects the fact that it takes substantial power to spin it in still air.


#3 "L/D of 50 to 1 means that a glider that weighs 500 pounds only requires 10 pounds of forward force to keep it from loosing altitude."

Much like #1, this is a misuse/misunderstanding of the true meaning of the L/D ratio. Forces are vector quantities having both a magnitude and a direction. The L/D ratio is representative (inversely proportional) of the steady state glide angle ratio of a given design. It is a statement of LOSS. It is NOT a statement of GAIN. There is no GAIN in an airfoil system. An L/D of 50:1 means that at a steady state glide, you loose 1 foot of altitude for every 50 feet of travel. If you wish to bring forces into play you must consider velocities and distances.

Let's talk real world numbers here to put it in perspective: If I'm cruising along in my 2400lb Cessna 172 at 82.8mph(121.5 ft/s) which has an L/D ratio of 10.75 under these conditions my throttle would be set to about 50hp. This means I am expending 27,500 ftlb/s of energy. Apply 27,500 ftlb/s of energy using a crane and you could lift 10 of those aircraft one foot off the floor in a second. There is loss in the "wings" of the propeller and again loss in the airfoil of the Cessna itself - NOT GAIN.

Once again, I urge anyone believing that the L/D ratio is a statement of system GAIN to Google "Propeller Efficiency Charts" to better educate yourself on it.

#4 "Iceboats do indeed go faster than the wind downwind. We are talking VMG here. The iceboat speed is much higher than the wind speed. This is not a debatable question, talk to any ice boater."

This is indeed a debatable question. At oblique angles upwind iceboats can certainly achieve incredible speeds and as they tack and their inertia can continue to carry them at higher VMG downwind briefly but then as they continue to tack back to best forward velocity their VMG downwind falls well below wind speed and the overall end result is a lower than VMG downwind. Argue it as you may these boasts of iceboats exceeding VMG downwind almost always EXCLUSIVELY appear in the DWFTTW debate. Ask any good yachtsman, land or water and he will tell you that is what a spinnaker is used for - sailing downwind - don't bother tacking it is a waste of time and energy. Talk to an ice boater and they will tell you that they try not to waste a moment of their day sailing downwind - they are in it for raw ground speed so they sail almost exclusively upwind and tack upwind as well.

Nevertheless, the challenge still stands for anyone: sailboat, land yacht, iceboat, or wind boarder to release a balloon into the wind and recapture it or pass beneath it. This challenge has yet to be accepted, accomplished and documented in any fashion. If it were indeed possible, this debate would be over.

#5 "This is merely a problem of understanding the principles of complex motion. If you had a room with a stationary floor and a ceiling that moved, you could build a cart with wheels to ride against the floor and ceiling that would move faster than the ceiling by using the proper gearing between the wheels."

Yes. That is completely possible and easy to understand - but that analogy is too dissimilar to what is discussed here. The cart, which now travels through the air is powered by a third external force - the ceiling. For the analogy to be more accurate, the ceiling and the floor would have to touch (no atmosphere) and the cart would have to bore it's way through the ceiling like a mole while it was traveling faster than the ceiling. Good luck.


Mr. Goodman,

What I am interested in most is the video of your cart on a level treadmill set to a steady speed in a windless room. I am not commenting on the video of the cart on the road. Your claim (as the treadmill video demonstrates) is that the cart has the power to move forward on the treadmill once a steady state speed is achieved. I am in total agreement that in order to achieve DWFTTW the cart would indeed have to move forward on the level treadmill set to a steady state speed. In your write-up, you claim that the cart is able to perform this feat because:

"At 4 mph the measured lift of the propeller is 92 grams and the force required to turn the wheels at that speed is 92 grams, for a L/D of 1 to 1. By ten mph the lift of the propeller is 552 grams and the force required to turn the wheels at that speed is 402 grams, for a L/D of 1.37 to 1."

And so by making this statement you have claimed to have developed a machine that produces power in excess of the power required to run it.

I will claim that if that were true then all of the world's energy issues are solved. So this is where I claim that this is a hoax. It may be a non-intentional hoax where the experiment was not correctly conducted - i.e. the speed of the treadmill was slowing down and the stored energy in the spinning blades moved the cart forward. Whatever the case, I claim flat out that if I am correct about points #1 and #2 above then it is impossible for your machine to produce more power out than is required to run it. It simply violates the laws of physics. At a steady state speed, the cart requires a certain amount of energy to spin the propeller. That energy is the total of all the friction components and the drag of the propeller through the air. If you understand that mankind is yet to produce a propeller that exceeds 100% efficiency then it is obvious that the output of the machine will be LESS than the forces required to operate it and therefore WILL NOT move forward as demonstrated on the video.

My apologies for the long winded response - it took a lot of reading to catch up on this topic.

I am afraid I don’t understand what you mean by “lift component”.

Why is it that we have to use so much effort to think about this with a propeller in the system but if the mechanism were joining two wheels we would never imagine some net increase in drive?

From the comments in here some appear to think the wind is turning the propeller, but it is not, it is going in the other direction – i.e. against the wind. So, in order to move at all, (including at less than wind speed) the wind on the rest of the vehicle has to be enough to overcome the effect of the wind on the propeller. But there is very little else for the wind to act on. The conclusion has to be that if the wind were powering it then it would be going in the other direction. Maybe if it had a big spinnaker attached to the front it might move in the direction shown but that would rather spoil the illusion.

I would love to see a video of it going upwind.


Guy

the lift component removes the force component F from the wheels.

Noone has explained what is wrong with my analysis.

1. The propeller thrust requires energy. (let’s call it E)

2. That energy is equal to the thrust (T) multiplied by the distance (D) the vehicle moves in a unit of time. (E=TxD, therefore T=E/D)

3. The energy to turn the propeller comes from the wheels.

4. If we assume an impossibly 100% efficient propeller then the energy input to the propeller is equal to E.

5. If we assume no frictional losses in the system then the energy needed from the wheels is also equal to E.

6. The force (F) required to generate energy E at the wheels is the energy divided by the distance moved in unit time. (F=E/D).

7. From 2 above, thrust also T= E/D

8. Therefore the thrust from the propeller T and the force F on the wheels are equal but in the reverse direction and thus cancel out.

So you can have thrust produced by the propeller downwind but it results in an equal and opposite force at the wheels.

I am keen to develop my understanding if anyone can explain how this analysis can be improved.


Of course in real life the propeller is not 100% efficient and there are frictional losses and so the mechanism results in slowing the vehicle. I don’t know why the video appears to show something different.

Guy

Yes it is.

If you can show that thrust from the propeller can be sustained at downwind, there you go. Either the wind helps sustenance (as proven by Jack's experiment), or it doesn't.

Do you still think Jack is a fraud? Why?

When tacking down wind, ice boats have to coast thru the eye to get on the other tack. At wind speed there is no wind thru the eye. At higher than wind speed, the sail streams straight back while it coast thru.

No it's not.

It doesn't work irrespective of the detailed mechanics - i.e. even if you assume Thrust x Distance Moved = Power in.


Guy

Isn't the question all about the pressure difference over the propeller, and how the surrounding wind affects it? For the steady state at downwind to hold, incoming wind must compensate for inefficencies in the rotor to maintain this pressure difference. It ought to be possible to describe this pressure difference by fluid dynamics, albeit complex and tedious (I failed my fluid dynamics exam twice; it would take some effort for me).

However, If I remember correctly, an earlier posting claimed that even computational models of sailing boats fail to predict observations, so the idealized nature of a model may not be adequate. Any faculty in rotor aerodynamics out there?

How do ice boats cope with being in irons for some time when VMG is close to windspeed?

Guy

  The car does go upwind but only if the gearing is reversed so that the windmill has more leverage than the wheels. In this case the windmill does turn the wheels.
  Iceboats do indeed go faster than the wind downwind. We are talking VMG here. The iceboat speed is much higher than the windspeed. This is not a debateable question, talk to any iceboater.
  Apparently down wind is not quite as simple and easy to model as you think.

"What is the theoretical maximum speed up wind in a zero friction 100% efficiency environment?"

I guess that would be infinity. Why not?

I don't think I have ever said speed in = speed out.

I don't understand why anyone would question that a boat can sail faster than the wind. If it were impossible then gliders, parachutes, hang gliders etc. would have a maximum glide slope of 1:1. But we all know that they can go substantial multiples of this – i.e. faster horizontally than vertically.

It is just like an inclined plane - of course the horizontal speed vector (equivalent to 90 degrees to the wind) can be greater than the vertical vector (direction of the wind).

I hope I have said nothing that contradicts this. It just doesn’t apply if you are going down wind because as you increase the angle downwind so you decrease the relative wind speed, which is generating the vessels speed.

I would say that the maximum speed across the wind is infinity (at 90 degrees to the wind and in a zero friction environment) but the maximum possible downwind component is equal to wind speed in all circumstances.

Frankly I don’t understand all the debate about down wind because it is such a simple situation and very easy to model and understand.

I find the up wind prospect far more interesting.

What is the theoretical maximum speed up wind in a zero friction 100% efficiency environment?

Guy

Guy,

How does this analysis treat a sailboat or iceboat traveling across the wind at a far greater speed? The idea that "speed in=speed out" doesn't work.

Woody, I am afraid that I did not receive your diagrams so the second part of your explanation is not totally clear to me.

However the question remains - what maximum speed does this machine achieve?

The answer is that speed at which the forces pushing it forward are equal to the forces resisting that movement. At that point there is no resultant force and thus no acceleration or deceleration.

I am entirely happy to do this analysis in an imaginary world with no mechanical friction and 100% efficiencies.

In that world, can you describe these forces and explain why you believe they become equal at a vehicle speed that is above the wind speed?

Mechanical advantage is a two edged sword. Double the mechanical advantage does double the output speed but it also doubles the input force required. The power input and the work done are always the same. I suggest that however you contrive a more complex machine these two effects inevitably cancel out and the point of balance of forces occurs when the vehicle speed is equal to the wind speed.

You can achieve this with a simple balloon blowing along the ground or (in a friction free environment) a complex machine with wheels, levers and propellers. In all cases the overall external forces on the machine are the same and the end point is the same viz. max speed = wind speed.



Guy

If the propellor is extracting energy from the wind, why does it not turn the other way to start with - like a windmill (something that actually is taking energy from the wind)?

By the way I've changed my mind on one point, with adequate gearing, it will go upwind.

Guy

The propeller IS the energy input to the vehicle. The wheels turn it so that it can go fast enough to get energy out of the wind. If the propeller wasn't driven by the wheels it wouldn't go fast enough relative to the wind to create the force needed to go downwind.

Energy comes in through the propeller, which pushes the vehicle forward, driving the wheels, which in turn maintain the spin on the propeller. The energy ALL enters the system from the wind initially.

The propeller is not an energy input to the vehicle it is an energy output - it is driven by the wheels not by the wind. If the propellor were to be driven by the wind (energy input the vehicle) it would turn the other way and drive it backwards.

That doesn't happen because it would need the energy output to the wheels to be greater than the energy input to the propller but, just as the other way round, (without friction + 100% propellor efficiency) these two forces ballance.

The claimed job of the propellor is to drive the vehicle forwards. It can't make any difference if that job were to be done by wheels. The real job of the propellor is to confuse thinking, sometimes it does that job!



Guy

Edited by author 04-13-2007 12:29 AM
[...] <--My post here had a problem, working on it

"Why would it not work by removing the propeller and connect the propeller drive mechanism to another wheel? A wheel is a more efficient drive mechanism than a propeller."

(I'm going to assume this isn't a facetious question.)

Because that way there's no energy input to the system. Wind-powered devices work becuase they're at the interface between two media, the air and either the water or ground, which are in motion relative to each other. If you're at the interface and you leave it -- enter one medium, for example by jumping into the air -- there's nothing holding you back against that sole medium, so you start to move with it, which is why kiteboarders always go downwind when they do really big jumps.

You can cheat, of course. The wind is pushing you one way, but once you've ditched the surface you still have gravity pulling you at right angles to the wind, so theoretically you could tack using that. I've never seen it, though. You'd have to dive like crazy, and the more wind there is the harder it would be because there would be more to fight against, and the less wind there is the harder it would be because larger kites fly slower.

This system is about using forces. Neither energy nor mass can be created or destroyed, but forces come and go as they please. The only limit is that they're balanced, one against one or more or less others.

I agree that boats can have a greater VMG by tacking downwind than by a dead run. Whether or not the VMG can be greater than the wind speed is moot as far as I am concerned. (It looks extremely unlikely - wouldn't the boat be in irons as it passed through VMG=windspeed? - however I havent thought it through yet.)

I'm not sure I accept your spiral tack analogy, I think the propeller is rotating the wrong way.

Why would it not work by removing the propeller and connect the propeller drive mechanism to another wheel? A wheel is a more efficient drive mechanism than a propeller.

Guy

The fact is that it works. Step back and take another look at the problem. Everyone agrees that ice boats can exceed the speed of the wind by tacking down wind. Even by going a longer distance, their VMG (velocity made good) is still faster than the wind. The propeller blade is on one long spiral tack down wind.

Edited by author 04-11-2007 05:18 AM
Zafner said “Look, surely you can concede that a machine on relatively low-friction wheels can be made to go downwind fairly close to windspeed, right?”

Yes. In a zero friction world it would go downwind at the windspeed.

”Once that's happening, the propeller is producing thrust, as energy is being added to the device from the ground. Any drag on the prop blades adds to the wheel friction, and the total of these is what has to make the machine slow down at wind speed. Thrust from the prop will increase in an almost linear fashion as the machine speeds up (it will increase with the speed of the wheels), but there's no guarantee that these will have a direct relation to the thrust from the prop.”


No. The prop gets its total power from the wheels. If the zero friction world also had 100% efficient propellers then the thrust from the propeller would be absolutely equal to the drag from the wheels so the two forces completely cancel out and there would be no change to the speed.

Of course in the real world there is friction and propellers do not turn 100% of input power into thrust and so the addition of the propeller slows the vehicle down.

Guy

Fredrick

You are right that energy is a scalar. But kinetic energy is a little unusual as it is relativistic, there is no absolute zero. Once the vehicle is at windspeed there is no relative kinetic energy available.

I think that the law of physics that is being broken is the conservation of energy.

Guy

Guy,

energy does not have direction, kinetic or not. Machines
convert energy to force, in the desired direction.
There are no violations of physics. Only a problem of machine
design, which the video, and many explanations below,
show can be overcome.

Look, surely you can concede that a machine on relatively low-friction wheels can be made to go downwind fairly close to windspeed, right?

Once that's happening, the propeller is producing thrust, as energy is being added to the device from the ground. Any drag on the prop blades adds to the wheel friction, and the total of these is what has to make the machine slow down at wind speed. Thrust from the prop will increase in an almost linear fashion as the machine speeds up (it will increase with the speed of the wheels), but there's no guarantee that these will have a direct relation to the thrust from the prop.

So, once the machine has reached approximately wind speed, if the bearings are good enough, the thrust produced by the prop can overcome the aerodynamic drag of the whole machine, which is zero, plus the aerodynamic drag of the prop blades, which can be pretty low if you use good blades. Equilibrium speed is reached at some speed higher than wind velocity downwind, where you start to get aerodynamic drag from the machine, and increased friction resistance from the wheels, but /primarily/ drag from the prop, which have a very high apparent wind speed indeed.

Yes?

Jack - Lift is the resultant of a downwards thrust caused by accelerating air downwards, this does require energy.


Fredrik - If the vehicle moves faster than the wind the its "kenetic" energy realtive to the vehicle becomes negative and thus acts to slow the vehicle.


Guy

Since the surrounding wind is an (almost) eternal energy source, there are no system energy violations. It is only a problem of work, to redirect kinetic energy in your favour. To maintain steady state in DTWFTTW at v _max, the kinetic energy of the wind must be input in favour of the system, to counterbalance dissipation. Isn't it this equilibrium that determines
v _max?

The force to move an aeroplane (10 lbs. @ 100 mph) is energy, the lifting force created by a wing is only holding the airplane up, not raising it. So it is not energy, or ft lbs / seconds

Yes it does. It is a measure of the inefficiency of the glider. The 10 pounds force represents totally lost energy, the glider is neither faster nor higher as a result. If the glider were 100% efficient it would require zero force. No aerofoil, be it a wing or a propeller, can deliver more energy output in lift or thrust than is put in to it, unfortunately they all deliver less.

Guy

PS I wish the above were not true, I am about to go fly in my glider!

L/D of 50 to 1 means that a glider that weighs 500 pounds only requires 10 pounds of forward force to keep it from losing altitude.

The L/D of a propeller is not as high as that of an airplane wing. Plus the L/D I gave you for the car includes all the rolling and gearing losses. The thrust provided by an airplane engine to move the airplane foward is almost never as much as the lift provided by the wings. There are very few airplanes that can fly straight up for any length of time. Pushing an airplane wing forwards is the same as rotating a propeller. The lift provided by the propeller is more than required to turn it. All the propeller has to do is to generate enough lift to remain stationary in the air to go windspeed.

The total energy in put to a wing is equal to the total lift + total drag.
The lift to drag ratio is a measure of efficiency. A wing that is 100% efficient has an L/D of infinity.

The glide slope of a glider is equal to its L/D.

If a glider was 100% efficient the glide slope would be zero and the glider would never loose height. The most efficient gliders these days have L/Ds of over 50, a lot better than the efficiency you state for your system.
If all airplanes were to produce more lift than the force required to push them gliders would climb all the time and aircraft engines would only need to be used to get off the runway and then could be turned off!

Guy


< replied-to message removed by QT >

The thrust of the propeller is in fact more than the force required to turn it. All airplanes fly with more lifting force than are required to push them, this is called the lift to drag ratio. The measured lift to drag (including frictional losses) on my wind car, is 1.5 to 1 @ 10 mph. This was measured on a treadmill. The forces to roll the wheels and turn the propeller at 10 mph is 280 grams, while the force produced by the propeller is 420 grams. The peak L to T is 1.65 to 1 at 7.5 mph. At 4 mph the lift to drag is 1 to 1. I hopes this helps.

Great exposition.

The problem with it is that the analysis is only looking at one part of the system at one very special instant in time - that in which the radius of the currently operating sail is vertical. The rest of the time the sail is operating (and there must be some absolute period of time when each sail operates) the sails acts against the direction the wheel is turning giving rise to a force at the road that acts to slow the vehicle. When the wheel is travelling slower than the wind this force is less than the force generated by the sail and thus the wheel accelerates. However when the wheel is moving at the same speed as the wind the forces become equal and if the wheel is travelling faster than the wind the road force becomes greater than the sail force thus acting to decelerate the wheel. (All in a perfect world of 100% efficiencies and zero friction).

To look at the forces on Jacks machine

T = the thrust developed by the propeller
D = the total drag of the airflow past the vehicle (-ve when the relative airflow is in the direction of travel)
R = the force from the road surface

When the vehicle reaches its steady state speed there is no resultant force acting to accelerate or decelerate it and therefore

T = D + R

Now the force at the road has two elements

P = the power to turn the propeller (zero if the propeller were not connected to a wheel)
F = the friction in the system

R = P + F

Therefore

T = D + P + F

or, to rearrange

T - P = D + F

i.e. the thrust delivered by the propeller HAS to be greater than the power used to turn it!

In an impossibly perfect world where there is no friction F = 0

T - P = D

In the same impossibly perfect world where the propeller has 100% efficiency T = P.

So in the impossibly perfect world steady state speed occurs when

P - P = D

i.e. when D = zero. This only occurs when the vehicle is travelling at exactly the speed of the wind.

In an impossibly perfect world the max speed attained is equal to the speed of the wind.

Guy

In the frame of reference of the wheel, every point of the wheel orbits around the center.

In the frame of reference of the ground, a rolling wheel rotates about its point of contact on the ground. Every point on the wheel orbits about that POC but after a very short time, the wheel rolls onto a new POC and the rotations shifts to rotating about this new point.

The sail is mounted somehow on the wheel. I've made this diagram extremely simple, leaving out all such detail as how the sail is mounted, or what happens when the sail rotates up out of position.

The wind pushes on the sail. Let's say the wind is blowing ten knots. Let's say the sail gets pushed to the right at 8 knots. It will have to go a little slower than the wind, so that the wind will blow past it to exert pressure.

If the sail is moving right at 8 knots, then the contact point where the wheel meets the ground being stationary, the center of the wheel must be moving right at 16 knots. That's faster than the wind which is moving at 10 knots.

Of course, after a very short amount of rotation the situation changes, the sail rotates up out of position. I haven't shown any mechanism to fix this in my diagram, but we could imagine some scheme which folds up that sail and unfurls a new one in the bottom position so there's continually a sail at that same place.

With just a bit more transformation we can arrive at Jack's machine.

Okay, you lost me. What makes you think this would move at all, let alone downwind? Are there some kind of gears inside or something?

Could I suggest another way to look at this? Look at this picture a few seconds and then decide if DWFTTW is really theoretically impossible.
http://users.sisna.com/wwbrison/bigwheel.gif

Guy
Come to Florida, and I will give you a demonstration so you can see for yourself.

Which one? You ignored so many.

What an impressive and well reasoned argument.

Ha ha ... another guy who hasn't done any research at all, even as little as reading the previous posts.

Way to go, Guy! Why don't you explain to all us dummies what a perpetual motion device is! Won't that be original!

Hey guys, this is an obvious hoax.

Look at it this way; the road exerts a force on the cart in the opposite direction to its travel. That force is equal to the force causing the propeller to turn plus all the related frictional losses.

In order for the propeller to accelerate the cart into the wind the thrust from the propeller must be greater than the sum of the air drag plus the force from the road.

Therefore, in order to work, the thrust delivered by the propeller must be greater than the force turning it!

Look at it another way; wheels are a far more efficient means of propulsion than propellers. If we dump the propeller and connected its drive to another wheel the cart should go even faster!

Guy

Woody, I think you've got it. And yes, if you could remove all losses, there is no limit to the speed or direction. One would just change the gear ratio and the angle of the fan.

OK, here y' go
http://users.sisna.com/wwbrison/cbgir.htm

Yes, after more thought I'm fairly sure (more than 75%) I understand the physics behind how it can work. I've deleted that webpage and am working on a better one. Wood

I've found an interesting lemma that applies here. I might have to reverse my position.

Wood

Look, it's very simple. I suggest that rather than make condescending comments about how "we could do the math" you actually DO the math. Then you will see that the lift from the blades can easily be positive at windspeed, as long as the system moving energy from the wheels to the prop is efficient enough and so is the prop.

Why don't you just read the guy's PDF? It's all right there.

Incidentally, you are not the first person on this board to bring up the idea of a perpetual motion machine. Repeating that phrase over and over as if it had anything to do with a system in which energy is continually being added from the outside just shows that you didn't read the earlier comments. Please do so.

Or better yet, try the experiment yourself.

/m181
Now you are taking an apologetic stance, rather than improving your reasoning.

There is no system imbalance. No physical laws are violated. The cart is surrounded by an inexhaustible energy source. Machines (in this case the propeller) do work on systems: they take energy input and direct this energy. To do that and resist the wind is challenging, but totally viable. Your other example with pulleys should work as fine, if you can overcome the practical difficulties.

All you need to explain, with or without math, is that the wind sustains the propeller speed (or that it doesn't sustain, if you want to disprove Jack's machine). I don't know enough aerodynamics to show this, but I am sure that any faculty or student of aerodynamics could do a better explanation.

OK, thanks for the feedback. I've put better words next to figures 2 and 4 (along with some other minor changes). Again, that's

http://users.sisna.com/wwbrison/dwfttw.htm

I'm not good at analyzing motives but I'm thinking mental derangement caused by the mother withholding her love when they were young, causing a paradoxical complex dominated by fear of not accomplishing enough in life (hence the deep inner symbolism of going faster than the wind.)

Or, maybe they are just having fun seeing how many people they can sucker in. I'm torn between the two theories.

(For those that want to see what I had before, edit the url to dwfttw_0.htm)

Wood

/m179
Woody, your provided diagrams are not helpful, and are misleading, because the analyses of force are incomplete. You are being ignorant about the arguments in the discussion here. It all comes down to the thrust and lift forces caused by the propeller, and how they are sustained by wind.

And I don't know how many times it has to be iterated: this is NOT perpetual motion, the wind is an (almost) eternal energy source.

You should also consider why any man would go to these lengths trying to fool everybody, and still be completely open and responsive to the debate, offering people to see for themselves.

Experts on propeller physics and/or aerodynamics could still contribute to the discussion, I think..

Edited by author 03-06-2007 06:14 PM
I've been fascinated with the subject of sailing since like age 7, when I got a new sailboat for Christmas. I put some pillows over it to protect it. Then I forgot it was there, and those pillows made a funny cracking sound when I landed on them. Only mistake I ever made.

I've thrown together some diagrams for you:
http://users.sisna.com/wwbrison/dwfttw.htm

Wood

I intended to add a few more notes/thoughts to this thread, but as I still haven't gotten around to doing that, I'd say it won't ever happen. Hence this post -- I don't want to be gone without having said: Thanks to all the fellow posters who helped me figure out where in my theories I've been right and where I've been horribly wrong. It was a fascinating discussion, I learned some new things and I'm a smarter person now.

Peter
You have got it. Once one gets around the lack of wind at windspeed it becomes easier. The lift from a helicopter rotor is more than the energy required to turn it. The power supplied by the wheels turns the propeller, which supplies more lift than is required to turn the wheels.
Pat
There is enough energy in converted in a 10 mph wind to overcome the frictional, rolling and aerodynamic drag, to drive the cart about 13 mph. It is more efficient at higher speeds since the friction drag is linear while the aerodynamic lift and drag are by the square. Excuse the video, I had strapped the camera and radio controls to my bicycle, and was trying not to wreck and steer at the same time. In the video my wife had pushed the car to start it on the rough road andI had accidentaly left the brake on. I had to find a day with a steady wind at about 8 mph going in the direction of a suitable road. Any more wind and the car rapidly gets away from me. In the AYRS publication I have total lift to drag numbers, that were derived from a tread mill. 4 mph is the crossover speed to exceed windspeed in laboratory conditions. In real life the wind gradient is a problem, and raises it to about 7 to 8 mph. There is almost no wind at 12 inches off the ground.

Edited by author 02-14-2007 04:16 PM
okay, so i've been thinking a ton about this and decided that it's possible that i was getting confused between having the wind turn the propeller like a turbine and having the propeller pushing wind backward, driven by the wheels.

this is how i think of it now...

assuming you have a very low friction system, and your propeller is nothing but two flat boards attached to a gear with a chain running to another gear on the wheels. one could see that eventually the cart will be blown by the wind until it's going ALMOST as fast as the wind speed, at which point rolling (and other) frictional forces will equal the force of the wind and the propeller will be happily spinning around doing nothing special.

now if we change the propeller blades to be wings instead of flat boards, then one could see that they would cause a marginal amount of additional drag while adding a significant amount of lift. this lift would manifest itself as an additional force acting to drive the vehicle forward faster... conceivably faster than the wind speed.

i'm not an equation person, so this whole concept has been very difficult to get my brain around. i think i'm starting to come out of the clouds now though... i'd like more than ever to build this thing :)

Jack:
With a NET headwind of 15 mph is stops.
With a tailwind of 10 mph (NET headwind of 5mph) it would accelerate.
So the smaller the headwind the more it accelerates = presumaby to infinity.
Why didn't you tell us that, in the video, the brakes were part on?

Caspian, thank you. My intuition first tells me
the wind should work against propulsion here,
but I think I get it now, everything makes sense.

A single differential equation of the evolution
of the pressure difference over the propeller would
make this very explicit and clear (Or is Reynolds
number or the like complicating matters?). Sounds like
an exercise in aerodynamics A course. Anyone up
to it?

Fredrik, in /m172 you say: There is no energy intake for v _cart >= v _wind, right?

There is energy input even when v _cart >= v _wind

The propeller converts some of its own rotational energy and some of the wind's kinetic energy into the cart's kinetic energy. The wind's kinetic energy is the energy input.

Reading along, my understandning is still incomplete. This is an awsome demonstration, so I really want to understand it. Thanks for sharing it with us, Jack.

From the point when v _cart = v _wind, you have a vertical
force equilibrium F _lift = mg, and the cart accelerates until
F _thrust = F _drag. OK. But then what? There is no energy
intake for v _cart >= v _wind, right? Why doesn't imperfections
make the system dissipate back to v _wind quickly? What mechanisms
make it sustainable?

And, to echo /m168, /m170, why does absolute wind speed matter?

/m170

magic, remember?

i really wish i lived in southern florida... Jack, can you post some more detailed schematics so Pat, Gilles, and myself can each build one and prove ourselves wrong?

So with a NET headwind of 15 mph is stops.
If it had a tailwind of 10 mph (NET headwind of 5mph) it would accelerate?
How so?

Pat
It slowsdown and stops.

Jack:What happens if, with Zero windspeed, you manually accelerate the cart to (say) 15mph and then let go?

GV
   The fan is very efficient, if you go to one of the back issues of
AYRS; there are instructions on how to build it. Suprisingly it looks exactly like the Wright Brothers props.
   The machine has all ball bearings and easily coast down a 1 inch in 12 foot slope. I may not be right about how it works, not suprising since the experts are still arguing over how sailboats work. Also it is geared to be most efficient at 1.4 times wind speed.

Hi Jack,

You've built a remarkable machine. I had never heard of the whole DWFTTW concept until I saw the BoingBoing post. The video was the clencher--if a picture is worth a thousand words, at 20 frames per second your video is amazing. I wish I was near Florida to see a demonstration.

I do have one thing to share, and I hope you find it interesting and not disrespectful. I think the process in which your machine gets up to speed and faster than the wind is more complicated than you've mentioned. Specifically, when the cart is moving faster than the wind, I believe it is acting like a windmill, taking energy from the headwind and transmitting it to the wheels. The reason I believe this is because if it were the other way around, taking energy from the wheels and sending it to the prop, there would be an energy loss at the prop (props are only 50-90% efficient). In other words, if you extract a given amount of energy from the wheels to turn the prop, the wheels (and thus the cart) will slow down. When this energy is transmitted it to the prop, the prop will use that exact same amount of energy, but only a fraction of that will go to usuable thrust, with a good portion going to drag (tip vortices, form drag).

Also, if the wheels were driving the prop, then theoretically, the cart should be able to accelerate from a slower speed, in a no-wind condition, and that is of course, impossible.

I've tried to explain this in more detail here: /m117

Regardless, you've built an incredible machine and I hope you continue to experiment! Cheers,

The wheels turn the fan, the fan blows backwards, creating enough force (lift) against the wind to stay ahead of it, and turn the wheels.

OK, possibly m162 already answered my question. I need to understand lift to drag in propellers.

OK, I'm having a hard time with this.

Rather than try to move faster than the wind, let's just discuss moving into a headwind from a stop.

Assuming high friction wheels so nothing slides, I say that the rotational force from the propeller transferred to the wheels can never exceed the drag on the propeller caused by the wind, so no motion of the propeller ever occurs.

In simple intuitive terms, why is this not the case?

It seems to me that the proposal that the rotational force from the propeller is greater than the propellers drag is perpetual motion. Drag is what "sucks the energy" out of the wind and causes the rotational force. There has to be loss, there certainly cannot be gain.

The wheels power the fan. The fan provides the lift to turn the wheels. All that is required is for the fan blades to have a greater than 1 to 1 lift to drag ratio. Somthing that any wing can do in spades. For information on the machine and instructions on how to build it, as well as the fan and many more odd and unusual ideas, join The Amateur Yacht Research Society, at office@ayrs.org , it is cheap and fun.

Edited by author 02-08-2007 08:50 AM
nex /m154
You can modify the rack and pinion solution by removing the teeth, leaving a friction drive (Bernado conveniently left the teeth out of the illustration at /m144), and then lubricate one of the "pinions" so it slips a lot on the "rack". That would be a closer analogy to a wind-powered device. I think with constant velocity "racks" and assuming no friction except against the slippage, it should smoothly approach the speed of the real rack and pinion device.

jack,
Congratulations on your machine! Where can we get more info on it? Do you have a website?

best,

Gilles

nex:

GV wrote a reply to me in /m135, trying to disprove my theorem with this: "We only have to allow the wind to push against the blades, not the windmill itself." The blades are part of the windmill. When the wind pushes against the blades, it does push against the windmill.

Correct. I was seperating the forces for simplicity's sake, attempting to demonstrate that the drag FORCE on the blades is less than the rotational FORCE imparted to them.

Resolve the drag and rotational vectors from the thrust in the following diagram and see for yourself. The top image is a powered prop, the bottom is a windmilling prop:
http://www.auf.asn.au/groundschool/windmilling.gif

What you see in the windmilling case is that the backwards force vector (drag) is smaller in magnitude than the rotational force component. In other words, the force causing the rotation of the blades is greater than the force slowing them down.

I built the DDFTTW machine. I can assure you that it is self starting, does not store energy, and will exceed the windspeed directly down wind by 1.5 times in 12 knots of true wind. It is also fastest straight downwind. I do demos in Southern Florida.

I'm convinced, you can outrun the wind (as long as you don't try to go straight downwind). I was just pointing out some inconsistencies (e.g. the diagram I was talking about is not the one you just mentioned) and interesting bits in an attempt to clear some things up ... so thanks for the clarification!

By the way: "Do the math (4 x sq. root of 2 divided by 2 = 2.8 or somesuch" ... so it's more like 2x than 4x -- what I said :-)

/m154- yo nex-
look at the diagram under "Why are eighteen footers always sailing upwind?" again. the component of vb parallel to vw is clearly greater than vw. And -guess what - that whole comment was on tacking, not on running directly downwind.
Also, look at the velocity chart again. land yachts are hitting their highest velocity of 4-5x the wind speed at about 45-60 degrees away from straight downwind. Do the math (4 x sq. root of 2 divided by 2 = 2.8 or somesuch. Or look at the chart here:
http://www.sevenravens.com/landsailing/
better than 90 mph downwind in a 30mph breeze.
and no, this comment is not about sailing directly downwind; it's about tacking a vehicle so that the component of it's velocity parallel to the wind is greater than the velocity of the wind.
just thought I'd get that out of the way.

True wind V apparent wind
Many of todays modern lightweight yachts sail faster than the true wind, and as written in some of the comments below ice boats sail at many X true wind strength. As speed increases, apparent wind moves forward relative to your direction of motion.
world spped sailing records and attempts http://www.sailspeedrecords.com/500.html
..or if you want to see a 60ft something triamaran doing 45+ knots in 25nk wind see http://www.hydroptere.com/index.php4?lang=EN

It's Nex's Monster Post(tm) time! I just revisited this thread and saw a few new things. A couple of notes regarding those:

/m153 Are you sure you didn't miss anything? Can you really simplify a machine with moving parts to a single, monolithic, rigid mass without compromising the validity of your diagram?

/m152 "If there is no wind" ... then you don't have a wind-powered vehicle. Duh. "This depends on the design of the vehicle" ... O rly? So you can't just put a loaf of bread on a skateboard?

/m150 ... Let's look at /m148 first, where ainamogel said: "the velocity component _parallel to the wind_ is 4x the wind speed." If you look more closely, it's more like 2x the wind speed. Still impressive. However, looking at that same polar velocity plot, you'll see that this land yacht can only achieve this feat when going at an angle to the wind -- straight downwind, the plot actually gives its speed as zero. Now in /m150, hibob seems to agree that you can outrun the wind, but, hibob, the very interesting link you provide actually contradicts your opinion!

First, looking at the diagrams under "How can boats sail faster than the wind?": Boat speed is > wind speed, but the velocity component _parellel to the wind_ is NOT greater than wind speed. Second, under "Why are eighteen footers always sailing upwind?" you'll find: "In a fast boat, there's no point going straight downwind: you can never go faster than the wind." So, very interesting page, thanks for the link, but nothing about outrunning the wind.

/m144, /m132 The proposed solution to the "rack and pinion" problem: Very simple and elegant. Obviously, if you turned the axle, the racks would move in the same direction, at different speeds, so it also must work the other way around. Now let's shift our frame of reference to be the faster moving rack; this is our fixed ground. Now the gear clearly moves faster than the other rack. So that problem is solved, and the answer is YES.

However, this contraption only works when the axle moves at exactly the right speed, the one at which all constraints of the system are fulfilled. At any other speed, it is deadlocked and either stops in its tracks or breaks apart, so it doesn't really tell us all about the forces acting on the wind-powered vehicle at any speed other than perfect equilibrium. When the vehicle moves just a little slower, this isn't much of a problem, there's just some slippage in the system. But what about speeds at which the apparent wind comes from the opposite direction? And what about a world in which racks and gears aren't made out of air? ;-p

Still, I think this thought experiment shows that DWFTTW ought to be possible in principle. Clever!

/m142, /m136 Of course there are air-powered vehicles that move faster than the wind; maybe you can even achieve factor 5. But whether you can even make the component of the speed that is parallel to the wind greater than wind speed, that is an entirely different question. And even if you can, there is yet another question: can you do it straight upwind or straight downwind? Well, not in an ice boat. A "downwind track" is not a track that goes _exactly_ downwind.

/m141 I think the claim that you can use wind power to move straight into the wind is still dubious. Yes, the apparent headwind could theoretically turn the propeller, which could add to the forward velocity of the vehicle. But it also pushes the prop back, reducing the vehicle's speed. You're saying the work the windmill does is overcompensating for the air resistance it provides. Yet, as long as the apparent wind is still a tailwind, it would 'try' to turn that same propeller in the other direction, making the wheels spin backwards, i.e. the tailwind reduces the forward velocity of the vehicle by way of the propeller rotation. The vehicle can still be blown forwards, but only if the air resistance is greater than the work that the windmill provides. So, in tailwind, sail effect > windmill effect, but in headwind, sail effect < windmill effect. Sounds like a pipe dream to me.

/m139 You're saying that depending on your frame of reference, either the windmill turns the wheels, or the wheels turn the propeller. However, this is completely impossible. Whether energy is transferred one way or the other depends on the gearing between the wheels and the propeller, and this gearing always stays the same, no matter how you change your frame of reference.

Also, I don't think that the vehicle in the video produces "lift in excess of drag". A sail going downwind produces only drag, no lift at all; I think this is a systematic constraint that won't change if you replace the sail by a propeller.

In the second half of that post, you're saying that tailwind pushes the vehicle forwards, reducing apparent wind ("The air has lost some velocity, that is a loss of kinetic energy which has been transfered to the cart."), but the apparent headwind is irrelevant ("The air powering the cart has indeed lost forward momentum but it has not gained any 'reverse momentum'") and doesn't push the vehicle back. You're contradicting yourself through rhetoric contortions worthy of a politician.

GV wrote a reply to me in /m135, trying to disprove my theorem with this: "We only have to allow the wind to push against the blades, not the windmill itself." The blades are part of the windmill. When the wind pushes against the blades, it does push against the windmill.

It's obviously impossible to build a vehicle that moves faster than the wind averaged over its entire period of movement just by drawing a free body diagram,
but it isn't that hard to imagine a similar vehicle to the one in the youtube video which operates in three phases, one in which the propeller spins up and stores momentum, a second in which the propeller's blades are either contracted and a sail is raised in order to bring it close to wind speed, and a third in which the propeller energy is put into the drive shaft, temporarily bringing the vehicle beyond wind speed.

or any manner of ways of storing wind energy, but this isn't what is being talked about.

Edited by author 02-07-2007 05:21 PM
case 1: DFTTW in SOME cases: This is easy to prove. If there is no wind, you're moving down faster than the wind, if there's a breeze, you're still faster -- there may or may not be a turning point, where you would be slower

case 2: DFTTW in ALL cases: This depends on the design of the vehicle, i.e. if you don't put some oil on the wheel axis, you might be very slow... wouldn't you say?

An important point, esp Re: hibob post 145.

Windmills are not 'free energy'. To make a windmill rotate it feels significant air resistance - imagine holding up a toy windmill, you feel the force of the wind pushing it back...

/m148 : right you are.

for other non-sailors,
http://www.phys.unsw.edu.au/~jw/sailing.html
 look at section "Why are eighteen footers always sailing upwind?"


so does the same vector math apply roughly to the prop on the cart?

Edited by author 02-07-2007 03:31 PM
ok.. i've read alot of the replies and i just can't understand why everyone is looking at this in such a complicated manner. Its understood that a tailwind (Fa) would over come the Ff of the wheels and give the cart velocity in the direction of the wind. This would happen to a point of equilibrium where the cart would reach a velocity slightly less than the total Fa.(less due to resistance(Ff)). But because the wind is not constant and gusts occur this would create a headwind. This head wind would act as a Fa due to the turbine effect of the prop.

So why not look at this problem in a much simpler way and turn it around so the cart initially starts into a headwind. Say this cart was stationary in a wind storm pointing directly into the the wind. Would the cart move towards the wind?
I say yes, so long as the wind force is great enough to power the turbine with enough revolution to overcome the Ff of drag and Ff used to move the wheels(drive train). If the wind velocity did over come the resistances the cart would accelerate but to a limited velocity itself. The velocity of the cart would reach a maximum due to the efficiency of the prop and the Ff - meaning, the wind could blow at any velocity over the velocity required to accel. the cart(Fa>Ff), but the cart would only reach a maximum velocity where Fa=Ff.

Bernardo pointed out that on a still day it would not move. This is true for the fact that the wind speed is 0 relative to the ground Ie. no energy could be used from the wind. Even if you pushed the cart up to a velocity where the wind was enough to power the machine, it would still decelerate because the wind is not moving over the ground. Although to keep the cart moving at the constant maximum speed would require very little secondary applied force - As in a tail wind
This is what i believe right now, I will think about it more.. i'm open to criticism.

/143
"/142, /136 : tacking and the vector math has been addressed upthread.
The component of the iceboat's velocity that is parallel to the wind is smaller than the velocity of the wind."

I'm sorry, but the above statement is false. See
http://www.sevenravens.com/landsailing/
for one counterexample, in which the velocity component _parallel to the wind_ is 4x the wind speed.
Google "iceboat polar velocity plot" for many many more examples.

Bernardo, (/m146)
I think you're confusing yourself with formulae. Your turbine example is correct, once the device is moving at wind speed there will be no more power generated by the turbine. however your prop mode example doesn't require wind to move it along, a simple push would start the perpetual motion machine moving at some speed greater than wind speed, which is zero.

"Is [some speed] ground speed or airspeed? If [some speed] is airspeed, then DWFTTW is possible, since airspeed is greater than ground speed. But if [some speed] is ground speed, then DWFTTW = perpetual motion."

No, I was wrong! And I just figured out how to prove (I think) that turbine-powered DWFTTW is impossible. (Airspeed is NOT greater than ground speed!)

turbine mode:

power = thrust X ground speed = resistance X airspeed

but ground speed > airspeed, so thrust < resistance

(and if you say "No, power = thrust X ground speed = resistance X ground speed", then you are suggesting a perpetual motion machine that could gain speed on a still day).

prop mode:

power = resistance X ground speed = thrust X airspeed

ground speed > airspeed, so thrust > resistance

Maybe. MAYBE. I might have made a mistake. But as far as I can tell, it looks like prop-based DWFTTW (as opposed to turbine-based DWFTTW) might be possible. Unless my calculations are in error.

GV- quoting from /m117:
"Once at windspeed, the cart is zipping along nicely, like a sailboat getting blown downwind, and rather smoothly because of all its momentum. From the cart's point of view, there is no wind! The wheels are spinning, and thus turning the prop, which is now making almost no thrust or drag because it's almost completely slicing through the air. Before, there was a tailwind. Now, nothing, so the prop isn't acting against much air at all."

Or alternatively, put the cart on a treadmill at a speed where the wheels and and prop are spinning and the combined forces keep the cart at a steady position on the treadmill. A neat trick in and of itself.

"Now, a slight lull in the wind comes along and the cart sees a headwind! The headwind hits the propeller and causes it to windmill Windmill! That's like discount energy! The prop is now a windmill, powering the wheels, and THAT'S what's causing the cart to speed up. It'll then speed up until the prop looses efficieny and drag balances out the whole thing."

Or alternatively, drop the velocity of the treadmill by 2 mph, or give the cart a 2 mph push. The cart is now moving into a headwind. Will it accelerate to a new equilibrium speed?

Good morning!

Nocens said: "... part of the confusion over the nature of the prop is due to the different frames of reference people are using. If your frame of reference is stationary with respect to the ground then the wind does work on the propeller which turns the wheels. On the other hand if your frame of reference is the cart then the ground is moving, doing work on the wheels, and turning the propeller against the wind."

Nope, you can't have both. Like I have said, the forces being exerted on the mast that holds the spinny thing, and on the wheels, and on the gears/belts that connect them, should tell you whether it's a turbine powering the wheels or the wheels powering a prop. It's can't be both at the same time. This, I am absolutely sure of. From the point of view of the cart, if the wind behind the spinny thing is faster than the headwind, then it's a prop, and if the wind behind the spinny thing is slower than the headwind, then it's a turbine. Or you could look at the spinny thing's RPM, its blade incidence angle, and the headwind speed: If it hits the air with a positive angle of attack (i.e. the "back" of each blade sees higher-pressure air), then it's a prop. If it hits the air with a negative angle of attack (i.e. the "front" of each blade sees high-pressure air), then it's a turbine. It can't be both.

Sure, it can switch from prop mode to turbine mode (or vice versa) as its airspeed changes, but once you're going DWFTTW and holding it (assuming that's possible), you have to stay either in prop mode or in turbine mode. Not both at the same time.

Oh, and Nex and Nocens say that the gear system is impossible. If this is true, then DWFTTW should be impossible, as far as I can tell. In any case, Zephyris did come up with a way, which I can illustrate for you:

http://www.airshowfan.com/solution.JPG

wbskeet37, on this thread we have already extensively debunked your claim using vector components, triangles, and Bernoulli. Haven't we? Yes, a sail-vehicle can go faster than the wind, but the component of its velocity along the wind direction is not greater than the total magnitude of the wind velocity.

And Nocens, your energy calculation is ALMOST right, except you mixed energy with power.

Here is the "proper" power calculation:

airspeed = speed of the headwind

propwash speed = speed of the air after it goes through the prop
(this is greater than airspeed if the prop is a thrust device, smaller than airspeed if the prop is a turbine)

groundspeed = speed of the ground rolling underneath the vehicle. Equal to wheel surface speed relative to vehicle. Greater than airspeed.

prop air flux = mass of air per second that makes it through the prop arc (i.e. that gets its speed changed from airspeed to propwash speed).

Assume no friction, no drag. There is only thrust and "resistance". If the prop is a thrust device, then "thrust" is the force it makes, and "resistance" is the force on the wheels that pulls the vehicle back (like the force on the non-powered wheels of a car). If the prop is a turbine, then "thrust" is the push of the wheels, and "resistance" is the force of the air pushing on the turbine when the turbine slows the air down to take energy from it.

Now here come the power calculations (energy per unit time):

power into turbine = power out of wheels

(half X prop flux X airspeed squared) - (half X prop flux X propwash speed squared) = thrust X groundspeed = power

The problem is that the power also equals

thrust X groundspeed = resistance X [some speed]

is [some speed] ground speed or airspeed? If [some speed] is airspeed, then DWFTTW is possible, since airspeed is greater than ground speed. But if [some speed] is ground speed, then DWFTTW = perpetual motion.

The work done is the force applied times the distance moved in the direction of the force. That's all I remember for sure and it doesn't seem to conclusively say whether it's one or the other - i.e. whether the maximum power the turbine can take is resistance X airspeed or resistance X ground speed.

/142, /136 : tacking and the vector math has been addressed upthread.
The component of the iceboat's velocity that is parallel to the wind is smaller than the velocity of the wind.

A slight shift - ice boats. According to the wiki article here
http://en.wikipedia.org/wiki/Ice_boat they can move upto 5 times as fast as the wind.

It always seemed counterintuitive to me too.

It's simple guys,

1) The cart gets pushed by the wind up to near the windspeed.

2) A miracle* happens and the cart is now travelling faster than the windspeed.

3) When it's travelling faster than the wind, the cart has a headwind. The propeller then becomes a windmill and uses this energy to drive the wheels. Same thing as a stationary windmill--getting energy from the wind to do work.

*The miracle is slimply a change in windspeed. A constant gust of 13mph slows to 11mph, giving the cart a headwind.

Posts /m102 and /m117 explain it in complete detail.

/m137 NRG, I'm afraid you are mistaken when you say "Going faster than the wind for a wind powered object would break a basic physics rule that energy cannot be created only transformed."

Consider, what does going faster than the wind really mean? A DWFTTW vehicle means that we have something which travels at a velocity greater than the velocity of the wind. This is not a thermodynamics violation because we are talking about the vehicle's final velocity, not its energy.

In order for a DWFTTW vehicle to work we need to construct one such that the vehicle's kinetic energy (0.5*vehicle_mass*vehicle_velocity^2) is less than the kinetic energy lost by the wind as it pushes the vehicle (0.5*air_mass*(wind_initial_velocity - wind_final_velocity)^2) and where vehicle_velocity is greater than wind_initial_velocity.

Energy is conserved as it must be. Velocity is not but there is no "law of conservation of velocity" for us to worry about. From a physics standpoint this is fine, we just need to determine if we are clever enough to build a device that can absorb energy from the wind while moving faster than it. Which is exactly what I'm trying to explain this cart does.

/m103 Bernardo, part of the confusion over the nature of the prop is due to the different frames of reference people are using. If your frame of reference is stationary with respect to the ground then the wind does work on the propeller which turns the wheels.
On the other hand if your frame of reference is the cart then the ground is moving, doing work on the wheels, and turning the propeller against the wind.
In both cases the actual work done is the same.

Your parallel racks analogies is almost exactly right and I think that you can construct a gear system which almost performs like a DWFTTW vehicle for that setup. However I think it will prove impossible because your racks will not allow a gear or other linkage to slip over them.
One of the key elements of the DWFTTW vehicle is the fact that a prop can produce lift in excess of its drag, I don't immediately see how you can construct an analogous gear, at least not simply enough for it to serve as an example of the principle.

/m133 Zethyris, you are confused by the same energy trick as some other have been in this thread. The statement "the air powering it must loose forward momentum, increasing its reverse momentum and accelerating. Now consider the conservation of energy; both the air and the object are gaining kinetic energy, both are gaining speed as they accelerate" is simply wrong.
The air powering the cart has indeed lost forward momentum but it has not gained any "reverse momentum", it has simply lost some (ideally all) of its forward momentum. The air has lost some velocity, that is a loss of kinetic energy which has been transfered to the cart.
A sail absorbs some energy from the wind to accelerate. This cart does that and then absorbs additional energy from the wind due to the action of the propeller, making it more effective than a simple sail. There is no perpetual motion or energy produced within the system.
It may also be worth noting that while the cart's final velocity is higher than the wind's, the cart's kinetic energy is less than (or equal too in ideal physics land) the kinetic energy lost by the wind.

I think this sums it all up neatly:

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Maybe I am wrong but, an object needs energy to move forward and resist the different friction forces from the wheels, gears. In the case of a wind propelled object this energy comes from the wind itself. If the object goes faster than the wind you loose this thrust. In a no friction world any wind powered object could only go at wind speed as a maximum. In the real world even this would be impossible. Going faster than the wind for a wind powered object would break a basic physics rule that energy cannot be created only transformed.

To answer the question "Can a vehicle move downwind faster than the wind?" it is yes. Go to Geneva or Green Lake WI this weekend and you will see iceboats go upto 5 times the speed of the wind on a downwind tack. www.iceboat.org

nex:

"Yes you could, but this creates a massively huge problem! In order to extract energy from the wind, you must allow the wind to push against your windmill. But because of the way you geared it, if the wind manages to push the windmill back just a couple of inches, the rotor will do 100 revolutions -- in the wrong direction! Everything considered, you end up with a deadlock. No engineering trick will make it exceed wind speed."

Not so. We only have to allow the wind to push against the blades, not the windmill itself. The "windmill" structure doesn't have to be anything more than a support for blades, so it theoretically could be an aerodynamic fairing with minimal drag. It is reasonable to assume that the blades have a L/D of greater than one, so for each unit of drag force on the windmill blades, we get (significantly) more lift force which is converted to work through the wheels, overcoming drag. It's not an infinite amount, it does get balanced.