How can an vehicle move faster than the wind that is powering it?

[nixy2]

I'll locate the video link. Are you convinced that an ice-boat can tack downwind such that its downwind velocity component is greater than the wind speed?

FWIW, Your vector diagram has convinced me you are right (I think). But also the vector diagram would also show an ice-boat can not go DDWFTTW, whereas the 'wind trolley' can?
With emphasis on the D

 

[rcgldr]

The air applies a forwards force to the device, while the treadmill applies a backwards force to the device.

This could only be true if the device is moving.

I was assuming the cart was moving in that example. Assume a long treadmill and nothing but air resisting the carts movement. The treadmill moves the cart backwards, and the air resists this movement with a forwards force. Assuming there is drag on the wheels, the treadmill exerts a backwards force onto the cart.

When you are running on the treadmill at 10mph in a room with still air does the air pressure on your back ...

The surrounding air isn't moving, only the air affected by the propeller.

Can you continuously absorb 10N of force from the belt and use it to continuously produce 10N of thrust in order to stay stationary on the belt?

Newtons' 3rd law at work here. The forces are always equal and opposite if the cart is not accelerating. The issue here is at what cart speed will the forces be equal? Can the forces be equal if the cart is moving forwards?

Back to the OP

How can an vehicle move faster than the wind that is powering it?

Because the source of power isn't the wind but the difference between wind speed and ground speed, which is independent of vehicle speed. The question is can the cart utiize this source of power while moving faster than the apparent wind on the cart, because the propeller blades experience a different apparent wind?

 

[ThinAirDesign]

If I run on the treadmill which is set to 10mph and I am in a room with still air do you think I feel a 10mph breeze on my face?

No.

The situation that you describe above is exactly the same as being on the street and running 10mph with a 10mph tailwind.

We really do need to get past this frame of reference issue before we move on -- it may well be a simple misunderstanding between us (and that may well be my fault).

This all started when Trond used the term "no wind" when discussing the cart on the treadmill. I'm just trying to make sure we are all using the term "no wind" the same. There's 'wind or not' relative to the chassis, 'wind or not' relative to the sails, 'wind or not' relative to the ground, 'wind or not' relative to the treadmill surface, and now there's 'wind or not' relative to my face. If when we say "no wind" and we don't establish *relative to what*, we can't have much of a productive conversation.

I don't mean to be difficult, but there can only be "simple answers" if all the small definitions are worked out.

JB

 

[PhysicsAddict]

Are one or both of you stating that the cart will respond/behave differently on the street with a 10mph wind as compared to in the basement on a treadmill set to 10mph?

It appears that you feel it will act differently in the two environments.

JB

And my answer is that I don't know for sure. Here is where I'm at:

1. The iceboaters of the planet certainly claim that a VMG downwind is a piece of cake. There's lots of them and only one of me so I'm inclined to follow along.
2. It would seem that you could take all the principles of the iceboats and squeeze them into a cart with rotating sails and the kinematic constraints of wheels to build a cart that will go DDWFTTW.
3. Jack Goodman claims to have built such a cart and posted the Youtube video which gets me excited but is hard to accept for documented evidence as "proof possible" since what we could be witnessing are artifacts of the experiment and like all good experiments really needs independent confirmation.
4. When I try to reduce it all down into an environment that would reduce the possibility of any such artifacts and would be much easier to test, control and document (the cart on a treadmill), I run into the issues I stated on my first post.

It is certainly a quandary.

After all, if they're not interested in an exchange -- only "it's violates the laws of physics", where else is there to go? It they're soooo right, it's easy money.
JB

You and I were having a nice exchange, Jeff and I were having a nice exchange. Nevertheless here we are with the betting.

I really only asked simple questions and expected only simple answers but the only one who would do so is you and Jeff.

Newtons' 3rd law at work here. The forces are always equal and opposite if the cart is not accelerating. The issue here is at what cart speed will the forces be equal? Can the forces be equal if the cart is moving forwards?

Hey! Just run the speed up on the treadmill until it appears to break even and there you have it. If you can get to that point I believe you can "go all the way".

What's boring is hearing from people who seem just as certain as I am until they're invited to put their money where their confidence is.

Why? How confident someone is on his/her position is irrelevant to this entire discussion. I know someone who was confident enough that the Patriots would win the Super Bowl that they dropped 25 large on it. It goes to show that how much money someone is willing to put on something has nothing to do with how correct they are. If you find it boring you should move along and we will continue to discuss it here.

This is a nice board and it appears to have lots of really bright contributors so I thought it would be nice to jump in the exchange here. I'm new here and only feel like I'm a guest so I am not going to hang around here while it turns into a slagging match.

Here is one thing I will leave you with:
I have now gone full circle on this. I originally argued that it was a "no-way no-how" thing. Then as it turned out to be possible with land yachts and iceboaters I could only believe that it's certainly possible to collapse it down to a cart heading directly downwind. When I saw Jack Goodman's video I thought "holy cow I got to build me one of those!" Then as I pondered the treadmill dilemma I started scratching my head again. But I didn't let it slow me down.

So here's mine:
http://s167.photobucket.com/albums/u123/DarwinAward/

I wish I had more but that was a hard drive crash ago. I built and rebuilt that cart 3 times after those pictures and video. Not shown in the photos or video is that in it's final form I could regear it at in only minutes. With the 4 sets of gears and 4 sets of wheels I had I could set it a full 300% above the cart pitch ratio that Mr. Goodman specified as well as 300% below. I had 5 different sets of blades including one homemade set laminated together using fanned out balsa that looked as close to Jack's as I could get. My cart had one other really nice attribute - I had variable pitch that I could adjust in real time. It was a blast to build and a blast to tinker on with one exception: it would never make forward progress on the treadmill.

But here is the thing that really bugs me: Jack Goodman built a cart and put it on a treadmill and he could run the treadmill from 0mph to 4mph where the cart would get lighter and lighter on the scale until it was "break-even" at 4mph. He could then increase the treadmill speed and it would increase the pull on his tensiometer as it would try to make forward progress on the treadmill.

I however, built my device and tested it using every combination of gearing, wheels, blades and pitch settings and in EVERY case my cart would only exhibit more force on the scale as the speed of the treadmill was increased. There was no combination of any of the variables that showed any promise of getting lighter on the scale as the treadmill speed was increased. Not only did I fail, I wasn't even in the ballpark.

The beauty of it all is that this only proves that I don't know how to build a cart that will make forward progress on the treadmill. I'll be the first to admit it. Whether it means that it is impossible to do or that I just suck at it I don't know. That is what is so cool about the whole deal - you can never disprove it but it may be possible to prove it can be done.

So here's my challenge to you, especially you "YaySayers": Get to it. What the hades is everyone waiting on? It didn't take me 4 hours to get it built the first time around and maybe $50 worth of old RC Helicopter parts. Go build one and put it on on a treadmill and give us some videos. I will certainly want to get with you afterwards and make mine work (no kidding, no sarchasim). Even if you are a "NaySayer" you will have a blast I promise. Just do it. Let me put it to you this way: I'd bet that there 100 folks on here and on 20 other forums on both sides of the argument that have spent 100 hours typing about it and STILL haven't run out to the shed and start wrenching about it! Go figure. Blows my mind.


Good luck and I will check back from time to time to see if anyone has gotten off of their lazy butts and posted up some videos!

 

[ThinAirDesign]

Hey PhysicsAddict, if you don't mind, I'd like to take you back to an earlier post of yours (quoted in full at the end of this post). I'm also going to reference a portion of an earlier post of mine.

The above is no different than taking two ice-boats on mirror zig-zag downwind tacks and placing a sliding beam between them -- give me two seats and a windsock right in the middle of the beam between the boats. You and I sit in those seats and watch the windsock. Yep, sure enough ... at the moment we reach the real wind speed, the sock hangs limp. Do the twin ice-boats that we are riding on care? ... of course not -- they are zigging and zagging and see plenty of wind as they accelerate us both to a VMG of greater that 1.0 and the sock turns into our face.

1: It's been established earlier in this thread via links to the NALSA website and forums that ice-boats and land yachts can and do regularly achieve VMGs far greater than 1.0. (if you don't agree, speak up now 'cause we need to backtrack and you might want to argue with them about it.)

2: Given "1", I would ask you to place the above twin ice-boats on your below treadmill (humor me please ... ok?). Remember, in the above scenario, you and I are sitting side by side between the boats(facing forward or downwind), riding an equally telescoping beam stretching from boat to boat, and we have a wind sock attached to our seat beam that is staring us in the face (in other words, it's operating in *our* frame of reference). We are in fact the *drivers* of this twin ice boat and our drivers seats are located in the exact dimensional, mechanical and CG center of this ship. We also happen to travel *directly* downwind.

In your below scenario, perform the exact same thought experiment with the twins as you do with the cart -- that is you and I take the twins up to the speed that the sock between us is hanging limp.

Now, apply all the same logic to the twins at this moment that you did to the cart (especially the part below that I bolded).

Of course, given "1", we both know that the twins will power right past this "zero" point and fill the windsock with what appears to us to be a headwind.

So now the question ... Are you and I, zipping across the ice with an apparent headwind (while actually having a ground referenced tailwind) a

A. A hoax?
B. Some other "artifact" captured on film?

Thanks in advance for your answer

JB

In order to understand this you need not understand sailing, relative wind, apparent wind or ANYTHING other than Newtons 1st law.

To get your head around this, imagine the cart facing west sitting on a long treadmill in a long windless hallway. Start the treadmill which runs towards the east and slowly increase the treadmill speed until the cart is at the perfect “break even” point. In other words, to an observer standing still in the hallway, the cart appears to also be standing perfectly still even though it is on the treadmill with its wheels spinning and propeller turning. This is the point where the cart goes EXACTLY as fast as the wind downwind. We don’t need it to go faster than the wind downwind yet. Right here at the break even point is the best place to get your head around it.

Now you don't need to understand anything more that two simple ideas:

1. You must understand Newton’s 1st law of motion - specifically pertaining to balanced and unbalanced forces. In order for the cart to appear to stand perfectly still on the treadmill, the forces pushing on the cart from the east must equal the forces pushing on the cart from the west.

In other words, let’s say that the treadmill is expending 10 Newtons of energy driving the cart east. Since the forces are balanced, the propeller on the cart must be expending 10 Newtons of energy driving the cart west in order to hold it stationary. Since the cart is not experiencing ANY wind pushing it at this point, all its energy driving it west must come from thrust generated by the propeller.

2. You must understand that mankind has yet to invent a machine simple or complex that outputs 100% of the energy it consumes. A propeller is at best 85% efficient. Add in the other components of friction and well it all goes downhill from there. In other words it would be impossible for the cart even get to this break even point. It will never generate thrust equal to the energy it consumes. Now to go even faster than the wind it will have to generate thrust IN EXCESS of the energy it consumes which of course is never going to happen.

Since you now understand these two simple ideas, you can now conclude that the video can only be either:

A. A hoax.
B. Some other "artifact" captured on film.

So here it is reduced to it's minimum components. Nothing to obfuscate here. Very simple.

If you contend that it is possible then all you need to answer is this simple non-obfuscated problem:

Let's suppose that the treadmill imparts a continuous 10 Newtons of force where the treadmill belt strikes the wheels. Please lay out the equations for me assuming your propeller is 90% efficient (that would be an awesome propeller BTW) and there is no friction in the inner gearing of the device. Show me where the device is able to generate continuous thrust in excess of 10 Newtons in order to break even and stand still.

It's a simple equation I assure you. If you need the equation I can point you toward it.

So if you would please lay it out for us where 10N into the propeller results in >= 10N of thrust out.

 

[ThinAirDesign]

Good luck and I will check back from time to time to see if anyone has gotten off of their lazy butts and posted up some videos!

Hey Physics ... if you're out and are not inclined to answer the above, I understand.

Just wanted to thank you for the exchange --- it was fun.

JB

 

[spork]

FWIW, Your vector diagram has convinced me you are right (I think)

That's the most exciting thing I've heard all day. Until now all I've gotten is that my vector diagram is completely wrong in every way - or people refusing to acknowledge it's existence -right or wrong.

But also the vector diagram would also show an ice-boat can not go DDWFTTW, whereas the 'wind trolley' can? D

That's absolutely right.

Because the source of power isn't the wind but the difference between wind speed and ground speed, which is independent of vehicle speed.

I continue to be impressed. It's clear that you understand the concepts and are open minded to the possibility. I'm very nearly certain you'll become a believer.

And my answer is that I don't know for sure. Here is where I'm at:

1. The iceboaters of the planet certainly claim that a VMG downwind is a piece of cake. There's lots of them and only one of me so I'm inclined to follow along.
2. It would seem that you could take all the principles of the iceboats and squeeze them into a cart with rotating sails and the kinematic constraints of wheels to build a cart that will go DDWFTTW.
3. Jack Goodman claims to have built such a cart and posted the Youtube video which gets me excited but is hard to accept for documented evidence as "proof possible" since what we could be witnessing are artifacts of the experiment and like all good experiments really needs independent confirmation.
4. When I try to reduce it all down into an environment that would reduce the possibility of any such artifacts and would be much easier to test, control and document (the cart on a treadmill), I run into the issues I stated on my first post.

It is certainly a quandary.

And that to me is VERY refreshing.

You and I were having a nice exchange, Jeff and I were having a nice exchange. Nevertheless here we are with the betting.

I really only asked simple questions and expected only simple answers but the only one who would do so is you and Jeff.

Well I'm sorry it seems that way. I have tried to answer all questions. The bet is only offered to people that are NOT asking questions - people that are sure they already know the answer.

Why? How confident someone is on his/her position is irrelevant to this entire discussion. I know someone who was confident enough that the Patriots would win the Super Bowl that they dropped 25 large on it.

You have it exactly backward. How much you bet isn't what makes you confident or right. How confident you are governs how much you'll bet. People are insisting they're absolutely right - and that others are absolutely wrong; but clearly they're not as confident as they claim to be.

Here is one thing I will leave you with:
I have now gone full circle on this. I originally argued that it was a "no-way no-how" thing.

And there we are. You didn't come on asking simple questions and wanting simple answers. You came on here ignoring all evidence and telling us we didn't understand physics.

Then as it turned out to be possible with land yachts and iceboaters I could only believe that it's certainly possible to collapse it down to a cart heading directly downwind. When I saw Jack Goodman's video I thought "holy cow I got to build me one of those!"

And all that is great. It proves you were in fact far more open minded than you let on. Don't get too upset if we took you at your word when you said "no way - no how".

Not only did I fail, I wasn't even in the ballpark.

Low drag and efficiency is key. Jack went to a lot of effort reducing drag and making an efficient prop.

The beauty of it all is that this only proves that I don't know how to build a cart that will make forward progress on the treadmill. I'll be the first to admit it. Whether it means that it is impossible to do or that I just suck at it I don't know. That is what is so cool about the whole deal - you can never disprove it but it may be possible to prove it can be done.

I'm glad to hear you say that.

 

[rcgldr]

So here's mine:

Well a heli rotor is designed for high speed, high lift, and has a lot of drag. You need a better propellor, one that can generate around 5 mph of air speed efficiently. I see 3 issues. Losses in the drive train, propeller efficiency with the induced wash issue, and most importantly, if the apparent wind on the blades or a propellor is really different than the apparent wind on the cart.

Drive train: in general, chain or belt drives are more efficient than geared drives.

Propeller - one similar to the Gossamer Albatross, but slower speed still (the Albatross flew at about 18mph), or similar to one of those rubber powered indoor models.

http://en.wikipedia.org/wiki/Gossamer_Albatross

 

[PhysicsAddict]

And there we are. You didn't come on asking simple questions and wanting simple answers. You came on here ignoring all evidence and telling us we didn't understand physics.

Not at all. You read my last post. You know where I stand on iceboats etc. I dropped in, restated the problem from a different angle so I could reduce it to the simplest of questions, then I started asking those very simple questions. Questions that if were met with simple answers would have helped me find my "kink". Questions that would be no different than I would pose to one of my engineers that came into my office with a design in order to have them defend it and help me understand it.

Low drag and efficiency is key. Jack went to a lot of effort reducing drag and making an efficient prop.

I was really shooting for that when I built a set of blades like his using balsa. Maybe fanned out balsa just doesn't scale down too well. Mine didn't even work as good as some of the heli blades. Any Ideas?

Well a heli rotor is designed for high speed, high lift, and has a lot of drag. You need a better propeller, one that can generate around 5 mph of air speed efficiently...

Thanks Jeff. As I mentioned, I did try to copy Jack's blades but that is where I may have snagged. I don't have accurate specs on Jacks blades or even a side-on shot of them to go from. I was just shooting from the hip on those. I was counting on the variable pitch system to cover the bases there. In that original video I also had the cart geared wrong compared to Jack's specs. That's why I rebuilt the cart later.

As for belt vs. gears, when it comes to smaller mechanics, the gears win. I have the components to re-make it using belt drive but I assure you this is far smoother and it almost seems frictionless.

AND if nobody is going to get up and get to carving then please post up a better shot of Jacks blades - a side on shot would be great. Dimensioned drawings would be awesome (Spork? can you get him to send you this info?). When I get back and if no one has made a move toward building their own cart then I will take another run at it if I can copy those blades. In fact, anyone building their own cart is going to need this info.

Thanks guys!

Later!

 

[PhysicsAddict]

Hey Physics ... if you're out and are not inclined to answer the above, I understand.

Just wanted to thank you for the exchange --- it was fun.

JB

Oh and Ditto! I enjoyed it! I'll be around I promise.

 

[spork]

Well a heli rotor is designed for high speed, high lift, and has a lot of drag. You need a better propellor, one that can generate around 5 mph of air speed efficiently.

Incidentally, all my heli blades have symmetrical airfoils. I assume yours does too. That would certainly cost you something. Also, heli blades have no twist. Jack's cart used a blade with "true pitch". That's probably fairly important.

Drive train: in general, chain or belt drives are more efficient than geared drives.

On Jack's cart the drive belt is as loose as he can use it. Also, the pulley's are exactly aligned on the tight side of the belt.

Spork? can you get him to send you this info?

I have most of the info. But how about I get you two in direct contact? He's a very easy guy to talk to.


Incidentally, I'm curious... are most of us believing at least that the ice-boats can and do achieve downwind tacks such that their downwind velocity component is faster than the wind? The cart is intriguing for sure, but I'm wondering if people still differ on the more basic "building block" to this brain teaser of sorts.

 

[Topher925]

Physics Addict,

So here's mine:
http://s167.photobucket.com/albums/u123/DarwinAward/

Great work! I just only wish I had time to finish up my theoretical analysis of this so we could compare it to your experiment and see if they verify each other. Unfortunately, these thermo labs won't grade themselves.

Also, try to keep this thread strictly based on the physical aspects of this device. Comments such as "take the bet" and "nasla says it can happen" are not valid arguments and don't prove or support anything. As I stated on spork's original thread, if posts using non-valid or irrelevant evidence or arguments are used to support your claim then they will be ignored by me and hopefully by all others as well.

 

[ThinAirDesign]

Comments such as "take the bet" and "nasla says it can happen" are not valid arguments and don't prove or support anything. As I stated on spork's original thread, if posts using non-valid or irrelevant evidence or arguments are used to support your claim then they will be ignored by me and hopefully by all others as well.

There is no better "analysis check" than the real world. If your analysis says that the balloon will win every time and the guys racing the NALSA races are beating the balloon every time, it's a pretty fair sign that your "analysis" is wrong.

Ignore the real world at your own peril.

JB

 

[OmCheeto]

There is no better "analysis check" than the real world. If your analysis says that the balloon will win every time and the guys racing the NALSA races are beating the balloon every time, it's a pretty fair sign that your "analysis" is wrong.

Ignore the real world at your own peril.

JB

I'm going to ignore the comments over the last 12 hours because I don't have time for 5 pages of nonsense, along with the fact that I figured it out last night, approaching sleep.

It's a similar effect to either roller skating or swinging on a swing.

Neither roller skates or swings have motors. But the devices in question just seemingly keep on going faster and faster.

It's the energy added by the RC steering mechanism that imparts the seemingly impossible forward thrust to the device.

And do not ask me for force vector diagrams... It's so second year university...

 

[ThinAirDesign]

It's the energy added by the RC steering mechanism that imparts the seemingly impossible forward thrust to the device.

Yes, you finally hit on the well known fact that if you jerk the front wheel of a tricycle back and forth with the right timing, a minicule amount of force can be amplified to astounding speeds unknown.

Brilliant.

JB

 

[Topher925]

Yes, you finally hit on the well known fact that if you jerk the front wheel of a tricycle back and forth with the right timing, a minicule amount of force can be amplified to astounding speeds unknown.

Brilliant.

JB

ThinAir, while I do still disagree with you I do have to admit that I did "lol" a little bit when I read your last post.

 

[spork]

And do not ask me for force vector diagrams...

No need to ask you for any force vector diagrams since I already derived, posted, and explained them in detail. What I just can't understand is how anyone could possibly deny this when such a trivial analysis shows it's completely doable.

If it's so "second year university" why can you not point out the flaw in my diagram?


So the evidence now exists in the form of a simple analysis, GPS data plots, the direct quotes from those that perform this "feat" regularly, and a video showing it in real-time. Not believing this is a lot like not believing we sent man to the moon, or that the 9-11 attacks were a U.S. government conspiracy. There's simply a landslide of information that this happens all the time, and no evidence to the contrary - but people have it all figured out I guess.

 

[spork]

I'm just completely baffled that people don't follow this. Forget about ice-boats tacking downwind (in fact it appears that everyone has conveniently forgotten that). Can we agree that a sailboat can tack upwind? If so - we're done. It's EXACTLY the same thing.

Now my bet is that no one will respond to whether a sailboat can tack upwind. People seem to like to ignore the simple hard evidence.

 

[Topher925]

Can we agree that a sailboat can tack upwind? If so - we're done. It's EXACTLY the same thing.

Of course a sailboat can tack upwind. But NO it is not exactly the same thing. If you actually believe it is the same thing then your logic is seriously flawed. This is not so much a matter of relativity but a matter of kinetic energy and how it is being transferred. The fact that you would even make a statement such as that demonstrates that you do not comprehend the phenomenon you are trying to convey.

As for your vector diagrams, is this the only one that you have made?

http://www.putfile.com/pic/8419299

I have ignored it because its a very poor diagram and really does nothing to model or demonstrate the subject at hand. I would like to see you create a diagram that has a summation of the forces inflicted on the boat assuming its sail is an actual airfoil as ThinAirDesign has suggested. I found that there are 5 significant force components acting on the boat and can be modeled as functions of velocity in the x and y directions an the velocity of the wind. The drag, lift, and wind force coefficients should be the only variables that define the system. Consider them as the eigenvalues or eigenvectors of the system. I used lift and drag coefficients for a NACA 0012 airfoil, perhaps thin air design can give me a more practical airfoil to reference.

 

[spork]

Of course a sailboat can tack upwind.

Well then we should be all done here - since all of us on the physics forum understand how inertial reference frames work.

But NO it is not exactly the same thing.

D'OH! It seems I spoke too soon. Are you actually telling me there's a difference between a boat in calm water with a 5 knot wind vs. a boat in calm wind and a 5 knot current? What if you were in the middle of the ocean with no GPS? How could you possibly tell the difference?

The fact that you would even make a statement such as that demonstrates that you do not comprehend the phenomenon you are trying to convey.

You're embarrassing yourself.

I have ignored it because its a very poor diagram and really does nothing to model or demonstrate the subject at hand.

Yes, you've demonstrated already that you don't understand my completely accurate vector diagram. Although you haven't been able to point out any specific problem with it.

I would like to see you create a diagram that has a summation of the forces inflicted on the boat assuming its sail is an actual airfoil as ThinAirDesign has suggested.

First of all, my diagram does exactly that. Secondly, ThinAir never made any such suggestion.

[lots of nonsense]... perhaps thin air design can give me a more practical airfoil to reference.

Of course - why trust someone with an M.S. in aero on something this simple?

 

[spork]

So, for everyone but Topher, I'm still at a loss on what's left to discuss. Is there honestly any real doubt that ice-boats are doing as claimed?

If so, how can you explain the sailboat tacking into the 5 knot relative wind (on a calm day with a 5 knot current) in the middle of the ocean?

 

[ThinAirDesign]

Of course a sailboat can tack upwind. But NO it is not exactly the same thing.

Topher, does this brainteaser sound familiar?

You're in a sailboat on a day with NO wind. However, there's a 10 knot current taking you directly toward your intended destination. What's the fastest way to get to your destination? Should you drop your sails to reduce drag, or use your sails to get there more quickly? You can only use the energy from the wind and/or water - no paddles, motors, etc.

If you can answer the above correctly, you will see that it IS exactly the same -- that is if your claim that the cart (or sailboat) cannot outrun it's power source was in fact valid, a sailboat would never be able to tack upwind.

You might want to think about it carefully, 'cause it's easy to look silly when dealing with the real world.

JB

 

[OmCheeto]

I must admit that I'm a bit new to this forum.

Is this a perennial Halloween joke kind of post?

 

[spork]

I must admit that I'm a bit new to this forum.

Is this a perennial Halloween joke kind of post?

I don't think so. I think Topher actually doesn't understand inertial reference frames.

 

[schroder]

So, for everyone but Topher, I'm still at a loss on what's left to discuss. Is there honestly any real doubt that ice-boats are doing as claimed?

If so, how can you explain the sailboat tacking into the 5 knot relative wind (on a calm day with a 5 knot current) in the middle of the ocean?

Look, sailboats tack into the wind at an angle, typically 40 degrees. This makes the wind curve around the sails, resulting in a delta velocity, in other words, acceleration. This acceleration is mainly to the side but does have a forward component as well. Also, the keel of the boat tends to redirect the sideways acceleration into a forward acceleration resulting in forward motion. Note, however, that the boat does not move directly forward into the wind as it is always tacking at an angle. Let’s say you have a twenty knot headwind and you tack into it at a forty degree angle. You might typically generate a twenty-four knot speed at an angle of forty degrees into the wind. This is why it can be said that a sailboat can go faster than the wind. But the velocity, as a vector is never faster than the wind. In the above example, the forward component would be about 18 knots, which is less than the 20 knot wind. The boat cannot sail directly into the wind. But I fail to see what all this has to do with a cart on a treadmill. The cart is initially getting ALL its drive power from the moving tread driving its wheels while the cart is held stationary against a backstop. Then the wheels drive a propeller through some sort of drive train. Now you expect me to believe that the force of the propeller can drive the cart forward on the treadmill? If that was true, you could turn the treadmill off and the cart would keep going! In other words, you are asking me to believe in a perpetual motion machine. This thread is an insult to the intelligence and it is about time that a moderator put it out of its misery.

 

[spork]

Look, sailboats tack into the wind at an angle, typically 40 degrees...

Yeah, I'm pretty familiar with how sailboats tack into the wind since I've been sailing for over 30 years.

This makes the wind curve around the sails...

Yeah, I'm pretty familiar with how the wind over an airfoil creates lift seeing as I have in M.S. in aero.

But I fail to see what all this has to do with a cart on a treadmill.

And I really can't imagine how it could possibly be made any simpler. I'll walk you through it. I'm going to number the steps, because I want someone to actually point out where this goes wrong.

1) I think we can agree that a sailboat can tack into the wind.

2) I hope we can agree that if you're in the middle of the ocean and you feel a 10 knot wind over your deck, you can tack into that wind. It doesn't matter whether you're in a 10 knot current and there's no "wind", or there's a 10 knot wind and no current. Afterall, what do we measure the wind relative to - the bottom of the ocean?

3) So... if we are in a 10 knot current, with no wind, and we tack into the relative wind, we'd have to say that we're tacking down-current rather than upwind. But we're going faster than the current. In other words we can tack faster than the fluid that's pushing us.

4) If a sailboat can tack faster than the fluid that's pushing it, an ice-boat can sure as heck do the same (which we already know from GPS data and testimony of the ice-boat racers).

5) Put an ice-boat or two in a huge frame with a seat in the middle and let them tack downwind faster than the wind all day long - while you sit in your seat going straight downwind faster than the wind.

There you go. A vehicle that goes straight downwind faster than the wind, powered only by the wind. Forget about the cart. The object is to build a vehicle that goes straight downwind faster than the wind - and this one does it.

It's now been shown with GPS data, vector analysis, testimony from the very ice-boat racers that do it every day, and finally we can see that exactly the same thing happens whenever a sailboat tacks into the wind.

Now you expect me to believe that the force of the propeller can drive the cart forward on the treadmill?

I would've said yes - but now I think it's a trick question.

If that was true, you could turn the treadmill off and the cart would keep going!

Now you're just messing with me - huh?

In other words, you are asking me to believe in a perpetual motion machine.

I'm curious to know how many times we'll have to explain that this is NOT a perpetual motion machine. How can it be so complicated to understand that this vehicle exploits the motion of the air relative to the ice or water?

This thread is an insult to the intelligence and it is about time that a moderator put it out of its misery.

You actually find this so challenging to your world view that you think a moderator should make it go away? That is an insult to "the" intelligence. But if it's REALLY so obviously impossible, why not take the bet that seems to be annoying everyone? You can claim the $100K and shut me up.

So without simply telling me this is a perpetual motion machine, or that it breaks every single law of physics, someone please point out the step where it all goes wrong. If a sailboat can tack upwind, then a wind-powered vehicle can go directly downwind, faster than the wind - in 5 easy steps.

 

[schroder]

3) So... if we are in a 10 knot current, with no wind, and we tack into the relative wind, we'd have to say that we're tacking down-current rather than upwind. But we're going faster than the current. This tells us that we can tack faster than the fluid that's pushing us.—spork--

This is where you are going wrong. When you tack into the relative wind, you can go faster than the relative wind, but you cannot go faster than the current! Can’t you see that? The sails resist the motion of the boat in the air, which will slow it in the water. But, at the angle of attack the slipstream of air will now be moving faster than the original relative wind. For example: the water current is ten knots. The boat is moving at zero relative velocity to the water but 10 knots relative to the wind. Now you hoist the sails and tack at a 40 degree angle. The wind coming across the sails will be at a greater angular velocity than ten knots (maybe 12 knots) but the boat will actually have a negative velocity in the water of about 1 or two knots. You will never outrun the current which is driving you in the first place!

You actually find this so challenging to your world view that you think a moderator should make it go away? That is an insult to "the" intelligence. But if it's REALLY so obviously impossible, why not take the bet that seems to be annoying everyone? You can claim the $100K and shut me up.—spork--

Where are the details of this bet you keep mentioning? I just might take you up and you can donate the money to Physics Forums after I win. About that video: why is there a need for a tensiometer to be attached to the rear of the cart? After all, if the cart can move forward on the treadmill, that should be very obvious for all to see. The tensiometer adds no useful information. However, the tensiometer might actually be a compressed spring which pushes the cart forward when the prop provides enough lift. That would explain the hoax!

 

[spork]

This is where you are going wrong. When you tack into the relative wind, you can go faster than the relative wind, but you cannot go faster than the current! Can’t you see that?

Of course you can. You're in the middle of the ocean. The current is moving you toward the north at 5 knots. There is no wind - but you feel the 5 knots of relative wind over your deck. You throw a buoy overboard as a current marker, put up your sails, and tack into the relative wind - leaving the buoy in your wake. You're now going north faster than the 5 knot current that's pushing you north. Can't you see that? This is where you are going wrong.

The sails resist the motion of the boat in the air, which will slow it in the water. But, at the angle of attack the slipstream of air will now be moving faster than the original relative wind.

Forget all about the details of how a boat sails. We agree it does. The question is this... how can you even tell whether you're in a 5 knot current with no wind or in a calm current with a 5 knot wind if you're in the middle of the ocean with no GPS etc? Serious question. Tell me what you do aboard that sailboat to tell me which situation you're in.

Where are the details of this bet you keep mentioning?

PM me with your contact info. We'll set it all up.

I just might take you up and you can donate the money to Physics Forums after I win.

Fine. Just don't sign that check until you actually see the experiment fail.

...That would explain the hoax!

Yup - there are lots of ways to explain the hoax - if there were a hoax. But why post a video hoax of an everyday event? This has been proven in just about every way imaginable - including GPS data, vector analysis, and testimony of the people that do it.


No one seems willing to answer the question any longer as to whether they believe ice-boats tack downwind with a downwind velocity component greater than the wind speed (as the racers, GPS data, and vector analysis clearly shows).

 

[Trond]

The bet is for people that are positive this is impossible - people like you.

Then you have misunderstood me completely, I said it was impossible at first on RR, then I pondered about it and changed my mind. However I have a different approach to the proeblem than you do.

 

[spork]

Then you have misunderstood me completely...

I think you're right. What is your current stance?

A) Sure it can be done (and happens every day)
B) Sure it can not be done
C) Unsure and interested in the analysis and evidence
C) Other

 

[Trond]

What is it? I'm trying to have a discussion about a cart and you want to discuss sailing. I'm not sure it means the same thing to you and me.

If you in A) as usual mean if an ice yacht can reach a point downwind faster than the ballon, then yes sure it can be done. Not sure how often tho

But as you know, I'm more interested in the cart.

How is your stance on whether the cart can advance on a treadmill with no wind relative the treadmill.

A) Sure it can
B) No it can't
C) Unsure
D) Other

 

[spork]

How is your stance on whether the cart can advance on a treadmill with no wind relative the treadmill.

I assume you mean no wind relative to the treadmill itself - not relative to the moving belt of the treadmill. In that case the cart can definitely advance on the moving belt.

 

[Trond]

Yes, that is what I mean. No wind relative the room, no wind relative the treadmill itself and consequently no wind relative the cart until it starts moving.

So it's rolling, at the start it's standing still on the belt, propeller turning, driven by the rolling wheels as the belt rolls underneath the cart. We get to the point where it starts to budge.

I trust we can agree that to continue from that point the blades will have to spin faster?

 

[schroder]

Of course you can. You're in the middle of the ocean. The current is moving you toward the north at 5 knots. There is no wind - but you feel the 5 knots of relative wind over your deck. You throw a buoy overboard as a current marker, put up your sails, and tack into the relative wind - leaving the buoy in your wake. You're now going north faster than the 5 knot current that's pushing you north. Can't you see that? This is where you are going wrong.





No one seems willing to answer the question any longer as to whether they believe ice-boats tack downwind with a downwind velocity component greater than the wind speed (as the racers, GPS data, and vector analysis clearly shows).

Yes, you leave the buoy in your wake because you are moving away from the direction of the current at an angle. Let's say the current, the boat and the buoy are moving directly from North to South at ten knots. You hoist your sails and tack into the apparent headwind at a forty degree angle. You are moving away from the buoy at the angle of tacking. Now, there is absolutely no way you can ever get back to a point directly South of where you started before the buoy does. If you think you can, that is the end of discussion! But I admit the same cannot be said about an iceboat and a balloon. However, much of the balloon’s velocity has a vertical component. Remember, the balloon is rising while the buoy drifts horizontally with the current. Also, while the buoy will drift along with the current, the balloon will allow some of the airstream to slip around the surface; it will not necessarily be carried along at wind velocity. Finally, the iceboat does achieve a higher peak velocity than a sailboat. But comparing the iceboat velocity with the balloon apparent velocity is not a direct comparison with the wind. But my part of this discussion is concerned primarily with that contraption moving steadily forward against the treadmill while being powered by the treadmill. I still say that is impossible.

 

[spork]

the boat and the buoy are moving directly from North to South at ten knots. You hoist your sails ... Now, there is absolutely no way you can ever get back to a point directly South of where you started before the buoy does. If you think you can, that is the end of discussion!

I don't just *think* I can get back to that point - I *know* I can get back to that point. In fact I can easily get back to a point further south than the buoy. That's what tacking is all about. So I guess this is the end of the discussion - but before you leave let me offer you a $100K bet on this as well. Frankly I can't imagine why anyone would take me up on a bet so blatently obvious - but it's there if you want it.

But my part of this discussion is concerned primarily with that contraption moving steadily forward against the treadmill while being powered by the treadmill. I still say that is impossible.

No need to go anywhere near the vehicle on the treadmill if we can't even agree that a sailboat can tack into the wind - particularly if the discussion is already over before it really began.

 

[spork]

For those still in the discussion...

Are we generally on board that the ice-boat racers aren't lying to us with their testimony, their GPS data, and their diagrams?

Do we not agree that a typical sailboat can tack into the wind - and thus it's easily shown that we can make a wind powered vehicle that can go directly downwind faster than the wind?

 

[ThinAirDesign]

Now, there is absolutely no way you can ever get back to a point directly South of where you started before the buoy does.

schroder, before you walk away from the conversation, humor me and answer the below question. I'd really appreciate it.


You and I are on a sailboat in the fog. We know that harbour is exactly South of us. As we pop our heads up above the deck, we see that we have a 10knot wind coming directly from the South. You and I both decide that we'll tack upwind to shore. (at this moment, we also drop a bouy into the water to mark our start point).

As we power away from our bouy, tacking zig-zag South towards land, will the bouy get there first, or will we?

Thanks

JB

 

[Trond]

I'll answer
That depends on your boat, sailing skills and whether there is a strong current going south directly to shore. If there were no current at all the buoy wouldn't go south as they seldom go directly against the wind...

And even if there were a 10 knot current going directly to shore it would be hard to beat you even with bad skills as you would then have both the current and the wind helping you...

 

[ThinAirDesign]

I'll answer
That depends on your boat, sailing skills and whether there is a strong current going south directly to shore. If there were no current at all the buoy wouldn't go south as they seldom go directly against the wind...

And even if there were a 10 knot current going directly to shore it would be hard to beat you even with bad skills as you would then have both the current and the wind helping you...

Until schroder gets back to us all I will say is that our sailing skills are perfectly adequate.

JB

 

[Trond]

I don't doubt that as it wouldn't take much to outsail a bouy tacking up wind now would it Jayson

 

[DaveC426913]

All this talk about a buoy is silly. A buoy is not wind-driven. A sailboat can sail circles around it.

We're getting off onto faulty analogies again.

 

[ThinAirDesign]

All this talk about a buoy is silly. A buoy is not wind-driven. A sailboat can sail circles around it.

We're getting off onto faulty analogies again.

At this point I couldn't care less about any analogies --- I just simply want to know the level of physics understanding of the folks in the exchange. If they don't understand simple inertial frames, I have to approach any explanation much differently.

JB

 

[schroder]

schroder, before you walk away from the conversation, humor me and answer the below question. I'd really appreciate it.


You and I are on a sailboat in the fog. We know that harbour is exactly South of us. As we pop our heads up above the deck, we see that we have a 10knot wind coming directly from the South. You and I both decide that we'll tack upwind to shore. (at this moment, we also drop a bouy into the water to mark our start point).

As we power away from our bouy, tacking zig-zag South towards land, will the bouy get there first, or will we?

Thanks

JB

I don’t know why I bother, but I will answer your question, and then ask one of my own. If the headwind is a true wind relative to still water, then the boat will get to port before the buoy. In fact, the buoy will never get to port! But, if the wind is a relative velocity caused by a ten knot current flowing towards the port, then the buoy will absolutely reach port first, regardless of how high performance the yacht is or how clever the skipper. Remember, there is no wind, only the relative wind to the current! And the discussion I had with spork was in reference to the latter scenario.

Now, let me ask you this: Suppose you have a very well designed auto rotation glide copter, the very best there is. You drop it in still air under the force of gravity. As it descends, the blades start to turn due to the relative velocity of the air as gravity pulls it towards the earth. Is there ever a point where the lift from the blades can stop the downward fall, or even reverse it so the copter goes up?

 

[ThinAirDesign]

I don’t know why I bother, but I will answer your question, and then ask one of my own. If the headwind is a true wind relative to still water, then the boat will get to port before the buoy. In fact, the buoy will never get to port! But, if the wind is a relative velocity caused by a ten knot current flowing towards the port, then the buoy will absolutely reach port first, regardless of how high performance the yacht is or how clever the skipper. Remember, there is no wind, only the relative wind to the current! And the discussion I had with spork was in reference to the latter scenario.

Thanks schroder. I will answer your below question and then I'll get back to the above.

Now, let me ask you this: Suppose you have a very well designed auto rotation glide copter, the very best there is. You drop it in still air under the force of gravity. As it descends, the blades start to turn due to the relative velocity of the air as gravity pulls it towards the earth. Is there ever a point where the lift from the blades can stop the downward fall, or even reverse it so the copter goes up?

I believe I understand the question, but let me be sure -- I assume by "glide copter", you are referring to say the equivalent of a gyrocopter without a motor. Am I right?

Assuming "Yes" to the above:

In a steady state situation, there is absolutely no version of this craft which could halt its descent or reverse it. The better designed the machine ... the slower the descent could be, but it will never get to zero or be able to reverse.

Hope I got that right.

Thanks for the quid pro quo. I hope it can continue with my next post.

JB

 

[schroder]

Thanks schroder. I will answer your below question and then I'll get back to the above.




I believe I understand the question, but let me be sure -- I assume by "glide copter", you are referring to say the equivalent of a gyrocopter without a motor. Am I right?

Assuming "Yes" to the above:

In a steady state situation, there is absolutely no version of this craft which could halt its descent or reverse it. The better designed the machine ... the slower the descent could be, but it will never get to zero or be able to reverse.

Hope I got that right.

Thanks for the quid pro quo. I hope it can continue with my next post.

JB

Thank you for your response, which is correct. Now can you please explain how a cart which is powered (through wheels and drive belt and propeller) running on a treadmill, can possibly reverse direction and move against the movement of the tread?

 

[ThinAirDesign]

Ok schroder, thanks again for the exchange (feel free to ask your own questions as before and I will do my best to answer them). I have posted my original question at the bottom of this post, just for reference.

Another question related to the original:

After you and I decide that we will tack upwind toward shore (South) and we drop our marker bouy, we set sail as planned. We start with a ~45 degree tack (or reach depending on whose terms we're using) to the SW and after a few hundred yards we tack back to the SE and return to a point directly South of our bouy. Just for conversation, let's say that the progress me made directly south was 500ft relative to the bouy.

Do you agree that the above progress relative to the bouy is possible?

Thanks

JB

You and I are on a sailboat in the fog. We know that harbour is exactly South of us. As we pop our heads up above the deck, we see that we have a 10knot wind coming directly from the South. You and I both decide that we'll tack upwind to shore. (at this moment, we also drop a bouy into the water to mark our start point).

As we power away from our bouy, tacking zig-zag South towards land, will the bouy get there first, or will we?

 

[ThinAirDesign]

I have to begin my commute schroder. I will continue a bit later (and will do my best with your question)

Thanks again.

JB

 

[uart]

Here's one train of thought that might help convince that the "treadmill in still air" situation is a least feasible.

Imagine for a moment that the rotating a propeller was replaced by a large “cork screw” (or similar). That is, the wheels were coupled through a suitable drive train to turn this large “cork screw”.

Now imagine that the corkscrew is started into a large block of soft foam attached to the front of the treadmill. If the treadmill is run then the wheels turn and the corkscrew turns and the vehicle will move forward as the corkscrew screws into the foam.

Perhaps we can think of the propeller in a similar was as "screwing" itself forward into the stationary air. I’ve got to admit that when I first saw the video I thought it was a hoax/impossible but right now I certainly think it’s at least feasible.

BTW. I also sail (just windsurfer ) and I’ve found this a very interesting discussion.

One last thing. Way back in this thread I posted a mathematical derivation of the maximum downwind speed as a function of the acute angle “phi” that a (sail or ice) boat could head into the apparent wind. The post was effectively lost to the forums current Latex problem so I’ll just briefly repost the main results here.

From the vector diagram attached,
W = wind velocity.
V = craft velocity.
A = relative (or apparent) wind velocity

Applying the sine rule (and simplifying) you get.

V / W = cos(theta) + cot(phi) sin(theta)

(note that “theta” is your boat heading off the wind and "phi" is your boats highest heading into the apparent wind)

From the above the VMG is

V cos(theta) / W = cos^2(theta) + 1/2 cot(phi) sin(2 theta)

Differentiating wrt theta the optimum heading theta was found to be,

theta_best = 45 – phi/2 degrees (assuming phi is acute)

And the resulting maximum VMG was found to be,

VMG_max = (1 + cosec(phi)) / 2

Clearly this is greater than W and I believe this proves that as long a phi is acute (which is the same as saying that the craft is capable of tacking up wind) then the maximum downwind VMG is greater than W.If anyone wants to see more details of the derivation take a look at post #62 in this thread when the latex bug is eventually fixed.

 

[spork]

All this talk about a buoy is silly. A buoy is not wind-driven. A sailboat can sail circles around it.

We're getting off onto faulty analogies again.

The sailboat tacking into the wind is not an analogy at all. It IS the device we seek to build. If you don't understand intertial reference frames, you won't see that.

However, you claim the sailboat can sail circles around the buoy. And I agree with that of course. In that case we know that the moving current can move the boat in the current's direction - faster than the current.

If the headwind is a true wind relative to still water...

We're in the middle of the ocean - 100's of miles from land, thousands of feet from the ocean floor. What IS "true wind". Do you honestly believe that what the air is doing relative to something so far away has any bearing on anything? Why not measure the wind speed relative to the moon in that case? Einstein tells us quite clearly that if we put a giant box around our boat (the fog for example) we have no way at all to distinguish between moving wind and still water vs. moving water and still wind. In fact Einstein would point out that even referring to either one as "moving" ONLY even makes sense relative to the other. After all, how fast is the "true" wind moving in an absolute sense? How fast is the Earth moving in an absolute sense? Ans: there is no answer - velocity is not absolute - it's relative.






I'll ask again. Are most of us on-board that the ice-boat can do as claimed by the ice-boating commnity (and backed up by GPS data and analysis)? At the start of this thread, most if not all said the ice-boat could never achieve a downwind VMG faster than the wind. I'd like to believe the evidence

 

[uart]

Hey I've always believed they could a achieve a VMG of W( 1 + cosec(phi) )/2