Sailing downwind faster than the wind: resolved?

[rcgldr]

... work done by the propeller is more than the work done by the wheels which are powering the propeller.

Not work, but force. The force at the propeller is greater than the force from the wheels, but the prop applies this force to air moving at much slower speed than the cart's speed relative to the ground. Assume the wind speed is 15 ft / sec (a bit over 10mph). Assume cart is moving directly downwind at 18 ft / sec, 3 ft/sec faster than the wind, and the relative wind through the prop is 5 ft / sec (2 ft / sec in addition to it's relative wind speed due to induced wash). Assume force from the wheels is 1/2 lb, and thrust at the prop is 1 lb. In a span of 1 second, the work done at the ground is 1/2 lb x 1 sec x 18 ft / sec = 9 lb ft. The work done by the prop is 1 lb x 1 sec x 5 ft / sec = 5 lb ft. Assuming the cart isn't accelerating, the losses are 4 lb ft, or about 44.5%. If efficiency is >= 55.5%, then the cart works with these parameters.

 

[yoavraz]

OOOPS. I knew there was a disconnect, but until now I have not realized we are talking about different experiments. I understand you have previous context. I apparently was thinking about a different forum from the one that was mentioned (I see this subject is popular...). At least we agree about the outdoor experiment description, I hope. Though I can guess now the scenario, I do not want to guess anymore.

Mender, Could you kindly refer me to your treadmill experiment description, or describe it here, or send me a private message. Also pls point me to the related video. Thnx

Thanks for video and info. See also the following treadmill DWFTTW video:
http://uk.youtube.com/watch?v=dgHBDESd38M&feature=related
that I picked in a search.

First of all, a substantial difference exists between a sailboat and a DWFTTW. I was completely in sailboats, and the headline "sailing downwind" completely misled me. Also the outdoor experiment misled me, though I was puzzled by the flag behavior (relative wind) a little. DWFTTW is definitely NOT SAILING. I stand behind all I said regarding a sailboat, also with wind turbine, but it is completely irrelevant to DWFTTW!

Second, what striked me the most, is the fact that a same machine architecture can be either a SAILBOAT, or DWFTTW, depending on parameters: The two major parameters that define the type are gear, TRANSMISSION RATIO and PROPELLER STEP.

In a SAILBOAT the wind pushes the vehicle. The wind (propeller) turns the wheels. The propeller step is low, the propeller is very high-speed (many revolutions per second), while the connected wheels are relatively very slow.
This behaves with all the characteristics of a sailboat, including the all the effects and physics with relative wind (apparent wind), which is the major factor (the propulsion source). Here all that I said earlier with the 180 direction applies. Here movement will start spontaneously at a certain minimum wind speed.

In a DWFTTW it is almost the opposite: The wheels turn the propeller, which generates relatively strong wind, thrust. The wheels turn fast, and the propeller relatively medium-slow. Now the propeller has a relatively large step to create max thrust. Here apparent wind does not play any major role (or any at all on the treadmill, if the air is really still - see below). Thus deviation from 180 wind does not matter much, only to the extent that its component from behind (180) pushes a little the vehicle. Here Gravitation and inertia play a major role. A little downhill makes a major contribution to wheel speed, and thus to propeller thrust. Inertia overcomes temporary disturbances that negatively affect wheel speed. I'm not sure at all about (relative) wind effect, though it may contribute a (little) force to overcome a little drag/friction. However, with a treadmill, when the vehicle is stationary, no relative wind exists (unless a substantial moving air boundary layer - wind - is generated close the the moving treadmill surface, but this in opposite direction!). Here you need a push (or downhill, or already running treadmill relatively to vehicle) to start movement.

In-between SAILBOAT and DWFTTW, I guess it has hybrid properties, depending on the two major parameters. I guess that in very strong winds it goes to a sailboat, and in relatively slow winds it will tend to be DWFTTW. I guess that in many parameter ranges it will not work at all because of conflict of forces.

All this brings us to the last question, the main subject of the discussion here, I understand: Is treadmill experiment equivalent to outdoor?

Now I'm not sure, and cannot tell by the videos without measurements. In the treadmill relative wind does not exist, and thus cannot play a role. This is the main difference with outdoor, where wind exists. Secondly, I'm not sure about the the slop. Uphill, or downhill, or horizontal. I do not know about the conditions in the experiments since a very small angle can make a big difference in tilting the equilibrium. I think I saw something about uphill on treadmill, but here the question is for how long. Inertia may sustain it a little, but then a little push is needed again. To try it you need guides/rails to keep the vehicle on the treadmill for long enough time.

 

[schroder]

Assume the wind speed is 15 ft / sec (a bit over 10mph). Assume cart is moving directly downwind at 18 ft / sec, 3 ft/sec faster than the wind, and the relative wind through the prop is 5 ft / sec (2 ft / sec in addition to it's relative wind speed due to induced wash).

What? Your argument consists of asking me to assume that the cart is already going faster than the wind? Are you serious?

 

[ThinAirDesign]

Thanks for video and info. See also the following treadmill In the treadmill relative wind does not exist, and thus cannot play a roll.

How someone can see a treadmill belt moving at 10mph in a still air room and say "relative wind does not exist" is simply amazing.

Actually, nothiing should amaze me anymore with this device -- It causes people to say some of the most mind bending things.

JB

 

[rcgldr]

Your argument consists of asking me to assume that the cart is already going faster than the wind?

Yes, assume the cart is already going faster than the wind. Assume something pushes the cart up to the desired speed then releases the cart. The question is what happens after the cart is then released to run on it's own with just the wind power. My point was that power output can be much less than power input, even when traveling faster than the wind. Look at the math again. I chose an example where prop thrust was double the wheel force, but for the real carts, it's probably less, maybe 3 to 2 or so.

 

[yoavraz]

How someone can see a treadmill belt moving at 10mph in a still air room and say "relative wind does not exist" is simply amazing.

Actually, nothiing should amaze me anymore with this device -- It causes people to say some of the most mind bending things.

JB

Very simple: If the AIR DOES NOT MOVE, there is NO WIND!

Look up definitions of "wind"

 

[rcgldr]

Is treadmill experiment equivalent to outdoor? In the treadmill relative wind does not exist.

The treadmill is equivalent. You don't need relative wind speed, or a relative ground speed, as these depend on a frame of reference. What is needed is a difference between wind speed and ground speed, independent of a frame of reference. For outdoors, you have +10 mph wind speed and 0 mph ground speed. For the treadmill, you have 0 mph wind speed and -10 mph ground speed. Both cases are equivalent. With a 10mph and a DDWFTTW cart, regardless of the frame of reference, if it's going DDWFTTW, then the cart's speed relative to the ground is a bit greater than +10mph, and the cart's speed relative to the air is a bit greater than 0 mph.

Relative to a ground (or treadmill) based observer, the wind moves at +10mph and the cart slightly faster. Relative to the air, the ground (or treadmill) moves at -10mph, while the cart moves forwards slowly. Relative to the cart, the ground moves a bit faster than -10mph backwards, and the air moves backwards at slow speed.

 

[ThinAirDesign]

Very simple: If the AIR DOES NOT MOVE, there is NO WIND!

Tell that to the fly on the hood of your car.

JB

 

[mender]

No Russ. What you are in effect saying is that the work done by the propeller is more than the work done by the wheels which are powering the propeller. You and I both know that is impossible.

Shroder, you are making a very common mistake. You have decided that the results that you are seeing are impossible and have come up with an explanation that allows you to accept that the cart is moving forward on the treadmill, yet conforms to what you think is happening. You are letting your decision/conclusion alter your interpretation of the data and conditions.

Things you need to understand to get past this: the test is valid, and the results are conclusive. The cart is demonstrating DDWFTTW when it moves forward on the treadmill. It is also demonstrating that it is harnessing energy from the difference in speed between the ground and the air - what most people understand as wind. It is also demonstrating a surplus when it is holding station against a 4.4 degree incline. It is not perpetual motion. It is not a hoax. It is non-intuitive, meaning that you have to work through the scenario and find out what is really happening, rather than depending on your gut reaction. It is all there to be found and calculated, a balance of forces that is straightforward (pun intended) once you go through the complete exercise.

Once you accept this and work through it (which may take some time off by yourself) you'll see the error in your "equivalent" frame of reference description.

Yoavraz, I looked up the definitions of wind, wind power, etc., to make sure I am dutifully following what you are saying. I'm hoping that you will do the same - actually I'm sure you will without me needing to coax you.

If what you are saying is true, my car won't feel any air resistance as it speeds up. After all, the air isn't moving, just the car. And I won't feel any "wind" if I stick my hand out the window at 60 mph because again there is no wind because the air isn't moving relative to the ground.

 

[yoavraz]

It is also demonstrating a surplus when it is holding station against a 4.4 degree incline.

Yoavraz, I looked up the definitions of wind, wind power, etc., to make sure I am dutifully following what you are saying. I'm hoping that you will do the same - actually I'm sure you will without me needing to coax you.

If what you are saying is true, my car won't feel any air resistance as it speeds up. After all, the air isn't moving, just the car. And I won't feel any "wind" if I stick my hand out the window at 60 mph because again there is no wind because the air isn't moving relative to the ground.

kjgilkgihghi

 

[yoavraz]

It is also demonstrating a surplus when it is holding station against a 4.4 degree incline.

Yoavraz, I looked up the definitions of wind, wind power, etc., to make sure I am dutifully following what you are saying. I'm hoping that you will do the same - actually I'm sure you will without me needing to coax you.

If what you are saying is true, my car won't feel any air resistance as it speeds up. After all, the air isn't moving, just the car. And I won't feel any "wind" if I stick my hand out the window at 60 mph because again there is no wind because the air isn't moving relative to the ground.

That is great, and actually I can now see how when having the initial momentum, with inertia an effective DWFTTW can sustain enough thrust to maintain it moving. No wind exists when the vehicle is stationary relatively to room. (Of course, the propeller makes wind backwards, but no external wind.)

As I wrote, only some possible wind close to the belt may exist due to boundary layer effect (the belt moves the close air layers; I remember quite strong wind from a conveyor belt), but in opposite direction! Thus it can only slow the vehicle a little, but apparently not stop it.Still I'm not sure if back-wind is essentially needed for the outdoor vehicle. It may provide the "last push" needed to overcome the drag for this particular vehicle, but in principle back wind looks secondary. For sure no wind exists indoor on treadmill.

----------------------
Added: Without the treadmill you must have wind, at least a little, to supply energy after the energy in first push of the vehicle is dissipated by drag and friction.

 

[ThinAirDesign]

You want an experiment to prove this? Gear up the cart so that it runs forward when sitting on a treadmill that runs in the same direction, the tread is running from behind the cart. That is a very simple reversal of gear and/or propeller pitch. The tread advancing from behind gives a truer representation of the wind blowing from behind. Hold your hand on the cart until it fully winds up and let it go. Tell me if it outruns the tread. That’s the challenge. I know that it will not but you all have a go at it and be sure to let me know how it works out!

Schroder is asking us to place the device on a belt in such a way that it advances across the belt in the same direction that the belt is traveling through the room. He wants to know if the cart can advance up the belt in this configuration -- he wants the device to 'beat the belt' or "outrun the tread" to the other end of the room.


In other words, he is asking if a wind powered device can move into the wind, powered by the wind.

Think about it -- he's asking the wheels to turn 1mph (beating the belt) into a 10mph relative headwind. Forget the treadmill -- just take the device out into the street with a 10mph wind and see if it advances down the street at 1mph against the headwind.

Proving any particular device can/cannot advance against a headwind in no way demonstrates that a device can/cannot go DDWFTTW.

(For what it's worth, we don't claim that our device will drive against a headwind powered only by that wind (though it's easy with regearing to make it do so). However the issue of whether a device can be built that will do so has been demonstrated so many countless times that it is of no interest to us.)

JB

 

[rcgldr]

In the treadmill relative wind does not exist, and thus cannot play a role.

In the treadmill case, a relative wind does exist, it's 0mph. It plays a role because the treadmill is not operating in a vacuum. The propeller is accelerating the still air backwards, and this generates forwards thrust. The treadmill surface moves at relative speed of -10mph. The cart works because it's forward speed relative to the air is much less than it's forwards speed relative to the treadmill, allowing the speed at the wheels to be geared down while at the same time increasing the torque applied to the propeller, so the propeller generates more force but at a lesser still speed than the wheels.

This is the main difference with outdoor, where wind exists.

Well outdoors the relative wind would be +10mph, and the ground's relative speed would be 0 mph. From the cart's frame of reference, the treadmill case and the outdoor case are the same (ignoring gusts).

I'm not sure about the the slope. Uphill, or downhill, or horizontal. I think I saw something about uphill on treadmill, but here the question is for how long.

It's uphill in this video, near equilibrium:

http://www.youtube.com/watch?v=dgHBDESd38M&fmt=18

Also uphill in the second part of this video:

http://www.youtube.com/watch?v=7xL8gRJ5F6k&fmt=18

I think someone mentioned this was 4.4 degrees uphill?

 

[mender]

The original question of whether a treadmill test is valid has introduced some new objections. This leads me to believe that yet another method of testing may be beneficial in developing a device. The treadmill test only shows the results of the total system, not each loss along the way nor the total amount of power that is being harnessed to counter the drag.

Shroder's assertion that the treadmill only serves to drive the wheels is correct. However, his reasoning that the treadmill can be oriented in any direction other than directly in line with the cart's path is not. That would change the direction of the force acting against the wheels, which is what the propeller has to overcome in order to work. A way to separately measure the two opposing forces should help when developing another design. For this discussion I'll use a propeller as the air interface.

I need a simple method of measuring how much resistance the air has to a moving propeller. What I propose to do is spin the wheels of the cart at the equivalent of 10 mph and measure how much force against the air is generated (lift in a forward direction), then measure how much force (or drag) is required to generate that lift force. From that, I can figure out the lift to drag ratio for the entire mechanism. Next, spin the prop by itself at the same rpm, measure the two forces and figure out the lift to drag ratio for just the prop. That will tell me how efficient my drive mechanism is and also how efficient my prop is. Finally, measure the rolling resistance of the cart with the drive mechanism disengaged so I know how efficient the vehicle is.

From doing this, I should be able to determine where my efforts can best be directed. After doing that, it should be a relatively simple matter of testing my other non-propeller air interface and fine-tuning its efficiency in isolation.

Is this reasonable? Can this be achieved with fairly common equipment? Or am I going to miss something?

 

[rcgldr]

Total amount of power.

If the specs for the propeller are known, that could be used. An electric motor with a known loss factor could be used to drive the propeller at the same rpm, and a watt meter used to determine the input power to the motor. I don't know if it's possible to drive the wheel axle with a motor, but if so, then again the input power to the motor required to drive the wheels which in turn drive the prop to a specific rpm could be measured. All the stuff I mentioned here should be available at a hobby shop or via hobby online store, although I don't know the cost as you need a watt meter, motor, motor controller and a power supply and/or rechargable batteries.

 

[ThinAirDesign]

Mender, I've only quickly reviewed your test request so bear with me.

Here is something I could do for you as it's something I've wondered about myself:

Test: 1
On a level treadmill we could nose the device up against a gram scale and show net thrust. we could do this at several speed.

Test 2:
On a level treadmill we remove the prop from it's shaft (leave the shaft and associated bearing drag) and "pull test" against the same scale. Again, this can be done as specific and associated to the above speed points.

Does this give you what you want? All? Some? Of no use?

Thanks

JB

 

[Subductionzon]

I am new to this forum, but on another I violently (well not quite) disagreed with spork on the veracity of the original video. In fact I can still see my comment on youtube.

Here are some points that will help clear things up, I hope. First off the treadmill tests are perfect proof of concept. If you don't think so imagine a treadmill arbitrarily large. If you are on a large enough treadmill you could not tell the difference between it moving 10 mph, and as a result you feeling a 10 mph apparent wind, or standing still on an open field and being hit by a 10 mph wind. There is no point in referring to the ground underneath the treadmill. Second, the wheels of the cart are coupled directly to the propeller. The propeller does not freewheel, so the cart's energy is coming from the difference between the speed of the wind and the speed of the ground. To those who think that what they are trying to do is approaching the idea of a perpetual motion machine you have to realize that with a air speed of zero (real and not apparent) the cart could not advance at all since the difference between ground speed and air speed is zero. It is a subtle difference but a very important one. If you think of the wind blowing on the cart you will be misled.

 

[rcgldr]

Test: 1
On a level treadmill we could nose the device up against a gram scale and show net thrust. we could do this at several speed.

Test 2:
On a level treadmill we remove the prop from it's shaft (leave the shaft and associated bearing drag) and "pull test" against the same scale. Again, this can be done as specific and associated to the above speed points.

Not enough information. One issue is that prop pitch increases both thrust and drag on the wheels, so the no prop pull test doesn't help much.

Replace the gearbox with a motor and drive the prop at the same rpm, and then measure the thrust with the gram scale. Then you'd know the thrust, and this reading minus the test 1 gram scale reading would give you the overall drag factors on the cart.

 

[mender]

Mender, I've only quickly reviewed your test request so bear with me.

Here is something I could do for you as it's something I've wondered about myself:

Test: 1
On a level treadmill we could nose the device up against a gram scale and show net thrust. we could do this at several speed.

Test 2:
On a level treadmill we remove the prop from it's shaft (leave the shaft and associated bearing drag) and "pull test" against the same scale. Again, this can be done as specific and associated to the above speed points.

Does this give you what you want? All? Some? Of no use?

Thanks

JB

Yes, JB, "all" will be very helpful! The first test should give me the L/D ratio of your cart and the second the rolling resistance of the cart and drivetrain.

Can you also tell me the gearing that you're using and repeat the prop specs? And measure the amount of force/resistance the prop generates at the same mph intervals? This may be asking a lot but ...?

With that data, we should be able to plot several curves and predict velocities - maybe even increase the L/D of your cart, although that may be hard to do!

 

[mender]

Jeff's suggestion echos my request for the force the prop generates at the 10 mph rate. However, if you can add the extra data points we can graph that and be able to provide numbers to prove what is happening. Sometimes the numbers are believed more than the eyes.

 

[rcgldr]

Well one alternative is to visit web sites that calculate thrust versus rpm for given prop diameter and pitch, then average those, since I don't trust any of them (the AMA one ignores the pitch aspect).

If the prop pitch is excessive, then it's adding both thrust and drag factors into the cart, and could be the dominant drag factor on the wheels. This is independent of L/D of the prop, and if the L/D is high, than it's just adding stress to the drive train, which could indirectly increase the drag factor.

The only way to know if the pitch is excessive is to try larger driving wheels to slow down the prop and see if the results improve or degrade.

 

[mender]

How about this site and calculator:

http://members.jcom.home.ne.jp/4223215501/staticthrust.htm

It sounds like I need to get a power supply, one or two decent size RC electric motors and a few props to evaluate and baseline, then compare my non-prop design against that baseline and develop as needed.

 

[schroder]

Those are all excellent tests you are proposing. I predict you will find without fail that the drive power necessary to turn the wheels will be significantly more than the available output thrust at the propeller. In cannot come out any other way. I am disappointed that no one can answer my question about the validity of using the floor as a common reference for both frames where frame one is a cart sitting on a stationary tread and being pushed from the rear by a wind; and frame two where the cart is now being driven by a moving tread in stationary air. The floor is stationary at all times with the tread in frame one and with the air in frame two. The floor is a valid reference in both cases. In frame one, the cart advances relative to the floor at close to wind speed. In frame two, the cart is also advancing relative to the floor, but at very much less than the tread speed. For some reason which you cannot clarify or justify, you use the moving tread as your reference in that frame, which is clearly not a demonstration of anything. I can place a cardboard box on a treadmill and run the tread fast enough so the air makes the box advance against the tread. What does that prove? The cart must advance relative to the floor in both frames as they are equivalent. Again, for a physics forum I am amazed and disappointed that I need to defend conservative physics principles such as Nothing powered by the wind can go faster than the wind going directly downwind. You really need to get sorted out on this issue if you are to avoid becoming the laughing stock of the physics world.

 

[ThinAirDesign]

Again, for a physics forum I am amazed and disappointed that I need to defend conservative physics principles such as Nothing powered by the wind can go faster than the wind going directly downwind.

You are confusing established principles of physics with opinion -- yours.

There are no principles of physics stating that the above is impossible and I have the device on my desk which upon demand (and even polite request) can demonstrate the fallacy of such a position.

JB

 

[yoavraz]

Again, for a physics forum I am amazed and disappointed that I need to defend conservative physics principles such as Nothing powered by the wind can go faster than the wind going directly downwind. You really need to get sorted out on this issue if you are to avoid becoming the laughing stock of the physics world.

Forget about the wind. The only place you have a (external) wind in a DWFTTW on a treadmill is in the name DWFTTW (the W's)... I thought we have cleared this.

Thus you have nothing to defend here. It boils down to a little energy from the treadmill that transforms in a quite sophisticated way to thrust and movement in the opposite direction. No law of Physics is broken...

Actually, after I wrote the last paragraph above I have realized that without the treadmill you must have wind, at least little, to supply energy after the energy in first push of the vehicle is dissipated by drag and friction.

 

[mheslep]

...Nothing powered by the wind can go faster than the wind going directly downwind. ...

That is not an apt description of what is happening with this cart. The propeller surface is not going directly 'downwind', downwind being the direction of the cart, it is moving across the direction of the wind. In that case it is just another mechanical device like a sail boat traveling across the wind that converts energy in the wind stream via mechanical means to the kinetic energy of the platform. As any sailor knows a sail boat traveling across the wind can travel faster than the prevailing wind speed over the surface of the water. Regards perpetual motion, physics only states that the device must convert somewhat less of the energy it captures from the wind stream to the overall kinetic energy of the device. Focusing on the 'faster than wind' aspect is fraught with missteps.

To further demonstrate how the wind speed/ cart speed coupling is a red herring: the propeller cart could be equipped with a small electric generator/motor and a battery to store energy. The cart is fixed for a time in wind speed X and charges the battery as a wind turbine. Later, the cart can take off under motor power and travel many times the wind speed X in whatever direction.

 

[mender]

Frame one: the cart is sitting on the stationary tread. It has a wind blowing from behind at 10 mph. The movement of the air relative to the ground is what we call wind. Therefore the cart feels that relative movement as wind. Just to make sure, the cart is tethered to hold it in position.

Extend this: tow the cart forward at 10 mph in the 10 mph wind. The cart no longer feels a relative wind even though the wind relative to the ground is still there. Correct? At that point the cart is moving at the same speed as the air.

Frame two: to duplicate the conditions in Frame one, a speed difference between the air and the ground needs to somehow be achieved so that the cart can feel a 10 mph wind from behind, just like Frame one. One way to do that would be to tow the cart backwards at 10 mph in still air. But that raises a problem. In Frame one, when the cart feels the 10 mph wind from behind, the wheels which are part of the drive system are stationary. In order for the conditions to match Frame one, the wheels need to stay stationary as the cart is towed backwards. Easy enough: we attach a long flat surface that can slide along the ground to the same tow line and pull both backwards at the same time. Now we have matched the conditions of Frame one exactly. The air flow relative to the cart is 10 mph from behind, The ground speed relative to the cart is zero. The cart is held in position.

An observer standing on the ground beside the cart in Frame one would feel the same 10 mph wind from behind as the cart. An observer standing on the surface being towed backwards with the cart in Frame two would also feel that wind. An observer in Frame two standing on the ground beside the surface being towed would not feel the same wind that the cart feels; therefore the ground reference in Frame two is invalid. The only valid reference in Frame two is the moving surface.

Shroder, your question about using the floor as the reference for the second case has been answered by several people. The answer is no. You are failing to accept that answer. Your reason for not accepting the answer is based on your belief that "Nothing powered by the wind can go faster than the wind going directly downwind."

I appreciate your recognition of the validity of the proposed tests:

"Those are all excellent tests you are proposing. I predict you will find without fail that the drive power necessary to turn the wheels will be significantly more than the available output thrust at the propeller. In cannot come out any other way."

I think I understand why you have this belief. You see the thrust generated by the propeller as being, at best, the same as the drag needed to spin it. Since a propeller is essentially a wing, a quick look at typical lift to drag ratios for wings and propellers should help you get past this. Consider the thrust as lift.

 

[Subductionzon]

I am disappointed that no one can answer my question about the validity of using the floor as a common reference for both frames where frame one is a cart sitting on a stationary tread and being pushed from the rear by a wind; and frame two where the cart is now being driven by a moving tread in stationary air. ... . You really need to get sorted out on this issue if you are to avoid becoming the laughing stock of the physics world.

Why would you want to use the floor as a point of reference. Look at it from the cart's point of view. On an long treadmill if the cart was stationary (we will give it some imaginary locked brakes for this) it will feel a ten mph tail wind. That is what spork et al were trying to simulate by running their belt. There is no point to using the floor as a frame of reference. So when the cart outruns the treadmill, that is when it advances forward on the treadmill as was evident on the videos then it is clearly outrunning its perceived tail wind. Not only did they outrun the wind, they also outran it even when the treadmill was sloping up. Please note the cart derives its power from the difference between the speed of the wind and the ground (or in the case of the treadmill the perceived wind) so if the treadmill is not moving or if the wind is not blowing the cart will not move. No wind equals no power.

Speaking of points of reference I don't know if this has been asked before but what could go faster: A boat sailing down a stream moving ten mph with no wind, or a boat sailing down the same ten mph river with a ten mph tail wind? If you can answer this correctly you can see why the cart on the treadmill is the same as the cart sailing directly downwind faster than the wind.

 

[schroder]

You are confusing established principles of physics with opinion -- yours.

There are no principles of physics stating that the above is impossible and I have the device on my desk which upon demand (and even polite request) can demonstrate the fallacy of such a position.

JB

Does it look like a cardboard box? I have one of those also and it will advance against the tread. Maybe I will put in youtube.

 

[ThinAirDesign]

Forget about the wind. The only place you have a (external) wind in a DWFTTW on a treadmill is in the name DWFTTW (the W's)...

Nowhere will you find the parenthetical "(external)" in our claim with all it's implications. This is apparently a requirement of yours, though definitely not ours.

Wind it merely relative motion between surface and air. IFOR physics principles dictate that one cannot actually determine which is moving and which is not for all motion is relative.

A sailor in the middle of the ocean could see a nice breeze across his derigged boat and say "ah ha! -- the wind finally arrived", but in truth perhaps it is not the air moving at all, but a current of the ocean pushing his hull. He nor the boat is none the wiser and his sailing day moves forward the same way in either case -- he can use this wind to reach his next waypoint.

The cart on the treadmill is truly going DDWFTTW -- you're just confused by the frame of reference you happen to be standing in. It's a common mistake -- people have a hard time realizing that physics isn't about 'them' and their particular frame.

... I thought we have cleared this.

Most here have -- you still have not.

JB

 

[ThinAirDesign]

Does it look like a cardboard box? I have one of those also and it will advance against the tread. Maybe I will put in youtube.

When you have a video of your cardboard box advancing against the motion of a treadmill in a still air room, using only said motion as power, send me the link and we'll chat. I'll be looking forward to it.

JB

 

[yoavraz]

Nowhere will you find the parenthetical "(external)" in our claim with all it's implications. This is apparently a requirement of yours, though definitely not ours.

Wind it merely relative motion between surface and air. IFOR physics principles dictate that one cannot actually determine which is moving and which is not for all motion is relative.

A sailor in the middle of the ocean could see a nice breeze across his derigged boat and say "ah ha! -- the wind finally arrived", but in truth perhaps it is not the air moving at all, but a current of the ocean pushing his hull. He nor the boat is none the wiser and his sailing day moves forward the same way in either case -- he can use this wind to reach his next waypoint.

The cart on the treadmill is truly going DDWFTTW -- you're just confused by the frame of reference you happen to be standing in. It's a common mistake -- people have a hard time realizing that physics isn't about 'them' and their particular frame.



Most here have -- you still have not.

JB

Forget external. Real wind only by the propeller. You can call any imaginary object "wind," but it exists only if air really flows. With the treadmill DWFTTW is an empty name.

 

[mender]

Forget about the wind. The only place you have a (external) wind in a DWFTTW on a treadmill is in the name DWFTTW (the W's)... I thought we have cleared this.

Wind: the cart needs a source of power to work. It uses the wind as that source. The amount of power available from the wind is measured by the wind speed. That always assumes (and rightly so) that the ground is stationary.

Yoavraz, let's say we want to check a wind turbine to see how much power it can harness from a 10 mph wind. We mount the wind turbine on a trailer and drive around until we find a place that is experiencing a 10 mph wind. We stop, point the wind turbine into the wind and start taking our measurements. Everything is good, we get our measurements before the wind goes calm. We pack up but forget to secure the wind turbine. As we get to 10 mph in the still air, we notice that the wind turbine is turning. For the fun of it, we again hook up our test equipment and find that when the wind turbine is being towed through the air at 10 mph, it acts exactly the same as when it is sitting still in a 10 mph wind. Therefore, from now on we decide that instead of wasting time looking for the right wind, we generate our own wind by moving the ground reference at 10 mph.

The wind turbine doesn't know the difference. When the air is still and the ground is moving, the wind turbine behaves exactly the same way as when the ground is still and the air is moving. Those are equivalent frames of reference, and both are perfectly satisfactory for testing. According to the wind turbine and the output that is measured, the air is flowing past the wind turbine. To the wind turbine, that is wind. To the cart, air flowing past is also wind and generates the same results. You can call it fake wind (most would call it relative wind which is the correct term - look it up) but the results are the same as a wind moving across the ground.

The treadmill allows us to "tow" the cart along the ground at 10 mph. If we had a really long treadmill that was moving at 10 mph, we could step onto the treadmill surface holding our cart, set it down facing "downwind" and let it go.

What are the possible outcomes of this?
1: The cart doesn't move.
2: The cart moves and reaches a speed of less than 10 mph in reference to the treadmill surface
3: The cart moves and reaches 10 mph in reference to the treadmill surface.
4: The cart moves and reaches a speed above 10 mph in reference to the treadmill surface

Since we only have a short treadmill (I hope that you now accept that the treadmill is a valid substitute for a wind - if not read the frames of reference again and ask questions), we can only test a short portion of the full scale outdoor test. That segment is with the cart at 10 mph, with only a few feet either way to indicate a trend. If we place the cart on the treadmill surface moving at 10 mph, the outcomes that I listed above would look like this:

1: The cart would quickly move to the back of the treadmill when it is released
2: The cart would slowly move to the back of the treadmill when released (may be hard to see the difference between this and #1 but in either case this would be a failure)
3: The cart would stay in position on the treadmill (this would be downwind at wind speed)
4: The cart would move forward on the treadmill ( this would indicate moving directly downwind faster than the wind)

 

[ThinAirDesign]

Forget external. Real wind only by the propeller. You can call any imaginary object "wind," but it exists only if air really flows. With the treadmill DWFTTW is an empty name.

And therein lies the crux of your misunderstanding. There is nothing "imaginary" about this wind. To any object on that treadmill, including the device, there is *exactly* the same wind in that room as out on the street in a tailwind.

I know it seems impossible, but not only is it possible, it's the law.

JB

 

[ThinAirDesign]

On a treadmill the treadmill provides the energy. No wind exists.

With a "conclusion first" position, facts to fit will follow.

JB