Down wind faster than the wind

[spork]

Why?

Mostly just making a joke. But it just seems it's never quite over. I suspect you'll continue to fight the good fight against the naysayers, and develop more analytical ammo in the process. I know I have. I originally conceived of this thing a few years ago (and later learned I wasn't the first to have done so). I certainly felt I knew everything I needed to know about just exactly how it worked. But I have to admit, in answering peoples questions (or more often claims of me scamming) I think I've come to understand some of the subtleties better. Perhaps more importantly, I've come to understand some of the different but valid ways it can be explained (as opposed to the many invalid ways that seek to explain it).

It confirms to my satisfaction that your device should theoretically work as advertised...

Interestingly, I had convinced myself back at the beginning with a simple vector analysis. It wasn't until my buddy JB insisted that we build it that we did so. And yes, it actually does work as advertised. I plan to post some simple plans and parts list so anyone can prove it to themselves. JB has even threatened to mail his to deniers (that seem trustworthy enough not to mistreat it).

If I may, I congratulate you on such a brilliant idea (I wouldn't have thought of that) and thank you for this very inspiring exercise in theoretical mechanics.

Careful what you say - that kind of talk puts you in the extreme minority (but thanks).

 

[my_wan]

Ahhh finally found the explanation as to why it doesn't work that you can comprehend. What happens when you are going faster than the wind? You have a headwind. What does the headwind do? It pushes the propellor. In what direction does the headwind push the propellor? The wrong direction. What will happen? The cart will stop and start going the other direction.

Think again. The headwind at above wind speed turns the prop in the same direction it takes to increase the speed of that wind in the same headwind direction. At below wind speed that same direction increases wind speed in the opposite direction as the tailwind. These descriptions do miss the relative force vectors operating the craft because it only considers the absolute direction.

I will not respond to the second half of your response because you were responding to a quote that didn't belong to me but failed to note that. Though Careyp74's who actually said it made a good point.

 

[my_wan]

so a couple of questions. First (thanks JWideman) how is this thing steering? Second, why does this thing slow down and stop so drastically in the end?

I think this is a fake. I think there is either a battery driven motor and steering servo on the car, or the car is being towed behind something.

Of course the craft had remote steering and breaks. It says so. I can't attest that he didn't power the wheels with a motor or drag line of any sort. I do say the craft can in principle work as filmed without doing so.

If you bring up the fact that it takes a couple of tries, so that proves it is real, then you really haven't been around long. That is an old trick. Oh, and Grandma couldn't be in on the prank, right?

If you listen to the video it took another try because they forgot to release the break that you made an issue of above. Of course Grandma can be in on a prank. It could even be her idea. My point is why would you fake something that can work. It would be like faking floating steal when it is trivial to get steel to float.

BTW, this operation has nothing to do with tacking the wind. The prop is not being blown by the wind, it is being driven by the wheels. As cool as the plane on a treadmill is, and what we can learn from it, this video here is nothing like it, and doesn't make sense.

This is the quote that technoextreme made appear as if it was my quote. Agreed that it's nothing like a plane on a treadmill. At below wind speeds the prop acts more like a progressively reactive sail than a prop. At ground wind speed the average wind speed relative to the craft is still greater than the craft speed due to the prop. Note that with the prop wind speed are quiet different at different points around the prop. In fact given the prop the craft will never exceed average wind speed relative to the craft itself. The only wind speed exceeded on average is the wind speed relative to the ground without the craft involved.

 

[spork]

The only wind speed exceeded on average is the wind speed relative to the ground without the craft involved.

But isn't that enough?

 

[my_wan]

Hey folks.

Hey spork. Good to see you here . I wish I could have continued the previous debate. Your claim that I debated is probably not as far off as you probably think I claimed. It simply lack a quantitative capacity that the ideas I was trying to instill in the debate could give. The craft dynamics do not have a singular mode of operation, they depend heavily on a number of variables that can change with varying speeds or be changed in the design itself. It all comes down to how a long series of vectors add up or cancel on a particular set of design choices and speeds. The analytical problems are due to force feedback in these vectors such that simple addition is not adequate. I'm quiet sure the basic idea can be massively improved and even made practical in some circumstances.

 

[my_wan]

But isn't that enough?

Yes, if the only question is if it will work. I want efficiency and practical applications.

 

[my_wan]

D. 0 < f < 1: The device will move forward at high gear; the equilibrium speed will be v_wind / f minus losses, making it possible for the device to move at higher than wind speed (with less "oomph", though). However, as f approaches zero (the gear is set too high), the force that drives the device towards v_wind / f will get progressively lower, to the point that it will begin to lose to the friction and drag forces - and this will lower the equilibrium speed. So there is a sweet-spot f in this range that maximizes the equilibrium speed for a given wind speed. This depends on the specific construction of the device.

Very good. I brought up the sweet spot case for the propellers "design point" on physicsforums. It does apply also to the gear ratio. If the force ratio between the prop and wheels is too high then efficiency drops exponentially. If they exactly equal prematurely you can lose potential acceleration. They should only equal when the craft is at the maximum speed allowed by the force and drag components. It really needs a transmission for best efficiency at all speeds but that adds more overall inefficiency.

 

[humber]

George Sychrovsky does not suggest cheating. The device runs on the inertial energy of the propeller. He means that if the treadmill were long enough, and the device remain undisturbed, it would eventually stop when that energy is dissipated. The device is restrained by the hand until the propeller comes to speed. Every time the device is stopped in the manner that is shown, the propeller picks up some energy in the same manner as when started.
If you remove a spinning device from the treadmill and place it on the ground, it will move forward, so of course it will run up the belt until losses dissipate that stored energy.
This is not a demonstration of the claimed effect.

 

[spork]

The device runs on the inertial energy of the propeller.

That's ridiculous. We posted a video tonight to address that very claim.

He means that if the treadmill were long enough, and the device remain undisturbed, it would eventually stop when that energy is dissipated.

It would stop when I failed to pay my electric bill or the wheels wear out. Watch the video. Try it for yourself. This thing is about as simple as can be.

This is not a demonstration of the claimed effect.

Thanks for that considered and in-depth analysis.

 

[humber]

You have not addressed the stored energy. That is why it works. No analysis is required until you can demonstrate that it will run continuously without being stopped by hand or other means.
Whilst spinning, it will run for sometime on the ground, won't it?

 

[spork]

Watch


Direct Downwind Faster Than The Wind #5 (DDWFTTW)

At spork33

Your concerns are addressed directly.

 

[humber]

No, same problem. As your commentator remarked, you are stopping the device again. It picks up energy. Practical considerations prevent you from waiting the time that you allow for the propellrr to stop when removed from the treadmill, before stopping it again. Replace the propeller with a mass, and you will see the same effect.

 

[spork]

You're kidding - right?

When removed from the treadmill the prop starts to slow down immediately. as soon as it starts to slow down, the cart moves backward on the treadmill. Our moves forward indefinitely. It will push on whatever we put in front of it... indefinitely. If we increase the incline of the treadmill sufficiently, it will just "hover" in one place - indefinitely - without ever running out of that 1/2 ounce of kinetic energy stored in a 10 gram plastic prop.

 

[humber]

Of course. The propeller creates drag, which also restrains the device. If the device were capable of taking the energy derived from the wheels, and converting it to equivalent thrust, then it would remain in the same position, but that would require 100% efficiency. Under these conditions, no work would be done ( the device would not accelerate). The stored energy adds this force, to drive it forward. Therefore, the time it takes to slow to a stop is extended beyond that time of the free-air case. This would also apply to a flywheel, but it will certainly not be dragged backwards at the same speed as the belt, but it is that differential velocity that is the indicator of the stored energy. Work is being done.only by the stored energy.

This is not a really connected to the actual cart. For all intents and purposes, the device can take as much energy from the belt as it the situation demands. In the wind-drive case, Bernoulli's law limits the energy that can be taken from the wind. The cases are not the same.

 

[spork]

Of course. The propeller creates drag, which also restrains the device. If the device were capable of taking the energy derived from the wheels, and converting it to equivalent thrust, then it would remain in the same position, but that would require 100% efficiency. Under these conditions, no work would be done ( the device would not accelerate). The stored energy adds this force, to drive it forward. Therefore, the time it takes to slow to a stop is extended beyond that time of the free-air case. This would also apply to a flywheel, but it will certainly not be dragged backwards at the same speed as the belt, but it is that differential velocity that is the indicator of the stored energy. Work is being done.only by the stored energy.

I WIN!!! I bet JB you would use exactly this argument. He laughed his butt off.

This is not a really connected to the actual cart. For all intents and purposes, the device can take as much energy from the belt as it the situation demands. In the wind-drive case, Bernoulli's law limits the energy that can be taken from the wind. The cases are not the same.

So you've figured out that the equivalency of inertial frames isn't really true (when Galileo, Newton, and Einstein failed to ever find an exception). Impressive!

 

[humber]

It says nothing about frames of reference. When you tilt the belt to make the device hover, no work is being done. When you restrain it with your hand, no work is being done. No laws are broken, this is quite in keeping with what Newtonian mechanics would predict. All you are seeing in these cases is that the motive and impeding forces are in balance. Choose your load, (gravity, drag or hand) and the belt will provide the energy to balance it.
As I said, if you disagree, replace the propeller with a flywheel and observe that the device will not move backwards at the speed of the belt.

 

[humber]

When the device is static upon a belt that is at an angle, what happens when the belt is lowered a little? It moves forward up the belt, until the forces are again in balance. You are confusing force and work, which is force x distance.
Lowering the belt lowers the devices gravitational potential energy, driving the device forward.
For the device to move forward relative to the belt, i.e. Vehicle velocity - belt velocity > 0, requires a source of energy that is not available from the belt. When level, that supply of energy comes from the energy that is stored in the angular momentum of the propeller when you first spin it up. Nature 'never forgets' this energy, so it will remain until dissipated. Waiting is otherwise of no importance.
These demonstrations perhaps show what the real device needs to achieve, but not that they are realised. That situation is quite different

 

[spork]

Boy - you have some pretty unique ideas about physics. Perhaps I'll help straighten you out when I'm awake.

 

[Acleron]

Not quiet. Once the vehicle reaches ground air speed the prop tied to the wheels then creates thrust that effectively increases the air speed relative to the craft. Of course this places more drag on the wheels but because ground speed and actual air speed still don't match the power is there to pay for this drag. The available power is the difference between air speed and ground speed regardless of the motion of the craft or extra air speed created by the prop.

Just taking the case of the vehicle reaching the air speed. Then with respect to the propellor, the air is motionless. How can it now get any energy to supply to the wheels? If the propellor is directly connected to the wheels, which seems the case in the first video, the propellor would now act to stop the wheels. If the vehicle somehow exceeded wind speed the propellor would now be forced to rotate in the opposite direction further slowing the vehicle.

 

[.13.]

Humber, think of the treadmill as an engine that drives the propeller. The treadmill uses a little more power from the grid when the device is running on it. Since the vehicle is not mounted on the treadmills frame the only forces pushing it back are the friction between the wheels and the treadmill, air resistance against the vehicle, and friction between different components of the vehicle. Did I miss anything? In any case, the sum of forces acting against the vehicle are smaller than the force generated by the propeller (which is powered by the treadmill). That's why the vehicle starts to move forward.