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Down wind faster than the wind

The wheels torque the prop? Huh?

The entire premise of the thread/idea is that the cart is wind powered.

This implies that the wind provides the torque.
 
The claim that the combination of the speed of the wind and the opposing thrust of the propeller causes the vehicle to travel faster than the wind is incorrect.

(1) All of the energy to move the vehicle comes from the wind.

(20 All of he energy to spin the propeller comes from the wind.

(3) The energy produced by the spinning propeller is less than the energy taken from the wind to create it because of friction.

(4) The combined energy of the wind and the propeller is therefore less than the speed of the wind.

Not only could this vehicle not exceed the speed of the wind, it couldn’t even achieve it. The same vehicle with a sail the same area as the sweep of the propeller would perform better as there would be less friction involved.

There’s no free lunch and there’s no free energy.
 
Seymour Butz said:
The wheels torque the prop? Huh?

The entire premise of the thread/idea is that the cart is wind powered.

This implies that the wind provides the torque.
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No, the tailwind provides the straight-ahead push that gets the wheels moving and ultimately spins the prop via the torque of the gears. When the cart is near, at, and above wind speed the wind also provides greater resistance for the prop to push against than still air would.

But when the tailwind is actually flowing over the prop vanes it applies torque to the prop in the opposite direction from how the prop actually spins. The gear torque wins out because of how the gear ratios and prop pitch are set. The prop pushes air backward as the cart runs.

Respectfully,
Myriad
 
Michael C said:
I think a possible source of confusion is talking about "wind" instead of talking about "speed of the air". Saying "there isn‘t any wind relative to the vehicle" is equivalent to saying "the air is not moving with respect to the vehicle". This does not mean that the air no longer has any effect, or cannot be considered as a factor in the equation: the vehicle is still in contact with the air, so it can push against it.

The movement of the propeller is indeed created by by the motion of the rolling treadmill surface relative to the vehicle, but this motion only continues because the propeller is thrusting against the air. Imagine what would happen if the propeller was not connected to the wheels: in this case, when the vehicle was lowered on the treadmill, the wheels would start spinning, but the prop wouldn't turn. The loss of energy due to friction would soon cause the wheels to spin slower and the vehicle would run off the left end of the treadmill (viewed as in Spork's YouTube videos). In fact, when the propeller is connected to the movement of the wheels, it thrusts against the air causing the vehicle to run off the other end of the treadmill.

The essential thing is that it's not "the wind" that is the motive force, it's the difference in speed between the air and the ground. If there's no difference, the vehicle won't run. If you go out on a day with no wind at all and put the vehicle on the ground, it won't do anything. If you now give it a push, there will indeed be a "wind" relative to the vehicle, but it won't help, since there is still no difference in speed between the air and the ground. In this case, the vehicle will run a certain distance but will be quickly slowed down by forces of drag and friction.

If there is a steady wind, the vehicle will accelerate up to the speed where the forces are in equilibrium, then just keep running. And it's important to point out that the point where the forces are in equilibrium is not necessarily the point where the vehicle is stationary with respect to the air. When it is stationary with respect to the air, its wheels are being turned by the ground, the propeller is being turned by the wheels and therefore thrusting against the air.

If the vehicle is going at exactly the speed of the wind, then all the extra thrust of the propeller is doing is compensating for any speed losses caused by drag or friction. If the vehicle is going at 10mph in a 7mph wind, then we might consider that the thrust of the propeller is accounting for the extra 3mph. It's a simplification, but it may be a step towards understanding what's going on.
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The thing is that for the vehicle to reach the speed of the wind it would take all of the energy of the wind to do so. There would be no energy left to spin the propeller to push against the “still“ air. There is simply not enough energy in the wind for the vehicle to reach the speed of the wind and spin the propeller.
 
ynot said:
The thing is that for the vehicle to reach the speed of the wind it would take all of the energy of the wind to do so. There would be no energy left to spin the propeller to push against the “still“ air. There is simply not enough energy in the wind for the vehicle to reach the speed of the wind and spin the propeller.
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If this were true, I'd immediatly want to know how traditional sailing rigs reach VMGs of greater than 3x.

Their sail doesn't go limp as they reach VMG 1.0 after all.

JB
 
ynot said:
(1) All of the energy to move the vehicle comes from the wind.
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Correct.

ynot said:
(2) All of the energy to spin the propeller comes from the wind.
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Correct (and equivalent to (1), as there is no difference between spinning the propeller and moving the vehicle).

ynot said:
(3) The energy produced by the spinning propeller is less than the energy taken from the wind to create it because of friction.
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The propeller does not produce any energy while the vehicle accelerates. It gains kinetic energy during acceleration, it doesn't lose it. Only if the wind stopped blowing would the spinning propeller be able to produce energy (and slow down doing that).

ETA: You could say that the kinetic energy gained by the vehicle is less than the energy taken from the wind. That is true.

ynot said:
(4) The combined energy of the wind and the propeller is therefore less than the speed of the wind.
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Comparing energy and velocity makes no sense.
 
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ynot said:
What's wrong with using a wind instead of a treadmill?
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It's all wind -- but it's more repeatable and accurate to create the wind with the treadmill rather than rely on the differential heating of the sun.

JB
 
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ynot said:
The thing is that for the vehicle to reach the speed of the wind it would take all of the energy of the wind to do so. There would be no energy left to spin the propeller to push against the “still“ air. There is simply not enough energy in the wind for the vehicle to reach the speed of the wind and spin the propeller.
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No, it does not take all the energy of the wind to get the vehicle to reach the speed of the wind. Don't confuse energy and velocity.
 
Gearing only moves things faster it doesn’t create extra or new energy. In fact because of friction gearing always reduces energy. Some clever guys worked all this out many years ago.

Conservation of energy is not just a good idea . . . it’s the law!
 
Dan O. said:
You got the direction right but your math is wrong. Try looking at the edge conditions for R1=R2 and R1=0.

To get the correct answer, it might help if you solve for the movement of the parachute when the yo-yo rolls forward 1 unit then invert the answer to get the motion of the yo-yo for a 1 unit movement of the parachute.
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Thanks: I stand corrected. I'll take more time before answering the second question!
 
I am so curious by the way. Does anyone here thinking that energy and velocity are equivalent REALLY think that the bat that batters swing when they hit a baseball is moving in excess of 100 mph? Really? Truly?
 
ynot said:
Gearing only moves things faster it doesn’t create extra or new energy. In fact because of friction gearing always reduces energy. Some clever guys worked all this out many years ago.
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And we agree with that clever guy completely.

Conservation of energy is not just a good idea . . . it’s the law!
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And we think it's a very good law.

Somehow folks who think this device must be over-unity forget the potential energy between the two moving mediums. This device slows that relative motion and uses the extracted energy to overcome a bit of prop drag, a very very small bit of rolling friction and bearing drag, and an even smaller bit of aero drag created by the chassis moving some tiny amount more than the wind.

We don't need very much and there is a lot available. This surplus is demonstrated easily by the 3-4x VMG that traditional sailing rigs can achieve. We after all are only looking for 1.01 to visibly prove the point.

JB
 
ThinAirDesigns said:
And we agree with that clever guy completely.



And we think it's a very good law.

Somehow folks who think this device must be over-unity forget the potential energy between the two moving mediums. This device slows that relative motion and uses the extracted energy to overcome a bit of prop drag, a very very small bit of rolling friction and bearing drag, and an even smaller bit of aero drag created by the chassis moving some tiny amount more than the wind.

We don't need very much and there is a lot available. This surplus is demonstrated easily by the 3-4x VMG that traditional sailing rigs can achieve. We after all are only looking for 1.01 to visibly prove the point.

JB
Click to expand...

Sailing ships can gather more energy than they would otherwise need for the same task, and then use a transfomer to achieve a higher velocity.
The cart cannot do this.
 
humber said:
Sailing ships can gather more energy than they would otherwise need for the same task, and then use a transfomer to achieve a higher velocity.
The cart cannot do this.
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You highlight transformer so avidly. Is there some magic that electricity has that mechanical linkages do not have? Is it crystal power energy?

They harvest the energy from the wind to move faster than the wind. This is over-unity, according to YOU. Over-unity is impossible. Over-unity is more output energy than input energy. Not more output velocity than input velocity (ever seen a collision between a large object and a small object? Overunity!)
 
humber said:
Sailing ships can gather more energy than they would otherwise need for the same task, and then use a transfomer to achieve a higher velocity.
The cart cannot do this.
Click to expand...

Ahhh yes -- those pesky sailing shipbuilders. They have cornered the market on transformers and won't let the poor cart builders have them.

:rolleyes::rolleyes::rolleyes:

JB
 
GreyICE said:
You highlight transformer so avidly. Is there some magic that electricity has that mechanical linkages do not have? Is it crystal power energy?

They harvest the energy from the wind to move faster than the wind. This is over-unity, according to YOU. Over-unity is impossible. Over-unity is more output energy than input energy. Not more output velocity than input velocity (ever seen a collision between a large object and a small object? Overunity!)
Click to expand...

When thinking about abstract ideas, it can be helpful to be completely abstract, but this is not an electrical analogue (hence the italics)

The potential energy can be gathered by larger sail area. Now work =f*d,
so you can use a transformer to change the ratio of force and distance, for the same work. If you can do it for "d" then you can for "v"' . Transformers may be purely mechanical devices, but may include vectoring of forces, either by the angle (or design) of the sail, or the boat itself.

The cart also has a transformer in the gearbox, you must trade a fixed power input that is only enough to drive the cart to a point where a transformer would be of use. So you will not succeed.

It's from first principles. I went sailing once, and thought it to be an expensive way of getting salt in my beer.

ETA:
Yes, the cart would need to be over-unity to get to windspeed. But it won't so you are right, it is not.
 
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