Down wind faster than the wind

[humber]

You just contradicted yourself. Either you end up at windspeed - which means zero speed relative to the air, which means the cart stays at fixed position on the treadmill - or you go slower. Make up your mind.

Of course you'll be wrong either way. You can't seem to understand that the motion of the cart is not powered by the wind alone, it's powered by the difference between the speed of the wind and the speed of the ground. That difference has nothing to do with the speed of the cart, and (in principle at least) one can always extract energy from it.

Well, I am truly benighted. If cart is said to be at windspeed when on the belt, and the propellor is in the air. If I get out of the car, I should be blown into the propellor. You model fails to predict this admittedly foolish behavior.
Perhaps you can enlighten me.
To anticipate your objection, you told me that the wheels are the ground.
So, if I hang my legs out of the car, and onto the ground, I will be subjected to torque, rather than the linear motion that we mortals would expect.
Try as I may, I still can't understand why there is wind blowing over the propellor, but not when I put my hand out of the window.
The only thing I could think of is that the belt might be the wind, but you say not.

 

[Ivor the Engineer]

It has taken me a while to "see" it, but drawing a picture of the cart held stationary on a moving treadmill in a 0m/s wind (which is *identical* to an observer on the cart moving at the speed of the wind on a stationary treadmill) makes it easy to see how thrust generated by the wheel-driven propeller accelerates the cart to a higher speed than the treadmill.

I think.

 

[humber]

I don't have the faintest clue. But if you find it you can put it in an escrow account with my $100K and we'll bet on what this cart does.

I wonder why you should suddenly be so coy about publishing calculations that you previously offered for free.

 

[humber]

It has taken me a while to "see" it, but drawing a picture of the cart held stationary on a moving treadmill in a 0m/s wind (which is *identical* to an observer on the cart moving at the speed of the wind on a stationary treadmill) makes it easy to see how thrust generated by the wheel-driven propeller accelerates the cart to a higher speed than the treadmill.

I think.

Yes. The cart is said to be travelling at windspeed, and the motion you see is the difference of the two. That motion is said to be the cart's speed above windspeed, which is oddly like zero.
They will affirm this.

 

[CyCrow]

I'll repeat myself a bit here: The correct analogy is downwind-tacking iceboats. It is pushed by the propeller, it's not like a geared windmill moving directly upwind. The force/torque to spin the prop is provided by the wheels, and the lift-to-drag ratio of the propeller airfoil allows the lift (push) to exceed the total drag (torque) which is transfered to the wheels. This requires a difference in wind and ground speed. As far as I can see, the top speed is not limited to the wind speed either, it depends on the total lift-to-drag achieved.

// CyCrow

 

[spork]

No the prop blades are directly analagous to a sail boat running directly into the wind.

I guess they are if the prop is not spinning. But if the cart is moving the prop is spinning.

 

[Modified]

Yes, but unless you show that the vehicles in question can average a downwind velocity component faster than the wind, connecting such vehicles doesn't get you there.

If you can achieve a speed faster than the wind in some direction, then with a small enough friction and drag, you can average faster than the wind in any direction. This can be done by turning in the desired direction, dropping the sail, coasting until the speed is below some threshold, turning back in a favorable direction, re-accelerating, and repeating this process.

 

[ThinAirDesigns]

You must have changed your frame of integrity.

-

Humber, you'll have to explain the above comment because it's a mystery to me.

I have repeatedly attempted to engage you and JW in a basic discussion of intertial frames of reference -- no one will discuss it and I'm wondering why. It appears to the be the elephant in the room.

Elephants are gray
Mice are gray
Mice are elephants

Perfect example. I asked a simple question upon which an exchange can be based and I get an answer from you that leads to nowhere.

My post requesting that you review my numbers and return your own carries no implication that you agree with me -- even if you agree with those numbers. It means that if you and I agree on those numbers we move on and look at other examples *until* we find where we *do* disagree.

This entire thread has deteriorated and currently has no hope of recovery unless we can determine the precise point of disagreement.

Ball is in your court -- animals answers will get us no closer to agreement ... numbers just might.

JB

 

[Ivor the Engineer]

I'll repeat myself a bit here: The correct analogy is downwind-tacking iceboats. It is pushed by the propeller, it's not like a geared windmill moving directly upwind. The force/torque to spin the prop is provided by the wheels, and the lift-to-drag ratio of the propeller airfoil allows the lift (push) to exceed the total drag (torque) which is transfered to the wheels. This requires a difference in wind and ground speed. As far as I can see, the top speed is not limited to the wind speed either, it depends on the total lift-to-drag achieved.

// CyCrow

The bolded section is what I'm not certain about.

 

[spork]

I wonder why you should suddenly be so coy about publishing calculations that you previously offered for free.

I have no idea what you're talking about. You said you wanted to accept my wager for $100K. Now you seem to be looking for your $100K. If you find it, let's get this bet on the road.

 

[CyCrow]

Yes. The cart is said to be travelling at windspeed, and the motion you see is the difference of the two. That motion is said to be the cart's speed above windspeed, which is oddly like zero.
They will affirm this.

Advancing on the treadmill in still air proves that it is able to exceed downwind speed. To measure top speed, you would need either a very long treadmill, or a combination treadmill and wind tunnel. Or you could do it in less controlled conditions outside. "Oddly like zero" is not zero.

// CyCrow

 

[spork]

I'll repeat myself a bit here: The correct analogy is downwind-tacking iceboats. It is pushed by the propeller, it's not like a geared windmill moving directly upwind. The force/torque to spin the prop is provided by the wheels, and the lift-to-drag ratio of the propeller airfoil allows the lift (push) to exceed the total drag (torque) which is transfered to the wheels. This requires a difference in wind and ground speed. As far as I can see, the top speed is not limited to the wind speed either, it depends on the total lift-to-drag achieved.

// CyCrow

I think we have to include CyCrow in the group of people that understand this cart. The only slight correction I'd make is that the top speed is governed by the advance ratio (prop pitch vs. wheel drive for a single prop rotation). the L/D only tells us how closely we can match that theoretical top speed.

 

[Thabiguy]

It has taken me a while to "see" it, but drawing a picture of the cart held stationary on a moving treadmill in a 0m/s wind (which is *identical* to an observer on the cart moving at the speed of the wind on a stationary treadmill) makes it easy to see how thrust generated by the wheel-driven propeller accelerates the cart to a higher speed than the treadmill.

Yes - if the transmission is right. If the propeller was just blowing air backwards at the same speed that the treadmill moves, then the thrust generated by the propeller would be cancelled by equal but opposite force exerted by the treadmill on the cart as it drives the propeller, and nothing would happen.

In order for the device to accelerate, the propeller must be geared to move the air slower (wrt device) than the ground moves (wrt device). Speed will be slower, but exerted force will be greater. This is what will generate the net forward force to accelerate the vehicle.

 

[mhaze]

This is an absolute train wreck....But you three can correct us all with no evidence or background whatever - based only on truly bizarre "theories" you make up on the fly?

Build the stupid cart....

Yep. At issue as far as I am concerned is the experimental paradimn (which you have not delivered) that would conclusively prove or disprove the claims made concerning the device.

"Build the stupid cart", is in fact, no more or less than a plea for more stupidity in the form of carts.

By the way in this thread I have not seen an aerodynamic approach to the issues at all. Here I am referring to the conceptual frameworks and grammer as used in such a discussion, as opposed to physics and vectors. Humber comes close with his noting that air close to the cart on the treadmill is stationary, and this is not the same as airflow in the open field. Further, when the prop imparts momentum to the air while on the treadmill, it creates only the local airflow effects of a prop. This is in still air a low performance implementation with high amounts of eddies and swirls behind the prop, which says that your machine would do best with large, very slow turning props.

Looks to me like a reinvention of the autogyro with the prop perpendicular to the earth, and with the treadmill test being a reinvention of the autogyro's "jump start".

 

[sol invictus]

I see. We have 450 years of understanding, yet it seems that you are suggesting that the understanding of these laws is yuckky?

No. Read it again.

What I said was that you are denying one of the most basic laws of physics (one which has been understood for 450 years) while simultaneously claiming that those same laws make this device impossible (although of course without ever specifying which law you think it violates).

Well, I am truly benighted. If cart is said to be at windspeed when on the belt, and the propellor is in the air. If I get out of the car, I should be blown into the propellor. You model fails to predict this admittedly foolish behavior.

Huh?

Is this really so hard for you to understand? If you've ever sailed downwind on a sailboat or a windsurfer you'd see immediately what your error is there. If you stand on deck while sailing straight downwind, you feel almost no wind at all (even when the boat is moving very fast with respect to the water). You don't seem to be able to grasp that.

To anticipate your objection, you told me that the wheels are the ground.
So, if I hang my legs out of the car, and onto the ground, I will be subjected to torque, rather than the linear motion that we mortals would expect.

What in the world are you talking about?

Try as I may, I still can't understand why there is wind blowing over the propellor, but not when I put my hand out of the window.
The only thing I could think of is that the belt might be the wind, but you say not.

Again, I have no idea what you're talking about. You evidently have some scenario in your head you haven't told the rest of us about, which makes it hard to understand you.

 

[spork]

In order for the device to accelerate, the propeller must be geared to move the air slower (wrt device) than the ground moves (wrt device). Speed will be slower, but exerted force will be greater. This is what will generate the net forward force to accelerate the vehicle.

As much pain as this thread brings me, it really is a comfort when I see postings from guys like Thabiguy that clearly lay out the reality of this little puzzle. It's like a glimmering beacon of hope for humanity.

 

[Ivor the Engineer]

As much pain as this thread brings me, it really is a comfort when I see postings from guys like Thabiguy that clearly lay out the reality of this little puzzle. It's like a glimmering beacon of hope for humanity.

Hey, you haven't seen the threads on the Monty Hall problem...

 

[spork]

Yep. At issue as far as I am concerned is the experimental paradimn (which you have not delivered) that would conclusively prove or disprove the claims made concerning the device.

I'm sorry that you're unable to follow my posts, and those of JB, sol, and Thabiguy.

"Build the stupid cart", is in fact, no more or less than a plea for more stupidity in the form of carts.

Actually it's more of a plea for you to follow the long standing scientific tradition of: STFU and try it yourself.

By the way in this thread I have not seen an aerodynamic approach to the issues at all.

That's because you haven't understood my vector analysis, and as yet not a single person has asked for any explanation of them. I can only assume that's because there are two kinds of people in the world - those who need no explanation, and those for whom no explanation will help.

 

[spork]

Hey, you haven't seen the threads on the Monty Hall problem...

Sad to admit I've actually started threads on that problem (on other forums).

 

[ThinAirDesigns]

Advancing on the treadmill in still air proves that it is able to exceed downwind speed. // CyCrow

Thanks CyCrow.

humbert, if you are willing to have an exchange regarding inertial frames of reference perhaps you too can join the group who agree with Galileo, Newton, Einstein, et al.

JB