Merged DDWFTTW in a “Real” Wind

[Llyricist]

That's right. It was put there to prove that the wheels drove the propeller.

Why do you keep repeating this lie? It was originally put there to protect the drive train. In fact, those pictures you keep posting tell the story, the original one broke on the dynamo, so they had to go without the ratchet at Ivanpah, which in turn caused the "blowout" that bent the sprocket that shows in the first picture you keep posting, which is another misrepresentation, since it happened later than the others.

The fact that the ratchet also satisfied the requirement that the prop could never use its inertia to drive the wheels was a side effect.

A claim of ground power. Nobody in the real world of was going to accept that the ground can power that cart, as Spork claimed, so a quick change of policy was demanded.

No change of policy was demanded or even done. In an FOR where the cart (or the air) is stationary, the ground DOES power the cart. (ETA: above wind speed in the case of the FOR defined by the cart)

So Spork adopted Steve Smith's ideas,

The leverage explanation was around long before Steve Smith got involved, how you expect anyone to buy into this revisionist non-history is beyond me.

but forgot about that ratchet that would prevent that idea from working.

No, the ratchet doesn't prevent any of the valid explanations of how the cart works, it only prevents the ones that are wrong.

The NALSA data says you have all been had.

No it doesn't. It shows pretty clearly that the cart works as advertised.

 

[windgrins]

Quarky's Thanks

Thanks. As mentioned, I was pretty sure I was wrong.
But am I also wrong about ddwfttw without prop and wheels?

Quarky, Please use the buttons on the right hand bottom like "quote" so we will know who you are directing your comment to and on what topic.

This forum moves pretty fast so its hard to keep up with what is being replied to.

Thanks,

Windgrins

 

[windgrins]

Humber-correct again.

There is no time in any known physical system, where momentum is not conserved.

Humber, you are correct, sir.

When dealing with momentum tranferred in jets and streams, it sometimes clarifies things to talk about momentum change over a described time to be specific about quantitative values in change in momentum over the period in question. I do hope this was more illuminating than confusing for the general audience. I corrected my post to (hopefully) clear this up.

Regards,

WindGrins

 

[jadebox]

I think a rocket works more efficiently in an atmosphere than in space.

Wrong.

A rocket motor is more efficient in the atmosphere (although the entire rocket-powered vehicle may not be because of atmospheric drag).

A rocket operates most efficiently when the exit pressure equals the ambient pressure. But, it's not because the rocket pushes against the air. The outside pressure affects the expansion of the gases exiting the nozzle which affects the speed of the gases and, hence, the "reaction" that moves the rocket. In space, a rocket motor is always "over-expanding" and, therefore, not as efficient as it would be in the atmosphere.

-- Roger

 

[windgrins]

Jadebox Rocket Thrust

A rocket motor is more efficient in the atmosphere (although the entire rocket-powered vehicle may not be because of atmospheric drag).

A rocket operates most efficiently when the exit pressure equals the ambient pressure. But, it's not because the rocket pushes against the air. The outside pressure affects the expansion of the gases exiting the nozzle which affects the speed of the gases and, hence, the "reaction" that moves the rocket. In space, a rocket motor is always "over-expanding" and, therefore, not as efficient as it would be in the atmosphere.

-- Roger

I believe what you are saying is correct for conventional rockets which achieve their thrust by combusting (chemical burning) conventional fuels. Some other rockets (such as ionic propulsion) create their thrust by electrically accelerating mass. So for these types of Rockets, they probably are most efficient in space since their is no gas to affect the ions acceleration. "Rockets" that work with incompressible media-such as jet boats, probably don't have the same exact physics behind their thrust either as rockets which have expanding gas generators with thermo considerations. This is subtle topic and I claim little knowledge here. Therefore, I more than willing to listen to others with respect to this topic. I've got a lot to learn.

Regards,

WindGrins

 

[jadebox]

I believe what you are saying is correct for conventional rockets which achieve their thrust by combusting (chemical burning) conventional fuels. Some other rockets (such as ionic propulsion) create their thrust by electrically accelerating mass. So for these types of Rockets, they probably are most efficient in space since their is no gas to affect the ions acceleration. "Rockets" that work with incompressible media-such as jet boats, probably don't have the same exact physics behind their thrust either as rockets which have expanding gas generators with thermo considerations. This is subtle topic and I claim little knowledge here. Therefore, I more than willing to listen to others with respect to this topic. I've got a lot to learn.

What I said is true of all rocket motors, but the specific case of the "ionic propulsion" rocket you mention effetively has a very small nozzle so the effect of the difference in pressure would be less (approaching zero).

In the case of the jet boat, the motor would be a little more efficient in the water (you can see the "over-expansion" of the "exhaust" in photos of jet boats that expell the water above the surface), but, according to Wikipedia (the fount of all knowledge), jet boats work better when the water jet is expelled about the surface of the water because it allows a cleaner hull line and less draft - i.e. less drag on the boat.

-- Roger

 

[CORed]

That's right. It was put there to prove that the wheels drove the propeller.
A claim of ground power. Nobody in the real world of was going to accept that the ground can power that cart, as Spork claimed, so a quick change of policy was demanded.

So Spork adopted Steve Smith's ideas, but forgot about that ratchet that would prevent that idea from working. The NALSA data says you have all been had.

What humber has repeatedly failed to realize is that there has been no change in the explanation of how the ddwfttw cart works. The explanations are equivalent, and differ only in frame of reference. Of course, clearly humber doesn't understand any frame of reference other than the earth. He gets all confused when a frame of reference other than the earth is mentioned.

 

[quarky]

Quarky, Please use the buttons on the right hand bottom like "quote" so we will know who you are directing your comment to and on what topic.

This forum moves pretty fast so its hard to keep up with what is being replied to.

Thanks,

Windgrins

I feel your pain, friend. I'm a simple wheelbarrow driver. Imagine my reaction to the post above that merely mentioned how wrong I was, in an insulting manner, with no link to the wrongness of my spewage. I will try to do better.
It wasn't you, of course.

I'm am more than ok with being wrong. My skin is tough. I come here seeking knowledge, not aggrandizement.
(Even that has a ring of moral hi-ground, which I don't intend.)

 

[windgrins]

Jadebox, I Don't get the jetboat example!

What I said is true of all rocket motors, but the specific case of the "ionic propulsion" rocket you mention effetively has a very small nozzle so the effect of the difference in pressure would be less (approaching zero).

In the case of the jet boat, the motor would be a little more efficient in the water (you can see the "over-expansion" of the "exhaust" in photos of jet boats that expell the water above the surface), but, according to Wikipedia (the fount of all knowledge), jet boats work better when the water jet is expelled about the surface of the water because it allows a cleaner hull line and less draft - i.e. less drag on the boat.

-- Roger

Please help me understand your jet boat example as water is effectively incompressible (at these working pressures) and unless it is partially flashing into steam, how can it do any expanding?

My guess is what the pictures illustrate would be a cavitation phenomenon or perhaps air mixing with the jet.

I do understand the "cleaner hull form" part.

Comments?

WindGrins

 

[windgrins]

Thanks Quarky!

I feel your pain, friend. I'm a simple wheelbarrow driver. Imagine my reaction to the post above that merely mentioned how wrong I was, in an insulting manner, with no link to the wrongness of my spewage. I will try to do better.
It wasn't you, of course.

I'm am more than ok with being wrong. My skin is tough. I come here seeking knowledge, not aggrandizement.
(Even that has a ring of moral hi-ground, which I don't intend.)

No problem Quarky. I'm here for the same reasons. When I feel like I can explain something well, I feel like I have learned the concept.

An old flying instructor once told me. If you really want to learn to fly well, try teaching it. Boy, was he right!

WindGrins

 

[quarky]

No problem Quarky. I'm here for the same reasons. When I feel like I can explain something well, I feel like I have learned the concept.

An old flying instructor once told me. If you really want to learn to fly well, try teaching it. Boy, was he right!

WindGrins

Cool.

There are things i understand well enough to teach.
And have been paid to do so.

This thread's zone is clearly out of my turf, and I am glad that you are here, with some humility and some smarts.
kudos

 

[A.T.]

What humber has repeatedly failed to realize is that there has been no change in the explanation of how the ddwfttw cart works. The explanations are equivalent,

The fact that he thinks they are somehow contradictory just demonstrates his inability to actually understand a general mechanism. He is just matching words.

 

[humber]

Humber, you are correct, sir.

When dealing with momentum tranferred in jets and streams, it sometimes clarifies things to talk about momentum change over a described time to be specific about quantitative values in change in momentum over the period in question. I do hope this was more illuminating than confusing for the general audience. I corrected my post to (hopefully) clear this up.

Regards,

WindGrins

Yes, windgrins, but it's also true that any machine, whether it works or not, can claim general support from the conservation of momentum. It never fails.
What is missing it not force, nor momentum, but the power and energy.

When the cert is at WS, there is no wind power, and it does not become available after that point. When the cart is moving slower than the wind, there is a potential energy difference between cart and wind, that puts the source as the wind. At WS, there is no difference, and above it, the cart would be the source.

 

[humber]

What humber has repeatedly failed to realize is that there has been no change in the explanation of how the ddwfttw cart works. The explanations are equivalent, and differ only in frame of reference. Of course, clearly humber doesn't understand any frame of reference other than the earth. He gets all confused when a frame of reference other than the earth is mentioned.

Totally different. Your "understanding" of FOR is a bowdlerized concoction of Galileo and Einstein's elevator experiment, bequeathed to you by TAD.

The latter, is where "can't tell" comes from. Inside the elevator, the occupant "can't tell" the difference between acceleration and gravity.

The latest attempt at a mathematical solution, is also ripped off from Smith.
Smith mentions an electrical cart in his letter.
Spork's earlier attempt at an analysis - posted here at JREF - was an attempt to shoehorn his claim into Drela's calculations.

Chalk and cheese.

 

[Llyricist]

Yes, windgrins, but it's also true that any machine, whether it works or not, can claim general support from the conservation of momentum. It never fails.
What is missing it not force, nor momentum, but the power and energy.

When the cert is at WS, there is no wind power, and it does not become available after that point. When the cart is moving slower than the wind, there is a potential energy difference between cart and wind, that puts the source as the wind. At WS, there is no difference, and above it, the cart would be the source.

Yeah, he has idea no that his statements here are only applicable in the FOR where the cart is stationary. And therefore there is plenty of wind power available from the ground.

 

[humber]

A rocket motor is more efficient in the atmosphere (although the entire rocket-powered vehicle may not be because of atmospheric drag).

A rocket operates most efficiently when the exit pressure equals the ambient pressure. But, it's not because the rocket pushes against the air. The outside pressure affects the expansion of the gases exiting the nozzle which affects the speed of the gases and, hence, the "reaction" that moves the rocket. In space, a rocket motor is always "over-expanding" and, therefore, not as efficient as it would be in the atmosphere.

-- Roger

Do any of you do any reading, or just go with whatever hunch passes by?


1) Energy from the fuel is lost in air drag and gravity drag and is used for the rocket to gain altitude and speed. However, much of the lost energy ends up in the exhaust.

2) 100% efficiency within the engine (engine efficiency ηc = 100%) would mean that all the heat energy of the combustion products is converted into kinetic energy of the jet. This is not possible, but the high expansion ratio nozzles that can be used with rockets come surprisingly close: when the nozzle expands the gas, the gas is cooled and accelerated, and an energy efficiency of up to 70% can be achieved. Most of the rest is heat energy in the exhaust that is not recovered.[98] The high efficiency is a consequence of the fact that rocket combustion can be performed at very high temperatures and the gas is finally released at much lower temperatures, and so giving good Carnot efficiency.

3) However, engine efficiency is not the whole story. In common with the other jet-based engines, but particularly in rockets due to their high and typically fixed exhaust speeds, rocket vehicles are extremely inefficient at low speeds irrespective of the engine efficiency. The problem is that at low speeds, the exhaust carries away a huge amount of kinetic energy rearward. This phenomenon is termed propulsive efficiency (ηp).[98]

4) However, as speeds rise, the resultant exhaust speed goes down, and the overall vehicle energetic efficiency rises, reaching a peak of around 100% of the engine efficiency when the vehicle is travelling exactly at the same speed that the exhaust is emitted*. In this case the exhaust would ideally stop dead in space behind the moving vehicle, taking away zero energy, and from conservation of energy, all the energy would end up in the vehicle. The efficiency then drops off again at even higher speeds as the exhaust ends up travelling forwards- trailing behind the vehicle.

etc.



From these principles it can be shown that the propulsive efficiency ηp for a rocket moving at speed u with an exhaust velocity c is:

[latex] \eta_p= \frac {2 \frac {u} {c}} {1 + ( \frac {u} {c} )^2 }[/latex]

And the overall energy efficiency η is:

η = ηpηc

*It is also obvious from Newton, that must be true, but not generally realizable, so will only happen at one speed of the rocket. Other demands, and physical conditions will see that happen. Generally, a problem of "load matching". Something of which carteers are totally unaware.

All engineers, and most people, can readily understand Galilean Relativity, but also understand there is more to it than a cartoon.

http://www.internationalskeptics.com/forums/attachment.php?attachmentid=21953&stc=1&d=1303752691

 

[A.T.]

A rocket motor is more efficient in the atmosphere.

Do you mean that the very same rocket motor, running with the same fuel consumption will produce more thrust in the atmosphere than in vacuum?

A rocket operates most efficiently when the exit pressure equals the ambient pressure.

Most efficiently among what cases? I understand that for a given ambient pressure you try to match the exit pressure to it. But as far I can see, that doesn't imply that higher ambient pressure allows more efficiency in the sense of thrust/consumption.

The outside pressure affects the expansion of the gases exiting the nozzle which affects the speed of the gases

How does the outside pressure affect the speed of the gases? Does higher outside pressure mean higher or lower speeds of the gases?

In space, a rocket motor is always "over-expanding" and, therefore, not as efficient as it would be in the atmosphere.

In space, a rocket motor is always underexpanded and therefore not as efficient as a rocket motor with a nozzle of infinite size. But as far I can see, that doesn't imply that it is less efficient than in atmosphere.

 

[CNY_Dave]

Yup. For a neutrally buoyant balloon, you got it exactly. If the balloon has positive or negative buoyancy, there can be other interesting factors as it ascends or descends through gradient (nothing that wouldn't be obvious to you).

More interesting perhaps is that the balloon even tracks wind gusts very well. Intuition might suggest the balloon takes time to come up to the new wind speed, but this isn't the case.

Is the car test is equivalent to a change in wind speed propagating through the air?

As the car accelerates, a pressure wave goes through air in the car from back to front, at the speed of sound I would presume. Easiest to picture as if there is a 'step' in the velocity, giving a nice distinct front. (As the velocity change is not in a step function there is no nicely trackable front.)

Is this an accurate picture of how a change in wind velocity works in open air?
Or is the open-air case more like a wave breaking on a beach (as compared to a wave front moving through the water at the speed of water)?


Dave

 

[windgrins]

Humber, Yes, we Disagree.

Yes, windgrins, but it's also true that any machine, whether it works or not, can claim general support from the conservation of momentum. It never fails.
What is missing it not force, nor momentum, but the power and energy.

When the cert is at WS, there is no wind power, and it does not become available after that point. When the cart is moving slower than the wind, there is a potential energy difference between cart and wind, that puts the source as the wind. At WS, there is no difference, and above it, the cart would be the source.

We have beat this one to death and I know you believe that:

"When the cert is at WS, there is no wind power, and it does not become available after that point."

Contrarily,

I believe that when the cart is at WS, its no different than slower or faster than WS and that there is plenty of power at the prop blades that aren't in a no-wind condition. Or to state it with positives, the prop blades (where the wind part of the force is harvested), is always in a relative wind situation from which they can harvest useful energy. I believe the blades can harvest this differential as lift perpendicular to the plane of the prop by propelling the air backwards with respect to the prop. It does have drag in the plane of the prop but all props do and they still do useful work. It doesn't violate COM, COE or any power argument.

That's our fundamental disagreement and I've seen nothing in your argument that disputes this. I've seen lots of hand waving, empty refutation, appeal to authority, and irrelevant tangents, dismissals by insult and diminishment, but no cogent logical argument to the contrary. Want to offer one?

ETA: PS please do not trot out your silly "Wind is Wind" argument and that the differential does not matter. The only reason this cart works is that it can harvest energy from the wheels to power the prop through the drivetrain. If the prop were unpowered, it could not harvest the wind energy to exceed windspeed. But since it is powered by the wheels, it can and it does harvest the wind energy differential.

If you have any desire to engage me anymore in a discussion-Which you certainly don't have to, then I think you need to define the terms as you use them such as:

Inertial Reference Frame
Energy
Wind

Since you have used these terms in a completely non-standard way throughout the posts and proceed to make non-sense arguments from your own private definitions.

Regards,

WindGrins

 

[tobermoryphil]

Yes, windgrins, but it's also true that any machine, whether it works or not, can claim general support from the conservation of momentum. It never fails.
What is missing it not force, nor momentum, but the power and energy.

When the cert is at WS, there is no wind power, and it does not become available after that point. When the cart is moving slower than the wind, there is a potential energy difference between cart and wind, that puts the source as the wind. At WS, there is no difference, and above it, the cart would be the source.

So, Humber, so how do land yachts and ice yachts manage to have speeds of several times the wind speed?

OK, they are not proceeding directly down wind, but neither is a spot on the cart's prop blade.

If the first craft can do what they obviously do, why not the cart, with it's prop blade airfoil following an identical (if helical) path to the land yacht's airfoil sail?