Merged DDWFTTW in a “Real” Wind

[humber]

Can explain to us the internal contortions required to be completely wrong about something, argue vigourously from that mistaken position, and then switch to the contrary position and argue just as vigourously from that position without skipping a beat and while insisting that you were right all along?

Still singing the same song?

Because that's some pretty impressive doublethink right there.

Play chess, D'rok?

I guess your ultimate position is this: "Whatever anyone who accepts that the cart goes ddwfttw says is wrong, even when they're right, and whatever I say is right, even when I'm wrong." It's a flexible position, because, to be right, all you have to do is contradict the carteers and it is impossible to contradict yourself even when you do just that.

There are no contradictions. I posted the case where the angle and line of force influenced the outcome before any of the rest. If you had understood that, then you should have remarked on the connection, rather than concentrating one me. The cart is a cult of personality.

ETA:
I think that if there is enough friction, an over the top reel can be made to climb a vertical face, but not the underneath version .

 

[D'rok]

Still singing the same song?


Play chess, D'rok?



There are no contradictions. I posted the case where the angle and line of force influenced the outcome before any of the rest. If you had understood that, then you should have remarked on the connection, rather than concentrating one me. The cart is a cult of personality.

ETA:
I think that if there is enough friction, an over the top reel can be made to climb a vertical face, but not the underneath version .

What I find most remarkable about all of this (besides getting a basic grasp of how the cart works) is that when reality contradicts your analyses, it is reality that has to give way. In this particular instance, you nearly caved in to reality but at the last moment you just concocted a different analysis and pretended that you had it right all along.

I find this to be hilarious.

 

[Jack by the hedge]

Sails cannot go faster than the wind ddw, so what is your point?

The propeller blades are not travelling directly downwind. They operate like sails, and they are "tacking" in a circular path.

That is the point.

 

[Jack by the hedge]

<stuff>
... the power is the same.

That's what I said. The power is the same.

You said "there is always a corresponding change in the amount of work that can be done over the same time".

If you change the amount of work done in the same time, you change the amount of power by definition. P = WD/T

 

[Jack by the hedge]

It will roll backwards on any slope when the force of gravity is large enough.

Only if something slips. Either the reel slips on the surface or the cord slips on the reel. No other way, unless something breaks. In that configuration, the reel cannot roll backwards down the slope, unwinding the cord.

 

[humber]

That's what I said. The power is the same.

You said "there is always a corresponding change in the amount of work that can be done over the same time".

If you change the amount of work done in the same time, you change the amount of power by definition. P = WD/T

No. Power = F*d/time
Work = f*d
Power = work/time

There is no "free lunch", ever.
In the case of the block and tackle, the distance the rope is pulled is doubled, and the force is halved, but work remains the same
2d*f/2 = W

If done in the same one second, then the power would be the same as the un-pulllied case, because P =w/t

The worker has limited power. He can only exert some product of force and velocity in any given physical situation. Power = force*velocity, but he can do any amount of work (Provided he has the energy, which comes from combustion of food) Using pulleys, he can lift huge weights, even though his power is still limited.
Power is reduced by doing the same work over more time. If the force reduction is at the expense of more distance, then V must fall, because time has increased. V =d/t
The wind has a finite amount over energy for any given volume. Power is the related to time that energy is expended. No more can be "extracted" than is available, no matter how you try to "demand" more by gearing.

The propeller blades are not traveling directly downwind. They operate like sails, and they are "tacking" in a circular path.

That is the point.

Back to the cart. I can echo Maurice Ledifficile
[/quote=Maurice Ledifficile]
As to the kart, the propeller is powered by the very wind it is resisting (wind moves cart, wheels turn, propeller turns). That hardly sounds like it can generate much of anything. The kart would be faster without. I have 0% confidence in the record run’s validity. There. Put them apples in your pipe.
[/quote]

I think there are enough examples of holes, shortcuts, technical errors, bias, data mishandling and and special-pleading, that I can ignore the trial without feeling the need to explain how it does what it does because the result has no interesting meaning. It tacks a gusty wind for a short time. Call the press.

The tacking prop is nonsense, and has no text book support. The "air-screw" is a notion that has been made real.

http://www.mh-aerotools.de/airfoils/propuls1.htm#TOC
Propeller or Airscrew?

"Propellers have also been called airscrew in the past, but this term may be misleading, because a propeller does not move like a mechanical screw through a rigid medium. You don't call a wing knife or slicer because it also does not slice through the air in the direction of its inclined mean line. Each section of a propeller (or of a wing) has a certain angle of incidence and is moving through the air at its unique angle of attack - both are independent. On the other hand, a mechanical screw or a knife moves through a rigid material exactly in the direction which is given by its pitch or angle of incidence - a screw with different pitches along its radius would get stuck, a propeller does not."

The "advance ratio" is a way of expressing the tip speed with respect to linear motion. It does not literally mean a screw. It is a "figure of merit" like L/D ratio,

Airscrew.
All types of screws with helical blades designed to rotate in air and more particularly power-driven screws designed to produce thrust by rotation. Synonymous with the term 'propeller'. Airscrew slip is the ratio of the actual advance per revolution of an airscrew to the theoretical r advance per revolution. Airscrew efficiency is an expression of this ratio, normally about 82 per cent"

If there is slip, it can't be a screw.

The distance and object travels is defined as the distance the centre of mass moves. The distance a car travels is defined by how far the chassis travels. Not the radiator fan tips, or even the wheel surface. There may be a fixed relationship to the number of turns of the wheel, but then again the wheel can slip. They do, as a matter of normal traction generation, but that's a detail.

If the blade is seen as being at angle to the head wind, so like a tacking sail,
that headwind will still drive the cart backwards, but the angled blade would mean it would not be in a straight line. Any "tacking force" would still oppose the cart, and not drive it. The turning has no influence upon that.
If an angled blade could produced a useful tacking force, then so could the same but static blade attached to the chassis.

 

[Modified]

There is no fixed relationship between mass and friction. If scaled, you will find that out the hard way.

Wrong again. To a good approximation, friction is proportional to weight and independent of contact patch.

 

[humber]

Only if something slips. Either the reel slips on the surface or the cord slips on the reel. No other way, unless something breaks. In that configuration, the reel cannot roll backwards down the slope, unwinding the cord.

But, the limit to the applied force is the friction. That makes the idea useless, because acceleration will also be limited. If you apply a sudden jerk to the over the top version, the reel will still roll forwards, even if the thread becomes slack.
Do that to the under version, and it will turn it the other way. There is a limit in one case, but not the other. And, to turn the other way, it must lose all of the KE it had in the CW direction before that can happen.
Useless!

ETA:
You may think I am "changing my story" but there are so many problems, that it looks that way as I mention them. There are more.

 

[sol invictus]

The intent is to show that you are tilting at windmills.

Maybe "humber" is an art project - a contemporary internet play on Don Quixote? A kind of Exit-Through-The-Gift-Shop-esque character?

 

[humber]

Wrong again. To a good approximation, friction is proportional to weight and independent of contact patch.

That is an over simplifiacton.
If cars were limited by the rolling resistance, then you would have wheel spin every time you tried to move. Under acceleration, the tyre distorts to increase that area, and through changes in the material at the surface, which increase the coefficient of friction, Crr.

If you kept that drag all of the time, and so when under constant velocity, you may find you are better off with blocks of wood. That's the magic of tyres.
Very complex behavior.

But for the same surface area, air has more influence on a leaf, than it does a brick.

 

[humber]

Maybe "humber" is an art project - a contemporary internet play on Don Quixote? A kind of Exit-Through-The-Gift-Shope-esque character?

Well, the mods are going to get this one, but you may be his donkey.

 

[Modified]

That is an over simplifiacton.

Just to satisfy my curiosity, will you at least admit that you spelled "simplification" wrong?

 

[Jack by the hedge]

If you change the amount of work done in the same time, you change the amount of power by definition. P = WD/T

No. Power = F*d/time
Work = f*d
Power = work/time

I'm going to assume you didn't spot my abbreviation of Work Done to "WD" and assumed I meant Work * Distance. Blame my old physics lecturers for "WD" , if you don't like it.

Otherwise the above makes even less sense than usual, because you definitely stated that "there is always a corresponding change in the amount of work that can be done over the same time".

Ah. I now see you edited your post to remove the remark. Never mind, then. Carry on.

 

[spork]

Maybe "humber" is an art project - a contemporary internet play on Don Quixote? A kind of Exit-Through-The-Gift-Shop-esque character?

Bad analogy. Both of those characters were highly delusional people that DID things. That sets them apart from humber in a big way.

 

[Jack by the hedge]

It tacks a gusty wind for a short time. Call the press.

Perhaps you should call the press. On the tiny bit of energy you think it extracts from a couple of random gusts, it accelerates by more than windspeed. It's positively magical.

The tacking prop is nonsense

Yet you are incapable of summoning any argument against the short video neatly demonstrating the equivalence. Unimpressive.

<irrelevant padding about airscrews vs screws>
The distance and object travels is defined as the distance the centre of mass moves.

Irrelevant. The interaction between an object and the medium through which it is moving depends on its path through the medium and not the different path taken by its centre of mass. To be more specific, the interaction of a propeller blade with the air depends on the relative motion of the blade and the air with which it actually comes into contact, and is therefore not usefully described by the path of its hub.

If the blade is seen as being at angle to the head wind, so like a tacking sail, that headwind will still drive the cart backwards, but the angled blade would mean it would not be in a straight line. Any "tacking force" would still oppose the cart, and not drive it. The turning has no influence upon that.
If an angled blade could produced a useful tacking force, then so could the same but static blade attached to the chassis.

You appear to be incapable of conceiving any difference in behaviour between a propeller blade which is turning and one which is not turning. You may be onto something which will save the aviation business a fortune in fuel, or you may just still be wrong. (Clue - it's the latter)

You accept, I hope, that a conventional land yacht can tack such that its downwind component is faster than the wind. It achieves the thrust required from its sail, whose velocity has a component which is directly downwind and a component which is perpendicular to the wind. Exactly what a propeller blade can do.

 

[Jack by the hedge]

But, the limit to the applied force is the friction. That makes the idea useless, because acceleration will also be limited.

This is an entirely spurious objection. The acceleration of my car is also limited by friction. That does not make it useless.

 

[Modified]

This is an entirely spurious objection. The acceleration of my car is also limited by friction. That does not make it useless.

But your car will not work on ice or go up a 90 degree slope. Useless.

 

[Llyricist]

Some people have decided that the cart is a pmm. Therefore, pointing out that analogous machines are not pmm's is the same as pointing out that they are not analogous.

It matters not that nobody else claims the cart is a pmm, and are actually using the analogous machines to drive that point home, because the actual claims made by others never penetrate the boundary layer of their universe.

 

[humber]

Just to satisfy my curiosity, will you at least admit that you spelled "simplification" wrong?

I will tell you what I told others so long ago. I do not use the PC and keyboard very much, but mostly transfer stuff from my hand-held keyboard.

It is wireless, and based on a former device called the Micro-writer.
http://en.wikipedia.org/wiki/Microwriter

It of course smaller, but has no display. I pick it up and put it down, typing as I go hither and aboooot. Often I make typos, and don't see them until I eventually read the screen. That annoys me, so sometimes I will edit several times.
Your remarks suggests that I should, and that you have little else to offer, Modified.

 

[humber]

But your car will not work on ice or go up a 90 degree slope. Useless.

But it will on a road. The surface also distorts under force, and is an essential part of the process. Tyre are designed to accommodate different surfaces, such as dirt, ice and tarmac.
The reel is limited in principle, and that limit can only be extended by creating more friction, than any of the alternatives.